model two-dimensional heat-transfer: Topics by WorldWideScience.org

Sample records for model two-dimensional heat-transfer

Two-dimensional finite element heat transfer model of softwood. Part II, Macrostructural effects

Science.gov (United States)

Hongmei Gu; John F. Hunt

2006-01-01

A two-dimensional finite element model was used to study the effects of structural features on transient heat transfer in softwood lumber with various orientations. Transient core temperature was modeled for lumber samples âcutâ from various locations within a simulated log. The effects of ring orientation, earlywood to latewood (E/L) ratio, and ring density were...
A one-dimensional heat transfer model for parallel-plate thermoacoustic heat exchangers

NARCIS (Netherlands)

de Jong, Anne; Wijnant, Ysbrand H.; de Boer, Andries

2014-01-01

A one-dimensional (1D) laminar oscillating flow heat transfer model is derived and applied to parallel-plate thermoacoustic heat exchangers. The model can be used to estimate the heat transfer from the solid wall to the acoustic medium, which is required for the heat input/output of thermoacoustic
A one-dimensional heat transfer model for parallel-plate thermoacoustic heat exchangers.

Science.gov (United States)

de Jong, J A; Wijnant, Y H; de Boer, A

2014-03-01

A one-dimensional (1D) laminar oscillating flow heat transfer model is derived and applied to parallel-plate thermoacoustic heat exchangers. The model can be used to estimate the heat transfer from the solid wall to the acoustic medium, which is required for the heat input/output of thermoacoustic systems. The model is implementable in existing (quasi-)1D thermoacoustic codes, such as DeltaEC. Examples of generated results show good agreement with literature results. The model allows for arbitrary wave phasing; however, it is shown that the wave phasing does not significantly influence the heat transfer.
Two dimensional heat transfer problem in flow boiling in a rectangular minichannel

Directory of Open Access Journals (Sweden)

Hożejowska Sylwia

2015-01-01

Full Text Available The paper presents mathematical modelling of flow boiling heat transfer in a rectangular minichannel asymmetrically heated by a thin and one-sided enhanced foil. Both surfaces are available for observations due to the openings covered with glass sheets. Thus, changes in the colour of the plain foil surface can be registered and then processed. Plain side of the heating foil is covered with a base coat and liquid crystal paint. Observation of the opposite, enhanced surface of the minichannel allows for identification of the gas-liquid two-phase flow patterns and vapour quality. A two-dimensional mathematical model of heat transfer in three subsequent layers (sheet glass, heating foil, liquid was proposed. Heat transfer in all these layers was described with the respective equations: Laplace equation, Poisson equation and energy equation, subject to boundary conditions corresponding to the observed physical process. The solutions (temperature distributions in all three layers were obtained by Trefftz method. Additionally, the temperature of the boiling liquid was obtained by homotopy perturbation method (HPM combined with Trefftz method. The heat transfer coefficient, derived from Robin boundary condition, was estimated in both approaches. In comparison, the results by both methods show very good agreement especially when restricted to the thermal sublayer.
One dimensional analysis model for condensation heat transfer in feed water heater

International Nuclear Information System (INIS)

Murase, Michio; Takamori, Kazuhide; Aihara, Tsuyoshi

1998-01-01

In order to simplify condensation heat transfer calculations for feed water heaters, one dimensional (1D) analyses were compared with three dimensional (3D) analyses. The results showed that average condensation heat transfer coefficients by 1D analyses with 1/2 rows of heat transfer tubes agreed with those by 3D analyses within 7%. Using the 1D analysis model, effects of the pitch of heat transfer tubes were evaluated. The results showed that the pitch did not affect much on heat transfer rates and that the size of heat transfer tube bundle could be decreased by a small pitch. (author)
Two dimensional finite element heat transfer models for softwood

Science.gov (United States)

Hongmei Gu; John F. Hunt

2004-01-01

The anisotropy of wood creates a complex problem for solving heat and mass transfer problems that require analyses be based on fundamental material properties of the wood structure. Most heat transfer models use average thermal properties across either the radial or tangential directions and have not differentiated the effects of cellular alignment, earlywood/latewood...
Two-dimensional thermal analysis of radial heat transfer of monoliths in small-scale steam methane reforming

DEFF Research Database (Denmark)

Cui, Xiaoti; Kær, Søren Knudsen

2018-01-01

Monolithic catalysts have received increasing attention for application in the small-scale steam methane reforming process. The radial heat transfer behaviors of monolith reformers were analyzed by two-dimensional computational fluid dynamic (CFD) modeling. A parameter study was conducted...... by a large number of simulations focusing on the thermal conductivity of the monolith substrate, washcoat layer, wall gap, radiation heat transfer and the geometric parameters (cell density, porosity and diameter of monolith). The effective radial thermal conductivity of the monolith structure, kr......,eff, showed good agreement with predictions made by the pseudo-continuous symmetric model. This influence of the radiation heat transfer is low for highly conductive monoliths. A simplified model has been developed to evaluate the importance of radiation for monolithic reformers under different conditions...
Numerical prediction of turbulent heat transfer augmentation in an annular fuel channel with two-dimensional square ribs

International Nuclear Information System (INIS)

Takase, Kazuyuki

1996-01-01

The square-ribbed fuel rod for high temperature gas-cooled reactors was developed in order to enhance the turbulent heat transfer in comparison with the standard fuel rod. To evaluate the heat transfer performance of the square-ribbed fuel rod, the turbulent heat transfer coefficients in an annular fuel channel with repeated two-dimensional square ribs were analyzed numerically on a fully developed incompressible flow using the k - ε turbulence model and the two-dimensional axisymmetrical coordinate system. Numerical analyses were carried out for a range of Reynolds numbers from 3000 to 20000 and ratios of square-rib pitch to height of 10, 20 and 40, respectively. The predicted values of the heat transfer coefficients agreed within an error of 10% for the square-rib pitch to height ratio of 10, 20% for 20 and 25% for 40, respectively, with the heat transfer empirical correlations obtained from the experimental data. It was concluded by the present study that the effect of the heat transfer augmentation by square ribs could be predicted sufficiently by the present numerical simulations and also a part of its mechanism could be explained by means of the change in the turbulence kinematic energy distribution along the flow direction. (author)
Numerical prediction of augmented turbulent heat transfer in an annular fuel channel with repeated two-dimensional square ribs

International Nuclear Information System (INIS)

Takase, K.

1996-01-01

The square-ribbed fuel rod for high temperature gas-cooled reactors was designed and developed so as to enhance the turbulent heat transfer in comparison with the previous standard fuel rod. The turbulent heat transfer characteristics in an annular fuel channel with repeated two-dimensional square ribs were analysed numerically on a fully developed incompressible flow using the k-ε turbulence model and the two-dimensional axisymmetrical coordinate system. Numerical analyses were carried out under the conditions of Reynolds numbers from 3000 to 20000 and ratios of square-rib pitch to height of 10, 20 and 40 respectively. The predictions of the heat transfer coefficients agreed well within an error of 10% for the square-rib pitch to height ratio of 10, 20% for 20 and 25% for 40 respectively, with the heat transfer empirical correlations obtained from the experimental data due to the simulated square-ribbed fuel rods. Therefore it was found that the effect of heat transfer augmentation due to the square ribs could be predicted by the present numerical simulations and the mechanism could be explained by the change in the turbulence kinematic energy distribution along the flow direction. (orig.)
Benchmark numerical solutions for radiative heat transfer in two-dimensional medium with graded index distribution

Energy Technology Data Exchange (ETDEWEB)

Liu, L.H. [School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001 (China)]. E-mail: lhliu@hit.edu.cn

2006-11-15

In graded index media, the ray goes along a curved path determined by Fermat principle. Generally, the curved ray trajectory in graded index media is a complex implicit function, and the curved ray tracing is very difficult and complex. Only for some special refractive index distributions, the curved ray trajectory can be expressed as a simple explicit function. Two important examples are the layered and the radial graded index distributions. In this paper, the radiative heat transfer problems in two-dimensional square semitransparent with layered and radial graded index distributions are analyzed. After deduction of the ray trajectory, the radiative heat transfer problems are solved by using the Monte Carlo curved ray-tracing method. Some numerical solutions of dimensionless net radiative heat flux and medium temperature are tabulated as the benchmark solutions for the future development of approximation techniques for multi-dimensional radiative heat transfer in graded index media.
Two Dimensional Heat Transfer around Penetrations in Multilayer Insulation

Science.gov (United States)

Johnson, Wesley L.; Kelly, Andrew O.; Jumper, Kevin M.

2012-01-01

The objective of this task was to quantify thermal losses involving integrating MLI into real life situations. Testing specifically focused on the effects of penetrations (including structural attachments, electrical conduit/feedthroughs, and fluid lines) through MLI. While there have been attempts at quantifying these losses both analytically and experimentally, none have included a thorough investigation of the methods and materials that could be used in such applications. To attempt to quantify the excess heat load coming into the system due to the integration losses, a calorimeter was designed to study two dimensional heat transfer through penetrated MLI. The test matrix was designed to take as many variables into account as was possible with the limited test duration and system size. The parameters varied were the attachment mechanism, the buffer material (for buffer attachment mechanisms only), the thickness of the buffer, and the penetration material. The work done under this task is an attempt to measure the parasitic heat loads and affected insulation areas produced by system integration, to model the parasitic loads, and from the model produce engineering equations to allow for the determination of parasitic heat loads in future applications. The methods of integration investigated were no integration, using a buffer to thermally isolate the strut from the MLI, and temperature matching the MLI on the strut. Several materials were investigated as a buffer material including aerogel blankets, aerogel bead packages, cryolite, and even an evacuated vacuum space (in essence a no buffer condition).
Effective method for construction of low-dimensional models for heat transfer process

Energy Technology Data Exchange (ETDEWEB)

Blinov, D.G.; Prokopov, V.G.; Sherenkovskii, Y.V.; Fialko, N.M.; Yurchuk, V.L. [National Academy of Sciences of Ukraine, Kiev (Ukraine). Inst. of Engineering Thermophysics

2004-12-01

A low-dimensional model based on the method of proper orthogonal decomposition (POD) and the method of polyargumental systems (MPS) for thermal conductivity problems with strongly localized source of heat has been presented. The key aspect of these methods is that they enable to avoid weak points of other projection methods, which consists in a priori choice of basis functions. It enables us to use the MPS method and the POD method as convenient means to construct low-dimensional models of heat and mass transfer problems. (Author)
Effect of two dimensional heat conduction within the wall on heat transfer of a tube partially heated on its circumference

International Nuclear Information System (INIS)

Satoh, Isao; Kurosaki, Yasuo

1987-01-01

This paper dealt with the numerical calculations of the heat transfer of a tube partially heated on its circumference, considering two-dimensional heat conduction within the wall. The contribution of the unheated region of the tube wall to heat tranfer of the heated region was explained by the term of 'fin efficiency of psuedo-fin', it was clarified that the fin efficiency of the unheated region was little affected by the temperature difference between the inner and outer surfaces of the wall, and could be approximated by the fin efficency of a rectangular fin. Both the circumferential and radial heat conductions within the wall affected the temperature difference between the inner and outer surfaces of the heated region; however, the effect of the temperature difference on the circumferentially average Nusselt number could be obtained by using the analytical solution of radially one-dimensional heat conduction. Using these results, a diagram showing the effect of wall conduction on heat transfer, which is useful for designing the circumferentially nonuniformly heated coolant passages, was obtained. (author)
The inaccuracy of conventional one-dimensional parallel thermal resistance circuit model for two-dimensional composite walls

International Nuclear Information System (INIS)

Wong, K.-L.; Hsien, T.-L.; Hsiao, M.-C.; Chen, W.-L.; Lin, K.-C.

2008-01-01

This investigation is to show that two-dimensional steady state heat transfer problems of composite walls should not be solved by the conventionally one-dimensional parallel thermal resistance circuits (PTRC) model because the interface temperatures are not unique. Thus PTRC model cannot be used like its conventional recognized analogy, parallel electrical resistance circuits (PERC) model which has the unique node electric voltage. Two typical composite wall examples, solved by CFD software, are used to demonstrate the incorrectness. The numerical results are compared with those obtained by PTRC model, and very large differences are observed between their results. This proves that the application of conventional heat transfer PTRC model to two-dimensional composite walls, introduced in most heat transfer text book, is totally incorrect. An alternative one-dimensional separately series thermal resistance circuit (SSTRC) model is proposed and applied to the two-dimensional composite walls with isothermal boundaries. Results with acceptable accuracy can be obtained by the new model
FireStem2D A two-dimensional heat transfer model for simulating tree stem injury in fires

Science.gov (United States)

Efthalia K. Chatziefstratiou; Gil Bohrer; Anthony S. Bova; Ravishankar Subramanian; Renato P.M. Frasson; Amy Scherzer; Bret W. Butler; Matthew B. Dickinson

2013-01-01

FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by...
Two-Dimensional Variable Property Conjugate Heat Transfer Simulation of Nanofluids in Microchannels

International Nuclear Information System (INIS)

Ramiar, A.; Ranjbar, A.A.

2013-01-01

Laminar two-dimensional forced convective heat transfer of CuO-water and Al 2 O 3 -water nanofluids in a horizontal microchannel has been studied numerically, considering axial conduction effects in both solid and liquid regions and variable thermal conductivity and dynamic viscosity. The results show that using nanoparticles with higher thermal conductivities will intensify enhancement of heat transfer characteristics and slightly increases shear stress on the wall. The obtained results show more steep changes in Nusselt number for lower diameters and also higher values of Nusselt number by decreasing the diameter of nanoparticles. Also, by utilizing conduction number as the criterion, it was concluded from the results that adding nanoparticles will intensify the axial conduction effect in the geometry considered.
Preparation of functions of computer code GENGTC and improvement for two-dimensional heat transfer calculations for irradiation capsules

International Nuclear Information System (INIS)

Nomura, Yasushi; Someya, Hiroyuki; Ito, Haruhiko.

1992-11-01

Capsules for irradiation tests in the JMTR (Japan Materials Testing Reactor), consist of irradiation specimens surrounded by a cladding tube, holders, an inner tube and a container tube (from 30mm to 65mm in diameter). And the annular gaps between these structural materials in the capsule are filled with liquids or gases. Cooling of the capsule is done by reactor primary coolant flowing down outside the capsule. Most of the heat generated by fission in fuel specimens and gamma absorption in structural materials is directed radially to the capsule container outer surface. In thermal performance calculations for capsule design, an one(r)-dimensional heat transfer computer code entitled (Generalyzed Gap Temperature Calculation), GENGTC, originally developed in Oak Ridge National Laboratory, U.S.A., has been frequently used. In designing a capsule, are needed many cases of parametric calculations with respect to changes materials and gap sizes. And in some cases, two(r,z)-dimensional heat transfer calculations are needed for irradiation test capsules with short length fuel rods. Recently the authors improved the original one-dimensional code GENGTC, (1) to simplify preparation of input data, (2) to perform automatic calculations for parametric survey based on design temperatures, ect. Moreover, the computer code has been improved to perform r-z two-dimensional heat transfer calculation. This report describes contents of the preparation of the one-dimensional code GENGTC and the improvement for the two-dimensional code GENGTC-2, together with their code manuals. (author)
Two-dimensional finite element heat transfer model of softwood. Part I, Effective thermal conductivity

Science.gov (United States)

John F. Hunt; Hongmei Gu

2006-01-01

The anisotropy of wood complicates solution of heat and mass transfer problems that require analyses be based on fundamental material properties of the wood structure. Most heat transfer models use average thermal properties across either the radial or tangential direction and do not differentiate the effects of cellular alignment, earlywood/latewood differences, or...
Application of linear and non-linear low-Re k-ε models in two-dimensional predictions of convective heat transfer in passages with sudden contractions

International Nuclear Information System (INIS)

Raisee, M.; Hejazi, S.H.

2007-01-01

This paper presents comparisons between heat transfer predictions and measurements for developing turbulent flow through straight rectangular channels with sudden contractions at the mid-channel section. The present numerical results were obtained using a two-dimensional finite-volume code which solves the governing equations in a vertical plane located at the lateral mid-point of the channel. The pressure field is obtained with the well-known SIMPLE algorithm. The hybrid scheme was employed for the discretization of convection in all transport equations. For modeling of the turbulence, a zonal low-Reynolds number k-ε model and the linear and non-linear low-Reynolds number k-ε models with the 'Yap' and 'NYP' length-scale correction terms have been employed. The main objective of present study is to examine the ability of the above turbulence models in the prediction of convective heat transfer in channels with sudden contraction at a mid-channel section. The results of this study show that a sudden contraction creates a relatively small recirculation bubble immediately downstream of the channel contraction. This separation bubble influences the distribution of local heat transfer coefficient and increases the heat transfer levels by a factor of three. Computational results indicate that all the turbulence models employed produce similar flow fields. The zonal k-ε model produces the wrong Nusselt number distribution by underpredicting heat transfer levels in the recirculation bubble and overpredicting them in the developing region. The linear low-Re k-ε model, on the other hand, returns the correct Nusselt number distribution in the recirculation region, although it somewhat overpredicts heat transfer levels in the developing region downstream of the separation bubble. The replacement of the 'Yap' term with the 'NYP' term in the linear low-Re k-ε model results in a more accurate local Nusselt number distribution. Moreover, the application of the non-linear k
Incorrectness of conventional one-dimensional parallel thermal resistance circuit model for two-dimensional circular composite pipes

International Nuclear Information System (INIS)

Wong, K.-L.; Hsien, T.-L.; Chen, W.-L.; Yu, S.-J.

2008-01-01

This study is to prove that two-dimensional steady state heat transfer problems of composite circular pipes cannot be appropriately solved by the conventional one-dimensional parallel thermal resistance circuits (PTRC) model because its interface temperatures are not unique. Thus, the PTRC model is definitely different from its conventional recognized analogy, parallel electrical resistance circuits (PERC) model, which has unique node electric voltages. Two typical composite circular pipe examples are solved by CFD software, and the numerical results are compared with those obtained by the PTRC model. This shows that the PTRC model generates large error. Thus, this conventional model, introduced in most heat transfer text books, cannot be applied to two-dimensional composite circular pipes. On the contrary, an alternative one-dimensional separately series thermal resistance circuit (SSTRC) model is proposed and applied to a two-dimensional composite circular pipe with isothermal boundaries, and acceptable results are returned

Composite heat transfer in a pipe with thermal radiation of two-dimensional propagation - in connection with the temperature rise in flowing medium upstream from heating section

International Nuclear Information System (INIS)

Echigo, R.; Hasegawa, S.; Kamiuto, K.

1975-01-01

An analytical procedure is presented for simultaneous convective and radiative heat transfer with a fully developed laminar flow in a pipe by taking account of the two-dimensional propagation of radiative transfer and also shows the numerical results on the temperature profiles and the heat-transfer characteristics. In order to solve the energy equation with two-dimensional radiative transfer the entire ranges of the temperature field have to be solved simultaneously both along the radial and flow directions. Moreover, the heat flux by thermal radiation emitted from the heating wall propagates upstream so that it is necessary to examine the temperature profiles of the flowing medium to a certain distance upstream from the entrance of the heating section. In this way in order to attempt to solve the governing equation numerically by a finite difference method the dimension of matrix becomes extremely large provided that a satisfactory validity of numerical calculation is required Consequently the band matrix method is used and the temperature profiles of the medium in both regions upstream and downstream from the entrance of the heating section are illustrated and the heat transfer results are discussed in some detail by comparing with those of the one-dimensional transfer of radiation.(auth)
Two-dimensional nonlinear transient heat transfer analysis of variable section pin fins

Energy Technology Data Exchange (ETDEWEB)

Malekzadeh, P. [Department of Mechanical Engineering, School of Engineering, Persian Gulf University, Boushehr 75168 (Iran); Rahideh, H. [Department of Chemical Engineering, School of Engineering, Persian Gulf University, Boushehr 75168 (Iran)

2009-04-15

The two-dimensional nonlinear transient heat transfer analysis of variable cross section pin-fins is studied using the incremental differential quadrature method (IDQM) as a simple, accurate, and computationally efficient numerical tool. The formulations are general so that it can easily be used for arbitrary continuously varying cross section pin fins with the spatial-temperature dependent thermal parameters. On all external surfaces of the pin fin, the convective-radiative condition is considered. The effects of two different types of boundary conditions at the base of pin fin are investigated: time and spatial dependent temperature, and the convection heat transfer. The thermal conductivity of the pin fin is assumed to vary as a linear function of the temperature. The accuracy of the method is demonstrated by comparing its results with those generated by finite difference method. It is shown that using few grid points, results in excellent agreements with those of FDM are obtained. Less computational efforts of the method with respect to finite difference method is shown. (author)
Numerical studies of heat transfer by simultaneous radiative-conduction and radiative-convection in a two dimensional semi-transparent medium

International Nuclear Information System (INIS)

Draoui, Abdeslam

1989-01-01

The works we present here are on numerical approaches of heat transfer coupling radiation-conduction and radiation-convection within semi-transparent two-dimensional medium. The first part deals with a review of equations of radiative transfer and introduces three numerical methods (Pl, P3, Hottel's zones) which enable one to solve this problem in a two-dimensional environment. After comparing the three methods in the case where radiation is the only mode of transfer, we introduce in the second chapter a study of the coupling of radiation with conduction. So, a fourth method is used to solve this problem. These comparisons lead us to various methods which enable us to show the interest of the spherical harmonics approximations. In the third part, the Pl approximation is kept because it is simple to use, moreover it enables us to introduce both the coupling of radiative transfers with laminar convective equations in a thermally driven two-dimensional cavity. The results show a significant influence of the radiative participation of the fluid on heat and dynamic transfer we met in this type of problem. (author) [fr
Three-dimensional numerical study of heat transfer enhancement in separated flows

Science.gov (United States)

Kumar, Saurav; Vengadesan, S.

2017-11-01

The flow separation appears in a wide range of heat transfer applications and causes poor heat transfer performance. It motivates the study of heat transfer enhancement in laminar as well as turbulent flows over a backward facing step by means of an adiabatic fin mounted on the top wall. Recently, we have studied steady, 2-D numerical simulations in laminar flow and investigated the effect of fin length, location, and orientation. It revealed that the addition of fin causes enhancement of heat transfer and it is very effective to control the flow and thermal behavior. The fin is most effective and sensitive when it is placed exactly above the step. A slight displacement of the fin in upstream of the step causes the complete change of flow and thermal behavior. Based on the obtained 2-D results it is interesting to investigate the side wall effect in three-dimensional simulations. The comparison of two-dimensional and three-dimensional numerical simulations with the available experimental results will be presented. Special attention has to be given to capture unsteadiness in the flow and thermal field.
Evaluation method for two-phase flow and heat transfer in a feed-water heater

International Nuclear Information System (INIS)

Takamori, Kazuhide; Minato, Akihiko

1993-01-01

A multidimensional analysis code for two-phase flow using a two-fluid model was improved by taking into consideration the condensation heat transfer, film thickness, and film velocity, in order to develop an evaluation method for two-phase flow and heat transfer in a feed-water heater. The following results were obtained by a two-dimensional analysis of a feed-water heater for a power plant. (1) In the model, the film flowed downward in laminar flow due to gravity, with droplet entrainment and deposition. For evaluation of the film thickness, Fujii's equation was used in order to account for forced convection of steam flow. (2) Based on the former experimental data, the droplet deposition coefficient and droplet entrainment rate of liquid film were determined. When the ratio at which the liquid film directly flowed from an upper heat transfer tube to a lower heat transfer tube was 0.7, the calculated total heat transfer rate agreed with the measured value of 130 MW. (3) At the upper region of a heat transfer tube bundle where film thickness was thin, and at the outer region of a heat transfer tube bundle where steam velocity was high, the heat transfer rate was large. (author)
A forced convective heat transfer model for two-phase hydrogen systems

International Nuclear Information System (INIS)

Pasch, J.; Anghaie, S.

2007-01-01

A consistent event in the use of hydrogen in nuclear thermal propulsion is film boiling, in which the wall heat is so large that liquid can not exist at the wall. Instead, vapor interfaces with the wall and liquid flows in the core of the duct. To better understand heat transfer under these conditions, a select set of hydrogen test data from these conditions are analyzed. This paper presents the results of an extensive literature search for film boiling heat transfer models. A representative cross-section of these models is then applied to the data. The heat transfer coefficient data were found difficult to predict and highly dependent upon the flow regime. Pre-critical heat flux correlations completely fail to predict the heat transfer of inverted film boiling conditions. Pool boiling models for inverted film boiling also are inappropriate. Current force convection models for inverted film boiling, while far better than the previous two classes of models, still generate large predictive errors. It is recommended that for the inverted annular film boiling flow regime the modified equilibrium bulk Dittus-Boelter model be used. For agitated inverted annular film boiling and dispersed film boiling regimes associated with positive equilibrium qualities, the Hendricks model should be used. (A.C.)
Two-dimensional model of coupled heat and moisture transport in frost-heaving soils

International Nuclear Information System (INIS)

Guymon, G.L.; Berg, R.L.; Hromadka, T.V.

1984-01-01

A two-dimensional model of coupled heat and moisture flow in frost-heaving soils is developed based upon well known equations of heat and moisture flow in soils. Numerical solution is by the nodal domain integration method which includes the integrated finite difference and the Galerkin finite element methods. Solution of the phase change process is approximated by an isothermal approach and phenomenological equations are assumed for processes occurring in freezing or thawing zones. The model has been verified against experimental one-dimensional freezing soil column data and experimental two-dimensional soil thawing tank data as well as two-dimensional soil seepage data. The model has been applied to several simple but useful field problems such as roadway embankment freezing and frost heaving
Two-dimensional numerical modeling and solution of convection heat transfer in turbulent He II

Science.gov (United States)

Zhang, Burt X.; Karr, Gerald R.

1991-01-01

Numerical schemes are employed to investigate heat transfer in the turbulent flow of He II. FEM is used to solve a set of equations governing the heat transfer and hydrodynamics of He II in the turbulent regime. Numerical results are compared with available experimental data and interpreted in terms of conventional heat transfer parameters such as the Prandtl number, the Peclet number, and the Nusselt number. Within the prescribed Reynolds number domain, the Gorter-Mellink thermal counterflow mechanism becomes less significant, and He II acts like an ordinary fluid. The convection heat transfer characteristics of He II in the highly turbulent regime can be successfully described by using the conventional turbulence and heat transfer theories.
Effect of the Presence of Semi-circular Cylinders on Heat Transfer From Heat Sources Placed in Two Dimensional Channel

Directory of Open Access Journals (Sweden)

Ahmed W. Mustava

2013-04-01

Full Text Available The effect of a semi-circular cylinders in a two dimensional channel on heat transfer by forced convection from two heat sources with a constant temperature has been studied numerically. Each channel contains two heat sources; one on the upper surface of the channel and the other on the lower surface of the channel. There is semi-circular cylinder under the source in upper surface and there is semi-circular cylinder above the source in lower surface. The location of the second heat source with its semi-cylinder has been changed and keeps the first source with its semi- cylinder at the same location. The flow and temperature field are studied numerically with different values of Reynolds numbers and for different spacing between the centers of the semi-cylinders. The laminar flow field is analyzed numerically by solving the steady forms of the two-dimensional incompressible Navier- Stokes and energy equations. The Cartesian velocity components and pressure on a collocated (non-staggered grid are used as dependent variables in the momentum equations, which discretized by finite volume method, body fitted coordinates are used to represent the complex channel geometry accurately, and grid generation technique based on elliptic partial differential equations is employed. SIMPLE algorithm is used to adjust the velocity field to satisfy the conservation of mass. The range of Reynolds number is (Re= 100 – 800 and the range of the spacing between the semi-cylinders is(1-4 and the Prandtl number is 0.7.The results showed that increasing the spacing between the semi-cylinders increases the average of Nusselt number of the first heat source for all Reynolds numbers. As well as the results show that the best case among the cases studied to enhance the heat transfer is when the second heat source and its semi-cylinder located on at the distance (S=1.5 from the first half of the cylinder and the Reynolds number is greater than (Re ≥ 400 because of the
Separate effects tests for GOTHIC condensation and evaporative heat transfer models

International Nuclear Information System (INIS)

George, T.L.; Singh, A.

1994-01-01

The GOTHIC computer program, under development at EPRI/NAI, is a general purpose thermal hydraulics computer program for design, licensing, safety and operating analysis of nuclear containments and other confinement buildings. The code solves a nine equation model for three dimensional multiphase flow with separate mass, momentum and energy equations for vapor, liquid and drop phases. The vapor phase can be a gas mixture of steam and non-condensing gases. The phase balance equations are coupled by mechanistic and empirical models for interface mass, energy and momentum transfer that cover the entire flow regime from bubbly flow to film/drop flow. A variety of heat transfer correlations are available to model the fluid coupling to active and passive solid conductors. This paper focuses on the application of GOTHIC to two separate effects tests; condensation heat transfer on a vertical flat plate with varying bulk velocity, steam concentration and temperature, and evaporative heat transfer from a hot pool to a dry (superheated) atmosphere. Comparisons with experimental data is included for both tests. Results show the validity of two condensation heat transfer correlations as incorporated into GOTHIC and the interfacial heat and mass transfer models for the range of the experimental test conditions. Comparisons are also made for lumped versus multidimensional modeling for buoyancy controlled flow with evaporative heat transfer. (author). 13 refs., 1 tab., 10 figs
Separate effects tests for GOTHIC condensation and evaporative heat transfer models

International Nuclear Information System (INIS)

George, T.L.; Singh, A.

1996-01-01

The GOTHIC computer program, under development at NAI for EPRI, is a general purpose thermal hydraulics computer program for design, licensing, safety and operating analysis of nuclear containments and other confinement buildings. The code solves a nine-equation model for three-dimensional multiphase flow with separate mass, momentum and energy equations for vapor, liquid and drop phases. The vapor phase can be a gas mixture of steam and non-condensing gases. The phase balance equations are coupled by mechanistic and empirical models for interface mass, energy and momentum transfer that cover the entire flow regime from bubbly flow to film-drop flow. A variety of heat transfer correlations are available to model the fluid coupling to active and passive solid conductors. This paper focuses on the application of GOTHIC to two separate effects tests: condensation heat transfer on a vertical flat plate with varying bulk velocity, steam concentration and temperature, and evaporative heat transfer from a hot pool to a dry (superheated) atmosphere. Comparisons with experimental data are included for both tests. Results show the validity of two condensation heat transfer correlations as incorporated into GOTHIC and the interfacial heat and mass transfer models for the range of the experimental test conditions. Comparisons are also made for lumped vs. multidimensional modeling for buoyancy-controlled flow with evaporative heat transfer. (orig.)
Numerical simulation of gas-liquid two-phase flow behavior with condensation heat transfer

International Nuclear Information System (INIS)

Takamori, Kazuhide; Murase, Michio; Baba, Yoshikazu; Aihara, Tsuyoshi.

1995-01-01

In this study, condensation heat transfer experiments were performed in order to verify a condensation heat transfer model coupled with a three-dimensional two-phase flow analysis. In the heat transfer model, the liquid film flow rate on the heat transfer tubes was calculated by a mass balance equation and the liquid film thickness was calculated from the liquid film flow rate using Nusselt's laminar flow model and Fujii's equation for steam velocity effect. In the experiments, 112 horizontal staggered tubes with an outer diameter of 16 mm and length of 0.55 m were used. Steam and spray water were supplied to the test section, and inlet quality was controlled by the spray water flow rate. The temperature was 100degC and the pressure was 0.1 MPa. The overall heat transfer coefficients were measured for inlet quality of 13-100%. From parameter calculations for the falling liquid film ratio from the upper tubes to the lower tubes, the calculated overall heat transfer coefficients agreed with the data to within ±5% at the falling liquid film ratio of 0.7. (author)
Convective heat transfer from rough surfaces with two-dimensional ribs - transitional and laminar flow

International Nuclear Information System (INIS)

Dalle Donne, M.; Meyer, L.

1978-01-01

Measurements of friction factor and heat transfer coefficients for two rods of 18.9 mm 0.D. with two-dimensional roughness, each in two different outer smooth tubes have been performed in turbulent and laminar flow. The turbulent flow results indicate that the flow was not thermally fully established, the isothermal data however agree reasonably well with our previously obtained general correlation. Laminar flow results can be correlated best when the Reynolds and Greatz numbers are evaluated at the temperature average between the temperature of the inner rod surface and of the outer smooth surface of the annulus, the average being weighted over the two surfaces. (orig.) [de
Modelling floor heating systems using a validated two-dimensional ground coupled numerical model

DEFF Research Database (Denmark)

Weitzmann, Peter; Kragh, Jesper; Roots, Peter

2005-01-01

This paper presents a two-dimensional simulation model of the heat losses and tempera-tures in a slab on grade floor with floor heating which is able to dynamically model the floor heating system. The aim of this work is to be able to model, in detail, the influence from the floor construction...... the floor. This model can be used to design energy efficient houses with floor heating focusing on the heat loss through the floor construction and foundation. It is found that it is impor-tant to model the dynamics of the floor heating system to find the correct heat loss to the ground, and further......, that the foundation has a large impact on the energy consumption of buildings heated by floor heating. Consequently, this detail should be in focus when designing houses with floor heating....
CFD modelling of convective heat transfer from a window with adjacent venetian blinds

Energy Technology Data Exchange (ETDEWEB)

Marjanovic, L. [Belgrade Univ., Belgrade (Yugoslavia). Faculty of Mechanical Engineering]|[DeMontfort Univ. (United Kingdom). Inst. of Energy and Sustainable Development; Cook, M; Hanby, V.; Rees, S. [DeMontfort Univ. (United Kingdom). Inst. of Energy and Sustainable Development

2005-07-01

There is a limited amount of 3-dimensional modeling information on the performance of glazing systems with blinds. Two-dimensional flow modeling has indicated that 1-dimensional heat transfer can lead to invalid results where 2- and 3-dimensional effects are present. In this study, a 3-dimensional numerical solution was obtained on the effect of a venetian blind on the conjugate heat transfer from an indoor window glazing system. The solution was obtained for the coupled laminar free convection and radiation heat transfer problem, including conduction along the blind slats. Continuity, momentum and energy equations for buoyant flow were solved using Computational Fluid Dynamics (CFD) software. Grey diffuse radiation exchange between the window, blind and air were considered using the Monte Carlo method. All thermophysical properties of air were assumed to be constant with the exception of density, which was modeled using the Bousinesq approximation. Both winter and summer conditions were considered. In the computational domain, the window represented an isothermal type boundary condition with no slip. The height of the domain was extended beyond the blinds to allow for inflow and outflow regions. Fluid was allowed to entrain into the domain at an ambient temperature in a direction perpendicular to the window. The results indicated that heat transfer between window and indoor air is influenced both quantitatively and qualitatively by the presence of an aluminium venetian blind, and that the cellular flow between the blind slats can have a significant effect on the convective heat transfer from the window surface that is more fully recognized and analyzed in 3 dimensions. refs., 2 tabs., 13 figs.
Two-dimensional heat flow apparatus

Science.gov (United States)

McDougall, Patrick; Ayars, Eric

2014-06-01

We have created an apparatus to quantitatively measure two-dimensional heat flow in a metal plate using a grid of temperature sensors read by a microcontroller. Real-time temperature data are collected from the microcontroller by a computer for comparison with a computational model of the heat equation. The microcontroller-based sensor array allows previously unavailable levels of precision at very low cost, and the combination of measurement and modeling makes for an excellent apparatus for the advanced undergraduate laboratory course.
The Mathematical Modelling of Heat Transfer in Electrical Cables

Directory of Open Access Journals (Sweden)

Bugajev Andrej

2014-05-01

Full Text Available This paper describes a mathematical modelling approach for heat transfer calculations in underground high voltage and middle voltage electrical power cables. First of the all typical layout of the cable in the sand or soil is described. Then numerical algorithms are targeted to the two-dimensional mathematical models of transient heat transfer. Finite Volume Method is suggested for calculations. Different strategies of nonorthogonality error elimination are considered. Acute triangles meshes were applied in two-dimensional domain to eliminate this error. Adaptive mesh is also tried. For calculations OpenFOAM open source software which uses Finite Volume Method is applied. To generate acute triangles meshes aCute library is used. The efficiency of the proposed approach is analyzed. The results show that the second order of convergence or close to that is achieved (in terms of sizes of finite volumes. Also it is shown that standard strategy, used by OpenFOAM is less efficient than the proposed approach. Finally it is concluded that for solving real problem a spatial adaptive mesh is essential and adaptive time steps also may be needed.
Heat transfer modelling of two-phase bubbles swarm condensing in three - phase direct - contact condenser

Directory of Open Access Journals (Sweden)

Mahood Hameed B.

2016-01-01

Full Text Available An analytical model for the convective heat transfer coefficient and the two-phase bubble size of a three-phase direct contact heat exchanger was developed. Until the present, there has only been a theoretical model available that deals with a single two-phase bubble and a bubble train condensation in an immiscible liquid. However, to understand the actual heat transfer process within the three-phase direct contact condenser, characteristic models are required. A quasi - steady energy equation in a spherical coordinate system with a potential flow assumption and a cell model configuration has been simplified and solved analytically. The convective heat transfer in terms of Nu number has been derived, and it was found to be a function to Pe number and a system void fraction. In addition, the two-phase bubble size relates to the system void fraction and has been developed by solving a simple energy balance equation and using the derived convective heat transfer coefficient expression. Furthermore, the model correlates well with previous experimental data and theoretical results.
Analytical method for steady state heat transfer in two-dimensional porous media

Energy Technology Data Exchange (ETDEWEB)

Siegal, R.; Goldstein, M.E.

1970-07-01

A general technique has been devised for obtaining exact solutions for the heat transfer behavior of a 2- dimensional porous cooled medium. Fluid flows through the porous medium from a reservoir at constant pressure and temperature to a second reservoir at a lower pressure. For the type of flow involved, the surfaces of the porous region that are each at constant pressure are boundaries of constant velocity potential. This fact is used to map the porous region into a strip bounded by parallel potential lines in a complex potential plane. The energy equation, derived by assuming the local matrix and fluid temperatures are equal, is transformed into a separable equation when its independent variables are changed to the coordinates of the potential plane. This allows the general solution for the temperature distribution to be found in the potential plane. The solution is then mapped into the physical plane to yield the heat transfer characteristics of the porous region. An example problem of a porous wall having a step in thickness and a specified surface temperature or heat flux is worked out in detail.
Numerical Modeling of Ablation Heat Transfer

Science.gov (United States)

Ewing, Mark E.; Laker, Travis S.; Walker, David T.

2013-01-01

A unique numerical method has been developed for solving one-dimensional ablation heat transfer problems. This paper provides a comprehensive description of the method, along with detailed derivations of the governing equations. This methodology supports solutions for traditional ablation modeling including such effects as heat transfer, material decomposition, pyrolysis gas permeation and heat exchange, and thermochemical surface erosion. The numerical scheme utilizes a control-volume approach with a variable grid to account for surface movement. This method directly supports implementation of nontraditional models such as material swelling and mechanical erosion, extending capabilities for modeling complex ablation phenomena. Verifications of the numerical implementation are provided using analytical solutions, code comparisons, and the method of manufactured solutions. These verifications are used to demonstrate solution accuracy and proper error convergence rates. A simple demonstration of a mechanical erosion (spallation) model is also provided to illustrate the unique capabilities of the method.

A two-dimensional model with three regions for the reflooding study

International Nuclear Information System (INIS)

Motta, A.M.T.; Kinrys, S.; Roberty, N.C.; Carmo, E.G.D. do; Oliveira, L.F.S. de

1982-01-01

A two-dimensional semi-analytical model, with three heat transfer regions is described for the calculation of flood ratio, the length of quenching front and the temperature distribution in the cladding. (E.G.) [pt
A two-dimensional model with three regions for the reflooding study

International Nuclear Information System (INIS)

Motta, A.M.T.; Kinrys, S.; Roberty, N.C.; Carmo, E.G.D. do; Oliveira, L.F.S. de.

1983-02-01

A two-dimensional semi-analytical model, with three heat transfer regions is described for the calculation of flood ratio, the lenght of quenching front and the temperature distribution in the cladding. (E.G.) [pt
Two-dimensional finite element heat transfer model of softwood. Part III, Effect of moisture content on thermal conductivity

Science.gov (United States)

Hongmei Gu; John F. Hunt

2007-01-01

The anisotropy of wood creates a complex problem for solving heat and mass transfer problems that require analyses be based on fundamental material properties of the wood structure. Most heat transfer models for softwood use average thermal properties across either the radial or tangential direction and do not differentiate the effects of cellular alignment or...
Heat and Mass Transfer Model in Freeze-Dried Medium

Science.gov (United States)

Alfat, Sayahdin; Purqon, Acep

2017-07-01

There are big problems in agriculture sector every year. One of the major problems is abundance of agricultural product during the peak of harvest season that is not matched by an increase in demand of agricultural product by consumers, this causes a wasted agricultural products. Alternative way was food preservation by freeze dried method. This method was already using heat transfer through conduction and convection to reduce water quality in the food. The main objective of this research was to design a model heat and mass transfer in freeze-dried medium. We had two steps in this research, the first step was design of medium as the heat injection site and the second was simulate heat and mass transfer of the product. During simulation process, we use physical property of some agriculture product. The result will show how temperature and moisture distribution every second. The method of research use finite element method (FEM) and will be illustrated in three dimensional.
Heat Transfer Modelling of Glass Media within TPV Systems

Science.gov (United States)

Bauer, Thomas; Forbes, Ian; Penlington, Roger; Pearsall, Nicola

2004-11-01

Understanding and optimisation of heat transfer, and in particular radiative heat transfer in terms of spectral, angular and spatial radiation distributions is important to achieve high system efficiencies and high electrical power densities for thermophtovoltaics (TPV). This work reviews heat transfer models and uses the Discrete Ordinates method. Firstly one-dimensional heat transfer in fused silica (quartz glass) shields was examined for the common arrangement, radiator-air-glass-air-PV cell. It has been concluded that an alternative arrangement radiator-glass-air-PV cell with increased thickness of fused silica should have advantages in terms of improved transmission of convertible radiation and enhanced suppression of non-convertible radiation.
Heat transfer from two-side heated helical channels

International Nuclear Information System (INIS)

Shimonis, V.; Ragaishis, V.; Poshkas, P.

1995-01-01

Experimental results are presented on the heat transfer from two-side heated helical channels to gas (air) flows. The study covered six configurations and wide ranges of geometrical (D/h=5.5 to 84.2) and performance (Re=10 3 to 2*10 5 ) parameters. Under the influence of Re and of the channel curvature, the heat transfer from both the convex and the concave surfaces for two-side heating (q w1 ≅ q w2 ) is augmented by 20-30% over one-side heating. Improved relations to predict the critical values of Reynolds Re cr1 and Re cr2 are suggested. They enable more exact predictions of the heat transfer from convex surface in transient flows for one-side heating. The relation for annular channels is suggested for the turbulent heat transfer from the convex and concave surfaces of two-side heated helical channels. It can be adapted by introducing earlier expresions for one-side heated helical channels. (author). 6 refs., 2 tabs., 3 figs
Three-Dimensional Heat Transfer Analysis of Metal Fasteners in Roofing Assemblies

Directory of Open Access Journals (Sweden)

Manan Singh

2016-11-01

Full Text Available Heat transfer analysis was performed on typical roofing assemblies using HEAT3, a three-dimensional heat transfer analysis software. The difference in heat transferred through the roofing assemblies considered is compared between two cases—without any steel fasteners and with steel fasteners. In the latter case, the metal roofing fasteners were arranged as per Factor Mutual Global (FMG approvals, in the field, perimeter, and corner zones of the roof. The temperature conditions used for the analysis represented summer and winter conditions for three separate Climate Zones (CZ namely Climate Zone 2 or CZ2 represented by Orlando, FL; CZ3 represented by Atlanta, GA; and CZ6 zone represented by St. Paul, MN. In all the climatic conditions, higher energy transfer was observed with increase in the number of metal fasteners attributed to high thermal conductivity of metals as compared to the insulation and other materials used in the roofing assembly. This difference in heat loss was also quantified in the form of percentage change in the overall or effective insulation of the roofing assembly for better understanding of the practical aspects. Besides, a comparison of 2D heat transfer analysis (using THERM software and 3D analysis using HEAT3 is also discussed proving the relevance of 3D over 2D heat transfer analysis.
Modelling heat transfer during flow through a random packed bed of spheres

Science.gov (United States)

Burström, Per E. C.; Frishfelds, Vilnis; Ljung, Anna-Lena; Lundström, T. Staffan; Marjavaara, B. Daniel

2018-04-01

Heat transfer in a random packed bed of monosized iron ore pellets is modelled with both a discrete three-dimensional system of spheres and a continuous Computational Fluid Dynamics (CFD) model. Results show a good agreement between the two models for average values over a cross section of the bed for an even temperature profiles at the inlet. The advantage with the discrete model is that it captures local effects such as decreased heat transfer in sections with low speed. The disadvantage is that it is computationally heavy for larger systems of pellets. If averaged values are sufficient, the CFD model is an attractive alternative that is easy to couple to the physics up- and downstream the packed bed. The good agreement between the discrete and continuous model furthermore indicates that the discrete model may be used also on non-Stokian flow in the transitional region between laminar and turbulent flow, as turbulent effects show little influence of the overall heat transfer rates in the continuous model.
Heat transfer in a one-dimensional mixed convection loop

International Nuclear Information System (INIS)

Kim, Min Joon; Lee, Yong Bum; Kim, Yong Kyun; Kim, Jong Man; Nam, Ho Yun

1999-01-01

Effects of non-uniform heating in the core and additional forced circulation during decay heat removal operation are studied with a simplified mixed convection loop. The heat transfer coefficient is calculated analytically and measured experimentally. The analytic solution obtained from a one-dimensional heat equation is found to agree well with the experimental results. The effects of the non-uniform heating and the forced circulation are discussed
Two and dimensional heat analysis inside a high pressure electrical discharge tube

International Nuclear Information System (INIS)

Aghanajafi, C.; Dehghani, A. R.; Fallah Abbasi, M.

2005-01-01

This article represents the heat transfer analysis for a horizontal high pressure mercury steam tube. To get a more realistic numerical simulation, heat radiation at different wavelength width bands, has been used besides convection and conduction heat transfer. The analysis for different gases with different pressure in two and three dimensional cases has been investigated and the results compared with empirical and semi empirical values. The effect of the environmental temperature on the arc tube temperature is also studied
Triangular node for Transmission-Line Modeling (TLM) applied to bio-heat transfer.

Science.gov (United States)

Milan, Hugo F M; Gebremedhin, Kifle G

2016-12-01

Transmission-Line Modeling (TLM) is a numerical method used to solve complex and time-domain bio-heat transfer problems. In TLM, rectangles are used to discretize two-dimensional problems. The drawback in using rectangular shapes is that instead of refining only the domain of interest, a large additional domain will also be refined in the x and y axes, which results in increased computational time and memory space. In this paper, we developed a triangular node for TLM applied to bio-heat transfer that does not have the drawback associated with the rectangular nodes. The model includes heat source, blood perfusion (advection), boundary conditions and initial conditions. The boundary conditions could be adiabatic, temperature, heat flux, or convection. A matrix equation for TLM, which simplifies the solution of time-domain problems or solves steady-state problems, was also developed. The predicted results were compared against results obtained from the solution of a simplified two-dimensional problem, and they agreed within 1% for a mesh length of triangular faces of 59µm±9µm (mean±standard deviation) and a time step of 1ms. Copyright Â© 2016 Elsevier Ltd. All rights reserved.
Modeling of quench front progression and heat transfer by radiation during reflooding of a tubular test section

International Nuclear Information System (INIS)

Clement, P.; Deruaz, R.

1976-01-01

Heat transfer modeling is presented in the scope of emergency core cooling. The rewetting of a hot dry wall during reflooding is a conduction-controlled phenomenon described by a model of heat-transfer coefficient. Upstream of the quench front, a two-dimensional approach involving both axial and transverse (or radial) heat conduction is discussed in view of thick walls, high quench front velocities and nucleate boiling. Downstream of the quench-front, high wall temperatures are reached so that a thermal radiation model is required to separate the different mechanisms of heat transfer. An attempt is made to consider radiation between walls, water droplets and vapor, with scattering emission and absorption of the two phases
Study of instantaneous unsteady heat transfer in a rapid compression-expansion machine using zero dimensional k- ε turbulence model

International Nuclear Information System (INIS)

Bakhshan, Y.; Karim, G. A.; Mansouri, S. H.

2003-01-01

In this investigation, the instantaneous unsteady heat transfer within a pneumatically driven rapid compression-expansion machine that offers simple, well-controlled and known boundary conditions was studied. Values of the instantaneous apparent overall heat flux from the cylinder gas to the wall surfaces were calculated using a thermodynamics analysis of the experimentally measured pressure and volume temporal development. Corresponding heat flux values were also calculated through the application of a zero-dimensional k- ε turbulence model the characteristic velocity is a contribution of turbulence kinetic energy, mean kinetic energy of charged air into cylinder and piston motion for the calculation of Reynolds, Nusselt and Prandtl numbers. Comparison of the zero-dimensional k- ε turbulence model prediction with experimental data shows good agreement for all compression ratios
Evaluation of Interfacial Heat Transfer Models for Flashing Flow with Two-Fluid CFD

Directory of Open Access Journals (Sweden)

Yixiang Liao

2018-06-01

Full Text Available The complexity of flashing flows is increased vastly by the interphase heat transfer as well as its coupling with mass and momentum transfers. A reliable heat transfer coefficient is the key in the modelling of such kinds of flows with the two-fluid model. An extensive literature survey on computational modelling of flashing flows has been given in previous work. The present work is aimed at giving a brief review on available theories and correlations for the estimation of interphase heat transfer coefficient, and evaluating them quantitatively based on computational fluid dynamics simulations of bubble growth in superheated liquid. The comparison of predictions for bubble growth rate obtained by using different correlations with the experimental as well as direct numerical simulation data reveals that the performance of the correlations is dependent on the Jakob number and Reynolds number. No generally applicable correlations are available. Both conduction and convection are important in cases of bubble rising and translating in stagnant liquid at high Jakob numbers. The correlations combining the analytical solution for heat diffusion and the theoretical relation for potential flow give the best agreement.
Numerical analysis of air flow, heat transfer, moisture transport and thermal comfort in a room heated by two-panel radiators

Energy Technology Data Exchange (ETDEWEB)

Sevilgen, Goekhan; Kilic, Muhsin [Uludag University, Faculty of Engineering and Architecture, Department of Mechanical Engineering, TR-16059 Bursa (Turkey)

2011-01-15

A three-dimensional steady-state numerical analysis was performed in a room heated by two-panel radiators. A virtual sitting manikin with real dimensions and physiological shape was added to the model of the room, and it was assumed that the manikin surfaces were subjected to constant temperature. Two different heat transfer coefficients for the outer wall and for the window were considered. Heat interactions between the human body surfaces and the room environment, the air flow, the temperature, the humidity, and the local heat transfer characteristics of the manikin and the room surfaces were computed numerically under different environmental conditions. Comparisons of the results are presented and discussed. The results show that energy consumption can be significantly reduced while increasing the thermal comfort by using better-insulated outer wall materials and windows. (author)
Solution to Two-Dimensional Steady Inverse Heat Transfer Problems with Interior Heat Source Based on the Conjugate Gradient Method

Directory of Open Access Journals (Sweden)

Shoubin Wang

2017-01-01

Full Text Available The compound variable inverse problem which comprises boundary temperature distribution and surface convective heat conduction coefficient of two-dimensional steady heat transfer system with inner heat source is studied in this paper applying the conjugate gradient method. The introduction of complex variable to solve the gradient matrix of the objective function obtains more precise inversion results. This paper applies boundary element method to solve the temperature calculation of discrete points in forward problems. The factors of measuring error and the number of measuring points zero error which impact the measurement result are discussed and compared with L-MM method in inverse problems. Instance calculation and analysis prove that the method applied in this paper still has good effectiveness and accuracy even if measurement error exists and the boundary measurement points’ number is reduced. The comparison indicates that the influence of error on the inversion solution can be minimized effectively using this method.
Subcooled boiling heat transfer on a finned surface

International Nuclear Information System (INIS)

Kowalski, J.E.; Tran, V.T.; Mills, P.J.

1992-01-01

Experimental and numerical studies have been performed to determine the heat transfer coefficients from a finned cylindrical surface to subcooled boiling water. The heat transfer rates were measured in an annular test section consisting of an electrically heated fuel element simulator (FES) with eight longitudinal, rectangular fins enclosed in a glass tube. A two-dimensional finite-element heat transfer model using the Galerkin method was employed to determine the heat transfer coefficients along the periphery of the FES surface. An empirical correlation was developed to predict the heat transfer coefficients during subcooled boiling. The correlation agrees well with the measured data. (6 figures) (Author)
Modeling microscale heat transfer using Calore.

Energy Technology Data Exchange (ETDEWEB)

Gallis, Michail A.; Rader, Daniel John; Wong, Chung-Nin Channy; Bainbridge, Bruce L.; Torczynski, John Robert; Piekos, Edward Stanley

2005-09-01

Modeling microscale heat transfer with the computational-heat-transfer code Calore is discussed. Microscale heat transfer problems differ from their macroscopic counterparts in that conductive heat transfer in both solid and gaseous materials may have important noncontinuum effects. In a solid material, three noncontinuum effects are considered: ballistic transport of phonons across a thin film, scattering of phonons from surface roughness at a gas-solid interface, and scattering of phonons from grain boundaries within the solid material. These processes are modeled for polycrystalline silicon, and the thermal-conductivity values predicted by these models are compared to experimental data. In a gaseous material, two noncontinuum effects are considered: ballistic transport of gas molecules across a thin gap and accommodation of gas molecules to solid conditions when reflecting from a solid surface. These processes are modeled for arbitrary gases by allowing the gas and solid temperatures across a gas-solid interface to differ: a finite heat transfer coefficient (contact conductance) is imposed at the gas-solid interface so that the temperature difference is proportional to the normal heat flux. In this approach, the behavior of gas in the bulk is not changed from behavior observed under macroscopic conditions. These models are implemented in Calore as user subroutines. The user subroutines reside within Sandia's Source Forge server, where they undergo version control and regression testing and are available to analysts needing these capabilities. A Calore simulation is presented that exercises these models for a heated microbeam separated from an ambient-temperature substrate by a thin gas-filled gap. Failure to use the noncontinuum heat transfer models for the solid and the gas causes the maximum temperature of the microbeam to be significantly underpredicted.
Experiment of flow regime map and local condensing heat transfer coefficients inside three dimensional inner microfin tubes

Science.gov (United States)

Du, Yang; Xin, Ming Dao

1999-03-01

This paper developed a new type of three dimensional inner microfin tube. The experimental results of the flow patterns for the horizontal condensation inside these tubes are reported in the paper. The flow patterns for the horizontal condensation inside the new made tubes are divided into annular flow, stratified flow and intermittent flow within the test conditions. The experiments of the local heat transfer coefficients for the different flow patterns have been systematically carried out. The experiments of the local heat transfer coefficients changing with the vapor dryness fraction have also been carried out. As compared with the heat transfer coefficients of the two dimensional inner microfin tubes, those of the three dimensional inner microfin tubes increase 47-127% for the annular flow region, 38-183% for the stratified flow and 15-75% for the intermittent flow, respectively. The enhancement factor of the local heat transfer coefficients is from 1.8-6.9 for the vapor dryness fraction from 0.05 to 1.
Condensation heat transfer of a feed-water heater and improvement of its performance

International Nuclear Information System (INIS)

Takamori, Kazuhide; Murase, Michio; Baba, Yoshikazu; Aihara, Tsuyoshi

1995-01-01

In this study, a condensation heat transfer model, coupled with a three-dimensional two-phase flow analysis, was developed. In the heat transfer model, the liquid film flow rate on the heat transfer tubes was calculated by a mass balance equation and the liquid film thickness was calculated from the liquid film flow rate using Nusselt's laminar flow model and Fujii's equation for the steam velocity effect. The model was verified by condensation heat transfer experiments. In the experiments, 112 horizontal, staggered tubes with an outer diameter of 16mm and length of 0.55m were used. The calculated over-all heat transfer coefficients agreed with the data within ±5% under the inlet quality conditions of 13-100%. Based on a three-dimensional two-phase flow analysis, an improved feed-water heater with support plates, which have flow holes between the upper and lower tube bundles, was designed. The total heat exchange capacity of the improved feed-water heater increased about 6%. (author)

A three-dimensional analyses of fluid flow and heat transfer for moderator integrity assessment in PHWR

International Nuclear Information System (INIS)

Bang, K. H.; Lee, J. Y.; Yoo, S. O.; Kim, M. W.; Kim, H. J.

2002-01-01

Three-dimensional analyses of fluid flow and heat transfer has been performed in this study. The simulation of SPEL experimental work and comparison with experimental data has been carried out to verify the analyses models. Moreover, to verify the CANDU-6 reactor type, analyses of fluid flow and heat transfer in the calandria under the condition of steady state has been performed using FLUENT code, which is the conventional code for a three-dimensional analyses of fluid flow and heat transfer for moderator integrity assessment in PHWR thermal-hydraulics. It is found that the maximum temperature in the moderator is 347K (74 ), so that the moderator has the enough subcoolability to ensure the integrity of pressure tube during LOCA conditions
HPTAM, a two-dimensional Heat Pipe Transient Analysis Model, including the startup from a frozen state

Science.gov (United States)

Tournier, Jean-Michel; El-Genk, Mohamed S.

1995-01-01

A two-dimensional Heat Pipe Transient Analysis Model, 'HPTAM,' was developed to simulate the transient operation of fully-thawed heat pipes and the startup of heat pipes from a frozen state. The model incorporates: (a) sublimation and resolidification of working fluid; (b) melting and freezing of the working fluid in the porous wick; (c) evaporation of thawed working fluid and condensation as a thin liquid film on a frozen substrate; (d) free-molecule, transition, and continuum vapor flow regimes, using the Dusty Gas Model; (e) liquid flow and heat transfer in the porous wick; and (f) thermal and hydrodynamic couplings of phases at their respective interfaces. HPTAM predicts the radius of curvature of the liquid meniscus at the liquid-vapor interface and the radial location of the working fluid level (liquid or solid) in the wick. It also includes the transverse momentum jump condition (capillary relationship of Pascal) at the liquid-vapor interface and geometrically relates the radius of curvature of the liquid meniscus to the volume fraction of vapor in the wick. The present model predicts the capillary limit and partial liquid recess (dryout) in the evaporator wick, and incorporates a liquid pooling submodel, which simulates accumulation of the excess liquid in the vapor core at the condenser end.
Heat transfer entropy resistance for the analyses of two-stream heat exchangers and two-stream heat exchanger networks

International Nuclear Information System (INIS)

Cheng, XueTao; Liang, XinGang

2013-01-01

The entropy generation minimization method is often used to analyze heat transfer processes from the thermodynamic viewpoint. In this paper, we analyze common heat transfer processes with the concept of entropy generation, and propose the concept of heat transfer entropy resistance. It is found that smaller heat transfer entropy resistance leads to smaller equivalent thermodynamic force difference with prescribed heat transfer rate and larger heat transfer rate with prescribed equivalent thermodynamic force difference. With the concept of heat transfer entropy resistance, the performance of two-stream heat exchangers (THEs) and two-stream heat exchanger networks (THENs) is analyzed. For the cases discussed in this paper, it is found that smaller heat transfer entropy resistance always leads to better heat transfer performance for THEs and THENs, while smaller values of the entropy generation, entropy generation numbers and revised entropy generation number do not always. -- Highlights: • The concept of entropy resistance is defined. • The minimum entropy resistance principle is developed. • Smaller entropy resistance leads to better heat transfer
CFD modeling of heat transfer performance of MgO-water nanofluid under turbulent flow

Directory of Open Access Journals (Sweden)

Reza Davarnejad

2015-12-01

Full Text Available In this paper, Computational fluid dynamics (CFD modeling of turbulent heat transfer behavior of Magnesium Oxide-water nanofluid in a circular tube was studied. The modeling was two dimensional under k–ε turbulence model. The base fluid was pure water and the volume fraction of nanoparticles in the base fluid was 0.0625%, 0.125%, 0.25%, 0.5% and 1%. The applied Reynolds number range was 3000–19000. Three individual models including single phase, Volume of Fluid (VOF and mixture were used. The results showed that the simulated data were in good agreement with the experimental ones available in the literature. According to the experimental work (literature and simulation (this research, Nusselt number (Nu increased with increasing the volume fraction of nanofluid. However friction factor of nanofluid increased but its effect was ignorable compared with the Nu on heat transfer increment. It was concluded that two phase models were more accurate than the others for heat transfer prediction particularly in the higher volume fractions of nanoparticle. The average deviation from experimental data for single phase model was about 11% whereas it was around 2% for two phase models.
Heat transfer analysis of parabolic trough solar receiver

International Nuclear Information System (INIS)

Padilla, Ricardo Vasquez; Demirkaya, Gokmen; Goswami, D. Yogi; Stefanakos, Elias; Rahman, Muhammad M.

2011-01-01

Highlights: → In this paper a detailed one dimensional numerical heat transfer analysis of a PTC is performed. → The receiver and envelope were divided into several segments and mass and energy balance were applied in each segment. → Improvements either in the heat transfer correlations or radiative heat transfer analysis are presented. → The proposed heat transfer model was validated with experimental data obtained from Sandia National Laboratory. → Our results showed a better agreement with experimental data compared to other models. -- Abstract: Solar Parabolic Trough Collectors (PTCs) are currently used for the production of electricity and applications with relatively higher temperatures. A heat transfer fluid circulates through a metal tube (receiver) with an external selective surface that absorbs solar radiation reflected from the mirror surfaces of the PTC. In order to reduce the heat losses, the receiver is covered by an envelope and the enclosure is usually kept under vacuum pressure. The heat transfer and optical analysis of the PTC is essential to optimize and understand its performance under different operating conditions. In this paper a detailed one dimensional numerical heat transfer analysis of a PTC is performed. The receiver and envelope were divided into several segments and mass and energy balance were applied in each segment. Improvements either in the heat transfer correlations or radiative heat transfer analysis are presented as well. The partial differential equations were discretized and the nonlinear algebraic equations were solved simultaneously. Finally, to validate the numerical results, the model was compared with experimental data obtained from Sandia National Laboratory (SNL) and other one dimensional heat transfer models. Our results showed a better agreement with experimental data compared to other models.
Maximal near-field radiative heat transfer between two plates

Science.gov (United States)

Nefzaoui, Elyes; Ezzahri, Younès; Drévillon, Jérémie; Joulain, Karl

2013-09-01

Near-field radiative transfer is a promising way to significantly and simultaneously enhance both thermo-photovoltaic (TPV) devices power densities and efficiencies. A parametric study of Drude and Lorentz models performances in maximizing near-field radiative heat transfer between two semi-infinite planes separated by nanometric distances at room temperature is presented in this paper. Optimal parameters of these models that provide optical properties maximizing the radiative heat flux are reported and compared to real materials usually considered in similar studies, silicon carbide and heavily doped silicon in this case. Results are obtained by exact and approximate (in the extreme near-field regime and the electrostatic limit hypothesis) calculations. The two methods are compared in terms of accuracy and CPU resources consumption. Their differences are explained according to a mesoscopic description of nearfield radiative heat transfer. Finally, the frequently assumed hypothesis which states a maximal radiative heat transfer when the two semi-infinite planes are of identical materials is numerically confirmed. Its subsequent practical constraints are then discussed. Presented results enlighten relevant paths to follow in order to choose or design materials maximizing nano-TPV devices performances.
Heat transfer in gas turbine engines and three-dimensional flows; Proceedings of the Symposium, ASME Winter Annual Meeting, Chicago, IL, Nov. 27-Dec. 2, 1988

Science.gov (United States)

Elovic, E. (Editor); O'Brien, J. E. (Editor); Pepper, D. W. (Editor)

1988-01-01

The present conference on heat transfer characteristics of gas turbines and three-dimensional flows discusses velocity-temperature fluctuation correlations at the flow stagnation flow of a circular cylinder in turbulent flow, heat transfer across turbulent boundary layers with pressure gradients, the effect of jet grid turbulence on boundary layer heat transfer, and heat transfer characteristics predictions for discrete-hole film cooling. Also discussed are local heat transfer in internally cooled turbine airfoil leading edges, secondary flows in vane cascades and curved ducts, three-dimensional numerical modeling in gas turbine coal combustor design, numerical and experimental results for tube-fin heat exchanger airflow and heating characteristics, and the computation of external hypersonic three-dimensional flow field and heat transfer characteristics.
An analytical model for annular flow boiling heat transfer in microchannel heat sinks

International Nuclear Information System (INIS)

Megahed, A.; Hassan, I.

2009-01-01

An analytical model has been developed to predict flow boiling heat transfer coefficient in microchannel heat sinks. The new analytical model is proposed to predict the two-phase heat transfer coefficient during annular flow regime based on the separated model. Opposing to the majority of annular flow heat transfer models, the model is based on fundamental conservation principles. The model considers the characteristics of microchannel heat sink during annular flow and eliminates using any empirical closure relations. Comparison with limited experimental data was found to validate the usefulness of this analytical model. The model predicts the experimental data with a mean absolute error 8%. (author)
Heat and mass transfer

CERN Document Server

Karwa, Rajendra

2017-01-01

This textbook presents the classical treatment of the problems of heat transfer in an exhaustive manner with due emphasis on understanding of the physics of the problems. This emphasis is especially visible in the chapters on convective heat transfer. Emphasis is laid on the solution of steady and unsteady two-dimensional heat conduction problems. Another special feature of the book is a chapter on introduction to design of heat exchangers and their illustrative design problems. A simple and understandable treatment of gaseous radiation has been presented. A special chapter on flat plate solar air heater has been incorporated that covers thermo-hydraulic modeling and simulation. The chapter on mass transfer has been written looking specifically at the needs of the students of mechanical engineering. The book includes a large number and variety of solved problems with supporting line diagrams. The author has avoided duplicating similar problems, while incorporating more application-based examples. All the end-...
Heat transfer in two-phase flow of helium

International Nuclear Information System (INIS)

Subbotin, V.I.; Deev, V.I.; Solodovnikov, V.V.; Arkhipov, V.V.

1986-01-01

The results of experimental study of heat transfer in two-phase helium flow are presented. The effect of operating parameters (pressure, mass velocity, heat flux and quality) on boiling heat transfer intensity was investigated. A significant influence of boiling process prehistory on heat transfer coefficients was demonstrated. On the basis of experimental data obtained three typical regimes of flow boiling heat transfer were found. Analogy of heat transfer in flow boiling and pool boiling of helium and noncryogenic liquids was established. Correlations were developed which are in close agreement with available heat transfer data
Numerical modeling of heat transfer during hydrogen absorption in thin double-layered annular ZrCo beds

Directory of Open Access Journals (Sweden)

Yehui Cui

2018-06-01

Full Text Available In this work a three-dimensional (3D hydrogen absorption model was proposed to study the heat transfer behavior in thin double-layered annular ZrCo beds. Numerical simulations were performed to investigate the effects of conversion layer thickness, thermal conductivity, cooling medium and its flow velocity on the efficiency of heat transfer. Results reveal that decreasing the layer thickness and improving the thermal conductivity enhance the ability of heat transfer. Compared with nitrogen and helium, water appears to be a better medium for cooling. In order to achieve the best efficiency of heat transfer, the flow velocity needs to be maximized. Keywords: Hydrogen storage, ZrCo metal hydride, Heat transfer, Three-dimensional simulation
CFD SIMULATION OF THE HEAT TRANSFER PROCESS IN A CHEVRON PLATE HEAT EXCHANGER USING THE SST TURBULENCE MODEL

Directory of Open Access Journals (Sweden)

Jan Skočilas

2015-08-01

Full Text Available This paper deals with a computational fluid dynamics (CFD simulation of the heat transfer process during turbulent hot water flow between two chevron plates in a plate heat exchanger. A three-dimensional model with the simplified geometry of two cross-corrugated channels provided by chevron plates, taking into account the inlet and outlet ports, has been designed for the numerical study. The numerical model was based on the shear-stress transport (SST k-! model. The basic characteristics of the heat exchanger, as values of heat transfer coefficient and pressure drop, have been investigated. A comparative analysis of analytical calculation results, based on experimental data obtained from literature, and of the results obtained by numerical simulation, has been carried out. The coefficients and the exponents in the design equations for the considered plates have been arranged by using simulation results. The influence on the main flow parameters of the corrugation inclination angle relative to the flow direction has been taken into account. An analysis of the temperature distribution across the plates has been carried out, and it has shown the presence of zones with higher heat losses and low fluid flow intensity.
Evaluation of empirical heat transfer models using TFG heat flux sensors

International Nuclear Information System (INIS)

De Cuyper, T.; Broekaert, S.; Chana, K.; De Paepe, M.; Verhelst, S.

2017-01-01

Thermodynamic engine cycle models are used to support the development of the internal combustion engine (ICE) in a cost and time effective manner. The sub model which describes the in-cylinder heat transfer from the working gases to the combustion chamber walls plays an important role in the accuracy of these simulation tools. The heat transfer affects the power output, engine efficiency and emissions of the engine. The most common heat transfer models in engine research are the models of Annand and Woschni. These models provide an instantaneous spatial averaged heat flux. In this research, prototype thin film gauge (TFG) heat flux sensors are used to capture the transient in-cylinder heat flux behavior within a production spark ignition (SI) engine as they are small, robust and able to capture the highly transient temperature swings. An inlet valve and two different zones of the cylinder head are instrumented with multiple TFG sensors. The heat flux traces are used to calculate the convection coefficient which includes all information of the convective heat transfer phenomena inside the combustion chamber. The implementation of TFG sensors inside the combustion chamber and the signal processing technique are discussed. The heat transfer measurements are used to analyze the spatial variation in heat flux under motored and fired operation. Spatial variation in peak heat flux was observed even under motored operation. Under fired operation the observed spatial variation is mainly driven by the flame propagation. Next, the paper evaluates the models of Annand and Woschni. These models fail to predict the total heat loss even with calibration of the models coefficients using a reference motored operating condition. The effect of engine speed and inlet pressure is analyzed under motored operation after calibration of the models. The models are able to predict the trend in peak heat flux value for a varying engine speed and inlet pressure. Next, the accuracy of the
Aluminum-based one- and two-dimensional micro fin array structures: high-throughput fabrication and heat transfer testing

International Nuclear Information System (INIS)

Primeaux, Philip A; Zhang, Bin; Zhang, Xiaoman; Miller, Jacob; Meng, W J; KC, Pratik; Moore, Arden L

2017-01-01

Microscale fin array structures were replicated onto surfaces of aluminum 1100 and aluminum 6061 alloy (Al1100/Al6061) sheet metals through room-temperature instrumented roll molding. Aluminum-based micro fin arrays were replicated at room temperature, and the fabrication process is one with high throughput and low cost. One-dimensional (1D) micro fin arrays were made through one-pass rolling, while two-dimensional (2D) micro fin arrays were made by sequential 90° cross rolling with the same roller sleeve. For roll molding of 1D micro fins, fin heights greater than 600 µ m were achieved and were shown to be proportional to the normal load force per feature width. At a given normal load force, the fin height was further shown to scale inversely with the hardness of the sheet metal. For sequential 90° cross rolling, morphologies of roll molded 2D micro fin arrays were examined, which provided clues to understand how plastic deformation occurred under cross rolling conditions. A series of pool boiling experiments on low profile Al micro fin array structures were performed within Novec 7100, a widely used commercial dielectric coolant. Results for both horizontal and vertical surface orientations show that roll molded Al micro fin arrays can increase heat flux at fixed surface temperature as compared to un-patterned Al sheet. The present results further suggest that many factors beyond just increased surface area can influence heat transfer performance, including surface finish and the important multiphase transport mechanisms in and around the fin geometry. These factors must also be considered when designing and optimizing micro fin array structures for heat transfer applications. (paper)
Heat transfer in Rockwool modelling and method of measurement. Modelling radiative heat transfer in fibrous materials

Energy Technology Data Exchange (ETDEWEB)

Dyrboel, Susanne

1998-05-01

Fibrous materials are some of the most widely used materials for thermal insulation. In this project the focus of interest has been on fibrous materials for building application. Interest in improving the thermal properties of insulation materials is increasing as legislation is being tightened to reduce the overall energy consumption. A knowledge of the individual heat transfer mechanisms - whereby heat is transferred within a particular material is an essential tool to improve continuously the thermal properties of the material. Heat is transferred in fibrous materials by four different transfer mechanisms: conduction through air, conduction through fibres, thermal radiation and convection. In a particular temperature range the conduction through air can be regarded as a constant, and conduction through fibres is an insignificant part of the total heat transfer. Radiation, however, constitutes 25-40% of the total heat transfer in light fibrous materials. In Denmark and a number of other countries convection in fibrous materials is considered as non-existent when calculating heat transmission as well as when designing building structures. Two heat transfer mechanisms have been the focus of the current project: radiation heat transfer and convection. The radiation analysis serves to develop a model that can be used in further work to gain a wider knowledge of the way in which the morphology of the fibrous material, i.e. fibre diameter distribution, fibre orientation distribution etc., influences the radiation heat transfer under different conditions. The convection investigation serves to examine whether considering convection as non-existent is a fair assumption to use in present and future building structures. The assumption applied in practically is that convection makes a notable difference only in very thick insulation, at external temperatures below -20 deg. C, and at very low densities. For lager thickness dimensions the resulting heat transfer through the
MODELING OF TRANSIENT HEAT TRANSFER IN FOAMED CONCRETE SLAB

Directory of Open Access Journals (Sweden)

MD AZREE OTHUMAN MYDIN

2013-06-01

Full Text Available This paper reports the basis of one-dimensional Finite Difference method to obtain thermal properties of foamed concrete in order to solve transient heat conduction problems in multi-layer panels. In addition, this paper also incorporates the implementation of the method and the validation of thermal properties model of foamed concrete. A one-dimensional finite difference heat conduction programme has been developed to envisage the temperature development through the thickness of the foamed concrete slab, based on an initial estimate of the thermal conductivity-temperature relationship as a function of porosity and radiation within the voids. The accuracy of the model was evaluated by comparing predicted and experimental temperature profiles obtained from small scale heat transfer test on foamed concrete slabs, so that the temperature history of the specimen calculated by the programme closely matches those recorded during the experiment. Using the thermal properties of foamed concrete, the validated heat transfer program predicts foamed concrete temperatures in close agreement with experimental results obtained from a number of high temperature tests. The proposed numerical and thermal properties are simple yet efficient and can be utilised to aid manufacturers to develop their products without having to conduct numerous large-scale fire tests.
Radiative heat transfer in low-dimensional systems -- microscopic mode

Science.gov (United States)

Woods, Lilia; Phan, Anh; Drosdoff, David

2013-03-01

Radiative heat transfer between objects can increase dramatically at sub-wavelength scales. Exploring ways to modulate such transport between nano-systems is a key issue from fundamental and applied points of view. We advance the theoretical understanding of radiative heat transfer between nano-objects by introducing a microscopic model, which takes into account the individual atoms and their atomic polarizabilities. This approach is especially useful to investigate nano-objects with various geometries and give a detailed description of the heat transfer distribution. We employ this model to study the heat exchange in graphene nanoribbon/substrate systems. Our results for the distance separations, substrates, and presence of extended or localized defects enable making predictions for tailoring the radiative heat transfer at the nanoscale. Financial support from the Department of Energy under Contract No. DE-FG02-06ER46297 is acknowledged.
A two-region simulation model of vertical U-tube ground heat exchanger and its experimental verification

Energy Technology Data Exchange (ETDEWEB)

Yang, Weibo; Liu, Guangyuan [School of Energy and Power Engineering, Yangzhou University, Yangzhou City (China); Shi, Mingheng; Chen, Zhenqian [School of Energy and Environment, Southeast University, Nanjing City (China)

2009-10-15

Heat transfer around vertical ground heat exchanger (GHE) is a common problem for the design and simulation of ground coupled heat pump (GCHP). In this paper, an updated two-region vertical U-tube GHE analytical model, which is fit for system dynamic simulation of GCHP, is proposed and developed. It divides the heat transfer region of GHE into two parts at the boundary of borehole wall, and the two regions are coupled by the temperature of borehole wall. Both steady and transient heat transfer method are used to analyze the heat transfer process inside and outside borehole, respectively. The transient borehole wall temperature is calculated for the soil region outside borehole by use of a variable heat flux cylindrical source model. As for the region inside borehole, considering the variation of fluid temperature along the borehole length and the heat interference between two adjacent legs of U-tube, a quasi-three dimensional steady-state heat transfer analytical model for the borehole is developed based on the element energy conservation. The implement process of the model used in the dynamic simulation of GCHPs is illuminated in detail and the application calculation example for it is also presented. The experimental validation on the model is performed in a solar-geothermal multifunctional heat pump experiment system with two vertical boreholes and each with a 30 m vertical 1 1/4 in nominal diameter HDPE single U-tube GHE, the results indicate that the calculated fluid outlet temperatures of GHE by the model are agreed well with the corresponding test data and the guess relative error is less than 6%. (author)
Implementation of a Transition Model in a NASA Code and Validation Using Heat Transfer Data on a Turbine Blade

Science.gov (United States)

Ameri, Ali A.

2012-01-01

The purpose of this report is to summarize and document the work done to enable a NASA CFD code to model laminar-turbulent transition process on an isolated turbine blade. The ultimate purpose of the present work is to down-select a transition model that would allow the flow simulation of a variable speed power turbine to be accurately performed. The flow modeling in its final form will account for the blade row interactions and their effects on transition which would lead to accurate accounting for losses. The present work only concerns itself with steady flows of variable inlet turbulence. The low Reynolds number k- model of Wilcox and a modified version of the same model will be used for modeling of transition on experimentally measured blade pressure and heat transfer. It will be shown that the k- model and its modified variant fail to simulate the transition with any degree of accuracy. A case is thus made for the adoption of more accurate transition models. Three-equation models based on the work of Mayle on Laminar Kinetic Energy were explored. The three-equation model of Walters and Leylek was thought to be in a relatively mature state of development and was implemented in the Glenn-HT code. Two-dimensional heat transfer predictions of flat plate flow and two-dimensional and three-dimensional heat transfer predictions on a turbine blade were performed and reported herein. Surface heat transfer rate serves as sensitive indicator of transition. With the newly implemented model, it was shown that the simulation of transition process is much improved over the baseline k- model for the single Reynolds number and pressure ratio attempted; while agreement with heat transfer data became more satisfactory. Armed with the new transition model, total-pressure losses of computed three-dimensional flow of E3 tip section cascade were compared to the experimental data for a range of incidence angles. The results obtained, form a partial loss bucket for the chosen blade
Heat transfer to air-water two-phase flow in slug/churn region

International Nuclear Information System (INIS)

Wadekar, V.V.; Tuzla, K.; Chen, J.C.

1996-01-01

Measured heat transfer data for air-water two-phase flow in the slug/churn flow region are reported. The measurements were obtained from a 1.3 m tall, 15.7 mm diameter vertical tube test-section. It is observed that the data exhibit different heat transfer characteristics to those predicted by the standard correlations for the convective component of flow boiling heat transfer. Comparison with the predictions of a slug flow model for evaporation shows a significant overprediction of the data. The reason for the overprediction is attributed to the sensible heating requirement of the gas phase. The slug flow model is therefore suitably modified for non-evaporating two-phase flow. This specially adapted model is found to give reasonably good predictions of the measured data

Finite element method for radiation heat transfer in multi-dimensional graded index medium

International Nuclear Information System (INIS)

Liu, L.H.; Zhang, L.; Tan, H.P.

2006-01-01

In graded index medium, ray goes along a curved path determined by Fermat principle, and curved ray-tracing is very difficult and complex. To avoid the complicated and time-consuming computation of curved ray trajectories, a finite element method based on discrete ordinate equation is developed to solve the radiative transfer problem in a multi-dimensional semitransparent graded index medium. Two particular test problems of radiative transfer are taken as examples to verify this finite element method. The predicted dimensionless net radiative heat fluxes are determined by the proposed method and compared with the results obtained by finite volume method. The results show that the finite element method presented in this paper has a good accuracy in solving the multi-dimensional radiative transfer problem in semitransparent graded index medium
Determination of heat flows inside turbochargers by means of a one dimensional lumped model

OpenAIRE

Olmeda González, Pablo Cesar; Dolz Ruiz, Vicente; Arnau Martínez, Francisco José; Reyes Belmonte, Miguel Angel

2013-01-01

In the present paper, a methodology to calculate the heat fluxes inside a turbocharger from diesel passenger car is presented. The heat transfer phenomenon is solved by using a one dimensional lumped model that takes into account both the heat fluxes between the different turbocharger elements, as well as the heat fluxes between the working fluids and the turbocharger elements. This heat transfer study is supported by the high temperature differences between the working fluids passing thr...
Heat transfer characteristics of the two-phase closed thermosyphon (wickless heat pipe)

International Nuclear Information System (INIS)

Andros, F.E.; Florschuetz, L.W.

1982-01-01

Steady-state heat transfer characteristics and heat transfer limits (dry-out) for a vertical stainless steel tubular two-phase closed thermosyphon with Freon-113 working fluid are reported as a function of certain geometric parameters and liquid fill quantity. Condenser section heat transfer characteristics agreed reasonably well with existing laminar film condensation correlations and were found to be independent of the evaporator section, except for larger liquid fills. Evaporator characteristics were quite complex and appeared, under some conditions, to be coupled to condenser characteristics through effects of system pressure and/or surface wave as present on the descending condensate film. A laminar thin film evaporation model was found to give reasonable agreement with local evaporator temperature measurements in those regions of the evaporator where a continuous film apparently persisted. The measured heat transfer characteristics are interpreted relative to an earlier investigation by the authors in which flow characteristics in a similar device were visually and photographically observed. 10 references
A porous media calculation for the isolation condenser heat transfer and circulation

International Nuclear Information System (INIS)

Jaakko, Miettinen; Ismo, Karppinen

2003-01-01

In the development of advanced light water reactors, thermohydraulic phenomena are versatile in comparison with the present concepts. The new features include, for example, passive safety systems, where energy transport takes place by natural circulation instead of forced flow. In the isolation condenser, the steam generated in the reactor vessel is conduced into the heat transfer tubes. The tube bundle has been submerged into a large water pool, where the heat flux through the tube wall initially is heating the subcooled water, but rather soon boiling take place. The temperature differences and void fraction in the pool create large two-phase circulation. For modeling of the entire condenser a combined application of two types of simulation models has been selected. For the whole geometry, a porous media solution has been developed, where the existence of the heat transfer tubes in the water pool and their heat generation is described by the porous media approach. The 3-dimensional solution of two-phase equations is based on the drift-flux formalism. The condensation and liquid film generation inside the heat transfer tube is modelled using a 1-dimensional model considering the steam core, liquid film and heat transfer tube. The heat flux through the tube wall defines the boundary conditions for the water pool. Parallel to the porous media development for the entire process facility, the phase change models have been improved for Fluent 6 mixture model, and the code is used for analysing in detail the heat transfer around the tubing. The purpose in the analyses is to obtain more detailed information of the flow field and vapour distribution around the tube bundle. By combining the porous media model for the entire facility, with the CFD models for the two-phase flow details around the heat transfer tubes and experimental studies the most important mechanisms around the condensation pool can be gathered. In this context the porous media model is considered. (author)
Use of CATHENA to model calandria-tube/moderator heat transfer after pressure-tube/calandria-tube ballooning contact

International Nuclear Information System (INIS)

Fan, H.Z.; Bilanovic, Z.; Nitheanandan, T.

2004-01-01

A study was performed to assess the effect of the calandria-tube/moderator heat transfer after pressure-tube/calandria tube ballooning contact using CATHENA. Results of this study indicated that the analytical tool, CATHENA, can be applied for pool boiling heat transfer on the external surface of a large diameter tube, such as the calandria tube used in CANDU reactors. The methodology in such CANDU-generic study can be used to simulate the tube surface with multiple boiling regimes and to assess the benefits of closely coupling thermalhydraulics modelling and fuel/fuel channel behaviour modelling. CATHENA (Canadian Algorithm for THErmalhydraulic Network Analysis) is a one-dimensional, two-fluid thermalhydraulic simulation code designed by AECL to analyse two-phase flow and heat transfer in piping networks. The detailed heat transfer package in CATHENA allows a connection to be established from the multiple solid surfaces of tubes to the surrounding large amount of moderator water, which acts as a heat sink during a postulated loss of coolant event. The generalized heat transfer package within CATHENA allows the tube walls to be divided into several layers in the radial direction and several sectors in the circumferential direction, to account for heat transfer conditions in these two directions. The CATHENA code with the generalized heat transfer package is capable of capturing key pool-boiling phenomena such as nucleate, transition and film boiling heat transfer as well as an ability to model the rewet phenomenon to some extent. A CATHENA input model was generated and used in simulations of selected contact boiling experiment test cases. The transient wall temperatures have been calculated in different portions of the calandria tube. By using this model an adequate agreement was achieved between CATHENA calculation and experimental measurement The CATHENA code enables one to investigate the transient and local thermal-mechanical behaviour of the calandria tube
Heat transfer corrected isothermal model for devolatilization of thermally-thick biomass particles

DEFF Research Database (Denmark)

Luo, Hao; Wu, Hao; Lin, Weigang

Isothermal model used in current computational fluid dynamic (CFD) model neglect the internal heat transfer during biomass devolatilization. This assumption is not reasonable for thermally-thick particles. To solve this issue, a heat transfer corrected isothermal model is introduced. In this model......, two heat transfer corrected coefficients: HT-correction of heat transfer and HR-correction of reaction, are defined to cover the effects of internal heat transfer. A series of single biomass devitalization case have been modeled to validate this model, the results show that devolatilization behaviors...... of both thermally-thick and thermally-thin particles are predicted reasonable by using heat transfer corrected model, while, isothermal model overestimate devolatilization rate and heating rate for thermlly-thick particle.This model probably has better performance than isothermal model when it is coupled...
Non-linear heat transfer computer code by finite element method

International Nuclear Information System (INIS)

Nagato, Kotaro; Takikawa, Noboru

1977-01-01

The computer code THETA-2D for the calculation of temperature distribution by the two-dimensional finite element method was made for the analysis of heat transfer in a high temperature structure. Numerical experiment was performed for the numerical integration of the differential equation of heat conduction. The Runge-Kutta method of the numerical experiment produced an unstable solution. A stable solution was obtained by the β method with the β value of 0.35. In high temperature structures, the radiative heat transfer can not be neglected. To introduce a term of the radiative heat transfer, a functional neglecting the radiative heat transfer was derived at first. Then, the radiative term was added after the discretion by variation method. Five model calculations were carried out by the computer code. Calculation of steady heat conduction was performed. When estimated initial temperature is 1,000 degree C, reasonable heat blance was obtained. In case of steady-unsteady temperature calculation, the time integral by THETA-2D turned out to be under-estimation for enthalpy change. With a one-dimensional model, the temperature distribution in a structure, in which heat conductivity is dependent on temperature, was calculated. Calculation with a model which has a void inside was performed. Finally, model calculation for a complex system was carried out. (Kato, T.)
Numerical investigation of two- and three-dimensional heat transfer in expander cycle engines

Science.gov (United States)

Burch, Robert L.; Cheung, Fan-Bill

1993-01-01

The concept of using tube canting for enhancing the hot-side convective heat transfer in a cross-stream tubular rocket combustion chamber is evaluated using a CFD technique in this study. The heat transfer at the combustor wall is determined from the flow field generated by a modified version of the PARC Navier-Stokes Code, using the actual dimensions, fluid properties, and design parameters of a split-expander demonstrator cycle engine. The effects of artificial dissipation on convergence and solution accuracy are investigated. Heat transfer results predicted by the code are presented. The use of CFD in heat transfer calculations is critically examined to demonstrate the care needed in the use of artificial dissipation for good convergence and accurate solutions.
Electron-phonon heat exchange in quasi-two-dimensional nanolayers

Science.gov (United States)

Anghel, Dragos-Victor; Cojocaru, Sergiu

2017-12-01

We study the heat power P transferred between electrons and phonons in thin metallic films deposited on free-standing dielectric membranes. The temperature range is typically below 1 K, such that the wavelengths of the excited phonon modes in the system is large enough so that the picture of a quasi-two-dimensional phonon gas is applicable. Moreover, due to the quantization of the components of the electron wavevectors perpendicular to the metal film's surface, the electrons spectrum forms also quasi two-dimensional sub-bands, as in a quantum well (QW). We describe in detail the contribution to the electron-phonon energy exchange of different electron scattering channels, as well as of different types of phonon modes. We find that heat flux oscillates strongly with thickness of the film d while having a much smoother variation with temperature (Te for the electrons temperature and Tph for the phonons temperature), so that one obtains a ridge-like landscape in the two coordinates, (d, Te) or (d, Tph), with crests and valleys aligned roughly parallel to the temperature axis. For the valley regions we find P ∝ Te3.5 - Tph3.5. From valley to crest, P increases by more than one order of magnitude and on the crests P cannot be represented by a simple power law. The strong dependence of P on d is indicative of the formation of the QW state and can be useful in controlling the heat transfer between electrons and crystal lattice in nano-electronic devices. Nevertheless, due to the small value of the Fermi wavelength in metals, the surface imperfections of the metallic films can reduce the magnitude of the oscillations of P vs. d, so this effect might be easier to observe experimentally in doped semiconductors.
Mountain scale modeling of transient, coupled gas flow, heat transfer and carbon-14 migration

International Nuclear Information System (INIS)

Lu, Ning; Ross, B.

1993-01-01

We simulate mountain-scale coupled heat transfer and gas flow at Yucca Mountain. A coupled rock-gas flow and heat transfer model, TGIF2, is used to simulate mountain-scale two-dimensional transient heat transfer and gas flow. The model is first verified against an analytical solution for the problem of an infinite horizontal layer of fluid heated from below. Our numerical results match very well with the analytical solution. Then, we obtain transient temperature and gas flow distributions inside the mountain. These distributions are used by a transient semianalytical particle tracker to obtain carbon-14 travel times for particles starting at different locations within the repository. Assuming that the repository is filled with 30-year-old waste at an initial areal power density of 57 kw/acre, we find that repository temperatures remain above 60 degrees C for more than 10,000 years. Carbon-14 travel times to the surface are mostly less than 1000 years, for particles starting at any time within the first 10,000 years
Numerical Simulation of One-Dimensional Fractional Nonsteady Heat Transfer Model Based on the Second Kind Chebyshev Wavelet

Directory of Open Access Journals (Sweden)

Fuqiang Zhao

2017-01-01

Full Text Available In the current study, a numerical technique for solving one-dimensional fractional nonsteady heat transfer model is presented. We construct the second kind Chebyshev wavelet and then derive the operational matrix of fractional-order integration. The operational matrix of fractional-order integration is utilized to reduce the original problem to a system of linear algebraic equations, and then the numerical solutions obtained by our method are compared with those obtained by CAS wavelet method. Lastly, illustrated examples are included to demonstrate the validity and applicability of the technique.
Estimates of error introduced when one-dimensional inverse heat transfer techniques are applied to multi-dimensional problems

International Nuclear Information System (INIS)

Lopez, C.; Koski, J.A.; Razani, A.

2000-01-01

A study of the errors introduced when one-dimensional inverse heat conduction techniques are applied to problems involving two-dimensional heat transfer effects was performed. The geometry used for the study was a cylinder with similar dimensions as a typical container used for the transportation of radioactive materials. The finite element analysis code MSC P/Thermal was used to generate synthetic test data that was then used as input for an inverse heat conduction code. Four different problems were considered including one with uniform flux around the outer surface of the cylinder and three with non-uniform flux applied over 360 deg C, 180 deg C, and 90 deg C sections of the outer surface of the cylinder. The Sandia One-Dimensional Direct and Inverse Thermal (SODDIT) code was used to estimate the surface heat flux of all four cases. The error analysis was performed by comparing the results from SODDIT and the heat flux calculated based on the temperature results obtained from P/Thermal. Results showed an increase in error of the surface heat flux estimates as the applied heat became more localized. For the uniform case, SODDIT provided heat flux estimates with a maximum error of 0.5% whereas for the non-uniform cases, the maximum errors were found to be about 3%, 7%, and 18% for the 360 deg C, 180 deg C, and 90 deg C cases, respectively
Advanced k-epsilon modeling of heat transfer

Science.gov (United States)

Kwon, Okey; Ames, Forrest E.

1995-01-01

This report describes two approaches to low Reynolds-number k-epsilon turbulence modeling which formulate the eddy viscosity on the wall-normal component of turbulence and a length scale. The wall-normal component of turbulence is computed via integration of the energy spectrum based on the local dissipation rate and is bounded by the isotropic condition. The models account for the anisotropy of the dissipation and the reduced mixing length due to the high strain rates present in the near-wall region. The turbulent kinetic energy and its dissipation rate were computed from the k and epsilon transport equations of Durbin. The models were tested for a wide range of turbulent flows and proved to be superior to other k-epsilon models, especially for nonequilibrium anisotropic flows. For the prediction of airfoil heat transfer, the models included a set of empirical correlations for predicting laminar-turbulent transition and laminar heat transfer augmentation due to the presence of freestream turbulence. The predictions of surface heat transfer were generally satisfactory.
Maximal near-field radiative heat transfer between two plates

OpenAIRE

Nefzaoui, Elyes; Ezzahri, Younès; Drevillon, Jérémie; Joulain, Karl

2013-01-01

International audience; Near-field radiative transfer is a promising way to significantly and simultaneously enhance both thermo-photovoltaic (TPV) devices power densities and efficiencies. A parametric study of Drude and Lorentz models performances in maximizing near-field radiative heat transfer between two semi-infinite planes separated by nanometric distances at room temperature is presented in this paper. Optimal parameters of these models that provide optical properties maximizing the r...
Three dimensional modeling on airflow, heat and mass transfer in partially impermeable enclosure containing agricultural produce during natural convective cooling

International Nuclear Information System (INIS)

Chourasia, M.K.; Goswami, T.K.

2007-01-01

A three dimensional model was developed to simulate the transport phenomena in heat and mass generating porous medium cooled under natural convective environment. Unlike the previous works on this aspect, the present model was aimed for bulk stored agricultural produce contained in a permeable package placed on a hard surface. This situation made the bottom of the package impermeable to fluid flow as well as moisture transfer and adiabatic to heat transfer. The velocity vectors, isotherms and contours of rate of moisture loss were presented during transient cooling as well as at steady state using the commercially available computational fluid dynamics (CFD) code based on the finite volume technique. The CFD model was validated using the experimental data on the time-temperature history as well as weight loss obtained from a bag of potatoes kept in a cold store. The simulated and experimental values on temperature and moisture loss of the product were found to be in good agreement
Forced convection heat transfer in He II

International Nuclear Information System (INIS)

Kashani, A.

1986-01-01

An investigation of forced convection heat transfer in He II is conducted. The study includes both experimental and theoretical treatments of the problem. The experiment consists of a hydraulic pump and a copper flow tube, 3 mm in ID and 2m long. The system allows measurements of one-dimensional heat and mass transfer in He II. The heat transfer experiments are performed by applying heat at the midpoint along the length of the flow tube. Two modes of heat input are employed, i.e., step function heat input and square pulse heat input. The heat transfer results are discussed in terms of temperature distribution in the tube. The experimental temperature profiles are compared with numerical solutions of an analytical model developed from the He II energy equation. The bath temperature is set at three different values of 1.65, 1.80, and 1.95 K. The He II flow velocity is varied up to 90 cm/s. Pressure is monitored at each end of the flow tube, and the He II pressure drop is obtained for different flow velocities. Results indicate that He II heat transfer by forced convention is considerably higher than that by internal convection. The theoretical model is in close agreement with the experiment. He II pressure drop and friction factor are very similar to those of an ordinary fluid
Three-Dimensional Unsteady Simulation of a Modern High Pressure Turbine Stage Using Phase Lag Periodicity: Analysis of Flow and Heat Transfer

Science.gov (United States)

Shyam, Vikram; Ameri, Ali; Luk, Daniel F.; Chen, Jen-Ping

2010-01-01

Unsteady three-dimensional RANS simulations have been performed on a highly loaded transonic turbine stage and results are compared to steady calculations as well as experiment. A low Reynolds number k- turbulence model is employed to provide closure for the RANS system. A phase-lag boundary condition is used in the periodic direction. This allows the unsteady simulation to be performed by using only one blade from each of the two rows. The objective of this paper is to study the effect of unsteadiness on rotor heat transfer and to glean any insight into unsteady flow physics. The role of the stator wake passing on the pressure distribution at the leading edge is also studied. The simulated heat transfer and pressure results agreed favorably with experiment. The time-averaged heat transfer predicted by the unsteady simulation is higher than the heat transfer predicted by the steady simulation everywhere except at the leading edge. The shock structure formed due to stator-rotor interaction was analyzed. Heat transfer and pressure at the hub and casing were also studied. Thermal segregation was observed that leads to the heat transfer patterns predicted by steady and unsteady simulations to be different.
ANL ITER high-heat-flux blanket-module heat transfer experiments

International Nuclear Information System (INIS)

Kasza, K.E.

1992-02-01

An Argonne National Laboratory facility for conducting tests on multilayered slab models of fusion blanket designs is being developed; some of its features are described. This facility will allow testing under prototypic high heat fluxes, high temperatures, thermal gradients, and variable mechanical loadings in a helium gas environment. Steady and transient heat flux tests are possible. Electrical heating by a two-sided, thin stainless steel (SS) plate electrical resistance heater and SS water-cooled cold panels placed symmetrically on both sides of the heater allow achievement of global one-dimensional heat transfer across blanket specimen layers sandwiched between the hot and cold plates. The heat transfer characteristics at interfaces, as well as macroscale and microscale thermomechanical interactions between layers, can be studied in support of the ITER engineering design effort. The engineering design of the test apparatus has shown that it is important to use multidimensional thermomechanical analysis of sandwich-type composites to adequately analyze heat transfer. This fact will also be true for the engineering design of ITER
Multiregional coupled conduction--convection model for heat transfer in an HTGR core

International Nuclear Information System (INIS)

Giles, G.E. Jr.; Childs, K.W.; Sanders, J.P.

1978-01-01

HEXEREI is a three-dimensional, coupled conduction-convection heat transfer and multichannel fluid dynamic analysis computer code with both steady-state and transient capabilities. The program was developed to provide thermal-fluid dynamic analysis of a core following the general design for high-temperature gas-cooled reactors (HTGRs); its purpose was to provide licensing evaluations for the U.S. Nuclear Regulatory Commission. In order to efficiently model the HTGR core, the nodal geometry of HEXEREI was chosen as a regular hexagonal array perpendicular to the axis of and bounded by a right circular cylinder. The cylindrical nodal geometry surrounds the hexagonal center portion of the mesh; these two different types of nodal geometries must be connected by interface nodes to complete the accurate modeling of the HTGR core. HEXEREI will automatically generate a nodal geometry that will accurately model a complex assembly of hexagonal and irregular prisms. The accuracy of the model was proven by a comparison of computed values with analytical results for steady-state and transient heat transfer problems. HEXEREI incorporates convective heat transfer to the coolant in many parallel axial flow channels. Forced and natural convection (which permits different flow directions in parallel channels) is included in the heat transfer and fluid dynamic models. HEXEREI incorporates a variety of steady-state and transient solution techniques that can be matched with a particular problem to minimize the computational time. HEXEREI was compared with a code of similar capabilities that was based on a Cartesian mesh. This code modeled only one specific core design, and the mesh spacing was closer than that generated by HEXEREI. Good agreement was obtained with the detail provided by the representations
Modeling of the heat transfer performance of plate-type dispersion nuclear fuel elements

Science.gov (United States)

Ding, Shurong; Huo, Yongzhong; Yan, XiaoQing

2009-08-01

Considering the mutual actions between fuel particles and the metal matrix, the three-dimensional finite element models are developed to simulate the heat transfer behaviors of dispersion nuclear fuel plates. The research results indicate that the temperatures of the fuel plate might rise more distinctly with considering the particle swelling and the degraded surface heat transfer coefficients with increasing burnup; the local heating phenomenon within the particles appears when their thermal conductivities are too low. With rise of the surface heat transfer coefficients, the temperatures within the fuel plate decrease; the temperatures of the fuel plate are sensitive to the variations of the heat transfer coefficients whose values are lower, but their effects are weakened and slight when the heat transfer coefficients increase and reach a certain extent. Increasing the heat generation rate leads to elevating the internal temperatures. The temperatures and the maximum temperature differences within the plate increase along with the particle volume fractions. The surface thermal flux goes up along with particle volume fractions and heat generation rates, but the effects of surface heat transfer coefficients are not evident.

Modeling of heat transfer into a heat pipe for a localized heat input zone

International Nuclear Information System (INIS)

Rosenfeld, J.H.

1987-01-01

A general model is presented for heat transfer into a heat pipe using a localized heat input. Conduction in the wall of the heat pipe and boiling in the interior structure are treated simultaneously. The model is derived from circumferential heat transfer in a cylindrical heat pipe evaporator and for radial heat transfer in a circular disk with boiling from the interior surface. A comparison is made with data for a localized heat input zone. Agreement between the theory and the model is good. This model can be used for design purposes if a boiling correlation is available. The model can be extended to provide improved predictions of heat pipe performance
Two-dimensional molecular line transfer for a cometary coma

Science.gov (United States)

Szutowicz, S.

2017-09-01

In the proposed axisymmetric model of the cometary coma the gas density profile is described by an angular density function. Three methods for treating two-dimensional radiative transfer are compared: the Large Velocity Gradient (LVG) (the Sobolev method), Accelerated Lambda Iteration (ALI) and accelerated Monte Carlo (MC).
Effect of heat transfer in the fog region during core reflooding

International Nuclear Information System (INIS)

Rouai, N. M.; El-sawy, H. M.

1993-01-01

Core reflooding following a loss of coolant accident (LOCA) in a pressurized water reactor (PWR) received considerable attention during the past thirty years. In this paper a one dimensional model is used to study the effect of the heat transfer in the fog region ahead of the wet front reflooding rate of a cylindrical fuel element following a LOCA in a PWR. The heat conduction equation in the cladding is solved in coordinate system moving with the wet front under a variety of condition to investigate the effects of such parameters as the initial cladding surface temperature, the decay heat generation rate in the fuel and the mode of heat transfer prevailing. The cladding surface is divided into three axial regions according to the mechanism of heat transfer, namely, a boiling region behind the wet front, a fog region ahead of the wet front and a dry region further downstream of the wet front. The effect of changing the heat transfer coefficient in the fog region on the rewetting rate and on the fog length is investigated. The results of this simple model show that increasing the heat transfer in the fog region increases the rewetting velocity and consequently decreases the fog length. The results are in general agreement with a more accurate two-dimensional model and experimental data. (author)
Fluid flow and heat transfer modeling for castings

International Nuclear Information System (INIS)

Domanus, H.M.; Liu, Y.Y.; Sha, W.T.

1986-01-01

Casting is fundamental to manufacturing of many types of equipment and products. Although casting is a very old technology that has been in existence for hundreds of years, it remains a highly empirical technology, and production of new castings requires an expensive and time-consuming trial-and-error approach. In recent years, mathematical modeling of casting has received increasing attention; however, a majority of the modeling work has been in the area of heat transfer and solidification. Very little work has been done in modeling fluid flow of the liquid melt. This paper presents a model of fluid flow coupled with heat transfer of a liquid melt for casting processes. The model to be described in this paper is an extension of the COMMIX code and is capable of handling castings with any shape, size, and material. A feature of this model is the ability to track the liquid/gas interface and liquid/solid interface. The flow of liquid melt through the sprue and runners and into the mold cavity is calculated as well as three-dimensional temperature and velocity distributions of the liquid melt throughout the casting process. 14 refs., 13 figs
Macroscopic modeling for heat and water vapor transfer in dry snow by homogenization.

Science.gov (United States)

Calonne, Neige; Geindreau, Christian; Flin, Frédéric

2014-11-26

Dry snow metamorphism, involved in several topics related to cryospheric sciences, is mainly linked to heat and water vapor transfers through snow including sublimation and deposition at the ice-pore interface. In this paper, the macroscopic equivalent modeling of heat and water vapor transfers through a snow layer was derived from the physics at the pore scale using the homogenization of multiple scale expansions. The microscopic phenomena under consideration are heat conduction, vapor diffusion, sublimation, and deposition. The obtained macroscopic equivalent model is described by two coupled transient diffusion equations including a source term arising from phase change at the pore scale. By dimensional analysis, it was shown that the influence of such source terms on the overall transfers can generally not be neglected, except typically under small temperature gradients. The precision and the robustness of the proposed macroscopic modeling were illustrated through 2D numerical simulations. Finally, the effective vapor diffusion tensor arising in the macroscopic modeling was computed on 3D images of snow. The self-consistent formula offers a good estimate of the effective diffusion coefficient with respect to the snow density, within an average relative error of 10%. Our results confirm recent work that the effective vapor diffusion is not enhanced in snow.
Pumped two-phase heat transfer loop

Science.gov (United States)

Edelstein, Fred

1988-01-01

A pumped loop two-phase heat transfer system, operating at a nearly constant temperature throughout, includes several independently operating grooved capillary heat exchanger plates supplied with working fluid through independent flow modulation valves connected to a liquid supply line, a vapor line for collecting vapor from the heat exchangers, a condenser between the vapor and the liquid lines, and a fluid circulating pump between the condenser and the heat exchangers.
Heat transfer characteristics and limitations analysis of heat-pipe-cooled thermal protection structure

International Nuclear Information System (INIS)

Guangming, Xiao; Yanxia, Du; Yewei, Gui; Lei, Liu; Xiaofeng, Yang; Dong, Wei

2014-01-01

The theories of heat transfer, thermodynamics and fluid dynamics are employed to develop the coupled heat transfer analytical methods for the heat-pipe-cooled thermal protection structure (HPC TPS), and a three-dimensional numerical method considering the sonic limit of heat pipe is proposed. To verify the calculation correctness, computations are carried out for a typical heat pipe and the results agree well with experimental data. Then, the heat transfer characteristics and limitations of HPC TPS are mainly studied. The studies indicate that the use of heat pipe can reduce the temperature at high heat flux region of structure efficiently. However, there is a frozen startup period before the heat pipe reaching a steady operating state, and the sonic limit will be a restriction on the heat transfer capability. Thus, the effects of frozen startup must be considered for the design of HPC TPS. The simulation model and numerical method proposed in this paper can predict the heat transfer characteristics of HPC TPS quickly and exactly, and the results will provide important references for the design or performance evaluation of HPC TPS. - Highlights: • Numerical methods for the heat-pipe-cooled thermal protection structure are studied. • Three-dimensional simulation model considering sonic limit of heat pipe is proposed. • The frozen startup process of the embedded heat pipe can be predicted exactly. • Heat transfer characteristics of TPS and limitations of heat pipe are discussed
Heat transfer modeling in exhaust systems of high-performance two-stroke engines

OpenAIRE

Lujan Martinez, José Manuel; Climent Puchades, Héctor; Olmeda González, Pablo Cesar; JIMENEZ MACEDO, VICTOR DANIEL

2014-01-01

Heat transfer from the hot gases to the wall in exhaust systems of high-performance two-stroke engines is underestimated using steady state with fully developed flow empirical correlations. This fact is detected when comparing measured and modeled pressure pulses in different positions in the exhaust system. This can be explained taking into account that classical expressions have been validated for fully developed flows, a situation that is far from the flow behavior in reciprocating interna...
A heat transfer model for evaporating micro-channel coalescing bubble flow

International Nuclear Information System (INIS)

Consolini, L.; Thome, J.R.

2009-01-01

The current study presents a one-dimensional model of confined coalescing bubble flow for the prediction of micro-channel convective boiling heat transfer. Coalescing bubble flow has recently been identified as one of the characteristic flow patterns to be found in micro-scale systems, occurring at intermediate vapor qualities between the isolated bubble and the fully annular regimes. As two or more bubbles bond under the action of inertia and surface tension, the passage frequency of the bubble liquid slug pair declines, with a redistribution of liquid among the remaining flow structures. Assuming heat transfer to occur only by conduction through the thin evaporating liquid film surrounding individual bubbles, the present model includes a simplified description of the dynamics of the thin film evaporation process that takes into account the added mass transfer by breakup of the bridging liquid slugs. The new model has been confronted against experimental data taken within the coalescing bubble flow mode that have been identified by a diabatic micro-scale flow pattern map. The comparisons for three different fluids (R-134a, R-236fa and R-245fa) gave encouraging results with 83% of the database predicted within a ± 30% error band. (author)
Coupled DQ-FE methods for two dimensional transient heat transfer analysis of functionally graded material

Energy Technology Data Exchange (ETDEWEB)

Golbahar Haghighi, M.R.; Eghtesad, M. [Department of Mechanical Engineering, School of Engineering, Shiraz University, Shiraz 71348-51154 (Iran, Islamic Republic of); Malekzadeh, P. [Department of Mechanical Engineering, School of Engineering, Persian Gulf University, Boushehr 75169-13798 (Iran, Islamic Republic of)], E-mail: malekzadeh@pgu.ac.ir

2008-05-15

In this paper, a mixed finite element (FE) and differential quadrature (DQ) method as a simple, accurate and computationally efficient numerical tool for two dimensional transient heat transfer analysis of functionally graded materials (FGMs) is developed. The method benefits from the high accuracy, fast convergence behavior and low computational efforts of the DQ in conjunction with the advantages of the FE method in general geometry, loading and systematic boundary treatment. Also, the boundary conditions at the top and bottom surfaces of the domain can be implemented more precisely and in strong form. The temporal derivatives are discretized using an incremental DQ method (IDQM), whose numerical stability is not sensitive to time step size. The effects of non-uniform convective-radiative conditions on the boundaries are investigated. The accuracy of the proposed method is demonstrated by comparing its results with those available in the literature. It is shown that using few grid points, highly accurate results can be obtained.
CFD modeling of heat transfer performance of MgO-water nanofluid under turbulent flow

OpenAIRE

Davarnejad, Reza; Jamshidzadeh, Maryam

2015-01-01

In this paper, Computational fluid dynamics (CFD) modeling of turbulent heat transfer behavior of Magnesium Oxide-water nanofluid in a circular tube was studied. The modeling was two dimensional under k–ε turbulence model. The base fluid was pure water and the volume fraction of nanoparticles in the base fluid was 0.0625%, 0.125%, 0.25%, 0.5% and 1%. The applied Reynolds number range was 3000–19000. Three individual models including single phase, Volume of Fluid (VOF) and mixture were used. T...
Problems of heat transfer and hydraulics of two-phase media

CERN Document Server

Kutateladze, S S

1969-01-01

Problems of Heat Transfer and Hydraulics of Two-Phase Media presents the theory of heat transfer and hydrodynamics. This book discusses the various aspects of heat transfer and the flow of two-phase systems. Organized into two parts encompassing 22 chapters, this book starts with an overview of the laws of similarity for heat transfer to or from a flowing liquid with various physical properties and allowed for variation in viscosity and thermal conductivity. This book then explores the general functional relationship that exists between viscosity and thermal conductivity for thermodynamically
Numerical simulations of heat transfer in an annular fuel channel with three-dimensional spacer ribs set up periodically under a fully developed turbulent flow

International Nuclear Information System (INIS)

Takase, Kazuyuki; Akino, Norio

1996-06-01

Thermal-hydraulic characteristics of an annular fuel channel with spacer ribs for high temperature gas-cooled reactors were analyzed numerically by three-dimensional heat transfer computations under a fully developed turbulent flow. The two-equations κ-ε turbulence model was applied to the present turbulent analysis. In particular, the κ-ε turbulence model constants and the turbulent Prandtl number were improved from the previous standard values proposed by Jones and Launder in order to obtain heat transfer predictions with higher accuracy. Consequently, heat transfer coefficients and friction factors in the spacer-ribbed fuel channel were predicted with sufficient accuracy in the range of Reynolds number exceeding 3000. It was clarified quantitatively from the present study that main mechanism for the heat transfer augmentation in the spacer-ribbed fuel channel was combined effects of the turbulence promoter effect by the spacer ribs and the velocity acceleration effect by a reduction in the channel cross-section. (author)
Simulation of heat and mass transfer in boiling water with the Melodif code

International Nuclear Information System (INIS)

Freydier, P.; Chen, O.; Olive, J.; Simonin, O.

1991-04-01

The Melodif code is developed at Electricite de France, Research and Development Division. It is an eulerian two dimensional code for the simulation of turbulent two phase flows (a three dimensional code derived from Melodif, ASTRID, is currently being prepared). Melodif is based on the two fluid model, solving the equations of conservation for mass, momentum and energy, for both phases. In such a two fluid model, the description of interfacial transfers between phases is a crucial issue. The model used applies to a dominant continuous phase, and a dispersed phase. A good description of interfacial momentum transfer exists in the standard MELODIF code: the drag force, the apparent mass force... are taken into account. An important factor for interfacial transfers is the interfacial area per volume unit. With the assumption of spherical gas bubbles, an equation has been written for this variable. In the present wok, a model has been tested for interfacial heat and mass transfer in the case of boiling water: it is assumed that mass transfer is controlled by heat transfer through the latent massic energy taken in the phase that vaporizes (or condenses). This heat and mass transfer model has been tested in various configurations: - a cylinder with water flowing inside, is being heated. Boiling takes place near the wall, while bubbles migrating to the core of the flow recondense. This roughly simulates a sub-cooled boiling phenomenon. - a box containing liquid water is depressurized. Boiling takes place in the whole volume of the fluid. The Melodif code can simulate this configuration due to the implicitation of the relation between interphase mass transfer and the pressure variable
Homogenization and two scales convergence of some stationary and non-stationary heat transfer problems, application to gas cooled nuclear rectors

International Nuclear Information System (INIS)

Habibi, Z.

2011-01-01

We are interested in the homogenization of heat transfer in periodic porous media modelling the geometry of a gas cooled nuclear reactor. This geometry is made of a solid media perforated by several long thin parallel cylinders, the diameter of which is of the same order than the period. The heat is transported by conduction in the solid part of the domain and by conduction, convection and radiative transfer in the fluid part (the cylinders). A non-local boundary condition models the radiative heat transfer on the cylinder walls. It is a stationary analysis corresponding to a nominal performance of the reactor core, and also non-stationary corresponding to a normal shut-down of the core. To obtain the homogenized problem we first use a formal two-scale asymptotic expansion method. The mathematical justification of our results is based on the notion of two-scale convergence. One feature of this work in dimension 3 is that it combines homogenization with a 3D to 2D asymptotic analysis since the radiative transfer in the limit cell problem is purely two-dimensional. A second feature of this work is the study of this heat transfer when it contains an oscillating thermal source at the microscopic level and a thermal exchange with the perforations. In this context, our numerical analysis shows a non-negligible contribution of the second order corrector which helps us to model the gradients appearing between the source area and the perforations. (author) [fr
Heat transfer to a dispersed two phase flow and detailed quench front velocity research

International Nuclear Information System (INIS)

De Boer, T.C.; Van der Molen, S.B.

1985-01-01

During the blow-down phase of a loss-off coolant accident (LOCA) in a pressurized water reactor the core will heat up dramatically. Water will be injected in the system, and by bottom flooding the core will be cooled. The use of one-dimensional computer models for the calculation of the reflood process in a bundle needs a better justification. The influence of an unheated shroud on prequench heat transfer is investigated in a tube, an annulus and a 4 rod bundle. By using a glass shroud for the annulus, optical analysis of the dispersed two-phase flow regime has been performed. The ECN 36-rod bundle tests as performed with axial uniform power profile are reflood and boil-down at 0.2 MPa pressure executed for different conditions. The experiment yield a data base suitable for code validation and development. Better understanding is obtained for the influence of the radial non-uniform temperature and/or power distributions on the reflood process. Heat transfer improvement induced by the presence of spacer grids is observed. 72 refs.; 220 figs.
Numerical simulation of heat transfer process in automotive brakes

OpenAIRE

Gonzalo Voltas, David

2013-01-01

This master thesis concerns the theoretical investigations of the heat transfer process in automotive brakes. The process of heat generation and heat transfer to ambient air in automotive brake was presented. The two–dimensional, axi-symmetrical model of transient heat conduction for the brake was applied. The relevant boundary conditions, that describe the heat generated in the brake and the heat transferred to ambient air, were used. The unsteady heat conduction problem was solved by the...
Comparison of CFD Natural Convection and Conduction-only Models for Heat Transfer in the Yucca Mountain Project Drifts

International Nuclear Information System (INIS)

Hadgu, T.; Webb, S.; Itamura, M.

2004-01-01

Yucca Mountain, Nevada has been designated as the nation's high-level radioactive waste repository and the U.S. Department of Energy has been approved to apply to the U.S. Nuclear Regulatory Commission for a license to construct a repository. Heat transfer in the Yucca Mountain Project (YMP) drift enclosures is an important aspect of repository waste emplacement. Canisters containing radioactive waste are to be emplaced in tunnels drilled 500 m below the ground surface. After repository closure, decaying heat is transferred from waste packages to the host rock by a combination of thermal radiation, natural convection and conduction heat transfer mechanism?. Current YMP mountain-scale and drift-scale numerical models often use a simplified porous medium code to model fluid and heat flow in the drift openings. To account for natural convection heat transfer, the thermal conductivity of the air was increased in the porous medium model. The equivalent thermal conductivity, defined as the ratio of total heat flow to conductive heat flow, used in the porous media models was based on horizontal concentric cylinders. Such modeling does not effectively capture turbulent natural convection in the open spaces as discussed by Webb et al. (2003) yet the approach is still widely used on the YMP project. In order to mechanistically model natural convection conditions in YMP drifts, the computational fluid dynamics (CFD) code FLUENT (Fluent, Incorporated, 2001) has been used to model natural convection heat transfer in the YMP emplacement drifts. A two-dimensional (2D) model representative of YMP geometry (e.g., includes waste package, drip shield, invert and drift wall) has been developed and numerical simulations made (Francis et al., 2003). Using CFD simulation results for both natural convection and conduction-only heat transfer in a single phase, single component fluid, equivalent thermal conductivities have been calculated for different Rayleigh numbers. Correlation
Kinetic Monte Carlo modeling of chemical reactions coupled with heat transfer.

Science.gov (United States)

Castonguay, Thomas C; Wang, Feng

2008-03-28

In this paper, we describe two types of effective events for describing heat transfer in a kinetic Monte Carlo (KMC) simulation that may involve stochastic chemical reactions. Simulations employing these events are referred to as KMC-TBT and KMC-PHE. In KMC-TBT, heat transfer is modeled as the stochastic transfer of "thermal bits" between adjacent grid points. In KMC-PHE, heat transfer is modeled by integrating the Poisson heat equation for a short time. Either approach is capable of capturing the time dependent system behavior exactly. Both KMC-PHE and KMC-TBT are validated by simulating pure heat transfer in a rod and a square and modeling a heated desorption problem where exact numerical results are available. KMC-PHE is much faster than KMC-TBT and is used to study the endothermic desorption of a lattice gas. Interesting findings from this study are reported.
Numerical modeling of heat transfer during hydrogen absorption in thin double-layered annular ZrCo beds

Science.gov (United States)

Cui, Yehui; Zeng, Xiangguo; Kou, Huaqin; Ding, Jun; Wang, Fang

2018-06-01

In this work a three-dimensional (3D) hydrogen absorption model was proposed to study the heat transfer behavior in thin double-layered annular ZrCo beds. Numerical simulations were performed to investigate the effects of conversion layer thickness, thermal conductivity, cooling medium and its flow velocity on the efficiency of heat transfer. Results reveal that decreasing the layer thickness and improving the thermal conductivity enhance the ability of heat transfer. Compared with nitrogen and helium, water appears to be a better medium for cooling. In order to achieve the best efficiency of heat transfer, the flow velocity needs to be maximized.

The analysis of two-phase flow and heat transfer using a multidimensional, four field, two-fluid model

International Nuclear Information System (INIS)

Lahey, Richard T.; Drew, Donald A.

2001-01-01

This paper reviews the state-of-the-art in the prediction of multidimensional multiphase flow and heat transfer phenomena using a four field, two-fluid model. It is shown that accurate mechanistic computational fluid dynamic (CFD) predictions are possible for a wide variety of adiabatic and diabatic flows using this computational model. In particular, the model is able to predict the bubbly air/water upflow data of Serizawa (Serizawa, A., 1974. Fluid dynamic characteristics of two-phase flow. Ph.D. thesis, (Nuclear Engineering), Kyoto University, Japan), the downflow data of Wang et al. (Wang, S.K., Lee, S.J., Lahey Jr., R.T., Jones, O.C., 1987. 3-D turbulence structure and phase distribution measurements in bubbly two-phase flows. Int. J. Multiphase Flow 13 (3), 327-343), the isosceles triangle upflow data of Lopez de Bertodano et al. (Lopez de Bertodano, M., Lahey Jr., R.T., Jones, O.C., 1994b. Phase distribution in bubbly two-phase flow in vertical ducts. Int. J. Multiphase Flow 20 (5), 805-818), the heated annular R-113 subcooled boiling data of Velidandala, et al. (Velidandla, V., Pulta, S., Roy, P., Kaira, S.P., 1995. Velocity field in turbulent subcooled boiling flow. ASME Preprint HTD-314, 107-123) and the R-113 CHF data of Hino and Ueda (Hino, R., Ueda, T., 1985. Studies on heat transfer and flow characteristics in subcooled boiling-part 2, flow characteristics. Int. J. Multiphase Flow 11, 283-297). It can also predict external two-phase flows, such as those for spreading two-phase jets (Bonetto, F., Lahey Jr., R.T., 1993. An experimental study on air carryunder due to a plunging liquid jet. Int. J. Multiphase Flow 19 (2), 281-294) and multiphase flows around the hull of naval surface ships (Carrica, P.M., Bonetto, F., Drew, D.A., Lahey, R.T., 1999. A polydispersed model for bubbly two-phase flow around a surface ship. Int. J. Multiphase Flow 25 (2), 257-305)
Best estimate radiation heat transfer model developed for TRAC-BD1

International Nuclear Information System (INIS)

Spore, J.W.; Giles, M.M.; Shumway, R.W.

1981-01-01

A best estimate radiation heat transfer model for analysis of BWR fuel bundles has been developed and compared with 8 x 8 fuel bundle data. The model includes surface-to-surface and surface-to-two-phase fluid radiation heat transfer. A simple method of correcting for anisotropic reflection effects has been included in the model
Two-phase flow heat transfer in nuclear reactor systems

International Nuclear Information System (INIS)

Koncar, Bostjan; Krepper, Eckhard; Bestion, Dominique; Song, Chul-Hwa; Hassan, Yassin A.

2013-01-01

occurring in at least two different spatial scales. Uncertainty in modelling of bubble departure diameter at boiling was studied by M. Matkovic and B. Koncar. In this article the propagation of input uncertainties for the simplified model of bubble departure size is evaluated. A methodology for estimating the prediction capability of a given correlation is provided taking into account its range of applicability. Aqueous nanofluids have a great potential for cooling applications, hence they have been studied in the article of P.N. Alekseev et al. as a possible coolant in pressurized water reactor (PWR). The theoretical study presents how a stable formation of nanoparticles in water solution can be established. Formation of fractal nanoparticles with a higher thermal conductivity than water can enhance the heat transfer of water used as a coolant in PWR. Apart from solid particles, also alternative formation of gaseous nanoparticles in density fluctuations of water is discussed. The article of R. Rzehak and E. Krepper provides a comprehensive overview of the state-of-the-art in the field of CFD modelling of subcooled flow boiling. The efficient predictive capability of current models requires calibration of model parameters over a wide range of measured data and operating conditions.The results presented in the article confirmed the great potential of the existing modelling approach for the 3D simulation of subcooled flow boiling in industrial applications but also highlight the need for specific model improvements to achieve highly accurate predictions. Two articles deal with one-dimensional analyses of two phase flows. In the article of O.Costa et al., a rapid depressurization in vertical heated pipe is simulated with the in-house 1D computer code WAHA, which was developed specifically for simulations of two-phase water hammer phenomena. The WAHA results were confronted with the simulations of the well-known system code RELAP5 on the same experimental data. The thermal
Thermal-Flow Code for Modeling Gas Dynamics and Heat Transfer in Space Shuttle Solid Rocket Motor Joints

Science.gov (United States)

Wang, Qunzhen; Mathias, Edward C.; Heman, Joe R.; Smith, Cory W.

2000-01-01

A new, thermal-flow simulation code, called SFLOW. has been developed to model the gas dynamics, heat transfer, as well as O-ring and flow path erosion inside the space shuttle solid rocket motor joints by combining SINDA/Glo, a commercial thermal analyzer. and SHARPO, a general-purpose CFD code developed at Thiokol Propulsion. SHARP was modified so that friction, heat transfer, mass addition, as well as minor losses in one-dimensional flow can be taken into account. The pressure, temperature and velocity of the combustion gas in the leak paths are calculated in SHARP by solving the time-dependent Navier-Stokes equations while the heat conduction in the solid is modeled by SINDA/G. The two codes are coupled by the heat flux at the solid-gas interface. A few test cases are presented and the results from SFLOW agree very well with the exact solutions or experimental data. These cases include Fanno flow where friction is important, Rayleigh flow where heat transfer between gas and solid is important, flow with mass addition due to the erosion of the solid wall, a transient volume venting process, as well as some transient one-dimensional flows with analytical solutions. In addition, SFLOW is applied to model the RSRM nozzle joint 4 subscale hot-flow tests and the predicted pressures, temperatures (both gas and solid), and O-ring erosions agree well with the experimental data. It was also found that the heat transfer between gas and solid has a major effect on the pressures and temperatures of the fill bottles in the RSRM nozzle joint 4 configuration No. 8 test.
Selection of heat transfer model for describing short-pulse laser heating silica-based sensor

International Nuclear Information System (INIS)

Hao Xiangnan; Nie Jinsong; Li Hua; Bian Jintian

2012-01-01

The fundamental equations of Fourier heat transfer model and non-Fourier heat transfer model were numerically solved, with the finite difference method. The relative changes between temperature curves of the two heat transfer models were analyzed under laser irradiation with different pulse widths of 10 ns, 1 ns, 100 ps, 10 ps. The impact of different thermal relaxation time on non-Fourier model results was discussed. For pulses of pulse width less than or equal to 100 ps irradiating silicon material, the surface temperature increases slowly and carrier effect happens, which the non-Fourier model can reflect properly. As for general material, when the pulse width is less than or equal to the thermal relaxation time of material, carrier effect occurs. In this case, the non-Fourier model should be used. (authors)
Effects of Movable-Baffle on Heat Transfer and Entropy Generation in a Cavity Saturated by CNT Suspensions: Three-Dimensional Modeling

Directory of Open Access Journals (Sweden)

Abdullah A.A.A. Al-Rashed

2017-04-01

Full Text Available Convective heat transfer and entropy generation in a 3D closed cavity, equipped with adiabatic-driven baffle and filled with CNT (carbon nanotube-water nanofluid, are numerically investigated for a range of Rayleigh numbers from 103 to 105. This research is conducted for three configurations; fixed baffle (V = 0, rotating baffle clockwise (V+ and rotating baffle counterclockwise (V− and a range of CNT concentrations from 0 to 15%. Governing equations are formulated using potential vector vorticity formulation in its three-dimensional form, then solved by the finite volume method. The effects of motion direction of the inserted driven baffle and CNT concentration on heat transfer and entropy generation are studied. It was observed that for low Rayleigh numbers, the motion of the driven baffle enhances heat transfer regardless of its direction and the CNT concentration effect is negligible. However, with an increasing Rayleigh number, adding driven baffle increases the heat transfer only when it moves in the direction of the decreasing temperature gradient; elsewhere, convective heat transfer cannot be enhanced due to flow blockage at the corners of the baffle.
Two Dimensional CFD Analyses on the Heat Transfer for a Supercritical Pressure CO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Cho, Bong Hyun; Kim, Young In; Bae, Yoon Yeong [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

2005-07-01

The Supercritical Water Cooled Reactor(SCWR) operates in a pressure around 25MPa and temperature of 293{approx}510 .deg. C. In order to study the heat transfer behaviors and good comparisons between the various fluids, a heat transfer test loop(SPHINX) using CO{sub 2} has been constructed in KAERI as a part of international research program, I-NERI. At a supercritical pressure, the heat transfer coefficient is much larger than that estimated from the Dittus-Boelter correlation for a relatively large flow rate with moderate wall heat flux conditions. This phenomenon was explained by the rapid variations of the physical properties near the wall with the temperature. On the contrary, the heat transfer becomes worse when the bulk fluid enthalpy is below the pseudo-critical enthalpy under a low flow rate with large heat flux conditions. This phenomenon is called 'deteriorated heat transfer', and which is explained as the modification of the shear stress distribution across the tube to a buoyancy and/or acceleration in a low density layer near the wall, with the consequence of a turbulence. The upward vertical flow of CO{sub 2} through a uniformly heated tube of 4.4 mm in diameter and 3m long(heated length is 2.1m) was investigated numerically using the CFD code, FLUENT. Through the numerical simulations, we have attempted to obtain a physically meaningful insight into the heat transfer mechanisms at a supercritical pressure.
Three-dimensional modelling of a dc non-transferred arc plasma torch

International Nuclear Information System (INIS)

Li Heping; Chen Xi

2001-01-01

Three-dimensional (3D) modelling results are presented concerning a direct current (dc) non-transferred arc plasma torch with axisymmetrical geometrical configuration and axisymmetrical boundary conditions. It is shown that the arc is locally attached at the anode surface of the plasma torch, and the heat transfer and plasma flow within the torch are of 3D features. The predicted arc root location at the anode surface and arc voltage of the torch are very consistent with corresponding experimental results. (author)
Modeling heat transfer in supercritical fluid using the lattice Boltzmann method.

Science.gov (United States)

Házi, Gábor; Márkus, Attila

2008-02-01

A lattice Boltzmann model has been developed to simulate heat transfer in supercritical fluids. A supercritical viscous fluid layer between two plates heated from the bottom has been studied. It is demonstrated that the model can be used to study heat transfer near the critical point where the so-called piston effect speeds up the transfer of heat and results in homogeneous heating in the bulk of the layer. We have also studied the onset of convection in a Rayleigh-Bénard configuration. It is shown that our model can well predict qualitatively the onset of convection near the critical point, where there is a crossover between the Rayleigh and Schwarzschild criteria.
Heat and mass transfer in air-fed pressurised suits

International Nuclear Information System (INIS)

Tesch, K.; Collins, M.W.; Karayiannis, T.G.; Atherton, M.A.; Edwards, P.

2009-01-01

Air-fed pressurised suits are used to protect workers against contamination and hazardous environments. The specific application here is the necessity for regular clean-up maintenance within the torus chamber of fusion reactors. The current design of suiting has been developed empirically. It is, therefore, very desirable to formulate a thermo-fluids model, which will be able to define optimum designs and operating parameters. Two factors indicate that the modelling should be as comprehensive as possible. Firstly, the overall thermo-fluids problem is three-dimensional and includes mass as well as heat transfer. The fluid field is complex, bounded on one side by the human body and on the other by what may be distensible, porous and multi-layer clothing. In this paper, we report firstly the modelling necessary for the additional mass and heat transport processes. This involves the use of Fick's and Fourier's laws and conjugate heat transfer. The results of an initial validation study are presented. Temperatures at the outlet of the suits were obtained experimentally and compared with those predicted by the overall CFD model. Realistic three-dimensional geometries were used for the suit and human body. Calculations were for turbulent flow with single- and two-component (species) models
Mathematical Model for Fluid Flow and Heat Transfer Processes in Plate Exchanger

Directory of Open Access Journals (Sweden)

Cvete B. Dimitrieska

2015-11-01

Full Text Available Within the analytical solution of the system of equations which solve fluid flow and heat transfer processes, the elliptical and parabolic differential equations based on initial and boundary conditions is usually unfamiliar in a closed form. Numerical solution of equation system is necessarily obtained by discretization of equations. When system of equations relate to estimation of two dimensional stationary problems, the applicable method for estimation in basic two – dimensional form is recommended.
Multiscale solutions of radiative heat transfer by the discrete unified gas kinetic scheme

Science.gov (United States)

Luo, Xiao-Ping; Wang, Cun-Hai; Zhang, Yong; Yi, Hong-Liang; Tan, He-Ping

2018-06-01

The radiative transfer equation (RTE) has two asymptotic regimes characterized by the optical thickness, namely, optically thin and optically thick regimes. In the optically thin regime, a ballistic or kinetic transport is dominant. In the optically thick regime, energy transport is totally dominated by multiple collisions between photons; that is, the photons propagate by means of diffusion. To obtain convergent solutions to the RTE, conventional numerical schemes have a strong dependence on the number of spatial grids, which leads to a serious computational inefficiency in the regime where the diffusion is predominant. In this work, a discrete unified gas kinetic scheme (DUGKS) is developed to predict radiative heat transfer in participating media. Numerical performances of the DUGKS are compared in detail with conventional methods through three cases including one-dimensional transient radiative heat transfer, two-dimensional steady radiative heat transfer, and three-dimensional multiscale radiative heat transfer. Due to the asymptotic preserving property, the present method with relatively coarse grids gives accurate and reliable numerical solutions for large, small, and in-between values of optical thickness, and, especially in the optically thick regime, the DUGKS demonstrates a pronounced computational efficiency advantage over the conventional numerical models. In addition, the DUGKS has a promising potential in the study of multiscale radiative heat transfer inside the participating medium with a transition from optically thin to optically thick regimes.
Three-Dimensional Superhydrophobic Nanowire Networks for Enhancing Condensation Heat Transfer

Energy Technology Data Exchange (ETDEWEB)

Yang, Ronggui [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Wen, Rongfu [University of Colorado; Xu, Shanshan [University of Colorado; Ma, Xuehu [Dalian University of Technology; Lee, Yung-Cheng [University of Colorado

2017-12-18

Spontaneous droplet jumping on nanostructured surfaces can potentially enhance condensation heat transfer by accelerating droplet removal. However, uncontrolled nucleation in the micro-defects of nanostructured superhydrophobic surfaces could lead to the formation of large pinned droplets, which greatly degrades the performance. Here, we experimentally demonstrate for the first time stable and efficient jumping droplet condensation on a superhydrophobic surface with three-dimensional (3D) copper nanowire networks. Due to the formation of interconnections among nanowires, the micro-defects are eliminated while the spacing between nanowires is reduced, which results in the formation of highly mobile droplets. By preventing flooding on 3D nanowire networks, we experimentally demonstrate a 100% higher heat flux compared with that on the state-of-the-art hydrophobic surface over a wide range of subcooling (up to 28 K). The remarkable water repellency of 3D nanowire networks can be applied to a broad range of water-harvesting and phase-change heat transfer applications.
Heat transfer coefficient for flow boiling in an annular mini gap

Directory of Open Access Journals (Sweden)

Hożejowska Sylwia

2016-01-01

Full Text Available The aim of this paper was to present the concept of mathematical models of heat transfer in flow boiling in an annular mini gap between the metal pipe with enhanced exterior surface and the external glass pipe. The one- and two-dimensional mathematical models were proposed to describe stationary heat transfer in the gap. A set of experimental data governed both the form of energy equations in cylindrical coordinates and the boundary conditions. The models were formulated to minimize the number of experimentally determined constants. Known temperature distributions in the enhanced surface and in the fluid helped to determine, from the Robin condition, the local heat transfer coefficients at the enhanced surface – fluid contact. The Trefftz method was used to find two-dimensional temperature distributions for the thermal conductive filler layer, enhanced surface and flowing fluid. The method of temperature calculation depended on whether the area of single-phase convection ended with boiling incipience in the gap or the two-phase flow region prevailed, with either fully developed bubbly flow or bubbly-slug flow. In the two–phase flow, the fluid temperature was calculated by Trefftz method. Trefftz functions for the Laplace equation and for the energy equation were used in the calculations.
Two-dimensional modeling of conduction-mode laser welding

International Nuclear Information System (INIS)

Russo, A.J.

1984-01-01

WELD2D is a two-dimensional finite difference computer program suitable for modeling the conduction-mode welding process when the molten weld pool motion can be neglected. The code is currently structured to treat butt-welded geometries in a plane normal to the beam motion so that dissimilar materials may be considered. The surface heat transfer models used in the code include a Gaussian beam or uniform laser source, and a free electron theory reflectance calculation. Temperature-dependent material parameters are used in the reflectance calculation. Measured cold reflection data are used to include surface roughness or oxide effects until melt occurs, after which the surface is assumed to be smooth and clean. Blackbody reradiation and a simple natural convection model are also included in the upper surface boundary condition. Either an implicit or explicit finite-difference representation of the heat conduction equation in an enthalpy form is solved at each time step. This enables phase transition energies to be easily and accurately incorporated into the formulation. Temperature-dependent 9second-order polynominal dependence) thermal conductivities are used in the conduction calculations. Constant values of specific heat are used for each material phase. At present, material properties for six metals are included in the code. These are: aluminium, nickel, steel, molybdenum, copper and silicon
Modelling radiative heat transfer inside a basin type solar still

International Nuclear Information System (INIS)

Madhlopa, A.

2014-01-01

Radiative heat transfer inside a basin type solar still has been investigated using two models with (model 1) and without (model 2) taking into account optical view factors. The coefficient of radiative heat exchange (h r,w-gc ) between the water and cover surfaces of a practical solar still was computed using the two models. Simulation results show that model 1 yields lower values of h r,w-gc and the root mean square error than model 2. It is therefore concluded that the accuracy of modelling the performance of a basin-type solar still can be improved by incorporating view factors. - Highlights: • Radiative heat transfer in a basin type solar still has been investigated. • Two models with and without view factors were used. • The model with view factors exhibits a lower magnitude of root mean square error. • View factors affect the accuracy of modelling the performance of the solar still
Heat Transfer Modeling for Rigid High-Temperature Fibrous Insulation

Science.gov (United States)

Daryabeigi, Kamran; Cunnington, George R.; Knutson, Jeffrey R.

2012-01-01

Combined radiation and conduction heat transfer through a high-temperature, high-porosity, rigid multiple-fiber fibrous insulation was modeled using a thermal model previously used to model heat transfer in flexible single-fiber fibrous insulation. The rigid insulation studied was alumina enhanced thermal barrier (AETB) at densities between 130 and 260 kilograms per cubic meter. The model consists of using the diffusion approximation for radiation heat transfer, a semi-empirical solid conduction model, and a standard gas conduction model. The relevant parameters needed for the heat transfer model were estimated from steady-state thermal measurements in nitrogen gas at various temperatures and environmental pressures. The heat transfer modeling methodology was evaluated by comparison with standard thermal conductivity measurements, and steady-state thermal measurements in helium and carbon dioxide gases. The heat transfer model is applicable over the temperature range of 300 to 1360 K, pressure range of 0.133 to 101.3 x 10(exp 3) Pa, and over the insulation density range of 130 to 260 kilograms per cubic meter in various gaseous environments.
Pressure drop and heat transfer in the sodium to air heat exchanger tube banks on advanced sodium-cooled fast reactor

International Nuclear Information System (INIS)

Kang, H.; Eoh, J.; Cha, J.; Kim, S.

2011-01-01

A numerical study was performed to investigate the thermal and hydraulic characteristics and build up design model of the AHX (sodium-to-air heat exchanger) unit of a sodium-cooled fast reactor. Helical-coiled tube banks in the AHX were modeled as porous media and simulated heat and momentum transfer. Two-dimensional flow characteristic appeared at the most region of AHX annulus. Pressure drop and heat transfer coefficient for rectangular, parallelogram and staggered tube banks as the main components of the AHX were evaluated and compared with Zhukauskas empirical correlations. (author)
Effect of different heat transfer models on HCCI engine simulation

International Nuclear Information System (INIS)

Neshat, Elaheh; Saray, Rahim Khoshbakhti

2014-01-01

Highlights: • A new multi zone model is developed for HCCI combustion modeling. • New heat transfer model is used for prediction of heat transfer in HCCI engines. • Model can predict engine combustion, performance and emission characteristics well. • Appropriate mass and heat transfer models cause to accurate prediction of CO, UHC and NOx. - Abstract: Heat transfer from engine walls has an important role on engine combustion, performance and emission characteristics. The main focus of this study is offering a new relation for calculation of convective heat transfer from in-cylinder charge to combustion chamber walls of HCCI engines and providing the ability of new model in comparison with the previous models. Therefore, a multi zone model is developed for homogeneous charge compression ignition engine simulation. Model consists of four different types of zones including core zone, boundary layer zone, outer zones, which are between core and boundary layer, and crevice zone. Conductive heat transfer and mass transfer are considered between neighboring zones. For accurate calculation of initial conditions at inlet valve closing, multi zone model is coupled with a single zone model, which simulates gas exchange process. Various correlations are used as convective heat transfer correlations. Woschni, modified Woschni, Hohenberg and Annand correlations are used as convective heat transfer models. The new convection model, developed by authors, is used, too. Comparative analyses are done to recognize the accurate correlation for prediction of engine combustion, performance and emission characteristics in a wide range of operating conditions. The results indicate that utilization of various heat transfer models, except for new convective heat transfer model, leads to significant differences in prediction of in-cylinder pressure and exhaust emissions. Using Woschni, Chang and new model, convective heat transfer coefficient increases near top dead center, sharply
Comparison of heat transfer models for reciprocating compressor

International Nuclear Information System (INIS)

Tuhovcak, J.; Hejcik, J.; Jicha, M.

2016-01-01

Highlights: • Comparison of integral heat transfer models. • Influence of heat transfer model on volumetric and isentropic efficiency. • Various gases used as working fluid. - Abstract: One of the main factors affecting the efficiency of reciprocating compressor is heat transfer inside the cylinder. An analysis of heat transfer could be done using numerical models or integral correlations developed mainly from approaches used in combustion engines; however their accuracy is not completely verified due to the complicated experimental set up. The goal of this paper is to analyse the effect of heat transfer on compressor efficiency. Various integral correlations were compared for different compressor settings and fluids. CoolProp library was used in the code to obtain the properties of common coolants and gases. A comparison was done using the in-house code developed in Matlab, based on 1st Law of Thermodynamics.

Model for heat and mass transfer in freeze-drying of pellets.

Science.gov (United States)

Trelea, Ioan Cristian; Passot, Stéphanie; Marin, Michèle; Fonseca, Fernanda

2009-07-01

Lyophilizing frozen pellets, and especially spray freeze-drying, have been receiving growing interest. To design efficient and safe freeze-drying cycles, local temperature and moisture content in the product bed have to be known, but both are difficult to measure in the industry. Mathematical modeling of heat and mass transfer helps to determine local freeze-drying conditions and predict effects of operation policy, and equipment and recipe changes on drying time and product quality. Representative pellets situated at different positions in the product slab were considered. One-dimensional transfer in the slab and radial transfer in the pellets were assumed. Coupled heat and vapor transfer equations between the temperature-controlled shelf, the product bulk, the sublimation front inside the pellets, and the chamber were established and solved numerically. The model was validated based on bulk temperature measurement performed at two different locations in the product slab and on partial vapor pressure measurement in the freeze-drying chamber. Fair agreement between measured and calculated values was found. In contrast, a previously developed model for compact product layer was found inadequate in describing freeze-drying of pellets. The developed model represents a good starting basis for studying freeze-drying of pellets. It has to be further improved and validated for a variety of product types and freeze-drying conditions (shelf temperature, total chamber pressure, pellet size, slab thickness, etc.). It could be used to develop freeze-drying cycles based on product quality criteria such as local moisture content and glass transition temperature.
Radiant heat transfers in turbojet engines. Two applications, three levels of modeling; Transferts radiatifs dans les foyers de turboreacteurs. Deux applications, trois niveaux de modelisation

Energy Technology Data Exchange (ETDEWEB)

Schultz, J L; Desaulty, M [SNECMA, Centre de Villaroche, 77 - Moissy-Cramayel (France); Taine, J [Ecole Centrale de Paris, Laboratoire EM2C. CNRS, 92 - Chatenay-Malabry (France)

1997-12-31

Several applications linked with the dimensioning of turbojet engines require the use of modeling of radiant heat transfers. Two different applications are presented in this study: the modeling of heat transfers in the main combustion chamber, and modeling of the infrared signature of the post-combustion chamber of a military engine. In the first application, two types of radiant heat transfer modeling are presented: a global modeling based on empirical considerations and used in rapid pre-dimensioning methods, and a modeling based on a grey gases concept and combined to a ray shooting type technique allowing the determination of local radiant heat flux values. In the second application, a specific modeling of the radiant heat flux is used in the framework of a ray shooting method. Each model represents a different level of successive approximations of the radiant heat transfer adapted to flow specificities and to the performance requested. (J.S.) 16 refs.
Radiant heat transfers in turbojet engines. Two applications, three levels of modeling; Transferts radiatifs dans les foyers de turboreacteurs. Deux applications, trois niveaux de modelisation

Energy Technology Data Exchange (ETDEWEB)

Schultz, J.L.; Desaulty, M. [SNECMA, Centre de Villaroche, 77 - Moissy-Cramayel (France); Taine, J. [Ecole Centrale de Paris, Laboratoire EM2C. CNRS, 92 - Chatenay-Malabry (France)

1996-12-31

Several applications linked with the dimensioning of turbojet engines require the use of modeling of radiant heat transfers. Two different applications are presented in this study: the modeling of heat transfers in the main combustion chamber, and modeling of the infrared signature of the post-combustion chamber of a military engine. In the first application, two types of radiant heat transfer modeling are presented: a global modeling based on empirical considerations and used in rapid pre-dimensioning methods, and a modeling based on a grey gases concept and combined to a ray shooting type technique allowing the determination of local radiant heat flux values. In the second application, a specific modeling of the radiant heat flux is used in the framework of a ray shooting method. Each model represents a different level of successive approximations of the radiant heat transfer adapted to flow specificities and to the performance requested. (J.S.) 16 refs.
Heat and mass transfer models to understand the drying mechanisms of a porous substrate.

Science.gov (United States)

Songok, Joel; Bousfield, Douglas W; Gane, Patrick A C; Toivakka, Martti

2016-02-01

While drying of paper and paper coatings is expensive, with significant energy requirements, the rate controlling mechanisms are not currently fully understood. Two two-dimensional models are used as a first approximation to predict the heat transfer during hot air drying and to evaluate the role of various parameters on the drying rates of porous coatings. The models help determine the structural limiting factors during the drying process, while applying for the first time the recently known values of coating thermal diffusivity. The results indicate that the thermal conductivity of the coating structure is not the controlling factor, but the drying rate is rather determined by the thermal transfer process at the structure surface. This underlines the need for ensuring an efficient thermal transfer from hot air to coating surface during drying, before considering further measures to increase the thermal conductivity of porous coatings.
Molecular dynamics simulation of heat transfer through a water layer between two platinum slabs

International Nuclear Information System (INIS)

Iype, E; Arlemark, E J; Nedea, S V; Rindt, C C M; Zondag, H A

2012-01-01

Heat transfer through micro channels is being investigated due to its importance in micro channel cooling applications. Molecular dynamics simulation is regarded as a potential tool for studying such microscopic phenomena in detail. However, the applicability of molecular dynamics method is limited due to scarcely known inter atomic interactions involved in complex fluids. In this study we use an empirical force field (ReaxFF), which is parameterized using accurate quantum chemical simulation results for water, to simulate heat transfer phenomena through a layer of water confined between two platinum slabs. The model for water seems to reproduce the macroscopic properties such as density, radial distribution function and diffusivity quite well. The heat transfer phenomena through a channel filled with water, which is confined by two platinum (100) surfaces are studied using ReaxFF. The model accurately predicts the formation of surface mono-layer. The heat transfer analysis shows temperature jumps near the walls which are creating significant heat transfer resistances. A low bulk density in the channel creates a multi-phase region with vapor transport in the region.
Multi-time-scale heat transfer modeling of turbid tissues exposed to short-pulsed irradiations.

Science.gov (United States)

Kim, Kyunghan; Guo, Zhixiong

2007-05-01

A combined hyperbolic radiation and conduction heat transfer model is developed to simulate multi-time-scale heat transfer in turbid tissues exposed to short-pulsed irradiations. An initial temperature response of a tissue to an ultrashort pulse irradiation is analyzed by the volume-average method in combination with the transient discrete ordinates method for modeling the ultrafast radiation heat transfer. This response is found to reach pseudo steady state within 1 ns for the considered tissues. The single pulse result is then utilized to obtain the temperature response to pulse train irradiation at the microsecond/millisecond time scales. After that, the temperature field is predicted by the hyperbolic heat conduction model which is solved by the MacCormack's scheme with error terms correction. Finally, the hyperbolic conduction is compared with the traditional parabolic heat diffusion model. It is found that the maximum local temperatures are larger in the hyperbolic prediction than the parabolic prediction. In the modeled dermis tissue, a 7% non-dimensional temperature increase is found. After about 10 thermal relaxation times, thermal waves fade away and the predictions between the hyperbolic and parabolic models are consistent.
A multi-phase ferrofluid flow model with equation of state for thermomagnetic pumping and heat transfer

Energy Technology Data Exchange (ETDEWEB)

Aursand, Eskil, E-mail: eskil.aursand@sintef.no; Gjennestad, Magnus Aa.; Yngve Lervåg, Karl; Lund, Halvor

2016-03-15

A one-dimensional multi-phase flow model for thermomagnetically pumped ferrofluid with heat transfer is proposed. The thermodynamic model is a combination of a simplified particle model and thermodynamic equations of state for the base fluid. The magnetization model is based on statistical mechanics, taking into account non-uniform particle size distributions. An implementation of the proposed model is validated against experiments from the literature, and found to give good predictions for the thermomagnetic pumping performance. However, the results reveal a very large sensitivity to uncertainties in heat transfer coefficient predictions. - Highlights: • A multi-phase flow model for thermomagnetically pumped ferrofluid is proposed. • An implementation is validated against experiments from the literature. • Predicted thermomagnetic pumping effect agrees with experiments. • However, a very large sensitivity to heat transfer coefficient is revealed.
Proceedings of the 29th heat transfer and fluid mechanics institute

International Nuclear Information System (INIS)

Reardon, F.H.; Ngo, D.T.

1985-01-01

This book presents the papers given at a conference on two-phase flow and heat transfer. Topics considered at the conference included two-phase flow in zero gravity, approximate characteristics for one-dimensional two-phase flows, Soret transport in the production of silicon for solar cells, the dynamics of heat transfer in packed beds, and heat transfer in variable-property MHD entrance flow with a generalized temperature boundary condition
On Two-Scale Modelling of Heat and Mass Transfer

International Nuclear Information System (INIS)

Vala, J.; Stastnik, S.

2008-01-01

Modelling of macroscopic behaviour of materials, consisting of several layers or components, whose microscopic (at least stochastic) analysis is available, as well as (more general) simulation of non-local phenomena, complicated coupled processes, etc., requires both deeper understanding of physical principles and development of mathematical theories and software algorithms. Starting from the (relatively simple) example of phase transformation in substitutional alloys, this paper sketches the general formulation of a nonlinear system of partial differential equations of evolution for the heat and mass transfer (useful in mechanical and civil engineering, etc.), corresponding to conservation principles of thermodynamics, both at the micro- and at the macroscopic level, and suggests an algorithm for scale-bridging, based on the robust finite element techniques. Some existence and convergence questions, namely those based on the construction of sequences of Rothe and on the mathematical theory of two-scale convergence, are discussed together with references to useful generalizations, required by new technologies.
On Two-Scale Modelling of Heat and Mass Transfer

Science.gov (United States)

Vala, J.; Št'astník, S.

2008-09-01

Modelling of macroscopic behaviour of materials, consisting of several layers or components, whose microscopic (at least stochastic) analysis is available, as well as (more general) simulation of non-local phenomena, complicated coupled processes, etc., requires both deeper understanding of physical principles and development of mathematical theories and software algorithms. Starting from the (relatively simple) example of phase transformation in substitutional alloys, this paper sketches the general formulation of a nonlinear system of partial differential equations of evolution for the heat and mass transfer (useful in mechanical and civil engineering, etc.), corresponding to conservation principles of thermodynamics, both at the micro- and at the macroscopic level, and suggests an algorithm for scale-bridging, based on the robust finite element techniques. Some existence and convergence questions, namely those based on the construction of sequences of Rothe and on the mathematical theory of two-scale convergence, are discussed together with references to useful generalizations, required by new technologies.
Heat transfer from rough surfaces

International Nuclear Information System (INIS)

Dalle Donne, M.

1977-01-01

Artificial roughness is often used in nuclear reactors to improve the thermal performance of the fuel elements. Although these are made up of clusters of rods, the experiments to measure the heat transfer and friction coefficients of roughness are performed with single rods contained in smooth tubes. This work illustrated a new transformation method to obtain data applicable to reactor fuel elements from these annulus experiments. New experimental friction data are presented for ten rods, each with a different artificial roughness made up of two-dimensional rectangular ribs. For each rod four tests have been performed, each in a different outer smooth tube. For two of these rods, each for two different outer tubes, heat transfer data are also given. The friction and heat transfer data, transformed with the present method, are correlated by simple equations. In the paper, these equations are applied to a case typical for a Gas Cooled Fast Reactor fuel element. (orig.) [de
Application of two-equation turbulence models to turbulent gas flow heated by a high heat flux

International Nuclear Information System (INIS)

Kawamura, Hiroshi

1978-01-01

Heat transfer in heated turbulent gas flow is analyzed using two-equation turbulence models. Four kinds of two-equation models are examined; that is, k-epsilon model by Jones-Launder, k-w model by Wilcox-Traci, k-kL model by Rotta, k-ω model by Saffman-Wilcox. The results are compared with more than ten experiments by seven authors. The k-kL model proposed originally by Rotta and modified by the present author is found to give relatively the best results. It well predicts the decrease in the heat transfer coefficient found in the heated turbulent gas flow; however, it fails to predict the laminarization due to a strong heating. (author)
Magnetohydrodynamics effect on three-dimensional viscous incompressible flow between two horizontal parallel porous plates and heat transfer with periodic injection/suction

Directory of Open Access Journals (Sweden)

R. C. Chaudhary

2004-11-01

Full Text Available We investigate the hydromagnetic effect on viscous incompressible flow between two horizontal parallel porous flat plates with transverse sinusoidal injection of the fluid at the stationary plate and its corresponding removal by periodic suction through the plate in uniform motion. The flow becomes three dimensional due to this injection/suction velocity. Approximate solutions are obtained for the flow field, the pressure, the skin-friction, the temperature field, and the rate of heat transfer. The dependence of solution on M (Hartmann number and ÃŽÂ» (injection/suction is investigated by the graphs and tables.
Boundary conditions for heat transfer and evaporative cooling in the trachea and air sac system of the domestic fowl: a two-dimensional CFD analysis.

Directory of Open Access Journals (Sweden)

Nina S Sverdlova

Full Text Available Various parts of the respiratory system play an important role in temperature control in birds. We create a simplified computational fluid dynamics (CFD model of heat exchange in the trachea and air sacs of the domestic fowl (Gallus domesticus in order to investigate the boundary conditions for the convective and evaporative cooling in these parts of the respiratory system. The model is based upon published values for respiratory times, pressures and volumes and upon anatomical data for this species, and the calculated heat exchange is compared with experimentally determined values for the domestic fowl and a closely related, wild species. In addition, we studied the trachea histologically to estimate the thickness of the heat transfer barrier and determine the structure and function of moisture-producing glands. In the transient CFD simulation, the airflow in the trachea of a 2-dimensional model is evoked by changing the volume of the simplified air sac. The heat exchange between the respiratory system and the environment is simulated for different ambient temperatures and humidities, and using two different models of evaporation: constant water vapour concentration model and the droplet injection model. According to the histological results, small mucous glands are numerous but discrete serous glands are lacking on the tracheal surface. The amount of water and heat loss in the simulation is comparable with measured respiratory values previously reported. Tracheal temperature control in the avian respiratory system may be used as a model for extinct or rare animals and could have high relevance for explaining how gigantic, long-necked dinosaurs such as sauropoda might have maintained a high metabolic rate.
Model for definition of heat transfer coefficient in an annular two-phase flow

International Nuclear Information System (INIS)

Khun, J.

1976-01-01

Near-wall heat exchange in a vertical tube at high vapor velocity in a two-phase vapor and liquid flow is investigated. The flow divides inside the tube into a near-wall liquid film and a vapor nucleus containing liquid droplets, with the boundaries being uniform. The liquid film thickness determines the main resistance during heat transfer between the wall and vapor nucleus. The theoretical model presented is verified in water vaporization experiments, the R12 cooling agent and certain hydrocarbons. The loss of friction pressure is determined by the Lockart-Martinelli method. The approximately universal Carman velocity profile is used to evaluate the velocity in film, and basing on this, film thickness is determined. The parameter ranges were: Resub(vap)=10 4 -3x10 6 , Resub(liq.)=0.9-10. The theoretical model ensures good correlation with the experiment
Convective heat transfer the molten metal pool heated from below and cooled by two-phase flow

International Nuclear Information System (INIS)

Cho, J. S.; Suh, K. Y.; Chung, C. H.; Park, R. J.; Kim, S. B.

1998-01-01

During a hypothetical servere accident in the nuclear power plant, a molten core material may form stratified fluid layers. These layers may be composed of high temperature molten debris pool and water coolant in the lower plenum of the reactor vessel or in the reactor cavity. This study is concerned with the experimental test and numerical analysis on the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. This work examines the crust formation and the heat transfer characteristics of the molten metal pool immersed in the boiling coolant. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. The simulant molten pool material is tin (Sn) with the melting temperature of 232 .deg. C. Demineralized water is used as the working coolant. Tests were performed under the condition of the bottom surface heating in the test section and the forced convection of the coolant being injected onto the molten metal pool. The constant temperature and constant heat flux conditions are adopted for the bottom heating. The test parameters included the heated bottom surface temperature of the molten metal pool, the input power to the heated bottom surface of the test section, and the coolant injection rate. Numerical analyses were simultaneously performed in a two-dimensional rectangular domain of the molten metal pool to check on the measured data. The numerical program has been developed using the enthalpy method, the finite volume method and the SIMPLER algorithm. The experimental results of the heat transfer show general agreement with the calculated values. In this study, the relationship between the Nusselt number and Rayleigh number in the molten metal pool region was estimated and compared with the dry experiment without coolant nor solidification of the molten metal pool, and with the crust formation experiment with subcooled coolant, and against other correlations. In the experiments, the
Heat transfer control in a plane magnetic fluid layer with a free surface

International Nuclear Information System (INIS)

Bashtovoi, V.G.; Pogirnitskaya, S.G.; Reks, A.G.

1993-01-01

The heat transfer mechanisms that are specific to a magnetic liquid have been already investigated extensively. The high sensitivity of the free magnetic liquid surface to the external magnetic field introduces a new feature into the heat transfer process. In the present work, the authors have investigated the possibility of controlling the heat transfer through the phenomenon of magnetic liquid surface instability in a uniform magnetic field. The conditions for heat transfer through a chamber, partially filled with a magnetic liquid, are governed by the characteristics of the free liquid surface and by its stability and development in the supercritical magnetic fields. The authors consider a model two-dimensional problem of heat transfer through a two-layer medium consisting of horizontally situated immiscible layers of magnetic and nonmagnetic liquids with given thermal conductivities. In the absence of an external magnetic field, the interface of the liquids represents a plane surface. In fields which exceed the critical magnitude, the interface is deformed along the wave. As the field intensity is increased, the amplitude of interface distortion becomes larger. The two-dimensional shape of the free magnetic liquid surface may be realized experimentally using two plane layers of magnetic and nonmagnetic liquids in a uniform magnetic field tangent to the interface of the component layers. 7 refs., 9 figs
An assessment of RELAP5 MOD3.1.1 condensation heat transfer modeling with GIRAFFE heat transfer tests

International Nuclear Information System (INIS)

Boyer, B.D.; Parlatan, Y.; Slovik, G.C.; Rohatgi, U.S.

1995-01-01

RELAP5 MOD3.1.1 is being used to simulate Loss of Coolant Accidents (LOCA) for the Simplified Boiling Water Reactor (SBWR) being proposed by General Electric (GE). One of the major components associated with the SBWR is the Passive Containment Cooling System (PCCS) which provides the long-term heat sink to reject decay heat. The RELAP5 MOD3.1.1 code is being assessed for its ability to represent accurately the PCCS. Data from the Phase 1, Step 1 Heat Transfer Tests performed at Toshiba's Gravity-Driven Integral Full-Height Test for Passive Heat Removal (GIRAFFE) facility will be used for assessing the ability of RELAP5 to model condensation in the presence of noncondensables. The RELAP5 MOD3.1.1 condensation model uses the University of California at Berkeley (UCB) correlation developed by Vierow and Schrock. The RELAP5 code uses this heat transfer coefficient with the gas velocity effect multiplier being limited to 2. This heat transfer option was used to analyze the condensation heat transfer in the GIRAFFE PCCS heat exchanger tubes in the Phase 1, Step 1 Heat Transfer Tests which were at a pressure of 3 bar and had a range of nitrogen partial pressure fractions from 0.0 to 0.10. The results of a set of RELAP5 calculations al these conditions were compared with the GIRAFFE data. The effects of PCCS cell nodings on the heat transfer process were also studied. The UCB correlation, as implemented in RELAP5, predicted the heat transfer to ±5% of the data with a three-node model. The three-node model has a large cell in the entrance region which smeared out the entrance effects on the heat transfer, which tend to overpredict the condensation. Hence, the UCB correlation predicts condensation heat transfer in the presence of noncondensable gases with only a coarse mesh. The cell length term in the condensation heat transfer correlation implemented in the code must be removed to allow for accurate calculations with smaller cell sizes
Models for fluid flows with heat transfer in mixed convection

International Nuclear Information System (INIS)

Mompean Munhoz da Cruz, G.

1989-06-01

Second order models were studied in order to predict turbulent flows with heat transfer. The equations used correspond to the characteristic scale of turbulent flows. The order of magnitude of the terms of the equation is analyzed by using Reynolds and Peclet numbers. The two-equation model (K-ε) is applied in the hydrodynamic study. Two models are developed for the heat transfer analysis: the Prt + teta 2 and the complete model. In the first model, the turbulent thermal diffusivity is calculated by using the Prandtl number for turbulent flow and an equation for the variance of the temperature fluctuation. The second model consists of three equations concerning: the turbulent heat flow, the variance of the temperature fluctuation and its dissipation ratio. The equations were validated by four experiments, which were characterized by the analysis of: the air flow after passing through a grid of constant average temperature and with temperature gradient, an axysymmetric air jet submitted to high and low heating temperature, the mixing (cold-hot) of two coaxial jets of sodium at high Peclet number. The complete model is shown to be the most suitable for the investigations presented [fr
Two-demensional analysis of heat and mass transfer in porous media using the strongly implicit procedure

Science.gov (United States)

Curry, D. M.

1974-01-01

Numerical results of the heat and mass transfer in a porous matrix are presented. The coupled, nonlinear partial differential equations describing this physical phenomenon are solved in finite difference form for two dimensions, using a new iterative technique (the strongly implicit procedure). The influence of the external environment conditions (heating and pressure) is shown to produce two-dimensional flow in the porous matrix. Typical fluid and solid temperature distributions in the porous matrix and internal pressure distributions are presented.

Conjugate Compressible Fluid Flow and Heat Transfer in Ducts

Science.gov (United States)

Cross, M. F.

2011-01-01

A computational approach to modeling transient, compressible fluid flow with heat transfer in long, narrow ducts is presented. The primary application of the model is for analyzing fluid flow and heat transfer in solid propellant rocket motor nozzle joints during motor start-up, but the approach is relevant to a wide range of analyses involving rapid pressurization and filling of ducts. Fluid flow is modeled through solution of the spatially one-dimensional, transient Euler equations. Source terms are included in the governing equations to account for the effects of wall friction and heat transfer. The equation solver is fully-implicit, thus providing greater flexibility than an explicit solver. This approach allows for resolution of pressure wave effects on the flow as well as for fast calculation of the steady-state solution when a quasi-steady approach is sufficient. Solution of the one-dimensional Euler equations with source terms significantly reduces computational run times compared to general purpose computational fluid dynamics packages solving the Navier-Stokes equations with resolved boundary layers. In addition, conjugate heat transfer is more readily implemented using the approach described in this paper than with most general purpose computational fluid dynamics packages. The compressible flow code has been integrated with a transient heat transfer solver to analyze heat transfer between the fluid and surrounding structure. Conjugate fluid flow and heat transfer solutions are presented. The author is unaware of any previous work available in the open literature which uses the same approach described in this paper.
Calculating the heat transfer coefficient of frame profiles with internal cavities

DEFF Research Database (Denmark)

Noyé, Peter Anders; Laustsen, Jacob Birck; Svendsen, Svend

2004-01-01

. The heat transfer coefficient is determined by two-dimensional numerical calculations and by measurements. Calculations are performed in Therm (LBNL (2001)), which is developed at Lawrence Berkeley National Laboratory, USA. The calculations are performed in accordance with the future European standards...... correspondence between measured and calculated values. Hence, when determining the heat transfer coefficient of frame profiles with internal cavities by calculations, it is necessary to apply a more detailed radiation exchange model than described in the prEN ISO 10077-2 standard. The ISO-standard offers......Determining the energy performance of windows requires detailed knowledge of the thermal properties of their different elements. A series of standards and guidelines exist in this area. The thermal properties of the frame can be determined either by detailed two-dimensional numerical methods...
Investigation of heat transfer of tube line of staggered tube bank in two-phase flow

Science.gov (United States)

Jakubcionis, Mindaugas

2015-06-01

This article presents the results of experimental investigation of heat transfer process, carried out using the model of heat exchanger. Two-phase statically stable foam flow was used as a heat transfer fluid. Heat exchanger model consisted of staggered tube bank. Experimental results are presented with the focus on influence of tube position in the line of the bank, volumetric void component and velocity of gas component of the foam. The phenomena of liquid draining in cellular foam flow and its influence on heat transfer rate has also been discussed. The experimental results have been generalized by relationship between Nusselt, Reynolds and Prandtl numbers.
Characterizing convective heat transfer using infrared thermography and the heated-thin-foil technique

International Nuclear Information System (INIS)

Stafford, Jason; Walsh, Ed; Egan, Vanessa

2009-01-01

Convective heat transfer, due to axial flow fans impinging air onto a heated flat plate, is investigated with infrared thermography to assess the heated-thin-foil technique commonly used to quantify two-dimensional heat transfer performance. Flow conditions generating complex thermal profiles have been considered in the analysis to account for dominant sources of error in the technique. Uncertainties were obtained in the measured variables and the influences on the resultant heat transfer data are outlined. Correction methods to accurately account for secondary heat transfer mechanisms were developed and results show that as convective heat transfer coefficients and length scales decrease, the importance of accounting for errors increases. Combined with flow patterns that produce large temperature gradients, the influence of heat flow within the foil on the resultant heat transfer becomes significant. Substantial errors in the heat transfer coefficient are apparent by neglecting corrections to the measured data for the cases examined. Methods to account for these errors are presented here, and demonstrated to result in an accurate measurement of the local heat transfer map on the surface
Application of flexibility model in modeling of flow boiling heat transfer

International Nuclear Information System (INIS)

Peng Jinfeng; Zhao Fuyu

2009-01-01

The mathematical modeling and computer simulation have been widely used in the analysis of system's dynamic characteristics, and often useful for system control. One of the popular methods for this purpose is the lumped parameter method. For flow boiling heat transfer system, the traditional lumped parameter modeling method has a problem that the heat transfer coefficients change suddenly at the boundary of coolant phase change. It can cause error. In this paper, an idea of flexibility model is developed to deal with the boundary problem and to improve the model of flow boiling heat transfer. The segments of coolant phase change's boundary are identified, and the membership functions which are derived from Fuzzy Mathematics are used to derive approximate expressions of heat transfer coefficient in those regions. The continuity of heat transfer coefficient can be described by those expressions. The membership functions are derived from mathematical analysis and transformation. The result shows that this idea is feasible and the conclusion is practicable.
An assessment of RELAP5 MOD3.1.1 condensation heat transfer modeling with GIRAFFE heat transfer tests

International Nuclear Information System (INIS)

Boyer, B.D.; Parlatan, Y.; Slovik, G.C.

1995-01-01

RELAP5 MOD3.1.1 is being used to simulate Loss of Coolant Accidents (LOCA) for the Simplified Boiling Water Reactor (SBWR) being proposed by General Electric (GE). One of the major components associated with the SBWR is the Passive Containment Cooling System (PCCS) which provides the long-term heat sink to reject decay heat. The RELAP5 MOD3.1.1 code is being assessed for its ability to represent accurately the PCCS. Data from the Phase 1, Step 1 Heat Transfer Tests performed at Toshiba's Gravity-Driven Integral Full-Height Test for Passive Heat Removal (GIRAFFE) facility will be used for assessing the ability of RELAP5 to model condensation in the presence of noncondensables. The RELAP5 MOD3.1.1 condensation model uses the University of California at Berkeley (UCB) correlation developed by Vierow and Schrock. The RELAP5 code uses this heat transfer coefficient with the gas velocity effect multiplier being limited to 2. This heat transfer option was used to analyze the condensation heat transfer in the GIRAFFE PCCS heat exchanger tubes in the Phase 1, Step 1 Heat Transfer Tests which were at a pressure of 3 bar and had a range of nitrogen partial pressure fractions from 0.0 to 0.10. The results of a set of RELAP5 calculations at these conditions were compared with the GIRAFFE data. The effects of PCCS cell noding on the heat transfer process were also studied. The UCB correlation, as implemented in RELAP5, predicted the heat transfer to ±5% of the data with a three--node model. The three-node model has a large cell in the entrance region which smeared out the entrance effects on the heat transfer, which tend to overpredict the condensation. Hence, the UCB correlation predicts condensation heat transfer correlation implemented in the code must be removed to allow for accurate calculations with smaller cell sizes
An assessment of RELAP5 MOD3.1.1 condensation heat transfer modeling with GIRAFFE heat transfer tests

Energy Technology Data Exchange (ETDEWEB)

Boyer, B.D.; Parlatan, Y.; Slovik, G.C. [and others

1995-09-01

RELAP5 MOD3.1.1 is being used to simulate Loss of Coolant Accidents (LOCA) for the Simplified Boiling Water Reactor (SBWR) being proposed by General Electric (GE). One of the major components associated with the SBWR is the Passive Containment Cooling System (PCCS) which provides the long-term heat sink to reject decay heat. The RELAP5 MOD3.1.1 code is being assessed for its ability to represent accurately the PCCS. Data from the Phase 1, Step 1 Heat Transfer Tests performed at Toshiba`s Gravity-Driven Integral Full-Height Test for Passive Heat Removal (GIRAFFE) facility will be used for assessing the ability of RELAP5 to model condensation in the presence of noncondensables. The RELAP5 MOD3.1.1 condensation model uses the University of California at Berkeley (UCB) correlation developed by Vierow and Schrock. The RELAP5 code uses this heat transfer coefficient with the gas velocity effect multiplier being limited to 2. This heat transfer option was used to analyze the condensation heat transfer in the GIRAFFE PCCS heat exchanger tubes in the Phase 1, Step 1 Heat Transfer Tests which were at a pressure of 3 bar and had a range of nitrogen partial pressure fractions from 0.0 to 0.10. The results of a set of RELAP5 calculations at these conditions were compared with the GIRAFFE data. The effects of PCCS cell noding on the heat transfer process were also studied. The UCB correlation, as implemented in RELAP5, predicted the heat transfer to {plus_minus}5% of the data with a three--node model. The three-node model has a large cell in the entrance region which smeared out the entrance effects on the heat transfer, which tend to overpredict the condensation. Hence, the UCB correlation predicts condensation heat transfer correlation implemented in the code must be removed to allow for accurate calculations with smaller cell sizes.
Modeling Xenon Tank Pressurization using One-Dimensional Thermodynamic and Heat Transfer Equations

Science.gov (United States)

Gilligan, Ryan P.; Tomsik, Thomas M.

2017-01-01

As a first step in understanding what ground support equipment (GSE) is required to provide external cooling during the loading of 5,000 kg of xenon into 4 aluminum lined composite overwrapped pressure vessels (COPVs), a modeling analysis was performed using Microsoft Excel. The goals of the analysis were to predict xenon temperature and pressure throughout loading at the launch facility, estimate the time required to load one tank, and to get an early estimate of what provisions for cooling xenon might be needed while the tanks are being filled. The model uses the governing thermodynamic and heat transfer equations to achieve these goals. Results indicate that a single tank can be loaded in about 15 hours with reasonable external coolant requirements. The model developed in this study was successfully validated against flight and test data. The first data set is from the Dawn mission which also utilizes solar electric propulsion with xenon propellant, and the second is test data from the rapid loading of a hydrogen cylindrical COPV. The main benefit of this type of model is that the governing physical equations using bulk fluid solid temperatures can provide a quick and accurate estimate of the state of the propellant throughout loading which is much cheaper in terms of computational time and licensing costs than a Computation Fluid Dynamics (CFD) analysis while capturing the majority of the thermodynamics and heat transfer.
Validation of heat transfer models for gap cooling

International Nuclear Information System (INIS)

Okano, Yukimitsu; Nagae, Takashi; Murase, Michio

2004-01-01

For severe accident assessment of a light water reactor, models of heat transfer in a narrow annular gap between overheated core debris and a reactor pressure vessel are important for evaluating vessel integrity and accident management. The authors developed and improved the models of heat transfer. However, validation was not sufficient for applicability of the gap heat flux correlation to the debris cooling in the vessel lower head and applicability of the local boiling heat flux correlations to the high-pressure conditions. Therefore, in this paper, we evaluated the validity of the heat transfer models and correlations by analyses for ALPHA and LAVA experiments where molten aluminum oxide (Al 2 O 3 ) at about 2700 K was poured into the high pressure water pool in a small-scale simulated vessel lower head. In the heating process of the vessel wall, the calculated heating rate and peak temperature agreed well with the measured values, and the validity of the heat transfer models and gap heat flux correlation was confirmed. In the cooling process of the vessel wall, the calculated cooling rate was compared with the measured value, and the validity of the nucleate boiling heat flux correlation was confirmed. The peak temperatures of the vessel wall in ALPHA and LAVA experiments were lower than the temperature at the minimum heat flux point between film boiling and transition boiling, so the minimum heat flux correlation could not be validated. (author)
Numerical modeling of heat transfer and pasteurizing value during thermal processing of intact egg.

Science.gov (United States)

Abbasnezhad, Behzad; Hamdami, Nasser; Monteau, Jean-Yves; Vatankhah, Hamed

2016-01-01

Thermal Pasteurization of Eggs, as a widely used nutritive food, has been simulated. A three-dimensional numerical model, computational fluid dynamics codes of heat transfer equations using heat natural convection, and conduction mechanisms, based on finite element method, was developed to study the effect of air cell size and eggshell thickness. The model, confirmed by comparing experimental and numerical results, was able to predict the temperature profiles, the slowest heating zone, and the required heating time during pasteurization of intact eggs. The results showed that the air cell acted as a heat insulator. Increasing the air cell volume resulted in decreasing of the heat transfer rate, and the increasing the required time of pasteurization (up to 14%). The findings show that the effect on thermal pasteurization of the eggshell thickness was not considerable in comparison to the air cell volume.
Development of design evaluation tools for the JSFR fuel transfer pot

Energy Technology Data Exchange (ETDEWEB)

Chikazawa, Yoshitaka, E-mail: chikazawa.yoshitaka@jaea.go.jp [Japan Atomic Energy Agency, 4002 Narita, Oarai, Higashi-ibaraki-gun, Ibaraki 311-1393 (Japan); Hirata, Shingo [Japan Atomic Energy Agency, 4002 Narita, Oarai, Higashi-ibaraki-gun, Ibaraki 311-1393 (Japan); Obata, Hiroyuki [Japan Atomic Power Company Ltd., 1-1, Mitoshiro-chyo, Kanda, Chiyoda-ku, Tokyo 101-0053 (Japan)

2014-07-01

Highlights: • JSFR is going to adopt an advanced fuel handling system. • A three dimensional analysis model for heat transfer evaluation of the JSFR fuel transfer pot has been developed. • The heat transfer models inside and outside the pot have been validated by reference experiments. • For a simpler design tool, a two dimensional analysis model has been developed. - Abstract: JSFR is going to adopt an advanced fuel handling system. As for ex-vessel spent fuel handling, a transfer pot with two fuel subassembly positions has been developed so as to shorten refueling period increasing plant availability. The pot is required to provide sufficient cooling capability in case of transportation malfunction. In this study, a three dimensional analysis model for heat transfer evaluation of the JSFR fuel transfer pot has been developed. The heat transfer models inside and outside the pot have been validated by reference experiments. Using the developed three-dimensional model, the JSFR fuel transfer pot has been analyzed. For a simpler design tool, a two dimensional analysis model has been developed. Comparison of the three and two dimensional analyses shows that two dimensional analyses could estimate pot cooling performance conservatively.
3D numerical simulation on heat transfer performance of a cylindrical liquid immersion solar receiver

International Nuclear Information System (INIS)

Xiang Haijun; Wang Yiping; Zhu Li; Han Xinyue; Sun Yong; Zhao Zhengjian

2012-01-01

Highlights: ► Establishment of a three-dimensional numerical simulation model of a cylindrical liquid immersion solar receiver. ► Determination of model parameters and validation of the model by using the real-collected data. ► Optimization of liquid flow rate and fin’s structure for better heat transfer performance. - Abstract: Liquid immersion cooling for a cylindrical solar receiver in a dish concentrator photovoltaic system has been experimentally verified to be a promising method of removing surplus heat from densely packed solar cells. In the present study, a three-dimensional (3D) numerical simulation model of the prototype was established for better understanding the mechanism of the direct-contact heat transfer process. With the selection of standard k–ε turbulent model, the detailed simulation results of velocity field and temperature characteristics were obtained. The heat transfer performance of two structural modules (bare module and finned module) under actual weather conditions was simulated. It was found that the predicted temperature distribution of the two structural modules at the axial and lateral direction was in good agreement with the experimental data. Based on the validated simulation model, the influence of liquid flow rate and module geometric parameters on the cell temperature was then investigated. The simulated results indicated that the cell module with fin height of 4 mm and fin number of 11 has the best heat transfer performance and will be used in further works.
A three-dimensional numerical study and comparison between the air side model and the air/water side model of a plain fin-and-tube heat exchanger

International Nuclear Information System (INIS)

Borrajo-Pelaez, R.; Ortega-Casanova, J.; Cejudo-Lopez, J.M.

2010-01-01

CFD is becoming an important heat exchanger research technique. It constitutes an inexpensive prediction method, avoiding the need of testing numerous prototypes. Current work in this field is mostly based on air flow models assuming constant temperature of fin-and-tube surface. The purpose of this paper is to present an enhanced model, whose innovation lies in considering additionally the water flow in the tubes and the conduction heat transfer through the fin and tubes, to demonstrate that the neglect of these two phenomena causes a simulation result accuracy reduction. 3-D Numerical simulations were accomplished to compare both an air side and an air/water side model. The influence of Reynolds number, fin pitch, tube diameter, fin length and fin thickness was studied. The exchanger performance was evaluated through two non-dimensional parameters: the air side Nusselt number and a friction factor. It was found that the influence of the five parameters over the mechanical and thermal efficiencies can be well reported using these non-dimensional coefficients. The results from the improved model showed more real temperature contours, with regard to those of the simplified model. Therefore, a higher accuracy of the heat transfer was achieved, yielding better predictions on the exchanger performance.
Measurement of critical heat flux in narrow gap with two-dimensional slices

International Nuclear Information System (INIS)

Kim, Yong Hoon; Kim, Sung Joong; Noh, Sang Woo; Suh, Kune Y.

2002-01-01

value because the power of the heaters was restricted by the three-dimensional (3D) geometry. The two-dimensional (2D) geometry relative to the 3D geometry enables the heaters to produce higher power. Experiments were conducted to develop the CHF correlation for gap cooling with the 2D slices. The experimental facility consisted of a heater, a pressure vessel, a heat exchanger and the pressure and temperature measurement system. Tests were carried out in the pressure range of 0.1 to 1 MPa for the gap sizes of 1mm and 2mm using demineralized water
FEHMN 1.0: Finite element heat and mass transfer code

International Nuclear Information System (INIS)

Zyvoloski, G.; Dash, Z.; Kelkar, S.

1991-04-01

A computer code is described which can simulate non-isothermal multiphase multicomponent flow in porous media. It is applicable to natural-state studies of geothermal systems and ground-water flow. The equations of heat and mass transfer for multiphase flow in porous and permeable media are solved using the finite element method. The permeability and porosity of the medium are allowed to depend on pressure and temperature. The code also has provisions for movable air and water phases and noncoupled tracers; that is, tracer solutions that do not affect the heat and mass transfer solutions. The tracers can be passive or reactive. The code can simulate two-dimensional, two-dimensional radial, or three-dimensional geometries. A summary of the equations in the model and the numerical solution procedure are provided in this report. A user's guide and sample problems are also included. The main use of FEHMN will be to assist in the understanding of flow fields in the saturated zone below the proposed Yucca Mountain Repository. 33 refs., 27 figs., 12 tabs
Heat transfer in window frames with internal cavities

Energy Technology Data Exchange (ETDEWEB)

Gustavsen, Arild

2001-07-01

Heat transfer in window frames with internal air cavities is studied in this thesis. Investigations focus on two- and three-dimensional natural convection effects inside air cavities, the dependence of the emissivity on the thermal transmittance, and the emissivity of anodized and untreated aluminium profiles. The investigations are mostly conducted on window frames which are the same size as real frames found in residential buildings. Numerical and experimental investigations were performed to study the effectiveness of one commercial Computational Fluid Dynamics (CFD) program for simulating combined natural convection and heat transfer in simple three-dimensional window frames with internal air cavities. The accuracy of the conjugate CFD simulations was evaluated by comparing results for surface temperature on the warm side of the specimens to results from experiments that use infrared (IR) thermography to map surface temperatures during steady-state thermal tests. In general, there was good agreement between the simulations and experiments. Two-dimensional computational fluid dynamic and conduction simulations are performed to study the difference between treating air cavities as a fluid and as a solid when calculating the thermal transmittance of window frames. The simulations show that traditional software codes, simulating only conduction and using equivalent conductivities for the air cavities, give Uvalues that compare well with results from fluid flow simulations. The difference between the two models are mostly limited to the temperature distribution inside air cavities. It is also found that cavities with an interconnection less than about 7 mm can be treated as separate cavities. Three-dimensional natural convection effects in simple and custom-made PVC and thermally broken aluminum window frames with one open internal cavity were studied, with the use of CFD simulations and thermography experiments. Focus was put on corner effects and heat transfer
A numerical model for boiling heat transfer coefficient of zeotropic mixtures

Science.gov (United States)

Barraza Vicencio, Rodrigo; Caviedes Aedo, Eduardo

2017-12-01

Zeotropic mixtures never have the same liquid and vapor composition in the liquid-vapor equilibrium. Also, the bubble and the dew point are separated; this gap is called glide temperature (Tglide). Those characteristics have made these mixtures suitable for cryogenics Joule-Thomson (JT) refrigeration cycles. Zeotropic mixtures as working fluid in JT cycles improve their performance in an order of magnitude. Optimization of JT cycles have earned substantial importance for cryogenics applications (e.g, gas liquefaction, cryosurgery probes, cooling of infrared sensors, cryopreservation, and biomedical samples). Heat exchangers design on those cycles is a critical point; consequently, heat transfer coefficient and pressure drop of two-phase zeotropic mixtures are relevant. In this work, it will be applied a methodology in order to calculate the local convective heat transfer coefficients based on the law of the wall approach for turbulent flows. The flow and heat transfer characteristics of zeotropic mixtures in a heated horizontal tube are investigated numerically. The temperature profile and heat transfer coefficient for zeotropic mixtures of different bulk compositions are analysed. The numerical model has been developed and locally applied in a fully developed, constant temperature wall, and two-phase annular flow in a duct. Numerical results have been obtained using this model taking into account continuity, momentum, and energy equations. Local heat transfer coefficient results are compared with available experimental data published by Barraza et al. (2016), and they have shown good agreement.
The thermodynamics of enhanced heat transfer: a model study

International Nuclear Information System (INIS)

Hovhannisyan, Karen; Allahverdyan, Armen E

2010-01-01

Situations where a spontaneous process of energy or matter transfer is enhanced by an external device are widespread in nature (the human sweating system, enzyme catalysis, facilitated diffusion across biomembranes, industrial heat-exchangers and so on). The thermodynamics of such processes remains, however, open. Here we study enhanced heat transfer by using a model junction immersed between two thermal baths at different temperatures T h and T c (T h > T c ). The transferred heat power is enhanced via controlling the junction by means of external time-dependent fields. Provided that the spontaneous heat flow process is optimized over the junction Hamiltonian, any enhancement of this spontaneous process demands consumption and subsequent dissipation of work. The efficiency of the enhancement is defined via the increment in the heat power divided by the amount of work done. We show that this efficiency is bounded from above by T c /(T h − T c ). Formally this is identical to the Carnot bound for the efficiency of ordinary refrigerators which transfer heat from cold to hot bodies. It also shares some (but not all) physical features of the Carnot bound
Numerical Modeling of Conjugate Heat Transfer in Fluid Network

Science.gov (United States)

Majumdar, Alok

2004-01-01

Fluid network modeling with conjugate heat transfer has many applications in Aerospace engineering. In modeling unsteady flow with heat transfer, it is important to know the variation of wall temperature in time and space to calculate heat transfer between solid to fluid. Since wall temperature is a function of flow, a coupled analysis of temperature of solid and fluid is necessary. In cryogenic applications, modeling of conjugate heat transfer is of great importance to correctly predict boil-off rate in propellant tanks and chill down of transfer lines. In TFAWS 2003, the present author delivered a paper to describe a general-purpose computer program, GFSSP (Generalized Fluid System Simulation Program). GFSSP calculates flow distribution in complex flow circuit for compressible/incompressible, with or without heat transfer or phase change in all real fluids or mixtures. The flow circuit constitutes of fluid nodes and branches. The mass, energy and specie conservation equations are solved at the nodes where as momentum conservation equations are solved at the branches. The proposed paper describes the extension of GFSSP to model conjugate heat transfer. The network also includes solid nodes and conductors in addition to fluid nodes and branches. The energy conservation equations for solid nodes solves to determine the temperatures of the solid nodes simultaneously with all conservation equations governing fluid flow. The numerical scheme accounts for conduction, convection and radiation heat transfer. The paper will also describe the applications of the code to predict chill down of cryogenic transfer line and boil-off rate of cryogenic propellant storage tank.
Post-dryout heat transfer analysis model with droplet Lagrangian simulation

International Nuclear Information System (INIS)

Keizo Matsuura; Isao Kataoka; Kaichiro Mishima

2005-01-01

Post-dryout heat transfer analysis was carried out considering droplet behavior by using the Lagrangian simulation method. Post-dryout heat transfer is an important heat transfer mechanism in many industrial appliances. Especially in recent Japanese BWR licensing, the standard for assessing the integrity of fuel that has experienced boiling transition is being examined. Although post-dryout heat transfer analysis is important when predicting wall temperature, it is difficult to accurately predict the heat transfer coefficient in the post-dryout regime because of the many heat transfer paths and non-equilibrium status between droplet and vapor. Recently, an analysis model that deals with many heat transfer paths including droplet direct contact heat transfer was developed and its results showed good agreement with experimental results. The model also showed that heat transfer by droplet could not be neglected in the low mass flux condition. However, the model deals with droplet deposition behavior by experimental droplet deposition correlation, so it cannot estimate the effect of droplet flow on turbulent flow field and heat transfer. Therefore, in this study we deal with many droplets separately by using the Lagrangian simulation method and hence estimate the effect of droplet flow on the turbulent flow field. We analyzed post-dryout experimental results and found that they correlated well with the analysis results. (authors)

A three-dimensional thermal and electromagnetic model of whole limb heating with a MAPA.

Science.gov (United States)

Charny, C K; Levin, R L

1991-10-01

Previous studies by the authors have shown that if properly implemented, the Pennes assumptions can be applied to quantify bioheat transfer during extremity heating. Given its relative numerical simplicity and its ability to predict temperatures in thermoregulated tissue, the Pennes model of bioheat transfer was utilized in a three-dimensional thermal model of limb heating. While the arterial blood temperature was assumed to be radially uniform within a cross section of the limb, axial gradients in the arterial and venous blood temperatures were computed with this three-dimensional model. A realistically shaped, three-dimensional finite element model of a tumor-bearing human lower leg was constructed and was "attached" mathematically to the whole body thermal model of man described in previous studies by the authors. The central as well as local thermoregulatory feedback control mechanisms which determine blood perfusion to the various tissues and rate of evaporation by sweating were input into the limb model. In addition, the temperature of the arterial blood which feeds into the most proximal section of the lower leg was computed by the whole body thermal model. The variations in the shape of the tissues which comprise the limb were obtained from computerized tomography scans. Axial variations in the energy deposition patterns along the length of the limb exposed to a miniannular phased array (MAPA) applicator were also input into this model of limb heating. Results indicate that proper positioning of the limb relative to the MAPA is a significant factor in determining the effectiveness of the treatment. A patient-specific hyperthermia protocol can be designed using this coupled electromagnetic and thermal model.
Modeling of condensation heat transfer in a reactor containment

International Nuclear Information System (INIS)

Kim, M.H.; Corradini, M.L.

1990-01-01

This paper proposes a set of condensation models for forced and natural convection in the presence of a noncondensable gas. A simple model is derived by using the analogy between mass, momentum and energy transfer. The effects of a wavy interface are implemented in this model by using correlations for a rough wall surface. A two-dimensional condensation model using a k-ε model for the turbulent vapor-air flow was also developed to investigate the effect of two-dimensional flow and to provide a sound theoretical basis for the simple model. Each model is compared with the available 'separate effects' experimental data. The forced convection model is then compared to the Carolinas Virginia Tube Reactor (CVTR) integral test by using the vapor-air velocity predicted by a separate two-dimensional fluid dynamics model. The effect of counter-current flow is also considered in this comparison. The natural convection model is also compared to the steady-state integral data of Tagami. The comparison shows good agreement with both sets of experimental data. (orig.)
Simulations and experiments of laminar heat transfer for Therminol heat transfer fluids in a rifled tube

International Nuclear Information System (INIS)

Xu, Weiguo; Ren, Depeng; Ye, Qing; Liu, Guodong; Lu, Huilin; Wang, Shuai

2016-01-01

Graphical abstract: Predicted laminar Nusselt number using regression correlation of Therminol-55 heat transfer fluid is in agreement with experiments in the rifled tube. - Highlights: • Heat transfer coefficient and friction factor are measured and predicted in the rifled tube. • Correlations for Nusselt number and friction factor are proposed. • The roughness height of 0.425 mm in transition SST model is suggested as an input parameter. • k–kl–ω transition and transition SST models are recommended for laminar–turbulent transition. • Thermal enhancement factor and synergy angle are predicted in the rifled tube. - Abstract: Simulations and experiments of flow and heat transfer behavior of Therminol-55 heat transfer fluid have been conducted in a horizontal rifled tube with outer diameter and inner diameter 25.0 and 20.0 mm, pitch and rib height of 12.0 and 1.0 mm, respectively. Numerical simulations of three-dimensional flow behavior of Therminol-55 heat transfer fluid are carried out using FLUENT code in the rifled tube. Experimental results show that the heat transfer and thermal performance of Therminol-55 heat transfer fluid in the rifled tube are considerably improved compared to those of the smooth tube. The Nusselt number increases with the increase of Reynolds number, and is from 3.5 to 5.1 times over the smooth tube. Also, the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.2 and 4.2 times over the smooth tube. Predictive Nusselt number and friction factor correlations have been presented. The numerical results show that the laminar flow model is valid only at lower Reynolds number in the developed laminar flow of rifled tube. The k–kl–ω transition model and transition SST model with roughness of 0.425 mm are recommended for the predictions of transition process from laminar to turbulent flow in the rifled tube.
Heat transfer in porous medium embedded with vertical plate: Non-equilibrium approach - Part B

Energy Technology Data Exchange (ETDEWEB)

Quadir, G. A., E-mail: Irfan-magami@Rediffmail.com, E-mail: gaquadir@gmail.com [School of Mechatronic Engineering, University Malaysia Perlis, Pauh Putra, 02600 Arau, Perlis (Malaysia); Badruddin, Irfan Anjum [Dept. of Mechanical Engineering, University of Malaya, Kuala Lumpur, 50603 (Malaysia)

2016-06-08

This work is continuation of the paper Part A. Due to large number of results, the paper is divided into two section with section-A (Part A) discussing the effect of various parameters such as heat transfer coefficient parameter, thermal conductivity ratio etc. on streamlines and isothermal lines. Section-B highlights the heat transfer characteristics in terms of Nusselt number The Darcy model is employed to simulate the flow inside the medium. It is assumed that the heat transfer takes place by convection and radiation. The governing partial differential equations are converted into non-dimensional form and solved numerically using finite element method.
Molten corium concrete interaction: investigation of heat transfer in two-phase flow

International Nuclear Information System (INIS)

Amizic, Milan

2014-01-01

In the context of severe accident research for the second and the third generation of nuclear power plants, there are still open issues concerning some aspects of the concrete cavity ablation during the molten corium - concrete interaction (MCCI). The determination of heat transfer along the interfacial region between the molten corium pool and the ablating basemat concrete is crucial for the assessment of concrete ablation progression and eventually the basemat melt through. For the purpose of experimental investigation of thermal hydraulics inside a liquid pool agitated by gas bubbles, the CLARA project has been launched. The CLARA experiments are performed using simulant materials and they reveal the influence of superficial gas velocity, liquid viscosity and pool geometry on the heat transfer coefficient between the internally heated liquid pool and vertical and horizontal pool walls maintained at uniform temperature. The first test campaign has been conducted with the small pool configuration (50 cm * 25 cm * 25 cm). The tests have been performed with liquids covering a wide range of dynamic viscosity from approximately 1 mPa s to 10000 mPa s and the superficial gas velocity is varied up to 8 cm/s. This thesis comprises a brief description of MCCI phenomenology, literature reviews on the existing heat transfer correlations for two phase flow and the void fraction, a description of CLARA setup, experimental results and their interpretation. The experimental results are compared with existing models and some new models for the assessment of heat transfer coefficient in two-phase flow. (author) [fr
Heat transfer in melt ponds with convection and radiative heating: observationally-inspired modelling

Science.gov (United States)

Wells, A.; Langton, T.; Rees Jones, D. W.; Moon, W.; Kim, J. H.; Wilkinson, J.

2016-12-01

Melt ponds have key impacts on the evolution of Arctic sea ice and summer ice melt. Small changes to the energy budget can have significant consequences, with a net heat-flux perturbation of only a few Watts per square metre sufficient to explain the thinning of sea ice over recent decades. Whilst parameterisations of melt-pond thermodynamics often assume that pond temperatures remain close to the freezing point, recent in-situ observations show more complex thermal structure with significant diurnal and synoptic variability. We here consider the energy budget of melt ponds and explore the role of internal convective heat transfer in determining the thermal structure within the pond in relatively calm conditions with low winds. We quantify the energy fluxes and temperature variability using two-dimensional direct numerical simulations of convective turbulence within a melt pond, driven by internal radiative heating and surface fluxes. Our results show that the convective flow dynamics are modulated by changes to the incoming radiative flux and sensible heat flux at the pond surface. The evolving pond surface temperature controls the outgoing longwave emissions from the pond. Hence the convective flow modifies the net energy balance of a melt pond, modulating the relative fractions of the incoming heat flux that is re-emitted to the atmosphere or transferred downward into the sea ice to drive melt.
Modeling of heat and mass transfer processes during core melt discharge from a reactor pressure vessel

Energy Technology Data Exchange (ETDEWEB)

Dinh, T.N.; Bui, V.A.; Nourgaliev, R.R. [Royal Institute of Technology, Stockholm (Sweden)] [and others

1995-09-01

The objective of the paper is to study heat and mass transfer processes related to core melt discharge from a reactor vessel is a severe light water reactor accident. The phenomenology of the issue includes (1) melt convection in and heat transfer from the melt pool in contact with the vessel lower head wall; (2) fluid dynamics and heat transfer of the melt flow in the growing discharge hole; and (3) multi-dimensional heat conduction in the ablating lower head wall. A program of model development, validation and application is underway (i) to analyse the dominant physical mechanisms determining characteristics of the lower head ablation process; (ii) to develop and validate efficient analytic/computational methods for estimating heat and mass transfer under phase-change conditions in irregular moving-boundary domains; and (iii) to investigate numerically the melt discharge phenomena in a reactor-scale situation, and, in particular, the sensitivity of the melt discharge transient to structural differences and various in-vessel melt progression scenarios. The paper presents recent results of the analysis and model development work supporting the simulant melt-structure interaction experiments.
Deterministic transfer of two-dimensional materials by all-dry viscoelastic stamping

International Nuclear Information System (INIS)

Castellanos-Gomez, Andres; Buscema, Michele; Molenaar, Rianda; Singh, Vibhor; Janssen, Laurens; Van der Zant, Herre S J; Steele, Gary A

2014-01-01

The deterministic transfer of two-dimensional crystals constitutes a crucial step towards the fabrication of heterostructures based on the artificial stacking of two-dimensional materials. Moreover, controlling the positioning of two-dimensional crystals facilitates their integration in complex devices, which enables the exploration of novel applications and the discovery of new phenomena in these materials. To date, deterministic transfer methods rely on the use of sacrificial polymer layers and wet chemistry to some extent. Here, we develop an all-dry transfer method that relies on viscoelastic stamps and does not employ any wet chemistry step. This is found to be very advantageous to freely suspend these materials as there are no capillary forces involved in the process. Moreover, the whole fabrication process is quick, efficient, clean and it can be performed with high yield. (letter)
Anisotropic scattering in three dimensional differential approximation of radiation heat transfer

International Nuclear Information System (INIS)

Condiff, D.W.

1987-01-01

The differential approximation is extended to account for anisotropic scattering in invariant three dimensional form. A moment method using polyadic Legendre functions establishes that pressure cross sections should take precedence over extinction cross sections for treating radiation heat transfer in an absorbing, emitting, and scattering medium, and that use of these cross sections accounts for the extent of preferred forward or backwards scattering. The procedure and principle is extended to polyadic P-N approximations
Lunar ash flow with heat transfer.

Science.gov (United States)

Pai, S. I.; Hsieh, T.; O'Keefe, J. A.

1972-01-01

The most important heat-transfer process in the ash flow under consideration is heat convection. Besides the four important nondimensional parameters of isothermal ash flow (Pai et al., 1972), we have three additional important nondimensional parameters: the ratio of the specific heat of the gas, the ratio of the specific heat of the solid particles to that of gas, and the Prandtl number. We reexamine the one dimensional steady ash flow discussed by Pai et al. (1972) by including the effects of heat transfer. Numerical results for the pressure, temperature, density of the gas, velocities of gas and solid particles, and volume fraction of solid particles as function of altitude for various values of the Jeffreys number, initial velocity ratio, and two different gas species (steam and hydrogen) are presented.
A Computer-Based Simulation for Teaching Heat Transfer across a Woody Stem

Science.gov (United States)

Maixner, Michael R.; Noyd, Robert K.; Krueger, Jerome A.

2010-01-01

To assist student understanding of heat transfer through woody stems, we developed an instructional package that included an Excel-based, one-dimensional simulation model and a companion instructional worksheet. Guiding undergraduate botany students to applying principles of thermodynamics to plants in nature is fraught with two main obstacles:…
Radiation heat transfer within an open-cycle MHD generator channel

Science.gov (United States)

Delil, A. A. M.

1983-05-01

Radiation heat transfer in an MHD generator was modeled using the Sparrow and Cess model for radiation in an emitting, absorbing and scattering medium. The resulting general equations can be considerably reduced by introducing simplifying approximations for the channel and MHD gas properties. The simplifications lead to an engineering model, which is very useful for one-dimensional channel flow approximation. The model can estimate thermo-optical MHD gas properties, which can be substituted in the energy equation. The model considers the contribution of solid particles in the MHD gas to radiation heat transfer, considerable in coal-fired closed cycle MHD generators. The modeling is applicable also for other types of flow at elevated temperatures, where radiation heat transfer is an important quantity.
Modelling mass and heat transfer in nano-based cancer hyperthermia.

Science.gov (United States)

Nabil, M; Decuzzi, P; Zunino, P

2015-10-01

We derive a sophisticated mathematical model for coupled heat and mass transport in the tumour microenvironment and we apply it to study nanoparticle delivery and hyperthermic treatment of cancer. The model has the unique ability of combining the following features: (i) realistic vasculature; (ii) coupled capillary and interstitial flow; (iii) coupled capillary and interstitial mass transfer applied to nanoparticles; and (iv) coupled capillary and interstitial heat transfer, which are the fundamental mechanisms governing nano-based hyperthermic treatment. This is an improvement with respect to previous modelling approaches, where the effect of blood perfusion on heat transfer is modelled in a spatially averaged form. We analyse the time evolution and the spatial distribution of particles and temperature in a tumour mass treated with superparamagnetic nanoparticles excited by an alternating magnetic field. By means of numerical experiments, we synthesize scaling laws that illustrate how nano-based hyperthermia depends on tumour size and vascularity. In particular, we identify two distinct mechanisms that regulate the distribution of particle and temperature, which are characterized by perfusion and diffusion, respectively.
Experimental study and calculation of boiling heat transfer on steel plates during runout table operation

International Nuclear Information System (INIS)

Liu, Z.D.; Fraser, D.; Samarasekera, I.V.

2002-01-01

Within a hot strip steel mill, red hot steel is hot rolled into a long continuous slab that is led onto what is called the runout table. Temperatures of the steel at the beginning of this table are around 900 o C. Above and below the runout table are banks of water jets, sprays or water curtains that rapidly cool the steel slab. The heat transfer process itself may be considered one of the most complicated in the industrial world. The cooling process that occurs on the runout table is crucial and governs the final mechanical properties and flatness of a steel strip. However, very limited data of industrial conditions has been available and that which is available is poorly understood. To study heat transfer during runout table cooling, an industrial scale pilot runout table facility was constructed at the University of British Columbia (UBC). This paper describes the experimental details, data acquisition and data handling techniques for steel plates during water jet impingement cooling by one circular water jet from industrial headers. The effect of cooling water temperature and initial steel plate temperature as well as varying water jet diameters on heat transfer was systematically investigated. A two-dimensional finite element scheme based inverse heat conduction model was developed to calculate surface heat transfer coefficients along the impinging surface. Heat flux curves at the stagnation area were obtained for selected tests. A quantitative relationship between adjustable processing parameters and heat transfer coefficients along the impinging surface during runout table operation is discussed. The results of the study were used to upgrade an extensive process model developed at UBC. The model ties in the cooling rate and hence two dimensional temperature gradients to the resulting microstructure and final mechanical properties of the steel. This process model is widely used by major steel industries in Canada and the United States. (author)
Two-phase flow pattern and heat transfer during core uncovery

International Nuclear Information System (INIS)

Osakabe, Masahiro; Koizumi, Yasuo; Tasaka, Kanji

1987-01-01

The low and high power core uncovery patterns were observed in the high-pressure quasi-steady core uncovery experiments in a 25-rod bundle. The boundary between the two patterns was obtained in the experiments. The difference of two patterns was considered to be due to the slug-annular transition below the dryout points. The Osakabe's slug-annular transition model was the good boundary between the two patterns. The small break loss-of-coolant accident (LOCA) experiments were conducted by using the integral experimental facility with the 1,168-rod core. The transient core uncovery pattern was expected as the low power core uncovery pattern based on the quasisteady experiments mentioned above. The transient core uncovery patterns were classified into the boiloff and hydraulic core uncovery. In the boiloff core uncovery, the dryout points were controlled with the mixture level like the quasi-steady state. In the hydraulic core uncovery, the dryout points were not controlled with the mixture level alone, and the multi-dimensional dryout process in the core and the relatively high heat transfer above the dryout points were observed. It was considered that a part of water was remained above the dryout points due to the rapid depression of core liquid level. (author)
Influence on Heat Transfer Coefficient of Heat Exchanger by Velocity and Heat Transfer Temperature Difference

Directory of Open Access Journals (Sweden)

WANG Fang

2017-04-01

Full Text Available Aimed to insufficient heat transfer of heat exchanger, research the influence on the heat transfer coefficient impacted by velocity and heat transfer temperature difference of tube heat exchanger. According to the different heat transfer temperature difference and gas velocity，the experimental data were divided into group. Using the control variable method，the above two factors were analyzed separately. K一△T and k一:fitting curve were clone to obtain empirical function. The entire heat exchanger is as the study object，using numerical simulation methods，porous media，k一￡model，second order upwind mode，and pressure一velocity coupling with SIMPLE algorithm，the entire heat exchanger temperature field and the heat transfer coefficient distribution were given. Finally the trend of the heat transfer coefficient effected by the above two factors was gotten.
Heat transfer in Rockwool modelling and method of measurement. The effect of natural convection on heat transfer in fibrous materials

Energy Technology Data Exchange (ETDEWEB)

Dyrboel, Susanne

1998-05-01

Fibrous materials are some of the most widely used materials for thermal insulation. In this project the focus of interest has been on fibrous materials for building application. Interest in improving the thermal properties of insulation materials is increasing as legislation is being tightened to reduce the overall energy consumption. A knowledge of the individual heat transfer mechanisms - whereby heat is transferred within a particular material is an essential tool to improve continuously the thermal properties of the material. Heat is transferred in fibrous materials by four different transfer mechanisms: conduction through air, conduction through fibres, thermal radiation and convection. In a particular temperature range the conduction through air can be regarded as a constant, and conduction through fibres is an insignificant part of the total heat transfer. Radiation, however, constitutes 25-40% of the total heat transfer in light fibrous materials. In Denmark and a number of other countries convection in fibrous materials is considered as non-existent when calculating heat transmission as well as when designing building structures. Two heat transfer mechanisms have been the focus of the current project: radiation heat transfer and convection. The radiation analysis serves to develop a model that can be used in further work to gain a wider knowledge of the way in which the morphology of the fibrous material, i.e. fibre diameter distribution, fibre orientation distribution etc., influences the radiation heat transfer under different conditions. The convection investigation serves to examine whether considering convection as non-existent is a fair assumption to use in present and future building structures. The assumption applied in practically is that convection makes a notable difference only in very thick insulation, at external temperatures below -20 deg. C, and at very low densities. For large thickness dimensions the resulting heat transfer through the
Heat transfer from internally-heated molten UO2 pools

International Nuclear Information System (INIS)

Stein, R.P.; Baker, L. Jr.; Gunther, W.H.; Cook, C.

1978-01-01

Experimental measurements of heat transfer from internally heated pools of molten UO 2 have been obtained for two cell sizes: 10 cm x 10 cm and 20 cm x 20 cm. The experiments with the large cell have supported a previous conclusion from early small data that the measured downward heat fluxes are higher than would be expected on the basis of considerations of thermal convection. A convective model underpredicts the downward heat fluxes by a factor of 2.5 to 4.5 for all but one early experiment. Arbitrary assumptions of increased thermal conductivity do not account for the discrepancy. A single model based on internal thermal radiation heat transfer is able to account for the high values. The model uses the optically thick Rosseland approximation. Because of this, it is tentatively concluded that thermal radiation plays a dominant role in controlling the heat transfer from internally heated molted fuel
Three-Dimensional Unsteady Simulation of Aerodynamics and Heat Transfer in a Modern High Pressure Turbine Stage

Science.gov (United States)

Shyam, Vikram; Ameri, Ali

2009-01-01

Unsteady 3-D RANS simulations have been performed on a highly loaded transonic turbine stage and results are compared to steady calculations as well as to experiment. A low Reynolds number k-epsilon turbulence model is employed to provide closure for the RANS system. A phase-lag boundary condition is used in the tangential direction. This allows the unsteady simulation to be performed by using only one blade from each of the two rows. The objective of this work is to study the effect of unsteadiness on rotor heat transfer and to glean any insight into unsteady flow physics. The role of the stator wake passing on the pressure distribution at the leading edge is also studied. The simulated heat transfer and pressure results agreed favorably with experiment. The time-averaged heat transfer predicted by the unsteady simulation is higher than the heat transfer predicted by the steady simulation everywhere except at the leading edge. The shock structure formed due to stator-rotor interaction was analyzed. Heat transfer and pressure at the hub and casing were also studied. Thermal segregation was observed that leads to the heat transfer patterns predicted by steady and unsteady simulations to be different.
A meshless method for modeling convective heat transfer

Energy Technology Data Exchange (ETDEWEB)

Carrington, David B [Los Alamos National Laboratory

2010-01-01

A meshless method is used in a projection-based approach to solve the primitive equations for fluid flow with heat transfer. The method is easy to implement in a MATLAB format. Radial basis functions are used to solve two benchmark test cases: natural convection in a square enclosure and flow with forced convection over a backward facing step. The results are compared with two popular and widely used commercial codes: COMSOL, a finite element model, and FLUENT, a finite volume-based model.

Numerical investigation of transient behaviour of the recuperative heat exchanger in a MR J-T cryocooler using different heat transfer correlations

Science.gov (United States)

Damle, R. M.; Ardhapurkar, P. M.; Atrey, M. D.

2016-12-01

In J-T cryocoolers operating with mixed refrigerants (nitrogen-hydrocarbons), the recuperative heat exchange takes place under two-phase conditions. Simultaneous boiling of the low pressure stream and condensation of the high pressure stream results in higher heat transfer coefficients. The mixture composition, operating conditions and the heat exchanger design are crucial for obtaining the required cryogenic temperature. In this work, a one-dimensional transient algorithm is developed for the simulation of the two-phase heat transfer in the recuperative heat exchanger of a mixed refrigerant J-T cryocooler. Modified correlation is used for flow boiling of the high pressure fluid while different condensation correlations are employed with and without the correction for the low pressure fluid. Simulations are carried out for different mixture compositions and numerical predictions are compared with the experimental data. The overall heat transfer is predicted reasonably well and the qualitative trends of the temperature profiles are also captured by the developed numerical model.
Newtonian heating effects in three-dimensional flow of viscoelastic fluid

International Nuclear Information System (INIS)

Qayyum, A.; Hayat, T.; Alhuthali, M. S.; Malaikah, H. M.

2014-01-01

A mathematical model is constructed to investigate the three-dimensional flow of a non-Newtonian fluid. An incompressible viscoelastic fluid is used in mathematical formulation. The conjugate convective process (in which heat the transfer rate from the bounding surface with a finite capacity is proportional to the local surface temperature) in three-dimensional flow of a differential type of non-Newtonian fluid is analyzed for the first time. Series solutions for the nonlinear differential system are computed. Plots are presented for the description of emerging parameters entering into the problem. It is observed that the conjugate heating phenomenon causes an appreciable increase in the temperature at the stretching wall. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Tetrahedral node for Transmission-Line Modeling (TLM) applied to Bio-heat Transfer.

Science.gov (United States)

Milan, Hugo F M; Gebremedhin, Kifle G

2016-12-01

Transmission-Line Modeling (TLM) is a numerical method used to solve complex and time-domain bio-heat transfer problems. In TLM, parallelepipeds are used to discretize three-dimensional problems. The drawback in using parallelepiped shapes is that instead of refining only the domain of interest, a large additional domain would also have to be refined, which results in increased computational time and memory space. In this paper, we developed a tetrahedral node for TLM applied to bio-heat transfer that does not have the drawback associated with the parallelepiped node. The model includes heat source, blood perfusion, boundary conditions and initial conditions. The boundary conditions could be adiabatic, temperature, heat flux, or convection. The predicted temperature and heat flux were compared against results from an analytical solution and the results agreed within 2% for a mesh size of 69,941 nodes and a time step of 5ms. The method was further validated against published results of maximum skin-surface temperature difference in a breast with and without tumor and the results agreed within 6%. The published results were obtained from a model that used parallelepiped TLM node. An open source software, TLMBHT, was written using the theory developed herein and is available for download free-of-charge. Copyright © 2016 Elsevier Ltd. All rights reserved.
Heat transfer with a split water channel

International Nuclear Information System (INIS)

Krinsky, S.

1978-01-01

The heat transfer problem associated with the incidence of synchrotron radiation upon a vacuum chamber wall cooled by a single water channel was previously studied, and a numerical solution to the potential problem was found using the two-dimensional magnet program POISSON. Calculations were extended to consider the case of a split water channel using POISSON to solve the potential problem for a given choice of parameters. By optimizing the dimensions, boiling of the water can be avoided. A copper chamber is a viable solution to the heat transfer problem at a beam port
A multi-fluid model to simulate heat and mass transfer in a PEM fuel cell

DEFF Research Database (Denmark)

Berning, Torsten; Odgaard, Madeleine; Kær, Søren Knudsen

2011-01-01

This article summarizes a multi-phase model of a polymer electrolyte membrane fuel cell based on the formerly commercial CFD code CFX-4. It is three-dimensional in nature and includes multiphase heat and mass transfer in porous media. An overview is given and some numerical issues are discussed...... heat and mass transfer properties are superior. Another important aspect of this study is the wetting status of the electrolyte menbrane and the effective drag of water through the menbrane, which indicates what fraction of the product water created at the cathode side diffuses through the membrane...
Ferromagnetism in the two-dimensional periodic Anderson model

International Nuclear Information System (INIS)

Batista, C. D.; Bonca, J.; Gubernatis, J. E.

2001-01-01

Using the constrained-path Monte Carlo method, we studied the magnetic properties of the two-dimensional periodic Anderson model for electron fillings between 1/4 and 1/2. We also derived two effective low-energy theories to assist in interpreting the numerical results. For 1/4 filling, we found that the system can be a Mott or a charge-transfer insulator, depending on the relative values of the Coulomb interaction and the charge-transfer gap between the two noninteracting bands. The insulator may be a paramagnet or antiferromagnet. We concentrated on the effect of electron doping on these insulating phases. Upon doping we obtained a partially saturated ferromagnetic phase for low concentrations of conduction electrons. If the system were a charge-transfer insulator, we would find that the ferromagnetism is induced by the well-known Ruderman-Kittel-Kasuya-Yosida interaction. However, we found a novel correlated hopping mechanism inducing the ferromagnetism in the region where the nondoped system is a Mott insulator. Our regions of ferromagnetism spanned a much smaller doping range than suggested by recent slave boson and dynamical mean-field theory calculations, but they were consistent with that obtained by density-matrix renormalization group calculations of the one-dimensional periodic Anderson model
Two-temperature chemically non-equilibrium modelling of transferred arcs

International Nuclear Information System (INIS)

Baeva, M; Kozakov, R; Gorchakov, S; Uhrlandt, D

2012-01-01

A two-temperature chemically non-equilibrium model describing in a self-consistent manner the heat transfer, the plasma chemistry, the electric and magnetic field in a high-current free-burning arc in argon has been developed. The model is aimed at unifying the description of a thermionic tungsten cathode, a flat copper anode, and the arc plasma including the electrode sheath regions. The heat transfer in the electrodes is coupled to the plasma heat transfer considering the energy fluxes onto the electrode boundaries with the plasma. The results of the non-equilibrium model for an arc current of 200 A and an argon flow rate of 12 slpm are presented along with results obtained from a model based on the assumption of local thermodynamic equilibrium (LTE) and from optical emission spectroscopy. The plasma shows a near-LTE behaviour along the arc axis and in a region surrounding the axis which becomes wider towards the anode. In the near-electrode regions, a large deviation from LTE is observed. The results are in good agreement with experimental findings from optical emission spectroscopy. (paper)
Experimental validation of a heat transfer model for concentrating photovoltaic system

International Nuclear Information System (INIS)

Sendhil Kumar, Natarajan; Matty, Katz; Rita, Ebner; Simon, Weingaertner; Ortrun, Aßländer; Alex, Cole; Roland, Wertz; Tim, Giesen; Tapas Kumar, Mallick

2012-01-01

In this paper, a three dimensional heat transfer model is presented for a novel concentrating photovoltaic design for Active Solar Panel Initiative System (ASPIS). The concentration ratio of two systems (early and integrated prototype) are 5× and 10× respectively, designed for roof-top integrated Photovoltaic systems. ANSYS 12.1, CFX package was effectively used to predict the temperatures of the components of the both ASPIS systems at various boundary conditions. The predicted component temperatures of an early prototype were compared with experimental results of ASPIS, which were carried out in Solecta – Israel and at the Austrian Institute of Technology (AIT) – Austria. It was observed that the solar cell and lens temperature prediction shows good agreement with Solecta measurements. The minimum and maximum deviation of 3.8% and 17.9% were observed between numerical and Solecta measurements and the maximum deviations of 16.9% were observed between modeling and AIT measurements. Thus, the developed validated thermal model enables to predict the component temperatures for concentrating photovoltaic systems. - Highlights: ► Experimentally validated heat transfer model for concentrating Photovoltaic system developed. ► Predictions of solar cell temperatures for parallactic tracking CPV system for roof integration. ► The ASPIS module contains 2 mm wide 216 solar cells manufactured based on SATURN technology. ► A solar cell temperature of 44 °C was predicted for solar radiation intensity was 1000 W/m 2 and ambient temperature was 20 °C. ► Average deviation was 6% and enabled to predict temperature of any CPV system.
Heat Transfer in Large Two-Stroke Marine Diesel Engines

DEFF Research Database (Denmark)

Jensen, Michael Vincent

Heat transfer between the cylinder gas and the piston surface during combustion in large two-stroke uniflow scavenged marine diesel engines has been investigated in the present work. The piston surface experiences a severe thermal load during combustion due to the close proximity of the combustion...... zone to the surface. At the same time, cooling of the piston crown is relatively complicated. This can cause large thermal stresses in the piston crown and weakening of the material strength, which may be critical as it can lead to formation of cracks. Information about the piston surface heat transfer...... is thus important for the engine manufactures. The piston surface heat transfer was studied in the event of impingement of hot combustion products on the piston during combustion, and an estimate was obtained of the peak heat flux level experienced on the piston surface. The investigation was carried out...
Entropy resistance analyses of a two-stream parallel flow heat exchanger with viscous heating

International Nuclear Information System (INIS)

Cheng Xue-Tao; Liang Xin-Gang

2013-01-01

Heat exchangers are widely used in industry, and analyses and optimizations of the performance of heat exchangers are important topics. In this paper, we define the concept of entropy resistance based on the entropy generation analyses of a one-dimensional heat transfer process. With this concept, a two-stream parallel flow heat exchanger with viscous heating is analyzed and discussed. It is found that the minimization of entropy resistance always leads to the maximum heat transfer rate for the discussed two-stream parallel flow heat exchanger, while the minimizations of entropy generation rate, entropy generation numbers, and revised entropy generation number do not always. (general)
Numerical analysis of the heat and mass transfer processes in selected M-Cycle heat exchangers for the dew point evaporative cooling

International Nuclear Information System (INIS)

Pandelidis, Demis; Anisimov, Sergey

2015-01-01

Highlights: • The comparative numerical study of the eight M-Cycle heat exchangers was presented. • The mathematical model is compared against the experimental data. • The results show, that the original M-Cycle heat and mass exchanger can be improved. • The effectiveness of the heat and mass exchangers depends strongly on the inlet air parameters. - Abstract: This paper investigates a mathematical simulation of heat and mass transfer in eight different types of the Maisotsenko Cycle (M-Cycle) heat and mass exchangers (HMXs) used for indirect evaporative air cooling. A two-dimensional heat and mass transfer model is developed to perform the thermal calculations of the indirect evaporative cooling process and quantifying the overall performance. The mathematical model was validated against experimental data. A numerical simulation reveals many unique features of the considered HMXs, enabling an accurate prediction of their performance. Results of the model allow for comparison of the analyzed devices in order to improve the performance of the original HMX
Two-dimensional heat conducting simulation of plasma armatures

International Nuclear Information System (INIS)

Huerta, M.A.; Boynton, G.

1991-01-01

This paper reports on our development of a two-dimensional MHD code to simulate internal motions in a railgun plasma armature. The authors use the equations of resistive MHD, with Ohmic heating, and radiation heat transport. The authors use a Flux Corrected Transport code to advance all quantities in time. Our runs show the development of complex flows, subsequent shedding of secondary arcs, and a drop in the acceleration of the armature
Heat transfer coefficient correlation for convective boiling inside plain and micro fin tubes using genetic algorithms

International Nuclear Information System (INIS)

Picanco, Marco Antonio Silva; Bandarra Filho, Enio Pedone; Passos, Julio Cesar

2006-01-01

Two-phase flow heat transfer has been exhaustively studied over recent years. However, in this field several questions remain unanswered. Heat transfer coefficient prediction related to nucleate and convective boiling have been studied using different approaches, numerical, analytical and experimental. In this work, an experimental analysis, data representation and heat transfer coefficient prediction on two-phase heat transfer on nucleate and convective boiling are presented. An empirical correlation is obtained based on genetic algorithms search engine over a dimensional analysis of the two-phase flow heat transfer problem. (author)
A numerical study of vorticity-enhanced heat transfer

Science.gov (United States)

Wang, Xiaolin; Alben, Silas

2012-11-01

The Glezer lab at Georgia Tech has found that vorticity produced by vibrated reeds can improve heat transfer in electronic hardware. Vortices enhance forced convection by boundary layer separation and thermal mixing in the bulk flow. In this work, we simulate the heat transfer process in a 3-dimensional plate-fin heat sink. We propose a simplified model by considering flow and temperature in a 2-D channel, and extend the model to the third dimension using a 1-D heat fin model. We simulate periodically steady-state solutions. We determine how the global Nusselt number is increased, depending on the vortices' strengths and spacings, in the parameter space of Reynolds and Peclet numbers. We find a surprising spatial oscillation of the local Nusselt number due to the vortices. Support from NSF-DMS grant 1022619 is acknowledged.
Heat transfer and thermal stress analysis in fluid-structure coupled field

International Nuclear Information System (INIS)

Li, Ming-Jian; Pan, Jun-Hua; Ni, Ming-Jiu; Zhang, Nian-Mei

2015-01-01

In this work, three-dimensional simulation on conjugate heat transfer in a fluid-structure coupled field was carried out. The structure considered is from the dual-coolant lithium-lead (DCLL) blanket, which is the key technology of International Thermo-nuclear Experimental Reactor (ITER). The model was developed based on finite element-finite volume method and was employed to investigate mechanical behaviours of Flow Channel Insert (FCI) and heat transfer in the blanket under nuclear reaction. Temperature distribution, thermal deformation and thermal stresses were calculated in this work, and the effects of thermal conductivity, convection heat transfer coefficient and flow velocity were analyzed. Results show that temperature gradients and thermal stresses of FCI decrease when FCI has better heat conductivity. Higher convection heat transfer coefficient will result in lower temperature, thermal deformations and stresses in FCI. Analysis in this work could be a theoretical basis of blanket optimization. - Highlights: • We use FVM and FEM to investigate FCI structural safety considering heat transfer and FSI effects. • Higher convective heat transfer coefficient is beneficial for the FCI structural safety without much affect to bulk flow temperature. • Smaller FCI thermal conductivity can better prevent heat leakage into helium, yet will increase FCI temperature gradient and thermal stress. • Three-dimensional simulation on conjugate heat transfer in a fluid-structure coupled field was carried out
Heat and mass transfer in a vertical flue ring furnace

Energy Technology Data Exchange (ETDEWEB)

Jacobsen, Mona

1997-12-31

The main emphasis of this thesis was the design of a mathematical simulation model for studying details in the baking of anodes in the Hydro Aluminium anode baking furnace. The change of thermal conductivity, density, porosity and permeability during heat treatment was investigated. The Transient Plane Source technique for measuring thermal conductivity of solids was used on green carbon materials during the baking process in the temperature range 20-600 {sup o}C. Next, change of mass, density, porosity and permeability of anode samples were measured after being baked to temperatures between 300 and 1200 {sup o}C. The experimental data were used for parameter estimation and verification of property models for use in the anode baking models. Two distinct mathematical models have been modified to study the anode baking. A transient one-dimensional model for studying temperature, pressure and gas evolution in porous anodes during baking was developed. This was extended to a two-dimensional model incorporating the flue gas flow. The mathematical model which included porous heat and mass transfer, pitch pyrolysis, combustion of volatiles, radiation and turbulent channel flow, was developed by source code modification of the Computational Fluid Dynamics code FLUENT. The two-dimensional geometry of a flue gas channel adjacent to a porous flue gas wall, packing coke and anode was used for studying the effect of different firing strategies, raw materials properties and packing coke thickness. The model proved useful for studying the effects of heating rate, geometry and anode properties. 152 refs., 73 figs, 11 tabs.
Improved heat transfer modeling of the eye for electromagnetic wave exposures.

Science.gov (United States)

Hirata, Akimasa

2007-05-01

This study proposed an improved heat transfer model of the eye for exposure to electromagnetic (EM) waves. Particular attention was paid to the difference from the simplified heat transfer model commonly used in this field. From our computational results, the temperature elevation in the eye calculated with the simplified heat transfer model was largely influenced by the EM absorption outside the eyeball, but not when we used our improved model.
Modelling of heat and mass transfer processes in neonatology

Energy Technology Data Exchange (ETDEWEB)

Ginalski, Maciej K [FLUENT Europe, Sheffield Business Park, Europa Link, Sheffield S9 1XU (United Kingdom); Nowak, Andrzej J [Institute of Thermal Technology, Silesian University of Technology, Konarskiego 22, 44-100 Gliwice (Poland); Wrobel, Luiz C [School of Engineering and Design, Brunel University, Uxbridge UB8 3PH (United Kingdom)], E-mail: maciej.ginalski@ansys.com, E-mail: Andrzej.J.Nowak@polsl.pl, E-mail: luiz.wrobel@brunel.ac.uk

2008-09-01

This paper reviews some of our recent applications of computational fluid dynamics (CFD) to model heat and mass transfer problems in neonatology and investigates the major heat and mass transfer mechanisms taking place in medical devices such as incubators and oxygen hoods. This includes novel mathematical developments giving rise to a supplementary model, entitled infant heat balance module, which has been fully integrated with the CFD solver and its graphical interface. The numerical simulations are validated through comparison tests with experimental results from the medical literature. It is shown that CFD simulations are very flexible tools that can take into account all modes of heat transfer in assisting neonatal care and the improved design of medical devices.
Modelling of heat and mass transfer processes in neonatology

International Nuclear Information System (INIS)

Ginalski, Maciej K; Nowak, Andrzej J; Wrobel, Luiz C

2008-01-01

This paper reviews some of our recent applications of computational fluid dynamics (CFD) to model heat and mass transfer problems in neonatology and investigates the major heat and mass transfer mechanisms taking place in medical devices such as incubators and oxygen hoods. This includes novel mathematical developments giving rise to a supplementary model, entitled infant heat balance module, which has been fully integrated with the CFD solver and its graphical interface. The numerical simulations are validated through comparison tests with experimental results from the medical literature. It is shown that CFD simulations are very flexible tools that can take into account all modes of heat transfer in assisting neonatal care and the improved design of medical devices
Computational study of energy transfer in two-dimensional J-aggregates

International Nuclear Information System (INIS)

Gallos, Lazaros K.; Argyrakis, Panos; Lobanov, A.; Vitukhnovsky, A.

2004-01-01

We perform a computational analysis of the intra- and interband energy transfer in two-dimensional J-aggregates. Each aggregate is represented as a two-dimensional array (LB-film or self-assembled film) of two kinds of cyanine dyes. We consider the J-aggregate whose J-band is located at a shorter wavelength to be a donor and an aggregate or a small impurity with longer wavelength to be an acceptor. Light absorption in the blue wing of the donor aggregate gives rise to the population of its excitonic states. The depopulation of these states is possible by (a) radiative transfer to the ground state (b) intraband energy transfer, and (c) interband energy transfer to the acceptor. We study the dependence of energy transfer on properties such as the energy gap, the diagonal disorder, and the exciton-phonon interaction strength. Experimentally observable parameters, such as the position and form of luminescence spectrum, and results of the kinetic spectroscopy measurements strongly depend upon the density of states in excitonic bands, rates of energy exchange between states and oscillator strengths for luminescent transitions originating from these states

Transient Heat Transfer Model for Car Body Primer Curing

OpenAIRE

D. Zabala; N. Sánchez; J. Pinto

2010-01-01

A transient heat transfer mathematical model for the prediction of temperature distribution in the car body during primer baking has been developed by considering the thermal radiation and convection in the furnace chamber and transient heat conduction governing equations in the car framework. The car cockpit is considered like a structure with six flat plates, four vertical plates representing the car doors and the rear and front panels. The other two flat plates are the...
A numerical and experimental study of two-phase flow and heat transfer in a porous formation with localized heating from below

International Nuclear Information System (INIS)

Easterday, O.T.; Wang, C.Y.; Cheng, P.

1995-01-01

Understanding and predicting two-phase flow and heat transfer in porous media is of fundamental interest for a number of engineering applications. Examples include thermal technologies for remediation of contaminated subsurfaces, the extraction of geothermal energy from vapor-dominated reservoirs, and the assessment of high-level nuclear waste repositories. A numerical and experimental study is reported for two-phase flow and heat transfer in a horizontal porous formation with water through flow and partial heating from below. Based on a newly developed two-phase mixture model, numerical results of the temperature distribution, liquid saturation, liquid and vapor phase velocity fields are presented for three representative cases with varying inlet velocities. It is found that the resulting two-phase structure and flow patterns are strongly dependent upon the water inlet velocity and the bottom heat flux. The former parameter measures the flow along the horizontal direction, while the latter creates a relative motion between the phases in the vertical direction. Experiments are also performed to measure temperature distributions and to visualize the two-phase flow patterns. Qualitative agreement between experiments and numerical predictions is achieved. Overall, this combined experimental and numerical study has provided new insight into conjugate single- and two-phase flow and heat transfer in porous media, although future research is required if accurate modeling of these complex problems is to be accomplished
RELAP4/MOD6 reflood heat transfer and data comparison

International Nuclear Information System (INIS)

Nelson, R.A.; Sullivan, L.H.

1981-01-01

This discussion of RELAP4/MOD6 will be limited to the reflood heat transfer models and evaluation of these models by comparison of calculation with results from three reflood experiments. The discussion of the model includes the heat transfer surface concept, the heat transfer correlations, the superheat model and the entrainment model which presents both the two-phase heat transfer and hydraulic models. In the discussion of the reflood heat transfer, the mathematical concept of a multidimensional surface is used to represent the heat flux of a given heat transfer correlation or correlations dependent upon such variables as quality, wall superheat and flux. This concept has been used to investigate the characteristics of the correlations, which are discusssed in detail, and the way they are applied to the two-phase mixture. Of primary importance in the reflood core heat transfer is the consideration of thermal nonequilibrium between the phases and the liquid entrainment, and its distribution up the core. Results obtained to date show the heat transfer and hydraulics to be closely coupled. Comparison of the RELAP4/MOD6 reflood calculations with the data from the forced feed FLECHT and gravity feed FLECHT-SET and Semiscale reflood experiments indicates that the heat transfer and hydraulic models are operational and yield good results
Free convection film flows and heat transfer laminar free convection of phase flows and models for heat-transfer analysis

CERN Document Server

Shang, De-Yi

2012-01-01

This book presents recent developments in our systematic studies of hydrodynamics and heat and mass transfer in laminar free convection, accelerating film boiling and condensation of Newtonian fluids, as well as accelerating film flow of non-Newtonian power-law fluids (FFNF). These new developments provided in this book are (i) novel system of analysis models based on the developed New Similarity Analysis Method; (ii) a system of advanced methods for treatment of gas temperature- dependent physical properties, and liquid temperature- dependent physical properties; (iii) the organically combined models of the governing mathematical models with those on treatment model of variable physical properties; (iv) rigorous approach of overcoming a challenge on accurate solution of three-point boundary value problem related to two-phase film boiling and condensation; and (v) A pseudo-similarity method of dealing with thermal boundary layer of FFNF for greatly simplifies the heat-transfer analysis and numerical calculati...
Mathematical Simulation of Convective Heat Transfer in the Low-Temperature Storage of Liquefied Natural Gas

OpenAIRE

Shestakov, Igor; Dolgova, Anastasia; Maksimov, Vyacheslav Ivanovich

2015-01-01

The article shows the results of mathematical modeling of convective heat transfer in the low-temperature storage of liquefied natural gas. Regime of natural convection in an enclosure with different intensity of the heat flux at the external borders are investigated. Was examined two-dimensional nonstationary problem within the model of Navier-Stokes in dimensionless variables “vorticity - stream function - temperature”. Distributions of hydrodynamic parameters and temperatures that characte...
HTCC - a heat transfer model for gas-steam mixtures

International Nuclear Information System (INIS)

Papadimitriou, P.

1983-01-01

The mathematical model HTCC (Heat Transfer Coefficient in Containment) has been developed for RALOC after a loss-of-coolant accident in order to determine the local heat transfer coefficients for transfer between the containment atmosphere and the walls of the reactor building. The model considers the current values of room and wall temperature, the concentration of steam and non-condensible gases, geometry data and those of fluid dynamics together with thermodynamic parameters and from these determines the heat transfer mechanisms due to convection, radiation and condensation. The HTCC is implemented in the RALOC program. Comparative analyses of computed temperature profiles, for HEDL Standard problems A and B on hydrogen distribution, and of computed temperature profiles determined during the heat-up phase in the CSE-A5 experiment show a good agreement with experimental data. (orig.) [de
Effect of radiation heat transfer on the performance of high temperature heat exchanger, (2)

International Nuclear Information System (INIS)

Yamada, Yukio; Mori, Yasuo; Hijikata, Kunio.

1977-01-01

In high temperature helium gas-cooled reactors, the nuclear energy can be utilized effectively, and the safety is excellent as compared with conventional reactors. They are advantageous also in view of environmental problems. In this report, the high temperature heat exchanger used for heating steam with the helium from a high temperature gas reactor is modeled, and the case that radiating gas flow between parallel plates is considered. Analysis was made on the case of one channel and constant heat flux and on the model for a counter-flow type heat exchanger with two channels, and the effect of radiation on the heat transfer in laminar flow and turbulent flow regions was clarified theoretically. The basic equations, the method of approximate solution and the results of calculation are explained. When one dimensional radiation was considered, the representative temperature Tr regarding fluid radiation was introduced, and its relation to mean mixing temperature Tm was determined. It was clarified that the large error in the result did not arise even if Tr was taken equally to Tm, especially in case of turbulent flow. The error was practically negligible when the rate of forced convection heat transfer in case of radiating medium flow was taken same as that in the case without radiation. (Kako, I.)
Heat transfer system

Science.gov (United States)

Not Available

1980-03-07

A heat transfer system for a nuclear reactor is described. Heat transfer is accomplished within a sealed vapor chamber which is substantially evacuated prior to use. A heat transfer medium, which is liquid at the design operating temperatures, transfers heat from tubes interposed in the reactor primary loop to spaced tubes connected to a steam line for power generation purposes. Heat transfer is accomplished by a two-phase liquid-vapor-liquid process as used in heat pipes. Condensible gases are removed from the vapor chamber through a vertical extension in open communication with the chamber interior.
Conjugated heat transfer of natural convection in pool with internal heat sources and convection in the tube

International Nuclear Information System (INIS)

Li Longjian; Liu Hongtao; Cui Wenzhi

2007-01-01

The conjugated heat transfer of natural convection in pool with internal heat source and the forced convection in the tube was analyzed, and the corresponding three-dimensional physical and mathematical model was proposed. A control volume based finite element method was employed to solve numerically the problem. The computations were performed for different internal heat source intensity of the pool and the different flow velocity in the tube. The computed heat transfer coefficients on the inner and outer wall showed well consistency of those calculated with the empirical correlations. Compared with the measured total heat transfer coefficients between the fluids in and out of the tube, the computed ones showed also the well consistency, which implied that the numerical model proposed in this paper was reliable. The research results revealed that the total heat transfer coefficients between the fluids were strongly affected by the internal heat source intensity of the pool liquid and the flow velocity in the tube. (authors)
Fundamental principles of heat transfer

CERN Document Server

Whitaker, Stephen

1977-01-01

Fundamental Principles of Heat Transfer introduces the fundamental concepts of heat transfer: conduction, convection, and radiation. It presents theoretical developments and example and design problems and illustrates the practical applications of fundamental principles. The chapters in this book cover various topics such as one-dimensional and transient heat conduction, energy and turbulent transport, forced convection, thermal radiation, and radiant energy exchange. There are example problems and solutions at the end of every chapter dealing with design problems. This book is a valuable int
The solution of heat transfer problems using HEATRAN

International Nuclear Information System (INIS)

Collier, W.D.

1976-07-01

HEATRAN solves the heat diffusion equation over a two dimensional area of any shape or material distribution. Transfer by radiation across voids is allowed and special provsion is made for narrow gaps. A wide range of boundary conditions is available. (author)
Heat transfer from the roughened surface of gas cooled fast breeder reactor fuel element

International Nuclear Information System (INIS)

Tang, I.M.

1979-01-01

The temperature distributions and the augmentation of heat transfer performance by artificial roughening of a gas cooled fast breeder reactor (GCFR) fuel rod cladding are studied. Numerical solutions are based on the axisymmetric assumption for a two-dimensional model for one rib pitch of axial distance. The local and axial clad temperature distributions are obtained for both the rectangular and ramp rib roughened surface geometries. The transformation of experimentally measured convective heat transfer coefficients, in terms of Stanton number, into GCFR values is studied. In addition, the heat transfer performance of a GCFR fuel rod cladding roughened surface design is evaluated. Approximate analytical solution for correlating an average Stanton number is also obtained and satisfactorily compared with the corresponding numerical result for a GCFR design. The analytical correlation is useful in assessing roughened surface heat transfer performance in scoping studies and conceptual design
Investigations on post-dryout heat transfer in bilaterally heated annular channels

International Nuclear Information System (INIS)

Tian, W.X.; Qiu, S.Z.; Jia, D.N.

2006-01-01

Post-dryout heat transfer in bilaterally heated vertical narrow annular channels with 1.0, 1.5 and 2.0 mm gap size has been experimentally investigated with deionized water under the condition of pressure ranging from 1.38 to 5.9 MPa and low mass flow rate from 42.9 to 150.2 kg/m 2 s. The experimental data was compared with well known empirical correlations including Groeneveld, Mattson, etc., and none of them gave an ideal prediction. Theoretical investigations were also carried out on post-dryout heat transfer in annular channels. Based on analysis of heat exchange processes arising among the droplets, the vapor and two tube walls of annular channel, a non-equilibrium mechanistic heat transfer model was developed. Comparison indicated that the present model prediction showed a good agreement with our experimental data. Theoretical calculation result showed that the forced convective heat transfer between the heated wall and vapor dominate the overall heat transfer. The heat transfer caused by the droplets direct contact to the wall and the interfacial convection/evaporation of droplets in superheated vapors also had an indispensable contribution. The radiation heat transfer would be neglected because of its small contribution (less than 0.11%) to the total heat transfer
Convective heat transfer

CERN Document Server

Kakac, Sadik; Pramuanjaroenkij, Anchasa

2014-01-01

Intended for readers who have taken a basic heat transfer course and have a basic knowledge of thermodynamics, heat transfer, fluid mechanics, and differential equations, Convective Heat Transfer, Third Edition provides an overview of phenomenological convective heat transfer. This book combines applications of engineering with the basic concepts of convection. It offers a clear and balanced presentation of essential topics using both traditional and numerical methods. The text addresses emerging science and technology matters, and highlights biomedical applications and energy technologies. What’s New in the Third Edition: Includes updated chapters and two new chapters on heat transfer in microchannels and heat transfer with nanofluids Expands problem sets and introduces new correlations and solved examples Provides more coverage of numerical/computer methods The third edition details the new research areas of heat transfer in microchannels and the enhancement of convective heat transfer with nanofluids....
Analysis and Modeling of Heat Generation in Overcharged Li-Ion Battery with Passive Cooling

DEFF Research Database (Denmark)

Coman, Paul Tiberiu; Veje, Christian

2013-01-01

This paper presents a dynamic model for simulating the heat generation in Lithium batteries and an investigation of the heat transfer as well as the capacity of Phase Change Materials (PCM’s) to store energy inside a battery cell module when the battery is overcharged. The study is performed...... by coupling a one-dimensional model of the electrochemical processes with a two-dimensional model for the heat transfer in a cross section of a battery pack. The heat generation and subsequent temperature rise is analyzed for different charging currents for the two cases where the cell is air......-cooled and passively cooled using a PCM, respectively. As expected, the results show that for high currents, the heat generation and implicitly the temperature increases. However, using a PCM the temperature increase is found to be limited allowing the battery to be overcharged to a certain degree. It is found...
Effect of velocity boundary conditions on the heat transfer and flow topology in two-dimensional Rayleigh-Bénard convection.

Science.gov (United States)

van der Poel, Erwin P; Ostilla-Mónico, Rodolfo; Verzicco, Roberto; Lohse, Detlef

2014-07-01

The effect of various velocity boundary condition is studied in two-dimensional Rayleigh-Bénard convection. Combinations of no-slip, stress-free, and periodic boundary conditions are used on both the sidewalls and the horizontal plates. For the studied Rayleigh numbers Ra between 10(8) and 10(11) the heat transport is lower for Γ=0.33 than for Γ=1 in case of no-slip sidewalls. This is, surprisingly, the opposite for stress-free sidewalls, where the heat transport increases for a lower aspect ratio. In wider cells the aspect-ratio dependence is observed to disappear for Ra ≥ 10(10). Two distinct flow types with very different dynamics can be seen, mostly dependent on the plate velocity boundary condition, namely roll-like flow and zonal flow, which have a substantial effect on the dynamics and heat transport in the system. The predominantly horizontal zonal flow suppresses heat flux and is observed for stress-free and asymmetric plates. Low aspect-ratio periodic sidewall simulations with a no-slip boundary condition on the plates also exhibit zonal flow. In all the other cases, the flow is roll like. In two-dimensional Rayleigh-Bénard convection, the velocity boundary conditions thus have large implications on both roll-like and zonal flow that have to be taken into consideration before the boundary conditions are imposed.
Accounting for the Effect of Noncondensing Gases on Interphasic Heat and Mass Transfer in the Two-Fluid Model Used in the KORSAR Code

Science.gov (United States)

Yudov, Yu. V.

2018-03-01

A model is presented of the interphasic heat and mass transfer in the presence of noncondensable gases for the KORSAR/GP design code. This code was developed by FGUP NITI and the special design bureau OKB Gidropress. It was certified by Rostekhnadzor in 2009 for numerical substantiation of the safety of reactor installations with VVER reactors. The model is based on the assumption that there are three types of interphasic heat and mass transfer of the vapor component: vapor condensation or evaporation on the interphase under any thermodynamic conditions of the phases, pool boiling of the liquid superheated above the saturation temperature at the total pressure, and spontaneous condensation in the volume of gas phase supercooled below the saturation temperature at the vapor partial pressure. Condensation and evaporation on the interphase continuously occur in a two-phase flow and control the time response of the interphase heat and mass transfer. Boiling and spontaneous condensation take place only at the metastable condition of the phases and run at a quite high speed. The procedure used for calculating condensation and evaporation on the interphase accounts for the combined diffusion and thermal resistance of mass transfer in all regimes of the two-phase flow. The proposed approach accounts for, in a natural manner, a decrease in the rate of steam condensation (or generation) in the presence of noncondensing components in the gas phase due to a decrease (or increase) in the interphase temperature relative to the saturation temperature at the vapor partial pressure. The model of the interphase heat transfer also accounts for the processes of dissolution or release of noncondensing components in or from the liquid. The gas concentration at the interphase and on the saturation curve is calculated by the Henry law. The mass transfer coefficient in gas dissolution is based on the heat and mass transfer analogy. Results are presented of the verification of the
Evaluation of Advanced Models for PAFS Condensation Heat Transfer in SPACE Code

Energy Technology Data Exchange (ETDEWEB)

Bae, Byoung-Uhn; Kim, Seok; Park, Yu-Sun; Kang, Kyung Ho [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Ahn, Tae-Hwan; Yun, Byong-Jo [Pusan National University, Busan (Korea, Republic of)

2015-10-15

The PAFS (Passive Auxiliary Feedwater System) is operated by the natural circulation to remove the core decay heat through the PCHX (Passive Condensation Heat Exchanger) which is composed of the nearly horizontal tubes. For validation of the cooling and operational performance of the PAFS, PASCAL (PAFS Condensing Heat Removal Assessment Loop) facility was constructed and the condensation heat transfer and natural convection phenomena in the PAFS was experimentally investigated at KAERI (Korea Atomic Energy Research Institute). From the PASCAL experimental result, it was found that conventional system analysis code underestimated the condensation heat transfer. In this study, advanced condensation heat transfer models which can treat the heat transfer mechanisms with the different flow regimes in the nearly horizontal heat exchanger tube were analyzed. The models were implemented in a thermal hydraulic safety analysis code, SPACE (Safety and Performance Analysis Code for Nuclear Power Plant), and it was evaluated with the PASCAL experimental data. With an aim of enhancing the prediction capability for the condensation phenomenon inside the PCHX tube of the PAFS, advanced models for the condensation heat transfer were implemented into the wall condensation model of the SPACE code, so that the PASCAL experimental result was utilized to validate the condensation models. Calculation results showed that the improved model for the condensation heat transfer coefficient enhanced the prediction capability of the SPACE code. This result confirms that the mechanistic modeling for the film condensation in the steam phase and the convection in the condensate liquid contributed to enhance the prediction capability of the wall condensation model of the SPACE code and reduce conservatism in prediction of condensation heat transfer.
Validation of the TASS/SMR-S Code for the PRHRS Condensation Heat Transfer Model

International Nuclear Information System (INIS)

Jun, In Sub; Yang, Soo Hyoung; Chung, Young Jong; Lee, Won Jae

2011-01-01

When some accidents or events are occurred in the SMART, the secondary system is used to remove the core decay heat for the long time such as a feedwater system. But if the feedwater system can't remove the residual core heat because of its malfunction, the core decay heat is removed using the Passive Residual Heat Removal System (PRHRS). The PRHRS is passive type safety system adopted to enhance the safety of the SMART. It can fundamentally eliminate the uncertainty of operator action. TASS/SMR-S (Transient And Setpoint Simulation/ System-integrated Modular Reactor-Safety) code has various heat transfer models reflecting the design features of the SMART. One of the heat transfer models is the PRHRS condensation heat transfer model. The role of this model is to calculate the heat transfer coefficient in the heat exchanger (H/X) tube side using the relevant heat transfer correlations for all of the heat transfer modes. In this paper, the validation of the condensation heat transfer model was carried out using the POSTECH H/X heat transfer test
Adiabatic partition effect on natural convection heat transfer inside a square cavity

DEFF Research Database (Denmark)

Mahmoudi Nezhad, Sajjad; Rezaniakolaei, Alireza; yousefi, Tooraj

2018-01-01

A steady state and two-dimensional laminar free convection heat transfer in a partitioned cavity with horizontal adiabatic and isothermal side walls is investigated using both experimental and numerical approaches. The experiments and numerical simulations are carried out using a Mach......-Zehnder interferometer and a finite volume code, respectively. A horizontal and adiabatic partition, with angle of θ is adjusted such that it separates the cavity into two identical parts. Effects of this angel as well as Rayleigh number on the heat transfer from the side-heated walls are investigated in this study...... partition angle, the results show that the average Nusselt number and consequently the heat transfer enhance as the Rayleigh number increases. However, for a given Rayleigh number the maximum and the minimum heat transfer occurs at θ = 45°and θ = 90°, respectively. Two responsible mechanisms...

Verification and Validation of Heat Transfer Model of AGREE Code

Energy Technology Data Exchange (ETDEWEB)

Tak, N. I. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Seker, V.; Drzewiecki, T. J.; Downar, T. J. [Department of Nuclear Engineering and Radiological Sciences, Univ. of Michigan, Michigan (United States); Kelly, J. M. [US Nuclear Regulatory Commission, Washington (United States)

2013-05-15

The AGREE code was originally developed as a multi physics simulation code to perform design and safety analysis of Pebble Bed Reactors (PBR). Currently, additional capability for the analysis of Prismatic Modular Reactor (PMR) core is in progress. Newly implemented fluid model for a PMR core is based on a subchannel approach which has been widely used in the analyses of light water reactor (LWR) cores. A hexagonal fuel (or graphite block) is discretized into triangular prism nodes having effective conductivities. Then, a meso-scale heat transfer model is applied to the unit cell geometry of a prismatic fuel block. Both unit cell geometries of multi-hole and pin-in-hole types of prismatic fuel blocks are considered in AGREE. The main objective of this work is to verify and validate the heat transfer model newly implemented for a PMR core in the AGREE code. The measured data in the HENDEL experiment were used for the validation of the heat transfer model for a pin-in-hole fuel block. However, the HENDEL tests were limited to only steady-state conditions of pin-in-hole fuel blocks. There exist no available experimental data regarding a heat transfer in multi-hole fuel blocks. Therefore, numerical benchmarks using conceptual problems are considered to verify the heat transfer model of AGREE for multi-hole fuel blocks as well as transient conditions. The CORONA and GAMMA+ codes were used to compare the numerical results. In this work, the verification and validation study were performed for the heat transfer model of the AGREE code using the HENDEL experiment and the numerical benchmarks of selected conceptual problems. The results of the present work show that the heat transfer model of AGREE is accurate and reliable for prismatic fuel blocks. Further validation of AGREE is in progress for a whole reactor problem using the HTTR safety test data such as control rod withdrawal tests and loss-of-forced convection tests.
Computational modeling of unsteady third-grade fluid flow over a vertical cylinder: A study of heat transfer visualization

Science.gov (United States)

Reddy, G. Janardhana; Hiremath, Ashwini; Kumar, Mahesh

2018-03-01

The present paper aims to investigate the effect of Prandtl number for unsteady third-grade fluid flow over a uniformly heated vertical cylinder using Bejan's heat function concept. The mathematical model of this problem is given by highly time-dependent non-linear coupled equations and are resolved by an efficient unconditionally stable implicit scheme. The time histories of average values of momentum and heat transport coefficients as well as the steady-state flow variables are displayed graphically for distinct values of non-dimensional control parameters arising in the system. As the non-dimensional parameter value gets amplified, the time taken for the fluid flow variables to attain the time-independent state is decreasing. The dimensionless heat function values are closely associated with an overall rate of heat transfer. Thermal energy transfer visualization implies that the heat function contours are compact in the neighborhood of the leading edge of the hot cylindrical wall. It is noticed that the deviations of flow-field variables from the hot wall for a non-Newtonian third-grade fluid flow are significant compared to the usual Newtonian fluid flow.
Heat transfer modeling an inductive approach

CERN Document Server

Sidebotham, George

2015-01-01

This innovative text emphasizes a "less-is-more" approach to modeling complicated systems such as heat transfer by treating them first as "1-node lumped models" that yield simple closed-form solutions. The author develops numerical techniques for students to obtain more detail, but also trains them to use the techniques only when simpler approaches fail. Covering all essential methods offered in traditional texts, but with a different order, Professor Sidebotham stresses inductive thinking and problem solving as well as a constructive understanding of modern, computer-based practice. Readers learn to develop their own code in the context of the material, rather than just how to use packaged software, offering a deeper, intrinsic grasp behind models of heat transfer. Developed from over twenty-five years of lecture notes to teach students of mechanical and chemical engineering at The Cooper Union for the Advancement of Science and Art, the book is ideal for students and practitioners across engineering discipl...
Condensation heat transfer in plate heat exchangers

International Nuclear Information System (INIS)

Panchal, C.B.

1985-01-01

An Alfa-Laval plate heat exchanger, previously tested as an evaporator, was retested as a condenser. Two series of tests with different chevron-angle plates were carried out using ammonia as a working fluid. The overall heat-transfer coefficient and pressure drop were measured, and the effects of operating parameters were determined. The experimental data were compared with theoretical predictions. In the analysis, a gravity-controlled condensation process was modeled theoretically, and the overall performance was calculated. The analysis shows that the overall heat-transfer coefficient can be predicted with an average uncertainty of about 10%. It is, however, important to consider the interfacial shear stress, because the effective friction factor is high for flow in plate heat exchangers
An experimental and numerical study of endwall heat transfer in a turbine blade cascade including tangential heat conduction analysis

Science.gov (United States)

Ratto, Luca; Satta, Francesca; Tanda, Giovanni

2018-06-01

This paper presents an experimental and numerical investigation of heat transfer in the endwall region of a large scale turbine cascade. The steady-state liquid crystal technique has been used to obtain the map of the heat transfer coefficient for a constant heat flux boundary condition. In the presence of two- and three-dimensional flows with significant spatial variations of the heat transfer coefficient, tangential heat conduction could lead to error in the heat transfer coefficient determination, since local heat fluxes at the wall-to-fluid interface tend to differ from point to point and surface temperatures to be smoothed out, thus making the uniform-heat-flux boundary condition difficult to be perfectly achieved. For this reason, numerical simulations of flow and heat transfer in the cascade including the effect of tangential heat conduction inside the endwall have been performed. The major objective of numerical simulations was to investigate the influence of wall heat conduction on the convective heat transfer coefficient determined during a nominal iso-flux heat transfer experiment and to interpret possible differences between numerical and experimental heat transfer results. Results were presented and discussed in terms of local Nusselt number and a convenient wall heat flux function for two values of the Reynolds number (270,000 and 960,000).
Turbulence Modeling and Computation of Turbine Aerodynamics and Heat Transfer

Science.gov (United States)

Lakshminarayana, B.; Luo, J.

1996-01-01

The objective of the present research is to develop improved turbulence models for the computation of complex flows through turbomachinery passages, including the effects of streamline curvature, heat transfer and secondary flows. Advanced turbulence models are crucial for accurate prediction of rocket engine flows, due to existance of very large extra strain rates, such as strong streamline curvature. Numerical simulation of the turbulent flows in strongly curved ducts, including two 180-deg ducts, one 90-deg duct and a strongly concave curved turbulent boundary layer have been carried out with Reynolds stress models (RSM) and algebraic Reynolds stress models (ARSM). An improved near-wall pressure-strain correlation has been developed for capturing the anisotropy of turbulence in the concave region. A comparative study of two modes of transition in gas turbine, the by-pass transition and the separation-induced transition, has been carried out with several representative low-Reynolds number (LRN) k-epsilon models. Effects of blade surface pressure gradient, freestream turbulence and Reynolds number on the blade boundary layer development, and particularly the inception of transition are examined in detail. The present study indicates that the turbine blade transition, in the presence of high freestream turbulence, is predicted well with LRN k-epsilon models employed. The three-dimensional Navier-Stokes procedure developed by the present authors has been used to compute the three-dimensional viscous flow through the turbine nozzle passage of a single stage turbine. A low Reynolds number k-epsilon model and a zonal k-epsilon/ARSM (algebraic Reynolds stress model) are utilized for turbulence closure. An assessment of the performance of the turbulence models has been carried out. The two models are found to provide similar predictions for the mean flow parameters, although slight improvement in the prediction of some secondary flow quantities has been obtained by the
Experiment on transient heat transfer in closed narrow channel

International Nuclear Information System (INIS)

Ochiai, Masaaki

1985-01-01

Heat transfer coefficients and transient pressures in closed narrow channels were obtained experimentally, in order to assess the gap heat transfer models in the computer code WTRLGD which were devised to analyze the internal pressure behavior of waterlogged fuel rods. Gap widths of channels are 0.1--0.5mm to simulate the gap region of waterlogged fuel rods, and test fluids are water (7--89.2 0 C) and Freon-113 (9.2 0 C). The results show that the heater temperature and the pressure measured in the experiments without the DNB occurrence are simulated fairly well by the calculational model of WTRLGD where the heat transfer in a closed narrow channel is evaluated with one-dimensional transient thermal conduction equation and Jens and Lottes' correlation for nucleate boiling. Consequently, it is also suggested that the above equations are available for evaluation of heat flux from fuel to internal water of waterlogged fuel rods. The film boiling heat transfer coefficient was in the same order of that evaluated by Bromley's correlation and the DNB heat flux was smaller than that obtained in quasi-steady experiments with ordinary systems, although the experimental data for them were not enough. (author)
Interface model conditions for a non-equilibrium heat transfer model for conjugate fluid/porous/solid domains

International Nuclear Information System (INIS)

Betchen, L.J.; Straatman, A.G.

2005-01-01

A mathematical and numerical model for the treatment of conjugate fluid flow and heat transfer problems in domains containing pure fluid, porous, and pure solid regions has been developed. The model is general and physically reasoned, and allows for local thermal non-equilibrium in the porous region. The model is developed for implementation on a simple collocated finite volume grid. Of particular novelty are the conditions implemented at the interfaces between porous regions, and those containing a pure solid or pure fluid. The model is validated by simulation of a three-dimensional porous plug problem for which experimental results are available. (author)
Drying process optimization for an API solvate using heat transfer model of an agitated filter dryer.

Science.gov (United States)

Nere, Nandkishor K; Allen, Kimberley C; Marek, James C; Bordawekar, Shailendra V

2012-10-01

Drying an early stage active pharmaceutical ingredient candidate required excessively long cycle times in a pilot plant agitated filter dryer. The key to faster drying is to ensure sufficient heat transfer and minimize mass transfer limitations. Designing the right mixing protocol is of utmost importance to achieve efficient heat transfer. To this order, a composite model was developed for the removal of bound solvent that incorporates models for heat transfer and desolvation kinetics. The proposed heat transfer model differs from previously reported models in two respects: it accounts for the effects of a gas gap between the vessel wall and solids on the overall heat transfer coefficient, and headspace pressure on the mean free path length of the inert gas and thereby on the heat transfer between the vessel wall and the first layer of solids. A computational methodology was developed incorporating the effects of mixing and headspace pressure to simulate the drying profile using a modified model framework within the Dynochem software. A dryer operational protocol was designed based on the desolvation kinetics, thermal stability studies of wet and dry cake, and the understanding gained through model simulations, resulting in a multifold reduction in drying time. Copyright © 2012 Wiley-Liss, Inc.
Modeling the scooping phenomenon for the heat transfer in liquid–gas horizontal slug flows

International Nuclear Information System (INIS)

Bassani, Carlos L.; Pereira, Fernando H.G.; Barbuto, Fausto A.A.; Morales, Rigoberto E.M.

2016-01-01

Highlights: • A low computational tool for heat transfer prediction on slug flows is presented. • The scooping phenomenon is modeled on a stationary approach. • The scooping phenomenon improved in 8% the heat transfer results. - Abstract: The heat transfer between the deep sea waters and the oil and gas mixtures flowing through production lines is a common situation in the petroleum industry. The optimum prediction of the liquid–gas flow parameters along those lines, when the intermittent flow pattern known as slug flow is dominant, has extreme importance in facilities' design. The mixture temperature drop caused by the colder sea waters, which can be regarded as an infinite medium with constant temperature, directly affects physical properties of the fluids such as the viscosity and specific mass. Gas expansion may also occur due to pressure and temperature gradients, thus changing the flow hydrodynamics. Finally, the temperature gradient affects the thermodynamic equilibrium between the phases, favoring wax deposition and thus increasing pressure drops or even blocking the production line. With those issues in mind, the present work proposes a stationary model to predict the mixture temperature distribution and the two-phase flow heat transfer coefficient based on the mass, momentum and energy conservation equations applied to different unit cell regions. The main contribution of the present work is the modeling of the thermal scooping phenomenon, i.e., the heat transfer between two adjacent unit cells due to the mass flux known as scooping. The model was implemented as a structured Fortran95 code with an upwind difference scheme. The results were compared to experimental data and presented good agreement. The analysis showed that the inclusion of the scooping phenomenon into the model resulted in an averaged 8% improvement in the temperature gradient calculation and heat transfer coefficient prediction for the flowing mixture.
A model for dispersed flow heat transfer in rod bundles during reflood

International Nuclear Information System (INIS)

Wong, S.

1980-01-01

The present model calculates the heat transfer characteristics of the non-equilibrium dispersed droplet flow regime above the quench front during reflood by solving simultaneously the wall-to-vapor interactions, wall-to-droplet interactions and vapor-to-droplet interactions by an iterative numerical method. The unique feature in the present study is various heat transfer mechanisms are combined in an overall energy balance equation, and the convective heat transfer to vapor is obtained by calculating the vapor temperature distributions at the heated walls. The reactor rod bundle geometry, axial variations of vapor temperature and flow properties, radiative heat transfers, and enhancement of heat transfer due to turbulence are considered carefully, so that the present model could be used to predict PWR (Pressurized Water Reactor) reflood heat transfers, and hence the fuel cladding wall temperature transients. In order to achieve closure of the problem formulations, the droplet size and its motion are determined from the FLECHT (Full Length Emergency Cooling Heat Transfer Program) low flooding rate series consine axial power shape test data. The model is then verified by comparing the heat transfer predictions with FLECHT low flooding rate series skewed axial power shape test data. Comparisons of predictions with data show satisfactory agreements
Radiation heat transfer model for the SCDAP code

International Nuclear Information System (INIS)

Sohal, M.S.

1984-01-01

A radiation heat transfer model has been developed for severe fuel damage analysis which accounts for anisotropic effects of reflected radiation. The model simplifies the view factor calculation which results in significant savings in computational cost with little loss of accuracy. Radiation heat transfer rates calculated by the isotropic and anisotropic models compare reasonably well with those calculated by other models. The model is applied to an experimental nuclear rod bundle during a slow boiloff of the coolant liquid, a situation encountered during a loss of coolant accident with severe fuel damage. At lower temperatures and also lower temperature gradients in the core, the anisotropic effect was not found to be significant
Large eddy simulations of turbulent flows with heat transfer

International Nuclear Information System (INIS)

Chatelain, Alexandre

2004-01-01

LES of turbulent flows with heat transfer was used within the framework of conjugate heat transfer problems. The objective of this work lies not only in identifying the various elements likely to impair temperature fluctuations estimations at the fluid/solid interface but also to introduce adequate wall modeling. The choice of a proper convection scheme for the transport of passive scalars led to the adoption of a high order upwind scheme with slope limiter. The use of classical wall models having shown some weaknesses as for the estimation of parietal temperature fluctuations, two new approaches are proposed and tested. The first one relies on a complete resolution of the Navier-Stokes equations on a refined grid close to the wall making it possible to rebuild the temperature fluctuations near the wall. The second one relies on the simultaneous and one dimensional resolution of a turbulent boundary layer equation and a variance transport equation near the wall. (author) [fr
[Two-dimensional model of a double-well potential: proton transfer when a hydrogen bond is deformed].

Science.gov (United States)

Krasilnikov, P M

2014-01-01

The potential energy cross-section profile along a hydrogen bond may contain two minima in certain conditions; it is so-called a double well potential. The H-bond double well potential is essential for proton transfer along this hydrogen bond. We have considered the two-dimensional model of such double well potential in harmonic approximation, and we have also investigated the proton tunneling in it. In real environments thermal motion of atoms or conformational changes may cause reorientation and relative shift of molecule fragment forming the hydrogen bond and, as a result, the hydrogen bond isdeformed. This deformation is liable to change the double well potential form and, hence, the probability of the proton tunneling is changed too. As it is shown the characteristic time of proton tunneling is essentially increased by even small relative shift of heavy atoms forming the H-bond and also rotational displacement of covalent bond generated by one of heavy atoms and the proton (hydrogen atom). However, it is also shown, at the certain geometry of the H-bond deformation the opposite effect occurred, i.e., the characteristic time is not increased and even decreased. Notice that such its behavior arises from two-dimensionality of potential wells; this and other properties of our model are discussed in detail.
Effects of stabilizers on the heat transfer characteristics of a nuclear waste canister

International Nuclear Information System (INIS)

Vafai, K.; Ettefagh, J.

1986-07-01

This report summarizes the feasibility and the effectiveness of using stabilizers (internal metal structural components) to augment the heat transfer characteristics of a nuclear waste canister. The problem was modeled as a transient two-dimensional heat transfer in two physical domains - the stabilizer and the wedge (a 30-degree-angle canister segment), which includes the heat-producing spent-fuel rods. This problem is solved by a simultaneous and interrelated numerical investigation of the two domains in cartesian and polar coordinate systems. The numerical investigations were performed for three cases. In the first case, conduction was assumed to be the dominant mechanism for heat transfer. The second case assumed that radiation was the dominant mechanism, and in the third case both radiation and conduction were considered as mechanisms of heat transfer. The results show that for typical conditions in a waste package design, the stabilizers are quite effective in reducing the overall temperature in a waste canister. Furthermore, the results show that increasing the stabilizer thickness over the thickness specified in the present design has a negligible effect on the temperature distribution in the canister. Finally, the presence of the stabilizers was found to shift the location of the peak temperature areas in the waste canister
Discussion on the Heat and Mass Transfer Model on the Pool Surface

Energy Technology Data Exchange (ETDEWEB)

Hong, Soon-Joon; Choo, Yeon-Jun [FNC Tech., Yongin (Korea, Republic of); Ha, Sang-Jun [KHNP Central Research Institute, Daejeon (Korea, Republic of)

2016-10-15

Heat transfer on the pool surface involves the evaporation and condensation of steam in the presence of non-condensable gas. It is a kind of inter-phase heat transfer. This phenomenon has been regarded as less important on the thermal hydraulic behaviors such as pressure, temperature, hydrogen distribution, and so on in the nuclear reactor containment building. As a matter of fact, several RAIs (requests for additional information) during the licensing review of the developed CAP have been presented. And early in 2000s the steam condensation on the water surface of IRWST was a concern of APR1400 design. Such an increased concern is believed because it is a newly adopted system. This study discusses the pool surface heat transfer by reviewing the models of several well-known containment analysis codes, and conducting the sensitivities. This study discussed the pool surface heat transfer. The related models of CAP, GOTHIC, CONTEMPT-LT, and CONTEMPT4 were compared. The sensitivity of heat transfer coefficient for SKN3 and 4 using conventional code CONTEMPT-LT/028-A showed little effect. And the sensitivity of relative humidity and heat transfer area for latent heat transfer shows that CAP locates between GOTHIC and CONTEMPT4/MOD. The sensitivity for sensible heat transfer also shows similar trend. Conclusively, current CAP model of pool surface heat transfer has no fatal defect.
Discussion on the Heat and Mass Transfer Model on the Pool Surface

International Nuclear Information System (INIS)

Hong, Soon-Joon; Choo, Yeon-Jun; Ha, Sang-Jun

2016-01-01

Heat transfer on the pool surface involves the evaporation and condensation of steam in the presence of non-condensable gas. It is a kind of inter-phase heat transfer. This phenomenon has been regarded as less important on the thermal hydraulic behaviors such as pressure, temperature, hydrogen distribution, and so on in the nuclear reactor containment building. As a matter of fact, several RAIs (requests for additional information) during the licensing review of the developed CAP have been presented. And early in 2000s the steam condensation on the water surface of IRWST was a concern of APR1400 design. Such an increased concern is believed because it is a newly adopted system. This study discusses the pool surface heat transfer by reviewing the models of several well-known containment analysis codes, and conducting the sensitivities. This study discussed the pool surface heat transfer. The related models of CAP, GOTHIC, CONTEMPT-LT, and CONTEMPT4 were compared. The sensitivity of heat transfer coefficient for SKN3 and 4 using conventional code CONTEMPT-LT/028-A showed little effect. And the sensitivity of relative humidity and heat transfer area for latent heat transfer shows that CAP locates between GOTHIC and CONTEMPT4/MOD. The sensitivity for sensible heat transfer also shows similar trend. Conclusively, current CAP model of pool surface heat transfer has no fatal defect
A two-cavity reactor for solar chemical processes: heat transfer model and application to carbothermic reduction of ZnO

International Nuclear Information System (INIS)

Wieckert, Christian; Palumbo, Robert; Frommherz, Ulrich

2004-01-01

A 5 kW two-cavity beam down reactor for the solar thermal decomposition of ZnO with solid carbon has been developed and tested in a solar furnace. Initial exploratory experiments show that it operates with a solar to chemical energy conversion efficiency of about 15% when the solar flux entering the reactor is 1300 kW/m 2 , resulting in a reaction chamber temperature of about 1500 K. The solid products have a purity of nearly 100% Zn. Furthermore, the reactor has been described by a numerical model that combines radiant and conduction heat transfer with the decomposition kinetics of the ZnO-carbon reaction. The model is based on the radiosity exchange method. For a given solar input, the model estimates cavity temperatures, Zn production rates, and the solar to chemical energy conversion efficiency. The model currently makes use of two parameters which are determined from the experimental results: conduction heat transfer through the reactor walls enters the model as a lumped term that reflects the conduction loss during the experiments, and the rate of the chemical reaction includes an experimentally determined term that reflects the effective amount of ZnO and CO participating in the reactor. The model output matches well the experimentally determined cavity temperatures. It suggests that reactors built with this two-cavity concept already on this small scale can reach efficiencies exceeding 25%, if operated with a higher solar flux or if one can reduce conduction heat losses through better insulation and if one can maintain or improve the effective amount of ZnO and CO that participates in the reaction
3-D Transient Heat Transfer Analysis of Slab Heating Characteristics in a Reheating Furnace in Hot Strip Mills

Science.gov (United States)

Jang, J. Y.; Lee, Y. W.; Lin, C. N.; Wang, C. H.

2016-05-01

A three-dimensional mathematical transient heat transfer model for the prediction of temperature distribution within the slab has been developed by considering the thermal radiation in the walking-beam-type reheating furnace chamber. The steel slabs are heated up through the non-firing, preheating, 1st-heating, 2nd-heating, and soaking zones in the furnace, respectively, where the furnace wall temperature is function of time. Comparison with the in-situ experimental data from Steel Company in Taiwan shows that the present heat transfer model works well for the prediction of thermal behavior of the slab in the reheating furnace. The effects of different skid button height (H=60mm, 90mm, and 120mm) and different gap distance between two slabs (S=50mm, 75mm, and 100mm) on the slab skid mark formation and temperature profiles are investigated. It is found that the skid mark severity decreases with an increase in the skid button height. The effect of gap distance is important only for the slab edge planes, while it is insignificant for the slab central planes.
Excitation transfer and trapping kinetics in plant photosystem I probed by two-dimensional electronic spectroscopy.

Science.gov (United States)

Akhtar, Parveen; Zhang, Cheng; Liu, Zhengtang; Tan, Howe-Siang; Lambrev, Petar H

2018-03-01

Photosystem I is a robust and highly efficient biological solar engine. Its capacity to utilize virtually every absorbed photon's energy in a photochemical reaction generates great interest in the kinetics and mechanisms of excitation energy transfer and charge separation. In this work, we have employed room-temperature coherent two-dimensional electronic spectroscopy and time-resolved fluorescence spectroscopy to follow exciton equilibration and excitation trapping in intact Photosystem I complexes as well as core complexes isolated from Pisum sativum. We performed two-dimensional electronic spectroscopy measurements with low excitation pulse energies to record excited-state kinetics free from singlet-singlet annihilation. Global lifetime analysis resolved energy transfer and trapping lifetimes closely matches the time-correlated single-photon counting data. Exciton energy equilibration in the core antenna occurred on a timescale of 0.5 ps. We further observed spectral equilibration component in the core complex with a 3-4 ps lifetime between the bulk Chl states and a state absorbing at 700 nm. Trapping in the core complex occurred with a 20 ps lifetime, which in the supercomplex split into two lifetimes, 16 ps and 67-75 ps. The experimental data could be modelled with two alternative models resulting in equally good fits-a transfer-to-trap-limited model and a trap-limited model. However, the former model is only possible if the 3-4 ps component is ascribed to equilibration with a "red" core antenna pool absorbing at 700 nm. Conversely, if these low-energy states are identified with the P 700 reaction centre, the transfer-to-trap-model is ruled out in favour of a trap-limited model.

Stokes flow heat transfer in an annular, rotating heat exchanger

International Nuclear Information System (INIS)

Saatdjian, E.; Rodrigo, A.J.S.; Mota, J.P.B.

2011-01-01

The heat transfer rate into highly viscous, low thermal-conductivity fluids can be enhanced significantly by chaotic advection in three-dimensional flows dominated by viscous forces. The physical effect of chaotic advection is to render the cross-sectional temperature field uniform, thus increasing both the wall temperature gradient and the heat flux into the fluid. A method of analysis for one such flow-the flow in the eccentric, annular, rotating heat exchanger-and a procedure to determine the best heat transfer conditions, namely the optimal values of the eccentricity ratio and time-periodic rotating protocol, are discussed. It is shown that in continuous flows, such as the one under consideration, there exists an optimum frequency of the rotation protocol for which the heat transfer rate is a maximum. - Highlights: → The eccentric, annular, rotating heat exchanger is studied for periodic Stokes flow. → Counter-rotating the inner tube with a periodic velocity enhances the heat transfer. → The heat-transfer enhancement under such conditions is due to chaotic advection. → For a given axial flow rate there is a frequency that maximizes the heat transfer. → There is also an optimum value of the eccentricity ratio.
A two-parameter nondiffusive heat conduction model for data analysis in pump-probe experiments

Science.gov (United States)

Ma, Yanbao

2014-12-01

Nondiffusive heat transfer has attracted intensive research interests in last 50 years because of its importance in fundamental physics and engineering applications. It has unique features that cannot be described by the Fourier law. However, current studies of nondiffusive heat transfer still focus on studying the effective thermal conductivity within the framework of the Fourier law due to a lack of a well-accepted replacement. Here, we show that nondiffusive heat conduction can be characterized by two inherent material properties: a diffusive thermal conductivity and a ballistic transport length. We also present a two-parameter heat conduction model and demonstrate its validity in different pump-probe experiments. This model not only offers new insights of nondiffusive heat conduction but also opens up new avenues for the studies of nondiffusive heat transfer outside the framework of the Fourier law.
Heat transfer prediction in a square porous medium using artificial neural network

Science.gov (United States)

Ahamad, N. Ameer; Athani, Abdulgaphur; Badruddin, Irfan Anjum

2018-05-01

Heat transfer in porous media has been investigated extensively because of its applications in various important fields. Neural network approach is applied to analyze steady two dimensional free convection flows through a porous medium fixed in a square cavity. The backpropagation neural network is trained and used to predict the heat transfer. The results are compared with available information in the literature. It is found that the heat transfer increases with increase in Rayleigh number. It is further found that the local Nusselt number decreases along the height of cavity. The neural network is found to predict the heat transfer behavior accurately for given parameters.
Modulation of near-field heat transfer between two gratings

OpenAIRE

Biehs , Svend-Age; Da Rosa , Felipe S. S.; Ben-Abdallah , Philippe

2011-01-01

International audience; We present a theoretical study of near-field heat transfer between two uniaxial anisotropic planar structures. We investigate how the distance and relative orientation (with respect to their optical axes) between the objects affect the heat flux. In particular, we show that by changing the angle between the optical axes it is possible in certain cases to modulate the net heat flux up to 90% at room temperature, and discuss possible applications of such a strong effect.
On heat transfer to pulsatile flow of a two-phase fluid

Directory of Open Access Journals (Sweden)

S. P. Chakraborty

2005-09-01

Full Text Available The problem of heat transfer to pulsatile flow of a two-phase fluid-particle system contained in a channel bounded by two infinitely long rigid impervious parallel walls has been studied in this paper. The solutions for the steady and the fluctuating temperature distributions are obtained. The rates of heat transfer at the walls are also calculated. The results are discussed numerically with graphical presentations. It is shown that the presence of the particles not only diminishes the steady and unsteady temperature fields but also decreases the reversal of heat flux at the hotter wall irrespective of the influences of other flow parameters.
Two-dimensional radiative transfer for the retrieval of limb emission measurements in the martian atmosphere

Science.gov (United States)

Kleinböhl, Armin; Friedson, A. James; Schofield, John T.

2017-01-01

The remote sounding of infrared emission from planetary atmospheres using limb-viewing geometry is a powerful technique for deriving vertical profiles of structure and composition on a global scale. Compared with nadir viewing, limb geometry provides enhanced vertical resolution and greater sensitivity to atmospheric constituents. However, standard limb profile retrieval techniques assume spherical symmetry and are vulnerable to biases produced by horizontal gradients in atmospheric parameters. We present a scheme for the correction of horizontal gradients in profile retrievals from limb observations of the martian atmosphere. It characterizes horizontal gradients in temperature, pressure, and aerosol extinction along the line-of-sight of a limb view through neighboring measurements, and represents these gradients by means of two-dimensional radiative transfer in the forward model of the retrieval. The scheme is applied to limb emission measurements from the Mars Climate Sounder instrument on Mars Reconnaissance Orbiter. Retrieval simulations using data from numerical models indicate that biases of up to 10 K in the winter polar region, obtained with standard retrievals using spherical symmetry, are reduced to about 2 K in most locations by the retrieval with two-dimensional radiative transfer. Retrievals from Mars atmospheric measurements suggest that the two-dimensional radiative transfer greatly reduces biases in temperature and aerosol opacity caused by observational geometry, predominantly in the polar winter regions.
Simultaneous heat and moisture transfer in soils combined with building simulation

Energy Technology Data Exchange (ETDEWEB)

Santos, G. H. dos; Mendes, N. [Pontifical Catholic University of Parana, PUCPR/CCET, Thermal Systems Laboratory (LST), Curitiba (Brazil)

2006-07-01

In order to precisely predict ground heat transfer, room air temperature and humidity, a combined model has been developed and conceived to calculate both the coupled heat and moisture transfer in soil and floor and the psychrometrics condition of indoor air. The present methodology for the soil is based on the theory of Philip and De Vries, using variable thermophysical properties for different materials. The governing equations were discretized using the finite-volume method and a three-dimensional model for describing the physical phenomena of heat and mass transfer in unsaturated moist porous soils and floor. Additionally, a lumped transient approach for a building room and a finite-volume multi-layer model for the building envelope have been developed to integrate with the soil model. Results are presented in terms of temperature, humidity and heat flux at the interface between room air and the floor, showing the importance of the approach presented and the model robustness for long-term simulations with a high time step. (author)
Bubble Dynamics, Two-Phase Flow, and Boiling Heat Transfer in Microgravity

Science.gov (United States)

Chung, Jacob N.

1998-01-01

This report contains two independent sections. Part one is titled "Terrestrial and Microgravity Pool Boiling Heat Transfer and Critical heat flux phenomenon in an acoustic standing wave." Terrestrial and microgravity pool boiling heat transfer experiments were performed in the presence of a standing acoustic wave from a platinum wire resistance heater using degassed FC-72 Fluorinert liquid. The sound wave was created by driving a half wavelength resonator at a frequency of 10.15 kHz. Microgravity conditions were created using the 2.1 second drop tower on the campus of Washington State University. Burnout of the heater wire, often encountered with heat flux controlled systems, was avoided by using a constant temperature controller to regulate the heater wire temperature. The amplitude of the acoustic standing wave was increased from 28 kPa to over 70 kPa and these pressure measurements were made using a hydrophone fabricated with a small piezoelectric ceramic. Cavitation incurred during experiments at higher acoustic amplitudes contributed to the vapor bubble dynamics and heat transfer. The heater wire was positioned at three different locations within the acoustic field: the acoustic node, antinode, and halfway between these locations. Complete boiling curves are presented to show how the applied acoustic field enhanced boiling heat transfer and increased critical heat flux in microgravity and terrestrial environments. Video images provide information on the interaction between the vapor bubbles and the acoustic field. Part two is titled, "Design and qualification of a microscale heater array for use in boiling heat transfer." This part is summarized herein. Boiling heat transfer is an efficient means of heat transfer because a large amount of heat can be removed from a surface using a relatively small temperature difference between the surface and the bulk liquid. However, the mechanisms that govern boiling heat transfer are not well understood. Measurements of
Vapordynamic thermosyphon - heat transfer two-phase device for wide applications

Science.gov (United States)

Vasiliev, Leonard; Vasiliev, Leonid; Zhuravlyov, Alexander; Shapovalov, Aleksander; Rodin, Aleksei

2015-12-01

Vapordynamic thermosyphon (VDT) is an efficient heat transfer device. The two-phase flow generation and dynamic interaction between the liquid slugs and vapor bubbles in the annular minichannel of the VDT condenser are the main features of such thermosyphon, which allowed to increase its thermodynamic efficiency. VDT can transfer heat in horizontal position over a long distance. The condenser is nearly isothermal with the length of tens of meters. The VDT evaporators may have different forms. Some practical applications of VDT are considered.
Heat transfer in porous medium embedded with vertical plate: Non-equilibrium approach - Part A

Energy Technology Data Exchange (ETDEWEB)

Badruddin, Irfan Anjum [Dept. of Mechanical Engineering, University of Malaya, Kuala Lumpur, 50603 (Malaysia); Quadir, G. A. [School of Mechatronic Engineering, University Malaysia Perlis, Pauh Putra, 02600 Arau, Perlis (Malaysia)

2016-06-08

Heat transfer in a porous medium embedded with vertical flat plate is investigated by using thermal non-equilibrium model. Darcy model is employed to simulate the flow inside porous medium. It is assumed that the heat transfer takes place by natural convection and radiation. The vertical plate is maintained at isothermal temperature. The governing partial differential equations are converted into non-dimensional form and solved numerically using finite element method. Results are presented in terms of isotherms and streamlines for various parameters such as heat transfer coefficient parameter, thermal conductivity ratio, and radiation parameter.
Heat transfer in porous medium embedded with vertical plate: Non-equilibrium approach - Part A

International Nuclear Information System (INIS)

Badruddin, Irfan Anjum; Quadir, G. A.

2016-01-01

Heat transfer in a porous medium embedded with vertical flat plate is investigated by using thermal non-equilibrium model. Darcy model is employed to simulate the flow inside porous medium. It is assumed that the heat transfer takes place by natural convection and radiation. The vertical plate is maintained at isothermal temperature. The governing partial differential equations are converted into non-dimensional form and solved numerically using finite element method. Results are presented in terms of isotherms and streamlines for various parameters such as heat transfer coefficient parameter, thermal conductivity ratio, and radiation parameter
Local heat transfer where heated rods touch in axially flowing water

International Nuclear Information System (INIS)

Kast, S.J.

1983-05-01

An anlaytic model is developed to predict the azimuthal width of a stablesteam blanket region near the line of contact between two heated rods cooled by axially flowing water at high pressure. The model is intended to aid analysis of reduced surface heat transfer capability for the abnormal configuration of nuclear fuel rods bowed into contact in the core of a pressurized water nuclear reactor. The analytic model predicts the azimuthal width of the steam blanket zone having reduced surface heat transfer as a function of rod average heat flux, subchannel coolant conditions and rod dimensions. The analytic model is developed from a heat balance between the heat generated in the wall of a heated empty tube and the heat transported away by transverse mixing and axial convection in the coolant subchannel. The model is developed for seveal geometries including heated rods in line contact, a heated rod touching a short insulating plane and a heated rod touching the inside of a metal guide tube
Thermal radiation heat transfer in participating media by finite volume discretization using collimated beam incidence

Science.gov (United States)

Harijishnu, R.; Jayakumar, J. S.

2017-09-01

The main objective of this paper is to study the heat transfer rate of thermal radiation in participating media. For that, a generated collimated beam has been passed through a two dimensional slab model of flint glass with a refractive index 2. Both Polar and azimuthal angle have been varied to generate such a beam. The Temperature of the slab and Snells law has been validated by Radiation Transfer Equation (RTE) in OpenFOAM (Open Field Operation and Manipulation), a CFD software which is the major computational tool used in Industry and research applications where the source code is modified in which radiation heat transfer equation is added to the case and different radiation heat transfer models are utilized. This work concentrates on the numerical strategies involving both transparent and participating media. Since Radiation Transfer Equation (RTE) is difficult to solve, the purpose of this paper is to use existing solver buoyantSimlpeFoam to solve radiation model in the participating media by compiling the source code to obtain the heat transfer rate inside the slab by varying the Intensity of radiation. The Finite Volume Method (FVM) is applied to solve the Radiation Transfer Equation (RTE) governing the above said physical phenomena.
Numerical prediction of flow, heat transfer, turbulence and combustion

CERN Document Server

Spalding, D Brian; Pollard, Andrew; Singhal, Ashok K

1983-01-01

Numerical Prediction of Flow, Heat Transfer, Turbulence and Combustion: Selected Works of Professor D. Brian Spalding focuses on the many contributions of Professor Spalding on thermodynamics. This compilation of his works is done to honor the professor on the occasion of his 60th birthday. Relatively, the works contained in this book are selected to highlight the genius of Professor Spalding in this field of interest. The book presents various research on combustion, heat transfer, turbulence, and flows. His thinking on separated flows paved the way for the multi-dimensional modeling of turbu
CFD modelling wall heat transfer inside a combustion chamber using ANSYS forte

Science.gov (United States)

Plengsa-ard, C.; Kaewbumrung, M.

2018-01-01

A computational model has been performed to analyze a wall heat transfer in a single cylinder, direct injection and four-stroke diesel engine. A direct integration using detailed chemistry CHEMKIN is employed in a combustion model and the Reynolds Averaged Navier Stokes (RANS) turbulence model is used to simulate the flow in the cylinder. To obtain heat flux results, a modified classical variable-density wall heat transfer model is also performed. The model is validated using experimental data from a CUMMINs engine operated with a conventional diesel combustion. One operating engine condition is simulated. Comparisons of simulated in-cylinder pressure and heat release rates with experimental data shows that the model predicts the cylinder pressure and heat release rates reasonably well. The contour plot of instantaneous temperature are presented. Also, the contours of predicted heat flux results are shown. The magnitude of peak heat fluxes as predicted by the wall heat transfer model is in the range of the typical measure values in diesel combustion.
Liquid metal heat transfer in heat exchangers under low flow rate conditions

International Nuclear Information System (INIS)

Mochizuki, Hiroyasu

2015-01-01

The present paper describes the liquid metal heat transfer in heat exchangers under low flow rate conditions. Measured data from some experiments indicate that heat transfer coefficients of liquid metals at very low Péclet number are much lower than what are predicted by the well-known empirical relations. The cause of this phenomenon was not fully understood for many years. In the present study, one countercurrent-type heat exchanger is analyzed using three, separated countercurrent heat exchanger models: one is a heat exchanger model in the tube bank region, while the upper and lower plena are modeled as two heat exchangers with a single heat transfer tube. In all three heat exchangers, the same empirical correlation is used in the heat transfer calculation on the tube and the shell sides. The Nusselt number, as a function of the Péclet number, calculated from measured temperature and flow rate data in a 50 MW experimental facility was correctly reproduced by the calculation result, when the calculated result is processed in the same way as the experiment. Finally, it is clarified that the deviation is a superficial phenomenon which is caused by the heat transfer in the plena of the heat exchanger. (author)
Heat transfer modelling in thermophotovoltaic cavities using glass media

Energy Technology Data Exchange (ETDEWEB)

Bauer, T.; Forbes, I.; Penlington, R.; Pearsall, N. [Northumbria University, Newcastle upon Tyne (United Kingdom). School of Engineering and Technology

2005-08-15

Optimisation of heat transfer, and in particular radiative heat transfer in terms of the spectral, angular and spatial radiation distributions, is required to achieve high efficiencies and high electrical power densities for thermophotovoltaic (TPV) conversion. This work examines heat transfer from the radiator to the PV cell in an infinite plate arrangement using three different arrangements of participating dielectric media. The modelling applies the Discrete Ordinates method and assumes fused silica (quartz glass) as the dielectric medium. The arrangement radiator-glass-PV cell (also termed dielectric photon concentration) was found to be superior in terms of efficiency and power density. (author)
Heat Transfer Model for Hot Air Balloons

OpenAIRE

Lladó Gambín, Adriana

2016-01-01

A heat transfer model and analysis for hot air balloons is presented in this work, backed with a flow simulation using SolidWorks. The objective is to understand the major heat losses in the balloon and to identify the parameters that affect most its flight performance. Results show that more than 70% of the heat losses are due to the emitted radiation from the balloon envelope and that convection losses represent around 20% of the total. A simulated heating source is also included in the mod...
Comprehensive analysis of heat transfer of gold-blood nanofluid (Sisko-model) with thermal radiation

Science.gov (United States)

Eid, Mohamed R.; Alsaedi, Ahmed; Muhammad, Taseer; Hayat, Tasawar

Characteristics of heat transfer of gold nanoparticles (Au-NPs) in flow past a power-law stretching surface are discussed. Sisko bio-nanofluid flow (with blood as a base fluid) in existence of non-linear thermal radiation is studied. The resulting equations system is abbreviated to model the suggested problem in non-linear PDEs. Along with initial and boundary-conditions, the equations are made non-dimensional and then resolved numerically utilizing 4th-5th order Runge-Kutta-Fehlberg (RKF45) technique with shooting integration procedure. Various flow quantities behaviors are examined for parametric consideration such as the Au-NPs volume fraction, the exponentially stretching and thermal radiation parameters. It is observed that radiation drives to shortage the thermal boundary-layer thickness and therefore resulted in better heat transfer at surface.
An Analytical Solution for Transient Heat Conduction in a Composite Slab with Time-Dependent Heat Transfer Coefficient

Directory of Open Access Journals (Sweden)

Ryoichi Chiba

2018-01-01

Full Text Available An analytical solution is derived for one-dimensional transient heat conduction in a composite slab consisting of n layers, whose heat transfer coefficient on an external boundary is an arbitrary function of time. The composite slab, which has thermal contact resistance at n-1 interfaces, as well as an arbitrary initial temperature distribution and internal heat generation, convectively exchanges heat at the external boundaries with two different time-varying surroundings. To obtain the analytical solution, the shifting function method is first used, which yields new partial differential equations under conventional types of external boundary conditions. The solution for the derived differential equations is then obtained by means of an orthogonal expansion technique. Numerical calculations are performed for two composite slabs, whose heat transfer coefficient on the heated surface is either an exponential or a trigonometric function of time. The numerical results demonstrate the effects of temporal variations in the heat transfer coefficient on the transient temperature field of composite slabs.

Modelling and Pareto optimization of heat transfer and flow coefficients in microchannels using GMDH type neural networks and genetic algorithms

International Nuclear Information System (INIS)

Amanifard, N.; Nariman-Zadeh, N.; Borji, M.; Khalkhali, A.; Habibdoust, A.

2008-01-01

Three-dimensional heat transfer characteristics and pressure drop of water flow in a set of rectangular microchannels are numerically investigated using Fluent and compared with those of experimental results. Two metamodels based on the evolved group method of data handling (GMDH) type neural networks are then obtained for modelling of both pressure drop (ΔP) and Nusselt number (Nu) with respect to design variables such as geometrical parameters of microchannels, the amount of heat flux and the Reynolds number. Using such obtained polynomial neural networks, multi-objective genetic algorithms (GAs) (non-dominated sorting genetic algorithm, NSGA-II) with a new diversity preserving mechanism is then used for Pareto based optimization of microchannels considering two conflicting objectives such as (ΔP) and (Nu). It is shown that some interesting and important relationships as useful optimal design principles involved in the performance of microchannels can be discovered by Pareto based multi-objective optimization of the obtained polynomial metamodels representing their heat transfer and flow characteristics. Such important optimal principles would not have been obtained without the use of both GMDH type neural network modelling and the Pareto optimization approach
High-velocity two-phase flow two-dimensional modeling

International Nuclear Information System (INIS)

Mathes, R.; Alemany, A.; Thilbault, J.P.

1995-01-01

The two-phase flow in the nozzle of a LMMHD (liquid metal magnetohydrodynamic) converter has been studied numerically and experimentally. A two-dimensional model for two-phase flow has been developed including the viscous terms (dragging and turbulence) and the interfacial mass, momentum and energy transfer between the phases. The numerical results were obtained by a finite volume method based on the SIMPLE algorithm. They have been verified by an experimental facility using air-water as a simulation pair and a phase Doppler particle analyzer for velocity and droplet size measurement. The numerical simulation of a lithium-cesium high-temperature pair showed that a nearly homogeneous and isothermal expansion of the two phases is possible with small pressure losses and high kinetic efficiencies. In the throat region a careful profiling is necessary to reduce the inertial effects on the liquid velocity field
Simulation of the heat and mass transfer processes during the vacuum frying of potato chips

Directory of Open Access Journals (Sweden)

Ram Yamsaengsung

2008-01-01

Full Text Available A fundamental two-dimensional model to predict the heat and mass transfer that occur during the vacuum frying of potato chips was solved using the Finite Element toolbox in MATLAB 6.1. The simulation of the heat transfer process included the convection of heat from the surface to the product, the conduction of heat into the product, and a loss of heat using the heat source term representing evaporation. The mass transfer process was divided into two periods: (1 water loss and (2 oil absorption. The first scenario included a diffusion term and a source term. The source term represented the convection and evaporation of water from the product. For the second period, the diffusion term represented the gradual absorption of oil through capillary diffusion.From the simulation, a good agreement between the experimental data and the predicted values was obtained. From the heat transfer model, the rapid increase in temperature of the product toward the boiling point of water (at the associated pressure followed by its steady increase toward the temperature of the oil was validated. Furthermore, by separating the rate of moisture loss into two parts to represent the constant rate and falling rate period of drying, the model was able to predict an initial period of rapid moisture loss followed by a decreasing rate of moisture loss. The simulation also demonstrated the formation of the crust and the gradual movement of the crust inward. Finally, using two sets of diffusion coefficients that correlated to the two schemes of moisture loss, the model predicted the rapid flux of oil into the product during the constant drying stage, followed by a small amount of oil absorption into its interior once the crust had been established.
Safety verification of radiation shielding and heat transfer for a model for dry

International Nuclear Information System (INIS)

Yu, Haiyan; Tang, Xiaobin; Wang, Peng; Chen, Feida; Chai, Hao; Chen, Da

2015-01-01

Highlights: • New type of dry spent fuel storage was designed. • MC method and FEM were used to verify the reliability of new storage. • Radiation shield and heat transfer both meet IAEA standards: 2 mSv/h, 0.1 mSv/h and 190 °C, 85 °C. • Provided possibilities for future implementation of this type of dry storage. - Abstract: The goal of this research is to develop a type of dry spent fuel storage called CHN-24 container, which could contain an equivalent load of 45 GWD/MTU of spent fuel after 10 years cooling. Basically, radiation shielding performance and safe removal of decay heat, which play important roles in the safety performance, were checked and validated using the Monte Carlo method and finite element analysis to establish the radiation dose rate calculation model and three-dimensional heat transfer model for the CHN-24 container. The dose rates at the surface of the container and at a distance of 1 m from the surface were 0.42 mSv/h and 0.06 mSv/h, respectively. These conform to the International Atomic Energy Agency (IAEA) radioactive material transportation safety standards 2 mSv/h and 0.1 mSv/h. The results shows that the CHN-24 container maintains its structural and material integrity under the condition of normal thermal steady-state heat transfer as well as in case of extreme fire as evinced by transient-state analysis. The temperature inside and on the surface of the container were 150.91 °C and 80 °C under normal storage conditions, which indicated that the design also conform to IAEA heat transfer safety standards of 190 °C and 85 °C
Visualization of Heat Transfer and Core Damage With RGUI 1.5

International Nuclear Information System (INIS)

Mesina, George L.

2002-01-01

Graphical User Interfaces (GUI) have become an integral and essential part of computer software. In the ever-changing world of computing, they provide the user with a valuable means to learn, understand, and use the application software while also helping applications adapt to and span different computing paradigms, such as different operating systems. For these reasons, GUI development for nuclear plant analysis programs has been ongoing for a decade and a half and much progress has been made. With the development of codes such as RELAP5-3D [1] and SCDAP/RELAP5 that have multi-dimensional modeling capability, it has become necessary to represent three-dimensional, calculated data. The RELAP5-3D Graphical User Interface (RGUI) [4] was designed specifically for this purpose. It reduces the difficulty of analyzing complex three-dimensional models and enhances the analysts' ability to recognize plant behavior visually. Previous versions of RGUI [5] focused on visualizing reactor coolant behavior during a simulated transient or accident. Recent work has extended RGUI to display two other phenomena, heat transfer and core damage. Heat transfer is depicted through the visualization of RELAP5-3D heat structures. Core damage is visualized by displaying fuel rods and other core structures in a reactor vessel screen. Conditions within the core are displayed via numerical results and color maps. These new features of RGUI 1.5 are described and illustrated. (authors)
Development of local heat transfer and pressure drop models for pebble bed high temperature gas-cooled reactor cores - HTR2008-58296

International Nuclear Information System (INIS)

McLaughlin, B.; Worsley, M.; Stainsby, R.; Grief, A.; Dennier, A.; Macintosh, S.; Van Heerden, E.

2008-01-01

This paper describes pressure drop and heat transfer coefficient predictions for a typical coolant flow within the core of a pebble bed reactor (PBR) by examining a representative group of pebbles remote from the reflector region. The three- dimensional steady state flow and heat transfer predictions utilized in this work are obtained from a computational fluid dynamics (CFD) model created in the commercial software ANSYS FLUENT TM . This work utilizes three RANS turbulence models and the Chilton-Colburn analogy for heat transfer. A methodology is included in this paper for creating a quality unstructured mesh with prismatic surface layers on a random arrangement of touching pebbles. The results of the model are validated by comparing them with the correlations of the German KTA rules for a PBR. (authors)
Effect of radiant heat transfer on the performance of high temperature heat exchanger

International Nuclear Information System (INIS)

Mori, Yasuo; Hijikata, Kunio; Yamada, Yukio

1975-01-01

The development of high temperature gas-cooled reactors is motivated by the consideration of the application of nuclear heat for industrial uses or direct steelmaking and chemical processes. For these purposes, reliable and efficient heat exchangers should be developed. This report analyzes the effect of radiant heat transfer on the performance of high temperature heat exchangers. The heat transfer model is as follows: the channel composed with two parallel adiabatic walls is divided with one parallel plate between the walls. Non-radiative fluid flows in the two separated channels in opposite direction. Heat transfer equations for this system were obtained, and these equations were solved by some approximate method and numerical analysis. The effect of radiation on heat transfer became larger as the radiant heat transfer between two walls was larger. In the heat exchangers of counter flow type, the thermal efficiency is controlled with three parameters, namely radiation-convection parameter, Stanton number and temperature difference. The thermal efficiency was larger with the increase of these parameters. (Iwase, T.)
Fluidized-Bed Heat Transfer Modeling for the Development of Particle/Supercritical-CO2 Heat Exchanger

Energy Technology Data Exchange (ETDEWEB)

Ma, Zhiwen [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Martinek, Janna G [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

2017-06-03

Concentrating solar power (CSP) technology is moving toward high-temperature and high-performance design. One technology approach is to explore high-temperature heat-transfer fluids and storage, integrated with a high-efficiency power cycle such as the supercritical carbon dioxide (s-CO2) Brayton power cycle. The s-CO2 Brayton power system has great potential to enable the future CSP system to achieve high solar-to-electricity conversion efficiency and to reduce the cost of power generation. Solid particles have been proposed as a possible high-temperature heat-transfer medium that is inexpensive and stable at high temperatures above 1,000 degrees C. The particle/heat exchanger provides a connection between the particles and s-CO2 fluid in the emerging s-CO2 power cycles in order to meet CSP power-cycle performance targets of 50% thermal-to-electric efficiency, and dry cooling at an ambient temperature of 40 degrees C. The development goals for a particle/s-CO2 heat exchanger are to heat s-CO2 to =720 degrees C and to use direct thermal storage with low-cost, stable solid particles. This paper presents heat-transfer modeling to inform the particle/s-CO2 heat-exchanger design and assess design tradeoffs. The heat-transfer process was modeled based on a particle/s-CO2 counterflow configuration. Empirical heat-transfer correlations for the fluidized bed and s-CO2 were used in calculating the heat-transfer area and optimizing the tube layout. A 2-D computational fluid-dynamics simulation was applied for particle distribution and fluidization characterization. The operating conditions were studied from the heat-transfer analysis, and cost was estimated from the sizing of the heat exchanger. The paper shows the path in achieving the cost and performance objectives for a heat-exchanger design.
Turbulent mixed buoyancy driven flow and heat transfer in lid driven enclosure

International Nuclear Information System (INIS)

Mishra, Ajay Kumar; Sharma, Anil Kumar

2015-01-01

Turbulent mixed buoyancy driven flow and heat transfer of air in lid driven rectangular enclosure has been investigated for Grashof number in the range of 10 8 to 10 11 and for Richardson number 0.1, 1 and 10. Steady two dimensional Reynolds-Averaged-Navier-Stokes equations and conservation equations of mass and energy, coupled with the Boussinesq approximation, are solved. The spatial derivatives in the equations are discretized using the finite-element method. The SIMPLE algorithm is used to resolve pressure-velocity coupling. Turbulence is modeled with the k-ω closure model with physical boundary conditions along with the Boussinesq approximation, for the flow and heat transfer. The predicted results are validated against benchmark solutions reported in literature. The results include stream lines and temperature fields are presented to understand flow and heat transfer characteristics. There is a marked reduction in mean Nusselt number (about 58%) as the Richardson number increases from 0.1 to 10 for the case of Ra=10 10 signifying the effect of reduction of top lid velocity resulting in reduction of turbulent mixing. (author)
Enhanced two phase flow in heat transfer systems

Science.gov (United States)

Tegrotenhuis, Ward E; Humble, Paul H; Lavender, Curt A; Caldwell, Dustin D

2013-12-03

A family of structures and designs for use in devices such as heat exchangers so as to allow for enhanced performance in heat exchangers smaller and lighter weight than other existing devices. These structures provide flow paths for liquid and vapor and are generally open. In some embodiments of the invention, these structures can also provide secondary heat transfer as well. In an evaporate heat exchanger, the inclusion of these structures and devices enhance the heat transfer coefficient of the evaporation phase change process with comparable or lower pressure drop.
Numerical study of turbulent heat transfer from confined impinging jets using a pseudo-compressibility method

Energy Technology Data Exchange (ETDEWEB)

Rahman, M.; Rautaheimo, P.; Siikonen, T.

1997-12-31

A numerical investigation is carried out to predict the turbulent fluid flow and heat transfer characteristics of two-dimensional single and three impinging slot jets. Two low-Reynolds-number {kappa}-{epsilon} models, namely the classical model of Chien and the explicit algebraic stress model of Gatski and Speziale, are considered in the simulation. A cell-centered finite-volume scheme combined with an artificial compressibility approach is employed to solve the flow equations, using a diagonally dominant alternating direction implicit (DDADI) time integration method. A fully upwinded second order spatial differencing is adopted to approximate the convective terms. Roe`s damping term is used to calculate the flux on the cell face. A multigrid method is utilized for the acceleration of convergence. On average, the heat transfer coefficients predicted by both models show good agreement with the experimental results. (orig.) 17 refs.
Optimization of heat saving in buildings using unsteady heat transfer model

Directory of Open Access Journals (Sweden)

Dedinec Aleksandra

2015-01-01

Full Text Available Reducing the energy consumption growth rate is increasingly becoming one of the main challenges for ensuring sustainable development, particularly in the buildings as the largest end-use sector in many countries. Along this line, the aim of this paper is to analyse the possibilities for energy savings in the construction of new buildings and reconstruction of the existing ones developing a tool that, in terms of the available heating technologies and insulation, provides answer to the problem of optimal cost effective energy consumption. The tool is composed of an unsteady heat transfer model which is incorporated into a cost-effective energy saving optimization. The unsteady heat transfer model uses annual hourly meteorological data, chosen as typical for the last ten-year period, as well as thermo physical features of the layers of the building walls. The model is tested for the typical conditions in the city of Skopje, Macedonia. The results show that the most cost effective heating technology for the given conditions is the wood fired stove, followed by the inverter air-conditioner. The centralized district heating and the pellet fired stoves are the next options. The least cost effective option is the panel that uses electricity. In this paper, the optimal insulation thickness is presented for each type of heating technology.
Development and Application of a Numerical Framework for Improving Building Foundation Heat Transfer Calculations

Science.gov (United States)

Kruis, Nathanael J. F.

Heat transfer from building foundations varies significantly in all three spatial dimensions and has important dynamic effects at all timescales, from one hour to several years. With the additional consideration of moisture transport, ground freezing, evapotranspiration, and other physical phenomena, the estimation of foundation heat transfer becomes increasingly sophisticated and computationally intensive to the point where accuracy must be compromised for reasonable computation time. The tools currently available to calculate foundation heat transfer are often either too limited in their capabilities to draw meaningful conclusions or too sophisticated to use in common practices. This work presents Kiva, a new foundation heat transfer computational framework. Kiva provides a flexible environment for testing different numerical schemes, initialization methods, spatial and temporal discretizations, and geometric approximations. Comparisons within this framework provide insight into the balance of computation speed and accuracy relative to highly detailed reference solutions. The accuracy and computational performance of six finite difference numerical schemes are verified against established IEA BESTEST test cases for slab-on-grade heat conduction. Of the schemes tested, the Alternating Direction Implicit (ADI) scheme demonstrates the best balance between accuracy, performance, and numerical stability. Kiva features four approaches of initializing soil temperatures for an annual simulation. A new accelerated initialization approach is shown to significantly reduce the required years of presimulation. Methods of approximating three-dimensional heat transfer within a representative two-dimensional context further improve computational performance. A new approximation called the boundary layer adjustment method is shown to improve accuracy over other established methods with a negligible increase in computation time. This method accounts for the reduced heat transfer
A computational model for viscous fluid flow, heat transfer, and melting in in situ vitrification melt pools

International Nuclear Information System (INIS)

McHugh, P.R.; Ramshaw, J.D.

1991-11-01

MAGMA is a FORTRAN computer code designed to viscous flow in in situ vitrification melt pools. It models three-dimensional, incompressible, viscous flow and heat transfer. The momentum equation is coupled to the temperature field through the buoyancy force terms arising from the Boussinesq approximation. All fluid properties, except density, are assumed variable. Density is assumed constant except in the buoyancy force terms in the momentum equation. A simple melting model based on the enthalpy method allows the study of the melt front progression and latent heat effects. An indirect addressing scheme used in the numerical solution of the momentum equation voids unnecessary calculations in cells devoid of liquid. Two-dimensional calculations can be performed using either rectangular or cylindrical coordinates, while three-dimensional calculations use rectangular coordinates. All derivatives are approximated by finite differences. The incompressible Navier-Stokes equations are solved using a new fully implicit iterative technique, while the energy equation is differenced explicitly in time. Spatial derivatives are written in conservative form using a uniform, rectangular, staggered mesh based on the marker and cell placement of variables. Convective terms are differenced using a weighted average of centered and donor cell differencing to ensure numerical stability. Complete descriptions of MAGMA governing equations, numerics, code structure, and code verification are provided. 14 refs
A computational model for viscous fluid flow, heat transfer, and melting in in situ vitrification melt pools

Energy Technology Data Exchange (ETDEWEB)

McHugh, P.R.; Ramshaw, J.D.

1991-11-01

MAGMA is a FORTRAN computer code designed to viscous flow in in situ vitrification melt pools. It models three-dimensional, incompressible, viscous flow and heat transfer. The momentum equation is coupled to the temperature field through the buoyancy force terms arising from the Boussinesq approximation. All fluid properties, except density, are assumed variable. Density is assumed constant except in the buoyancy force terms in the momentum equation. A simple melting model based on the enthalpy method allows the study of the melt front progression and latent heat effects. An indirect addressing scheme used in the numerical solution of the momentum equation voids unnecessary calculations in cells devoid of liquid. Two-dimensional calculations can be performed using either rectangular or cylindrical coordinates, while three-dimensional calculations use rectangular coordinates. All derivatives are approximated by finite differences. The incompressible Navier-Stokes equations are solved using a new fully implicit iterative technique, while the energy equation is differenced explicitly in time. Spatial derivatives are written in conservative form using a uniform, rectangular, staggered mesh based on the marker and cell placement of variables. Convective terms are differenced using a weighted average of centered and donor cell differencing to ensure numerical stability. Complete descriptions of MAGMA governing equations, numerics, code structure, and code verification are provided. 14 refs.
Heat Transfer Analysis for a Fixed CST Column

International Nuclear Information System (INIS)

Lee, S.Y.

2004-01-01

In support of a small column ion exchange (SCIX) process for the Savannah River Site waste processing program, a transient two-dimensional heat transfer model that includes the conduction process neglecting the convection cooling mechanism inside the crystalline silicotitanate (CST) column has been constructed and heat transfer calculations made for the present design configurations. For this situation, a no process flow condition through the column was assumed as one of the reference conditions for the simulation of a loss-of-flow accident. A series of the modeling calculations has been performed using a computational heat transfer approach. Results for the baseline model indicate that transit times to reach 130 degrees Celsius maximum temperature of the CST-salt solution column are about 96 hours when the 20-in CST column with 300 Ci/liter heat generation source and 25 degrees Celsius initial column temperature is cooled by natural convection of external air as a primary heat transfer mechanism. The modeling results for the 28-in column equipped with water jacket systems on the external wall surface of the column and water coolant pipe at the center of the CST column demonstrate that the column loaded with 300 Ci/liter heat source can be maintained non-boiling indefinitely. Sensitivity calculations for several alternate column sizes, heat loads of the packed column, engineered cooling systems, and various ambient conditions at the exterior wall of the column have been performed under the reference conditions of the CST-salt solution to assess the impact of those parameters on the peak temperatures of the packed column for a given transient time. The results indicate that a water-coolant pipe at the center of the CST column filled with salt solution is the most effective one among the potential design parameters related to the thermal energy dissipation of decay heat load. It is noted that the cooling mechanism at the wall boundary of the column has significant
Development of a UF{sub 6} cylinder transient heat transfer/stress analysis model

Energy Technology Data Exchange (ETDEWEB)

Williams, W.R. [Martin Marietta Energy Systems, Inc., Oak Ridge, TN (United States)

1991-12-31

A heat transfer/stress analysis model is being developed to simulate the heating to a point of rupture of a cylinder containing UF{sub 6} when it is exposed to a fire. The assumptions underlying the heat transfer portion of the model, which has been the focus of work to date, will be discussed. A key aspect of this model is a lumped parameter approach to modeling heat transfer. Preliminary results and future efforts to develop an integrated thermal/stress model will be outlined.
Measurement and modeling of interface heat transfer coefficients

International Nuclear Information System (INIS)

Rollett, A.D.; Lewis, H.D.; Dunn, P.S.

1985-01-01

The results of preliminary work on the modeling and measurement of the heat transfer coefficients of metal/mold interfaces is reported. The system investigated is the casting of uranium in graphite molds. The motivation for the work is primarily to improve the accuracy of process modeling of prototype mold designs at the Los Alamos Foundry. The evolution in design of a suitable mold for unidirectional solidification is described, illustrating the value of simulating mold designs prior to use. Experiment indicated a heat transfer coefficient of 2 kW/m 2 /K both with and without superheat. It was possible to distinguish between solidification due to the mold and that due to radiative heat loss. This permitted an experimental estimate of the emissivity, epsilon = 0.2, of the solidified metal
Heat transfer modelling of pulsed laser-tissue interaction

Science.gov (United States)

Urzova, J.; Jelinek, M.

2018-03-01

Due to their attributes, the application of medical lasers is on the rise in numerous medical fields. From a biomedical point of view, the most interesting applications are the thermal interactions and the photoablative interactions, which effectively remove tissue without excessive heat damage to the remaining tissue. The objective of this work is to create a theoretical model for heat transfer in the tissue following its interaction with the laser beam to predict heat transfer during medical laser surgery procedures. The dimensions of the ablated crater (shape and ablation depth) were determined by computed tomography imaging. COMSOL Multiphysics software was used for temperature modelling. The parameters of tissue and blood, such as density, specific heat capacity, thermal conductivity and diffusivity, were calculated from the chemical ratio. The parameters of laser-tissue interaction, such as absorption and reflection coefficients, were experimentally determined. The parameters of the laser beam were power density, repetition frequency, pulse length and spot dimensions. Heat spreading after laser interaction with tissue was captured using a Fluke thermal camera. The model was verified for adipose tissue, skeletal muscle tissue and heart muscle tissue.
Simplified analytical model for thermal transfer in vertical hollow brick

Energy Technology Data Exchange (ETDEWEB)

Lorente, S [Lab. d` Etudes Thermiques et Mecaniques, INSA, UPS, Toulouse (France); Petit, M [Lab. d` Etudes Thermiques et Mecaniques, INSA, UPS, Toulouse (France); Javelas, R [Lab. d` Etudes Thermiques et Mecaniques, INSA, UPS, Toulouse (France)

1996-12-01

A modern building envelope has a lot of little cavities. Most of them are vertical with a high height to thickness ratio. We present here the conception of a software to determine heat transfer through terra-cotta bricks full of large vertical cavities. After a bibliographic study on convective heat transfer in such cavities, we made an analytical model based on Karman-Polhausen`s method for convection and on the radiosity method for radiative heat transfer. We used a test apparatus of a single cavity to determine the temperature field inside the cavity. Using these experimental results, we showed that the exchange was two-dimensional. We also realised heat flux measurements. Then we expose our theoretical study: We propose relations between central core temperatures and active face temperatures, then between outside and inside active face temperatures. We calculate convective superficial heat transfer because we noticed we have boundary layers along the active faces. We realise a heat flux balance between convective plus radiative heat transfer and conductive heat transfer, so we propose an algorithm to calculate global heat transfer through a single cavity. Finally, we extend our model to a whole hollow brick with lined-up cavities and propose an algorithm to calculate heat flux and thermal resistance with a good accuracy ({approx}7.5%) compared to previous experimental results. (orig.)

Numerical Modeling of Transient Heat Transfer in Longitudinal Fin

Directory of Open Access Journals (Sweden)

Farshad Panahizadeh

2017-11-01

Full Text Available The main objective of the present numerical study is to investigate the transient heat transfer in one kind of all-purpose longitudinal fin with the triangular profile. The lateral surface of the concerned fin and the tip of it are subjected to general situations included heat flux at the base and insulation on the tip. For this study developed a one dimensional in house code written by Fortran 90 programming language by using finite difference method with an implicit scheme in unsteady state condition. Generally, the result of this study in time variation state after 700 seconds is steady. The results also show the fin efficiency by increasing the time of study decreases due to a reduction in the total heat transfer which is happened in the fin. The grid independence study shows that for the number of nodes greater than 20 the result will not be changed and same as before. Finally, the result of Fortran code verified by commercial CFD code which relies on finite difference method and it was shown have a consistent agreement
Thermal non-equilibrium heat transfer in a porous cavity in the presence of bio-chemical heat source

Directory of Open Access Journals (Sweden)

Nazari Mohsen

2015-01-01

Full Text Available This paper is concerned with thermal non-equilibrium natural convection in a square cavity filled with a porous medium in the presence of a biomass which is transported in the cavity. The biomass can consume a secondary moving substrate. The physics of the presented problem is related to the analysis of heat and mass transfer in a composting process that controlled by internal heat generation. The intensity of the bio-heat source generated in the cavity is equal to the rate of consumption of the substrate by the biomass. It is assumed that the porous medium is homogeneous and isotropic. A two-field model that represents the fluid and solid phase temperature fields separately is used for energy equation. A simplified Monod model is introduced along with the governing equations to describe the consumption of the substrate by the biomass. In other word, the transient biochemical heat source which is dependent on a solute concentration is considered in the energy equations. Investigation of the biomass activity and bio-chemical heat generation in the case of thermal non-equilibrium assumption has not been considered in the literature and they are open research topics. The effects of thermal non-equilibrium model on heat transfer, flow pattern and biomass transfer are investigated. The effective parameters which have a direct impact on the generated bio-chemical heat source are also presented. The influences of the non-dimensional parameters such as fluid-to-solid conductivity ratio on the temperature distribution are presented.
Internally Heated Screw Pyrolysis Reactor (IHSPR) heat transfer performance study

Science.gov (United States)

Teo, S. H.; Gan, H. L.; Alias, A.; Gan, L. M.

2018-04-01

1.5 billion end-of-life tyres (ELT) were discarded globally each year and pyrolysis is considered the best solution to convert the ELT into valuable high energy-density products. Among all pyrolysis technologies, screw reactor is favourable. However, conventional screw reactor risks plugging issue due to its lacklustre heat transfer performance. An internally heated screw pyrolysis reactor (IHSPR) was developed by local renewable energy industry, which serves as the research subject for heat transfer performance study of this particular paper. Zero-load heating test (ZLHT) was first carried out to obtain the operational parameters of the reactor, followed by the one dimensional steady-state heat transfer analysis carried out using SolidWorks Flow Simulation 2016. Experiments with feed rate manipulations and pyrolysis products analyses were conducted last to conclude the study.
An experimental investigation of heat transfer from a reactor fuel channel to surrounding water

International Nuclear Information System (INIS)

Gillespie, G.E.

An important feature of the CANDU-PHW reactor is that each fuel channel is surrounded by cool heavy-water moderator that can act as a sink for heat generated in the fuel if other means of heat removal were to fail. During postulated loss-of-coolant accidents there are two scenarios in which the primary cooling system may not prevent fuel-channel overheating. These situations arise when: (1) for a particular break size and location, called the critical break, the coolant flow through a portion of the reactor core stagnates before the emergency coolant injection system restores circulation, or, (2) the emergency coolant injection system fails to operate. In either case, the heat generated in the fuel is transferred mainly by radiation to the pressure tube and calandria tube, and then by boiling heat transfer to the moderator. This paper describes a simple one-dimensional model developed to analyse the thermal behaviour of a fuel channel when the internal pressure is high. Also described is a series of experiments in which the pressure-tube segment is pressurized and heated at a constant rate until it contacts a surrounding calandria-tube segment. Predictions of the one-dimensional model are compared with the experimental results
Supercritical heat transfer in an annular channel with two-sided heaing

International Nuclear Information System (INIS)

Sergeev, V.V.; Remizov, O.V.; Gal'chenko, Eh.F.

1986-01-01

The paper deals with experimental inestigation into worsening of heat transfer at forced up flow in steam-water mixture in a vertical annular channel with two-sided heating and development of technique for calculation of supercritical heat exchange in this channel. Bench-scale experiments are carried out at high-pressure at mass rates of the coolant equal to 300-865 kg/(m 2 x s), pressure of 9.8-17.8 MPa and heat flux on the internal surface - 20-400 kW/m 2 , on the external surface - 35-450 kW/m 2 . Technique for calculation of supercritical heat exchange in channels with one- and two-sided heating is suggested. Analysis of the obtained experimental data permits to determine conditions for arising departure nucleate boiling on the internal and external surfaces and on both surfaces simultaneously. It is concluded that the suggested technique of calculation adequately reflects the effect of regime parameters of coolant flow on temperature regime of heat transferring surfaces in the supercritical area
Analytical model for bottom reflooding heat transfer in light water reactors (the UCFLOOD code)

International Nuclear Information System (INIS)

Arrieta, L.; Yadigaroglu, G.

1978-08-01

The UCFLOOD code is based on mechanistic models developed to analyze bottom reflooding of a single flow channel and its associated fuel rod, or a tubular test section with internal flow. From the hydrodynamic point of view the flow channel is divided into a single-phase liquid region, a continuous-liquid two-phase region, and a dispersed-liquid region. The void fraction is obtained from drift flux models. For heat transfer calculations, the channel is divided into regions of single-phase-liquid heat transfer, nucleate boiling and forced-convection vaporization, inverted-annular film boiling, and dispersed-flow film boiling. The heat transfer coefficients are functions of the local flow conditions. Good agreement of calculated and experimental results has been obtained. A code user's manual is appended
Numerical Modeling of Fin and Tube Heat Exchanger for Waste Heat Recovery

DEFF Research Database (Denmark)

Singh, Shobhana; Sørensen, Kim; Condra, Thomas Joseph

In the present work, multiphysics numerical modeling is carried out to predict the performance of a liquid-gas fin and tube heat exchanger design. Three-dimensional (3D) steady-state numerical model using commercial software COMSOL based on finite element method (FEM) is developed. The study...... associates conjugate heat transfer phenomenon with the turbulent flow to describe the variable temperature and velocity profile. The performance of heat exchanger design is investigated in terms of overall heat transfer coefficient, Nusselt number, Colburn j-factor, flow resistance factor, and efficiency...... between fin and tube. The present numerical model predicts the performance of the heat exchanger design, therefore, can be applied to existing waste heat recovery systems to improve the overall performance with optimized design and process-dependent parameters....
Heat transfer in intermediate heat exchanger under low flow rate conditions

International Nuclear Information System (INIS)

Mochizuki, H.

2008-01-01

The present paper describes the heat transfer in intermediate heat exchangers (IHXs) of liquid metal cooled fast reactors when flow rate is low such as a natural circulation condition. Although empirical correlations of heat transfer coefficients for IHX were derived using test data at the fast reactor 'Monju' and 'Joyo' and also at the 50 MW steam generator facility, the heat transfer coefficient was very low compared to the well known correlation for liquid metals proposed by Seban-Shimazaki. The heat conduction in IHX was discussed as a possible cause of the low Nusselt number. As a result, the heat conduction is not significant under the natural circulation condition, and the heat conduction term in the energy equation can be neglected in the one-dimensional plant dynamics calculation. (authors)
Inter-subchannel heat transfer modeling for a subchannel analysis of liquid metal-cooled reactors

International Nuclear Information System (INIS)

Hae-Yong, Jeong; Kwi-Seok, Ha; Young-Min, Kwon; Yong-Bum, Lee; Dohee, Hahn

2007-01-01

In a subchannel approach, the temperature, pressure and velocity in a subchannel are averaged, and one representative thermal-hydraulic condition specifies the state of a subchannel. To enhance the predictability of a subchannel analysis code, it is required to model the inter-subchannel heat transfer between the adjacent subchannels as accurately as possible. One of the critical parameters which determine the thermal-hydraulic behavior of the coolant in subchannels is the heat conduction between two neighboring sub-channels. This portion of a heat transfer becomes more important in the design of an LMR (Liquid Metal-cooled Reactor) because of the high heat capacity of the liquid metal coolant. The other important part of heat transfer is the mixing of flow as a form of cross flow. Especially, the turbulent mixing caused by the eddy motion of fluid across the gap between the subchannels enhances the exchange of the momentum and the energy through the gap with no net transport of the mass. Major results of recent efforts on these modeling have been implemented in a subchannel analysis code MATRA-LMR-FB. The analysis shows that the accuracy of a subchannel analysis code is improved by enhancing the models describing the conduction heat transfer and the cross-flow mixing, especially at low flow rate. (authors)
Modeling of Compressible Flow with Friction and Heat Transfer Using the Generalized Fluid System Simulation Program (GFSSP)

Science.gov (United States)

Bandyopadhyay, Alak; Majumdar, Alok

2007-01-01

The present paper describes the verification and validation of a quasi one-dimensional pressure based finite volume algorithm, implemented in Generalized Fluid System Simulation Program (GFSSP), for predicting compressible flow with friction, heat transfer and area change. The numerical predictions were compared with two classical solutions of compressible flow, i.e. Fanno and Rayleigh flow. Fanno flow provides an analytical solution of compressible flow in a long slender pipe where incoming subsonic flow can be choked due to friction. On the other hand, Raleigh flow provides analytical solution of frictionless compressible flow with heat transfer where incoming subsonic flow can be choked at the outlet boundary with heat addition to the control volume. Nonuniform grid distribution improves the accuracy of numerical prediction. A benchmark numerical solution of compressible flow in a converging-diverging nozzle with friction and heat transfer has been developed to verify GFSSP's numerical predictions. The numerical predictions compare favorably in all cases.
The improvement of the heat transfer model for sodium-water reaction jet code

International Nuclear Information System (INIS)

Hashiguchi, Yoshirou; Yamamoto, Hajime; Kamoshida, Norio; Murata, Shuuichi

2001-02-01

For confirming the reasonable DBL (Design Base Leak) on steam generator (SG), it is necessary to evaluate phenomena of sodium-water reaction (SWR) in an actual steam generator realistically. The improvement of a heat transfer model on sodium-water reaction (SWR) jet code (LEAP-JET ver.1.40) and application analysis to the water injection tests for confirmation of propriety for the code were performed. On the improvement of the code, the heat transfer model between a inside fluid and a tube wall was introduced instead of the prior model which was heat capacity model including both heat capacity of the tube wall and inside fluid. And it was considered that the fluid of inside the heat exchange tube was able to treat as water or sodium and typical heat transfer equations used in SG design were also introduced in the new heat transfer model. Further additional work was carried out in order to improve the stability of the calculation for long calculation time. The test calculation using the improved code (LEAP-JET ver.1.50) were carried out with conditions of the SWAT-IR·Run-HT-2 test. It was confirmed that the SWR jet behavior on the result and the influence to the result of the heat transfer model were reasonable. And also on the improved code (LEAP-JET ver.1.50), user's manual was revised with additional I/O manual and explanation of the heat transfer model and new variable name. (author)
A simple heat transfer model for a heat flux plate under transient conditions

International Nuclear Information System (INIS)

Ryan, L.; Dale, J.D.

1985-01-01

Heat flux plates are used for measuring rates of heat transfer through surfaces under steady state and transient conditions. Their usual construction is to have a resistive layer bounded by thermopiles and an exterior layer for protection. If properly designed and constructed a linear relationship between the thermopile generated voltage and heat flux results and calibration under steady state conditions is straight forward. Under transient conditions however the voltage output from a heat flux plate cannot instantaneously follow the heat flux because of the thermal capacitance of the plate and the resulting time lag. In order to properly interpret the output of a heat flux plate used under transient conditions a simple heat transfer model was constructed and tested. (author)
Conjugate heat transfer analysis for in-vessel retention with external reactor vessel cooling

International Nuclear Information System (INIS)

Park, Jong-Woon; Bae, Jae-ho; Song, Hyuk-Jin

2016-01-01

Highlights: • A conjugate heat transfer analysis method is applied for in-vessel corium retention. • 3D heat diffusion has a formidable effect in alleviating focusing heat load from metallic layer. • The focusing heat load is decreased by about 2.5 times on the external surface. - Abstract: A conjugate heat transfer analysis method for the thermal integrity of a reactor vessel under external reactor vessel cooling conditions is developed to resolve light metal layer focusing effect issue for in-vessel retention. The method calculates steady-state three-dimensional temperature distribution of a reactor vessel using coupled conjugate heat transfer between in-vessel three-layered stratified corium (metallic pool, oxide pool and heavy metal and polar-angle dependent boiling heat transfer at the outer surface of a reactor vessel). The three-layer corium heat transfer model is utilizing lumped-parameter thermal-resistance circuit method. For the ex-vessel boiling boundary conditions, nucleate, transition and film boiling are considered. The thermal integrity of a reactor vessel is addressed in terms of heat flux at the outer-most nodes of the vessel and remaining thickness profile. The vessel three-dimensional heat conduction is validated against a commercial code. It is found that even though the internal heat flux from the metal layer goes far beyond critical heat flux (CHF) the heat flux from the outermost nodes of the vessel may be maintained below CHF due to massive vessel heat diffusion. The heat diffusion throughout the vessel is more pronounced for relatively low heat generation rate in an oxide pool. Parametric calculations are performed considering thermal conditions such as peak heat flux from a light metal layer, heat generation in an oxide pool and external boiling conditions. The major finding is that the most crucial factor for success of in-vessel retention is not the mass of the molten light metal above the oxide pool but the heat generation rate
Specific heat study of quasi-one-dimensional antiferromagnetic model for an organic polymer chain

International Nuclear Information System (INIS)

Qu Shaohua; Zhu Lin

2008-01-01

The specific heat of an infinite one-dimensional polymer chain bearing periodically arranged side radicals connected to the even sites is studied by means of quantum transfer-matrix method based on a Ising-Heisenberg model. In the absence of the exchange interactions between side radicals and the main chain, the curves of specific heat show a round peak due to the antiferromagnetic excitations for the all antiferromagnetic interactions along the polymer chain. Considering the exchange interactions between the side radicals and the main chain, the curves of the specific heat show double-peak structure for ferromagnetic interactions between the radicals and main chain, indicating that a competition between ferromagnetic and antiferromagnetic interactions and the possibility of the occurrence of the stable ferrimagnetic state along the polymer chain
Analytical modeling of heat transfer during the reflooding phase of the LOCA: the UCFLOOD code

International Nuclear Information System (INIS)

Yadigaroglu, G.; Arrieta, L.A.

1980-01-01

A mechanistic model of bottom-reflooding heat transfer is described. From the hydrodynamic point of view the flow channel is divided into a single-phase liquid region, a continuous-liquid two-phase region, and a dispersed-liquid region. The void fraction is obtained from drift flux models. The onset of liquid entrainment is determined using a criterion based on the instability of the liquid core in the inverted-annular flow regime. For heat transfer calculations, the channel is also divided into a number of regions. The heat transfer coefficients are functions of the local flow conditions. Quench front propagation is treated separately by a model including the effects of axial conduction. Good agreement of calculated and experimental results has been obtained
Numerical simulation of heat transfer process in solar enhanced natural draft dry cooling tower with radiation model

International Nuclear Information System (INIS)

Wang, Qiuhuan; Zhu, Jialing; Lu, Xinli

2017-01-01

Graphical abstract: A 3-D numerical model integrated with a discrete ordinate (DO) solar radiation model (considering solar radiation effect in the room of solar collector) was developed to investigate the influence of solar radiation intensity and ambient pressure on the efficiency and thermal characteristics of the SENDDCT. Our study shows that introducing such a radiation model can more accurately simulate the heat transfer process in the SENDDCT. Calculation results indicate that previous simulations overestimated solar energy obtained by the solar collector and underestimated the heat loss. The cooling performance is improved when the solar radiation intensity or ambient pressure is high. Air temperature and velocity increase with the increase of solar radiation intensity. But ambient pressure has inverse effects on the changes of air temperature and velocity. Under a condition that the solar load increases but the ambient pressure decreases, the increased rate of heat transferred in the heat exchanger is not obvious. Thus the performance of the SENDDCT not only depends on the solar radiation intensity but also depends on the ambient pressure. - Highlights: • A radiation model has been introduced to accurately simulate heat transfer process. • Heat transfer rate would be overestimated if the radiation model was not introduced. • The heat transfer rate is approximately proportional to solar radiation intensity. • The higher the solar radiation or ambient pressure, the better SENDDCT performance. - Abstract: Solar enhanced natural draft dry cooling tower (SENDDCT) is more efficient than natural draft dry cooling tower by utilizing solar radiation in arid region. A three-dimensional numerical model considering solar radiation effect was developed to investigate the influence of solar radiation intensity and ambient pressure on the efficiency and thermal characteristics of SENDDCT. The numerical simulation outcomes reveal that a model with consideration of
Numerical simulations of thermal conductivity in dissipative two-dimensional Yukawa systems.

Science.gov (United States)

Khrustalyov, Yu V; Vaulina, O S

2012-04-01

Numerical data on the heat transfer constants in two-dimensional Yukawa systems were obtained. Numerical study of the thermal conductivity and diffusivity was carried out for the equilibrium systems with parameters close to conditions of laboratory experiments with dusty plasma. For calculations of heat transfer constants the Green-Kubo formulas were used. The influence of dissipation (friction) on the heat transfer processes in nonideal systems was investigated. The approximation of the coefficient of thermal conductivity is proposed. Comparison of the obtained results to the existing experimental and numerical data is discussed.
Homogenization of some radiative heat transfer models: application to gas-cooled reactor cores

International Nuclear Information System (INIS)

El Ganaoui, K.

2006-09-01

In the context of homogenization theory we treat some heat transfer problems involving unusual (according to the homogenization) boundary conditions. These problems are defined in a solid periodic perforated domain where two scales (macroscopic and microscopic) are to be taken into account and describe heat transfer by conduction in the solid and by radiation on the wall of each hole. Two kinds of radiation are considered: radiation in an infinite medium (non-linear problem) and radiation in cavity with grey-diffuse walls (non-linear and non-local problem). The derived homogenized models are conduction problems with an effective conductivity which depend on the considered radiation. Thus we introduce a framework (homogenization and validation) based on mathematical justification using the two-scale convergence method and numerical validation by simulations using the computer code CAST3M. This study, performed for gas cooled reactors cores, can be extended to other perforated domains involving the considered heat transfer phenomena. (author)
Proceedings of the 33rd national heat transfer conference NHTC'99

International Nuclear Information System (INIS)

Jensen, M.K.; Di Marzo, M.

1999-01-01

The papers in this conference were divided into the following sections: Radiation Heat Transfer in Fires; Computational Fluid Dynamics Methods in Two-Phase Flow; Heat Transfer in Microchannels; Thin Film Heat Transfer; Thermal Design of Electronics; Enhanced Heat Transfer I; Porous Media Convection; Contact Resistance Heat Transfer; Materials Processing in Solidification and Crystal Growth; Fundamentals of Combustion; Challenging Modeling Aspects of Radiative Transfer; Fundamentals of Microscale Transport; Laser Processing and Diagnostics for Manufacturing and Materials Processing; Experimental Studies of Multiphase Flow; Enhanced Heat Transfer II; Heat and Mass Transfer in Porous Media; Heat Transfer in Turbomachinery and Gas Turbine Systems; Conduction Heat Transfer; General Papers; Open Forum on Combustion; Combustion and Instrumentation and Diagnostics I; Radiative Heat Transfer and Interactions in Participating and Nonparticipating Media; Applications of Computational Heat Transfer; Heat Transfer and Fluid Aspects of Heat Exchangers; Two-Phase Flow and Heat Transfer Phenomena; Fundamentals of Natural and Mixed Convection Heat Transfer I; Fundamental of Natural and Mixed Convection Heat Transfer II; Combustion and Instrumentation and Diagnostics II; Computational Methods for Multidimensional Radiative Transfer; Process Heat Transfer; Advances in Computational Heat and Mass Transfer; Numerical Methods for Porous Media; Transport Phenomena in Manufacturing and Materials Processing; Practical Combustion; Melting and Solidification Heat Transfer; Transients in Dynamics of Two-Phase Flow; Basic Aspects of Two-Phase Flow; Turbulent Heat Transfer; Convective Heat Transfer in Electronics; Thermal Problems in Radioactive and Mixed Waste Management; and Transport Phenomena in Oscillatory Flows. Separate abstracts were prepared for most papers in this conference
Two-dimensional models

International Nuclear Information System (INIS)

Schroer, Bert; Freie Universitaet, Berlin

2005-02-01

It is not possible to compactly review the overwhelming literature on two-dimensional models in a meaningful way without a specific viewpoint; I have therefore tacitly added to the above title the words 'as theoretical laboratories for general quantum field theory'. I dedicate this contribution to the memory of J. A. Swieca with whom I have shared the passion of exploring 2-dimensional models for almost one decade. A shortened version of this article is intended as a contribution to the project 'Encyclopedia of mathematical physics' and comments, suggestions and critical remarks are welcome. (author)

Heat transfer between immiscible liquids enhanced by gas bubbling

International Nuclear Information System (INIS)

Greene, G.A.; Schwarz, C.E.; Klages, J.; Klein, J.

1982-08-01

The phenomena of core-concrete interactions impact upon containment integrity of light water reactors (LWR) following postulated complete meltdown of the core by containment pressurization, production of combustible gases, and basemat penetration. Experiments have been performed with non-reactor materials to investigate one aspect of this problem, heat transfer between overlying immiscible liquids whose interface is disturbed by a transverse non-condensable gas flux emanating from below. Hydrodynamic studies have been performed to test a criterion for onset of entrainment due to bubbling through the interface and subsequent heat transfer studies were performed to assess the effect of bubbling on interfacial heat transfer rates, both with and without bubble induced entrainment. Non-entraining interfacial heat transfer data with mercury-water/oil fluid pairs were observed to be bounded from below within a factor of two to three by the Szekeley surface renewal heat transfer model. However heat transfer data for fluid pairs which are found to entrain (water-oil), believed to be characteristic of molten reactor core-concrete conditions, were measured to be up to two orders of magnitude greater than surface renewal predictions and are calculated by a simple entrainment heat transfer model
Heat transfer and velocity characteristics of single- and two-phase flows in a subsonic model gun

International Nuclear Information System (INIS)

Bicen, A.F.; Khezzar, L.; Schmidt, M.; Whitelaw, J.H.

1989-01-01

Heat transfer and velocity measurements are reported for single- and two-phase flows in the wake of an in-bore projectile propelled by an inert gas at an initial gauge pressure of 8 bars to an exit velocity over 40 m/s in ∼ 33 ms. The results show that with the single phase the turbulent velocity boundary layers occupy over 20% of the barrel radius and that the wall heat transfer increases with distance from the breech and decreases with time during the shot. In the initial chamber, and later in the shot, the heat transfer results are close to those obtained from a convection correlation for a steady turbulent boundary layer, contrary to those at locations swept by the projectile, which are higher by up to 50% throughout the shot. The two-phase flow results show that 55-μm particles with loadings of 1.3% and 4% by volume initially lag the fluid and this lag increases with distance from the breech. Later in the shot the particles catch up and lead the decelerating fluid by an amount that is greater, with the higher particle loading and with a tendency for the particle velocity to increase around the edge of the boundary layer
Effects of heat and mass transfer on unsteady boundary layer flow of a chemical reacting Casson fluid

Science.gov (United States)

Khan, Kashif Ali; Butt, Asma Rashid; Raza, Nauman

2018-03-01

In this study, an endeavor is to observe the unsteady two-dimensional boundary layer flow with heat and mass transfer behavior of Casson fluid past a stretching sheet in presence of wall mass transfer by ignoring the effects of viscous dissipation. Chemical reaction of linear order is also invoked here. Similarity transformation have been applied to reduce the governing equations of momentum, energy and mass into non-linear ordinary differential equations; then Homotopy analysis method (HAM) is applied to solve these equations. Numerical work is done carefully with a well-known software MATHEMATICA for the examination of non-dimensional velocity, temperature, and concentration profiles, and then results are presented graphically. The skin friction (viscous drag), local Nusselt number (rate of heat transfer) and Sherwood number (rate of mass transfer) are discussed and presented in tabular form for several factors which are monitoring the flow model.
Film boiling heat transfer from a hot sphere falling in two-phase pool

International Nuclear Information System (INIS)

Bang, K. H.; Kim, K. Y.

1998-01-01

The purpose of the present study is to experimentally investigate film boiling heat trasfer from a hot sphere falling in steam-water two-phase pool, which is the key heat transfer mode in molten fuel and coolant mixing. To measure film boiling heat transfer coefficients on a spere falling in two-phase pool, a heated sphere with a thermocouple embedded at the center is dropped in a vertical tube filled with steam-water mixture. The present experiment is unique in making the heated sphere fall through the two-phase pool while the previous experiments were performed with stationary spheres in flowing fluid. The falling speed of the sphere is measured using a set of magnet pickup coils distributed along the tube. The ranges of the experimental conditions are: spere fall speed 0-0.5 m/s, average void fraction 0-25,% steam superficial velocity 0-0.25 m/s. The results show that the forced convection film boiling heat transfer coefficient decrease slightly as the steam superficial velocity (void fraction) is increased
Coupled heat transfer model and experiment study of semitransparent barrier materials in aerothermal environment

Science.gov (United States)

Wang, Da-Lin; Qi, Hong

Semi-transparent materials (such as IR optical windows) are widely used for heat protection or transfer, temperature and image measurement, and safety in energy , space, military, and information technology applications. They are used, for instance, ceramic coatings for thermal barriers of spacecrafts or gas turbine blades, and thermal image observation under extreme or some dangerous environments. In this paper, the coupled conduction and radiation heat transfer model is established to describe temperature distribution of semitransparent thermal barrier medium within the aerothermal environment. In order to investigate this numerical model, one semi-transparent sample with black coating was considered, and photothermal properties were measured. At last, Finite Volume Method (FVM) was used to solve the coupled model, and the temperature responses from the sample surfaces were obtained. In addition, experiment study was also taken into account. In the present experiment, aerodynamic heat flux was simulated by one electrical heater, and two experiment cases were designed in terms of the duration of aerodynamic heating. One case is that the heater irradiates one surface of the sample continually until the other surface temperature up to constant, and the other case is that the heater works only 130 s. The surface temperature responses of these two cases were recorded. Finally, FVM model of the coupling conduction-radiation heat transfer was validated based on the experiment study with relative error less than 5%.
Heat Transfer Modeling and Validation for Optically Thick Alumina Fibrous Insulation

Science.gov (United States)

Daryabeigi, Kamran

2009-01-01

Combined radiation/conduction heat transfer through unbonded alumina fibrous insulation was modeled using the diffusion approximation for modeling the radiation component of heat transfer in the optically thick insulation. The validity of the heat transfer model was investigated by comparison to previously reported experimental effective thermal conductivity data over the insulation density range of 24 to 96 kg/cu m, with a pressure range of 0.001 to 750 torr (0.1 to 101.3 x 10(exp 3) Pa), and test sample hot side temperature range of 530 to 1360 K. The model was further validated by comparison to thermal conductivity measurements using the transient step heating technique on an insulation sample at a density of 144 kg/cu m over a pressure range of 0.001 to 760 torr, and temperature range of 290 to 1090 K.
Mathematical Simulation of Convective Heat Transfer in the Low-Temperature Storage of Liquefied Natural Gas

Directory of Open Access Journals (Sweden)

Shestakov Igor A.

2015-01-01

Full Text Available The article shows the results of mathematical modeling of convective heat transfer in the low-temperature storage of liquefied natural gas. Regime of natural convection in an enclosure with different intensity of the heat flux at the external borders are investigated. Was examined two-dimensional nonstationary problem within the model of Navier-Stokes in dimensionless variables “vorticity - stream function - temperature”. Distributions of hydrodynamic parameters and temperatures that characterize the basic regularities of the processes are obtained. Circulating flows are determined and carried out the analysis of vortices formation mechanism and the temperature distribution in solution at conditions of natural convection when the Grashof number (Gr = 106. A significant influence of heat transfer rate on solutions boundary on flow structure and temperature field in LNG storage tanks.
Numerical Investigation of Fluid Flow and Heat Transfer Inside a 2D Enclosure with Three Hot Obstacles on the Ramp under the Influence of a Magnetic Field

Directory of Open Access Journals (Sweden)

M. M. Keshtkar

2017-06-01

Full Text Available This paper focuses on solving the fluid flow and heat transfer equations inside a two-dimensional square enclosure containing three hot obstacles affected by gravity and magnetic force placed on a ramp using Boltzmann method (LBM applying multiple relaxation times (MRT. Although, the Lattice Boltzmann with MRT is a complex technique, it is a relatively new, stable, fast and high-accurate one. The main objective of this research was to numerically model the fluid flow and ultimately obtaining the velocity field, flow and temperature contour lines inside a two-dimensional enclosure. The results and their comparisons for different types of heat transfer revealed that free or forced heat transfer has a considerable impact on the heat transfer and stream lines. This can be controlled by modifying the Richardson number. It is revealed that changing the intensity of the magnetic field (Hartman number has an appreciable effect on the heat transfer.
Two-phase heat and mass transfer in turbulent parallel and countercurrent flows of liquid film and gas

International Nuclear Information System (INIS)

Kholpanov, L.P.; Babak, T.B.; Babak, V.N.; Malyusov, V.A.; Zhavoronkov, N.M.; AN SSSR, Moscow. Inst. Obshchej i Neorganicheskoj Khimii)

1980-01-01

To determine the ways of intensification of heat and mass transfer processes, the direct flow and counterflow heat and mass transfer is analytically investigated during the turbulent flow of a liquid and gas film on the basis of solving the energy equation for liquid and gas film, i.e. the two-phase film heat transfer is investigated from the position of a conjugate task. The analysis of the two-phase heat transfer has shown that it is necessary to know the position of each point in a plane before using this or that formula. Depending on its position on this plane, the heat transfer process will be determined by one or two phases only. It is found, that in the case of a single-phase heat transfer the temperature on the surface remains stable over the channel length. In the case of a two-phase heat transfer it can significantly change over the channel length [ru
Numerical study on pressure drop and heat transfer for designing sodium-to-air heat exchanger tube banks on advanced sodium-cooled fast reactor

International Nuclear Information System (INIS)

Kang, Hie-Chan; Eoh, Jae-Hyuk; Cha, Jae-Eun; Kim, Seong-O.

2013-01-01

Highlights: ► Numerical simulation for the heat flow characteristic of the sodium-to-air heat exchanger (AHX) and tube banks. ► Parallelogram tube banks showed almost similar thermal and hydraulic characteristics to the rectangular tube banks. ► Pressure drop and heat transfer of the staggered and rectangular tube banks compared with Zhukauskas’ correlation. ► AHX was modeled as porous media and suggested design guide to enhance the performance. - Abstract: A numerical study is performed to investigate the thermal and hydraulic characteristics and build up design model of the AHX (sodium-to-air heat exchanger) unit of a sodium-cooled fast reactor. Helical-coiled tube banks in the AHX are modeled as porous media and simulated heat and momentum transfer by a commercial program. Two-dimensional flow characteristic appears differently at the inlet region of the AHX annulus, and the required length of the inlet region is shorter for an inlet having a 45 degree chamber or a round shape than for one with a perpendicular corner. Pressure drop and heat transfer coefficient for rectangular, parallelogram and staggered tube banks as the main components of the AHX are evaluated and discussed. Pressure drop and heat transfer shows similar trends and underestimated values, respectively, when compared with Zhukauskas empirical correlations. The parallelogram tube bank shows similar results to the rectangular arrangement.
Heat transfer model for quenching by submerging

International Nuclear Information System (INIS)

Passarella, D N; Varas, F; MartIn, E B

2011-01-01

In quenching by submerging the workpiece is cooled due to vaporization, convective flow and interaction of both mechanisms. The dynamics of these phenomena is very complex and the corresponding heat fluxes are strongly dependent on local flow variables such as velocity of fluid and vapor fraction. This local dependence may produce very different cooling rates along the piece, responsible for inappropriate metallurgical transformations, variability of material properties and residual stresses. In order to obtain an accurate description of cooling during quenching, a mathematical model of heat transfer is presented here. The model is based on the drift-flux mixture-model for multiphase flows, including an equation of conservation of energy for the liquid phase and specific boundary conditions that account for evaporation and presence of vapor phase on the surface of the piece. The model was implemented on Comsol Multiphysics software. Generation of appropriate initial and boundary conditions, as well as numerical resolution details, is briefly discussed. To test the model, a simple flow condition was analyzed. The effect of vapor fraction on heat transfer is assessed. The presence of the typical vapor blanket and its collapse can be recovered by the model, and its effect on the cooling rates on different parts of the piece is analyzed. Comparisons between numerical results and data from literature are made.
Heat transfer model for quenching by submerging

Energy Technology Data Exchange (ETDEWEB)

Passarella, D N; Varas, F [Departamento de Matematica Aplicada II, E.T.S. de Ing. de Telecomunicacion, Universidad de Vigo, Campus Marcosende, 36310 Vigo (Spain); MartIn, E B, E-mail: diego@dma.uvigo.es, E-mail: fvaras@uvigo.es, E-mail: emortega@uvigo.es [Area de Mecanica de Fluidos, E.T.S. de Ing. Industriales, Universidad de Vigo, Campus Marcosende, 36310 Vigo (Spain)

2011-05-01

In quenching by submerging the workpiece is cooled due to vaporization, convective flow and interaction of both mechanisms. The dynamics of these phenomena is very complex and the corresponding heat fluxes are strongly dependent on local flow variables such as velocity of fluid and vapor fraction. This local dependence may produce very different cooling rates along the piece, responsible for inappropriate metallurgical transformations, variability of material properties and residual stresses. In order to obtain an accurate description of cooling during quenching, a mathematical model of heat transfer is presented here. The model is based on the drift-flux mixture-model for multiphase flows, including an equation of conservation of energy for the liquid phase and specific boundary conditions that account for evaporation and presence of vapor phase on the surface of the piece. The model was implemented on Comsol Multiphysics software. Generation of appropriate initial and boundary conditions, as well as numerical resolution details, is briefly discussed. To test the model, a simple flow condition was analyzed. The effect of vapor fraction on heat transfer is assessed. The presence of the typical vapor blanket and its collapse can be recovered by the model, and its effect on the cooling rates on different parts of the piece is analyzed. Comparisons between numerical results and data from literature are made.
Indirectly heated biomass gasification using a latent-heat ballast-part 3: refinement of the heat transfer model

International Nuclear Information System (INIS)

Cummer, Keith; Brown, Robert C.

2005-01-01

An indirectly heated gasifier is under development at Iowa State University. This gasifier integrates a latent-heat ballast with a fluidized-bed reactor. The latent heat ballast is an array of stainless-steel tubes filled with lithium fluoride, which is a high-temperature phase-change material (PCM). Previous studies have presented experimental results from the gasifier and described a mathematical model of the pyrolysis phase of the cyclic gasification process. This model considers both heat transfer and chemical reactions that occur during pyrolysis, but discrepancies between model predictions and experimental data have demonstrated the need to refine the model. In particular, cooling curves for the ballasting system are not well predicted during phase change of the lithium fluoride. A reformulated model, known as the Receding Interface (RI) model, postulates the existence of a receding liquid phase within the ballast tubes as they cool, which progressively decreases the rate of heat transfer from the tubes. The RI model predicts behavior that is more consistent with experimental results during the phase-change process, while retaining accuracy before and after the process of phase change
Finite element solution of two dimensional time dependent heat equation

International Nuclear Information System (INIS)

Maaz

1999-01-01

A Microsoft Windows based computer code, named FHEAT, has been developed for solving two dimensional heat problems in Cartesian and Cylindrical geometries. The programming language is Microsoft Visual Basic 3.0. The code makes use of Finite element formulation for spatial domain and Finite difference formulation for time domain. Presently the code is capable of solving two dimensional steady state and transient problems in xy- and rz-geometries. The code is capable excepting both triangular and rectangular elements. Validation and benchmarking was done against hand calculations and published results. (author)
Theory of Periodic Conjugate Heat Transfer

CERN Document Server

Zudin, Yuri B

2012-01-01

This book presents the theory of periodic conjugate heat transfer in a detailed way. The effects of thermophysical properties and geometry of a solid body on the commonly used and experimentally determined heat transfer coefficient are analytically presented from a general point of view. The main objective of the book is a simplified description of the interaction between a solid body and a fluid as a boundary value problem of the heat conduction equation for the solid body. At the body surface, the true heat transfer coefficient is composed of two parts: the true mean value resulting from the solution of the steady state heat transfer problem and a periodically variable part, the periodic time and length to describe the oscillatory hydrodynamic effects. The second edition is extended by (i) the analysis of stability boundaries in helium flow at supercritical conditions in a heated channel with respect to the interaction between a solid body and a fluid; (ii) a periodic model and a method of heat transfer sim...
[Modeling of processes of heat transfer in whole-body hyperthermia].

Science.gov (United States)

Kinsht, D N

2006-01-01

The method of whole-body hyperthermia in which the body temperature for a short time reaches values up to 43-44 degrees C holds currently much promise. However, at body temperatures above 42 degrees C, the risks associated with the hemodynamic instability and the appearance of arrhythmia in the patient increase. A model of heat transfer has been created to increase the efficiency and safety of the immersion-convectional method of whole-body hyperthermia. This model takes into account changes in the skin blood flow and the dynamics of pulse rate depending on body temperature. The model of heat transfer adequately reflects processes of heating of the organism and can form a basis for the calculation of distribution of heat inside the organism.
Discrete vessel heat transfer in perfused tissue - model comparison

NARCIS (Netherlands)

Stanczyk, M.; Leeuwen, van G.M.J.; Steenhoven, van A.A.

2007-01-01

The aim of this paper is to compare two methods of calculating heat transfer in perfused biological tissue using a discrete vessel description. The methods differ in two important aspects: the representation of the vascular system and the algorithm for calculating the heat flux between tissue and
Preliminary Numerical Analysis of Convective Heat Transfer Loop Using MARS Code

Energy Technology Data Exchange (ETDEWEB)

Lee, Yongjae; Seo, Gwang Hyeok; Jeun, Gyoodong; Kim, Sung Joong [Hanyang Univ., Seoul (Korea, Republic of)

2014-05-15

The MARS has been developed adopting two major modules: RELAP5/MOD3 (USA) for one-dimensional (1D) two-fluid model for two-phase flows and COBRA-TF code for a three-dimensional (3D), two-fluid, and three-field model. In addition to the MARS code, TRACE (USA) is a modernized thermal-hydraulics code designed to consolidate and extend the capabilities of NRC's 3 legacy safety code: TRAC-P, TRAC-B and RELAP. CATHARE (French) is also thermal-hydraulic system analysis code for Pressurized Water Reactor (PWR) safety. There are several researches on comparing experimental data with simulation results by the MARS code. Kang et al. conducted natural convection heat transfer experiments of liquid gallium loop, and the experimental data were compared to MARS simulations. Bang et al. examined the capability of the MARS code to predict condensation heat transfer experiments with a vertical tube containing a non-condensable gas. Moreover, Lee et al. adopted MELCOR, which is one of the severe accident analysis codes, to evaluate several strategies for the severe accident mitigation. The objective of this study is to conduct the preliminary numerical analysis for the experimental loop at HYU using the MARS code, especially in order to provide relevant information on upcoming experiments for the undergraduate students. In this study, the preliminary numerical analysis for the convective heat transfer loop was carried out using the MARS Code. The major findings from the numerical simulations can be summarized as follows. In the calculations of the outlet and surface temperatures, the several limitations were suggested for the upcoming single-phase flow experiments. The comparison work for the HTCs shows validity for the prepared input model. This input could give useful information on the experiments. Furthermore, the undergraduate students in department of nuclear engineering, who are going to be taken part in the experiments, could prepare the program with the input, and will
Preliminary Numerical Analysis of Convective Heat Transfer Loop Using MARS Code

International Nuclear Information System (INIS)

Lee, Yongjae; Seo, Gwang Hyeok; Jeun, Gyoodong; Kim, Sung Joong

2014-01-01

The MARS has been developed adopting two major modules: RELAP5/MOD3 (USA) for one-dimensional (1D) two-fluid model for two-phase flows and COBRA-TF code for a three-dimensional (3D), two-fluid, and three-field model. In addition to the MARS code, TRACE (USA) is a modernized thermal-hydraulics code designed to consolidate and extend the capabilities of NRC's 3 legacy safety code: TRAC-P, TRAC-B and RELAP. CATHARE (French) is also thermal-hydraulic system analysis code for Pressurized Water Reactor (PWR) safety. There are several researches on comparing experimental data with simulation results by the MARS code. Kang et al. conducted natural convection heat transfer experiments of liquid gallium loop, and the experimental data were compared to MARS simulations. Bang et al. examined the capability of the MARS code to predict condensation heat transfer experiments with a vertical tube containing a non-condensable gas. Moreover, Lee et al. adopted MELCOR, which is one of the severe accident analysis codes, to evaluate several strategies for the severe accident mitigation. The objective of this study is to conduct the preliminary numerical analysis for the experimental loop at HYU using the MARS code, especially in order to provide relevant information on upcoming experiments for the undergraduate students. In this study, the preliminary numerical analysis for the convective heat transfer loop was carried out using the MARS Code. The major findings from the numerical simulations can be summarized as follows. In the calculations of the outlet and surface temperatures, the several limitations were suggested for the upcoming single-phase flow experiments. The comparison work for the HTCs shows validity for the prepared input model. This input could give useful information on the experiments. Furthermore, the undergraduate students in department of nuclear engineering, who are going to be taken part in the experiments, could prepare the program with the input, and will
Mathematical modeling of heat transfer in production premises heated by gas infrared emitters

Directory of Open Access Journals (Sweden)

Maksimov Vyacheslav I.

2017-01-01

Full Text Available The results of numerical modeling of the process of free convective heat transfer in the regime of turbulent convection in a closed rectangular region heated by an infrared radiator are presented. The system of Navier-Stokes equations in the Boussinesq approximation is solved, the energy equation for the gas and the heat conduction equations for the enclosing vertical and horizontal walls. A comparative analysis of the heat transfer regimes in the considered region for different Grashof numbers is carried out. The features of the formation of heated air flows relative to the infrared emitter located at some distance from the upper horizontal boundary of the region are singled out.

Heat Transfer Enhancement By Three-Dimensional Surface Roughness Technique In Nuclear Fuel Rod Bundles

Science.gov (United States)

Najeeb, Umair

This thesis experimentally investigates the enhancement of single-phase heat transfer, frictional loss and pressure drop characteristics in a Single Heater Element Loop Tester (SHELT). The heater element simulates a single fuel rod for Pressurized Nuclear reactor. In this experimental investigation, the effect of the outer surface roughness of a simulated nuclear rod bundle was studied. The outer surface of a simulated fuel rod was created with a three-dimensional (Diamond-shaped blocks) surface roughness. The angle of corrugation for each diamond was 45 degrees. The length of each side of a diamond block is 1 mm. The depth of each diamond block was 0.3 mm. The pitch of the pattern was 1.614 mm. The simulated fuel rod had an outside diameter of 9.5 mm and wall thickness of 1.5 mm and was placed in a test-section made of 38.1 mm inner diameter, wall thickness 6.35 mm aluminum pipe. The Simulated fuel rod was made of Nickel 200 and Inconel 625 materials. The fuel rod was connected to 10 KW DC power supply. The Inconel 625 material of the rod with an electrical resistance of 32.3 kO was used to generate heat inside the test-section. The heat energy dissipated from the Inconel tube due to the flow of electrical current flows into the working fluid across the rod at constant heat flux conditions. The DI water was employed as working fluid for this experimental investigation. The temperature and pressure readings for both smooth and rough regions of the fuel rod were recorded and compared later to find enhancement in heat transfer coefficient and increment in the pressure drops. Tests were conducted for Reynold's Numbers ranging from 10e4 to 10e5. Enhancement in heat transfer coefficient at all Re was recorded. The maximum heat transfer co-efficient enhancement recorded was 86% at Re = 4.18e5. It was also observed that the pressure drop and friction factor increased by 14.7% due to the increased surface roughness.
Two models for the dynamics of a cross flow heat exchanger

Energy Technology Data Exchange (ETDEWEB)

Hopkinson, A [Control and Instrumentation Division, Atomic Energy Establishment, Winfrith, Dorchester, Dorset (United Kingdom)

1962-12-15

Two models of a cross flow heat exchanger, a concentric tube counter flow model and a cross flow model, are studied theoretically. Differential equations describing the behaviour of the models are derived and from them equations for the steady state temperatures and the temperature transfer functions are obtained. (author)
A mechanistic model of heat transfer for gas-liquid flow in vertical wellbore annuli.

Science.gov (United States)

Yin, Bang-Tang; Li, Xiang-Fang; Liu, Gang

2018-01-01

The most prominent aspect of multiphase flow is the variation in the physical distribution of the phases in the flow conduit known as the flow pattern. Several different flow patterns can exist under different flow conditions which have significant effects on liquid holdup, pressure gradient and heat transfer. Gas-liquid two-phase flow in an annulus can be found in a variety of practical situations. In high rate oil and gas production, it may be beneficial to flow fluids vertically through the annulus configuration between well tubing and casing. The flow patterns in annuli are different from pipe flow. There are both casing and tubing liquid films in slug flow and annular flow in the annulus. Multiphase heat transfer depends on the hydrodynamic behavior of the flow. There are very limited research results that can be found in the open literature for multiphase heat transfer in wellbore annuli. A mechanistic model of multiphase heat transfer is developed for different flow patterns of upward gas-liquid flow in vertical annuli. The required local flow parameters are predicted by use of the hydraulic model of steady-state multiphase flow in wellbore annuli recently developed by Yin et al. The modified heat-transfer model for single gas or liquid flow is verified by comparison with Manabe's experimental results. For different flow patterns, it is compared with modified unified Zhang et al. model based on representative diameters.
Study of stream wise transverse magnetic fluid flow with heat transfer around an obstacle embedded in a porous medium

Energy Technology Data Exchange (ETDEWEB)

Rashidi, S. [Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad 91775-1111 (Iran, Islamic Republic of); Dehghan, M. [Department of Mechanical Engineering, Semnan University, P.O. Box: 35196-45399, Semnan (Iran, Islamic Republic of); Ellahi, R., E-mail: rellahi@engr.ucr.edu [Department of Mathematics and Statistics, FBAS, IIUI, 44000 Islamabad (Pakistan); Department of Mechanical Engineering, Bourns Hall, University of California, Riverside, CA 92521 (United States); Riaz, M. [Department of QEC, National Defense University, E-9 Sector, 44000 Islamabad (Pakistan); Jamal-Abad, M.T. [Department of Mechanical Engineering, Semnan University, P.O. Box: 35196-45399, Semnan (Iran, Islamic Republic of)

2015-03-15

A mathematical model for two-dimensional fluid flow under the influence of stream wise transverse magnetic fields in laminar regime is simulated in this study. Heat transfer past a square diamond shaped porous obstacle is also taken into account. The attention is focused to investigate the effects of intensity and direction of magnetic field, Darcy and Reynolds numbers on the mechanism of convective heat transfer and flow structures. The Darcy–Brinkman–Forchheimer model along with the Maxwell equations is used. The nonlinear coupled equations using a finite volume approach (FVA) are solved numerically. The calculations are performed for different governing parameters such as Reynolds number, Nusselt number, Stuart number and Prandtl Number. The physical interpretation of velocity and isothermal contours is assigned through graphs. It is shown that the effects of a transverse magnetic field on flow behavior and heat transfer mechanism are more than that of the stream wise magnetic field. The configuration of streamlines and vorticity contours phenomena are also presented for porous diamond obstacle. Comparison of the numerical solutions with existing literature is also made. - Highlights: • This paper analyses two-dimensional fluid flow under the influence of stream wise transverse magnetic field. • Heat transfer past a square diamond shaped porous obstacle is taken into account. • The Darcy–Brinkman–Forchheimer model is used. • Finite volume approach is used to find numerical solutions. • The configuration of streamlines and vorticity contours phenomena are presented through graphs.
NCEL: two dimensional finite element code for steady-state temperature distribution in seven rod-bundle

International Nuclear Information System (INIS)

Hrehor, M.

1979-01-01

The paper deals with an application of the finite element method to the heat transfer study in seven-pin models of LMFBR fuel subassembly. The developed code NCEL solves two-dimensional steady state heat conduction equation in the whole subassembly model cross-section and enebles to perform the analysis of thermal behaviour in both normal and accidental operational conditions as eccentricity of the central rod or full or partial (porous) blockage of some part of the cross-flow area. The heat removal is simulated by heat sinks in coolant under conditions of subchannels slug flow approximation
One-dimensional two-phase thermal hydraulics (ENSTA course)

International Nuclear Information System (INIS)

Olive, J.

1995-11-01

This course is part of the ENSTA 3rd year thermal hydraulics program (nuclear power option). Its purpose is to provide the theoretical basis and main physical notions pertaining to two-phase flow, mainly focussed on water-steam flows. The introduction describes the physical specificities of these flows, emphasizing their complexity. The mathematical bases are then presented (partial derivative equations), leading to a one-dimensional type, simplified description. Balances drawn up for a pipe length volume are used to introduce the mass conservation. motion and energy equations for each phase. Various postulates used to simplify two-phase models are presented, culminating in homogeneous model definitions and equations, several common examples of which are given. The model is then applied to the calculation of pressure drops in two-phase flows. This involves presenting the models most frequently used to represent pressure drops by friction or due to pipe irregularities, without giving details (numerical values of parameters). This chapter terminates with a brief description of static and dynamic instabilities in two-phase flows. Finally, heat transfer conditions frequently encountered in liquid-steam flows are described, still in the context of a 1D model. This chapter notably includes reference to under-saturated boiling conditions and the various forms of DNB. The empirical heat transfer laws are not discussed in detail. Additional material is appended, some of which is in the form of corrected exercises. (author). 6 appends
About the possible options for models of convective heat transfer in closed volumes with local heating source

Directory of Open Access Journals (Sweden)

Maksimov Vyacheslav I.

2015-01-01

Full Text Available Results of mathematical modeling of convective heat transfer in air area surrounded on all sides enclosing structures, in the presence of heat source at the lower boundary of the media are presented. Solved the system of differential equations of unsteady Navier-Stokes equations with the appropriate initial and boundary conditions. The process of convective heat transfer is calculated using the models of turbulence Prandtl and Prandtl-Reichard. Takes into account the processes of heat exchange region considered with the environment. Is carried out the analysis of the dimensionless heat transfer coefficient at interfaces “air – enclosures”. The distributions average along the gas temperature range are obtained.
Assessment of interfacial heat transfer models under subcooled flow boiling

Energy Technology Data Exchange (ETDEWEB)

Ribeiro, Guilherme B.; Braz Filho, Francisco A., E-mail: gbribeiro@ieav.cta.br, E-mail: fbraz@ieav.cta.br [Instituto de Estudos Avançados (DCTA/IEAv), São José dos Campos, SP (Brazil). Div. de Energia Nuclear

2017-07-01

The present study concerns a detailed analysis of subcooled flow boiling characteristics under high pressure systems using a two-fluid Eulerian approach provided by a Computational Fluid Dynamics (CFD) solver. For this purpose, a vertical heated pipe made of stainless steel with an internal diameter of 15.4 mm was considered as the modeled domain. An uniform heat flux of 570 kW/m2 and saturation pressure of 4.5 MPa were applied to the channel wall, whereas water mass flux of 900 kg/m2s was considered for all simulation cases. The model was validated against a set of experimental data and results have indicated a promising use of CFD technique for the estimation of wall temperature, the liquid bulk temperature and the location of the departure of nucleate boiling. Different sub-models of interfacial heat transfer coefficient were applied and compared, allowing a better prediction of void fraction along the heated channel. (author)
Assessment of reflood heat transfer model of COBRA-TIF against ABB-CE evaluation model

Energy Technology Data Exchange (ETDEWEB)

Lee, S. I.; Lee, S. Y.; Park, C. E.; Choi, H. R.; Choi, C. J. [Korea Power Engineering Company Inc., Taejon (Korea, Republic of)

2000-05-01

According to 10 CFR 50 Appendix K, ECCS performance evaluation model should be based on the experimental data of FLECHT and have the conservatism compared with experimental data. To meet this requirement ABB-CE has the complicate code structure as follows: COMPERC-II calculates three reflood rates, and FLELAPC and HTCOF calculate the reflood heat transfer coefficients, and finally STRIKIN-II calculates the cladding temperature using the reflood heat transfer calculated in previous stage. In this paper, to investigate whether or not COBRA-TF satisfies the requirement of Appendix K, the reflood heat transfer coefficient of COBRA-TF was assessed against ABB-CE MOD-2C model. It was found out that COBRA-TF predicts properly the experimental data and has more conservatism than the results of ABB-CE MOD-2C model. Based on these results, it can be concluded that the reflood heat transfer coefficients calculated by COBRA-TF meet the requirement of Appendix K.
Containment condensing heat transfer

International Nuclear Information System (INIS)

Gido, R.G.; Koestel, A.

1983-01-01

This report presents a mechanistic heat-transfer model that is valid for large scale containment heat sinks. The model development is based on the determination that the condensation is controlled by mass diffusion through the vapor-air boundary layer, and the application of the classic Reynolds' analogy to formulate expressions for the transfer of heat and mass based on hydrodynamic measurements of the momentum transfer. As a result, the analysis depends on the quantification of the shear stress (momentum transfer) at the interface between the condensate film and the vapor-air boundary layer. In addition, the currently used Tagami and Uchida test observations and their range of applicability are explained
Condensation heat transfer coefficient with noncondensible gases for heat transfer in thermal hydraulic codes

International Nuclear Information System (INIS)

Banerjee, S.; Hassan, Y.A.

1995-01-01

Condensation in the presence of noncondensible gases plays an important role in the nuclear industry. The RELAP5/MOD3 thermal hydraulic code was used to study the ability of the code to predict this phenomenon. Two separate effects experiments were simulated using this code. These were the Massachusetts Institute of Technology's (MIT) Pressurizer Experiment, the MIT Single Tube Experiment. A new iterative approach to calculate the interface temperature and the degraded heat transfer coefficient was developed and implemented in the RELAP5/MOD3 thermal hydraulic code. This model employs the heat transfer simultaneously. This model was found to perform much better than the reduction factor approach. The calculations using the new model were found to be in much better agreement with the experimental values
Condensation heat transfer coefficient with noncondensible gases for heat transfer in thermal hydraulic codes

Energy Technology Data Exchange (ETDEWEB)

Banerjee, S.; Hassan, Y.A. [Texas A& M Univ., College Station, TX (United States)

1995-09-01

Condensation in the presence of noncondensible gases plays an important role in the nuclear industry. The RELAP5/MOD3 thermal hydraulic code was used to study the ability of the code to predict this phenomenon. Two separate effects experiments were simulated using this code. These were the Massachusetts Institute of Technology`s (MIT) Pressurizer Experiment, the MIT Single Tube Experiment. A new iterative approach to calculate the interface temperature and the degraded heat transfer coefficient was developed and implemented in the RELAP5/MOD3 thermal hydraulic code. This model employs the heat transfer simultaneously. This model was found to perform much better than the reduction factor approach. The calculations using the new model were found to be in much better agreement with the experimental values.
A study of the flow boiling heat transfer in an annular heat exchanger with a mini gap

Directory of Open Access Journals (Sweden)

Musiał Tomasz

2017-01-01

Full Text Available In this paper the research on flow boiling heat transfer in an annular mini gap was discussed. A one- dimensional mathematical approach was proposed to describe stationary heat transfer in the gap. The mini gap 1 mm wide was created between a metal pipe with enhanced exterior surface and an external tempered glass pipe positioned along the same axis. The experimental test stand consists of several systems: the test loop in which distilled water circulates, the data and image acquisition system and the supply and control system. Known temperature distributions of the metal pipe with enhanced surface and of the working fluid helped to determine, from the Robin boundary condition, the local heat transfer coefficients at the fluid - heated surface contact. In the proposed mathematical model it is assumed that the cylindrical wall is a planar multilayer wall. The numerical results are presented on a chart as function of the heat transfer coefficient along the length of the mini gap.
Study of two-phase flow redistribution between two passes of a heat exchanger

International Nuclear Information System (INIS)

Mendes de Moura, L.F.

1989-04-01

The object of the present thesis deals with the study of two-phase flow redistribution between two passes of a heat exchanger. Mass flow rate measurements of each component performed at each channel outlet of the second pass allowed us to determine the influence of mass flow, gas quality, flow direction (upward or downward) and common header geometry upon flow redistribution. Local void fraction inside common header was measured with an optical probe. A two-dimensional two-phase flow computational code was developed from a two-fluid model. Modelling of interfacial momentum transfer was used in order to take into account twp-phase flow patterns in common headers. Numerical simulation results show qualitative agreement with experimental results. Present theoretical model limitations are analysed and future improvements are proposed [fr
Lattice Boltzmann heat transfer model for permeable voxels

Science.gov (United States)

Pereira, Gerald G.; Wu, Bisheng; Ahmed, Shakil

2017-12-01

We develop a gray-scale lattice Boltzmann (LB) model to study fluid flow combined with heat transfer for flow through porous media where voxels may be partially solid (or void). Heat transfer in rocks may lead to deformation, which in turn can modulate the fluid flow and so has significant contribution to rock permeability. The LB temperature field is compared to a finite difference solution of the continuum partial differential equations for fluid flow in a channel. Excellent quantitative agreement is found for both Poiseuille channel flow and Brinkman flow. The LB model is then applied to sample porous media such as packed beds and also more realistic sandstone rock sample, and both the convective and diffusive regimes are recovered when varying the thermal diffusivity. It is found that while the rock permeability can be comparatively small (order milli-Darcy), the temperature field can show significant variation depending on the thermal convection of the fluid. This LB method has significant advantages over other numerical methods such as finite and boundary element methods in dealing with coupled fluid flow and heat transfer in rocks which have irregular and nonsmooth pore spaces.
A Multi-Dimensional Heat Transfer Model of a Tie-Tube and Hexagonal Fuel Element for Nuclear Thermal Propulsion

Science.gov (United States)

Gomez, C. F.; Mireles, O. R.; Stewart, E.

2016-01-01

The Space Capable Cryogenic Thermal Engine (SCCTE) effort considers a nuclear thermal rocket design based around a Low-Enriched Uranium (LEU) design fission reactor. The reactor core is comprised of bundled hexagonal fuel elements that directly heat hydrogen for expansion in a thrust chamber and hexagonal tie-tubes that house zirconium hydride moderator mass for the purpose of thermalizing fast neutrons resulting from fission events. Created 3D steady state Hex fuel rod model with 1D flow channels. Hand Calculation were used to set up initial conditions for fluid flow. The Hex Fuel rod uses 1D flow paths to model the channels using empirical correlations for heat transfer in a pipe. Created a 2-D axisymmetric transient to steady state model using the CFD turbulent flow and Heat Transfer module in COMSOL. This model was developed to find and understand the hydrogen flow that might effect the thermal gradients axially and at the end of the tie tube where the flow turns and enters an annulus. The Hex fuel rod and Tie tube models were made based on requirements given to us by CSNR and the SCCTE team. The models helped simplify and understand the physics and assumptions. Using pipe correlations reduced the complexity of the 3-D fuel rod model and is numerically more stable and computationally more time-efficient compared to the CFD approach. The 2-D axisymmetric tie tube model can be used as a reference "Virtual test model" for comparing and improving 3-D Models.
A new approach to the modeling of ultimate heat sink cooling ponds

International Nuclear Information System (INIS)

Policastro, A.J.; Wastag, M.; Paul, J.; Carhart, R.A.

1996-01-01

Ultimate heat sink (UHS) cooling pond thermal performance is analyzed by a new method in which zero, one, and three-dimensional models are used in combination. A typical UHS pond has an irregular shape covering 20 hectares at an average depth of 4 m with a heavy thermal load of 40 MWt (megawatts thermal) per hectare. The resulting flow field can be one, two or three dimensional. A three-dimensional numerical model (Paul 1983) is modified and used to determine the effective dimensionality of the pond under accident conditions. The model's surface heat transfer formulas and its predictions of thermal hydraulics are verified using laboratory and field data. The Paul model shows that, unlike normal cooling ponds, a typical UHS pond is vertically-mixed with only a longitudinal temperature variation. Buoyancy-driven circulations, strong discharge-to-intake flow, and rapid surface heat removal break down the usual vertical stratification. Predictions of the one-dimensional MITEMP model are shown to agree with Paul model predictions for a typical UHS pond at the Catawba Nuclear Power Plant
Effect of heat transfer tube leak on dynamic characteristic of steam generator

International Nuclear Information System (INIS)

Sun Baozhi; Shi Jianxin; Li Na; Zheng Lusong; Liu Shanghua; Lei Yu

2015-01-01

Taking the steam generator of Daya Bay Nuclear Power Station as the research object, one-dimensional dynamic model of the steam generator based on drift flux theory and leak model of heat transfer tube were established. Steady simulation of steam generator under different conditions was carried out. Based on verifying the drift flux model and leak model of heat transfer tube, the effect of leak location and flow rate under different conditions on steam generator's key parameters was studied. The results show that the drift flux model and leak model can reflect the law of key parameter change accurately such as vapor mass fraction and steam pressure under different leak cases. The variation of the parameters is most apparent when the leak is at the entrance of boiling section and vapor mass fraction varies from 0.261 to 0.163 when leakage accounts for 5% of coolant flow rate. The successful prediction of the effect of heat transfer tube leak on dynamic characteristics of the steam generator based on drift flux theory supplies some references for monitoring and taking precautionary measures to prevent heat transfer tube leak accident. (authors)
Parametric analyses of DEMO Divertor using two dimensional transient thermal hydraulic modelling

Science.gov (United States)

Domalapally, Phani; Di Caro, Marco

2018-05-01

Among the options considered for cooling of the Plasma facing components of the DEMO reactor, water cooling is a conservative option because of its high heat removal capability. In this work a two-dimensional transient thermal hydraulic code is developed to support the design of the divertor for the projected DEMO reactor with water as a coolant. The mathematical model accounts for transient 2D heat conduction in the divertor section. Temperature-dependent properties are used for more accurate analysis. Correlations for single phase flow forced convection, partially developed subcooled nucleate boiling, fully developed subcooled nucleate boiling and film boiling are used to calculate the heat transfer coefficients on the channel side considering the swirl flow, wherein different correlations found in the literature are compared against each other. Correlation for the Critical Heat Flux is used to estimate its limit for a given flow conditions. This paper then investigates the results of the parametric analysis performed, whereby flow velocity, diameter of the coolant channel, thickness of the coolant pipe, thickness of the armor material, inlet temperature and operating pressure affect the behavior of the divertor under steady or transient heat fluxes. This code will help in understanding the basic parameterś effect on the behavior of the divertor, to achieve a better design from a thermal hydraulic point of view.
New flow boiling heat transfer model for hydrocarbons evaporating inside horizontal tubes

International Nuclear Information System (INIS)

Chen, G. F.; Gong, M. Q.; Wu, J. F.; Zou, X.; Wang, S.

2014-01-01

Hydrocarbons have high thermodynamic performances, belong to the group of natural refrigerants, and they are the main components in mixture Joule-Thomson low temperature refrigerators (MJTR). New evaluations of nucleate boiling contribution and nucleate boiling suppression factor in flow boiling heat transfer have been proposed for hydrocarbons. A forced convection heat transfer enhancement factor correlation incorporating liquid velocity has also been proposed. In addition, the comparisons of the new model and other classic models were made to evaluate its accuracy in heat transfer prediction

Heat transfer models for fusion blanket first walls

International Nuclear Information System (INIS)

Fillo, J.A.

1977-01-01

In the development of magnetically confined fusion reactors, the ability to cool the first wall, i.e., the first material surface interfacing the plasma, appears to be a critical factor involved in establishing the wall load limit. In order to understand the thermal behavior of the first wall time-dependent, one-dimensional heat conduction models are reviewed with differing modes of heat extraction and cooling
Simultaneous heat and mass transfer on oscillatory free convection boundary layer flow

International Nuclear Information System (INIS)

Hossain, M.A.

1985-11-01

The problem of simultaneous heat and mass transfer in two-dimensional free convection from a semi-infinite vertical flat plate is investigated. An integral method is used to find a solution for zero wall velocity and for a mass transfer velocity at the wall with small-amplitude oscillatory wall temperature. Low and high-frequency solutions are developed separately and are discussed graphically with the effects of the parameters Gr (the Grashof number for heat transfer), Gc (the Grashof number for mass transfer) and Sc (the Schmidt number) for Pr=0.71 representing aid at 20 deg. C. (author)
Numerical analysis of temperature and flow effects in a dry, two-dimensional, porous-media reservoir used for compressed air energy storage

Energy Technology Data Exchange (ETDEWEB)

Wiles, L.E.

1979-10-01

The purpose of the work is to define the hydrodynamic and thermodynamic response of a CAES dry porous media reservoir subjected to simulated air mass cycling. The knowledge gained will provide, or will assist in providing, design guidelines for the efficient and stable operation of the air storage reservoir. The analysis and results obtained by two-dimensional modeling of dry reservoirs are presented. While the fluid/thermal response of the underground system is dependent on many parameters, the two-dimensional model was applied only to those parameters that entered the analysis by virtue of inclusion of the vertical dimension. In particular, the parameters or responses that were quantified or characterized include wellbore heat transfer, heat losses to the vertical boundaries of the porous zone, gravitationally induced flows, producing length of the wellbore, and the effects of nonuniform permeability. The analysis of the wellbore heat transfer included consideration of insulation, preheating (bubble development with heated air), and air mass flow rate.
Heat transfer and pressure drop of a reactor fuel element model with polyzonal spiral finning

Energy Technology Data Exchange (ETDEWEB)

Oka, S; Becirspahic, S [Institute of Nuclear Sciences Boris Kidric, Heat Transfer Department, Vinca, Beograd (Serbia and Montenegro)

1964-10-15

Heat transfer and pressure drop of a reactor fuel element model with polyzonal spiral finning have been investigated. The St-number distribution over length and perimeter of he finning are given. The mean and minimum St{sub k}-number are plotted against the Re-number. The influence of the gap between two fuel elements upon heat transfer and pressure drop, in dependence on the Re-number, and the influence of the length of the fuel element on pressure drop across the gap are shown. The influence of the relative position of the splitters of two neighboring fuel elements on pressure drop and heat transfer is shown. The investigations were performed in the Re-number range 15,000 to 100,000 (author)
A Heat Transfer Investigation of Liquid and Two-Phase Methane

Science.gov (United States)

VanNoord, Jonathan

2010-01-01

A heat transfer investigation was conducted for liquid and two-phase methane. The tests were conducted at the NASA Glenn Research Center Heated Tube Facility (HTF) using resistively heated tube sections to simulate conditions encountered in regeneratively cooled rocket engines. This testing is part of NASA s Propulsion and Cryogenics Advanced Development (PCAD) project. Nontoxic propellants, such as liquid oxygen/liquid methane (LO2/LCH4), offer potential benefits in both performance and safety over equivalently sized hypergolic propulsion systems in spacecraft applications. Regeneratively cooled thrust chambers are one solution for high performance, robust LO2/LCH4 engines, but cooling data on methane is limited. Several test runs were conducted using three different diameter Inconel 600 tubes, with nominal inner diameters of 0.0225-, 0.054-, and 0.075-in. The mass flow rate was varied from 0.005 to 0.07 lbm/sec. As the current focus of the PCAD project is on pressure fed engines for LO2/LCH4, the average test section outlet pressures were targeted to be 200 psia or 500 psia. The heat flux was incrementally increased for each test condition while the test section wall temperatures were monitored. A maximum average heat flux of 6.2 Btu/in.2 sec was achieved and, at times, the temperatures of the test sections reached in excess of 1800 R. The primary objective of the tests was to produce heat transfer correlations for methane in the liquid and two-phase regime. For two-phase flow testing, the critical heat flux values were determined where the fluid transitions from nucleate boiling to film boiling. A secondary goal of the testing was to measure system pressure drops in the two-phase regime.
Heat transfer modeling of double-side arc welding

International Nuclear Information System (INIS)

Sun Junsheng; Wu Chuansong

2002-01-01

If a plasma arc and a TIG arc are connected in serial and with the plasma arc placed on the obverse side and the TIG arc on the opposite side of the workpiece, a special double-side arc welding (DSAW) system will be formed, in which the PAW current is forced to flow through the keyhole along the thickness direction so as to compensate the energy consumed for melting the workpiece and improve the penetration capacity of the PAW arc. By considering the mechanics factors which influence the DSAW pool geometric shape, the control equations of the pool surface deformation are derived, and the mathematics mode for DSAW heat transfer is established by using boundary-fitted non-orthogonal coordinate systems. With this model, the difference between DSAW and PAW heat transfer is analyzed and the reason for the increase of DSAW penetration is explained from the point of heat transfer. The welding process experiments show that calculated results are in good agreement with measured ones
Heat transfer analysis of short helical borehole heat exchangers

International Nuclear Information System (INIS)

Zarrella, Angelo; De Carli, Michele

2013-01-01

Highlights: ► Vertical ground heat exchanger with a helical shaped pipe is analyzed. ► The model considers the interaction between the ground and the environment. ► The results of the model are in good agreement with the experimental values. ► The weather conditions considerably affect the fluid heat carrier temperature. ► The pitch between the turns does not affect the behaviour of the heat exchanger. -- Abstract: In this paper a numerical model to analyze the thermal behaviour of vertical ground heat exchangers with a helical shaped pipe is presented. This type of configuration can be a suitable alternative to conventional ground heat exchangers, especially when the heating and cooling loads of the building are very low. The model describes the heat transfer problem by means of a network of interconnected thermal resistances and capacitances. Moreover, as the investigated ground heat exchanger is usually installed in shallow depth, the model takes into account the interaction between the ground and the ambient environment which affects the fluid heat carrier temperature into the heat exchanger and, as a consequence, the energy efficiency of the heat pump. After a sensitivity analysis on the mesh parameters, the presented model is compared with experimental data and the simulation results show good agreement with the measurements. Finally, analyses to investigate the influence of the weather conditions, of the axial heat transfer and of the pitch between the turns of the helical pipe for two types of ground are carried out.
Modeling heat and mass transfer in the heat treatment step of yerba maté processing

Directory of Open Access Journals (Sweden)

J. M. Peralta

2007-03-01

Full Text Available The aim of this research was to estimate the leaf and twig temperature and moisture content of yerba maté branches (Ilex paraguariensis Saint Hilaire during heat treatment, carried out in a rotary kiln dryer. These variables had to be estimated (modeling the heat and mass transfer due to the difficulty of experimental measurement in the dryer. For modeling, the equipment was divided into two zones: the flame or heat treatment zone and the drying zone. The model developed fit well with the experimental data when water loss took place only in leaves. In the first zone, leaf temperature increased until it reached 135°C and then it slowly decreased to 88°C at the exit, despite the gas temperature, which varied in this zone from 460°C to 120°C. Twig temperature increased in the two zones from its inlet temperature (25°C up to 75°C. A model error of about 3% was estimated based on theoretical and experimental data on leaf moisture content.
SCDAP/RELAP5 Modeling of Heat Transfer and Flow Losses in Lower Head Porous Debris

International Nuclear Information System (INIS)

Coryell, E.W.; Siefken, L.J.; Paik, S.

1998-01-01

Designs are described for implementing models for calculating the heat transfer and flow losses in porous debris in the lower head of a reactor vessel. The COUPLE model in SCDAP/RELAP5 represents both the porous and non-porous debris that results from core material slumping into the lower head. Currently, the COUPLE model has the capability to model convective and radiative heat transfer from the surfaces of non-porous debris in a detailed manner and to model only in a simplistic manner the heat transfer from porous debris. In order to advance beyond the simplistic modeling for porous debris, designs are developed for detailed calculations of heat transfer and flow losses in porous debris. Correlations are identified for convective heat transfer in porous debris for the following modes of heat transfer; (1) forced convection to liquid, (2) forced convection to gas, (3) nucleate boiling, (4) transition boiling, and (5) film boiling. Interphase heat transfer is modeled in an approximate manner. A design is also described for implementing a model of heat transfer by radiation from debris to the interstitial fluid. A design is described for implementation of models for flow losses and interphase drag in porous debris. Since the models for heat transfer and flow losses in porous debris in the lower head are designed for general application, a design is also described for implementation of these models to the analysis of porous debris in the core region. A test matrix is proposed for assessing the capability of the implemented models to calculate the heat transfer and flow losses in porous debris. The implementation of the models described in this report is expected to improve the COUPLE code calculation of the temperature distribution in porous debris and in the lower head that supports the debris. The implementation of these models is also expected to improve the calculation of the temperature and flow distribution in porous debris in the core region
Heat transfer of phase-change materials in two-dimensional cylindrical coordinates

Science.gov (United States)

Labdon, M. B.; Guceri, S. I.

1981-01-01

Two-dimensional phase-change problem is numerically solved in cylindrical coordinates (r and z) by utilizing two Taylor series expansions for the temperature distributions in the neighborhood of the interface location. These two expansions form two polynomials in r and z directions. For the regions sufficiently away from the interface the temperature field equations are numerically solved in the usual way and the results are coupled with the polynomials. The main advantages of this efficient approach include ability to accept arbitrarily time dependent boundary conditions of all types and arbitrarily specified initial temperature distributions. A modified approach using a single Taylor series expansion in two variables is also suggested.
Radiative heat transfer

CERN Document Server

Modest, Michael F

2013-01-01

The third edition of Radiative Heat Transfer describes the basic physics of radiation heat transfer. The book provides models, methodologies, and calculations essential in solving research problems in a variety of industries, including solar and nuclear energy, nanotechnology, biomedical, and environmental. Every chapter of Radiative Heat Transfer offers uncluttered nomenclature, numerous worked examples, and a large number of problems-many based on real world situations-making it ideal for classroom use as well as for self-study. The book's 24 chapters cover the four major areas in the field: surface properties; surface transport; properties of participating media; and transfer through participating media. Within each chapter, all analytical methods are developed in substantial detail, and a number of examples show how the developed relations may be applied to practical problems. It is an extensive solution manual for adopting instructors. Features: most complete text in the field of radiative heat transfer;...
Aerodynamics, heat and mass transfer in steam-aerosol turbulent flows in containment

Energy Technology Data Exchange (ETDEWEB)

Nigmatulin, B.I.; Pershukov, V.A.; Ris, V.V. [Research & Engineering Centre of Nuclear Plants Safety, Moscow (Russian Federation)] [and others

1995-09-01

In this report an analysis of aerodynamic and heat transfer processes at the blowdown of gas-dispersed mixture into the containment volume is presented. A few models for description of the volume averaged and local characteristics are analyzed. The mathematical model for description of the local characteristics of the turbulent gas-dispersed flows was developed. The calculation of aerodynamic, heat and mass transfer characteristics was based on the Navier-Stokes, energy and gas mass fractions conservation equations. For calculation of dynamics and deposition of the aerosols the original diffusion-inertia model is developed. The pulsating characteristics of the gaseous phase were calculated on the base (k-{xi}) model of turbulence with modification to account thermogravitational force action and influence of particle mass loading. The appropriate boundary conditions using the {open_quotes}near-wall function{close_quotes} approach was obtained. Testing of the mathematical models and boundary conditions has shown a good agreement between computation and data of comparison. The described mathematical models were applied to two- and three dimensional calculations of the turbulent flow in containment at the various stages of the accident.
Entropy Generation Analysis of Natural Convection in Square Enclosures with Two Isoflux Heat Sources

Directory of Open Access Journals (Sweden)

S. Z. Nejad

2017-04-01

Full Text Available This study investigates entropy generation resulting from natural convective heat transfer in square enclosures with local heating of the bottom and symmetrical cooling of the sidewalls. This analysis tends to optimize heat transfer of two pieces of semiconductor in a square electronic package. In this simulation, heaters are modeled as isoflux heat sources and sidewalls of the enclosure are isothermal heat sinks. The top wall and the non-heated portions of the bottom wall are adiabatic. Flow and temperature fields are obtained by numerical simulation of conservation equations of mass, momentum and energy in laminar, steady and two dimensional flows. With constant heat energy into the cavity, effect of Rayleigh number, heater length, heater strength ratios and heater position is evaluated on flow and temperature fields and local entropy generation. The results show that a minimum entropy generation rate is obtained under the same condition in which a minimum peak heater temperature is obtained.
Two-dimensional heat flow analysis applied to heat sterilization of ponderosa pine and Douglas-fir square timbers

Science.gov (United States)

William T. Simpson

2004-01-01

Equations for a two-dimensional finite difference heat flow analysis were developed and applied to ponderosa pine and Douglas-fir square timbers to calculate the time required to heat the center of the squares to target temperature. The squares were solid piled, which made their surfaces inaccessible to the heating air, and thus surface temperatures failed to attain...
Analysis of Heat Transfer in Cooling of a Hot Plate by Planar Impingement Jet

International Nuclear Information System (INIS)

Ahn, Dae Hwan; Kim, Dong Sik

2009-01-01

Water jet impingement cooling is used to remove heat from high-temperature surfaces such as hot steel plates in the steel manufacturing process (thermo-mechanical cooling process; TMCP). In those processes, uniform cooling is the most critical factor to ensure high strength steel and good quality. In this study, experiments are performed to measure the heat transfer coefficient together with the inverse heat conduction problem (IHCP) analysis for a plate cooled by planar water jet. In the inverse heat transfer analysis, spatial and temporal variations of heat transfer coefficient, with no information regarding its functional form, are determined by employing the conjugate gradient method with an adjoint problem. To estimate the two dimensional distribution of heat transfer coefficient and heat flux for planar waterjet cooling, eight thermo-couple are installed inside the plate. The results show that heat transfer coefficient is approximately uniform in the span-wise direction in the early stage of cooling. In the later stage where the forced-convection effect is important, the heat transfer coefficient becomes larger in the edge region. The surface temperature vs. heat flux characteristics are also investigated for the entire boiling regimes. In addition, the heat transfer rate for the two different plate geometries are compared at the same Reynolds number
Heat transfer 1990. Proceedings of the ninth international heat transfer conference

International Nuclear Information System (INIS)

Hetsroni, G.

1990-01-01

This book contains the proceedings of the Ninth International Heat Transfer Conference. Included in Volume 3 are the following chapters: Refrigerant vapor condensation on a horizontal tube bundle. Local heat transfer in a reflux condensation inside a closed two-phase thermosyphon and surface temperature by means of a pulsed photothermal effects
Three-dimensional numerical study of heat transfer characteristics of plain plate fin-and-tube heat exchangers from view point of field synergy principle

International Nuclear Information System (INIS)

He, Y.L.; Tao, W.Q.; Song, F.Q.; Zhang, W.

2005-01-01

In this paper, 3-D numerical simulations were performed for laminar heat transfer and fluid flow characteristics of plate fin-and-tube heat exchanger. The effects of five factors were examined: Re number, fin pitch, tube row number, spanwise and longitudinal tube pitch. The Reynolds number based on the tube diameter varied from 288 to 5000, the non-dimensional fin pitch based on the tube diameter varied from 0.04 to 0.5, the tube row number from 1 to 4, the spanwise tube pitch S 1 /d varies from 1.2 to 3, and the longitudinal tube pitch S 2 /d from 1.0 to 2.4. The numerical results were analyzed from the view point of field synergy principle, which says that the reduction of the intersection angle between velocity and fluid temperature gradient is the basic mechanism to enhance convective heat transfer. It is found that the effects of the five parameters on the heat transfer performance of the finned tube banks can be well described by the field synergy principle, i.e., the enhancement or deterioration of the convective heat transfer across the finned tube banks is inherently related to the variation of the intersection angle between the velocity and the fluid temperature gradient. It is also recommended that to further enhance the convective heat transfer, the enhancement techniques, such as slotting the fin, should be adopted mainly in the rear part of the fin where the synergy between local velocity and temperature gradient become worse
Measuring of heat transfer coefficient

DEFF Research Database (Denmark)

Henningsen, Poul; Lindegren, Maria

Subtask 3.4 Measuring of heat transfer coefficient Subtask 3.4.1 Design and setting up of tests to measure heat transfer coefficient Objective: Complementary testing methods together with the relevant experimental equipment are to be designed by the two partners involved in order to measure...... the heat transfer coefficient for a wide range of interface conditions in hot and warm forging processes. Subtask 3.4.2 Measurement of heat transfer coefficient The objective of subtask 3.4.2 is to determine heat transfer values for different interface conditions reflecting those typically operating in hot...
Heat transport in two-dimensional materials by directly solving the phonon Boltzmann equation under Callaway's dual relaxation model

Science.gov (United States)

Guo, Yangyu; Wang, Moran

2017-10-01

The single mode relaxation time approximation has been demonstrated to greatly underestimate the lattice thermal conductivity of two-dimensional materials due to the collective effect of phonon normal scattering. Callaway's dual relaxation model represents a good approximation to the otherwise ab initio solution of the phonon Boltzmann equation. In this work we develop a discrete-ordinate-method (DOM) scheme for the numerical solution of the phonon Boltzmann equation under Callaway's model. Heat transport in a graphene ribbon with different geometries is modeled by our scheme, which produces results quite consistent with the available molecular dynamics, Monte Carlo simulations, and experimental measurements. Callaway's lattice thermal conductivity model with empirical boundary scattering rates is examined and shown to overestimate or underestimate the direct DOM solution. The length convergence of the lattice thermal conductivity of a rectangular graphene ribbon is explored and found to depend appreciably on the ribbon width, with a semiquantitative correlation provided between the convergence length and the width. Finally, we predict the existence of a phonon Knudsen minimum in a graphene ribbon only at a low system temperature and isotope concentration so that the average normal scattering rate is two orders of magnitude stronger than the intrinsic resistive one. The present work will promote not only the methodology for the solution of the phonon Boltzmann equation but also the theoretical modeling and experimental detection of hydrodynamic phonon transport in two-dimensional materials.
Experimental study of interfacial shear stress for an analogy model of evaporative heat transfer

International Nuclear Information System (INIS)

Kwon, Hyuk; Park, GoonCherl; Min, ByungJoo

2008-01-01

In this study, we conducted measurements of an evaporative interfacial shear stress in a passive containment cooling system (PCCS). An interfacial shear stress for a counter-current flow was measured from a momentum balance equation and the interfacial friction factor for evaporation was evaluated by using experimental data. A model for the evaporative heat transfer coefficient of a vertical evaporative flat surface was developed based on an analogy between heat and momentum transfer. It was found that the interfacial shear stress increases with the Jacob number, which incorporates the evaporation rate, and the air and water Reynolds numbers. The relationship between the evaporative heat transfer and the interfacial shear stress was evaluated by using the experimental results. This relationship was used to develop a model for an evaporative heat transfer coefficient by using an analogy between heat and mass transfer. The prediction of this model were found to be in good agreement with the experimental data obtained for evaporative heat transfer by Kang and Park. (author)

COBRA/TRAC analysis of two-dimensional thermal-hydraulic behavior in SCTF reflood tests

International Nuclear Information System (INIS)

Iwamura, Takamichi; Ohnuki, Akira; Sobajima, Makoto; Adachi, Hiromichi

1987-01-01

The effects of radial power distribution and non-uniform upper plenum water accumulation on thermal-hydraulic behavior in the core were observed in the reflood tests with Slab Core Test Facility (SCTF). In order to examine the predictability of these two effects by a multi-dimensional analysis code, the COBRA/TRAC calculations were made. The calculated results indicated that the heat transfer enhancement in high power bundles above quench front was caused by high vapor flow rate in those bundles due to the radial power distribution. On the other hand, the heat transfer degradation in the peripheral bundles under the condition of non-uniform upper plenum water accumulation was caused by the lower flow rates of vapor and entrained liquid above the quench front in those bundles by the reason that vapor concentrated in the center bundles due to the cross flow induced by the horizontal pressure gradient in the core. The above-mentioned two-dimensional heat transfer behaviors calculated with the COBRA/TRAC code is similar to those observed in SCTF tests and therefore those calculations are useful to investigate the mechanism of the two-dimensional effects in SCTF reflood tests. (author)
Comparison of Two Models for Radiative Heat Transfer in High Temperature Thermal Plasmas

Directory of Open Access Journals (Sweden)

Matthieu Melot

2011-01-01

Full Text Available Numerical simulation of the arc-flow interaction in high-voltage circuit breakers requires a radiation model capable of handling high-temperature participating thermal plasmas. The modeling of the radiative transfer plays a critical role in the overall accuracy of such CFD simulations. As a result of the increase of computational power, CPU intensive methods based on the radiative transfer equation, leading to more accurate results, are now becoming attractive alternatives to current approximate models. In this paper, the predictive capabilities of the finite volume method (RTE-FVM and the P1 model are investigated. A systematic comparison between these two models and analytical solutions are presented for a variety of relevant test cases. Two implementations of each approach are compared, and a critical evaluation is presented.
Recent developments in the modeling of boiling heat transfer mechanisms

International Nuclear Information System (INIS)

Podowski, M.Z.

2009-01-01

Due to the importance of boiling for the analysis of operation and safety of nuclear reactors, extensive efforts have been made in the past to develop a variety of methods and tools to study boiling heat transfer for various geometries and operating conditions. Recent progress in the computational multiphase fluid dynamics (CMFD) methods of two- and multiphase flows has already started opening up new exciting possibilities for using complete multidimensional models to predict the operation of boiling systems under both steady-state and transient conditions. However, such models still require closure laws and boundary conditions, the accuracy of which determines the predictive capabilities of the overall models and the associated CMFD simulations. Because of the complexity of the underlying physical phenomena, boiling heat transfer has traditionally been quantified using phenomenological models and correlations obtained by curve-fitting extensive experimental data. Since simple heuristic formulae are not capable of capturing the effect of various specific experimental conditions and the associated wide scattering of data points, most existing correlations are characterized by large uncertainties which are typically hidden behind the 'logarithmic scale' format of plots. Furthermore, such an approach provides only limited insight into the local phenomena of: nucleation, heated surface material properties, temperature fluctuations, and others. The objectives of this paper are two-fold. First, the state of the art is reviewed in the area of modeling concepts for both pool boiling and forced-convection (bulk and subcooled) boiling. Then, new results are shown concerning the development of new mechanistic models and their validation against experimental data. It is shown that a combination of the proposed theoretical approach with advanced computational methods leads to a dramatic improvement in both our understanding of the physics of boiling and the predictive
The influence of nanoparticle migration on forced convective heat transfer of nanofluid under heating and cooling regimes.

Science.gov (United States)

Kozlova, Sofya V; Ryzhkov, Ilya I

2014-09-01

In this paper, laminar convective heat transfer of water-alumina nanofluid in a circular tube with uniform heat flux at the tube wall is investigated. The investigation is performed numerically on the basis of two-component model, which takes into account nanoparticle transport by diffusion and thermophoresis. Two thermal regimes at the tube wall, heating and cooling, are considered and the influence of nanoparticle migration on the heat transfer is analyzed comparatively. The intensity of thermophoresis is characterized by a new empirical model for thermophoretic mobility. It is shown that the nanoparticle volume fraction decreases (increases) in the boundary layer near the wall under heating (cooling) due to thermophoresis. The corresponding variations of nanofluid properties and flow characteristics are presented and discussed. The intensity of heat transfer for the model with thermophoresis in comparison to the model without thermophoresis is studied by plotting the dependence of the heat transfer coefficient on the Peclet number. The effectiveness of water-alumina nanofluid is analyzed by plotting the average heat transfer coefficient against the required pumping power. The analysis of the results reveals that the water-alumina nanofluid shows better performance in the heating regime than in the cooling regime due to thermophoretic effect.
Comparison of heat transfer in straight and corrugated minichannels with two-phase flow

Directory of Open Access Journals (Sweden)

Peukert P.

2014-03-01

Full Text Available Measurements of heat transfer rates performed with an experimental condensation heat exchanger are reported for a corrugated minichannel tube and for a straight minichannel tube. The two cases were compared at same flow regimes. The corrugation appears advantageous for relatively low steam pressures and flow rates where much higher heat transfer rates were observed close to the steam entrance, thus allowing shortening the heat exchanger with the associated advantages of costs lowering and smaller built-up space. At high steam pressures and high flow rates both tubes performed similarly.
Heat transfer correlations in mantle tanks

DEFF Research Database (Denmark)

Furbo, Simon; Knudsen, Søren

2005-01-01

on calculations with a CFD-model, which has earlier been validated by means of experiments. The CFD-model is used to determine the heat transfer between the solar collector fluid in the mantle and the walls surrounding the mantle in all levels of the mantle as well as the heat transfer between the wall...... transfer correlations are suitable as input for a detailed simulation model for mantle tanks. The heat transfer correlations determined in this study are somewhat different from previous reported heat transfer correlations. The reason is that this study includes more mantle tank designs and operation......Small solar domestic hot water systems are best designed as low flow systems based on vertical mantle tanks. Theoretical investigations of the heat transfer in differently designed vertical mantle tanks during different operation conditions have been carried out. The investigations are based...
Proposed heat transfer model for the gas-liquid heat transfer effects observed in the Stanford Research Institute scaled tests

International Nuclear Information System (INIS)

Corradini, M.; Sonin, A.A.; Todreas, N.

1976-12-01

In 1971-72, the Stanford Research Institute conducted a series of scaled experiments which simulated a sodium-vapor expansion in a hypothetical core disruptive accident (HCDA) for the Fast Flux Test Facility. A non-condensible explosive source was used to model the pressure-volume expansion characteristics of sodium vapor as predicted by computer code calculations. Rigid piston-cylinder experiments ( 1 / 10 and 1 / 30 scale) were undertaken to determine these expansion characteristics. The results showed that the pressure-volume characteristics depend significantly on the presence of water in the cylinder reducing the work output by about 50 percent when a sufficient water depth was present. The study presented proposes that the mechanism of heat transfer between the water and high temperature gas was due to area enhancement by Taylor instabilities at the gas-liquid interface. A simple heat transfer model is proposed which describes this energy transport process and agrees well with the experimental data from both scaled experiments. The consequences of this analysis suggest that an estimate of the heat transfer to the cold slug during a full-scale HCDA due to sodium vapor expansion and the accompanying reduction in mechanical work energy warrants further investigation. The implication of this analysis is that for either sodium or fuel vapor expansion in an HCDA, there is an inherent heat transfer mechanism which significantly reduces the work output of the expanding bubble
Comparison of correlations for heat transfer in sphere-pac beds

International Nuclear Information System (INIS)

Fundamenski, W.R.; Gierszewski, P.J.

1991-08-01

The design of a tritium breeding blanket for a fusion reactor requires the knowledge of heat transfer within the blanket. In this paper three models for effective bed heat transfer are compared against the experimental database in order to choose a reference correlation to be used in blanket design. Two parameters are used to describe heat transfer in a packed bed: effective thermal conductivity of the bed, and a heat transfer coefficient at the bed-solid interface
Heat and mass transfer effects in a direct methanol fuel cell: A 1D model

Energy Technology Data Exchange (ETDEWEB)

Oliveira, V.B.; Falcao, D.S.; Pinto, A.M.F.R. [Centro de Estudos de Fenomenos de Transporte, Departamento de Eng. Quimica, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto (Portugal); Rangel, C.M. [INETI - Unidade de Electroquimica e Materiais, Paco do Lumiar, 22,1649-038 (Portugal)

2008-07-15

Models are a fundamental tool for the design process of fuel cells and fuel cell systems. In this work, a steady-state, one-dimensional model accounting for coupled heat and mass transfer, along with the electrochemical reactions occurring in the DMFC, is presented. The model output is the temperature profile through the cell and the water balance and methanol crossover between the anode and the cathode. The model predicts the correct trends for the influence of current density and methanol feed concentration on both methanol and water crossover. The model estimates the net water transfer coefficient through the membrane, {alpha}, a very important parameter to describe water management in the DMFC. Suitable operating ranges can be set up for different MEA structures maintaining the crossover of methanol and water within acceptable levels. The model is rapidly implemented and is therefore suitable for inclusion in real-time system level DMFC calculations. (author)
Heat transfer

International Nuclear Information System (INIS)

Saad, M.A.

1985-01-01

Heat transfer takes place between material systems as a result of a temperature difference. The transmission process involves energy conversions governed by the first and second laws of thermodynamics. The heat transfer proceeds from a high-temperature region to a low-temperature region, and because of the finite thermal potential, there is an increase in entropy. Thermodynamics, however, is concerned with equilibrium states, which includes thermal equilibrium, irrespective of the time necessary to attain these equilibrium states. But heat transfer is a result of thermal nonequilibrium conditions, therefore, the laws of thermodynamics alone cannot describe completely the heat transfer process. In practice, most engineering problems are concerned with the rate of heat transfer rather than the quantity of heat being transferred. Resort then is directed to the particular laws governing the transfer of heat. There are three distinct modes of heat transfer: conduction, convection, and radiation. Although these modes are discussed separately, all three types may occur simultaneously
A one-dimensional material transfer model for HECTR version 1.5

International Nuclear Information System (INIS)

Geller, A.S.; Wong, C.C.

1991-08-01

HECTR (Hydrogen Event Containment Transient Response) is a lumped-parameter computer code developed for calculating the pressure-temperature response to combustion in a nuclear power plant containment building. The code uses a control-volume approach and subscale models to simulate the mass, momentum, and energy transfer occurring in the containment during a loss-of-collant-accident (LOCA). This document describes one-dimensional subscale models for mass and momentum transfer, and the modifications to the code required to implement them. Two problems were analyzed: the first corresponding to a standard problem studied with previous HECTR versions, the second to experiments. The performance of the revised code relative to previous HECTR version is discussed as is the ability of the code to model the experiments. 8 refs., 5 figs., 3 tabs
Heat transfer--Orlando (Symposium), 1980

International Nuclear Information System (INIS)

Stein, R.P.

1980-01-01

This conference proceedings contains 36 papers of which 3 appear as abstracts. 23 papers are indexed separately. Topics covered include: thermodynamics of PWR and LMFBR Steam Generators; two-phase flow in parallel channels; geothermal heat transfer; natural circulation in complex geometries; heat transfer in non-Newtonian systems; and process heat transfer
Radiation effects on heat transfer in heat exchangers, (2)

International Nuclear Information System (INIS)

Mori, Yasuo; Watanabe, Kenji; Taira, Tatsuji.

1980-01-01

In a high temperature gas-cooled reactor system, in which the working fluid exchanges heat at high temperature near 1000 deg C, the heat transfer acceleration by positively utilizing the radiation heat transfer between solid surfaces should be considered. This paper reports on the results of experiment and analysis for the effects of radiant heat on the heat transfer performance at elevated temperature by applying the heat transfer-accelerating method using radiators to the heat exchanger with tube bundle composed of two channels of heating and heated sides. As the test heat exchangers, a parallel counter flow exchanger and the cross flow exchanger simulating helical tubes were employed, and the results studied on the characteristics of each heat exchanger are described. The plates placed in parallel to flow in every space of the tube bundle arranged in a matrix were used as the heat transfer accelerator. The effects of acceleration with the plates were the increase of heat transmission from 12 to 24% and 12 to 38% in the parallel flow and cross flow heat exchangers, respectively. Also, it was clarified that the theoretical analysis, in which it was assumed that the region within pitch S and two radiator plates, with a heat-transferring tube placed at the center, is the minimum domain for calculation, and that the heat exchange by radiation occurs only between the domain and the adjacent domains, can estimate the heat transfer-accelerating effect and the temperature distribution in a heat exchanger with sufficient accuracy. (Wakatsuki, Y.)
Analytical heat transfer modeling of a new radiation calorimeter

Energy Technology Data Exchange (ETDEWEB)

Obame Ndong, Elysée [Department of Industrial Engineering and Maintenance, University of Sciences and Technology of Masuku (USTM), BP 941 Franceville (Gabon); Grenoble Electrical Engineering Laboratory (G2Elab), University Grenoble Alpes and CNRS, G2Elab, F38000 Grenoble (France); Gallot-Lavallée, Olivier [Grenoble Electrical Engineering Laboratory (G2Elab), University Grenoble Alpes and CNRS, G2Elab, F38000 Grenoble (France); Aitken, Frédéric, E-mail: frederic.aitken@g2elab.grenoble-inp.fr [Grenoble Electrical Engineering Laboratory (G2Elab), University Grenoble Alpes and CNRS, G2Elab, F38000 Grenoble (France)

2016-06-10

Highlights: • Design of a new calorimeter for measuring heat power loss in electrical components. • The calorimeter can operate in a temperature range from −50 °C to 150 °C. • An analytical model of heat transfers for this new calorimeter is presented. • The theoretical sensibility of the new apparatus is estimated at ±1 mW. - Abstract: This paper deals with an analytical modeling of heat transfers simulating a new radiation calorimeter operating in a temperature range from −50 °C to 150 °C. The aim of this modeling is the evaluation of the feasibility and performance of the calorimeter by assessing the measurement of power losses of some electrical devices by radiation, the influence of the geometry and materials. Finally a theoretical sensibility of the new apparatus is estimated at ±1 mW. From these results the calorimeter has been successfully implemented and patented.
Analytical heat transfer modeling of a new radiation calorimeter

International Nuclear Information System (INIS)

Obame Ndong, Elysée; Gallot-Lavallée, Olivier; Aitken, Frédéric

2016-01-01

Highlights: • Design of a new calorimeter for measuring heat power loss in electrical components. • The calorimeter can operate in a temperature range from −50 °C to 150 °C. • An analytical model of heat transfers for this new calorimeter is presented. • The theoretical sensibility of the new apparatus is estimated at ±1 mW. - Abstract: This paper deals with an analytical modeling of heat transfers simulating a new radiation calorimeter operating in a temperature range from −50 °C to 150 °C. The aim of this modeling is the evaluation of the feasibility and performance of the calorimeter by assessing the measurement of power losses of some electrical devices by radiation, the influence of the geometry and materials. Finally a theoretical sensibility of the new apparatus is estimated at ±1 mW. From these results the calorimeter has been successfully implemented and patented.
Heat and mass transfer during the cryopreservation of a bioartificial liver device: a computational model.

Science.gov (United States)

Balasubramanian, Saravana K; Coger, Robin N

2005-01-01

Bioartificial liver devices (BALs) have proven to be an effective bridge to transplantation for cases of acute liver failure. Enabling the long-term storage of these devices using a method such as cryopreservation will ensure their easy off the shelf availability. To date, cryopreservation of liver cells has been attempted for both single cells and sandwich cultures. This study presents the potential of using computational modeling to help develop a cryopreservation protocol for storing the three dimensional BAL: Hepatassist. The focus is upon determining the thermal and concentration profiles as the BAL is cooled from 37 degrees C-100 degrees C, and is completed in two steps: a cryoprotectant loading step and a phase change step. The results indicate that, for the loading step, mass transfer controls the duration of the protocol, whereas for the phase change step, when mass transfer is assumed negligible, the latent heat released during freezing is the control factor. The cryoprotocol that is ultimately proposed considers time, cooling rate, and the temperature gradients that the cellular space is exposed to during cooling. To our knowledge, this study is the first reported effort toward designing an effective protocol for the cryopreservation of a three-dimensional BAL device.
Stochastic modelling of conjugate heat transfer in near-wall turbulence

International Nuclear Information System (INIS)

Pozorski, Jacek; Minier, Jean-Pierre

2006-01-01

The paper addresses the conjugate heat transfer in turbulent flows with temperature assumed to be a passive scalar. The Lagrangian approach is applied and the heat transfer is modelled with the use of stochastic particles. The intensity of thermal fluctuations in near-wall turbulence is determined from the scalar probability density function (PDF) with externally provided dynamical statistics. A stochastic model for the temperature field in the wall material is proposed and boundary conditions for stochastic particles at the solid-fluid interface are formulated. The heated channel flow with finite-thickness walls is considered as a validation case. Computation results for the mean temperature profiles and the variance of thermal fluctuations are presented and compared with available DNS data
Stochastic modelling of conjugate heat transfer in near-wall turbulence

Energy Technology Data Exchange (ETDEWEB)

Pozorski, Jacek [Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Fiszera 14, 80952 Gdansk (Poland)]. E-mail: jp@imp.gda.pl; Minier, Jean-Pierre [Research and Development Division, Electricite de France, 6 quai Watier, 78400 Chatou (France)

2006-10-15

The paper addresses the conjugate heat transfer in turbulent flows with temperature assumed to be a passive scalar. The Lagrangian approach is applied and the heat transfer is modelled with the use of stochastic particles. The intensity of thermal fluctuations in near-wall turbulence is determined from the scalar probability density function (PDF) with externally provided dynamical statistics. A stochastic model for the temperature field in the wall material is proposed and boundary conditions for stochastic particles at the solid-fluid interface are formulated. The heated channel flow with finite-thickness walls is considered as a validation case. Computation results for the mean temperature profiles and the variance of thermal fluctuations are presented and compared with available DNS data.
Three-dimensional numerical study of flow and heat transfer from a cube placed in a uniform flow

International Nuclear Information System (INIS)

Saha, A.K.

2006-01-01

The fluid flow and heat transfer from a stationary cube placed in a uniform flow is studied numerically. The three-dimensional unsteady Navier Stokes and energy equations are solved using higher order temporal and spatial discretizations. Computations are carried out for a Reynolds number range of 50-400. At Re = 218, the symmetry seen at Re = 216 breaks down in one of the orthogonal planes while remains symmetric on the other thus showing a planar symmetry. The flow experiences a Hopf bifurcation at a Reynolds number between 265 and 270 and becomes unsteady. The thermal field also shows all the transitions same as those of flow transitions. The drag coefficient decreases while the heat transfer shows an increasing trend with Reynolds number. The transition from a steady to an unsteady flow does not show any significant increase in the heat transfer. Both the flow and thermal fields show multiple frequencies at high Reynolds number and the number of frequencies increases with the increase in Reynolds number. The instantaneous flow and temperature field are seen to deviate from planar symmetry at Re = 400
Smouldering (thermal) remediation of soil contaminated with industrial organic liquids: novel insights into heat transfer and kinetics uncovered by integrating experiments and modelling

Science.gov (United States)

Gerhard, J.; Zanoni, M. A. B.; Torero, J. L.

2017-12-01

Smouldering (i.e., flameless combustion) underpins the technology Self-sustaining Treatment for Active Remediation (STAR). STAR achieves the in situ destruction of nonaqueous phase liquids (NAPLs) by generating a self-sustained smouldering reaction that propagates through the source zone. This research explores the nature of the travelling reaction and the influence of key in situ and engineered characteristics. A novel one-dimensional numerical model was developed (in COMSOL) to simulate the smouldering remediation of bitumen-contaminated sand. This model was validated against laboratory column experiments. Achieving model validation depended on correctly simulating the energy balance at the reaction front, including properly accounting for heat transfer, smouldering kinetics, and heat losses. Heat transfer between soil and air was demonstrated to be generally not at equilibrium. Moreover, existing heat transfer correlations were found to be inappropriate for the low air flow Reynold's numbers (Re remediation systems. Therefore, a suite of experiments were conducted to generate a new heat transfer correlation, which generated correct simulations of convective heat flow through soil. Moreover, it was found that, for most cases of interest, a simple two-step pyrolysis/oxidation set of kinetic reactions was sufficient. Arrhenius parameters, calculated independently from thermogravimetric experiments, allowed the reaction kinetics to be validated in the smouldering model. Furthermore, a simple heat loss term sufficiently accounted for radial heat losses from the column. Altogether, these advances allow this simple model to reasonably predict the self-sustaining process including the peak reaction temperature, the reaction velocity, and the complete destruction of bitumen behind the front. Simulations with the validated model revealed numerous unique insights, including how the system inherently recycles energy, how air flow rate and NAPL saturation dictate contaminant

Experimental and theoretical analysis of the local condensation heat transfer in a plate heat exchanger

International Nuclear Information System (INIS)

Grabenstein, V; Kabelac, S

2012-01-01

Plate heat exchanger (PHE) are today widely used in industrial heat transfer applications due to their good thermal performance, modest space requirement, easy accessibility to all areas and their lower capital and operating costs as compared to shell-and-tube heat exchangers. Although authoritative models for the design of PHE used as condensers are missing, the number of applications where a PHE is operating as a condenser increases. On the way to a reliable model based on physical approaches for the prediction of heat transfer and pressure drop during the condensation process inside a PHE, the flow and heat interactions as well as their dependence on the geometrical parameters of the corrugated plates and the operating conditions must be studied in detail. In this work the stepwise procedure for the fundamental construction of such a model is described. An experimental setup was built to analyze the characteristics of the two-phase-flow in PHE. A single gap, consisting of two transparent corrugated plates, was tested with a two-phase flow of air/water and also with boiling refrigerant R365mfc. Flow pattern maps were constructed for plates with corrugation angles of 27 and 63 degrees relative to the direction of flow. Investigations of the local heat transfer coefficients and the pressure drop were done with the same plates. The measurement of the local heat transfer coefficients was carried out by the use of the 'Temperature Oscillation InfraRed Thermography' (TOIRT) method. Based on these results three main flow patterns are defined: film flow, bubbly flow and slug flow. For each of the three flow patterns an own model for the heat transfer and pressure drop mechanism are developed and the heat transfer coefficient and the friction factor is calculated with different equations depending on the actual steam quality, mass flow and geometrical parameters by means of a flow pattern map. The theory of the flow pattern based prediction models is proved with own
Near-field heat transfer between graphene/hBN multilayers

Science.gov (United States)

Zhao, Bo; Guizal, Brahim; Zhang, Zhuomin M.; Fan, Shanhui; Antezza, Mauro

2017-06-01

We study the radiative heat transfer between multilayer structures made by a periodic repetition of a graphene sheet and a hexagonal boron nitride (hBN) slab. Surface plasmons in a monolayer graphene can couple with hyperbolic phonon polaritons in a single hBN film to form hybrid polaritons that can assist photon tunneling. For periodic multilayer graphene/hBN structures, the stacked metallic/dielectric array can give rise to a further effective hyperbolic behavior, in addition to the intrinsic natural hyperbolic behavior of hBN. The effective hyperbolicity can enable more hyperbolic polaritons that enhance the photon tunneling and hence the near-field heat transfer. However, the hybrid polaritons on the surface, i.e., surface plasmon-phonon polaritons, dominate the near-field heat transfer between multilayer structures when the topmost layer is graphene. The effective hyperbolic regions can be well predicted by the effective medium theory (EMT), thought EMT fails to capture the hybrid surface polaritons and results in a heat transfer rate much lower compared to the exact calculation. The chemical potential of the graphene sheets can be tuned through electrical gating and results in an additional modulation of the heat transfer. We found that the near-field heat transfer between multilayer structures does not increase monotonously with the number of layers in the stack, which provides a way to control the heat transfer rate by the number of graphene layers in the multilayer structure. The results may benefit the applications of near-field energy harvesting and radiative cooling based on hybrid polaritons in two-dimensional materials.
Analysis of radiative heat transfer impact in cross-flow tube and fin heat exchangers

Directory of Open Access Journals (Sweden)

Hanuszkiewicz-Drapała Małgorzata

2016-03-01

Full Text Available A cross-flow, tube and fin heat exchanger of the water – air type is the subject of the analysis. The analysis had experimental and computational form and was aimed for evaluation of radiative heat transfer impact on the heat exchanger performance. The main element of the test facility was an enlarged recurrent segment of the heat exchanger under consideration. The main results of measurements are heat transfer rates, as well as temperature distributions on the surface of the first fin obtained by using the infrared camera. The experimental results have been next compared to computational ones coming from a numerical model of the test station. The model has been elaborated using computational fluid dynamics software. The computations have been accomplished for two cases: without radiative heat transfer and taking this phenomenon into account. Evaluation of the radiative heat transfer impact in considered system has been done by comparing all the received results.
Determination of two dimensional axisymmetric finite element model for reactor coolant piping nozzles

International Nuclear Information System (INIS)

Choi, S. N.; Kim, H. N.; Jang, K. S.; Kim, H. J.

2000-01-01

The purpose of this paper is to determine a two dimensional axisymmetric model through a comparative study between a three dimensional and an axisymmetric finite element analysis of the reactor coolant piping nozzle subject to internal pressure. The finite element analysis results show that the stress adopting the axisymmetric model with the radius of equivalent spherical vessel are well agree with that adopting the three dimensional model. The radii of equivalent spherical vessel are 3.5 times and 7.3 times of the radius of the reactor coolant piping for the safety injection nozzle and for the residual heat removal nozzle, respectively
Measurement of Two-Phase Flow and Heat Transfer Parameters using Infrared Thermometry

Science.gov (United States)

Kim, Tae-Hoon; Kommer, Eric; Dessiatoun, Serguei; Kim, Jungho

2012-01-01

A novel technique to measure heat transfer and liquid film thickness distributions over relatively large areas for two-phase flow and heat transfer phenomena using infrared (IR)thermometry is described. IR thermometry is an established technology that can be used to measure temperatures when optical access to the surface is available in the wavelengths of interest. In this work, a midwave IR camera (3.6-5.1 microns) is used to determine the temperature distribution within a multilayer consisting of a silicon substrate coated with a thin insulator. Since silicon is largely transparent to IR radiation, the temperature of the inner and outer walls of the multilayer can be measured by coating selected areas with a thin, IR opaque film. If the fluid used is also partially transparent to IR, the flow can be visualized and the liquid film thickness can be measured. The theoretical basis for the technique is given along with a description of the test apparatus and data reduction procedure. The technique is demonstrated by determining the heat transfer coefficient distributions produced by droplet evaporation and flow boiling heat transfer.
Finite-elements modeling of radiant heat transfers between mobile surfaces; Modelisation par elements finis de transferts radiatifs entre surfaces mobiles

Energy Technology Data Exchange (ETDEWEB)

Daurelle, J V; Cadene, V; Occelli, R [Universite de Provence, 13 - Marseille (France)

1997-12-31

In the numerical modeling of thermal industrial problems, radiant heat transfers remain difficult to take into account and require important computer memory and long computing time. These difficulties are enhanced when radiant heat transfers are coupled with finite-elements diffusive heat transfers because finite-elements architecture is complex and requires a lot of memory. In the case of radiant heat transfers along mobile boundaries, the methods must be optimized. The model described in this paper concerns the radiant heat transfers between diffuse grey surfaces. These transfers are coupled with conduction transfers in the limits of the diffusive opaque domain. 2-D and 3-D geometries are analyzed and two configurations of mobile boundaries are considered. In the first configuration, the boundary follows the deformation of the mesh, while in the second, the boundary moves along the fixed mesh. Matter displacement is taken into account in the term of transport of the energy equation, and an appropriate variation of the thermophysical properties of the transition elements between the opaque and transparent media is used. After a description of the introduction of radiative limit conditions in a finite-elements thermal model, the original methods used to optimize calculation time are explained. Two examples of application illustrate the approach used. The first concerns the modeling of radiant heat transfers between fuel rods during a reactor cooling accident, and the second concerns the study of heat transfers inside the air-gap of an electric motor. The method of identification of the mobile surface on the fixed mesh is described. (J.S.) 12 refs.
Finite-elements modeling of radiant heat transfers between mobile surfaces; Modelisation par elements finis de transferts radiatifs entre surfaces mobiles

Energy Technology Data Exchange (ETDEWEB)

Daurelle, J.V.; Cadene, V.; Occelli, R. [Universite de Provence, 13 - Marseille (France)

1996-12-31

In the numerical modeling of thermal industrial problems, radiant heat transfers remain difficult to take into account and require important computer memory and long computing time. These difficulties are enhanced when radiant heat transfers are coupled with finite-elements diffusive heat transfers because finite-elements architecture is complex and requires a lot of memory. In the case of radiant heat transfers along mobile boundaries, the methods must be optimized. The model described in this paper concerns the radiant heat transfers between diffuse grey surfaces. These transfers are coupled with conduction transfers in the limits of the diffusive opaque domain. 2-D and 3-D geometries are analyzed and two configurations of mobile boundaries are considered. In the first configuration, the boundary follows the deformation of the mesh, while in the second, the boundary moves along the fixed mesh. Matter displacement is taken into account in the term of transport of the energy equation, and an appropriate variation of the thermophysical properties of the transition elements between the opaque and transparent media is used. After a description of the introduction of radiative limit conditions in a finite-elements thermal model, the original methods used to optimize calculation time are explained. Two examples of application illustrate the approach used. The first concerns the modeling of radiant heat transfers between fuel rods during a reactor cooling accident, and the second concerns the study of heat transfers inside the air-gap of an electric motor. The method of identification of the mobile surface on the fixed mesh is described. (J.S.) 12 refs.
Integrated conjugate heat transfer analysis method for in-vessel retention with external reactor vessel cooling - 15477

International Nuclear Information System (INIS)

Park, J.W.; Bae, J.H.; Seol, W.C.

2015-01-01

An integrated conjugate heat transfer analysis method for the thermal integrity of a reactor vessel under external reactor vessel cooling conditions is developed to resolve light metal layer focusing effect issue. The method calculates steady-state 3-dimensional temperature distribution of a reactor vessel using coupled conjugate heat transfer between in-vessel 3-layered stratified corium (metallic pool, oxide pool and heavy metal) and polar-angle dependent boiling heat transfer at the outer surface of a reactor vessel. The 3-layer corium heat transfer model is utilizing lumped-parameter thermal-resistance circuit method and ex-vessel boiling regimes are parametrically considered. The thermal integrity of a reactor vessel is addressed in terms of un-molten thickness profile. The vessel 3-dimensional heat conduction is validated against a commercial code. It is found that even though the internal heat flux from the metal layer goes far beyond critical heat flux (CHF) the heat flux from the outermost nodes of the vessel may be maintained below CHF due to massive vessel heat diffusion. The heat diffusion throughout the vessel is more pronounced for relatively low heat generation rate in an oxide pool. Parametric calculations are performed considering thermal conditions such as peak heat flux from a light metal layer, heat generation in an oxide pool and external boiling conditions. The major finding is that the most crucial factor for success of in-vessel retention is not the mass of the molten light metal above the oxide pool but the heat generation rate inside the oxide pool and the 3-dimensional vessel heat transfer provides a much larger minimum vessel wall thickness. (authors)
Modelling of heat transfer to fluids at a supercritical pressure

International Nuclear Information System (INIS)

Shuisheng, He

2014-01-01

A key feature of Supercritical Water-cooled Reactor (SCWR) is that, by raising the pressure of the reactor coolant fluid above the critical value, a phase change crisis is avoided. However, the changes in water density as it flows through the core of an SCWR are actually much higher than in the current water-cooled reactors. In a typical design, the ratio of the density of water at the core inlet to that at exit is as high as 7:1. Other fluid properties also vary significantly, especially around the pseudo-critical temperature (at which the specific heat capacity peaks). As a result, turbulent flow and heat transfer behaviour in the core is extremely complex and under certain conditions, significant heat transfer deterioration can potentially occur. Consequently, understanding and being able to predict flow and heat transfer phenomena under normal steady operation conditions and in start-up and hypothetical fault conditions are fundamental to the design of SCWR. There have been intensive studies on flow and heat transfer to fluids at supercritical pressure recently and several excellent review papers have been published. In the talk, we will focus on some turbulence modelling issues encountered in CFD simulations. The talk will first discuss some flow and heat transfer issues related to fluids at supercritical pressures and their potential implications in SCWR, and some recent developments in the understanding and modelling techniques of such problems, which will be followed by an outlook for some future developments.Factors which have a major influence on the flow and will be discussed are buoyancy and flow acceleration due to thermal expansion (both are due to density variations but involve different mechanisms) and the nonuniformity of other fluid properties. In addition, laminar-turbulent flow transition coupled with buoyancy and flow acceleration plays an important role in heat transfer effectiveness and wall temperature in the entrance region but such
SCDAP/RELAP5 Modeling of Heat Transfer and Flow Losses in Lower Head Porous Debris

International Nuclear Information System (INIS)

Siefken, Larry James; Coryell, Eric Wesley; Paik, Seungho; Kuo, Han Hsiung

1999-01-01

Designs are described for implementing models for calculating the heat transfer and flow losses in porous debris in the lower head of a reactor vessel. The COUPLE model in SCDAP/RELAP5 represents both the porous and nonporous debris that results from core material slumping into the lower head. Currently, the COUPLE model has the capability to model convective and radiative heat transfer from the surfaces of nonporous debris in a detailed manner and to model only in a simplistic manner the heat transfer from porous debris. In order to advance beyond the simplistic modeling for porous debris, designs are developed for detailed calculations of heat transfer and flow losses in porous debris. Correlations are identified for convective heat transfer in porous debris for the following modes of heat transfer; (1) forced convection to liquid, (2) forced convection to gas, (3) nucleate boiling, (4) transition boiling, and (5) film boiling. Interphase heat transfer is modeled in an approximate manner. Designs are described for models to calculate the flow losses and interphase drag of fluid flowing through the interstices of the porous debris, and to apply these variables in the momentum equations in the RELAP5 part of the code. Since the models for heat transfer and flow losses in porous debris in the lower head are designed for general application, a design is also described for implementation of these models to the analysis of porous debris in the core region. A test matrix is proposed for assessing the capability of the implemented models to calculate the heat transfer and flow losses in porous debris. The implementation of the models described in this report is expected to improve the COUPLE code calculation of the temperature distribution in porous debris and in the lower head that supports the debris. The implementation of these models is also expected to improve the calculation of the temperature and flow distribution in porous debris in the core region
Numerical study of the conjugate heat transfer in a horizontal pipe heated by Joulean effect

Directory of Open Access Journals (Sweden)

Touahri Sofiane

2012-01-01

Full Text Available The three dimensional mixed convection heat transfer in a electrically heated horizontal pipe conjugated to a thermal conduction through the entire solid thickness is investigated by taking into account the thermal dependence of the physical properties of the fluid and the outer heat losses. The model equations of continuity, momentum and energy are numerically solved by the finite volume method. The pipe thickness, the Prandtl and the Reynolds numbers are fixed while the Grashof number is varied from 104to107. The results obtained show that the dynamic and thermal fields for mixed convection are qualitatively and quantitatively different from those of forced convection, and the local Nusselt number at the interface solid-fluid is not uniform: it has considerable axial and azimuthally variations. The effect of physical variables of the fluid depending on temperature is significant, which justifies its inclusion. The heat transfer is quantified by the local and average Nusselt numbers. We found that the average Nusselt number of solid-fluid interface of the duct increases with the increase of Grashof number. We have equally found out that the heat transfer is improved thanks to the consideration of the thermo dependence of the physical properties. We have tried modelling the average Nusselt number as a function of Richardson number. With the parameters used, the heat transfer is quantified by the correlation: NuA=12.0753 Ri0.156
Numerical study on the heat transfer performance of non-Newtonian fluid flow in a manifold microchannel heat sink

International Nuclear Information System (INIS)

Li, Si-Ning; Zhang, Hong-Na; Li, Xiao-Bin; Li, Qian; Li, Feng-Chen; Qian, Shizhi; Joo, Sang Woo

2017-01-01

Highlights: • Heat transfer performance of non-Newtonian fluid flow in a MHS is studied. • Pseudo-plastic fluid flow can clearly promote the heat transfer efficiency in MMC. • Heat transfer enhancement is attributed to the emergence of secondary flow. • The heat transfer uniformity can also be improved by pseudo-plastic fluid flow. - Abstract: As the miniaturization and integration become the leading trend of the micro-electro-mechanical systems, it is of great significance to improve the microscaled heat transfer performance. This paper presents a three-dimensional (3D) numerical simulation on the flow characteristics and heat transfer performance of non-Newtonian fluid flow in a manifold microchannel (MMC) heat sink and traditional microchannel (TMC) heat sink. The non-Newtonian fluid was described by the power-law model. The analyses concentrated on the non-Newtonian fluid effect on the heat transfer performance, including the heat transfer efficiency and uniformity of temperature distribution, as well as the influence of inlet/outlet configurations on fluid flow and heat transfer. Comparing with Newtonian fluid flow, pseudo-plastic fluid could reduce the drag resistance in both MMC and TMC, while the dilatant fluid brought in quite larger drag resistance. For the heat transfer performance, the introduction of pseudo-plastic fluid flow greatly improved the heat transfer efficiency owing to the generation of secondary flow due to the shear-thinning property. Besides, the temperature distribution in MMC was more uniform by using pseudo-plastic fluid. Moreover, the inlet/outlet configuration was also important for the design and arrangement of microchannel heat sinks, since the present work showed that the maximum temperature was prone to locating in the corners near the inlet and outlet. This work provides guidance for optimal design of small-scale heat transfer devices in many cooling applications, such as biomedical chips, electronic systems, and
Survey of studies on the flow and heat transfer of two-component, two-phase flow of liquid metal in magnetic field

International Nuclear Information System (INIS)

Kumamaru, Hiroshige

1980-01-01

Brief review of the studies on the flow and heat transfer of two-component, two-phase flow of liquid metal in magnetic field is presented. R.J. Thome measured the distribution of void rate, slip ratio and pressure loss for the two-phase flow of NaK-N 2 under vertical magnetic field. The void rate distribution became even and the slip ratio increased with the increasing magnetic field. The experimental results of pressure loss was compared with the calculation by an equation derived from the homogeneous flow model. R.G. Owen et al. made the analytical studies of the MHD friction loss of two phase flow. Michiyoshi et al. made experimental studies on the hydrodynamic local properties of Hg-Ar two-phase flow of slug region in a vertically ascending tube under magnetic field, and Kimi et al. also made studies on the heat transfer of Hg-Ar flow under magnetic field. Saito et al. measured the slip ratio and pressure loss of NaK-N 2 flow. As a whole, it can be said that the average void rate decreases, and its distribution becomes even under magnetic field. The slip ratio increases, and the friction loss factor becomes nearly one. It was hard to make clear the heat transfer characteristics. (Kato, T.)
A study of the flow boiling heat transfer in a minichannel for a heated wall with surface texture produced by vibration-assisted laser machining

International Nuclear Information System (INIS)

Piasecka, Magdalena; Strąk, Kinga; Grabas, Bogusław; Maciejewska, Beata

2016-01-01

The paper presents results concerning flow boiling heat transfer in a vertical minichannel with a depth of 1.7 mm and a width of 16 mm. The element responsible for heating FC-72, which flowed laminarly in the minichannel, was a plate with an enhanced surface. Two types of surface textures were considered. Both were produced by vibration-assisted laser machining. Infrared thermography was used to record changes in the temperature on the outer smooth side of the plate. Two-phase flow patterns were observed through a glass pane. The main aim of the study was to analyze how the two types of surface textures affect the heat transfer coefficient. A two-dimensional heat transfer approach was proposed to determine the local values of the heat transfer coefficient. The inverse problem for the heated wall was solved using a semi-analytical method based on the Trefftz functions. The results are presented as relationships between the heat transfer coefficient and the distance along the minichannel length and as boiling curves. The experimental data obtained for the two types of enhanced heated surfaces was compared with the results recorded for the smooth heated surface. The highest local values of the heat transfer coefficient were reported in the saturated boiling region for the plate with the type 1 texture produced by vibration-assisted laser machining. (paper)
Investigation of heat transfer and flow using ribs within gas turbine blade cooling passage: Experimental and hybrid LES/RANS modeling

Science.gov (United States)

Kumar, Sourabh

Gas turbines are extensively used for aircraft propulsion, land based power generation and various industrial applications. Developments in innovative gas turbine cooling technology enhance the efficiency and power output, with an increase in turbine rotor inlet temperatures. These advancements of turbine cooling have allowed engine design to exceed normal material temperature limits. For internal cooling design, techniques for heat extraction from the surfaces exposed to hot stream are based on the increase of heat transfer areas and on promotion of turbulence of the cooling flow. In this study, it is obtained by casting repeated continuous V and broken V shaped ribs on one side of the two pass square channel into the core of blade. Despite extensive research on ribs, only few papers have validated the numerical data with experimental results in two pass channel. In the present study, detailed experimental investigation is carried out for two pass square channels with 180° turn. Detailed heat transfer distribution occurring in the ribbed passage is reported for steady state experiment. Four different combinations of 60° and Broken 60° V ribs in channel are considered. Thermocouples are used to obtain the temperature on the channel surface and local heat transfer coefficients are obtained for various Reynolds numbers, within the turbulent flow regime. Area averaged data are calculated in order to compare the overall performance of the tested ribbed surface and to evaluate the degree of heat transfer enhancement induced by the ribs with. Flow within the channels is characterized by heat transfer enhancing ribs, bends, rotation and buoyancy effects. Computational Fluid Dynamics (CFD) simulations were carried out for the same geometries using different turbulence models such as k-o Shear stress transport (SST) and Reynolds stress model (RSM). These CFD simulations were based on advanced computing in order to improve the accuracy of three dimensional metal
Numerical study on heat transfer characteristics of thermosyphon heat pipes using nanofluids

International Nuclear Information System (INIS)

Huminic, Gabriela; Huminic, Angel

2013-01-01

Highlights: • Numerical study of nanofluid heat transfer in thermosyphon heat pipes is performed. • Effect of nanoparticle concentration and operating temperature are studied. • Fe 2 O 3 –water nanofluid with 5.3% volume concentration shows the best performance. • Results show the improvement the thermal performances of thermosyphon heat pipe with nanofluids. - Abstract: In this work, a three-dimensional analysis is used to investigate the heat transfer of thermosyphon heat pipe using water and nanofluids as the working fluid. The study focused mainly on the effects of volume concentrations of nanoparticles and the operating temperature on the heat transfer performance of the thermosyphon heat pipe using the nanofluids. The analysis was performed for water and γ-Fe 2 O 3 nanoparticles, three volume concentrations of nanoparticles (0 vol.%, 2 vol.% and 5.3 vol.%) and four operating temperatures (60, 70, 80 and 90 °C). The numerical results show that the volume concentration of nanoparticles had a significant effect in reducing the temperature difference between the evaporator and condenser. Experimental and numerical results show qualitatively that the thermosyphon heat pipe using the nanofluid has better heat transfer characteristics than the thermosyphon heat pipe using water
Modeling of zero gravity venting: Studies of two-phase heat transfer under reduced gravity

Science.gov (United States)

Merte, H., Jr.

1986-01-01

The objective is to predict the pressure response of a saturated liquid-vapor system when undergoing a venting or depressurization process in zero gravity at low vent rates. An experimental investigation of the venting of cylindrical containers partially filled with initially saturated liquids was previously conducted under zero-gravity conditions and compared with an analytical model which incorporated the effect of interfacial mass transfer on the ullage pressure response during venting. A new model is presented to improve the estimation of the interfacial mass transfer. Duhammel's superposition integral is incorporated to approximate the transient temperature response of the interface, treating the liquid as a semi-infinite solid with conduction heat transfer. Account is also taken of the condensation taking place within the bulk of a saturated vapor as isentropic expansion takes place. Computational results are presented for the venting of R-11 from a given vessel and initial state for five different venting rates over a period of three seconds, and compared to prior NASA experiments. An improvement in the prediction of the final pressure takes place, but is still considerably below the measurements.
Heat transfer studies in waste repository design

International Nuclear Information System (INIS)

Boehm, R.F.; Chen, Y.T.; Izzeldin, A.; Kuharic, W.; Sudan, N.

1994-01-01

The main task of this project is the development of visualization methods in heat transfer through porous media. Experiments have been performed related to the determination of the wavelength that gives equality of the refractive indices of the porous material and the liquid. The work has been accomplished using the calibration setup consisting of a 2-in. long test cell filled with 2-mm diameter soda-lime glass beads. A supplemental task is an unsaturated flow experiment with heat transfer in porous media. For this work the medium of interest in quartz beads. Essentially two-dimensional flows of admitted water are able to be examined. During this quarter, the setup and calibration of the experimental instrumentation was done. Also the modification of the main experimental tank and the inflow system was carried out. Initial testing was done
Direct numerical simulations of flow and heat transfer over a circular cylinder at Re = 2000

NARCIS (Netherlands)

Vidya, Mahening Citra; Beishuizen, N.A.; van der Meer, Theodorus H.

2016-01-01

Unsteady direct numerical simulations of the flow around a circular cylinder have been performed at Re = 2000. Both two-dimensional and three-dimensional simulations were validated with laminar cold flow simulations and experiments. Heat transfer simulations were carried out and the time-averaged
2-dimensional numerical modeling of active magnetic regeneration

DEFF Research Database (Denmark)

Nielsen, Kaspar Kirstein; Pryds, Nini; Smith, Anders

2009-01-01

Various aspects of numerical modeling of Active Magnetic Regeneration (AMR) are presented. Using a 2-dimensional numerical model for solving the unsteady heat transfer equations for the AMR system, a range of physical effects on both idealized and non-idealized AMR are investigated. The modeled...

Heat and mass transfer and hydrodynamics in two-phase flows in nuclear power plants

International Nuclear Information System (INIS)

Styrikovich, M.A.; Polonskii, V.S.; Tsiklauri, G.V.

1986-01-01

This book examines nuclear power plant equipment from the point of view of heat and mass transfer and the behavior of impurities contained in water and in steam, with reference to real water regimes of nuclear power plants. The transfer processes of equipment are considered. Heat and mass transfer are analyzed in the pre-crisis regions of steam-generating passages with non-permeable surfaces, and in capillary-porous structures. Attention is given to forced convection boiling crises and top post-DNB heat transfer. Data on two-phase hydrodynamics in straight and curved channels are correlated and safety aspects of nuclear power plants are discussed
CHAP-2 heat-transfer analysis of the Fort St. Vrain reactor core

International Nuclear Information System (INIS)

Kotas, J.F.; Stroh, K.R.

1983-01-01

The Los Alamos National Laboratory is developing the Composite High-Temperature Gas-Cooled Reactor Analysis Program (CHAP) to provide advanced best-estimate predictions of postulated accidents in gas-cooled reactor plants. The CHAP-2 reactor-core model uses the finite-element method to initialize a two-dimensional temperature map of the Fort St. Vrain (FSV) core and its top and bottom reflectors. The code generates a finite-element mesh, initializes noding and boundary conditions, and solves the nonlinear Laplace heat equation using temperature-dependent thermal conductivities, variable coolant-channel-convection heat-transfer coefficients, and specified internal fuel and moderator heat-generation rates. This paper discusses this method and analyzes an FSV reactor-core accident that simulates a control-rod withdrawal at full power
Heat transfer at a beam port corner

International Nuclear Information System (INIS)

Krinsky, S.

Along the general run of the vacuum chamber synchrotron radiation strikes the wall at a glancing angle of about 5.6 0 . The heat source is well-approximated by a ribbon of uniform power density having a small vertical height and an infinite azimuthal length. The heat transfer problem reduces to one in two-dimensions and it has been considered in a previous note. At the corner of a beam port the angle of incidence becomes 90 0 , so the temperature rises much higher than elsewhere. Since the power density at the corner is not uniform in its azimuthal dependence, but is strongly peaked at the point of normal incidence, two-dimensional heat flow is not a good approximation. The rectangular 3d problem is considered. This is easily solved and yields a good first estimate of the temperature rise at the corner
Numerical Investigation of Jet Impingement Heat Transfer on a Flat plate

Directory of Open Access Journals (Sweden)

Asem Nabadavis

2016-12-01

Full Text Available The numerical investigation emphasizes on studying the heat transfer characteristics when a high velocity air jet impinges upon a flat plate having constant heat flux. Numerical analysis has been conducted by solving conservation equations of momentum, mass and energy with two equations based k- ε turbulence model to determine the wall temperature and Nu of the plate considering the flow to be incompressible. It was found from the investigation that the heat transfer rate increases with the increase of Reynolds number of the jet (Rej. It was also found that there is an optimum value for jet distance to nozzle diameter ratio (H/d for maximum heat transfer when all the other parameters were kept fixed. Similar results as above were found when two jets of air were used instead of one jet keeping the mass flow rate constant. For a two jets case it was also found that heat transfer rate over the surface increases when the jets are inclined outward compared to vertical and inward jets and also there exists an optimum angle of jet for maximum heat transfer. Further investigation was carried out for different jetto-jet separation distance for a twin jet impingement model where it was noted that heat transfer is more distributed in case of larger values of L and the rate of heat transfer increases as the separation between the jet increases till a certain point after which the rate of heat transfer decreases.
Turbulence modeling and surface heat transfer in a stagnation flow region

Science.gov (United States)

Wang, C. R.; Yeh, F. C.

1987-01-01

Analysis for the turbulent flow field and the effect of freestream turbulence on the surface heat transfer rate of a stagnation flow is presented. The emphasis is on modeling and its augmentation of surface heat transfer rate. The flow field considered is the region near the forward stagnation point of a circular cylinder in a uniform turbulent mean flow.
A computationally efficient method for full-core conjugate heat transfer modeling of sodium fast reactors

Energy Technology Data Exchange (ETDEWEB)

Hu, Rui, E-mail: rhu@anl.gov; Yu, Yiqi

2016-11-15

Highlights: • Developed a computationally efficient method for full-core conjugate heat transfer modeling of sodium fast reactors. • Applied fully-coupled JFNK solution scheme to avoid the operator-splitting errors. • The accuracy and efficiency of the method is confirmed with a 7-assembly test problem. • The effects of different spatial discretization schemes are investigated and compared to the RANS-based CFD simulations. - Abstract: For efficient and accurate temperature predictions of sodium fast reactor structures, a 3-D full-core conjugate heat transfer modeling capability is developed for an advanced system analysis tool, SAM. The hexagon lattice core is modeled with 1-D parallel channels representing the subassembly flow, and 2-D duct walls and inter-assembly gaps. The six sides of the hexagon duct wall and near-wall coolant region are modeled separately to account for different temperatures and heat transfer between coolant flow and each side of the duct wall. The Jacobian Free Newton Krylov (JFNK) solution method is applied to solve the fluid and solid field simultaneously in a fully coupled fashion. The 3-D full-core conjugate heat transfer modeling capability in SAM has been demonstrated by a verification test problem with 7 fuel assemblies in a hexagon lattice layout. Additionally, the SAM simulation results are compared with RANS-based CFD simulations. Very good agreements have been achieved between the results of the two approaches.
Heat transfer enhancement

International Nuclear Information System (INIS)

Hasatani, Masanobu; Itaya, Yoshinori

1985-01-01

In order to develop energy-saving techniques and new energy techniques, and also most advanced techniques by making industrial equipment with high performance, heat transfer performance frequently becomes an important problem. In addition, the improvement of conventional heat transfer techniques and the device of new heat transfer techniques are often required. It is most proper that chemical engineers engage in the research and development for enhancing heat transfer. The research and development for enhancing heat transfer are important to heighten heat exchange efficiency or to cool equipment for preventing overheat in high temperature heat transfer system. In this paper, the techniques of enhancing radiative heat transfer and the improvement of radiative heat transfer characteristics are reported. Radiative heat transfer is proportional to fourth power of absolute temperature, and it does not require any heat transfer medium, but efficient heat-radiation converters are necessary. As the techniques of enhancing radiative heat transfer, the increase of emission and absorption areas, the installation of emissive structures and the improvement of radiative characteristics are discussed. (Kako, I.)
"Nanotechnology Enabled Advanced Industrial Heat Transfer Fluids"

Energy Technology Data Exchange (ETDEWEB)

Dr. Ganesh Skandan; Dr. Amit Singhal; Mr. Kenneth Eberts; Mr. Damian Sobrevilla; Prof. Jerry Shan; Stephen Tse; Toby Rossmann

2008-06-12

ABSTRACT Nanotechnology Enabled Advanced industrial Heat Transfer Fluids” Improving the efficiency of Industrial Heat Exchangers offers a great opportunity to improve overall process efficiencies in diverse industries such as pharmaceutical, materials manufacturing and food processing. The higher efficiencies can come in part from improved heat transfer during both cooling and heating of the material being processed. Additionally, there is great interest in enhancing the performance and reducing the weight of heat exchangers used in automotives in order to increase fuel efficiency. The goal of the Phase I program was to develop nanoparticle containing heat transfer fluids (e.g., antifreeze, water, silicone and hydrocarbon-based oils) that are used in transportation and in the chemical industry for heating, cooling and recovering waste heat. Much work has been done to date at investigating the potential use of nanoparticle-enhanced thermal fluids to improve heat transfer in heat exchangers. In most cases the effect in a commercial heat transfer fluid has been marginal at best. In the Phase I work, we demonstrated that the thermal conductivity, and hence heat transfer, of a fluid containing nanoparticles can be dramatically increased when subjected to an external influence. The increase in thermal conductivity was significantly larger than what is predicted by commonly used thermal models for two-phase materials. Additionally, the surface of the nanoparticles was engineered so as to have a minimal influence on the viscosity of the fluid. As a result, a nanoparticle-laden fluid was successfully developed that can lead to enhanced heat transfer in both industrial and automotive heat exchangers
Two phase nonequilibrium heat transfer in the TRAC-PD2 code

International Nuclear Information System (INIS)

Mandell, D.A.; Liles, D.R.

1980-01-01

TRAC is a best-estimate, multidimensional, nonequilibrium computer code intended for the analysis of loss-of-coolant accidents (LOCA's) in light water reactors. TRAC-PD2 is the third, detailed, pressurized water reactor version of the code. The TRAC code is modular both by components and by function. That is, vessels, pipes, pumps, etc. can be coupled together in any manner in order to simulate a reactor or a particular experimental facility. Individual physical phenomena are also coded in separate subroutines. This paper discusses the wall to fluid heat transfer coefficient correlations, the interfacial heat transfer models, and presents results for several experimental facilities
Flow and heat transfer of MHD graphene oxide-water nanofluid between two non-parallel walls

Directory of Open Access Journals (Sweden)

Azimi Mohammadreza

2017-01-01

Full Text Available The steady 2-D heat transfer and flow between two non-parallel walls of a graphene oxide nanofluid in presence of uniform magnetic field are investigated in this paper. The analytical solution of the non-linear problem is obtained by Galerkin optimal homotopy asymptotic method. At first a similarity transformation is used to reduce the partial differential equations modeling the flow and heat transfer to ordinary non-linear differential equation systems containing the semi angle between the plate’s parameter, Reynolds number, the magnetic field strength, nanoparticle volume fraction, Eckert and Prandtl numbers. Finally, the obtained analytical results have been compared with results achieved from previous works in some cases.
Heat and mass transfer in a reforming catalyst bed. Analytical prediction of distributions in the catalyst bed; Kaishitsu shokubaiso ni okeru netsu oyobi busshitsu ido. Suchi kaiseki ni yoru sonai bunpu no yosoku

Energy Technology Data Exchange (ETDEWEB)

Usami, Y [Tokyo Electric Power Co. Inc., Tokyo (Japan); Fukusako, S; Yamada, M [Hokkaido University, Sapporo (Japan)

2000-01-25

Heat and mass transfer characteristics within a reforming catalyst bed have been analytically investigated. A numerical analysis was carried out in a two-dimensional steady-state model of reforming catalyst layer. Reforming tube was filled with catalyst and the tube wall was uniformly heated, a mixture of steam and methane was reformed through the catalyst bed. Predicted temperature, formed gas composition, methane conversion rate, and heat transfer coefficient distributions in the catalyst layer showed good agreement with experimental data. The effects of space velocity, steam carbon molar ratio, and wall temperature on the heat transfer coefficient were analytically presented. From temperature and composition distributions simulated by two-dimensional analysis, the effects of these factors above mentioned and diffusion on the transport phenomena were qualitatively predicted. (author)
The experimental study of heat transfer around molds inside a model autoclave

Science.gov (United States)

Ghamlouch, Taleb; Roux, Stéphane; Lefèvre, Nicolas; Bailleul, Jean-Luc; Sobotka, Vincent

2018-05-01

The temperature distribution within composite parts manufactured inside autoclaves plays a key role in determining the parts quality at the end of the curing cycle. Indeed, heat transfer between the parts and the surroundings inside an autoclave is strongly coupled with the flow field around the molds and can be modeled through the convective heat transfer coefficient (HTC). The aerodynamically unsuitable geometry of the molds generates complex turbulent non-uniform flows around them accompanied with the presence of dead zones. This heterogeneity can imply non-uniform convective heat transfers leading to temperature gradients inside parts that can be prejudicial. Given this fact, the purpose of this study is to perform experimental measurements in order to describe the flow field and the convective heat transfer behavior around representative industrial molds installed inside a home-made model. A key point of our model autoclave is the ease of use of non-intrusive measuring instruments: the Particle Image Velocimetry (PIV) technique and infrared imaging camera for the study of the flow field and the heat transfer coefficient distribution around the molds respectively. The experimental measurements are then compared to computational fluid dynamics (CFD) calculations performed on the computer code ANSYS Fluent 16.0®. This investigation has revealed, as expected, a non-uniform distribution of the convective heat transfer coefficient around the molds and therefore the presence of thermal gradients which can reduce the composite parts quality during an autoclave process. A good agreement has been achieved between the experimental and the numerical results leading then to the validation of the performed numerical simulations.
Heat transfer, condensation and fog formation in crossflow plastic heat exchangers

NARCIS (Netherlands)

Brouwers, H.J.H.

1996-01-01

In this paper heat transfer of air-water-vapour mixtures in plastic crossflow heat exchangers is studied theoretically and experimentally. First, a model for heat transfer without condensation is derived, resulting in a set of classical differential equations. Subsequently, heat transfer with wall
Bayesian inference of the heat transfer properties of a wall using experimental data

KAUST Repository

Iglesias, Marco

2016-01-06

A hierarchical Bayesian inference method is developed to estimate the thermal resistance and volumetric heat capacity of a wall. We apply our methodology to a real case study where measurements are recorded each minute from two temperature probes and two heat flux sensors placed on both sides of a solid brick wall along a period of almost five days. We model the heat transfer through the wall by means of the one-dimensional heat equation with Dirichlet boundary conditions. The initial/boundary conditions for the temperature are approximated by piecewise linear functions. We assume that temperature and heat flux measurements have independent Gaussian noise and derive the joint likelihood of the wall parameters and the initial/boundary conditions. Under the model assumptions, the boundary conditions are marginalized analytically from the joint likelihood. ApproximatedGaussian posterior distributions for the wall parameters and the initial condition parameter are obtained using the Laplace method, after incorporating the available prior information. The information gain is estimated under different experimental setups, to determine the best allocation of resources.
Two-phase flow patterns and their relationship to two-phase heat transfer

International Nuclear Information System (INIS)

Hewitt, G.F.

1977-01-01

The objective of this lecture was to discuss the general nature of two phase flows, to define the various regimes of flow and to discuss the influence of these regimes on the heat transfer processes taking place. The methods of regime delineation are briefly described and regime descriptions introduced for both vertical and horizontal flows in tubes. ''Flow regime maps'' have been widely used as an aid to determination of the regime which occurs in a given situation. Some of the more widely used maps are described and the limitations of this approach discussed. There have been many attempts to obtain a better phenomenological description of two phase flow patterns. In this lecture, these attempts will be reviewed in the context of the bubble/plug, plug/churn and churn/annular flow transitions in vertical flow. The latter two transitions are related to the flooding/flow reversal phenomena. For horizontal flows, recent work on the onset of slugging will be reviewed. In flows with evaporation or condensation, the situation is influenced by departures from thermodynamic equilibrium and the types of departure observed are discuss briefly. Flow patterns and their relationships with heat transfer regimes are then reviewed for the case of condensation in horizontal tubes and evaporation in vertical tubes
Numerical simulation of convection and heat transfer in Czochralski crystal growth by multiple-relaxation-time LBM

Science.gov (United States)

Liu, Ding; Huang, Weichao; Zhang, Ni

2017-07-01

A two-dimensional axisymmetric swirling model based on the lattice Boltzmann method (LBM) in a pseudo Cartesian coordinate system is posited to simulate Czochralski (Cz) crystal growth in this paper. Specifically, the multiple-relaxation-time LBM (MRT-LBM) combined with the finite difference method (FDM) is used to analyze the melt convection and heat transfer in the process of Cz crystal growth. An incompressible axisymmetric swirling MRT-LB D2Q9 model is applied to solve for the axial and radial velocities by inserting thermal buoyancy and rotational inertial force into the two-dimensional lattice Boltzmann equation. In addition, the melt temperature and the azimuthal velocity are solved by MRT-LB D2Q5 models, and the crystal temperature is solved by FDM. The comparison results of stream functions values of different methods demonstrate that our hybrid model can be used to simulate the fluid-thermal coupling in the axisymmetric swirling model correctly and effectively. Furthermore, numerical simulations of melt convection and heat transfer are conducted under the conditions of high Grashof (Gr) numbers, within the range of 105 ˜ 107, and different high Reynolds (Re) numbers. The experimental results show our hybrid model can obtain the exact solution of complex crystal-growth models and analyze the fluid-thermal coupling effectively under the combined action of natural convection and forced convection.
Experimental studies on heat transfer to supercritical water in 2 × 2 rod bundle with two channels

International Nuclear Information System (INIS)

Gu, H.Y.; Hu, Z.X.; Liu, D.; Xiao, Y.; Cheng, X.

2015-01-01

Highlights: • Heat transfer to supercritical water in a 2 × 2 rod bundle is investigated. • Effects of system parameters on heat transfer in bundle are analyzed. • The test data were compared with twenty heat transfer correlations. - Abstract: The experiment of heat transfer to supercritical water in 2 × 2 rod bundle is performed at Shanghai Jiao Tong University. The test section consists of two channels separated by a square steel assembly box with rounded corners. Water flows downward in the first channel and then turns upward in the second channel to cool the 2 × 2 rod bundle installed inside the assembly box. The bundle consists of four heated rods of 10 mm in O.D. and 1.18 in pitch-to-diameter ratio. The fluid enthalpy in the first channel increases due to the heat transfer through the assembly box when flowing downward. The minimum fluid enthalpy increase in the first channel appears at the pseudo-critical region due to the small temperature difference between the two channels. Effects of various parameters on heat transfer behavior inside the 2 × 2 rod bundle are similar to those observed in tube or annuli. No special phenomenon in heat transfer is observed during the mass flux and power transient. The steady-state heat transfer correlation is applicable to predict the heat transfer in the mass or power transient sequence. In addition, the importance of several dimensionless numbers and the accuracy of 20 heat transfer correlations are assessed. It is concluded that the buoyancy parameter proposed by Cheng et al. (2009) shows unique effect on heat transfer coefficient. Among the 20 selected heat transfer correlations, the correlations of Jackson and Fewster (1975) and Bishop et al. (1964) give the best predictions when compared with the experimental data
Modeling of Heat Transfer in Rooms in the Modelica "Buildings" Library

Energy Technology Data Exchange (ETDEWEB)

Wetter, Michael [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Zuo, Wangda [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Nouidui, Thierry Stephane [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

2011-11-01

This paper describes the implementation of the room heat transfer model in the free open-source Modelica \\Buildings" library. The model can be used as a single room or to compose a multizone building model. We discuss how the model is decomposed into submodels for the individual heat transfer phenomena. We also discuss the main physical assumptions. The room model can be parameterized to use different modeling assumptions, leading to linear or non-linear differential algebraic systems of equations. We present numerical experiments that show how these assumptions affect computing time and accuracy for selected cases of the ANSI/ASHRAE Standard 140- 2007 envelop validation tests.
A general one-dimensional model for conduction-controlled rewetting of a surface

International Nuclear Information System (INIS)

Elias, E.; Yadigaroglu, G.

1977-01-01

A computer-oriented analytical method for predicting the rewetting rate of a hot dry wall is proposed. The wall, which is modeled as a thin flat plate with internal heat generation, receives a variable heat flux from one side while it is cooled from the other side. The model accounts for the large variations of the heat transfer coefficient near the wet front and for the temperature dependence of the thermal and physical properties of the wall. The one-dimensional heat-conduction equation is solved by dividing the quenching zone into small segments of arbitrary temperature increment and constant properties and heat transfer coefficient. A trial-and-error method is developed to predict the velocity of the wet front, the length of the quenching zone and the temperature profile. The one-dimensional models of other authors can be obtained as particular cases of the present model. (Auth.)
Solution of the two- dimensional heat equation for a rectangular plate

Directory of Open Access Journals (Sweden)

Nurcan BAYKUŞ SAVAŞANERİL

2015-11-01

Full Text Available Laplace equation is a fundamental equation of applied mathematics. Important phenomena in engineering and physics, such as steady-state temperature distribution, electrostatic potential and fluid flow, are modeled by means of this equation. The Laplace equation which satisfies boundary values is known as the Dirichlet problem. The solutions to the Dirichlet problem form one of the most celebrated topics in the area of applied mathematics. In this study, a novel method is presented for the solution of two-dimensional heat equation for a rectangular plate. In this alternative method, the solution function of the problem is based on the Green function, and therefore on elliptic functions.

The effect of plate heat exchanger’s geometry on heat transfer

Directory of Open Access Journals (Sweden)

Oana GIURGIU

2014-11-01

Full Text Available The study presents further Computational Fluid Dynamics (CFD numerical analysis for two models of plate heat exchangers. Comparatively was studied the influence of geometric characteristics of plates on the intensification process of heat exchange. For this purpose, it was examined the distribution of velocity and temperatures fields on active plate height. Heat transfer characteristics were analysed through the variation of mass flow on the primary heat agent.
Multiphysics Numerical Modeling of a Fin and Tube Heat Exchanger

DEFF Research Database (Denmark)

Singh, Shobhana; Sørensen, Kim; Condra, Thomas Joseph

2015-01-01

In the present research work, a modeling effort to predict the performance of a liquid-gas type fin and tube heat exchanger design is made. Three dimensional (3D) steady state numerical model is developed using commercial software COMSOL Multiphysics based on finite element method (FEM......). For the purposes here, only gas flowing over the fin side is simulated assuming constant inner tube wall temperature. The study couples conjugate heat transfer mechanism with turbulent flow in order to describe the temperature and velocity profile. In addition, performance characteristics of the heat exchanger...... design in terms of heat transfer and pressure loss are determined by parameters such as overall heat transfer coefficient, Colburn j-factor, flow resistance factor, and efficiency index. The model provides useful insights necessary for optimization of heat exchanger design....
Modelling of the processes of heat and mass transfer in adiabatic steam and drop flows

International Nuclear Information System (INIS)

Andrizhievskij, A.A.; Mikhalevich, A.A.; Nesterenko, V.B.; Trifonov, A.G.

1983-01-01

The mathematical models for investigating the local and integral characteristics of heat and mass transfer processes during simultaneous motion of adiabatic steam and drop flow and a flux of impurity particles are given. The mathematical model is constrUcted on the basis of one-dimensional stationary eqUations of conservation of mass, thermal energy and momentum of liquid and vapor phases. Dispersion composition of condensed moisture is described by the Nukiyama-Tanasava distribution function formed taking into account the Veber number critical value. Equations of motion and mass balance conservation for impurity particles are included into the mathematical model. These equations are considered as additional inactive phase
A stydy on the heat transfer characteristics in the composite heat pipe as modeling turbine rotor

International Nuclear Information System (INIS)

Kwon, Sun Sok; Jang, Yeong Suc; Yoo, Byung Wook

1993-01-01

The purpose of this research is to study the characteristics of heat transfer in composite rotary heat pipe as modeled turbine rotating by a finite element analysis and experiment. Nu number, Re number, Pr number and dimensionless condensate layer thickness by thermal input and revolutions per minute were given as analysis factors. The comparison between calculated and experimental data showed similar tendency. Therefore the analysis method may be useful to predict the performance of composite heat pipe. The resistance on heat pipe showed the best effect of heat transfer by film condensation, by decreasing film condensation, the heat transfer rate from condenser was increased rapidly. The dimensionless condensate layer thickness according to Re number at given Pr number showed constant values, the dimensionless condensate layer thickness is proportionate to the square root of inverse of revolution number per minute. In this study Nu = A(δ(ω/ν) -1/2 Re B ) is used to the convection heat transfer coefficient and A = 0.963, B = 0.5025 were obtained as analysis predicts. (Author)
HEAT TRANSFER ANALYSIS FOR FIXED CST AND RF COLUMNS

International Nuclear Information System (INIS)

Lee, S

2007-01-01

In support of a small column ion exchange (SCIX) process for the Savannah River Site waste processing program, transient and steady state two-dimensional heat transfer models have been constructed for columns loaded with cesium-saturated crystalline silicotitanate (CST) or spherical Resorcinol-Formaldehyde (RF) beads and 6 molar sodium tank waste supernate. Radiolytic decay of sorbed cesium results in heat generation within the columns. The models consider conductive heat transfer only with no convective cooling and no process flow within the columns (assumed column geometry: 27.375 in ID with a 6.625 in OD center-line cooling pipe). Heat transfer at the column walls was assumed to occur by natural convection cooling with 35 C air. A number of modeling calculations were performed using this computational heat transfer approach. Minimal additional calculations were also conducted to predict temperature increases expected for salt solution processed through columns of various heights at the slowest expected operational flow rate of 5 gpm. Results for the bounding model with no process flow and no active cooling indicate that the time required to reach the boiling point of ∼130 C for a CST-salt solution mixture containing 257 Ci/liter of Cs-137 heat source (maximum expected loading for SCIX applications) at 35 C initial temperature is about 6 days. Modeling results for a column actively cooled with external wall jackets and the internal coolant pipe (inlet coolant water temperature: 25 C) indicate that the CST column can be maintained non-boiling under these conditions indefinitely. The results also show that the maximum temperature of an RF-salt solution column containing 133 Ci/liter of Cs-137 (maximum expected loading) will never reach boiling under any conditions (maximum predicted temperature without cooling: 88 C). The results indicate that a 6-in cooling pipe at the center of the column provides the most effective cooling mechanism for reducing the maximum
Heat transfer and hydrodynamics of nonstationary dispersed-film flow in complex shape channels

International Nuclear Information System (INIS)

Nigmatulin, B.I.; Klebanov, L.A.; Kroshilin, A.E.; Kroshilin, V.E.

1980-01-01

The mathematical model has been used to investigate the dispersed-film regime of a liquid flow and condition for the appearance of heat transfer crisis. One-dimensional motion equations are used for each component of the mixture. The model developed is used to describe the hydrodynamics and the crisis of heat transfer in rod bundles and round tubes under stationary and nonstationary conditions. The account of a separate flow of a liquid film and a vapourdrop nucleus permits to describe the main regularities of a dispersed film flow. A good agreement of calculation and experimental results is obtained [ru
Theoretical study of evaporation heat transfer in horizontal microfin tubes: stratified flow model

Energy Technology Data Exchange (ETDEWEB)

Honda, H; Wang, Y S [Kyushu Univ., Inst. for Materials Chemistry and Engineering, Kasuga, Fukuoka (Japan)

2004-08-01

The stratified flow model of evaporation heat transfer in helically grooved, horizontal microfin tubes has been developed. The profile of stratified liquid was determined by a theoretical model previously developed for condensation in horizontal microfin tubes. For the region above the stratified liquid, the meniscus profile in the groove between adjacent fins was determined by a force balance between the gravity and surface tension forces. The thin film evaporation model was applied to predict heat transfer in the thin film region of the meniscus. Heat transfer through the stratified liquid was estimated by using an empirical correlation proposed by Mori et al. The theoretical predictions of the circumferential average heat transfer coefficient were compared with available experimental data for four tubes and three refrigerants. A good agreement was obtained for the region of Fr{sub 0}<2.5 as long as partial dry out of tube surface did not occur. (Author)
PORFLO - a continuum model for fluid flow, heat transfer, and mass transport in porous media. Model theory, numerical methods, and computational tests

International Nuclear Information System (INIS)

Runchal, A.K.; Sagar, B.; Baca, R.G.; Kline, N.W.

1985-09-01

Postclosure performance assessment of the proposed high-level nuclear waste repository in flood basalts at Hanford requires that the processes of fluid flow, heat transfer, and mass transport be numerically modeled at appropriate space and time scales. A suite of computer models has been developed to meet this objective. The theory of one of these models, named PORFLO, is described in this report. Also presented are a discussion of the numerical techniques in the PORFLO computer code and a few computational test cases. Three two-dimensional equations, one each for fluid flow, heat transfer, and mass transport, are numerically solved in PORFLO. The governing equations are derived from the principle of conservation of mass, momentum, and energy in a stationary control volume that is assumed to contain a heterogeneous, anisotropic porous medium. Broad discrete features can be accommodated by specifying zones with distinct properties, or these can be included by defining an equivalent porous medium. The governing equations are parabolic differential equations that are coupled through time-varying parameters. Computational tests of the model are done by comparisons of simulation results with analytic solutions, with results from other independently developed numerical models, and with available laboratory and/or field data. In this report, in addition to the theory of the model, results from three test cases are discussed. A users' manual for the computer code resulting from this model has been prepared and is available as a separate document. 37 refs., 20 figs., 15 tabs
Generalisation of two-layer turbulent model for passive cooling in a channel

International Nuclear Information System (INIS)

Bennacer, R.; Hammami, T.; Mohamad, A.A.; Beji, H.

2003-01-01

Turbulent natural convection still under improvement and no perfect compromise exist. The near wall region modelisation poses numerical difficulties and current modeling are either expensive or lack universality. Uncertainness in evaluating the good heat transfer rate can be catastrophically in causing local overheat and materials destruction which can be of heavy consequence as cooling nuclear component (rodes). Using the recent DNS done on natural convection flow in an infinite channel differentially heated for (10 4 6 ) a scaling analysis is developed and a one-equation near-wall turbulence model is deduced (inner layer). The inner model is coupled with a Low Reynolds Model (LRM) in the outer region (second layer) and applied to calculate natural flow for different Ra numbers. It yields good performance, computation time reduction and much better heat transfer prediction compared to the diffusive Jones Launder LRM. The efficiency is tested in one-dimensional and two-dimensional case. (author)
Cryogenic heat transfer

CERN Document Server

Barron, Randall F

2016-01-01

Cryogenic Heat Transfer, Second Edition continues to address specific heat transfer problems that occur in the cryogenic temperature range where there are distinct differences from conventional heat transfer problems. This updated version examines the use of computer-aided design in cryogenic engineering and emphasizes commonly used computer programs to address modern cryogenic heat transfer problems. It introduces additional topics in cryogenic heat transfer that include latent heat expressions; lumped-capacity transient heat transfer; thermal stresses; Laplace transform solutions; oscillating flow heat transfer, and computer-aided heat exchanger design. It also includes new examples and homework problems throughout the book, and provides ample references for further study.
Heat engine in the three-dimensional spacetime

Energy Technology Data Exchange (ETDEWEB)

Mo, Jie-Xiong [Institute of Theoretical Physics, Lingnan Normal University,Zhanjiang, 524048, Guangdong (China); Department of Physics, Lingnan Normal University,Zhanjiang, 524048, Guangdong (China); Liang, Feng [Department of Physics, Lingnan Normal University,Zhanjiang, 524048, Guangdong (China); Li, Gu-Qiang [Institute of Theoretical Physics, Lingnan Normal University,Zhanjiang, 524048, Guangdong (China); Department of Physics, Lingnan Normal University,Zhanjiang, 524048, Guangdong (China)

2017-03-02

We define a kind of heat engine via three-dimensional charged BTZ black holes. This case is quite subtle and needs to be more careful. The heat flow along the isochores does not equal to zero since the specific heat C{sub V}≠0 and this point completely differs from the cases discussed before whose isochores and adiabats are identical. So one cannot simply apply the paradigm in the former literatures. However, if one introduces a new thermodynamic parameter associated with the renormalization length scale, the above problem can be solved. We obtain the analytical efficiency expression of the three-dimensional charged BTZ black hole heat engine for two different schemes. Moreover, we double check with the exact formula. Our result presents the first specific example for the sound correctness of the exact efficiency formula. We argue that the three-dimensional charged BTZ black hole can be viewed as a toy model for further investigation of holographic heat engine. Furthermore, we compare our result with that of the Carnot cycle and extend the former result to three-dimensional spacetime. In this sense, the result in this paper would be complementary to those obtained in four-dimensional spacetime or ever higher. Last but not the least, the heat engine efficiency discussed in this paper may serve as a criterion to discriminate the two thermodynamic approaches introduced in ref. https://www.doi.org/10.1103/PhysRevD.92.124069 and our result seems to support the approach which introduces a new thermodynamic parameter R=r{sub 0}.
Finite Element Modeling in 3D of the Impact of Superfluid Helium Filled Micro-channels on the Heat Transfer through LHC Type Cable Insulation

CERN Document Server

Bielert, E; ten Kate, H

2012-01-01

For a future luminosity upgrade of CERN’s Large Hadron Collider, a drastically improved heat removal in the inner triplet quadrupole magnets is required. One of the necessary improvements involves the cable insulation. A porous all-polyimide insulation scheme has been proposed recently. Essentially the insulation features a network of micro channels filled with superfluid helium that significantly increases the heat transfer through the insulation layer. A three dimensional Finite Element model required to simulate and study the enhanced heat transfer through the micro channels is presented here. The thermal coupling between heated cable and helium as well as the heat flux through the micro-channels are investigated. The model is validated by comparison of results with published measured data. Finally a sensitivity analysis is performed concerning the stability of the cables in magnet windings.
Development and preliminary assessment of the wall condensation heat transfer models for the SPACE code

International Nuclear Information System (INIS)

Park, Hyun Sik; Choi, Ki Yong; Moon, Sang Ki; Kim, Jung Woo; Kim, Kyung Doo

2009-01-01

The wall condensation heat transfer models are developed for the SPACE code and are assessed for various condensation conditions. Both default and alternative models were selected through an extensive literature survey. For a pure steam condensation, a maximum value among the Nusselt, Chato, and Shah's correlations is used in order to consider the geometric and turbulent effects. In the presence of non-condensable gases, the Colburn-Hougen's diffusion model was used as a default model and a non-iterative condensation model proposed by No and Park was selected as an alternative model. The wall condensation heat transfer models were assessed preliminarily by using arbitrary test conditions. Both wall condensation models could simulate the heat transfer coefficients and heat fluxes in the vertical, horizontal and turbulent conditions quite reasonably for a pure steam condensation. Both the default and alternative wall condensation models were also verified for the condensation heat transfer coefficient and heat flux in the presence of noncondensable gas. However, some improvements and further detailed verification are necessary for the condensation phenomena in the presence of noncondensable gas
A Numerical Analysis of Heat Transfer and Effectiveness on Film Cooled Turbine Blade Tip Models

Science.gov (United States)

Ameri, A. A.; Rigby, D. L.

1999-01-01

A computational study has been performed to predict the distribution of convective heat transfer coefficient on a simulated blade tip with cooling holes. The purpose of the examination was to assess the ability of a three-dimensional Reynolds-averaged Navier-Stokes solver to predict the rate of tip heat transfer and the distribution of cooling effectiveness. To this end, the simulation of tip clearance flow with blowing of Kim and Metzger was used. The agreement of the computed effectiveness with the data was quite good. The agreement with the heat transfer coefficient was not as good but improved away from the cooling holes. Numerical flow visualization showed that the uniformity of wetting of the surface by the film cooling jet is helped by the reverse flow due to edge separation of the main flow.
Photon-exchange energy transfer of an electron–hole plasma between quasi-two-dimensional semiconductor layers

International Nuclear Information System (INIS)

Lyo, S.K.

2012-01-01

Photon-mediated energy transfer is shown to play an important role for transfer of an electron–hole plasma between two quasi-two-dimensional quantum wells separated by a wide barrier. The magnitude and the dependence of the transfer rate of an electron–hole plasma on the temperature, the well-to-well distance, and the plasma density are compared with those of the standard Förster (i.e., dipolar) rate and also with the exciton transfer rate. The plasma transfer rate through the photon-exchange mechanism decays very slowly as a function of the well-to-well distance and is larger than the dipolar rate except for short distances. The transfer rate of plasmas saturates at high densities and decays rapidly with the temperature. - Highlights: ► We study energy transfer (ET) between two two-dimensional semiconductor quantum wells. ► We compare the ET rates of an electron–hole plasma (at a high density) and Mott excitons. ► We show that the proposed photon-exchange rate is practically dominant over the Förster rate. ► We examine the dependences of the ET rate on the temperature, density, and well-to-well distance.
Numerical simulation of potato slices drying using a two-dimensional finite element model

Directory of Open Access Journals (Sweden)

Beigi Mohsen

2017-01-01

Full Text Available An experimental and numerical study was conducted to investigate the process of potato slices drying. For simulating the moisture transfer in the samples and predict the dehydration curves, a two-dimensional finite element model was developed and programmed in Compaq Visual Fortran, version 6.5. The model solved the Fick’s second law for slab in a shrinkage system to calculate the unsteady two-dimensional moisture transmission in rectangular coordinates (x,y. Moisture diffusivity and moisture transfer coefficient were determined by minimizing the sum squares of residuals between experimental and numerical predicted data. Shrinkage kinetics of the potato slices during dehydration was determined experimentally and found to be a linear function of removed moisture. The determined parameters were used in the mathematical model. The predicted moisture content values were compared to the experimental data and the validation results demonstrated that the dynamic drying curves were predicted by the methodology very well.
A three-dimensional thermal-fluid analysis of flat heat pipes

Energy Technology Data Exchange (ETDEWEB)

Xiao, Bin; Faghri, Amir [Department of Mechanical Engineering, University of Connecticut, 261 Glenbrook Road, Unit 2337, Storrs, CT 06269 (United States)

2008-06-15

A detailed, three-dimensional model has been developed to analyze the thermal hydrodynamic behaviors of flat heat pipes without empirical correlations. The model accounts for the heat conduction in the wall, fluid flow in the vapor chambers and porous wicks, and the coupled heat and mass transfer at the liquid/vapor interface. The flat pipes with and without vertical wick columns in the vapor channel are intensively investigated in the model. Parametric effects, including evaporative heat input and size on the thermal and hydrodynamic behavior in the heat pipes, are investigated. The results show that, the vertical wick columns in the vapor core can improve the thermal and hydrodynamic performance of the heat pipes, including thermal resistance, capillary limit, wall temperature, pressure drop, and fluid velocities due to the enhancement of the fluid/heat mechanism form the bottom condenser to the top evaporator. The results predict that higher evaporative heat input improves the thermal and hydrodynamic performance of the heat pipe, and shortening the size of heat pipe degrades the thermal performance of the heat pipe. (author)
A new heat transfer analysis in machining based on two steps of 3D finite element modelling and experimental validation

Science.gov (United States)

Haddag, B.; Kagnaya, T.; Nouari, M.; Cutard, T.

2013-01-01

Modelling machining operations allows estimating cutting parameters which are difficult to obtain experimentally and in particular, include quantities characterizing the tool-workpiece interface. Temperature is one of these quantities which has an impact on the tool wear, thus its estimation is important. This study deals with a new modelling strategy, based on two steps of calculation, for analysis of the heat transfer into the cutting tool. Unlike the classical methods, considering only the cutting tool with application of an approximate heat flux at the cutting face, estimated from experimental data (e.g. measured cutting force, cutting power), the proposed approach consists of two successive 3D Finite Element calculations and fully independent on the experimental measurements; only the definition of the behaviour of the tool-workpiece couple is necessary. The first one is a 3D thermomechanical modelling of the chip formation process, which allows estimating cutting forces, chip morphology and its flow direction. The second calculation is a 3D thermal modelling of the heat diffusion into the cutting tool, by using an adequate thermal loading (applied uniform or non-uniform heat flux). This loading is estimated using some quantities obtained from the first step calculation, such as contact pressure, sliding velocity distributions and contact area. Comparisons in one hand between experimental data and the first calculation and at the other hand between measured temperatures with embedded thermocouples and the second calculation show a good agreement in terms of cutting forces, chip morphology and cutting temperature.
Generalized irreversible heat-engine experiencing a complex heat-transfer law

International Nuclear Information System (INIS)

Chen Lingen; Li Jun; Sun Fengrui

2008-01-01

The fundamental optimal relation between optimal power-output and efficiency of a generalized irreversible Carnot heat-engine is derived based on a generalized heat-transfer law, including a generalized convective heat-transfer law and a generalized radiative heat-transfer law, q ∝ (ΔT n ) m . The generalized irreversible Carnot-engine model incorporates several internal and external irreversibilities, such as heat resistance, bypass heat-leak, friction, turbulence and other undesirable irreversibility factors. The added irreversibilities, besides heat resistance, are characterized by a constant parameter and a constant coefficient. The effects of heat-transfer laws and various loss terms are analyzed. The results obtained corroborate those in the literature
Study of Variable Turbulent Prandtl Number Model for Heat Transfer to Supercritical Fluids in Vertical Tubes

Science.gov (United States)

Tian, Ran; Dai, Xiaoye; Wang, Dabiao; Shi, Lin

2018-06-01

In order to improve the prediction performance of the numerical simulations for heat transfer of supercritical pressure fluids, a variable turbulent Prandtl number (Prt) model for vertical upward flow at supercritical pressures was developed in this study. The effects of Prt on the numerical simulation were analyzed, especially for the heat transfer deterioration conditions. Based on the analyses, the turbulent Prandtl number was modeled as a function of the turbulent viscosity ratio and molecular Prandtl number. The model was evaluated using experimental heat transfer data of CO2, water and Freon. The wall temperatures, including the heat transfer deterioration cases, were more accurately predicted by this model than by traditional numerical calculations with a constant Prt. By analyzing the predicted results with and without the variable Prt model, it was found that the predicted velocity distribution and turbulent mixing characteristics with the variable Prt model are quite different from that predicted by a constant Prt. When heat transfer deterioration occurs, the radial velocity profile deviates from the log-law profile and the restrained turbulent mixing then leads to the deteriorated heat transfer.

Modelling of convective heat and mass transfer in rotating flows

CERN Document Server

Shevchuk, Igor V

2016-01-01

This monograph presents results of the analytical and numerical modeling of convective heat and mass transfer in different rotating flows caused by (i) system rotation, (ii) swirl flows due to swirl generators, and (iii) surface curvature in turns and bends. Volume forces (i.e. centrifugal and Coriolis forces), which influence the flow pattern, emerge in all of these rotating flows. The main part of this work deals with rotating flows caused by system rotation, which includes several rotating-disk configurations and straight pipes rotating about a parallel axis. Swirl flows are studied in some of the configurations mentioned above. Curvilinear flows are investigated in different geometries of two-pass ribbed and smooth channels with 180° bends. The author demonstrates that the complex phenomena of fluid flow and convective heat transfer in rotating flows can be successfully simulated using not only the universal CFD methodology, but in certain cases by means of the integral methods, self-similar and analyt...
Potential for PET scanning as an aid to heat transfer modeling

International Nuclear Information System (INIS)

Samulski, T.V.; Harris, C.; Winget, J.M.; Dewhirst, M.W.

1987-01-01

Positron Emission Tomography (PET) using /sup 68/Ga labelled microspheres (15μ diam.) for quantitative imaging of perfusion is being investigated for its potential to aid in verification of parameter estimation techniques. Such techniques have been used in bioheat transfer modeling where direct measurement of perfusion has not been possible. Perfusion is needed, to utilize bioheat transfer to predict temperatures between measured points during hyperthermia therapy. A preliminary study showing that PET could be used for verification of parameter estimation was done by heating a melanoma in a dog in which multiple thermometry catheters were placed in a central plane. Microspheres were injected at the end of a one hour heat treatment session before power down. CT and PET images of the same plane were aligned so that relative counts/pixel in 2 cm regions of interest of the PET image were measured along several catheter tracks. In all tracks measured an inverse correlation was shown between relative perfusion and temperature along the catheter during thermal steady state. These data strongly imply that PET scans obtained in the manner described bear relevance to bioheat transfer and for verification of perfusion in heated tissues as estimated by heat transfer modeling
Experimental Study and a Mathematical Model of the Processes in Frozen Soil Under a Reservoir with a Hot Heat-Transfer Agent

Science.gov (United States)

Kislitsyn, A. A.; Shastunova, U. Yu.; Yanbikova, Yu. F.

2018-05-01

On an experimental setup, the authors have measured temperature fields in frozen soil during the filling of a reservoir with hot heat-transfer agent (oil), and also the change in the shape and position of the front of ice melting (isotherms T = 0°C) with time. The approximate solution of a two-dimensional Stefan problem on thawing of frozen soil has been given; it has been shown that satisfactory agreement with experimental results can only be obtained with account taken of the convective transfer of heat due to the water motion in the region of thawed soil.
A model for radiative heat transfer in mixtures of a hot solid or molten material with water and steam

International Nuclear Information System (INIS)

Vaeth, L.

1997-05-01

A model has been devised for describing the radiative heat transfer in mixtures of a hot radiant material with water and steam, to be used, e.g., in the framework of a multiphase, multicomponent flow simulation. The main features of the model are: 1. The radiative heat transfer is modelled for a homogeneous mixture of one continuous material with droplets/bubbles of the other two, of the kind normally assumed for the material distribution in one cell of a bigger calculational problem. Neither the heat transfer over the cell boundaries nor the finite dimensions of the cell are taken into account. 2. The geometry of the mixture (radiant material continuous or discontinuous, droplet/bubble diameters and number densities) is taken into account. 3. The optical properties of water and water vapour are modelled as functions of the temperature of the radiant and, in the case of water vapour, also of the absorbing material. 4. The model distinguishes between heat transfer to the surface of the water (leading to evaporation) and into the bulk of the water (pure heating). (orig./DG) [de
Point kinetics model with one-dimensional (radial) heat conduction formalism

International Nuclear Information System (INIS)

Jain, V.K.

1989-01-01

A point-kinetics model with one-dimensional (radial) heat conduction formalism has been developed. The heat conduction formalism is based on corner-mesh finite difference method. To get average temperatures in various conducting regions, a novel weighting scheme has been devised. The heat conduction model has been incorporated in the point-kinetics code MRTF-FUEL. The point-kinetics equations are solved using the method of real integrating factors. It has been shown by analysing the simulation of hypothetical loss of regulation accident in NAPP reactor that the model is superior to the conventional one in accuracy and speed of computation. (author). 3 refs., 3 tabs
Heat transfer

Indian Academy of Sciences (India)

First page Back Continue Last page Overview Graphics. Heat transfer. Heat conduction in solid slab. Convective heat transfer. Non-linear temperature. variation due to flow. HEAT FLUX AT SURFACE. conduction/diffusion.
Super-Planckian far-field radiative heat transfer

Science.gov (United States)

Fernández-Hurtado, V.; Fernández-Domínguez, A. I.; Feist, J.; García-Vidal, F. J.; Cuevas, J. C.

2018-01-01

We present here a theoretical analysis that demonstrates that the far-field radiative heat transfer between objects with dimensions smaller than the thermal wavelength can overcome the Planckian limit by orders of magnitude. To guide the search for super-Planckian far-field radiative heat transfer, we make use of the theory of fluctuational electrodynamics and derive a relation between the far-field radiative heat transfer and the directional absorption efficiency of the objects involved. Guided by this relation, and making use of state-of-the-art numerical simulations, we show that the far-field radiative heat transfer between highly anisotropic objects can largely overcome the black-body limit when some of their dimensions are smaller than the thermal wavelength. In particular, we illustrate this phenomenon in the case of suspended pads made of polar dielectrics like SiN or SiO2. These structures are widely used to measure the thermal transport through nanowires and low-dimensional systems and can be employed to test our predictions. Our work illustrates the dramatic failure of the classical theory to predict the far-field radiative heat transfer between micro- and nanodevices.
Three-dimensional analyses of fluid flow and heat transfer for moderator integrity assessment in PHWR

International Nuclear Information System (INIS)

Yu, S.-O.; Kim, M.; Kim, H.-J.

2002-01-01

A CANDU reactor has the unique features and the intrinsic safety related characteristics that distinguish it from other water-cooled thermal reactors. If there is the loss of coolant accident (LOCA) and a coincident failure of the emergency coolant injection (ECI) system, the heavy water moderator is continuously cooled, providing a heat sink for decay heat produced in the fuel. Therefore, it is one of major concerns to estimate the local subcooling of moderator inside the calandria vessel under postulated accident in CANDU safety analyses. The Canadian Nuclear Safety Commission (CNSC), a regulatory body in Canada, categorized the integrity of moderator as a generic safety issue and recommended that a series of experimental works be performed to verify the safety evaluation codes for individual simulated condition of nuclear power plant, comparing with the results of three-dimensional experimental data. In this study, three-dimensional analyses of fluid flow and heat transfer have been performed to assess thermal-hydraulic characteristics for moderator simulation conducted by SPEL (Sheridan Park Experimental Laboratory) experimental facility. The parametric study has also carried out to investigate the effect of major parameters such as flowrate, temperature, and heat load generated from the heaters on the temperature and flow distribution inside the moderator. Three flow patterns have been identified in the moderator with flowrate, heat generation, or both. As the transition of fluid flow is progressed, it is found that the dimensionless numbers (Ar) and the ratio of buoyancy to inertia forces are constant. (author)
Developing of two-dimensional model of the corium cooling and behavior with non-condensible gas injection

Energy Technology Data Exchange (ETDEWEB)

Chung, Chang Hyun; Cho, Jae Seon; Kim, Ju Youl; Kim, Do Hyoung [Seoul National University, Seoul (Korea, Republic of)

1997-07-01

The purpose of this study is to understand the effect of the non-condensible gas injection into the molten corium on the heat transfer and dynamic behavior within the melt when molten core-concrete interaction occurs during the hypothetical severe accident. Corium behavior with gas injection effect is two phase fluid pattern in which droplet has dispersed gas phase in continuous liquid phase of corium. To analyze this behavior, two dimensional governing equation using the governing equation, the computer program is accomplished using the finite difference method and SIMPLER algorithm. And benchmarking calculation is performed for the KfK experiment, which consider the gas injection effect. After this pre-calculation, an analyses is performed with typical corium under severe accidents. It is concluded that the heat transfer within corium increases as the metal components of the corium and gas injection velocity increase. 88 refs., 23 tabs., 35 figs. (author)
CFD evaluation of turbulence model on heat transfer in 5 × 5 rod bundles

International Nuclear Information System (INIS)

Chao Yanmeng; Yang Lixin; Zhang Yuxiang; Pang Zhengzheng

2014-01-01

Different turbulence models may lead to different results when analyzing fuel assemblies using computational fluid dynamics (CFD) method. In this paper, a 5 × 5 rod bundle model was built to analyze the relationship between flow and heat transfer. The pressure drop and Nu were calculated using ANSYS CFX. Three factors evaluating swirling flow and cross-flow were used to analyze the inner relationship between flow field and heat transfer. The performances of various turbulence models, including eddy viscosity model and Reynold stress model, were evaluated. The comparison between numerical and similar experimental results indicates that Reynold stress model is more appropriate for modeling flow features and heat transfer in spacer grids discussed in this paper. (authors)
Robust Modelling of Heat and Mass Transfer in Processing of Solid Foods

DEFF Research Database (Denmark)

Feyissa, Aberham Hailu

The study is focused on combined heat and mass transfer during processing of solid foods such as baking and frying processes. Modelling of heat and mass transfer during baking and frying is a significant scientific challenge. During baking and frying, the food undergoes several changes...... in microstructure and other physical properties of the food matrix. The heat and water transport inside the food is coupled in a complex way, which for some food systems it is not yet fully understood. A typical example of the latter is roasting of meat in convection oven, where the mechanism of water transport...... is unclear. Establishing the robust mathematical models describing the main mechanisms reliably is of great concern. A quantitative description of the heat and mass transfer during the solid food processing, in the form of mathematical equations, implementation of the solution techniques, and the value...
Simultaneous Heat and Mass Transfer Model for Convective Drying of Building Material

Science.gov (United States)

Upadhyay, Ashwani; Chandramohan, V. P.

2018-04-01

A mathematical model of simultaneous heat and moisture transfer is developed for convective drying of building material. A rectangular brick is considered for sample object. Finite-difference method with semi-implicit scheme is used for solving the transient governing heat and mass transfer equation. Convective boundary condition is used, as the product is exposed in hot air. The heat and mass transfer equations are coupled through diffusion coefficient which is assumed as the function of temperature of the product. Set of algebraic equations are generated through space and time discretization. The discretized algebraic equations are solved by Gauss-Siedel method via iteration. Grid and time independent studies are performed for finding the optimum number of nodal points and time steps respectively. A MATLAB computer code is developed to solve the heat and mass transfer equations simultaneously. Transient heat and mass transfer simulations are performed to find the temperature and moisture distribution inside the brick.
Analytical Solutions of Heat Transfer and Film Thickness with Slip Condition Effect in Thin-Film Evaporation for Two-Phase Flow in Microchannel

Directory of Open Access Journals (Sweden)

Ahmed Jassim Shkarah

2015-01-01

Full Text Available Physical and mathematical model has been developed to predict the two-phase flow and heat transfer in a microchannel with evaporative heat transfer. Sample solutions to the model were obtained for both analytical analysis and numerical analysis. It is assumed that the capillary pressure is neglected (Morris, 2003. Results are provided for liquid film thickness, total heat flux, and evaporating heat flux distribution. In addition to the sample calculations that were used to illustrate the transport characteristics, computations based on the current model were performed to generate results for comparisons with the analytical results of Wang et al. (2008 and Wayner Jr. et al. (1976. The calculated results from the current model match closely with those of analytical results of Wang et al. (2008 and Wayner Jr. et al. (1976. This work will lead to a better understanding of heat transfer and fluid flow occurring in the evaporating film region and develop an analytical equation for evaporating liquid film thickness.
On development of analytical closure relationships for local wall friction, heat and mass transfer coefficients for sub-channel codes

International Nuclear Information System (INIS)

Kornienko, Y.

2000-01-01

The purpose has been to describe an approach suggested for constructing generalized closure relationships for local and subchannel wall friction, heat and mass transfer coefficients, with not only axial and transversal parameters taken into account, but azimuthal substance transfer effects as well. These constitutive relations that are primary for description of one- and two-phase one-dimensional flow models can be derived from the initial 3-D drift flux formulation. The approach is based on the Reynolds flux, boundary layer and generalized coefficient of substance transfer. One more task has been to illustrate the validity of the 'conformity principle' for the limiting cases. The method proposed is based on the similarity theory, boundary layer model, and a phenomenological description of the regularities of the substance transfer (momentum, heat, and mass), as well as on an adequate simulation of the forms of flow structure by a generalized approach to build (an integrated in form and semi-empirical in maintenance structure) analytical relationships for wall friction, heat and mass transfer coefficients. (author)
Modeling conductive heat transfer during high-pressure thawing processes: determination of latent heat as a function of pressure.

Science.gov (United States)

Denys, S; Van Loey, A M; Hendrickx, M E

2000-01-01

A numerical heat transfer model for predicting product temperature profiles during high-pressure thawing processes was recently proposed by the authors. In the present work, the predictive capacity of the model was considerably improved by taking into account the pressure dependence of the latent heat of the product that was used (Tylose). The effect of pressure on the latent heat of Tylose was experimentally determined by a series of freezing experiments conducted at different pressure levels. By combining a numerical heat transfer model for freezing processes with a least sum of squares optimization procedure, the corresponding latent heat at each pressure level was estimated, and the obtained pressure relation was incorporated in the original high-pressure thawing model. Excellent agreement with the experimental temperature profiles for both high-pressure freezing and thawing was observed.
Numerical investigations of opposing mixed convection heat transfer in vertical flat channel 2. Vortex flow in case of symmetrical heating

International Nuclear Information System (INIS)

Sirvydas, A.; Poskas, R.

2006-01-01

We present the results on numerical investigation of the local opposing mixed convection heat transfer in a vertical flat channel with symmetrical heating at low Reynolds numbers. Numerical two-dimensional simulation was performed for the same channel and for the same conditions as in the experiment using the FLUENT 6.1 code. The unsteady flow investigations were performed in airflow for the experimental conditions at the Reynolds number 2130 and Grashof number 6.2* 10 8 . Quasi-steady flow investigations were performed for two Reynolds numbers (2130 and 4310) and the Grashof number up to 3.1*10 9 in order to simulate the buoyancy effect on the flow structure. In both steady and quasi-steady modelling cases the results demonstrated that under the high buoyancy effect the chequerwise local circular flow took place near the heated walls. This made velocity profiles asymmetrical and caused pulsations of the wall temperature. Wall temperature had a pulsatory character, however, the resulting averaged values correlated rather well with experimental data for steady and quasi-steady cases for Re in = 2130. For Re in = 4310, the resulting averaged values for x/d e ≤25 correlated rather well with experimental data. When x/d e > 25, the difference between the experimental and the calculated wall temperature was increasing, increasing, possibly due to a steady flow and heat transfer modelling. (author)
Encyclopedia of two-phase heat transfer and flow III macro and micro flow boiling and numerical modeling fundamentals

CERN Document Server

2018-01-01

Set III of this encyclopedia is a new addition to the previous Sets I and II. It contains 26 invited chapters from international specialists on the topics of numerical modeling of two-phase flows and evaporation, fundamentals of evaporation and condensation in microchannels and macrochannels, development and testing of micro two-phase cooling systems for electronics, and various special topics (surface wetting effects, microfin tubes, two-phase flow vibration across tube bundles). The chapters are written both by renowned university researchers and by well-known engineers from leading corporate research laboratories. Numerous "must read" chapters cover the fundamentals of research and engineering practice on boiling, condensation and two-phase flows, two-phase heat transfer equipment, electronics cooling systems, case studies and so forth. Set III constitutes a "must have" reference together with Sets I and II for thermal engineering researchers and practitioners.
Heat transfer in an asymmetrically heated duct, 2

International Nuclear Information System (INIS)

Satoh, Isao; Kurosaki, Yasuo

1986-01-01

The objective of this article is to study theoretically and experimentally the effects of nonuniform heating on turbulent heat transfer characteristics for flow in a horizontal rectangular duct ; a vertical side wall was uniformly heated, and the other wall were insulated. In our theoretical approach, the zero-equation model for turbulent eddy viscosity was employed. The effects of mesh size of finite difference on the calculation results were examined, and some refined compensation for wall temperatures and wall shear stresses by no use of fine mesh were proposed to reduce the calculation time. The heat transfer coefficients in thermally developing region for a nonuniformly heated duct obtained from numerical solutions are larger than the one for uniformly heated case. The buoyancy effects on heat transfer were evaluated. However, it was seen that the secondary flow due to buoyancy force was hardly expected to enhance heat transfer in a turbulent duct flow. Experiments were performed to measure the velocity and temperature profiles in a turbulent duct flow with a nonuniform heated wall. The experimental results were in good agreement with the theoretical ones. (author)
Handbook of heat and mass transfer. Volume 2

International Nuclear Information System (INIS)

Cheremisinoff, N.P.

1986-01-01

This two-volume series, the work of more than 100 contributors, presents advanced topics in industrial heat and mass transfer operations and reactor design technology. Volume 2 emphasizes mass transfer and reactor design. Some of the contents discussed are: MASS TRANSFER PRINCIPLES - Effect of turbulence promoters on mass transfer. Mass transfer principles with homogeneous and heterogeneous reactions. Convective diffusion with reactions in a tube. Transient mass transfer onto small particles and drops. Modeling heat and mass transport in falling liquid films. Heat and mass transfer in film absorption. Multicomponent mass transfer: theory and applications. Diffusion limitation for reaction in porous catalysts. Kinetics and mechanisms of catalytic deactivation. DISTILLATION AND EXTRACTION - Generalized equations of state for process design. Mixture boiling. Estimating vapor pressure from normal boiling points of hydrocarbons. Estimating liquid and vapor molar fractions in distillation columns. Principles of multicomponent distillation. Generalized design methods for multicomponent distillation. Interfacial films in inorganic substances extraction. Liquid-liquid extraction in suspended slugs. MULTIPHASE REACTOR SYSTEMS - Reaction and mass transport in two-phase reactors. Mass transfer and kinetics in three-phase reactors. Estimating liquid film mass transfer coefficients in randomly packed columns. Designing packed tower wet scrubbers - emphasis on nitrogen oxides. Gas absorption in aerated mixers. Axial dispersion and heat transfer in gas-liquid bubble columns. Operation and design of trickle-bed reactors
TWO-DIMENSIONAL CORE-COLLAPSE SUPERNOVA MODELS WITH MULTI-DIMENSIONAL TRANSPORT

International Nuclear Information System (INIS)

Dolence, Joshua C.; Burrows, Adam; Zhang, Weiqun

2015-01-01

We present new two-dimensional (2D) axisymmetric neutrino radiation/hydrodynamic models of core-collapse supernova (CCSN) cores. We use the CASTRO code, which incorporates truly multi-dimensional, multi-group, flux-limited diffusion (MGFLD) neutrino transport, including all relevant O(v/c) terms. Our main motivation for carrying out this study is to compare with recent 2D models produced by other groups who have obtained explosions for some progenitor stars and with recent 2D VULCAN results that did not incorporate O(v/c) terms. We follow the evolution of 12, 15, 20, and 25 solar-mass progenitors to approximately 600 ms after bounce and do not obtain an explosion in any of these models. Though the reason for the qualitative disagreement among the groups engaged in CCSN modeling remains unclear, we speculate that the simplifying ''ray-by-ray'' approach employed by all other groups may be compromising their results. We show that ''ray-by-ray'' calculations greatly exaggerate the angular and temporal variations of the neutrino fluxes, which we argue are better captured by our multi-dimensional MGFLD approach. On the other hand, our 2D models also make approximations, making it difficult to draw definitive conclusions concerning the root of the differences between groups. We discuss some of the diagnostics often employed in the analyses of CCSN simulations and highlight the intimate relationship between the various explosion conditions that have been proposed. Finally, we explore the ingredients that may be missing in current calculations that may be important in reproducing the properties of the average CCSNe, should the delayed neutrino-heating mechanism be the correct mechanism of explosion

Non-Uniform Heat Transfer in Thermal Regenerators

DEFF Research Database (Denmark)

Jensen, Jesper Buch

, a numerical model, which simulates a single-blow operation in a parallel-plate regenerator, was developed and used to model the heat transfer under various conditions. In addition to the modeling of the heat transfer, a series of experiments on passive regenerators with non-uniform, but precisely controlled....... Additionally, the experiments gave real comparative results, whereas the model to a certain degree more served to provide insight to the heat transfer processes taking place inside the regenera- tors, something that would be - if not impossible - then highly impractical to do experimentally. It has been found......This thesis presents investigations on the heat transfer in complex heat ex- changers in general and in regenerative heat exchangers (regenerators) in par- ticular. The motivation for this work is a result of inconsistencies obeserved in the results from a series of experiments on active magnetic...
Experimental Study on Natural Convection Heat Transfer From two Parallel Horizontal Cylinders in Horizontal Cylindrical Enclosure

Directory of Open Access Journals (Sweden)

Ahmed T. Ahmed

2013-05-01

Full Text Available An experimental study on natural convection heat transfer from two parallel horizontal cylinders in horizontal cylindrical enclosure was carried out under condition of constant surfaces temperature for two cylinders and cylindrical enclosure. The study included the effect of Rayleigh number, rotation angle that represent the confined angle between the passing horizontal plane in cylindrical enclosure center and passing line in two cylinders centers, and the spaces between two cylinders on their heat loss ability.39An experimental set-up was used for this purpose which consist watercontainer, test section which is formed of plastic cylinder that represent the cylindrical enclosure, and two heating elements which are formed of two copper cylinders with (19 mm in diameters heated internally by electrical sources that represents transfer and heat loss elements through this set-up. The experiments were done at the range of Rayleigh number between ( , cylinders rotation angle at ( , and spacing ratio at ( . The study showed that the ability of heat loss from two cylinders is a function of Rayleigh number, cylinders rotation angle, and the spaces between them. This ability is increased by increasing of Rayleigh number and it was showed that this ability reaches maximum value at the first cylinder ( and minimum value at the second cylinder ( at spacing ratio (S/D=3 and rotation angle ( for the first and ( for the second cylinder respectively. The effective variables on natural convection heat transfer from the above two cylinders are related by two correlating equations, each one explains dimensionless relation of heat transfer from each cylinder that represented by Nusselt number against Rayleigh number, rotation angle, and the spacing ratio between two cylinders.
A two-dimensional analytical model of laminar flame in lycopodium dust particles

Energy Technology Data Exchange (ETDEWEB)

Rahbari, Alireza [Shahid Rajaee Teacher Training University, Tehran (Iran, Islamic Republic of); Shakibi, Ashkan [Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Bidabadi, Mehdi [Combustion Research Laboratory, Narmak, Tehran (Iran, Islamic Republic of)

2015-09-15

A two-dimensional analytical model is presented to determine the flame speed and temperature distribution of micro-sized lycopodium dust particles. This model is based on the assumptions that the particle burning rate in the flame front is controlled by the process of oxygen diffusion and the flame structure consists of preheat, reaction and post flame zones. In the first step, the energy conservation equations for fuel-lean condition are expressed in two dimensions, and then these differential equations are solved using the required boundary condition and matching the temperature and heat flux at the interfacial boundaries. Consequently, the obtained flame temperature and flame speed distributions in terms of different particle diameters and equivalence ratio for lean mixture are compared with the corresponding experimental data for lycopodium dust particles. Consequently, it is shown that this two-dimensional model demonstrates better agreement with the experimental results compared to the previous models.
A two-dimensional analytical model of laminar flame in lycopodium dust particles

International Nuclear Information System (INIS)

Rahbari, Alireza; Shakibi, Ashkan; Bidabadi, Mehdi

2015-01-01

A two-dimensional analytical model is presented to determine the flame speed and temperature distribution of micro-sized lycopodium dust particles. This model is based on the assumptions that the particle burning rate in the flame front is controlled by the process of oxygen diffusion and the flame structure consists of preheat, reaction and post flame zones. In the first step, the energy conservation equations for fuel-lean condition are expressed in two dimensions, and then these differential equations are solved using the required boundary condition and matching the temperature and heat flux at the interfacial boundaries. Consequently, the obtained flame temperature and flame speed distributions in terms of different particle diameters and equivalence ratio for lean mixture are compared with the corresponding experimental data for lycopodium dust particles. Consequently, it is shown that this two-dimensional model demonstrates better agreement with the experimental results compared to the previous models.
Two-temperature theory in magneto-thermoelasticity with fractional order dual-phase-lag heat transfer

Energy Technology Data Exchange (ETDEWEB)

Ezzat, Magdy A., E-mail: maezzat2000@yahoo.com [Department of Mathematics, Faculty of Sciences and Letters in Al Bukayriyyah, Al-Qassim University, Al-Qassim (Saudi Arabia); El-Karamany, Ahmed S., E-mail: qaramani@gmail.com [Department of Mathematical and Physical Sciences, Nizwa University, P.O. Box 1357, Nizwa 611 (Oman); Ezzat, Shereen M. [Department of Mathematics, Faculty of Sciences and Letters in Al Bukayriyyah, Al-Qassim University, Al-Qassim (Saudi Arabia)

2012-11-15

Highlights: Black-Right-Pointing-Pointer We model fractional order dual-phase-lag heat conduction law. Black-Right-Pointing-Pointer We applied the model on a perfect conducting half-space of elastic material. Black-Right-Pointing-Pointer Some theories of generalized thermoelasticity follow as limit cases. Black-Right-Pointing-Pointer State space approach is adopted for the solution of one-dimensional problems. Black-Right-Pointing-Pointer The model will improve the efficiency of thermoelectric material. - Abstract: A new mathematical model of two-temperature magneto-thermoelasticity is constructed where the fractional order dual-phase-lag heat conduction law is considered. The state space approach developed in Ezzat (2008) is adopted for the solution of one-dimensional application for a perfect conducting half-space of elastic material, which is thermally shocked in the presence of a transverse magnetic field. The Laplace transform technique is used. A numerical method is employed for the inversion of the Laplace transforms. According to the numerical results and its graphs, conclusion about the new theory has been constructed. Some theories of generalized thermoelasticity follow as limit cases. Some comparisons have been shown in figures to estimate effects of temperature discrepancy and fractional order parameter on all the studied fields.
3-D Transient Heat Transfer Analysis of Slab Heating Characteristics in a Reheating Furnace in Hot Strip Mills

OpenAIRE

J. Y. Jang; Y. W. Lee; C. N. Lin; C. H. Wang

2015-01-01

The reheating furnace is used to reheat the steel slabs before the hot-rolling process. The supported system includes the stationary/moving beams, and the skid buttons which block some thermal radiation transmitted to the bottom of the slabs. Therefore, it is important to analyze the steel slab temperature distribution during the heating period. A three-dimensional mathematical transient heat transfer model for the prediction of temperature distribution within the slab ha...
Heat transfer and fire spread

Science.gov (United States)

Hal E. Anderson

1969-01-01

Experimental testing of a mathematical model showed that radiant heat transfer accounted for no more than 40% of total heat flux required to maintain rate of spread. A reasonable prediction of spread was possible by assuming a horizontal convective heat transfer coefficient when certain fuel and flame characteristics were known. Fuel particle size had a linear relation...
Radiation heat transfer model in a spent fuel pool by TRACE code

International Nuclear Information System (INIS)

Sanchez-Saez, F.; Carlos, S.; Villanueva, J.F.; Martorell, S.

2014-01-01

Nuclear policies have experienced an important change since Fukushima Daiichi nuclear plant accident and the safety of spent fuels has been in the spot issue among all the safety concerns. The work presented consists of the thermohydraulic simulation of spent fuel pool behavior after a loss of coolant throughout transfer channel with loss of cooling transient is produced. The simulation is done with the TRACE code. One of the most important variables that define the behavior of the pool is cladding temperature, which evolution depends on the heat emission. In this work convection and radiation heat transfer is considered. When both heat transfer models are considered, a clear delay in achieving the maximum peak cladding temperature (1477 K) is observed compared with the simulation in which only convection heat transfer is considered. (authors)
Numerical simulation of heat transfer in metal foams

Science.gov (United States)

Gangapatnam, Priyatham; Kurian, Renju; Venkateshan, S. P.

2018-02-01

This paper reports a numerical study of forced convection heat transfer in high porosity aluminum foams. Numerical modeling is done considering both local thermal equilibrium and non local thermal equilibrium conditions in ANSYS-Fluent. The results of the numerical model were validated with experimental results, where air was forced through aluminum foams in a vertical duct at different heat fluxes and velocities. It is observed that while the LTE model highly under predicts the heat transfer in these foams, LTNE model predicts the Nusselt number accurately. The novelty of this study is that once hydrodynamic experiments are conducted the permeability and porosity values obtained experimentally can be used to numerically simulate heat transfer in metal foams. The simulation of heat transfer in foams is further extended to find the effect of foam thickness on heat transfer in metal foams. The numerical results indicate that though larger foam thicknesses resulted in higher heat transfer coefficient, this effect weakens with thickness and is negligible in thick foams.
In vitro investigation of heat transfer phenomenon in human immature teeth.

Science.gov (United States)

Talebi, Maryam; Moghimi, Sahar; Shafagh, Mina; Kalani, Hadi; Mazhari, Fatemeh

2014-01-01

Background and aims. Heat generated within tooth during clinical dentistry can cause thermally induced damage to hard and soft components of the tooth (enamel, dentin and pulp). Geometrical characteristics of immature teeth are different from those of mature teeth. The purpose of this experimental and theoretical study was to investigate thermal changes in immature permanent teeth during the use of LED light-curing units (LCU). Materials and methods. This study was performed on the second mandibular premolars. This experimental investiga-tion was carried out for recording temperature variations of different sites of tooth and two dimensional finite element models were used for heat transfer phenomenon in immature teeth. Sensitivity analysis and local tests were included in the model validation phase. Results. Overall, thermal stimulation for 30 seconds with a low-intensity LED LCU increased the temperature from 28°C to 38°C in IIT (intact immature tooth) and PIT (cavity-prepared immature tooth). When a high-intensity LED LCU was used, tooth temperature increased from 28°C to 48°C. The results of the experimental tests and mathematical modeling illustrated that using LED LCU on immature teeth did not have any detrimental effect on the pulp temperature. Conclusion. Using LED LCU in immature teeth had no effect on pulp temperature in this study. Sensitivity analysis showed that variations of heat conductivity might affect heat transfer in immature teeth; therefore, further studies are required to determine thermal conductivity of immature teeth.
An experimental study of heat transfer and pressure drop of two-phas flow in an inclined annular channel

International Nuclear Information System (INIS)

Khattab, M.S.; Mariy, A.H.; Hilal, M.M.; El-Morshdy, S.E.

1999-01-01

The phenomena of two-phase flow through horizontal, vertical and inclined tubes has many engineering applications in heat exchangers, boilers, nuclear reactors, steam generators and refrigerators..etc. In the present investigation, two-phase flow heat transfer and pressure drop have been experimentally studied at different orientations of an annular channel test section subjected to uniform heat flux. The annular test section was internally heated by a DC power supply. The experimental investigation has been classified onto three steady state groups of (heat flux, mass flux, and inlet temperature). The first group was at 522.41 kw/m 2 , 310 kg/m 2 s and 89.4 degree C; the second was at 779.72 kw/m 2 , 507 Hg/m 2 s and 94.3 degree C and the third was at 1019.97 kw/m 2 s 701 kg/m 2 100 degree C. The effect of inclination on the two-phase heat transfer coefficient and pressure drop are presented and discussed. The present experimental results are compared with some existing correlations for two phase flow boiling heat transfer in horizontal and vertical tubes at their range of validity. The comparison shows a good agreement. The behavior of the two-phase mean heat transfer coefficient shows a small enhancement due to inclination from horizontal to vertical orientation. The enhancement factor relating the two-phase heat transfer coefficient with the inclination angle is predicted
Influence of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and time to ignition

Directory of Open Access Journals (Sweden)

Guo Zerong

2016-01-01

Full Text Available To study the effect of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and time to ignition, considering the heat transfer coefficient as the power function of temperature, mathematical thermal explosion steady state and unsteady-state model of finite cylindrical fireworks and crackers with complex shell structures are established based on two-dimensional steady state thermal explosion theory. The influence of variable heat transfer coefficient on thermal explosion critical ambient temperature and time to ignition are analyzed. When heat transfer coefficient is changing with temperature and in the condition of natural convection heat transfer, critical ambient temperature lessen, thermal explosion time to ignition shorten. If ambient temperature is close to critical ambient temperature, the influence of variable heat transfer coefficient on time to ignition become large. For firework with inner barrel in example analysis, the critical ambient temperature of propellant is 463.88 K and the time to ignition is 4054.9s at 466 K, 0.26 K and 450.8s less than without considering the change of heat transfer coefficient respectively. The calculation results show that the influence of variable heat transfer coefficient on thermal explosion time to ignition is greater in this example. Therefore, the effect of variable heat transfer coefficient should be considered into thermal safety evaluation of fireworks to reduce potential safety hazard.
Molten pool-lower head integrity. Heat transfer models including advanced numerical simulations (DNS)

Energy Technology Data Exchange (ETDEWEB)

Seiler, J.M.; Bonnet, J.M.; Bernaz, L. [CEA Grenoble (France)

2001-07-01

Extensive studies have been performed to investigate the heat transfer within a molten corium pool (homogeneous, stratified and with miscibility gap): Synthesis of heat transfer correlations in molten pool (homogeneous and stratified), Focusing effect in stratified metal layer, DNS analysis of Rayleigh Benard instabilities at the top boundary; interpretation of the different convection regimes and exponents affecting the Rayleigh number in the heat transfer correlations, Molten pool model for corium presenting a miscibility gap. Condition for de-stratification. (authors)
Molten pool-lower head integrity. Heat transfer models including advanced numerical simulations (DNS)

International Nuclear Information System (INIS)

Seiler, J.M.; Bonnet, J.M.; Bernaz, L.

2001-01-01

Extensive studies have been performed to investigate the heat transfer within a molten corium pool (homogeneous, stratified and with miscibility gap): Synthesis of heat transfer correlations in molten pool (homogeneous and stratified), Focusing effect in stratified metal layer, DNS analysis of Rayleigh Benard instabilities at the top boundary; interpretation of the different convection regimes and exponents affecting the Rayleigh number in the heat transfer correlations, Molten pool model for corium presenting a miscibility gap. Condition for de-stratification. (authors)
Mixed convection heat transfer from confined tandem square cylinders in a horizontal channel

KAUST Repository

Huang, Zhu

2013-11-01

This paper presents a numerical study on the two-dimensional laminar mixed convective flow and heat transfer around two identical isothermal square cylinders arranged in tandem and confined in a channel. The spacing between the cylinders is fixed with four widths of the cylinder and the blockage ratio and the Prandtl number are fixed at 0.1 and 0.7 respectively. The mixed convective flow and heat transfer is simulated by high accuracy multidomain pseudospectral method. The Reynolds number (Re) is studied in the range 80 ≤ Re ≤ 150, the Richardson number (Ri) demonstrating the influence of thermal buoyancy ranges from 0 to 1. Numerical results reveal that, with the thermal buoyancy effect, the mixed convective flow sheds vortex behind the cylinders and keeps periodic oscillating. The variations of characteristic quantities related to flow and heat transfer processes, such as the overall drag and lift coefficients and the Nusselt numbers, are presented and discussed. Furthermore, the influence of thermal buoyancy on the fluid flow and heat transfer are discussed and analysed. © 2013 Elsevier Ltd. All rights reserved.
Probing heat transfer, fluid flow and microstructural evolution during fusion welding of alloys

Science.gov (United States)

Zhang, Wei

The composition, geometry, structure and properties of the welded joints are affected by the various physical processes that take place during fusion welding. Understanding these processes has been an important goal in the contemporary welding research to achieve structurally sound and reliable welds. In the present thesis research, several important physical processes including the heat transfer, fluid flow and microstructural evolution in fusion welding were modeled based on the fundamentals of transport phenomena and phase transformation theory. The heat transfer and fluid flow calculation is focused on the predictions of the liquid metal convection in the weld pool, the temperature distribution in the entire weldment, and the shape and size of the fusion zone (FZ) and heat affected zone (HAZ). The modeling of microstructural evolution is focused on the quantitative understanding of phase transformation kinetics during welding of several important alloys under both low and high heating and cooling conditions. Three numerical models were developed in the present thesis work: (1) a three-dimensional heat transfer and free surface flow model for the gas metal arc (GMA) fillet welding considering the complex weld joint geometry, (2) a phase transformation model based on the Johnson-Mehl-Avrami (JMA) theory, and (3) a one-dimensional numerical diffusion model considering multiple moving interfaces. To check the capabilities of the developed models, several cases were investigated, in which the predictions from the models were compared with the experimental results. The cases studied are the follows. For the modeling of heat transfer and fluid flow, the welding processes studied included gas tungsten arc (GTA) linear welding, GTA transient spot welding, and GMA fillet welding. The calculated weldment geometry and thermal cycles was validated against the experimental data under various welding conditions. For the modeling of microstructural evolution, the welded
Natural convection heat transfer on two horizontal cylinders in liquid sodium

Energy Technology Data Exchange (ETDEWEB)

Hata, K.; Shiotsu, M.; Takeuchi, Y. [Institute of Atomic Energy, Kyoto Univ. (Japan)] [and others

1995-09-01

Natural convection heat transfer on two horizontal 7.6 mm diameter test cylinders assembled with the ratio of the distance between each cylinder axis to the cylinder diameter, S/D, of 2 in liquid sodium was studied experimentally and theoretically. The heat transfer coefficients on the cylinder surface due to the same heat inputs ranging from 1.0 X 10{sup 7} to 1.0 x 10{sup 9} W/m{sup 3} were obtained experimentally for various setting angeles, {gamma}, between vertical direction and the plane including both of these cylinder axis over the range of zero to 90{degrees}. Theoretical equations for laminar natural convection heat transfer from the two horizontal cylinders were numerically solved for the same conditions as the experimental ones considering the temperature dependence of thermophysical properties concerned. The average Nusselt numbers, Nu, values on the Nu versus modified Rayleigh number, R{sub f}, graph. The experimental values of Nu for the upper cylinder are about 20% lower than those for the lower cylinder at {gamma} = 0{degrees} for the range of R{sub f} tested here. The value of Nu for the upper cylinder becomes higher and approaches that for the lower cylinder with the increase in {gamma} over range of 0 to 90{degrees}. The values of Nu for the lower cylinder at each {gamma} are almost in agreement with those for a single cylinder. The theoretical values of Nu on two cylinders except those for R{sub f}<4 at {gamma} = 0{degrees} are in agreement with the experimental data at each {gamma} with the deviations less than 15%. Correlations for Nu on the upper and lower cylinders were obtained as functions of S/D and {gamma} based n the theoretical solutions for the S/D ranged over 1.5 to 4.0.
Phase change heat transfer device for process heat applications

International Nuclear Information System (INIS)

Sabharwall, Piyush; Patterson, Mike; Utgikar, Vivek; Gunnerson, Fred

2010-01-01

The next generation nuclear plant (NGNP) will most likely produce electricity and process heat, with both being considered for hydrogen production. To capture nuclear process heat, and transport it to a distant industrial facility requires a high temperature system of heat exchangers, pumps and/or compressors. The heat transfer system is particularly challenging not only due to the elevated temperatures (up to ∼1300 K) and industrial scale power transport (≥50 MW), but also due to a potentially large separation distance between the nuclear and industrial plants (100+ m) dictated by safety and licensing mandates. The work reported here is the preliminary analysis of two-phase thermosyphon heat transfer performance with alkali metals. A thermosyphon is a thermal device for transporting heat from one point to another with quite extraordinary properties. In contrast to single-phased forced convective heat transfer via 'pumping a fluid', a thermosyphon (also called a wickless heat pipe) transfers heat through the vaporization/condensing process. The condensate is further returned to the hot source by gravity, i.e., without any requirement of pumps or compressors. With this mode of heat transfer, the thermosyphon has the capability to transport heat at high rates over appreciable distances, virtually isothermally and without any requirement for external pumping devices. Two-phase heat transfer by a thermosyphon has the advantage of high enthalpy transport that includes the sensible heat of the liquid, the latent heat of vaporization, and vapor superheat. In contrast, single-phase forced convection transports only the sensible heat of the fluid. Additionally, vapor-phase velocities within a thermosyphon are much greater than single-phase liquid velocities within a forced convective loop. Thermosyphon performance can be limited by the sonic limit (choking) of vapor flow and/or by condensate entrainment. Proper thermosyphon requires analysis of both.
3-D heat transfer computer calculations of the performance of the IAEA's air-bath calorimeters

International Nuclear Information System (INIS)

Elias, E.; Kaizermann, S.; Perry, R.B.; Fiarman, S.

1989-01-01

A three dimensional (3-D) heat transfer computer code was developed to study and optimize the design parameters and to better understand the performance characteristics of the IAEA's air-bath calorimeters. The computer model accounts for heat conduction and radiation in the complex materials of the calorimeter and for heat convection and radiation at its outer surface. The temperature servo controller is modelled as an integral part of the heat balance equations in the system. The model predictions will be validated against test data using the ANL bulk calorimeter. 11 refs., 6 figs
Use of two-phase flow heat transfer method in spacecraft thermal system

Science.gov (United States)

Hye, A.

1985-01-01

In space applications, weight, volume and power are critical parameters. Presently liquid freon is used in the radiator planels of the Space Shuttle to dissipate heat. This requires a large amount of freon, large power for pumps, large volume and weight. Use of two-phase flow method to transfer heat can reduce them significantly. A modified commercial vapor compression refrigerator/freezer was sucessfully flown in STS-4 to study the effect of zero-gravity on the system. The duty cycle was about 5 percent higher in flight as compared to that on earth due to low flow velocity in condenser. The vapor Reynolds number at exit was about 4000 as compared to about 12,000. Efforts are underway to design a refrigerator/freezer using an oil-free compressor for Spacelab Mission 4 scheduled to fly in January 1986. A thermal system can be designed for spacecraft using the two-phase flow to transfer heat economically.

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