Present-day heat flow model of Mars
Parro, Laura M.; Jiménez-Díaz, Alberto; Mansilla, Federico; Ruiz, Javier
2017-04-01
Until the acquisition of in-situ measurements, the study of the present-day heat flow of Mars must rely on indirect methods, mainly based on the relation between the thermal state of the lithosphere and its mechanical strength, or on theoretical models of internal evolution. Here, we present a first-order global model for the present-day surface heat flow for Mars, based on the radiogenic heat production of the crust and mantle, on scaling of heat flow variations arising from crustal thickness and topography variations, and on the heat flow derived from the effective elastic thickness of the lithosphere beneath the North Polar Region. Our preferred model finds heat flows varying between 14 and 25 mW m-2, with an average value of 19 mW m-2. Similar results (although about ten percent higher) are obtained if we use heat flow based on the lithospheric strength of the South Polar Region. Moreover, expressing our results in terms of the Urey ratio (the ratio between total internal heat production and total heat loss through the surface), we estimate values close to 0.7-0.75, which indicates a moderate contribution of secular cooling to the heat flow of Mars (consistent with the low heat flow values deduced from lithosphere strength), unless heat-producing elements abundances for Mars are subchondritic.
Present-day heat flow model of Mars.
Parro, Laura M; Jiménez-Díaz, Alberto; Mansilla, Federico; Ruiz, Javier
2017-04-03
Until the acquisition of in-situ measurements, the study of the present-day heat flow of Mars must rely on indirect methods, mainly based on the relation between the thermal state of the lithosphere and its mechanical strength, or on theoretical models of internal evolution. Here, we present a first-order global model for the present-day surface heat flow for Mars, based on the radiogenic heat production of the crust and mantle, on scaling of heat flow variations arising from crustal thickness and topography variations, and on the heat flow derived from the effective elastic thickness of the lithosphere beneath the North Polar Region. Our preferred model finds heat flows varying between 14 and 25 mW m(-2), with an average value of 19 mW m(-2). Similar results (although about ten percent higher) are obtained if we use heat flow based on the lithospheric strength of the South Polar Region. Moreover, expressing our results in terms of the Urey ratio (the ratio between total internal heat production and total heat loss through the surface), we estimate values close to 0.7-0.75, which indicates a moderate contribution of secular cooling to the heat flow of Mars (consistent with the low heat flow values deduced from lithosphere strength), unless heat-producing elements abundances for Mars are subchondritic.
An analytical model for annular flow boiling heat transfer in microchannel heat sinks
Energy Technology Data Exchange (ETDEWEB)
Megahed, A.; Hassan, I. [Concordia University, Montreal, QC (Canada). Dept. of Mechanical and Industrial Engineering
2009-07-01
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)
Thermal performance modeling of cross-flow heat exchangers
Cabezas-Gómez, Luben; Saíz-Jabardo, José Maria
2014-01-01
This monograph introduces a numerical computational methodology for thermal performance modeling of cross-flow heat exchangers, with applications in chemical, refrigeration and automobile industries. This methodology allows obtaining effectiveness-number of transfer units (e-NTU) data and has been used for simulating several standard and complex flow arrangements configurations of cross-flow heat exchangers. Simulated results have been validated through comparisons with results from available exact and approximate analytical solutions. Very accurate results have been obtained over wide ranges
Modeling Io's Heat Flow: Constraints from Galileo PPR Data
Rathbun, J. A.; Spencer, J. R.; Tamppari, L. K.
2000-01-01
We attempt to improve on previous Io heat flow estimates by using higher resolution data from Galileo Photopolarimeter Radiometer (PPR) and improved thermophysical models of the surface, including finite thermal inertia, the pedestal effect, and disk-resolved radiance.
Multilevel Flow Modeling of Domestic Heating Systems
DEFF Research Database (Denmark)
Hu, Junjie; Lind, Morten; You, Shi
2012-01-01
of complementing this reasoning methodology. Domestic heating systems, as the main resource to meet the thermal requirements of end-users, have different implementations in Europe in order to achieve various degrees of controllability and heating efficiencies. As all the heating systems serve the same basic needs...... i.e. supplying and transferring thermal energy, it is off interest to use MFM to investigate similarities and differences between different implementations. In this paper, three typical domestic European heating systems, which differ from each other in the number of temperature sensors and auxiliary...
A heat transfer model for slug flow boiling within microchannels
Magnini, Mirco; Thome, John
2016-11-01
We propose a novel physics-based model for the fluid mechanics and heat transfer associated with slug flow boiling in horizontal circular microchannels, to update the widely used three-zone model for the design of multi-microchannel evaporators. The flow is modelled as the cyclic passage of a liquid slug, an elongated bubble which traps a thin liquid film against the channel wall, and a dry vapor plug. The capillary flow theory, extended to incorporate evaporation effects, is applied to estimate the bubble velocity along the channel. A liquid film thickness prediction method considering bubble proximity effects, which may limit the radial extension of the film, is included. Theoretical heat transfer models accounting for the thermal inertia of the liquid film and for the recirculating flow within the liquid slug are utilized. The heat transfer model is compared to experimental data taken from three independent studies: 833 slug flow boiling data points covering R134a, R245fa and R236fa and channel diameters from 0.4 mm to 1 mm. The new model predicts more than 80% of the database to within +/- 30 % and it represents an important step toward a complete physics-based modelling of bubble dynamics and heat transfer within microchannels under evaporating flow conditions.
Heat source models in simulation of heat flow in friction stir welding
DEFF Research Database (Denmark)
Schmidt, Henrik Nikolaj Blich; Hattel, Jesper
2004-01-01
. The convective heat transfer due to the material flow affects the temperature fields. Models presented previously in the literature allow the heat to flow through the probe volume, and the majority neglects the influence of the contact condition as the sliding condition is assumed. In this work, a number......The objective of the present paper is to investigate the effect of including the tool probe and the material flow in the numerical modelling of heat flow in friction stir welding (FSW). The contact condition at the interface between the tool and workpiece controls the heat transfer mechanisms...... of cases is established. Each case represents a combination of a contact condition, i.e. sliding and sticking, and a stage of refinement regarding the heat source distribution. In the most detailed models, the heat flow is forced around the probe volume by prescribing a velocity field in shear layers...
Heat Source Models in Simulation of Heat Flow in Friction Stir Welding
DEFF Research Database (Denmark)
Schmidt, Henrik Nikolaj Blich; Hattel, Jesper
2004-01-01
. The convective heat transfer due to the material flow affects the temperature fields. Models presented previously in literature allow the heat to flow through the probe volume, and the majority of them neglect the influence of the contact condition as the sliding condition is assumed. In the present work......The objective of the present paper is to investigate the effect of including the tool probe and the material flow in the numerical modelling of heat flow in Friction Stir Welding (FSW). The contact condition at the interface between the tool and workpiece controls the heat transfer mechanisms......, a number of cases are established. Each case represents a combination of a contact condition, i.e. sliding and sticking, and a stage of refinement regarding the heat source distribution. In the most detailed models the heat flow is forced around the probe volume by prescribing a velocity field in shear...
New shear-free relativistic models with heat flow
Msomi, A M; Maharaj, S D
2013-01-01
We study shear-free spherically symmetric relativistic models with heat flow. Our analysis is based on Lie's theory of extended groups applied to the governing field equations. In particular, we generate a five-parameter family of transformations which enables us to map existing solutions to new solutions. All known solutions of Einstein equations with heat flow can therefore produce infinite families of new solutions. In addition, we provide two new classes of solutions utilising the Lie infinitesimal generators. These solutions generate an infinite class of solutions given any one of the two unknown metric functions.
Modeling heat efficiency, flow and scale-up in the corotating disc scraped surface heat exchanger
DEFF Research Database (Denmark)
Friis, Alan; Szabo, Peter; Karlson, Torben
2002-01-01
A comparison of two different scale corotating disc scraped surface heat exchangers (CDHE) was performed experimentally. The findings were compared to predictions from a finite element model. We find that the model predicts well the flow pattern of the two CDHE's investigated. The heat transfer...
Modelling of convective heat and mass transfer in rotating flows
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...
Heat Flow Pattern and Thermal Resistance Modeling of Anisotropic Heat Spreaders
Falakzaadeh, F.; Mehryar, R.
2017-01-01
To ensure safe operating temperatures of the ever smaller heat generating electronic devices, drastic measures should be taken. Heat spreaders are used to increase surface area, by spreading the heat without necessarily transferring it to the ambient in the first place. The heat flow pattern is investigated in heat spreaders and the fundamental differences regarding how heat conducts in different materials is addressed. Isotropic materials are compared with anisotropic ones having a specifically higher in-plane thermal conductivity than through plane direction. Thermal resistance models are proposed for anisotropic and isotropic heat spreaders in compliance with the order of magnitude of dimensions used in electronics packaging. After establishing thermal resistance models for both the isotropic and anisotropic cases, numerical results are used to find a correlation for predicting thermal resistance in anisotropic heat spreaders with high anisotropy ratios.
Numerical heat conduction in hydrodynamical models of colliding hypersonic flows
Parkin, E R
2010-01-01
Hydrodynamical models of colliding hypersonic flows are presented which explore the dependence of the resulting dynamics and the characteristics of the derived X-ray emission on numerical conduction and viscosity. For the purpose of our investigation we present models of colliding flow with plane-parallel and cylindrical divergence. Numerical conduction causes erroneous heating of gas across the contact discontinuity which has implications for the rate at which the gas cools. We find that the dynamics of the shocked gas and the resulting X-ray emission are strongly dependent on the contrast in the density and temperature either side of the contact discontinuity, these effects being strongest where the postshock gas of one flow behaves quasi-adiabatically while the postshock gas of the other flow is strongly radiative. Introducing additional numerical viscosity into the simulations has the effect of damping the growth of instabilities, which in some cases act to increase the volume of shocked gas and can re-he...
Calibrated Heat Flow Model for Determining the Heat Conduction Losses in Laser Cutting of CFRP
Mucha, P.; Weber, R.; Speker, N.; Berger, P.; Sommer, B.; Graf, T.
Laser machining has great potential regarding automation in fabrication of CFRP (carbon-fiber-reinforced plastics) parts, due to the nearly force and tool-wear free processing at high process speeds. The high vaporization temperatures and the large heat conductivity of the carbon fibers lead to a large heat transport into the sample. This causes the formation of a heat-affected zone and a decrease of the process speed. In the present paper,an analytical heat flow model was adapted in order to understand and investigate the heat conduction losses. Thermal sensors were embedded in samples at different distances from the kerf to fit the calculated to the measured temperatures. Heat conduction losses of up to 30% of the laser power were determined. Furthermore, the energy not absorbed by the sample, the energy for sublimating the composite material in the kerf, the energy for the formation of the HAZ, and the residual heat in the sample are compared in an energy balance.
A Variable Refrigerant Flow Heat Pump Computer Model in EnergyPlus
Energy Technology Data Exchange (ETDEWEB)
Raustad, Richard A. [Florida Solar Energy Center
2013-01-01
This paper provides an overview of the variable refrigerant flow heat pump computer model included with the Department of Energy's EnergyPlusTM whole-building energy simulation software. The mathematical model for a variable refrigerant flow heat pump operating in cooling or heating mode, and a detailed model for the variable refrigerant flow direct-expansion (DX) cooling coil are described in detail.
Wees, J.D. van; Bonte, D.; Nelskamp, S.
2009-01-01
Basement heat flow is one of the most influential parameters on basin maturity. Although rapid progress has been made in the development of tectonic models capable of modelling the thermal consequences of basin formation, these models are hardly used in basin modelling. To better predict heat flows
Probabilistic tectonic heat flow modeling for basin maturation: Assessment method and applications
Wees, J.D. van; Bergen, F. van; David, P.; Nepveu, M.; Beekman, F.; Cloetingh, S.; Bonté, D.
2009-01-01
Tectonic modeling is often neglected in the basin modeling workflow and heat flow is most times considered a user input. Such heat flows can, therefore, result in erroneous basin modeling outcomes, resulting in false overoptimistic identification of prospective areas or failure to identify prospects
Probabilistic tectonic heat flow modeling for basin maturation: Assessment method and applications
Wees, J.D. van; Bergen, F. van; David, P.; Nepveu, M.; Beekman, F.; Cloetingh, S.; Bonté, D.
2009-01-01
Tectonic modeling is often neglected in the basin modeling workflow and heat flow is most times considered a user input. Such heat flows can, therefore, result in erroneous basin modeling outcomes, resulting in false overoptimistic identification of prospective areas or failure to identify
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...
Flow regimes and mechanistic modeling of critical heat flux under subcooled flow boiling conditions
Le Corre, Jean-Marie
Thermal performance of heat flux controlled boiling heat exchangers are usually limited by the Critical Heat Flux (CHF) above which the heat transfer degrades quickly, possibly leading to heater overheating and destruction. In an effort to better understand the phenomena, a literature review of CHF experimental visualizations under subcooled flow boiling conditions was performed and systematically analyzed. Three major types of CHF flow regimes were identified (bubbly, vapor clot and slug flow regime) and a CHF flow regime map was developed, based on a dimensional analysis of the phenomena and available data. It was found that for similar geometric characteristics and pressure, a Weber number (We)/thermodynamic quality (x) map can be used to predict the CHF flow regime. Based on the experimental observations and the review of the available CHF mechanistic models under subcooled flow boiling conditions, hypothetical CHF mechanisms were selected for each CHF flow regime, all based on a concept of wall dry spot overheating, rewetting prevention and subsequent dry spot spreading. It is postulated that a high local wall superheat occurs locally in a dry area of the heated wall, due to a cyclical event inherent to the considered CHF two-phase flow regime, preventing rewetting (Leidenfrost effect). The selected modeling concept has the potential to span the CHF conditions from highly subcooled bubbly flow to early stage of annular flow. A numerical model using a two-dimensional transient thermal analysis of the heater undergoing nucleation was developed to mechanistically predict CHF in the case of a bubbly flow regime. In this type of CHF two-phase flow regime, the high local wall superheat occurs underneath a nucleating bubble at the time of bubble departure. The model simulates the spatial and temporal heater temperature variations during nucleation at the wall, accounting for the stochastic nature of the boiling phenomena. The model has also the potential to evaluate
Institute of Scientific and Technical Information of China (English)
张寅平; 胡先旭; 郝磬; 王馨
2003-01-01
This paper analyzes the convective heat transfer enhancement mechanism of latent heat functionally thermal fluid. By using the proposed internal heat source model, the influence of each factor affecting the heat transfer enhancement of laminar flow in a circular tube with constant heat flux is analyzed. The main influencing factors and the mechanisms of heat transfer enhancement are clarified, and the influences of the main factors on the heat transfer enhancement are quantitatively analyzed. A modified Nusselt number for internal flow is introduced to describe more effectively the degree of heat transfer enhancement for latent functionally thermal fluid.
three-step model of dispersed flow heat transfer (post chf vertical flow)
African Journals Online (AJOL)
user
The resulting equation gives the total heat transferred to the flow in terms of the mass flux, flow quality, .... superheated vapour, helps of course to desuperheat ... differential evaporation around the drop. The ... Thus we must first obtain the total.
Directory of Open Access Journals (Sweden)
Huijun Feng, Lingen Chen, Fengrui Sun
2010-11-01
Full Text Available An irreversible universal steady flow heat pump cycle model with variable-temperature heat reservoirs and the losses of heat-resistance and internal irreversibility is established by using the theory of finite time thermodynamics. The universal heat pump cycle model consists of two heat-absorbing branches, two heat-releasing branches and two adiabatic branches. Expressions of heating load, coefficient of performance (COP and profit rate of the universal heat pump cycle model are derived, respectively. By means of numerical calculations, heat conductance distributions between hot- and cold-side heat exchangers are optimized by taking the maximum profit rate as objective. There exist an optimal heat conductance distribution and an optimal thermal capacity rate matching between the working fluid and heat reservoirs which lead to a double maximum profit rate. The effects of internal irreversibility, total heat exchanger inventory, thermal capacity rate of the working fluid and heat capacity ratio of the heat reservoirs on the optimal finite time exergoeconomic performance of the cycle are discussed in detail. The results obtained herein include the optimal finite time exergoeconomic performances of endoreversible and irreversible, constant- and variable-temperature heat reservoir Brayton, Otto, Diesel, Atkinson, Dual, Miller and Carnot heat pump cycles.
An improved mechanistic critical heat flux model for subcooled flow boiling
Energy Technology Data Exchange (ETDEWEB)
Kwon, Young Min [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of); Chang, Soon Heung [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)
1997-12-31
Based on the bubble coalescence adjacent to the heated wall as a flow structure for CHF condition, Chang and Lee developed a mechanistic critical heat flux (CHF) model for subcooled flow boiling. In this paper, improvements of Chang-Lee model are implemented with more solid theoretical bases for subcooled and low-quality flow boiling in tubes. Nedderman-Shearer`s equations for the skin friction factor and universal velocity profile models are employed. Slip effect of movable bubbly layer is implemented to improve the predictability of low mass flow. Also, mechanistic subcooled flow boiling model is used to predict the flow quality and void fraction. The performance of the present model is verified using the KAIST CHF database of water in uniformly heated tubes. It is found that the present model can give a satisfactory agreement with experimental data within less than 9% RMS error. 9 refs., 5 figs. (Author)
CONJUGATE MODEL FOR HEAT AND MASS TRANSFER OF POROUS WALL IN THE HIGH TEMPERATURE GAS FLOW
Institute of Scientific and Technical Information of China (English)
A.F. Polyakov; D.L.Reviznikov; 沈青; 魏叔如
2001-01-01
Heat and mass transfer of a porous permeable wall in a high temperature gas dynamical flow is considered. Numerical simulation is conducted on the ground of the conjugate mathematical model which includes filtration and heat transfer equations in a porous body and boundary layer equations on its surface. Such an approach enables one to take into account complex interaction between heat and mass transfer in the gasdynamical flow and in the structure subjected to this flow.The main attention is given to the impact of the intraporous heat transfer intensity on the transpiration cooling efficiency.
A simple and accurate numerical network flow model for bionic micro heat exchangers
Energy Technology Data Exchange (ETDEWEB)
Pieper, M.; Klein, P. [Fraunhofer Institute (ITWM), Kaiserslautern (Germany)
2011-05-15
Heat exchangers are often associated with drawbacks like a large pressure drop or a non-uniform flow distribution. Recent research shows that bionic structures can provide possible improvements. We considered a set of such structures that were designed with M. Hermann's FracTherm {sup registered} algorithm. In order to optimize and compare them with conventional heat exchangers, we developed a numerical method to determine their performance. We simulated the flow in the heat exchanger applying a network model and coupled these results with a finite volume method to determine the heat distribution in the heat exchanger. (orig.)
Heat Transfer in MHD Squeezing Flow using Brinkman Model
Directory of Open Access Journals (Sweden)
Satish Chandra RAJVANSHI
2014-01-01
Full Text Available This study investigates squeezing flow of viscous incompressible fluid in a highly permeable medium between 2 parallel, permeable, unsteadily rotating plates in the presence of a magnetic field and radiation. The plates at time t* are separated by a distance H(1-at*1/2. Using a similarity transformation, the governing equations have been transformed into a system of non-linear ordinary differential equations. The resulting equations have been solved numerically by a shooting method. Graphs are presented to depict the temperature and heat transfer profiles. The results show a decline in the temperature profiles under the effect of enhanced radiation.doi:10.14456/WJST.2014.68
FEFLOW finite element modeling of flow, mass and heat transport in porous and fractured media
Diersch, Hans-Jörg G
2013-01-01
Placing advanced theoretical and numerical methods in the hands of modeling practitioners and scientists, this book explores the FEFLOW system for solving flow, mass and heat transport processes in porous and fractured media. Offers applications and exercises.
One-dimensional model for heat transfer to a supercritical water flow in a tube
Sallevelt, J.L.H.P.; Withag, J.A.M.; Bramer, E.A.; Brilman, D.W.F.; Brem, G.
2012-01-01
Heat transfer in water at supercritical pressures has been investigated numerically using a one-dimensional modeling approach. A 1D plug flow model has been developed in order to make fast predictions of the bulk-fluid temperature in a tubular flow. The chosen geometry is a vertical tube with an inn
Analytical modeling for the heat transfer in sheared flows of nanofluids
Ferrari, Claudio; L'vov, Victor S; Procaccia, Itamar; Rudenko, Oleksii; Boonkkamp, J H M ten Thije; Toschi, Federico
2012-01-01
We developed a model for the enhancement of the heat flux by spherical and elongated nano- particles in sheared laminar flows of nano-fluids. Besides the heat flux carried by the nanoparticles the model accounts for the contribution of their rotation to the heat flux inside and outside the particles. The rotation of the nanoparticles has a twofold effect, it induces a fluid advection around the particle and it strongly influences the statistical distribution of particle orientations. These dynamical effects, which were not included in existing thermal models, are responsible for changing the thermal properties of flowing fluids as compared to quiescent fluids. The proposed model is strongly supported by extensive numerical simulations, demonstrating a potential increase of the heat flux far beyond the Maxwell-Garnet limit for the spherical nanoparticles. The road ahead which should lead towards robust predictive models of heat flux enhancement is discussed.
Directory of Open Access Journals (Sweden)
Sangwoo Park
2016-04-01
Full Text Available Groundwater flow is one of the most important factors for the design of a ground heat exchanger (GHEX since the thermal environment of the ground around the buried GHEX is significantly affected by heat convection due to the groundwater flow. Several preceding studies have been conducted to develop analytical solutions to the heat transfer model of GHEX with consideration of groundwater flow. One of these solutions is the combined heat transfer model of conduction and convection. However, the developed combined analytical models are inapplicable to all of the configurations of ordinary GHEXs because these solutions assume that the inner part of the borehole is thermally inert or consists of the same material as that of the surrounding ground. In this paper, the applicability of the combined solid cylindrical heat source model, which is the most suitable to energy piles until now, was evaluated by performing a series of numerical analyses. In the numerical analysis, the inner part of the borehole was modeled as two different materials (i.e., permeable ground formation and impermeable fill such as concrete to evaluate applicability of the analytical solution along with different diameter-length (D/L ratios of borehole. In a small value of the D/L ratio, the analytical solution to the combined heat transfer model is in good agreement with the result of numerical analysis. On the other hand, when increasing the D/L ratio, the analytical solution significantly overestimates the effect of groundwater flow on the heat transfer of GHEXs because the analytical solution disregards the existence of the impermeable region in the borehole. Consequently, such tendency is more critical in the GHEX with a large D/L ratio such as large-diameter energy piles.
Three-dimensional Oldroyd-B fluid flow with Cattaneo-Christov heat flux model
Shehzad, S. A.; Hayat, T.; Abbasi, F. M.; Javed, Tariq; Kutbi, M. A.
2016-04-01
The impact of Cattaneo-Christov heat flux in three-dimensional flow of an Oldroyd-B fluid over a bidirectional stretching surface is explored in this article. The boundary layer flow of an incompressible fluid is considered. Heat transfer analysis is discussed via the Cattaneo-Christov model of heat flux. Similarity transformations lead to the nonlinear ordinary differential systems. Convergent solutions of dimensionless velocities and temperature have been computed. Convergence analysis is presented graphically and numerically. The influence of physical parameters on the velocities and temperature are plotted and discussed. We observed that the values of temperature gradient are higher for the Cattaneo-Christov heat flux model when we compare it with the values obtained by the simple Fourier's law of heat conduction.
Modeling Heat Flow In a Calorimeter Equipped With a Textured Solar Collector
Jaworske, Donald A.; Allen, Bradley J.
2001-01-01
Heat engines are being considered for generating electric power for minisatellite applications, particularly for those missions in high radiation threat orbits. To achieve this objective, solar energy must be collected and transported to the hot side of the heat engine. A solar collector is needed having the combined properties of high solar absorptance, low infrared emittance, and high thermal conductivity. To test candidate solar collector concepts, a simple calorimeter was designed, manufactured, and installed in a bench top vacuum chamber to measure heat flow. In addition, a finite element analysis model of the collector/calorimeter combination was made to model this heat flow. The model was tuned based on observations from the as-manufactured collector/calorimeter combination. In addition, the model was exercised to examine other collector concepts, properties, and scale up issues.
Rosa Duque, Maria
2016-04-01
Reinterpretation of old heat flow data or use of new data and new techniques of detection of the temperature under the surface have conducted to new heat flow density values in some regions of the globe. The problem of ice melting in Greenland and Antarctica caught the public's attention to the importance of knowledge on heat flow values and thermal structure of the globe. In the last years, several models were presented trying to obtain lithosphere and Moho thickness of the Iberia Peninsula. The work we intend to present is related with the SW part of the Iberia Peninsula ( south of the Ossa Morena zone, South Portuguese Zone and Algarve). The results obtained show a decrease in the thickness of the crust and the lithosphere in this region. Density anomalies in the crust are also referred. I intend to make the connection between the results of these models and the heat flow thermal conductivity, heat production and geological data available for the region, trying to explain the results of heat flow density data obtained.
Adaptive neuro-fuzzy modeling of transient heat transfer in circular duct air flow
Energy Technology Data Exchange (ETDEWEB)
Hasiloglu, Abdulsamet [Department of Electronics and Telecommunications Engineering, Engineering Faculty, Ataturk University, Erzurum (Turkey); Yilmaz, Mehmet; Comakli, Omer [Department of Mechanical Engineering, Engineering Faculty, Ataturk University, Erzurum (Turkey); Ekmekci, Ismail [Department of Mechanical Engineering, Engineering Faculty, Sakarya University, Sakarya (Turkey)
2004-11-01
The aim of this study is to demonstrate the usefulness of an adaptive neuro-fuzzy inference system (ANFIS) for the prediction of transient heat transfer. An ANFIS has been applied for the transient heat transfer in thermally and simultaneously developing circular duct flow, subjected to a sinusoidally varying inlet temperature. The experiments covered Reynolds numbers in the 2528{<=}Re{<=}4265 range and inlet heat input in the 0.01{<=}{beta}{<=}0.96 Hz frequency range. The accuracy of predictions and the adaptability of the ANFIS were examined, and good predictions were achieved for the temperature amplitudes of the transient heat transfer in thermally and simultaneously developing circular duct flow. The results show that the neuro-fuzzy can be used for modeling transient heat transfer in ducts. The results obtained with the ANFIS are also compared to those of a multiple linear regression and a neural network with a multi-layered feed-forward back-propagation algorithm. (authors)
Modelling of coupled heat and moisture flows around a buried electrical cable
Directory of Open Access Journals (Sweden)
Eslami Hossein
2016-01-01
Full Text Available The admissible current within a buried electrical power cable is limited by the maximum allowed temperature of the cable (Joule effect. The thermal properties of the surrounding soil controls heat dissipation around the cable. The main focus of the study was to evaluate the coupled heat and moisture flow around such buried electrical cables. The heat dissipation of a buried power cable was simulated in the surrounding soil at unsteady conditions. The hydro-thermal coupling was modelled by taking into account the moisture flow of liquid water and vapour, and the heat flow in the soil by convection and advection. As the thermal vapour diffusion enhancement factor (η appears to be a key parameter, the sensitivity study of the coupled heat and moisture flow in the ground regarding this parameter was performed. The variations of the degree of saturation and the temperature of the surrounding soil were studied over 180 days of heating. The results showed that the moisture flow was mainly caused by the vapour transport under temperature gradients. These results emphasized the significant effect of the hydrothermal characteristics of surrounding soil. The radius of influence of the power cable was also evaluated.
Calibration of a Numerical Model for Heat Transfer and Fluid Flow in an Extruder
DEFF Research Database (Denmark)
Hofstätter, Thomas; Pedersen, David Bue; Nielsen, Jakob Skov
2016-01-01
This paper discusses experiments performed in order to validate simulations on a fused deposition modelling (FDM) extruder. The nozzle has been simulated in terms of heat transfer and fluid flow. In order to calibrate and validate these simulations, experiments were performed giving a significant...... dynamical parameters. This research sets the foundation for further research within melted extrusion based additive manufacturing. The heating process of the extruder will be described and a note on the material feeding will be given....
Constraints on Pacific midplate swells from global depth-age and heat flow-age models
Stein, Carol A.; Stein, Seth
Oceanic midplate swells are identified by shallow seafloor depths. In turn, models of the processes giving rise to these regions rely on assessments of how their depths, surface heat flow, and flexural properties differ from those for lithosphere which is presumed not to have been affected by these processes. Such comparisons have been inhibited because reference thermal models, which are assumed to describe unperturbed lithosphere, predict deeper depths and lower heat flow than typically observed for lithosphere older than 70 Ma. As a result, both depth and heat flow anomalies can be overestimated. To address this difficulty, we have derived model GDH1 (Global Depth and Heat flow) by joint fitting of heat flow and bathymetry. GDH1, which has a hotter and thinner lithosphere than previous models, fits the depth and heat flow data significantly better, including the data from older lithosphere previously treated as anomalous. It also provides an improved fit to depth-to-basement data for ocean drilling sites, and to geoid offsets across fracture zones. The improved fit occurs for depth-age data from both the DBDB-5 digital bathymetry, and from regional medians from ship tracks, which yield comparable depth-age curves. We use GDH1 to study three classes of midplate swells: the Hawaiian and other hot spot swells, the Darwin Rise area of widespread Cretaceous volcanism, and the Superswell, considered a present analogue to the Darwin Rise. Heat flow on the Hawaiian swell, though anomalously high with respect to previous reference models, is at most slightly high relative to GDH1. The situation is similar for the Bermuda, Cape Verde, and Crozet hot spots. The absence of a significant heat flow anomaly favors a primarily dynamic, rather than thermal, origin for these swells. Similarly, the present depths and heat flow for the Darwin Rise are consistent with GDH1, although they were anomalous with respect to previous reference models. The depth and heat flow data thus
Two-Phase Flow Modeling in a Single Closed Loop Pulsating Heat Pipes
Institute of Scientific and Technical Information of China (English)
YANG Hong-hai; Sameer Khandekar; Sanka V. V. S. N. S. Manyam; Manfred Groll
2007-01-01
Mathematical modeling of pulsating heat pipes through 'first’ principles is a contemporary problem which remains quite elusive. Simplifications and assumptions made in all the modeling approaches developed so far render them unsuitable for engineering design. In this paper, a more realistic modeling scheme is presented which provides considerable try for thought toward the next progressive step. At high enough heat flux level, closed loop pulsating heat pipes experience a bulk internal unidirectional fluid circulation. Under such a condition, conventional two-phaseflow modeling in capillary tubes may be applied. This has been attempted for single-loop PHPs. A homogeneous model and a separated two-fluid flow model based on simultaneous conservation of mass, momentum and energy, have been developed for an equivalent 'open flow' system. The model allows prediction of two-phase flow parameters in each subsection of the device thereby providing important insights into its operation. The concept of 'void fraction constraint'in pulsating heat pipe operation is introduced and its relevance to future modeling attempts is outlined.
Metz, P. D.
A FORTRAN computer program called GROCS (GRound Coupled Systems) has been developed to study 3-dimensional underground heat flow. Features include the use of up to 30 finite elements or blocks of Earth which interact via finite difference heat flow equations and a subprogram which sets realistic time and depth dependent boundary conditions. No explicit consideration of mositure movement or freezing is given. GROCS has been used to model the thermal behavior of buried solar heat storage tanks (with and without insulation) and serpentine pipe fields for solar heat pump space conditioning systems. The program is available independently or in a form compatible with specially written TRNSYS component TYPE subroutines. The approach taken in the design of GROCS, the mathematics contained and the program architecture, are described. Then, the operation of the stand-alone version is explained. Finally, the validity of GROCS is discussed.
Calibration of a Numerical Model for Heat Transfer and Fluid Flow in an Extruder
DEFF Research Database (Denmark)
Hofstätter, Thomas; Pedersen, David Bue; Nielsen, Jakob Skov
2016-01-01
This paper discusses experiments performed in order to validate simulations on a fused deposition modelling (FDM) extruder. The nozzle has been simulated in terms of heat transfer and fluid flow. In order to calibrate and validate these simulations, experiments were performed giving a significant...
Tarlow, S.; Lev, E.; Zappa, C. J.; Karson, J.; Wysocki, B.
2011-12-01
Observation and investigation of surface cooling rates of active lava flows can help constrain thermal parameters necessary for creating of more precise lava flow models. To understand how the lava cools, temperature data was collected using an infrared video camera. We explored three models of the release of heat from lava stream; one based on heat conduction, another based on crust thickness and radiation, and a third model based on radiative cooling and variable crust thickness. The lava flow, part of the Syracuse University Lava Project (http://lavaproject.syr.edu), was made by pouring molten basalt at 1300 Celsius from a furnace into a narrow trench of sand. Hanging roughly 2 m over the trench, the infrared camera, records the lava's surface temperature for the duration of the flow. We determine the average surface temperature of the lava flow at a fixed location downstream as the mean of the lateral cross section of each frame of the IR imagery. From the recorded IR frames, we calculate the mean cross-channel temperature for each downstream distance. We then examine how this mean temperature evolves over time, and plot cooling curves for selected down-stream positions. We then compared the observed cooling behavior to that predicted by three cooling models: a conductive cooling model, a radiative cooling model with constant crust thickness, and a radiative cooling model with variable crust thickness. All three models are solutions to the one-dimensional heat equation. To create the best fit for the conductive model, we constrained thermal diffusivity and to create the best fit for the radiative model, we constrained crust thickness. From the comparison of our data to the models we can conclude that the lava flow's cooling is primarily driven by radiation.
Numerical modeling of electromagnetic heating of a liquid flowing in a pipeline
Kireev, Victor; Kovaleva, Liana; Shrubkovskiy, Ivan; Zinnatullin, Rasul
2016-12-01
The problem of the influence of radio-frequency electromagnetic field on the temperature distribution in laminar flow of dielectric liquid in a pipeline using numerical modeling has been investigated. The mathematical model of the process is based on the convective heat transfer equation and takes into account the effect of the electromagnetic radiation and heat exchange with the environment. The thermal effect of the electromagnetic field is considered by the introduction of volumetric heat sources. The results of the numerical modeling by comparing with the results of own experiment have been validated. It was shown that the use of an electromagnetic radiator can effectively heat a dielectric liquid with providing optimal temperature regime.
Applied research in hydraulics and heat flow
Asli, Kaveh Hariri; Asli, Hossein Hariri; Motlaghzadeh, Kasra
2014-01-01
PrefaceModeling for Heat Flow ProcessFluid and Fluid MechanicsTwo Phases Flow and Vapor BubbleDynamic Modeling for Heat and Mass TransferVapor Pressure and Saturation TemperatureFinite Difference and Method of Characteristics for Transitional FlowLagrangian and Eulerian Transitional FlowDynamic Modeling for Water FlowModeling for Flow ProcessDynamic Modeling for Mass and Momentum TransportIndex
Analysis of 2D flow and heat transfer modeling in fracture of porous media
Guo, Chunsheng; Nian, Xianbo; Liu, Yong; Qi, Chao; Song, Jinsheng; Yu, Wenhe
2017-08-01
Heat and mass transfer between porous media and fluid is a complex coupling process, which is widely used in various fields of engineering applications, especially for natural and artificial fractures in oil and gas extraction. In this study, a new method is proposed to deal with the flow and heat transfer problem of steady flow in a fracture. The fluid flow in a fracture was described using the same method as Mohais, who considered a fracture as a channel with porous wall, and the perturbation method was used to solve the mathematical model. Unlike previous studies, the shear jump boundary condition proposed by Ochoa-Tapia and Whitaker was used at the interface between the fluid and porous media. The main methods were perturbation analysis and the application of shear jump boundary conditions. The influence of permeability, channel width, shear jump degree and effective dynamic viscosity on the flow and heat transfer in the channel was studied by analysing the analytical solution. The distribution of axial velocity in the channel with the change of the typical parameters and the sensitivity of the heat transfer was obtained.
Calibration of a Numerical Model for Heat Transfer and Fluid Flow in an Extruder
DEFF Research Database (Denmark)
Hofstätter, Thomas; Pedersen, David Bue; Nielsen, Jakob Skov;
2016-01-01
This paper discusses experiments performed in order to validate simulations on a fused deposition modelling (FDM) extruder. The nozzle has been simulated in terms of heat transfer and fluid flow. In order to calibrate and validate these simulations, experiments were performed giving a significant...... look into the physical behaviour of the nozzle, heating and cooling systems. Experiments on the model were performed at different sub-mm diameters of the extruder. Physical parameters of the model – especially temperature dependent parameters – were set into analytical relationships in order to receive...... dynamical parameters. This research sets the foundation for further research within melted extrusion based additive manufacturing. The heating process of the extruder will be described and a note on the material feeding will be given....
Energy Technology Data Exchange (ETDEWEB)
Sundberg, Jan; Back, Paer-Erik; Laendell, Maerta; Sundberg, Anders (GEO INNOVA AB, Linkoeping (Sweden))
2009-06-15
This report presents modelling of temperature and temperature gradients in boreholes in Laxemar and Forsmark and fitting to measured temperature data. The modelling is performed with an analytical expression including thermal conductivity, thermal diffusivity, heat flow, internal heat generation and climate events in the past. As a result of the fitting procedure it is also possible to evaluate local heat flow values for the two sites. However, since there is no independent evaluation of the heat flow, uncertainties in for example thermal conductivity, diffusivity and the palaeoclimate temperature curve are transferred into uncertainties in the heat flow. Both for Forsmark and Laxemar, reasonably good fits were achieved between models and data on borehole temperatures. However, none of the general models achieved a fit within the 95% confidence intervals of the measurements. This was achieved in some cases for the additional optimised models. Several of the model parameters are uncertain. A good model fit does not automatically imply that 'correct' values have been used for these parameters. Similar model fits can be expected with different sets of parameter values. The palaeoclimatically corrected surface mean heat flow at Forsmark and Laxemar is suggested to be 61 and 56 mW/m2 respectively. If all uncertainties are combined, including data uncertainties, the total uncertainty in the heat flow determination is judged to be within +12% to -14% for both sites. The corrections for palaeoclimate are quite large and verify the need of site-specific climate descriptions. Estimations of the current ground surface temperature have been made by extrapolations from measured temperature logging. The mean extrapolated ground surface temperature in Forsmark and Laxemar is estimated to 6.5 deg and 7.3 deg C respectively. This is approximately 1.7 deg C higher for Forsmark, and 1.6 deg C higher for Laxemar compared to data in the report SKB-TR-06-23. Comparison with
Drying and Heating Modelling of Granular Flow: Application to the Mix-Asphalt Processes
Directory of Open Access Journals (Sweden)
L Le Guen
2011-01-01
Full Text Available Concrete asphalt is a hydrocarbon material that includes a mix of mineral components along with a bituminous binder. Prior to mixing, its production protocol requires drying and heating the aggregates. Generally performed in a rotary drum, these drying and heating steps within mix asphalt processes have never been studied from a physical perspective. We are thus proposing in the present paper to analyze the drying and heating mechanisms when granular materials and hot gases are involved in a co-current flow. This process step accounts for a large proportion of the overall energy consumed during hot-mix asphalt manufacturing. In the present context, the high energy cost associated with this step has encouraged developing new strategies specifically for the drying process. Applying new asphalt techniques so that an amount of moisture can be preserved in the asphalt concrete appears fundamental to such new strategies. This low-energy asphalt, also referred to as the "warm technique", depends heavily on a relevant prediction of the actual moisture content inside asphalt concrete during the mixing step. The purpose of this paper is to present a physical model dedicated to the evolution in temperature and moisture of granular solids throughout the drying and heating steps carried out inside a rotary drum. An initial experimental campaign to visualize inside a drum at the pilot scale (i.e. 1/3 scale has been carried out in order to describe the granular flow and establish the necessary physical assumptions for the drying and heating model. Energy and mass balance equations are solved by implementing an adequate heat and mass transfer coupling, yielding a 1D model from several parameters that in turn drives the physical modeling steps. Moreover, model results will be analyzed and compared to several measurements performed in an actual asphalt mix plant at the industrial scale (i.e. full scale.
A full 3D model of fluid flow and heat transfer in an E.B. heated liquid metal bath
Matveichev, A.; Jardy, A.; Bellot, J. P.
2016-07-01
In order to study the dissolution of exogeneous inclusions in the liquid metal during processing of titanium alloys, a series of dipping experiments has been performed in an Electron Beam Melting laboratory furnace. Precise determination of the dissolution kinetics requires knowing and mastering the exact thermohydrodynamic behavior of the melt pool, which implies full 3D modeling of the process. To achieve this goal, one needs to describe momentum and heat transfer, phase change, as well as the development of flow turbulence in the liquid. EB power input, thermal radiation, heat loss through the cooling circuit, surface tension effects (i.e. Marangoni-induced flow) must also be addressed in the model. Therefore a new solver dealing with all these phenomena was implemented within OpenFOAM platform. Numerical results were compared with experimental data from actual Ti melting, showing a pretty good agreement. In the second stage, the immersion of a refractory sample rod in the liquid pool was simulated. Results of the simulations showed that the introduction of the sample slightly disturbs the flow field inside the bath. The amount of such disturbance depends on the exact location of the dipping.
Modeling the Material Flow and Heat Transfer in Reverse Dual-Rotation Friction Stir Welding
Shi, L.; Wu, C. S.; Liu, H. J.
2014-08-01
Reverse dual-rotation friction stir welding (RDR-FSW) is a novel modification of conventional friction stir welding (FSW) process. During the RDR-FSW process, the tool pin and the assisted shoulder are separated and rotate with opposite direction independently, so that there are two material flows with reverse direction. The material flow and heat transfer in RDR-FSW have significant effects on the microstructure and properties of the weld joint. A 3D model is developed to quantitatively analyze the effects of the separated tool pin and the assisted shoulder which rotate in reverse direction on the material flow and heat transfer during RDR-FSW process. Numerical simulation is conducted to predict the temperature profile, material flow field, streamlines, strain rate, and viscosity distributions near the tool. The calculated results show that as the rotation speed of the tool pin increases, the temperature near the tool gets higher, the zone with higher temperature expands, and approximately symmetric temperature distribution is obtained near the tool. Along the workpiece thickness direction, the calculated material flow velocity and its layer thickness near the tool get lowered because the effect of the shoulder is weakened as the distance away from the top surface increases. The model is validated by comparing the predicted values of peak temperature at some typical locations with the experimentally measured ones.
Lachenbruch, Arthur H.; Marshall, B. Vaughan
1969-01-01
Defines heat flow as the flux at the earth's solid surface of heat conducted from the interior; the heat-flow-unit (hfu) is on the order of 1-millionth calorie through each sq cm of the surface/sec, which is enough to melt a 4-mm layer of ice over the earth's surface/yr. Earth heat originates from radioactive decay of U, Th and K in the crust and mantle. Although land heat-flow measurements in the Arctic are too few for regional interpretation, those from Cape Thompson, Barrow and Cape Simpson, Northern Alaska are discussed and figured to show what they contribute to understanding of permafrost, climatic change and shoreline movements. Measuring thermal conductivity and gradient is much simpler in ocean basins than on land. Locations of such measurements are mapped, the results for the Alaskan quadrant in more detail. The sharp change in heat flow at the edge of the Alpha Cordillera, shown in a geothermal model, suggests that this feature is a huge accumulation of basalt, rather than mantle material or remnant of a foundering continent as previously postulated. Future Arctic heat flow studies are discussed.
Modelling flow and heat transfer in two-fluid interfacial flows, with applications to drops and jets
Mehdi-Nejad, Vala
2003-10-01
A two-dimensional, axi-symmetric model is developed to calculate flow and heat transfer in a two-fluid system. The model uses one set of the governing equations combined with a volume tracking method on a fixed structured mesh to model the simultaneous movement of mass, momentum and energy across cell boundaries. Both first and second-order methods are used to approximate temperature fields with sharp gradients that exist near a fluid-fluid interface. The model is first used to simulate the effect of surrounding air during a droplet impact. Bubble entrapment is observed in both numerical simulation and experimental photographs. The impact of water, n-heptane and molten nickel droplets on a solid surface is simulated. When a droplet approaches another surface, air in the gap between them was forced out. Increased air pressure below the droplet creates a depression in its surface, in which air is trapped. Different behaviors observed for water and n-heptane simulations are attributed to differences in wetting behavior. Next, to demonstrate the capabilities of the model, the interfacial heat transfer from molten tin droplets falling in an oil bath is modelled. The development of vortices behind droplets is simulated and the effect of fluid recirculation and oil thermal conductivity on heat dissipation is studied. The thesis concludes with application of the model to a study of interfacial heat transfer during jet break up. It is demonstrated that the change of fluid properties associated with interfacial heat transfer affects the jet break up and the resulting droplet size. It is also shown that obtaining a desirable droplet size during jet break up not only depends on hydrodynamic conditions such as nozzle diameter, jet initial velocity, and pressure, but also on thermal conditions such as the initial jet temperature and the surrounding fluid thermal properties.
Directory of Open Access Journals (Sweden)
Yu Zhang
2015-10-01
Full Text Available In this article, we begin with the non-homogeneous model for the non-differentiable heat flow, which is described using the local fractional vector calculus, from the first law of thermodynamics in fractal media point view. We employ the local fractional variational iteration algorithm II to solve the fractal heat equations. The obtained results show the non-differentiable behaviors of temperature fields of fractal heat flow defined on Cantor sets.
Mathematical Modeling of Magneto Pulsatile Blood Flow Through a Porous Medium with a Heat Source
Directory of Open Access Journals (Sweden)
Sharma B.K
2015-05-01
Full Text Available In the present study a mathematical model for the hydro-magnetic non-Newtonian blood flow in the non-Darcy porous medium with a heat source and Joule effect is proposed. A uniform magnetic field acts perpendicular to the porous surface. The governing non-linear partial differential equations have been solved numerically by applying the explicit finite difference Method (FDM. The effects of various parameters such as the Reynolds number, hydro-magnetic parameter, Forchheimer parameter, Darcian parameter, Prandtl number, Eckert number, heat source parameter, Schmidt number on the velocity, temperature and concentration have been examined with the help of graphs. The present study finds its applications in surgical operations, industrial material processing and various heat transfer operations.
Conder, J. R.; Gunn, D. J.; Shaikh, M. A.
1982-08-01
A mathematical model is presented for the vaporisation of liquid from a laminar film flowing down the inside surface of a smooth tube into a countercurrent laminar flow of gas. The partial differential equations that describe temperature and composition distributions are integrated across the tube to give a set of four coupled ordinary differential equations. A numerical method for the solution of the equations is proposed and examined; the method is posed to solve the transient response for heat and mass transfer. A satisfactory solution is found for a range of space and time intervals. The mathematical model has been validated by experimental measurements on a falling film evaporator with evaporation occurring at sub-boiling temperatures from a laminar liquid film into a laminar gas stream. The performance of the evaporator is assessed.
Numerical modeling of fluid flow and heat transfer in a narrow Taylor-Couette-Poiseuille system
Energy Technology Data Exchange (ETDEWEB)
Poncet, Sebastien, E-mail: poncet@l3m.univ-mrs.f [Laboratoire M2P2, UMR 6181 CNRS, Universite d' Aix-Marseille, Ecole Centrale Marseille, IMT la Jetee, 38 rue Joliot-Curie, 13451 Marseille (France); Haddadi, Sofia, E-mail: sofia.haddadi@gmail.co [Laboratoire M2P2, UMR 6181 CNRS, Universite d' Aix-Marseille, Ecole Centrale Marseille, IMT la Jetee, 38 rue Joliot-Curie, 13451 Marseille (France); Viazzo, Stephane, E-mail: stephane.viazzo@l3m.univ-mrs.f [Laboratoire M2P2, UMR 6181 CNRS, Universite d' Aix-Marseille, Ecole Centrale Marseille, IMT la Jetee, 38 rue Joliot-Curie, 13451 Marseille (France)
2011-02-15
Research highlights: {yields} Turbulence modeling of opened Taylor-Couette flows. {yields} Parametric study of the flow parameters on the hydrodynamic and thermal fields. {yields} The RSM as an adequate level of closure for rotating flows. - Abstract: We consider turbulent flows in a differentially heated Taylor-Couette system with an axial Poiseuille flow. The numerical approach is based on the Reynolds Stress Modeling (RSM) of widely validated in various rotor-stator cavities with throughflow () and heat transfer (). To show the capability of the present code, our numerical predictions are compared very favorably to the velocity measurements of in the isothermal case, for both the mean and turbulent fields. The RSM model improves, in particular, the predictions of the k-{epsilon} model of . Then, the second order model is applied for a large range of rotational Reynolds (3744 {<=} Re{sub i} {<=} 37,443) and Prandtl numbers (0.01 {<=} Pr {<=} 12), flow rate coefficient (0 {<=} C{sub w} {<=} 30,000) in a very narrow cavity of radius ratio s = R{sub i}/R{sub o} = 0.961 and aspect ratio L = (R{sub o} - R{sub i})/h = 0.013, where R{sub i} and R{sub o} are the radii of the inner and outer cylinders respectively and h is the cavity height. Temperature gradients are imposed between the incoming fluid and the inner and outer cylinders. The mean hydrodynamic and thermal fields reveal three distinct regions across the radial gap with a central region of almost constant axial and tangential mean velocities and constant mean temperature. Turbulence, which is weakly anisotropic, is mainly concentrated in that region and vanishes towards the cylinders. The mean velocity distributions are not clearly affected by the rotational Reynolds number and the flow rate coefficient. The effects of the flow parameters on the thermal field are more noticeable and considered in details. Correlations for the averaged Nusselt numbers along both cylinders are finally provided according to the
Mathematical modeling of fluid flow, heat transfer and inclusion transport in a four strand tundish
Institute of Scientific and Technical Information of China (English)
Yufeng Wang; Guanghua Wen; Ping Tang; Mingmei Zhu; Yuanqing Chen; Weizhao Song
2007-01-01
Mathematical simulation was used for trouble-shooting and optimization.By the mathematical simulation,fluid flow and heat transfer of molten-steel in a four-strand tundish of a billet caster under different conditions (bare tundish and tundish with flow control device) were analyzed.The results showed that (1) the tundish with flow control device (FCD) has an important effect on the fluid pattern and temperature distribution; (2) the unsteady solving method was used to model the inclusion motions at different time periods,and it showed that the FCD is advantageous to separate the nonmetallic inclusions.According to the simulation results,the main problem existing in the industry production was found,and some helpful measurements were executed.Consequently,the large nonmetallic inclusions were separated,and the content of total oxygen was reduced.The quality of steel was greatly improved.
On Cattaneo-Christov heat flux model for Carreau fluid flow over a slendering sheet
Hashim; Khan, Masood
The underlying intentions of this article are to investigate the impact of non-Fourier heat flux model on the stagnation-point flow of non-Newtonian Carreau fluid. In this study, the innovative Cattaneo-Christov constitutive model is introduced to study the characteristics of thermal relaxation time. The flow is impelled by a slendering surface which is of the variable thickness. In the model, the physical mechanism responsible for homogeneous-heterogeneous reactions are further taken into account. Also, the diffusion coefficients of the reactant and auto catalyst are considered to be equal. The governing non-linear partial differential equations consisting of the momentum, energy and concentration equations are reduced to the coupled ordinary differential equations by means of local similarity transformations. The transformed ODEs are tackled numerically by employing an effective shooting algorithm along with the Runge-Kutta Fehlberg scheme. The physical characteristics of the fluid velocity, temperature and concentration profiles are illuminated with the variation of numerous governing factors and are presented graphically. For instance, our result indicates that the temperature and thermal boundary layer thickness are lower in case of Cattaneo-Christov heat flux model when compared to classical Fourier's heat model. Meanwhile, the rate of heat transfer is significantly improved by a high wall thickness parameter and an opposite influence is found due to the thermal relaxation parameter. We further noticed that a higher value of homogeneous and heterogeneous reaction parameter corresponds to a deceleration in the concentration field and it shows an inverse relation for the Schmidt number. A correlation with accessible results for specific cases is found with fabulous consent.
A model for heat flow in deep borehole disposals of high-level nuclear waste
Gibb, Fergus G. F.; Travis, Karl P.; McTaggart, Neil A.; Burley, David
2008-05-01
Deep borehole disposal (DBD) is emerging as a viable alternative to mined repositories for many forms of highly radioactive waste. It is geologically safer, more secure, less environmentally disruptive and potentially more cost-effective. All high-level wastes generate heat leading to elevated temperatures in and around the disposal. In some versions of DBD this heat is an essential part of the disposal while in others it affects the performances of materials and waste forms and can threaten the success of the disposal. Different versions of DBD are outlined, for all of which it is essential to predict the distribution of temperature with time. A generic physical model is established and a mathematical model set up involving the transient conductive heat flow differential equation for a cylindrical source term with realistic decay. This equation is solved using the method of Finite Differences. A Fortran computer code (GRANITE) has been developed for the model in the context of DBD and validated against theoretical and other benchmarks. The limitations of the model, code, input parameters and data used are discussed and it is concluded that the model provides a satisfactory basis for predicting temperatures in DBD. Examples of applications to some DBD scenarios are given and it is shown that the results are essential to the design strategy of the DBD versions, geometric details and choice of materials used. Without such modeling it would be impossible to progress DBD of nuclear wastes; something that is now being given serious consideration in several countries.
Directory of Open Access Journals (Sweden)
S. Yamoah
2012-06-01
Full Text Available The pebble bed type high temperature gas cooled nuclear reactor is a promising option for next generation reactor technology and has the potential to provide high efficiency and cost effective electricity generation. The reactor unit heat transfer poses a challenge due to the complexity associated with the thermalflow design. Therefore to reliably simulate the flow and heat transport of the pebble bed modular reactor necessitates a heat transfer model that deals with radiation as well as thermal convection and conduction. In this study, a model with the capability to simulate fluid flow and heat transfer in the pebble bed modular reactor core has been developed. The developed model was implemented on a personal computer using FORTRAN 95 programming language. Several important fluid flow and heat transfer parameters have been examined: including the pressure drop over the reactor core, the heat transfer coefficient, the Nusselt number and the effective thermal conductivity of the fuel pebbles. Results obtained from the simulation experiments show a uniform pressure in the radial direction for a core to fuel element diameter (D/d ratio>20 and the heat transfer coefficient increases with increasing temperature and coolant mass flow rate. The model can adequately account for the flow and heat transfer phenomenon and the loss of pressure through friction in the pebble bed type high temperature nuclear reactor.
Energy Technology Data Exchange (ETDEWEB)
Mansoori, Zohreh; Saffar-Avval, Majid; Basirat-Tabrizi, Hassan; Ahmadi, Goodarz; Lain, Santiago
2002-12-01
A thermo-mechanical turbulence model is developed and used for predicting heat transfer in a gas-solid flow through a vertical pipe with constant wall heat flux. The new four-way interaction model makes use of the thermal k{sub {theta}}-{tau}{sub {theta}} equations, in addition to the hydrodynamic k-{tau} transport, and accounts for the particle-particle and particle-wall collisions through a Eulerian/Lagrangian formulation. The simulation results indicate that the level of thermal turbulence intensity and the heat transfer are strongly affected by the particle collisions. Inter-particle collisions attenuate the thermal turbulence intensity near the wall but somewhat amplify the temperature fluctuations in the pipe core region. The hydrodynamic-to-thermal times-scale ratio and the turbulent Prandtl number in the region near the wall increase due to the inter-particle collisions. The results also show that the use of a constant or the single-phase gas turbulent Prandtl number produces error in the thermal eddy diffusivity and thermal turbulent intensity fields. Simulation results also indicate that the inter-particle contact heat conduction during collision has no significant effect in the range of Reynolds number and particle diameter studied.
Modeling of flow and heat transfer for fluids at supercritical conditions
Gallaway, Tara
2011-12-01
The Supercritical Water Reactor (SCWR) has been proposed as one of the six Generation IV reactor design concepts under consideration. The key feature of the SCWR is that water at supercritical pressures is used as the reactor coolant. At supercritical pressures, the working fluid does not undergo phase change as it is heated, but rather the fluid properties experience dramatic variations throughout what is known as the pseudo-critical region. Highly nonuniform temperature and uid property distributions are expected in the reactor core, which will have a significant impact on turbulence and heat transfer as well as stability limits for future SCWRs. The goal of this work is to understand and predict the effects of these fluid property variations on turbulence and heat transfer throughout the reactor core and to predict the potential onset of dynamic instabilities. CO2 at supercritical conditions is included in the current study due in some part to its use as a viable simulant fluid in place of water for experimental studies. The use of CO2 at supercritical conditions as a reactor coolant has also gained popularity in recent years. Spline-type property models have been developed for both water and CO2 at supercritical pressures in order to include the property variations into a numerical solver. Turbulence and heat transfer models for fluids at supercritical conditions have been developed and implemented into the NPHASE-CMFD computer code. The results of predictions using the proposed models have been compared to experimental data from the Korea Atomic Energy Research Institute (KAERI) for various heat transfer regimes. While no model is without some deficiency, the Chien Low-Reynolds k -- epsilon model performs best at predicting the experimental data. A stability model has been developed and is presented in this dissertation as well. This model utilizes three different solution methods and tests the effects of inlet temperature, mass flow rate, local loss
Modeling tangent hyperbolic nanoliquid flow with heat and mass flux conditions
Hayat, T.; Ullah, I.; Alsaedi, A.; Ahmad, B.
2017-03-01
This attempt predicts the hydromagnetic flow of a tangent hyperbolic nanofluid originated by a non-linear impermeable stretching surface. The considered nanofluid model takes into account the Brownian diffusion and thermophoresis characteristics. An incompressible liquid is electrically conducted in the presence of a non-uniformly applied magnetic field. Heat and mass transfer phenomena posses flux conditions. Mathematical formulation is developed by utilizing the boundary layer approach. A system of ordinary differential equations is obtained by employing adequate variables. Convergence for obtained series solutions is checked and explicitly verified through tables and plots. Effects of numerous pertinent variables on velocity, temperature and concentration fields are addressed. Computations for surface drag coefficient, heat transfer rate and mass transfer rate are presented and inspected for the influence of involved variables. Temperature is found to enhance for a higher magnetic variable. Present and previous outcomes in limiting sense are also compared.
Energy Technology Data Exchange (ETDEWEB)
Raustad, Richard; Nigusse, Bereket; Domitrovic, Ron
2013-09-30
The University of Central Florida/Florida Solar Energy Center, in cooperation with the Electric Power Research Institute and several variable-refrigerant-flow heat pump (VRF HP) manufacturers, provided a detailed computer model for a VRF HP system in the United States Department of Energy's (U.S. DOE) EnergyPlus? building energy simulation tool. Detailed laboratory testing and field demonstrations were performed to measure equipment performance and compare this performance to both the manufacturer's data and that predicted by the use of this new model through computer simulation. The project goal was to investigate the complex interactions of VRF HP systems from an HVAC system perspective, and explore the operational characteristics of this HVAC system type within a laboratory and real world building environment. Detailed laboratory testing of this advanced HVAC system provided invaluable performance information which does not currently exist in the form required for proper analysis and modeling. This information will also be useful for developing and/or supporting test standards for VRF HP systems. Field testing VRF HP systems also provided performance and operational information pertaining to installation, system configuration, and operational controls. Information collected from both laboratory and field tests were then used to create and validate the VRF HP system computer model which, in turn, provides architects, engineers, and building owners the confidence necessary to accurately and reliably perform building energy simulations. This new VRF HP model is available in the current public release version of DOE?s EnergyPlus software and can be used to investigate building energy use in both new and existing building stock. The general laboratory testing did not use the AHRI Standard 1230 test procedure and instead used an approach designed to measure the field installed full-load operating performance. This projects test methodology used the air
Quasi-steady-state model of a counter flow air-to-air heat exchanger with phase change
DEFF Research Database (Denmark)
Rose, Jørgen; Nielsen, Toke Rammer; Kragh, Jesper;
2008-01-01
into account the effects of condensation and frost formation. The model is developed as an Excel spreadsheet, and specific results are compared with laboratory measurements. As an example, the model is used to determine the most energy-efficient control strategy for a specific heat-exchanger under northern......Using mechanical ventilation with highly efficient heat-recovery in northern European or arctic climates is a very efficient way of reducing the energy use for heating in buildings. However, it also presents a series of problems concerning condensation and frost formation in the heat......-exchanger. Developing highly efficient heat-exchangers and strategies to avoid/remove frost formation implies the use of detailed models to predict and evaluate different heat-exchanger designs and strategies. This paper presents a quasi-steady-state model of a counter-flow air-to-air heat-exchanger that takes...
Numerical modeling of heat transfer and fluid flow in laser metal deposition by powder injection
Fan, Zhiqiang
Laser metal deposition is an additive manufacturing technique which allows quick fabrication of fully-dense metallic components directly from Computer Aided Design (CAD) solid models. A self-consistent three-dimensional model was developed for the laser metal deposition process by powder injection, which simulates heat transfer, phase changes, and fluid flow in the melt pool. The governing equations for solid, liquid and gas phases in the calculation domain have been formulated using the continuum model. The free surface in the melt pool has been tracked by the Volume of Fluid (VOF) method, while the VOF transport equation was solved using the Piecewise Linear Interface Calculation (PLIC) method. Surface tension was modeled by taking the Continuum Surface Force (CSF) model combined with a force-balance flow algorithm. Laser-powder interaction was modeled to account for the effects of laser power attenuation and powder temperature rise during the laser metal deposition process. The governing equations were discretized in the physical space using the finite volume method. The advection terms were approximated using the MUSCL flux limiter scheme. The fluid flow and energy equations were solved in a coupled manner. The incompressible flow equations were solved using a two-step projection method, which requires a solution of a Poisson equation for the pressure field. The discretized pressure Poisson equation was solved using the ICCG (Incomplete Cholesky Conjugate Gradient) solution technique. The energy equation was solved by an enthalpy-based method. Temperature-dependent thermal-physical material properties were considered in the numerical implementation. The numerical model was validated by comparing simulations with experimental measurements.
A porosity model for flow resistance calculation of heat exchanger with louvered fins
Energy Technology Data Exchange (ETDEWEB)
Kim, Taek Keun [Halla Visteon Climate Control Corp. Daejeon (Korea, Republic of); Kang, Hie Chan [Kunsan National University, Gunsan (Korea, Republic of); Lee, Joon Sik [Seoul National University, Seoul (Korea, Republic of)
2016-04-15
A full 3-dimensional flow simulation of a louvered fin heat exchanger assembly requires a huge number of grid points and enormous computing time. This work proposes a porous media model for the flow resistance calculation of the louvered fin side in order to efficiently simulate a complex 3-dimensional flow over the louvered fins. In the present model, we determine the permeability and Ergun constant in the modified Darcy equation. We first build up a database of the friction factor from the available experimental data and our own CFD data, and then develop the friction factor correlation in the range of the Reynolds number based on the louver pitch from 0.001 to 20000 for 14 different louvered fin types. We use the non-linear and multi-linear regression analyses to obtain the friction factor correlation as a function of louvered fin geometric parameters such as louver pitch, louver angle and fin pitch. The present friction factor correlation shows an excellent agreement with the previous experimental and CFD data. The modified Darcy equation with the proposed permeability and Ergun constant for the louvered fin side can easily be coupled with the 3-dimensional computation of the main tube flow.
Modeling of dissociation and energy transfer in shock-heated nitrogen flows
Energy Technology Data Exchange (ETDEWEB)
Munafò, A., E-mail: munafo@illinois.edu [Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Talbot Laboratory, 104 S. Wright St., Urbana, Illinois 61801 (United States); NASA Ames Research Center, Moffett Field, California 94035 (United States); Liu, Y., E-mail: yen.liu@nasa.gov [NASA Ames Research Center, Moffett Field, California 94035 (United States); Panesi, M., E-mail: mpanesi@illinois.edu [Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Talbot Laboratory, 104 S. Wright St., Urbana, Illinois 61801 (United States)
2015-12-15
This work addresses the modeling of dissociation and energy transfer processes in shock heated nitrogen flows by means of the maximum entropy linear model and a newly proposed hybrid bin vibrational collisional model. Both models aim at overcoming two of the main limitations of the state of the art non-equilibrium models: (i) the assumption of equilibrium between rotational and translational energy modes of the molecules and (ii) the reliance on the quasi-steady-state distribution for the description of the population of the internal levels. The formulation of the coarse-grained models is based on grouping the energy levels into bins, where the population is assumed to follow a Maxwell-Boltzmann distribution at its own temperature. Different grouping strategies are investigated. Following the maximum entropy principle, the governing equations are obtained by taking the zeroth and first-order moments of the rovibrational master equations. The accuracy of the proposed models is tested against the rovibrational master equation solution for both flow quantities and population distributions. Calculations performed for free-stream velocities ranging from 5 km/s to 10 km/s demonstrate that dissociation can be accurately predicted by using only 2-3 bins. It is also shown that a multi-temperature approach leads to an under-prediction of dissociation, due to the inability of the former to account for the faster excitation of high-lying vibrational states.
UNSAT-H Version 2. 0: Unsaturated soil water and heat flow model
Energy Technology Data Exchange (ETDEWEB)
Fayer, M.J.; Jones, T.L.
1990-04-01
This report documents UNSAT-H Version 2.0, a model for calculating water and heat flow in unsaturated media. The documentation includes the bases for the conceptual model and its numerical implementation, benchmark test cases, example simulations involving layered soils and plant transpiration, and the code listing. Waste management practices at the Hanford Site have included disposal of low-level wastes by near-surface burial. Predicting the future long-term performance of any such burial site in terms of migration of contaminants requires a model capable of simulating water flow in the unsaturated soils above the buried waste. The model currently used to meet this need is UNSAT-H. This model was developed at Pacific Northwest Laboratory to assess water dynamics of near-surface, waste-disposal sites at the Hanford Site. The code is primarily used to predict deep drainage as a function of such environmental conditions as climate, soil type, and vegetation. UNSAT-H is also used to simulate the effects of various practices to enhance isolation of wastes. 66 refs., 29 figs., 7 tabs.
Naphon, P.; Arisariyawong, T.; Nualboonrueng, T.
2017-07-01
A computation fluid dynamics study has been performed to analyze the nanofluids heat transfer and flow characteristics in the spirally coiled tubes. Eulerian two-phase turbulent model is applied to simulate the heat transfer and flow characteristics in the vertical spirally coiled tube. The spirally coiled tubes are fabricated by bending a 8.50 mm inner diameter straight copper tube into a spiral-coil with two different curvature ratios of 0.035, 0.060. The predicted results are verified with the present measured data. Reasonable agreement is obtained from the comparison between the measured data and the predicted results. In addition, due to the centrifugal force, the induced secondary flow has significant effect on the heat transfer enhancement as flowing through the spirally coiled tube. Effects of curvature, nanofluids concentration and hot water temperature on the nanofluids heat transfer characteristics and pressure drop are considered.
Institute of Scientific and Technical Information of China (English)
Wei LU; Yan-yong XIANG
2012-01-01
Experiments of saturated water flow and heat transfer were conducted for a meter-scale model of regularly fractured granite.The fractured rock model (height 1502.5 mm,width 904 mm,and thickness 300 mm),embedded with two vertical and two horizontal fractures of pre-set apertures,was constructed using 18 pieces of intact granite.The granite was taken from a site currently being investigated for a high-level nuclear waste repository in China.The experiments involved different heat source temperatures and vertical water fluxes in the embedded fractures either open or filled with sand.A finite difference scheme and computer code for calculation of water flow and heat transfer in regularly fractured rocks was developed,verified against both the experimental data and calculations from the TOUGH2 code,and employed for parametric sensitivity analyses.The experiments revealed that,among other things,the temperature distribution was influenced by water flow in the fractures,especially the water flow in the vertical fracture adjacent to the heat source,and that the heat conduction between the neighboring rock blocks in the model with sand-filled fractures was enhanced by the sand,with larger range of influence of the heat source and longer time for approaching asymptotic steady-state than those of the model with open fractures.The temperatures from the experiments were in general slightly smaller than those from the numerical calculations,probably due to the fact that a certain amount of outward heat transfer at the model perimeter was unavoidable in the experiments.The parametric sensitivity analyses indicated that the temperature distribution was highly sensitive to water flow in the fractures,and the water temperature in the vertical fracture adjacent to the heat source was rather insensitive to water flow in other fractures.
Review:Liquid film dryout model for predicting critical heat flux in annular two-phase flow
Institute of Scientific and Technical Information of China (English)
Bo JIAO; Li-min QIU; Jun-liang LU; Zhi-hua GAN
2009-01-01
Gas-liquid two-phase flow and heat transfer can be encountered in numerous fields, such as chemical engineering, refrigeration, nuclear power reactor, metallurgical industry, spaceflight. Its critical heat flux (CHF) is one of the most important factors for the system security of engineering applications. Since annular flow is the most common flow pattern in gas-liquid two-phase flow, predicting CHF of annular two-phase flow is more significant. Many studies have shown that the liquid film dryout model is successful for that prediction, and determining the following parameters will exert predominant effects on the accuracy of this model: onset of annular flow, inception criterion for droplets entrainment, entrainment fraction, droplets deposi-tion and entrainment rates. The main theoretical results achieved on the above five parameters are reviewed; also, limitations in the existing studies and problems for further research are discussed.
Conry, Patrick; Sharma, Ashish; Leo, Laura; Fernando, H. J. S.; Potosnak, Mark; Hellmann, Jessica
2013-11-01
The modeling of urban heat island (UHI) requires a multi-scale approach as it involves numerous physical phenomena spanning a range of scales. We have performed a comprehensive study of Chicago's UHI via coupling of mesoscale Weather Research and Forecasting (WRF) and micro-scale ENVI-met models. The application of the latter model to a Lincoln Park neighborhood and a parallel observational campaign will be the primary focus of this presentation. ENVI-met employs a computational fluid dynamics model to represent heterogeneity of urban areas, providing fine resolution output of UHI dynamics. In the field campaign, two stations located on rooftops of DePaul University buildings were each equipped with a sonic anemometer and vertical array of thermocouples, allowing investigations of spatial variability of flow, turbulent fluxes, and temperature profiles in an urban roughness sublayer. One of these was located above a rooftop garden and the other above a conventional rooftop. Downscaled output from the WRF model or a set of observational data served as initial and boundary conditions for the ENVI-met model. The model's predicative capabilities were assessed through comparison with another set of observational data, and dynamical causes for the model's poor behavior were identified. Funded by NSF Grant No. 0934592 and ND-ECI.
Energy Technology Data Exchange (ETDEWEB)
Raustad, Richard; Nigusse, Bereket; Domitrovic, Ron
2013-09-30
The University of Central Florida/Florida Solar Energy Center, in cooperation with the Electric Power Research Institute and several variable-refrigerant-flow heat pump (VRF HP) manufacturers, provided a detailed computer model for a VRF HP system in the United States Department of Energy's (U.S. DOE) EnergyPlus? building energy simulation tool. Detailed laboratory testing and field demonstrations were performed to measure equipment performance and compare this performance to both the manufacturer's data and that predicted by the use of this new model through computer simulation. The project goal was to investigate the complex interactions of VRF HP systems from an HVAC system perspective, and explore the operational characteristics of this HVAC system type within a laboratory and real world building environment. Detailed laboratory testing of this advanced HVAC system provided invaluable performance information which does not currently exist in the form required for proper analysis and modeling. This information will also be useful for developing and/or supporting test standards for VRF HP systems. Field testing VRF HP systems also provided performance and operational information pertaining to installation, system configuration, and operational controls. Information collected from both laboratory and field tests were then used to create and validate the VRF HP system computer model which, in turn, provides architects, engineers, and building owners the confidence necessary to accurately and reliably perform building energy simulations. This new VRF HP model is available in the current public release version of DOE?s EnergyPlus software and can be used to investigate building energy use in both new and existing building stock. The general laboratory testing did not use the AHRI Standard 1230 test procedure and instead used an approach designed to measure the field installed full-load operating performance. This projects test methodology used the air
Directory of Open Access Journals (Sweden)
Shih-Cheng Hu
2016-12-01
Full Text Available A mathematical model is developed using the Matlab/Simulink platform to investigate heat and mass transfer performance of cross-flow and counterflow dehumidifiers with Lithium Chloride (LiCl solution. In the liquid desiccant dehumidifier, the orthogonal polynomial basis is used to simulate the combined processes of heat and mass transfer. The temperature profiles on cross-flow and countercurrent flow dehumidifiers are demonstrated. The resultant counter flow air changes the temperature profile of the LiCl solution in the longitudinal direction because of the drag forces. In addition, when inlet airflow rate reaches 15 kg·s−1, the temperature effect becomes less obvious and may be reasonably negligible. Under these conditions, the air changes the design factor and determines the interfacial temperature. It is demonstrated that the mathematical model can be of great value in the design and improvement of cross-flow and countercurrent flow dehumidifiers.
Modeling of Air Temperature for Heat Exchange due to Vertical Turbulence and Horizontal Air Flow
Institute of Scientific and Technical Information of China (English)
ZHANG Lei; MENG Qing-lin
2009-01-01
In order to calculate the air temperature of the near surface layer in urban environment,the Sur-face layer air was divided into several layers in the vertical direction,and some energy bakmce equations were de-veloped for each air layer,in which the heat exchange due to vertical turbulence and horizontal air flow was tak-en into account.Then,the vertical temperature distribution of the surface layer air was obtained through the coupled calculation using the energy balance equations of underlying surfaces and building walls.Moreover,the measured air temperatures in a small area (with a horizontal scale of less than 500 m) and a large area (with ahorizontal scale of more than 1000 m) in Guangzhou in summer were used to validate the proposed model.The calculated results agree well with the measured ones,with a maximum relative error of 4.18%.It is thus con-cluded that the proposed model is a high-accuracy method to theoretically analyze the urban heat island and the thermal environment.
Magnetic field effect on unsteady nanofluid flow and heat transfer using Buongiorno model
Sheikholeslami, M.; Ganji, D. D.; Rashidi, M. M.
2016-10-01
In this study, heat and mass transfer characteristic of unsteady nanofluid flow between parallel plates is investigated. The important effect of Brownian motion and thermophoresis has been included in the model of nanofluid. The governing equations are solved via Differential Transformation Method. The validity of this method was verified by comparison previous work which is done for viscous fluid. The analytical investigation is carried out for different governing parameters namely; the squeeze number, Hartmann number, Schmidt number, Brownian motion parameter, thermophoretic parameter and Eckert number. The results indicate that skin friction coefficient has direct relationship with Hartmann number and squeeze number. Also it can be found that Nusselt number increases with increase of Hartmann number, Eckert number and Schmidt number but it is decreases with augment of squeeze number.
A dry-spot model for the prediction of critical heat flux in water boiling in bubbly flow regime
Energy Technology Data Exchange (ETDEWEB)
Ha, Sang Jun; No, Hee Cheon [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)
1997-12-31
This paper presents a prediction of critical heat flux (CHF) in bubbly flow regime using dry-spot model proposed recently by authors for pool and flow boiling CHF and existing correlations for forced convective heat transfer coefficient, active site density and bubble departure diameter in nucleate boiling region. Without any empirical constants always present in earlier models, comparisons of the model predictions with experimental data for upward flow of water in vertical, uniformly-heated round tubes are performed and show a good agreement. The parametric trends of CHF have been explored with respect to variations in pressure, tube diameter and length, mass flux and inlet subcooling. 16 refs., 6 figs., 1 tab. (Author)
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.
Eninger, J. E.
1982-01-01
Metal-foil reed valve in conventional slab-wick heat pipe limits heat flow to one direction only. With sink warmer than source, reed is forced closed and fluid returns to source side through annular transfer wick. When this occurs, wick slab on sink side of valve dries out and heat pipe ceases to conduct heat.
Bauer, Christopher
1993-11-01
Stirling engine heat exchangers are shell-and-tube type with oscillatory flow (zero-mean velocity) for the inner fluid. This heat transfer process involves laminar-transition turbulent flow motions under oscillatory flow conditions. A low Reynolds number kappa-epsilon model, (Lam-Bremhorst form), was utilized in the present study to simulate fluid flow and heat transfer in a circular tube. An empirical transition model was used to activate the low Reynolds number k-e model at the appropriate time within the cycle for a given axial location within the tube. The computational results were compared with experimental flow and heat transfer data for: (1) velocity profiles, (2) kinetic energy of turbulence, (3) skin friction factor, (4) temperature profiles, and (5) wall heat flux. The experimental data were obtained for flow in a tube (38 mm diameter and 60 diameter long), with the maximum Reynolds number based on velocity being Re(sub max) = 11840, a dimensionless frequency (Valensi number) of Va = 80.2, at three axial locations X/D = 16, 30 and 44. The agreement between the computations and the experiment is excellent in the laminar portion of the cycle and good in the turbulent portion. Moreover, the location of transition was predicted accurately. The Low Reynolds Number kappa-epsilon model, together with an empirical transition model, is proposed herein to generate the wall heat flux values at different operating parameters than the experimental conditions. Those computational data can be used for testing the much simpler and less accurate one dimensional models utilized in 1-D Stirling Engine design codes.
Magnetic heat pump flow director
Howard, Frank S. (Inventor)
1995-01-01
A fluid flow director is disclosed. The director comprises a handle body and combed-teeth extending from one side of the body. The body can be formed of a clear plastic such as acrylic. The director can be used with heat exchangers such as a magnetic heat pump and can minimize the undesired mixing of fluid flows. The types of heat exchangers can encompass both heat pumps and refrigerators. The director can adjust the fluid flow of liquid or gas along desired flow directions. A method of applying the flow director within a magnetic heat pump application is also disclosed where the comb-teeth portions of the director are inserted into the fluid flow paths of the heat pump.
A Model of Solar Radiation and Joule Heating in Flow of Third Grade Nanofluid
Hussain, Tariq; Hayat, Tasawar; Shehzad, Sabir Ali; Alsaedi, Ahmed; Chen, Bin
2015-03-01
The flow problem resulting from the stretching of a surface with convective conditions in a magnetohydrodynamic nanofluid with solar radiation is examined. Both heat and nanoparticle mass transfer convective conditions are employed. An incompressible third grade fluid which exhibits shear thinning and shear thickening characteristics is used as a base fluid. Concept of convective nanoparticle mass condition is introduced. Effects of Brownian motion and thermophoresis on magnetohydrodynamic flow of nanofluid are accounted in the presence of thermal radiation. Energy equation incorporates the features of Joule heating. The impact of physical parameters on the temperature and nanoparticle concentration has been pointed out. Numerical values of skin-friction coefficient are presented and analysed. It is hoped that this present investigation serves as a stimulus for the next generation of solar film collectors, heat exchangers technology, material processing, geothermal energy storage, and all those processes which are highly affected by the heat enhancement concept.
Modelling of fluid flow and heat transfer in a reciprocating compressor
Tuhovcak, J.; Hejcik, J.; Jicha, M.
2015-08-01
Efficiency of reciprocating compressor is strongly dependent on several parameters. The most important are valve behaviour and heat transfer. Valves affect the flow through the suction and discharge line. Heat flow from the walls to working fluid increases the work of the cycle. Understanding of these phenomena inside the compressor is a necessary step in the development process. Commercial CFD tools offer wide range of opportunities how to simulate the flow inside the reciprocating compressor nowadays, however they are too demanding in terms of computational time and mesh creation. Several approaches using various correlation equation exist to describe the heat transfer inside the cylinder, however none of them was validated by measurements due to the complicated settings. The goal of this paper is to show a comparison between these correlations using in-house code based on energy balance through the cycle.
Numerical modeling of the Joule heating effect on electrokinetic flow focusing.
Huang, Kuan-Da; Yang, Ruey-Jen
2006-05-01
In electrokinetically driven microfluidic systems, the driving voltage applied during operation tends to induce a Joule heating effect in the buffer solution. This heat source alters the solution's characteristics and changes both the electrical potential field and the velocity field during the transport process. This study performs a series of numerical simulations to investigate the Joule heating effect and analyzes its influence on the electrokinetic focusing performance. The results indicate that the Joule heating effect causes the diffusion coefficient of the sample to increase, the potential distribution to change, and the flow velocity field to adopt a nonuniform profile. These variations are particularly pronounced under tighter focusing conditions and at higher applied electrical intensities. In numerical investigations, it is found that the focused bandwidth broadens because thermal diffusion effect is enhanced by Joule heating. The variation in the potential distribution induces a nonuniform flow field and causes the focused bandwidth to tighten and broaden alternately as a result of the convex and concave velocity flow profiles, respectively. The present results confirm that the Joule heating effect exerts a considerable influence on the electrokinetic focusing ratio.
Modelling of flow boiling heat transfer in a cylindrical annulus mini gap
Directory of Open Access Journals (Sweden)
Piasecka Magdalena
2017-01-01
Full Text Available This paper presents the results of investigations into flow boiling heat transfer in a mini gap 1 mm wide. The mathematical approaches of the heat transfer coefficient determination were also proposed. It was considered two ways of describing layers in a measurement module with a cylindrical annulus mini gap. In the first approach, the measurement module was treated as a planar multilayer wall and in the second approach - as a multilayer cylindrical wall. The values of the local heat transfer coefficients, determined from two approaches, were compared. Both approaches gave similar results.
Implementation of an Integrated Thermal Building Model for Investigations of Heat Flows
Directory of Open Access Journals (Sweden)
Morozov Maxim N.
2017-01-01
Full Text Available A model of the building heating system, consisting of energy source, a distributed automatic control system, elements of individual heating unit and heating system is designed. Application Simulink of mathematical package Matlab is selected as a platform for the model. There are the specialized application Simscape libraries in aggregate with a wide range of Matlab mathematical tools allow to apply the “acausal” modeling concept. Implementation the “physical” representation of the object model gave improving the accuracy of the models.
Aursand, Eskil; Lervåg, Karl Yngve; Lund, Halvor
2016-01-01
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.
A Preliminary Heat Flow Model for Cooling a Batholith near Ica, Peru
Gonzalez, L. U.; Clausen, B. L.; Molano, J. C.; Martinez, A. M.; Poma, O.
2014-12-01
This research models the cooling of a suite in the Linga Super-unit located at the north end of the Arequipa segment in the Cretaceous Peruvian Coastal Batholith. The monzogabbro to granite Linga suite is approximately 50 km long and 15 km wide, with an estimated vertical extent of about 5 km originally intruded to a depth of 3 km. The emplacement was in andesitic volcanics on the west and the Pampahuasi diorite Super-unit on the east and has incorporated earlier gabbroic bodies. The Linga suite is thought to be the result of a sequence of three pulses: an elongate unit to the west then two elliptical units to the northeast and southeast. The data for modeling comes from field observations on internal and external contacts, some well-defined magma chamber walls and roof, pendant and stoped blocks, magma chamber zoning, the nature and distribution of enclaves and xenoliths, magmatic fabric, evidences of magma mingling, rock porosity, mineralogical associations in metamorphic aureoles, extensive mineralization and brecciated conduits, and the types of hydrothermal alteration varying with distance from contacts. More than forty hand samples, thin sections, and geochemical analyses were used to estimate water content, magma and country rock temperature, liquid density, and viscosity. Further data will come from: zircon U-Pb ages for country rock and magma batch timeframes, fluid inclusions for magma pressure and temperature, and δ18O data for source of hydrothermal fluids. Simple heat conduction calculations using MATLAB and HEAT 3D for a single tabular intrusion estimated a cooling time to solidus of about 300 k.y. More complex modeling includes magma convection and multiple intrusions. Extensive veining and pervasive alteration suggested the use of HYDROTHERM to model possible additional heat flow effects from hydrothermal fluids. Extensive propylitic and significant potassic alteration were observed and, with TerraSpec infrared spectroscopy to identify
Frampton, Andrew; Destouni, Georgia
2016-04-01
In cold regions, flow in the unsaturated zone is highly dynamic with seasonal variability and changes in temperature, moisture, and heat and water fluxes, all of which affect ground freeze-thaw processes and influence transport of inert and reactive waterborne substances. In arctic permafrost environments, near-surface groundwater flow is further restricted to a relatively shallow and seasonally variable active layer, confined by perennially frozen ground below. The active layer is typically partially saturated with ice, liquid water and air, and is strongly dependent on seasonal temperature fluctuations, thermal forcing and infiltration patterns. Here there is a need for improved understanding of the mechanisms controlling subsurface solute transport in the partially saturated active layer zone. Studying solute transport in cold regions is relevant to improve the understanding of how natural and anthropogenic pollution may change as activities in arctic and sub-arctic regions increase. It is also particularly relevant for understanding how dissolved carbon is transported in coupled surface and subsurface hydrological systems under climate change, in order to better understand the permafrost-hydrological-carbon climate feedback. In this contribution subsurface solute transport under surface warming and degrading permafrost conditions is studied using a physically based model of coupled cryotic and hydrogeological flow processes combined with a particle tracking method. Changes in subsurface water flows and solute transport travel times are analysed for different modelled geological configurations during a 100-year warming period. Results show that for all simulated cases, the minimum and mean travel times increase non-linearly with warming irrespective of geological configuration and heterogeneity structure. The travel time changes are shown to depend on combined warming effects of increase in pathway length due to deepening of the active layer, reduced transport
Convection Heat Transfer and Flow Calculations Suitable for Electric Machines Thermal Models
Cavagnino, Andrea
2008-01-01
This paper deals with the formulations used to predict convection cooling and flow in electric machines. Empirical dimensionless analysis formulations are used to calculate convection heat transfer. The particular formulation used is selected to match the geometry of the surface under consideration and the cooling type used. Flow network analysis, which is used to study the ventilation inside the machine, is also presented. In order to focus the discussion using examples, a commercial softwar...
Using xRage to Model Heat Flow for Experiments to Measure Opacities in HED Plasmas
Elgin, L.; Vandervort, R.; Keiter, P.; Drake, R. P.; Mussack, K.; Orban, C.
2015-11-01
We are developing a NIF proposal to measure opacities of C, N and O at temperatures and densities relevant to the base of the solar convection zone. Our proposed experiments would provide the first opacity measurements for these elements within this HED regime. A critical feature of our experimental platform is a super-sonic radiation front propagating within the targets. Under these conditions, density remains constant across the radiation front for a couple nanoseconds, enabling a window during which the opacities of the hot and cold target may be measured simultaneously. Afterwards, hydrodynamic effects create temperature and density gradients, which would obfuscate analysis of opacity data. We are using xRage to simulate heat flow within our targets in order to estimate the time scale over which temperature and density gradients evolve. These simulations will better inform our target design and diagnostic requirements. If successful, our experiments could yield the data necessary to validate existing opacity models or provide physical insights to inform the development of new opacity models. Accurate opacity models are essential to the understanding of radiation transport within HED systems, with applications ranging from astrophysics to ICF. U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant #DE-NA0001840. Los Alamos National Laboratory, LA-UR-15-25490.
Compare Energy Use in Variable Refrigerant Flow Heat Pumps Field Demonstration and Computer Model
Energy Technology Data Exchange (ETDEWEB)
Sharma, Chandan; Raustad, Richard
2013-07-01
Variable Refrigerant Flow (VRF) heat pumps are often regarded as energy efficient air-conditioning systems which offer electricity savings as well as reduction in peak electric demand while providing improved individual zone setpoint control. One of the key advantages of VRF systems is minimal duct losses which provide significant reduction in energy use and duct space. However, there is limited data available to show their actual performance in the field. Since VRF systems are increasingly gaining market share in the US, it is highly desirable to have more actual field performance data of these systems. An effort was made in this direction to monitor VRF system performance over an extended period of time in a US national lab test facility. Due to increasing demand by the energy modeling community, an empirical model to simulate VRF systems was implemented in the building simulation program EnergyPlus. This paper presents the comparison of energy consumption as measured in the national lab and as predicted by the program. For increased accuracy in the comparison, a customized weather file was created by using measured outdoor temperature and relative humidity at the test facility. Other inputs to the model included building construction, VRF system model based on lab measured performance, occupancy of the building, lighting/plug loads, and thermostat set-points etc. Infiltration model inputs were adjusted in the beginning to tune the computer model and then subsequent field measurements were compared to the simulation results. Differences between the computer model results and actual field measurements are discussed. The computer generated VRF performance closely resembled the field measurements.
Modeling and Simulation of Radiative Compressible Flows in Aerodynamic Heating Arc-Jet Facility
Bensassi, Khalil; Laguna, Alejandro A.; Lani, Andrea; Mansour, Nagi N.
2016-01-01
Numerical simulations of an arc heated flow inside NASA's 20 [MW] Aerodynamics heating facility (AHF) are performed in order to investigate the three-dimensional swirling flow and the current distribution inside the wind tunnel. The plasma is considered in Local Thermodynamics Equilibrium(LTE) and is composed of Air-Argon gas mixture. The governing equations are the Navier-Stokes equations that include source terms corresponding to Joule heating and radiative cooling. The former is obtained by solving an electric potential equation, while the latter is calculated using an innovative massively parallel ray-tracing algorithm. The fully coupled system is closed by the thermodynamics relations and transport properties which are obtained from Chapman-Enskog method. A novel strategy was developed in order to enable the flow solver and the radiation calculation to be preformed independently and simultaneously using a different number of processors. Drastic reduction in the computational cost was achieved using this strategy. Details on the numerical methods used for space discretization, time integration and ray-tracing algorithm will be presented. The effect of the radiative cooling on the dynamics of the flow will be investigated. The complete set of equations were implemented within the COOLFluiD Framework. Fig. 1 shows the geometry of the Anode and part of the constrictor of the Aerodynamics heating facility (AHF). Fig. 2 shows the velocity field distribution along (x-y) plane and the streamline in (z-y) plane.
Modelling flow and heat transfer around a seated human body by computational fluid dynamics
DEFF Research Database (Denmark)
Sørensen, Dan Nørtoft; Voigt, Lars Peter Kølgaard
2003-01-01
A database (http://www.ie.dtu.dk/manikin) containing a detailed representation of the surface geometry of a seated female human body was created from a surface scan of a thermal manikin (minus clothing and hair). The radiative heat transfer coefficient and the natural convection flow around...
Computational Modelling of Couette Flow of Nanofluids with Viscous Heating and Convective Cooling
Directory of Open Access Journals (Sweden)
Oluwole Daniel Makinde
2014-01-01
Full Text Available The combined effect of viscous heating and convective cooling on Couette flow and heat transfer characteristics of water base nanofluids containing Copper Oxide (CuO and Alumina (Al2O3 as nanoparticles is investigated. It is assumed that the nanofluid flows in a channel between two parallel plates with the channel’s upper plate accelerating and exchange heat with the ambient surrounding following the Newton’s law of cooling, while the lower plate is stationary and maintained at a constant temperature. Using appropriate similarity transformation, the governing Navier-Stokes and the energy equations are reduced to a set of nonlinear ordinary differential equations. These equations are solved analytically by regular perturbation method with series improvement technique and numerically by an efficient Runge-Kutta-Fehlberg integration technique coupled with shooting method. The effects of the governing parameters on the dimensionless velocity, temperature, skin friction, pressure drop and Nusselt number are presented graphically, and discussed quantitatively.
Rubab, Khansa; Mustafa, M
2016-01-01
This letter investigates the MHD three-dimensional flow of upper-convected Maxwell (UCM) fluid over a bi-directional stretching surface by considering the Cattaneo-Christov heat flux model. This model has tendency to capture the characteristics of thermal relaxation time. The governing partial differential equations even after employing the boundary layer approximations are non linear. Accurate analytic solutions for velocity and temperature distributions are computed through well-known homotopy analysis method (HAM). It is noticed that velocity decreases and temperature rises when stronger magnetic field strength is accounted. Penetration depth of temperature is a decreasing function of thermal relaxation time. The analysis for classical Fourier heat conduction law can be obtained as a special case of the present work. To our knowledge, the Cattaneo-Christov heat flux model law for three-dimensional viscoelastic flow problem is just introduced here.
Directory of Open Access Journals (Sweden)
Khansa Rubab
Full Text Available This letter investigates the MHD three-dimensional flow of upper-convected Maxwell (UCM fluid over a bi-directional stretching surface by considering the Cattaneo-Christov heat flux model. This model has tendency to capture the characteristics of thermal relaxation time. The governing partial differential equations even after employing the boundary layer approximations are non linear. Accurate analytic solutions for velocity and temperature distributions are computed through well-known homotopy analysis method (HAM. It is noticed that velocity decreases and temperature rises when stronger magnetic field strength is accounted. Penetration depth of temperature is a decreasing function of thermal relaxation time. The analysis for classical Fourier heat conduction law can be obtained as a special case of the present work. To our knowledge, the Cattaneo-Christov heat flux model law for three-dimensional viscoelastic flow problem is just introduced here.
Heat transfer optimization of SCO2 porous flow based on Brinkman model
Directory of Open Access Journals (Sweden)
Lin David T.W.
2016-01-01
Full Text Available The purpose of this study is to obtain the optimal operating condition in order to find the maximum supercritical CO2 heat extraction in the enhanced geothermal system (EGS. In this study, the heat transfer model conjugated with the Brinkman model is used to evaluate the thermal behavior in the reservoir of the EGS. This numerical model is validated by experiment. Optimization is processed based on the Nelder-Mead approach. The optimal operating conditions are proposed with different pressure, porosity. This study will build the optimal platform of heat source of geothermal power plant.
Abdul Fattah, R.; Meekes, S.; Bouman, J.; Ebbing, J.; Haagmans, R.
2014-01-01
A 3D basin modeling study was carried out to reconstruct the regional heat flow and source rock maturity in the Rub'al-Khali basin. Gravity gradient data from the GOCE satellite were used to model deep structures, such as the Moho interface. Tectonic heat flow was modeled using the GOCE-based Moho i
Berg, Matthew; Hartley, Brian; Richters, Oliver
2015-01-01
By synthesizing stock-flow consistent models, input-output models, and aspects of ecological macroeconomics, a method is developed to simultaneously model monetary flows through the financial system, flows of produced goods and services through the real economy, and flows of physical materials through the natural environment. This paper highlights the linkages between the physical environment and the economic system by emphasizing the role of the energy industry. A conceptual model is developed in general form with an arbitrary number of sectors, while emphasizing connections with the agent-based, econophysics, and complexity economics literature. First, we use the model to challenge claims that 0% interest rates are a necessary condition for a stationary economy and conduct a stability analysis within the parameter space of interest rates and consumption parameters of an economy in stock-flow equilibrium. Second, we analyze the role of energy price shocks in contributing to recessions, incorporating several propagation and amplification mechanisms. Third, implied heat emissions from energy conversion and the effect of anthropogenic heat flux on climate change are considered in light of a minimal single-layer atmosphere climate model, although the model is only implicitly, not explicitly, linked to the economic model.
Burns, Erick R.; Williams, Colin F.; Ingebritsen, Steven E.; Voss, Clifford I.; Spane, Frank A.; DeAngelo, Jacob
2015-01-01
Heat-flow mapping of the western USA has identified an apparent low-heat-flow anomaly coincident with the Columbia Plateau Regional Aquifer System, a thick sequence of basalt aquifers within the Columbia River Basalt Group (CRBG). A heat and mass transport model (SUTRA) was used to evaluate the potential impact of groundwater flow on heat flow along two different regional groundwater flow paths. Limited in situ permeability (k) data from the CRBG are compatible with a steep permeability decrease (approximately 3.5 orders of magnitude) at 600–900 m depth and approximately 40°C. Numerical simulations incorporating this permeability decrease demonstrate that regional groundwater flow can explain lower-than-expected heat flow in these highly anisotropic (kx/kz ~ 104) continental flood basalts. Simulation results indicate that the abrupt reduction in permeability at approximately 600 m depth results in an equivalently abrupt transition from a shallow region where heat flow is affected by groundwater flow to a deeper region of conduction-dominated heat flow. Most existing heat-flow measurements within the CRBG are from shallower than 600 m depth or near regional groundwater discharge zones, so that heat-flow maps generated using these data are likely influenced by groundwater flow. Substantial k decreases at similar temperatures have also been observed in the volcanic rocks of the adjacent Cascade Range volcanic arc and at Kilauea Volcano, Hawaii, where they result from low-temperature hydrothermal alteration.
Energy Technology Data Exchange (ETDEWEB)
Burns, Erick R.; Williams, Colin F.; Ingebritsen, Steven E.; Voss, Clifford I.; Spane, Frank A.; DeAngelo, Jacob
2015-02-01
Heat-flow mapping of the western USA has identified an apparent low-heat-flow anomaly coincident with the Columbia Plateau Regional Aquifer System, a thick sequence of basalt aquifers within the Columbia River Basalt Group (CRBG). A heat and mass transport model (SUTRA) was used to evaluate the potential impact of groundwater flow on heat flow along two different regional groundwater flow paths. Limited in situ permeability (k) data from the CRBG are compatible with a steep permeability decrease (approximately 3.5 orders of magnitude) at 600–900 m depth and approximately 40°C. Numerical simulations incorporating this permeability decrease demonstrate that regional groundwater flow can explain lower-than-expected heat flow in these highly anisotropic (kx/kz ~ 104) continental flood basalts. Simulation results indicate that the abrupt reduction in permeability at approximately 600 m depth results in an equivalently abrupt transition from a shallow region where heat flow is affected by groundwater flow to a deeper region of conduction-dominated heat flow. Most existing heat-flow measurements within the CRBG are from shallower than 600 m depth or near regional groundwater discharge zones, so that heat-flow maps generated using these data are likely influenced by groundwater flow. Substantial k decreases at similar temperatures have also been observed in the volcanic rocks of the adjacent Cascade Range volcanic arc and at Kilauea Volcano, Hawaii, where they result from low-temperature hydrothermal alteration.
Magnetic Heat Pump Containing Flow Diverters
Howard, Frank S.
1995-01-01
Proposed magnetic heat pump contains flow diverters for suppression of undesired flows. If left unchecked, undesired flows mix substantial amounts of partially heated and partially cooled portions of working fluid, effectively causing leakage of heat from heated side to cooled side. By reducing leakage of heat, flow diverters increase energy efficiency of magnetic heat pump, potentially offering efficiency greater than compressor-driven refrigerator.
Magnetic Heat Pump Containing Flow Diverters
Howard, Frank S.
1995-01-01
Proposed magnetic heat pump contains flow diverters for suppression of undesired flows. If left unchecked, undesired flows mix substantial amounts of partially heated and partially cooled portions of working fluid, effectively causing leakage of heat from heated side to cooled side. By reducing leakage of heat, flow diverters increase energy efficiency of magnetic heat pump, potentially offering efficiency greater than compressor-driven refrigerator.
Zheng, Y.; Liu, Q.; Li, Y.
2012-03-01
Solids moving with a gas stream in a pipeline can be found in many industrial processes, such as power generation, chemical, pharmaceutical, food and commodity transfer processes. A mass flow rate of the solids is important characteristic that is often required to be measured (and controlled) to achieve efficient utilization of energy and raw materials in pneumatic conveying systems. The methods of measuring the mass flow rate of solids in a pneumatic pipeline can be divided into direct and indirect (inferential) measurements. A thermal solids' mass flow-meter, in principle, should ideally provide a direct measurement of solids flow rate, regardless of inhomogeneities in solids' distribution and environmental impacts. One key issue in developing a thermal solids' mass flow-meter is to characterize the heat transfer between the hot pipe wall and the gas-solids dense phase flow. The Eulerian continuum modeling with gas-solid two phases is the most common method for pneumatic transport. To model a gas-solid dense phase flow passing through a heated region, the gas phase is described as a continuous phase and the particles as the second phase. This study aims to describe the heat transfer characteristics between the hot wall and the gas-solids dense phase flow in pneumatic pipelines by modeling a turbulence gas-solid plug passing through the heated region which involves several actual and crucial issues: selections of interphase exchange coefficient, near-wall region functions and different wall surface temperatures. A sensitivity analysis was discussed to identify the influence on the heat transfer characteristics by selecting different interphase exchange coefficient models and different boundary conditions. Simulation results suggest that sensitivity analysis in the choice of models is very significant. The simulation results appear to show that a combination of choosing the Syamlal-O'Brien interphase exchange coefficient model and the standard k-ɛ model along with
Mathematical Model for Fluid Flow and Heat Transfer Processes in Plate Exchanger
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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.
Development of Soft-Sphere Contact Models for Thermal Heat Conduction in Granular Flows
Energy Technology Data Exchange (ETDEWEB)
Morris, A. B.; Pannala, S.; Ma, Zhiwen; Hrenya, C. M.
2016-12-01
Conductive heat transfer to flowing particles occurs when two particles (or a particle and wall) come into contact. The direct conduction between the two bodies depends on the collision dynamics, namely the size of the contact area and the duration of contact. For soft-sphere discrete-particle simulations, it is computationally expensive to resolve the true collision time because doing so would require a restrictively small numerical time step. To improve the computational speed, it is common to increase the 'softness' of the material to artificially increase the collision time, but doing so affects the heat transfer. In this work, two physically-based correction terms are derived to compensate for the increased contact area and time stemming from artificial particle softening. By including both correction terms, the impact that artificial softening has on the conductive heat transfer is removed, thus enabling simulations at greatly reduced computational times without sacrificing physical accuracy.
DEFF Research Database (Denmark)
Fuchs, Sven; Balling, Niels
parameterization with a spatial distribution of rock thermal conductivity and new heat-flow values. The latter one are used to setup the numerical lower boundary condition. Measured heat flow and borehole temperature observations (59 values from 24 wells) are used to constrain the modelling results (calibration...... and validation). The prediction uncertainties between observed and modelled temperatures at deep borehole sites are small (rms = 3.5 °C). For eight deep boreholes, new values of terrestrial surface heat flow are derived, ranging between 72 and 84 mW/m² (mean of 80 ± 5 mW/m²). Those values are up to 20 m......W/m² higher than low values reported in some previous studies for this region. Heat flow from the mantle is estimated to be between 33 and 40 mW/m² (q1–q3; mean of 37 ± 7 mW/m²). Pronounced lateral temperature variations are caused mainly by complex geological structures, including a large amount of salt...
Joule heating in electrokinetic flow.
Xuan, Xiangchun
2008-01-01
Electrokinetic flow is an efficient means to manipulate liquids and samples in lab-on-a-chip devices. It has a number of significant advantages over conventional pressure-driven flow. However, there exists inevitable Joule heating in electrokinetic flow, which is known to cause temperature variations in liquids and draw disturbances to electric, flow and concentration fields via temperature-dependent material properties. Therefore, both the throughput and the resolution of analytic studies performed in microfluidic devices are affected. This article reviews the recent progress on the topic of Joule heating and its effect in electrokinetic flow, particularly the theoretical and experimental accomplishments from the aspects of fluid mechanics and heat/mass transfer. The primary focus is placed on the temperature-induced flow variations and the accompanying phenomena at the whole channel or chip level.
Heat flow in northwest Pacific marginal seas
Institute of Scientific and Technical Information of China (English)
JIANG Lili; LI Guanbao; LI Naisheng
2004-01-01
Heat flow studies in Northwest Pacific marginal seas has a more than 40 years history with more than 4000 heat flow values obtained. The regional average value is 80.4 mW/m2, which is lower than the world's 87 mW/m2, but higher than those of the Eurasia continent and the Pacific Ocean. This reflects the regional crust property in the area. The studies on distribution of the heat flow and contour pattern of heat flow in 1°×1°and 2°×2°scales in Northwest Pacific marginal seas revealed that the most high heat flow anomalies in the area were found along back-arc basins and island arc in an obviously northeasterly track. Exceptions are the Komandoskaya Basin (KMB), the Izu-Bonin Trough (IBT) and the Mariana Trough (MT), which extend in northwest. The contours of low heat flow marked the boundaries of the continent and the ocean. The present heat flow values reflect the imprint of the last thermal event and relate closely to tectonic activity. The high heat flow gradient areas have high frequency of earthquake. Therefore, the area of faulting controlled the pattern of the heat flow anomalies. Heat flow gradient in 135°direction indicated a major lithosphere transformation oceanward resulting from movement of the earth's material. In this paper, we described patterns of heat flow distribution in the Northwest Pacific, heat flow value changes in horizontal and vertical directions, combining the studies of Shi (1997) on the landforms of the island arcs in east Asia and plate movement, and the results of Shi and Zhang (1998) on heat simulation of subduction of active ocean mountain and the activity of islands arc. A preliminary model of geodynamics in the Northwest Pacific and its adjacent area was put forward. There is a great lateral heat flow gradient on the surface of the mantle between ocean and continent, which indicates that the materials in asthenosphere move from continent to ocean causing movement of the crust.
Modelling snowpack surface temperature in the Canadian Prairies using simplified heat flow models
Singh, Purushottam Raj; Yew Gan, Thian
2005-11-01
Three practical schemes for computing the snow surface temperature Ts, i.e. the force-restore method (FRM), the surface conductance method (SCM), and the Kondo and Yamazaki method (KYM), were assessed with respect to Ts retrieved from cloud-free, NOAA-AVHRR satellite data for three land-cover types of the Paddle River basin of central Alberta. In terms of R2, the mean Ts, the t-test and F-test, the FRM generally simulated more accurate Ts than the SCM and KYM. The bias in simulated Ts is usually within several degrees Celsius of the NOAA-AVHRR Ts for both the calibration and validation periods, but larger errors are encountered occasionally, especially when Ts is substantially above 0 °C. Results show that the simulated Ts of the FRM is more consistent than that of the SCM, which in turn was more consistent than that of the KYM. This is partly because the FRM considers two aspects of heat conduction into snow, a stationary-mean diurnal (sinusoidal) temperature variation at the surface coupled to a near steady-state ground heat flux, whereas the SCM assumes a near steady-state, simple heat conduction, and other simplifying assumptions, and the KYM does not balance the snowpack heat fluxes by assuming the snowpack having a vertical temperature profile that is linear. Copyright
Modelling and simulation of turbulence and heat transfer in wall-bounded flows
Popovac, M.
2006-01-01
At present it is widely accepted that there is no universal turbulence model, i.e. no turbulence model can give acceptably good predictions for all turbulent flows that are found in nature or engineering. Every turbulence model is based on certain assumptions, and hence it is aimed at certain type o
Investigation of RANS Model Deficiencies for Flow and Heat Transfer Simulations in a Pin-Fin Array
Hao, Zengrong; Gorle, Catherine; Civil; Environmental Engineering Department Team
2016-11-01
Quantifying turbulence model-form uncertainties of Reynolds-averaged Navier-Stokes (RANS) models is a challenging topic, largely because model inaccuracies can vary greatly across flow regions. The objective of the present study is to gain knowledge on where and how RANS models violate reality in representative heat exchanger geometries, such that a UQ method for use in optimization studies can be developed. To achieve this objective we performed a large-eddy simulation (LES) of the flow and heat transfer for a pin-fin array, and analyzed where RANS fails to predict the key features. The LES results are validated against experimental data available from Ames et al. (J. Turbo., 2005) and Ames and Dvorak (J. Turbo., 2006). The RANS simulations showed significant deviations from the LES for mean velocity profiles downstream of certain pins and for the Nusselt number distribution on the fins. A detailed comparison of the turbulent quantities illustrates a general underestimation of the Reynolds stresses and turbulent heat fluxes in near-fin regions, and incorrect trends in some pin-wake regions near the channel center plane. Based on this analysis, we draw conclusions that will support the development of a turbulence model UQ method for heat exchangers. This work is supported by IWT SBO project EUFORIA.
Directory of Open Access Journals (Sweden)
Hożejowska Sylwia
2014-03-01
Full Text Available The paper presents results of heat transfer research on flow boiling in a rectangular minichannel positioned vertically, with an enhanced surface. One of the channel walls was made of thin foil powered by direct current. This foil is enhanced on the side contacting fluid in the minichannel. It is possible to observe both surfaces of the minichannel through two openings covered with glass panes. One allows detecting temperature of the plain side of the foil by liquid crystal thermography. The opposite surface of the minichannel (from the enhanced side of the foil can be observed through the other glass pane. The observations of the flow structures allowed to calculate the void fraction for some cross-sections of selected two phase flow images. In mathematical modelling of the considered process stationary heat transfer in a glass pane, heating foil and boiling liquid can be described with Laplace equation, Poisson equation and energy equation, respectively. For completeness of the model a corresponding system of boundary conditions was given. The two-dimensional temperature fields of glass pane, heating foil and fluid was computed with the Trefftz method. The equalizing calculus used to smooth the measured data has reduced errors.
A Laboratory Model for the Flow in Urban Street Canyons Induced by Bottom Heating
Institute of Scientific and Technical Information of China (English)
刘辉志; 梁彬; 朱凤荣; 张伯寅; 桑建国
2003-01-01
Water tank experiments are carried out to investigate the convection flow induced by bottom heating and the effects of the ambient wind on the flow in non-symmetrical urban street canyons based on the PIV (Particle Image Visualization) technique. Fluid experiments show that with calm ambient wind,the flows in the street canyon are completely driven by thermal force, and the convection can reach the upper atmosphere of the street canyon. Horizontal and vertical motions also appear above the roofs of the buildings. These are the conditions which favor the exchange of momentum and air mass between the street canyon and its environment. More than two vortices are induced by the convection, and the complex circulation pattern will vary with time in a wider street canyon. However， in a narrow street canyon， just one vortex appears. With a light ambient wind, the bottom heating and the associated convection result in just one main vortex. As the ambient wind speed increases, the vortex becomes more organized and its center shifts closer to the leeward building.
Flow between two stretchable rotating disks with Cattaneo-Christov heat flux model
Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed
An analysis is performed to investigate flow between two stretchable rotating disks. Thermal equation is constructed by Cattaneo-Christov heat flux theory. Porous medium is also taken into account. The nonlinear partial differential equations are first converted to ordinary differential equations and then computed for the convergent series solutions. Discussion about impact of dimensionless parameters on velocities, temperature and skin friction coefficient is given. It is observed that the radial velocity at upper disk enhances for larger values of ratio of corresponding stretching rate to angular velocity. Velocity in y-direction decays with an increase in rotational parameter. Magnitude of temperature profile decays for larger Prandtl number and thermal relaxation parameter.
Directory of Open Access Journals (Sweden)
A. Mushtaq
2016-01-01
Full Text Available Present work studies the well-known Sakiadis flow of Maxwell fluid along a moving plate in a calm fluid by considering the Cattaneo-Christov heat flux model. This recently developed model has the tendency to describe the characteristics of relaxation time for heat flux. Some numerical local similarity solutions of the associated problem are computed by two approaches namely (i the shooting method and (ii the Keller-box method. The solution is dependent on some interesting parameters which include the viscoelastic fluid parameter β, the dimensionless thermal relaxation time γ and the Prandtl number Pr. Our simulations indicate that variation in the temperature distribution with an increase in local Deborah number γ is non-monotonic. The results for the Fourier’s heat conduction law can be obtained as special cases of the present study.
Kamonpatana, Pitiya; Mohamed, Hussein M H; Shynkaryk, Mykola; Heskitt, Brian; Yousef, Ahmed E; Sastry, Sudhir K
2013-11-01
To accomplish continuous flow ohmic heating of a low-acid food product, sufficient heat treatment needs to be delivered to the slowest-heating particle at the outlet of the holding section. This research was aimed at developing mathematical models for sterilization of a multicomponent food in a pilot-scale ohmic heater with electric-field-oriented parallel to the flow and validating microbial inactivation by inoculated particle methods. The model involved 2 sets of simulations, one for determination of fluid temperatures, and a second for evaluating the worst-case scenario. A residence time distribution study was conducted using radio frequency identification methodology to determine the residence time of the fastest-moving particle from a sample of at least 300 particles. Thermal verification of the mathematical model showed good agreement between calculated and experimental fluid temperatures (P > 0.05) at heater and holding tube exits, with a maximum error of 0.6 °C. To achieve a specified target lethal effect at the cold spot of the slowest-heating particle, the length of holding tube required was predicted to be 22 m for a 139.6 °C process temperature with volumetric flow rate of 1.0 × 10(-4) m3/s and 0.05 m in diameter. To verify the model, a microbiological validation test was conducted using at least 299 chicken-alginate particles inoculated with Clostridium sporogenes spores per run. The inoculated pack study indicated the absence of viable microorganisms at the target treatment and its presence for a subtarget treatment, thereby verifying model predictions.
Chan, B. C.
1986-05-01
A basic, limited scope, fast-running computer model is presented for the solution of two-dimensional, transient, thermally-coupled fluid flow problems. This model is to be the module in the SSC (an LMFBR thermal-hydraulic systems code) for predicting complex flow behavior, as occurs in the upper plenum of the loop-type design or in the sodium pool of the pool-type design. The nonlinear Navier-Stokes equations and the two-equation (two-variable) transport model of turbulence are reduced to a set of linear algebraic equations in an implicit finite difference scheme, based on the control volume approach. These equations are solved iteratively in a line-by-line procedure using the tri-diagonal matrix algorithm. The results of calculational examplers are shown in the computer-generated plots.
Mucha, P.; Berger, P.; Weber, R.; Speker, N.; Sommer, B.; Graf, T.
2015-03-01
Laser machining has great potential for automated manufacturing of parts made of carbon-fiber-reinforced plastic (CFRP) due to the nearly force and tool-wear free processing. The high vaporization temperatures and the large heat conductivity of the carbon fibers, however, lead to unintentional heat conduction into the material causing damage in zones close to the process. In this paper, the matrix damage zone (MDZ) is subdivided into a matrix sublimation zone (MSZ) where the matrix material was sublimated and a zone where the temperature temporarily exceeded a value causing structural damage in the matrix. In order to investigate the extent of these zones, a one-dimensional heat flow model was applied, which was calibrated by cutting experiments using temperature sensors embedded in the CFRP samples. The investigations showed that the extents of the MSZ and MDZ are dominated by a total interaction time, which includes the passage of the laser beam and the continued interaction of the cloud of hot ablation products with the carbon fibers at the kerf wall and that from a practical point of view, the experimentally determined effective heat conductivity is suitable for simple estimations of the heat-affected zones in CFRP.
Risius, Steffen; Beck, Walter H.; Klein, Christian; Henne, Ulrich; Wagner, Alexander
2017-09-01
Heat loads on spacecraft traveling at hypersonic speed are of major interest for their designers. Several tests using temperature-sensitive paints (TSP) have been carried out in long duration shock tunnels to determine these heat loads; generally paint layers were thin, so that certain assumptions could be invoked to enable a good estimate of the thermal parameter ρck (a material property) to be obtained—the value of this parameter is needed to determine heat loads from the TSP. Very few measurements have been carried out in impulse facilities [viz. shock tunnels such as the High Enthalpy Shock Tunnel Göttingen (HEG)], where test times are much shorter. Presented here are TSP temperature measurements and subsequently derived heat loads on a ramp model placed in a hypersonic flow in HEG (specific enthalpy h 0 = 3.3 MJ kg-1, Mach number M = 7.4, temperature T ∞ = 277 K, density ρ ∞ = 11 g m-3). A number of fluorescence intensity images were acquired, from which, with the help of calibration data, temperature field data on the model surface were determined. From these the heat load into the surface was calculated, using an assumption of a 1D, semi-infinite heat transfer model. ρck for the paint was determined using an insitu calibration with a Medtherm coaxial thermocouple mounted on the model; Medtherm ρck is known. Finally presented are sources of various measurement uncertainties, arising from: (1) estimation of ρck; (2) intensity measurement in the chosen interrogation area; (3) paint time response.
Geophysical models of heat and fluid flow in damageable poro-elastic continua
Roubíček, Tomáš
2017-03-01
A rather general model for fluid and heat transport in poro-elastic continua undergoing possibly also plastic-like deformation and damage is developed with the goal to cover various specific models of rock rheology used in geophysics of Earth's crust. Nonconvex free energy at small elastic strains, gradient theories (in particular the concept of second-grade nonsimple continua), and Biot poro-elastic model are employed, together with possible large displacement due to large plastic-like strains evolving during long time periods. Also the additive splitting is justified in stratified situations which are of interest in modelling of lithospheric crust faults. Thermodynamically based formulation includes entropy balance (in particular the Clausius-Duhem inequality) and an explicit global energy balance. It is further outlined that the energy balance can be used to ensure, under suitable data qualification, existence of a weak solution and stability and convergence of suitable approximation schemes at least in some particular situations.
Geophysical models of heat and fluid flow in damageable poro-elastic continua
Roubíček, Tomáš
2017-01-01
A rather general model for fluid and heat transport in poro-elastic continua undergoing possibly also plastic-like deformation and damage is developed with the goal to cover various specific models of rock rheology used in geophysics of Earth's crust. Nonconvex free energy at small elastic strains, gradient theories (in particular the concept of second-grade nonsimple continua), and Biot poro-elastic model are employed, together with possible large displacement due to large plastic-like strains evolving during long time periods. Also the additive splitting is justified in stratified situations which are of interest in modelling of lithospheric crust faults. Thermodynamically based formulation includes entropy balance (in particular the Clausius-Duhem inequality) and an explicit global energy balance. It is further outlined that the energy balance can be used to ensure, under suitable data qualification, existence of a weak solution and stability and convergence of suitable approximation schemes at least in some particular situations.
Directory of Open Access Journals (Sweden)
M. A. Daha
2012-02-01
Full Text Available The evolution of temperature profiles and weld pool geometry during dissimilar welding between 2205 duplex stainless steel and A36 low carbon steel using keyhole plasma arc welding has been simulated using a three dimensional numerical heat transfer and fluid flow model. An adaptive heat source is proposed as a heat source model for performing a non-linear transient thermal analysis, based on the configuration feature of keyhole plasma arc welds. Temperature profiles and solidified weld pool geometry are presented for three different welding heat input. The reversed bugle shape parameters (width of fusion zone at both top and bottom surfaces of the weld pool geometry features for a dissimilar 2205–A36 weld joint are summarized to successfully explain the observations. The model was also applied to keyhole plasma welding of 6.8 mm thick similar 2205 duplex stainless steel joint for validation. The simulation results were compared with independently obtained experimental data and good agreements have been obtained.
Characteristics of heat flow in recuperative heat exchangers
Directory of Open Access Journals (Sweden)
Lalović Milisav
2005-01-01
Full Text Available A simplified model of heat flow in cross-flow tube recuperative heat exchangers (recuperators was presented in this paper. One of the purposes of this investigation was to analyze changes in the values of some parameters of heat transfer in recuperators during combustion air preheating. The logarithmic mean temperature (Atm and overall heat transfer coefficient (U, are two basic parameters of heat flow, while the total heated area surface (A is assumed to be constant. The results, presented as graphs and in the form of mathematical expressions, were obtained by analytical methods and using experimental data. The conditions of gaseous fuel combustions were defined by the heat value of gaseous fuel Qd = 9263.894 J.m-3, excess air ratio λ= 1.10, content of oxygen in combustion air ν(O2 = 26%Vol, the preheating temperature of combustion air (cold fluid outlet temperature tco = 100-500°C, the inlet temperature of combustion products (hot fluid inlet temperature thi = 600-1100°C.
Energy Technology Data Exchange (ETDEWEB)
Amanifard, N.; Nariman-Zadeh, N.; Borji, M.; Khalkhali, A.; Habibdoust, A. [Department of Mechanical Engineering, The University of Guilan, P.O. Box 3756, Rasht (Iran)
2008-02-15
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 ({delta}P) 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 ({delta}P) 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. (author)
COMPUTATIONAL FLOW MODELLING OF FORMULA-SAE SIDEPODS FOR OPTIMUM RADIATOR HEAT MANAGEMENT
Directory of Open Access Journals (Sweden)
C. M. DE SILVA
2011-02-01
Full Text Available Formula SAE vehicles, over the program’s history have showcased a myriad of aerodynamic packages, each claiming specific quantitative and qualitative features. This paper attempts to critique differing aerodynamic sidepod designs and their effect upon radiator heat management. Various features from inlet size, sidepod shape and size, presence of an undertray, suspension cover, gills and chimneys are analysed for their effects. Computational Fluid Dynamics (CFD analyses are performed in the FLUENT environment, with the aid of GAMBIT meshing software and SolidWorks modelling.
Energy Technology Data Exchange (ETDEWEB)
Steinberg, A.M.; Boxx, I.; Stoehr, M.; Meier, W. [Institute for Combustion Technology, German Aerospace Centre (DLR), 70569 Stuttgart (Germany); Carter, C.D. [Air Force Research Laboratory, Wright-Patterson AFB, OH (United States)
2010-12-15
A detailed analysis of the flow-flame interactions associated with acoustically coupled heat-release rate fluctuations was performed for a 10 kW, CH{sub 4}/air, swirl stabilized flame in a gas turbine model combustor exhibiting self-excited thermo-acoustic oscillations at 308 Hz. High-speed stereoscopic particle image velocimetry, OH planar laser induced fluorescence, and OH* chemiluminescence measurements were performed at a sustained repetition rate of 5 kHz, which was sufficient to resolve the relevant combustor dynamics. Using spatio-temporal proper orthogonal decomposition, it was found that the flow-field contained several simultaneous periodic motions: the reactant flux into the combustion chamber periodically oscillated at the thermo-acoustic frequency (308 Hz), a helical precessing vortex core (PVC) circumscribed the burner nozzle at 515 Hz, and the PVC underwent axial contraction and extension at the thermo-acoustic frequency. The global heat release rate fluctuated at the thermo-acoustic frequency, while the heat release centroid circumscribed the combustor at the difference between the thermo-acoustic and PVC frequencies. Hence, the three-dimensional location of the heat release fluctuations depended on the interaction of the PVC with the flame surface. This motivated the compilation of doubly phase resolved statistics based on the phase of both the acoustic and PVC cycles, which showed highly repeatable periodic flow-flame configurations. These include flames stabilized between the inflow and inner recirculation zone, large-scale flame wrap-up by the PVC, radial deflection of the inflow by the PVC, and combustion in the outer recirculation zones. Large oscillations in the flame surface area were observed at the thermo-accoustic frequency that significantly affected the total heat-release oscillations. By filtering the instantaneous reaction layers at different scales, the importance of the various flow-flame interactions affecting the flame area was
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The flow disturbance and heat transfer mechanism in the tube bundle of rod baffle shell-and-tube heat exchanger were analyzed, on the basis of which and combined with the concept of heat transfer enhancement in the core flow, a new type of shell-and-tube heat exchanger with combination of rod and van type spoiler was designed. Corresponding mathematical and physical models on the shell side about the new type heat exchanger were established, and fluid flow and heat transfer characteristics were numerically analyzed. The simulation results showed that heat transfer coefficient of the new type of heat exchanger approximated to that of rod baffle heat exchanger, but flow pressure drop was much less than the latter, indicating that comprehensive performance of the former is superior to that of the latter. Compared with rod baffle heat exchanger, heat transfer coefficient of the heat exchanger under investigation is higher under same pressure drop, especially under the high Reynolds numbers.
DEFF Research Database (Denmark)
Fuchs, Sven; Balling, Niels
We present a regional 3D numerical crustal temperature model and analyze the present-day conductive thermal field of the Danish-German border region located in the North German Basin. A comprehensive analysis of borehole and well-log data on a regional scale is conducted to derive both the model...... structures and marked lateral variations in the thickness of basin sediments. The associated variations in rock thermal conductivity generate significant variations in model heat flow and large variations in temperature gradients. Major geothermal sandstone reservoirs (e.g. Rhaetian and Middle Buntsandstein......-Graben area). In combination with the structural geological model and information on reservoir hydraulic properties, the presented temperature model will constitute a very valuable base for planning and management the subsurface geothermal resources and help preventing conflicts of use in the Danish...
Role of radiogenic heat generation in surface heat flow formation
Khutorskoi, M. D.; Polyak, B. G.
2016-03-01
Heat generation due to decay of long-lived radioactive isotopes is considered in the Earth's crust of the Archean-Proterozoic and Paleozoic provinces of Eurasia and North America. The heat flow that forms in the mantle is calculated as the difference between the heat flow observed at the boundary of the solid Earth and radiogenic heat flow produced in the crust. The heat regime in regions with anomalously high radiogenic heat generation is discussed. The relationship between various heat flow components in the Precambrian and Phanerozoic provinces has been comparatively analyzed, and the role of erosion of the surfaceheat- generating layer has been estimated.
UNSAT-H Version 3.0: Unsaturated Soil Water and Heat Flow Model Theory, User Manual, and Examples
Energy Technology Data Exchange (ETDEWEB)
MJ Fayer
2000-06-12
The UNSAT-H model was developed at Pacific Northwest National Laboratory (PNNL) to assess the water dynamics of arid sites and, in particular, estimate recharge fluxes for scenarios pertinent to waste disposal facilities. During the last 4 years, the UNSAT-H model received support from the Immobilized Waste Program (IWP) of the Hanford Site's River Protection Project. This program is designing and assessing the performance of on-site disposal facilities to receive radioactive wastes that are currently stored in single- and double-shell tanks at the Hanford Site (LMHC 1999). The IWP is interested in estimates of recharge rates for current conditions and long-term scenarios involving the vadose zone disposal of tank wastes. Simulation modeling with UNSAT-H is one of the methods being used to provide those estimates (e.g., Rockhold et al. 1995; Fayer et al. 1999). To achieve the above goals for assessing water dynamics and estimating recharge rates, the UNSAT-H model addresses soil water infiltration, redistribution, evaporation, plant transpiration, deep drainage, and soil heat flow as one-dimensional processes. The UNSAT-H model simulates liquid water flow using Richards' equation (Richards 1931), water vapor diffusion using Fick's law, and sensible heat flow using the Fourier equation. This report documents UNSAT-H .Version 3.0. The report includes the bases for the conceptual model and its numerical implementation, benchmark test cases, example simulations involving layered soils and plants, and the code manual. Version 3.0 is an, enhanced-capability update of UNSAT-H Version 2.0 (Fayer and Jones 1990). New features include hysteresis, an iterative solution of head and temperature, an energy balance check, the modified Picard solution technique, additional hydraulic functions, multiple-year simulation capability, and general enhancements.
Magnetohydrodynamic two-phase dusty fluid flow and heat model over deforming isothermal surfaces
Turkyilmazoglu, Mustafa
2017-01-01
This paper is devoted to the mathematical analysis of a magnetohydrodynamic viscous two-phase dusty fluid flow and heat transfer over permeable stretching or shrinking bodies. The wall boundary is subjected to a linear deformation as well as to a quadratic surface temperature. Such a highly nonlinear phenomenon, for the first time in the literature, is attacked to search for occurrence of exact solutions, whose numerical correspondences are already available for limited wall transpiration velocities. The obtained analytical solutions are found be in perfect line with the numerical computations. Besides this, exact solutions point to the existence of dual solutions for both permeable stretching and shrinking cases, which were not detected from the numerical studies up to date. The existence of such exact solutions and their parameter domain particularly depending on the wall suction or injection are successfully analyzed. The physical outcomes concerning the effects of suspended particles on the momentum and thermal boundary layers well-documented in the open literature can be best understood from the presented exact solutions.
Energy Technology Data Exchange (ETDEWEB)
Sheikholeslami, Mohsen; Domiri Ganji, Davood [Department of Mechanical Engineering, Babol University of Technology, Babol (Iran, Islamic Republic of); Younus Javed, M. [National University of Sciences and Technology, College of Electrical and Mechanical Engineering Islamabad (Pakistan); Ellahi, R., E-mail: rellahi@engr.ucr.edu [Department of Mechanical Engineering, University of California Riverside, Bourns Hall A373 (United States); Department of Mathematics and Statistics, FBAS, IIUI, H-10 Sector, Islamabad (Pakistan)
2015-01-15
In this study, effect of thermal radiation on magnetohydrodynamics nanofluid flow between two horizontal rotating plates is studied. The significant effects of Brownian motion and thermophoresis have been included in the model of nanofluid. By using the appropriate transformation for the velocity, temperature and concentration, the basic equations governing the flow, heat and mass transfer are reduced to a set of ordinary differential equations. These equations, subjected to the associated boundary conditions are solved numerically using the fourth-order Runge–Kutta method. The effects of Reynolds number, magnetic parameter, rotation parameter, Schmidt number, thermophoretic parameter, Brownian parameter and radiation parameter on heat and mass characteristics are examined. Results show that Nusselt number has direct relationship with radiation parameter and Reynolds number while it has reverse relationship with other active parameters. It can also be found that concentration boundary layer thickness decreases with the increase of radiation parameter. - Highlights: • This paper analyses thermal radiation on magnetohydrodynamic nanofluid. • Fourth-order Runge–Kutta method is used. • The effects of Reynolds number, magnetic parameter, rotation parameter, Schmidt number thermophoretic parameter, Brownian parameter and radiation parameter on heat and mass characteristics are examined. • Comparison is also made with the existing literature.
CFD modelling of longwall goaf gas flow to improve gas capture and prevent goaf self-heating
Institute of Scientific and Technical Information of China (English)
REN Ting-xiang
2009-01-01
CFD models have been developed to investigate the Iongwall goaf gas flow pat-terns under different mining and geological control conditions. The Iongwall goaf was treated as porous regions and gas flow was modelled as a momentum sink added to the momentum equation. Gas desorption from the caved goaf and destressed coal seams within the mining disturbed area was modelled as additional mass sources in the continu-ity equation. These CFD models were developed according to specific Iongwall layouts and calibrated against field monitoring data. Two case studies were presented demon-strating the application of CFD modelling of goaf gas flow characteristics for improved goaf gas capture and the reduction of oxygen ingress into the goaf areas for self-heating pre-vention. Results from the case studies indicate that the optimum goaf drainage strategy would be a combination of shallow (near the face) and deep holes to improve the overall drainage efficiency and gas purity. For gassy longwall faces retreating against the seam dip, it is recommended to conduct cross-measure roof hole drainage targeting the fractured zones overlying the return comer, rather than high capacity surface goaf drainage deep in the goaf.
Sui, Jize; Zhao, Peng; Cheng, Zhengdong; Zheng, Liancun; Zhang, Xinxin
2017-02-01
The rheological and heat-conduction constitutive models of micropolar fluids (MFs), which are important non-Newtonian fluids, have been, until now, characterized by simple linear expressions, and as a consequence, the non-Newtonian performance of such fluids could not be effectively captured. Here, we establish the novel nonlinear constitutive models of a micropolar fluid and apply them to boundary layer flow and heat transfer problems. The nonlinear power law function of angular velocity is represented in the new models by employing generalized "n-diffusion theory," which has successfully described the characteristics of non-Newtonian fluids, such as shear-thinning and shear-thickening fluids. These novel models may offer a new approach to the theoretical understanding of shear-thinning behavior and anomalous heat transfer caused by the collective micro-rotation effects in a MF with shear flow according to recent experiments. The nonlinear similarity equations with a power law form are derived and the approximate analytical solutions are obtained by the homotopy analysis method, which is in good agreement with the numerical solutions. The results indicate that non-Newtonian behaviors involving a MF depend substantially on the power exponent n and the modified material parameter K 0 introduced by us. Furthermore, the relations of the engineering interest parameters, including local boundary layer thickness, local skin friction, and Nusselt number are found to be fitted by a quadratic polynomial to n with high precision, which enables the extraction of the rapid predictions from a complex nonlinear boundary-layer transport system.
Free convection film flows and heat transfer
Shang, Deyi
2010-01-01
Presents development of systematic studies for hydrodynamics and heat and mass transfer in laminar free convection, accelerating film boiling and condensation of Newtonian fluids, and accelerating film flow of non-Newtonian power-law fluids. This book provides a system of analysis models with a developed velocity component method.
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.
Allègre, C. J.; Jaupart, C.; Nolet, G.
2007-12-01
The question of layered versus whole mantle convection has been pending since early models of mantle convection (Oxburgh and Turcotte, 1967; McKenzie and Richter, 1978). In a first phase, layered mantle models appeared to be the winners, because they explained most of geochemical observations. They of course also explained the seismic focal solutions (compressive/ non compressive) in subducting plate and the heat flow constraints (Richter, 1980). Later on, the discovery that slabs could penetrate the lower mantle was considered as proof of whole mantle convection. Most numerical experiments were then developed in this context, overlooking many geochemical observations such as rare gas isotopes or radioactive elements. In this presentation, we will examine the different data one by one. a) geochemical constraints include the budget equations for Sr, Nd, Hf, isotopes, the budget equation for He, Ne, Ar, the budget for heat producing elements U, Th, K (including Th/U and K/U ratios). (Allègre and al., 1979, 1982; De Paolo and Wasserburg, 1977; O'Nions and al.,1977). b) Constrains linking geochemical observations and geodynamics. How the so-called depleted mantle is generated ? Continuities and affinities between MORB and OIB, including the Dupal and Non Dupal provinces: The non-pristine source for OIB based on Pb isotope data. The marble cake structure for upper mantle. Continental crust recycling via sediments and delamination processes. In thise respect, we emphasize the difference in statistical variance of isotope or trace element ratios in the different/types of basalts reflecting the difference in stirring intensity in their sources. We also use information from extinct radioactivities 142Nd and 129Xe. In each case, we estimate the errors for measurements and models. c) The seismic evidence of slab penetration into the lower mantle are from Creager and Jordan(1984) to Van der Hilst et al.(1991), Sparkman and al.(1993), with the counter example of non
Energy Technology Data Exchange (ETDEWEB)
Wu, Y.S.; Chen, G.; Bodvarsson, G.
1995-12-01
The US Department of Energy is performing detailed site characterization studies at Yucca Mountain to determine its suitability as a geological repository site for high level nuclear wastes. As part of these research efforts, a three-dimensional, site-scale unsaturated-zone model has been developed at Lawrence Berkeley National Laboratory (LBNL) in collaboration with the US Geological Survey (USGS). The primary objectives of developing the 3-D site-scale model are to predict the ambient hydrogeological conditions and the movement of moisture and gas within the unsaturated zone of the mountain. In addition, the model has the capability of modeling non-isothermal flow and transport phenomena at the mountain. Applications of such a site-scale model should include evaluation of effects of thermal loading on heated gas and heat flow through the mountain for long-term performance assessment of the repository. Emplacement of heat-generating, high-level nuclear wastes at Yucca Mountain would create complex multiphase fluid flow and heat transfer processes. The physical mechanisms include conductive and convective heat transfer, phase change phenomena (vaporization and condensation), flow of liquid and gas phases under variably-saturated condition, diffusion and dispersion of vapor and gas, vapor sorption, and vapor-pressure lowering effects. The heterogeneity of complicated geological setting at Yucca Mountain, such as alternating, layers of porous-fractured rocks, will significantly affect the processes of fluid and heat flow.
The present-day heat flow structure of Mars
Parro, L. M.; Jiménez-Díaz, A.; Mansilla, F.; Ruiz, J.
2016-12-01
Until the arrival of in-situ measurements, the study of the current heat flow of Mars goes through indirect methods, mainly based on the relation between the thermal state of lithosphere and their mechanical strength, or on theoretical models of internal evolution. Here, we present a first-order global model for the present-day surface heat flow for Mars, based on the current radiogenic heat production of the crust and mantle, scaling heat flow variations arising from crustal thickness and topography crustal thickness variations, and on the heat flow derived from the effective elastic thickness of the lithosphere beneath the North Polar Region. Our preferred model find heat flows varying between 14 and 23 mW m-2, with an average value of 18.6 mW m-2. Similar results are obtained if we use heat flow based on the lithosphere strength of the South Polar Region. Moreover, expressing our results in terms of the Urey ratio (the ratio between total internal heat production and heat loss), we have values close to 0.8, which indicates a moderate contribution of secular cooling to the heat flow of Mars (consistent with low heat flow values deduced from lithosphere strength), unless that heat-producing elements abundances for Mars are subchondritics.
Heat flow distribution in Chinese continent and its adjacent areas
Institute of Scientific and Technical Information of China (English)
Wei Tao; Zhengkang Shen
2008-01-01
Using a compilation of 6980 heat flow measurements, we produce a new heat flow map for the Chinese continent and its adjacent areas. We develop an objective and integrated method to interpolate the heat flow data, taking into account both the uniformity within geological units and coherency of regional heat flow. The geologic units are outlined based on Zhang et al.'s active tectonic block model.Our heat flow model is presented in two formats: a contour map and a heat flow dataset with values on a 1 × 1° grid for the Chinese continent and its adjacent areas, reflecting detailed variations in some regions. Also provided is a resolution map which helps understand the reliability of the heat flow model. Our results reveal that (1) Heat flows in the eastern part of the Chinese continent are relatively higher than those in the western part except that in the Tibetan Plateau area. (2) Heat flows in the Ordos and North China blocks are around 60 mW/m2, and are 50-55 mW/m2 in South China except for the continental marginal sea regions. (3) Heat flow is the lowest in the Jtmggar Basin, only 35-45 mW/m2, and is 45-55 mW/m2 in the Tarim Basin. The results of this study provide an important data-set for studies on thermal and rheological structures of the Chinese continent and its adjacent areas.
Engeler, I.; Hendricks Franssen, H. J.; Müller, R.; Stauffer, F.
2011-02-01
SummaryThis paper focuses on the role of heat transport in river-aquifer interactions for the study area Hardhof located in the Limmat valley within the city of Zurich (Switzerland). On site there are drinking water production facilities of Zurich water supply, which pump groundwater and infiltrate bank filtration water from river Limmat. The artificial recharge by basins and by wells creates a hydraulic barrier against the potentially contaminated groundwater flow from the city. A three-dimensional finite element model of the coupled variably saturated groundwater flow and heat transport was developed. The hydraulic conductivity of the aquifer and the leakage coefficient of the riverbed were calibrated for isothermal conditions by inverse modelling, using the pilot point method. River-aquifer interaction was modelled using a leakage concept. Coupling was considered by temperature-dependent values for hydraulic conductivity and for leakage coefficients. The quality of the coupled model was tested with the help of head and temperature measurements. Good correspondence between simulated and measured temperatures was found for the three pumping wells and seven piezometers. However, deviations were observed for one pumping well and two piezometers, which are situated in an area, where zones with important hydrogeological heterogeneity are expected. A comparison of simulation results with isothermal leakage coefficients with those of temperature-dependent leakage coefficients shows that the temperature dependence is able to reduce the head residuals close to the river by up to 30%. The largest improvements are found in the zone, where the river stage is considerably higher than the groundwater level, which is in correspondence with the expectations. Additional analyses also showed that the linear leakage concept cannot reproduce the seepage flux in a downstream section during flood events. It was found that infiltration is enhanced during flood events, which is
CFD modelling of supercritical water flow and heat transfer in a 2 × 2 fuel rod bundle
Energy Technology Data Exchange (ETDEWEB)
Podila, Krishna, E-mail: krishna.podila@cnl.ca; Rao, Yanfei, E-mail: yanfei.rao@cnl.ca
2016-05-15
Highlights: • Bare and wire wrapped 2 × 2 fuel rod bundles were modelled with CFD. • Sensitivity of predictions to SST k–ω, v{sup 2}–f and turbulent Prandtl number was tested. • CFD predictions were assessed with experimentally reported fuel wall temperatures. - Abstract: In the present assessment of the CFD code, two heat transfer experiments using water at supercritical pressures were selected: a 2 × 2 rod bare bundle; and a 2 × 2 rod wire-wrapped bundle. A systematic 3D CFD study of the fluid flow and heat transfer at supercritical pressures for the rod bundle geometries was performed with the key parameter being the fuel rod wall temperature. The sensitivity of the prediction to the steady RANS turbulence models of SST k–ω, v{sup 2}–f and turbulent Prandtl number (Pr{sub t}) was tested to ensure the reliability of the predicted wall temperature obtained for the current analysis. Using the appropriate turbulence model based on the sensitivity analysis, the mesh refinement, or the grid convergence, was performed for the two geometries. Following the above sensitivity analyses and mesh refinements, the recommended CFD model was then assessed against the measurements from the two experiments. It was found that the CFD model adopted in the current work was able to qualitatively capture the trends reported by the experiments but the degree of temperature rise along the heated length was underpredicted. Moreover, the applicability of turbulence models varied case-by-case and the performance evaluation of the turbulence models was primarily based on its ability to predict the experimentally reported fuel wall temperatures. Of the two turbulence models tested, the SST k–ω was found to be better at capturing the measurements at pseudo-critical and supercritical test conditions, whereas the v{sup 2}–f performed better at sub-critical test conditions. Along with the appropriate turbulence model, CFD results were found to be particularly sensitive to
Heat flow model for pulsed laser melting and rapid solidification of ion implanted GaAs
Kim, Taeseok; Pillai, Manoj R.; Aziz, Michael J.; Scarpulla, Michael A.; Dubon, Oscar D.; Yu, Kin M.; Beeman, Jeffrey W.; Ridgway, Mark C.
2010-07-01
In order to further understand the pulsed-laser melting (PLM) of Mn and N implanted GaAs, which we have used to synthesize thin films of the ferromagnetic semiconductor Ga1-xMnxAs and the highly mismatched alloy GaNxAs1-x, we have simulated PLM of amorphous (a-) and crystalline (c-) GaAs. We present a numerical solution to the one-dimensional heat equation, accounting for phase-dependent reflectivity, optical skin depth, and latent heat, and a temperature-dependent thermal conductivity and specific heat. By comparing the simulations with experimental time-resolved reflectivity and melt depth versus laser fluence, we identify a set of thermophysical and optical properties for the crystalline, amorphous, and liquid phases of GaAs that give reasonable agreement between experiment and simulation. This work resulted in the estimation of thermal conductivity, melting temperature and latent heat of fusion of a-GaAs of 0.008 W/cm K at 300 K, 1350 K, and 2650 J/cm3, respectively. These materials properties also allow the prediction of the solidification velocity of crystalline and ion-amorphized GaAs.
DEFF Research Database (Denmark)
Guerrier, Patrick; Tosello, Guido; Nielsen, Kaspar Kirstein
2016-01-01
Using elevated mold temperature is known to have a positive influence of final injection molded parts. Induction heating is a method that allow obtaining a rapid thermal cycle, so the overall molding cycle time is not increased. In the present research work, an integrated multi-turn induction hea...
Warsta, L.; Turunen, M.; Koivusalo, H. J.; Paasonen-Kivekäs, M.; Karvonen, T.; Taskinen, A.
2012-12-01
Simulation of hydrological processes for the purposes of agricultural water management and protection in boreal environment requires description of winter time processes, including heat transport, soil freezing and thawing, and snow accumulation and melt. Finland is located north of the latitude of 60 degrees and has one third to one fourth of the total agricultural land area (2.3 milj. ha) on clay soils (> 30% of clay). Most of the clayey fields are subsurface drained to provide efficient drainage and to enable heavy machines to operate on the fields as soon as possible after the spring snowmelt. Generation of drainflow and surface runoff in cultivated fields leads to nutrient and sediment load, which forms the major share of the total load reaching surface waters at the national level. Water, suspended sediment, and soluble nutrients on clayey field surface are conveyed through the soil profile to the subsurface drains via macropore pathways as the clayey soil matrix is almost impermeable. The objective of the study was to develop the missing winter related processes into the FLUSH model, including soil heat transport, snow pack simulation and the effects of soil freezing and thawing on the soil hydraulic conductivity. FLUSH is an open source (MIT license), distributed, process-based model designed to simulate surface runoff and drainflow in clayey, subsurface drained agricultural fields. 2-D overland flow is described with the diffuse wave approximation of the Saint Venant equations and 3-D subsurface flow with a dual-permeability model. Both macropores and soil matrix are simulated with the Richards equation. Soil heat transport is described with a modified 3-D convection-diffusion equation. Runoff and groundwater data was available from different periods from January 1994 to April 1999 measured in a clayey, subsurface drained field section (3.6 ha) in southern Finland. Soil temperature data was collected in two locations (to a depth of 0.8 m) next to the
Bauer, Christopher
1993-01-01
Stirling engine heat exchangers are shell-and-tube type with oscillatory flow (zero-mean velocity) for the inner fluid. This heat transfer process involves laminar-transition turbulent flow motions under oscillatory flow conditions. A low Reynolds number kappa-epsilon model, (Lam-Bremhorst form), was utilized in the present study to simulate fluid flow and heat transfer in a circular tube. An empirical transition model was used to activate the low Reynolds number k-e model at the appropriate time within the cycle for a given axial location within the tube. The computational results were compared with experimental flow and heat transfer data for: (1) velocity profiles, (2) kinetic energy of turbulence, (3) skin friction factor, (4) temperature profiles, and (5) wall heat flux. The experimental data were obtained for flow in a tube (38 mm diameter and 60 diameter long), with the maximum Reynolds number based on velocity being Re(sub max) = 11840, a dimensionless frequency (Valensi number) of Va = 80.2, at three axial locations X/D = 16, 30 and 44. The agreement between the computations and the experiment is excellent in the laminar portion of the cycle and good in the turbulent portion. Moreover, the location of transition was predicted accurately. The Low Reynolds Number kappa-epsilon model, together with an empirical transition model, is proposed herein to generate the wall heat flux values at different operating parameters than the experimental conditions. Those computational data can be used for testing the much simpler and less accurate one dimensional models utilized in 1-D Stirling Engine design codes.
Axial flow heat exchanger devices and methods for heat transfer using axial flow devices
Energy Technology Data Exchange (ETDEWEB)
Koplow, Jeffrey P.
2016-02-16
Systems and methods described herein are directed to rotary heat exchangers configured to transfer heat to a heat transfer medium flowing in substantially axial direction within the heat exchangers. Exemplary heat exchangers include a heat conducting structure which is configured to be in thermal contact with a thermal load or a thermal sink, and a heat transfer structure rotatably coupled to the heat conducting structure to form a gap region between the heat conducting structure and the heat transfer structure, the heat transfer structure being configured to rotate during operation of the device. In example devices heat may be transferred across the gap region from a heated axial flow of the heat transfer medium to a cool stationary heat conducting structure, or from a heated stationary conducting structure to a cool axial flow of the heat transfer medium.
Computation and Modeling of Heat Transfer in Wall-Bounded Turbulent Flows
2010-05-31
Dissimilarity in a Turbulent Channel Flow, Mecánica Computacional , Vol. XXVI, pp. 3644-3663, Ed. by Elaskar, S.A., E.A. Pilotta, and G.A. Torres. (http...Natural Dissimilarity in a Turbulent Plane Couette Flow, In Mecánica Computacional Vol. XXVII, Ed. by A. Cardona, M. Storti, and C. Zuppa, pp.1619-1636...Past a Circular Cylinder , In Mecánica Computacional Vol. XXVII, Ed. by A. Cardona, M. Storti, and C. Zuppa, pp.249-264, 2008. http://venus.ceride.gov.ar/twiki/bin/view/AMCA/ListadoDePublicaciones). xii
Planetary heat flow from shallow subsurface measurements: Mars
Cornwall, Marc; Hagermann, Axel
2016-10-01
Planetary heat flow probes measure heat flow (depth-resolved temperature and thermal conductivity) to provide insight into the internal state of a planet. The probes have been utilized extensively on Earth, twice on the Moon, and once on the Surface of comet 67P-CG. Mars is an important target for heat flow measurement as heat flow is a critical parameter in Martian thermal history models. Earlier studies indicate that Martian planetary heat flow can be accessed at 5 m below the surface in dry regolith monitored over at least one Martian year. A one Martian year monitoring period is necessary because, in the shallow subsurface, heat flow from the interior is superposed with time varying heat flow contributions, primarily due to insolation. Given that a heat flow probe may not achieve its target depth or monitoring period, this study investigates how the depth (2-5 m), duration (0-1 Martian year) and quality of measurements influence the accuracy of planetary heat flow. An inverse model is used to show that, in the preceding scenarios, the accuracy of planetary heat flow directly estimated from depth-dependent thermal conductivity with 10-20% precision errors, temperatures with 50-100 mK precision errors and modelling uncertainties up to 500 mK, can, on average, be improved by a factor of 27 with optimization to 13%. Accuracies increase with sensor penetration depth and regolith monitoring period. Heat flow optimized from instantaneous measurements or those with the shortest regolith monitoring periods have increased accuracy where the frequency and amplitude of the temperature variation are lowest. The inverse model is based on the Function Specification Inversion method. This study demonstrates that a solution subspace can be identified within a space of uncertainties modelled for the temperature measurements and planetary heat flow: the subspace is defined by a constant log-ratio of their respective standard deviations. Optimized heat flow estimates display
Nonequilibrium invariant measure under heat flow.
Delfini, Luca; Lepri, Stefano; Livi, Roberto; Politi, Antonio
2008-09-19
We provide an explicit representation of the nonequilibrium invariant measure for a chain of harmonic oscillators with conservative noise in the presence of stationary heat flow. By first determining the covariance matrix, we are able to express the measure as the product of Gaussian distributions aligned along some collective modes that are spatially localized with power-law tails. Numerical studies show that such a representation applies also to a purely deterministic model, the quartic Fermi-Pasta-Ulam chain.
Ocłoń, Paweł; Łopata, Stanisław; Nowak, Marzena
2015-04-01
This study presents a novel, simplified model for the time-efficient simulation of transient conjugate heat transfer in round tubes. The flow domain and the tube wall are modeled in 1D and 2D, respectively and empirical correlations are used to model the flow domain in 1D. The model is particularly useful when dealing with complex physics, such as flow boiling, which is the main focus of this study. The tube wall is assumed to have external fins. The flow is vertical upwards. Note that straightforward computational fluid dynamics (CFD) analysis of conjugate heat transfer in a system of tubes, leads to 3D modeling of fluid and solid domains. Because correlation is used and dimensionality reduced, the model is numerically more stable and computationally more time-efficient compared to the CFD approach. The benefit of the proposed approach is that it can be applied to large systems of tubes as encountered in many practical applications. The modeled equations are discretized in space using the finite volume method, with central differencing for the heat conduction equation in the solid domain, and upwind differencing of the convective term of the enthalpy transport equation in the flow domain. An explicit time discretization with forward differencing was applied to the enthalpy transport equation in the fluid domain. The conduction equation in the solid domain was time discretized using the Crank-Nicholson scheme. The model is applied in different boundary conditions and the predicted boiling patterns and temperature fields are discussed.
Rodriguez-Sinobas, Leonor; Zubelzu, Sergio; Sobrino, Fernando Fernando; Sánchez, Raúl
2017-04-01
Most of the studies dealing with the development of water flow simulation models in soils, are calibrated using experimental data measured by soil probe sensors or tensiometers which locate at specific points in the study area. However since the beginning of the XXI century, the use of Distributed Fiber Optic Temperature Measurement for estimating temperature variation along a cable of fiber optic has been assessed in multiple environmental applications. Recently, its application combined with an active heating pulses technique (AHFO) has been reported as a sensor to estimate soil moisture. This method applies a known amount of heat to the soil and monitors the temperature evolution, which mainly depends on the soil moisture content. Thus, it allows estimations of soil water content every 12.5 cm along the fiber optic cable, as long as 1500 m , with 2 % accuracy , every second. This study presents the calibration of a soil water flow model (developed in Hydrus 2D) with the AHFO technique. The model predicts the distribution of soil water content of a green area irrigated by sprinkler irrigation. Several irrigation events have been evaluated in a green area located at the ETSI Agronómica, Agroalimentaria y Biosistemas in Madrid where an installation of 147 m of fiber optic cable at 15 cm depth is deployed. The Distribute Temperature Sensing unit was a SILIXA ULTIMA SR (Silixa Ltd, UK) and has spatial and temporal resolution of 0.29 m. Data logged in the DTS unit before, during and after the irrigation event were used to calibrate the estimations in the Hydrus 2D model during the infiltration and redistribution of soil water content within the irrigation interval. References: Karandish, F., & Šimůnek, J. (2016). A field-modeling study for assessing temporal variations of soil-water-crop interactions under water-saving irrigation strategies. Agricultural Water Management, 178, 291-303. Li, Y., Šimůnek, J., Jing, L., Zhang, Z., & Ni, L. (2014). Evaluation of
Boiling heat transfer of refrigerant R-21 in upward flow in plate-fin heat exchanger
Kuznetsov, V. V.; Shamirzaev, A. S.
2015-11-01
The article presents the results of experimental investigation of boiling heat transfer of refrigerant R-21 in upward flow in a vertical plate-fin heat exchanger with transverse size of the channels that is smaller than the capillary constant. The heat transfer coefficients obtained in ranges of small mass velocities and low heat fluxes, which are typical of the industry, have been poorly studied yet. The characteristic patterns of the upward liquid-vapor flow in the heat exchanger channels and the regions of their existence are detected. The obtained data show a weak dependence of heat transfer coefficient on equilibrium vapor quality, mass flow rate, and heat flux density and do not correspond to calculations by the known heat transfer models. A possible reason for this behavior is a decisive influence of evaporation of thin liquid films on the heat transfer at low heat flux.
Laboratory Investigations of Lava Flow Heat Transfer
Fagents, S. A.; Rumpf, M. E.; Hamilton, C. W.
2011-12-01
To investigate the effectiveness with which lava can heat substrates of different types, we conducted a suite of experiments in which molten basalt was poured onto solid or particulate materials, and the downward propagation of the heat pulse was measured. The motivation for this work lies in seeking to understand how lava flows on the Moon would have heated the underlying regolith, and thus to determine the depths at which solar wind particles implanted in the regolith would have been protected from the heat of the overlying flow. Extraction and analysis of ancient solar wind samples would provide a wealth of information on the evolution and fate of the Sun. Our experimental device consists of a box constructed from 1"-thick calcium silicate sheeting with interior dimensions of 20 x 20 x 25 cm. The substrate material (a particulate lunar regolith simulant or solid basalt) occupies the lower 15 cm of the box, which is embedded with an array of 8 thermocouples. Up to 6 kg of crushed basalt collected from the 2010 Kilauea lava flows is heated to supraliquidus temperatures and poured directly onto the substrate. The evolution of the temperature profile within the lava flow and substrate is recorded as the basalt cools, and the surface temperature distribution is recorded using a Forward Looking Infrared Radiometer (FLIR) video camera. We have been using the experimental data sets to validate a numerical model of substrate heating. If the physics is appropriately formulated, the model will accurately predict both surface and internal temperature distribution as a function of time. A key issue has been incorporation of valid temperature-dependent thermophysical properties, because particulate materials are not well characterized at elevated temperatures. Regolith thermal conductivity in particular exerts a strong control over the depth of penetration of the thermal wave, so its accurate description is essential for a robust model. Comparison of experimental vs. modeled
Underworld and multi-basin heat flow
Quenette, S. M.; O'Neill, C.; Moresi, L. N.; Danis, C. R.; Mansour, J.
2011-12-01
We present an over arching method for non-linear heat flow assessments of large, multi-basin systems. Our example is the Sydney-, Gunnedah-, Bowen basins (Danis et al 2011), which covers an area of 800kms by 1900kms and depth of 5kms, on the east coast of Australia. It is used as a baseline towards further fluid and structural geodynamics oriented analysis. In contrast to reservoir scale geothermal models - basin, multi-basin and towards lithosphere scale models exhibit their own challenges in terms of physical/rheological behaviour and computational tractability. For instance we model a non-linear heat flow by means of temperature dependent conductivity, as indicated by Clauser and Huenges (1995), which allows crystalline basement rocks, such as granites, to show for example a significant decrease in conductivity from ambient temperature up to around 400C, dropping from around 3 mK**(units) to around 2. For this modelling, a specialisation of the geodynamics code 'Underworld' (Moresi et al 2007) called Underworld-GT is used. A toolbox is added to the otherwise un-touched Underworld code adding geothermal workflow and context to Underworld. A particular novel feature is the ability to load stratigraphic layers, and/or GoCAD or GeoModeller voxel sets as the constraining geological geometry, whilst allowing the heat assessment models to scale from 1 process to 1000s. Another is the ability to prescribe synthetic drill holes, and its use in stochastic-oriented assessments of model parameters. Following the Underworld platform's approach and its simple PDE abstraction layer, these model configurations from a baseline for further additions to the governing equations such as fluid flow and structure, enabling a bridge between reservoir and continental scale dynamics, albeit with their own computational challenges.
DEFF Research Database (Denmark)
Haertel, Jan Hendrik Klaas; Nellis, Gregory F.
2017-01-01
. The conductance of the heat exchanger is maximized for a prescribed pressure drop and prescribed air-side temperature change across the heat exchanger. Polymer with infilled thermally conducting metal filaments is considered as the heat exchanger material which allows cost effective additive manufacturing...... optimized slot channel model in order to demonstrate the superior performance of the topology optimized designs. Thus, this work demonstrates the usefulness of topology optimization to fully exploit the design freedom afforded by additive manufacturing technologies....
Simulation Studies on A Cross Flow Plate Fin Heat Exchanger
Directory of Open Access Journals (Sweden)
M. Thirumarimurugan
2008-01-01
Full Text Available Compact heat exchangers which were initially developed for the aerospace industries in the1940s have been considerably improved in the past few years. The main reasons for the goodperformance of compact heat exchangers are their special design which includes turbulent which inturn use high heat transfer coefficient and resists fouling, and maximum temperature driving forcebetween the hot and cold fluids. Numerous types use special enhancement techniques to achieve therequired heat transfer in smaller plot areas and, in many cases, less initial investment. One such type ofcompact heat exchanger is the Plate-fin heat exchanger. The complexity of compact heat exchangerdesign equations results from the exchangers unique ability to transfer heat between multiple processstreams and a wide array of possible flow configurations. This paper presents the performanceevaluation of cross flow plate fin heat exchanger with several different Gas-Liquid systems.Experimental results such as exchanger effectiveness, overall heat transfer coefficients were calculatedfor the flow systems of Cross flow Heat Exchangers. A steady state model for the outlet temperature ofboth the cold and hot fluid and overall heat transfer coefficient of a plate-fin cross flow heat exchangerwas developed and simulated using MATLAB, which was verified with the experiments conducted.
Institute of Scientific and Technical Information of China (English)
文先太; 梁彩华; 刘成兴; 张小松
2012-01-01
As a new heat and mass transfer device, heat-source tower plays an important role in the heat-source tower heat pump system. Heat is absorbed from the ambient in winter and supplied to the evaporator of heat pump. There are some similarities and differences in heat and mass transfer between heat-source tower and cooling tower. Six primary differences are pointed out as follows: heat resistance, physical property of liquid, ratio of latent heat percentage, flow rate of circular water/liquid, effect of liquid float on the whole system, and direction and rate of heat transfer. Based on the similarities and differences of heat-source tower and cooling tower, the mathematical model of heat and mass transfer in the cross heat-source tower is proposed and the model is confirmed by experiments. Results show that the latent heat percentage of cross flow heat-source tower is less than 35% and the error of heat transfer rate between simulation and experiment is less than 10%. The model is accurate enough to simulate the heat transfer characteristic in the heat-source tower.%热源塔作为新型的热质交换设备,在热源塔热泵机组运行过程中起着重要作用.其在冬季运行时从空气中吸收热量,为热泵机组提供低品位热量.热源塔与冷却塔在传热传质上存在一定异同点,指出了冷却塔与热源塔在传热传质上存在热阻、液体物性、潜热换热量比例、循环水／液体流量、飘液对系统的影响、热量传递方向和换热量大小等方面的差异.根据热源塔与冷却塔差异建立叉流热源塔传热传质数学模型,并采用实验验证模型的准确性.结果表明叉流热源塔潜热百分比低于35％,模型结果与实验结果相比换热性能误差低于10％,该模型能够较为精确地对叉流热源塔换热性能进行模拟.
Cerminara, Matteo; Esposti Ongaro, Tomaso; Carlo Berselli, Luigi
2014-05-01
We have developed a compressible multiphase flow model to simulate the three-dimensional dynamics of turbulent volcanic ash plumes. The model describes the eruptive mixture as a polydisperse fluid, composed of different types of gases and particles, treated as interpenetrating Eulerian phases. Solid phases represent the discrete ash classes into which the total granulometric spectrum is discretized, and can differ by size and density. The model is designed to quickly and accurately resolve important physical phenomena in the dynamics of volcanic ash plumes. In particular, it can simulate turbulent mixing (driving atmospheric entrainment and controlling the heat transfer), thermal expansion (controlling the plume buoyancy), the interaction between solid particles and volcanic gas (including kinetic non-equilibrium effects) and the effects of compressibility (over-pressured eruptions and infrasonic measurements). The model is based on the turbulent dispersed multiphase flow theory for dilute flows (volume concentration <0.001, implying that averaged inter-particle distance is larger than 10 diameters) where particle collisions are neglected. Moreover, in order to speed up the code without losing accuracy, we make the hypothesis of fine particles (Stokes number <0.2 , i.e., volcanic ash particles finer then a millimeter), so that we are able to consider non-equilibrium effects only at the first order. We adopt LES formalism (which is preferable in transient regimes) for compressible flows to model the non-linear coupling between turbulent scales and the effect of sub-grid turbulence on the large-scale dynamics. A three-dimensional numerical code has been developed basing on the OpenFOAM computational framework, a CFD open source parallel software package. Numerical benchmarks demonstrate that the model is able to capture important non-equilibrium phenomena in gas-particle mixtures, such as particle clustering and ejection from large-eddy turbulent structures, as well
Analysis of the flow structure and heat transfer in a vertical mantle heat exchanger
DEFF Research Database (Denmark)
Knudsen, Søren; Morrison, GL; Behnia, M
2005-01-01
initially mixed and initially stratified inner tank and mantle. The analysis of the heat transfer showed that the flow in the mantle near the inlet is mixed convection flow and that the heat transfer is dependent on the mantle inlet temperature relative to the core tank temperature at the mantle level. (C......The flow structure inside the inner tank and inside the mantle of a vertical mantle heat exchanger was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the inner tank and in the mantle were measured using a Particle Image...... Velocimetry (PIV) system. A Computational Fluid Dynamics (CFD) model of the vertical mantle heat exchanger was also developed for a detailed evaluation of the heat flux at the mantle wall and at the tank wall. The flow structure was evaluated for both high and low temperature incoming flows and for both...
Analytical and Numerical Modelling of Flow Driven by Surface Differential Heating.
1982-09-01
of theoretical studies of the sea-breeze phenom- enon have appeared in the literature. Most of these are based on numerical modelling ( Estoque 1961... ESTOQUE , M.A. (1961). A Theoretical Investigation of the Sea Breeze. Quart. J. Roy. Meteor. Soc. 87, 136-146. GEISLER, J.E. and BRETHERTON, F.P. (1968
Crustal Heat Production and Mantle Heat Flow in Southeast China
Institute of Scientific and Technical Information of China (English)
胡圣标; 汪集旸
1994-01-01
The correlation between seismic velocity （vp） and radiogenic heat production （A） en-ables the distribution of crustal heat production to be evaluated,from which the mantle heat flow for 21seismic velocity-depth profiles located along the two continental geotraverses in Southeast China can bededuced.Several approaches have been proposed to special problems connected with the conversion ofseismic velocities into heat production in orogenic areas.The results show that the crustal heat flow inSoutheast China is quite inhomogeneous,varying between 17.8 and 46 mW·m-2,which can be attribut-ed to the complicated crustal structure related to overthrusting and overlapping in the upper crust.The re-markable regional variation in the mantle heat flow,ranging from 23.2 to 41.6 mW·m-2,correspondsto the large-scale tectonothermal evolution of the orogenic belts.
A study of the dispersed flow interfacial heat transfer model of RELAP5/MOD2.5 and RELAP5/MOD3
Energy Technology Data Exchange (ETDEWEB)
Andreani, M. [Swiss Federal Institute of Technology, Zurich (Switzerland); Analytis, G.T.; Aksan, S.N. [Paul Scherrer Institute, Villigen (Switzerland)
1995-09-01
The model of interfacial heat transfer for the dispersed flow regime used in the RELAP5 computer codes is investigated in the present paper. Short-transient calculations of two low flooding rate tube reflooding experiments have been performed, where the hydraulic conditions and the heat input to the vapour in the post-dryout region were controlled for the predetermined position of the quench front. Both RELAP5/MOD2.5 and RELAP5/MOD3 substantially underpredicted the exit vapour temperature. The mass flow rate and quality, however, were correct and the heat input to the vapour was larger than the actual one. As the vapour superheat at the tube exit depends on the balance between the heat input from the wall and the heat exchange with the droplets, the discrepancy between the calculated and the measured exit vapour temperature suggested that the inability of both codes to predict the vapour superheat in the dispersed flow region is due to the overprediction of the interfacial heat transfer rate.
Heat transfer and fluid flow in microchannels
Mala, Ghulam Mohiuddin
Fluid flow and heat transfer characteristics in microchannels of different cross-sections; parallel plate, cylindrical and trapezoidal microchannels were studied. The trapezoidal microchannels were etched in silicon and glass by photolithographic techniques. The cylindrical microchannels of fused silica and stainless steel were readily available. Channels with depths of 18 μm to 300 μm were studied. The study was divided into three parts viz. theoretical modeling, numerical simulation and experimentation. Electrokinetic effects such as the effects of electrical double layer (EDL) at the solid-liquid interface and surface roughness effects were considered. An experimental apparatus was constructed and a procedure devised to measure the flow rate, pressure drop, temperatures and electrokinetic parameters like streaming potential, streaming current, and conductivity of the working fluid. Great care was taken so that the measurements were accurate and repeatable. For steady state laminar flow and heat transfer in microchannels, mathematical models were developed that consider the effects of electrical double layer and surface roughness at the microchannel walls. The non- linear, 2-D, Poisson-Boltzmann equation that describes the potential distribution at the solid liquid interface was solved numerically and results were compared with a linear approximate solution that overestimates the potential distribution for higher values of zeta potential. Effects of the EDL field at the solid-liquid interface, surface roughness at the microchannel walls and the channel size, on the velocity distribution, streaming potential, apparent viscosity, temperature distribution and heat transfer characteristics are discussed. The experimental results indicate significant departure in flow characteristics from the predictions of the Navier-Stokes equations, referred to as conventional theory. The difference between the experimental results and theoretical predictions decreases as the
Indian Academy of Sciences (India)
HARI MOHAN KUSHWAHA; SANTOSH K SAHU
2016-06-01
This paper presents an analytical investigation to study the heat transfer and fluid flow characteristics in the slip flow region for hydrodynamically and thermally fully developed flow between parallel plates.Both upper and lower plates are subjected to asymmetric heat flux boundary conditions. The effect of first ordervelocity slip, temperature jump, asymmetric heat flux ratio and viscous dissipation on the heat transfer performance is analyzed. Closed form expressions are obtained for the temperature distribution and Nusselt number. Present predictions are verified for the cases that neglect the viscous heating and microscale effects. The effect of asymmetric heat flux ratio with and without viscous dissipation on Nusselt number for both macroscale and microscale is highlighted. The heat transfer characteristics are found to depend on various modeling parameters, namely, modified Brinkman number, Knudsen number and heat flux ratio
Fullea, J.; Muller, M. R.; Jones, A. G.
2012-04-01
Little is known of Ireland's deep, low-enthalpy geothermal resources and the potential for space heating and/or electricity generation based on geothermal energy to displace Ireland's significant reliance on carbon-based fuels. IRETHERM (www.iretherm.ie) is a four-and-a-half year, all-island, academic-government-industry collaborative project, initiated in 2011, with the overarching objective of developing a strategic and holistic understanding of Ireland's geothermal energy potential through integrated modelling of new and existing geophysical and geological data. One of the challenges in searching for deep geothermal resources in the relatively unexplored setting of Ireland lies in identifying those areas most likely to support significantly elevated temperatures at depth. Available borehole data, although sparse and clustered around areas of mineral and hydrocarbon interest, suggest a marked regional increase in surface heat-flow across Ireland, from ~40 mW/m2 in the south to >80 mW/m2 in the north. The origins of both the observed regional heat-flow trend and local temperature anomalies have not been investigated and are not currently understood. Although variations in the structure of the crust and lithosphere have been revealed by a number of active-source seismic and teleseismic experiments, their effects on surface heat-flow have not been modelled. Bulk 3-D variation in crustal heat-production across Ireland, which may contribute significantly to the observed regional and local temperature variations, has also not been determined. We investigate the origins of Ireland's regional heat-flow trend and regional and local temperature variations using the software package LitMod. This software combines petrological and geophysical modelling of the lithosphere and sub-lithospheric upper mantle within an internally consistent thermodynamic-geophysical framework, where all relevant properties are functions of temperature, pressure and chemical composition. The major
Energy Technology Data Exchange (ETDEWEB)
Yamamoto, Yoshinobu, E-mail: yamamotoy@yamanashi.ac.jp [Division of Mechanical Engineering, University of Yamanashi, 4-3-11 Takeda, Kofu 400-8511 (Japan); Kunugi, Tomoaki, E-mail: kunugi@nucleng.kyoto-u.ac.jp [Department of Nuclear Engineering, Kyoto University, C3-d2S06, Kyoto-Daigaku Katsura, Nishikyo-Ku 615-8540, Kyoto (Japan)
2016-11-01
Highlights: • We show the applicability to predict the heat transfer imposed on a uniform wall-normal magnetic field by means of the zero-equation heat transfer model. • Quasi-theoretical turbulent Prandtl numbers with various molecular Prandtl number fluids were obtained. • Improvements of the prediction accuracy in turbulent kinetic energy and turbulent dissipation rate under the magnetic fields were accomplished. - Abstract: Zero-equation heat transfer models based on the constant turbulent Prandtl number are evaluated using direct numerical simulation (DNS) data for fully developed channel flows imposed on a uniform wall-normal magnetic field. Quasi-theoretical turbulent Prandtl numbers are estimated by DNS data of various molecular Prandtl number fluids. From the viewpoint of highly-accurate magneto-hydrodynamic (MHD) heat transfer prediction, the parameters of the turbulent eddy viscosity of the k–É› model are optimized under the magnetic fields. Consequently, we use the zero-equation model based on a constant turbulent Prandtl number to demonstrate MHD heat transfer, and show the applicability of using this model to predict the heat transfer.
Pneumatic Proboscis Heat-Flow Probe
Zacny, Kris; Hedlund, Magnus; Mumm, Eric; Shasho, Jeffrey; Chu, Philip; Kumar, Nishant
2013-01-01
Heat flow is a fundamental property of a planet, and provides significant constraints on the abundance of radiogenic isotopes, the thermal evolution and differentiation history, and the mechanical properties of the lithosphere. Heat-flow measurements are also essential in achieving at least four of the goals set out by the National Research Council for future lunar exploration. The heat-flow probe therefore directly addresses the goal of the Lunar Geophysical Network, which is to understand the interior structure and composition of the Moon. A key challenge for heat flow measurement is to install thermal sensors to the depths approximately equal to 3 m that are not influenced by the diurnal, annual, and longer-term fluctuations of the surface thermal environment. In addition, once deployed, the heat flow probe should cause little disturbance to the thermal regime of the surrounding regolith. A heat-flow probe system was developed that has two novel features: (1) it utilizes a pneumatic (gas) approach, excavates a hole by lofting the lunar soil out of the hole, and (2) deploys the heat flow probe, which utilizes a coiled up tape as a thermal probe to reach greater than 3-meter depth. The system is a game-changer for small lunar landers as it exhibits extremely low mass, volume, and simple deployment. The pneumatic system takes advantage of the helium gas used for pressurizing liquid propellant of the lander. Normally, helium is vented once the lander is on the surface, but it can be utilized for powering pneumatic systems. Should sufficient helium not be available, a simple gas delivery system may be taken specifically for the heat flow probe. Either way, the pneumatic heat flow probe system would be much lighter than other systems that entirely rely on the electrical power of the lander.
Tham, Leony; Nazar, Roslinda; Pop, Ioan
2016-09-01
The steady laminar mixed convection boundary layer flow from a horizontal circular cylinder in a nanofluid embedded in a porous medium, which is maintained at a constant surface heat flux, has been studied by using the Buongiorno-Darcy nanofluid model for both cases of a heated and cooled cylinder. The resulting system of nonlinear partial differential equations is solved numerically using an implicit finite-difference scheme known as the Keller box method. The solutions for the flow and heat transfer characteristics are evaluated numerically and studied for various values of the governing parameters, namely the Lewis number, Brownian number, mixed convection parameter, buoyancy ratio parameter and thermophoresis parameter. It is also found that the boundary layer separation occurs at the opposing fluid flow, that is when the mixed convection parameter is negative. It is also observed that increasing the mixed convection parameter delays the boundary layer separation and the separation can be completely suppressed for sufficiently large values of the mixed convection parameter. The Brownian and buoyancy ratio parameters appear to affect the fluid flow and heat transfer profiles.
Garven, G.; Raffensperger, J.P.; Dumoulin, J.A.; Bradley, D.A.; Young, L.E.; Kelley, K.D.; Leach, D.L.
2003-01-01
The Red Dog deposit is a giant 175 Mton (16% Zn, 5% Pb), shale-hosted Pb-Zn-Ag-Ba ore district situated in the Carboniferous Kuna Basin, Western Brooks Range, Alaska. These SEDEX-type ores are thought to have formed in calcareous turbidites and black mudstone at elevated sub-seafloor temperatures (120-150??C) within a hydrogeologic framework of submarine convection that was structurally organized by large normal faults. The theory for modeling brine migration and heat transport in the Kuna Basin is discussed with application to evaluating flow patterns and heat transport in faulted rift basins and the effects of buoyancy-driven free convection on reactive flow and ore genesis. Finite element simulations show that hydrothermal fluid was discharged into the Red Dog subbasin during a period of basin-wide crustal heat flow of 150-160 mW/m2. Basinal brines circulated to depths as great as 1-3 km along multiple normal faults flowed laterally through thick clastic aquifers acquiring metals and heat, and then rapidly ascended a single discharge fault zone at rates ??? 5 m/year to mix with seafloor sulfur and precipitate massive sulfide ores. ?? 2003 Elsevier Science B.V. All rights reserved.
Thermodynamics of Flow Boiling Heat Transfer
Collado, F. J.
2003-05-01
Convective boiling in sub-cooled water flowing through a heated channel is essential in many engineering applications where high heat flux needs to be accommodated. It has been customary to represent the heat transfer by the boiling curve, which shows the heat flux versus the wall-minus-saturation temperature difference. However it is a rather complicated problem, and recent revisions of two-phase flow and heat transfer note that calculated values of boiling heat transfer coefficients present many uncertainties. Quite recently, the author has shown that the average thermal gap in the heated channel (the wall temperature minus the average temperature of the coolant) was tightly connected with the thermodynamic efficiency of a theoretical reversible engine placed in this thermal gap. In this work, whereas this correlation is checked again with data taken by General Electric (task III) for water at high pressure, a possible connection between this wall efficiency and the reversible-work theorem is explored.
Kuhn, Philipp P.; Echtler, Helmut; Littke, Ralf; Alfaro, Guillermo
2010-11-01
The Arauco basin is part of the coastal forearc domain in South-Central Chile. During its evolution since the Late Cretaceous it was subject to multiple deposition cycles and the erosion of lower bathyal to beach and lagoon sediments. These different environments were established in alternating accretional and erosive subduction tectonic settings along the South Andean active margin. Whereas the general development is well understood, inconsistencies arise regarding the origin of the high thermal maturity of Eocene coals and the estimates of vertical movements of the whole area during the Cenozoic. Thermal modelling of this forearc basin provides new insights regarding its thermal evolution and evaluation of the magnitudes of subsidence and inversion. Results are based on the analysis of coal samples from surface outcrops, mines and drill cores of ten onshore wells from ENAP/Sipetrol. Newly derived vitrinite reflectance (VR r) measurements indicated a temperature in the range of 135-150 °C for the oldest sediment unit of the Arauco basin, which was reached in post Eocene times. Furthermore, 1D basin modelling techniques indicate scenarios that could explain the coalification values in the basin's sediments. The models were calibrated against VR r data from drill core samples supplied by ENAP/Sipetrol. A Miocene and an Oligocene subsidence/inversion scenario were considered, while neither could be securely discarded based on the modelling results. Furthermore, it can be shown that the current thermal maturity was not reached by an increased heat flow (HF) or a deep subsidence only. Consequently, a structural inversion accompanied by the erosion of ~ 3.0 ± 0.4 km depending on the locality in combination with a high HF of ~ 64 ± 4 mW/m 2 is the best explanation of the available data. The HF, which is high for a forearc setting, can be attributed to the increased temperature of the relatively young subducted Nazca Plate and an additional influence of ascending hot
Conjugate Compressible Fluid Flow and Heat Transfer in Ducts
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.
The role of Compton heating in cluster cooling flows
Ciotti, L; Pellegrini, S
2003-01-01
Recent observations by Chandra and XMM-Newton demonstrate that the central gas in "cooling flow" galaxy clusters has a mass cooling rate that decreases rapidly with decreasing temperature. This contrasts the predictions of a steady state cooling flow model. On the basis of these observational results, the gas can be in a steady state only if a steady temperature dependent heating mechanism is present; alternatively the gas could be in an unsteady state, i.e., heated intermittently. Intermittent heating can be produced by accretion on the supermassive black hole residing in the central cluster galaxy, via Compton heating. This mechanism can be effective provided that the radiation temperature of the emitted spectrum is higher than the gas temperature. Here we explore whether this heating mechanism can be at the origin of the enigmatic behavior of the hot gas in the central regions of ``cooling flow'' clusters. Although several characteristics of Compton heating appear attractive in this respect, we find that t...
Modeling of the Radial Heat Flow and Cooling Processes in a Deep Ultraviolet Cu+ Ne-CuBr Laser
Directory of Open Access Journals (Sweden)
Iliycho Petkov Iliev
2009-01-01
Full Text Available An improved theoretical model of the gas temperature profile in the cross-section of an ultraviolet copper ion excited copper bromide laser is developed. The model is based on the solution of the one-dimensional heat conduction equation subject to special nonlinear boundary conditions, describing the heat interaction between the laser tube and its surroundings. It takes into account the nonuniform distribution of the volume power density along with the radius of the laser tube. The problem is reduced to the boundary value problem of the first kind. An explicit solution of this model is obtained. The model is applied for the evaluation of the gas temperature profiles of the laser in the conditions of free and forced air-cooling. Comparison with other simple models assumed constant volume power density is made. In particular, a simple expression for calculating the average gas temperature is found.
Pneumatic Proboscis Heat Flow Probe Project
National Aeronautics and Space Administration — The heat flow probe directly answers requirements in the topic: S1.11 Lunar Science Instruments and Technology: "Geophysical Measurements: Systems, subsystems, and...
Laminar fluid flow and heat transfer in a fin-tube heat exchanger with vortex generators
Energy Technology Data Exchange (ETDEWEB)
Yanagihara, J.I.; Rodriques, R. Jr. [Polytechnic School of Univ. of Sao Paolo, Sao Paolo (Brazil). Dept. of Mechanical Engineering
1996-12-31
Development of heat transfer enhancement techniques for fin-tube heat exchangers has great importance in industry. In recent years, heat transfer augmentation by vortex generators has been considered for use in plate fin-tube heat exchangers. The present work describes a numerical investigation about the influence of delta winglet pairs of vortex generators on the flow structure and heat transfer of a plate fin-tube channel. The Navier-Stokes and Energy equations are solved by the finite volume method using a boundary-fitted coordinate system. The influence of vortex generators parameters such as position, angle of attack and aspect ratio were investigated. Local and global influences of vortex generators in heat transfer and flow losses were analyzed by comparison with a model using smooth fin. The results indicate great advantages of this type of geometry for application in plate fin-tube heat exchangers, in terms of large heat transfer enhancement and small pressure loss penalty. (author)
Burnett simulations of gas flow and heat transfer in microchannels
Institute of Scientific and Technical Information of China (English)
Fubing BAO; Jianzhong LIN
2009-01-01
In micro- and nanoscale gas flows, the flow falls into the transition flow regime. There are not enough molecule collisions and the gas deviates from the equilibrium. The Navier-Stokes equations fail to describe the gas flow in this regime. The direct simulation Monte Carlo method converges slowly and requires lots of computational time. As a result, the high-order Burnett equations are used to study the gas flow and heat transfer characteristics in micro- and nanoscale gas flows in this paper. The Burnett equations are first reviewed, and the augmented Burnett equations with high-order slip bound-ary conditions are then used to model the gas flow and heat transfer in Couette and Poiseuille flows in the transition regime.
Heat and mass transfer and hydrodynamics in swirling flows (review)
Leont'ev, A. I.; Kuzma-Kichta, Yu. A.; Popov, I. A.
2017-02-01
Research results of Russian and foreign scientists of heat and mass transfer in whirling flows, swirling effect, superficial vortex generators, thermodynamics and hydrodynamics at micro- and nanoscales, burning at swirl of the flow, and technologies and apparatuses with the use of whirling currents for industry and power generation were presented and discussed at the "Heat and Mass Transfer in Whirling Currents" 5th International Conference. The choice of rational forms of the equipment flow parts when using whirling and swirling flows to increase efficiency of the heat-power equipment and of flow regimes and burning on the basis of deep study of the flow and heat transfer local parameters was set as the main research prospect. In this regard, there is noticeable progress in research methods of whirling and swirling flows. The number of computational treatments of swirling flows' local parameters has been increased. Development and advancement of the up to date computing models and national productivity software are very important for this process. All experimental works are carried out with up to date research methods of the local thermoshydraulic parameters, which enable one to reveal physical mechanisms of processes: PIV and LIV visualization techniques, high-speed and infrared photography, high speed registration of parameters of high-speed processes, etc. There is a problem of improvement of researchers' professional skills in the field of fluid mechanics to set adequately mathematics and physics problems of aerohydrodynamics for whirling and swirling flows and numerical and pilot investigations. It has been pointed out that issues of improvement of the cooling system and thermal protection effectiveness of heat-power and heat-transfer equipment units are still actual. It can be solved successfully using whirling and swirling flows as simple low power consumption exposing on the flow method and heat transfer augmentation.
Heat flow and hydrocarbon generation in the Transylvanian basin, Romania
Energy Technology Data Exchange (ETDEWEB)
Cranganu, C.; Deming, D. [Univ. of Oklahoma, Norman (United States)
1996-10-01
The Transylvanian basin in central Romania is a Neogene depression superimposed on the Cretaceous nappe system of the Carpathian Mountains. The basin contains the main gas reserves of Romania, and is one of the most important gas-producing areas of continental Europe; since 1902, gas has been produced from more than 60 fields. Surface heat flow in the Transylvanian basin as estimated in other studies ranges from 26 to 58 mW/m{sup 2}, with a mean value of 38 mW/m{sup 2}, relatively low compared to surrounding areas. The effect of sedimentation on heat flow and temperature in the Transylvanian basin was estimated with a numerical model that solved the heat equation in one dimension. Because both sediment thickness and heat flow vary widely throughout the Transylvanian basin, a wide range of model variables were used to bracket the range of possibilities. Three different burial histories were considered (thin, average, and thick), along with three different values of background heat flow (low, average, and high). Altogether, nine different model permutations were studied. Modeling results show that average heat flow in the Transylvanian basin was depressed approximately 16% during rapid Miocene sedimentation, whereas present-day heat flow remains depressed, on average, about 17% below equilibrium values. We estimated source rock maturation and the timing of hydrocarbon generation by applying Lopatin`s method. Potential source rocks in the Transylvanian basin are Oligocene-Miocene, Cretaceous, and Jurassic black shales. Results show that potential source rocks entered the oil window no earlier than approximately 13 Ma, at depths of between 4200 and 8800 m. Most simulations encompassing a realistic range of sediment thicknesses and background heat flows show that potential source rocks presently are in the oil window; however, no oil has ever been discovered or produced in the Transylvanian basin.
Heat flow measurements on the Lomonosov Ridge, Arctic Ocean
Institute of Scientific and Technical Information of China (English)
XIAO Wentao; ZHANG Tao; ZHENG Yulong; GAO Jinyao
2013-01-01
Heat flow was measured on the Lomonosov Ridge during the 5th Chinese National Arctic Expedition in 2012. To derive the time-temperature curve, resistivity data were transformed to temperature by the resistivity-temperature program. Direct reading and linear regression methods were used to calculate the equilibrium temperature, which were regressed against the depth of the probes in sediment to derive the geothermal gradient. Then, heat flow was calculated as the product of geothermal gradient and thermal conductivity of sediments. The heat flow values on the basis of the two methods were similar (i.e., 67.27 mW/m2 and 63.99 mW/m2, respectively). The results are consistent with the measurements carried out at adjacent sites. The age of the Lomonosov Ridge predicted by the heat flow-age model was 62 Ma, which is in accordance with the inference that the ridge was separated from Eurasia at about 60 Ma.
Bakar, Nor Ashikin Abu; Bachok, Norfifah; Arifin, Norihan Md.
2016-06-01
The study of the steady two dimensional boundary layer flow of a copper (Cu)-water nanofluid on a moving plate is investigated. The assumption is the plate moves in the same or opposite direction to the free stream. The nonlinear partial differential equations are transformed into nonlinear ordinary differential equations using a similarity variables,then a shooting technique is used to solved it numerically. The numerical results for skin friction coefficient, the local Nusselt number, the local Sherwood number as well as the velocity, temperature and concentration profiles are obtained. The effect of nanoparticle volume fraction, Brownian motion and thermophoresis parameters on heat transfer are examined. The results show that the local Nusselt number and the local Sherwood number increase with increasing in the Brownian motion parameter Nb and thermophoresis parameter Nt.
DEFF Research Database (Denmark)
Nielsen, Toke Rammer; Rose, Jørgen; Kragh, Jesper
2009-01-01
In cold climates heat recovery in the ventilation system is essential to reduce heating energy demand. Condensation and freezing occur often in efficient heat exchangers used in cold climates. To develop efficient heat exchangers and defrosting strategies for cold climates, heat and mass transfer...
Paolini, C.; Park, A. J.; Mellors, R. J.; Castillo, J.
2009-12-01
A typical CO2 sequestration scenario involves the use of multiple simulators for addressing multiphase fluid and heat flow, water-rock interaction and mass-transfer, rock mechanics, and other chemical and physical processes. The benefit of such workflow is that each model can be constrained rigorously; however, the drawback is final modeling results may achieve only a limited extent of the theoretically possible capabilities of each model. Furthermore, such an approach in modeling carbon sequestration cannot capture the nonlinearity of the various chemical and physical processes. Hence, the models can only provide guidelines for carbon sequestration processes with large margins of error. As an alternative, a simulator is being constructed by a multi-disciplinary team with the aim of implementing a large array of fundamental phenomenologies, including, but not limited to: water-rock interaction using elemental mass-balance and explicit mass-transfer and reaction coupling methods; multi-phase and heat flow, including super-critical CO2 and oil; fracture mechanics with anisotropic permeabilities; rheological rock mechanics based on incremental stress theory; and a composite petrophysics model capable of describing changing rock composition and properties. The modules representing the processes will be solved using a layered iteration method, with the goal of capturing the nonlinear feedback among all of the processes. The simulator will be constructed using proven optimization and modular, object-oriented, and service-oriented programming methods. Finally, a novel AJAX (asynchronous JavaScript and XML) user interface is being tested to host the simulator that will allow usage through an Internet browser. Currently, the water-rock interaction, composite petrophysics, and multi-phase fluid and heat flow modules are available for integration. Results of the water-rock interaction and petrophysics coupling has been used to model interaction between a CO2-charged water and
Analysis of flow and heat transfer characteristics of porous heat-storage wall in greenhouse
Institute of Scientific and Technical Information of China (English)
Li OUYANG; Wei LIU
2008-01-01
The flow and heat transfer characteristics of porous heat-storage wall in greenhouse are studied by using the one-dimensional steady energy two-equation model for saturated porous medium. The results show that the heat exchange between the air and the solid matrix of the porous heat-storage wall depends upon the inlet air velocity, the porosity and the permeability of porous medium, and the thermal conductivity of the solid matrix. Because the incidence of solar radiation on the porous heat-storage wall is not uniform, the new compos-ite porous solar wall with different porosity is proposed to reduce the disadvantageous effect.
Analytical heat and fluid flow in microchannels and microsystems
Cotta, Renato M; Naveira-Cotta, Carolina P
2016-01-01
This book focuses on the modeling and analysis of heat and fluid flow in microchannels and micro-systems, compiling a number of analytical and hybrid numerical-analytical solutions for models that account for the relevant micro-scale effects, with the corresponding experimental analysis validation when applicable. The volume stands as the only available compilation of easy to use analytically-based solutions for micro-scale heat and fluid flow problems, that systematically incorporates the most relevant micro-scale effects into the mathematical models, followed by their physical interpretation on the micro-system behavior.
Numerical prediction of flow, heat transfer, turbulence and combustion
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
Stirling Engine With Radial Flow Heat Exchangers
Vitale, N.; Yarr, George
1993-01-01
Conflict between thermodynamical and structural requirements resolved. In Stirling engine of new cylindrical configuration, regenerator and acceptor and rejector heat exchangers channel flow of working gas in radial direction. Isotherms in regenerator ideally concentric cylinders, and gradient of temperature across regenerator radial rather than axial. Acceptor and rejector heat exchangers located radially inward and outward of regenerator, respectively. Enables substantial increase in power of engine without corresponding increase in diameter of pressure vessel.
Heat transfer mechanisms in microgravity flow boiling.
Ohta, Haruhiko
2002-10-01
The objective of this paper is to clarify the mechanisms of heat transfer and dryout phenomena in flow boiling under microgravity conditions. Liquid-vapor behavior in annular flow, encountered in the moderate quality region, has extreme significance for practical application in space. To clarify the gravity effect on the heat transfer observed for an upward flow in a tube, the research described here started from the measurement of pressure drop for binary gas-liquid mixture under various gravity conditions. The shear stress acting on the surface of the annular liquid film was correlated by an empirical method. Gravity effects on the heat transfer due to two-phase forced convection were investigated by the analysis of velocity and temperature profiles in the film. The results reproduce well the trends of heat transfer coefficients varying with the gravity level, quality, and mass velocity. Dryout phenomena in the moderate quality region were observed in detail by the introduction of a transparent heated tube. At heat fluxes just lower and higher than CHF value, a transition of the heat transfer coefficient was calculated from oscillating wall temperature, where a series of opposing heat transfer trends--the enhancement due to the quenching of dried areas or evaporation from thin liquid films and the deterioration due to the extension of dry patches--were observed between the passage of disturbance waves. The CHF condition that resulted from the insufficient decrease of wall temperature in the period of enhanced heat transfer was overcome by a temperature increase in the deterioration period. No clear effect of gravity on the mechanisms of dryout was observed within the range of experiments.
Directory of Open Access Journals (Sweden)
Korzeń Anna
2017-01-01
The results of the numerical simulations of a heat exchanger using experimentally determined air and water-side heat transfer formulas for calculation of heat transfer coefficient were compared with the experimental data. Very good agreement of computation results (i.e. air and water temperature at the outlet of the heat exchanger with the experimental data was obtained.
Analysis of radiative heat transfer impact in cross-flow tube and fin heat exchangers
Hanuszkiewicz-Drapała, Małgorzata; Bury, Tomasz; Widziewicz, Katarzyna
2016-03-01
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.
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.
Energy Technology Data Exchange (ETDEWEB)
Kneafsey, T.J.; Pruess, K. [Lawrence Berkeley National Lab., CA (United States). Earth Sciences Div.
1997-06-01
Water flow in fractures under the conditions of partial saturation and thermal drive may lead to fast flow along preferential localized pathways and heat pipe conditions. Water flowing in fast pathways may ultimately contact waste packages at Yucca Mountain and transport radionuclides to the accessible environment. Sixteen experiments were conducted to visualize liquid flow in glass fracture models, a transparent epoxy fracture replica, and a rock/replica fracture assembly. Spatially resolved thermal monitoring was performed in seven of these experiments to evaluate heat-pipe formation. Depending on the fracture apertures and flow conditions, various flow regimes were observed including continuous rivulet flow for high flow rates, intermittent rivulet flow and drop flow for intermediate flow rates, and film flow for low flow rates and wide apertures. These flow regimes were present in both fracture models and in the replica of a natural fracture. Heat-pipe conditions indicated by low thermal gradients were observed in five experiments. Conditions conducive to heat-pipe formation include an evaporation zone, condensation zone, adequate space for vapor and liquid to travel, and appropriate fluid driving forces. In one of the two experiments where heat pipe conditions were not observed, adequate space for liquid-vapor counterflow was not provided. Heat pipe conditions were not established in the other, because liquid flow was inadequate to compensate for imbibition and the quantity of heat contained within the rock.
Heat transfer in vapour-liquid flow of carbon dioxide
Energy Technology Data Exchange (ETDEWEB)
Yagov, V.V. [Moscow Power Engineering Institute (Technical University), Moscow (Russian Federation)], e-mail: YagovVV@mpei.ru
2009-07-01
During the last decade a number of studies of boiling heat transfer in carbon dioxide notably increase. As a field of CO{sub 2} practical using corresponds to high reduced pressures, and a majority of available experimental data on CO{sub 2} flow boiling even in submillimetric channels relate to turbulent liquid flow regimes, a possibility arises to develop sufficiently general method for HTC predicting. Under the above conditions nucleate boiling occurs up to rather high flow quality, even in annular flow regime due to extremely small size of an equilibrium vapour bubble. This conclusion is in agreement with the available experimental data. The predicting equation for nucleate boiling heat transfer developed by the present author in 1988 is valid for any nonmetallic liquid. A contribution of forced convection in heat transfer is calculated according to the Petukhov et al. equation with correction factor, which accounted for an effect of velocity increase due to evaporation. This effect can be essential at relatively small heat fluxes and rather high mass flow rates. The Reynolds analogy and homogeneous model are used in order to account for the convective heat transfer augmentation in two-phase flow. Due to low ratio of liquid and vapour densities at high reduced pressures the homogeneous approximation of two-phase flow seems to be warranted. A total heat transfer coefficient is calculated as an interpolated value of boiling and convective HTCs. The experimental data on CO{sub 2} flow boiling related to regimes before heated wall dryout incipience are in rather good agreement with the calculations. (author)
Heat transfer in vapour-liquid flow of carbon dioxide
Energy Technology Data Exchange (ETDEWEB)
Yagov, V.V. [Moscow Power Engineering Institute (Technical University), Moscow (Russian Federation)], e-mail: YagovVV@mpei.ru
2009-07-01
During the last decade a number of studies of boiling heat transfer in carbon dioxide notably increase. As a field of CO{sub 2} practical using corresponds to high reduced pressures, and a majority of available experimental data on CO{sub 2} flow boiling even in submillimetric channels relate to turbulent liquid flow regimes, a possibility arises to develop sufficiently general method for HTC predicting. Under the above conditions nucleate boiling occurs up to rather high flow quality, even in annular flow regime due to extremely small size of an equilibrium vapour bubble. This conclusion is in agreement with the available experimental data. The predicting equation for nucleate boiling heat transfer developed by the present author in 1988 is valid for any nonmetallic liquid. A contribution of forced convection in heat transfer is calculated according to the Petukhov et al. equation with correction factor, which accounted for an effect of velocity increase due to evaporation. This effect can be essential at relatively small heat fluxes and rather high mass flow rates. The Reynolds analogy and homogeneous model are used in order to account for the convective heat transfer augmentation in two-phase flow. Due to low ratio of liquid and vapour densities at high reduced pressures the homogeneous approximation of two-phase flow seems to be warranted. A total heat transfer coefficient is calculated as an interpolated value of boiling and convective HTCs. The experimental data on CO{sub 2} flow boiling related to regimes before heated wall dryout incipience are in rather good agreement with the calculations. (author)
Heat Transfer & Periodic Flow Analysis of Heat Exchanger by CFD with Nano Fluids
Directory of Open Access Journals (Sweden)
Mr.V.V.Ramakrishna
2016-01-01
Full Text Available Many heat transfer applications such as steam generators in a boiler or air cooling coil of an air conditioner, can be modelled in a bank of tubes containing a fluid flowing at one temperature that is immersed in a second fluid in a cross flow at different temperature. CFD simulations are a useful tool for understanding flow and heat transfer principles as well as for modelling these types of geometries. Both the fluids considered in the present study are CUO Nano fluids, and flow is classified as laminar and steady with Reynolds number between 100- 600.The mass flow rate of the cross flow and diameter has been varied (such as 0.05, 0.1, 0.15, 0.20, 0.25, 0.30 kg/sec and 0.8, 1.0.1.2 &1.4cm and the models are used to predict the flow and temperature fields that result from convective heat transfer. Due to symmetry of the tube bank and the periodicity of the flow inherent in the tube bank geometry, only a portion of the geometry will be modelled and with symmetry applied to the outer boundaries. The inflow boundary will be redefined as a periodic zone and the outflow boundary is defined as the shadow. The various static pressures, velocities, and temperatures obtained are reported. In this present project tubes of different diameters and different mass flow rates are considered to examine the optimal flow distribution. Further the problem has been subjected to effect of materials used for tubes manufacturing on heat transfer rate. Materials considered are copper and Nickle Chromium alloys. Results emphasize the utilization of alloys in place of copper as tube material serves better heat transfer with most economical way.
The management of heat flow in deep mines
Energy Technology Data Exchange (ETDEWEB)
Wagner, Horst [Montanuniv. Leoben (Austria). Dept. Mineral Resources and Petroleum Engineering
2013-04-15
With the ever-increasing depth of mines, the management of heat has become a key issue for their design and operation. There are two main sources of heat: heat transfer from the rock mass into the mine workings and heat associated with mining operations. The principles of heat transfer from the rock mass are discussed and basic relationships presented. Sources of heat linked to mining operations are discussed. It is shown that in deep-level mines, heat transfer from the rock mass accounts more than 75 % of total mine heat load. In highly mechanized coal mines, heat from the use of mining machinery is also significant. Some models of heat flow prediction for deep gold mines are presented. It is shown that in the case of deep mines, control of heat flow is more important than increasing refrigeration capacity. Examples of heat flow management methods are given. Furthermore, the paper deals with the effects of heat on the human body and mine cooling strategies for deep mines. In detail the effects of heat on a worker are examined, heat stress and heat tolerance discussed and methods of assessing heat stress in different mining situations presented. Experiences from deep South African gold mines highlight the adverse effects of heat stress environment on safety and labour productivity. The principal methods of cooling of deep and ultra deep mines are discussed. It is shown that auto-compression of ventilation air is a deciding factor governing the choice of surface or underground cooling of ventilation air. In the case of deep and ultra deep mines, the use of chilled service water and ice slurry has shown to be the most cost effective means of mine cooling. In the case of ice slurry as cooling medium advantage is taken of the latent heat of ice which significantly reduces the amount of water required for mine cooling and hence the cost of pumping the water to surface. Cooling strategies for moderately deep, deep and ultra deep mines are discussed. Examples of cooling
Yayla, Sedat; Beyin, Seyfettin; Oztekin, Alparslan
2012-11-01
Transient 3-D dimensional turbulent flow simulations are conducted to examine flow and heat transfer characteristics in inline and staggered slotted semi-cylinders placed in a rectangular cross sectioned fin tube heat exchanger. Both Reynolds averaged Navier's equation and Large Eddy simulations model are employed to conduct simulations using Fluent-ANSYS. Predictions of transient simulations are compared against the results of the PIV flow visualization observations at Reynolds number 1500 and 4000. Measured and predicted velocity and the vorticity field in the wake of cylinders agree well with each other at both Reynolds number. The effect of the angle between the slotted semi cylinders and the flow direction is investigated for various values of Reynolds number in both laminar and turbulent flow regimes. Transient nature of the three dimensional flow structures with flow separation, reattachment and vortices are characterized. The effects of the flow structure on the heat transfer characteristics are determined by calculating the heat transfer coefficient along the surface of the semi cylinders.
Lu, C.; Deng, S.; Podgorney, R. K.; Huang, H.
2011-12-01
Reliable reservoir performance predictions of enhanced geothermal reservoir systems require accurate and robust modeling for the coupled thermal-hydrological-mechanical processes. Conventionally, in order to reduce computational cost, these types of problems are solved using operator splitting method, usually by sequentially coupling a subsurface flow and heat transport simulator with a solid mechanics simulator via input files. However, such operator splitting approaches are applicable only to loosely coupled problems and usually converge slowly. As in most enhanced geothermal systems (EGS), fluid flow, heat transport, and rock deformation are typically strongly nonlinearly coupled, an alternative is to solve the system of nonlinear partial differential equations that govern the system simultaneously using a fully coupled solution procedure for fluid flow, heat transport, and solid mechanics. This procedure solves for all solution variables (fluid pressure, temperature and rock displacement fields) simultaneously, which leads to one large nonlinear algebraic system that needs to be solved by a strongly convergent nonlinear solver. Development over the past 10 years in the area of physics-based conditioning, strongly convergent nonlinear solvers (such as Jacobian Free Newton methods) and efficient linear solvers (such as GMRES, AMG), makes such an approach competitive. In this presentation, we will introduce a continuum-scaled parallel physics-based, fully coupled, modeling tool for predicting the dynamics of fracture initiation and propagation, fluid flow, rock deformation, and heat transport in a single integrated code named FALCON (Fracturing And Liquid-steam CONvection). FALCON is built upon a parallel computing framework developed at Idaho National Laboratory (INL) for solving coupled systems of nonlinear equations with finite element method with unstructured and adaptively refined/coarsened grids. Currently, FALCON contains poro- and thermal- elastic models
Bianchi type-V cosmological models with perfect fluid and heat flow in Saez–Ballester theory
Indian Academy of Sciences (India)
Shri Ram; M Zeyauddin; C P Singh
2009-02-01
In this paper we discuss the variation law for Hubble's parameter with average scale factor in a spatially homogeneous and anisotropic Bianchi type-V space-time model, which yields constant value of the deceleration parameter. We derive two laws of variation of the average scale factor with cosmic time, one is of power-law type and the other is of exponential form. Exact solutions of Einstein field equations with perfect fluid and heat conduction are obtained for Bianchi type-V space-time in these two types of cosmologies. In the cosmology with the power-law, the solutions correspond to a cosmological model which starts expanding from the singular state with positive deceleration parameter. In the case of exponential cosmology, we present an accelerating non-singular model of the Universe. We find that the constant value of deceleration parameter is reasonable for the present day Universe and gives an appropriate description of evolution of Universe. We have also discussed different types of physical and kinematical behaviour of the models in these two types of cosmologies.
Convective heat flow in space cryogenics plugs - Critical and moderate He II heat flux densities
Yuan, S. W. K.; Frederking, T. H. K.
1990-01-01
Plug flow rates of entropy, heat and normal fluid in phase separators and in zero net mass flow systems are, to some extent, quite similar. A simplified analysis of critical conditions is presented in agreement with data trends. A critical temperature gradient arises on the basis of the He II two-fluid model at the stability limit constraining the thermohydrodynamics of the system. Thus, the question of critical thermodynamic fluctuations associated with nucleation versus the possibility of critical gradients in externally imposed parameters is answered in favor of the latter route toward turbulence. Furthermore, a similarity equation is presented which incorporates size dependent rates for moderate heat flow densities observed in experiments.
Constraints on lithospheric thermal structure for the Indian Ocean from depth and heat flow data
Shoberg, Tom; Stein, Carol A.; Stein, Seth
1993-06-01
Models for the thermal evolution of oceanic lithosphere are primarily constrained by variations in seafloor depth and heat flow with age. These models have been largely based on data from the Pacific and Atlantic Ocean basins. We construct seafloor age relations for the Indian Ocean which we combine with bathymetric, sediment isopach and heat flow data to derive curves for depth and heat flow versus age. Comparison of these curves with predictions from three thermal models shows that they are better fit by the shallower depths and higher heat flow for the GDH1 model, which is characterized by a thinner and hotter lithosphere than previous models.
A one-dimensional heat transfer model for parallel-plate thermoacoustic heat exchangers
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
Garven, G.; Dumoulin, J. A.; Bradley, D. A.; Young, L. E.; Kelley, K. D.; Leach, D. L.
2002-12-01
Crustal heat flow can provide a strong mechanism for driving groundwater flow, particularly in submarine basins where other mechanisms for driving pore fluid flow such as topography, compaction and crustal deformation are too weak or too slow to have a significant effect on disturbing conductive heat flow. Fault zones appear to play a crucial role in focusing fluid migration in basins, as inferred in ancient rocks by many examples of hydrothermal deposits of sediment-hosted ores worldwide. Many rift-hosted deposits of lead, zinc, and barite ore appear to have formed at or near the seafloor by focused venting of hot basinal fluids and modified seawater, although the geophysical nature of these systems is not so well known. For example, the upper Kuna Formation, a finely laminated, black, organic-rich siliceous mudstone and shale in the Western Brooks Range of northwest Alaska, is host to the largest resources of zinc yet discovered in the Earth's crust, containing ore reserves in excess of 175 Mt averaging about 16% Zn and 5% Pb. Although situated today in a highly-deformed series of structural allocthonous plates thrusted during the Jurassic to Cretaceous Brookian Orogeny, the stratiform ores are thought to have formed much earlier in the anoxic, mud-rich Carboniferous-age Kuna Basin when adjacent carbonate platforms were drowned by rifting and tectonic subsidence. Fluid inclusion studies of ore-stage sphalerite and gangue minerals indicate sub-seafloor mineralization temperatures less than 200oC and most likely between 120 to 150 oC, during a period of sediment diagenesis and extensional faulting. We have constructed fully-coupled numerical models of heat and fluid flow to test hydrologic theories for free convection, submarine venting and subsequent ore formation, as constrained by paleoheat flow and petrologic observations. A finite element grid was designed and adapted for a cross section of the Kuna Basin, geologically restored to latest Mississippian time
Numerical and Experimental Approaches Toward Understanding Lava Flow Heat Transfer
Rumpf, M.; Fagents, S. A.; Hamilton, C.; Crawford, I. A.
2013-12-01
We have performed numerical modeling and experimental studies to quantify the heat transfer from a lava flow into an underlying particulate substrate. This project was initially motivated by a desire to understand the transfer of heat from a lava flow into the lunar regolith. Ancient regolith deposits that have been protected by a lava flow may contain ancient solar wind, solar flare, and galactic cosmic ray products that can give insight into the history of our solar system, provided the records were not heated and destroyed by the overlying lava flow. In addition, lava-substrate interaction is an important aspect of lava fluid dynamics that requires consideration in lava emplacement models Our numerical model determines the depth to which the heat pulse will penetrate beneath a lava flow into the underlying substrate. Rigorous treatment of the temperature dependence of lava and substrate thermal conductivity and specific heat capacity, density, and latent heat release are imperative to an accurate model. Experiments were conducted to verify the numerical model. Experimental containers with interior dimensions of 20 x 20 x 25 cm were constructed from 1 inch thick calcium silicate sheeting. For initial experiments, boxes were packed with lunar regolith simulant (GSC-1) to a depth of 15 cm with thermocouples embedded at regular intervals. Basalt collected at Kilauea Volcano, HI, was melted in a gas forge and poured directly onto the simulant. Initial lava temperatures ranged from ~1200 to 1300 °C. The system was allowed to cool while internal temperatures were monitored by a thermocouple array and external temperatures were monitored by a Forward Looking Infrared (FLIR) video camera. Numerical simulations of the experiments elucidate the details of lava latent heat release and constrain the temperature-dependence of the thermal conductivity of the particulate substrate. The temperature-dependence of thermal conductivity of particulate material is not well known
Directory of Open Access Journals (Sweden)
Hongsheng Chen
2015-12-01
Full Text Available Coupled heat transfer and chemical reaction of fluid flow in complex boundaries are explored by introducing two additional properties, i.e. particle type and energy state into the Lattice gas automata (LGA Frisch–Hasslacher–Pomeau (FHP-II model. A mix-redistribute of energy and type of particles is also applied on top of collision rules to ensure randomness while maintaining the conservation of mass, momentum and energy. Simulations of heat transfer and heterogeneous reaction of gas flow passing a circular porous cylinder in a channel are presented. The effects of porosity of cylinder, gas inlet velocity, and reaction probability on the reaction process are further analyzed with respect to the characteristics of solid morphology, product concentration, and temperature profile. Numerical results indicate that the reaction rate increases with increasing reaction probability as well as gas inlet velocity. Cylinders with a higher value of porosity and more homogeneous structure also react with gas particles faster. These results agree well with the basic theories of gas–solid reactions, indicating the present model provides a method for describing gas–solid reactions in complex boundaries at mesoscopic level.
Heat flow through the sea bottom around the Yucatan Peninsula
Energy Technology Data Exchange (ETDEWEB)
Khutorskoy, M.D.; Kononov, V.I.; Polyak, B.G. (Geological Inst., Moscow (USSR)); Fernandez, R. (Centro de Investigacion Cientifica y Educacion Superior de Ensenada, Baja California (Mexico)); Matveev, V.G.; Rot, A.A. (Polytechnical Inst., Kuybyshev (USSR))
1990-02-10
Heat flow studies were conducted in January-February 1987, off the Atlantic Coast of Mexico on board the R/V Akademik Nikolai Strakhov. Two areas were surveyed, one transecting the Salt Dome Province and the Campeche Canyon, in the Gulf of Mexico, and the other, on the eastern flank of the Yucatan Peninsula. Conductive heat flow through the bottom sediments was determined as the product of vertical temperature gradient and in situ thermal conductivity, measured with a thermal probe using a multithermistor array and real-time processing capabilities. Forward two-dimensional modeling allows one to estimate heat flow variations at both sites from local disturbances and to obtain average heat flow values of 51 mW/m{sup 2} for the transect within the Gulf of Mexico and 38 and 69 mW/m{sup 2} for two basins within the Yucatan area. Sea bottom relief has a predominant effect over other environmental factors in the scatter of heat flow determination in the Gulf of Mexico.
Cook, S. J.
2009-05-01
Aquarius is a Windows application that models fluid flow and heat transport under conditions in which fluid buoyancy can significantly impact patterns and magnitudes of fluid flow. The package is designed as a visualization tool through which users can examine flow systems in environments, both low temperature aquifers and regions with elevated PT regimes such as deep sedimentary basins, hydrothermal systems, and contact thermal aureoles. The package includes 4 components: (1) A finite-element mesh generator/assembler capable of representing complex geologic structures. Left-hand, right-hand and alternating linear triangles can be mixed within the mesh. Planer horizontal, planer vertical and cylindrical vertical coordinate sections are supported. (2) A menu-selectable system for setting properties and boundary/initial conditions. The design retains mathematical terminology for all input parameters such as scalars (e.g., porosity), tensors (e.g., permeability), and boundary/initial conditions (e.g., fixed potential). This makes the package an effective instructional aide by linking model requirements with the underlying mathematical concepts of partial differential equations and the solution logic of boundary/initial value problems. (3) Solution algorithms for steady-state and time-transient fluid flow/heat transport problems. For all models, the nonlinear global matrix equations are solved sequentially using over-relaxation techniques. Matrix storage design allows for large (e.g., 20000) element models to run efficiently on a typical PC. (4) A plotting system that supports contouring nodal data (e.g., head), vector plots for flux data (e.g., specific discharge), and colour gradient plots for elemental data (e.g., porosity), water properties (e.g., density), and performance measures (e.g., Peclet numbers). Display graphics can be printed or saved in standard graphic formats (e.g., jpeg). This package was developed from procedural codes in C written originally to
2012-01-01
One of the most important industrial processes is heat transfer, carried out by heat exchangers in single and multiphase flow applications. Despite the existence of well-developed theoretical models for different heat transfer mechanisms, the expanding need for industrial applications requiring the design and optimization of heat exchangers, has created a solid demand for experimental work and effort. This thesis concerns the use of numerical approaches to analyze and optimize heat transfer a...
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
A coupled model among flow field,solid temperature,species concentration and gas radiation,which was based on statistical narrow-band correlated-k model,was employed to predict the infrared radiations from hot exhausting nozzles. The parameters of narrow-band model were deduced from HITEMP line-by-line database. Several methods to increase computational efficiency and to save computational resources were employed,thus all the complicated computations could be operated on a personal computer. The predictions for three cases have been conducted to validate the accuracy of the methods mentioned above,including the temperature distribution of a water-cooling nozzle in rocket engines,the carbon dioxide absorptivity at the wavelength of 4.3 micron and the infrared radiation of a cylindrical furnace. Finally,the aerothermodynamic and infrared characteristics of two nozzles were predicted. It was shown that the infrared radiation intensity of chevron ejecting nozzle were obviously smaller than that of common axisymmetric convergent-divergent nozzle.
Business models of heat entrepreneurship in Finland
Energy Technology Data Exchange (ETDEWEB)
Okkonen, Lasse [North Karelia University of Applied Sciences, Yliopistokatu 6, FI-80100 Joensuu (Finland); Suhonen, Niko [University of Eastern Finland, Department of Law, P.O. Box 111, FI-80101 Joensuu (Finland)
2010-07-15
This paper presents the business models of small-scale heat energy production in Finland. Firstly, the development of heat entrepreneurship in the country is presented, including the remarkable growth of small and medium size enterprises (SMEs) in the last 15 years. Secondly, the concept of business model (business architecture of product/service flows and earning logics) is modified to the framework of wood heat production. The business model concept, and its sub-concepts, is applied in a brief review of current heat energy businesses in Finland. We arrive at a business model of heat entrepreneurships that are public companies/utilities, public-private partnerships, private companies and cooperatives, Energy Saving Company (ESCO), network model of large enterprise and franchising. Descriptive cases of these models are presented. Finally, the paper concludes with a discussion on the applicability of the business models in different operational environments and geographical contexts. (author)
Brune, James N.; Brown, Stephen; Johnson, Peggy A.
1993-02-01
Spontaneous stick-slip along the interface between stressed foam rubber blocks is a simple analog of earthquake rupture and stick-slip. Results from this model are used to elucidate the role of normal stress variations along the interface in the stick-slip process. Observations indicate significant normal interface vibrations and separation during slip, suggesting that dynamic changes in normal stress (rather than a drop in the coefficient of friction) may control stick-slip, as suggested, for example, by Tolstoi, Oden and Martins and Brune and co-workers. Observations of particle trajectories indicate that stick-slip shear motion is associated with various degrees of fault separation. For an asymmetric model, the motion is consistent with slipping motion of the type suggested by Schallamach and Price. For a symmetric model, the motion is similar to that suggested by Comninou and Dundurs. If interface waves of this type, involving separation during slip, occur in earthquakes, they may be a solution to the heat flow paradox, since a major part of the slip occurs during separation and during low normal stress. Thus frictional heat generation is reduced. Normal interface vibrations during stick-slip may explain the high corner frequency of P wave spectra and the generally high levels of P wave spectra beyond the corner frequency. Schallamach-Comninou type waves are consistent with the partial stress drop-abrupt locking-self healing models of Brune and Heaton.
Heat flow diagnostics for helicon plasmasa)
Berisford, Daniel F.; Bengtson, Roger D.; Raja, Laxminarayan L.; Cassady, Leonard D.; Chancery, William J.
2008-10-01
We present experimental studies of power balance in an argon helicon discharge. An infrared camera measures the heating of the dielectric tube containing a helicon discharge based on measurement of temperature profiles of the tube surface before and after a rf pulse. Using this diagnostic, we have measured surface heating trends at a variety of operating conditions on two helicon systems: the 10kW VASIMR VX-50 experiment and the University of Texas at Austin 1kW helicon experiment. Power losses downstream from the antenna are measured using thermocouples and probes. The heating of the dielectric tube increases with decreasing magnetic fields, higher gas flow rates, and higher molecular mass of the gas. These preliminary results suggest that cross-field particle diffusion contributes a significant proportion of the energy flux to the wall.
Visualization of working fluid flow in gravity assisted heat pipe
Directory of Open Access Journals (Sweden)
Nemec Patrik
2015-01-01
Full Text Available Heat pipe is device working with phase changes of working fluid inside hermetically closed pipe at specific pressure. The phase changes of working fluid from fluid to vapor and vice versa help heat pipe to transport high heat flux. The article deal about construction and processes casing in heat pipe during operation. Experiment visualization of working fluid flow is performed with glass heat pipe filed with ethanol. The visualization of working fluid flow explains the phenomena as working fluid boiling, nucleation of bubbles, vapor flow, vapor condensation on the wall, vapor and condensate flow interaction, flow down condensate film thickness on the wall, occurred during the heat pipe operation.
Visualization of working fluid flow in gravity assisted heat pipe
Nemec, Patrik; Malcho, Milan
2015-05-01
Heat pipe is device working with phase changes of working fluid inside hermetically closed pipe at specific pressure. The phase changes of working fluid from fluid to vapor and vice versa help heat pipe to transport high heat flux. The article deal about construction and processes casing in heat pipe during operation. Experiment visualization of working fluid flow is performed with glass heat pipe filed with ethanol. The visualization of working fluid flow explains the phenomena as working fluid boiling, nucleation of bubbles, vapor flow, vapor condensation on the wall, vapor and condensate flow interaction, flow down condensate film thickness on the wall, occurred during the heat pipe operation.
Flow characteristics and heat transfer in wavy walled channels
Mills, Zachary; Shah, Tapan; Monts, Vontravis; Warey, Alok; Balestrino, Sandro; Alexeev, Alexander
2013-11-01
Using lattice Boltzmann simulations, we investigated the effects of wavy channel geometry on the flow and heat transfer within a parallel plate heat exchanger. We observed three distinct flow regimes that include steady flow with and without recirculation and unsteady time-periodic flow. We determined the critical Reynolds numbers at which the flow transitions between different flow regimes. To validate our computational results, we compared the simulated flow structures with the structures observed in a flowing soap film. Furthermore, we examine the effects of the wavy channel geometry on the heat transfer. We find that the unsteady flow regime drastically enhances the rate of heat transfer and show that heat exchangers with wavy walls outperform currently used heat exchangers with similar volume and power characteristics. Results from our study point to a simple and efficient method for increasing performance in compact heat exchangers.
Study on heat transfer for falling liquid film flow with consideration of interfacial evaporation
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The interfacial evaporative heat transfer was included in the semi-empirical study of the heat transfer for the falling liquid film flow. The investigations showed that, the inclusion of the interfacial evaporative heat transfer in the turbulent model would lower the predicted convective heat transfer coefficient. Predictions of the new model resulted in a prominent deviation from that predictions of the normal model in the case of large mass flow rate and low wall heat flux. This deviation will be decreased with increasing wall heat flux, such that it will be asymptotic zero at very high wall heat flux. Predictions of the new model agreed well with the current experimental measurements. This study has verified that the Reynolds number is not the sole crucial parameter for heat transfer of falling liquid film flow, and wall heat flux will be another important independent parameter. This result is consistent with our previous studies.
Gai, S. L.; Cain, T.; Joe, W. S.; Sandeman, R. J.; Miller, C. G.
1988-01-01
Heat transfer rate measurements have been obtained at 0, 5, 15, and 21 deg angles-of-attack for a straight biconic scale model of an aeroassisted orbital vehicle proposed for planetary probe missions. Heat-transfer distributions were measured using palladium thin-film resistance gauges deposited on a glass-ceramic substrate. The windward heat transfer correlations were based on equilibrium flow in the shock layer of the model, although the flow may depart from equilibrium in the flow-field.
Fractal density and singularity analysis of heat flow over ocean ridges
Qiuming, Cheng
2016-01-01
Peak heat flow occurs at mid-ocean ridges and decreases with the age of the oceanic lithosphere. Several plate models, including the Parsons and Sclater (PSM) model, Global Depth and Heat (GDH1) model and Constant Heat flow Applied on the Bottom Lithospheric Isotherm (CHABLIS) model, have been used to predict heat flow in the ocean lithosphere. The discrepancy between the predicted and measured heat flow in the younger lithosphere (i.e. younger than 55 Myr) influenced by local hydrothermal circulation has been used to estimate hydrothermal heat flux and investigate hydrothermal processes. We can modify the cooling models by substituting the ordinary mass density of lithosphere by fractal density with singularity. This new model provides a modified solution to fit the observed heat flow data used in other models in the literature throughout the age range. This model significantly improves the results for prediction of heat flow that were obtained using the PSM, GDH1 and CHABLIS models. Furthermore, the heat flow model does not exhibit special characteristics around any particular age of lithosphere. This raises a fundamental question about the existence of a “sealing” age and accordingly the hydrothermal flux estimation based on the cooling models.
Fractal density and singularity analysis of heat flow over ocean ridges.
Qiuming, Cheng
2016-01-13
Peak heat flow occurs at mid-ocean ridges and decreases with the age of the oceanic lithosphere. Several plate models, including the Parsons and Sclater (PSM) model, Global Depth and Heat (GDH1) model and Constant Heat flow Applied on the Bottom Lithospheric Isotherm (CHABLIS) model, have been used to predict heat flow in the ocean lithosphere. The discrepancy between the predicted and measured heat flow in the younger lithosphere (i.e. younger than 55 Myr) influenced by local hydrothermal circulation has been used to estimate hydrothermal heat flux and investigate hydrothermal processes. We can modify the cooling models by substituting the ordinary mass density of lithosphere by fractal density with singularity. This new model provides a modified solution to fit the observed heat flow data used in other models in the literature throughout the age range. This model significantly improves the results for prediction of heat flow that were obtained using the PSM, GDH1 and CHABLIS models. Furthermore, the heat flow model does not exhibit special characteristics around any particular age of lithosphere. This raises a fundamental question about the existence of a "sealing" age and accordingly the hydrothermal flux estimation based on the cooling models.
Heating Cooling Flows with Weak Shock Waves
Mathews, W G; Brighenti, F
2006-01-01
The discovery of extended, approximately spherical weak shock waves in the hot intercluster gas in Perseus and Virgo has precipitated the notion that these waves may be the primary heating process that explains why so little gas cools to low temperatures. This type of heating has received additional support from recent gasdynamical models. We show here that outward propagating, dissipating waves deposit most of their energy near the center of the cluster atmosphere. Consequently, if the gas is heated by (intermittent) weak shocks for several Gyrs, the gas within 30-50 kpc is heated to temperatures that far exceed observed values. This heating can be avoided if dissipating shocks are sufficiently infrequent or weak so as not to be the primary source of global heating. Local PV and viscous heating associated with newly formed X-ray cavities are likely to be small, which is consistent with the low gas temperatures generally observed near the centers of groups and clusters where the cavities are located.
Directory of Open Access Journals (Sweden)
Américo Scotti
2012-06-01
Full Text Available O objetivo do presente trabalho é propor um modelo global para descrever o fluxo de calor em soldagem a arco, visando o entendimento dos fenômenos relacionados com o fluxo de calor. A tentativa é suprir uma lacuna do conhecimento gerado entre a aplicação de modelos analíticos simplificados (não totalmente realistas e de modelos numéricos (que mascaram a visão física dos fenômenos. Inicia-se propondo uma descrição mais física para a razão da queda de tensão num arco, baseada na geração e perda de calor para se manter o equilíbrio da desionização e reionização, em contraste com a abordagem em que o arco é comparável a um resistor elétrico. Em seguida, se propõe um modelo descritivo da subsistência térmica de um arco, para qualificar as formas de transferência de calor do arco para a chapa. Um segundo modelo descritivo é então proposto para explicar como o calor entra, difunde e sai da chapa durante a soldagem. Finalmente, é discutido como a aplicação destes dois modelos de forma global permite entender que nem todo o fluxo de calor do arco para a chapa vai afetar a velocidade de resfriamento nas regiões do material aquecidas. Culmina-se com a proposta do emprego do termo Calor Imposto Efetivo como meio de evidenciar o parâmetro de calor de importância a ser determinado em soldagem.The objective of the present paper is to propose a global model for describing heat flow in arc welding, aiming the understanding of the phenomena involved. The attempt is to fill out a gap of knowledge which has been generated between the application of simplified analytical models (not totally realistic and numerical models (that disguises the physics of the phenomena. Initially, a physic-oriented description of the reasons for welding arc voltage drop is presented. This description is based on the heat generation and its losses to maintain the balance between deionization and reionization, in contrast to the approach that the arc
Geothermal heat exchanger with coaxial flow of fluids
Directory of Open Access Journals (Sweden)
Pejić Dragan M.
2005-01-01
Full Text Available The paper deals with a heat exchanger with coaxial flow. Two coaxial pipes of the secondary part were placed directly into a geothermal boring in such a way that geothermal water flows around the outer pipe. Starting from the energy balance of the exchanger formed in this way and the assumption of a study-state operating regime, a mathematical model was formulated. On the basis of the model, the secondary circle output temperature was determined as a function of the exchanger geometry, the coefficient of heat passing through the heat exchange areas, the average mass isobaric specific heats of fluid and mass flows. The input temperature of the exchanger secondary circle and the temperature of the geothermal water at the exit of the boring were taken as known values. Also, an analysis of changes in certain factors influencing the secondary water temperature was carried out. The parameters (flow temperature of the deep boring B-4 in Sijarinska Spa, Serbia were used. The theoretical results obtained indicate the great potential of this boring and the possible application of such an exchanger.
Homotopy perturbation method for heat transfer flow of a third grade fluid between parallel plates
Energy Technology Data Exchange (ETDEWEB)
Siddiqui, A.M. [Pennsylvania State University, York Campus, York, PA 17403 (United States); Zeb, A. [COMSATS Institute of Information Technology, 30 H-8/1, Islamabad (Pakistan)], E-mail: amtaz56@yahoo.co.uk; Ghori, Q.K. [COMSATS Institute of Information Technology, 30 H-8/1, Islamabad (Pakistan); Benharbit, A.M. [Pennsylvania State University, York Campus, York, PA 17403 (United States)
2008-04-15
The present paper studies the heat transfer flow of a third grade fluid between two heated parallel plates for the constant viscosity model. Three flow problems, namely plane Couette flow, plane Poiseuille flow and plane Couette-Poiseuille flow have been considered. In each case the non-linear momentum equation and the energy equation have been solved using the homotopy perturbation method. Explicit analytical expressions for the velocity field and the temperature distribution have been derived.
OPTIMISATION OF MANTLE TANKS FOR LOW FLOW SOLAR HEATING SYSTEMS
DEFF Research Database (Denmark)
Shah, Louise Jivan; Furbo, Simon
1996-01-01
A model, describing the heat transfer coefficients in the mantle of a mantle tank has been developed. The model is validated by means of measurements with varying operational conditions for different designed mantle tanks. The model has been implemented in an existing detailed mathematical...... programme that simulates the thermal behaviour of low flow SDHW systems. The yearly thermal performance of low flow SDHW systems with different designed mantle tanks has been calculated. The influence of the mantle tank design on the thermal performance is investigated by means of the calculations...... with the programme and by means of tests of three SDHW systems with different designed mantle tanks. Based on the investigations design rules for mantle tanks are proposed. The model, describing the heat transfer coefficients in the mantle is approximate. In addition, the measurements have revealed...
Numerical simulations of heat transfer in plane channel flow
Gharbi, Najla El; Benzaoui, Ahmed
2010-01-01
Reynolds-averaged Navier-Stokes (RANS) turbulence models (such as k-{\\epsilon} models) are still widely used for engineering applications because of their relatively simplicity and robustness. In fully developed plane channel flow (i.e. the flow between two infinitely large plates), even if available models and near-wall treatments provide adequate mean flow velocities, they fail to predict suitable turbulent kinetic energy "TKE" profiles near walls. TKE is involved in determination of eddy viscosity/diffusivity and could therefore provide inaccurate concentrations and temperatures. In order to improve TKE a User Define Function "UDF" based on an analytical profile for TKE was developed and implemented in Fluent. Mean streamwise velocity and turbulent kinetic energy "TKE" profiles were compared to DNS data for friction Reynolds number $Re_{\\tau}$ = 150. Simulation results for TKE show accurate profiles. Simulation results for horizontal heated channel flows obtained with Fluent are presented. Numerical result...
MODEL OF LASER-TIG HYBRID WELDING HEAT SOURCE
Institute of Scientific and Technical Information of China (English)
Chen Yanbin; Li Liqun; Feng Xiaosong; Fang Junfei
2004-01-01
The welding mechanism of laser-TIG hybrid welding process is analyzed. With the variation of arc current, the welding process is divided into two patterns: deep-penetration welding and heat conductive welding. The heat flow model of hybrid welding is presented. As to deep-penetration welding, the heat source includes a surface heat flux and a volume heat flux. The heat source of heat conductive welding is composed of two Gaussian distribute surface heat sources. With this heat source model, a temperature field is calculated. The finite element code MARC is employed for this purpose. The calculation results show a good agreement with the experimental data.
Indian Academy of Sciences (India)
Om Prakash; Devendra Kumar; Y K Dwivedi
2012-12-01
The paper investigates the effects of heat transfer in MHD flow of viscoelastic stratified fluid in porous medium on a parallel plate channel inclined at an angle . A laminar convection flow for incompressible conducting fluid is considered. It is assumed that the plates are kept at different temperatures which decay with time. The partial differential equations governing the flow are solved by perturbation technique. Expressions for the velocity of fluid and particle phases, temperature field, Nusselt number, skin friction and flow flux are obtained within the channel. The effects of various parameters like stratification factor, magnetic field parameter, Prandtl number on temperature field, heat transfer, skin friction, flow flux, velocity for both the fluid and particle phases are displayed through graphs and discussed numerically.
Energy Technology Data Exchange (ETDEWEB)
Flyckt, V M M; Raaymakers, B W; Lagendijk, J J W [Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX Utrecht (Netherlands)
2006-10-07
Prediction of the temperature distribution in the eye depends on how the impact of the blood flow is taken into account. Three methods will be compared: a simplified eye anatomy that applies a single heat transfer coefficient to describe all heat transport mechanisms between the sclera and the body core, a detailed eye anatomy in which the blood flow is accounted for either by the bioheat approach, or by including the discrete vasculature in the eye and the orbit. The comparison is done both for rabbit and human anatomies, normo-thermally and when exposed to homogeneous power densities. The first simplified model predicts much higher temperatures than the latter two. It was shown that the eye is very hard to heat when taking physiological perfusion correctly into account. It was concluded that the heat transfer coefficient describing the heat transport from the sclera to the body core reported in the literature for the first simplified model is too low. The bioheat approach is appropriate for a first-order approximation of the temperature distribution in the eye when exposed to a homogeneous power density, but the discrete vasculature down to 0.2 mm in diameter needs to be taken into account when the heterogeneity of the temperature distribution at a mm scale is of interest.
Flyckt, V. M. M.; Raaymakers, B. W.; Lagendijk, J. J. W.
2006-10-01
Prediction of the temperature distribution in the eye depends on how the impact of the blood flow is taken into account. Three methods will be compared: a simplified eye anatomy that applies a single heat transfer coefficient to describe all heat transport mechanisms between the sclera and the body core, a detailed eye anatomy in which the blood flow is accounted for either by the bioheat approach, or by including the discrete vasculature in the eye and the orbit. The comparison is done both for rabbit and human anatomies, normo-thermally and when exposed to homogeneous power densities. The first simplified model predicts much higher temperatures than the latter two. It was shown that the eye is very hard to heat when taking physiological perfusion correctly into account. It was concluded that the heat transfer coefficient describing the heat transport from the sclera to the body core reported in the literature for the first simplified model is too low. The bioheat approach is appropriate for a first-order approximation of the temperature distribution in the eye when exposed to a homogeneous power density, but the discrete vasculature down to 0.2 mm in diameter needs to be taken into account when the heterogeneity of the temperature distribution at a mm scale is of interest.
Mathematical Modeling of Spiral Heat Exchanger
Directory of Open Access Journals (Sweden)
Probal Guha , Vaishnavi Unde
2014-04-01
Full Text Available Compact Heat Exchangers (CHEs are increasingly being used on small and medium scale industries. Due to their compact size and efficient design, they facilitate more efficient heat transfer. Better heat transfer would imply lesser fuel consumption for the operations of the plant, giving improvement to overall efficiency. This reduction in consumption of fuel is a step towards sustainable development. This report exclusively deals with the study the spiral heat exchanger.The design considerations for spiral heat exchanger is that the flow within the spiral has been assumed as flow through a duct and by using Shah London empirical equation for Nusselt number design parameters are further optimized.This is accompanied by a detailed energy balance to generate a concise mathematical model
Predicting Turbulent Convective Heat Transfer in Fully Developed Duct Flows
Rokni, Masoud; Gatski, Thomas B.
2001-01-01
The performance of an explicit algebraic stress model (EASM) is assessed in predicting the turbulent flow and forced heat transfer in both straight and wavy ducts, with rectangular, trapezoidal and triangular cross-sections, under fully developed conditions. A comparison of secondary flow patterns. including velocity vectors and velocity and temperature contours, are shown in order to study the effect of waviness on flow dynamics, and comparisons between the hydraulic parameters. Fanning friction factor and Nusselt number, are also presented. In all cases. isothermal conditions are imposed on the duct walls, and the turbulent heat fluxes are modeled using gradient-diffusion type models. The formulation is valid for Reynolds numbers up to 10(exp 5) and this minimizes the need for wall functions that have been used with mixed success in previous studies of complex duct flows. In addition, the present formulation imposes minimal demand on the number of grid points without any convergence or stability problems. Criteria in terms of heat transfer and friction factor needed to choose the optimal wavy duct cross-section for industrial applications among the ones considered are discussed.
On Inverting the Heat Flow with Engineering Materials
Zhou, Li
2016-02-01
Transformation thermodynamics enriches our understanding of heat flow and makes it possible to manipulate the heat flow at will, like shielding, concentrating and inverting. The inverting of heat flow is the extreme one, which has not been studied specifically yet. In this study we firstly inverted the heat flow by transformation thermodynamics and provided the formula for the transformed thermal conductivity. Finite element simulations were conducted to realize the steady and non-steady inverting of heat flow, based on the eccentric-semi-ring structures with natural materials. To do the inverting of heat flow, a simple "L"-shape conductive structure was proposed and verified with an infrared camera. It is concluded that inverting heat flow can be done by both complex engineering materials and some simple structures.
Flow Regimes of Mesoscale Circulations Forced by Inhomogeneous Surface Heating
Hossain, M Alamgir
2016-01-01
Urbanization is one of the extreme process that increases uncertainty in future climate projections. Flow regimes of mesoscale circulations associated with surface heating due to urbanization have been investigated using a wavelet based computational fluid dynamics~(CFD) model. The results of our numerical model have been validated against that of a laboratory model, as well as reference numerical simulations. Characteristics of urban induced circulations have been studied for surface heat flux perturbation ($H_0$) between $28.93$Wm$^{-2}$ and $925.92$Wm$^{-2}$, and the results have been analyzed against available boundary layer measurements under similar physical conditions. Our primary study shows that urban/rural heat flux anomalies introduce strong oscillations in the convective boundary layer (CBL), and transfers a fraction of the turbulent kinetic energy vertically through internal waves. Such results complement previous investigators' hypothesis that temporal oscillations in urban-induced mesoscale cir...
Pereira, Emmanuel; Mendonça, Mateus S.; Lemos, Humberto C. F.
2015-09-01
We investigate a chain of oscillators with anharmonic on-site potentials, with long range interparticle interactions, and coupled both to external and internal stochastic thermal reservoirs of Ornstein-Uhlenbeck type. We develop an integral representation, a` la Feynman-Kac, for the correlations and the heat current. We assume the approximation of discrete times in the integral formalism (together with a simplification in a subdominant part of the harmonic interaction) and develop a suitable polymer expansion for the model. In the regime of strong anharmonicity, strong harmonic pinning, and for the interparticle interaction with integrable polynomial decay, we prove the convergence of the polymer expansion uniformly in volume (number of sites and time). We also show that the two-point correlation decays in space such as the interparticle interaction. The existence of a convergent polymer expansion is of practical interest: it establishes a rigorous support for a perturbative analysis of the heat flow problem and for the computation of the thermal conductivity in related anharmonic crystals, including those with inhomogeneous potentials and long range interparticle interactions. To show the usefulness and trustworthiness of our approach, we compute the thermal conductivity of a specific anharmonic chain, and make a comparison with related numerical results presented in the literature.
Visualization of working fluid flow in gravity assisted heat pipe
Nemec Patrik; Malcho Milan
2015-01-01
Heat pipe is device working with phase changes of working fluid inside hermetically closed pipe at specific pressure. The phase changes of working fluid from fluid to vapor and vice versa help heat pipe to transport high heat flux. The article deal about construction and processes casing in heat pipe during operation. Experiment visualization of working fluid flow is performed with glass heat pipe filed with ethanol. The visualization of working fluid flow explains the phenomena as working fl...
Vapor Flow Patterns During a Start-Up Transient in Heat Pipes
Issacci, F.; Ghoniem, N, M.; Catton, I.
1996-01-01
The vapor flow patterns in heat pipes are examined during the start-up transient phase. The vapor core is modelled as a channel flow using a two dimensional compressible flow model. A nonlinear filtering technique is used as a post process to eliminate the non-physical oscillations of the flow variables. For high-input heat flux, multiple shock reflections are observed in the evaporation region. The reflections cause a reverse flow in the evaporation and circulations in the adiabatic region. Furthermore, each shock reflection causes a significant increase in the local pressure and a large pressure drop along the heat pipe.
A review of the heat flow data of NE Morocco
Chiozzi, Paolo; Barkaoui, Alae-Eddine; Rimi, Abdelkrim; Verdoya, Massimo; Zarhloule, Yassine
2016-04-01
The Atlas chain is characterised by a SW-NE trending volcanic belt roughly extending from the Atlantic to the Mediterranean Sea and showing activity that spans in age mainly from Middle Miocene to Quaternary (14.6-0.3 Ma). The geochemical features of volcanism are mostly intraplate and alkaline with the exception of the northeastern termination of the belt where calc-alkaline series crop out. Lithospheric thermal and density models so far proposed, constrained by heat flow, gravity anomalies, geoid, and topography data, show that the Atlas chain is not supported isostatically by a thickened crust and a thin, hot and low-density lithosphere explains the high topography. One of the possible explanations for lithospheric mantle thinning, possibly in relation with the observed alkaline volcanism, is thermal erosion produced by either small-scale convection or activation of a small mantle plume, forming part of a hot and deep mantle reservoir system extending from the Canary Islands. This paper focuses on the several geothermal data available in the northeastern sector of the volcanic belt. The occurrence of an extensive, often artesian, carbonatic reservoir hosting moderately hot groundwater might boost the temperature gradient in the overlying impermeable cover, and consequently mask the deep thermal regime. We therefore revised the available dataset and investigated the contribution of advection. Temperature data available from water and oil wells were reprocessed and analysed in combination with thermal conductivity measurements on a wide set of lithotypes. Data were filtered according to rigid selection criteria, and, in the deeper boreholes, the heat flow was inferred by taking into account the porosity variation with depth and the temperature effect on the matrix and pore-filling fluid conductivity. Moreover, the possible effect of advection was evaluated with simple analytical models which envisage the carbonatic layers as confined aquifers heated by the
Multiple nonequilibrium steady states for one-dimensional heat flow.
Zhang, F; Isbister, D J; Evans, D J
2001-08-01
A nonequilibrium molecular dynamics model of heat flow in one-dimensional lattices is shown to have multiple steady states for any fixed heat field strength f(e) ranging from zero to a certain positive value. We demonstrate that, depending on the initial conditions, there are at least two possibilities for the system's evolution: (i) formation of a stable traveling wave (soliton), and (ii) chaotic motion throughout the entire simulation. The percentage of the soliton-generating trajectories is zero for small field strength f(e), but increases sharply to unity over a critical region of the parameter f(e).
Directory of Open Access Journals (Sweden)
. Dr. S. Rawat
2014-01-01
Full Text Available A mathematical model is presented for the steady, two-dimensional magneto-convection heat transfer of a two-phase, electrically-conducting, particle-suspension in a channel containing a non-Darcian porous medium intercalated between two parallel plates, in the presence of a transverse magnetic field. The channel walls are assumed to be isothermal but at different temperatures. The governing equations for the one-dimensional steady flow are formulated following Marble (1970 and extended to include the influence of Darcian porous drag, Forcheimmer quadratic drag, buoyancy effects, Lorentz body force (hydromagnetic retardation force and particle-phase viscous stresses. Special boundary conditions for the particle-phase wall conditions are implemented. The governing coupled, non-linear differential equations are reduced from an (x,y coordinate system to a one-dimensional (y coordinate system. A series of transformations is then employed to non-dimensionalize the model in terms of a single independent variable, , yielding a quartet of coupled ordinary differential equations which are solved numerically using the finite element method, under appropriate transformed boundary conditions. The influence of for example Grashof free convection number (Gr, Hartmann hydromagnetic number (Ha, inverse Stokes number (Skm, Darcy number (Da, Forcheimmer number (Fs,particle loading parameter (PL, buoyancy parameter (B on the fluid-phase velocity and particle-phase velocity are presented graphically. A number of special cases of the transformed model are also studied. The mathematical model finds applications in solar collector devices, electronic fabrication, jet nozzle flows, industrial materials processing transport phenomena, MHD energy generator systems etc.
A laser-induced heat flux technique for convective heat transfer measurements in high speed flows
Porro, A. R.; Keith, T. G., Jr.; Hingst, W. R.
1991-01-01
A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high-speed flowfields.
Flow Boiling Heat Transfer in Two-Phase Micro Channel Heat Sink at Low Water Mass Flux
Kuznetsov, Vladimir V.; Shamirzaev, Alisher S.
2009-08-01
Boiling heat transfer at water flow with low mass flux in heat sink which contained rectangular microchannels was studied. The stainless steel heat sink contained ten parallel microchannels with a size of 640 × 2050 μm in cross-section with typical wall roughness of 10-15 μm. The local flow boiling heat transfer coefficients were measured at mass velocity of 17 and 51 kg/m2s, heat flux on 30 to 150 kW/m2 and vapor quality of up to 0.8 at pressure in the channels closed to atmospheric one. It was observed that Kandlikar nucleate boiling correlation is in good agreement with the experimental data at mass flow velocity of 85 kg/m2s. At smaller mass flux the Kandlikar model and Zhang, Hibiki and Mishima model demonstrate incorrect trend of heat transfer coefficients variation with vapor quality.
Heat sink analytical modelling
Guitart Corominas, Joaquim
2010-01-01
Electronics has leaded most technological advances of the past 60 years. There are technologies with domains particularly developed for electronics such as material science, electromagnetism, system dynamics and also heat transfer. The relation to heat transfer is because the heat generation of electronics devices. Commonly, these devices need additional cooling in order to avoid extreme temperatures inside it. Heat sinks allow this supplementary cooling, so they are omnipresent i...
DEFF Research Database (Denmark)
Knudsen, Torben
2011-01-01
The purpose with this deliverable 2.5 is to use fresh experimental data for validation and selection of a flow model to be used for control design in WP3-4. Initially the idea was to investigate the models developed in WP2. However, in the project it was agreed to include and focus on a additive...... model turns out not to be useful for prediction of the flow. Moreover, standard Box Jenkins model structures and multiple output auto regressive models proves to be superior as they can give useful predictions of the flow....
Titarenko, S.; McCaig, A. M.
2014-12-01
A perennial problem in near-ridge hydrothermal circulation is that the only directly measurable data to test models is often vent fluid temperature. Surface heat flow measurements may be available but without the underlying thermal structure it is not known if they are transient and affected by local hydrothermal flow, or conductive. The Atlantis Massif oceanic core complex at 30 °N on the mid-Atlantic Ridge, offers a unique opportunity to better constrain hydrothermal circulation models. The temperature profile in gabbroic rocks of IODP Hole 1309D was measured in IODPExpedition 340T, and found to be near-conductive, but with a slight inflexion at ~750 mbsf indicating downward advection of fluid above that level. The lack of deep convection is especially remarkable given that the long-lived Lost City Hydrothermal Field (LCHF) is located only 5km to the south. We have modelled hydrothermal circulation in the Massif using Comsol Multiphysics, comparing 2-D and 3-D topographic models and using temperature-dependent conductivity to give the best estimate of heatflow into the Massif. We can constrain maximum permeability in gabbro below 750 mbsf to 5e-17 m2. The thermal gradient in the upper part of the borehole can be matched with a permeability of 3e-14 m2 in a 750 m thick layer parallel to the surface of the massif, with upflow occurring in areas of high topography and downflow at the location of the borehole. However in 3-D the precise flow pattern is quite model dependent, and the thermal structure can be matched either by downflow centred on the borehole at lower permeability or centred a few hundred metres from the borehole at higher permeability. The borehole gradient is compatible with the longevity (>120 kyr) and outflow temperature (40-90 °C) of the LCHF either with a deep more permeable (1e-14 m2 to 1e-15 m2) domain beneath the vent site in 2-D or a permeable fault slot 500 to 1000m wide and parallel to the transform fault in 3-D. In both cases topography
Heat transfer and fluid flow in minichannels and microchannels
Kandlikar, Satish; Li, Dongqing; Colin, Stephane; King, Michael R
2013-01-01
Heat exchangers with minichannel and microchannel flow passages are becoming increasingly popular due to their ability to remove large heat fluxes under single-phase and two-phase applications. Heat Transfer and Fluid Flow in Minichannels and Microchannels methodically covers gas, liquid, and electrokinetic flows, as well as flow boiling and condensation, in minichannel and microchannel applications. Examining biomedical applications as well, the book is an ideal reference for anyone involved in the design processes of microchannel flow passages in a heat exchanger. Each chapter is accompan
Influence of Ohmic Heating on Advection-Dominated Accretion Flows
Bisnovatyi-Kogan, G S
1997-01-01
Advection-dominated, high-temperature, quasi-spherical accretion flow onto a compact object of mass M, recently considered by a number of authors, assume that the dissipation of turbulent energy of the flow heats the ions and that a constant fraction f of the dissipated energy is advected inward. It is suggested that the efficiency of conversion of accretion energy to radiation can be very much smaller than unity. However, it is likely that the flows have an equipartition magnetic field with the result that dissipation of magnetic energy at a rate comparable to that for the turbulence must occur by Ohmic heating. We argue that this heating occurs as a result of plasma instabilities and that the relevant instabilities are current driven in response to the strong electric fields parallel to the magnetic field. We argue further that these instabilities heat predominantly the electrons. We analyze a model for the radial dependence of the ion and electron temperatures of a general, possibly quasi-spherical accreti...
Melt Flow and Heat Transfer in Laser Drilling
Yang, Youqing; Zhang, Yuwen
2016-01-01
During the laser drilling process the recoil pressure drives melt flow and affects the heat transfer and material removal rate. To get a more realistic picture of the melt flow, a series of differential equations are formulated here that govern the process from pre-heating to melting and evaporation. In particular, the Navier-Stokes equation governing the melt flow is solved with the use of the boundary layer theory and integral methods. Heat conduction in solid is investigated by using the classical method with the corrections that reflect the change in boundary condition from the constant heat flux to Stefan condition. The dependence of saturation temperature on the vapor pressure is taken into account by using the Clausius-Clapeyron equation. Both constantly rising radial velocity profiles and rising-fall velocity profiles are considered. The proposed approach is compared with existing ones. In spite of the assumed varying velocity profiles, the proposed model predicts that the drilling hole profiles are v...
Evaluation of heat and water flow in porosity permeable horizons
Pasquale, Vincenzo; Verdoya, Massimo; Chiozzi, Paolo
2010-05-01
Several strategies have been developed to explore the circulation of geofluids, which can yield heat transport over large spatial scales. Groundwater flow from recharge areas, where precipitation seeps downwards beneath the ground surface and reaches the saturated zone, to discharge areas, where subsurface water is discharged to streams, lakes, ponds or swamps, forms an additional mechanism of heat transfer to pure conduction, which is generally assumed for the underground thermal regime. In this paper we discuss and apply two different analytical models of heat and water flow, both valid for steady-state thermal conditions and for uniform, isotropic, homogeneous, and saturated porous media. By combining conductive and groundwater advective heat transfer, a first model assumes heat and water flow in vertical direction and neglects thermal gradient along the horizontal. The thermal field is influenced only by the flow of water parallel to the thermal gradient, whereas perpendicular water flow if any has no effect. Because most layers are sloping and because surface topographic relief usually exists across the aquifer, usually isotherms are not horizontal. Hence, we applied a second model for heat and water flow, neither purely horizontal nor purely vertical. In the governing equation of heat conduction-advection we take account of the horizontal flow of heat and water. The flow rate is assumed to be constant and sufficient small that thermal equilibrium is maintained between the water and the rock matrix. Examples of application are given for a set of boreholes drilled for geothermal exploration. Hydrothermal parameters (vertical and horizontal components of the Darcy velocity and the Péclet number) are determined by matching temperature and thermal gradient versus depth data with the two models. Thermal information is completed by a set of thermal conductivity measurements carried out on core samples recovered during drillings. The analysed underground
Convective heat transfer measurement involving flow past stationary circular disks
Energy Technology Data Exchange (ETDEWEB)
Wedekind, G.L. (Oakland Univ., Rochester, MI (United States))
1989-11-01
Considerable empirical data exist in the literature for forced convection heat transfer involving external flow over a variety of geometries, and for various ranges of Reynolds number. This author is not aware of any published empirical data for forced convection heat transfer involving flow past a simple stationary circular disk, whose axis is perpendicular to the flow. Such is the purpose of this paper.
Kavi, K. M.
1984-01-01
There have been a number of simulation packages developed for the purpose of designing, testing and validating computer systems, digital systems and software systems. Complex analytical tools based on Markov and semi-Markov processes have been designed to estimate the reliability and performance of simulated systems. Petri nets have received wide acceptance for modeling complex and highly parallel computers. In this research data flow models for computer systems are investigated. Data flow models can be used to simulate both software and hardware in a uniform manner. Data flow simulation techniques provide the computer systems designer with a CAD environment which enables highly parallel complex systems to be defined, evaluated at all levels and finally implemented in either hardware or software. Inherent in data flow concept is the hierarchical handling of complex systems. In this paper we will describe how data flow can be used to model computer system.
Cluster banding heat source model
Institute of Scientific and Technical Information of China (English)
Zhang Liguo; Ji Shude; Yang Jianguo; Fang Hongyuan; Li Yafan
2006-01-01
Concept of cluster banding heat source model is put forward for the problem of overmany increment steps in the process of numerical simulation of large welding structures, and expression of cluster banding heat source model is deduced based on energy conservation law.Because the expression of cluster banding heat source model deduced is suitable for random weld width, quantitative analysis of welding stress field for large welding structures which have regular welds can be made quickly.
Multidimensional numerical modeling of heat exchangers
Sha, W. T.; Yang, C. I.; Kao, T. T.; Cho, S. M.
A comprehensive, multidimensional, thermal-hydraulic model is developed for the analysis of shell-and-tube heat exchangers for liquid-metal services. For the shellside fluid, the conservation equations of mass, momentum, and energy for continuum fluids are modified using the concept of porosity, surface permeability and distributed resistance to account for the blockage effects due to the presence of heat-transfer tubes, flow baffles/shrouds, the support plates, etc. On the tubeside, the heat-transfer tubes are connected in parallel between the inlet and outlet plenums, and tubeside flow distribution is calculated based on the plenum-to-plenum pressure difference being equal for all tubes. It is assumed that the fluid remains single-phase on the shell side and may undergo phase-change on the tube side, thereby simulating the conditions of Liquid Metal Fast Breeder Reactor (LMFBR) intermediate heat exchangers (IHX) and steam generators (SG).
Makinde, O. D.; Chinyoka, T.
2010-12-01
This present study consists of a numerical investigation of transient heat transfer in channel flow of an electrically conducting variable viscosity Boussinesq fluid in the presence of a magnetic field and thermal radiation. The temperature dependent nature of viscosity is assumed to follow an exponentially model and the system exchanges heat with the ambient following Newton's law of cooling. The governing nonlinear equations of momentum and energy transport are solved numerically using a semi-implicit finite difference method. Solutions are presented in graphical form and given in terms of fluid velocity, fluid temperature, skin friction and heat transfer rate for various parametric values. Our results reveal that combined effect of thermal radiation, magnetic field, viscosity variation and convective cooling have significant impact in controlling the rate of heat transfer in the boundary layer region.
Inverted annular flow heat transfer in a natural circulation loop
Energy Technology Data Exchange (ETDEWEB)
Ozawa, M.; Umekawa, H.; Shiba, Y.; Yano, T. [Kansai Univ., Osaka (Japan)
1998-07-01
Gravity-feed reflooding experiment was conducted in a natural circulation loop of liquid nitrogen. The cooling curve of high temperature tube wall had a characteristic feature, i.e. initial rapid cooling with steam binding, relatively long-time plateau, gradual decrease with or without flow oscillation, and final drastic decrease during quenching process. Such phenomena had close relationship to the heated wall dynamics and heating power transient. To provide fundamental understanding on the present phenomena, the heat transfer data in inverted annular and dispersed flows were obtained under steady or oscillatory flow condition. The experimental data suggested that the heat transfer coefficient in the inverted annular or dispersed flow regimes is a slightly increasing function of heat flux but significantly depended on the tube diameter. The flow oscillation deteriorated heat transfer slightly in the inverted annular and dispersed flow regimes but significantly in the quenching process.
Modelling of Temperature Profiles and Transport Scaling in Auxiliary Heated Tokamaks
DEFF Research Database (Denmark)
Callen, J.D.; Christiansen, J.P.; Cordey, J.G.;
1987-01-01
The temperature profiles produced by various heating profiles are calculated from local heat transport models. The models take the heat flux to be the sum of heat diffusion and a non-diffusive heat flow, consistent with local measurements of heat transport. Two models are developed analytically i...
Multiphysics Numerical Modeling of a Fin and Tube Heat Exchanger
DEFF Research Database (Denmark)
Singh, Shobhana; Sørensen, Kim; Condra, Thomas Joseph
2015-01-01
). 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....
Coupled Seepage and Heat Transfer Intake Model
Institute of Scientific and Technical Information of China (English)
WU Junhua; YOU Shijun; ZHANG Huan; LI Haishan
2009-01-01
In the beach well intake system, heat is transferred from soil to fluid when seawater is filtered through the aquifer, providing higher temperature source water to the seawater source heat pump (SWHP) system in winter. A 3-D coupled seepage and heat transfer model for studying beach well intake system is established by adopting the computer code FLUENT. Numerical results of this model are compared with the experimental results under the same conditions. Based on the experiment-verified coupled model, numerical simulation of the supply water temperature is studied over a heating season. Results show that the minimum temperature of supply water is 275.2 K when this intake system continuously provides seawater with flow rate of 35 m3/h to SWHP. Results also indicate that the supply water temperature is higher than seawater, and that the minimum temperature of supply water lags behind seawater, ensuring effective and reliable operation of SWHP.
Slip Flow in Elliptic Microducts with Constant Heat Flux
Directory of Open Access Journals (Sweden)
Marco Spiga
2012-01-01
Full Text Available This paper outlines a numerical model for determining the dynamic and thermal performances of a rarefied fluid flowing in a microduct with elliptical cross-section. A slip flow is considered, in laminar steady state condition, in fully developed forced convection, with Knudsen number in the range 0.001−0.1, in H1 boundary conditions. The velocity and temperature distributions are determined in the elliptic cross-section, for different values of both aspect ratio γ and Knudsen number, resorting to the Comsol Multiphysics software, to solve the momentum and energy equations. The friction factors (or Poiseuille numbers and the convective heat transfer coefficients (or Nusselt numbers are calculated and presented in graphs and tables. The numerical solution is validated resorting to data available in literature for continuum flow in elliptic cross-sections (Kn = 0 and for slip flow in circular ducts (γ=1. A further benchmark is carried out for the velocity profile for slip flow in ellipticalcross-sections, thanks to a recent analytical solution obtained using elliptic cylinder coordinates and the separation of variables method. The Poiseuille and Nusselt numbers for elliptic cross-sections are discussed. The results may be used to predict pressure drop and heat transfer performance in metallic microducts with elliptic cross-section, produced by microfabrication for microelectromechanical systems (MEMS.
Numerical modeling of microwave heating
Directory of Open Access Journals (Sweden)
Shukla A.K.
2010-01-01
Full Text Available The present study compares the temperature distribution within cylindrical samples heated in microwave furnace with those achieved in radiatively-heated (conventional furnace. Using a two-dimensional finite difference approach the thermal profiles were simulated for cylinders of varying radii (0.65, 6.5, and 65 cm and physical properties. The influence of susceptor-assisted microwave heating was also modeled for the same. The simulation results reveal differences in the heating behavior of samples in microwaves. The efficacy of microwave heating depends on the sample size and its thermal conductivity.
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.
A New Determination of Io's Heat Flow Using Diurnal Heat Balance Constraints
Spencer, J. R.; Rathbun, J. A.; McEwen, A. S.; Pearl, J. C.; Bastos, A.; Andrade, J.; Correia, M.; Barros, S.
2002-01-01
We use heat balance arguments to obtain a new estimate of Io's heat flow that does not depend on assumptions about the temperatures of its thermal anomalies. Our estimated heat flow is somewhat less than 2.2 +/- 0.9 W/sq m. Additional information is contained in the original extended abstract.
NUMERICAL STUDY ON FLOW DISTRIBUTION IN PLATE-FIN HEAT EXCHANGERS
Institute of Scientific and Technical Information of China (English)
张哲; 厉彦忠
2003-01-01
Objective To investigate the flow distribution in plate-fin heat exchangers and optimize the design of header configuration for plate-fin heat exchangers. Methods A mathematical model of header was proposed. The effects of the header configuration on the flow distribution in plate-fin heat exchangers were investigated by CFD. The second header configuration with a two-stage-distributing structure was brought forward to improve the performance of flow distribution. Results It is found that the flow maldistribution is very serious in the direction of header length for the conventional header used in industry. The numerical predictions indicate that the improved header configurations can effectively improve the performance of flow distribution in plate-fin heat exchangers. Conclusion The numerical simulation confirms that CFD should be a suitable tool for predicting the flow distribution. The method has a wide variety of applications in the design of plate-fin heat exchangers.
Working fluid flow visualization in gravity heat pipe
Directory of Open Access Journals (Sweden)
Nemec Patrik
2016-01-01
Full Text Available Heat pipe is device working with phase changes of working fluid inside hermetically closed pipe at specific pressure. The phase changes of working fluid from fluid to vapour and vice versa help heat pipe to transport high heat flux. The article deal about gravity heat pipe construction and processes casing inside during heat pipe operation. Experiment working fluid flow visualization is performed with two glass heat pipes with different inner diameter (13 mm and 22 mm and filled with water. The working fluid flow visualization explains the phenomena as a working fluid boiling, nucleation of bubbles, and vapour condensation on the wall, vapour and condensate flow interaction, flow down condensate film thickness on the wall occurred during the heat pipe operation.
Working fluid flow visualization in gravity heat pipe
Nemec, Patrik; Malcho, Milan
2016-03-01
Heat pipe is device working with phase changes of working fluid inside hermetically closed pipe at specific pressure. The phase changes of working fluid from fluid to vapour and vice versa help heat pipe to transport high heat flux. The article deal about gravity heat pipe construction and processes casing inside during heat pipe operation. Experiment working fluid flow visualization is performed with two glass heat pipes with different inner diameter (13 mm and 22 mm) and filled with water. The working fluid flow visualization explains the phenomena as a working fluid boiling, nucleation of bubbles, and vapour condensation on the wall, vapour and condensate flow interaction, flow down condensate film thickness on the wall occurred during the heat pipe operation.
Anibas, Christian; Kukral, Janik; Touhidul Mustafa, Syed Md; Huysmans, Marijke
2017-04-01
Urban areas have a great potential for shallow geothermal systems. Their energy demand is high, but currently they have only a limited potential to cover their own energy demand. The transition towards a low-carbon energy regime offers alternative sources of energy an increasing potential. Urban areas however pose special challenges for the successful exploitation of shallow geothermal energy. High building densities limit the available space for drillings and underground investigations. Urban heat island effects and underground structures influence the thermal field, groundwater pollution and competing water uses limit the available subsurface. To tackle these challenges in the Brussels Capital Region, Belgium two projects 'BruGeo' and the recently finished 'Prospective Research of Brussels project 2015-PRFB-228' address the investigation in urban geothermal systems. They aim to identify the key factors of the underground with respect to Aquifer Thermal Energy Storage (ATES) installations like thermal properties, aquifer thicknesses, groundwater flow velocities and their heterogeneity. Combined numerical groundwater and heat transport models are applied for the assessment of both open and closed loop shallow geothermal systems. The Brussels Capital Region comprises of the Belgian Capital, the City of Brussels and 18 other municipalities covering 161 km2 with almost 1.2 million inhabitants. Beside the high population density the Brussels Capital Region has a pronounced topography and a relative complex geology. This is both a challenge and an opportunity for the exploitation of shallow geothermal energy. The most important shallow hydrogeological formation in the Brussels-Capital Region are the Brussels Sands with the Brussels Sands Aquifer. Scenarios where developed using criteria for the hydrogeological feasibility of ATES installations such as saturated aquifer thickness, groundwater flow velocity and the groundwater head below surface. The Brussels Sands
Numerical analysis of the steam flow field in shell and tube heat exchanger
Directory of Open Access Journals (Sweden)
Bartoszewicz Jarosław
2016-06-01
Full Text Available In the paper, the results of numerical simulations of the steam flow in a shell and tube heat exchanger are presented. The efficiency of different models of turbulence was tested. In numerical calculations the following turbulence models were used: k-ε, RNG k-ε, Wilcox k-ω, Chen-Kim k-ε, and Lam-Bremhorst k-ε. Numerical analysis of the steam flow was carried out assuming that the flow at the inlet section of the heat exchanger were divided into three parts. The angle of steam flow at inlet section was determined individually in order to obtain the best configuration of entry vanes and hence improve the heat exchanger construction. Results of numerical studies were verified experimentally for a real heat exchanger. The modification of the inlet flow direction according to theoretical considerations causes the increase of thermal power of a heat exchanger of about 14%.
Numerical analysis of the steam flow field in shell and tube heat exchanger
Bartoszewicz, Jarosław; Bogusławski, Leon
2016-06-01
In the paper, the results of numerical simulations of the steam flow in a shell and tube heat exchanger are presented. The efficiency of different models of turbulence was tested. In numerical calculations the following turbulence models were used: k-ɛ, RNG k-ɛ, Wilcox k-ω, Chen-Kim k-ɛ, and Lam-Bremhorst k-ɛ. Numerical analysis of the steam flow was carried out assuming that the flow at the inlet section of the heat exchanger were divided into three parts. The angle of steam flow at inlet section was determined individually in order to obtain the best configuration of entry vanes and hence improve the heat exchanger construction. Results of numerical studies were verified experimentally for a real heat exchanger. The modification of the inlet flow direction according to theoretical considerations causes the increase of thermal power of a heat exchanger of about 14%.
Estimation of respiratory heat flows in prediction of heat strain among Taiwanese steel workers
Chen, Wang-Yi; Juang, Yow-Jer; Hsieh, Jung-Yu; Tsai, Perng-Jy; Chen, Chen-Peng
2017-01-01
International Organization for Standardization 7933 standard provides evaluation of required sweat rate (RSR) and predicted heat strain (PHS). This study examined and validated the approximations in these models estimating respiratory heat flows (RHFs) via convection ( C res) and evaporation ( E res) for application to Taiwanese foundry workers. The influence of change in RHF approximation to the validity of heat strain prediction in these models was also evaluated. The metabolic energy consumption and physiological quantities of these workers performing at different workloads under elevated wet-bulb globe temperature (30.3 ± 2.5 °C) were measured on-site and used in the calculation of RHFs and indices of heat strain. As the results show, the RSR model overestimated the C res for Taiwanese workers by approximately 3 % and underestimated the E res by 8 %. The C res approximation in the PHS model closely predicted the convective RHF, while the E res approximation over-predicted by 11 %. Linear regressions provided better fit in C res approximation ( R 2 = 0.96) than in E res approximation ( R 2 ≤ 0.85) in both models. The predicted C res deviated increasingly from the observed value when the WBGT reached 35 °C. The deviations of RHFs observed for the workers from those predicted using the RSR or PHS models did not significantly alter the heat loss via the skin, as the RHFs were in general of a level less than 5 % of the metabolic heat consumption. Validation of these approximations considering thermo-physiological responses of local workers is necessary for application in scenarios of significant heat exposure.
Heat flow and thermal maturity in the Williston Basin
Energy Technology Data Exchange (ETDEWEB)
Gosnold, W.; LeFever, R. [North Dakota Univ., Grand Forks, ND (United States)
2009-07-01
This presentation discussed steady-state heat sources, transient disturbances, and the chemical kinetics and hydrocarbon potential of the Williston Basin. Global average heat flow has been estimated at 87 mW per m{sup 2}, while total surface heat flux is 44.2 x TW. Heat flow within ocean basins correlates with age, while heat flow on continents is related to radioactive heat production in the continental crust. The mantle flux of the continental crust averages 27 mW per m{sup 2}. Heat flow correlates with tectonic age. Transient signals in continental heat flow include groundwater flow, ground cover changes, and climatic changes. However, subsurface temperatures can be calculated when heat flow and thermal conductivity are known, using Fourier's law of heat conduction. Thermal maturity is a measure of the degree of kerogen metamorphism in a formation, and can provide an estimate of the maximum temperature that a formation has reached when combined with an understanding of chemical kinetics and thermal history. The kinetic reaction rate depends on the absolute temperature as well as the amount of reactants. The reaction rate is a function of absolute temperature, frequency factor, and activation energy. The hydrocarbon potential can then be estimated for different kerogen types across a range of activation energies. tabs., figs.
Institute of Scientific and Technical Information of China (English)
GIOVANGIGLI; Vincent
2012-01-01
We present multicomponent flow models derived from the kinetic theory of gases and investigate the symmetric hyperbolic-parabolic structure of the resulting system of partial differential equations.We address the Cauchy problem for smooth solutions as well as the existence of deflagration waves,also termed anchored waves.We further discuss related models which have a similar hyperbolic-parabolic structure,notably the SaintVenant system with a temperature equation as well as the equations governing chemical equilibrium flows.We next investigate multicomponent ionized and magnetized flow models with anisotropic transport fluxes which have a different mathematical structure.We finally discuss numerical algorithms specifically devoted to complex chemistry flows,in particular the evaluation of multicomponent transport properties,as well as the impact of multicomponent transport.
Dag, Yusuf
Forced convection over traditional surfaces such as flat plate, cylinder and sphere have been well researched and documented. Data on forced convection over airfoil surfaces, however, remain very scanty in literature. High altitude vehicles that employ airfoils as lifting surfaces often suffer leading edge ice accretions which have tremendous negative consequences on the lifting capabilities and stability of the vehicle. One of the ways of mitigating the effect of ice accretion involves judicious leading edge convective cooling technique which in turn depends on the accuracy of convective heat transfer coefficient used in the analysis. In this study empirical investigation of convective heat transfer measurements on asymmetric airfoil is presented at different angle of attacks ranging from 0° to 20° under subsonic flow regime. The top and bottom surface temperatures are measured at given points using Senflex hot film sensors (Tao System Inc.) and used to determine heat transfer characteristics of the airfoils. The model surfaces are subjected to constant heat fluxes using KP Kapton flexible heating pads. The monitored temperature data are then utilized to determine the heat convection coefficients modelled empirically as the Nusselt Number on the surface of the airfoil. The experimental work is conducted in an open circuit-Eiffel type wind tunnel, powered by a 37 kW electrical motor that is able to generate subsonic air velocities up to around 41 m/s in the 24 square-inch test section. The heat transfer experiments have been carried out under constant heat flux supply to the asymmetric airfoil. The convective heat transfer coefficients are determined from measured surface temperature and free stream temperature and investigated in the form of Nusselt number. The variation of Nusselt number is shown with Reynolds number at various angles of attacks. It is concluded that Nusselt number increases with increasing Reynolds number and increase in angle of attack from 0
A study of sensing heat flow through thermal walls by using thermoelectric module
Sippawit Noppawit; Leephakpreeda Thananchai
2015-01-01
Demands on heat flow detection at a plane wall via a thermoelectric module have drawn researchers’ attention to quantitative understanding in order to properly implement the thermoelectric module in thermal engineering practices. Basic mathematical models of both heat transfer through a plane wall and thermoelectric effects are numerically solved to represent genuine behaviors of heat flow detection by mounting a thermoelectric module at a plane wall. The h...
Approximate Model for Turbulent Stagnation Point Flow.
Energy Technology Data Exchange (ETDEWEB)
Dechant, Lawrence [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2016-01-01
Here we derive an approximate turbulent self-similar model for a class of favorable pressure gradient wedge-like flows, focusing on the stagnation point limit. While the self-similar model provides a useful gross flow field estimate this approach must be combined with a near wall model is to determine skin friction and by Reynolds analogy the heat transfer coefficient. The combined approach is developed in detail for the stagnation point flow problem where turbulent skin friction and Nusselt number results are obtained. Comparison to the classical Van Driest (1958) result suggests overall reasonable agreement. Though the model is only valid near the stagnation region of cylinders and spheres it nonetheless provides a reasonable model for overall cylinder and sphere heat transfer. The enhancement effect of free stream turbulence upon the laminar flow is used to derive a similar expression which is valid for turbulent flow. Examination of free stream enhanced laminar flow suggests that the rather than enhancement of a laminar flow behavior free stream disturbance results in early transition to turbulent stagnation point behavior. Excellent agreement is shown between enhanced laminar flow and turbulent flow behavior for high levels, e.g. 5% of free stream turbulence. Finally the blunt body turbulent stagnation results are shown to provide realistic heat transfer results for turbulent jet impingement problems.
Heat flow map of Europe: brief summary of the geophysical implications
Energy Technology Data Exchange (ETDEWEB)
Cermak, V.
1981-01-01
The map of the surface heat flow in Europe was supplemented with the crustal thickness pattern, data on crustal radioactivity and conductivity and with available information on the heat flow-tectonic age, heat flow-heat generation and heat flow-crustal thickness relationships. Using this material and discussing it in terms of the crustal structure, generalized one-dimensional steady-state conductive temperature-depth curves were calculated for major tectonic provinces of Europe. Converting the seismic velocities to heat generation data, a preliminary pattern of the Moho heat flow was proposed. The Mohorovicic discontinuity is clearly not an isothermal surface, neither is the outflow of heat from the upper mantle constant, but both parameters may vary in broad ranges. For a more refined model of the crust and upper mantle, the characteristic geotherms were computed, using surface heat flow as the determining parameter. By equating the depths, at which geotherms intersect the mantle solidus, with the depth of the lithosphere base, the surface heat flow pattern was used to map regional variations of the lithospheric thickness. 52 references, 11 figures.
Xin Gu; Bing Liu; Yongqing Wang; Ke Wang
2016-01-01
Effect of main structural parameters of shutter baffle heat exchanger with a triangle tube layout in the shell side on heat transfer and flow resistance performance is studied in the article. A periodic whole cross-sectional computation model is built for the heat exchanger in the numerical study. The effects of structural parameters are analyzed, including assembly mode of shutter baffles, shutter baffle pitch, strip inclination angles, and strip widths. The correctness and accuracy of numer...
A one-dimensional heat transfer model for parallel-plate thermoacoustic heat exchangers.
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.
Analytical skin friction and heat transfer formula for compressible internal flows
Dechant, Lawrence J.; Tattar, Marc J.
1994-01-01
An analytic, closed-form friction formula for turbulent, internal, compressible, fully developed flow was derived by extending the incompressible law-of-the-wall relation to compressible cases. The model is capable of analyzing heat transfer as a function of constant surface temperatures and surface roughness as well as analyzing adiabatic conditions. The formula reduces to Prandtl's law of friction for adiabatic, smooth, axisymmetric flow. In addition, the formula reduces to the Colebrook equation for incompressible, adiabatic, axisymmetric flow with various roughnesses. Comparisons with available experiments show that the model averages roughly 12.5 percent error for adiabatic flow and 18.5 percent error for flow involving heat transfer.
Latent Heat Flow in Light Weight Roofs and its Influence on the Thermal Performance
DEFF Research Database (Denmark)
Rode, Carsten; Rudbeck, Claus Christian
1998-01-01
on a colder surface. In these cases, themagnitude of the latent heat flux can be of the same order as the heat transfer by conduction. The latent heat transfer may result in a heat gain which coincides with other gains of an occupied building, and thus can cause an extra requirement for cooling. The paper...... reviews and quantifies the importance of heat flow processes in moist insulation systems. It then employs modeling to analyze the effect of extra heat gain caused bylatent heat transfer in the envelope on the thermal load on an office building chosen asan example. An extra cooling requirement of 6......Under certain conditions, migration of small amounts of moisture in the envelope of buildings can cause heat flow through permeable thermal insulation materials due to the conversion of latent heat when moisture evaporates from a warm surface, diffuses through the insulation, and condenses...
Latent Heat Flow in Light Weight Roofs and its Influence on the Thermal Performance
DEFF Research Database (Denmark)
Rode, Carsten; Rudbeck, Claus Christian
1998-01-01
Under certain conditions, migration of small amounts of moisture in the envelope of buildings can cause heat flow through permeable thermal insulation materials due to the conversion of latent heat when moisture evaporates from a warm surface, diffuses through the insulation, and condenses...... reviews and quantifies the importance of heat flow processes in moist insulation systems. It then employs modeling to analyze the effect of extra heat gain caused bylatent heat transfer in the envelope on the thermal load on an office building chosen asan example. An extra cooling requirement of 6...... on a colder surface. In these cases, themagnitude of the latent heat flux can be of the same order as the heat transfer by conduction. The latent heat transfer may result in a heat gain which coincides with other gains of an occupied building, and thus can cause an extra requirement for cooling. The paper...
Institute of Scientific and Technical Information of China (English)
Maunu KUOSA; Petri SALLINEN; Arttu REUNANEN; Jari BACKMAN; Jaakko LARJOLA; Lasse KOSKELAINEN
2005-01-01
The study deals with the cooling of a high-speed electric machine through an air gap with numerical and experimental methods. The rotation speed of the test machine is between 5000～40000 r/min and the machine is cooled by a forced gas flow through the air gap. In the previous part of the research the friction coefficient was measured for smooth and grooved stator cases with a smooth rotor. The heat transfer coefficient was recently calculated by a numerical method and measured for a smooth stator-rotor combination. In this report the cases with axial groove slots at the stator and/or rotor surfaces are studied. Numerical flow simulations and measurements have been done for the test machine dimensions at a large velocity range. At constant mass flow rate the heat transfer coefficients by the numerical method attain bigger values with groove slots on the stator or rotor surfaces. The results by the numerical method have been confirmed with measurements. The RdF-sensor was glued to the stator and rotor surfaces to measure the heat flux through the surface, as well as the temperature.
Heat transfer in flow past a continuously moving porous flat plate with heat flux
Digital Repository Service at National Institute of Oceanography (India)
Murty, T.V.R.; Sarma, Y.V.B.
The analysis of the heat transfer in flow past a continuously moving semi-infinite plate in the presence of suction/ injection with heat flux has been presented. Similarity solutions have been derived and the resulting equations are integrated...
A heterogeneous model for heat transfer in packed beds
Wijngaarden, R.J.; Westerterp, K.R.
1993-01-01
If transient heat transfer occurs in a packed bed or a reaction is carried out on the pellets, the heterogeneity of the bed is essential because of the heat flow between pellets and gas. Global heat parameters for the packed bed, such as λeff and αw, are usually derived from homogeneous models. Ther
Flow in a model turbine stator
Buggeln, R. C.; Shamroth, S. J.; Briley, W. R.
1985-10-01
In view of the complex nature of the flowfield in the hot section of gas turbine engines, the need to predict heat transfer and flow losses, the possible appearance of separation and strong secondary flows, etc., the present effort is focusing upon a Navier-Stokes approach to the three dimensional turbine stator problem. The advantages of a full Navier-Stokes approach are clear since when combined with a suitable turbulence model these equations represent the flow and heat transfer physics. In particular, the Navier-Stokes equations accurately represent possible separated regions and regions of significant secondary flow. In addition, the Navier-Stokes approach allows representation of the entire flow field by a single set of equations, thus avoiding problems associated with representing different regions of the flow by different equations and then matching flow regions.
Critical heat flux in flow boiling in microchannels
Saha, Sujoy Kumar
2015-01-01
This Brief concerns the important problem of critical heat flux in flow boiling in microchannels. A companion edition in the SpringerBrief Subseries on Thermal Engineering and Applied Science to “Heat Transfer and Pressure Drop in Flow Boiling in Microchannels,” by the same author team, this volume is idea for professionals, researchers, and graduate students concerned with electronic cooling.
Computational fluid flow and heat transfer. An engineering tool
Salcudean, Martha
1991-05-01
The purpose, method, and potential of computational fluid dynamics (CFD) are discussed. Some examples of CFD and heat transfer applied to engineering problems are described. Simulation of casting in a permanent mold, gallium arsenide crystal growth, and the computation of discharge coefficients in film cooling of turbine blades are briefly described. It is shown the the CFD methods help to improve the understanding of the physics involved. They allow the influence of various parameters on the product or process to be investigated in a relatively inexpensive way. CFD constitutes a predictive tool which allows for product or process optimization. Discretization and solution methods used in the present examples are briefly described. Some limitations of the CFD methods are illustrated. The error introduced by false diffusion is shown for laminar flow around a bluff body. The improvement obtained by a higher order scheme is discussed. Some difficulties related to turbulence modelling are illustrated for the flow and heat transfer around the same bluff body. Turbulent swirling flow between concentric annuli is also discussed. Problems related to the slow convergence rate and major improvements obtained through applying multigrid convergence acceleration methods are shown for two and three dimensional opposing jets penetrating into a main flow.
Nanoscale Heat Transfer Due to Near Field Radiation and Nanofluidic Flows
2015-07-21
AFRL-OSR-VA-TR-2015-0205 Nanoscale heat transfer due to near field radiation and nanofluidic flows Peter Taborek UNIVERSITY OF CALIFORNIA IRVINE...TITLE AND SUBTITLE Nanoscale heat transfer due to near field radiation and nanofluidic flows 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA9550-12-1-0065...liquid flows through the pipe would spontaneously form a liquid/vapor interface either inside the pie or near the exit. We developed a model which
Batir, Joseph F.; Blackwell, David D.; Richards, Maria C.
2016-06-01
The objective of this research is to contribute to the understanding of the thermal regime of Alaska and its relationship to geology, regional tectonics, and to suggest potential sites for future geothermal energy production. New heat flow data were collected and are combined with existing published and unpublished data, although large sections of Alaska still lack data. Fault traces were implemented into the heat flow contouring as an additional gridding constraint, to incorporate both heat flow measurements and geology. New heat flow data supported the use of geologic trends in the heat flow mapping procedure, and a heat flow map of Alaska was produced with this added constraint. The multi-input contouring strategy allows production of a map with a regional interpretation of heat flow, in addition to site-specific heat flow and thermal model interpretations in areas with sufficient data density. Utilizing the new heat flow map, temperature-at-depth curves were created for example areas. Temperature-at-depth curves are calculated to 10 km depth for the areas of Anchorage, Fairbanks, Juneau, the Alaska Peninsula, Bristol Bay, and the Copper River Basin. The temperatures-at-depth predicted near the population centers of Anchorage and Juneau are relatively low, limiting the geothermal resource potential. The Fairbanks area temperature estimates are near conventional power production temperatures (150 °C) between 3.5 and 4 km. All data areas, except at Juneau, have temperatures sufficient for low temperature geothermal applications (40 °C) by 2 km. A high heat flow region exists within the Aleutian Volcanic Arc, although new data show heat flow variations from 59 to 120 mW m-2, so individual geothermal resources within the arc will be irregularly located.
Temperatures and Heat Flows in a Soil Enclosing a Slinky Horizontal Heat Exchanger
Directory of Open Access Journals (Sweden)
Pavel Neuberger
2014-02-01
Full Text Available Temperature changes and heat flows in soils that host “slinky”-type horizontal heat exchangers are complex, but need to be understood if robust quantification of the thermal energy available to a ground-source heat pump is to be achieved. Of particular interest is the capacity of the thermal energy content of the soil to regenerate when the heat exchangers are not operating. Analysis of specific heat flows and the specific thermal energy regime within the soil, including that captured by the heat-exchangers, has been characterised by meticulous measurements. These reveal that high concentrations of antifreeze mix in the heat-transfer fluid of the heat exchanger have an adverse impact on heat flows discharged into the soil.
Effect of flow maldistribution and axial conduction on compact microchannel heat exchanger
Baek, Seungwhan; Lee, Cheonkyu; Jeong, Sangkwon
2014-03-01
When a compact microchannel heat exchanger is operated at cryogenic environments, it has potential problems of axial conduction and flow maldistribution. To analyze these detrimental effects, the heat exchanger model that includes both axial conduction and flow maldistribution effect is developed in consideration of the microchannel heat exchanger geometry. A dimensionless axial conduction parameter (λ) is used to describe the axial conduction effect, and the coefficient of variation (CoV) is introduced to quantify the flow maldistribution condition. The effectiveness of heat exchanger is calculated according to the various values of the axial conduction parameter and the CoV. The analysis results show that the heat exchanger effectiveness is insensitive when λ is less than 0.005, and effectiveness is degraded with the large value of CoV. Three microchannel heat exchangers are fabricated with printed circuit heat exchanger (PCHE) technology for validation purpose of the heat exchanger model. The first heat exchanger is a conventional heat exchanger, the second heat exchanger has the modified cross section to eliminate axial conduction effect, and the third heat exchanger has the modified cross section and the cross link in parallel channel to mitigate flow maldistribution effect. These heat exchangers are tested in cryogenic single-phase, and two-phase environments. The third heat exchanger shows the ideal thermal characteristic, while the other two heat exchangers experience some performance degradation due to axial conduction or flow maldistribution. The impact of axial conduction and flow maldistribution effects are verified by the simulation results and compared with the experimental results.
Heat transfer and flow in solar energy and bioenergy systems
Xu, Ben
The demand for clean and environmentally benign energy resources has been a great concern in the last two decades. To alleviate the associated environmental problems, reduction of the use of fossil fuels by developing more cost-effective renewable energy technologies becomes more and more significant. Among various types of renewable energy sources, solar energy and bioenergy take a great proportion. This dissertation focuses on the heat transfer and flow in solar energy and bioenergy systems, specifically for Thermal Energy Storage (TES) systems in Concentrated Solar Power (CSP) plants and open-channel algal culture raceways for biofuel production. The first part of this dissertation is the discussion about mathematical modeling, numerical simulation and experimental investigation of solar TES system. First of all, in order to accurately and efficiently simulate the conjugate heat transfer between Heat Transfer Fluid (HTF) and filler material in four different solid-fluid TES configurations, formulas of an e?ective heat transfer coe?cient were theoretically developed and presented by extending the validity of Lumped Capacitance Method (LCM) to large Biot number, as well as verifications/validations to this simplified model. Secondly, to provide design guidelines for TES system in CSP plant using Phase Change Materials (PCM), a general storage tank volume sizing strategy and an energy storage startup strategy were proposed using the enthalpy-based 1D transient model. Then experimental investigations were conducted to explore a novel thermal storage material. The thermal storage performances were also compared between this novel storage material and concrete at a temperature range from 400 °C to 500 °C. It is recommended to apply this novel thermal storage material to replace concrete at high operating temperatures in sensible heat TES systems. The second part of this dissertation mainly focuses on the numerical and experimental study of an open-channel algae
Inductive heating with magnetic materials inside flow reactors.
Ceylan, Sascha; Coutable, Ludovic; Wegner, Jens; Kirschning, Andreas
2011-02-07
Superparamagnetic nanoparticles coated with silica gel or alternatively steel beads are new fixed-bed materials for flow reactors that efficiently heat reaction mixtures in an inductive field under flow conditions. The scope and limitations of these novel heating materials are investigated in comparison with conventional and microwave heating. The results suggest that inductive heating can be compared to microwave heating with respect to rate acceleration. It is also demonstrated that a very large diversity of different reactions can be performed under flow conditions by using inductively heated flow reactors. These include transfer hydrogenations, heterocyclic condensations, pericyclic reactions, organometallic reactions, multicomponent reactions, reductive cyclizations, homogeneous and heterogeneous transition-metal catalysis. Silica-coated iron oxide nanoparticles are stable under many chemical conditions and the silica shell could be utilized for further functionalization with Pd nanoparticles, rendering catalytically active heatable iron oxide particles. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Low-Flow Film Boiling Heat Transfer on Vertical Surfaces
DEFF Research Database (Denmark)
Munthe Andersen, J. G.; Dix, G. E.; Leonard, J. E.
1976-01-01
The phenomenon of film boiling heat transfer for high wall temperatures has been investigated. Based on the assumption of laminar flow for the film, the continuity, momentum, and energy equations for the vapor film are solved and a Bromley-type analytical expression for the heat transfer...... length, an average film boiling heat transfer coefficient is obtained....
Forsyth, Peter; McGilvray, Matthew; Gillespie, David R. H.
2017-01-01
This paper reports an experimental and numerical study of the development and coupling of aerodynamic flows and heat transfer within a model ribbed internal cooling passage to provide insight into the development of secondary flows. Static instrumentation was installed at the end of a long smooth passage and used to measure local flow features in a series of experiments where ribs were incrementally added upstream. This improves test turnaround time and allows higher-resolution heat transfer coefficient distributions to be captured, using a hybrid transient liquid crystal technique. A composite heat transfer coefficient distribution for a 12-rib-pitch passage is reported: notably the behaviour is dominated by the development of the secondary flow in the passage throughout. Both the aerodynamic and heat transfer test data were compared to numerical simulations developed using a commercial computational fluid dynamics solver. By conducting a number of simulations it was possible to interrogate the validity of the underlying assumptions of the experimental strategy; their validity is discussed. The results capture the developing size and strength of the vortical structures in secondary flow. The local flow field was shown to be strongly coupled to the enhancement of heat transfer coefficient. Comparison of the experimental and numerical data generally shows excellent agreement in the level of heat transfer coefficient predicted, though the numerical simulations fail to capture some local enhancement on both the ribbed and smooth surfaces. Where this was the case, the coupled flow and heat transfer measurements were able to identify missing velocity field characteristics.
Heat transfer measurements of the 1983 kilauea lava flow.
Hardee, H C
1983-10-07
Convective heat flow measurements of a basaltic lava flow were made during the 1983 eruption of Kilauea volcano in Hawaii. Eight field measurements of induced natural convection were made, giving heat flux values that ranged from 1.78 to 8.09 kilowatts per square meter at lava temperatures of 1088 and 1128 degrees Celsius, respectively. These field measurements of convective heat flux at subliquidus temperatures agree with previous laboratory measurements in furnace-melted samples of molten lava, and are useful for predicting heat transfer in magma bodies and for estimating heat extraction rates for magma energy.
Energy Technology Data Exchange (ETDEWEB)
Park, Chun Dong; Lee, Dong Hyun; Park, Byung-Sik; Choi, Jaejoon [Korea Institute of Energy Research (KIER), Daejeon (Korea, Republic of)
2017-02-15
In this study, the flow and heat transfer characteristics of the finned annular passage were investigated numerically. The annular passage simulates co-axial geothermal heat exchanger, and fins are installed on its inner wall to reduce heat loss from the production passage (annulus) to injection passage (inner pipe). A commercial CFD program, Ansys Fluent, was used with SST k-ω turbulence model. The effects of the geometric parameters of the fin on the inner tube were analyzed under the periodic boundary condition. The result indicated that most parameters had a tendency to increase with an increase in the height and angle of the fin. However, it was confirmed that the Nusselt number of the inner tube on the coaxial 15, 5, 0.3 was lower than that of the smooth tube. Additionally, the Nusselt number of the inner tube exhibited a tendency of decreasing with a decrease in the spacing in Coaxial 15, S{sub f}, 0.3.
Two-phase Flow Distribution in Heat Exchanger Manifolds
Vist, Sivert
2004-01-01
The current study has investigated two-phase refrigerant flow distribution in heat exchange manifolds. Experimental data have been acquired in a heat exchanger test rig specially made for measurement of mass flow rate and gas and liquid distribution in the manifolds of compact heat exchangers. Twelve different manifold designs were used in the experiments, and CO2 and HFC-134a were used as refrigerants.
Heat transfer and pressure drop in flow boiling in microchannels
Saha, Sujoy Kumar
2016-01-01
This Brief addresses the phenomena of heat transfer and pressure drop in flow boiling in micro channels occurring in high heat flux electronic cooling. A companion edition in the Springer Brief Subseries on Thermal Engineering and Applied Science to “Critical Heat Flux in Flow Boiling in Micro channels,” by the same author team, this volume is idea for professionals, researchers and graduate students concerned with electronic cooling.
Heat transfer and fluid flow in biological processes advances and applications
Becker, Sid
2015-01-01
Heat Transfer and Fluid Flow in Biological Processes covers emerging areas in fluid flow and heat transfer relevant to biosystems and medical technology. This book uses an interdisciplinary approach to provide a comprehensive prospective on biofluid mechanics and heat transfer advances and includes reviews of the most recent methods in modeling of flows in biological media, such as CFD. Written by internationally recognized researchers in the field, each chapter provides a strong introductory section that is useful to both readers currently in the field and readers interested in learning more about these areas. Heat Transfer and Fluid Flow in Biological Processes is an indispensable reference for professors, graduate students, professionals, and clinical researchers in the fields of biology, biomedical engineering, chemistry and medicine working on applications of fluid flow, heat transfer, and transport phenomena in biomedical technology. Provides a wide range of biological and clinical applications of fluid...
Feru, E.; Willems, F.P.T.; Rojer, C.; Jager, B. de; Steinbuch, M.
2013-01-01
To meet future CO2 emission targets, Waste Heat Recovery systems have recently attracted much attention for automotive applications, especially for long haul trucks. This paper focuses on the development of a dynamic counter-flow heat exchanger model for control purposes. The model captures the dyna
Feru, E.; Willems, F.P.T.; Rojer, C.; Jager, B. de; Steinbuch, M.
2013-01-01
To meet future CO2 emission targets, Waste Heat Recovery systems have recently attracted much attention for automotive applications, especially for long haul trucks. This paper focuses on the development of a dynamic counter-flow heat exchanger model for control purposes. The model captures the dyna
Demand modelling for central heating systems
Energy Technology Data Exchange (ETDEWEB)
Heller, A.
2000-07-01
involving fluid flows brings along a problem called 'numerical diffusion'. This subject will be discussed in much detail. The objective of doing so is to find a solution that is generally applicable for the simulations of flows in e.g. solar collector tubes, thermal tank models and so on. In some cases the implementation of heat loads involves assumptions to meteorological parameters. In this report two methods representing such data are discussed: 1) Simple function models. 2) Climatic reference data sets. The methods will here be examined and discussed. To estimate the reality of generated heat demand 'profiles', measurements from a distric heating case are used for comparison. No comprehensive validation is carried out here. The comparison with the measurements shows that the generation tool is not able to represent the real system. However, the tool can be applied for the modelling of new settlements where the heat load is not known and must be estimated by other means. A rather comprehensive section with discussion and conclusions closes the report. (au)
Cryogenic Heat Exchanger with Turbulent Flows
Amrit, Jay; Douay, Christelle; Dubois, Francis; Defresne, Gerard
2012-01-01
An evaporator-type cryogenic heat exchanger is designed and built for introducing fluid-solid heat exchange phenomena to undergraduates in a practical and efficient way. The heat exchanger functions at liquid nitrogen temperature and enables cooling of N[subscript 2] and He gases from room temperatures. We present first the experimental results of…
Cryogenic Heat Exchanger with Turbulent Flows
Amrit, Jay; Douay, Christelle; Dubois, Francis; Defresne, Gerard
2012-01-01
An evaporator-type cryogenic heat exchanger is designed and built for introducing fluid-solid heat exchange phenomena to undergraduates in a practical and efficient way. The heat exchanger functions at liquid nitrogen temperature and enables cooling of N[subscript 2] and He gases from room temperatures. We present first the experimental results of…
Simulation of rarefied gas flow and heat transfer in microchannels
Institute of Scientific and Technical Information of China (English)
王娴; 王秋旺; 陶文铨; 郑平
2002-01-01
Analysis and simulation of rarefied nitrogen gas flow and heat transfer were performed with the Knusden number ranging from 0.05 to 1.0, using the direct simulation of Monte Carlo (DSMC) method. The influences of the Kn number and the aspect ratio on the gas temperature and wall heat flux in the microchannels were studied parametrically. The total and local heat fluxes of the microchannel walls varying with the channel inlet velocities were also investigated in detail. It was found that the Kn number and the aspect ratio greatly influence the heat transfer performance of microchannels, and both the channel inlet and outlet have higher heat fluxes while the heat flux in the middle part of channels is very low. It is also found that the inlet free stream flow velocity has small affect on the wall total heat flux while it changes the distribution of local heat flux.
Numerical analysis of fluid flow and heat transfer in a helical ...
African Journals Online (AJOL)
DR OKE
numerical study to investigate three-dimensional turbulent developing convective ... numerical study on double-pipe helical heat exchanger modeled for laminar fluid flow and ... Boundary layer mesh was generated for both nozzle and helix.
Microgravity two-phase flow regime modeling
Energy Technology Data Exchange (ETDEWEB)
Lee, D.; Best, F.R.; Faget, N.
1987-01-01
A flow pattern or flow regime is the characteristics spatial distribution of the phases of fluid in a duct. Since heat transfer and pressure drop are dependent on the characteristic distribution of the phases, it is necessary to describe flow patterns in an appropriate manner so that a hydrodynamic or heat transfer theory applicable to that pattern can be chosen. The objective of the present analysis is to create a flow regime map based on physical modeling of vapor/liquid interaction phenomena in a microgravity environment. In the present work, four basic flow patterns are defined: dispersed flow, stratified flow, slug flow, and annular flow. Fluid properties, liquid and vapor flow rates, and pipe size were chosen as the principal parameters. It is assumed that a transition from one flow pattern to another will occur when there is a change in the dominant force which controls that flow pattern. The forces considered in this modeling are surface tension force, both force, inertial force, friction, and turbulent fluctuations.
Joule-Thomson effect and internal convection heat transfer in turbulent He II flow
Walstrom, P. L.
1988-01-01
The temperature rise in highly turbulent He II flowing in tubing was measured in the temperature range 1.6-2.1 K. The effect of internal convection heat transport on the predicted temperature profiles is calculated from the two-fluid model with mutual friction. The model predictions are in good agreement with the measurements, provided that the pressure gradient term is retained in the expression for internal convection heat flow.
Joule-Thomson effect and internal convection heat transfer in turbulent He II flow
Walstrom, P. L.
1988-03-01
The temperature rise in highly turbulent He II flowing in tubing was measured in the temperature range 1.6-2.1 K. The effect of internal convection heat transport on the predicted temperature profiles is calculated from the two-fluid model with mutual friction. The model predictions are in good agreement with the measurements, provided that the pressure gradient term is retained in the expression for internal convection heat flow.
Heat transfer and flow characteristics on a gas turbine shroud.
Obata, M; Kumada, M; Ijichi, N
2001-05-01
The work described in this paper is an experimental investigation of the heat transfer from the main flow to a turbine shroud surface, which may be applicable to ceramic gas turbines. Three kinds of turbine shrouds are considered with a flat surface, a taper surface and a spiral groove surface opposite to the blades in an axial flow turbine of actual turbo-charger. Heat transfer measurements were performed for the experimental conditions of a uniform heat flux or a uniform wall temperature. The effects of the inlet flow angle, rotational speed, and tip clearance on the heat transfer coefficient were clarified under on- and off-design flow conditions. The mean heat transfer coefficient was correlated to the blade Reynolds number and tip clearance, and compared with an experimental correlation and measurements of a flat surface. A comparison was also made for the measurement of static pressure distributions.
Flow Patterns and Thermal Drag in Supersonic Duct Flow with Heating
Institute of Scientific and Technical Information of China (English)
Zeng－YuanGuo; Zhi－HongLiu
1994-01-01
The supersonic duct flow with fixed back pressure to stagnation pressure ratio Pb/P0 under heating is investigated analytically.A “Flow Pattern Diagram” Which consists of six pattern zones is developed.By this diagram the actual flow state in supersonic duct flow system can be determined conveniently when Pb/Po and heating intensity are knows.It is impossible for flow with heavy heating to become supersonic,even though the pressure ratio is much smaller than the critical pressure ratio,Based on the analogy between viscous effect and heating effect a thermal drag factor has een defined.which can predict the flow property variation due to heating and the relaive importance of viscous effect and heating effect.
Flow and heat transfer in compact offset strip fin surfaces
Institute of Scientific and Technical Information of China (English)
Junqi DONG; Jiangping CHEN; Zhijiu CHEN
2008-01-01
Experimental studies of air-side heat transfer and pressure drop characteristics of offset strip fins and flat tube heat exchangers were performed. A series of tests were conducted for 9 heat exchangers with different fin space, fin height, fin strip length and flow length, at a constant tube-side water flow rate of 2.5 m3/h. The char-acteristics of the heat transfer and pressure drop of differ-ent fin space, fin height and fin length were analyzed and compared. The curves of the heat transfer coefficients vs. The pumping power per unit frontal area were then plot-ted. Moreover, the enhanced heat transfer mechanism of offset strip fins was analyzed using field synergy theory. The results showed that fin length and flow length have more obviously effect on the thermal hydraulic character-istics of offset strip fins.
Heat flow and ground water flow in the Great Plains of the United States
Gosnold, William D.
1985-12-01
Regional groundwater flow in deep aquifers adds advective components to the surface heat flow over extensive areas within the Great Plains province. The regional groundwater flow is driven by topographically controlled piezometric surfaces for confined aquifers that recharge either at high elevations on the western edge of the province or from subcrop contacts. The aquifers discharge at lower elevations to the east. The assymetrical geometry for the Denver and Kennedy Basins is such that the surface areas of aquifer recharge are small compared to the areas of discharge. Consequently, positive advective heat flow occurs over most of the province. The advective component of heat flow in the Denver Basin is on the order of 15 mW m -2 along a zone about 50 km wide that parallels the structure contours of the Dakota aquifer on the eastern margin of the Basin. The advective component of heat flow in the Kennedy Basin is on the order of 20 mW m -2 and occurs over an extensive area that coincides with the discharge areas of the Madison (Mississippian) and Dakota (Cretaceous) aquifers. Groundwater flow in Paleozoic and Mesozoic aquifers in the Williston Basin causes thermal anomalies that are seen in geothermal gradient data and in oil well temperature data. The pervasive nature of advective heat flow components in the Great Plains tends to mask the heat flow structure of the crust, and only heat flow data from holes drilled into the crystalline basement can be used for tectonic heat flow studies.
The Helical Oscillating Heat Pipe: Flow Pattern Behaviour Study
Directory of Open Access Journals (Sweden)
Y. Sriudom
2015-01-01
Full Text Available This research aims to study the effect of evaporator temperature, pitch distance, and working fluid on the internal flow pattern and the heat transfer characteristics of the helical oscillating heat pipe. A Pyrex tube with an inner diameter of 2.4 mm was used to study the flow pattern in the evaporator section. The pitch distance varied at 1, 1.5, and 2 cm. Water and R-123 were used as working fluid with a filling ratio of 80% by total volume. In the evaporator section, the water temperature varied at 60, 75, and 90°C to supply heat to the heat pipe. In the condenser section, air with a temperature of 25°C was used as heat sink. From the results, it was found that 4 internal flow patterns, bubble flow, slug flow, annular flow, and stratified wavy flow, were observed in the evaporator section for both working fluids. The heat transfer rate decreased when the pitch distance was increased from 1 to 2 cm. The maximum heat flux was 2,132.6 and 1,773.4 W/m2 for the working fluid of R-123 and water, respectively. Both occurred at a pitch distance of 1 cm and an evaporator temperature of 90°C.
Mechanism and control of convective heat transfer-- Coordination of velocity and heat flow fields
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
A second look has been given at the mechanism of convective heat transfer based on the analogy between convection and conduction with heat sources. The strength of convective heat transfer depends not only on the fluid velocity and fluid properties, but also on the coordination of fluid velocity and heat flow fields. Hence, based on the included angle of velocity and temperature gradient vectors, the presence of fluid motion may enhance or reduce heat transfer. With this concept, the known heat transfer phenomena may be understood in a deeper way. More important is that some novel approaches of heat transfer control can be developed.
Directory of Open Access Journals (Sweden)
Xin Gu
2016-03-01
Full Text Available Effect of main structural parameters of shutter baffle heat exchanger with a triangle tube layout in the shell side on heat transfer and flow resistance performance is studied in the article. A periodic whole cross-sectional computation model is built for the heat exchanger in the numerical study. The effects of structural parameters are analyzed, including assembly mode of shutter baffles, shutter baffle pitch, strip inclination angles, and strip widths. The correctness and accuracy of numerical simulation method are confirmed with a laser Doppler velocimeter experiment. Based on the research results, correlations for heat transfer coefficient and pressure drop in shell side are presented. Using the field synergy principle, the heat transfer enhancement mechanisms of segmental baffle heat exchanger and shutter baffle heat exchanger in shell side are analyzed.
MODEL OF HEAT SIMULATOR FOR DATA CENTERS
Directory of Open Access Journals (Sweden)
Jan Novotný
2016-08-01
Full Text Available The aim of this paper is to present a design and a development of a heat simulator, which will be used for a flow research in data centers. The designed heat simulator is based on an ideological basis of four-processor 1U Supermicro server. The designed heat simulator enables to control the flow and heat output within the range of 10–100 %. The paper covers also the results of testing measurements of mass flow rates and heat flow rates in the simulator. The flow field at the outlet of the server was measured by the stereo PIV method. The heat flow rate was determined, based on measuring the temperature field at the inlet and outlet of the simulator and known mass flow rate.
Despagne, Wilfried; Frenod, Emmanuel
2014-01-01
Purpose: The purpose of this paper is to investigate the road freight haulage activity. Using the physical and data flow information from a freight forwarder, we intend to model the flow of inbound and outbound goods in a freight transport hub. Approach: This paper presents the operation of a road haulage group. To deliver goods within two days to any location in France, a haulage contractor needs to be part of a network. This network handles the processing of both physical goods and data. We...
Temperatures and Heat Flows in a Soil Enclosing a Slinky Horizontal Heat Exchanger
Pavel Neuberger; Radomír Adamovský; Michaela Šeďová
2014-01-01
Temperature changes and heat flows in soils that host “slinky”-type horizontal heat exchangers are complex, but need to be understood if robust quantification of the thermal energy available to a ground-source heat pump is to be achieved. Of particular interest is the capacity of the thermal energy content of the soil to regenerate when the heat exchangers are not operating. Analysis of specific heat flows and the specific thermal energy regime within the soil, including that captured by the ...
Numerical Modeling of Fin and Tube Heat Exchanger for Waste Heat Recovery
DEFF Research Database (Denmark)
Singh, Shobhana; Sørensen, Kim; Condra, Thomas Joseph
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......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...... 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....
An analytical theory of heated duct flows in supersonic combustors
Directory of Open Access Journals (Sweden)
Chenxi Wu
2014-01-01
Full Text Available One-dimensional analytical theory is developed for supersonic duct flow with variation of cross section, wall friction, heat addition, and relations between the inlet and outlet flow parameters are obtained. By introducing a selfsimilar parameter, effects of heat releasing, wall friction, and change in cross section area on the flow can be normalized and a self-similar solution of the flow equations can be found. Based on the result of self-similar solution, the sufficient and necessary condition for the occurrence of thermal choking is derived. A relation of the maximum heat addition leading to thermal choking of the duct flow is derived as functions of area ratio, wall friction, and mass addition, which is an extension of the classic Rayleigh flow theory, where the effects of wall friction and mass addition are not considered. The present work is expected to provide fundamentals for developing an integral analytical theory for ramjets and scramjets.
Role of plate-driven mantle flow in distribution of the global heat flow
Institute of Scientific and Technical Information of China (English)
叶正仁; 安镇文
1999-01-01
Heat flow in the Earth, from its hot interior to its relatively cool exterior, is the primary energy flow responsible for the dynamic nature of our planet. The motion of the plates excites a forced convective motion in the mantle, and this plate-driven mantle flow will strongly modulate the temperature field in the mantle because of the relatively high Peeler number of the mantle dynamic system. Here the role of the plate-driven mantle flow in the observed global heat flow is examined. The result reveals that the main feature of the distribution of the observed heat flow at the surface of the Earth matches well with the prediction and nearly one half of the average heat flow can be attributed to the thermal effect of the plate-driven mantle flow.
The porosity in a fluidized bed heat transfer model
Visser, G; Visser, G.; Valk, M.
1993-01-01
A mathematical model of heat transfer between a fluidized bed and an immersed surface and a model of gas flow and porosity, both recently published, were combined and further modified in the area of low velocities where the particle convective component of heat transfer is low or neglectable. Experi
The porosity in a fluidized bed heat transfer model
Visser, G.; Valk, M.
1993-01-01
A mathematical model of heat transfer between a fluidized bed and an immersed surface and a model of gas flow and porosity, both recently published, were combined and further modified in the area of low velocities where the particle convective component of heat transfer is low or neglectable. Experi
Terrestrial heat flow in Junggar Basin,Northwest China
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Based on temperature logs of 117 boreholes and thermal conductivity of 119 rock samples,the first group of 35 heat flow data in the Junggar Basin are presented.The thermal gradients vary between 11.6 and 26.5℃/km ,and the thermal conductivity changes from 0.17 to 3.6 W/mK.Heat flow ranges from 23.4 to 53.7 mW/m2 with a mean of (42.3± 7.7) mW/m2.The heat flow pattern shows that heat flow is higher in the uplifts and lower in the depressions.The factors affecting the heat flow and its distribution include basin type,basement structure,sediment thickness,radioactive heat generation,etc.The overall low present-day heat flow in the Junggar Basin reflected its tectonothermal evolution characterized by lithospheric thickening,thrust and fault at shallow crust as well as consequently quick subsidence during the Late Cenozoic.
The surface heat flow of the Arabian Shield in Jordan
Förster, A.; Förster, H.-J.; Masarweh, R.; Masri, A.; Tarawneh, K.; Desert Group
2007-04-01
Surface heat flow in southern Jordan (western part of the Arabian Plate) was determined in a dense cluster of five, up to 900-m-deep boreholes that have encountered sedimentary rocks of Paleozoic (Ordovician and Silurian) age. These rocks are underlain by an igneous and metamorphic basement, which has been studied for its radiogenic heat production, along the eastern margin of the Dead Sea Transform (DST) fault system. The heat flow, calculated from continuous temperature logs and laboratory-measured thermal conductivity of drillcores and surface samples, averages to 60.3 ± 3.4 mW m -2 and contrasts the common view of the late Proterozoic-consolidated Arabian Shield constituting a low heat-flow province of ⩽45 mW m -2. Although only characterizing an area of about 300 km 2, this average is unlikely representing a positive local anomaly caused by voluminous HHP granites/rhyolites at shallow depths. Instead, a heat flow of 60 mW m -2 is considered a robust estimate of the Phanerozoic conductive surface heat flow not only for Jordan, but for the Arabian Shield in areas unaffected by younger reactivation. The large variation in conductive heat flow (36-88 mW m -2) previously observed in Jordan, southern Syria, and Saudi Arabia is irreconcilable with their broad similarity in lithosphere structure and composition and rather reflects a combination of factors including low-quality temperature data and insufficient knowledge on thermal rock properties.
Hasterok, D.; Gard, M.
2016-09-01
While surface heat flow relates to the heat loss through the lithosphere, it can be difficult to quantify and separate the heat produced internally through radiogenic decay from the heat transferred across the base of the lithosphere by mantle convection. In this study, we apply a thermo-isostatic analysis to Australia and estimate the sub-lithospheric and radiogenic heat flow components by employing a simple 1-D conservation of energy model. We estimate an anomalous radiogenic heat production across much of eastern Australia generally accounting for >50 mW m-2, while western Australia appears to have high crustal compositionally corrected elevation, possibly related to chemical buoyancy of the mantle lithosphere. A moderately high sub-lithospheric heat flow (∼40 mW m-2) along the eastern and southeastern coast, including Tasmania, is coincident with locations of Cenozoic volcanism and supports an edge-driven convection hypothesis. However, the pattern of sub-lithospheric heat flow along the margin does not support the existence of hotspot tracks. Thermo-isostatic models such as these improve our ability to identify and quantify crustal from mantle sources of heat loss and add valuable constraints on tectonic and geodynamic models of the continental lithosphere's physical state and evolution.
Energy Technology Data Exchange (ETDEWEB)
Mechitoua, N.; Dalsecco, S.; Delalondre, C.; Simonin, O. [Electricite de France (EDF), 78 - Chatou (France). Lab. National d`Hydraulique
1996-12-31
The direction of studies and researches (DER) of Electricite de France (EdF) has been involved for several years in a research program on turbulent reactive flows. The objectives of this program concern: the reduction of pollutant emissions from existing fossil-fueled power plants, the study of new production means (fluidized beds), and the promotion of electric power applications in the industry. An important part of this program is devoted to the development and validation of 3-D softwares and to the modeling of physical phenomena. This paper presents some industrial applications (furnaces, boilers, electric arcs) for which radiant heat transfers play an important role and the radiation models used. (J.S.) 8 refs.
Fluid flow and heat transfer investigation of pebble bed reactors using mesh-adaptive LES
Energy Technology Data Exchange (ETDEWEB)
Pavlidis, Dimitrios; Lathouwers, Danny, E-mail: d.lathouwers@tudelft.nl
2013-11-15
The very high temperature reactor is one of the designs currently being considered for nuclear power generation. One its variants is the pebble bed reactor in which the coolant passes through complex geometries (pores) at high Reynolds numbers. A computational fluid dynamics model with anisotropic mesh adaptivity is used to investigate coolant flow and heat transfer in such reactors. A novel method for implicitly incorporating solid boundaries based on multi-fluid flow modelling is adopted. The resulting model is able to resolve and simulate flow and heat transfer in randomly packed beds, regardless of the actual geometry, starting off with arbitrarily coarse meshes. The model is initially evaluated using an orderly stacked square channel of channel-height-to-particle diameter ratio of unity for a range of Reynolds numbers. The model is then applied to the face-centred cubical geometry. coolant flow and heat transfer patterns are investigated.
Fluid flow and heat transfer in rotating porous media
Vadasz, Peter
2016-01-01
This Book concentrates the available knowledge on rotating fluid flow and heat transfer in porous media in one single reference. Dr. Vadasz develops the fundamental theory of rotating flow and heat transfer in porous media and introduces systematic classification and identification of the relevant problems. An initial distinction between rotating flows in isothermal heterogeneous porous systems and natural convection in homogeneous non-‐isothermal porous systems provides the two major classes of problems to be considered. A few examples of solutions to selected problems are presented, highlighting the significant impact of rotation on the flow in porous media.
Novel Heat Flow Probe Design and Deployment Project
National Aeronautics and Space Administration — We propose to develop a novel method for deploying heat flow sensors/heaters in a hole and also a novel approach to subsurface access using a percussive method. The...
New determinations of geothermal heat flow in France
Energy Technology Data Exchange (ETDEWEB)
Bertaux, M.G. (Universite Pierre-et-Marie Curie, Paris); Bienfait, G.; Bottinga, Y.
1978-03-28
A brief analysis of geothermal heat flow determinations obtained in France during the past few years is presented. General trends were compared with older measurements and new data published in Europe.
Flow boiling heat transfer in circulating fluidized bed
Institute of Scientific and Technical Information of China (English)
Xiaoguang REN; Jiangdong ZHENG; Sefiane KHELLII; Arumemi-Ikhide MICHAEL
2009-01-01
In order to enhance heat transfer and mitigate contamination in the boiling processes, a new type of vapor-liquid-solid (3-phase) circulating fluidized bed boil-ing system has been designed, combining a circulating fluidized bed with boiling heat transfer. Experimental results show an enhancement of the boiling curve. Flow visualization studies concerning flow hydrodynamics within the riser column are also conducted whose results are presented and discussed.
Heat flow and thermal history of the Anadarko basin, Oklahoma
Carter, L.S.; Kelley, S.A.; Blackwell, D.D.; Naeser, N.D.
1998-01-01
New heat-flow values for seven sites in the Anadarko basin, Oklahoma, were determined using high-precision temperature logs and thermal conductivity measurements from nearly 300 core plugs. Three of the sites are on the northern shelf, three sites are in the deep basin, and one site is in the frontal fault zone of the northern Wichita Mountains. The heat flow decreased from 55 to 64 mW/m2 in the north, and from 39 to 54 mW/m2 in the south, due to a decrease in heat generation in the underlying basement rock toward the south. Lateral lithologic changes in the basin, combined with the change in heat flow across the basin, resulted in an unusual pattern of thermal maturity. The vitrinite reflectance values of the Upper Devonian-Lower Mississippian Woodford formation are highest 30-40 km north-northwest of the deepest part of the basin. The offset in highest reflectance values is due to the contrast in thermal conductivity between the Pennsylvanian "granite wash" section adjacent to the Wichita uplift and the Pennsylvanian shale section to the north. The geothermal gradient in the low-conductivity shale section is elevated relative to the geothermal gradient in the high-conductivity "granite wash" section, thus displacing the highest temperatures to the north of the deepest part of the basin. Apatite fission-track, vitrinite reflectance, and heat-flow data were used to constrain regional aspects of the burial history of the Anadarko basin. By combining these data sets, we infer that at least 1.5 km of denudation has occurred at two sites in the deep Anadarko basin since the early to middle Cenozoic (40 ?? 10 m.y.). The timing of the onset of denudation in the southern Anadarko basin coincides with the period of late Eocene erosion observed in the southern Rocky Mountains and in the northern Great Plains. Burial history models for two wells from the deep Anadarko basin predict that shales of the Woodford formation passed through the hydrocarbon maturity window by the
Energy Technology Data Exchange (ETDEWEB)
Manservisi, Sandro, E-mail: sandro.manservisi@unibo.it; Menghini, Filippo, E-mail: filippo.menghini3@unibo.it
2015-12-15
Highlights: • Turbulent heat transfer with a κ–ϵ–κ{sub θ}–ϵ{sub θ} turbulence model is investigated. • Numerical simulations with different pitch-to-diameter ratios are performed. • The results are compared with SED model and a few available experimental correlations. - Abstract: The study of heat transfer in heavy liquid metals has gained more attention in the last several years due to their applications in new advanced nuclear reactors. These fluids are characterized by low Prandtl numbers and a peculiar heat transfer that cannot be accurately reproduced with standard turbulence approximations, such as the Simple Eddy Diffusivity model (SED), commonly used in commercial codes. In this paper we report the results obtained for the SED and a more advanced κ–ϵ–κ{sub θ}–ϵ{sub θ} four parameter turbulence model for simulations in square lattice bare rod bundle geometries with different pitch-to-diameter ratios. We compare these numerical results with the available experimental data and correlations for the prediction of the Nusselt number.
Internal (Annular) and Compressible External (Flat Plate) Turbulent Flow Heat Transfer Correlations.
Energy Technology Data Exchange (ETDEWEB)
Dechant, Lawrence [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Smith, Justin [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2016-01-01
Here we provide a discussion regarding the applicability of a family of traditional heat transfer correlation based models for several (unit level) heat transfer problems associated with flight heat transfer estimates and internal flow heat transfer associated with an experimental simulation design (Dobranich 2014). Variability between semi-empirical free-flight models suggests relative differences for heat transfer coefficients on the order of 10%, while the internal annular flow behavior is larger with differences on the order of 20%. We emphasize that these expressions are strictly valid only for the geometries they have been derived for e.g. the fully developed annular flow or simple external flow problems. Though, the application of flat plate skin friction estimate to cylindrical bodies is a traditional procedure to estimate skin friction and heat transfer, an over-prediction bias is often observed using these approximations for missile type bodies. As a correction for this over-estimate trend, we discuss a simple scaling reduction factor for flat plate turbulent skin friction and heat transfer solutions (correlations) applied to blunt bodies of revolution at zero angle of attack. The method estimates the ratio between axisymmetric and 2-d stagnation point heat transfer skin friction and Stanton number solution expressions for sub-turbulent Reynolds numbers %3C1x10 4 . This factor is assumed to also directly influence the flat plate results applied to the cylindrical portion of the flow and the flat plate correlations are modified by
Cao, Guoliang; Han, Dongmei; Currell, Matthew J.; Zheng, Chunmiao
2016-09-01
Groundwater flow in deep sedimentary basins results from complex evolution processes on geological timescales. Groundwater flow systems conceptualized according to topography and/or groundwater table configuration generally assume a near-equilibrium state with the modern landscape. However, the time to reach such a steady state, and more generally the timescales of groundwater flow system evolution are key considerations for large sedimentary basins. This is true in the North China Basin (NCB), which has been studied for many years due to its importance as a groundwater supply. Despite many years of study, there remain contradictions between the generally accepted conceptual model of regional flow, and environmental tracer data. We seek to reconcile these contractions by conducting simulations of groundwater flow, age and heat transport in a three dimensional model, using an alternative conceptual model, based on geological, thermal, isotope and historical data. We infer flow patterns under modern hydraulic conditions using this new model and present the theoretical maximum groundwater ages under such a flow regime. The model results show that in contrast to previously accepted conceptualizations, most groundwater is discharged in the vicinity of the break-in-slope of topography at the boundary between the piedmont and central plain. Groundwater discharge to the ocean is in contrast small, and in general there are low rates of active flow in the eastern parts of the basin below the central and coastal plain. This conceptualization is more compatible with geochemical and geothermal data than the previous model. Simulated maximum groundwater ages of ∼1 Myrs below the central and coastal plain indicate that residual groundwater may be retained in the deep parts of the basin since being recharged during the last glacial period or earlier. The groundwater flow system has therefore probably not reached a new equilibrium state with modern-day hydraulic conditions. The
Mathematical Model of Moving Heat-Transfer Agents
Directory of Open Access Journals (Sweden)
R. I. Yesman
2010-01-01
Full Text Available A mathematical model of moving heat-transfer agents which is applied in power systems and plants has been developed in the paper. A paper presents the mathematical model as a closed system of differential convective heat-transfer equations that includes a continuity equation, a motion equation, an energy equation.Various variants of boundary conditions on the surfaces of calculation flow and heat exchange zone are considered in the paper.
Creeping Viscous Flow around a Heat-Generating Solid Sphere
DEFF Research Database (Denmark)
Krenk, Steen
1981-01-01
The velocity field for creeping viscous flow around a solid sphere due to a spherically symmetric thermal field is determined and a simple thermal generalization of Stokes' formula is obtained. The velocity field due to an instantaneous heat source at the center of the sphere is obtained in close...... form and an application to the storage of heat-generating nuclear waste is discussed....
New terrestrial heat flow measurements on the Nazca Plate
Energy Technology Data Exchange (ETDEWEB)
Anderson, R.N. (Columbia Univ., Palisades, NY); Langseth, M.G.; Vacquier, V.; Francheteau, J.
1976-03-01
Sixty-seven new heat flow measurements on the Nazca Plate are reported, and the thermal regimes of three specific areas on the plate are examined. The Nazca Ridge is an aseismic ridge which may have been generated as an ''island trail'' from the Easter Island ''hot spot'' and/or may be a fossil transform fault. The Nazca Ridge has lower heat flow than the surrounding sea floor implying that the ridge might have low ''effective'' thermal conductivity causing heat to preferentially flow or refract to surrounding ocean crust which has higher conductivity, or, the low heat flow values may be caused by hydrothermal circulation on the ridge. The Carnegie Plateau is an elevated region south of the Carnegie Ridge on the northeastern Nazca Plate with high heat flow and shallow topography consistent with an age of less than 20 m.y. B.P. The central Nazca Plate is an area of highly variable heat flow which is possibly related to thin sediment and to rough regional topography.
Directory of Open Access Journals (Sweden)
Emad H. Aly
2015-01-01
Full Text Available In existence of the velocity slip model, suction/injection, and heat source/sink, the boundary layer flow near a stagnation-point over a heated stretching sheet in a porous medium saturated by a nanofluid, with effect of the thermal radiation and magnetic field, has been studied. The governing system of partial differential equations was transformed into a system of nonlinear ordinary equations using the appropriate similarity transforms. Then, the obtained system has been numerically solved by the Chebyshev pseudospectral differentiation matrix (ChPDM approach. It was found that, at some special cases, the current results are in a very good agreement with those presented in the literature. In addition, the flow velocity, surface shear stress, temperature, and concentration are strongly influenced on applying the slip model, which is, therefore, extremely important to predict the flow characteristics accurately in the nanofluid mechanics. It was proved that this velocity slip condition is mandatory and should be taken into account in nanoscale research; otherwise, false results and a spurious physical sight are to be gained. Further, it was deduced that the influence of the stream velocity and shear stress reaches very rapidly the stable manner for both cases of the velocity ratio. However, when this ratio is equal to one, the skin friction coefficient, reduced Nusselt number, and reduced Sherwood number are constant and equal to zero, 0.721082, and 3.06155, respectively. Furthermore, it was proved that the reduced Nusselt number decreases with increase of Brownian motion and thermophoresis; has a very weak effect on increasing Lewis number; increases with increase of Prandtl number; and is higher in the cases of suction, velocity ratio > 1 and heat source in comparison with injection, velocity ratio 1 in comparison with injection and velocity ratio < 1, respectively; and is approximately the same in the heat source and heat sink cases. Finally
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.
Laminar Flow and Heat Transfer Characteristics in Jackets of Triangular Flow Channels
Institute of Scientific and Technical Information of China (English)
王翠华; 刘胜举; 吴剑华; 李雅侠
2013-01-01
Laminar flow and heat transfer characteristics of jacketed vessel with triangular flow channels were numerically studied under hydrodynamically and thermally fully developed conditions. Constant heat flux at the heated wall was assumed. The numerical program code in terms of vorticity, stream function, axial velocity com-ponent and energy equations was written based on a finite volume method. Based on the numerical results, the flow and temperature field were given, and the effects of Dean and Prandtl numbers on flow and heat transfer were ex-amined, and the correlations of flow resistance and mean Nusselt number were developed for the jacket. The results show that the structure of secondary flow is steady two vortices in the investigated range of dimensionless curvature ratio and Reynolds number. Two peaks of local Nusselt number increase significantly with Prandtl and Dean num-ber increasing, but the local Nusselt numbers near two ends and at the center of the heated wall increase only slightly. The center and two ends of heated wall are the poor positions for heat transfer in the jacket. Compared with the outer half coil jacket at the same area of heated wall, curvature radius, Reynolds number and Prandtl number, the jacket of triangular flow channel has lower flow resistance and less mean Nusselt number.
Herman, Cila; Chen, Yuwen
2006-08-01
A simplified model of heat transfer was developed to investigate the thermal behavior of heat exchangers and stack plates of thermoacoustic devices. The model took advantage of previous results describing the thermal behavior of the thermoacoustic core and heat transfer in oscillating flow to study the performance of heat exchangers attached to the core. The configuration considered is a flat tube (with a working fluid flowing in the tube) of the thickness of the stack plate attached to both ends of the stack plate. Geometrical and operational parameters as well as thermophysical properties of the heat exchangers, transport fluids in the heat exchangers, stack plate and the thermoacoustic working fluid were organized into dimensionless groups that allowed accounting for their impact on the performance of the heat exchangers. Two types of thermal boundary conditions were considered: constant temperature and constant heat flux along the heat exchanger tubes. Numerical simulations were carried out with the model introduced in the paper. The temperature distributions and heat fluxes near the edge of the stack plate were found to be nonlinear. The influence of system parameters on the thermal performance of the heat exchangers was analyzed.
Effect of particle loading on heat transfer enhancement in a gas-solid suspension cross flow
Institute of Scientific and Technical Information of China (English)
周劲松; 骆仲泱; 高翔; 倪明江; 岑可法
2002-01-01
Heat transfer between gas-solid multiphase flow and tubes occurs in many industry processes, such as circulating fluidized bed process, pneumatic conveying process, chemical process, drying process, etc. (This paper focuses on the influence of the presence of particles on the heat transfer between a tube and gas-solid sus-pension. The presence of particles causes positive enhancement of heat transfer in the case of high solid loading ratio, but heat transfer reduction has been found for in the case of very low soliding ratio (Ms of less than 0.05 kg/kg). A usefial correlation ineorpomting solid lolling ratio, particle size and flow Reytmlds number was derived from experimental data. In addition, the κ-ε two-equation model and the Fluctuation-Spectrum-Random-Trajectory Model (FSRT Model) are used to simulate the flow field and heat transit of the gas-phase and the solid-phase, respectively. Through coupling of the two phases the model can predict the local and total heat transfer characteristics of tube in gas-solid cross flow. For the total heat transfer enhancement due to particles loading the model predictions agreed well wih experimental data.
Sari, I. M.
2017-02-01
Teacher plays a crucial role in Education. Helping students construct scientifically mental model is one of obligation of Physics Education Department of Teacher Education Institute that produce physics teacher. Excavating students’ mental model is necessary to be done in physics education. This research was first to identify 23 physics students’ mental model of heat and heat conduction. A series of semi-structured interviews was conducted to excavate the students’ understanding of heat and mental models on heat conduction. The students who involved in this study come from different level from sophomore to master degree in Physics Education Department. This study adopted a constant comparison method to obtain the patterns of the participants’ responses through the students’ writing, drawing and verbal utterances. The framework for assessing mental model and the instruments were adopted and adapted from Chiou and Anderson (2010). We also compared the students’ understanding of heat and mental models on heat conduction. The result shows that Heat is treated as Intrinsic property, material substances, and caloric flow. None of students expressed heat as transfer of thermal energy. Moreover, there are two kinds of students’ fundamental component of mental model in heat conduction were found: medium and molecules. Students understanding of heat and fundamental components of mental model in heat conduction are not resulted from running mental model.
Entropy resistance analyses of a two-stream parallel flow heat exchanger with viscous heating
Institute of Scientific and Technical Information of China (English)
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.
Experimental stand for investigation of fluid flow in heat exchangers with cross-flow arrangement
Directory of Open Access Journals (Sweden)
Łopata Stanisław
2017-01-01
Full Text Available The operation analysis of high-performance heat exchanger with tubes elliptical indicated that the heat exchangers can be subject to damage. The reason for this is probably improper distribution of working fluid in tubular space of heat exchanger. Therefore, a part of the tubes may be improperly cooled and subject to compressible stresses. The paper presents an experimental stand allowing to confirm the given assumption. The experimental investigation enables to examine the mass flow rate in heat exchanger tubes. Also, it is possible to assess the impact of the construction of inlet, intermediate and outlet chambers on the flow distribution within the heat exchanger tubes.
Understanding heat transfer in 2D channel flows including recirculation
Dirkse, M.H.; Loon, van W.K.P.; Stigter, J.D.; Bot, G.P.A.
2007-01-01
Inviscid, irrotational two-dimensional flows can be modelled using the Schwarz¿Christoffel integral. Although bounded flows including boundary layer separation and recirculation are not irrotational, a model is presented that uses the Schwarz¿Christoffel integral to model these flows. The model sepa
Directory of Open Access Journals (Sweden)
A. Al-Witry
2013-05-01
Full Text Available This study compares CFD analyses of the fluid flow and heat transfer phenomena in a popular pin-fin geometry of X/D = 2.5, S/D = 2.5 and H/D = 1 for a range of Re = 5,000 to 30,000 to those from experiment to aid in the benchmarking the performance of the CFD code FLUENT. The CFD analyses use three ANSYS-FLUENT (version 13 near wall treatments available within the code: 1 the Standard Wall Function (SWF, 2 the Non-Equilibrium Wall Function (NEWF and 3 the enhanced wall treatment. Experimental data used in this study were obtained from two papers: 1 by Chyu et al. (1998 for heat transfer predictions and another 2 by Metzgeret al. (1984 for pressure loss predictions, both for the same setup. The study also differentiates between the heat transfer occurring by the body of the pin-fin itself and that by the end-wall areas surrounding it. Results from the CFD analyses based on the fourth pin-fin from the inlet (commonly assumed to have a stable flow around it, show very good prediction accuracies of heat transfer coefficients for the pin-fin body itself but rather low accuracies for the end-wall areas (based on heat flux and inlet temperature values. Better accuracies were obtained when using the enhanced wall treatment where pin-fin body heat transfer coefficients were almost identical between the CFD and experimental results. An alternative definition of heat transfer based on the averaged local temperatures around the fourth pin-fin showed that the heat transfer coefficient then (with CFD's capability to establish the local thermal field is really between 1.5 to 3.5 times that predicted by using the inlet temperature in deducing the local h values. The same accuracies cannot be said about its predictions of pressure loss coefficients where CFD results tended to be lower by 50-100%h.
Modelling of the Czochralski flow
Jan Franc
1998-01-01
The Czochralski method of the industrial production of a silicon single crystal consists of pulling up the single crystal from the silicon melt. The flow of the melt during the production is called the Czochralski flow. The mathematical description of the flow consists of a coupled system of six P.D.E. in cylindrical coordinates containing Navier-Stokes equations (with the stream function), heat convection-conduction equations, convection-diffusion equation for oxygen impurity and an equation...
A fictitious domain method for particulate flows with heat transfer
Yu, Z.; Yu, Zhaosheng; Shao, Xueming; Wachs, Anthony
2006-01-01
The distributed-Lagrange-multiplier/fictitious-domain (DLM/FD) method of Glowinski et al. [R. Glowinski, T.-W. Pan, T.I. Hesla, D.D. Joseph, A distributed Lagrange multiplier/fictitious domain method for particulate flows, Int. J. Multiphase Flow 25 (1999) 755–794] is extended to deal with heat
An Immersed Boundary Method for Complex Flow and Heat Transfer
Paravento, F.; Pourquie, M.J.; Boersma, B.J.
2007-01-01
The need to predict flow and heat transfer problems requires a flexible and fast tool able to simulate complex geometries without increasing the complexity of the flow solver architecture. Here we use a finite volume code that uses a direct solver with pressure correction. A new immersed boundary me
A fictitious domain method for particulate flows with heat transfer
Yu, Zhaosheng; Shao, Xueming; Wachs, Anthony
2006-01-01
The distributed-Lagrange-multiplier/fictitious-domain (DLM/FD) method of Glowinski et al. [R. Glowinski, T.-W. Pan, T.I. Hesla, D.D. Joseph, A distributed Lagrange multiplier/fictitious domain method for particulate flows, Int. J. Multiphase Flow 25 (1999) 755–794] is extended to deal with heat tran
Site-Scale Saturated Zone Flow Model
Energy Technology Data Exchange (ETDEWEB)
G. Zyvoloski
2003-12-17
The purpose of this model report is to document the components of the site-scale saturated-zone flow model at Yucca Mountain, Nevada, in accordance with administrative procedure (AP)-SIII.lOQ, ''Models''. This report provides validation and confidence in the flow model that was developed for site recommendation (SR) and will be used to provide flow fields in support of the Total Systems Performance Assessment (TSPA) for the License Application. The output from this report provides the flow model used in the ''Site-Scale Saturated Zone Transport'', MDL-NBS-HS-000010 Rev 01 (BSC 2003 [162419]). The Site-Scale Saturated Zone Transport model then provides output to the SZ Transport Abstraction Model (BSC 2003 [164870]). In particular, the output from the SZ site-scale flow model is used to simulate the groundwater flow pathways and radionuclide transport to the accessible environment for use in the TSPA calculations. Since the development and calibration of the saturated-zone flow model, more data have been gathered for use in model validation and confidence building, including new water-level data from Nye County wells, single- and multiple-well hydraulic testing data, and new hydrochemistry data. In addition, a new hydrogeologic framework model (HFM), which incorporates Nye County wells lithology, also provides geologic data for corroboration and confidence in the flow model. The intended use of this work is to provide a flow model that generates flow fields to simulate radionuclide transport in saturated porous rock and alluvium under natural or forced gradient flow conditions. The flow model simulations are completed using the three-dimensional (3-D), finite-element, flow, heat, and transport computer code, FEHM Version (V) 2.20 (software tracking number (STN): 10086-2.20-00; LANL 2003 [161725]). Concurrently, process-level transport model and methodology for calculating radionuclide transport in the saturated zone at Yucca
Energy Technology Data Exchange (ETDEWEB)
Hsieh, Huai-En; Chen, Mei-Shiue; Chen, Jyun-Wei; Lin, Wei-Keng; Pei, Bau-Shei [National Tsing Hua Univ., Taiwan (China). Inst. of Nuclear Engineering and Science
2015-05-15
Boiling heat transfer has a high heat removal capability in convective cooling. However, the heat removal capability of downward-facing boiling is significantly worse than that of upward-facing cases because of the confined buoyancy effect. This study was inspired by the conception of external reactor vessel cooling (ERVC) condition relevant to the in-vessel retention (IVR) design of Westinghouse AP1000 plant. In the present study, a small-scale test facility had been established to investigate the local phenomena of boiling heat transfer under a downward-facing horizontal heated surface with impinging coolant flow. In this study, the surface temperature, heat flux information and several specific scenes of bubbles are taken down throughout the boiling processes for detailed investigation. It is observed that bubbles are confined under the downward-facing heated surface, which causes a worse heat transfer rate and a lower critical heat flux (CHF) limit than upward-facing boiling. Nevertheless, the impinging coolant flow is found to disturb the thermal boundary layer formed by the heated surface, so the CHF increases with an increase of coolant flow rate. In addition, during nucleate boiling, it is discovered that the growth, combination and dissipation of bubbles induce turbulent wakes and therefore enhance the heat transfer capability.
Flow and heat transfer of petal shaped double tube
Shakouchi, Toshihiko; Kawashima, Yuki; Tsujimoto, Koichi; Ando, Toshitake
2014-06-01
In this study, the flow and heat transfer characteristics of petal-shaped double tube with 6 petals are examined experimentally for a compact heat exchanger. As results, the heat transfer rate, Q, of the 6 petal shaped double tube (6-p tube) is much larger than that, Qp, of conventional circular double tube in all Reynolds number Rein,h (where, the reference length is hydraulic diameter) ranges. For example, at Rein,h =(0.5～1.0)× 104 it is about 4 times of Qp. The heat transfer enhancement of 6-p tube is by the increase of heat transfer area, wetting perimeter, and a highly fluctuating flow, and Q of the 6-p tube can be expressed by Q [kW/m] = 0.54Rein,h + 2245.
DNS of turbulent channel flow subject to oscillatory heat flux
Directory of Open Access Journals (Sweden)
Bukhvostova Anastasia
2014-01-01
Full Text Available In this paper we study the heat transfer in a turbulent channel flow, which is periodically heated through its walls. We consider the flow of air and water vapor using direct numerical simulation. We consider the fluid as a compressible Newtonian gas. We focus on the heat transfer properties of the system, e.g., the temperature difference between the walls and the Nusselt number. We consider the dependence of these quantities on the frequency of the applied heat flux. We observe that the mean temperature difference is quite insensitive to the frequency and that the amplitude of its oscillations is such that its value multiplied by the square root of frequency is approximately constant. Next we add droplets to the channel, which can undergo phase transitions. The heat transfer properties of the channel in the case with droplets are found to increase by more than a factor of two, compared to the situation without droplets.
Majorowicz, Jacek; Chan, Judith; Crowell, James; Gosnold, Will; Heaman, Larry M.; Kück, Jochem; Nieuwenhuis, Greg; Schmitt, Douglas R.; Unsworth, Martyn; Walsh, Nathaniel; Weides, Simon
2014-05-01
relationship determined for other provinces of the Canadian Shield. However, this relationship could not be established for Q estimates from industrial temperatures data for the study area that includes the Taltson Magmatic Zone and neighbouring Buffalo High and Buffalo Utikuma domains to the west. It appears that the spatial wavelength of heat generation change is much smaller than that of heat flow. Thermal modelling of heat flow and heat generation data from the Hunt Well, using mantle heat flow contributions of 15 ± 5 mW m-2 results in lithosphere-asthenosphere boundary depth estimates of near 200 km. This mantle heat flow value is consistent with the range for the stable continental areas, 15 (±3) mW m-2.
A novel compact heat exchanger using gap flow mechanism
Liang, J. S.; Zhang, Y.; Wang, D. Z.; Luo, T. P.; Ren, T. Q.
2015-02-01
A novel, compact gap-flow heat exchanger (GFHE) using heat-transfer fluid (HTF) was developed in this paper. The detail design of the GFHE coaxial structure which forms the annular gap passage for HTF is presented. Computational fluid dynamics simulations were introduced into the design to determine the impacts of the gap width and the HTF flow rate on the GFHE performance. A comparative study on the GFHE heating rate, with the gap widths ranged from 0.1 to 1.0 mm and the HTF flow rates ranged from 100 to 500 ml/min, was carried out. Results show that a narrower gap passage and a higher HTF flow rate can yield a higher average heating rate in GFHE. However, considering the compromise between the GFHE heating rate and the HTF pressure drop along the gap, a 0.4 mm gap width is preferred. A testing loop was also set up to experimentally evaluate the GFHE capability. The testing results show that, by using 0.4 mm gap width and 500 ml/min HTF flow rate, the maximum heating rate in the working chamber of the as-made GFHE can reach 18 °C/min, and the average temperature change rates in the heating and cooling processes of the thermal cycle test were recorded as 6.5 and 5.4 °C/min, respectively. These temperature change rates can well satisfy the standard of IEC 60068-2-14:2009 and show that the GFHE developed in this work has sufficient heat exchange capacity and can be used as an ideal compact heat exchanger in small volume desktop thermal fatigue test apparatus.
A survey of oscillating flow in Stirling engine heat exchangers
Simon, Terrence W.; Seume, Jorge R.
1988-01-01
Similarity parameters for characterizing the effect of flow oscillation on wall shear stress, viscous dissipation, pressure drop and heat transfer rates are proposed. They are based on physical agruments and are derived by normalizing the governing equations. The literature on oscillating duct flows, regenerator and porous media flows is surveyed. The operating characteristics of the heat exchanger of eleven Stirling engines are discribed in terms of the similarity parameters. Previous experimental and analytical results are discussed in terms of these parameters and used to estimate the nature of the oscillating flow under engine operating conditions. The operating points for many of the modern Stirling engines are in or near the laminar to turbulent transition region. In several engines, working fluid does not pass entirely through heat exchangers during a cycle. Questions that need to be addressed by further research are identified.
Experimental investigation on Heat Transfer Performance of Annular Flow Path Heat Pipe
Energy Technology Data Exchange (ETDEWEB)
Kim, In Guk; Kim, Kyung Mo; Jeong, Yeong Shin; Bang, In Cheol [UNIST, Ulsan (Korea, Republic of)
2015-05-15
Mochizuki et al. was suggested the passive cooling system to spent nuclear fuel pool. Detail analysis of various heat pipe design cases was studied to determine the heat pipes cooling performance. Wang et al. suggested the concept PRHRS of MSR using sodium heat pipes, and the transient performance of high temperature sodium heat pipe was numerically simulated in the case of MSR accident. The meltdown at the Fukushima Daiichi nuclear power plants alarmed to the dangers of station blackout (SBO) accident. After the SBO accident, passive decay heat removal systems have been investigated to prevent the severe accidents. Mochizuki et al. suggested the heat pipes cooling system using loop heat pipes for decay heat removal cooling and analysis of heat pipe thermal resistance for boiling water reactor (BWR). The decay heat removal systems for pressurized water reactor (PWR) were suggested using natural convection mechanisms and modification of PWR design. Our group suggested the concept of a hybrid heat pipe with control rod as Passive IN-core Cooling System (PINCs) for decay heat removal for advanced nuclear power plant. Hybrid heat pipe is the combination of the heat pipe and control rod. In the present research, the main objective is to investigate the effect of the inner structure to the heat transfer performance of heat pipe containing neutron absorber material, B{sub 4}C. The main objective is to investigate the effect of the inner structure in heat pipe to the heat transfer performance with annular flow path. ABS pellet was used instead of B{sub 4}C pellet as cylindrical structures. The thermal performances of each heat pipes were measured experimentally. Among them, concentric heat pipe showed the best performance compared with others. 1. Annular evaporation section heat pipe and annular flow path heat pipe showed heat transfer degradation. 2. AHP also had annular vapor space and contact cooling surface per unit volume of vapor was increased. Heat transfer
Heat Transfer Enhancement Due to Marangoni Flow Around Moving Bubbles During Nucleate Boiling
Institute of Scientific and Technical Information of China (English)
David M. Christopher; WANG Hao; PENG Xiaofeng
2006-01-01
Nucleate boiling is a very efficient method for generating high heat transfer rates from solid surfaces; however, the fundamental physical mechanisms governing nucleate boiling heat transfer are not well understood. The heat transfer mechanisms around stationary and moving bubbles on very thin microwires were analyzed numerically to evaluate the effect of the bubble motion on the heat transfer from the wire surface. The numerical analysis accurately models the experimentally observed bubble movement and fluid velocities. The analytical model includes the effects of the Marangoni flow around the bubble and the evaporation and condensation within the bubble. The analysis shows that the heat transfer was significantly enhanced by the Marangoni flow around the outside of the bubble which transfers at least twice as much energy from the wire as the heat transfer directly from the wire to the bubble. The enhanced heat transfer due to the Marangoni flow was evident for both stationary and moving bubbles. The moving bubbles also created a wake that further enhanced the heat transfer from the wire. Since the Marangoni number for water is greater than for ethanol for the same conditions, the Marangoni flow and, hence, the bubble velocities are predicted to be greater in water than in ethanol.
Heat flow distribution and thermal structure of the Nankai subduction zone off the Kii Peninsula
Hamamoto, Hideki; Yamano, Makoto; Goto, Shusaku; Kinoshita, Masataka; Fujino, Keiko; Wang, Kelin
2011-10-01
Detailed heat flow surveys were carried out in the central part of the Nankai Trough southeast of the Kii Peninsula (off Kumano) for investigation of the thermal structure of the subducting plate interface. At stations in the Kumano Trough (forearc basin) and its vicinity, long-term monitoring of temperature profiles in surface sediments was conducted because bottom water temperature variations (BTV) significantly disturb subbottom sediment temperatures. Heat flow values were successfully determined at seven stations by removing the influence of BTV from temperature records for 300 to 400 days. The surface heat flow data were combined with estimates from depths of methane hydrate bottom simulating reflectors to construct a heat flow profile across the subduction zone. Heat flow decreases from 90-110 mW/m2 on the floor of the Nankai Trough to 50-60 mW/m2 at around 30 km from the deformation front, while it is rather uniform, 40-60 mW/m2, in the Kumano Trough. The values measured on the Nankai Trough floor are concordant with the value estimated from the age of the subducting Philippine Sea plate, about 20 m.y., taking into account the effect of sedimentation. The obtained heat flow profile was used to constrain thermal models of the subduction zone. The subsurface thermal structure was calculated using a two-dimensional, steady state model, in which the frictional heating along the plate interface and the radioactive heat production are treated as unknown parameters. Comparison of the calculated surface heat flow in the Kumano Trough with the observed data indicates that the effective coefficient of friction is small, about 0.1 or less, and thus the shear stress on the plate interface is very low in this subduction zone.
Xu, Huijin; Zhao, Changying; Vafai, Kambiz
2017-08-01
Fully developed forced convective heat transfer in an annulus filled with a porous medium subject to asymmetrical heating is investigated analytically with different models in this work. The classic Darcy and Brinkman models were employed for the fluid flow, while the local thermal equilibrium (LTE) and the local thermal non-equilibrium (LTNE) models were employed to describe the heat transfer process in porous media. An analytical model based on fin theory was also employed for analyzing this problem. Exact solutions with Darcy-LTNE, Darcy-LTE, Brinkman-LTNE, Brinkman-LTE, and the fin models were obtained. Among these solutions, the Brinkman-LTNE solution can be treated as the benchmark, as it is a complete model, which covers the effect of viscous force near the solid wall and the temperature difference between the solid and fluid phases. The basic parameters that affect the velocity and temperature fields were analyzed in depth. The velocity and temperature profiles with these different models were also presented. The effects of some critical parameters on thermal performance of asymmetrically heated annulus fitted with a porous medium were discussed. The cited different analytical models were compared in detail with each other. The critical heat flux (HF) ratios for the inner and outer walls were presented in terms of a Nu- ξ curve for the five models. These solutions were developed for an asymmetrically heated annular channel filled with a porous medium, which can predict the thermal performance within a wide range of radii and HF ratios.
Modelling fluid flow in a reciprocating compressor
Directory of Open Access Journals (Sweden)
Tuhovcak Jan
2015-01-01
Full Text Available Efficiency of reciprocating compressor is strongly dependent on the valves characteristics, which affects the flow through the suction and discharge line. Understanding the phenomenon inside the compressor is necessary step in development process. Commercial CFD tools offer wide capabilities to simulate the flow inside the reciprocating compressor, however they are too complicated in terms of computational time and mesh creation. Several parameters describing compressor could be therefore examined without the CFD analysis, such is valve characteristic, flow through the cycle and heat transfer. The aim of this paper is to show a numerical tool for reciprocating compressor based on the energy balance through the cycle, which provides valve characteristics, flow through the cycle and heat losses from the cylinder. Spring-damping-mass model was used for the valve description. Boundary conditions were extracted from the performance test of 4-cylinder semihermetic compressor and numerical tool validation was performed with indicated p-V diagram comparison.
Modelling fluid flow in a reciprocating compressor
Tuhovcak, Jan; Hejčík, Jiří; Jícha, Miroslav
2015-05-01
Efficiency of reciprocating compressor is strongly dependent on the valves characteristics, which affects the flow through the suction and discharge line. Understanding the phenomenon inside the compressor is necessary step in development process. Commercial CFD tools offer wide capabilities to simulate the flow inside the reciprocating compressor, however they are too complicated in terms of computational time and mesh creation. Several parameters describing compressor could be therefore examined without the CFD analysis, such is valve characteristic, flow through the cycle and heat transfer. The aim of this paper is to show a numerical tool for reciprocating compressor based on the energy balance through the cycle, which provides valve characteristics, flow through the cycle and heat losses from the cylinder. Spring-damping-mass model was used for the valve description. Boundary conditions were extracted from the performance test of 4-cylinder semihermetic compressor and numerical tool validation was performed with indicated p-V diagram comparison.
Heat transfer intensification by increasing vapor flow rate in flat heat pipes
Sprinceana, Silviu; Mihai, Ioan; Beniuga, Marius; Suciu, Cornel
2015-02-01
Flat heat pipes have various technical applications, one of the most important being the cooling of electronic components[9]. Their continuous development is due to the fact that these devices permit heat transfer without external energetic contribution. The practical exploitation of flat heat pipes however is limited by the fact that dissipated power can only reach a few hundred watts. The present paper aims to advance a new method for the intensification of convective heat transfer. A centrifugal mini impeller, driven by a turntable which incorporates four permanent magnets was designed. These magnets are put in motion by another rotor, which in its turn includes two permanent magnets and is driven by a mini electrical motor. Rotation of the centrifugal blades generates speed and pressure increase of the cooling agent brought to vapor state within the flat micro heat pipe. It's well known that the liquid suffers biphasic transformations during heat transfer inside the heat pipe. Over the hotspot (the heat source being the electronic component) generated at one end of the heat pipe, convective heat transfer occurs, leading to sudden vaporization of the liquid. Pressures generated by newly formed vapors push them towards the opposite end of the flat heat pipe, where a finned mini heat sink is usually placed. The mini-heat exchanger is air-cooled, thus creating a cold spot, where vapors condensate. The proposed method contributes to vapor flow intensification by increasing their transport speed and thus leading to more intense cooling of the heat pipe.
Heat flow, heat transfer and lithosphere rheology in geothermal areas: Features and examples
Ranalli, G.; Rybach, L.
2005-10-01
Surface heat flow measurements over active geothermal systems indicate strongly positive thermal anomalies. Whereas in "normal" geothermal settings, the surface heat flow is usually below 100-120 mW m - 2 , in active geothermal areas heat flow values as high as several watts per meter squared can be found. Systematic interpretation of heat flow patterns sheds light on heat transfer mechanisms at depth on different lateral, depth and time scales. Borehole temperature profiles in active geothermal areas show various signs of subsurface fluid movement, depending on position in the active system. The heat transfer regime is dominated by heat advection (mainly free convection). The onset of free convection depends on various factors, such as permeability, temperature gradient and fluid properties. The features of heat transfer are different for single or two-phase flow. Characteristic heat flow and heat transfer features in active geothermal systems are demonstrated by examples from Iceland, Italy, New Zealand and the USA. Two main factors affect the rheology of the lithosphere in active geothermal areas: steep temperature gradients and high pore fluid pressures. Combined with lithology and structure, these factors result in a rheological zonation with important consequences both for geodynamic processes and for the exploitation of geothermal energy. As a consequence of anomalously high temperature, the mechanical lithosphere is thin and its total strength can be reduced by almost one order of magnitude with respect to the average strength of continental lithosphere of comparable age and thickness. The top of the brittle/ductile transition is located within the upper crust at depths less than 10 km, acts as the root zone of listric normal faults in extensional environments and, at least in some cases, is visible on seismic reflection lines. These structural and rheological features are well illustrated in the Larderello geothermal field in Tuscany.
Assessment of heat sources on the control of fast flow of Vestfonna ice cap, Svalbard
Schäfer, M.; Gillet-Chaulet, F.; Gladstone, R.; Pettersson, R.; Pohjola, V. A.; Strozzi, T.; Zwinger, T.
2014-10-01
Understanding the response of fast flowing ice streams or outlet glaciers to changing climate is crucial in order to make reliable projections of sea level change over the coming decades. Motion of fast outlet glaciers occurs largely through basal motion governed by physical processes at the glacier bed, which are not yet fully understood. Various subglacial mechanisms have been suggested for fast flow but common to most of the suggested processes is the requirement of presence of liquid water, and thus temperate conditions. We use a combination of modelling, field, and remote observations in order to study links between different heat sources, the thermal regime and basal sliding in fast flowing areas on Vestfonna ice cap. A special emphasis lies on Franklinbreen, a fast flowing outlet glacier which has been observed to accelerate recently. We use the ice flow model Elmer/Ice including a Weertman type sliding law and a Robin inverse method to infer basal friction parameters from observed surface velocities. Firn heating, i.e. latent heat release through percolation of melt water, is included in our model; its parameterisation is calibrated with the temperature record of a deep borehole. We found that strain heating is negligible, whereas friction heating is identified as one possible trigger for the onset of fast flow. Firn heating is a significant heat source in the central thick and slow flowing area of the ice cap and the essential driver behind the ongoing fast flow in all outlets. Our findings suggest a possible scenario of the onset and maintenance of fast flow on the Vestfonna ice cap based on thermal processes and emphasise the role of latent heat released through refreezing of percolating melt water for fast flow. However, these processes cannot yet be captured in a temporally evolving sliding law. In order to simulate correctly fast flowing outlet glaciers, ice flow models not only need to account fully for all heat sources, but also need to incorporate
A study of sensing heat flow through thermal walls by using thermoelectric module
Directory of Open Access Journals (Sweden)
Sippawit Noppawit
2015-01-01
Full Text Available Demands on heat flow detection at a plane wall via a thermoelectric module have drawn researchers’ attention to quantitative understanding in order to properly implement the thermoelectric module in thermal engineering practices. Basic mathematical models of both heat transfer through a plane wall and thermoelectric effects are numerically solved to represent genuine behaviors of heat flow detection by mounting a thermoelectric module at a plane wall. The heat transfer through the plane wall is expected to be detected. It is intriguing from simulation results that the heat rejected at the plane wall is identical to the heat absorbed by the thermoelectric module when the area of the plane wall is the same as that of the thermoelectric module. Furthermore, both the area sizes of the plane walls and the convective heat transfer coefficients at the wall influence amount of the heat absorbed by the thermoelectric module. Those observational data are modeled for development of sensing heat flow through a plane wall by a thermoelectric module in practical uses.
Analytical models for complex swirling flows
Borissov, A.; Hussain, V.
1996-11-01
We develops a new class of analytical solutions of the Navier-Stokes equations for swirling flows, and suggests ways to predict and control such flows occurring in various technological applications. We view momentum accumulation on the axis as a key feature of swirling flows and consider vortex-sink flows on curved axisymmetric surfaces with an axial flow. We show that these solutions model swirling flows in a cylindrical can, whirlpools, tornadoes, and cosmic swirling jets. The singularity of these solutions on the flow axis is removed by matching them with near-axis Schlichting and Long's swirling jets. The matched solutions model flows with very complex patterns, consisting of up to seven separation regions with recirculatory 'bubbles' and vortex rings. We apply the matched solutions for computing flows in the Ranque-Hilsch tube, in the meniscus of electrosprays, in vortex breakdown, and in an industrial vortex burner. The simple analytical solutions allow a clear understanding of how different control parameters affect the flow and guide selection of optimal parameter values for desired flow features. These solutions permit extension to other problems (such as heat transfer and chemical reaction) and have the potential of being significantly useful for further detailed investigation by direct or large-eddy numerical simulations as well as laboratory experimentation.
Atomistic-Continuum Hybrid Simulation of Heat Transfer between Argon Flow and Copper Plates
Mao, Yijin; Chen, C L
2016-01-01
A simulation work aiming to study heat transfer coefficient between argon fluid flow and copper plate is carried out based on atomistic-continuum hybrid method. Navier-Stokes equations for continuum domain are solved through the Pressure Implicit with Splitting of Operators (PISO) algorithm, and the atom evolution in molecular domain is solved through the Verlet algorithm. The solver is validated by solving Couette flow and heat conduction problems. With both momentum and energy coupling method applied, simulations on convection of argon flows between two parallel plates are performed. The top plate is kept as a constant velocity and has higher temperature, while the lower one, which is modeled with FCC copper lattices, is also fixed but has lower temperature. It is found that, heat transfer between argon fluid flow and copper plate in this situation is much higher than that at macroscopic when the flow is fully developed.
Heat flow effect on the plasma line frequency
Energy Technology Data Exchange (ETDEWEB)
Kofman, W.; St.Maurice, J.P. (Centre d' Etude des Phenomenes Aleatories et Geophysique, St. Martin d' Heres (France)); Eyken A.P. van (EISCAT Scientific Association, Ramfjordmoen (Norway))
1993-04-01
The authors report on new electron plasma line experiments performed from the Tromso radar station, in the backscatter mode, which means they used the downshifted and upshifted plasma lines. The data were collected in May, 1992, on three days which were very quiet magnetically. They observe a bias between the upshifted and downshifted lines and the calculated results from evaluation of the standard dispersion relations. The authors are able to account for this difference by adding a heat flow term involving electrons to the standard theoretical model. This correction is important if one is looking at systematics in the differences in these two measurement modes with accuracies in the kHz range. It is also a factor of import if one is making measurements in areas where the temperature gradient can be 1 K/km or more.
Loyd, S J; Becker, T W; Conrad, C P; Lithgow-Bertelloni, C; Corsetti, F A
2007-09-04
The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by approximately 0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past.
Directory of Open Access Journals (Sweden)
Hosahalli S. Ramaswamy
2011-01-01
Full Text Available A domestic microwave oven (1000 W was modified to permit the continuous flow of liquids run through a helical coil centrally located inside the oven cavity. Heating characteristics were evaluated by measuring inlet and outlet temperatures of coil as a function of system variables. The influence of number of turns, coil diameter, tube diameter, pitch and initial temperature were evaluated at different flow rates. The average residence time of water was computed by dividing the coil volume by the volumetric flow rate. The influence of Dean number was evaluated. Results from this study showed that (1 higher number of turns resulted in lower heating rate, lower temperature fluctuations, higher exit temperature and longer time to achieve temperature equilibrium; (2 larger tube or coil diameter gave larger coil volume causing the heating rate to decrease; (3 faster flow rates resulted in lower exit temperatures, lower temperature fluctuation, higher Dean number and slightly higher heating rate; (4 higher initial temperatures resulted in higher exit temperatures; (5 higher Dean number resulted in more uniform heating and slightly higher heating rate. Overall, the coil volume was the more dominant factor affecting heating rate as compared with flow rate and Dean number.
Institute of Scientific and Technical Information of China (English)
卢威; 黄家荣; 范宇峰; 钟奇
2011-01-01
In order to solve the complex heat lransfer problem coupled with air flow, solid conduction and radiacion in a manned spacecraft pressurized cabin, a numerical model of flow and heat transfer for the manned spacecraft pressurized cabin is built. The simulation and analysis of air flow and heat transfer are performed under ground test conditions, and the numerical model is suhsequently validated by test results. The results indicate that the numerical model is reliable wiih a high fidelity, and the simulation results using this model are found to highly agree with the ground test data, which could be further used for performance assessment of thermal control system( TCS) , orbit support and failure management.%为求解载人航天器密封舱内复杂的空气对流、导热和辐射三者耦合的传热问题,本文建立了载人航天器密封舱的流动与传热数值模型,对地面试验状态下密封舱内的空气流动与传热进行了仿真分析,并利用试验结果对数值模型进行了验证.结果表明,建立的数值模型可靠且具有较高精度,仿真结果与地面试验数据吻合性较好,可进一步用于热控系统性能评估、在轨支持和故障处理.
Traffic flow modeling: a Genealogy
Van Wageningen-Kessels, F.L.M.; Hoogendoorn, S.P.; Vuik, C.; Van Lint, J.W.C.
2014-01-01
80 years ago, Bruce Greenshields presented the first traffic flow model at the Annual Meeting of the Highway Research Board. Since then, many models and simulation tools have been developed. We show a model tree with four families of traffic flow models, all descending from Greenshields' model. The
Convective Heat Transfer Analysis in Fluid Flow with Turbulence Promoters with Heat Pipes
Directory of Open Access Journals (Sweden)
Theodor Mateescu
2007-01-01
Full Text Available The present paper proposes the analysis and the simulation of the convection heat transfer into the fluid flow with turbulence promoters utilizing heat pipes. The study is based on the necesity of the unconventional energy forms capitalization, increasing of the energy efficiency and leads to the energy consumtion decrease in concordance with the sustainable development concept.
Analysis of the heat transfer in unsymmetrically heated triangular microchannels in slip flow regime
Institute of Scientific and Technical Information of China (English)
ZHU; Xun; LIAO; Qiang; XIN; Mingdao
2004-01-01
A theoretical analysis of heat transfer characteristics is presented for the fully developed laminar flow of the incompressible gas in the triangular microchannels heated unsymmetrically with constant axial heat flux. Through solving the energy equation with temperature jump boundary conditions in slip flow regime by virtue of a computationoriented method of the orthonormal function analysis, the dimensionless temperature profiles and the average Nusselt number for various thermal boundary conditions are obtained. The effects of Knudsen number, aspect ratio, and thermal boundary conditions on the heat transfer are discussed. The calculated results show that the orthonormal function method can be used to study the heat transfer characteristics of the unsymmetrically heated triangular microchannels. The average Nusselt number in triangular microchannels is lower for slip flow than for no-slip flow, and decreases with increasing Knudsen number. The aspect ratios and thermal boundary conditions of triangular microchannels have significant influences on the change of average Nusselt numbers with the increase in the Knudsen number. For the equilateral triangular microchannels, the decrease of the Nusselt number ratio due to temperature jump is smaller at large Knudsen number and larger at small Knudsen number on the boundary condition of bottom wall heated alone as compared with the one on the boundary condition of two heated hypotenuse walls. The correlations of the average Nusselt number with the Knudsen number for equilateral triangular microchannels are obtained.
Transectional heat transfer in thermoregulating bigeye tuna (Thunnus obesus) - a 2D heat flux model.
Boye, Jess; Musyl, Michael; Brill, Richard; Malte, Hans
2009-11-01
We developed a 2D heat flux model to elucidate routes and rates of heat transfer within bigeye tuna Thunnus obesus Lowe 1839 in both steady-state and time-dependent settings. In modeling the former situation, we adjusted the efficiencies of heat conservation in the red and the white muscle so as to make the output of the model agree as closely as possible with observed cross-sectional isotherms. In modeling the latter situation, we applied the heat exchanger efficiencies from the steady-state model to predict the distribution of temperature and heat fluxes in bigeye tuna during their extensive daily vertical excursions. The simulations yielded a close match to the data recorded in free-swimming fish and strongly point to the importance of the heat-producing and heat-conserving properties of the white muscle. The best correspondence between model output and observed data was obtained when the countercurrent heat exchangers in the blood flow pathways to the red and white muscle retained 99% and 96% (respectively) of the heat produced in these tissues. Our model confirms that the ability of bigeye tuna to maintain elevated muscle temperatures during their extensive daily vertical movements depends on their ability to rapidly modulate heating and cooling rates. This study shows that the differential cooling and heating rates could be fully accounted for by a mechanism where blood flow to the swimming muscles is either exclusively through the heat exchangers or completely shunted around them, depending on the ambient temperature relative to the body temperature. Our results therefore strongly suggest that such a mechanism is involved in the extensive physiological thermoregulatory abilities of endothermic bigeye tuna.
Flow Structure and Heat Transfer Between Two Disks Rotating Independently
Institute of Scientific and Technical Information of China (English)
Chyi-Yeou Soong
2003-01-01
In the present paper, fluid flow and convective heat transfer between two co-axial disks rotating independently are dealt with mainly based on the author's recent research on that topic. Three rotational modes, i.e. co-rotation, rotor-stator, and counter-rotation, are considered. Theory of rotating non-isothermal fluids with the presence of disk rotation and thermal effects is addressed. Rotational buoyancy effects on the flow structure development are highlighted. Results of flow visualization and heat transfer measurements are discussed to explore the thermal flow mechanisms involved in the two-disk flows at various rotational and geometric conditions. Potential issues open to the future investigation are also proposed.
Degradation of the performance of microchannel heat exchangers due to flow maldistribution
DEFF Research Database (Denmark)
Nielsen, Kaspar Kirstein; Engelbrecht, Kurt; Christensen, Dennis;
2012-01-01
The effect of flow maldistribution on the performance of microchannel parallel plate heat exchangers is investigated using an established single blow numerical model and cyclic steady-state regenerator experiments. It is found that as the variation of the individual channel thickness...... in a particular stack (heat exchanger) increases the actual performance of the heat exchanger decreases significantly, deviating from the expected nominal performance. We show that this is due to both the varying fluid flow velocities in each individual channel and the thermal cross talk between the channels...
Institute of Scientific and Technical Information of China (English)
Jihua HU; Yanjun ZHANG; Danyan DU; Gang WU; Ziwang YU; Chen WANG; Fuquan NI
2008-01-01
Energy utilization in the aquifers is a new technology closely related to development of heat pump technique. It is significant for the flow distribution to be predicted in the aquifer surrounding the Groundwater Source Heat Pump System (GSHPS). The authors presented a new concept of "flow transfixion" by analyzing general features of aquifers, and then discussed interaction of the flow transfixion with the heat transfixion, which has practical significance to projects. A numerical model of groundwater flow was established based on the basic tenets of water-heat transferring in the aquifer. On this basis the flow field and the temperature field of GSHPS for a site in Shenyang City were numerically simulated. The basis of the flow transfixion was obtained; it was discussed for the influence of the flow transfixion on the heat transfixion. To a certain extent, the study offers some reference for the projects' design of GSHP in the studied area.
Energy Technology Data Exchange (ETDEWEB)
Lee, Juhyung; Chang, Soon Heung [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of); Jo, Daeseong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2013-10-15
Subcooled flow boiling in a vertical rectangular channel was experimentally investigated to enhance the understanding of the CHF and the effect of the two-phase flow instability on it under low pressure conditions, especially for downward flow which was adopted for Jordan Research and Training Reactor (JRTR) and Kijang research reactor (KJRR) to achieve easier fuel and irradiation rig loading. In addition, visual observations of subcoold flow boiling was conducted by using high-speed video (HSV) for a clear understanding of both phenomena. We concluded that flow excursion (which is static instability) could be induced due to the OPDF (which is dynamic instability) when a system has no resistibility to the pressure drop perturbation, which is caused by the coalescence of facing bubbles on opposing heated surfaces. In more stable system with throttling applied, flow rate could be maintained and stable CHF could be reached. The static flow instability (FI) and critical heat flux (CHF) for subcooled flow boiling in a vertical narrow channels under low pressure condition are fairly crucial phenomena relative to thermal-hydraulic design and safety analysis for pool-type research reactors. It has been recommended that RRs and MTRs be designed to have sufficient margins for CHF and the onset of FI as well, since unstable flow could leads to premature CHF under very low wall heat flux in comparison to stable CHF. Even the fact and previous studies, however, the understanding of relationship among FI, premature CHF and stable CHF is not sufficient to date.
LARGE EDDY SIMULATION OF FREE SURFACE TURBULENT CHANNEL FLOW WITH HEAT TRANSFER
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
In this paper, the Large Eddy Simulation (LES) was used to study the free-surface turbulent channel flow with passive heat transfer. The three-dimensional filtered incompressible Navier-Stokes equations and energy equation were numerically solved with dynamic Subgrid Scale (SGS) models for modeling turbulent stresses and heat flux. To compare the turbulent behavior of the free-surface and two-walled channel flows, the LES of two-walled turbulent channel flow was performed. The statistical quantities and flow structures of the free-surface turbulence with heat transfer in the vicinity of the free-surface were investigated. The results are also in good agreement with theoretical analysis and available results by Direct Numerical Simulation (DNS).
Influence of magmatism on mantle cooling, surface heat flow and Urey ratio
Nakagawa, Takashi; Tackley, Paul J.
2012-05-01
Two-dimensional thermo-chemical mantle convection simulations are used to investigate the influence of melting-inducted differentiation on the thermal evolution of Earth's mantle, focussing in particular on matching the present-day surface heat flow and the 'Urey ratio'. The influence of internal heating rate, initial mantle temperature and partitioning of heat-producing elements into basaltic crust are studied. High initial mantle temperatures, which are expected following Earth's accretion, cause major differences in early mantle thermo-chemical structures, but by the present-day surface heat flux and internal structures are indistinguishable from cases with a low initial temperature. Assuming three different values of mantle heat production that vary by more than a factor of two results in small differences in present-day heat flow, as does assuming different partitioning ratios of heat-producing elements into crust. Indeed, all of the cases presented here, regardless of exact parameters, have approximately Earth's present-day heat flow, with substantial fractions coming from the core and from mantle cooling. As a consequence of the model present-day surface heat flow varying only slightly with parameters, the Urey ratio (the ratio of total heat production to the total surface heat flow) is highly dependent on the amount of internal heat production, and due to the large uncertainty in this, the Urey ratio is considered to be a much poorer constraint on thermal evolution than the heat flow. The range of present-day Urey ratio observed in simulations here is about 0.3 to 0.5, which is consistent with observational and geochemical constraints (Jaupart et al., 2007). Magmatic heat transport contributes an upper bound of 9% to Earth's present-day heat loss but a much higher fraction at earlier times—often more than convective heat loss—so neglecting this causes an overestimation of the Urey ratio. Magmatic heat transport also plays an important role in mantle
An experimental investigation of flow boiling heat transfer of R-141b and R-1234yf in microchannels
Directory of Open Access Journals (Sweden)
Shamirzaev Alisher
2017-01-01
Full Text Available This study presents experimental results of flow boiling heat transfer of refrigerants R-141b and R-1234yf in a horizontal microchannel heat sink. The copper microchannel heat sink contains 21 microchannels with 335×930 μm cross-section. Distribution of local heat transfer coefficients along the length and width of the microchannel plate were measured in the range of external heat fluxes from 50 to 550 kW/m2. Finally, comparisons with predictions according to the model of flow boiling heat transfer are reported for the data sets.
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.
Directory of Open Access Journals (Sweden)
M. Das
2015-12-01
Full Text Available The influence of Newtonian heating on heat and mass transfer in unsteady hydromagnetic flow of a Casson fluid past a vertical plate in the presence of thermal radiation and chemical reaction is studied. The Casson fluid model is used to distinguish the non-Newtonian fluid behavior. The fluid flow is induced due to periodic oscillations of the plate along its length and a uniform transverse magnetic field is applied in a direction which is normal to the direction of fluid flow. The partial differential equations governing the flow, heat, and mass transfer are transformed to non-dimensional form using suitable non-dimensional variables which are then solved analytically by using Laplace transform technique. The numerical values of the fluid velocity, fluid temperature, and species concentration are depicted graphically whereas the values of skin-friction, Nusselt number, and Sherwood number are presented in tabular form. It is noticed that the fluid velocity and temperature decrease with increasing values of Casson parameter while concentration decreases with increasing values of chemical reaction parameter and Schmidt number. Such a fluid flow model has several industrial and medical applications such as in glass manufacturing, paper production, purification of crude oil and study of blood flow in the cardiovascular system.
Diffusive heat and mass transfer in oscillatory pipe flow
Brereton, G. J.; Jalil, S. M.
2017-07-01
The enhancement of axial heat and mass transfer by laminar flow oscillation in pipes with axial gradients in temperature and concentration has been studied analytically for the cases of insulated and conducting walls. The axial diffusivity can exceed its molecular counterpart by many orders of magnitude, with a quadratic scaling on the pressure-gradient amplitude and the Prandtl or Schmidt number, and is a bimodal function of oscillatory frequency: quasi-steady behavior at low frequencies and a power-law decay at high frequencies. When the pipe wall is conductive and of sufficient thickness, and the flow oscillation is quasi-steady, the axial diffusivity may be enhanced by a further factor of about ten as a result of increased radial diffusion, for liquid and gas flows in pipes with walls with a wide range of thermal conductivities. Criteria for the wall thickness required to achieve this additional enhancement and for the limits placed on the validity of these solutions by viscous dissipation are also deduced. When the heat transfer per unit flow work achieved by oscillatory pipe flow is contrasted with that of a conventional parallel-flow heat exchanger, it is found to be of comparable size and the ratio of the two is shown to be a function only of the pipe geometry, heat-exchanger mean velocity, and fluid viscosity.
Brine flow in heated geologic salt.
Energy Technology Data Exchange (ETDEWEB)
Kuhlman, Kristopher L.; Malama, Bwalya
2013-03-01
This report is a summary of the physical processes, primary governing equations, solution approaches, and historic testing related to brine migration in geologic salt. Although most information presented in this report is not new, we synthesize a large amount of material scattered across dozens of laboratory reports, journal papers, conference proceedings, and textbooks. We present a mathematical description of the governing brine flow mechanisms in geologic salt. We outline the general coupled thermal, multi-phase hydrologic, and mechanical processes. We derive these processes governing equations, which can be used to predict brine flow. These equations are valid under a wide variety of conditions applicable to radioactive waste disposal in rooms and boreholes excavated into geologic salt.
Duangthongsuk Weerapun
2017-01-01
This article presents an experimental investigation on the heat transfer performance and pressure drop characteristic of two types of nanofluids flowing through microchannel heat sink with multiple zigzag flow channel structures (MZMCHS). SiO2 nanoparticles dispersed in DI water with concentrations of 0.3 and 0.6 vol.% were used as working fluid. MZMCHS made from copper material with dimension of 28 × 33 mm. Hydraulic diameter of MZMCHs is designed at 1 mm, 7 number of flow channels and heat ...
Experimental and Exergy Analysis of A Double Pipe Heat Exchanger for Parallel Flow Arrangement
Directory of Open Access Journals (Sweden)
Parth P. Parekh
2014-07-01
Full Text Available This paper presents For Experimental and Exergy Analysis of a Double Pipe Heat Exchanger for Parallel- flow Arrangement. The Double pipe heat exchanger is one of the Different types of heat exchangers. double-pipe exchanger because one fluid flows inside a pipe and the other fluid flows between that pipe and another pipe that surrounds the first.In a parallel flow, both the hot and cold fluids enter the Heatexchanger at same end andmove in same direction. The present work is taken up to carry experimental work and the exergy analysis based on second law analysis of a Double-Pipe Heat Exchanger. In experimental set up hot water and cold water will be used working fluids. The inlet Hot water will be varied from 40 0C and 50 0C and cold water temperature will be varied from between 15 and 20 0C. It has been planned to find effects of the inlet condition of both working fluid flowing through the heat exchanger on the heat transfer characteristics, entropy generation, and Exergy loss. The Mathematical modelling of heat exchanger will based on the conservation equation of mass, energy and based on second law of thermodynamics to find entropy generation and exergy losses.
Energy Technology Data Exchange (ETDEWEB)
Park, Cheol
1998-02-15
Empirical and phenomenological investigations have been performed for countercurrent and cocurrent annular flow critical heat fluxes(CHFs) under low flow conditions. The CHF characteristics on finned surfaces were also examined by experiments and analyses for finned and unfinned geometries. A new form of C{sub w}{sup 2} in the Wallis flooding correlation was proposed for a general use in predicting the flooding limited CHF at tubes, annuli and rectangular channels under zero and very low flow conditions. The suggested correlation showed reasonable predictions compared to the measured CHF with an root-mean-square(RMS) error of 18.8%. A physical model for the prediction of a CHF location at a zero inlet flow condition was improved to take into account entrainment from the liquid film and to extend the applicable range to subcooled inlet flow conditions. The improved model showed reasonable agreements with the Katto data, and provided details of the CHF mechanism due to flooding. It was analytically confirmed that the flooding is a triggering mechanism of a countercurrent annular flow CHF under zero and very low flow conditions. It was also revealed that the heat flux effect such as the nucleation induced entrainment in the liquid film should be considered for the analysis of a flooding limited CHF, especially in small L/D geometry. In addition, an attempt was made to predict CHF values by applying the improved model with predetermined CHF locations. The results showed that the predictions by the improved physical model agreed reasonably with the experimental data. Annular flow hydrodynamic models of Whalley, Levy and Katto, which were developed for high flow conditions, were compared with available low flow CHF data to make out the applicability of the models to low flow conditions. As a result, it was found that Katto model, which improved the fault of Whally and Levy models, could be applied to predict low flow CHF with some improvements although the model
Heat Transfer Model for Hot Air Balloons
Llado-Gambin, Adriana
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 modeling based on typical thermal input from a balloon propane burner. The burner duty cycle to keep a constant altitude can vary from 10% to 28% depending on the atmospheric conditions, and the ambient temperature is the parameter that most affects the total thermal input needed. The simulation and analysis also predict that the gas temperature inside the balloon decreases at a rate of -0.25 K/s when there is no burner activity, and it increases at a rate of +1 K/s when the balloon pilot operates the burner. The results were compared to actual flight data and they show very good agreement indicating that the major physical processes responsible for balloon performance aloft are accurately captured in the simulation.
Effect of particle loading on heat transfer enhancement in a gas-solid suspension cross flow
Institute of Scientific and Technical Information of China (English)
周劲松; 骆仲泱; 高翔; 倪明江; 岑可法
2002-01-01
Heat transfer between gas-solid multiphase flow and tubes occurs in m a ny industry processes, such as circulating fluidized bed process, pneumatic conv eying process, chemical process, drying process, etc. This paper focuses on the influence of the presence of particles on the heat transfer between a tube and g as-solid suspension. The presence of particles causes positive enhancement of h e at transfer in the case of high solid loading ratio, but heat transfer reduction has been found for in the case of very low solid loading ratio (Ms of les s than 0.05 kg/kg). A useful correlation incorporating solid loading ratio, particle s ize and flow Reynolds number was derived from experimental data. In addition, th e k-ε two-equation model and the Fluctuation-Spectrum- Random-Trajecto ry Model ( FSRT Model) are used to simulate the flow field and heat transfer of the gas-ph a se and the solid-phase, respectively. Through coupling of the two phases the mo d el can predict the local and total heat transfer characteristics of tube in gas - solid cross flow. For the total heat transfer enhancement due to particles loadi ng the model predictions agreed well with experimental data.
DEFF Research Database (Denmark)
Heiselberg, Per; Nielsen, Peter V.
Air distribution in ventilated rooms is a flow process that can be divided into different elements such as supply air jets, exhaust flows, thermal plumes, boundary layer flows, infiltration and gravity currents. These flow elements are isolated volumes where the air movement is controlled...... by a restricted number of parameters, and the air movement is fairly independent of the general flow in the enclosure. In many practical situations, the most convenient· method is to design the air distribution system using flow element theory....
Locally-rotationally-symmetric Bianchi type-V cosmology with heat flow
Indian Academy of Sciences (India)
C P Singh; A Beesham
2009-10-01
In this paper we present a spatially homogeneous locally-rotationally-symmetric (LRS) Bianchi type-V cosmological model with perfect fluid and heat flow. A general approach is introduced to solve Einstein’s field equations using a law of variation for the mean Hubble parameter, which is related to average scale factor of the model that yields a constant value for the deceleration parameter. Exact solutions that correspond to singular and non-singular models are found with heat flow. The physical constraints on the solution and, in particular, the thermodynamical laws that govern such solutions are discussed in some detail.
An investigation of flow characteristics and critical heat flux in vertical upward round tube
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Prediction of critical heat flux (CHF) in annular flow is important for the safety of once- through steam generator and the reactor core under accident conditions. The dryout in annular flow occurs at the point where the film is depleted due to entrainment, deposition, and evaporation. The film thickness, film mass flow rate along axial distribution, and CHF are calculated in vertical upward round tube on the basis of a separated flow model of annular flow. The theoretical CHF values are higher than those derived from experimental data, with error being within 30%.
Heat transfer from cylinders in subsonic slip flows
Nagabushana, K. A.; Stainback, P. C.
1992-01-01
The heat transfer in heated wires was measured using a constant temperature anemometer over a Mach number range from 0.05 to 0.4 and pressures from 0.5 to 8.0 atmospheres. The total temperature ranged from 80 to 120 F and the wire diameters were 0.00015, 0.00032, and 0.00050 inch. The heat transfer data is presented in the form of a corrected Nusselt number. Based on suggested criteria, much of the data was obtained in the slip flow regime. Therefore, the data is compared with data having comparable flow conditions. The possible application of the heat transfer data to hot wire anemometry is discussed. To this end, the sensitivity of the wires to velocity, density, and total temperature is computed and compared using two different types of correlations.
Performance of parallel flow HeII heat exchangers
Huang, Y.; Chang, Y.; Witt, R. J.; Van Sciver, S. W.
Previous studies of HeII heat exchangers have focused on tube-in-shell designs. The present paper examines the properties of a parallel flow HeII heat exchanger formed from two 254 mm lengths of copper channel having nominal rectangular dimensions 2 mm × 4 mm. Heaters positioned at the inlets and outlets of both channels permit the simulation of a variety of physically plausible boundary conditions. An iterative numerical method, based on one-dimensional energy balances in each channel with coupling through a heat transfer term, is presented and agrees well with the experimental results. As with tube-in-shell designs, parallel flow HeII heat exchangers may exhibit unusual temperature profiles.
MHD non-Newtonian micropolar fluid flow and heat transfer in channel with stretching walls
Institute of Scientific and Technical Information of China (English)
M. ASHRAF; N. JAMEEL; K. ALI
2013-01-01
A study is presented for magnetohydrodynamics (MHD) flow and heat trans-fer characteristics of a viscous incompressible electrically conducting micropolar fluid in a channel with stretching walls. The micropolar model introduced by Eringen is used to describe the working fluid. The transformed self similar ordinary differential equations together with the associated boundary conditions are solved numerically by an algorithm based on quasi-linearization and multilevel discretization. The effects of some physical parameters on the flow and heat transfer are discussed and presented through tables and graphs. The present investigations may be beneficial in the flow and thermal control of polymeric processing.
Directory of Open Access Journals (Sweden)
Ai-Min Yang
2014-03-01
Full Text Available The fractal heat flow within local fractional derivative is investigated. The nonhomogeneous heat equations arising in fractal heat flow are discussed. The local fractional Fourier series solutions for one-dimensional nonhomogeneous heat equations are obtained. The nondifferentiable series solutions are given to show the efficiency and implementation of the present method.
Bubbles as tracers of heat input to cooling flows
Binney, J; Omma, H
2007-01-01
We examine the distribution of injected energy in three-dimensional, adaptive-grid simulations of the heating of cooling flows. We show that less than 10 percent of the injected energy goes into bubbles. Consequently, the energy input from the nucleus is underestimated by a factor of order 6 when it is taken to be given by PVgamma/(gamma-1), where P and V are the pressure and volume of the bubble, and gamma the ratio of principal specific heats.
Synthesis of Bottom Hole Temperatures and Heat Flow Data
Gosnold, W. D.; Crowell, A. M.
2012-12-01
The development of a National Geothermal Data System (http://www.geothermaldata.org/) promises to provide industry, governmental agencies and researchers with a wealth of data on United States geothermal resources. Two of the larger data sets in the NDGS effort are the bottom-hole temperature data set from oil and gas drilling and the heat flow data set. The BHT data are being compiled by state geological surveys in a Bore Hole Observation Template that can include up to 76 different attributes for each well. The heat flow data are being compiled by a consortium led by the SMU Geothermal Laboratory in a Heat Flow Template that can include up to 63 different atrributes for each heat flow site. The key data for geothermal resource development are temperature, depth and the reservoir properties that control production capacity. The UND geothermal laboratory has assembled the BHT and heat flow data sets for North Dakota, Nebraska and Minnesota and we have compared how accurately the key geothermal data may be independently determined from each data set and by synthesis of both data sets. The BHT data provide temperature at depth, but it is well-documented that BHT data were recorded at non-equilibrium conditions and generally underestimate actual formation temperatures. Heat flow data include a measured temperature gradient, although the gradient may apply to only a short segment of the borehole temperature measurement. Synthesis of these two data sets provides checks that can prevent errors in data interpretation. We compared BHT data from the Denver Basin and Williston Basin to equilibrium temperature vs. depth profiles measured in deep boreholes and developed a thermal stratigraphy approach that permits correction of the BHT data for each basin.
Numerical Simulation of Different Models of Heat Pipe Heat Exchanger Using AcuSolve
Directory of Open Access Journals (Sweden)
Zainal Nurul Amira
2017-01-01
Full Text Available In this paper, a numerical simulation of heat pipe heat exchanger (HPHE is computed by using CFD solver program i.e. AcuSolve. Two idealized model of HPHE are created with different variant of entry’s dimension set to be case 1 and case 2. The geometry of HPHE is designed in SolidWorks and imported to AcuSolve to simulate the fluid flow numerically. The design of HPHE is the key to provide a heat exchanger system to work proficient as expected. Finally, the result is used to optimize and improving heat recovery systems of the increasing demand for energy efficiency in industry.
Preliminary heat flow map of Europe. Explanatory text
Energy Technology Data Exchange (ETDEWEB)
Cermak, V.; Hurtig, E.
1977-08-08
A preliminary heat flow map of Europe was prepared, based on data contained in 401 references. The map was prepared on a scale of 1:5,000,000 and shows broad-scale geological structure (e.g., platforms, shields, foredeeps) and specialized rock suites (ophiolites, volcanites). Primary faults and thrust faults are indicated, and contours showing the depth of crystalline basement are given. Heat flow is plotted using 10.0 mW/m/sup 2/ isotherms. The accompanying explanatory text describes data acquisition and techniques of correction, and discusses some implications of the results.
Flow Pattern and Heat Transfer Behavior of Boiling Two—Phase flow in Inclined Pipes
Institute of Scientific and Technical Information of China (English)
LiuDezhang; OuyangNing
1992-01-01
Movable Electrical Conducting Probe (MECP),a kind of simple and reliable measuring transducer,used for predicting full-flow-path flow pattern in a boiling vapor/liquid two-phase flow is introduced in this paper when the test pipe is set at different inclination angles,several kinds of flow patterns,such as bubble,slug,churn,intermittent,and annular flows,may be observed in accordance with the locations of MECP.By means of flow pattern analysis,flow fleld numerical calculations have been carried out,and heat transfer coeffcient correlations along full-flow-path derived.The results show that heat transfer performance of boiling two-phase flow could be significanfly augmanted as expected in some flow pattern zones.The results of the investigation,measuring techniques and conclusions contained in this paper would be a useful reference in foundational research for prediction of flow pattern and heat transfer behavior in boiling two-phase flow,as well as for turbine vane liquid-cooling design.
Buoyancy driven flow in a hot water tank due to standby heat loss
DEFF Research Database (Denmark)
Fan, Jianhua; Furbo, Simon
2012-01-01
show that the CFD model predicts satisfactorily water temperatures at different levels of the tank during cooling by standby heat loss. It is elucidated how the downward buoyancy driven flow along the tank wall is established by the heat loss from the tank sides and how the natural convection flow......Results of experimental and numerical investigations of thermal behavior in a vertical cylindrical hot water tank due to standby heat loss of the tank are presented. The effect of standby heat loss on temperature distribution in the tank is investigated experimentally on a slim 150l tank...... parts of the tank is measured by experiments and used as input to the CFD model. Water temperatures at different levels of the tank are measured and compared to CFD calculated temperatures. The investigations focus on validation of the CFD model and on understanding of the CFD calculations.The results...
Flow structure and heat exchange analysis in internal cooling channel of gas turbine blade
Szwaba, Ryszard; Kaczynski, Piotr; Doerffer, Piotr; Telega, Janusz
2016-08-01
This paper presents the study of the flow structure and heat transfer, and also their correlations on the four walls of a radial cooling passage model of a gas turbine blade. The investigations focus on heat transfer and aerodynamic measurements in the channel, which is an accurate representation of the configuration used in aeroengines. Correlations for the heat transfer coefficient and the pressure drop used in the design of radial cooling passages are often developed from simplified models. It is important to note that real engine passages do not have perfect rectangular cross sections, but include corner fillet, ribs with fillet radii and special orientation. Therefore, this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which possesses very realistic features.
An experimental investigation of heat-transfer and flow in channels with streamwise-periodic flow
Energy Technology Data Exchange (ETDEWEB)
Habib, M.A. (King Fahd Univ. of Petroleum and Minerals, Dhahran (Saudi Arabia)); Mobarak, A.M.; Attya, A.M.; Aly, A.Z. (Cairo Univ. (Egypt). Faculty of Engineering)
1992-11-01
We investigate the enhancement of heat transfer and the consequent conservation of energy in channels with segmented baffles. The influence of Reynolds number, baffle spacing, baffle material, and heat flux on local and average heat-transfer coefficients have been studied. Our results show that the flow must pass over three to six baffles before it becomes periodic and fully-developed. Augmentation of heat transfer was obtained with increases in Reynolds number, thermal conductivity of the baffles and decreases in baffle spacing and wall heat flux. (Author).
Thermal heat-balance mode flow-to-frequency converter
Pawlowski, Eligiusz
2016-11-01
This paper presents new type of thermal flow converter with the pulse frequency output. The integrating properties of the temperature sensor have been used, which allowed for realization of pulse frequency modulator with thermal feedback loop, stabilizing temperature of sensor placed in the flowing medium. The system assures balancing of heat amount supplied in impulses to the sensor and heat given up by the sensor in a continuous way to the flowing medium. Therefore the frequency of output impulses is proportional to the heat transfer coefficient from sensor to environment. According to the King's law, the frequency of those impulses is a function of medium flow velocity around the sensor. The special feature of presented solution is total integration of thermal sensor with the measurement signal conditioning system. Sensor and conditioning system are not the separate elements of the measurement circuit, but constitute a whole in form of thermal heat-balance mode flow-to-frequency converter. The advantage of such system is easiness of converting the frequency signal to the digital form, without using any additional analogue-to-digital converters. The frequency signal from the converter may be directly connected to the microprocessor input, which with use of standard built-in counters may convert the frequency into numerical value of high precision. Moreover, the frequency signal has higher resistance to interference than the voltage signal and may be transmitted to remote locations without the information loss.
Van Buer, N. J.
2015-12-01
Arc magmatic processes, from differentiation to emplacement, depend crucially on the rate at which heat and magma are supplied to the arc crust. In active arcs, the total heat flow can be estimated relatively directly by measuring and quantifying the amounts of heat lost via conduction, hydrothermal circulation, and eruption. This total heat flow can be used to calculate the implied magmatic flux at depth. Alternatively, magmatic flux in active arcs can be estimated from measured rates of volatile emissions, usually SO2. Unfortunately, heat flow and volatile flux data sufficiently detailed to make these calculations exist for only a handful of active arcs. In the geologic record, rates of arc magmatic flux have most frequently been estimated by measuring the preserved volumes of intrusive and extrusive products and dividing by the geochronologically determined duration of arc activity. This can be converted to heat flow by assuming a certain amount of heat carried per volume of magma. The ranges of magmatic flux estimated via either heat flow or SO2 are similar for modern arcs, but, on average, estimates from the geologic record are lower by about a factor of three (Fig. 1). This discrepancy may indicate that the assumption that preserved igneous rock volumes represent the total advective flux is a poor choice when interpreting the geologic record. Recycling of early solidified magma and loss of cumulates to the mantle may be important, i.e., the time-integrated advective flux might significantly exceed the net preserved intrusive volume. This is also supported by other lines of evidence, including geochemical mass-balance arguments, thermal models of basalt flux needed to allow substantial assimilation and/or crystal fractionation in the lower crust, high-temperature thermochronology in arcs, and thermal models of the conditions necessary to cause large, explosive eruptions from upper crustal magma chambers. Substantial recycling or convection within the arc crust
FLOW RESISTANCE AND HEAT TRANSFER CHARACTERISTICS OF A NEW-TYPE PLATE HEAT EXCHANGER
Institute of Scientific and Technical Information of China (English)
LUAN Zhi-jian; ZHANG Guan-min; TIAN Mao-cheng; FAN Ming-xiu
2008-01-01
A new-type corrugation Plate Heat Exchanger (PHE) was designed. Results from both numerical simulations and experiments showed that the flow resistance of the working fluid in this new corrugation PHE, compared with the traditional chevron-type one, was decreased by more than 50%, and corresponding heat transfer performance was decreased by about 25%. The flow field of the working fluid in the corrugation PHE was transformed and hence performance difference in both flow resistance and heat transfer was generated. Such a novel plate, consisting of longitudinal and transverse corrugations, can effectively avoid the problem of flow path blockage, which will help to extend the application of PHEs to the situation with unclean working fluids.
DEFF Research Database (Denmark)
Nielsen, Kaspar Kirstein; Engelbrecht, Kurt; Bahl, Christian R.H.
2013-01-01
The heat transfer performance of inhomogeneous parallel plate heat exchangers in transient operation is investigated using an established model. A performance parameter, denoted the Nusselt-scaling factor, is used as benchmark and calculated using a well-established single blow technique. A sample...... of 50 random stacks having equal average channel thicknesses with 20 channels each are used to provide a statistical base. The standard deviation of the stacks is varied as are the flow rate (Reynolds number) and the thermal conductivity of the solid heat exchanger material. It is found that the heat...... transfer performance of inhomogeneous stacks of parallel plates may be reduced significantly due to the maldistribution of the fluid flow compared to the ideal homogeneous case. The individual channels experience different flow velocities and this further induces an inter-channel thermal cross talk....
MHD Casson nanofluid flow past a wedge with Newtonian heating
Ahmad, Kartini; Hanouf, Zahir; Ishak, Anuar
2017-02-01
The problem of steady Casson nanofluid flow past a wedge is studied in this paper. The presence of magnetic field along with Newtonian heating at the surface is considered. The governing partial differential equations are first transformed into a set of nonlinear ordinary differential equations by similarity transformations, before being solved numerically using the Keller-box method. The effects of the wedge angle Ω from 0° (horizontal plate) to 180° (vertical plate) as well as of as the magnetic parameter M on the non-Newtonian fluid flow and heat transfer characteristics are investigated. It is found that the surface temperature is slightly higher for the flow over a horizontal plate compared to that over a vertical plate. It is also found that the magnetic field decreases the surface temperature but increases the skin friction. The flow of a Newtonian fluid is found to give higher skin friction as compared to that of Casson fluid.
Marangoni mixed convection flow with Joule heating and nonlinear radiation
Directory of Open Access Journals (Sweden)
Tasawar Hayat
2015-07-01
Full Text Available Marangoni mixed convective flow of Casson fluid in a thermally stratified medium is addressed. Flow analysis has been carried out in presence of inclined magnetic field. Heat transfer analysis is discussed in the presence of viscous dissipation, Joule heating and nonlinear thermal radiation. The governing nonlinear partial differential equations are first converted into ordinary differential systems and then developed the convergent series solutions. Flow pattern with the influence of pertinent parameters namely the magnetic parameter, Casson fluid parameter, temperature ratio parameter, stratification parameter, Prandtl number, Eckert number and radiation parameter is investigated. Expression of local Nusselt number is computed and analyzed. It is found that the Nusselt number decreases by increasing magnetic parameter, temperature ratio parameter, angle of inclination and stratification parameter. Moreover the effect of buoyancy parameter on the velocity distribution is opposite in both the opposing and assisting flow phenomena. Thermal field and associated layer thickness are enhanced for larger radiation parameter.
Transient flow and heating characteristics in a pinched plasma column.
York, T. M.; Stover, E. K.
1972-01-01
The generation of axial flow and heating of an argon plasma in a pinched plasma column of a pulsed, linear z-pinch device was examined experimentally and analytically. Transient (about 5 microsec) axial pressure profiles identify three characteristic periods in the column history. These include (1) strong axial pressure asymmetry indicative of plasma streaming, (2) isotropic, rapidly rising plasma pressure indicative of plasma heating, and (3) column breakup. An efficient conversion of radial collapse to axial streaming velocity is identified. Mechanisms for such an effect and subsequent heating are evaluated; significance to transients in pulsed plasma accelerators is identified.
A Study of Heat Transfer and Flow Characteristics of Rising Taylor Bubbles
Scammell, Alexander David
2016-01-01
Practical application of flow boiling to ground- and space-based thermal management systems hinges on the ability to predict the systems heat removal capabilities under expected operating conditions. Research in this field has shown that the heat transfer coefficient within two-phase heat exchangers can be largely dependent on the experienced flow regime. This finding has inspired an effort to develop mechanistic heat transfer models for each flow pattern which are likely to outperform traditional empirical correlations. As a contribution to the effort, this work aimed to identify the heat transfer mechanisms for the slug flow regime through analysis of individual Taylor bubbles.An experimental apparatus was developed to inject single vapor Taylor bubbles into co-currently flowing liquid HFE 7100. The heat transfer was measured as the bubble rose through a 6 mm inner diameter heated tube using an infrared thermography technique. High-speed flow visualization was obtained and the bubble film thickness measured in an adiabatic section. Experiments were conducted at various liquid mass fluxes (43-200 kgm2s) and gravity levels (0.01g-1.8g) to characterize the effect of bubble drift velocityon the heat transfer mechanisms. Variable gravity testing was conducted during a NASA parabolic flight campaign.Results from the experiments showed that the drift velocity strongly affects the hydrodynamics and heat transfer of single elongated bubbles. At low gravity levels, bubbles exhibited shapes characteristic of capillary flows and the heat transfer enhancement due to the bubble was dominated by conduction through the thin film. At moderate to high gravity, traditional Taylor bubbles provided small values of enhancement within the film, but large peaks in the wake heat transfer occurred due to turbulent vortices induced by the film plunging into the trailing liquid slug. Characteristics of the wake heat transfer profiles were analyzed and related to the predicted velocity field
Coupling between entropy and unsteady heat release in a thermoacoustic system with a mean flow
Li, Lei; Zhao, Dan
2016-11-01
In this work, the coupling between entropy and unsteady heat release in a one dimensional duct in the presence of a mean flow is considered. As acoustic disturbances impinge on a compact heat source enclosed in the duct, entropy disturbances are generated. The transfer function between the generated entropy waves and oncoming flow velocity fluctuations is deduced by conducting order analysis of the linearized governing equations. The effects of the mean flow are emphasized for different forms of unsteady heat release model. It is shown that there is a strong coupling between entropy, heat release, mean flow and acoustic impedance at the heat source. To validate our theoretical analysis, numerical investigation is conducted by using a low order model. Comparing the theoretical and the low order model's results reveals that a good agreement is observed. It is found that when the mean flow Mach number is not negligible, the term of O(M1) in the identified entropy transfer function is as important as that of O(M0). Neglecting the term of O(M1) may lead to wrong prediction of the entropy waves produced in the system.
Stochastic power flow modeling
Energy Technology Data Exchange (ETDEWEB)
1980-06-01
The stochastic nature of customer demand and equipment failure on large interconnected electric power networks has produced a keen interest in the accurate modeling and analysis of the effects of probabilistic behavior on steady state power system operation. The principle avenue of approach has been to obtain a solution to the steady state network flow equations which adhere both to Kirchhoff's Laws and probabilistic laws, using either combinatorial or functional approximation techniques. Clearly the need of the present is to develop sound techniques for producing meaningful data to serve as input. This research has addressed this end and serves to bridge the gap between electric demand modeling, equipment failure analysis, etc., and the area of algorithm development. Therefore, the scope of this work lies squarely on developing an efficient means of producing sensible input information in the form of probability distributions for the many types of solution algorithms that have been developed. Two major areas of development are described in detail: a decomposition of stochastic processes which gives hope of stationarity, ergodicity, and perhaps even normality; and a powerful surrogate probability approach using proportions of time which allows the calculation of joint events from one dimensional probability spaces.
Adamczyk, John J.
1997-01-01
Last year, researchers at the NASA Lewis Research Center used the average passage code APNASA to complete the largest three-dimensional simulation of a multistage axial flow compressor to date. Consisting of 29 blade rows, the configuration is typical of those found in aeroengines today. The simulation, which was executed on the High Performance Computing and Communications (HPCC) Program IBM SP2 parallel computer located at the NASA Ames Research Center, took nearly 90 hr to complete. Since the completion of this activity, a fine-grain, parallel version of APNASA has been written by a team of researchers from General Electric, NASA Lewis, and NYMA. Timing studies performed on the SP2 have shown that, with eight processors assigned to each blade row, the simulation time is reduced by a factor of six. For this configuration, the simulation time would be 15 hr. The reduction in computing time indicates that an overnight turnaround of a multistage configuration simulation is feasible. In addition, average passage forms of two-equation turbulence models were formulated. These models are currently being incorporated into APNASA.
Heat flow characterization and baseline of sandstone using infra-red thermography
Ibrahim, Y.; Padmanabhan, E.; Ano, A. B.; Ismail, W.
2016-11-01
Infra-red thermography was applied to sandstone to characterize and obtain a baseline or a reference thermal image for sandstone. The sample was imaged at room temperature and then heated and imaged again at different time intervals. The thermal images and the optical gradient obtained were analyzed, calibrated, and equated to actual-temperature measured geothermal gradient under controlled heat flux. Heat flow propagation is not consistent in the first time intervals (below 25 minutes). However, after that, the difference in temperature in the distal part and the proximal parts to the heat source almost remained constant. In general, the heat flow could fit to a linear model that is directly proportional to time. The results can be useful when applied to borehole thermal imaging, as well as in thermal conductivity and geothermal gradient determination.
Abnormal high surface heat flow caused by the Emeishan mantle plume
Jiang, Qiang; Qiu, Nansheng; Zhu, Chuanqing
2016-04-01
It is commonly believed that increase of heat flow caused by a mantle plume is small and transient. Seafloor heat flow data near the Hawaiian hotspot and the Iceland are comparable to that for oceanic lithosphere elsewhere. Numerical modeling of the thermal effect of the Parana large igneous province shows that the added heat flow at the surface caused by the magmatic underplating is less than 5mW/m2. However, the thermal effect of Emeishan mantle plume (EMP) may cause the surface hear-flow abnormally high. The Middle-Late Emeishan mantle plume is located in the western Yangtze Craton. The Sichuan basin, to the northeast of the EMP, is a superimposed basin composed of Paleozoic marine carbonate rocks and Mesozoic-Cenozoic terrestrial clastic rocks. The vitrinite reflectance (Ro) data as a paleogeothermal indicator records an apparent change of thermal regime of the Sichuan basin. The Ro profiles from boreholes and outcrops which are close to the center of the basalt province exhibit a 'dog-leg' style at the unconformity between the Middle and Upper Permian, and they show significantly higher gradients in the lower subsection (pre-Middle Permian) than the Upper subsection (Upper Permian to Mesozoic). Thermal history inversion based on these Ro data shows that the lower subsection experienced a heat flow peak much higher than that of the upper subsection. The abnormal heat flow in the Sichuan basin is consistent with the EMP in temporal and spatial distribution. The high-temperature magmas from deep mantle brought heat to the base of the lithosphere, and then large amount of heat was conducted upwards, resulting in the abnormal high surface heat flow.
A fictitious domain method for particulate flows with heat transfer
Yu, Zhaosheng; Shao, Xueming; Wachs, Anthony
2006-09-01
The distributed-Lagrange-multiplier/fictitious-domain (DLM/FD) method of Glowinski et al. [R. Glowinski, T.-W. Pan, T.I. Hesla, D.D. Joseph, A distributed Lagrange multiplier/fictitious domain method for particulate flows, Int. J. Multiphase Flow 25 (1999) 755-794] is extended to deal with heat transfer in particulate flows in two dimensions. The Boussinesq approximation is employed for the coupling between the flow and temperature fields. The fluid-flow equations are solved with the finite-difference projection method on a half-staggered grid. In our operator splitting scheme, the Lagrange multipliers at the previous time level are kept in the fluid equations, and the new Lagrange multipliers for the rigid-body motion constraint and the Dirichlet temperature boundary condition are determined from the reduced saddle-point problem, whereas a very simple scheme based on the fully explicit computation of the Lagrange multiplier is proposed for the problem in which the solid heat conduction inside the particle boundary is also considered. Our code for the case of fixed temperature on the immersed boundary is verified by comparing favorably our results on the natural convection driven by a hot cylinder eccentrically placed in a square box and on the sedimentation of a cold circular particle in a vertical channel to the data in the literature. The code for the case of freely varying temperature on the boundaries of freely moving particles is applied to analyze the motion of a catalyst particle in a box and in particular the heat conductivities of nanofluids and sheared non-colloidal suspensions, respectively. Our preliminary computational results support the argument that the micro-heat-convection in the fluids is primarily responsible for the unusually high heat conductivity of nanofluids. It is shown that the Peclet number plays a negative role in the diffusion-related heat conductivity of a sheared non-colloidal suspension, whereas the Reynolds number does the
Flow and Convective Heat Transfer of Cylinder Misaligned from Aerodynamic Axis of Cyclone Flow
Directory of Open Access Journals (Sweden)
I. L. Leukhin
2008-01-01
Full Text Available The paper provides and analyzes results of experimental investigations on physical specific features of hydrodynamics and convective heat transfer of a cyclone flow with a group of round cylinders located symmetrically relative to its aerodynamic axis, calculative equations for average and local heat transfer factors at characteristic sections of cylinder surface.
Modelling of the Czochralski flow
Directory of Open Access Journals (Sweden)
Jan Franc
1998-01-01
Full Text Available The Czochralski method of the industrial production of a silicon single crystal consists of pulling up the single crystal from the silicon melt. The flow of the melt during the production is called the Czochralski flow. The mathematical description of the flow consists of a coupled system of six P.D.E. in cylindrical coordinates containing Navier-Stokes equations (with the stream function, heat convection-conduction equations, convection-diffusion equation for oxygen impurity and an equation describing magnetic field effect.
Energy Technology Data Exchange (ETDEWEB)
Jo, Youngchul; Son, Seokkwon; Kim, Hyungmo; Eoh, Jaehyuk; Jeong, Jiyoung [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2015-10-15
DHR systems consist of two diverse heat removal loops such as passive and active DHR systems, and the heat load imposed on the primary sodium pool is safely rejected into the environment through different kinds of sodium-to-air heat exchangers, e.g. M-shape and helical-coil type air-coolers. The former is called as an FHX(Forced-draft sodium-to-air Heat Exchanger) and the latter is simply called as an AHX(natural-draft sodium-to-Air Heat Exchanger). In a general sodium-to-air heat exchanger design, convection resistance in a shell-side air flow path becomes dominant factor affecting the mechanism of conjugate heat transfer from the sodium flow inside the tube to the air path across the sodium tube wall. Hence verification of the flow and heat transfer characteristics is one of the most important tasks to demonstrate decay heat removal performance. To confirm a kind of ultimate heat sink heat exchanger, a medium-scale Sodium thermal-hydraulic Experiment Loop for Finned-tube sodium-to-Air Heat exchanger (here after called the SELFA) has been designed and is recently being constructed at KAERI site. The introduction of the flow baffle inside the upper sodium chamber of the model FHX unit in the SELFA facility is briefly proposed and discussed as well. The present study aims at introducing a flow baffle design inside the upper sodium chamber to make more equalized flowrates flowing into each heat transfer tube of the model FHX unit. In the cases without the flow baffle geometry, it was observed lager discrepancies in flowrates at the heat transfer tubes. However it was also found that those kinds of discrepancies could be definitely decreased at around 1/10 by employing a flow baffle.
Electromagnetohydrodynamic flow of blood and heat transfer in a capillary with thermal radiation
Energy Technology Data Exchange (ETDEWEB)
Sinha, A. [Department of Mathematics, Jadavpur University, Kolkata 700032 (India); Shit, G.C., E-mail: gopal_iitkgp@yahoo.co.in [Department of Mathematics, Jadavpur University, Kolkata 700032 (India); Institute of Mathematical Sciences, Chennai 600113 (India)
2015-03-15
This paper presents a comprehensive theoretical study on heat transfer characteristics together with fully developed electromagnetohydrodynamic flow of blood through a capillary, having electrokinetic effects by considering the constant heat flux at the wall. The effect of thermal radiation and velocity slip condition have been taken into account. A rigorous mathematical model for describing Joule heating in electro-osmotic flow of blood including the Poisson–Boltzmann equation, the momentum equation and the energy equation is developed. The alterations in the thermal transport phenomenon, induced by the variation of imposed electromagnetic effects, are thoroughly explained through an elegant mathematical formalism. Results presented here pertain to the case where the height of the capillary is much greater than the thickness of electrical double layer comprising the stern and diffuse layers. The essential features of the electromagnetohydrodynamic flow of blood and associated heat transfer characteristics through capillary are clearly highlighted by the variations in the non-dimensional parameters for velocity profile, temperature profile and the Nusselt number. The study reveals that the temperature of blood can be controlled by regulating Joule heating parameter. - Highlights: • Electromagnetohydrodynamic flow of blood in capillary is studied. • Potential electric field is applied for driving elecroosmotic flow of blood. • Effect of thermal radiation, Joule heating and velocity slip is investigated. • Thermal radiation bears the significant change in the temperature field.
Comparison of Frictional Heating Models
Energy Technology Data Exchange (ETDEWEB)
Davies, Nicholas R [ORNL; Blau, Peter Julian [ORNL
2013-10-01
The purpose of this work was to compare the predicted temperature rises using four well-known models for frictional heating under a few selected conditions in which similar variable inputs are provided to each model. Classic papers by Archard, Kuhlmann-Wilsdorf, Lim and Ashby, and Rabinowicz have been examined, and a spreadsheet (Excel ) was developed to facilitate the calculations. This report may be used in conjunction with that spreadsheet. It explains the background, assumptions, and rationale used for the calculations. Calculated flash temperatures for selected material combinations, under a range of applied loads and sliding speeds, are tabulated. The materials include AISI 52100 bearing steel, CDA 932 bronze, NBD 200 silicon nitride, Ti-6Al-4V alloy, and carbon-graphite material. Due to the assumptions made by the different models, and the direct way in which certain assumed quantities, like heat sink distances or asperity dimensions, enter into the calculations, frictional hearing results may differ significantly; however, they can be similar in certain cases in light of certain assumptions that are shared between the models.
Energy Technology Data Exchange (ETDEWEB)
P. Dixon
2004-02-11
The purpose of this Model Report is to document the unsaturated zone (UZ) fluid flow and tracer transport models and submodels as well as the flow fields generated utilizing the UZ Flow and Transport Model of Yucca Mountain (UZ Model), Nevada. This work was planned in ''Technical Work Plan (TWP) for: Performance Assessment Unsaturated Zone'' (BSC 2002 [160819], Section 1.10, Work Package AUZM06). The UZ Model has revised, updated, and enhanced the previous UZ Flow Model REV 00 ICN 01 (BSC 2001 [158726]) by incorporation of the conceptual repository design with new grids, recalibration of property sets, and more comprehensive validation effort. The flow fields describe fracture-fracture, matrix-matrix, and fracture-matrix liquid flow rates and their spatial distributions as well as moisture conditions in the UZ system. These 3-D UZ flow fields are used directly by Performance Assessment (PA). The model and submodels evaluate important hydrogeologic processes in the UZ as well as geochemistry and geothermal conditions. These provide the necessary framework to test conceptual hypotheses of flow and transport at different scales and predict flow and transport behavior under a variety of climatic conditions. In addition, this Model Report supports several PA activities, including abstractions, particle-tracking transport simulations, and the UZ Radionuclide Transport Model.
Heat transfer in thin, compact heat exchangers with circular, rectangular, or pin-fin flow passages
Olson, D. A.
1992-01-01
Heat transfer and pressure drop have been measured of three thin, compact heat exchangers in helium gas at 3.5 MPa and higher, with Reynolds numbers of 450 to 36,000. The flow geometries for the three heat exchanger specimens were: circular tube, rectangular channel, and staggered pin fin with tapered pins. The specimens were heated radiatively at heat fluxes up to 77 W/sq cm. Correlations were developed for the isothermal friction factor as a function of Reynolds number, and for the Nusselt number as a function of Reynolds number and the ratio of wall temperature to fluid temperature. The specimen with the pin fin internal geometry had significantly better heat transfer than the other specimens, but it also had higher pressure drop. For certain conditions of helium flow and heating, the temperature more than doubled from the inlet to the outlet of the specimens, producing large changes in gas velocity, density, viscosity, and thermal conductivity. These changes in properties did not affect the correlations for friction factor and Nusselt number in turbulent flow.
Shalaginova, Z. I.
2016-03-01
The mathematical model and calculation method of the thermal-hydraulic modes of heat points, based on the theory of hydraulic circuits, being developed at the Melentiev Energy Systems Institute are presented. The redundant circuit of the heat point was developed, in which all possible connecting circuits (CC) of the heat engineering equipment and the places of possible installation of control valve were inserted. It allows simulating the operating modes both at central heat points (CHP) and individual heat points (IHP). The configuration of the desired circuit is carried out automatically by removing the unnecessary links. The following circuits connecting the heating systems (HS) are considered: the dependent circuit (direct and through mixing elevator) and independent one (through the heater). The following connecting circuits of the load of hot water supply (HWS) were considered: open CC (direct water pumping from pipelines of heat networks) and a closed CC with connecting the HWS heaters on single-level (serial and parallel) and two-level (sequential and combined) circuits. The following connecting circuits of the ventilation systems (VS) were also considered: dependent circuit and independent one through a common heat exchanger with HS load. In the heat points, water temperature regulators for the hot water supply and ventilation and flow regulators for the heating system, as well as to the inlet as a whole, are possible. According to the accepted decomposition, the model of the heat point is an integral part of the overall heat-hydraulic model of the heat-supplying system having intermediate control stages (CHP and IHP), which allows to consider the operating modes of the heat networks of different levels connected with each other through CHP as well as connected through IHP of consumers with various connecting circuits of local systems of heat consumption: heating, ventilation and hot water supply. The model is implemented in the Angara data
Laminar hydromagnetic flows in an inclined heated layer
Directory of Open Access Journals (Sweden)
Paolo Falsaperla
2016-05-01
Full Text Available In this paper we investigate, analytically, stationary laminar flow solutions of an inclined layer filled with a hydromagnetic fluid heated from below and subject to the gravity field. In particular we describe in a systematic way the many basic solutions associated to the system. This extensive work is the basis to linear instability and nonlinear stability analysis of such motions.
Heat Flow for the Minimal Surface with Plateau Boundary Condition
Institute of Scientific and Technical Information of China (English)
Kung Ching CHANG; Jia Quan LIU
2003-01-01
The heat flow for the minimal surface under Plateau boundary condition is defined to be aparabolic variational inequality, and then the existence, uniqueness, regularity, continuous dependenceon the initial data and the asymptotics are studied. It is applied as a deformation of the level sets inthe critical point theory.
On the Curvature and Heat Flow on Hamiltonian Systems
Directory of Open Access Journals (Sweden)
Ohta Shin-ichi
2014-01-01
Full Text Available We develop the differential geometric and geometric analytic studies of Hamiltonian systems. Key ingredients are the curvature operator, the weighted Laplacian, and the associated Riccati equation.We prove appropriate generalizations of the Bochner-Weitzenböck formula and Laplacian comparison theorem, and study the heat flow.
Fluid Flow and Heat Transfer over a Permeable Stretching Cylinder
Directory of Open Access Journals (Sweden)
K Vajravelu
2014-01-01
Full Text Available In this paper, we analyze the effects of thermo-physical properties on the axisymmetric flow of a viscous fluid induced by a stretching cylinder in the presence of internal heat generation/absorption. It is assumed that the cylinder is stretched in the axial direction with a linear velocity and the surface temperature of the cylinder is subjected to vary linearly. Here, the temperature dependent thermo-physical properties namely, the fluid viscosity and the fluid thermal conductivity are respectively assumed to vary as an inverse function of the temperature and a linear function of the temperature. The governing system of partial differential equations is converted into a system of coupled non-linear ordinary differential equations with variable coefficients. The resulting system is solved numerically using a second order finite difference scheme known as the Keller-box method. The governing equations of the problem show that the flow and heat transfer characteristics depend on six parameters, namely the curvature parameter, fluid viscosity parameter, injection/suction parameter, variable thermal conductivity parameter, heat source/sink parameter and the Prandtl number. The numerical values obtained for the velocity, temperature, skin friction, and the Nusselt number are presented through graphs and tables for several sets of values of the pertinent parameters. The results obtained for the flow and heat transfer characteristics reveal many interesting behaviors that warrant further study on the axisymmetric flow phenomena. Comparisons with the available results in the literature are presented as special cases.
Single phase channel flow forced convection heat transfer
Energy Technology Data Exchange (ETDEWEB)
Hartnett, J.P.
1999-04-01
A review of the current knowledge of single phase forced convection channel flow of liquids (Pr > 5) is presented. Two basic channel geometries are considered, the circular tube and the rectangular duct. Both laminar flow and turbulent flow are covered. The review begins with a brief overview of the heat transfer behavior of Newtonian fluids followed by a more detailed presentation of the behavior of purely viscous and viscoelastic Non-Newtonian fluids. Recent developments dealing with aqueous solutions of high molecular weight polymers and aqueous solutions of surfactants are discussed. The review concludes by citing a number of challenging research opportunities.
Heat transfer in nonequilibrium boundary layer flow over a partly catalytic wall
Wang, Zhi-Hui
2016-11-01
Surface catalysis has a huge influence on the aeroheating performance of hypersonic vehicles. For the reentry flow problem of a traditional blunt vehicle, it is reasonable to assume a frozen boundary layer surrounding the vehicles' nose, and the catalytic heating can be decoupled with the heat conduction. However, when considering a hypersonic cruise vehicle flying in the medium-density near space, the boundary layer flow around its sharp leading-edge is likely to be nonequilibrium rather than frozen due to rarefied gas effects. As a result, there will be a competition between the heat conduction and the catalytic heating. In this paper, the theoretical modeling and the direct simulation Monte Carlo (DSMC) method are employed to study the corresponding rarefied nonequilibrium flow and heat transfer phenomena near the leading edge of the near space hypersonic vehicles. It is found that even under identical rarefication degree, the nonequilibrium degree of the flow and the corresponding heat transfer performance of the sharp leading edges could be different from that of the big blunt noses. A generalized model is preliminarily proposed to describe and to evaluate the competitive effects between the homogeneous recombination of atoms inside the nonequilibrium boundary layer and the heterogeneous recombination of atoms on the catalytic wall surface. The introduced nonequilibrium criterion and the analytical formula are validated and calibrated by the DSMC results, and the physical mechanism is discussed.
Thermal-hydraulic issues of flow boiling and condensation in organic Rankine cycle heat exchangers
Mikielewicz, Jarosław; Mikielewicz, Dariusz
2012-08-01
In the paper presented are the issues related to the design and operation of micro heat exchangers, where phase changes can occur, applicable to the domestic micro combined heat and power (CHP) unit. Analysed is the stability of the two-phase flow in such unit. A simple hydraulic model presented in the paper enables for the stability analysis of the system and analysis of disturbance propagation caused by a jump change of the flow rate. Equations of the system dynamics as well as properties of the working fluid are strongly non-linear. A proposed model can be applicable in designing the system of flow control in micro heat exchangers operating in the considered CHP unit.
Turbulent Heat Transfer Characteristics in the Shear Layer of a Separated Flow
Jovic, S.; Kutler, Paul F. (Technical Monitor)
1994-01-01
Experiments were performed to study the evolution of the heat transfer structure in a separated free shear layer region of an incompressible separated turbulent boundary layer flow behind a backward-facing step. While there is an abundance of velocity field measurements of separated flows, heat transfer measurements are rather scarce, thus limiting assessment of the heat transfer physics and its accurate modeling. The purpose of the paper is twofold: to improve an understanding of effects of flow separation on heat transfer characteristics, and to provide data for turbulence modeling and computation. The boundary layer upstream of the step was turbulent and fully developed. A constant temperature surface boundary condition was imposed upstream and downstream of the step for the heat transfer study. An internal mixing-layer like flow forms and grows from the step lip within the original boundary layer. The turbulent structure of the flow evolving downstream, however, does not switch immediately to that of a mixing layer over the entire shear layer thickness. Measurements of mean and fluctuating velocity and temperature fields indicate that the internal layer spreads gradually in the transverse direction while the outer part of the original boundary layer is effectively unperturbed. The results in this paper have not been previously reported.
Heat Transfer Coefficient Measurement for Downward Facing Flow Boiling Heat Transfer
Energy Technology Data Exchange (ETDEWEB)
Jung, Jun Yeong; Jeong, Yong Hoon [KAIST, Daejeon (Korea, Republic of)
2016-05-15
To evaluate heat transfer capability of the ERVC, estimating heat transfer coefficient (HTC) is important. In this study, the HTCs were experimentally measured, and large break loss of coolant accident (LLOCA) was used as basic accident. At the lower head outer wall, heat transfer phenomenon was downward facing flow boiling heat transfer. Because, natural circulation occurred. Hence, to simulate the flow boiling, water loop was designed. The reactor vessel lower head was simulated as 2-D slice main heater. To simulate the heat transfer characteristics of material and geometry, the main heater was made of SA508 consisting the reactor vessel, and its radius curvature was 2.5 m. The main heater outer surface (facing to air) temperature was measured by infrared (IR) camera, and the inner surface (facing to working fluid) temperature was calculated by solving conduction equation of main heater. The main heater heat flux was under CHF value of previous research. The results of 60 .deg. and 90 .deg. were used as representative angular location data. LLOCA was used as basic accident. Through this experiment, the HTC data was produced for SA508 heat transfer surface material and 2.5 m of radius curvature. The HTCs result shown different trend at each angular location. The HTCs commonly increased with heat flux increment, but the trends were different for angular location.
Mathematical model of induction heating
Rak, Josef
2017-07-01
One of mathematical models of induction heating can be described by a parabolic differential equation with the specific Joule looses in the body. Advantage of this method is that the detailed knowledge of the 3D-magnetic field is not necessary and move of the body or the inductor can be easily implemented. The specific Joule looses can computed by solving the Fredholm integral equation of the second kind for the eddy current of density by the Nyström method with the singularity subtraction.
A heat transfer model of a horizontal ground heat exchanger
Mironov, R. E.; Shtern, Yu. I.; Shtern, M. Yu.; Rogachev, M. S.
2016-04-01
Ground-source heat pumps are gaining popularity in Eastern Europe, especially those which are using the horizontal ground heat exchanger (GHX). Due to the difficulty of accessing GHX after the installation, materials and the quality of the installation must satisfy the very high requirements. An inaccurate calculation of GHX can be the reason of a scarcity of heat power in a crucial moment. So far, there isn't any appropriate mathematical description of the horizontal GHX which takes into account the mutual influence of GHX pipes on each other. To solve this problem we used the temperature wave approach. As a result, a mathematical model which describes the dependence of the heat transfer rate per unit length of the horizontal GHX pipe on the thermal properties of soil, operating time of GHX and the distance between pipes was obtained. Using this model, heat transfer rates per unit length of a horizontal GHX were plotted as functions of the distance between pipes and operating time. The modeling shows that heat transfer rates decreases rapidly with the distance between pipes lower then 2 meters. After the launch of heat pump, heat power of GHX is reduced during the first 20 - 30 days and get steady after that. The obtained results correlate with experimental data. Therefore the proposed mathematical model can be used to design a horizontal GHX with the optimal characteristics, and predict its capability during operation.
Institute of Scientific and Technical Information of China (English)
安刚; 李俊明; 王补宣
2001-01-01
Theoretical investigations have been performed on the convective heat transfer for incompressible laminar flow of gases through microtube and parallel-plates micropassages with constant wall temperature. Considering the change in thermal conductivity and viscosity of gas in wall adjacent region from the kinetic theory, mathematical models are built for both of the micropassages. The dimensionless temperature distribution and the corresponding heat transfer characteristics are simulated numerically, and the results discussed briefly.
Directory of Open Access Journals (Sweden)
A. O. Morais
2015-06-01
Full Text Available AbstractEnhanced heat transfer in tubes under laminar flow conditions can be found in coils or corrugated tubes or in the presence of high wall relative roughness, curves, pipe fittings or mechanical vibration. Modeling these cases can be complex because of the induced secondary flow. A modification of the Graetz problem for non-Newtonian power-law flow is proposed to take into account the augmented heat transfer by the introduction of an effective radial thermal diffusivity. The induced mixing was modeled as an increased radial heat transfer in a straight tube. Three experiments using a coiled tube and a tubular heat exchanger with high relative wall roughness are presented in order to show how this parameter can be obtained. Results were successfully correlated with Reynolds number. This approach can be useful for modeling laminar flow reactors (LFR and tubular heat exchangers available in the chemical and food industries.
Chein, Reiyu; Yang, Yeong Chin; Lin, Yushan
2006-02-01
In this study we present simple analytical models that predict the temperature and pressure variations in electrokinetic-driven microchannel flow under the Joule heating effect. For temperature prediction, a simple model shows that the temperature is related to the Joule heating parameter, autothermal Joule heating parameter, external cooling parameter, Peclet number, and the channel length to channel hydraulic diameter ratio. The simple model overpredicted the thermally developed temperature compared with the full numerical simulation, but in good agreement with the experimental measurements. The factors that affect the external cooling parameters, such as the heat transfer coefficient, channel configuration, and channel material are also examined based on this simple model. Based on the mass conservation, a simple model is developed that predicts the pressure variations, including the temperature effect. An adverse pressure gradient is required to satisfy the mass conservation requirement. The temperature effect on the pressure gradient is via the temperature-dependent fluid viscosity and electroosmotic velocity.
Nathenson, Menuel; Tilling, Robert I.; ,
1993-01-01
A steady-state solution for heat transfer from an isothermal, spherical magma chamber, with an imposed regional geothermal gradient far from the chamber, is developed. The extensive published heat-flow data set for Mount Hood, Oregon, is dominated by conductive heat transfer in the deeper parts of most drill holes and provides an ideal application of such a model. Magma-chamber volumes or depths needed to match the distribution of heat-flow data are larger or shallower than those inferred from geologic evidence.
Directory of Open Access Journals (Sweden)
Jing Cui
2015-06-01
Full Text Available The surface characteristics, such as wettability and roughness, play an important role in heat transfer performance in the field of microfluidic flow. In this paper, the process of a hot liquid flowing through a microchannel with cold walls, which possesses different surface wettabilities and microstructures, is simulated by a transient double-distribution function (DDF two-phase thermal lattice Boltzmann BGK (LBGK model. The Shan-Chen multiphase LBGK model is used to describe the flow field and the independent distribution function is introduced to solve the temperature field. The simulation results show that the roughness of the channel wall improves the heat transfer, no matter what the surface wettability is. These simulations reveal that the heat exchange characteristics are directly related to the flow behavior. For the smooth-superhydrophobic-surface flow, a gas film forms that acts as an insulating layer since the thermal conductivity of the gas is relatively small in comparison to that of a liquid. In case of the rough-superhydrophobic-surface flow, the vortex motion of the gas within the grooves significantly enhances the heat exchange between the fluid and wall.
THE HEAT AND FLUID FLOW ANALYSIS FOR WATER HEATER
Directory of Open Access Journals (Sweden)
Chien-Nan Lin
2011-01-01
Full Text Available In this paper, the heat transfer and fluid flow are studied for the water heater of RV cars, in which the hot water is heated by the combustion energy of liquefied petroleum gases. Three types of combustion tubes are performed in this investigation, which are circular tube, elliptic tube and elliptic tube with screwed wire inserted. The heat transfer performances of numerical simulation results are compared with those of the experimental works; they are in good trend agreement. The elliptic combustion tube performs better than the circular one, which indicates the average 7% energy saving for the elliptic combustion tube and 12% energy saving for the elliptic combustion tube with screwed wire under static heating.
Tracer technology modeling the flow of fluids
Levenspiel, Octave
2012-01-01
A vessel’s behavior as a heat exchanger, absorber, reactor, or other process unit is dependent upon how fluid flows through the vessel. In early engineering, the designer would assume either plug flow or mixed flow of the fluid through the vessel. However, these assumptions were oftentimes inaccurate, sometimes being off by a volume factor of 100 or more. The result of this unreliable figure produced ineffective products in multiple reaction systems. Written by a pioneering researcher in the field of chemical engineering, the tracer method was introduced to provide more accurate flow data. First, the tracer method measured the actual flow of fluid through a vessel. Second, it developed a suitable model to represent the flow in question. Such models are used to follow the flow of fluid in chemical reactors and other process units, like in rivers and streams, or solid and porous structures. In medicine, the tracer method is used to study the flow of chemicals—harmful and harmless—in the...
Influence of heat and mass flux conditions in hydromagnetic flow of Jeffrey nanofluid
Energy Technology Data Exchange (ETDEWEB)
Abbasi, F. M. [Department of Mathematics, Comsats Institute of Information Technology, Islamabad 44000 (Pakistan); Shehzad, S. A., E-mail: ali-qau70@yahoo.com [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Hayat, T. [Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000 (Pakistan); Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah (Saudi Arabia); Alsaedi, A.; Obid, Mustafa A. [Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah (Saudi Arabia)
2015-03-15
This article explores the hydromagnetic steady flow of Jeffrey fluid in the presence of thermal radiation. The chosen nanofluid model takes into account the Brownian motion and thermophoresis effects. Flow and heat transfer characteristics are determined by a stretching surface with flux conditions. The nonlinear boundary layer flow through partial differential systems is converted into the ordinary differential systems. The resulting reduced systems are computed for the convergent solutions of velocity, temperature and nanoparticle concentration. Graphs of dimensionless temperature and nanoparticle concentration profiles are presented for different values of emerging parameters. Skin-friction coefficient are computed and analyzed in both hydrodynamic and hydromagnetic flow situations.
Influence of heat and mass flux conditions in hydromagnetic flow of Jeffrey nanofluid
Directory of Open Access Journals (Sweden)
F. M. Abbasi
2015-03-01
Full Text Available This article explores the hydromagnetic steady flow of Jeffrey fluid in the presence of thermal radiation. The chosen nanofluid model takes into account the Brownian motion and thermophoresis effects. Flow and heat transfer characteristics are determined by a stretching surface with flux conditions. The nonlinear boundary layer flow through partial differential systems is converted into the ordinary differential systems. The resulting reduced systems are computed for the convergent solutions of velocity, temperature and nanoparticle concentration. Graphs of dimensionless temperature and nanoparticle concentration profiles are presented for different values of emerging parameters. Skin-friction coefficient are computed and analyzed in both hydrodynamic and hydromagnetic flow situations.
Capillary flow through heat-pipe wicks
Eninger, J. E.
1975-01-01
Theoretical expressions are obtained for the capillary-pressure limit and permeability of a fibrous wick in terms of the porosity and fiber diameter. Hysteresis in capillary pressure is included through the introduction of an empirical hysteresis constant. A partial-saturation model based on the statistical distribution of local porosity requires an additional empirical constant, the standard deviation. The theory is compared to results of a beta-ray absorption experiment that measured the liquid content of a partially saturated wick and to results of permeability measurements on partially and fully saturated wicks. A simple wick-weighing experiment is described that yields values for the empirical hysteresis constant and the standard deviation. Theoretical results are used to design an optimum wick.
EXPERIMENTAL STUDY OF ENHANCED HEAT TRANSFER BY FLOW-INDUCED VIBRATION OF ELASTIC TUBE BUNDLES
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
A new concept of heat transfer enhancement by flow-induced vibration was put forward, and a novel heat transfer element called elastic tube bundles was designed. The experimental investigation was performed on its characteristics of flow-induced virbration in out-tube or in-tube flow. Under the conditions of fixed heat flux and steam-water heat transfer, the regularity of heat transfer enhancement by flow-induced vibration was examined.
Energy Technology Data Exchange (ETDEWEB)
Liu, Q.S. [Kobe Univ. of Mercantile Marine, Dept. of Nuclear Engineering (Japan); Shiotsu, M. [Kyoto Univ., Dept. of Energy Sci. and Tech. (Japan); Sakurai, A. [Kyoto Univ. (Japan)
2001-07-01
The knowledge of flow film boiling heat transfer on a horizontal cylinder in various liquids flowing upward perpendicular to the cylinder is important as the database for the safety evaluation of the accidents such as rapid power burst and pressure reduction in the nuclear power plants. Flow film boiling heat transfer from single horizontal cylinders in water and Freon-113 flowing upward perpendicular to the cylinder under subcooled conditions was measured under wide experimental conditions. The flow velocities ranged from 0 to 1 m/s, the system pressures ranged from 100 to 500 kPa, and the surface superheats were raised up to 800 K for water and 400 K for Freon-113, respectively. Platinum horizontal cylinders with diameters ranging from 0.7 to 5 mm were used as the test heaters. The test heater was heated by direct electric current. The experimental data of film boiling heat transfer coefficients show that they increase with the increase of flow velocity, liquid subcooling, system pressure and with the decrease of cylinder diameter. Based on the experimental data, a correlation for subcooled flow film boiling heat transfer including the effects of liquid subcooling and radiation was presented, which can describe the experimental data obtained within 20% for the flow velocities below 0.7 m/s, and within -30% to +20% for the higher flow velocities. The correlation also predicted well the data by Shigechi (1983), Motte and Bromley (1957), and Sankaran and Witte (1990) obtained for the larger diameter cylinders and higher flow velocities in various liquids at the pressures of near atmospheric. The Shigechi's data were in the range from about -20% to +15%, the data of Motte and Bromley were about 30%,and the data of Sankaran and Witte were within +20 % of the curves given by the corresponding predicted values. (authors)
Investigation into flow boiling heat transfer in a minichannel with enhanced heating surface
Directory of Open Access Journals (Sweden)
Piasecka Magdalena
2012-04-01
Full Text Available The paper presents results of flow boiling in a minichannel of 1.0 mm depth. The heating element for the working fluid (FC-72 that flows along the minichannel is a single-sided enhanced alloy foil made from Haynes-230. Microrecesses were formed on the selected area of the heating foil by laser technology. The observations of the flow structure were carried out through a piece of glass. Simultaneously, owing to the liquid crystal layer placed on the opposite side of the enhanced foil surface, it was possible to measure temperature distribution on the heating wall through another piece of glass. The experimental research has been focused on the transition from single phase forced convection to nucleate boiling, i.e. the zone of boiling incipience and further development of boiling. The objective of the paper is determining of the void fraction for some cross-sections of selected images for increasing heat fluxes supplied to the heating surface. The flow structure photos were processed in Corel graphics software and binarized. The analysis of phase volumes was developed in Techystem Globe software.
Heat transfer enhancement in cross-flow heat exchangers using oval tubes and multiple delta winglets
Energy Technology Data Exchange (ETDEWEB)
Tiwari, S.; Maurya, D.; Biswas, G.; Eswaran, V. [Indian Institute of Technology, Kanpur (India). Dept. of Mechanical Engineering
2003-07-01
A three-dimensional study of laminar flow and heat transfer in a channel with built-in oval tube and delta winglets is carried out through the solution of the complete Navier-Stokes and energy equations using a body-fitted grid and a finite-volume method. The geometrical configuration represents an element of a gas-liquid fin-tube cross-flow heat exchanger. The size of such heat exchangers can be reduced through enhancement of transport coefficients on the air (gas) side, which are usually small compared to the liquid side. In a suggested strategy, oval tubes are used in place of circular tubes, and delta-winglet type vortex generators in various configuration's are mounted on the fin-surface. An evaluation of the strategy is attempted in this investigation. The investigation is carried out for different angles of attack of the winglets to the incoming flow for the case of two winglet pairs. The variation of axial location of the winglets is also considered for one pair of winglets mounted in common-flow-down configuration. The structures of the velocity field and the heat transfer characteristics have been presented. The results indicate that vortex generators in conjunction with the oval tube show definite promise for the improvement of fin-tube heat exchangers. (author)
Hass, Bridget; Harris, Robert N.
2016-06-01
Heat flow analysis of the Costa Rica convergent margin is carried out for seven sites drilled during Integrated Ocean Drilling Program (IODP) Expeditions 334 and 344 as part of the Costa Rica Seismogenesis Project (CRISP). These expeditions are designed to better understand erosional subduction zones. Heat flow measurements were made to improve estimates of the thermal structure of this erosive margin and are located on the incoming plate, toe, lower, middle, and upper slopes of the margin. Heat flow values corrected for the effects of seafloor bathymetry and sedimentation are on average 15% higher than uncorrected values and range from approximately 158-200 mW/m2 on the incoming plate to values of approximately 50 mW/m2 on the middle and upper slopes of the margin. These values are consistent with previous estimates of heat flow showing a landward decrease in heat flow consistent with subduction of the Cocos plate. Preferred thermal models of the shallow subduction zone successfully predicting observed values of heat flow incorporate fluid flow within the upper oceanic aquifer have an uppermost permeability of 10-9.5 m2 and a plate boundary effective coefficient of friction of 0.06. These models suggest that temperatures on the subduction thrust reach 100°C at distances between 30 and 35 km landward of the deformation front. The updip limit of seismicity, as defined by aftershocks events of ML 1-4 recorded following the Mw 6.9 Quepos earthquake, occurs at 25 km landward of the deformation front at temperatures cooler than the 100-150°C typically predicted.
Boundary layer flow and heat transfer to Carreau fluid over a nonlinear stretching sheet
Masood Khan; Hashim
2015-01-01
This article studies the Carreau viscosity model (which is a generalized Newtonian model) and then use it to obtain a formulation for the boundary layer equations of the Carreau fluid. The boundary layer flow and heat transfer to a Carreau model over a nonlinear stretching surface is discussed. The Carreau model, adequate for many non-Newtonian fluids, is used to characterize the behavior of the fluids having shear thinning properties and fluids with shear thickening properties for numerical ...
Witte, A.; Cabrera, A.; Polifke, W.
2016-09-01
The steady-state heat transfer from a cylinder in cross-flow is a prototype problem in thermo-fluiddynamics. However, in many applications such as the Rijke tube, the flow may fluctuate. This work analyses the phenomenon combining numerical simulation with system identification. Direct numerical simulation of laminar flow and Large Eddy Simulation at subcritical flow at Reynolds number equal to 3900 are used, respectively. Fluctuations of the inlet velocity in the simulation are excited over a wide range of frequencies. Time series of unsteady heat release and velocity are post-processed to identify dynamic models, which may be represented as transfer functions. They accurately describe the dynamic behavior and can be used for further modeling.
Energy Technology Data Exchange (ETDEWEB)
Choi, Gil Sik; Jeong, Yong Hun [KAIST, Daejeon (Korea, Republic of); Chang, Soon Heung [Handong Univ., Pohang (Korea, Republic of)
2015-12-15
There is an increasing need to understand the thermal-hydraulic phenomena, including the critical heat flux (CHF), in narrow rectangular channels and consider these in system design. The CHF mechanism under a saturated flow boiling condition involves the depletion of the liquid film of an annular flow. To predict this type of CHF, the previous representative liquid film dryout models (LFD models) were studied, and their shortcomings were reviewed, including the assumption that void fraction or quality is constant at the boundary condition for the onset of annular flow (OAF). A new LFD model was proposed based on the recent constitutive correlations for the droplet deposition rate and entrainment rate. In addition, this LFD model was applied to predict the CHF in vertical narrow rectangular channels that were uniformly heated. The predicted CHF showed good agreement with 284 pieces of experimental data, with a mean absolute error of 18. 1 % and root mean square error of 22.9 %.
Energy Technology Data Exchange (ETDEWEB)
Hurtado, F. J.; Kaiser, A. S.; Zamora, B.; Lucas, M.; Viedma, A.
2008-07-01
A thermodynamic analysis for solar chimney power plant has been carried out by numerical simulation. A numerical model has been developed using the general purpose code Fluent to study heat transfer and convective flow within the chimney power plant. The {kappa}-{epsilon} turbulence model has been employed. A heat transfer, mass flow and power production numerical analysis has been carried out on different hours during the day, assuming steady state conditions. The numeric values obtained are 10% different from experimental measures. Once model has been validated, a numeric study about flow within power plant, heat transfer and mass flow has been carry out, and the non-dimensional parameters obtained have been compared with studies about free convection. (Author)
How the propagation of heat-flux modulations triggers E × B flow pattern formation.
Kosuga, Y; Diamond, P H; Gürcan, O D
2013-03-08
We propose a novel mechanism to describe E×B flow pattern formation based upon the dynamics of propagation of heat-flux modulations. The E × B flows of interest are staircases, which are quasiregular patterns of strong, localized shear layers and profile corrugations interspersed between regions of avalanching. An analogy of staircase formation to jam formation in traffic flow is used to develop an extended model of heat avalanche dynamics. The extension includes a flux response time, during which the instantaneous heat flux relaxes to the mean heat flux, determined by symmetry constraints. The response time introduced here is the counterpart of the drivers' response time in traffic, during which drivers adjust their speed to match the background traffic flow. The finite response time causes the growth of mesoscale temperature perturbations, which evolve to form profile corrugations. The length scale associated with the maximum growth rate scales as Δ(2) ~ (v(thi)/λT(i))ρ(i)sqrt[χ(neo)τ], where λT(i) is a typical heat pulse speed, χ(neo) is the neoclassical thermal diffusivity, and τ is the response time of the heat flux. The connection between the scale length Δ(2) and the staircase interstep scale is discussed.
Energy Technology Data Exchange (ETDEWEB)
Y. Wu
2004-11-01
The purpose of this report is to document the unsaturated zone (UZ) flow models and submodels, as well as the flow fields that have been generated using the UZ flow model(s) of Yucca Mountain, Nevada. In this report, the term ''UZ model'' refers to the UZ flow model and the several submodels, which include tracer transport, temperature or ambient geothermal, pneumatic or gas flow, and geochemistry (chloride, calcite, and strontium) submodels. The term UZ flow model refers to the three-dimensional models used for calibration and simulation of UZ flow fields. This work was planned in the ''Technical Work Plan (TWP) for: Unsaturated Zone Flow Analysis and Model Report Integration'' (BSC 2004 [DIRS 169654], Section 1.2.7). The table of included Features, Events, and Processes (FEPs), Table 6.2-11, is different from the list of included FEPs assigned to this report in the ''Technical Work Plan for: Unsaturated Zone Flow Analysis and Model Report Integration'' (BSC 2004 [DIRS 169654], Table 2.1.5-1), as discussed in Section 6.2.6. The UZ model has revised, updated, and enhanced the previous UZ model (BSC 2001 [DIRS 158726]) by incorporating the repository design with new grids, recalibration of property sets, and more comprehensive validation effort. The flow fields describe fracture-fracture, matrix-matrix, and fracture-matrix liquid flow rates, and their spatial distributions as well as moisture conditions in the UZ system. These three-dimensional UZ flow fields are used directly by Total System Performance Assessment (TSPA). The model and submodels evaluate important hydrogeologic processes in the UZ as well as geochemistry and geothermal conditions. These provide the necessary framework to test hypotheses of flow and transport at different scales, and predict flow and transport behavior under a variety of climatic conditions. In addition, the limitations of the UZ model are discussed in Section 8.11.
Anomalous heat flow belt along the continental margin of Brazil
Hamza, Valiya M.; Vieira, Fabio P.; Silva, Raquel T. A.
2017-06-01
A comprehensive analysis of thermal gradient and heat flow data was carried out for sedimentary basins situated in the continental margin of Brazil (CMB). The results point to the existence of a narrow belt within CMB, where temperature gradients are higher than 30 °C/km and the heat flow is in excess of 70 mW/m2. This anomalous geothermal belt is confined between zones of relatively low to normal heat flow in the adjacent continental and oceanic regions. The width of the belt is somewhat variable, but most of it falls within the range of 100-300 km. The spatial extent is relatively large in the southern (in the basins of Pelotas, Santos and Campos) and northern (in the basins of Potiguar and Ceará) parts, when compared with those in the central parts (in the basins of South Bahia, Sergipe and Alagoas). The characteristics of heat flow anomalies appear to be compatible with those produced by thermal sources at depths in the lower crust. Hence, magma emplacement at the transition zone between lower crust and upper mantle is considered the likely mechanism producing such anomalies. Seismicity within the belt is relatively weak, with focal depths less than 10 km for most of the events. Such observations imply that "tectonic bonding" between continental and oceanic segments, at the transition zone of CMB, is relatively weak. Hence, it is proposed that passive margins like CMB be considered as constituting a type of plate boundary that is aseismic at sub-crustal levels, but allows for escape of significant amounts of earth's internal heat at shallow depths.
Flow patterns and heat convection in a rectangular water bolus for use in superficial hyperthermia.
Birkelund, Yngve; Jacobsen, Svein; Arunachalam, Kavitha; Maccarini, Paolo; Stauffer, Paul R
2009-07-07
This paper investigates both numerically and experimentally the spatio-temporal effects of water flow in a custom-made water bolus used for superficial hyperthermia generated by a 915-MHz, 4 x 3 microwave applicator array. Similar hyperthermia models referenced in the literature use a constant water temperature and uniform heat flux to describe conduction and convection energy exchange within the heating apparatus available to cool the tissue surface. The results presented in this paper show that the spatially varying flow pattern and rate are vital factors for the overall heat control applicability of the 5 mm thick bolus under study. Regions with low flow rates and low heat convection clearly put restrictions on the maximum microwave energy possible within the limits of skin temperature rise under the bolus. Our analysis is illustrated by experimental flow front studies using a contrast liquid set-up monitored by high definition video and complemented by numerical analysis of liquid flow and heat exchange within the rectangular water bolus loaded by malignant tissue. Important factors for the improvement of future bolus designs are also discussed in terms of diameter and configuration of the water input and output tubing network.
On the Flow of a Paramagnetic Fluid in a Differentially Heated Channel
Directory of Open Access Journals (Sweden)
H. Sadat
2011-01-01
Full Text Available In the present study, we investigate the flow of a paramagnetic fluid in a two dimensional heated channel when an external magnetic gradient is imposed. In the fully developed regime, an analytical solution shows that a flow reversal may occur; the condition of this is given n terms of the Reynolds number. Numerical simulations are then carried out for more general situations. It is shown that the analytical model gives good qualitative predictions.
ANALYTICAL AND EXPERIMENTAL INVESTIGATION OF FLOW DISTRIBUTION IN MANIFOLDS FOR HEAT EXCHANGERS
Institute of Scientific and Technical Information of China (English)
LU Fang; LUO Yong-hao; YANG Shi-ming
2008-01-01
The prediction of flow distribution in flow manifolds is important for the design of heat exchangers. The pressure drop along the flow in the header is the most influential factor in flow distribution. Various continuous models available in literature have failed to satisfactorily predict the pressure distribution in the headers of the flow manifolds. In this article, a discrete model matching the real physical phenomena has been proposed, to predict the pressure distribution in headers. An experimental evaluation of relevant flow characteristic parameters has been carried out to support the discrete model calculations. The validity of the theoretical discrete model has been performed with experimental results, under specific conditions. Refined experimental probes, for pressure heads with ultrasonic measuring devices, have been used to obtain accurate results. The experimental results fully substantiate the soundness of the theoretical prediction. In addition, the advantage of the ability to accommodate local disturbances in the discrete model has been pointed out. The effect of some local disturbances may be substantial. As a result of the analysis presented in this article, improved designs of flow manifolds in heat exchangers can be realized, to assure operation safety under severe operating conditions.
Measuring Heat Flow on the Moon and Mars- The Heat Flow and Physical Properties Package HP-cubed
Spohn, T.; Grott, M.; Ho, T.; van Zoest, T.; Kargl, G.; Smrekar, S. E.; Hudson, T. L.
2010-12-01
With only two successful heat flow measurements performed on the surface of the Moon to date, the thermal state of the Moon remains poorly constrained. Furthermore, measurements were taken close to the boundary of the Procellarum KREEP terraine, and the obtained values may not be representative for the bulk of the planet. For Mars, no heat flow measurement is yet available. Here we will present the Heat Flow and Physical Properties Package HP-cubed a self-penetrating, robotic heat flow probe. The instrument consists of electrical and temperature sensors that will be emplaced into the lunar subsurface by means of an electro-mechanical hammering mechanism. The instruement is foreseen to penetrate 3-5 m into the planet’s soil and will perform depth resolved measurements, from which the surface planetary heat flow can be directly deduced. The instrument has been pre-developed in two ESA funded precursor studies and has been further developed in the framework of ESA’s ExoMars mission. The current readiness level of the instrument is TRL 5.62 (ESA PDR Apr. 2009) which has been achieved with several Breadboards developed and tested between 2004 and 2009. As no drilling is required to achieve soil penetration, HP-cubed is a relatively lightweight heat flow probe, weighting less than 1800 g. It has been further studied as parts of the discovery proposals Lunette and GEMS and for the proposed Japanese lunar mission SELENE 2 The instrument consists of an electro-mechanic mole, a pay-load compartment, and a tether equipped with temperature sensors. The latter can be actively heated for thermal conductivity measurements. A tiltmeter and acceleraometer will help to track the path of the mole. The payload compartment has room for sensors such as a permittivity probe, a bore-hole camera, and/or a masspectrometer. Following deployment of the instrument, instrument operations will be split into two phases: During the penetration phase soil intrusion is achieved by means of the
Directory of Open Access Journals (Sweden)
Tsz Leung Yip
2013-03-01
Full Text Available A model is developed for studying marine traffic flow through classical traffic flow theories, which can provide us with a better understanding of the phenomenon of traffic flow of ships. On one hand, marine traffic has its special features and is fundamentally different from highway, air and pedestrian traffic. The existing traffic models cannot be simply extended to marine traffic without addressing marine traffic features. On the other hand, existing literature on marine traffic focuses on one ship or two ships but does not address the issues in marine traffic flow.
Heat Transfer Enhancement in Turbulent Flows by Blocked Surfaces
Directory of Open Access Journals (Sweden)
Onur YEMENİCİ
2013-04-01
Full Text Available In this study, the heat transfer analyses over flat and blocked surfaces were carried out in turbulent flow under the influence of the block height. A constant-temperature hot wire anemometer was used to the velocity and turbulent intensity measurements, while temperature values were measured by copper-constantan thermocouples. The average Stanton numbers for block heights of 15 and 25 mm were higher than those of flat surface by %38 and %84, respectively. The results showed that the presence of the blocks increased the heat transfer and the enhancement rose with block heights
Heat transfer and fluid flow in nuclear systems
Fenech, Henri
1982-01-01
Heat Transfer and Fluid in Flow Nuclear Systems discusses topics that bridge the gap between the fundamental principles and the designed practices. The book is comprised of six chapters that cover analysis of the predicting thermal-hydraulics performance of large nuclear reactors and associated heat-exchangers or steam generators of various nuclear systems. Chapter 1 tackles the general considerations on thermal design and performance requirements of nuclear reactor cores. The second chapter deals with pressurized subcooled light water systems, and the third chapter covers boiling water reacto
Boundary Layer Flow of Second Grade Fluid in a Cylinder with Heat Transfer
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S. Nadeem
2012-01-01
Full Text Available An analysis is carried out to obtain the similarity solution of the steady boundary layer flow and heat transfer of a second grade through a horizontal cylinder. The governing partial differential equations along with the boundary conditions are reduced to dimensionless form by using the boundary layer approximation and applying suitable similarity transformation. The resulting nonlinear coupled system of ordinary differential equations subject to the appropriate boundary conditions is solved by homotopy analysis method (HAM. The effects of the physical parameters on the flow and heat transfer characteristics of the model are presented. The behavior of skin friction coefficient and Nusselt numbers is studied for different parameters.
TOUGH Simulations of the Updegraff's Set of Fluid and Heat Flow Problems
Energy Technology Data Exchange (ETDEWEB)
Moridis, G.J.; Pruess (editor), K.
1992-11-01
The TOUGH code [Pruess, 1987] for two-phase flow of water, air, and heat in penneable media has been exercised on a suite of test problems originally selected and simulated by C. D. Updegraff [1989]. These include five 'verification' problems for which analytical or numerical solutions are available, and three 'validation' problems that model laboratory fluid and heat flow experiments. All problems could be run without any code modifications (*). Good and efficient numerical performance, as well as accurate results were obtained throughout. Additional code verification and validation problems from the literature are briefly summarized, and suggestions are given for proper applications of TOUGH and related codes.
Thielen, L.; Hanjalić, K.; Jonker, H.; Manceau, R.
2005-01-01
We present numerical computations of flow and heat transfer in multiple jets impinging normally on a flat heated surface, obtained with a new second-moment turbulence closure combined with an elliptic blending model of non-viscous wall blocking effect. This model provides the mean velocity and turbu
Experimental And Analytical Study Of Heat Transfer And Fluid Flow Through Aluminum Foams
Mancin, Simone; Zilio, Claudio; Rossetto, Luisa; Cavallini, Alberto
2010-05-01
This paper aims at investigating the air heat transfer and fluid flow through eight Aluminum open cell foam samples with different number of pores per linear inch (PPI ranging between 5 and 40), almost constant porosity (around 0.92-0.93) and different foam core heights (20 and 40 mm). The experimental heat transfer coefficient and pressure drop measurements have been collected in a test rig built at Dipartimento di Fisica Tecnica of the University of Padova. Three different heat fluxes have been imposed: 25.0, 32.5 and 40.0 kW m-2 and the air mass flow rate has been varied between 0.005 and 0.025 kg s-1, with air approach velocity between 2 and 5 m s-1. The effect of the foam height on the heat transfer has been experimentally analysed. Finally, the pressure drop measurements have been compared against an analytical model suggested in the open literature.
Heat-flow equation motivated by the ideal-gas shock wave.
Holian, Brad Lee; Mareschal, Michel
2010-08-01
We present an equation for the heat-flux vector that goes beyond Fourier's Law of heat conduction, in order to model shockwave propagation in gases. Our approach is motivated by the observation of a disequilibrium among the three components of temperature, namely, the difference between the temperature component in the direction of a planar shock wave, versus those in the transverse directions. This difference is most prominent near the shock front. We test our heat-flow equation for the case of strong shock waves in the ideal gas, which has been studied in the past and compared to Navier-Stokes solutions. The new heat-flow treatment improves the agreement with nonequilibrium molecular-dynamics simulations of hard spheres under strong shockwave conditions.
Improvement of Heating Method for Measuring the Wetness of Flowing Wet Steam
Institute of Scientific and Technical Information of China (English)
无
1998-01-01
In this paper,an improvement of heating method for measuring wetness of the flowing wet steam is developed,the basic principle of the heating method is presented and the mathematical model has been built for analyzing the thermodynamics problems during the process of heating,Moreover,an instrument for measuring wetness of wet steam flow was designed and made out.This instument has been used for measuring wetness of the wet steam flow at the outlet of the nozzle rig in Thermal Turbine Laboratory,Xi'an Jiaotong University,By analyzing the relative error of the result,it was found that this instrument has fairly high accuracy,it can be used as the prototype of practical instrument and has an important applicable value in engineering.
Numerical Prediction of Heat Transfer Characteristics of Nanofluids in a Minichannel Flow
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Arjumand Adil
2014-01-01
Full Text Available CFD simulation of the heat transfer and pressure drop characteristics of different nanofluids in a minichannel flow has been explained using FLUENT version 6.3.26. Different nanofluids with nanoparticles of Al2O3, CuO, SiO2, and TiO2 have been used in the simulation process. A comparison of the experimental and computational results has been made for the heat transfer and pressure drop characteristics for the case of Al2O3-water nanofluid for the laminar flow. Also, computations have been made by considering Brownian motion as well as without considering Brownian motion of the nanoparticles. After verification of the computational model with the experimental results for Al2O3-water nanofluid, the simulations were performed for the same experimental readings for different nanofluids in the laminar flow regime to find out the heat transfer and pressure drop characteristics.
Directory of Open Access Journals (Sweden)
Mikielewicz Dariusz
2014-09-01
Full Text Available In the paper a method developed earlier by authors is applied to calculations of pressure drop and heat transfer coefficient for flow boiling and also flow condensation for some recent data collected from literature for such fluids as R404a, R600a, R290, R32,R134a, R1234yf and other. The modification of interface shear stresses between flow boiling and flow condensation in annular flow structure are considered through incorporation of the so called blowing parameter. The shear stress between vapor phase and liquid phase is generally a function of nonisothermal effects. The mechanism of modification of shear stresses at the vapor-liquid interface has been presented in detail. In case of annular flow it contributes to thickening and thinning of the liquid film, which corresponds to condensation and boiling respectively. There is also a different influence of heat flux on the modification of shear stress in the bubbly flow structure, where it affects bubble nucleation. In that case the effect of applied heat flux is considered. As a result a modified form of the two-phase flow multiplier is obtained, in which the nonadiabatic effect is clearly pronounced.
New and classical applications of heat flow studies
Clauser, C.
2005-12-01
This special issue of Journal of Geophysics and Engineering is dedicated to a collection of papers which resulted from an international workshop held in Aachen, Germany, on 4-7 October 2004, called 'New and Classical Applications of Heat Flow Studies'. This was the third in a series of topical geothermal workshops arranged by the Geothermal Working Group of the German Geophysical Society (DGG) and was organized by the Institute of Applied Geophysics at RWTH Aachen University under the auspices of the International Heat Flow Commission of the International Association of Seismology and Physics (IASPEI). The meeting was attended by some 60 scientists from 14 countries and three continents. Financial assistance, granted by DGG and IASPEI, allowed us to provide partial support for a total of eight students, young scientists and eminent researchers from eastern Europe and overseas. The convenors of the meeting were Christoph Clauser (Aachen), Thomas Kohl (Zürich) and Makoto Taniguchi (Kyoto). The main local organizers were Volker Rath (scientific programme) and Ute Kreutz (accommodation and financial affairs). The topics addressed in more than 50 oral and poster presentations indicated that today intriguing new applications of heat flow studies have emerged, complementing the classical topics of heat flow mapping and the tectonic implications of heat flow. In classical applications, for instance, thermal signatures of water flow or downward diffusion of variations in the Earth's mean temperature are considered as noise which needs to be corrected prior to further use of the data. In contrast, in several new applications it is exactly the information contained in these signatures which has been extracted and interpreted. For instance, over the past two decades, work on the most prominent of these new applications has been devoted to inverting the variation of the Earth's past mean ground surface temperature (GST). As of today, GST provided by the geothermal method has
Modeling of Methods to Control Heat-Consumption Efficiency
Tsynaeva, E. A.; Tsynaeva, A. A.
2016-11-01
In this work, consideration has been given to thermophysical processes in automated heat consumption control systems (AHCCSs) of buildings, flow diagrams of these systems, and mathematical models describing the thermophysical processes during the systems' operation; an analysis of adequacy of the mathematical models has been presented. A comparison has been made of the operating efficiency of the systems and the methods to control the efficiency. It has been determined that the operating efficiency of an AHCCS depends on its diagram and the temperature chart of central quality control (CQC) and also on the temperature of a low-grade heat source for the system with a heat pump.
Jiménez, Juan; Smits, Alexander
2003-11-01
Experimental investigation over a DARPA SUBOFF submarine model (SUBOFF Model) was performed using flow visualization and Digital Particle Image Velocimetry (DPIV). The model has an axisymmetric body with sail and fins, and it was supported by a streamlined strut that was formed by the extension of the sail appendage. The range of flow conditions studied correspond to a Reynolds numbers based on model length, Re_L, of about 10^5. Velocity vector fields, turbulence intensities, vorticity fields, and flow visualization in the vicinity of the junction flows are presented. In the vicinity of the control surface and sail hull junctions, the presence of streamwise vortices in the form of horseshoe or necklace vortices locally dominates the flow. The effects of unsteady motions about an axis passing through the sail are also investigated to understand the evolution of the unsteady wake.
Stromberger, Jorg Hermann
Numerous experimental and theoretical investigations on two-phase flow instability and burnout in heated microchannels have been reported in the literature. However none of these investigations deals with the possible effects of wall vibrations on such flow boiling processes within microchannels. Fluid-structure interaction in ultra high power density systems cooled by high velocity single phase forced convection in microchannels may result in vibration amplitudes that are a significant fraction of the diameter of the channel. Such vibrations may significantly impact vapor bubble dynamics at the wall and, hence, the limiting heat fluxes corresponding to the onset of flow instability and/or burnout. The primary purpose of this research was to experimentally quantify the effect of forced wall vibration on the onset of flow instability (OFI) and the critical heat flux (CHF) in uniformly-heated annular microchannels. The secondary interest of this investigation was to compare the experimental data collected in the single-phase regime to commonly used single-phase forced convection correlations. Experimental data acquired in the flow boiling regime were to be utilized to confirm the validity of common flow boiling correlations for microchannel flow. The influence of forced wall vibration on subcooled single-phase forced convection and flow boiling was examined. The Georgia Tech Microchannel Test Facility (GTMTF) was modified to allow such experiments to be conducted at controlled values of transverse wall vibration amplitudes and accelerations for a range of frequencies. The channel demand curves were obtained for various inner and outer surface heat fluxes. Experiments were conducted for broad ranges of transverse wall vibration amplitudes over a range of frequencies. The experiments conducted in this investigation provide designers of high power density systems cooled by forced convection in microchannels with the appropriate data and correlations to confidently
Heat string model of bi-dimensional dc Glidarc
Pellerin, S.; Richard, F.; Chapelle, J.; Cormier, J.-M.; Musiol, K.
2000-10-01
The gliding arc discharge (`Glidarc') is the subject of renewed interest in application to a variety of chemical reactions. The gliding arc creates a weakly ionized gas `string' between two horn-shaped electrodes. In this paper, we present a simple model for a bi-dimensional dc Glidarc working in air, in which the conducting zone of the discharge that is heated by the Joule effect is considered as a hot wire cooled by an air flow. Inside this wire, the heat transfer results from thermal conduction. The exchange of heat between the hot wire and the air flow is assured by convection and depends on the wire radius and the relative velocity of the arc with respect to the gas flow. The model correctly describes experimental results and allows us to predict the working parameters of the Glidarc in different experimental situations.
Heat transfer coefficient for flow boiling in an annular mini gap
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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.
Heat transfer coefficient for flow boiling in an annular mini gap
Hożejowska, Sylwia; Musiał, Tomasz; Piasecka, Magdalena
2016-03-01
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 ca