Measurement of heat transfer effectiveness during collision of a Leidenfrost droplet with a heated wall - 15447

International Nuclear Information System (INIS)

Park, J.S.; Kim, H.; Bae, S.W.; Kim, K.D.

2015-01-01

Droplet-wall collision heat transfer during dispersed flow film boiling plays a role in predicting cooling rate and peak cladding temperature of overheated fuels during reflood following a LOCA accident in nuclear power plants. This study aims at experimentally studying effects of collision velocity and angle, as dynamic characteristics of the colliding droplet, on heat transfer. The experiments were performed by varying collision velocity from 0.2 to 1.5 m/s and collision angle between the droplet path and the wall in the range from 30 to 90 degrees under atmosphere condition. A single droplet was impinged on an infrared-opaque Pt film deposited on an infrared-transparent sapphire plate, which combination permits to measure temperature distribution of the collision surface using a high-speed infrared camera from below. The instantaneous local surface heat flux was obtained by solving transient heat conduction equation for the heated substrate using the measured surface temperature data as the boundary condition of the collision surface. Total heat transfer amount of a single droplet collision was calculated by integrating the local heat flux distribution on the effective heat transfer area during the collision time. The obtained results confirmed the finding from the previous studies that with increasing collision velocity, the heat transfer effectiveness increases due to the increase of the heat transfer area and the local heat flux value. Interestingly, it was found that as collision angle of a droplet with a constant collision velocity decreases from 90 to 50 degrees and thus the vertical velocity component of the collision decreases, the total heat transfer amount per a collision increases. It was observed that the droplet colliding with an angle less than 90 degrees slides on the surface during the collision and the resulting collision area is larger than that in the normal collision. On the other hand, further decrease of collision angle below 40 degrees

Temperature fluctuations in fully-developed turbulent channel flow with heated upper wall

Science.gov (United States)

Bahri, Carla; Mueller, Michael; Hultmark, Marcus

2013-11-01

The interactions and scaling differences between the velocity field and temperature field in a wall-bounded turbulent flow are investigated. In particular, a fully developed turbulent channel flow perturbed by a step change in the wall temperature is considered with a focus on the details of the developing thermal boundary layer. For this specific study, temperature acts as a passive scalar, having no dynamical effect on the flow. A combination of experimental investigation and direct numerical simulation (DNS) is presented. Velocity and temperature data are acquired with high accuracy where, the flow is allowed to reach a fully-developed state before encountering a heated upper wall at constant temperature. The experimental data is compared with DNS data where simulations of the same configuration are conducted.

Bed-To-Wall Heat Transfer in a Supercritical Circulating Fluidised Bed Boiler

Directory of Open Access Journals (Sweden)

Błaszczuk Artur

2014-06-01

Full Text Available The purpose of this work is to find a correlation for heat transfer to walls in a 1296 t/h supercritical circulating fluidised bed (CFB boiler. The effect of bed-to-wall heat transfer coefficient in a long active heat transfer surface was discussed, excluding the radiation component. Experiments for four different unit loads (i.e. 100% MCR, 80% MCR, 60% MCR and 40% MCR were conducted at a constant excess air ratio and high level of bed pressure (ca. 6 kPa in each test run. The empirical correlation of the heat transfer coefficient in a large-scale CFB boiler was mainly determined by two key operating parameters, suspension density and bed temperature. Furthermore, data processing was used in order to develop empirical correlation ranges between 3.05 to 5.35 m·s-1 for gas superficial velocity, 0.25 to 0.51 for the ratio of the secondary to the primary air, 1028 to 1137K for bed temperature inside the furnace chamber of a commercial CFB boiler, and 1.20 to 553 kg·m-3 for suspension density. The suspension density was specified on the base of pressure measurements inside the boiler’s combustion chamber using pressure sensors. Pressure measurements were collected at the measuring ports situated on the front wall of the combustion chamber. The obtained correlation of the heat transfer coefficient is in agreement with the data obtained from typical industrial CFB boilers.

Experimental study on the heat transfer characteristics of a nuclear reactor containment wall cooled by gravitationally falling water

Science.gov (United States)

Pasek, Ari D.; Umar, Efrison; Suwono, Aryadi; Manalu, Reinhard E. E.

2012-06-01

Gravitationally falling water cooling is one of mechanism utilized by a modern nuclear Pressurized Water Reactor (PWR) for its Passive Containment Cooling System (PCCS). Since the cooling is closely related to the safety, water film cooling characteristics of the PCCS should be studied. This paper deals with the experimental study of laminar water film cooling on the containment model wall. The influences of water mass flow rate and wall heat rate on the heat transfer characteristic were studied. This research was started with design and assembly of a containment model equipped with the water cooling system, and calibration of all measurement devices. The containment model is a scaled down model of AP 1000 reactor. Below the containment steam is generated using electrical heaters. The steam heated the containment wall, and then the temperatures of the wall in several positions were measure transiently using thermocouples and data acquisition. The containment was then cooled by falling water sprayed from the top of the containment. The experiments were done for various wall heat rate and cooling water flow rate. The objective of the research is to find the temperature profile along the wall before and after the water cooling applied, prediction of the water film characteristic such as means velocity, thickness and their influence to the heat transfer coefficient. The result of the experiments shows that the wall temperatures significantly drop after being sprayed with water. The thickness of water film increases with increasing water flow rate and remained constant with increasing wall heat rate. The heat transfer coefficient decreases as film mass flow rate increase due to the increases of the film thickness which causes the increasing of the thermal resistance. The heat transfer coefficient increases slightly as the wall heat rate increases. The experimental results were then compared with previous theoretical studied.

Conduction and convection heat transfer characteristics of water-based au nanofluids in a square cavity with differentially heated side walls subjected to constant temperatures

Directory of Open Access Journals (Sweden)

Ternik Primož

2014-01-01

Full Text Available The present work deals with the natural convection in a square cavity filled with the water-based Au nanofluid. The cavity is heated on the vertical and cooled from the adjacent wall, while the other two horizontal walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles’ volume fraction on the heat transfer characteristics of Au nanofluids at the given base fluid’s (i.e. water Rayleigh number. Accurate results are presented over a wide range of the base fluid Rayleigh number and the volume fraction of Au nanoparticles. It is shown that adding nanoparticles in a base fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the use of nanofluids can reduce the heat transfer rate instead of increasing it.

Transient forced convection with viscous dissipation to power-law fluids in thermal entrance region of circular ducts with constant wall heat flux

International Nuclear Information System (INIS)

Dehkordi, Asghar Molaei; Mohammadi, Ali Asghar

2009-01-01

A numerical investigation was conducted on the transient behavior of a hydrodynamically, fully developed, laminar flow of power-law fluids in the thermally developing entrance region of circular ducts taking into account the effect of viscous dissipation but neglecting the effect of axial conduction. In this regard, the unsteady state thermal energy equation was solved by using a finite difference method, whereas the steady state thermal energy equation without wall heat flux was solved analytically as the initial condition of the former. The effects of the power-law index and wall heat flux on the local Nusselt number and thermal entrance length were investigated. Moreover, the local Nusselt number of steady state conditions was correlated in terms of the power-law index and wall heat flux and compared with literature data, which were obtained by an analytic solution for Newtonian fluids. Furthermore, a relationship was proposed for the thermal entrance length

Heat transfer models for fusion blanket first walls

International Nuclear Information System (INIS)

Fillo, J.A.

1977-01-01

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

Effect of two dimensional heat conduction within the wall on heat transfer of a tube partially heated on its circumference

International Nuclear Information System (INIS)

Satoh, Isao; Kurosaki, Yasuo

1987-01-01

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

A study on post impingement effects of urea-water solution spray on the heated wall of automotive SCR systems

Science.gov (United States)

Shahariar, G. M. H.; Wardana, M. K. A.; Lim, O. T.

2018-04-01

The post impingement effects of urea-water solution spray on the heated wall of automotive SCR systems was numerically investigated in a constant volume chamber using STAR CCM+ CFD code. The turbulence flow was modelled by realizable k-ε two-layer model together with standard wall function and all y+ treatment was applied along with two-layer approach. The Eulerian-Lagrangian approach was used for the modelling of multi phase flow. Urea water solution (UWS) was injected onto the heated wall for the wall temperature of 338, 413, 473, 503 & 573 K. Spray development after impinging on the heated wall was visualized and measured. Droplet size distribution and droplet evaporation rates were also measured, which are vital parameters for the system performance but still not well researched. Specially developed user defined functions (UDF) are implemented to simulate the desired conditions and parameters. The investigation reveals that wall temperature has a great impact on spray development after impingement, droplet size distribution and evaporation. Increasing the wall temperature leads to longer spray front projection length, smaller droplet size and faster droplet evaporation which are preconditions for urea crystallization reduction. The numerical model and parameters are validated comparing with experimental data.

Mixed convection in a nanofluid filled-cavity with partial slip subjected to constant heat flux and inclined magnetic field

Energy Technology Data Exchange (ETDEWEB)

Ismael, Muneer A. [Mechanical Engineering Department, Engineering College, University of Basrah, Basrah (Iraq); Mansour, M.A. [Department of Mathematics, Assuit University, Faculty of Science, Assuit (Egypt); Chamkha, Ali J. [Mechanical Engineering Department, Prince Mohammad Bin Fahd University, Al-Khobar 31952 (Saudi Arabia); Prince Sultan Endowment for Energy and Environment, Prince Mohammad Bin Fahd University, Al-Khobar 31952 (Saudi Arabia); Rashad, A.M., E-mail: am_rashad@yahoo.com [Department of Mathematics, Aswan University, Faculty of Science, Aswan 81528 (Egypt)

2016-10-15

Mixed convection in a lid-driven square cavity filled with Cu-water nanofluid and subjected to inclined magnetic field is investigated in this paper. Partial slip effect is considered along the lid driven horizontal walls. A constant heat flux source on the left wall is considered, meanwhile the right vertical wall is cooled isothermally. The remainder cavity walls are thermally insulted. A control finite volume method is used as a numerical appliance of the governing equations. Six pertinent parameters were studied these; the orientation of the magnetic field (Φ=0–360°), Richardson number (Ri=0.001–1000), Hartman number (Ha=0–100), the size and position of the heat source (B=0.2–0.8, D=0.3–0.7, respectively), nanoparticles volume fraction (ϕ=0.0–0.1), and the lid-direction of the horizontal walls (λ=±1) where the positive sign means lid-driven to the right while the negative sign means lid-driven to the left. The results show that the orientation and the strength of the magnetic field can play a significant role in controlling the convection under the effect of partial slip. It is also found that the natural convection decreases with increasing the length of the heat source for all ranges of the studied parameters, while it is do so due to the vertical distance up to Hartman number of 50, beyond this value the natural convection decreases with lifting the heat source narrower to the top wall. - Highlights: • Partial slip along moving walls of MHD cavity filled with nanofluid is considered. • The suppression exerted by the magnetic field decreases with its orientation. • Nusselt number is enhanced slightly with nanoparticles at shortest heat source. • Nusselt number is enhanced with nanoparticles at stronger magnetic field.

Mixed convection in a nanofluid filled-cavity with partial slip subjected to constant heat flux and inclined magnetic field

International Nuclear Information System (INIS)

Ismael, Muneer A.; Mansour, M.A.; Chamkha, Ali J.; Rashad, A.M.

2016-01-01

Mixed convection in a lid-driven square cavity filled with Cu-water nanofluid and subjected to inclined magnetic field is investigated in this paper. Partial slip effect is considered along the lid driven horizontal walls. A constant heat flux source on the left wall is considered, meanwhile the right vertical wall is cooled isothermally. The remainder cavity walls are thermally insulted. A control finite volume method is used as a numerical appliance of the governing equations. Six pertinent parameters were studied these; the orientation of the magnetic field (Φ=0–360°), Richardson number (Ri=0.001–1000), Hartman number (Ha=0–100), the size and position of the heat source (B=0.2–0.8, D=0.3–0.7, respectively), nanoparticles volume fraction (ϕ=0.0–0.1), and the lid-direction of the horizontal walls (λ=±1) where the positive sign means lid-driven to the right while the negative sign means lid-driven to the left. The results show that the orientation and the strength of the magnetic field can play a significant role in controlling the convection under the effect of partial slip. It is also found that the natural convection decreases with increasing the length of the heat source for all ranges of the studied parameters, while it is do so due to the vertical distance up to Hartman number of 50, beyond this value the natural convection decreases with lifting the heat source narrower to the top wall. - Highlights: • Partial slip along moving walls of MHD cavity filled with nanofluid is considered. • The suppression exerted by the magnetic field decreases with its orientation. • Nusselt number is enhanced slightly with nanoparticles at shortest heat source. • Nusselt number is enhanced with nanoparticles at stronger magnetic field.

Enhanced heat sink with geometry induced wall-jet

Energy Technology Data Exchange (ETDEWEB)

Hossain, Md. Mahamudul, E-mail: sohel0991@gmail.com; Tikadar, Amitav; Bari, Fazlul; Morshed, A. K. M. M. [Department of Mechanical Engineering Bangladesh University of Engineering and Technology, Dhaka-1000. Bangladesh (Bangladesh)

2016-07-12

Mini-channels embedded in solid matrix have already proven to be a very efficient way of electronic cooling. Traditional mini-channel heat sinks consist of single layer of parallel channels. Although mini-channel heat sink can achieve very high heat flux, its pumping requirement for circulating liquid through the channel increase very sharply as the flow velocity increases. The pumping requirements of the heat sink can be reduced by increasing its performance. In this paper a novel approach to increase the thermal performance of the mini-channel heat sink is proposed through geometry induced wall jet which is a passive technique. Geometric irregularities along the channel length causes abrupt pressure change between the channels which causes cross flow through the interconnections thus one channel faces suction and other channel jet action. This suction and jet action disrupts boundary layer causing enhanced heat transfer performance. A CFD model has been developed using commercially available software package FLUENT to evaluate the technique. A parametric study of the velocities and the effect of the position of the wall-jets have been performed. Significant reduction in thermal resistance has been observed for wall-jets, it is also observed that this reduction in thermal resistance is dependent on the position and shape of the wall jet.

Heat transfer characteristics of building walls using phase change material

Science.gov (United States)

Irsyad, M.; Pasek, A. D.; Indartono, Y. S.; Pratomo, A. W.

2017-03-01

Minimizing energy consumption in air conditioning system can be done with reducing the cooling load in a room. Heat from solar radiation which passes through the wall increases the cooling load. Utilization of phase change material on walls is expected to decrease the heat rate by storing energy when the phase change process takes place. The stored energy is released when the ambient temperature is low. Temperature differences at noon and evening can be utilized as discharging and charging cycles. This study examines the characteristics of heat transfer in walls using phase change material (PCM) in the form of encapsulation and using the sleeve as well. Heat transfer of bricks containing encapsulated PCM, tested the storage and released the heat on the walls of the building models were evaluated in this study. Experiments of heat transfer on brick consist of time that is needed for heat transfer and thermal conductivity test as well. Experiments were conducted on a wall coated by PCM which was exposed on a day and night cycle to analyze the heat storage and heat release. PCM used in these experiments was coconut oil. The measured parameter is the temperature at some points in the brick, walls and ambient temperature as well. The results showed that the use of encapsulation on an empty brick can increase the time for thermal heat transfer. Thermal conductivity values of a brick containing encapsulated PCM was lower than hollow bricks, where each value was 1.3 W/m.K and 1.6 W/m.K. While the process of heat absorption takes place from 7:00 am to 06:00 pm, and the release of heat runs from 10:00 pm to 7:00 am. The use of this PCM layer can reduce the surface temperature of the walls of an average of 2°C and slows the heat into the room.

The Cosmological Constant and Domain Walls in Orientifold Field Theories and N=1 Gluodynamics

CERN Document Server

Armoni, Adi

2003-01-01

We discuss domain walls and vacuum energy density (cosmological constant) in N=1 gluodynamics and in non-supersymmetric large N orientifold field theories which have been recently shown to be planar equivalent (in the boson sector) to N=1 gluodynamics. A relation between the vanishing force between two parallel walls and vanishing cosmological constant is pointed out. This relation may explain why the cosmological constant vanishes in the orientifold field theory at leading order although the hadronic spectrum of this theory does not contain fermions in the limit N-->infinity. The cancellation is among even and odd parity bosonic contributions, due to NS-NS and R-R cancellations in the annulus amplitude of the underlying string theory. We use the open-closed string channel duality to describe interaction between the domain walls which is interpreted as the exchange of composite ``dilatons'' and ``axions'' coupled to the walls. Finally, we study some planar equivalent pairs in which both theories in the parent...

Selective Internal Heat Distribution in Modified Trombe Wall

Science.gov (United States)

Szyszka, Jerzy; Kogut, Janusz; Skrzypczak, Izabela; Kokoszka, Wanda

2017-12-01

At present, the requirements for thermal insulation of the external walls in buildings are being increased. There is a need to reduce energy consumption for heating rooms during the winter season. This may be achieved by increasing the thermal resistance of the outer partitions, using solutions that utilize either recuperation or solar radiation. The most popular systems include either solar collectors, or heat pump links or ground exchangers. Trombe walls (TW) are a very promising passive heating system, which requires little or no effort to operate, and may be very convenient in different climate conditions. A typical TW consists of a masonry wall painted a dark, heat absorbing paint colour and faced with a single or double layer of glass. The principle of operation is based on the photothermal conversion of solar radiation. There are various modifications of TW. They may improve the energy efficiency in relation to the climate conditions in which they operate. The hybrid solutions are also known. The efficiency of walls is related to the use of proper materials. In TW, the compromise should be sought between the thermal resistance and the ability to distribute heat from the absorbed energy of solar radiation. The paper presents an overview of the most commonly used solutions and discusses its own concept dedicated to the climate conditions of Central Europe.

Fluid-Structure Simulations of a Ruptured Intracranial Aneurysm: Constant versus Patient-Specific Wall Thickness

Directory of Open Access Journals (Sweden)

S. Voß

2016-01-01

Full Text Available Computational Fluid Dynamics is intensively used to deepen the understanding of aneurysm growth and rupture in order to support physicians during therapy planning. However, numerous studies considering only the hemodynamics within the vessel lumen found no satisfactory criteria for rupture risk assessment. To improve available simulation models, the rigid vessel wall assumption has been discarded in this work and patient-specific wall thickness is considered within the simulation. For this purpose, a ruptured intracranial aneurysm was prepared ex vivo, followed by the acquisition of local wall thickness using μCT. The segmented inner and outer vessel surfaces served as solid domain for the fluid-structure interaction (FSI simulation. To compare wall stress distributions within the aneurysm wall and at the rupture site, FSI computations are repeated in a virtual model using a constant wall thickness approach. Although the wall stresses obtained by the two approaches—when averaged over the complete aneurysm sac—are in very good agreement, strong differences occur in their distribution. Accounting for the real wall thickness distribution, the rupture site exhibits much higher stress values compared to the configuration with constant wall thickness. The study reveals the importance of geometry reconstruction and accurate description of wall thickness in FSI simulations.

Analysis of Forced Convection Heat Transfer for Axial Annular Flow of Giesekus Viscoelastic Fluid

Energy Technology Data Exchange (ETDEWEB)

Mohseni, Mehdi Moayed; Rashidi, Fariborz; Movagar, Mohammad Reza Khorsand [Amirkabir University of Technology, Tehran (Iran, Islamic Republic of)

2015-02-15

Analytical solutions for the forced convection heat transfer of viscoelastic fluids obeying the Giesekus model are obtained in a concentric annulus under laminar flow for both thermal and hydrodynamic fully developed conditions. Boundary conditions are assumed to be (a) constant fluxes at the walls and (b) constant temperature at the walls. Temperature profiles and Nusselt numbers are derived from dimensionless energy equation. Subsequently, effects of elasticity, mobility parameter and viscous dissipation are discussed. Results show that by increasing elasticity, Nusselt number increases. However, this trend is reversed for constant wall temperature when viscous dissipation is weak. By increasing viscous dissipation, the Nusselt number decreases for the constant flux and increases for the constant wall temperature. For the wall cooling case, when the viscous dissipation exceeds a critical value, the generated heat overcomes the heat which is removed at the walls, and fluid heats up longitudinally.

On the Partitioning of Wall Heat Flux in Subcooled Flow Boiling

International Nuclear Information System (INIS)

Chu, In-Cheol; Hoang, Nhan Hien; Euh, Dong-Jin; Song, Chul-Hwa

2015-01-01

This region has been treated successfully by two-fluid model coupled with a population balance model or interfacial area transport equation (IATE). The second region is near-wall heat transfer which has been commonly described by a wall heat flux partitioning model coupled with models of nucleation site density (NSD), bubble departure diameter and bubble release frequency. Since the phase change process in the near-wall heat transfer is really complex, comprising different heat transfer mechanisms, bubble dynamics, bubble nucleation and thermal response of heated surface, the modeling of the second region is still a great challenge despite intensive efforts. Numerous models and correlations have been proposed to aim for computing the near-wall heat transfer. The models of nucleation site density, bubble departure diameter and bubble release frequency are used to quantify these components. The models closely related to each other. The heat flux partitioning model controls the wall and liquid temperatures. Then, it turns to control the boiling parameters, i.e. nucleation site density, bubble departure diameter and bubble release frequency. In this study, the partitioning of wall heat flux is taken into account. The existing issues occurred with previous models of the heat flux partitioning are pointed out and then a new model which considers the heat transfer caused by evaporation of superheated liquid at bubble boundary and the actual period of transient conduction term is formulated. The new model is then validated with a collected experimental database. This paper presented a new heat flux partitioning model in which the heat transfer by evaporation of the superheated liquid at the bubble boundary and the active period of the transient conduction were considered. The new model was validated with the experimental data of the subcooled flow boiling of water obtained by Phillips

Flow and heat transfer in a curved channel

Science.gov (United States)

Brinich, P. F.; Graham, R. W.

1977-01-01

Flow and heat transfer in a curved channel of aspect ratio 6 and inner- to outer-wall radius ratio 0.96 were studied. Secondary currents and large longitudinal vortices were found. The heat-transfer rates of the outer and inner walls were independently controlled to maintain a constant wall temperature. Heating the inner wall increased the pressure drop along the channel length, whereas heating the outer wall had little effect. Outer-wall heat transfer was as much as 40 percent greater than the straight-channel correlation, and inner-wall heat transfer was 22 percent greater than the straight-channel correlation.

The effect of external boundary conditions on condensation heat transfer in rotating heat pipes

Science.gov (United States)

Daniels, T. C.; Williams, R. J.

1979-01-01

Experimental evidence shows the importance of external boundary conditions on the overall performance of a rotating heat pipe condenser. Data are presented for the boundary conditions of constant heat flux and constant wall temperature for rotating heat pipes containing either pure vapor or a mixture of vapor and noncondensable gas as working fluid.

An analytical wall-function for turbulent flows and heat transfer over rough walls

International Nuclear Information System (INIS)

Suga, K.; Craft, T.J.; Iacovides, H.

2006-01-01

This paper reports the development of a refined wall-function strategy for the modelling of turbulent forced convection heat transfer over smooth and rough surfaces. In order to include the effects of fine-grain surface roughness, the present study extends a more fundamental work by Craft et al. [Craft, T.J., Gerasimov, A.V., Iacovides, H., Launder, B.E., 2002. Progress in the generalisation of wall-function treatment. Int. J. Heat Fluid Flow 23, 148-160] on the development of advanced wall-functions of general applicability. The presently proposed model is validated through comparisons with data available for internal flows through channels and for external flows over flat and curved plates with both smooth and rough surfaces. Then, its further validation in separating flows over a sand dune and a sand-roughened ramp is discussed. The validation results suggest that the presently proposed form can be successfully applied to a wide range of attached and separated turbulent flows with heat transfer over smooth and fine-grain rough surfaces

Thermodynamic optimization of a coiled tube heat exchanger under constant wall heat flux condition

International Nuclear Information System (INIS)

Satapathy, Ashok K.

2009-01-01

In this paper the second law analysis of thermodynamic irreversibilities in a coiled tube heat exchanger has been carried out for both laminar and turbulent flow conditions. The expression for the scaled non-dimensional entropy generation rate for such a system is derived in terms of four dimensionless parameters: Prandtl number, heat exchanger duty parameter, Dean number and coil to tube diameter ratio. It has been observed that for a particular value of Prandtl number, Dean number and duty parameter, there exists an optimum diameter ratio where the entropy generation rate is minimum. It is also found that with increase in Dean number or Reynolds number, the optimum value of the diameter ratio decreases for a particular value of Prandtl number and heat exchanger duty parameter.

Experimental investigation into heating and airflow in trombe walls and solar chimneys

International Nuclear Information System (INIS)

Habib, A.; Burek, S.

2006-01-01

Trombe Walls and solar chimneys are examples of passive solar air heating systems. However, the airflow and thermal efficiency characteristics of this type of system are not well understood, and partly for this reason, they are not commonly utilised. This paper reports on an experimental investigation into buoyancy-driven convection in a test rig designed to simulate the operation of a passive solar collector. The test rig comprised a vertical open-ended channel, approximately 1a square, heated from one side. The channel depth could be varied from 20mm to 110mm, and heating inputs varied from 200W to 1000W. Temperatures and airflow rates were measured and recorded, to characterise both steady-state and transient performance. The principal findings are: 1. Time constants (for heating)ranged typically between 30 and 70 minutes. 2. Flow regimes were mainly laminar (Reynolds number varing from ∼500 to ∼4000, depending on heat input and channel depth. 3. The thermal efficiency (as a solar collector and the heat transfer coefficient were functions of heat input, and were not depended on the channel depth. 4. The mass flow rate through the channel increased bath as the heat input increased and as the channel depth increased. The paper presents these findings and discusses their implications in more detail.(Author)

Stochastic modelling of conjugate heat transfer in near-wall turbulence

International Nuclear Information System (INIS)

Pozorski, Jacek; Minier, Jean-Pierre

2006-01-01

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

Stochastic modelling of conjugate heat transfer in near-wall turbulence

Energy Technology Data Exchange (ETDEWEB)

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

2006-10-15

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

Thermal energy storage system using phase change materials: Constant heat source

Directory of Open Access Journals (Sweden)

Reddy Meenakshi R.

2012-01-01

Full Text Available The usage of phase change materials (PCM to store the heat in the form of latent heat is increased, because large quantity of thermal energy is stored in smaller volumes. In the present experimental investigation paraffin and stearic acid are employed as PCMs in thermal energy storage (TES system to store the heat as sensible and latent heat also. A constant heat source is used to supply heat transfer fluid (HTF at constant temperature to the TES system. In the TES system PCMs are stored in the form of spherical capsules of 38 mm diameter made of high density poly ethylene (HDPE. The results of the investigation are related to the charging time and recovery of stored energy from the TES system.

Conjugate heat transfer in a porous cavity filled with nano-fluids and heated by a triangular thick wall

International Nuclear Information System (INIS)

Chamkha, Ali J.; Ismael, Muneer A.

2013-01-01

The conjugate natural convection-conduction heat transfer in a square domain composed of nano-fluids filled porous cavity heated by a triangular solid wall is studied under steady-state conditions. The vertical and horizontal walls of the triangular solid wall are kept isothermal and at the same hot temperature Th. The other boundaries surrounding the porous cavity are kept adiabatic except the right vertical wall where it is kept isothermally at the lower temperature T c . Equations governing the heat transfer in the triangular wall and heat and nano-fluid flow, based on the Darcy model, in the nano-fluid-saturated porous medium together with the derived relation of the interface temperature are solved numerically using the over-successive relaxation finite-difference method. A temperature independent nano-fluids properties model is adopted. Three nano-particle types dispersed in one base fluid (water) are investigated. The investigated parameters are the nano-particles volume fraction φ (0-0.2), Rayleigh number Ra (10-1000), solid wall to base-fluid saturated porous medium thermal conductivity ratio K ro (0.44, 1, 23.8), and the triangular wall thickness D (0.1-1). The results are presented in the conventional form; contours of streamlines and isotherms and the local and average Nusselt numbers. At a very low Rayleigh number Ra = 10, a significant enhancement in heat transfer within the porous cavity with φ is observed. Otherwise, the heat transfer may be enhanced or deteriorated with φ depending on the wall thickness D and the Rayleigh number Ra. At high Rayleigh numbers and low conductivity ratios, critical values of D, regardless of 4, are observed and accounted. (authors)

Steady natural convection in a horizontal channel containing heated rectangular blocks periodically mounted on its lower wall

International Nuclear Information System (INIS)

Bakkas, M.; Amahmid, A.; Hasnaoui, M.

2006-01-01

In this paper, we perform a numerical investigation of laminar steady natural convection flows in a two-dimensional horizontal channel containing heating rectangular blocks, periodically mounted on its lower wall. The blocks are heated at a constant temperature, T H ' and connected with adiabatic surfaces. The upper wall of the channel is maintained at a cold temperature T C ' . The parameters governing the problem are the Rayleigh number (10 2 = 6 ), the geometric parameter C (0.25=< C=l'/H'=<0.75) and the relative height of the blocks (1/8=< B=h'/H'=<1/2). The effect of the computational domain choice on the multiplicity of solutions is also investigated. The results obtained using air (Pr=0.72) as the working fluid show that the parameters B and C have a significant effect on the fluid flow and temperature fields. The symmetry of the flow is not always maintained although the boundary conditions for this problem are symmetrical, and the difference between two multiple solutions in terms of heat transfer may reach 34% for a given set of the governing parameters

Prediction of vertical expansion pressure stresses in coke oven heating walls

Energy Technology Data Exchange (ETDEWEB)

Duerselen, H; Janicka, J

1987-08-01

The paper describes an accurate method developed by Krupp Koppers for calculating stresses in the central areas of coke oven heating walls. The results of this calculation model have provided the following conclusions for the design of coke ovens: 1) a rising pre-stressing of the heating walls caused by the weight of the top deck of the coke oven leads - compared with the stress limits of W. Ahlers - to lower permissible expansion pressures. 2) A given heating wall width has its corresponding maximum feasible oven height. Heating wall width and top deck weight are not interchangeable parameters. 3) The dependence of the permissible expansion pressure on the stretcher brick thickness should not be overlooked. Stretcher brick thicknesses of under 90 mm are not recomended for tall ovens and heavily swelling coal. 4) The capacity of mortar to absorb tensile stresses is ultimately an undesirable property, because the stresses at the points where the mortar is not holding are higher than in a straightforward stretch of brickwork.

Estimation of transient heat flux density during the heat supply of a catalytic wall steam methane reformer

Science.gov (United States)

Settar, Abdelhakim; Abboudi, Saïd; Madani, Brahim; Nebbali, Rachid

2018-02-01

Due to the endothermic nature of the steam methane reforming reaction, the process is often limited by the heat transfer behavior in the reactors. Poor thermal behavior sometimes leads to slow reaction kinetics, which is characterized by the presence of cold spots in the catalytic zones. Within this framework, the present work consists on a numerical investigation, in conjunction with an experimental one, on the one-dimensional heat transfer phenomenon during the heat supply of a catalytic-wall reactor, which is designed for hydrogen production. The studied reactor is inserted in an electric furnace where the heat requirement of the endothermic reaction is supplied by electric heating system. During the heat supply, an unknown heat flux density, received by the reactive flow, is estimated using inverse methods. In the basis of the catalytic-wall reactor model, an experimental setup is engineered in situ to measure the temperature distribution. Then after, the measurements are injected in the numerical heat flux estimation procedure, which is based on the Function Specification Method (FSM). The measured and estimated temperatures are confronted and the heat flux density which crosses the reactor wall is determined.

Investigation and assessment of wall heat transfer correlations in SPACE code

International Nuclear Information System (INIS)

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

2010-06-01

SPACE, which is a safety analysis code for nuclear power plants, has been developed to analyze the multidimensional, two-component and three-field flow. This code can be applied to safety analysis for approval which is thermal-hydraulic analysis to support the nuclear power station design, establishment of accident ease strategy, development of operating guide line, experiment plan and analysis. To do so, SPACE code has 12 wall heat transfer mode and the corresponding models and correlations to deal with the physical heat transfer phenomenon in wall surface. In this report, the physical correlation models regarding the wall heat transfer are explained and their performance is assessed against several SET

Rough-wall turbulent boundary layers with constant skin friction

KAUST Repository

Sridhar, A.

2017-03-28

A semi-empirical model is presented that describes the development of a fully developed turbulent boundary layer in the presence of surface roughness with length scale ks that varies with streamwise distance x . Interest is centred on flows for which all terms of the von Kármán integral relation, including the ratio of outer velocity to friction velocity U+∞≡U∞/uτ , are streamwise constant. For Rex assumed large, use is made of a simple log-wake model of the local turbulent mean-velocity profile that contains a standard mean-velocity correction for the asymptotic fully rough regime and with assumed constant parameter values. It is then shown that, for a general power-law external velocity variation U∞∼xm , all measures of the boundary-layer thickness must be proportional to x and that the surface sand-grain roughness scale variation must be the linear form ks(x)=αx , where x is the distance from the boundary layer of zero thickness and α is a dimensionless constant. This is shown to give a two-parameter (m,α) family of solutions, for which U+∞ (or equivalently Cf ) and boundary-layer thicknesses can be simply calculated. These correspond to perfectly self-similar boundary-layer growth in the streamwise direction with similarity variable z/(αx) , where z is the wall-normal coordinate. Results from this model over a range of α are discussed for several cases, including the zero-pressure-gradient ( m=0 ) and sink-flow ( m=−1 ) boundary layers. Trends observed in the model are supported by wall-modelled large-eddy simulation of the zero-pressure-gradient case for Rex in the range 108−1010 and for four values of α . Linear streamwise growth of the displacement, momentum and nominal boundary-layer thicknesses is confirmed, while, for each α , the mean-velocity profiles and streamwise turbulent variances are found to collapse reasonably well onto z/(αx) . For given α , calculations of U+∞ obtained from large-eddy simulations are streamwise

CFD modelling wall heat transfer inside a combustion chamber using ANSYS forte

Science.gov (United States)

Plengsa-ard, C.; Kaewbumrung, M.

2018-01-01

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

Heat transfer enhancement of free surface MHD-flow by a protrusion wall

International Nuclear Information System (INIS)

Hulin Huang; Bo Li

2010-01-01

Due to the magnetohydrodynamic (MHD) effect on the flow, which degrades heat transfer coefficients by pulsation suppression of external magnetic field on the flow, a hemispherical protrusion wall is applied to free surface MHD-flow system as a heat transfer enhancement, because the hemispherical protrusion wall has some excellent characteristics including high heat transfer coefficients, low friction factors and high overall thermal performances. So, the characteristics of the fluid flow and heat transfer of the free surface MHD-flow with hemispherical protrusion wall are simulated numerically and the influence of some parameters, such as protrusion height δ/D, and Hartmann number, are also discussed in this paper. It is found that, in the range of Hartmann number 30 ≤ Ha ≤ 70, the protrusion wall assemblies can achieve heat transfer enhancements (Nu/Nu 0 ) of about 1.3-2.3 relative to the smooth channel, while the friction loss (f/f 0 ) increases by about 1.34-1.45. Thus, the high Nusselt number can be obtained when the protrusion wall with a radically lower friction loss increase, which may help get much higher overall thermal performances.

Development of platform to compare different wall heat transfer packages for system analysis codes

International Nuclear Information System (INIS)

Kim, Min-Gil; Lee, Won Woong; Lee, Jeong Ik; Shin, Sung Gil

2016-01-01

System thermal hydraulic (STH) analysis code is used for analyzing and evaluating the safety of a designed nuclear system. The system thermal hydraulic analysis code typically solves mass, momentum and energy conservation equations for multiple phases with sets of selected empirical constitutive equations to close the problem. Several STH codes are utilized in academia, industry and regulators, such as MARS-KS, SPACE, RELAP5, COBRA-TF, TRACE, and so on. Each system thermal hydraulic code consists of different sets of governing equations and correlations. However, the packages and sets of correlations of each code are not compared quantitatively yet. Wall heat transfer mode transition maps of SPACE and MARS-KS have a little difference for the transition from wall nucleate heat transfer mode to wall film heat transfer mode. Both codes have the same heat transfer packages and correlations in most region except for wall film heat transfer mode. Most of heat transfer coefficients calculated for the range of selected variables of SPACE are the same with those of MARS-KS. For the intervals between 500K and 540K of wall temperature, MARS-KS selects the wall film heat transfer mode and Bromley correlation but SPACE select the wall nucleate heat transfer mode and Chen correlation. This is because the transition from nucleate boiling to film boiling of MARS-KS is earlier than SPACE. More detailed analysis of the heat transfer package and flow regime package will be followed in the near future

Heat transfer augmentation in a tube using nanofluids under constant heat flux boundary condition: A review

International Nuclear Information System (INIS)

Singh, Vinay; Gupta, Munish

2016-01-01

Highlights: • Reviews heat transfer augmentation of nanofluids in a tube with constant heat flux. • Recent advances in hybrid nanofluids are reviewed. • Identifies and compares significant results. • Scope of future research in this area is discussed. - Abstract: In the last few decades, research on nanofluids has increased rapidly. Traditional heat transfer fluids with order of nanometer sized particles (1–100 nm) suspended in them are termed as nanofluids. Nanofluids have been proved as better heat transfer fluids despite of various contradictions in results by different research groups. The aim of this article is to review and summarize the recent experimental and theoretical studies on convective heat transfer in heat exchangers using constant heat flux boundary condition. The use of different types of nanoparticles with different base fluids by different research groups has been presented and compared. Further an overview of experimental results about heat transfer abilities of hybrid nanofluids from available literature sources is also presented. Finally, the challenges and future directions in which research can be further progress are discussed.

Fully-developed heat transfer in annuli with viscous dissipation

Energy Technology Data Exchange (ETDEWEB)

Coelho, P.M. [Universidade do Porto, Porto (Portugal). Centro de Estudos de Fenomenos de Transporte, DEMEGI, Faculdade de Engenharia; Pinho, F.T. [Universidade do Porto, Porto (Portugal). Centro de Estudos de Fenomenos de Transporte, Faculdade de Engenharia

2006-09-15

For Newtonian concentric annular flows analytical solutions are obtained under imposed asymmetric constant wall heat fluxes as well as under imposed asymmetric constant wall temperatures, taking into account viscous dissipation and for fluid dynamic and thermally fully-developed conditions. Results for the special case of the heat flux ratio for identical wall temperatures and the critical Brinkman numbers marking changes of sign in wall heat fluxes are also derived. Equations are presented for the Nusselt numbers at the inner and outer walls, bulk temperature and normalised temperature distribution as a function of all relevant non-dimensional numbers. Given the complexity of the derived equations, simpler exact expressions are presented for the Nusselt numbers for ease of use, with their coefficients given in tables as a function of the radius ratio. (author)

A new wall function boundary condition including heat release effect for supersonic combustion flows

International Nuclear Information System (INIS)

Gao, Zhen-Xun; Jiang, Chong-Wen; Lee, Chun-Hian

2016-01-01

Highlights: • A new wall function including heat release effect is theoretically derived. • The new wall function is a unified form holding for flows with/without combustion. • The new wall function shows good results for a supersonic combustion case. - Abstract: A new wall function boundary condition considering combustion heat release effect (denoted as CWFBC) is proposed, for efficient predictions of skin friction and heat transfer in supersonic combustion flows. Based on a standard flow model including boundary-layer combustion, the Shvab–Zeldovich coupling parameters are introduced to derive a new velocity law-of-the-wall including the influence of combustion. For the temperature law-of-the-wall, it is proposed to use the enthalpy–velocity relation, instead of the Crocco–Busemann equation, to eliminate explicit influence of chemical reactions. The obtained velocity and temperature law-of-the-walls constitute the CWFBC, which is a unified form simultaneously holding for single-species, multi-species mixing and multi-species reactive flows. The subsequent numerical simulations using this CWFBC on an experimental case indicate that the CWFBC could accurately reflect the influences on the skin friction and heat transfer by the chemical reactions and heat release, and show large improvements compared to previous WFBC. Moreover, the CWFBC can give accurate skin friction and heat flux for a coarse mesh with y"+ up to 200 for the experimental case, except for slightly larger discrepancy of the wall heat flux around ignition position.

Study of the Relap5/mod3.2 wall heat flux partitioning model

International Nuclear Information System (INIS)

Hari, S.; Hassan, Y.A.

2001-01-01

The performance of the subcooled boiling model adapted in RELAP5/MOD3.2 computer code has been assessed in detail for low-pressure conditions and it has been found that the void fraction profile is under-predicted. In general, any subcooled boiling model is composed of individual sub-models that account for the different physical mechanism that govern the overall process, as the wall vapor generation, interfacial shear and condensation etc. The wall heat flux partitioning model is one of the important sub-models that is a constituent of any subcooled boiling model. The function of this model is to apportion the wall heat flux to the different components (as the single/two phase fluid or bubble), as the case may be, in a two-phase flow-boiling scenario adjacent to a heated wall. The ''pumping factor'' approach is generally followed by most of the wall heat flux partitioning models, for partitioning the wall heat flux. In this work, the wall heat flux partitioning model of RELAP5/MOD3.2 computer code is studied; in particular, the ''pumping factor'' formulation in the present code version is assessed for its performance under low-pressure conditions. In addition, three different ''pumping factor'' formulations available in the literature have been introduced into the RELAP5/MOD3.2 code. Simulations of two low-pressure subcooled flow boiling experiments were performed with the refined code versions to determine the appropriate pumping factor to be used under these conditions. (author)

Numerical study of natural convection heat transfer in a horizontal channel provided with rectangular blocks releasing uniform heat flux and mounted on its lower wall

International Nuclear Information System (INIS)

Bakkas, M.; Amahmid, A.; Hasnaoui, M.

2008-01-01

Two-dimensional laminar steady natural convection in a horizontal channel with the upper wall maintained cold at a constant temperature and the lower one provided with rectangular heating blocks, periodically distributed, has been studied numerically. The blocks are connected with adiabatic segments and their surfaces are assumed to release a uniform heat flux. The study is performed using air as the working fluid (Pr = 0.72). The spacing between the blocks is maintained constant (C = l'/H' = 0.5) while the Rayleigh number and the relative height of the blocks are respectively varied in the ranges 10 2 ≤ Ra ≤ 2 x 10 6 and 1/8 ≤ B = h'/H' ≤ 1/2. The effect of the computational domain length on the multiplicity of solutions is investigated. Flow and temperature fields are also produced for various combinations of the governing parameters. It is demonstrated that, depending on the length of the computational domain and the governing parameters, different flow structures can be obtained

Thermo-hydraulic characterization of a self-pumping corrugated wall heat exchanger

International Nuclear Information System (INIS)

Schmidmayer, Kevin; Kumar, Prashant; Lavieille, Pascal; Miscevic, Marc; Topin, Frédéric

2017-01-01

Compactness, efficiency and thermal control of the heat exchanger are of critical significance for many electronic industry applications. In this view, a new concept of heat exchanger at millimeter scale is proposed and numerically studied. It consists in dynamically deforming at least one of its walls by a progressive wave in order to create an active corrugated channel. Systematic studies were performed in single-phase flow on the different deformation parameters that allow obtaining the thermo-hydraulic characteristics of the system. It has been observed the dynamic wall deformation induces a significant pumping effect. Intensification of heat transfer remains very important even for highly degraded waveforms although the pumping efficiency is reduced in this case. The mechanical power applied on the upper wall to deform it dynamically is linked to the wave shape, amplitude, frequency and outlet-inlet pressure difference. The overall performance of the proposed system has been evaluated and compared to existing static channels. The performance of the proposed heat exchanger evolved in two steps for a given wall deformation. It declines slightly up to a critical value of mechanical power applied on the wall. When this critical value is exceeded, it deteriorates significantly, reaching the performance of existing conventional systems. - Highlights: • A new concept of heat exchanger within channel at millimeter scale is proposed. • Upper wall is deformed dynamically by applying external mechanical power. • Pumping effect is observed and is linked to the wave shape, amplitude and frequency. • Efficient proposed system in low Reynolds number range. • Overall performance is significantly high compared to static corrugated and straight channels.

Reducing heat transfer across the insulated walls of refrigerated truck trailers by the application of phase change materials

International Nuclear Information System (INIS)

Ahmed, Mashud; Meade, Oliver; Medina, Mario A.

2010-01-01

A general estimate shows that 80% of communities across the United States receive their goods exclusively by transport trucks, of which a significant number are climate-controlled because they carry perishable goods, pharmaceutical items and many other temperature-sensitive commodities. Keeping the inside of a truck trailer at a constant temperature and relative humidity requires exact amounts of heat and/or moisture management throughout the shipment period, which is regulated via small refrigeration units, placed outside the truck, that operate by burning fuel. These trucks, known as refrigerated truck trailers, are the focus of this paper. In the research presented herein, the conventional method of insulation of the refrigerated truck trailer was modified using phase change materials (PCMs). The limited research carried out in refrigerated transport compared to other refrigeration processes has left spaces for innovative solutions in this area. The research investigated the inclusion of paraffin-based PCMs in the standard trailer walls as a heat transfer reduction technology. An average reduction in peak heat transfer rate of 29.1% was observed when all walls (south, east, north, west, and top) were considered. For individual walls, the peak heat transfer rate was reduced in the range of 11.3-43.8%. Overall average daily heat flow reductions into the refrigerated compartment of 16.3% were observed. These results could potentially translate into energy savings, pollution abatement from diesel-burning refrigeration units, refrigeration equipment size reduction, and extended equipment operational life. The research and its results will help to better understand the scope of this technology.

Bayesian inference of the heat transfer properties of a wall using experimental data

KAUST Repository

Iglesias, Marco

2016-01-06

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

Influence of Joule heating on current-induced domain wall depinning

Energy Technology Data Exchange (ETDEWEB)

Moretti, Simone, E-mail: simone.moretti@usal.es; Raposo, Victor; Martinez, Eduardo [University of Salamanca, Plaza de los Caidos, 37008 Salamanca (Spain)

2016-06-07

The domain wall depinning from a notch in a Permalloy nanostrip on top of a SiO{sub 2}/Si substrate is studied theoretically under application of static magnetic fields and the injection of short current pulses. The influence of Joule heating on current-induced domain wall depinning is explored self-consistently by coupling the magnetization dynamics in the ferromagnetic strip to the heat transport throughout the system. Our results indicate that Joule heating plays a remarkable role in these processes, resulting in a reduction in the critical depinning field and/or in a temporary destruction of the ferromagnetic order for typically injected current pulses. In agreement with experimental observations, similar pinning-depinning phase diagrams can be deduced for both current polarities when the Joule heating is taken into account. These observations, which are incompatible with the sole contribution of spin transfer torques, provide a deeper understanding of the physics underlying these processes and establish the real scope of the spin transfer torque. They are also relevant for technological applications based on current-induced domain-wall motion along soft strips.

The role of the velocity gradient in laminar convective heat transfer through a tube with a uniform wall heat flux

International Nuclear Information System (INIS)

Wang Liangbi; Zhang Qiang; Li Xiaoxia

2009-01-01

This paper aims to contribute to a better understanding of convective heat transfer. For this purpose, the reason why thermal diffusivity should be placed before the Laplacian operator of the heat flux, and the role of the velocity gradient in convective heat transfer are analysed. The background to these analyses is that, when the energy conservation equation of convective heat transfer is used to explain convective heat transfer there are two points that are difficult for teachers to explain and for undergraduates to understand: thermal diffusivity is placed before the Laplacian operator of temperature; on the wall surface (the fluid side) the velocity is zero, a diffusion equation of temperature is gained from energy conservation equation, however, temperature cannot be transported. Consequently, the real physical meaning of thermal diffusivity is not clearly reflected in the energy conservation equation, and whether heat transfer occurs through a diffusion process or a convection process on the wall surface is not clear. Through a simple convective heat transfer case: laminar convective heat transfer in a tube with a uniform wall heat flux on the tube wall, this paper explains these points more clearly. The results declare that it is easier for teachers to explain and for undergraduates to understand these points when a description of heat transfer in terms of the heat flux is used. In this description, thermal diffusivity is placed before the Laplacian operator of the heat flux; the role of the velocity gradient in convective heat transfer appears, on the wall surface, the fact whether heat transfer occurs through a diffusion process or a convection process can be explained and understood easily. The results are not only essential for teachers to improve the efficiency of university-level physics education regarding heat transfer, but they also enrich the theories for understanding heat transfer

Laminar free convection in a vertical tube with constant wall temperature considering the variation of fluid properties

International Nuclear Information System (INIS)

Senna, J.G.

1981-01-01

A model to analyze Laminar Free convection with variable properties in the entrance of a vertical open tube with constant wall temperature and for one Prandtl number (0.7), is studied. The velocity and temperature profiles are determined by finite difference methods for different rates of wall to ambient temperatures and different values of the velocity in the entrance of the tube. The results will be compared with those obtained in the same problem with constant properties. (Author) [pt

Random generation of bubble sizes on the heated wall during subcooled boiling

International Nuclear Information System (INIS)

Koncar, B.; Mavko, B.

2003-01-01

In subcooled flow boiling, a locally averaged bubble diameter significantly varies in the transverse direction to the flow. From the experimental data of Bartel, a bent crosssectional profile of local bubble diameter with the maximum value shifted away from the heated wall may be observed. In the present paper, the increasing part of the profile (near the heated wall) is explained by a random generation of bubble sizes on the heated wall. The hypothesis was supported by a statistical analysis of different CFD simulations, varying by the size of the generated bubble (normal distribution) and the number of generated bubbles per unit surface. Local averaging of calculated void fraction distributions over different bubble classes was performed. The increasing curve of the locally averaged bubble diameter in the near-wall region was successfully predicted. (author)

Options for a high heat flux enabled helium cooled first wall for DEMO

Energy Technology Data Exchange (ETDEWEB)

Arbeiter, Frederik, E-mail: f.arbe@kit.edu; Chen, Yuming; Ghidersa, Bradut-Eugen; Klein, Christine; Neuberger, Heiko; Ruck, Sebastian; Schlindwein, Georg; Schwab, Florian; Weth, Axel von der

2017-06-15

Highlights: • Design challenges for helium cooled first wall reviewed and otimization approaches explored. • Application of enhanced heat transfer surfaces to the First Wall cooling channels. • Demonstrated a design point for 1 MW/m{sup 2} with temperatures <550 °C and acceptable stresses. • Feasibility of several manufacturing processes for ribbed surfaces is shown. - Abstract: Helium is considered as coolant in the plasma facing first wall of several blanket concepts for DEMO fusion reactors, due to the favorable properties of flexible temperature range, chemical inertness, no activation, comparatively low effort to remove tritium from the gas and no chemical corrosion. Existing blanket designs have shown the ability to use helium cooled first walls with heat flux densities of 0.5 MW/m{sup 2}. Average steady state heat loads coming from the plasma for current EU DEMO concepts are expected in the range of 0.3 MW/m{sup 2}. The definition of peak values is still ongoing and depends on the chosen first wall shape, magnetic configuration and assumptions on the fraction of radiated power and power fall off lengths in the scrape off layer of the plasma. Peak steady state values could reach and excess 1 MW/m{sup 2}. Higher short-term transient loads are expected. Design optimization approaches including heat transfer enhancement, local heat transfer tuning and shape optimization of the channel cross section are discussed. Design points to enable a helium cooled first wall capable to sustain heat flux densities of 1 MW/m{sup 2} at an average shell temperature lower than 500 °C are developed based on experimentally validated heat transfer coefficients of structured channel surfaces. The required pumping power is in the range of 3–5% of the collected thermal power. The FEM stress analyses show code-acceptable stress intensities. Several manufacturing methods enabling the application of the suggested heat transfer enhanced first wall channels are explored. An

A constant heat flux plasma limiter for TEXTOR

International Nuclear Information System (INIS)

Mioduszewski, P.

1980-10-01

In future large tokamak machines heat removal from the plasma is going to play an important role. In TEXTOR the total plasma power is expected to be in the range of 0.5-2.5 MW. Typical fractions of about 50% of this power have to be removed from the plasma by limiters. The power flux from the limiter scrape-off layer to the limiter surface decays rapidly with distance into the scrape-off layer resulting in a highly space-dependent heat load on the limiter. Therefore, limiters are shaped in a way to smooth of the heat load, and the ideal limiter shape should produce a constant heat flux over the whole limiter surface. The ideally shaped limiter offers a better chance to handle the high heat loads with the preferred materials like stainless steel (or inconel 625 as in the case of TEXTOR). (orig./GG)

On the assumption of vanishing temperature fluctuations at the wall for heat transfer modeling

Science.gov (United States)

Sommer, T. P.; So, R. M. C.; Zhang, H. S.

1993-01-01

Boundary conditions for fluctuating wall temperature are required for near-wall heat transfer modeling. However, their correct specifications for arbitrary thermal boundary conditions are not clear. The conventional approach is to assume zero fluctuating wall temperature or zero gradient for the temperature variance at the wall. These are idealized specifications and the latter condition could lead to an ill posed problem for fully-developed pipe and channel flows. In this paper, the validity and extent of the zero fluctuating wall temperature condition for heat transfer calculations is examined. The approach taken is to assume a Taylor expansion in the wall normal coordinate for the fluctuating temperature that is general enough to account for both zero and non-zero value at the wall. Turbulent conductivity is calculated from the temperature variance and its dissipation rate. Heat transfer calculations assuming both zero and non-zero fluctuating wall temperature reveal that the zero fluctuating wall temperature assumption is in general valid. The effects of non-zero fluctuating wall temperature are limited only to a very small region near the wall.

Effect of guide wall on jet impingement cooling in blade leading edge channel

International Nuclear Information System (INIS)

Zhao, Qing-Yang; Chung, Heeyoon; Choi, Seok Min; Cho, Hyung Hee

2016-01-01

The characteristics of fluid flow and heat transfer, which are affected by the guide wall in a jet impinged leading edge channel, have been investigated numerically using three-dimensional Reynolds-averaged Navier-Stokes analysis via the shear stress transport turbulence model and gamma theta transitional turbulence model. A constant wall heat flux condition has been applied to the leading edge surface. The jet-to-surface distance is constant, which is three times that of the jet diameter. The arrangement of the guide wall near the jet hole is set as a variable. Results presented in this study include the Nusselt number contour, velocity vector, streamline with velocity, and local Nusselt number distribution along the central line on the leading edge surface. The average Nusselt number and average pressure loss between jet nozzle and channel exit are calculated to assess the thermal performance. The application of the guide wall is aimed at improving heat transfer uniformity on the leading edge surface. Results indicated that the streamwise guide wall ensures the vertical jet impingement flow intensity and prevents the flow after impingement to reflux into jet flow. Thus, a combined rectangular guide wall benefits the average heat transfer, thermal performance and heat transfer distribution uniformity

The Heat Transfer Coefficient of Recycled Concrete Bricks Combination with EPS Insulation Board Wall

Directory of Open Access Journals (Sweden)

Jianhua Li

2015-01-01

Full Text Available Four tectonic forms samples were conducted to test their heat transfer coefficients. By analyzing and comparing the test values and theoretical values of the heat transfer coefficient, a corrected-value calculation method for determining the heat transfer coefficient was proposed; the proposed method was proved to be reasonably correct. The results indicated that the recycled concrete brick wall heat transfer coefficient is higher than that of the clay brick wall, the heat transfer coefficient of recycled concrete brick wall could be effectively reduced when combined with the EPS insulation board, and the sandwich insulation type was better than that of external thermal insulation type.

Exact Solutions for Unsteady Free Convection Flow of Casson Fluid over an Oscillating Vertical Plate with Constant Wall Temperature

Directory of Open Access Journals (Sweden)

Asma Khalid

2015-01-01

Full Text Available The unsteady free flow of a Casson fluid past an oscillating vertical plate with constant wall temperature has been studied. The Casson fluid model is used to distinguish the non-Newtonian fluid behaviour. The governing partial differential equations corresponding to the momentum and energy equations are transformed into linear ordinary differential equations by using nondimensional variables. Laplace transform method is used to find the exact solutions of these equations. Expressions for shear stress in terms of skin friction and the rate of heat transfer in terms of Nusselt number are also obtained. Numerical results of velocity and temperature profiles with various values of embedded flow parameters are shown graphically and their effects are discussed in detail.

Type I ELM filament heat fluxes on the KSTAR main chamber wall

Directory of Open Access Journals (Sweden)

M.-K. Bae

2017-08-01

Full Text Available Heat loads deposited on the first wall by mitigated Type I ELMs are expected to be the dominant contributor to the total thermal plasma wall load of the International Thermonuclear Experimental Reactor (ITER, particularly in the upper main chamber regions during the baseline H-mode magnetic equilibrium, due to the fast radial convective heat propagation of ELM filaments before complete loss to the divertor. Specific Type I ELMing H-mode discharges have been performed with a lower single null magnetic geometry, where the outboard separatrix position is slowly (∼7s scanned over a radial distance of 7cm, reducing the wall probe–separatrix distance to a minimum of ∼9cm, and allowing the ELM filament heat loss to the wall to be analyzed as a function of radial propagation distance. A fast reciprocating probe (FRP head is separately held at fixed position toroidally close and 4.7cm radially in front of the wall probe. This FRP monitors the ELM ion fluxes, allowing an average filament radial propagation speed, found to be independent of ELM energy, of 80–100ms−1 to be extracted. Radial dependence of the peak filament wall parallel heat flux is observed to be exponential, with the decay length of λq, ELM ∼25 ± 4mm and with the heat flux of q∥, ELM= 0.05MWm−2 at the wall, corresponding to q∥ ∼ 7.5MWm−2 at the second separatrix. Along with the measured radial propagation speed and the calculated radial profile of the magnetic connection lengths across the SOL, these data could be utilized to analyze filament energy loss model for the future machines.

Energy balance of droplets impinging onto a wall heated above the Leidenfrost temperature

International Nuclear Information System (INIS)

Dunand, P.; Castanet, G.; Gradeck, M.; Maillet, D.; Lemoine, F.

2013-01-01

Highlights: • Measurement techniques are combined to characterize the heat lost due to liquid vaporization. • The wall heat flux is estimated by infrared thermography associated with inverse heat conduction. • The liquid heating is characterized by the two-color Laser-Induced Fluorescence thermometry. • Results reveal how the heat fluxes vary with the droplet sizes and the Weber number. -- Abstract: This work is an experimental study aiming at characterizing the heat transfers induced by the impingement of water droplets (diameter 80–180 μm) on a thin nickel plate heated by electromagnetic induction. The temperature of the rear face of the nickel sample is measured by means of an infrared camera and the heat removed from the wall due to the presence of the droplets is estimated using a semi-analytical inverse heat conduction model. In parallel, the temperature of the droplets is measured using the two-color Laser-Induced Fluorescence thermometry (2cLIF) which has been extended to imagery for the purpose of these experiments. The measurements of the variation in the droplet temperature occurring during an impact allow determining the sensible heat removed by the liquid. Measurements are performed at wall conditions well above the Leidenfrost temperature. Different values of the Weber numbers corresponding to the bouncing and splashing regimes are tested. Comparisons between the heat flux removed from the wall and the sensible heat gained by the liquid allows estimating the heat flux related to liquid evaporation. Results reveal that the respective level of the droplet sensible heat and the heat lost due to liquid vaporization can vary significantly with the droplet sizes and the Weber number

Study of an active wall solar heating system

International Nuclear Information System (INIS)

Kassem, Talal

2006-01-01

An active wall solar heating system was built and tested. In the same time a compatible computer program has been according to set the recommended dimensions for the solar collectors where (F-Chart) method used to set the ratio of monthly solar sharing average for the examined heating system. Some parameters, such as collectors' areas, its tilt angle and near earth reflecting were experimentally investigated, affecting the executed active solar heating system performance. The study explain the ability of using this system which is simple, Low coast and high performance in heating residential and public buildings and heating water with ratio of yearly solar sharing achieves the needed saving of using this system.(Author)

Heat transfer improvement due to the imposition of non-uniform wall heating for in-tube laminar forced convection

International Nuclear Information System (INIS)

Hajmohammadi, M.R.; Poozesh, S.; Rahmani, M.; Campo, A.

2013-01-01

This paper explores the bearing that a non-uniform distribution of heat flux used as a wall boundary condition exerts on the heat transfer improvement in a round pipe. Because the overall heat load is considered fixed, the heat transfer improvement is viewed through a reduction in the maximum temperature (‘hot spot’) by imposing optimal distribution of heat flux. Two cases are studied in detail 1) fully developed and 2) developing flow. Peak temperatures in the heated pipe wall are calculated via an analytical approach for the fully developed case, while a numerical simulation based on CFD is employed for the developing case. By relaxing the heat flux distribution on the pipe wall, the numerical results imply that the optimum distribution of heat flux, which minimizes the peak temperatures corresponds with the ‘descending’ distribution. Given that the foregoing approach is quite different from the ‘ascending’ heat flux distribution recommended in the literature by means of the entropy generation minimization (EGM) method, it is inferred that the optimization of heat transfer and fluid flow, in comparison with the thermodynamic optimization, may bring forth quite different guidelines for the designs of thermal systems under the same constraints and circumstances. -- Highlights: • Considered the bearing of non-uniform distribution of heat flux on the hot spots. • Determined the optimal distribution of heat flux that minimizes the hot spots. • Results are compared with those obtained by EGM method

Heat transfer and carryover of low pressure water in a heated vertical tube

International Nuclear Information System (INIS)

Smith, T.A.

1976-01-01

Local heat transfer coefficients in the stable film boiling and dispersed flow regimes were studied for the upward flow of low pressure water in a heated vertical tube. Wall temperatures were maintained constant with time and along the tube so that both axial and time temperature gradients approached zero. Heat flux along the tube was not constant but was applied so as to maintain a steady state temperature profile. A preheater was used to bring the liquid to saturation before it entered the main portion of the test section and in some cases the equilibrium quality was greater than zero at the entrance to the main test section. The test section was made of stainless steel, and the lower portion, the preheater, was heated directly by dc current. Copper block heat spikes were clamped to the upper test section and were used to apply the heat flux to maintain the wall temperature constant with time. Several theories for the different possible types of flow (laminar or turbulent, tube or film) were compared with the experimental data. The carry-over point for low flooding rates (1 inch/sec or less) was inferred from these comparisons and gave good agreement with the Plummer critical mass criterion for liquid carry-over

ICRF heating in JET during initial operations with the ITER-like wall

Energy Technology Data Exchange (ETDEWEB)

Jacquet, P.; Brix, M.; Graham, M.; Mayoral, M.-L.; Meigs, A.; Monakhov, I.; Sirinelli, A. [Euratom/CCFE Fusion Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Bobkov, V.; Drewelow, P.; Pütterich, T. [Max-Planck-Institut für Plasmaphysik, EURATOM-Assoziation, Garching (Germany); Brezinsek, S. [IEK-4, Forschungszentrum Jülich, Association EURATOM-FZJ (Germany); Campergue, A-L. [Ecole Nationale des Ponts et Chaussées, F77455 Marne-la-Vallée (France); Colas, L. [CEA, IRFM, F-13108 Saint-Paul-Lez-Durance (France); Czarnecka, A. [Association Euratom-IPPLM, Hery 23, 01-497 Warsaw (Poland); Klepper, C. C. [Oak Ridge National Laboratory, Oak Ridge, TN 37831-6169 (United States); Lerche, E.; Van-Eester, D. [Association EURATOM-Belgian State, ERM-KMS, Brussels (Belgium); Milanesio, D. [Politecnico di Torino, Department of Electronics, Torino (Italy); Mlynar, J. [Association EURATOM-IPP.CR, Za Slovankou 3, 182 21 Praha 8 (Czech Republic); Collaboration: JET-EFDA Contributors

2014-02-12

In 2011/12, JET started operation with its new ITER-Like Wall (ILW) made of a tungsten (W) divertor and a beryllium (Be) main chamber wall. The impact of the new wall material on the JET Ion Cyclotron Resonance Frequency (ICRF) operation was assessed and also the properties of JET plasmas heated with ICRF were studied. No substantial change of the antenna coupling resistance was observed with the ILW as compared with the carbon wall. Heat-fluxes on the protecting limiters close the antennas quantified using Infra-Red (IR) thermography (maximum 4.5 MW/m{sup 2} in current drive phasing) are within the wall power load handling capabilities. A simple RF sheath rectification model using the antenna near-fields calculated with the TOPICA code can well reproduce the heat-flux pattern around the antennas. ICRF heating results in larger tungsten and nickel (Ni) contents in the plasma and in a larger core radiation when compared to Neutral Beam Injection (NBI) heating. Some experimental facts indicate that main-chamber W components could be an important impurity source: the divertor W influx deduced from spectroscopy is comparable when using RF or NBI at same power and comparable divertor conditions; the W content is also increased in ICRF-heated limiter plasmas; and Be evaporation in the main chamber results in a strong and long lasting reduction of the impurity level. The ICRF specific high-Z impurity content decreased when operating at higher plasma density and when increasing the hydrogen concentration from 5% to 20%. Despite the higher plasma bulk radiation, ICRF exhibited overall good plasma heating efficiency; The ICRF power can be deposited at plasma centre and the radiation is mainly from the outer part of the plasma. Application of ICRF heating in H-mode plasmas started, and the beneficial effect of ICRF central electron heating to prevent W accumulation in the plasma core could be observed.

Radiant and convective heat transfer for flow of a transparent gas in a short tube with prescribed sinusoidal wall heat flux

International Nuclear Information System (INIS)

de Lemos, M.J.S.

1982-01-01

The present analysis accounts for radiant and convective heat transfer for a transparent fluid flowing in a short tube with prescribed wall heat flux. The heat flux distribution used was of sine shape with maximum at the middle of the tube. Such a solution is the approximate one for axial power in a nuclear reactor. The solutions for the tube wall and gas bulk temperatures were obtained by successive substitutions for the wall and gas balance energy equations. The results show a decrease of 30% for the maximum wall temperature using black surface (e = 1). In this same case, the increasing in the gas temperature shows a decrease of 58%

Experimental observation for the heat transfer in fluids

International Nuclear Information System (INIS)

Salinas R, G.A.

1996-01-01

The heat transfer that occurs into a cavity with a relation 2/1 with constant heat supply in a vertical wall and on the opposed wall at constant temperature is studied. The energy transfer process causes the heat convection that occurs mainly due to energy transport that is present by means of the motion of the fluid itself. Also the heat conduction process by molecular exchange is obtained. During the fluid particle displacements, the high energy regions take contact with the low energy regions resulting by this way the free convection by density differences. The flow can be followed by means of tracers and the changes of density can be registered by optical techniques like interferometry. (Author)

A Study on Aspect Ratio of Heat Dissipation Fin for the Heat Dissipation Performance of Ultra Constant Discharge Lamp

Science.gov (United States)

Ko, Dong Guk; Cong Ge, Jun; Im, Ik Tae; Choi, Nag Jung; Kim, Min Soo

2018-01-01

In this study, we analyzed the heat dissipation performance of UCD lamp ballast fin with various aspect ratios. The minimum grid size was 0.02 mm and the number of grid was approximately 11,000. In order to determine the influence of the aspect ratio on the heat dissipation performance of UCD lamp ballast fin, the heat transfer area of the fin was kept constant at 4 mm2. The aspect ratios of the fin were 2 mm: 2 mm (basic model), 1.5 mm: 2.7 mm and 2.7 mm: 1.5 mm, respectively. The heat flux and heat flux time at fin were kept constant at 1×105 W/m2 and 10 seconds, respectively. The heat dissipation performance by the fin was the best at an aspect ratio of 1.5 mm: 2.7 mm.

The combined effects of wall longitudinal heat conduction and inlet fluid flow maldistribution in crossflow plate-fin heat exchangers

Energy Technology Data Exchange (ETDEWEB)

Ranganayakulu, C. [Aeronautical Development Agency, Bangalore (India); Seetharamu, K.N. [School of Mechanical Engineering, Univ. of Southern Malaysia (KCP), Tronoh (Malaysia)

2000-05-01

An analysis of a crossflow plate-fin compact heat exchanger, accounting for the combined effect of two-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow distribution on both hot and cold fluid sides is carried out using a finite element method. Using the fluid flow maldistribution models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction and flow nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performance deteriorations are quite significant in some typical applications due to the combined effects of wall longitudinal heat conduction and inlet fluid flow nonuniformity on crossflow plate-fin heat exchanger. (orig.)

The thermal response of a homogeneous slab to a constant heat flux

Energy Technology Data Exchange (ETDEWEB)

Bunn, J.P.

1983-01-01

An approximate solution of the one-dimensional heat flow equation for a homogeneous slab subject to a constant heat flux at its inner face and bounded at its outer face by a surface resistance to a medium at constant temperature is presented. This solution is used to find the temperature of the inner face as a function of time. It is also used to investigate the approach to steady state enabling the time required to reach a given percentage of the steady state temperature to be calculated.

Methods for monitoring heat flow intensity in the blast furnace wall

Directory of Open Access Journals (Sweden)

L'. Dorčák

2010-04-01

Full Text Available In this paper we present the main features of an online system for real-time monitoring of the bottom part of the blast furnace. Firstly, monitoring concerns the furnace walls and furnace bottom temperatures measurement and their visualization. Secondly, monitored are the heat flows of the furnace walls and furnace bottom. In the case of two measured temperatures, the heat flow is calculated using multi-layer implicit difference scheme and in the case of only one measured temperature, the heat flow is calculated using a method based on application of fractional-order derivatives. Thirdly, monitored is the theoretical temperature of the blast furnace combustion process in the area of tuyeres.

Numerical analysis of heat transfer in the first wall of CFETR WCSB blanket

Energy Technology Data Exchange (ETDEWEB)

Zhao, Pinghui, E-mail: phzhao@mail.ustc.edu.cn; Deng, Weiping; Ge, Zhihao; Li, Yuanjie

2016-04-15

Highlights: • Detailed numerical analysis of heat transfer in a water-cooling first wall was carried out based on the conceptual design of CFETR WCSB blanket. • Investigation of the influences of buoyancy effect and surface roughness on heat transfer in the water-cooling first wall was presented. • Analysis of the effect of the front wall thickness on temperature was carried out for the water-cooling first wall design. • Simulation results of two 1D CFD methods were evaluated by the 3D CFD data. - Abstract: China Fusion Engineering Test Reactor (CFETR), the first fusion reactor experiment project planned in China, is now being investigated in detail. Recently, a conceptual structural design of the Water-Cooled-Solid-Breeder (WCSB) blanket was proposed as one of the breeding blanket candidates for CFETR. In this research, based on the present design of the CFETR WCSB blanket, the heat transfer performance in the first wall (FW) under the pressurized water cooling condition was analyzed. The 3D computational fluid dynamics (CFD) results show that the maximal temperature of the FW will not exceed the limited temperature under normal or even higher heat flux condition. In addition, the effect of buoyancy on heat transfer is negligible under both conditions. The influence of roughness becomes increasingly important when the roughness height lies in the fully turbulent regime. The maximal temperature increases approximately linearly as the thickness of the front wall increases. It is also found that the heat flux and the local heat transfer coefficient are extremely non-uniform in the circumferential direction. Two 1D CFD methods are also evaluated by 3D CFD data, with the conclusion that both 1D results have some differences with the 3D data. The improved 1D method is more accurate than the former one. However, we ascertain that 1D methods should be used with caution for the water-cooling FW design.

Characteristics of turbulent velocity and temperature in a wall channel of a heated rod bundle

Energy Technology Data Exchange (ETDEWEB)

Krauss, T.; Meyer, L. [Forschungszentrum Karlsruhe (Germany)

1995-09-01

Turbulent air flow in a wall sub-channel of a heated 37-rod bundle (P/D = 1.12, W/D = 1.06) was investigated. measurements were performed with hot-wire probe with X-wires and a temperature wire. The mean velocity, the mean fluid temperature, the wall shear stress and wall temperature, the turbulent quantities such as the turbulent kinetic energy, the Reynolds-stresses and the turbulent heat fluxes were measured and are discussed with respect to data from isothermal flow in a wall channel and heated flow in a central channel of the same rod bundle. Also, data on the power spectral densities of the velocity and temperature fluctuations are presented. These data show the existence of large scale periodic fluctuations are responsible for the high intersubchannel heat and momentum exchange.

Mixed convection heat transfer enhancement in a cubic lid-driven cavity containing a rotating cylinder through the introduction of artificial roughness on the heated wall

Science.gov (United States)

Kareem, Ali Khaleel; Gao, Shian

2018-02-01

The aim of the present numerical investigation is to comprehensively analyse and understand the heat transfer enhancement process using a roughened, heated bottom wall with two artificial rib types (R-s and R-c) due to unsteady mixed convection heat transfer in a 3D moving top wall enclosure that has a central rotating cylinder, and to compare these cases with the smooth bottom wall case. These different cases (roughened and smooth bottom walls) are considered at various clockwise and anticlockwise rotational speeds, -5 ≤ Ω ≤ 5, and Reynolds numbers of 5000 and 10 000. The top and bottom walls of the lid-driven cavity are differentially heated, whilst the remaining cavity walls are assumed to be stationary and adiabatic. A standard k-ɛ model for the Unsteady Reynolds-Averaged Navier-Stokes equations is used to deal with the turbulent flow. The heat transfer improvement is carefully considered and analysed through the detailed examinations of the flow and thermal fields, the turbulent kinetic energy, the mean velocity profiles, the wall shear stresses, and the local and average Nusselt numbers. It has been concluded that artificial roughness can strongly affect the thermal fields and fluid flow patterns. Ultimately, the heat transfer rate has been dramatically increased by involving the introduced artificial rips. Increasing the cylinder rotational speed or Reynolds number can enhance the heat transfer process, especially when the wall roughness exists.

Development and preliminary assessment of the wall condensation heat transfer models for the SPACE code

International Nuclear Information System (INIS)

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

2009-01-01

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

Conjugate heat transfer for turbulent flow in a thick walled plain pipe

Directory of Open Access Journals (Sweden)

Canli Eyub

2018-01-01

Full Text Available Laminar and turbulent flow have their own characteristics in respect of heat transfer in pipes. While conjugate heat transfer is a major concern for a thick walled pipe with laminar flow inside it, there are limited studies about a turbulent flow in a thick walled plain pipe considering the conjugate heat transfer. In order to conduct such a work by means of in-house developed code, it was desired to make a preliminary investigation with commercially available CFD codes. ANSYS CFD was selected as the tool since it has a positive reputation in the literature for reliability. Defined heat transfer problem was solved with SIMPLE and Coupled Schemes for pressure velocity coupling and results are presented accordingly.

Positioning a thin-wall round wrapper within a heavy wall out-of-round shell of a heat exchanger

International Nuclear Information System (INIS)

Hargrove, H.G.; Thompson, E.G.; Bayless, J.R.

1983-01-01

A thin-wall, generally round wrapper is installed within a heavy wall, rolled heat exchanger shell which has greater out-of-round tolerances than the wrapper and the wrapper is maintained in its round state by utilizing a plurality of jacks disposed adjacent spaced tube support plates within the wrapper. (author)

Flow laminarization and heat transfer crisis in tubes while intense heating of turbulent flow of a gas endothermically dissociating on a wall

International Nuclear Information System (INIS)

Kurganov, V.A.; Gladuntsov, A.I.

1977-01-01

Analysed are the experimental data obtained for heat transfer to gaseous dissociating ammonium (NH 3 ) under heating in round pipes (steel Kh18N10T) at developed eddying input flow and marginal condition of heat supply gsub(c) approximately equal to const in the ranges of the following parameters: p=3-10 atm; Tsub(input)=310-720 K; Tsub(c) ( 3 ; gsub(c)/-anti rho W 8.8 kJ/kg; gsub(c)/(anti rho WCsub(p) sub(input)Tsub(input)) (<=) 0.0104; 1/d (<=) 150 (where Tsub(c) is the wall temperature, gsub(c) the heat flow density on wall, and anti rho W velocity). The discussion involves phenomena of worsened heat transfer at high heat loads. The authors show the basic relationship between these phenomena and laminarization of the near-wall flow at the input site of the pipe. The regularities of heat transfer were noted to undergo substantial transformation under laminarized flow

Experimental demonstration of a tailored-width microchannel heat exchanger configuration for uniform wall temperature

International Nuclear Information System (INIS)

Riera, S; Barrau, J; Rosell, J I; Omri, M; Fréchette, L G

2013-01-01

In this work, an experimental study of a novel microfabricated heat sink configuration that tends to uniform the wall temperature, even with increasing flow temperature, is presented. The design consists of a series of microchannel sections with stepwise varying width. This scheme counteracts the flow temperature increase by reducing the local thermal resistance along the flow path. A test apparatus with uniform heat flux and distributed wall temperature measurements was developed for microchannel heat exchanger characterisation. The energy balance is checked and the temperature distribution is analysed for each test. The results show that the wall temperature decreases slightly along the flow path while the fluid temperature increases, highlighting the strong impact of this approach. For a flow rate of 16 ml/s, the mean thermal resistance of the heat sink is 2,35·10 −5 m 2 ·K/W which enhances the results compared to the millimeter scale channels nearly three-fold. For the same flow rate and a heat flux of 50 W/cm 2 , the temperature uniformity, expressed as the standard deviation of the wall temperature, is around 6 °C

Systems with a constant heat flux with applications to radiative heat transport across nanoscale gaps and layers

Science.gov (United States)

Budaev, Bair V.; Bogy, David B.

2018-06-01

We extend the statistical analysis of equilibrium systems to systems with a constant heat flux. This extension leads to natural generalizations of Maxwell-Boltzmann's and Planck's equilibrium energy distributions to energy distributions of systems with a net heat flux. This development provides a long needed foundation for addressing problems of nanoscale heat transport by a systematic method based on a few fundamental principles. As an example, we consider the computation of the radiative heat flux between narrowly spaced half-spaces maintained at different temperatures.

An analysis of the vapor flow and the heat conduction through the liquid-wick and pipe wall in a heat pipe with single or multiple heat sources

Science.gov (United States)

Chen, Ming-Ming; Faghri, Amir

1990-01-01

A numerical analysis is presented for the overall performance of heat pipes with single or multiple heat sources. The analysis includes the heat conduction in the wall and liquid-wick regions as well as the compressibility effect of the vapor inside the heat pipe. The two-dimensional elliptic governing equations in conjunction with the thermodynamic equilibrium relation and appropriate boundary conditions are solved numerically. The solutions are in agreement with existing experimental data for the vapor and wall temperatures at both low and high operating temperatures.

Analytical solution to the problem of heat transfer in an MHD flow inside a channel with prescribed sinusoidal wall heat flux

International Nuclear Information System (INIS)

Zniber, K.; Oubarra, A.; Lahjomri, J.

2005-01-01

An MHD laminar flow through a two dimensional channel subjected to a uniform magnetic field and heated at the walls of the conduit over the whole length with a sinusoidal heat flux of vanishing mean value or not, is studied analytically. General expressions of the temperature distribution and of the local and mean Nusselt numbers are obtained by using the technique of linear operators in the case of negligible Joule and viscous dissipation and by taking into account the axial conduction effect. The principal results show that an increase of the local Nusselt number with Hartmann number is observed, and, far from the inlet section, the average heat transfer between the fluid and the walls shows a significant improvement at all values of Hartmann number used when the frequency of the prescribed sinusoidal wall heat flux is increasing in the case of vanishing mean value of the heat flux and this is true especially at low Peclet numbers

'Eco-house 99' - Full-scale demonstration of solar walls with building integrated heat storages

Energy Technology Data Exchange (ETDEWEB)

Hummelshoej, R.M.; Rahbek, J.E. [COWI Consulting Engineers and Planners AS (Denmark)

2000-07-01

A critical issue for solar systems in northern latitudes is the economic profitability. It is often said that the techniques for solar utilisation are expensive and unprofitable. This is, however, not always the case. A new project with 59 low energy terrace houses was carried out in Kolding, Denmark. The houses are designed as ecological buildings with emphasis on total economy based on low operation and maintenance costs, energy conservation and passive/hybrid solar utilisation. Besides direct solar gain through windows, each house has a solar wall of 6-8.5 m{sup 2} on the south facade. The solar walls are used both for heating of ventilation air and for space heating. The solar walls deliver heat to the dwellings during the heating season. To optimise the energy utilisation from the solar walls, the energy is stored internally in building integrated heat storages. Two different new types of prefabricated heat storages are built into the houses. One is an internal concrete wall with embedded ventilation pipes, and the other is a hollow concrete element with integrated stone bed. The heat storages are mainly designed to store solar energy from the day to the evening and the night. Because the solar walls and the heat storages have been a part of the design process from the start, the additional expenses are as low as 30-140 Euro/m{sup 2} solar wall compared with the alternative facade. This is far less than what it costs to add a solar wall on an existing building. Measurements over one year show that the yield of the solar walls is in the range of 115-125 kWh/m{sup 2}/year as expected. With the actual financing, the annual payment of the additional expenses for the solar systems is between 1-6 Euro/m{sup 2} solar wall, while the annual savings are about 5 Euro/year/m{sup 2} (with an energy price of 0.042 Euro/kWh). Dependent on which alternative facade construction the solar wall system is compared with, the profit of the system is in the range of 1 to +4 Euro

On calculation of difference in specific heats at constant pressure and constant volume using an empiric Nernst-Lindeman equation

International Nuclear Information System (INIS)

Leont'ev, K.L.

1981-01-01

Known theoretical and empirical formulae are considered for the difference in specific heats at constant pressure and volume. On the basis of the Grunaiser law on the ratio of specific heat to thermal expansion and on the basis of the correlation proposed by the author, between this ratio and average velocity of elastic waves obtained in a new expression for the difference in specific heats and determined are conditions at which empiric Nernst-Lindeman equation can be considered to be strict. Results of calculations for metals with fcc lattice are presented

Heat release determination in a constant volume combustion chamber from the instantaneous cylinder pressure

International Nuclear Information System (INIS)

Lapuerta, Magín; Sanz-Argent, Josep; Raine, Robert

2014-01-01

A diagnostic method has been developed to interpret the results of basic combustion studies with diesel-like fuels performed in a constant volume reactor originally conceived for cetane number measurements. The main target of the method is to calculate the instantaneous heat release over time from the chamber pressure experimental signal. The method incorporates filtering of the raw data to eliminate the oscillations recorded as a consequence of the location of the pressure sensor. It considers homogeneity of the gaseous mixture (single zone model) and change in its composition due to the combustion process. A semi-empirical heat transfer model was also proposed and its coefficients were fitted from experimental results obtained in the constant volume chamber using diesel fuel. -- Highlights: • A diagnostic model for constant volume reactors has been developed and tested. • Updating the gas composition after combustion improves accuracy of the method. • Heat transfer coefficients are used for the fulfillment of boundary conditions. • The model provides a deeper insight than the apparent heat release analysis

On the challenge of plasma heating with the JET metallic wall

NARCIS (Netherlands)

Mayoral, M. L.; Bobkov, V.; Czarnecka, A.; Day, I.; Ekedahl, A.; Jacquet, P.; Goniche, M.; King, R.; Kirov, K.; Lerche, E.; J. Mailloux,; Van Eester, D.; Asunta, O.; Challis, C.; Ciric, D.; Coenen, J. W.; Colas, L.; Giroud, C.; Graham, M.; Jenkins, I.; Joffrin, E.; Jones, T.; King, D.; Kiptily, V.; Klepper, C. C.; Maggi, C.; Maggiora, R.; Marcotte, F.; Matthews, G.; Milanesio, D.; Monakhov, I.; Nightingale, M.; Neu, R.; Ongena, J.; T. Puetterich,; Riccardo, V.; Rimini, F.; Strachan, J.; Surrey, E.; Thompson, V.; van Rooij, G. J.

2014-01-01

The major aspects linked to the use of the JET auxiliary heating systems: NBI, ICRF and LHCD, in the new JET ITER-like wall are presented. We show that although there were issues related to the operation of each system, efficient and safe plasma heating was obtained with room for higher power. For

Heat pipe

International Nuclear Information System (INIS)

Triggs, G.W.; Lightowlers, R.J.; Robinson, D.; Rice, G.

1986-01-01

A heat pipe for use in stabilising a specimen container for irradiation of specimens at substantially constant temperature within a liquid metal cooled fast reactor, comprises an evaporator section, a condenser section, an adiabatic section therebetween, and a gas reservoir, and contains a vapourisable substance such as sodium. The heat pipe further includes a three layer wick structure comprising an outer relatively fine mesh layer, a coarse intermediate layer and a fine mesh inner layer for promoting unimpeded return of condensate to the evaporation section of the heat pipe while enhancing heat transfer with the heat pipe wall and reducing entrainment of the condensate by the upwardly rising vapour. (author)

TRAC-BDl/MOD1 post-dryout wall heat transfer

International Nuclear Information System (INIS)

Shumway, R.W.

1984-01-01

A comparison of TRAC-BWR heat transfer package with 766 data points is presented. On the average, TRAC-BWR provides a better prediction of the data compared to any single correlation although there is still a large scatter in TRAC-BWR prediction. Regarding any potential changes in the TRAC-BD1/MOD1 wall heat transfer package, it is concluded that no significant improvement in the film boiling area can be made until data with better measurements are obtained and analyzed. Specifically, data is needed which has a wide range of accurately measured void fractions. Heated tube data is also needed which addresses the countercurrent flow transition conditions

Performance Analysis of Thermoelectric Modules Consisting of Square Truncated Pyramid Elements Under Constant Heat Flux

Science.gov (United States)

Oki, Sae; Natsui, Shungo; Suzuki, Ryosuke O.

2018-06-01

System design of a thermoelectric (TE) power generation module is pursued in order to improve the TE performance. Square truncated pyramid shaped P-N pairs of TE elements are connected electronically in series in the open space between two flat insulator boards. The performance of the TE module consisting of 2-paired elements is numerically simulated using commercial software and original TE programs. Assuming that the heat radiating into the hot surface is regulated, i.e., the amount of heat from the hot surface to the cold one is steadily constant, as it happens for solar radiation heating, the performance is significantly improved by changing the shape and the alignment pattern of the elements. When the angle θ between the edge and the base is smaller than 72°, and when the cold surface is kept at a constant temperature, two patterns in particular, amongst the 17 studied, show the largest TE power and efficiency. In comparison to other geometries, the smarter square truncated pyramid shape can provide higher performance using a large cold bath and constant heat transfer by heat radiation.

Influence of presence of inclined centered baffle and corrugation frequency on natural convection heat transfer flow of air inside a square enclosure with corrugated side walls

Energy Technology Data Exchange (ETDEWEB)

Hussain, Salam Hadi; Jabbar, Mohammed Yousif; Mohamad, Ahmad Saddy [Mechanical Engineering Department, College of Engineering, Babylon University, Babylon Province (Iraq)

2011-09-15

The main objective of this study is to investigate the effect of presence of insulated inclined centered baffle and corrugation frequency on the steady natural convection in a sinusoidal corrugated enclosure. The present study is based on such a configuration where the two vertical sinusoidal walls are maintained at constant low temperature whereas a constant heat flux source whose length is 80% of the width of the enclosure is discretely embedded in the bottom wall. The remaining parts of the bottom wall and the top wall are adiabatic. The finite volume method has been used to solve the governing Navier-Stokes and the energy conservation equations of the fluid medium in the enclosure in order to investigate the effects of baffle inclination angles, corrugation frequencies and Grashof numbers on the fluid flow and heat transfer in the enclosure. The values of the governing parameters are the Grashof number Gr (10{sup 3}-10{sup 6}), the corrugation frequencies CF (1, 2 and 3), baffle inclination angles (0 deg. {<=} {phi} {<=} 150 deg.) and Prandtl number Pr (0.71). Results are presented in the form of streamline and isotherm plots. The results of this investigation are illustrated that the average Nusselt number increases with increase in both the Grashof number and corrugation frequency for different baffle inclination angles and the presence of inclined baffle and increasing the corrugation frequency have significant effects on the average Nusselt numbers, streamlines and isotherms inside the enclosure. The obtained numerical results have been compared with literature ones, and it gives a reliable agreement. (authors)

Creep collapse of thick-walled heat transfer tube subjected to external pressure at high temperature

International Nuclear Information System (INIS)

Ioka, Ikuo; Kaji, Yoshiyuki; Terunuma, Isao; Nekoya, Shin-ichi; Miyamoto, Yoshiaki

1994-09-01

A series of creep collapse tests of thick-walled heat transfer tube were examined experimentally and analytically to confirm an analytical method for creep deformation behavior of a heat transfer tube of an intermediate heat exchanger (IHX) at a depressurization accident of secondary cooling system of HTTR (High Temperature Engineering Test Reactor). The tests were carried out using thick-walled heat transfer tubes made of Hastelloy XR at 950degC in helium gas environment. The predictions of creep collapse time obtained by a general purpose FEM-code ABAQUS were in good agreement with the experimental results. A lot of cracks were observed on the outer surface of the test tubes after the creep collapse. However, the cracks did not pass through the tube wall and, therefore, the leak tightness was maintained regardless of a collapse deformation for all tubes tested. (author)

An assessment of CFD-based wall heat transfer models in piston engines

Energy Technology Data Exchange (ETDEWEB)

Sircar, Arpan [Pennsylvania State Univ., University Park, PA (United States); Paul, Chandan [Pennsylvania State Univ., University Park, PA (United States); Ferreyro-Fernandez, Sebastian [Pennsylvania State Univ., University Park, PA (United States); Imren, Abdurrahman [Pennsylvania State Univ., University Park, PA (United States); Haworth, Daniel C [Pennsylvania State Univ., University Park, PA (United States)

2017-04-26

The lack of accurate submodels for in-cylinder heat transfer has been identified as a key shortcoming in developing truly predictive, physics-based computational fluid dynamics (CFD) models that can be used to develop combustion systems for advanced high-efficiency, low-emissions engines. Only recently have experimental methods become available that enable accurate near-wall measurements to enhance simulation capability via advancing models. Initial results show crank-angle dependent discrepancies with respect to previously used boundary-layer models of up to 100%. However, available experimental data is quite sparse (only few data points on engine walls) and limited (available measurements are those of heat flux only). Predictive submodels are needed for medium-resolution ("engineering") LES and for unsteady Reynolds-averaged simulations (URANS). Recently, some research groups have performed DNS studies on engine-relevant conditions using simple geometries. These provide very useful data for benchmarking wall heat transfer models under such conditions. Further, a number of new and more sophisticated models have also become available in the literature which account for these engine-like conditions. Some of these have been incorporated while others of a more complex nature, which include solving additional partial differential equations (PDEs) within the thin boundary layer near the wall, are underway. These models will then be tested against the available DNS/experimental data in both SI (spark-ignition) and CI (compression-ignition) engines.

Transient convective heat transfer to laminar flow from a flat plate with constant heat capacity

International Nuclear Information System (INIS)

Hanawa, Juichi

1980-01-01

Most basic transient heat transfer problem is the transient response characteristics of forced convection heat transfer in the flow along a flat plate or in a tube. In case of the laminar flow along a flat plate, the profile method using steady temperature distribution has been mostly adopted, but its propriety has not been clarified yet. About the unsteady heat transfer in the laminar flow along a flat plate, the analysis or experiment evaluating the heat capacity of the flat plate exactly was never carried out. The purpose of this study is to determine by numerical calculation the unsteady characteristics of the boundary layer in laminar flow and to confirm them by experiment concerning the unsteady heat transfer when a flat plate with a certain heat capacity is placed in parallel in uniform flow and given a certain quantity of heat generation suddenly. The basic equation and the solution are given, and the method of numerical calculation and the result are explained. The experimental setup and method, and the experimental results are shown. Both results were in good agreement, and the response of wall temperature, the response of Nusselt number and the change of temperature distribution in course of time were able to be determined by applying Laplace transformation and numerical Laplace inverse transformation to the equation. (Kako, I.)

Inverse heat conduction estimation of inner wall temperature fluctuations under turbulent penetration

Science.gov (United States)

Guo, Zhouchao; Lu, Tao; Liu, Bo

2017-04-01

Turbulent penetration can occur when hot and cold fluids mix in a horizontal T-junction pipe at nuclear plants. Caused by the unstable turbulent penetration, temperature fluctuations with large amplitude and high frequency can lead to time-varying wall thermal stress and even thermal fatigue on the inner wall. Numerous cases, however, exist where inner wall temperatures cannot be measured and only outer wall temperature measurements are feasible. Therefore, it is one of the popular research areas in nuclear science and engineering to estimate temperature fluctuations on the inner wall from measurements of outer wall temperatures without damaging the structure of the pipe. In this study, both the one-dimensional (1D) and the two-dimensional (2D) inverse heat conduction problem (IHCP) were solved to estimate the temperature fluctuations on the inner wall. First, numerical models of both the 1D and the 2D direct heat conduction problem (DHCP) were structured in MATLAB, based on the finite difference method with an implicit scheme. Second, both the 1D IHCP and the 2D IHCP were solved by the steepest descent method (SDM), and the DHCP results of temperatures on the outer wall were used to estimate the temperature fluctuations on the inner wall. Third, we compared the temperature fluctuations on the inner wall estimated by the 1D IHCP with those estimated by the 2D IHCP in four cases: (1) when the maximum disturbance of temperature of fluid inside the pipe was 3°C, (2) when the maximum disturbance of temperature of fluid inside the pipe was 30°C, (3) when the maximum disturbance of temperature of fluid inside the pipe was 160°C, and (4) when the fluid temperatures inside the pipe were random from 50°C to 210°C.

Heat Conductivity Resistance of Concrete Wall Panel by Water Flowing in Different Orientations of Internal PVC pipe

Science.gov (United States)

Umi, N. N.; Norazman, M. N.; Daud, N. M.; Yusof, M. A.; Yahya, M. A.; Othman, M.

2018-04-01

Green building technology and sustainability development is current focus in the world nowadays. In Malaysia and most tropical countries the maximum temperature recorded typically at 35°C. Air-conditioning system has become a necessity in occupied buildings, thereby increasing the cost of electric consumption. The aim of this study is to find out the solution in minimizing heat transfer from the external environment and intentions towards going green. In this study, the experimental work includes testing three types of concrete wall panels. The main heat intervention material in this research is 2 inch diameter Polyvinyl Chloride (PVC) pipe embedded at the center of the concrete wall panel, while the EPS foam beads were added to the cement content in the concrete mix forming the outer layer of the wall panel. Water from the rainwater harvesting system is regulated in the PVC pipe to intervene with the heat conductivity through the wall panel. Results from the experimental works show that the internal surface temperature of these heat resistance wall panels is to 3□C lower than control wall panel from plain interlocking bricks.

Scalar and joint velocity-scalar PDF modelling of near-wall turbulent heat transfer

International Nuclear Information System (INIS)

Pozorski, Jacek; Waclawczyk, Marta; Minier, Jean-Pierre

2004-01-01

The temperature field in a heated turbulent flow is considered as a dynamically passive scalar. The probability density function (PDF) method with down to the wall integration is explored and new modelling proposals are put forward, including the explicit account for the molecular transport terms. Two variants of the approach are considered: first, the scalar PDF method with the use of externally-provided turbulence statistics; and second, the joint (stand-alone) velocity-scalar PDF method where a near-wall model for dynamical variables is coupled with a model for temperature. The closure proposals are formulated in the Lagrangian setting and resulting stochastic evolution equations are solved with a Monte Carlo method. The near-wall region of a heated channel flow is taken as a validation case; the second-order thermal statistics are of a particular interest. The PDF computation results agree reasonably with available DNS data. The sensitivity of results to the molecular Prandtl number and to the thermal wall boundary condition is accounted for

MATHEMATICAL MODELING OF HEAT EXCHANGE IN DIRECT FLAT CHANNELS AND DIRECT ROUND PIPES WITH ROUGH WALLS UNDER THE SYMMETRIC HEAT SUPPLY

Directory of Open Access Journals (Sweden)

I E. Lobanov

2017-01-01

Full Text Available Objectives. The aim of present work was to carry out mathematical modelling of heat transfer with symmetrical heating in flat channels and round pipes with rough walls.Methods. The calculation was carried out using the L'Hôpital-Bernoulli's method. The solution of the problem of intensified heat transfer in a round tube with rough walls was obtained using the Lyon's integral.Results. Different from existing theories, a methodology of theoretical computational heat transfer determination for flat rough channels and round pipes with rough walls is developed on the basis of the principle of full viscosity superposition in a turbulent boundary layer. The analysis of the calculated heat transfer and hydroresistivity values for flat rough channels and round rough pipes shows that the increase in heat transfer is always less than the corresponding increase in hydraulic resistance, which is a disadvantage as compared to channels with turbulators, with all else being equal. The results of calculating the heat transfer for channels with rough walls in an extended range of determinant parameters, which differ significantly from the corresponding data for the channels with turbulators, determine the level of heat exchange intensification.Conclusion. An increase in the calculated values of the relative average heat transfer Nu/NuGL for flat rough channels and rough pipes with very high values of the relative roughness is significantly contributed by both an increase in the relative roughness height and an increase in the Reynolds number Re. In comparison with empirical dependencies, the main advantage of solutions for averaged heat transfer in rough flat channels and round pipes under symmetrical thermal load obtained according to the developed theory is that they allow the calculation of heat exchange in rough pipes to be made in the case of large and very large relative heights of roughness protrusions, including large Reynolds numbers, typical for pipes

Heat transfer of natural convection in a rectangular cavity with vertical walls of different temperatures

International Nuclear Information System (INIS)

Seki, Nobuhiro; Fukusako, Shoichiro; Inaba, Hideo

1978-01-01

In the present study the behavior of heat transfer in a rectangular cavity with one isothermal vertical wall heated and the other cooled is investigated. Heat transfer coefficients on the vertical walls are measured for fluids with Prandtl number Pr of 3 to 40,000 in case of aspect-ratio H/W from 5 to 47.5 and their correlated results are presented for laminar, transition and turbulent regions, respectively. It is shown that the present arrangement (Nu sub(H) - Ra sub(H)) using the height of cavity as a representative length may significantly be useful in the various heat transfer modes accompanied with flow patterns of them. (auth.)

Buoyancy effects laminar slot jet impinging on a surface with constant heat flux

International Nuclear Information System (INIS)

Shokouhmand, H.; Esfahanian, V.; Masoodi, R.

2004-01-01

The two-dimensional laminar air jet issuing from a nozzle of half which terminates at height above a flat plate normal to the jet is numerically on the flow and thermal structure of the region near impingement. The impinging surface is maintained at a constant heat flux condition. The full Navier-Stocks and energy equations are solved by a finite difference method to evaluate the velocity profiles and temperature distribution. The governing parameters and their ranges are: Reynolds number Re, 10-50, Grashof number Gr, 0-50, Richardson number Ri=Gr/ Re 2 , Non dimensional nozzle height H,2-3. Results of the free streamline, local friction factor and heat transfer coefficient are graphically presented. It is found that enhancement of the heat transfer rate is substantial for high Richardson number conditions. Although the laminar jet impingement for isothermal condition has been already studied, however the constant heat flux has not been studied enough. the present paper will analyze a low velocity air jet, Which can be used for cooling of a simulated electronics package

Heat deposition on the first wall due to ICRF-induced loss of fast ions in JT-60U

International Nuclear Information System (INIS)

Kusama, Y.; Tobita, K.; Kimura, H.; Hamamatsu, K.; Fujii, T.; Nemoto, M.; Saigusa, M.; Moriyama, S.; Tani, K.; Koide, Y.; Sakasai, A.; Nishitani, T.; Ushigusa, K.

1995-01-01

In JT-60U, the heat deposition on the first wall due to the ICRF-induced loss of fast ions was investigated by changing the position of the resonance layer in the ripple-trapping region. A heat spot appears on the first wall of the same major radius as the resonance layer of the ICRF waves. The broadening of the heat spot in the major radius direction is consistent with that of the resonance layer due to the Doppler broadening. The heat spot is considered to be formed by the ICRF-induced ripple-trapped loss of fast ions. Although the total ICRF-induced loss power to the heat spot is as low as 2% of the total ICRF power, the additional heat flux will become a new issue because of the localized heat deposition on the first wall. ((orig.))

Experimental and numerical study of heat transfer across insulation wall of a refrigerated integral panel van

International Nuclear Information System (INIS)

Glouannec, Patrick; Michel, Benoit; Delamarre, Guillaume; Grohens, Yves

2014-01-01

This paper presents an experimental and numerical design study of an insulation wall for refrigerated vans. The thermophysical properties of the insulating multilayer panel, the external environment impact (solar irradiation, temperature, etc.) and durability are taken into account. Different tools are used to characterize the thermal performances of the insulation walls and the thermal properties of the insulation materials are measured. In addition, an experiment at the wall scale is carried out and a 2D FEM model of heat and mass transfer within the wall is formulated. Three configurations are studied with this design approach. Multilayer insulation walls containing reflective multi-foil insulation, aerogel and phase change materials (PCM) are tested. Promising results are obtained with these materials, especially the reduction of peak heat transfer and energy consumption during the daytime period. Furthermore, the major influence of solar irradiation is highlighted as it can increase the peak heat transfer crossing the insulation wall by up to 43%. Nevertheless, we showed that the use of reflective multi-foil insulation and aerogel layers allowed decreasing this impact by 27%. - Highlights: • A design study of an insulation wall for a refrigerated van is carried out. • Experimental and numerical studies of multilayer insulation walls are performed. • The major influence of solar irradiation is highlighted. • New insulation materials (reflective multi-foil, aerogel and PCM) are tested

Local heat transfer around a wall-mounted cube. Case of the attack angle of 45 deg.; Rippotai tokki mawari no kyokusho netsu dentatsu. Katamukikaku 45 degrees no baai

Energy Technology Data Exchange (ETDEWEB)

Nakamura, H.; Igarashi, T.; Tsutsui, T. [National Defense Academy, Kanagawa (Japan)

1999-11-25

An experimental study was performed to investigate the local heat transfer around a cube mounted on the wall. The cube lied in the turbulent boundary layer. The flow angle of attack to the cube was 15 degree. The Reynolds number ranged from 4.2 x 10{sup 3} to 3.3 x 10{sup 4}. The surface temperature distributions around time cube were measured with thermocouples tinder the condition of a constant heat flux. The local h eat transfer is very high near the front corner on the top face of the cube. This high heat transfer region extends from the front corner to downstream along both edges. This is caused by the formation of lamb horn vortex. The local heat transfer is also high in time region of horseshoe vortex formed a round the cube. On the wall behind the cube, there is a pair of minimum heat transfer region. The average Nusselt number on each face of the cube is given as a function of Reynolds number. The overall Nusselt number of time cube is expressed by Nu{sub m}=0.43Re{sup 0.58}. (author)

Bayesian inferences of the thermal properties of a wall using temperature and heat flux measurements

KAUST Repository

Iglesias, Marco; Sawlan, Zaid A; Scavino, Marco; Tempone, Raul; Wood, Christopher

2017-01-01

and heat flux over extended time periods. The one-dimensional heat equation with unknown Dirichlet boundary conditions is used to model the heat transfer process through the wall. In Ruggeri et al. (2017), it was assessed the uncertainty about the thermal

Axial slit wall effect on the flow instability and heat transfer in rotating concentric cylinders

Energy Technology Data Exchange (ETDEWEB)

Liu, Dong; Chao, Chang Qing; Wang, Ying Ze; Zhu, Fang Neng [School of Energy and Power Engineering, Jiangsu University, Zhenjiang (China); Kim, Hyoung Bum [School of Mechanical and Aerospace Engineering, Gyeongsang National University, Jinju (Korea, Republic of)

2016-12-15

The slit wall effect on the flow instability and heat transfer characteristics in Taylor-Couette flow was numerically studied by changing the rotating Reynolds number and applying the negative temperature gradient. The concentric cylinders with slit wall are seen in many rotating machineries. Six different models with the slit number 0, 6, 9, 12, 15 and 18 were investigated in this study. The results show the axial slit wall enhances the Taylor vortex flow and suppresses the azimuthal variation of wavy Taylor vortex flow. When negative temperature gradient exists, the results show that the heat transfer augmentation appears from laminar Taylor vortex to turbulent Taylor flow regime. The heat transfer enhancement become stronger as increasing the Reynolds number and slit number. The larger slit number model also accelerates the flow transition regardless of the negative temperature gradient or isothermal condition.

Axial slit wall effect on the flow instability and heat transfer in rotating concentric cylinders

International Nuclear Information System (INIS)

Liu, Dong; Chao, Chang Qing; Wang, Ying Ze; Zhu, Fang Neng; Kim, Hyoung Bum

2016-01-01

The slit wall effect on the flow instability and heat transfer characteristics in Taylor-Couette flow was numerically studied by changing the rotating Reynolds number and applying the negative temperature gradient. The concentric cylinders with slit wall are seen in many rotating machineries. Six different models with the slit number 0, 6, 9, 12, 15 and 18 were investigated in this study. The results show the axial slit wall enhances the Taylor vortex flow and suppresses the azimuthal variation of wavy Taylor vortex flow. When negative temperature gradient exists, the results show that the heat transfer augmentation appears from laminar Taylor vortex to turbulent Taylor flow regime. The heat transfer enhancement become stronger as increasing the Reynolds number and slit number. The larger slit number model also accelerates the flow transition regardless of the negative temperature gradient or isothermal condition

An experimental and numerical study of endwall heat transfer in a turbine blade cascade including tangential heat conduction analysis

Science.gov (United States)

Ratto, Luca; Satta, Francesca; Tanda, Giovanni

2018-06-01

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

Phonon and thermal properties of achiral single wall carbon ...

Indian Academy of Sciences (India)

A detailed theoretical study of the phonon and thermal properties of achiral single wall carbon nanotubes has been carried out using force constant model considering up to third nearest-neighbor interactions. We have calculated the phonon dispersions, density of states, radial breathing modes (RBM) and the specific heats ...

Heat transfer augmentation along the tube wall of a louvered fin heat exchanger using practical delta winglets

Energy Technology Data Exchange (ETDEWEB)

Lawson, Michael J.; Thole, Karen A. [Mechanical and Nuclear Engineering Department, The Pennsylvania State University, University Park, PA 16802 (United States)

2008-05-15

Delta winglets are known to induce the formation of streamwise vortices and increase heat transfer between a working fluid and the surface on which the winglets are placed. This study investigates the use of delta winglets to augment heat transfer on the tube surface of louvered fin heat exchangers. It is shown that delta winglets placed on louvered fins produce augmentations in heat transfer along the tube wall as high as 47% with a corresponding increase of 19% in pressure losses. Manufacturing constraints are considered in this study whereby piercings in the louvered fins resulting from stamping the winglets into the louvered fins are simulated. Comparisons of measured heat transfer coefficients with and without piercings indicate that piercings reduce average heat transfer augmentations, but significant increases still occur with respect to no winglets present. (author)

Simultaneous measurements of thickness and temperature profile in a wavy liquid film falling freely on a heating wall

International Nuclear Information System (INIS)

Lyu, T.; Mudawar, I.

1990-01-01

This paper reports on a technique for measuring the thickness of liquid films that was developed and tested. The feasibility of this technique was demonstrated in stagnant liquid films as well as in liquid jets. A procedure for in-situ calibration of the thickness probe was developed, allowing the adaptation of the probe to measurements of wavy liquid films. The thickness probe was constructed from a platinum-rhodium wire that was stretched across the film. A constant DC current was supplied through the probe wire, and film thickness was determined from variations in the probe voltage drop resulting from the large differences in the electrical resistances of the wetted and unwetted segments of the wire. Unlike electrical admittance thickness probes, the new probe did not require dissolving an electrolyte in the liquid, making the new probe well suited to studies involving sensible heating of a film of pure dielectric liquid that is in direct contact with a current- carrying wall. Also presented is a composite probe that facilitated simultaneous measurements of temperature profile across a wavy liquid film and film thickness. Experimental results demonstrate a strong influence of waviness on liquid temperature in a film of deionized water falling freely on the outside wall of a vertical, electrically heated tube for film Reynolds numbers smaller than 10,000

Analysis of the dual phase lag bio-heat transfer equation with constant and time-dependent heat flux conditions on skin surface

Directory of Open Access Journals (Sweden)

Ziaei Poor Hamed

2016-01-01

Full Text Available This article focuses on temperature response of skin tissue due to time-dependent surface heat fluxes. Analytical solution is constructed for DPL bio-heat transfer equation with constant, periodic and pulse train heat flux conditions on skin surface. Separation of variables and Duhamel’s theorem for a skin tissue as a finite domain are employed. The transient temperature responses for constant and time-dependent boundary conditions are obtained and discussed. The results show that there is major discrepancy between the predicted temperature of parabolic (Pennes bio-heat transfer, hyperbolic (thermal wave and DPL bio-heat transfer models when high heat flux accidents on the skin surface with a short duration or propagation speed of thermal wave is finite. The results illustrate that the DPL model reduces to the hyperbolic model when τT approaches zero and the classic Fourier model when both thermal relaxations approach zero. However for τq = τT the DPL model anticipates different temperature distribution with that predicted by the Pennes model. Such discrepancy is due to the blood perfusion term in energy equation. It is in contrast to results from the literature for pure conduction material, where the DPL model approaches the Fourier heat conduction model when τq = τT . The burn injury is also investigated.

Method and apparatus for active control of combustion rate through modulation of heat transfer from the combustion chamber wall

Science.gov (United States)

Roberts, Jr., Charles E.; Chadwell, Christopher J.

2004-09-21

The flame propagation rate resulting from a combustion event in the combustion chamber of an internal combustion engine is controlled by modulation of the heat transfer from the combustion flame to the combustion chamber walls. In one embodiment, heat transfer from the combustion flame to the combustion chamber walls is mechanically modulated by a movable member that is inserted into, or withdrawn from, the combustion chamber thereby changing the shape of the combustion chamber and the combustion chamber wall surface area. In another embodiment, heat transfer from the combustion flame to the combustion chamber walls is modulated by cooling the surface of a portion of the combustion chamber wall that is in close proximity to the area of the combustion chamber where flame speed control is desired.

Influence of heat-treatment on lithium ion anode properties of mesoporous carbons with nanosheet-like walls

Energy Technology Data Exchange (ETDEWEB)

Zeng, Fanyan [College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082 (China); Hou, Zhaohui, E-mail: zhqh96@163.com [College of Chemistry and Chemical Engineering, Hunan Institute of Science and Technology, Yueyang 414006 (China); He, Binhong [College of Chemistry and Chemical Engineering, Hunan Institute of Science and Technology, Yueyang 414006 (China); Ge, Chongyong; Cao, Jianguo [College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082 (China); Kuang, Yafei, E-mail: yafeik@163.com [College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082 (China)

2012-08-15

Highlights: ► Mesoporous carbons possess unique nanosheet-like pore walls which can be changed by heat treatment. ► Lithium ion anode properties of mesoporous carbons could be influenced by the nanosheet-like walls. ► Mesoporous carbons with nanosheet-like walls exhibit enhanced electrochemical properties LIBs. -- Abstract: Mesoporous carbons (MCs) with nanosheet-like walls have been prepared as electrodes for lithium-ion batteries by a simple one-step infiltrating method under the action of capillary flow. The influence of heat treatment temperature on the surface topography, pore/phase structure and anode performances of as-prepared materials has been investigated. The results reveal that melted liquid-crystal polycyclic aromatic hydrocarbons could be anchored on liquid/silica interfaces by molecule engineering. After carbonization, the nanosheets are formed as the pore walls of MCs and are perpendicular to the long axis of pores. The anode properties demonstrate that C-1200 displays higher reversible capacitance than those treated in higher temperature. The rate performances of C-1200 and C-1800 are similar and more excellent than that of C-2400. These improved lithium ion anode properties could be attributed to the nanosheet-like walls of MCs which can be influenced by the heat treatment temperature.

Evaporation and condensation heat transfer in a suppression chamber of the water wall type passive containment cooling system

International Nuclear Information System (INIS)

Fujii, Tadashi; Kataoka, Yoshiyuki; Murase, Michio

1996-01-01

To evaluate the system pressure response of a water wall type containment cooling system, which is one of the passive safety systems, the evaporation and condensation behaviors in a suppression chamber have been experimentally examined. In the system, the suppression pool water evaporates from the pool surface, passing into the wetwell due to pool temperature rise, while steam in the wetwell condenses on the steel containment vessel wall due to the heat release through the wall. The wetwell is a gas phase region in the suppression chamber and its pressure, which is expressed as the sum of the noncondensable gas pressure and saturated steam pressure, is strongly affected by the evaporation heat transfer from the suppression pool surface and condensation heat transfer on the containment vessel wall. Based on the measured temperature profiles near the heat transfer surface and the wetwell pressure using two apparatuses, evaporation and condensation heat transfer coefficients were evaluated. The following results were obtained. (1) Both heat transfer coefficients increased as the ratio of the steam partial pressure to the total pressure increased. (2) Comparison of the results from two types of test apparatuses confirmed that the size of the heat transfer surface did not affect the heat transfer characteristics within these tests. (3) The heat transfer coefficients were expressed by the ratio of the steam to noncondensable gas logarithmic mean concentration, which considered the steam and gas concentration gradient from the heat transfer surface to the wetwell bulk. (author)

Radiometric measurements of wall temperatures in the 800 K to 1150 K range for a quartz radiant heating tube

International Nuclear Information System (INIS)

Blevins, L.G.; Sivathanu, Y.R.; Gore, J.P.; Shahien, M.A.

1995-01-01

Many industrial applications require heat transfer to a load in an inert environment, which can be achieved by using gas-fired radiant tubes. A radiant tube consists of a flame confined in a cylindrical metal or ceramic chamber. The flame heats the tube wall, which in turn radiates to the load. One important characteristic of radiant heating tubes is wall temperature uniformity. Numerical models of radiant tubes have been used to predict wall temperatures, but there is a lack of experimental data for validation. Recently, Namazian et al., Singh and Gorski, and Peters et al. have measured wall temperature profiles of radiant tubes using thermocouples. 13 refs., 3 figs

Evaluation of Thermo-Fluid Performance of Compact Heat Exchanger with Corrugated Wall Channels

International Nuclear Information System (INIS)

Tak, Nam Il; Lee, Won Jae

2006-01-01

One of the key components of an indirect nuclear hydrogen production system is an intermediate heat exchanger (IHX). For the IHX, a printed circuit heat exchanger (PCHE) is known as one of the promising types due to its compactness and ability to operate at high temperatures and under high pressures. The PCHE is a relatively new heat exchanger. It has been commercially manufactured only since 1985 and solely by one British vendor, HeatricTM. Due to its short history and limited production, sufficient information about the PCHE is not available for the design of the IHX in open literatures. The predominant shape of flow channels of the PCHE is laterally corrugated. The flow in a corrugated wall channel is very interesting since a variety of flow phenomena can be considered by changing the amplitude-to-wavelength ratio. In the present paper, thermo-fluid performance of a heat exchanger with a typical PCHE geometry has been evaluated. Computational fluid dynamics (CFD) analysis was performed to analyze a gas flow behavior in a corrugated wall channel

Numerical simulation of heat fluxes in a two-temperature plasma at shock tube walls

International Nuclear Information System (INIS)

Kuznetsov, E A; Poniaev, S A

2015-01-01

Numerical simulation of a two-temperature three-component Xenon plasma flow is presented. A solver based on the OpenFOAM CFD software package is developed. The heat flux at the shock tube end wall is calculated and compared with experimental data. It is shown that the heat flux due to electrons can be as high as 14% of the total heat flux. (paper)

Numerical simulation of heat fluxes in a two-temperature plasma at shock tube walls

Science.gov (United States)

Kuznetsov, E. A.; Poniaev, S. A.

2015-12-01

Numerical simulation of a two-temperature three-component Xenon plasma flow is presented. A solver based on the OpenFOAM CFD software package is developed. The heat flux at the shock tube end wall is calculated and compared with experimental data. It is shown that the heat flux due to electrons can be as high as 14% of the total heat flux.

Detailed Dynamic Heat Transfer in Thick Brick Walls Typical of Lille Metropolis

Directory of Open Access Journals (Sweden)

Antczak E.

2012-10-01

Full Text Available The study of thermal transfer in old houses massive walls offers a big interest permitting the understanding of their specificities and the choice of a suitable material for their eventual insulation. We propose to study the thermal transfer in massive brick walls that characterize the Northern Europe old houses. To do so, we will begin by defining the thermal transfer mode: we proved that the transfer mode can be reduced to a unidirectional transfer. Then, an experimental wall is built and submitted to two different solicitation types (constant temperature in steady state mode and sinusoidal temperature through a wooden insulated box containing a radiator. The interest of these solicitations is to determine the thermal properties of the wall: the steady-state regime permits to determine the thermal resistances of the system when the harmonic regime permits to determine the thermal capacities of the system.

Wall-resolved Large Eddy Simulations of turbulent heat transfer in a T-junction

Science.gov (United States)

Georgiou, Michail; Papalexandris, Miltiadis V.

2017-11-01

In this talk we report on wall-resolved Large Eddy Simulations of turbulent heat transfer between a cold crossflow and a hot incoming jet in a T-junction. Due to their high efficiency in mixing and heat transfer, T-junctions are encountered in numerous industrial applications. Our study is motivated by the need to assess phenomena related to thermal fatigue that are often encountered at their walls. We first describe the important features of the flow with emphasis on the shear layers that are formed at the entry of the jet and the recirculation regions. We also show results for first- and second-order statistics of the flow and compare our predictions with previous experimental data. Lastly, we present results from the spectral analysis of the temperature signal that we performed in order to assess the oscillating mechanisms that dominate the flow and the risk of thermal fatigue at the walls of the T-junction.

Convective heat transfer for a gaseous slip flow in micropipe and parallel-plate microchannel with uniform wall heat flux: effect of axial heat conduction

Science.gov (United States)

Haddout, Y.; Essaghir, E.; Oubarra, A.; Lahjomri, J.

2018-06-01

Thermally developing laminar slip flow through a micropipe and a parallel plate microchannel, with axial heat conduction and uniform wall heat flux, is studied analytically by using a powerful method of self-adjoint formalism. This method results from a decomposition of the elliptic energy equation into a system of two first-order partial differential equations. The advantage of this method over other methods, resides in the fact that the decomposition procedure leads to a selfadjoint problem although the initial problem is apparently not a self-adjoint one. The solution is an extension of prior studies and considers a first order slip model boundary conditions at the fluid-wall interface. The analytical expressions for the developing temperature and local Nusselt number in the thermal entrance region are obtained in the general case. Therefore, the solution obtained could be extended easily to any hydrodynamically developed flow and arbitrary heat flux distribution. The analytical results obtained are compared for select simplified cases with available numerical calculations and they both agree. The results show that the heat transfer characteristics of flow in the thermal entrance region are strongly influenced by the axial heat conduction and rarefaction effects which are respectively characterized by Péclet and Knudsen numbers.

Methods for determining the wall thickness variation of tubular heaters used in thermalhydraulic studies

International Nuclear Information System (INIS)

Cubizolles, G.; Garnier, J.; Groeneveld, D.; Tanase, A.

2009-01-01

) Onset of Nucleate Boiling data. The three predicted wall thickness variations were in excellent agreement with each other and also agreed very well with subsequent direct measurements with a precision caliper, and photography-based measurements using slices of the test section. The wall thickness derivation methods used at CEA and UofO are thought to be especially valuable for future thermalhydraulic studies on fuel bundle simulators where heater tubes with a nominal constant wall thickness can have a wall thickness variation of ± 5% and result in a similar variation in surface heat flux. Better knowledge of the wall thickness variation will permit more precise measurements of the local single-phase and boiling heat transfer coefficients. (author)

Heat-affected-zone toughness in heavy wall pipe: Final report

Energy Technology Data Exchange (ETDEWEB)

Dyck, K.; Glover, A.G.; Varo, D.B.

1988-02-01

The objective of this program has been to determine the significance of low toughness regions on the service performance of heat-affected zones in heavy wall pipe materials. The low temperature HAZ toughness of welds in microalloyed and quenched and tempered materials at two heat inputs was established, a test technique to produce fatigue cracks in the HAZ was developed, and four full scale fracture tests were completed at /minus/49/degree/F. Publication available from the American Gas Association Order Processing Department, 1515 Wilson Boulevard, Arlington, Virginia 22209-2470 (703/841-8558). 17 refs. (JL)

Direct numerical simulation of turbulent pipe flow with nonuniform surface heat flux

International Nuclear Information System (INIS)

Satake, Shin-ichi; Kunugi, Tomoaki

1998-01-01

Turbulent transport computations of a scalar quantity for fully-developed turbulent pipe flow were carried out by means of a direct numerical simulation (DNS) procedure. In this paper, three wall-heating boundary conditions were considered as follows: Case-1) a uniform heat-flux condition along the wall, Case-2) a nonuniform wall-heating condition, that is, a cosine heat-flux distribution along the wall and Case-3) a nonuniform wall-heating condition with a constant temperature over a half of the pipe wall. The number of computational grids used in this paper is 256 x 128 x 128. Prandtl number of the working fluid is 0.71. The Nusselt number in case of Case-1 is in good agreement with the empirical correlation. In case of Case-3, the distributions of the turbulent quantity and the Nusselt number seem to be reasonable. However, as for Case-2, the distributions of the turbulent quantity and the Nusselt number seem to be unrealistic. Two numerical treatments of thermal boundary condition on the wall were applied and their results were discussed from the viewpoint of the turbulent transport feature. (author)

Flow and heat transfer characteristics in a channel having furrowed wall based on sinusoidal wave

Energy Technology Data Exchange (ETDEWEB)

Wang, Jiansheng; Gao, Xiaoming; Li, Weiyi [Tianjin University, Tianjin (Switzerland)

2015-11-15

The effect of wall geometry on the flow and heat transfer in a channel with one lower furrowed and an upper flat wall kept at a uniform temperature is investigated by large eddy simulation. Three channels, one with sinusoidal wavy surface having the ratio (amplitude to wavelength) α/λ=0.05 and the other two with furrowed surface derived from the sinusoidal curve, are considered. The numerical results show that the streamwise vortices center is located near the lower wall and vary along the streamwise on various furrow surfaces. The furrow geometry increases the pressure drag and decreases the friction drag of the furrowed surface compared with that of the smooth surface; consequently, the total drag is increased for the augment of pressure drag. As expected, the heat transfer performance has been improved. Finally, a thermal performance factor is defined to evaluate the performance of the furrowed wall.

Operation experiences of the JT-60 first walls during high-power additional heating experiments

International Nuclear Information System (INIS)

Takatsu, H.; Ando, T.; Yamamoto, M.; Arai, T.; Kodama, K.; Suzuki, M.; Shimizu, M.

1989-01-01

JT-60 started its operation in May 1985 with TiC-coated molybdenum or Inconel 625 first walls. They provided very clean surfaces as well as superior plasma characteristics during Joule heating discharges. Though 20 μm-thick TiC coatings showed good adhesion characteristics, melting of the TiC coating and also the molybdenum or Inconel 625 substrate was observed at some specific spots, and an influx of heavy metals to the main plasma was inevitable during discharges. Initial results of the additional heating experiments showed degrading effects of locally melted TiC-coated molybdenum or Inconel 625 on plasma operation. Therefore, about a half of the TiC-coated first walls were removed and new graphite first walls were installed during the venting period from April to May 1987. The start-up of the discharge conditioning after installation of a significant number of graphite tiles was very rapid. Flexibility in plasma operation was increased, and JT-60 extended the operation region beyond its original specifications. The graphite first walls of the main chamber performed admirably and maintained their integrity under the conditions of plasma current and additional heating power up to 3.2 MA and 30 MW, respectively. On the other hand, the number of damaged divertor plates was much larger than that expected. The reason of unexpected failure is now under examination. (orig.)

Wall ablation of heated compound-materials into non-equilibrium discharge plasmas

Science.gov (United States)

Wang, Weizong; Kong, Linghan; Geng, Jinyue; Wei, Fuzhi; Xia, Guangqing

2017-02-01

The discharge properties of the plasma bulk flow near the surface of heated compound-materials strongly affects the kinetic layer parameters modeled and manifested in the Knudsen layer. This paper extends the widely used two-layer kinetic ablation model to the ablation controlled non-equilibrium discharge due to the fact that the local thermodynamic equilibrium (LTE) approximation is often violated as a result of the interaction between the plasma and solid walls. Modifications to the governing set of equations, to account for this effect, are derived and presented by assuming that the temperature of the electrons deviates from that of the heavy particles. The ablation characteristics of one typical material, polytetrafluoroethylene (PTFE) are calculated with this improved model. The internal degrees of freedom as well as the average particle mass and specific heat ratio of the polyatomic vapor, which strongly depends on the temperature, pressure and plasma non-equilibrium degree and plays a crucial role in the accurate determination of the ablation behavior by this model, are also taken into account. Our assessment showed the significance of including such modifications related to the non-equilibrium effect in the study of vaporization of heated compound materials in ablation controlled arcs. Additionally, a two-temperature magneto-hydrodynamic (MHD) model accounting for the thermal non-equilibrium occurring near the wall surface is developed and applied into an ablation-dominated discharge for an electro-thermal chemical launch device. Special attention is paid to the interaction between the non-equilibrium plasma and the solid propellant surface. Both the mass exchange process caused by the wall ablation and plasma species deposition as well as the associated momentum and energy exchange processes are taken into account. A detailed comparison of the results of the non-equilibrium model with those of an equilibrium model is presented. The non-equilibrium results

Effect of wall conductances on hydromagnetic flow and heat transfer in a rotating channel

International Nuclear Information System (INIS)

Mazumder, B.S.

1977-01-01

Wall conductance effects on the hydromagnetic flow and heat transfer between two parallel plates in a rotating frame of reference has been studied when the liquid is permeated by a transverse magnetic field. An exact solution of the governing equation has been obtained. It is found that the velocity current density and the temperature depend only on the sum of the wall conductances phi 1 + phi 2 = phi but magnetic field depends on the individual values of phi 1 and phi 2 where phi 1 and phi 2 are respectively the wall conductance ratios of the upper and lower walls. (Auth.)

Investigation the effect of outdoor air infiltration on the heat-shielding characteristics the outer walls of high-rise buildings

Science.gov (United States)

Vytchikov, Yu. S.; Kostuganov, A. B.; Saparev, M. E.; Belyakov, I. G.

2018-03-01

The presented article considers the influence of infiltrated outdoor air on the heat-shielding characteristics of the exterior walls of modern residential and public buildings. A review of the sources devoted to this problem confirmed its relevance at the present time, especially for high-rise buildings. The authors of the article analyzed the effect of longitudinal and transverse air infiltration on the heat-shielding characteristics of the outer wall of a 25-story building that was built in Samara. The results showed a significant reduction of the reduced resistance to the heat transfer of the outer wall when air is infiltrated through it. There are the results of full-scale examination of external walls to confirm the calculated data. Based on the results of the study carried out by the authors of the article, general recommendations on the internal finishing of the outer walls of high-rise buildings are given.

A new divided-wall heat integrated distillation column (HIDiC) for batch processing: Feasibility and analysis

International Nuclear Information System (INIS)

Jana, Amiya K.

2016-01-01

Highlights: • A novel heat integrated configuration is proposed for batch distillation. • The shell is divided into two closed semi-cylinders by a metal wall. • An open-loop variable manipulation policy is formulated. • The column improves its energy efficiency and economic performance. - Abstract: This work introduces a new heat integrated distillation column (HIDiC) for batch processing. Under this scheme, the entire cylindrical shell is proposed to divide vertically by a metal wall into two closed semi-cylinders. Aiming to generate an internal heat source, a heat pump system is employed over the left hand division to elevate the pressure of the right hand part with the application of HIDiC concept. This new divided-wall HIDiC column utilizes its own energy source by transferring heat from the high pressure (HP) to low pressure (LP) side, thereby reducing the utility consumption in both the still and condenser. To make this thermal integration technology more effective, a typical tray configuration is proposed in both sides of the divided-wall. Unlike the continuous flow distillation, the batch column shows unsteady state process characteristics that make its operation more challenging. With this, an open-loop variable manipulation policy is formulated so that the dynamics of the heat integrated column remain close, if not same, with its conventional counterpart. This is a necessary condition required for a fair comparison between them. Finally, the proposed configuration is illustrated by a binary column, showing an improvement in energy savings, entropy generation and cost over its conventional analogous. This thermally integrated configuration is relatively simple than the traditional HIDiC in terms of design and operation.

Slug-flow dynamics with phase change heat transfer in compact heat exchangers with oblique wavy walls

Science.gov (United States)

Morimoto, Kenichi; Kinoshita, Hidenori; Matsushita, Ryo; Suzuki, Yuji

2017-11-01

With abundance of low-temperature geothermal energy source, small-scale binary-cycle power generation system has gained renewed attention. Although heat exchangers play a dominant role in thermal efficiency and the system size, the optimum design strategy has not been established due to complex flow phenomena and the lack of versatile heat transfer models. In the present study, the concept of oblique wavy walls, with which high j/f factor is achieved by strong secondary flows in single-phase system, is extended to two-phase exchangers. The present analyses are based on evaporation model coupled to a VOF technique, and a train of isolated bubbles is generated under the controlled inlet quality. R245fa is adopted as a low boiling-point working media, and two types of channels are considered with a hydraulic diameter of 4 mm: (i) a straight circular pipe and (ii) a duct with oblique wavy walls. The focus is on slug-flow dynamics with evaporation under small capillary but moderate Weber numbers, where the inertial effect as well as the surface tension is of significance. A possible direction of the change in thermo-physical properties is explored by assuming varied thermal conductivity. Effects of the vortical motions on evaporative heat transfer are highlighted. This work has been supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Numerical analysis of air flow, heat transfer, moisture transport and thermal comfort in a room heated by two-panel radiators

Energy Technology Data Exchange (ETDEWEB)

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

2011-01-15

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

Jet Impingement Heat Transfer at High Reynolds Numbers and Large Density Variations

DEFF Research Database (Denmark)

Jensen, Michael Vincent; Walther, Jens Honore

2010-01-01

Jet impingement heat transfer from a round gas jet to a flat wall has been investigated numerically in a configuration with H/D=2, where H is the distance from the jet inlet to the wall and D is the jet diameter. The jet Reynolds number was 361000 and the density ratio across the wall boundary...... layer was 3.3 due to a substantial temperature difference of 1600K between jet and wall. Results are presented which indicate very high heat flux levels and it is demonstrated that the jet inlet turbulence intensity significantly influences the heat transfer results, especially in the stagnation region....... The results also show a noticeable difference in the heat transfer predictions when applying different turbulence models. Furthermore calculations were performed to study the effect of applying temperature dependent thermophysical properties versus constant properties and the effect of calculating the gas...

Analytical Solution of Flow and Heat Transfer over a Permeable Stretching Wall in a Porous Medium

Directory of Open Access Journals (Sweden)

M. Dayyan

2013-01-01

Full Text Available Boundary layer flow through a porous medium over a stretching porous wall has seen solved with analytical solution. It has been considered two wall boundary conditions which are power-law distribution of either wall temperature or heat flux. These are general enough to cover the isothermal and isoflux cases. In addition to momentum, both first and second laws of thermodynamics analyses of the problem are investigated. The governing equations are transformed into a system of ordinary differential equations. The transformed ordinary equations are solved analytically using homotopy analysis method. A comprehensive parametric study is presented, and it is shown that the rate of heat transfer increases with Reynolds number, Prandtl number, and suction to the surface.

Effect of constant heat flux at outer cylinder on stability of viscous ...

African Journals Online (AJOL)

In this paper, the stability of the Couette flow of a viscous incompressible fluid between two concentric rotating cylinders is studied in the presence of a radial temperature gradient, when the outer cylinder is maintained at a constant heat flux. The analytical solution of the eigen-value problem is obtained by using the ...

Extension of the master sintering curve for constant heating rate modeling

Science.gov (United States)

McCoy, Tammy Michelle

The purpose of this work is to extend the functionality of the Master Sintering Curve (MSC) such that it can be used as a practical tool for predicting sintering schemes that combine both a constant heating rate and an isothermal hold. Rather than just being able to predict a final density for the object of interest, the extension to the MSC will actually be able to model a sintering run from start to finish. Because the Johnson model does not incorporate this capability, the work presented is an extension of what has already been shown in literature to be a valuable resource in many sintering situations. A predicted sintering curve that incorporates a combination of constant heating rate and an isothermal hold is more indicative of what is found in real-life sintering operations. This research offers the possibility of predicting the sintering schedule for a material, thereby having advanced information about the extent of sintering, the time schedule for sintering, and the sintering temperature with a high degree of accuracy and repeatability. The research conducted in this thesis focuses on the development of a working model for predicting the sintering schedules of several stabilized zirconia powders having the compositions YSZ (HSY8), 10Sc1CeSZ, 10Sc1YSZ, and 11ScSZ1A. The compositions of the four powders are first verified using x-ray diffraction (XRD) and the particle size and surface area are verified using a particle size analyzer and BET analysis, respectively. The sintering studies were conducted on powder compacts using a double pushrod dilatometer. Density measurements are obtained both geometrically and using the Archimedes method. Each of the four powders is pressed into ¼" diameter pellets using a manual press with no additives, such as a binder or lubricant. Using a double push-rod dilatometer, shrinkage data for the pellets is obtained over several different heating rates. The shrinkage data is then converted to reflect the change in relative

Bayesian inferences of the thermal properties of a wall using temperature and heat flux measurements

KAUST Repository

Iglesias, Marco

2017-09-20

The assessment of the thermal properties of walls is essential for accurate building energy simulations that are needed to make effective energy-saving policies. These properties are usually investigated through in situ measurements of temperature and heat flux over extended time periods. The one-dimensional heat equation with unknown Dirichlet boundary conditions is used to model the heat transfer process through the wall. In Ruggeri et al. (2017), it was assessed the uncertainty about the thermal diffusivity parameter using different synthetic data sets. In this work, we adapt this methodology to an experimental study conducted in an environmental chamber, with measurements recorded every minute from temperature probes and heat flux sensors placed on both sides of a solid brick wall over a five-day period. The observed time series are locally averaged, according to a smoothing procedure determined by the solution of a criterion function optimization problem, to fit the required set of noise model assumptions. Therefore, after preprocessing, we can reasonably assume that the temperature and the heat flux measurements have stationary Gaussian noise and we can avoid working with full covariance matrices. The results show that our technique reduces the bias error of the estimated parameters when compared to other approaches. Finally, we compute the information gain under two experimental setups to recommend how the user can efficiently determine the duration of the measurement campaign and the range of the external temperature oscillation.

Effects of Liquid Transpiration Cooling on Heat Transfer to the Diverging Region of a Porous-Walled Nozzle

National Research Council Canada - National Science Library

Schieb, Daniel

1997-01-01

This research effort investigated the effects of evaporation of water on the heat transferred to the wall of the diverging portion of a porous walled nozzle The AFIT High Pressure Shock Tube was used...

Beam heat load due to geometrical and resistive wall impedance in COLDDIAG

Science.gov (United States)

Casalbuoni, S.; Migliorati, M.; Mostacci, A.; Palumbo, L.; Spataro, B.

2012-11-01

One of the still open issues for the development of superconductive insertion devices is the understanding of the heat intake from the electron beam. With the aim of measuring the beam heat load to a cold bore and the hope to gain a deeper understanding in the underlying mechanisms, a cold vacuum chamber for diagnostics (COLDDIAG) was built. It is equipped with the following instrumentation: retarding field analyzers to measure the electron flux, temperature sensors to measure the beam heat load, pressure gauges, and mass spectrometers to measure the gas content. Possible beam heat load sources are: synchrotron radiation, wakefield effects due to geometrical and resistive wall impedance and electron/ion bombardment. The flexibility of the engineering design will allow the installation of the cryostat in different synchrotron light sources. COLDDIAG was first installed in the Diamond Light Source (DLS) in 2011. Due to a mechanical failure of the thermal transition of the cold liner, the cryostat had to be removed after one week of operation. After having implemented design changes in the thermal liner transition, COLDDIAG has been reinstalled in the DLS at the end of August 2012. In order to understand the beam heat load mechanism it is important to compare the measured COLDDIAG parameters with theoretical expectations. In this paper we report on the analytical and numerical computation of the COLDDIAG beam heat load due to coupling impedances deriving from unavoidable step transitions, ports used for pumping and diagnostics, surface roughness, and resistive wall. The results might have an important impact on future technological solutions to be applied to cold bore devices.

On the characteristics and application of thin wall welded titanium tubes for heat transfer

International Nuclear Information System (INIS)

Nishimura, Takashi; Miyamoto, Yoshiyuki

1985-01-01

Because of the excellent corrosion resistance, thin wall welded titanium tubes have become to be used in large number as the heat transfer tubes of condensers and seawater desalting plants using seawater in place of conventional copper alloy tubes. Especially in nuclear power plants, the all titanium condensers using thin wall welded titanium tubes and titanium tube plates were adopted in the almost all plants under construction or expected to be constructed. In this report, the various characteristics of thin wall welded titanium tubes required for using them as heat transfer tubes, such as corrosion resistance, heat transfer characteristics, fatigue strength and expanding characteristics, are outlined, and the state of use is described. At first, relatively thick seamless titanium tubes were used for chemical industry, but thereafter, due to the advance of the mass production techniques, the welded titanium tubes of less than 0.7 mm thickness and high quality have become to be supplied at low cost. In 1969, titanium tubes were used for the first time in Japan for the air cooler in the condenser of Akita Power Station, Tohoku Electric Power Co., Inc. The features of titanium are small specific gravity, small linear expansion coefficient and small Young's modulus. (Kako, I.)

The effects of heat generation and wall interaction on freezing and melting in a finite slab

International Nuclear Information System (INIS)

Cheung, F.B.; Chawla, T.C.; Pedersen, D.R.

1984-01-01

The processes of freezing and melting occurring in a heat-generating slab bounded by two semi-infinite cold walls is studied numerically. The method of collocation is employed to solve the various sets of governing equations describing the unsteady behavior of the system during different periods of time. Depending on the rate of internal heat generation and the thermal properties of the wall and the slab, several changes may take place in the system. These changes, as indicated by the transient locations of the solid-liquid interface, include transitions from freezing directly to melting, from freezing to cooling with phase change, from cooling to heating without phase change, and from heating to melting. Numerical predictions of the occurrence of these transitions, the rates of freezing and melting, and the duration of the transients are obtained as functions of several controlling dimensionless parameters of the system. Comparison is made with the case of a heat-generating sphere to further explore the effect of system geometry. (author)

Heating characteristics of billet in a walking hearth type reheating furnace

International Nuclear Information System (INIS)

Emadi, Ali; Saboonchi, Ahmad; Taheri, Mahdi; Hassanpour, Saeid

2014-01-01

The heating characteristics of billet in a walking hearth type reheating furnace were studied by developing a mathematical heat transfer model. Radiation calculations were conducted by means of zone method and considering all radiation exchange paths. The weighted-sum-of-gray-gas-model was used for better accuracy of gas radiation prediction. Convective heat flux was calculated by considering suitable value of convective heat transfer coefficient at any location of the furnace. The model was substantiated through its comparison to experimental data. A comparison was drawn to evaluate the effect of constant and variable convective coefficient on convective flux distribution and billet thermal behavior. The effect of furnace wall's emissivity of each zone and whole of the furnace on the billet thermal behavior was investigated. The obtained results revealed that by increasing furnace wall's emissivity for a determined residence time, billet's temperature in primary zones rises but it has no significant effect on its final temperature. However, by increasing wall's emissivity from 0.7 to 0.95, the residence time can be declined by about 5%. Moreover, emissivity increase in non-firing and preheating zones as compared to heating and soaking zones has greater impact on the billet thermal behavior. -- Highlights: • 3D radiation modeling by considering all possible paths of radiation exchange. • Using WSGG model for better prediction of gas radiation. • Using non-constant convection coefficient to consider variation of gas mass flow. • Investigation of effect of convection coefficient on billet temperature behavior. • Investigation of wall emissivity of furnace zones

Detection of heat abduction on the walls by artificial neural network and selection of materials with decision support system

Directory of Open Access Journals (Sweden)

Egemen Tekkanat

2017-08-01

Full Text Available Today energy conservation is a very important issue in the world and Turkey. The aim of this study is to minimize the heat abduction, thus to save energy by utilizing the factors to prevent the heat abduction on the walls of buildings. First of all, a back-propagation network model with artificial neural network model was used for the factors that can cause heat loss on the walls. Whether the walls have insulation were considered. After that, Decision Support Systems were used for heat insulation to select the appropriate materials. A Decision Support Model with Analytic Hierarchy Process (AHP was recommended to meet the needs of a customer best and to make better decisions for the selection of the materials. The method was used by construction firms for their decision processes for the best materials and the results were evaluated. After the evaluations were done, the factors that cause heat loss were considered and it became clear which factors were more important for the prevention of heat loss.

Heat transfer and thermodynamic performance of convective–radiative cooling double layer walls with temperature-dependent thermal conductivity and internal heat generation

International Nuclear Information System (INIS)

Torabi, Mohsen; Zhang, Kaili

2015-01-01

Highlights: • First and second laws of thermodynamics have been investigated in a composite wall. • Convective–radiative heat transfer is assumed on both surfaces. • Optimum interface location is calculated to minimize the total entropy generation rate. • Thermal conductivities ratio has great effects on the temperature and entropy generation. - Abstract: Composite geometries have numerous applications in industry and scientific researches. This work investigates the temperature distribution, and local and total entropy generation rates within two-layer composite walls using conjugate convection and radiation boundary conditions. Thermal conductivities of the materials of walls are assumed temperature-dependent. Temperature-dependent internal heat generations are also incorporated into the modeling. The differential transformation method (DTM) is used as an analytical technique to tackle the highly nonlinear system of ordinary differential equations. Thereafter, the local and total entropy generation rates are calculated using the DTM formulated temperature distribution. An exact analytical solution, for the temperature-independent model without radiation effect, is also derived. The correctness and accuracy of the DTM solution are checked against the exact solution. After verification, effects of thermophysical parameters such as location of the interface, convection–conduction parameters, radiation–conduction parameters, and internal heat generations, on the temperature distribution, and both local and total entropy generation rates are examined. To deliver the minimum total entropy generation rate, optimum values for some parameters are also found. Since composite walls are widely used in many fields, the abovementioned investigation is a beneficial tool for many engineering industries and scientific fields to minimize the entropy generation, which is the exergy destruction, of the system

Laminar free convection with variable fluid properties in vertical ducts having uniform wall temperature

International Nuclear Information System (INIS)

Aihara, Toshio; Maruyama, Shigenao; Choi, Jun-Seop.

1985-01-01

Recently, the research on free convection in vertical ducts has become active again concerning the problem of cooling in nuclear reactor accidents and the cooling of electronic equipment. Generally, in the convection heat transfer in ducts, when the wall temperature is high, the fluid temperature in the ducts conspicuously changes, accordingly, the temperature dependence of the properties cannot be neglected. In this study, about the laminar free convection in parallel plates and a circular pipe having uniform wall temperature, the numerical analysis taking the temperature dependence of all properties into account was carried out, thus the effect of the temperature dependence of properties exerted on free convection heat transfer was clarified, and the relation to the solution in constant properties was examined. Moreover, by introducing a new representative dimension, it was attempted to express mean heat transfer coefficient which is independent of the form of ducts in unified way. The mean Nusselt number of the constant property solution using entrance pressure condition agreed very well with the exact numerical solution. (Kako, I.)

The roles of thermal insulation and heat storage in the energy performance of the wall materials: a simulation study.

Science.gov (United States)

Long, Linshuang; Ye, Hong

2016-04-07

A high-performance envelope is the prerequisite and foundation to a zero energy building. The thermal conductivity and volumetric heat capacity of a wall are two thermophysical properties that strongly influence the energy performance. Although many case studies have been performed, the results failed to give a big picture of the roles of these properties in the energy performance of an active building. In this work, a traversal study on the energy performance of a standard room with all potential wall materials was performed for the first time. It was revealed that both heat storage materials and insulation materials are suitable for external walls. However, the importances of those materials are distinct in different situations: the heat storage plays a primary role when the thermal conductivity of the material is relatively high, but the effect of the thermal insulation is dominant when the conductivity is relatively low. Regarding internal walls, they are less significant to the energy performance than the external ones, and they need exclusively the heat storage materials with a high thermal conductivity. These requirements for materials are consistent under various climate conditions. This study may provide a roadmap for the material scientists interested in developing high-performance wall materials.

Measurement of the nonaxisymmetric heat load distribution on the first wall of TFTR due to locked modes

International Nuclear Information System (INIS)

Janos, A.C.; Fredrickson, E.; McGuire, K.M.; Nagayama, Y.; Owens, D.K.

1992-01-01

The first wall of TFTR is covered in large part (23%) by an inner-wall bumper limiter which is the primary power handling structure in TFTR. The limiter is comprised of more than 2000 tiles, and is instrumented with a large number (>100) of thermocouples in a two-dimensional (2D) array, primarily for protection of the wall. While only about 5% of the tiles are monitored, this thermocouple system is nevertheless capable of mapping details in the nonaxisymmetric, as well as symmetric, heat load patterns encountered under different conditions. In particular, helical heating patterns are observed in discharges which have locked modes. The helical patterns clearly match the expected trajectories based on the m/n mode numbers obtained from Mirnov coils (m/n=2/1 and 4/1), so that the thermocouple system can and was used to identify the existence and mode number of a locked mode. While TFTR discharges rarely suffer from locked modes, locked modes always alter the heating pattern. The locked modes are found to very significantly redistribute the heat load for both ohmic and NBI heated discharges. Locked modes can make what were the coldest areas into the hottest areas, and vice versa. Locked modes also can alter the heat pattern resulting from the frequent disruptions which occur as a result of a locked mode

Calculation of local bed to wall heat transfer in a fluidized-bed

International Nuclear Information System (INIS)

Kilkis, B.I.

1987-01-01

Surface to bed heat transfer in a fluidized-bed largely depends upon its local and global hydrodynamical behavior including particle velocity, particle trajectory, gas velocity, and void fraction. In this study, a computer program was developed in order to calculate the local bed to wall heat transfer, by accounting for the local and global instantaneous hydrodynamics of the bed. This is accomplished by utilizing the CHEMFLUB computer program. This information at a given location is interpreted so that the most appropriate heat transfer model is utilized for each time increment. These instantaneous heat transfer coefficient for the given location. Repeating the procedure for different locations, a space average heat transfer coefficient is also calculated. This report briefly summarizes the various heat transfer models employed and gives sample computer results reporting the case study for Mickley - Trilling's experimental set-up. Comparisons with available experimental data and correlations are also provided in order to compare and evaluate the computer results

Wall heat flux influence on the thermodynamic optimisation of irreversibilities of a circulating fluidised bed combustor

CSIR Research Space (South Africa)

Baloyi, J

2016-07-01

Full Text Available . The irreversibilities generated were arrived at by computing the entropy generation rates due to the combustion and frictional pressure drop processes. For the combustor where the wall condition was changed from adiabatic to negative heat flux (that is heat leaving...

Influence of internal and external boundary conditions on the decrement factor and time lag heat flux of building walls in steady periodic regime

International Nuclear Information System (INIS)

Mazzeo, D.; Oliveti, G.; Arcuri, N.

2016-01-01

Highlights: • Dynamic behaviour of building walls subjected to sinusoidal and actual loadings. • The joint action of more temperature and heat flux loadings has been considered. • Dynamic parameters were defined by the internal and external fluctuating heat flux. • Use of the Total Harmonic Distortion to determine the number of harmonics required. • Study of the influence of external and internal loadings on dynamic parameters. - Abstract: The dynamic behaviour of opaque components of the building envelope in steady periodic regime is investigated using parameters defined by the fluctuating heat flux that is transferred in the wall. The use of the heat flux allows for the joint action of the loadings that characterise both the outdoor environment and the indoor air-conditioned environment to be taken into account. The analysis was developed in sinusoidal conditions to determine the frequency response of the wall and in non-sinusoidal conditions to identify the actual dynamic behaviour of the wall. The use of non-dimensional periodic thermal transmittance is proposed for the sinusoidal analysis in order to evaluate the decrement factor and the time lag that the heat flux undergoes in crossing the wall as well as the efficiency of heat storage. In the presence of non-sinusoidal loadings, the identification of the dynamic behaviour of the wall is obtained using several dynamic parameters: the decrement factor in terms of energy, defined as the ratio between the energy in a semi-period entering and exiting the wall; the decrement factor and the time lag in terms of heat flux, considering the maximum peak and the minimum peak. These parameters allow for the identification of how the form of the heat flux trend crossing the wall is modified. The number of harmonics to be considered for an accurate representation of heat fluxes is determined by means of the introduction of the Total Harmonic Distortion (THD), which quantifies the distortion of a non

Interacting effects of uniform flow, plane shear, and near-wall proximity on the heat and mass transfer of respiratory aerosols

Energy Technology Data Exchange (ETDEWEB)

Worth Longest, P. [Virginia Commonwealth University, Richmond, VA (United States). Dept. of Mechanical Engineering; Kleinstreuer, C. [North Carolina State University, Raleigh, NC (United States). Dept. of Mechanical and Aerospace Engineering

2004-10-01

Individual and interacting effects of uniform flow, plane shear, and near-wall proximity on spherical droplet heat and mass transfer have been assessed for low Reynolds number conditions beyond the creeping flow regime. Validated resolved volume simulations were used to compute heat and mass transfer surface gradients of two-dimensional axisymmetric droplets and three-dimensional spherical droplets near planar wall boundaries for conditions consistent with inhalable aerosols (5 {<=} d {<=} 300 {mu}m) in the upper respiratory tract. Results indicate that planar shear significantly impacts droplet heat and mass transfer for shear-based Reynolds numbers greater than 1, which occur for near-wall respiratory aerosols with diameters in excess of 50 {mu}m. Wall proximity is shown to significantly enhance heat and mass transfer due to conduction and diffusion at separation distances less than five particle diameters and for small Reynolds numbers. For the Reynolds number conditions of interest, significant non-linear effects arise due to the concurrent interaction of uniform flow and shear such that linear superposition of Sherwood or Nusselt number terms is not allowable. Based on the validated numeric simulations, multivariable Sherwood and Nusselt number correlations are provided to account for individual flow characteristics and concurrent non-linear interactions of uniform flow, planar shear, and near-wall proximity. These heat and mass transfer correlations can be applied to effectively compute condensation and evaporation rates of potentially toxic or therapeutic aerosols in the upper respiratory tract, where non-uniform flow and wall proximity are expected to significantly affect droplet transport, deposition, and vapor formation. (author)

Heat transfer effects on the performance of an air standard Dual cycle

International Nuclear Information System (INIS)

Hou, S.-S.

2004-01-01

There are heat losses during the cycle of a real engine that are neglected in ideal air standard analysis. In this paper, the effects of heat transfer on the net work output and the indicated thermal efficiency of an air standard Dual cycle are analyzed. Heat transfer from the unburned mixture to the cylinder walls has a negligible effect on the performance for the compression process. Additionally, the heat transfer rates to the cylinder walls during combustion are the highest and extremely important. Therefore, we assume that the compression and power processes proceed instantaneously so that they are reversible adiabatics, and the heat losses during the heat rejection process can be neglected. The heat loss through the cylinder wall is assumed to occur only during combustion and is further assumed to be proportional to the average temperature of both the working fluid and the cylinder wall. The results show that the net work output versus efficiency characteristics and the maximum net work output and the corresponding efficiency bounds are strongly influenced by the magnitude of the heat transfer. Higher heat transfer to the combustion chamber walls lowers the peak temperature and pressure and reduces the work per cycle and the efficiency. The effects of other parameters, in conjunction with the heat transfer, including combustion constants, cut-off ratio and intake air temperature, are also reported. The results are of importance to provide good guidance for the performance evaluation and improvement of practical Diesel engines

Heat-Induced, Pressure-Induced and Centrifugal-Force-Induced Exact Axisymmetric Thermo-Mechanical Analyses in a Thick-Walled Spherical Vessel, an Infinite Cylindrical Vessel, and a Uniform Disk Made of an Isotropic and Homogeneous Material

Directory of Open Access Journals (Sweden)

Vebil Yıldırım

2017-07-01

Full Text Available Heat-induced, pressure-induced, and centrifugal force-induced axisymmetric exact deformation and stresses in a thick-walled spherical vessel, a cylindrical vessel, and a uniform disk are all determined analytically at a specified constant surface temperature and at a constant angular velocity. The inner and outer pressures are both included in the formulation of annular structures made of an isotropic and homogeneous linear elastic material. Governing equations in the form of Euler-Cauchy differential equation with constant coefficients are solved and results are presented in compact forms. For disks, three different boundary conditions are taken into account to consider mechanical engineering applications. The present study is also peppered with numerical results in graphical forms.

Assessment of hypervapotron heat sink performance using CFD under DEMO relevant first wall conditions

Energy Technology Data Exchange (ETDEWEB)

Domalapally, Phani, E-mail: p_kumar.domalapally@cvrez.cz

2016-11-01

Highlights: • Performance of Hypervapotron heat sink was tested for First wall limiter application. • Two different materials were tested Eurofer 97 and CuCrZr at PWR conditions. • Simulations were performed to see the effect of the different inlet conditions and materials on the maximum temperature. • It was found that CuCrZr heat sink performance is far better than Eurofer heat sink at the same operating conditions. - Abstract: Among the proposed First Wall (FW) cooling concepts for European Demonstration Fusion Power Plant (DEMO), water cooled FW is one of the options. The heat flux load distribution on the FW of the DEMO reactor is not yet precisely defined. But if the heat loads on the FW are extrapolated from ITER conditions, the numbers are quite high and have to be handled none the less. The design of the FW itself is challenging as the thermal conductivity ratio of heat sink materials in ITER (CuCrZr) and in DEMO (Eurofer 97) is ∼10–12 and the operating conditions are of Pressurized Water Reactor (PWR) in DEMO instead of 70 °C and 4 MPa as in ITER. This paper analyzes the performance of Hypervapotron (HV) heat sink for FW limiter application under DEMO conditions. Where different materials, temperatures, heat fluxes and velocities are considered to predict the performance of the HV, to establish its limits in handling the heat loads before reaching the upper limits from temperature point of view. In order to assess the performance, numerical simulations are performed using commercial CFD code, which was previously validated in predicting the thermal hydraulic performance of HV geometry. Based on the results the potential usage of HV heat sink for DEMO will be assessed.

Optimum diameter of a circulating fluidised bed combustor with negative wall heat flux

CSIR Research Space (South Africa)

Baloyi, J

2015-07-01

Full Text Available on irreversibilities in a 7 m circulating fluidised bed combustor with a negative wall heat flux, firing a mixture of air and solid pitch pine wood, was investigated. An analytical expression was derived that predicts the entropy generation rate, thereby...

First results of out-of-pile experiments concerning cooling phenomena of molten layers with internal heat sources

International Nuclear Information System (INIS)

Fieg, G.

1977-01-01

After severe hypothetical reactor accidents, large amounts of molten core material with internal heat generation may appear. It must be guaranteed that these materials can be kept within the containment. To clarify this situation, the knowledge of heat transport from liquid layers with internal heat generation is needed. First experimental results on heat transport from internally heated horizontal fluid layers are presented. The experiments have been performed in a smooth horizontal vessel with the base of 15 x 15 cm 2 . The Joule-heated liquid layer (depth L = 1 cm - 3.5 cm) is enclosed between two isothermal horizontal walls. They are polished fore parts of heat exchangers. The temperatures of the walls were held constant with thermostatically controlled water circulating through the heat exchangers. Horizontal heat fluxes were depressed by appropriate insulation of the side walls. The total heat transport to the upper and lower boundaries has been measured by the mass transport through the heat exchangers and the temperature rise of the cooling water

Augmentation of forced-convection heat transfer by applying electric fields to disturb flow near a wall

International Nuclear Information System (INIS)

Nariai, H.; Ishiguro, H.; Nagata, S.; Yabe, A.

1991-01-01

This paper reports on the augmentation effect of electrohydrodynamically (EHD) induced flow disturbance on forced-convection heat transfer in a channel that was experimentally investigated in order to determine the applicability of the enhanced heat transfer into a low- pressure drop heat exchanger, such as a high-performance oil cooler. The investigation is mainly based on the study carried out on the unique point where the flow is disturbed actively and controllably by applying electric fields between the wall and array of wire electrodes installed near the wall along the main stream. The liquid mixture of refrigerant R113 (96 wt %) and ethanol (4 wt %), called Fronsorubu AE, was selected as a working fluid. Heat transfer was found to be promoted intensely in the turbulent flow as well as in the laminar flow, up to a factor of about twenty-three in the case of laminar flow. It is noteworthy that the rate of increase in heat transfer coefficient is larger compared to that in the pressure drop. From a measurement of velocities by a laser Doppler velocimeter, it was made clear that the electrohydrodynamically induced flow disturbance brings about large heat transfer coefficients

Influence of thermal gradient on gas turbine combustor wall using impingement/effusion cooling techniques: CHT CFD predictions

Directory of Open Access Journals (Sweden)

A. M. El-jummah

2017-04-01

Full Text Available Internal wall heat transfer relevant to impingement/effusion cooling techniques was investigated using conjugate heat transfer (CHT computational fluid dynamics (CFD with ANSYS Fluent and ICEM commercial software. This work concentrates on the development of CHT CFD design procedures that are applicable to combustor wall and turbine blade heat transfer optimisation in gas turbine (GT. It specifically modelled and compares two configuration which are specifically relevant to the impingement and effusion holes density n (m-2 and is the ratio of the hole pitch X2. The configurations investigated are equal and unequal impingement and effusion holes density n (m-2, respectively, whereby in each case the variation in the number of cooling holes were carried out. The ratio of impingement and effusion number of holes/m2 (or hole density n, investigated were impingement/effusion: 4306/4306 and 1076/4306, respectively. The geometries were for impingement wall, hole pitch X to diameter D, X/D ratio of ~ 11 but different number of holes N for both n geometries, at a constant offset effusion wall, hole X/D of 4.7 of the same N for both the two configurations. The model geometries have a constant impingement gap of 8 mm with both impingement and effusion walls at 6.35 mm thick Nimonic - 75 material and were computed for varied air mass flux G from 0.1 - 0.94 kg/sm2. Symmetrical applications were employed in modelling each of the geometry, whereby for the impingement hole, only quarter of one hole was modelled, while for the effusion side the holes were either quarter or half modelled. The two n geometries were computed with k - ɛ turbulence model using standard wall functions, which also applies to all G. The predicted locally surface X2 (or hole square area average heat transfer coefficient (HTC h values compared with with previously published experimental data showed good agreement. The reduced internal gap flow recirculation with reduced heat transfer to

Numerical investigation of heat transfer enhancement in ribbed channel for the first wall of DFLL-TBM in ITER

International Nuclear Information System (INIS)

Jin Qiang; Liu Songlin; Li Min; Wang Weihua

2012-01-01

As an important component of Dual Functional Lithium Lead-Test Blanket Module (DFLL-TBM), the first wall (FW) must withstand and remove the heat flux from the plasma (q″ = 0.3 MW/m 2 ) and high nuclear power deposited in the structure at normal plasma operation scenario of ITER. In this paper the transverse ribs arranged along the plasma facing inner wall surface were used to enhance the heat transfer capability. After the validation compared with empirical correlations the Standard k–ω model was employed to do the numerical simulation using FLUENT code to investigate the heat transfer efficiency and flow performance of coolant in the ribbed channel preliminarily. The perforation on the bottom of rib was proposed near the lower heat transfer area (LHTA) to improve the heat transfer performance according to results of analyses.

Study on the L–H transition power threshold with RF heating and lithium-wall coating on EAST

DEFF Research Database (Denmark)

Chen, Leifeng; Xu, G.S.; Nielsen, Anders Henry

2016-01-01

The power threshold for low (L) to high (H) confinement mode transition achieved by radio-frequency (RF) heating and lithium-wall coating is investigated experimentally on EAST for two sets of walls: an all carbon wall (C) and molybdenum chamber and a carbon divertor (Mo/C). For both sets of walls...... Ploss increases with neutral density near the lower X-point in EAST with the Mo/C wall, consistent with previous results in the C wall (Xu et al 2011 Nucl. Fusion 51 072001). These findings suggest that the edge neutral density, the ion ∇B drift as well as the divertor pumping capability play important...

Development of laser cladding system to repair wall thinning of 1-inch heat exchanger tube

International Nuclear Information System (INIS)

Terada, Takaya

2013-01-01

We developed a laser cladding system to repair the inner wall wastage of heat exchanger tubes. Our system, which is designed to repair thinning tube walls within 100 mm from the edge of a heat exchanger tube, consists of a fiber laser, a composite-type optical fiberscope, a coupling device, a laser processing head, and a wire-feeding device. All of these components were reconfigured from the technologies of FBR maintenance. The laser processing head, which has a 15-mm outer diameter, was designed to be inserted into a 1-inch heat exchanger tube. We mounted a heatproof broadband mirror for laser cladding and fiberscope observation with visible light inside the laser processing head. The wire-feeding device continuously supplied 0.4-mm wire to the laser irradiation spot with variable feeding speeds from 0.5 to 20 mm/s. We are planning to apply our proposed system to the maintenance of aging industrial plants. (author)

Transient thermal performance analysis of micro heat pipes

International Nuclear Information System (INIS)

Liu, Xiangdong; Chen, Yongping

2013-01-01

A theoretical analysis of transient fluid flow and heat transfer in a triangular micro heat pipes (MHP) has been conducted to study the thermal response characteristics. By introducing the system identification theory, the quantitative evaluation of the MHP's transient thermal performance is realized. The results indicate that the evaporation and condensation processes are both extended into the adiabatic section. During the start-up process, the capillary radius along axial direction of MHP decreases drastically while the liquid velocity increases quickly at the early transient stage and an approximately linear decrease in wall temperature arises along the axial direction. The MHP behaves as a first-order LTI control system with the constant input power as the 'step input' and the evaporator wall temperature as the 'output'. Two corresponding evaluation criteria derived from the control theory, time constant and temperature constant, are able to quantitatively evaluate the thermal response speed and temperature level of MHP under start-up, which show that a larger triangular groove's hydraulic diameter within 0.18–0.42 mm is able to accelerate the start-up and decrease the start-up temperature level of MHP. Additionally, the MHP starts up fastest using the fluid of ethanol and most slowly using the working fluid of methanol, and the start-up temperature reaches maximum level for acetone and minimum level for the methanol. -- Highlights: • Transient thermal response of micro heat pipe is simulated by an improved model. • Control theory is introduced to quantify the thermal response of micro heat pipe. • Evaluation criteria are proposed to represent thermal response of micro heat pipe. • Effects of groove dimensions and working fluids on start-up of micro heat pipe are evaluated

Improving the conductivity of single-walled carbon nanotubes films by heat treatment

Energy Technology Data Exchange (ETDEWEB)

Wang Jiaping [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Superfine Microstructures, 1295 Dingxi Road, Shanghai 200050 (China); Sun Jing, E-mail: jingsun@mail.sic.ac.c [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Superfine Microstructures, 1295 Dingxi Road, Shanghai 200050 (China); Gao Lian, E-mail: liangaoc@online.sh.c [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Superfine Microstructures, 1295 Dingxi Road, Shanghai 200050 (China); Liu Yangqiao; Wang Yan; Zhang Jing [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Superfine Microstructures, 1295 Dingxi Road, Shanghai 200050 (China); Kajiura, Hisashi; Li Yongming; Noda, Kazuhiro [Advanced Materials Laboratories, Sony Corporation, Atsugi Tec. No. 2, 4-16-1 Okata Atsugi, Kanagawa 243-0021 (Japan)

2009-10-19

A simple heat treatment method was applied to remove surfactants remaining in the single-walled carbon nanotubes (SWNTs) films at 300 deg. C for 5 h in air. Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and reflected light interference microscope (RLIM) were employed to verify the elimination of surfactants. The comprehensive performance, especially the conductivity, could be improved by more than one order after heat treatment. For example, using SDBS as dispersant, the sheet resistance decreased from 782,600 OMEGA/square to 40,460 OMEGA/square with the transmittance of about 99.5% at 550 nm.

Numerical Simulation of a Turbulent Flow Over a Backward Facing Step With Heated Wall: Effect of Pulsating Velocity and Oscillating Wall

NARCIS (Netherlands)

Pozarlik, Artur Krzysztof; Kok, Jacobus B.W.

2012-01-01

An accurate prediction of the flow and the thermal boundary layer is required to properly simulate gas to wall heat transfer in a turbulent flow. This is studied with a view to application to gas turbine combustors. A typical gas turbine combustion chamber flow presents similarities with the

Influence of fluid-property variation on turbulent convective heat transfer in vertical annular CHANNEL FLOWS

International Nuclear Information System (INIS)

Joong Hun Bae; Jung Yul Yoo; Haecheon Choi

2005-01-01

Full text of publication follows: The influence of variable fluid property on turbulent convective heat transfer is investigated using direct numerical simulations. We consider thermally-developing flows of air and supercritical-pressure CO 2 in a vertical annular channel where the inner wall is heated with a constant heat flux and the outer wall is insulated. Turbulence statistics show that the heat and momentum transport characteristics of variable-property flows are significantly different from those of constant-property flows. The difference is mainly caused by the spatial and temporal variations of fluid density. The non-uniform density distribution causes fluid particles to be accelerated either by expansion or buoyancy force, while the temporal density fluctuations change the heat and momentum transfer via transport of turbulent mass flux, ρ'u' i . Both effects of the spatial and temporal variations of density are shown to be important in the analysis of turbulent convective heat transfer for supercritical-pressure fluids. For variable-property heated air flows, however, the effect of temporal density fluctuations can be neglected at low Mach number, which is in good accordance with the Morkovin's hypothesis. (authors)

EFFECT OF DISCRETE HEATER AT THE VERTICAL WALL OF THE CAVITY OVER THE HEAT TRANSFER AND ENTROPY GENERATION USING LBM

Directory of Open Access Journals (Sweden)

Mousa Farhadi

2011-01-01

Full Text Available In this paper Lattice Boltzmann Method (LBM was employed for investigation the effect of the heater location on flow pattern, heat transfer and entropy generation in a cavity. A 2D thermal lattice Boltzmann model with 9 velocities, D2Q9, is used to solve the thermal flow problem. The simulations were performed for Rayleigh numbers from 103 to 106 at Pr = 0.71. The study was carried out for heater length of 0.4 side wall length which is located at the right side wall. Results are presented in the form of streamlines, temperature contours, Nusselt number and entropy generation curves. Results show that the location of heater has a great effect on the flow pattern and temperature fields in the enclosure and subsequently on entropy generation. The dimensionless entropy generation decreases at high Rayleigh number for all heater positions. The ratio of averaged Nusselt number and dimensionless entropy generation for heater located on vertical and horizontal walls was calculated. Results show that higher heat transfer was observed from the cold walls when the heater located on vertical wall. On the other hand, heat transfer increases from the heater surface when it located on the horizontal wall.

Numerical calculation of wall-to-bed heat transfer coefficients in gas-fluidized beds

NARCIS (Netherlands)

Kuipers, J.A.M.; Prins, W.; van Swaaij, W.P.M.

1992-01-01

A computer model for a hot gas-fluidized bed has been developed. The theoretical description is based on a two-fluid model (TFM) approach in which both phases are considered to be continuous and fully interpenetrating. Local wall-to-bed heat-transfer coefficients have been calculated by the

Simulation and measurement of enhanced turbulent heat transfer in a channel with periodic ribs on one principal wall

International Nuclear Information System (INIS)

Tongmin Liou; Jennjiang Hwang; Shihhui Chen

1993-01-01

This paper performs a numerical and experimental analysis to investigate the heat transfer and fluid flow behaviour in a rectangular channel flow with streamwise-periodic ribs mounted on one of the principal walls. The k --A PDM turbulence model together with a smoothed hybrid central/skew upstream difference scheme (SCSUDS) and the PISO pressure-velocity coupling algorithm was applied to solving the accelerated, separated and recirculating flows. The real-time holographic interferometry technique was adopted to measure the time-dependent temperature field in the ribbed duct. The predicted fluid flow and temperature field were tested by previous laser-Doppler velocimetry measurements and present holographic interferometry data, and reasonable agreement was achieved. By the examination of the local wall temperature distribution for the uniform wall heat flux (UHF) boundary condition the regions susceptible to the hot spots are identified. Moreover, the study provided the numerical solution to investigate the effect of geometry and flow parameters on the local as well as average heat transfer coefficients. The compact correlation of the average heat transfer coefficient was further developed and accounted for the rib height, rib spacing, and Reynolds number. (Author)

NON-LINEAR TRANSIENT HEAT CONDUCTION ANALYSIS OF INSULATION WALL OF TANK FOR TRANSPORTATION OF LIQUID ALUMINUM

Directory of Open Access Journals (Sweden)

Miroslav M Živković

2010-01-01

Full Text Available This paper deals with transient nonlinear heat conduction through the insulation wall of the tank for transportation of liquid aluminum. Tanks designed for this purpose must satisfy certain requirements regarding temperature of loading and unloading, during transport. Basic theoretical equations are presented, which describe the problem of heat conduction finite element (FE analysis, starting from the differential equation of energy balance, taking into account the initial and boundary conditions of the problem. General 3D problem for heat conduction is considered, from which solutions for two- and one-dimensional heat conduction can be obtained, as special cases. Forming of the finite element matrices using Galerkin method is briefly described. The procedure for solving equations of energy balance is discussed, by methods of resolving iterative processes of nonlinear transient heat conduction. Solution of this problem illustrates possibilities of PAK-T software package, such as materials properties, given as tabular data, or analytical functions. Software also offers the possibility to solve nonlinear and transient problems with incremental methods. Obtained results for different thicknesses of the tank wall insulation materials enable its comparison in regards to given conditions

A fundamental study of fission product deposition on the wall surface

International Nuclear Information System (INIS)

Ishiguro, R.; Sakashita, H.; Sugiyama, K.

1987-01-01

Deposition of soluble matters on wall surfaces is studied in the present report for the purpose to understand a mechanism of fission product deposition on the wall surface in a molten salt reactor. Calcium carbonate solution is used to observe the fundamental mechanism of deposition. The experiments are performed under conditions of turbulent flow of the solution over a heated wall. According to the experimental results a model is proposed to estimate deposition rate. The model consists of two parts, one is the initial nucleus formation on a clean wall surface and the other is the constant increase of deposition succeeding to the first stage. The model is assessed by comparing it with the experimental results. Both results coincide well in some parameters, but not so well in others. (author)

Transition to chaos in a square enclosure containing internal heat sources

Energy Technology Data Exchange (ETDEWEB)

Baytas, A.C. [Institute For Nuclear Energy, Istanbul (Turkey)

1995-09-01

A numerical investigation is performed to study the transition from steady to chaotic flow of a fluid confined in a two-dimensional square cavity. The cavity has rigid walls of constant temperature containing uniformly distributed internal heat source. Effects of the Rayleigh number of flow and heat transfer rates are studied. In addition to, same problem is solved for sinusoidally changing internal heat source to show its effect on the flow model and heat transfer of the enclosures. Details of oscillatory solutions and flow bifurcations are presented.

Heat transfer and critical heat flux in a asymmetrically heated tube helicoidal flow

International Nuclear Information System (INIS)

Boscary, J.

1995-10-01

The design of plasma facing components is crucial for plasma performance in next fusion reactors. These elements will be submitted to very high heat flux. They will be actively water-cooled by swirl tubes in the subcooled boiling regime. High heat flux experiments were conducted in order to analyse the heat transfer and to evaluate the critical heat flux. Water-cooled mock-ups were one-side heated by an electron beam gun for different thermal-hydraulic conditions. The critical heat flux was detected by an original method based on the isotherm modification on the heated surface. The wall heat transfer law including forced convection and subcooled boiling regimes was established. Numerical calculations of the material heat transfer conduction allowed the non-homogeneous distribution of the wall temperature and of the wall heat flux to be evaluated. The critical heat flux value was defined as the wall maximum heat flux. A critical heat flux model based on the liquid sublayer dryout under a vapor blanket was established. A good agreement with test results was found. (author). 198 refs., 126 figs., 21 tabs

Simplified model for determining local heat flux boundary conditions for slagging wall

Energy Technology Data Exchange (ETDEWEB)

Bingzhi Li; Anders Brink; Mikko Hupa [Aabo Akademi University, Turku (Finland). Process Chemistry Centre

2009-07-15

In this work, two models for calculating heat transfer through a cooled vertical wall covered with a running slag layer are investigated. The first one relies on a discretization of the velocity equation, and the second one relies on an analytical solution. The aim is to find a model that can be used for calculating local heat flux boundary conditions in computational fluid dynamics (CFD) analysis of such processes. Two different cases where molten deposits exist are investigated: the black liquor recovery boiler and the coal gasifier. The results show that a model relying on discretization of the velocity equation is more flexible in handling different temperature-viscosity relations. Nevertheless, a model relying on an analytical solution is the one fast enough for a potential use as a CFD submodel. Furthermore, the influence of simplifications to the heat balance in the model is investigated. It is found that simplification of the heat balance can be applied when the radiation heat flux is dominant in the balance. 9 refs., 7 figs., 10 tabs.

Fractional derivatives of constant and variable orders applied to anomalous relaxation models in heat transfer problems

Directory of Open Access Journals (Sweden)

Yang Xiao-Jun

2017-01-01

Full Text Available In this paper, we address a class of the fractional derivatives of constant and variable orders for the first time. Fractional-order relaxation equations of constants and variable orders in the sense of Caputo type are modeled from mathematical view of point. The comparative results of the anomalous relaxation among the various fractional derivatives are also given. They are very efficient in description of the complex phenomenon arising in heat transfer.

Heat transfer nanofluid based on curly ultra-long multi-wall carbon nanotubes

Science.gov (United States)

Boncel, Sławomir; Zniszczoł, Aurelia; Pawlyta, Mirosława; Labisz, Krzysztof; Dzido, Grzegorz

2018-02-01

The main challenge in the use of multi-wall carbon nanotube (MWCNT) as key components of nanofluids is to transfer excellent thermal properties from individual nanotubes into the bulk systems. We present studies on the performance of heat transfer nanofluids based on ultra-long ( 2 mm), curly MWCNTs - in the background of various other nanoC-sp2, i.e. oxidized MWCNTs, commercially available Nanocyl™ MWCNTs and spherical carbon nanoparticles (SCNs). The nanofluids prepared via ultrasonication from water and propylene glycol were studied in terms of heat conductivity and heat transfer in a scaled up thermal circuit containing a copper helical heat exchanger. Ultra-long curly MWCNT (1 wt.%) nanofluids (stabilized with Gum Arabic in water) emerged as the most thermally conducting ones with a 23-30%- and 39%-enhancement as compared to the base-fluids for water and propylene glycol, respectively. For turbulent flows ( Re = 8000-11,000), the increase of heat transfer coefficient for the over-months stable 1 wt.% ultra-long MWCNT nanofluid was found as high as >100%. The findings allow to confirm that longer MWCNTs are promising solid components in nanofluids and hence to predict their broader application in heat transfer media.

First wall of thermonuclear device

International Nuclear Information System (INIS)

Kizawa, Makoto; Koizumi, Makoto; Nishihara, Yoshihiro.

1990-01-01

The first wall of a thermonuclear device is constituted with inner wall tiles, e.g. made of graphite and metal substrates for fixing them. However, since the heat expansion coefficient is different between the metal substrates and intermediate metal members, thermal stresses are caused to deteriorate the endurance of the inner wall tiles. In view of the above, low melting metals are disposed at the portion of contact between the inner wall tiles and the metal substrates and, further, a heat pipe structure is incorporated into the metal substrates. Under the thermal load, for example, during operation of the thermonuclear device, the low melting metals at the portion of contact are melted into liquid metals to enhance the state of contact between the inner wall tiles and the metal substrate to reduce the heat resistance and improve the heat conductivity. Even if there is a difference in the heat expansion coefficient between the inner wall tiles and the metal substrates, neither sharing stresses not thermal stresses are caused. Further, since the heat pipe structure is incorporated into the metal substrates, the lateral unevenness of the temperature in the metal substrates can be eliminated. Thus, the durability of the inner wall tiles can be improved. (N.H.)

Experimental investigation of heat transfer in the transition region

International Nuclear Information System (INIS)

Johannsen, K.; Weber, P.; Feng, Q.

1990-10-01

An experimental study of forced convective boiling heat transfer for upflow of water in a circular tube has been performed using a heat transfer system with temperature-controlled indirect Joule heating. By this way, complete boiling curves from incipience of boiling to fully established film boiling could be measured including the transition boiling regime. The boiling curves were traversed in a quasi-steady mode, usually by increasing the set-point wall temperature average at a constant time rate of 3.5 K/min. The vast majority of results covers the pressure range from 0.1 to 1.0 MPa, mass flux range from 25 to 200 kg/(m 2 s) and inlet subcooling from 5 to 30 K. The experimental results of transition boiling heat transfer obtained in the centre of the test section were correlated in terms of a heat flux/surface superheat relationship that was normalized by the maximum heat flux (local CHF) and its associated wall superheat, respectively, to anchor the transition boiling curve to its low temperature limit. The upper surface temperature limit of the transition boiling regime was determined by inspection of measured axial distributions of surface heat flux and corresponding wall temperature. The critical heat flux (CHF) and its corresponding wall superheat has been measured, too. These temperature-controlled results were compared also with power-controlled experiments. The data are presented in terms of a table and accurate empirical correlations following Katto's generalized correlation scheme. Taking into account previous CHF data at L/D ≤ 100 and same range of flow conditions the length effect was found to further depend on pressure and mass flux. The data for the critical wall superheat show a distinct dependence upon pressure, mass flux and inlet quality that has not been observed before with comparable clarity

Heat transfer in an asymmetrically heated duct, 2

International Nuclear Information System (INIS)

Satoh, Isao; Kurosaki, Yasuo

1986-01-01

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

Symmetry Methods of Flow and Heat Transfer between Slowly Expanding or Contracting Walls

Directory of Open Access Journals (Sweden)

Gabriel Magalakwe

2013-01-01

Full Text Available An analysis has been carried out for the flow and heat transfer of an incompressible laminar and viscous fluid in a rectangular domain bounded by two moving porous walls which enable the fluid to enter or exit during successive expansions or contractions. The basic equations governing the flow are reduced to the ordinary differential equations using Lie-group analysis. Effects of the permeation Reynolds number , porosity , and the dimensionless wall dilation rate on the self-axial velocity are studied both analytically and numerically. The solutions are represented graphically. The analytical procedure is based on double perturbation in the permeation Reynolds number and the wall expansion ratio , whereas the numerical solution is obtained using Runge-Kutta method with shooting technique. Results are correlated and compared for some values of the physical parameters. Lastly, we look at the temperature distribution.

Enhancement of heat transfer for thermal energy storage application using stearic acid nanocomposite with multi-walled carbon nanotubes

International Nuclear Information System (INIS)

Li, TingXian; Lee, Ju-Hyuk; Wang, RuZhu; Kang, Yong Tae

2013-01-01

A latent heat storage nanocomposite made of stearic acid (SA) and multi-walled carbon nanotube (MWCNT) is prepared for thermal energy storage application. The thermal properties of the SA/MWCNT nanocomposite are characterized by SEM (scanning electron microscopy) and DSC (differential scanning calorimeter) analysis techniques, and the effects of different volume fractions of MWCNT on the heat transfer enhancement and thermal performance of stearic acid are investigated during the charging and discharging phases. The SEM analysis shows that the additive of MWCNT is uniformly distributed in the phase change material of stearic acid, and the DSC analysis reveals that the melting point of SA/MWCNT nanocomposite shifts to a lower temperature during the charging phase and the freezing point shifts to a higher temperature during the discharging phase when compared with the pure stearic acid. The experimental results show that the addition of MWCNT can improve the thermal conductivity of stearic acid effectively, but it also weakens the natural convection of stearic acid in liquid state. In comparison with the pure stearic acid, the charging rate can be decreased by about 50% while the discharging rate can be improved by about 91% respectively by using the SA/5.0% MWCNT nanocomposite. It appears that the MWCNT is a promising candidate for enhancing the heat transfer performance of latent heat thermal energy storage system. - Highlights: • A nanocomposite made of stearic acid and multi-walled carbon nanotube is prepared for thermal energy storage application. • Effects of multi-walled carbon nanotube on the thermal performance of the nanocomposite are investigated. • Multi-walled carbon nanotube enhances the thermal conductivity but weakens the natural convection of stearic acid. • Discharging/charging rates of stearic acid are increased/decreased by using multi-walled carbon nanotube

A solution for the Graetz problem in parallel plates, with axial heat conduction in the fluid and in the wall

International Nuclear Information System (INIS)

Biage, M.

1983-04-01

A heat transfer problem in parallel plates with infinite with has been solved, with axial heat conduction in the fluid and in the wall, considering steady-state laminar flow for a Newtonian fluid and a fully developed velocity profile. The duct consists of an infinite inicial part, insulated on both plates, an intermediale part of finite length, with a prescribed heat flux in the upper plate and insulated on the botton plate, and by another infinite part also insulated on both plates. The problem has been solved by a numerical combination of the integral equation method and the variational method. Both, the performance of the numerical technique employed and results obtained are analyzed in this work. It is demostrated that the heat conduction in the wall significantly modifies the heat transfer parameters. (Author) [pt

A Methodology to Determine Self-Similarity, Illustrated by Example: Transient Heat Transfer with Constant Flux

Science.gov (United States)

Monroe, Charles; Newman, John

2005-01-01

This simple example demonstrates the physical significance of similarity solutions and the utility of dimensional and asymptotic analysis of partial differential equations. A procedure to determine the existence of similarity solutions is proposed and subsequently applied to transient constant-flux heat transfer. Short-time expressions follow from…

High heat load experiments for first wall materials by high power ion beams

Energy Technology Data Exchange (ETDEWEB)

Kuroda, Tsutomu; Kaneko, Osamu; Sakurai, Keiichi; Oka, Yoshihide; Shibui, Masanao; Ohmori, Junji

1985-09-01

Preliminary results are presented with some analytical calculations for thermal shock fractures of first-wall material candidates under plasma disruption heating conditions. A 120 keV - 90 A ion source has been used as an energy source to heat large specimens with heat fluxes of about 9 kW/cm/sup 2/ for pulse length of about 57 msec. Materials examined here are graphite (POCO), SiC, AlN, TiC-coated graphite, and sus 304. The SiC and AlN specimens were completely broken by only one thermal shock. The web-like surface cracks with a depth of about 0.6 mm were created in the tungsten specimen during five shots. No apparent destructive changes were observed in the graphite specimen.

Boiling Heat Transfer Mechanisms in Earth and Low Gravity: Boundary Condition and Heater Aspect Ratio Effects

Science.gov (United States)

Kim, Jungho

2004-01-01

Boiling is a complex phenomenon where hydrodynamics, heat transfer, mass transfer, and interfacial phenomena are tightly interwoven. An understanding of boiling and critical heat flux in microgravity environments is of importance to space based hardware and processes such as heat exchange, cryogenic fuel storage and transportation, electronic cooling, and material processing due to the large amounts of heat that can be removed with relatively little increase in temperature. Although research in this area has been performed in the past four decades, the mechanisms by which heat is removed from surfaces in microgravity are still unclear. Recently, time and space resolved heat transfer data were obtained in both earth and low gravity environments using an array of microheaters varying in size between 100 microns to 700 microns. These heaters were operated in both constant temperature as well as constant heat flux mode. Heat transfer under nucleating bubbles in earth gravity were directly measured using a microheater array with 100 m resolution operated in constant temperature mode with low and high subcooled bulk liquid along with images from below and from the side. The individual bubble departure diameter and energy transfer were larger with low subcooling but the departure frequency increased at high subcooling, resulting in higher overall heat transfer. The bubble growth for both subcoolings was primarily due to energy transfer from the superheated liquid layer relatively little was due to wall heat transfer during the bubble growth process. Oscillating bubbles and sliding bubbles were also observed in highly subcooled boiling. Transient conduction and/or microconvection was the dominant heat transfer mechanism in the above cases. A transient conduction model was developed and compared with the experimental data with good agreement. Data was also obtained with the heater array operated in a constant heat flux mode and measuring the temperature distribution across

Studies on first wall and plasma wall interaction in JT-60

International Nuclear Information System (INIS)

Nakamura, Hiroo

1988-12-01

This paper describes studies on first wall and plasma wall interaction in JT-60. Main results are as follows; (1) To select JT-60 first wall material, various RandD were done in FY1975 ∼ 1976. Mo was selected as first wall materials of limiters and divertor plates because of its reliability under a high heat flux condition. (2) Development of low-Z material has been done to reduce impurity problem of Mo first wall. As a result, titanium carbide (TiC) was selected as a coating material on the Mo. High heat load testing has been done for TiC coated Mo limiter same as JT-60. This material can survive under the condition of 1 kW/cm 2 x 10 s, expected in JT-60 limiter design. (3) To reduce high heat load on the divertor plate, separatrix swing is proposed. Optimum frequency of the sweeping is evaluated to be 2 Hz in JT-60. For a discharge with heating power of 30 MW and duration time of 10 s, in addition to the separatrix swing, remote radiative cooling in the divertor region is necessary. Moreover, calculations of erosion thickness have been done for stainless steel, Mo, graphite, TiC and silicon caibide under high heat flux during plasma disruption. (4) In divertor experiments in JT-60, divertor functions on particle, heat load and impurity controls have been demonstrated. In elctron density of 6 x 10 19 m -3 , particle fueling rate of 20 MW NB heating (3 Pa m 3 /s) can be exhausted by divertor pumping system. Effectiveness of remote radiative cooling is demonstrated under the condition of 20 MW NB heating power. Also, separatrix swing is demonstrated to reduce heat load on the divertor plate. Total radiation in main plasma is 5 ∼ 10% of total absorbed power. (author) 120 refs

A novel transient wall heat transfer approach for the start-up of SI engines with gasoline direct injection

Science.gov (United States)

Lejsek, David; Kulzer, André; Hammer, Jürgen

2010-11-01

The introduction of CO2-reduction technologies like Start-Stop or the Hybrid-Powertrain and the worldwide stringent emission legislation require a detailed optimization of the engine start-up. The combustion concept development as well as the calibration of the engine control unit makes an explicit thermodynamic analysis of the combustion process during the start-up necessary. Initially, the well-known thermodynamic analysis of in-cylinder pressure at stationary condition was transmitted to the highly non-stationary engine start-up. For this running mode of the engine the current models for calculation of the transient wall heat fluxes were found to be misleading. With a fraction of nearly 45% of the burned fuel energy, the wall heat is very important for the calculation of energy balance and for the combustion process analysis. Based on the measurements of transient wall heat transfer densities during the start-up presented in a former work (Lejsek and Kulzer in Investigations on the transient wall heat transfer at start-up for SI engines with gasoline direct injection. SAE Paper), the paper describes the development of adaptations to the known correlations by Woschni (MTZ 31:491, 1970), Hohenberg (Experimentelle Erfassung der Wandwärme von Kolbenmotoren. TU Graz, Habil., 1980) and Bargende (Ein Gleichungsansatz zur Berechnung der instationären Wandwärmeverluste im Hochdruckteil von Ottomotoren. TH Darmstadt, PhD-Thesis, 1991) for the application during engine start-up. To demonstrate the high accuracy of the model, the results of the cyclic resolved thermodynamic analysis using the presented novel approaches were compared with the results of the measurements. It is shown, that the novel heat flux models for the engine start-up process gives a cyclic resolved thermodynamic analysis to optimize the engine start-up pretty efficient.

Heat transfer and critical heat flux in a spiral flow in an asymmetrical heated tube

International Nuclear Information System (INIS)

Boscary, J.; Association Euratom-CEA, Centre d'Etudes Nucleaires de Cadarache, 13 - Saint-Paul-lez-Durance

1997-03-01

The design of plasma facing components is crucial for plasma performance in next fusion reactors. These elements will be submitted to very high heat flux. They will be actively water-cooled by swirl tubes in the subcooled boiling regime. High heat flux experiments were conducted in order to analyse the heat transfer and to evaluate the critical heat flux. Water-cooled mock-ups were one-side heated by an electron beam gun for different thermal-hydraulic conditions. The critical heat flux was detected by an original method based on the isotherm modification on the heated surface. The wall heat transfer law including forced convection and subcooled boiling regimes was established. Numerical calculations of the material heat transfer conduction allowed the non-homogeneous distribution of the wall temperature and of the wall heat flux to be evaluated. The critical heat flux value was defined as the wall maximum heat flux. A critical heat flux model based on the liquid sublayer dryout under a vapor blanket was established. A good agreement with test results was found. (author)

Local heat transfer around a wall-mounted cube at 45 deg. to flow in a turbulent boundary layer

International Nuclear Information System (INIS)

Nakamura, Hajime; Igarashi, Tamotsu; Tsutsui, Takayuki

2003-01-01

The flow and local heat transfer around a wall-mounted cube oriented 45 deg. to the flow is investigated experimentally in the range of Reynolds number 4.2 x 10 3 -3.3 x 10 4 based on the cube height. The distribution of local heat transfer on the cube and its base wall are examined, and it is clarified that the heat transfer distribution under the angled condition differs markedly to that for cube oriented perpendicular to the flow, particularly on the top face of the cube. The surface pressure distribution is also investigated, revealing a well-formed pair of leading-edge vortices extending from the front corner of the top face downstream along both front edges for Re>(1-2)x10 4 . Regions of high heat transfer and low pressure are formed along the flow reattachment and separation lines caused by these vortices. In particular, near the front corner of the top face, pressure suction and heat transfer enhancement are pronounced. The average heat transfer on the top face is enhanced at Re>(1-2)x10 4 over that of a cube aligned perpendicular to the flow

Resistive wall heating due to image current on the beam chamber for a superconducting undulator.

Energy Technology Data Exchange (ETDEWEB)

Kim, S. H. (Accelerator Systems Division (APS))

2012-03-27

The image-current heating on the resistive beam chamber of a superconducting undulator (SCU) was calculated based on the normal and anomalous skin effects. Using the bulk resistivity of copper for the beam chamber, the heat loads were calculated for the residual resistivity ratios (RRRs) of unity at room temperature to 100 K at a cryogenic temperature as the reference. Then, using the resistivity of the specific aluminum alloy 6053-T5, which will be used for the SCU beam chamber, the heat loads were calculated. An electron beam stored in a storage ring induces an image current on the inner conducting wall, mainly within a skin depth, of the beam chamber. The image current, with opposite charge to the electron beam, travels along the chamber wall in the same direction as the electron beam. The average current in the storage ring consists of a number of bunches. When the pattern of the bunched beam is repeated according to the rf frequency, the beam current may be expressed in terms of a Fourier series. The time structure of the image current is assumed to be the same as that of the beam current. For a given resistivity of the chamber inner wall, the application ofthe normal or anomalous skin effect will depend on the harmonic numbers of the Fourier series of the beam current and the temperature of the chamber. For a round beam chamber with a ratius r, much larger than the beam size, one can assume that the image current density as well as the density square, may be uniform around the perimeter 2{pi}r. For the SCU beam chamber, which has a relatively narrow vertical gap compared to the width, the effective perimeter was estimated since the heat load should be proportional to the inverse of the perimeter.

Numerical analysis of flow instability in the water wall of a supercritical CFB boiler with annular furnace

Science.gov (United States)

Xie, Beibei; Yang, Dong; Xie, Haiyan; Nie, Xin; Liu, Wanyu

2016-08-01

In order to expand the study on flow instability of supercritical circulating fluidized bed (CFB) boiler, a new numerical computational model considering the heat storage of the tube wall metal was presented in this paper. The lumped parameter method was proposed for wall temperature calculation and the single channel model was adopted for the analysis of flow instability. Based on the time-domain method, a new numerical computational program suitable for the analysis of flow instability in the water wall of supercritical CFB boiler with annular furnace was established. To verify the code, calculation results were respectively compared with data of commercial software. According to the comparisons, the new code was proved to be reasonable and accurate for practical engineering application in analysis of flow instability. Based on the new program, the flow instability of supercritical CFB boiler with annular furnace was simulated by time-domain method. When 1.2 times heat load disturbance was applied on the loop, results showed that the inlet flow rate, outlet flow rate and wall temperature fluctuated with time eventually remained at constant values, suggesting that the hydrodynamic flow was stable. The results also showed that in the case of considering the heat storage, the flow in the water wall is easier to return to stable state than without considering heat storage.

Behaviour of the Callovo-Oxfordian clay around a converging heated borehole: thermal free wall experiment

International Nuclear Information System (INIS)

Garitte, B.; Gens, A.; Vaunat, J.; Armand, G.; Conil, N.

2012-01-01

Document available in extended abstract form only. ANDRA has launched several heating experiments in the Meuse-Haute Marne Underground Laboratory (e.g. TER and TED). In these experiments, the heater-rock contact was ensured by a metal tubing that prevented any convergence of the heating borehole. The Thermal Free Wall experiment was run by ANDRA to investigate whether the rock behaviour around an un-cased borehole was similar as in the previous experiments. Additionally, the temperature increase in the TFW was applied faster than in the previous experiments in order to investigate the rock response to a heavier thermal load. It consists in a main borehole containing the heater and two instrumentation boreholes equipped with a temperature and a pore water pressure sensor each. The sensors installed in borehole TER1906 are at approximately 40 cm from the heater borehole wall in the bedding plane. The TER1907 sensors are in the direction perpendicular to the bedding planes at about 70 cm from the heater borehole. The boreholes were drilled from the GEX gallery in the direction of the major in situ stress (16 MPa). The heater has an effective heating length of 3.29 m and is located between 7 and 10 m from the GEX gallery. It was emplaced on a base to centre it in the borehole and to have a void between the heater and the rock mass for free convergence. Heating started on 10 January 2011 and lasted 56 days. One of the requirements of the experiment was to apply a relatively fast heating ramp in comparison with the previous tests in order to investigate the rock behaviour under stronger thermal load. The increase from 21 C to 90 C at the external heater wall was achieved in 14 hours. The initial pore water pressure is about 3.2 MPa, somewhat lower than the undisturbed pore water pressure at the level of the laboratory (4.5 MPa). This difference is attributed to the presence of the GEX gallery that was excavated in July-September 2005. In this work, we present the

Entropy Generation during Turbulent Flow of Zirconia-water and Other Nanofluids in a Square Cross Section Tube with a Constant Heat Flux

Directory of Open Access Journals (Sweden)

Hooman Yarmand

2014-11-01

Full Text Available The entropy generation based on the second law of thermodynamics is investigated for turbulent forced convection flow of ZrO2-water nanofluid through a square pipe with constant wall heat flux. Effects of different particle concentrations, inlet conditions and particle sizes on entropy generation of ZrO2-water nanofluid are studied. Contributions from frictional and thermal entropy generations are investigated, and the optimal working condition is analyzed. The results show that the optimal volume concentration of nanoparticles to minimize the entropy generation increases when the Reynolds number decreases. It was also found that the thermal entropy generation increases with the increase of nanoparticle size whereas the frictional entropy generation decreases. Finally, the entropy generation of ZrO2-water was compared with that from other nanofluids (including Al2O3, SiO2 and CuO nanoparticles in water. The results showed that the SiO2 provided the highest entropy generation.

Influence of Slip Condition on Unsteady Free Convection Flow of Viscous Fluid with Ramped Wall Temperature

Directory of Open Access Journals (Sweden)

Sami Ul Haq

2015-01-01

Full Text Available The objective of this study is to explore the influence of wall slip condition on a free convection flow of an incompressible viscous fluid with heat transfer and ramped wall temperature. Exact solution of the problem is obtained by using Laplace transform technique. Graphical results to see the effects of Prandtl number Pr, time t, and slip parameter η on velocity and skin friction for the case of ramped and constant temperature of the plate are provided and discussed.

Numerical study of effect of wall parameters on catalytic combustion characteristics of CH4/air in a heat recirculation micro-combustor

International Nuclear Information System (INIS)

Yan, Yunfei; Wang, Haibo; Pan, Wenli; Zhang, Li; Li, Lixian; Yang, Zhongqing; Lin, Changhai

2016-01-01

Highlights: • Combustion in heat recuperation micro-combustors with different materials was studied. • Heat concentration is more obvious with thermal conductivity decreasing. • Combustor with copper baffles has uniform temperature distribution and best preheating effectiveness. • Influence of wall thermal conductivity is negligible on OH(s) coverage. • Methane conversion rate firstly increases and then decreases with h increasing. - Abstract: Premixed combustion of methane/air mixture in heat recuperation micro-combustors made of different materials (corundum, quartz glass, copper and ferrochrome) was investigated. The effects of wall parameters on the combustion characters of a CH 4 /air mixture under Rhodium catalyst as well as the influence of wall materials and convection heat transfer coefficients on the stable combustion limit, temperature field, and free radicals was explored using numerical analysis methodology. The results show that with a decrease of thermal conductivity of wall materials, the temperature of the reaction region increases and hot spots becomes more obvious. The combustor with copper baffles has uniform temperature distribution and best preheating effectiveness, but when inlet velocity is too small, the maximum temperature in the combustor with copper or ferrochrome baffles is well beyond the melting point of the materials. With an increase in thermal conductivity, the preheat zone for premixed gas increases, but the influence of thermal conductivity on OH(s) coverage is negligible. With an increase of the wall convection heat transfer coefficient, the methane conversion rate firstly increases, then decreases reaching a maximum value at h = 8.5 W/m 2 K, however, the average temperature of both the axis and exterior surface of the combustor decrease.

Simulations of the near-wall heat transfer at medium prandtl numbers

International Nuclear Information System (INIS)

Bergant, R.; Tiselj, I.

2003-01-01

A heat transfer from a wall to a fluid at low Reynolds and Prandtl numbers can be described by means of Direct Numerical Simulation (DNS). At higher Prandtl numbers (Pr > 20) so-called under-resolved DNS can be performed to carry out turbulent heat transfer. Three different under-resolved DNSs of the fully developed turbulent flow in the channel at Reynolds number Re = 4580 and at Prandtl numbers Pr = 100, Pr = 200 and Pr 500 are presented in this paper. These simulations describe all velocity scales, but they are not capable to describe smallest temperature scales. However, very good agreement of heat transfer coefficients was achieved with the correlation of Hasegawa [1] or with the correlation of Papavassiliou [2], who performed DNS by means of Lagrangian method instead of Eulerian method, which was applied in our simulations. We estimate that under resolved DNS simulations based on Eulerian method are useful up to approximately Pr = 200, whereas at Pr = 500 instabilities appear due to the unresolved smallest thermal scales. (author)

Erosion simulation of first wall beryllium armour after ITER transient heat loads and runaway electrons action

Energy Technology Data Exchange (ETDEWEB)

Bazylev, B., E-mail: boris.bazylev@kit.edu [Karlsruhe Institute of Technology, IHM, P.O. Box 3640, D-76021 Karlsruhe (Germany); Igitkhanov, Yu.; Landman, I.; Pestchanyi, S. [Karlsruhe Institute of Technology, IHM, P.O. Box 3640, D-76021 Karlsruhe (Germany); Loarte, A. [ITER Organisation, Cadarache, 13108 Saint Paul Lez Durance Cedex (France)

2011-10-01

Beryllium is foreseen as plasma facing armour for the first wall (FW) in ITER in form of Be-clad blanket modules in macrobrush design with brush size about 8-10 cm. In ITER significant heat loads during transient events (TE) and runaway electrons impact are expected at the main chamber wall that may leads to the essential damage of the Be armour. The main mechanisms of metallic target damage remain surface melting, evaporation, and melt motion, which determine the life-time of the plasma facing components. The melt motion damages of Be macrobrush armour caused by the tangential friction force and the J x B forces are analyzed for bulk Be and different sizes of Be-brushes. The damage of the FW due to heat loads caused by runaway electrons is numerically simulated.

Erosion simulation of first wall beryllium armour after ITER transient heat loads and runaway electrons action

International Nuclear Information System (INIS)

Bazylev, B.; Igitkhanov, Yu.; Landman, I.; Pestchanyi, S.; Loarte, A.

2011-01-01

Beryllium is foreseen as plasma facing armour for the first wall (FW) in ITER in form of Be-clad blanket modules in macrobrush design with brush size about 8-10 cm. In ITER significant heat loads during transient events (TE) and runaway electrons impact are expected at the main chamber wall that may leads to the essential damage of the Be armour. The main mechanisms of metallic target damage remain surface melting, evaporation, and melt motion, which determine the life-time of the plasma facing components. The melt motion damages of Be macrobrush armour caused by the tangential friction force and the J x B forces are analyzed for bulk Be and different sizes of Be-brushes. The damage of the FW due to heat loads caused by runaway electrons is numerically simulated.

Dynamics and control of a heat pump assisted extractive dividing-wall column for bioethanol dehydration

NARCIS (Netherlands)

Patraşcu, Iulian; Bildea, Costin Sorin; Kiss, Anton A.

Recently, a novel heat-pump-assisted extractive distillation process taking place in a dividing-wall column was proposed for bioethanol dehydration. This integrated design combines three distillation columns into a single unit that allows over 40% energy savings and low specific energy requirements

Differentiated heated lid driven cavity interacting with tube: A lattice Boltzmann study

Directory of Open Access Journals (Sweden)

Bennacer Rachid

2017-01-01

Full Text Available The multiple-relaxation-time (MRT lattice-Boltzmann method is implemented to investigate combined natural and forced convection occurring in a two-dimensional square cavity. The top wall slides to the right at constant speed, while the other three remain stationary. The solution is performed for a left vertical wall at a constant temperature, which is higher than of the right wall. This yields a “cooperating” case, in which dynamic and buoyancy forces are added together. The enclosure is filled with air and contains a heat conducting circular cylinder, which is placed at various positions. The double distribution model used in lattice Boltzmann methods has been adopted to simulate the hydrodynamic and thermal fields, with the D2Q9 and D2Q5 lattices selected to perform the corresponding computations. Simulations have been conducted over a wide range of Rayleigh (Ra and Reynolds (Re numbers, and the features of dynamic and thermal fields are presented for the spectra of this mixed convection phenomenon. The flow and heat transfer characteristics of the cylinder position are described and analyzed in terms of the average Nusselt number (Nu. The computed results show the influence of the cylinder on the corresponding heat transfer in the enclosure. It has been found that the power (i.e. shear stress needed to lid the upper surface will depend on the governing parameters.

Analytical solutions for hydromagnetic natural convection flow of a particulate suspension through isoflux-isothermal channels in the presence of a heat source or sink

International Nuclear Information System (INIS)

Chamkha, Ali J.; Al-Rashidi, Seham S.

2010-01-01

This work considers the problem of steady natural convection hydromagnetic flow of a particulate suspension through an infinitely long channel in the presence of heat generation or absorption effects. The channel walls are maintained at isoflux-isothermal condition. That is, the thermal boundary conditions are such that one of the channel walls is maintained at constant heat flux while the other is maintained at a constant temperature. Various closed-form solutions of the governing equations for different special cases are obtained. A parametric study of the physical parameters involved in the problem is done to illustrate the influence of these parameters on the velocity and temperature profiles of both phases.

Effects of radiation and high heat flux on the performance of first-wall components. Final report

International Nuclear Information System (INIS)

Wolfer, W.G.

1985-10-01

The performance of high-heat-flux components in present and future fusion devices is strongly affected by materials properties and their changes with radiation exposure and helium content. In addition, plasma disruptions and thermal fatigue are major life-limiting aspects. A multidisciplinary approach is therefore required in the performance analysis, and the following results have been accomplished. An equation of state for helium has been derived and applied to helium bubble formation by various growth processes. Models for various radiation effects have been developed and perfected to analyze radiation-induced swelling and embrittlement for high-heat flux materials. Computer codes have been developed to predict melting, evaporation, and melt-layer stability during plasma disruptions. A structural analysis code was perfected to evaluate the stress distribution and crack propagation in a high-heat-flux component or first wall. This code was applied to a duplex structure consisting of a beryllium coating on a copper substrate. It was also used to compare the lifetimes of a first wall in a tokamak reactor made of ferritic or austenitic steel

Molecular dynamics study on heat transport from single-walled carbon nanotubes to Si substrate

Energy Technology Data Exchange (ETDEWEB)

Feng, Ya; Zhu, Jie, E-mail: zhujie@iet.cn; Tang, Da-Wei

2015-02-06

In this paper, non-equilibrium molecular dynamics simulations were performed to investigate the heat transport between a vertically aligned single-walled carbon nanotube (SWNT) and Si substrate, to find out the influence of temperature and system sizes, including diameter and length of SWNT and measurements of substrate. Results revealed that high temperature hindered heat transport in SWNT itself but was a beneficial stimulus for heat transport at interface of SWNT and Si. Furthermore, the system sizes strongly affected the peaks in vibrational density of states of Si, which led to interfacial thermal conductance dependent on system sizes. - Highlights: • NEMD is performed to simulate the heat transport from SWNT to Si substrate. • We analyze both interfacial thermal conductance and thermal conductivity of SWNT. • High temperature is a beneficial stimulus for heat transport at the interface. • Interfacial thermal conductance strongly depends on the sizes of SWNT and substrate. • We calculate VDOS of C and Si atoms to analyze phonon couplings between them.

Annual investigation of vertical type ground source heat pump system performance on a wall heating and cooling system in Istanbul

Energy Technology Data Exchange (ETDEWEB)

Akbulut, U.; Yoru, Y.; Kincay, O. [Department of Mechanical Engineering, Yildiz Technical University (Turkey)], email: akbulutugur@yahoo.com, email: yilmazyoru@gmail.com, email: okincay@yildiz.edu.tr

2011-07-01

Wall heating and cooling systems (WHCS) are equipped with heating serpentines or panels for water circulation. These systems operate in a low temperature range so they are preferable to other, conventional systems. Furthermore, when these systems are connected to a ground source heat pump (GSHP) system, energy performance and thermal comfort are further enhanced. The purpose of this paper is to report the results of an annual inspection done on a vertical type ground-coupled heat pump systems (V-GSHP) WHCS in Istanbul and present the results. The performance data from the Yildiz Renewable Energy House at Davutpasa Campus of Yildiz Technical University, Istanbul, Turkey, during the year 2010 were collected and analyzed. The conclusions drawn from the inspection and analysis were listed in this paper. Using renewable energy sources effectively will bring both economic and environmental benefits and it is hoped that the use of these energy efficient WHCS systems will become widespread.

Entropy Generation Analysis of Natural Convection in Square Enclosures with Two Isoflux Heat Sources

Directory of Open Access Journals (Sweden)

S. Z. Nejad

2017-04-01

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

Inverse problem of estimating transient heat transfer rate on external wall of forced convection pipe

International Nuclear Information System (INIS)

Chen, W.-L.; Yang, Y.-C.; Chang, W.-J.; Lee, H.-L.

2008-01-01

In this study, a conjugate gradient method based inverse algorithm is applied to estimate the unknown space and time dependent heat transfer rate on the external wall of a pipe system using temperature measurements. It is assumed that no prior information is available on the functional form of the unknown heat transfer rate; hence, the procedure is classified as function estimation in the inverse calculation. The accuracy of the inverse analysis is examined by using simulated exact and inexact temperature measurements. Results show that an excellent estimation of the space and time dependent heat transfer rate can be obtained for the test case considered in this study

A Wind Tunnel Investigation of the Influence of Solar-Induced Wall-Heating on the Flow Regime within a Simulated Urban Street Canyon

International Nuclear Information System (INIS)

Kovar-Panskus, A.; Moulinneuf, L.; Savory, E.; Abdelqari, A.; Sini, J.-F.; Rosant, J.-M.; Robins, A.; Toy, N.

2002-01-01

A wind tunnel study has been undertaken to assess the influence of solar-induced wall heating on the airflow pattern within a street canyon under low-speed wind conditions. This flow is normally dominated by large-scale vortical motion, such that the wind moves downwards at the downstream wall. In the present work the aim has been to examine whether the buoyancy forces generated at this wall by solar-induced heating are of sufficient strength to oppose the downward inertial forces and, thereby, change the canyon flow pattern. Such changes will also influence the dispersion of pollutants within the street. In the experiments the windward-facing wall of a canyon has been uniformly heated to simulate the effect of solar radiation.Four different test cases, representing different degrees of buoyancy (defined by a test Froude number, Fr), have been examined using a simple, 2-D, square-section canyon model in a wind tunnel. For reference purposes, the neutral case (no wall heating), has also been studied. The approach flow boundary layer conditions have been well defined, with the wind normal to the main canyon axis, and measurements have been taken of canyon wall and air temperatures and profiles of mean velocities and turbulence intensities.Analysis of the results shows clear differences in the flow patterns. As Fr decreases from the neutral case there are reductions of up to 50% in the magnitudes of the reverseflow velocities near the ground and in the upward motion near the upstream wall. A marked transition occurs at Fr ∼ 1, where the single dominant vortex, existing at higher Fr values, weakens and moves upwards whilst a lower region of relatively stagnant flow appears. This transition had previously been observed in numerical model predictions but at a Fr at least an order of magnitude higher

Unsteady laminar flow with convective heat transfer through a rotating curved square duct with small curvature

Energy Technology Data Exchange (ETDEWEB)

Mondal, Rabindra Nath, E-mail: rnmondal71@yahoo.com; Shaha, Poly Rani [Department of Mathematics, Jagannath University, Dhaka-1100 (Bangladesh); Roy, Titob [Department of Mathematics, Vikarunnesa Nun School and College, Boshundhara, Dhaka (Bangladesh); Yanase, Shinichiro, E-mail: yanase@okayama-u.ac.jp [Department of Mechanical and Systems Engineering, Okayama University, Okayama 700-8530 (Japan)

2016-07-12

Unsteady laminar flow with convective heat transfer through a curved square duct rotating at a constant angular velocity about the center of curvature is investigated numerically by using a spectral method, and covering a wide range of the Taylor number −300≤Tr≤1000 for the Dean number Dn = 1000. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr = 100, where the outer wall is heated and the inner wall cooled, the top and bottom walls being adiabatic. Flow characteristics are investigated with the effects of rotational parameter, Tr, and the pressure-driven parameter, Dn, for the constant curvature 0.001. Time evolution calculations as well as their phase spaces show that the unsteady flow undergoes through various flow instabilities in the scenario ‘multi-periodic → chaotic → steady-state → periodic → multi-periodic → chaotic’, if Tr is increased in the positive direction. For negative rotation, however, time evolution calculations show that the flow undergoes in the scenario ‘multi-periodic → periodic → steady-state’, if Tr is increased in the negative direction. Typical contours of secondary flow patterns and temperature profiles are obtained at several values of Tr, and it is found that the unsteady flow consists of two- to six-vortex solutions if the duct rotation is involved. External heating is shown to generate a significant temperature gradient at the outer wall of the duct. This study also shows that there is a strong interaction between the heating-induced buoyancy force and the centrifugal-Coriolis instability in the curved channel that stimulates fluid mixing and consequently enhances heat transfer in the fluid.

An approximate analysis of the diffusing flow in a self-controlled heat pipe.

Science.gov (United States)

Somogyi, D.; Yen, H. H.

1973-01-01

Constant-density two-dimensional axisymmetric equations are presented for the diffusing flow of a class of self-controlled heat pipes. The analysis is restricted to the vapor space. Condensation of the vapor is related to its mass fraction at the wall by the gas kinetic formula. The Karman-Pohlhausen integral method is applied to obtain approximate solutions. Solutions are presented for a water heat pipe with neon control gas.

Flow and heat transfer in parallel channel attached with equally-spaced ribs, 2

International Nuclear Information System (INIS)

Kunugi, Tomoaki; Takizuka, Takakazu

1980-09-01

Using a computer code for the analysis of the flow and heat transfer in a parallel channel attached with equally-spaced ribs, calculations are performed when a pitch to rib-width ratio is 7 : 1, a rib-width to rib-height ratio is 2 : 1 and a channel-height to rib-height is 3 : 1. Assuming that the fluid properties and the heat-flux at the wall of this channel are constant, characteristics of the flow and heat transfer are analyzed in the range of Reynolds number from 10 to 250. The following results are obtained: (1) The separation region behind a rib grows downstream with the increase of Reynolds number. (2) The pressure drop of ribbed channel is greater than that of the smooth channel, and increases as Reynolds number increases. (3) The mean Nusselt number of ribbed channel is about 10 - 11 at the upper wall and about 7.5 at the lower wall in the range of Reynolds number from 10 to 250. (author)

OSCILLATING LIGHT WALL ABOVE A SUNSPOT LIGHT BRIDGE

Energy Technology Data Exchange (ETDEWEB)

Yang, Shuhong; Zhang, Jun; Jiang, Fayu [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Xiang, Yongyuan, E-mail: shuhongyang@nao.cas.cn [Fuxian Solar Observatory, Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China)

2015-05-10

With the high tempo-spatial Interface Region Imaging Spectrograph 1330 Å images, we find that many bright structures are rooted in the light bridge of NOAA 12192, forming a light wall. The light wall is brighter than the surrounding areas, and the wall top is much brighter than the wall body. The New Vacuum Solar Telescope Hα and the Solar Dynamics Observatory 171 and 131 Å images are also used to study the light-wall properties. In 1330, 171, and 131 Å, the top of the wall has a higher emission, while in the Hα line, the wall-top emission is very low. The wall body corresponds to bright areas in 1330 Å and dark areas in the other lines. The top of the light wall moves upward and downward successively, performing oscillations in height. The deprojected mean height, amplitude, oscillation velocity, and the dominant period are determined to be 3.6 Mm, 0.9 Mm, 15.4 km s{sup −1}, and 3.9 minutes, respectively. We interpret the oscillations of the light wall as the leakage of p-modes from below the photosphere. The constant brightness enhancement of the wall top implies the existence of some kind of atmospheric heating, e.g., via the persistent small-scale reconnection or the magneto-acoustic waves. In another series of 1330 Å images, we find that the wall top in the upward motion phase is significantly brighter than in the downward phase. This kind of oscillation may be powered by the energy released due to intermittent impulsive magnetic reconnection.

Analysis of heat transfer and frost layer formation on a cryogenic tank wall exposed to the humid atmospheric air

International Nuclear Information System (INIS)

Kim, Kyoung-Hoon; Ko, Hyung-Jong; Kim, Kyoungjin; Kim, Yong-Wook; Cho, Kie-Joo

2009-01-01

In this paper heat transfer characteristics and frost layer formation are investigated numerically on the surface of a cryogenic oxidizer tank for a liquid propulsion rocket, where a frost layer could be a significant factor in maintaining oxidizer temperature within a required range. Frost formation is modeled by considering mass diffusion of water vapor in the air into the frost layer and various heat transfer modes such as natural and forced convection, latent heat, solar radiation of short wavelength, and ambient radiation of long wavelength. Computational results are first compared with the available measurements and show favorable agreement on thickness and effective thermal conductivity of the frost layer. In the case of the cryogenic tank, a series of parametric studies is presented in order to examine the effects of important parameters such as temperature and wind speed of ambient air, air humidity, and tank wall temperature on the frost layer formation and the amount of heat transfer into the tank. It is found that the heat transfer by solar radiation is significant and also that heat transfer strongly depends on air humidity, ambient air temperature, and wind speed but not tank wall temperature.

Erosion simulation of first wall beryllium armour under ITER transient heat loads

Energy Technology Data Exchange (ETDEWEB)

Bazylev, B.; Janeschitz, G. [Forschungszentrum Karlsruhe GmbH, FZK, Karlsruhe (Germany); Landman, I.; Pestchanyi, S. [FZK-Forschungszentrum Karlsruhe, Association Euratom-FZK, Technik und Umwelt, Karlsruhe (Germany); Loarte, A. [EFDA Close Support Unit Garching, Garching bei Munchen(Germany)

2007-07-01

Full text of publication follows: Operation of ITER at high fusion gain is assumed to be the H-mode. A characteristic feature of this regime is the transient release of energy from the confined plasma onto divertor and the first wall by multiple ELMs (about 10{sup 4} ELMs per ITER discharge), which can play a determining role in the erosion rate and lifetime of these components. It is expected that about 50-70 % of the ELM energy releases onto divertor armour and the rest is dumped onto the First Wall (FW) armour. The expected energy heat loads on the ITER divertor and FW during Type I ELM are in range 0.5 - 4 MJ/m{sup 2} in timescales of 0.3-0.6 ms. In case of the ITER disruptions the material evaporated from the divertor expands into the SOL and generates significant radiation heating of the FW armour up to several GW/m2 during a few milliseconds that can also lead to the its melting and noticeable damage. Beryllium macro-brush armour (Be-brushes) is foreseen as plasma FW facing component (PFC) in ITER. During the intense transient events in ITER the surface melting, melt motion, melt splashing and evaporation are seen as the main mechanisms of Be-erosion. The expected erosion of the ITER plasma facing components under transient energy loads can be properly estimated by numerical simulations using the codes MEMOS and PHEMOBRID validated against experimental data obtained at the plasma gun facilities QSPA-T, MK-200UG and QSPA-Kh50 that provide a way to simulate the energy loads expected in ITER in laboratory experiments. The numerical simulations were carried out for the expected ITER ELMs for the heat loads in the range 0.5 - 3.0 MJ/m{sup 2} and the timescale up 0.6 ms and ITER disruptions for the heat loads in the range 2 - 13 MJ/m{sup 2} in timescales of 1-5 ms. Radiation heat loads at the FW armour from the vapour expanded into the SOL were calculated using the codes FOREV-2 and TOKES for both ITER ELM and ITER disruption scenarios. Melt layer damage of the Be

Erosion simulation of first wall beryllium armour under ITER transient heat loads

International Nuclear Information System (INIS)

Bazylev, B.; Janeschitz, G.; Landman, I.; Pestchanyi, S.; Loarte, A.

2007-01-01

Full text of publication follows: Operation of ITER at high fusion gain is assumed to be the H-mode. A characteristic feature of this regime is the transient release of energy from the confined plasma onto divertor and the first wall by multiple ELMs (about 10 4 ELMs per ITER discharge), which can play a determining role in the erosion rate and lifetime of these components. It is expected that about 50-70 % of the ELM energy releases onto divertor armour and the rest is dumped onto the First Wall (FW) armour. The expected energy heat loads on the ITER divertor and FW during Type I ELM are in range 0.5 - 4 MJ/m 2 in timescales of 0.3-0.6 ms. In case of the ITER disruptions the material evaporated from the divertor expands into the SOL and generates significant radiation heating of the FW armour up to several GW/m2 during a few milliseconds that can also lead to the its melting and noticeable damage. Beryllium macro-brush armour (Be-brushes) is foreseen as plasma FW facing component (PFC) in ITER. During the intense transient events in ITER the surface melting, melt motion, melt splashing and evaporation are seen as the main mechanisms of Be-erosion. The expected erosion of the ITER plasma facing components under transient energy loads can be properly estimated by numerical simulations using the codes MEMOS and PHEMOBRID validated against experimental data obtained at the plasma gun facilities QSPA-T, MK-200UG and QSPA-Kh50 that provide a way to simulate the energy loads expected in ITER in laboratory experiments. The numerical simulations were carried out for the expected ITER ELMs for the heat loads in the range 0.5 - 3.0 MJ/m 2 and the timescale up 0.6 ms and ITER disruptions for the heat loads in the range 2 - 13 MJ/m 2 in timescales of 1-5 ms. Radiation heat loads at the FW armour from the vapour expanded into the SOL were calculated using the codes FOREV-2 and TOKES for both ITER ELM and ITER disruption scenarios. Melt layer damage of the Be FW macro

A constant-density Gurney approach to the Cylinder test

Energy Technology Data Exchange (ETDEWEB)

Reaugh, John E.; Souers, P. Clark [Energetic Materials Center, Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States)

2004-04-01

The previous analysis of the Cylinder test required the treatment of different wall thicknesses and wall materials separately. To fix this, the Gurney analysis is used, but this results in low values for full-wall standard, ideal explosives relative to CHEETAH analyses. A new constant metal-density model is suggested, which takes account of the thinning metal wall as the cylinder expands. With this model, the inner radius of the metal cylinder moves faster than the measured outer radius. Additional small corrections occur in all cylinders because of energy trapped in the copper walls. Also, the half-wall cylinders have a small correction because the relative volumes of the gas products are smaller at a given outside wall displacement. The Fabry-Perot and streak camera measurements are compared. The Fabry method is shown to equate to the constant density model. (Abstract Copyright [2004], Wiley Periodicals, Inc.)

Conjugate heat transfer effects on wall bubble nucleation in subcooled flashing flows

International Nuclear Information System (INIS)

Peterson, P.F.; Hijikata, K.

1990-01-01

A variety of models have been proposed to explain observations that large liquid superheat is required to initiate nucleation in flashing flows of subcooled liquids in nozzles, cracks and pipes. In such flows an abrupt change in the fluid temperature occurs downstream of the nucleating cavities. This paper examines the subcooling of the nucleating cavities due to conjugate heat transfer to the cold downstream fluid. This examination suggests a mechanism limiting the maximum active cavity size. Simple analysis shows that, of the total superheat required to initiate flashing, a substantial portion results from conjugate wall subcooling, which decreases the cavity vapor pressure. The specific case of flashing critical nozzle flow is examined in detail. Here boundary-layer laminarization due to the strong favorable pressure gradient aids the analysis of conjugate heat transfer

HELCZA-High heat flux test facility for testing ITER EU first wall components.

Czech Academy of Sciences Publication Activity Database

Prokůpek, J.; Samec, K.; Jílek, R.; Gavila, P.; Neufuss, S.; Entler, Slavomír

2017-01-01

Roč. 124, November (2017), s. 187-190 ISSN 0920-3796. [SOFT 2016: Symposium on Fusion Technology /29./. Prague, 05.09.2016-09.09.2016] Institutional support: RVO:61389021 Keywords : HELCZA * High heat flux * Electron beam testing * Test facility * Plasma facing components * First wall * Divertora Subject RIV: JF - Nuclear Energetics OBOR OECD: Nuclear related engineering Impact factor: 1.319, year: 2016 www.sciencedirect.com/science/article/pii/S0920379617302818

Steady state ensembles of thermal radiation in a layered media with a constant heat flux

International Nuclear Information System (INIS)

Budaev, Bair V.; Bogy, David B.

2013-01-01

This paper describes steady-state ensembles of thermally excited electromagnetic radiation in nano-scale layered media with a constant non-vanishing heat flux across the layers. It is shown that Planck's law of thermal radiation, the principle of equivalence, and the laws of wave propagation in layered media, imply that in order for the ensemble of thermally excited electromagnetic fields to exist in a medium consisting of a stack of layers between two half-space, the net heat flux across the layers must exceed a certain threshold that is determined by the temperatures of the half spaces and by the reflective properties of the entire structure. The obtained results provide a way for estimating the radiative heat transfer coefficient of nano-scale layered structures. (copyright 2013 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Flow patterns and thermal comfort in a room with panel, floor and wall heating

Energy Technology Data Exchange (ETDEWEB)

Myhren, Jonn Are; Holmberg, Sture [Fluid and Climate Technology, Department of Constructional Engineering and Design, KTH, School of Technology and Health, Marinens vaeg 30, SE-13640 Haninge-Stockholm (Sweden)

2008-07-01

Thermal comfort aspects in a room vary with different space heating methods. The main focus in this study was how different heating systems and their position affect the indoor climate in an exhaust-ventilated office under Swedish winter conditions. The heat emitters used were a high and a medium-high temperature radiator, a floor heating system and large wall heating surfaces at low temperature. Computational fluid dynamics (CFD) simulations were used to investigate possible cold draught problems, differences in vertical temperature gradients, air speed levels and energy consumption. Two office rooms with different ventilation systems and heating needs were evaluated. Both systems had high air exchange rates and cold infiltration air. The general conclusions from this study were that low temperature heating systems may improve indoor climate, giving lower air speeds and lower temperature differences in the room than a conventional high temperature radiator system. The disadvantage with low temperature systems is a weakness in counteracting cold down-flow from ventilation supply units. For that reason the location of heat emitters and the design of ventilation systems proved to be of particular importance. Measurements performed in a test chamber were used to validate the results from the CFD simulations. (author)

Solar Energy Gain and Space-Heating Energy Supply Analyses for Solid-Wall Dwelling Retrofitted with the Experimentally Achievable U-value of Novel Triple Vacuum Glazing

Directory of Open Access Journals (Sweden)

Saim Memon

2017-06-01

Full Text Available A considerable effort is devoted to devising retrofit solutions for reducing space-heating energy in the domestic sector. Existing UK solid-wall dwellings, which have both heritage values and historic fabric, are being improved but they tend to have meagre thermal performance, partly, due to the heat-loss through glazings. This paper takes comparative analyses approach to envisage space-heating supply required in order to maintain thermal comfort temperatures and attainable solar energy gains to households with the retrofit of an experimentally achievable thermal performance of the fabricated sample of triple vacuum glazing to a UK solid-wall dwelling. 3D dynamic thermal models (timely regimes of heating, occupancy, ventilation and internal heat gains of an externally-insulated solid-wall detached dwelling with a range of existing glazing types along with triple vacuum glazings are modelled. A dramatic decrease of space-heating load and moderate increase of solar gains are resulted with the dwelling of newly achievable triple vacuum glazings (having centre-of-pane U-value of 0.33 Wm-2K-1 compared to conventional glazing types. The space-heating annual cost of single glazed dwellings was minimised to 15.31% (≈USD 90.7 with the retrofit of triple-vacuum glazings. An influence of total heat-loss through the fabric of solid-wall dwelling was analysed with steady-state calculations which indicates a fall of 10.23 % with triple vacuum glazings compared to single glazings.

Wall-to-bed heat transfer in gas-solid fluidized beds: a computational and experimental study

NARCIS (Netherlands)

Patil, D.J.; Smit, J.; van Sint Annaland, M.; Kuipers, J.A.M.

2006-01-01

The wall-to-bed heat transfer in gas-solid fluidized beds is mainly determined by phenomena prevailing in a thermal boundary layer with a thickness in the order of magnitude of the size of a single particle. In this thermal boundary layer the temperature gradients are very steep and the local

Sealing of transmitted-heat lines at wall piercings; Abdichtung von Fernwaermeleitungen in Mauerdurchfuehrungen

Energy Technology Data Exchange (ETDEWEB)

Werner, A.; Ney, K. [Doyma GmbH und Co., Oyten (Germany)

1998-04-01

Flexible sealing systems are necessary to provide permanent protection of transmitted-heat pipe wall penetrations against the ingress of water. Unlike the rigid sealing methods in widespread use, flexible sealing systems are capable of absorbing thermally induced pipe movements and thus of preventing leaks around such piercings. The following article provides an introduction to the subject and offers practical suggestions for the ideal design of transmitted-heat pipe wall penetrations. Sealing system variants with a range of degrees of flexibility are discussed, in addition to measures which need to be taken into account as early as the installation of the pipe itself. Prime attention is devoted not to methods already practised, but to recent, potentially marketable developments. (orig.) [Deutsch] Um Mauerdurchfuehrungen von Fernwaermeleitungen dauerhaft gegen das Eindringen von Wasser zu schuetzen, sind flexible Abdichtsysteme notwendig. Im Gegensatz zu den verbreiteten starren Abdichtungsmethoden koennen flexible Systeme die thermisch bedingten Rohrbewegungen aufnehmen und damit Undichtigkeiten im Bereich der Durchfuehrungen verhindern. Der folgende Beitrag fuehrt in die Thematik ein und gibt praktische Hinweise, wie eine Mauerdurchfuehrung von Fernwaermeleitungen idealerweise gestaltet werden sollte. Neben Massnahmen, die bereits bei der Rohrverlegung zu beachten sind, werden Abdichtvarianten mit unterschiedlichem Flexibilitaetsgrad skizziert. Schwerpunkt der Untersuchung liegt hier nicht nur auf bereits bekannten Verfahren sondern auch auf marktfaehigen Neuentwicklungen. (orig.)

A thin-walled pressurized sphere exposed to external general corrosion and nonuniform heating

Science.gov (United States)

Sedova, Olga S.; Pronina, Yulia G.; Kuchin, Nikolai L.

2018-05-01

A thin-walled spherical shell subjected to simultaneous action of internal and external pressure, nonuniform heating and outside mechanochemical corrosion is considered. It is assumed that the shell is homogeneous, isotropic and linearly elastic. The rate of corrosion is linearly dependent on the equivalent stress, which is the sum of mechanical and temperature stress components. Paper presents a new analytical solution, which takes into account the effect of the internal and external pressure values themselves, not only their difference. At the same time, the new solution has a rather simple form as compared to the results based on the solution to the Lame problem for a thick-walled sphere under pressure. The solution obtained can serve as a benchmark for numerical analysis and for a qualitative forecast of durability of the vessel.

Evaluation on double-wall-tube residual stress distribution of sodium-heated steam generator by neutron diffraction and numerical analysis

International Nuclear Information System (INIS)

Kisohara, N.; Suzuki, H.; Akita, K.; Kasahara, N.

2012-01-01

A double-wall-tube is nominated for the steam generator heat transfer tube of future sodium fast reactors (SFRs) in Japan, to decrease the possibility of sodium/water reaction. The double-wall-tube consists of an inner tube and an outer tube, and they are mechanically contacted to keep the heat transfer of the interface between the inner and outer tubes by their residual stress. During long term SG operation, the contact stress at the interface gradually falls down due to stress relaxation. This phenomenon might increase the thermal resistance of the interface and degrade the tube heat transfer performance. The contact stress relaxation can be predicted by numerical analysis, and the analysis requires the data of the initial residual stress distributions in the tubes. However, unclear initial residual stress distributions prevent precious relaxation evaluation. In order to resolve this issue, a neutron diffraction method was employed to reveal the tri-axial (radius, hoop and longitudinal) initial residual stress distributions in the double-wall-tube. Strain gauges also were used to evaluate the contact stress. The measurement results were analyzed using a JAEA's structural computer code to determine the initial residual stress distributions. Based on the stress distributions, the structural computer code has predicted the transition of the relaxation and the decrease of the contact stress. The radial and longitudinal temperature distributions in the tubes were input to the structural analysis model. Since the radial thermal expansion difference between the inner (colder) and outer (hotter) tube reduces the contact stress and the tube inside steam pressure contributes to increasing it, the analytical model also took these effects into consideration. It has been conduced that the inner and outer tubes are contacted with sufficient stresses during the plant life time, and that effective heat transfer degradation dose not occur in the double-wall-tube SG. (authors)

The influence of insulation of walls of industrial objects on thermal regime at the heating system of gas infrared radiators

Directory of Open Access Journals (Sweden)

Nagornova Tatiana

2017-01-01

Full Text Available The results of a numerical study of the process of heat transfer from the gas infrared emitters in the heated accommodation are represented. Simulation was conducted taking into account the heat withdrawal in the enclosing constructions and of heat exchange with the environment. The estimation of the average values of temperatures of air indoors in the dependence on the different intensity of heat withdrawal into the vertical walls is carried out (when the layer of insulation is present, and without it.

Erosion simulation of first wall beryllium armour under ITER transient heat loads

Science.gov (United States)

Bazylev, B.; Janeschitz, G.; Landman, I.; Pestchanyi, S.; Loarte, A.

2009-04-01

The beryllium is foreseen as plasma facing armour for the first wall in the ITER in form of Be-clad blanket modules in macrobrush design with brush size about 8-10 cm. In ITER significant heat loads during transient events (TE) are expected at the main chamber wall that may leads to the essential damage of the Be armour. The main mechanisms of metallic target damage remain surface melting and melt motion erosion, which determines the lifetime of the plasma facing components. Melting thresholds and melt layer depth of the Be armour under transient loads are estimated for different temperatures of the bulk Be and different shapes of transient loads. The melt motion damages of Be macrobrush armour caused by the tangential friction force and the Lorentz force are analyzed for bulk Be and different sizes of Be-brushes. The damage of FW under radiative loads arising during mitigated disruptions is numerically simulated.

Erosion simulation of first wall beryllium armour under ITER transient heat loads

Energy Technology Data Exchange (ETDEWEB)

Bazylev, B. [Forschungszentrum Karlsruhe, IHM, P.O. Box 3640, 76021 Karlsruhe (Germany)], E-mail: bazylev@ihm.fzk.de; Janeschitz, G. [Forschungszentrum Karlsruhe, Fusion, P.O. Box 3640, 76021 Karlsruhe (Germany); Landman, I.; Pestchanyi, S. [Forschungszentrum Karlsruhe, IHM, P.O. Box 3640, 76021 Karlsruhe (Germany); Loarte, A. [ITER Organisation, Cadarache, 13108 Saint Paul Lez Durance Cedex (France)

2009-04-30

The beryllium is foreseen as plasma facing armour for the first wall in the ITER in form of Be-clad blanket modules in macrobrush design with brush size about 8-10 cm. In ITER significant heat loads during transient events (TE) are expected at the main chamber wall that may leads to the essential damage of the Be armour. The main mechanisms of metallic target damage remain surface melting and melt motion erosion, which determines the lifetime of the plasma facing components. Melting thresholds and melt layer depth of the Be armour under transient loads are estimated for different temperatures of the bulk Be and different shapes of transient loads. The melt motion damages of Be macrobrush armour caused by the tangential friction force and the Lorentz force are analyzed for bulk Be and different sizes of Be-brushes. The damage of FW under radiative loads arising during mitigated disruptions is numerically simulated.

Erosion simulation of first wall beryllium armour under ITER transient heat loads

International Nuclear Information System (INIS)

Bazylev, B.; Janeschitz, G.; Landman, I.; Pestchanyi, S.; Loarte, A.

2009-01-01

The beryllium is foreseen as plasma facing armour for the first wall in the ITER in form of Be-clad blanket modules in macrobrush design with brush size about 8-10 cm. In ITER significant heat loads during transient events (TE) are expected at the main chamber wall that may leads to the essential damage of the Be armour. The main mechanisms of metallic target damage remain surface melting and melt motion erosion, which determines the lifetime of the plasma facing components. Melting thresholds and melt layer depth of the Be armour under transient loads are estimated for different temperatures of the bulk Be and different shapes of transient loads. The melt motion damages of Be macrobrush armour caused by the tangential friction force and the Lorentz force are analyzed for bulk Be and different sizes of Be-brushes. The damage of FW under radiative loads arising during mitigated disruptions is numerically simulated.

Multiphysics Numerical Modeling of a Fin and Tube Heat Exchanger

DEFF Research Database (Denmark)

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

2015-01-01

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

Asymptotic analysis, direct numerical simulation and modeling of premixed turbulent flame-wall interaction; Etude asymptotique, simulation numerique directe et modelisation de l`interaction flamme turbulente premelangee-paroi

Energy Technology Data Exchange (ETDEWEB)

Bruneaux, G.

1996-05-20

Premixed turbulent flame-wall interaction is studied using theoretical and numerical analysis. Laminar interactions are first investigated through a literature review. This gives a characterization of the different configurations of interaction and justifies the use of simplified kinetic schemes to study the interaction. Calculations are then performed using Direct Numerical Simulation with a one-step chemistry model, and are compared with good agreements to asymptotic analysis. Flame-wall distances and wall heat fluxes obtained are compared successfully with those of the literature. Heat losses decrease the consumption rate, leading to extinction at the maximum of wall heat flux. It is followed by a flame retreat, when the fuel diffuses into the reaction zone, resulting in low unburnt hydrocarbon levels. Then, turbulent regime is investigated, using two types of Direct Numerical Simulations: 2D variable density and 3D constant density. Similar results are obtained: the local turbulent flame behavior is identical to a laminar interaction, and tongues of fresh gases are expelled from the wall region, near zones of quenching. In the 2D simulations, minimal flame-wall distances and maximum wall heat fluxes are similar to laminar values. However, the structure of the turbulence in the 3D calculations induces smaller flame-wall distances and higher wall heat fluxes. Finally, a flame-wall interaction model is built and validated. It uses the flamelet approach, where the flame is described in terms of consumption speed and flame surface density. This model is simplified to produce a law of the wall, which is then included in a averaged CFD code (Kiva2-MB). It is validated in an engine calculation. (author) 36 refs.

A heat transfer analysis of laminar flow over a flat plate with unheated starting region for low Prandtl number fluids

International Nuclear Information System (INIS)

Ahola, M.P.; Karimi, A.

1996-01-01

In boundary layer analyses involving heat transfer, the Prandtl number (Pr) relates the diffusion of momentum to the diffusion of heat, and can be shown to directly correlate to the ratio of the thermal boundary layer thickness to the velocity boundary layer thickness. For large Prandtl number fluids (i.e., Pr > 1) the velocity boundary layer thickness is larger than the thermal boundary layer thickness, and vice versa. In some applications in the industry heating does not occur over the entire plate, such as in the case of an unheated starting region or spot heating along a finite segment of the plate. For such applications solutions only exist for the simpler case of large Prandtl number fluids where the thermal boundary layer is assumed to be smaller than the velocity boundary layer. The analyses presented in this paper extends the solution to the unheated starting region problem for small Prandtl number fluids, where the thermal boundary layer grows larger and crosses the velocity boundary layer. The solution is based on the integral method approach assuming laminar flow, and both cases of constant wall temperature as well as constant wall heat flux are analyzed

Tuberlent heat transfer and friction in four-wall convergent/divergent square channels with one ribbed wall

Energy Technology Data Exchange (ETDEWEB)

Ahn, Soo Whan; Lee, Myung Sung [Dept. of Mechanical System Engineering, Institute of Marine Industry, Gyeongsang National University, Jinju (Korea, Republic of)

2015-10-15

The local heat transfer and pressure drop of developed turbulent flows in convergent/divergent channels with square axial cross-sectional areas were experimentally investigated to improve the channel design, such as a gas turbine cooling system. Square convergent/divergent channels with one ribbed wall were manufactured with a fixed rib height e of 10 mm and a ratio of rib spacing p to height e of 10. The measurement was conducted for Reynolds numbers from 15,000 to 89,000. Convergent, divergent, and straight channels with ratios D{sub ho}/D{sub hi} of 0.75, 1.33, and 1.0, respectively, are considered. Of the three channel types, the ribbed divergent channel was found to produce the best thermal performance under identical flow rate, pumping power, and pressure loss conditions.

Thermal performance evaluation of a massive brick wall under real weather conditions via the Conduction Transfer function method

Directory of Open Access Journals (Sweden)

Emilio Sassine

2017-12-01

Full Text Available The reliable estimation of buildings energy needs for cooling and heating is essential for any eventual thermal improvement of the envelope or the HVAC equipment. This paper presents an interesting method to evaluate the thermal performance of a massive wall by using the frequency-domain regression (FDR method to calculate CTF coefficients by means of the Fourier transform. The method is based on the EN ISO 13786 (2007 procedure by using the Taylor expansion for the elements of the heat matrix. Numerical results were validated through an experimental heating box with stochastic boundary conditions on one side of the wall representing real weather conditions and constant temperature profile on the other side representing the inside ambiance in real cases. Finally, a frequency analysis was performed in order to assess the validity and accuracy of the method used. The results show that development to the second order is sufficient to predict the thermal behavior of the studied massive wall in the range of frequencies encountered in the building applications (one hour time step. This method is useful for thermal transfer analysis in real weather conditions where the outside temperature is stochastic; it also allows the evaluation of the thermal performance of a wall through a frequency analysis.

Near wall combustion modeling in spark ignition engines. Part A: Flame–wall interaction

International Nuclear Information System (INIS)

Demesoukas, Sokratis; Caillol, Christian; Higelin, Pascal; Boiarciuc, Andrei; Floch, Alain

2015-01-01

Highlights: • A model for flame–wall interaction in addition to flame wrinkling by turbulence is proposed. • Two sparkplug positions and two lengths are used in a test engine for model validation. • Flame–wall interaction decreases the maximum values of cylinder pressure and heat release rates. • The impact of combustion chamber geometry is taken into account by the flame–wall interaction model. - Abstract: Research and design in the field of spark ignition engines seek to achieve high performance while conserving fuel economy and low pollutant emissions. For the evaluation of various engine configurations, numerical simulations are favored, since they are quick and less expensive than experiments. Various zero-dimensional combustion models are currently used. Both flame front reactions and post-flame processes contribute to the heat release rate. The first part of this study focuses on the role of the flame front on the heat release rate, by modeling the interaction of the flame front with the chamber wall. Post-flame reactions are dealt with in Part B of the study. The basic configurations of flame quenching in laminar flames are also applicable in turbulent flames, which is the case in spark ignition engines. A simplified geometric model of the combustion chamber was used to calculate the mean flame surface, the flame volume and the distribution of flame surface as a function of the distance from the wall. The flame–wall interaction took into account the geometry of the combustion chamber and of the flame, aerodynamic turbulence and the in-cylinder pressure and temperature conditions, through a phenomenological attenuation function of the wrinkling factor. A modified global wrinkling factor as a function of the mean surface distance distribution from the wall was calculated. The impact of flame–wall interaction was simulated for four configurations of the sparkplug position and length: centered and lateral position, and standard and projected

Flow Boiling on a Downward-Facing Inclined Plane Wall of Core Catcher

International Nuclear Information System (INIS)

Kim, Hyoung Tak; Bang, Kwang Hyun; Suh, Jung Soo

2013-01-01

In order to investigate boiling behavior on downward-facing inclined heated wall prior to the CHF condition, an experiment was carried out with 1.2 m long rectangular channel, inclined by 10 .deg. from the horizontal plane. High speed video images showed that the bubbles were sliding along the heated wall, continuing to grow and combining with the bubbles growing at their nucleation sites in the downstream. These large bubbles continued to slide along the heated wall and formed elongated slug bubbles. Under this slug bubble thin liquid film layer on the heated wall was observed and this liquid film prevents the wall from dryout. The length, velocity and frequency of slug bubbles sliding on the heated wall were measured as a function of wall heat flux and these parameters were used to develop wall boiling model for inclined, downward-facing heated wall. One approach to achieve coolable state of molten core in a PWR-like reactor cavity during a severe accident is to retain the core melt on a so-called core catcher residing on the reactor cavity floor after its relocation from the reactor pressure vessel. The core melt retained in the core catcher is cooled by water coolant flowing in an inclined cooling channel underneath as well as the water pool overlaid on the melt layer. Two-phase flow boiling with downward-facing heated wall such as this core catcher cooling channel has drawn a special attention because this orientation of heated wall may reach boiling crisis at lower heat flux than that of a vertical or upward-facing heated wall. Nishikawa and Fujita, Howard and Mudawar, Qiu and Dhir have conducted experiments to study the effect of heater orientation on boiling heat transfer and CHF. SULTAN experiment was conducted to study inclined large-scale structure coolability by water in boiling natural convection. In this paper, high-speed visualization of boiling behavior on downward-facing heated wall inclined by 10 .deg. is presented and wall boiling model for the

Kinetic wall from Israel

Energy Technology Data Exchange (ETDEWEB)

Godolphin, D.

1985-05-01

An unusual solar mass wall is described. At the turn of a handle it can change from a solar energy collector to a heat-blocker. An appropriate name for it might be the rotating prism wall. An example of the moving wall is at work in an adobe test home in Sede Boqer. Behind a large south-facing window stand four large adobe columns that are triangular in plan. One face of each of them is painted black to absorb sunlight, a second is covered with panels of polystyrene insulation, and a third is painted to match the room decor. These columns can rotate. On winter nights, the insulated side faces the glass, keeping heat losses down. The same scheme works in summer to keep heat out of the house. Small windows provide ventilation.

Heat and mass transfer in porous cavity: Assisting flow

Energy Technology Data Exchange (ETDEWEB)

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

2016-06-08

In this paper, investigation of heat and mass transfer in a porous cavity is carried out. The governing partial differential equations are non-dimensionalised and solved using finite element method. The left vertical surface of the cavity is maintained at constant temperature and concentration which are higher than the ambient temperature and concentration applied at right vertical surface. The top and bottom walls of the cavity are adiabatic. Heat transfer is assumed to take place by natural convection and radiation. The investigation is carried out for assisting flow when buoyancy and gravity force act in same direction.

Magnon specific heat and free energy of Heisenberg ferromagnetic single-walled nanotubes: Green's function approach

Energy Technology Data Exchange (ETDEWEB)

Mi, Bin-Zhou, E-mail: mbzfjerry2008@126.com [Department of Basic Curriculum, North China Institute of Science and Technology, Beijing 101601 (China); Department of Physics, School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083 (China); Zhai, Liang-Jun [The School of Mathematics and Physics, Jiangsu University of Technology, Changzhou 213001 (China); Hua, Ling-Ling [Department of Basic Curriculum, North China Institute of Science and Technology, Beijing 101601 (China)

2016-01-15

The effect of magnetic spin correlation on the thermodynamic properties of Heisenberg ferromagnetic single-walled nanotubes are comprehensively investigated by use of the double-time Green's function method. The influence of temperature, spin quantum number, diameter of the tube, anisotropy strength and external magnetic field to internal energy, free energy, and magnon specific heat are carefully calculated. Compared to the mean field approximation, the consideration of the magnetic correlation effect significantly improves the internal energy values at finite temperature, while it does not so near zero temperature, and this effect is related to the diameter of the tube, anisotropy strength, and spin quantum number. The magnetic correlation effect lowers the internal energy at finite temperature. As a natural consequence of the reduction of the internal energy, the specific heat is reduced, and the free energy is elevated. - Highlights: • Magnon specific heat and free energy of Heisenberg ferromagnetic single-walled nanotubes (HFM-SWNTs) are investigated. • The magnetic correlations effect has a considerable contribution to the thermodynamics properties of HFM-SWNTs. • Magnetic correlation effects are always to lower the internal energy at finite temperature. • At Curie point, magnetic correlation energy is much less than zero. • The peak values of magnon specific heat curves rise and shift right towards higher temperatures with the diameter of tubes, the anisotropy strength, and the spin quantum number rising.

Heat release effects on mixing scales of non-premixed turbulent wall-jets: A direct numerical simulation study

International Nuclear Information System (INIS)

Pouransari, Zeinab; Vervisch, Luc; Johansson, Arne V.

2013-01-01

Highlights: ► A non-premixed turbulent flame close to a solid surface is studied using DNS. ► Heat release effects delay transition and enlarge fluctuation of density and pressure. ► The fine-scale structures damped and surface wrinkling diminished due to heat-release. ► Using semilocal scaling improves the collapse of turbulence statistic in inner region. ► There are regions of the flame where considerable (up to 10%) premixed burning occurs. -- Abstract: The present study concerns the role of heat release effects on characteristics mixing scales of turbulence in reacting wall-jet flows. Direct numerical simulations of exothermic reacting turbulent wall-jets are performed and compared to the isothermal reacting case. An evaluation of the heat-release effects on the structure of turbulence is given by examining the mixture fraction surface characteristics, diagnosing vortices and exploring the dissipation rate of the fuel and passive scalar concentrations, and moreover by illustration of probability density functions of reacting species and scatter plots of the local temperature against the mixture fraction. Primarily, heat release effects delay the transition, enlarge the fluctuation intensities of density and pressure and also enhance the fluctuation level of the species concentrations. However, it has a damping effect on all velocity fluctuation intensities and the Reynolds shear stress. A key result is that the fine-scale structures of turbulence are damped, the surface wrinkling is diminished and the vortices become larger due to heat-release effects. Taking into account the varying density by using semi-local scaling improves the collapse of the turbulence statistics in the inner region, but does not eliminate heat release induced differences in the outer region. Examining the two-dimensional premultiplied spanwise spectra of the streamwise velocity fluctuations indicates a shifting in the positions of the outer peaks, associated with large

Report on the joint meeting of the Division of Development and Technology Plasma/Wall Interaction and High Heat Flux Materials and Components Task Groups

International Nuclear Information System (INIS)

Wilson, K.L.

1985-10-01

This report of the Joint Meeting of the Division of Development and Technology Plasma/Wall Interaction and High Heat Flux Materials and Components Task Groups contains contributing papers in the following areas: Plasma/Materials Interaction Program and Technical Assessment, High Heat Flux Materials and Components Program and Technical Assessment, Pumped Limiters, Ignition Devices, Program Planning Activities, Compact High Power Density Reactor Requirements, Steady State Tokamaks, and Tritium Plasma Experiments. All these areas involve the consideration of High Heat Flux on Materials and the Interaction of the Plasma with the First Wall. Many of the Test Facilities are described as well

Analytical method for steady state heat transfer in two-dimensional porous media

Energy Technology Data Exchange (ETDEWEB)

Siegal, R.; Goldstein, M.E.

1970-07-01

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

Simple method for calculation of heat loss through floor/beam-wall intersections according to ISO 9164

International Nuclear Information System (INIS)

Dilmac, Sukran; Guner, Abdurrahman; Senkal, Filiz; Kartal, Semiha

2007-01-01

The international standards for calculation of energy consumption for heating are ISO 9164 and EN 832. Although they are based on similar principles, there are significant differences in the calculation procedure of transmission heat loss coefficient, H T , especially in the evaluation of thermal bridges. The calculation of H T and the way thermal bridges are to be taken into consideration are explained in detail in EN 832 and in a series of other linked standards. In ISO 9164, the parameters used in the relevant equations are cited, but there is a lack of explanation about how they will be determined or calculated. Although in ISO 6946-2, the earlier version of the same standard, the calculation methods of these quantities were explained for column-wall intersections; in the revised ISO 6946, these explanations have been removed. On the other hand, these parameters had never been defined for floor/beam-wall intersections. In this paper, a new method is proposed for calculation of the parameters cited in ISO 9164 for floor/beam-wall intersections. The results obtained by the proposed method for typical floor with beam sections are compared with the results obtained by the methods stated in EN 832/EN 13789/EN ISO 14683 and the results obtained from 2D analysis. Different methods are evaluated as to their simplicity and agreement

Wall temperature control of low-speed body drag

Science.gov (United States)

Lin, J. C.; Ash, R. L.

1986-01-01

The use of thermal means to control drag under turbulent boundary layer conditions is examined. Numerical calculations are presented for both skin friction and (unseparated) pressure drag for turbulent boundary-layer flows over a fuselage-like body with wall heat transfer. In addition, thermal control of separation on a bluff body is investigated. It is shown that a total drag reduction of up to 20 percent can be achieved for wall heating with a wall-to-total-freestream temperature ratio of 2. For streamlined slender bodies, partial wall heating of the forebody can produce almost the same order of total drag reduction as the full body heating case. For bluff bodies, the separation delay from partial wall cooling of the afterbody is approximately the same as for the fully cooled body.

Heat and mass transfer in turbulent chemically nonequilibrium flow in the tube with boundary second kind conditions. The section with the stabilized heat and mass transfer

International Nuclear Information System (INIS)

Kritsuk, E.L.; Mishina, L.V.; Shegidevich, L.N.

1986-01-01

The hydrodynamically stabilized chemically nonequilibrium turbulent flow in a tube with the inert impermeable surface and constant specific heat flow on the wall is considered. The reversible homogeneous reaction of nitrogen dioxide dissociation 2NO 2 ↔ 2NO+O 2 takes place in the flow. Chemically equilibrium flow with homogeneous profile of temperature and concentration arrives into the channel inlet. After application of simplifying assumptions, the expressions for characteristics of heat and mass transfer have been written down, which are valid in the whole range of the flow parameter variation from frozen up to chemically equilibrium flow. An integral transformation method is suggested for a radial coordinate which allows a wall region to be extended, thereby essentially extending the step of integration. A solution in quadratures has been obtained for the heat and mass transfer problem in an inert fluid flow for the developed process section. The elimination method has been employed to solve the boundary-value second-kind problem for the function governing heat and mass transfer in a chemically nonequilibrium turbulent flow over the developed heat and mass transfer section. The results of calculations are presented

Group solution for unsteady free-convection flow from a vertical moving plate subjected to constant heat flux

Science.gov (United States)

Kassem, M.

2006-03-01

The problem of heat and mass transfer in an unsteady free-convection flow over a continuous moving vertical sheet in an ambient fluid is investigated for constant heat flux using the group theoretical method. The nonlinear coupled partial differential equation governing the flow and the boundary conditions are transformed to a system of ordinary differential equations with appropriate boundary conditions. The obtained ordinary differential equations are solved numerically using the shooting method. The effect of Prandlt number on the velocity and temperature of the boundary-layer is plotted in curves. A comparison with previous work is presented.

Numerical study of evaporation in a vertical annulus heated at the inner wall

International Nuclear Information System (INIS)

Ben Radhia, R.; Ben Jabrallah, S.; Ben Jabrallah, S.; Corriou, J.P.; Harmand, S.

2011-01-01

Mixed convection during evaporation of a water falling film in a vertical concentric annulus was studied numerically. The water thin film falls on the inner tube and is subjected to a constant heat flux density, whereas the outer cylinder is assumed to be insulated and dry. An imposed air flow circulates within the gap between the two concentric tubes. The objective of this work is to understand the evaporation phenomenon in order to improve the average evaporated mass flux density and heat and mass transfer. Conservative equations governing the gas phase are solved numerically using the finite volume method. In the liquid phase, a method based on local heat and mass balances on each level is used. Thus, the following liquid film parameters, feed water mass flow, feed temperature and heat flux density, are taken into account. The obtained results are analyzed to emphasize and evaluate the influence of the previous operating parameters and the annulus curvature on the effective evaporation surface and on the mass flux density of evaporated water. (authors)

A theory for natural convection turbulent boundary layers next to heated vertical surfaces

International Nuclear Information System (INIS)

George, W.K. Jr.; Capp, S.P.

1979-01-01

The turbulent natural convection boundary layer next to a heated vertical surface is analyzed by classical scaling arguments. It is shown that the fully developed turbulent boundary layer must be treated in two parts: and outer region consisting of most of the boundary layer in which viscous and conduction terms are negligible and an inner region in which the mean convection terms are negligible. The inner layer is identified as a constant heat flux layer. A similarity analysis yields universal profiles for velocity and temperature in the outer and constant heat flux layers. An asymptotic matching of these profiles in an intermediate layer (the buoyant sublayer) yields analytical expressions for the buoyant sublayer profiles. Asymptotic heat transfer and friction laws are obtained for the fully developed boundary layers. Finally, conductive and thermo-viscous sublayers characterized by a linear variation of velocity and temperature are shown to exist at the wall. All predictions are seen to be in excellent agreement with the abundant experimental data. (author)

Electronic setup for fluorescence emission measurements and long-time constant-temperature maintenance of Single-Walled Carbon Nano-Tubes in water solutions

Directory of Open Access Journals (Sweden)

De Rosa Matteo

2017-03-01

Full Text Available In our previous research we have observed that the fluorescence emission from water solutions of Single-Walled Carbon Nano-Tubes (SWCNT, excited by a laser with a wavelength of 830nm, diminishes with the time. We have already proved that such a fading is a function of the storage time and the storage temperature. In order to study the emission of the SWCNT as a function of these two parameters we have designed and realized a special measurement compartment with a cuvette holder where the SWCNT solutions can be measured and stored at a fixed constant temperature for periods of time as long as several weeks. To maintain the measurement setup under a constant temperature we have designed special experimental setup based on two Peltier cells with electronic temperature control.

Mixed convection boundary-layer flow from a horizontal circular cylinder with a constant surface heat flux

Energy Technology Data Exchange (ETDEWEB)

Nazar, R.; Amin, N. [Department of Mathematics, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor (Malaysia); Pop, I. [Faculty of Mathematics, University of Cluj, R-3400 Cluj, CP 253 (Romania)

2004-02-01

The laminar mixed convection boundary-layer flow of a viscous and incompressible fluid past a horizontal circular cylinder, which is maintained at a constant heat flux and is placed in a stream flowing vertically upward has been theoretically studied in this paper. The solutions for the flow and heat transfer characteristics are evaluated numerically for different values of the mixed convection parameter {lambda} with the Prandtl number Pr = 1 and 7, respectively. It is found, as for the case of a heated or cooled cylinder, considered by Merkin [5], that assisting flow delays separation of the boundary-layer and can, if the assisting flow is strong enough, suppress it completely. The opposing flow, on the other side, brings the separation point nearer to the lower stagnation point and for sufficiently strong opposing flows there will not be a boundary-layer on the cylinder. (orig.)

Local wall power loading variations in thermonuclear fusion devices

International Nuclear Information System (INIS)

Carroll, M.C.; Miley, G.H.

1989-01-01

A 2 1/2-dimensional geometric model is presented that allows calculation of power loadings at various points on the first wall of a thermonuclear fusion device. Given average wall power loadings for brems-strahlung, cyclotron radiation charged particles, and neutrons, which are determined from various plasma-physics computation models, local wall heat loads are calculated by partitioning the plasma volume and surface into cells and superimposing the heating effects of the individual cells on selected first-wall differential areas. Heat loads from the entire plasma are thus determined as a function of position on the first-wall surface. Significant differences in local power loadings were found for most fusion designs, and it was therefore concluded that the effect of local power loading variations must be taken into account when calculating temperatures and heat transfer rates in fusion device first walls

Lean premixed reacting flows with swirl and wall-separation zones in a contracting chamber

Science.gov (United States)

Zhang, Yuxin; Rusak, Zvi; Wang, Shixiao

2017-11-01

Low Mach number lean premixed reacting swirling flows with wall-separation zones in a contracting circular finite-length open chamber are studied. Assuming a complete reaction with high activation energy and chemical equilibrium behind the reaction zone, a nonlinear partial differential equation is derived for the solution of the flow stream function behind the reaction zone in terms of the inlet total enthalpy for a reacting flow, specific entropy and the circulation functions. Bifurcation diagrams of steady flows are described as the inlet swirl level is increased at fixed chamber contraction and reaction heat release. The approach is applied to an inlet solid-body rotation flow with constant profiles of the axial velocity, temperature and mixture reactant mass fraction. The computed results provide predictions of the critical inlet swirl levels for the first appearance of wall-separation states and for the size of the separation zone as a function of the inlet swirl ratio, Mach number, chamber contraction and heat release of the reaction. The methodology developed in this paper provides a theoretical feasibility for the development of the technology of swirl-assisted combustion where the reaction zone is supported and stabilized by a wall-separation zone.

Study of plasma wall interactions in the long-pulse NB-heated discharges of JT-60U towards steady-state operation

International Nuclear Information System (INIS)

Takenaga, H.; Asakura, N.; Higashijima, S.; Nakano, T.; Kubo, H.; Konoshima, S.; Oyama, N.; Isayama, A.; Ide, S.; Fujita, T.; Miura, Y.

2005-01-01

Long time scale variation of plasma-wall interactions and its impact on particle balance, main plasma performance and particle behavior have been investigated in ELMy H-mode plasmas by extending the discharge pulse and the neutral beam heating pulse to 65 s and 30 s, respectively. The wall pumping rate starts to decrease in the latter phase by repeating the long-pulse discharges with 60% of Greenwald density sustained by gas-puffing. After several discharges, the wall inventory is saturated in the latter phase and, consequently, the density increases with neutral beam fuelling only. The edge pressure in the main plasma is reduced and ELMs are close to the type III regime under conditions of wall saturation. The intensities of C II emission near the X-point and CD band emission in the inner divertor start to increase before the wall saturates and continue to increase after the wall is saturated

Analytical solutions of heat transfer for laminar flow in rectangular channels

Directory of Open Access Journals (Sweden)

Rybiński Witold

2014-12-01

Full Text Available The paper presents two analytical solutions namely for Fanning friction factor and for Nusselt number of fully developed laminar fluid flow in straight mini channels with rectangular cross-section. This type of channels is common in mini- and microchannel heat exchangers. Analytical formulae, both for velocity and temperature profiles, were obtained in the explicit form of two terms. The first term is an asymptotic solution of laminar flow between parallel plates. The second one is a rapidly convergent series. This series becomes zero as the cross-section aspect ratio goes to infinity. This clear mathematical form is also inherited by the formulae for friction factor and Nusselt number. As the boundary conditions for velocity and temperature profiles no-slip and peripherally constant temperature with axially constant heat flux were assumed (H1 type. The velocity profile is assumed to be independent of the temperature profile. The assumption of constant temperature at the channel’s perimeter is related to the asymptotic case of channel’s wall thermal resistance: infinite in the axial direction and zero in the peripheral one. It represents typical conditions in a minichannel heat exchanger made of metal.

Computation of wall bounded flows with heat transfer in the framework of SRS approaches

Science.gov (United States)

Gritskevich, M. S.; Garbaruk, A. V.; Menter, F. R.

2014-12-01

A detailed assessment of Scale Adaptive Simulation (SAS) and Improved Delayed Detached Eddy Simulation (IDDES) is performed for prediction of heat transfer for several wall bounded flow. For that purpose a zero pressure gradient boundary layer, a backward facing step, and a thermal mixing in a T-Junction test cases are considered. The results, obtained with the use of ANSYS-FLUENT, show that both approaches are capable to predict both mean and RMS velocity and temperature with sufficient accuracy.

Liquid metal heat exchanger for efficient heating of soils and geologic formations

Science.gov (United States)

DeVault, Robert C [Knoxville, TN; Wesolowski, David J [Kingston, TN

2010-02-23

Apparatus for efficient heating of subterranean earth includes a well-casing that has an inner wall and an outer wall. A heater is disposed within the inner wall and is operable within a preselected operating temperature range. A heat transfer metal is disposed within the outer wall and without the inner wall, and is characterized by a melting point temperature lower than the preselected operating temperature range and a boiling point temperature higher than the preselected operating temperature range.

On development of analytical closure relationships for local wall friction, heat and mass transfer coefficients for sub-channel codes

International Nuclear Information System (INIS)

Kornienko, Y.

2000-01-01

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

Heat conduction in double-walled carbon nanotubes with intertube additional carbon atoms.

Science.gov (United States)

Cui, Liu; Feng, Yanhui; Tan, Peng; Zhang, Xinxin

2015-07-07

Heat conduction of double-walled carbon nanotubes (DWCNTs) with intertube additional carbon atoms was investigated for the first time using a molecular dynamics method. By analyzing the phonon vibrational density of states (VDOS), we revealed that the intertube additional atoms weak the heat conduction along the tube axis. Moreover, the phonon participation ratio (PR) demonstrates that the heat transfer in DWCNTs is dominated by low frequency modes. The added atoms cause the mode weight factor (MWF) of the outer tube to decrease and that of the inner tube to increase, which implies a lower thermal conductivity. The effects of temperature, tube length, and the number and distribution of added atoms were studied. Furthermore, an orthogonal array testing strategy was designed to identify the most important structural factor. It is indicated that the tendencies of thermal conductivity of DWCNTs with added atoms change with temperature and length are similar to bare ones. In addition, thermal conductivity decreases with the increasing number of added atoms, more evidently for atom addition concentrated at some cross-sections rather than uniform addition along the tube length. Simultaneously, the number of added atoms at each cross-section has a considerably more remarkable impact, compared to the tube length and the density of chosen cross-sections to add atoms.

Flow and heat transfer of MHD graphene oxide-water nanofluid between two non-parallel walls

Directory of Open Access Journals (Sweden)

Azimi Mohammadreza

2017-01-01

Full Text Available The steady 2-D heat transfer and flow between two non-parallel walls of a graphene oxide nanofluid in presence of uniform magnetic field are investigated in this paper. The analytical solution of the non-linear problem is obtained by Galerkin optimal homotopy asymptotic method. At first a similarity transformation is used to reduce the partial differential equations modeling the flow and heat transfer to ordinary non-linear differential equation systems containing the semi angle between the plate’s parameter, Reynolds number, the magnetic field strength, nanoparticle volume fraction, Eckert and Prandtl numbers. Finally, the obtained analytical results have been compared with results achieved from previous works in some cases.

A study of the flow boiling heat transfer in a minichannel for a heated wall with surface texture produced by vibration-assisted laser machining

International Nuclear Information System (INIS)

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

2016-01-01

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

Ion cyclotron resonance frequency heating in JET during initial operations with the ITER-like wall

Czech Academy of Sciences Publication Activity Database

Jacquet, P.; Bobkov, V.; Colas, L.; Czarnecka, A.; Lerche, E.; Mayoral, M.-L.; Monakhov, I.; Van-Eester, D.; Arnoux, G.; Brezinsek, S.; Brix, M.; Campergue, A.-L.; Devaux, S.; Drewelow, P.; Graham, M.; Klepper, C.C.; Meigs, A.; Milanesio, D.; Mlynář, Jan; Pütterich, T.; Sirinelli, A.

2014-01-01

Roč. 21, č. 6 (2014), 061510-061510 ISSN 1070-664X. [Topical conference on radio frequency power in plasmas/20./. Sorrento, 25.06.2013-28.06.2013] Institutional support: RVO:61389021 Keywords : JET * ITER-like wall * ICRF heating * impurities * sawtooth * simulation * transport Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.142, year: 2014 http://scitation.aip.org/content/aip/journal/pop/21/6/10.1063/1.4884354

AN EXPERIMENTAL STUDY FOR HEAT TRANSFER ENHANCEMENT BY LAMINAR FORCED CONVECTION FROM HORIZONTAL AND INCLINED TUBE HEATED WITH CONSTANT HEAT FLUX, USING TWO TYPES OF POROUS MEDIA

Directory of Open Access Journals (Sweden)

Thamir K. Jassem

2015-02-01

Full Text Available An experimental forced laminar study was presented in this research for an air flowing through a circular channel for different angles ( ,30o,45o,60o, the channel was heated at constant heat flux , the channel also was packed with steel and glass spheres respectively . The tests were done for three values of Peclets number (2111.71,3945.42,4575.47 with changing the heat flux for each case and five times for each number.The results showed that the dimensionless temperature distribution  will decrease with increasing the dimensionless channel length for all cases with changing Peclet number, heat flux and inclination angles, and its lowest value will be for glass spheres at highest flux, while at lower flux for , and the decreasing in dimensionless temperature was closed for both types of packed at other inclination angles.The study declared that the local Nusselt number decreases with increasing the dimensionless length of the channel for both packeds and for different applied heat flux, also through this study it was declared that the average Nusselt increases as Peclet number increases for both packed. Its value for the glass spheres is greater than the steel spheres with percentage (98.3% at small Peclet, and percentage (97.2% at large Peclet number for the horizontal tube, and (98.3% at small Peclet number and (97.8% at large Peclet number at  .Through this study its was found that average Nusselt number increases along the channel as the heat flux increases, because the bulk temperature will increase as the flow proceeds toward the end of the channel , so the heat transfer coefficient will increase.  It was declared from this study that in the case of the steel packed the heat transfer will occur mainly by conduction, while in the case of glass packed the heat transfer will occur mainly by laminar forced convection, where the lowest Nusselt number (Nu=3.8 was found when the pipe is horizontal and lowest heat flux and lowest Peclet number.  

A heat transfer model for the analysis of transient heating of the slab in a direct-fired walking beam type reheating furnace

Energy Technology Data Exchange (ETDEWEB)

Kim, Man Young [School of Mechanical and Aerospace Systems Engineering, Research Center of Industrial Technology, Chonbuk National University, 664-14 Duckjin-Dong, Duckjin-Gu, Jeonju, Chonbuk 561-756 (Korea)

2007-09-15

A mathematical heat transfer model for the prediction of heat flux on the slab surface and temperature distribution in the slab has been developed by considering the thermal radiation in the furnace chamber and transient heat conduction governing equations in the slab, respectively. The furnace is modeled as radiating medium with spatially varying temperature and constant absorption coefficient. The steel slabs are moved on the next fixed beam by the walking beam after being heated up through the non-firing, charging, preheating, heating, and soaking zones in the furnace. Radiative heat flux calculated from the radiative heat exchange within the furnace modeled using the FVM by considering the effect of furnace wall, slab, and combustion gases is introduced as the boundary condition of the transient conduction equation of the slab. Heat transfer characteristics and temperature behavior of the slab is investigated by changing such parameters as absorption coefficient and emissivity of the slab. Comparison with the experimental work show that the present heat transfer model works well for the prediction of thermal behavior of the slab in the reheating furnace. (author)

Numerical Study of Natural Convection within a Wavy Enclosure Using Meshfree Approach: Effect of Corner Heating

Directory of Open Access Journals (Sweden)

Sonam Singh

2014-01-01

Full Text Available This paper presents a numerical study of natural convection within a wavy enclosure heated via corner heating. The considered enclosure is a square enclosure with left wavy side wall. The vertical wavy wall of the enclosure and both of the corner heaters are maintained at constant temperature, Tc and Th, respectively, with Th>Tc while the remaining horizontal, bottom, top and side walls are insulated. A penalty element-free Galerkin approach with reduced gauss integration scheme for penalty terms is used to solve momentum and energy equations over the complex domain with wide range of parameters, namely, Rayleigh number (Ra, Prandtl number (Pr, and range of heaters in the x- and y-direction. Numerical results are represented in terms of isotherms, streamlines, and Nusselt number. It is observed that the rate of heat transfer depends to a great extent on the Rayleigh number, Prandtl number, length of the corner heaters and the shape of the heat transfer surface. The consistent performance of the adopted numerical procedure is verified by comparison of the results obtained through the present meshless technique with those existing in the literature.

Experimental study of no-frost refrigerator. Part 1: heat transfer through the walls; Estudo experimental de um refrigerador no-frost. Parte 1: transferencia de calor atraves das paredes

Energy Technology Data Exchange (ETDEWEB)

Goncalves, Joaquim Manoel [Escola Tecnica Federal de Santa Catarina, Sao Jose, SC (Brazil)]. E-mail: joaquim@nrva.ufsc.br; Melo, Claudio; Vieira, Luis Antonio Torquato [Santa Catarina Univ., Florianopolis, SC (Brazil). Dept. de Engenharia Mecanica

2000-07-01

This paper approaches the heat transfer in permanent regimen trough the walls of a no-frost refrigerator with two compartments with forced internal ventilation. The presented methodology allows the determination of thermal resistances of the walls externally. Also, the heating effect due to the compressor, the condenser and the air distribution between the compartments are investigated.

LES of fluid and heat flow over a wall-bounded short cylinder at different inflow conditions

Energy Technology Data Exchange (ETDEWEB)

Borello, D [Dipartmento di Ingegneria Meccanica e Aerospaziale, Sapienza University of Rome (Italy); Hanjalic, K, E-mail: borello@dma.ing.uniroma1.it [Department of Multi-scale Physics, Delft University of Technology (Netherlands)

2011-12-22

We report on LES studies of flow patterns, vortical structures and heat transfer in flows over a short single cylinder of diameter D placed in a plane channel of height h = 0.4D in which the bottom wall is heated. The Reynolds number of 6150, based on D, corresponds to the water experiments reported by Sahin et al. (2008). For the basic computational domain of 24 Multiplication-Sign 14 Multiplication-Sign 0.4D three different inflow conditions have been considered: a non-turbulent flow with a uniform initial velocity developing along the channel (NT), a fully developed channel flows (FD) (generated a priori) and periodic conditions (PC). The latter boundary conditions have also been considered for two shorter domain lengths of 6D and 3D corresponding to a cylinder in a compact matrix. For the long domain, despite the length of the channel of 9.5 D before (and after) the cylinder, the inlet conditions show strong effects on the formation and evolution of the multiple vortex systems both in front and behind the cylinder, influencing significantly also friction and heat transfer. Simulations show some agreement with experimental data though the comparison is impaired by the uncertainty in the experimental inflow conditions. For the shortest cylinder spacing the wake never closes and the flow shows enhanced unsteadiness and turbulence level. Interestingly, the comparison for the same short domain (3Dx3D) using the mean temperature at the inflow to this domain as a reference shows the lowest average base-wall Nusselt number in the PC 3D case that corresponds to compact heat exchangers.

Transient Heat Conduction

DEFF Research Database (Denmark)

Rode, Carsten

1998-01-01

Analytical theory of transient heat conduction.Fourier's law. General heat conducation equation. Thermal diffusivity. Biot and Fourier numbers. Lumped analysis and time constant. Semi-infinite body: fixed surface temperature, convective heat transfer at the surface, or constant surface heat flux...

Heat transfer and critical heat flux in a asymmetrically heated tube helicoidal flow; Transfert thermique et flux critique dans un ecoulement helicoidal en tube chauffe asymetriquement

Energy Technology Data Exchange (ETDEWEB)

Boscary, J

1995-10-01

The design of plasma facing components is crucial for plasma performance in next fusion reactors. These elements will be submitted to very high heat flux. They will be actively water-cooled by swirl tubes in the subcooled boiling regime. High heat flux experiments were conducted in order to analyse the heat transfer and to evaluate the critical heat flux. Water-cooled mock-ups were one-side heated by an electron beam gun for different thermal-hydraulic conditions. The critical heat flux was detected by an original method based on the isotherm modification on the heated surface. The wall heat transfer law including forced convection and subcooled boiling regimes was established. Numerical calculations of the material heat transfer conduction allowed the non-homogeneous distribution of the wall temperature and of the wall heat flux to be evaluated. The critical heat flux value was defined as the wall maximum heat flux. A critical heat flux model based on the liquid sublayer dryout under a vapor blanket was established. A good agreement with test results was found. (author). 198 refs., 126 figs., 21 tabs.

On computation of relaxation constant α in Landau–Lifshitz–Gilbert equation

Energy Technology Data Exchange (ETDEWEB)

Gladkov, Serguey, E-mail: sglad@newmail.ru; Bogdanova, Sofiya, E-mail: sonjaf@list.ru

2014-11-15

Due to the quasi-classical kinetic equation (QKE) for the magnon distribution function to calculate the velocity of the domain wall motion V in magnetic fields H>H{sub a}, where H{sub a}− magnetic anisotropy field. Based on the comparison of this formula for Vthe analytic expression of relaxation constant α in Landau–Lifshitz–Gilbert equation was found. We used the detected correlation between the system's entropy and the environment's resistance force, and obtained an expression for the spin-lattice braking force that is applied to the moving domain wall. We calculated the mobility ratio of the domain wall. - Highlights: • The resistance force acting on the domain wall was calculated. • Mobility coefficient of domain wall was calculated. • The strict calculation of relaxation constant in equation Landau-Lifshitz- Gilbert.

ANALYSIS OF THERMAL PROPERTIES AND HEAT LOSS IN CONSTRUCTION AND ISOTHERMAL MATERIALS OF MULTILAYER BUILDING WALLS

Directory of Open Access Journals (Sweden)

Arkadiusz Urzędowski

2017-06-01

Full Text Available The article discusses the impact of vertical partition, technology on thermal insulation of the building, and the resulting savings and residents thermal comfort. The study is carried out as an analysis of three selected design solutions including such materials as: aerated concrete elements, polystyrene, ceramic elements, concrete, mineral plaster. Simulation results of heat transfer in a multi-layered wall, are subjected to detailed analysis by means of thermal visual methods. The study of existing structures, helped to identify the local point of heat loss by means of infrared technology leading to determination of U-value reduction by 36% in maximum for the described 3 types of structure.

Experimental facility design for a gap heat transfer in a double wall tube

International Nuclear Information System (INIS)

Nam, Ho Yun; Hong, Jong Gan; Kim, Jong Man; Kim, Jong Bum; Jeong, Ji Young

2012-01-01

A reliable steam generator design is one of the most critical issues in developing a sodium cooled fast reactor (SFR), and various efforts to avoid potential sodium water reaction (SWR) have been made. For this reason, SFR steam generators have been developed to improve its reliability using a double wall tube (DWT), which has two barriers between the sodium and water. Most steam generators for SFRs are the shell and tube type. Steam at high pressure and low temperature flows inside the inner tubes, which are heated by the shell side sodium at low pressure and high temperature. Since the inner and outer tubes of conventional DWTs are made of identical materials, the degree of thermal expansion is somewhat different between the two concentric tubes owing to their temperature difference. Therefore, a greater temperature difference results in less contact pressures between the inner and outer tubes. This feature results in a deterioration of the heat transfer capability of DWTs. Current developments are focused on an improvement of heat transfer capability by investigating the gap conductance between the two concentric tubes. To improve the heat transfer capability of DWTs, it is preferable to use different tube materials (Fig. 1). It is recommended to choose the inner tube material whose thermal expansion coefficient is greater than that of the outer tube by 10 to 15%

Report on the joint meeting of the Division of Development and Technology Plasma Wall Interaction and High Heat Flux Materials and Components task groups

International Nuclear Information System (INIS)

Nygren, R.E.

1992-04-01

The Plasma/Wall Interaction and High Heat Flux Materials and Components Task Groups typically hold a joint meeting each year to provide a forum for discussion of technical issues of current interest as well as an opportunity for program reviews by the Department of Energy (DOE). At the meeting in September 1990, reported here, research programs in support of the International Thermonuclear Experimental Reactor (ITER) were highlighted. The first part of the meeting was devoted to research and development (R ampersand D) for ITER on plasma facing components plus introductory presentations on some current projects and design studies. The balance of the meeting was devoted to program reviews, which included presentations by most of the participants in the Small Business Innovative Research (SBIR) Programs with activities related to plasma wall interactions. The Task Groups on Plasma/Wall Interaction and on High Heat Flux Materials and Components were chartered as continuing working groups by the Division of Development and Technology in DOE's Magnetic Fusion Program. This report is an addition to the series of ''blue cover'' reports on the Joint Meetings of the Plasma/Wall Interaction and High Heat Flux Materials and Components Task Groups. Among several preceding meetings were those in October 1989 and January 1988

Study of Variable Turbulent Prandtl Number Model for Heat Transfer to Supercritical Fluids in Vertical Tubes

Science.gov (United States)

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

2018-06-01

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

Effects of ion beam heating on Raman spectra of single-walled carbon nanotubes

International Nuclear Information System (INIS)

Hulman, Martin; Skakalova, Viera; Krasheninnikov, A. V.; Roth, S.

2009-01-01

Free standing films of single-wall carbon nanotubes were irradiated with energetic N + and C 4+ ions. The observed changes in the Raman line shape of the radial breathing mode and the G band of the C 4+ irradiated samples were similar to those found for a thermally annealed sample. We ascribe these changes to thermal desorption of volatile dopants from the initially doped nanotubes. A simple geometry of the experiment allows us to estimate the temperature rise by one-dimensional heat conductance equation. The calculation indicates that irradiation-mediated increase in temperature may account for the observed Raman spectra changes

Preparation and property investigation of multi-walled carbon nanotube (MWCNT/epoxy composite films as high-performance electric heating (resistive heating element

Directory of Open Access Journals (Sweden)

F. X. Wang

2018-04-01

Full Text Available A series of multi-walled carbon nanotube (MWCNT/epoxy composite films with a thickness of ~700 µm is prepared by a sequential process of premixing, post dispersing, film casting, and thermal curing. The effects of the physical shear dispersion on the properties of conductive polymer composites as the electric heating element are investigated. The scanning electron microscope (SEM images show that highly efficient conductive networks form with shear dispersions of MWCNTs in the polymer matrix. The electrical resistivity decreases sharply from ~1015 Ω·cm for the neat epoxy resin to ~102 Ω·cm for the composite film with 2.0 wt% MWCNTs in accordance with the percolation behaviour, and a low percolation threshold of ~0.018 wt% is fitted. The electric heating behaviour of the composite film is observed at a low MWCNT content of 0.05 wt% due to the high electrical conductivity. For the composite film with 2.0 wt% MWCNTs, an equilibrium temperature of 115 °C is reached at an applied voltage of 40 V within 30 s. The excellent electric heating behaviour, including the rapid temperature response, electric heating efficiency, and operational stability, is primarily related to the conductive two-dimensional networks consisting of MWCNTs and the thermodynamically stable polymer matrix.

Experimental Assessment of Mechanical Night Ventilation on Inner Wall Surfaces

DEFF Research Database (Denmark)

Ji, Wenhui; Heiselberg, Per Kvols; Wang, Houhua

2016-01-01

The cooling potential of night ventilation largely depends on the heat exchange at the internal room surfaces. During night time, increased heat transfer on a vertical wall is expected due to cool supply air that flows along the internal wall surface from the top of the wall. This paper presents ...... an experimental study of the cooling of wall surfaces in a test room by mechanical night-time ventilation. Significant improvement of indoor thermal environment is presented resulting from the enhanced internal convection heat transfer....

Effect of variable heat transfer coefficient on tissue temperature next to a large vessel during radiofrequency tumor ablation

Directory of Open Access Journals (Sweden)

Pinheiro Cleber

2008-07-01

Full Text Available Abstract Background One of the current shortcomings of radiofrequency (RF tumor ablation is its limited performance in regions close to large blood vessels, resulting in high recurrence rates at these locations. Computer models have been used to determine tissue temperatures during tumor ablation procedures. To simulate large vessels, either constant wall temperature or constant convective heat transfer coefficient (h have been assumed at the vessel surface to simulate convection. However, the actual distribution of the temperature on the vessel wall is non-uniform and time-varying, and this feature makes the convective coefficient variable. Methods This paper presents a realistic time-varying model in which h is a function of the temperature distribution at the vessel wall. The finite-element method (FEM was employed in order to model RF hepatic ablation. Two geometrical configurations were investigated. The RF electrode was placed at distances of 1 and 5 mm from a large vessel (10 mm diameter. Results When the ablation procedure takes longer than 1–2 min, the attained coagulation zone obtained with both time-varying h and constant h does not differ significantly. However, for short duration ablation (5–10 s and when the electrode is 1 mm away from the vessel, the use of constant h can lead to errors as high as 20% in the estimation of the coagulation zone. Conclusion For tumor ablation procedures typically lasting at least 5 min, this study shows that modeling the heat sink effect of large vessels by applying constant h as a boundary condition will yield precise results while reducing computational complexity. However, for other thermal therapies with shorter treatment using a time-varying h may be necessary.

An experimental investigation of transient heat transfer in surrounding rock mass of high geothermal roadway

Directory of Open Access Journals (Sweden)

Zhang Yuan

2016-01-01

Full Text Available A self-designed experimental installation for transient heat transfer in the modelling surrounding rock mass of high geothermal roadways was elaborated in this paper. By utilizing the new installation, the temperature variation rules in surrounding rock mass of the high geothermal roadway during mechanical ventilation were studied. The results show that the roadway wall temperature decreases dramatically at the early stage of ventilation, and the temperature at every position of the surrounding rock mass is decreasing constantly with time passing by. From roadway wall to deep area, the temperature gradually increases until reaching original rock temperature. The relationship between dimensionless temperature and dimensionless radius demonstrates approximately exponential function. Meanwhile, the temperature disturbance range in the simulated surrounding rock mass extends gradually from the roadway wall to deep area in the surrounding rock mass. Besides, as the air velocity increases, heat loss in the surrounding rock mass rises and the ratio of temperature reduction becomes larger, the speed of disturbance range expansion also gets faster.

An integrated heat pipe-thermal storage design for a solar receiver

Science.gov (United States)

Keddy, E.; Sena, J. T.; Woloshun, K.; Merrigan, M. A.; Heidenreich, G.

Light-weight heat pipe wall elements that incorporate a thermal storage subassembly within the vapor space are being developed as part of the Organic Rankine Cycle Solar Dynamic Power System (ORC-SDPS) receiver for the Space Station application. The operating temperature of the heat pipe elements is in the 770 to 810 K range with a design power throughput of 4.8 kW per pipe. The total heat pipe length is 1.9 M. The Rankine cycle boiler heat transfer surfaces are positioned within the heat pipe vapor space, providing a relatively constant temperature input to the vaporizer. The heat pipe design employs axial arteries and distribution wicked thermal storage units with potassium as the working fluid. Performance predictions for this configuration have been conducted and the design characterized as a function of artery geometry, distribution wick thickness, porosity, pore size, and permeability.

Influence of PCMs on thermal behavior of building walls: experimental study using the walls of a reduced scale room

Directory of Open Access Journals (Sweden)

Gounni Ayoub

2017-01-01

Full Text Available Using Phase-Change Materials (PCM for lightweight building applications can increase equivalent thermal mass and provide energy savings. In the present experimental work, the heat transfer performance testing of some building walls, with or without PCM, is carried out using a reduced-scale cubic room (the test-cell. The cubic cell is heated by an incandescent bulb placed on its centre, and it is housed in an air-conditioned large-scale room that allows to control the ambient air temperature. The effect of the double PCM layer and of its location relatively to the outside surface of the wall is tested and discussed in terms of overall transmitted heat flux and in terms of reduction of the inside and outside surface temperatures. Findings shows that the additional inertia introduced by the PCM leads to a reduced overall heat flux transmission by the wall and to a lesser daily temperature amplitude on the surface of the wall that enhances the thermal comfort inside the building. In the next step of this work, the case of sandwich walls with air gap, and with wood and PCM layers will be considered.

Influence of PCMs on thermal behavior of building walls: experimental study using the walls of a reduced scale room

Science.gov (United States)

Gounni, Ayoub; Tahar Mabrouk, Mohamed; Kheiri, Abdelhamid; El alami, Mustapha

2017-11-01

Using Phase-Change Materials (PCM) for lightweight building applications can increase equivalent thermal mass and provide energy savings. In the present experimental work, the heat transfer performance testing of some building walls, with or without PCM, is carried out using a reduced-scale cubic room (the test-cell). The cubic cell is heated by an incandescent bulb placed on its centre, and it is housed in an air-conditioned large-scale room that allows to control the ambient air temperature. The effect of the double PCM layer and of its location relatively to the outside surface of the wall is tested and discussed in terms of overall transmitted heat flux and in terms of reduction of the inside and outside surface temperatures. Findings shows that the additional inertia introduced by the PCM leads to a reduced overall heat flux transmission by the wall and to a lesser daily temperature amplitude on the surface of the wall that enhances the thermal comfort inside the building. In the next step of this work, the case of sandwich walls with air gap, and with wood and PCM layers will be considered.

Heat and mass transfer in a liquid pool with wall ablation and composition effects

International Nuclear Information System (INIS)

Pham, Q.T.

2013-01-01

This work deals with the thermal-hydraulics of a melt pool coupled with the physical chemistry for the purpose of describing the behaviour of mixtures of materials (non-eutectic). Evolution of transient temperature in a liquid melt pool heated by volumetric power dissipation has been described with solidification on the cooled wall. The model has been developed and is validated for the experimental results given by LIVE experiment, performed at Karlsruhe Institute of Technology (KIT) in Germany. Under the conditions of these tests, it is shown that the interface temperature follows the liquidus temperature (corresponding to the composition of the liquid bath) during the whole transient. Assumption of interface temperature as liquidus temperature allows recalculating the evolution of the maximum melt temperature as well as the local crust thickness. Furthermore, we propose a model for describing the interaction between a non-eutectic liquid melt pool (subjected to volumetric power dissipation) and an ablated wall whose melting point is below the liquidus temperature of the melt. The model predictions are compared with results of ARTEMIS 2D tests. A new formulation of the interface temperature between the liquid melt and the solid wall (below liquidus temperature) has been proposed. (author) [fr

Numerical calculation of unsteady turbulent heat transfer in a circular tube considering for heat dissipation in a wale

International Nuclear Information System (INIS)

Groshev, A.I.; Slobodchuk, V.I.

1986-01-01

The results of numerical calculation of the conjugated problem of convective heat transfer under unsteady conditions are presented. The equations describing heat transfer take into account longitudinal heat diffusion in liquid and in a wall. The formulae for calculating local heat flows at the wall-liquid surface in the case of an arbitrary law of temperature variation at the outer wall surface along the channel length are proposed for steady-state heat transfer conditions

Heat flux characteristics of spray wall impingement with ethanol, butanol, iso-octane, gasoline and E10 fuels

International Nuclear Information System (INIS)

Serras-Pereira, J.; Aleiferis, P.G.; Walmsley, H.L.; Davies, T.J.; Cracknell, R.F.

2013-01-01

Highlights: • Heat flux sensors used to characterise the locations of fuel spray wall impingement. • Droplet evaporation modelling used to study the effect of fuel properties. • Behaviour of ethanol and butanol distinctively different to hydrocarbons. -- Abstract: Future fuel stocks for spark-ignition engines are expected to include a significant portion of bio-derived components with quite different chemical and physical properties to those of liquid hydrocarbons. State-of-the-art high-pressure multi-hole injectors for latest design direct-injection spark-ignition engines offer some great benefits in terms of fuel atomisation, as well as flexibility in in-cylinder fuel targeting by selection of the exact number and angle of the nozzle’s holes. However, in order to maximise such benefits for future spark-ignition engines and minimise any deteriorating effects with regards to exhaust emissions, it is important to avoid liquid fuel impingement onto the cylinder walls and take into consideration various types of biofuels. This paper presents results from the use of heat flux sensors to characterise the locations and levels of liquid fuel impingement onto the engine’s liner walls when injected from a centrally located multi-hole injector with an asymmetric pattern of spray plumes. Ethanol, butanol, iso-octane, gasoline and a blend of 10% ethanol with 90% gasoline (E10) were tested and compared. The tests were performed in the cylinder of a direct-injection spark-ignition engine at static conditions (i.e. quiescent chamber at 1.0 bar) and motoring conditions (at full load with inlet plenum pressure of 1.0 bar) with different engine temperatures in order to decouple competing effects. The collected data were analysed to extract time-resolved signals, as well as mean and standard deviation levels of peak heat flux. The results were interpreted with reference to in-cylinder spray formation characteristics, as well as fuel evaporation rates obtained by modelling

Heat transfer and critical heat flux in a spiral flow in an asymmetrical heated tube; Transfert thermique et flux critique dans un ecoulement helicoidal en tube chauffe asymetriquement

Energy Technology Data Exchange (ETDEWEB)

Boscary, J [CEA Centre d` Etudes de Cadarache, 13 - Saint-Paul-lez-Durance (France). Direction des Sciences de la Matiere; [Association Euratom-CEA, Centre d` Etudes Nucleaires de Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee

1997-03-01

The design of plasma facing components is crucial for plasma performance in next fusion reactors. These elements will be submitted to very high heat flux. They will be actively water-cooled by swirl tubes in the subcooled boiling regime. High heat flux experiments were conducted in order to analyse the heat transfer and to evaluate the critical heat flux. Water-cooled mock-ups were one-side heated by an electron beam gun for different thermal-hydraulic conditions. The critical heat flux was detected by an original method based on the isotherm modification on the heated surface. The wall heat transfer law including forced convection and subcooled boiling regimes was established. Numerical calculations of the material heat transfer conduction allowed the non-homogeneous distribution of the wall temperature and of the wall heat flux to be evaluated. The critical heat flux value was defined as the wall maximum heat flux. A critical heat flux model based on the liquid sublayer dryout under a vapor blanket was established. A good agreement with test results was found. (author) 197 refs.

Dynamics and control of a heat pump assisted extractive dividing-wall column for bioethanol dehydration

OpenAIRE

Patraşcu, Iulian; Bildea, Costin Sorin; Kiss, Anton A.

2017-01-01

Recently, a novel heat-pump-assisted extractive distillation process taking place in a dividing-wall column was proposed for bioethanol dehydration. This integrated design combines three distillation columns into a single unit that allows over 40% energy savings and low specific energy requirements of 1.24 kWh/kg ethanol. However, these economic benefits are possible only if this highly integrated system is also controllable to ensure operational availability. This paper is the first to addre...

Analysis of Hydrodynamics and Heat Transfer in a Thin Liquid Film Flowing over a Rotating Disk by Integral Method

Science.gov (United States)

Basu, S.; Cetegen, B. M.

2005-01-01

An integral analysis of hydrodynamics and heat transfer in a thin liquid film flowing over a rotating disk surface is presented for both constant temperature and constant heat flux boundary conditions. The model is found to capture the correct trends of the liquid film thickness variation over the disk surface and compare reasonably well with experimental results over the range of Reynolds and Rossby numbers covering both inertia and rotation dominated regimes. Nusselt number variation over the disk surface shows two types of behavior. At low rotation rates, the Nusselt number exhibits a radial decay with Nusselt number magnitudes increasing with higher inlet Reynolds number for both constant wall temperature and heat flux cases. At high rotation rates, the Nusselt number profiles exhibit a peak whose location advances radially outward with increasing film Reynolds number or inertia. The results also compare favorably with the full numerical simulation results from an earlier study as well as with the reported experimental results.

Shielding wall for thermonuclear device

International Nuclear Information System (INIS)

Uchida, Takaho.

1989-01-01

This invention concerns shielding walls opposing to plasmas of a thermonuclear device and it is an object thereof to conduct reactor operation with no troubles even if a portion of shielding wall tiles should be damaged. That is, the shielding wall tiles are constituted as a dual layer structure in which the lower base tiles are connected by means of bolts to first walls. Further, the upper surface tiles are bolt-connected to the layer base tiles. In this structure, the plasma thermal loads are directly received by the surface layer tiles and heat is conducted by means of conduction and radiation to the underlying base tiles and the first walls. Even upon occurrence of destruction accidents to the surface layer tiles caused by incident heat or electromagnetic force upon elimination of plasmas, since the underlying base tiles remain as they are, the first walls constituted with stainless steels, etc. are not directly exposed to the plasmas. Accordingly, the integrity of the first walls having cooling channels can be maintained and sputtering intrusion of atoms of high atom number into the plasmas can be prevented. (I.S.)

Parametric investigation of a non-constant cross sectional area air to air heat exchanger

International Nuclear Information System (INIS)

Cárdenas, Bruno; Garvey, Seamus; Kantharaj, Bharath; Simpson, Michael

2017-01-01

Highlights: • Evaluation of complex geometry aimed at minimizing volume per unit of exergy transfer. • The use of a non-constant cross-section for the heat exchanger is proposed. • The performance gains attainable via modern manufacturing techniques are discussed. • The trade-off between overall exergy efficiency and cost is thoroughly analysed. • A quadratic proportion between volume and characteristic dimension has been found. - Abstract: The present article addresses the design, mathematical modelling and analysis of a novel highly exergy-efficient air to air heat exchanger. An intricate design based on an hexagonal mesh is proposed for the cross-sectional area of the heat exchanger with aims to explore the performance gains that can be obtained by exploiting the capabilities and benefits offered by modern fabrication techniques such as additive manufacturing. Special attention is paid to understanding the relationship or trade-off that exists between the overall exergy efficiency of the heat exchanger and its cost. The iterative algorithm used to find the geometrical parameters that yield the best performance in terms of volume of material required per unit of exergy transfer at a certain level of efficiency, as well as the assumptions and simplifications made, are comprehensively explained. It has been found through the analyses carried out performed, which are thoroughly discussed throughout the paper, that if the characteristic dimension of the heat exchanger is scaled up by a factor of n, the volume of material per kW of exergy transfer at certain exergy efficiency will increase by a factor of n squared. This is a very important observation, possibly applicable to other types of heat exchangers, that indicates that performance improves dramatically at smaller scales. The overall performance of the case study presented is satisfactory, a volume of material as low as 84.8 cm"3 for one kW of exergy transfer can be achieved with a 99% exergy

Melting of a phase change material in a horizontal annulus with discrete heat sources

Directory of Open Access Journals (Sweden)

Mirzaei Hooshyar

2015-01-01

Full Text Available Phase change materials have found many industrial applications such as cooling of electronic devices and thermal energy storage. This paper investigates numerically the melting process of a phase change material in a two-dimensional horizontal annulus with different arrangements of two discrete heat sources. The sources are positioned on the inner cylinder of the annulus and assumed as constant-temperature boundary conditions. The remaining portion of the inner cylinder wall as well as the outer cylinder wall is considered to be insulated. The emphasis is mainly on the effects of the arrangement of the heat source pair on the fluid flow and heat transfer features. The governing equations are solved on a non-uniform O type mesh using a pressure-based finite volume method with an enthalpy porosity technique to trace the solid and liquid interface. The results are obtained at Ra=104 and presented in terms of streamlines, isotherms, melting phase front, liquid fraction and dimensionless heat flux. It is observed that, depending on the arrangement of heat sources, the liquid fraction increases both linearly and non-linearly with time but will slow down at the end of the melting process. It can also be concluded that proper arrangement of discrete heat sources has the great potential in improving the energy storage system. For instance, the arrangement C3 where the heat sources are located on the bottom part of the inner cylinder wall can expedite the melting process as compared to the other arrangements.

Numerical Investigation of Jet Impingement Heat Transfer on a Flat plate

Directory of Open Access Journals (Sweden)

Asem Nabadavis

2016-12-01

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

Developing Buoyancy Driven Flow of a Nanofluid in a Vertical Channel Subject to Heat Flux

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Nirmal C. Sacheti

2014-01-01

Full Text Available The developing natural convective flow of a nanofluid in an infinite vertical channel with impermeable bounding walls has been investigated. It is assumed that the nanofluid is dominated by two specific slip mechanisms and that the channel walls are subject to constant heat flux and isothermal temperature, respectively. The governing nonlinear partial differential equations coupling different transport processes have been solved numerically. The variations of velocity, temperature, and nanoparticles concentration have been discussed in relation to a number of physical parameters. It is seen that the approach to the steady-state profiles of velocity and temperature in the present work is different from the ones reported in a previous study corresponding to isothermal wall conditions.

Convective boundary layer flow and heat transfer in a nanofluid in the presence of second order slip, constant heat flux and zero nanoparticles flux

Energy Technology Data Exchange (ETDEWEB)

Rahman, M.M., E-mail: mansurdu@yahoo.com [Department of Mathematics and Statistics, College of Science, Sultan Qaboos University, PO Box 36, PC 123 Al-Khod, Muscat (Oman); Al-Rashdi, Maryam H. [Department of Mathematics and Statistics, College of Science, Sultan Qaboos University, PO Box 36, PC 123 Al-Khod, Muscat (Oman); Pop, I. [Department of Mathematics, Faculty of Mathematics and Computer Science, Babeş-Bolyai University, Cluj-Napoca 400084 (Romania)

2016-02-15

Highlights: • Convective boundary layer flow and heat transfer in a nanofluid is investigated. • Second order slip increases the rate of shear stress and decreases the rate of heat transfer in a nanofluid. • In nanofluid flow zero normal flux of the nanoparticles at the surface is realistic to apply. • Multiple solutions are identified for certain values of the parameter space. • The upper branch solution is found to be stable, hence physically realizable. - Abstract: In this work, the effects of the second order slip, constant heat flux, and zero normal flux of the nanoparticles due to thermophoresis on the convective boundary layer flow and heat transfer characteristics in a nanofluid using Buongiorno's model over a permeable shrinking sheet is studied theoretically. The nonlinear coupled similarity equations are solved using the function bvp4c using Matlab. Similarity solutions of the flow, heat transfer and nanoparticles volume fraction are presented graphically for several values of the model parameters. The results show that the application of second order slip at the interface is found to be increased the rate of shear stress and decreased the rate of heat transfer in a nanofluid, so need to be taken into account in nanofluid modeling. The results further indicate that multiple solutions exist for certain values of the parameter space. The stability analysis provides guarantee that the lower branch solution is unstable, while the upper branch solution is stable and physically realizable.

Role of wall heat transfer and other system variables on fuel compaction and recriticality

International Nuclear Information System (INIS)

Dhir, V.K.; Castle, J.N.; Catton, I.; Kastenberg, W.E.; Doshi, J.B.

1976-01-01

The assessment of the molten fuel gaining recriticality after a hypothetical core disruptive accident in a fast reactor is an important safety consideration. Recriticality of the disrupted core can be envisioned to occur, if the fuel rearranges itself into a denser configuration either due to gravity slumping of the molten fuel or due to pressure or heat transfer driven compaction of the earlier dispersed fuel. In this paper the role played by wall heat transfer, internal radiation and the bottle pressure on the physical state of the molten fuel pool is discussed. It is suggested that in the absence of a solid crust the heat transfer process from the molten fuel to the surrounding steel will be very efficient because of melting and buoyancy driven removal of less dense steel through the pool of heavier UO 2 . The internal radiation at the high fuel temperature significantly increase the effective thermal conductivity of the molten fuel and lead to increased heat transfer in situations where a solid crust of UO 2 exists between molten UO 2 and molten steel. IN a boiled-up bottled pool, the pool pressure is shown to increase very rapidly with time and thus necessitate higher fission heating of the fuel to maintain it in a certain boiled up state. Finally, the results of the above discussion are applied to study the recriticality of a fuel pool formed during a hypothetical core disrupted accident in a fast reactor

Investigations on post-dryout heat transfer in bilaterally heated annular channels

International Nuclear Information System (INIS)

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

2006-01-01

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

Heat exchange and pressure drop of herring-bone fin surfaces. Experimental cell results at constant wall temperature; Echange de chaleur et perte de charge de surfaces a ailettes en chevrons. Resultats experimentaux en cellule a temperature de paroi constante

Energy Technology Data Exchange (ETDEWEB)

NONE

1968-07-01

The increase in the specific power of nuclear reactors of the gas-graphite type has necessitated the use of high performance exchange surfaces for canning the fuel (natural uranium). For this, experiments were carried out on cans fitted with herring-bone fins, at constant wall temperature; a flow of water at 100 deg. C passes inside the can which is cooled externally by a flow of CO{sub 2} at 15 bars pressure. This experimental set-up makes it possible to compare the aero-thermal performances of the different cans with an accuracy of 5 per cent. This report presents the results obtained in the form of a friction coefficient f{sub 0} and mean Margoulis number m{sub 0} as a function of the Reynolds number Re{sub 0}, this latter varying from 3 x 10{sup 5} to 9 x 10{sup 5}. (authors) [French] L'augmentation de la puissance specifique des reacteurs nucleaires de la filiere graphite-gaz a necessite l'utilisation de surfaces d'echange a hautes performances pour gainer le combustible (uranium naturel). Dans cette optique, des gaines munies d'ailettes disposees en chevron ont ete experimentees a temperature de paroi constante: un courant d'eau a 100 deg. C circule a l'interieur de la gaine qui est refroidie exterieurement par un ecoulement de CO{sub 2} sous une pression de 15 bars. Cette methode experimentale permet de situer les performances aerothermiques des gaines les unes par rapport aux autres a 5 pour cent pres. Ce rapport presente les resultats obtenus sous la forme d'un coefficient de frottement f{sub 0} et d'un nombre de Margoulis moyen m{sub 0} en fonction du nombre de Reynolds Re{sub 0}, ce dernier pouvant varier de 3. 10{sup 5} a 9. 10{sup 5}. (auteurs)

Experimental and numerical investigation on natural convection heat transfer in nanofluids

International Nuclear Information System (INIS)

Kulkarni, P.P.; Nayak, A.K.; Vijayan, P.K.

2014-01-01

Currently, a lot of research is being carried out on the potential application of nanofluids as a coolant in nuclear reactors owing to their enhanced heat transfer characteristics as compared to base fluid. In this regards, an experimental study has been undertaken concerning natural convection heat transfer of nanofluids over a cylindrical heater with a constant wall heat flux condition. The heat flux was varied from 0-50000 W/m 2 and Rayleigh number range is 30000 to 1.65 X 10 5 . Results show that there was a reduction in natural convection heat transfer coefficient of nanofluids as compared to water. Experimental results were compared with existing models for similar geometry. However, the available correlation was found to be unable to predict experimental data. A new empirical model was developed based on the experimental data including the effect of nanoparticles concentration which predicts the experimental data satisfactorily. (author)

A numerical model for boiling heat transfer coefficient of zeotropic mixtures

Science.gov (United States)

Barraza Vicencio, Rodrigo; Caviedes Aedo, Eduardo

2017-12-01

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

Heat flux microsensor measurements

Science.gov (United States)

Terrell, J. P.; Hager, J. M.; Onishi, S.; Diller, T. E.

1992-01-01

A thin-film heat flux sensor has been fabricated on a stainless steel substrate. The thermocouple elements of the heat flux sensor were nickel and nichrome, and the temperature resistance sensor was platinum. The completed heat flux microsensor was calibrated at the AEDC radiation facility. The gage output was linear with heat flux with no apparent temperature effect on sensitivity. The gage was used for heat flux measurements at the NASA Langley Vitiated Air Test Facility. Vitiated air was expanded to Mach 3.0 and hydrogen fuel was injected. Measurements were made on the wall of a diverging duct downstream of the injector during all stages of the hydrogen combustion tests. Because the wall and the gage were not actively cooled, the wall temperature reached over 1000 C (1900 F) during the most severe test.

Antenna-coupled terahertz radiation from joule-heated single-wall carbon nanotubes

Directory of Open Access Journals (Sweden)

M. Muthee

2011-12-01

Full Text Available In this letter an experimental method is introduced that allows detection of terahertz (THz radiation from arrays of joule-heated Single-Walled Carbon Nanotubes (SWCNTs, by coupling this radiation through integrated antennas and a silicon lens. The radiation forms a diffraction-limited beam with a total maximum radiated power of 450 nW, significantly greater than the power estimated from Nyquist thermal noise (8 nW. The physical radiation process is unknown at this stage, but possible explanations for the high radiated power are discussed briefly. The emission has a typical bandwidth of 1.2 THz and can be tuned to different frequencies by changing the dimensions of the antennas. Arrays of the devices could be integrated in CMOS integrated circuits, and find application in THz systems, such as in near-range medical imaging.

The Effects of Channel Curvature and Protrusion Height on Nucleate Boiling and the Critical Heat Flux of a Simulated Electronic Chip

Science.gov (United States)

1994-05-01

parameters and geometry factor. 57 3.2 Laminar sublayer and buffer layer thicknesses for geometry of Mudawar and Maddox.ŝ 68 3.3 Correlation constants...transfer from simulated electronic chip heat sources that are flush with the flow channel wall. Mudawar and Maddox2" have studied enhanced surfaces...bias error was not estimated; however, the percentage of heat loss measured compares with that previously reported by Mudawar and Maddox19 for a

Improvement and validation of the wall heat transfer package of RELAP5/MOD3.3

International Nuclear Information System (INIS)

Wu, Pan; Xiong, Xiaofei; Shan, Jianqiang; Gou, Junli; Zhang, Bin; Zhang, Bo

2016-01-01

Highlights: • A new heat transfer package has been developed. • It has been incorporated into RELAP5/MOD3.3 to verify its advantages. • The results of modified code were compared with available experimental data. • The results showed that higher prediction accuracy was achieved. - Abstract: The process of energy transfer from heat structure to control volume is determined by the wall-to-fluid heat transfer package, which is crucial for nuclear reactor safety analysis codes. The current logic for selection of heat transfer modes of RELAP5/MOD3.3 code is too complex and may result in incorrect heat transfer mode judgment. Also, the narrow application scope of film boiling heat transfer correlations may result in large errors in film boiling region which is of paramount importance for the predicted peak clad temperatures during hypothetical LB-LOCAs in PWRs. In this study, a new heat transfer package has been developed and incorporated into the RELAP5/MOD3.3 code. Differing from the original package, the modified one consists of twelve heat transfer modes and proposes a new logic for selection of heat transfer modes. For each mode, the models in the existing safety analysis codes and the leading models in literature have been reviewed in order to determine the best model which can easily be applicable to the RELAP5/MOD3.3 code. Particularly (1) a new package of heat transfer correlations are produced; (2) a new logic for selection of film boiling and transition boiling heat transfer modes is proposed which use minimum film boiling temperature and critical heat flux temperature as distinguished points. The modified code has been validated by comparing the analysis results with available experimental data from tube post dryout experiments and loss-of-fluid test (LOFT) facility. The calculation results showed that the improved package could better predict the experimental phenomena with higher prediction accuracy.

Improvement and validation of the wall heat transfer package of RELAP5/MOD3.3

Energy Technology Data Exchange (ETDEWEB)

Wu, Pan; Xiong, Xiaofei; Shan, Jianqiang, E-mail: jqshan@mail.xjtu.edu.cn; Gou, Junli; Zhang, Bin; Zhang, Bo

2016-12-15

Highlights: • A new heat transfer package has been developed. • It has been incorporated into RELAP5/MOD3.3 to verify its advantages. • The results of modified code were compared with available experimental data. • The results showed that higher prediction accuracy was achieved. - Abstract: The process of energy transfer from heat structure to control volume is determined by the wall-to-fluid heat transfer package, which is crucial for nuclear reactor safety analysis codes. The current logic for selection of heat transfer modes of RELAP5/MOD3.3 code is too complex and may result in incorrect heat transfer mode judgment. Also, the narrow application scope of film boiling heat transfer correlations may result in large errors in film boiling region which is of paramount importance for the predicted peak clad temperatures during hypothetical LB-LOCAs in PWRs. In this study, a new heat transfer package has been developed and incorporated into the RELAP5/MOD3.3 code. Differing from the original package, the modified one consists of twelve heat transfer modes and proposes a new logic for selection of heat transfer modes. For each mode, the models in the existing safety analysis codes and the leading models in literature have been reviewed in order to determine the best model which can easily be applicable to the RELAP5/MOD3.3 code. Particularly (1) a new package of heat transfer correlations are produced; (2) a new logic for selection of film boiling and transition boiling heat transfer modes is proposed which use minimum film boiling temperature and critical heat flux temperature as distinguished points. The modified code has been validated by comparing the analysis results with available experimental data from tube post dryout experiments and loss-of-fluid test (LOFT) facility. The calculation results showed that the improved package could better predict the experimental phenomena with higher prediction accuracy.

Effect of radiant heat transfer on the performance of high temperature heat exchanger

International Nuclear Information System (INIS)

Mori, Yasuo; Hijikata, Kunio; Yamada, Yukio

1975-01-01

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

Free convective heat loss from cavity-type solar furnace; Solar receiver kara no shizen tairyu ni yoru netsusonshitsu

Energy Technology Data Exchange (ETDEWEB)

Fujii, I; Ito, N [Meiji University, Tokyo (Japan)

1996-10-27

Free convective heat loss from solar heat receivers was studied, using three laboratory model receivers (different in depth L and aperture diameter d) heated by electric heaters. Most of the heat produced by heaters was transmitted to the air inside. The cylindrical vessel walls were fully insulated against heat. Heat loss being supposed to result mainly from transfer by free convection, the experiment results were edited by use of Nusselt number Nu and Rayley number Ra. Relations between Nu(D/d){sup m1} and Ra(L/D){sup m2} were plotted in a chart. Here, D is the receiver inner diameter, and m1 and m2 are constants that can be determined by computation. Tests points were provided approximately lineally, irrespective of D, L, or receiver inclination. Air currents were found to produce one or more swirls inside, thanks to the current visualization technique, when the receiver inclination was not sharper than 120{degree} (except 0{degree}). The number of swirls increased as the inner wall temperature rose. This kind of behavior of air currents directly affects the degree of heat loss. 9 refs., 4 figs.

Analysis of prestressed concrete wall segments

International Nuclear Information System (INIS)

Koziak, B.D.P.; Murray, D.W.

1979-06-01

An iterative numerical technique for analysing the biaxial response of reinforced and prestressed concrete wall segments subject to combinations of prestressing, creep, temperature and live loads is presented. Two concrete constitutive relations are available for this analysis. The first is a uniaxially bilinear model with a tension cut-off. The second is a nonlinear biaxial relation incorporating equivalent uniaxial strains to remove the Poissons's ratio effect under biaxial loading. Predictions from both the bilinear and nonlinear model are compared with observations from experimental wall segments tested in tension. The nonlinear model results are shown to be close to those of the test segments, while the bilinear results are good up to cracking. Further comparisons are made between the nonlinear analysis using constant membrane force-moment ratios, constant membrane force-curvature ratios, and a nonlinear finite difference analysis of a test containment structure. Neither nonlinear analysis could predict the reponse of every wall segment within the structure, but the constant membrane force-moment analysis provided lower bound results. (author)

Axion-dilaton domain walls and fake supergravity

International Nuclear Information System (INIS)

Sonner, Julian; Townsend, Paul K

2007-01-01

Dynamical systems methods are used to investigate domain-wall solutions of a two-parameter family of models in which gravity is coupled to an axion and to a dilaton with an exponential potential of either sign. A complete global analysis is presented for (i) constant axion and (ii) flat walls, including a study of bifurcations and a new exact domain-wall solution with non-constant axion. We reconsider 'fake-supergravity' issues in light of these results. We show, by example, how domain walls determine multi-valued superpotentials that branch at stationary points that are not stationary points of the potential, and we apply this result to potentials with anti-de Sitter vacua. We also show by example that 'adapted' truncation to a single-scalar model may be inconsistent, and we propose a 'generalized' fake-supergravity formalism that applies in some such cases

A numerical study of external building walls containing phase change materials (PCM)

International Nuclear Information System (INIS)

Izquierdo-Barrientos, M.A.; Belmonte, J.F.; Rodríguez-Sánchez, D.; Molina, A.E.; Almendros-Ibáñez, J.A.

2012-01-01

Phase Change Materials (PCMs) have been receiving increased attention, due to their capacity to store large amounts of thermal energy in narrow temperature ranges. This property makes them ideal for passive heat storage in the envelopes of buildings. To study the influence of PCMs in external building walls, a one-dimensional transient heat transfer model has been developed and solved numerically using a finite difference technique. Different external building wall configurations were analyzed for a typical building wall by varying the location of the PCM layer, the orientation of the wall, the ambient conditions and the phase transition temperature of the PCM. The integration of a PCM layer into a building wall diminished the amplitude of the instantaneous heat flux through the wall when the melting temperature of the PCM was properly selected according to the season and wall orientation. Conversely, the results of the work show that there is no significant reduction in the total heat lost during winter regardless of the wall orientation or PCM transition temperature. Higher differences were observed in the heat gained during the summer period, due to the elevated solar radiation fluxes. The high thermal inertia of the wall implies that the inclusion of a PCM layer increases the thermal load during the day while decreasing the thermal load during the night. - Highlights: ► A comparative simulation of a building wall with and without PCMs has been conducted. ► PCM is selected according with the season, the wall orientation and the melting temperature. ► PCM in a building wall help to diminish the internal air temperature swings and to regulate the heat transfer.

Fire resistance of a steel plate reinforced concrete bearing wall

International Nuclear Information System (INIS)

Kodaira, Akio; Kanchi, Masaki; Fujinaka, Hideo; Akita, Shodo; Ozaki, Masahiko

2003-01-01

Samples from a steel plate reinforced concrete bearing wall composed of concrete slab sandwiched between studded steel plates, were subjected to loaded fire resistance tests. There were two types of specimens: some were 1800 mm high while the rest were 3000 mm high ; thickness and width were the same for all specimens, at 200 mm and 800 mm, respectively. Under constant load conditions, one side of each specimen was heated along the standard fire-temperature curve. The results enabled us to approximate the relationship between the ratio of working load to concrete strength N/(Ac x c σ b) and the fire resistance time (t: minutes), as equation (1) for the 1800 mm - high specimen, and equation (2) for the 3000 mm - high specimen. N/(Ac x c σ b) = 2.21 x (1/t) 0.323 (1), .N/(Ac x c σ b) 2.30 x (1/t) 0.378 (2) In addition, the temperature of the unheated side of the specimens was 100degC at 240 minutes of continuous heating, clearly indicating that there was sufficient heat insulation. (author)

Small scale structure in the wall region of a turbulent boundary layer

International Nuclear Information System (INIS)

Bogar, T.J.

1975-01-01

This paper is a report of the construction and application of an extremely small hot-wire X-probe (typical dimensions of 100 μ) to the measurement of Reynolds stress in the wall region of the turbulent boundary layer of a flat plate at high Reynolds number (Re/sub theta/ = 11,300). In the present flow, the size of the probe corresponds to a dimensionless length based on wall parameters of lu/sub tau//ν = 3. Probe construction methods are described. The Wyngaard-Lumley constant temperature anemometer used to heat the wire is analyzed, and a direct acoustical frequency calibration of the wire is made. This calibration shows the small wire to have uniform frequency response to 15 kHz. A novel calibration technique is employed using a high speed, digital mini-computer to determine the velocity in the stream direction and in a direction normal to the wall by matching the unique voltage pairs produced by the X-wire array in a turbulent flow to the voltage pairs produced when the probe is exposed to a known uniform flow inclined at various angles

External corners as heat bridges

Energy Technology Data Exchange (ETDEWEB)

Berber, J.

1984-08-01

The maximum additional heat loss in vertical external corners depending on wall thickness is determined. In order to amire at a low k-value, a much smaller wall thickness is required in externally insulated walls than in monolithic constructions; the greater loss of heat bridge with external insulation stands in contrast to a higher loss in thick, monolithic walls. In relation to total losses, the additional losses through external corners are practically negligible.

Mixed convection from a discrete heat source in enclosures with two adjacent moving walls and filled with micropolar nanofluids

Directory of Open Access Journals (Sweden)

Sameh E. Ahmed

2016-03-01

Full Text Available This paper examines numerically the thermal and flow field characteristics of the laminar steady mixed convection flow in a square lid-driven enclosure filled with water-based micropolar nanofluids by using the finite volume method. While a uniform heat source is located on a part of the bottom of the enclosure, both the right and left sidewalls are considered adiabatic together with the remaining parts of the bottom wall. The upper wall is maintained at a relatively low temperature. Both the upper and left sidewalls move at a uniform lid-driven velocity and four different cases of the moving lid ordinations are considered. The fluid inside the enclosure is a water based micropolar nanofluid containing different types of solid spherical nanoparticles: Cu, Ag, Al2O3, and TiO2. Based on the numerical results, the effects of the dominant parameters such as Richardson number, nanofluid type, length and location of the heat source, solid volume fractions, moving lid orientations and dimensionless viscosity are examined. Comparisons with previously numerical works are performed and good agreements between the results are observed. It is found that the average Nusselt number along the heat source decreases as the heat source length increases while it increases when the solid volume fraction increases. Also, the results of the present study indicate that both the local and the average Nusselt numbers along the heat source have the highest value for the fourth case (C4. Moreover, it is observed that both the Richardson number and moving lid ordinations have a significant effect on the flow and thermal fields in the enclosure.

Modular first wall concept for steady state operation

International Nuclear Information System (INIS)

Kotzlowski, H.E.

1981-01-01

On the basis of the limiter design proposed for ZEPHYR a first wall concept has been developed which can also be used as a large area limiter, heat shield or beam pump. Its specific feature is the thermal contact of the wall armour elements with the water-cooled base plates. The combination of radiation and contact cooling, compared with radiation only, helps to lower the steady state temperatures of the first wall by approximately 50 % and to reduce the cooling-time between discharges. Particulary the lower wall temperature give a larger margin for additional heating of the wall by plasma disruption or neutral beams until excessive erosion or damage of the armour takes place

Heat transfer enhancement in a tube using circular cross sectional rings separated from wall

International Nuclear Information System (INIS)

Ozceyhan, Veysel; Gunes, Sibel; Buyukalaca, Orhan; Altuntop, Necdet

2008-01-01

A numerical study was undertaken for investigating the heat transfer enhancement in a tube with the circular cross sectional rings. The rings were inserted near the tube wall. Five different spacings between the rings were considered as p = d/2, p = d, p = 3d/2, p = 2d and p = 3d. Uniform heat flux was applied to the external surface of the tube and air was selected as working fluid. Numerical calculations were performed with FLUENT 6.1.22 code, in the range of Reynolds number 4475-43725. The results obtained from a smooth tube were compared with those from the studies in literature in order to validate the numerical method. Consequently, the variation of Nusselt number, friction factor and overall enhancement ratios for the tube with rings were presented and the best overall enhancement of 18% was achieved for Re = 15,600 for which the spacing between the rings is 3d

Developing the laminar MHD forced convection flow of water/FMWNT carbon nanotubes in a microchannel imposed the uniform heat flux

Energy Technology Data Exchange (ETDEWEB)

Karimipour, Arash; Taghipour, Abdolmajid [Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad (Iran, Islamic Republic of); Malvandi, Amir, E-mail: amirmalvandi@aut.ac.ir [Department of Mechanical Engineering, Neyshabur Branch, Islamic Azad University, Neyshabur (Iran, Islamic Republic of)

2016-12-01

This paper aims to investigate magnetic field and slip effects on developing laminar forced convection of nanofluids in the microchannels. A novel mixture of water and FMWNT carbon nanotubes is used as the working fluid. To do this, fluid flow and heat transfer through a microchannel is simulated by a computer code in FORTRAN language. The mixture of FMWNT carbon nanotubes suspended in water is considered as the nanofluid. Slip velocity is supposed as the hydrodynamic boundary condition while the microchannel's lower wall is insulated and the top wall is under the effect of a constant heat flux. Moreover, the flow field is subjected to a magnetic field with a constant strength. The results are presented as the velocity, temperature and Nusselt number profiles. It is observed that nanofluid composed of water and carbon nanotubes (FMWNT) can work well to increase the heat transfer rate along the microchannel walls. Furthermore, it is indicated that imposing the magnetic field is very effective at the thermally developing region. In contrast, the magnetic field effect at fully developed region is insignificant, especially at low values of Reynolds number. - Highlights: • Simulation of water/FMWNT carbon nanotubes flow in a microchannel. • The effects of magnetic field strength on nanofluid's slip velocity. • The effects of Ha, Re, ϕ and slip coefficient on averaged Nusselt number. • Magnetic field effect at developing flow region is significant.

Heat transfer measurements of internally heated liquids in cylindrical convection cells

International Nuclear Information System (INIS)

Fieg, G.

1978-10-01

In hypothetical reactor accidents, the thermohydraulic behaviour of core melts heated by the after-heat must be analyzed. For this purpose model experiments have been performed to study the stationary, natural convective heat transfer of internally heated fluids in cylindrical convertion cells investigating also the influence of geometry (aspect ratio) as well as of difference thermal wall conditions on to the heat transport characteristics. Axial temperature profiles, local heat flux densities at the vertical walls and their dependence, on the external Rayleigh number ar in detail reported, besides the Nusselt vs Rayleigh correlations for the aspect ratios HID=1 and 0,25. The results of these experiments are compared, as for ar possible, with existing thermohydraulic codes and simpler model asoumptions like the zone-model of Baker et. al. and after experimental verification, be used to study realistic PAHR situations. Velocity measurements by means of Laser-Doppler-Method yield information about the flow characteristics near the vertical walls and within the central part of the convecting fluid. (GL) [de

Moisture Research - Optimizing Wall Assemblies

Energy Technology Data Exchange (ETDEWEB)

Arena, L.; Mantha, P.

2013-05-01

The Consortium for Advanced Residential Buildings (CARB) evaluated several different configurations of wall assemblies to determine the accuracy of moisture modeling and make recommendations to ensure durable, efficient assemblies. WUFI and THERM were used to model the hygrothermal and heat transfer characteristics of these walls.

Current-induced domain wall motion: Separating spin torque and Oersted-field effects in Co/Pt nanowires

Energy Technology Data Exchange (ETDEWEB)

Heinen, Jan; Boulle, Olivier; Rousseau, Kevin; Malinowski, Gregory; Klaeui, Mathias [Universitaet Konstanz, Fachbereich Physik, D-78457 Konstanz (Germany); Swagton, Henk J.; Koopmans, Bert [Eindhoven University of Technology, Department of Applied Physics, MB 5600 (Netherlands); Ulysse, Christian; Faini, Giancarlo [CNRS, Phynano team, Laboratoire de Photonique et de Nanostructures, 91460 Marcoussis (France)

2010-07-01

We report on magnetotransport studies on perpendicularly magnetized nanowires with narrow domain wall (DW) structures. Using Co/Pt multilayer nanowires, we have previously shown that Joule heating is concealing most of the current induced domain wall effects, but using a constant sample temperature a large non-adiabacity factor {beta} has been deduced. Here, we carry out experiments for both applied field directions and current polarities, starting from different DW configurations within a Hall cross. We clearly show, using the different symmetries of spin torque and Oersted-field, that the much debated Oersted-field does not contribute to the DW depinning significantly. This allows us to extract the spin torque contribution and the non-adiabacity factor {beta}, which turns out to be in line with previous measurements.

An investigation of the heat transfer and static pressure on the over-tip casing wall of an axial turbine operating at engine representative flow conditions. (II). Time-resolved results

International Nuclear Information System (INIS)

Thorpe, S.J.; Yoshino, S.; Ainsworth, R.W.; Harvey, N.W.

2004-01-01

This article reports the measurements of time-resolved heat transfer rate and time-resolved static pressure that have been made on the over-tip casing of a transonic axial-flow turbine operating at flow conditions that are representative of those found in modern gas turbine engines. This data is discussed and analysed in the context of explaining the physical mechanisms that influence the casing heat flux. The physical size of the measurement domain was one nozzle guide vane-pitch and from -20% to +80% rotor axial chord. Additionally, measurements of the time-resolved adiabatic wall temperature are presented. The time-mean data from the same set of experiments is presented and discussed in Part I of this article. The nozzle guide vane exit flow conditions in these experiments were a Mach number of 0.93 and a Reynolds number of 2.7 x 10 6 based on nozzle guide vane mid-height axial chord. The data reveal large temporal variations in heat transfer characteristics to the casing wall that are associated with blade-tip passing events and in particular the blade over-tip leakage flow. The highest instantaneous heat flux to the casing wall occurs within the blade-tip gap, and this has been found to be caused by a combination of increasing flow temperature and heat transfer coefficient. The time-resolved static pressure measurements have enabled a detailed understanding of the tip-leakage aerodynamics to be established, and the physical mechanisms influencing the casing heat load have been determined. In particular, this has focused on the role of the unsteady blade lift distribution that is produced by upstream vane effects. This has been seen to modulate the tip-leakage flow and cause subsequent variations in casing heat flux. The novel experimental techniques employed in these experiments have allowed the measurement of the time-resolved adiabatic wall temperature on the casing wall. These data clearly show the falling flow temperatures as work is extracted from the gas

Generalized irreversible heat-engine experiencing a complex heat-transfer law

International Nuclear Information System (INIS)

Chen Lingen; Li Jun; Sun Fengrui

2008-01-01

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

Location and optimization analysis of capillary tube network embedded in active tuning building wall

International Nuclear Information System (INIS)

Niu, Fuxin; Yu, Yuebin

2016-01-01

In this study, a building wall with a thermal tuning function is further investigated. This design turns the building wall from a passive thermal system to an active system. A capillary tube network is installed inside the wall to manipulate the thermodynamics and realize more flexibility and potentials of the wall. This novel building wall structure performs efficiently in terms of building load reduction and supplementary heating and cooling, and the structure is convenient for applying low grade or natural energy with a wider temperature range. The capillary tube network's location inside the wall greatly impacts the thermal and energy performance of the building wall. The effects of three locations including external, middle and internal side are analyzed. The results indicate that the internal wall surface temperature can be neutralized from the ambient environment when the embedded tubes are fed with thermal water. The wall can work with a wide range of water temperature and the optimal location of the tube network is relatively constant in different modes. Power benefit with the wall changes from 2 W to 39 W when the outdoor air temperature changes, higher in summer than in winter. - Highlights: • A building wall with a tuning function is proposed using a capillary pipe network. • Low-grade thermal water can be used to actively manipulate the thermal mass. • Location of the capillary network is investigated to maximize the performance. • The innovation can potentially lower down the grade of energy use in buildings.

Integrity of the first wall in fusion reactors

International Nuclear Information System (INIS)

Kurihara, Ryoichi

2004-07-01

Future fusion power reactors DREAM and A-SSTR2, which have been conceptually designed in the Japan Atomic Energy Research Institute, use the SiC/SiC composite material as the first wall of the blanket because of its characteristics of high heat-resistance and low radiation material. DEMO reactor, which was conceptually designed in 2001, uses the low activation ferritic steel as the first-wall material of the blanket. The problems in the thermal structural design of the plasma facing component such as the blanket first wall and the divertor plate which receives very high heat flux were examined in the design of the fusion power reactors. Compact high fusion power reactor must give high heat flux and high-speed neutron flux from the plasma to the first wall and the divertor plate. In this environmental situation, the micro cracks should be generated in material of the first wall. Structural integrity of the first wall would be very low during the operation of the reactor, if those micro-cracks grow in a crack having significant size by the fatigue or the creep. The crack penetration in the first wall can be a factor which threatens the safety of the fusion power reactor. This paper summarizes the problems on the structural integrity in the first wall made of the SiC/SiC composite material or the ferritic steel. (author)

B-meson decay constants from 2+1-flavor lattice QCD with domain-wall light quarks and relativistic heavy quarks

Energy Technology Data Exchange (ETDEWEB)

Christ, Norman H. [Columbia Univ., New York, NY (United States); Flynn, Jonathan M. [Univ. of Southampton, Southampton (United Kingdom); Izubuchi, Taku [Brookhaven National Lab. (BNL), Upton, NY (United States); Kawanai, Taichi [RIKEN, Wako (Japan); Brookhaven National Lab. (BNL), Upton, NY (United States); Lehner, Christoph [Brookhaven National Lab. (BNL), Upton, NY (United States); Soni, Amarjit [Brookhaven National Lab. (BNL), Upton, NY (United States); Van de Water, Ruth S. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Witzel, Oliver [Boston Univ., Boston, MA (United States)

2015-03-10

We calculate the B-meson decay constants f_B, f_Bs, and their ratio in unquenched lattice QCD using domain-wall light quarks and relativistic b-quarks. We use gauge-field ensembles generated by the RBC and UKQCD collaborations using the domain-wall fermion action and Iwasaki gauge action with three flavors of light dynamical quarks. We analyze data at two lattice spacings of a ≈ 0.11, 0.086 fm with unitary pion masses as light as M_π ≈ 290 MeV; this enables us to control the extrapolation to the physical light-quark masses and continuum. For the b-quarks we use the anisotropic clover action with the relativistic heavy-quark interpretation, such that discretization errors from the heavy-quark action are of the same size as from the light-quark sector. We renormalize the lattice heavy-light axial-vector current using a mostly nonperturbative method in which we compute the bulk of the matching factor nonperturbatively, with a small correction, that is close to unity, in lattice perturbation theory. We also improve the lattice heavy-light current through O(α_sa). We extrapolate our results to the physical light-quark masses and continuum using SU(2) heavy-meson chiral perturbation theory, and provide a complete systematic error budget. We obtain f_B⁰ = 196.2(15.7) MeV, f_B⁺ = 195.4(15.8) MeV, f_Bs = 235.4(12.2) MeV, f_Bs/f_B⁰ = 1.193(59), and f_Bs/f_B⁺ = 1.220(82), where the errors are statistical and total systematic added in quadrature. In addition, these results are in good agreement with other published results and provide an important independent cross check of other three-flavor determinations of B-meson decay constants using staggered light quarks.

Behavior of lithium ions in the turbulent near-wall tokamak plasma under heating of ions and electrons of the main plasma

International Nuclear Information System (INIS)

Shurygin, R. V.; Morozov, D. Kh.

2014-01-01

Turbulent dynamics of the near-wall tokamak plasma is simulated by numerically solving the nonlinear reduced Braginskii magnetohydrodynamic equations with allowance for a lithium ion admixture. The effects of turbulence and radiation of the admixture are analyzed in the framework of a self-consistent approach. The radial distributions of the radiative loss power and the density of Li 0 atoms and Li +1 ions are obtained as functions of the electron and ion temperatures of the main plasma in the near-wall layer. The results of numerical simulations show that supply of lithium ions into the low-temperature near-wall plasma substantially depends on whether the additional power is deposited into the electron or ion component of the main plasma. If the electron temperature in the layer increases (ECR heating), then the ion density drops. At the same time, an increase in the temperature of the main ions (ICR heating) leads to an increase in the density of Li +1 ions. The results of numerical simulations are explained by the different influence of the electron and ion temperatures on the atomic processes governing the accumulation and loss of particles in the balance equations for neutral Li 0 atoms and Li +1 ions in the admixture. The radial profile of the electron temperature and the corresponding distribution of the radiative loss power for different densities of neutral Li 0 atoms on the wall are obtained. The calculations show that the presence of Li +1 ions affects turbulent transport of the main ions. In this case, the electron heat flux increases by 20–30% with increasing Li +1 density, whereas the flux of the main ions drops by nearly the same amount. The radial profile of the turbulent flux of lithium ions is obtained. It is demonstrated that the appearance of the pinch effect is related to the positive density gradient of lithium ions across the calculation layer. For the parameters of the T-10 tokamak, the effect of radiative cooling of the near-wall plasma

Analysis and optimization of the heat-insulating light concrete hollow brick walls design by the finite element method

International Nuclear Information System (INIS)

Coz Diaz, J.J. del; Garcia Nieto, P.J.; Betegon Biempica, C.; Prendes Gero, M.B.

2007-01-01

Department of Public Works, owners and building proprietors are demanding high-capacity heat-insulating exterior masonry components specifically for further energy savings. For housing and industrial structures there is also a great interest in light building materials with good physical material behaviour, with respect to an energy conscious and ecological design, which fulfils all strength and serviceability requirements. The major variables influencing the thermal conductivity of masonry materials are illustrated in this work by taking blocks made from no-fine lightweight concrete and different mortar properties. The finite element method (FEM) is used for finding accurate solutions of the heat transfer equation for five different light concrete hollow brick walls. Mathematically, the non-linearity is due to the radiation boundary condition inside the inner recesses of the bricks. The conduction and convection phenomena are taking into account in this study for three different values of the mortar conductivity and three different values for the bricks. Optimization of the walls is carried out from the finite element analysis of five hollow brick geometries by means of the mass overall thermal efficiency and the equivalent thermal conductivity. Finally, conclusions of this work are exposed

Analysis and optimization of the heat-insulating light concrete hollow brick walls design by the finite element method

Energy Technology Data Exchange (ETDEWEB)

Coz Diaz, J.J. del; Betegon Biempica, C.; Prendes Gero, M.B. [Edificio Departamental Viesques, No 7, 33204 Gijon (Asturias) (Spain); Garcia Nieto, P.J. [Departamento de Matematicas, Facultad de Ciencias, C/Calvo Sotelo s/n, 33007 Oviedo (Asturias) (Spain)

2007-06-15

Department of Public Works, owners and building proprietors are demanding high-capacity heat-insulating exterior masonry components specifically for further energy savings. For housing and industrial structures there is also a great interest in light building materials with good physical material behaviour, with respect to an energy conscious and ecological design, which fulfils all strength and serviceability requirements. The major variables influencing the thermal conductivity of masonry materials are illustrated in this work by taking blocks made from no-fine lightweight concrete and different mortar properties. The finite element method (FEM) is used for finding accurate solutions of the heat transfer equation for five different light concrete hollow brick walls. Mathematically, the non-linearity is due to the radiation boundary condition inside the inner recesses of the bricks. The conduction and convection phenomena are taking into account in this study for three different values of the mortar conductivity and three different values for the bricks. Optimization of the walls is carried out from the finite element analysis of five hollow brick geometries by means of the mass overall thermal efficiency and the equivalent thermal conductivity. Finally, conclusions of this work are exposed. (author)

Design studies of an aluminum first wall for INTOR

International Nuclear Information System (INIS)

Powell, J.R.; Fillo, J.A.; Yu, W.S.; Hsieh, S.Y.; Pearlman, H.; Kramer, R.; Franz, E.; Craig, A.; Farrell, K.

1980-01-01

Besides the high erosion rates (including evaporation) expected for INTOR, there may also be high heat fluxes to the first wall, e.g., approx. 9 (Case I) to 24 (Case II) W/cm 2 , from two sources - radiation and charge exchange neutrals. There will also be internal heat generation by neutron and gamma deposition. An aluminum first wall design is analyzed, which substantially reduces concerns about survivability of the first wall during INTOR's operating life

Heat Loss Evaluation of the SMART-ITL Primary System

International Nuclear Information System (INIS)

Ryu, Sung Uk; Bae, Hwang; Kim, Dong Eok; Park, Keun Tae; Park, Hyun Sik; Yi, Sung Jae

2013-01-01

It is considered that the heat loss rate is one of the critical factors affecting the transient behavior of an integral effect test facility. This paper presents the experimental results of the heat loss rate for the primary system of a SMART-ITL (System-Integrated Modular Advanced ReacTor-Integral Test Loop) facility including the pressurizer (PZR). To evaluate the heat loss rate of the primary system, two different approaches were pursued, i. e., integral and differential approaches. The integral approach is a constant temperature method which controls the core and PZR powers at a desired temperature condition and the differential approach is a natural cooling-down measurement method that lasts for a long period of time. In the present work, the heat losses derived from integral and differential approaches were acquired for the primary system of the SMART-ITL. The results obtained by the two approaches were very similar. In addition, an empirical correlation with respect to the difference between the wall temperature and the ambient temperature was proposed to represent the heat loss characteristics of the SMART-ITL facility. The estimated heat losses could be used to estimate the heat loss during the tests and code simulations

Production of Cu/diamond composites for first-wall heat sinks

International Nuclear Information System (INIS)

Nunes, D.; Correia, J.B.; Carvalho, P.A.; Shohoji, N.; Fernandes, H.; Silva, C.; Alves, L.C.; Hanada, K.; Osawa, E.

2011-01-01

Due to their suitable thermal conductivity and strength, copper-based materials have been considered appropriate heat sinks for first wall panels in nuclear fusion devices. However, increased thermal conductivity and mechanical strength are demanded and the concept of property tailoring involved in the design of metal matrix composites advocates for the potential of nanodiamond dispersions in copper. Copper-nanodiamond composite materials can be produced by mechanical alloying followed by a consolidation operation. Yet, this powder metallurgy route poses several challenges: nanodiamond presents intrinsically difficult bonding with copper; contamination by milling media must be closely monitored; and full densification and microstructural homogeneity should be obtained with consolidation. The present line of work is aimed at an optimization of the processing conditions of Cu-nanodiamond composites. The challenges mentioned above have been addressed, respectively, by incorporating chromium in the matrix to form a stable carbide interlayer binding the two components; by assessing the contamination originating from the milling operation through particle-induced X-ray emission spectroscopy; and by comparing the densification obtained by spark plasma sintering with hot-extrusion data from previous studies.

Connection of thin-walled casings

Energy Technology Data Exchange (ETDEWEB)

Druyan, V.M.; Grinev, A.F.; Gruzdev, V.D.; Perchanik, V.V.; Syplenko, V.T.

1981-08-28

A connection is suggested for castings which contains a nipple and coupling part with conical triangular threading. in order to improve the strength of the connection of thin-walled casings with ratio D/S>22, where D is the outer diameter of the casing, S is the thickness of the wall of the casing, the end of the pipe on the length from the end to the main plane of the thread is conical with constant thickness of the wall and conicity eqal to the conicity of the thread.

Optical measurement of water over-heating in contact with a wall submitted to a quick temperature rise under atmospheric pressure

International Nuclear Information System (INIS)

Ebrardt, Jacques

1981-01-01

As a technique is necessary for the instantaneous measurement of a liquid temperature at the immediate vicinity of a wall submitted to a quick unsteady heating, this research thesis reports the development of such a technique, and its use for the determination of the temperature reached by the liquid before boiling in unsteady regime. After a report of a literature survey on the unsteady heating of liquid (by thermal shock or progressive heating), and on various theoretical aspects, the author reports the use of a measurement installation which is based on the use of optical interferometry, and on the exploitation of raw experimental data. Results of overheating at boiling initiation are interpreted [fr

Wall roughness induces asymptotic ultimate turbulence

NARCIS (Netherlands)

Zhu, Xiaojue; Verschoof, Ruben Adriaan; Bakhuis, Dennis; Huisman, Sander Gerard; Verzicco, Roberto; Sun, Chao; Lohse, Detlef

2018-01-01

Turbulence governs the transport of heat, mass and momentum on multiple scales. In real-world applications, wall-bounded turbulence typically involves surfaces that are rough; however, characterizing and understanding the effects of wall roughness on turbulence remains a challenge. Here, by

Effects of quantum entropy on bag constant

International Nuclear Information System (INIS)

Miller, D.E.; Tawfik, A.

2012-01-01

The effects of quantum entropy on the bag constant are studied at low temperatures and for small chemical potentials. The inclusion of the quantum entropy of the quarks in the equation of state provides the hadronic bag with an additional heat which causes a decrease in the effective latent heat inside the bag. We have considered two types of baryonic bags, Δ and Ω - . In both cases we have found that the bag constant without the quantum entropy almost does not change with temperature and quark chemical potential. The contribution from the quantum entropy to the equation of state clearly decreases the value of the bag constant. Furthermore, we construct states densities for quarks using the 'Thomas Fermi model' and take into consideration a thermal potential for the interaction. (author)

Heat transfer, condensation and fog formation in crossflow plastic heat exchangers

NARCIS (Netherlands)

Brouwers, H.J.H.

1996-01-01

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

Natural convective flows in a horizontal channel provided with heating isothermal blocks: Effect of the inter blocks spacing

International Nuclear Information System (INIS)

Bakkas, M.; Hasnaoui, M.; Amahmid, A.

2010-01-01

A numerical study of laminar steady natural convection induced in a two dimensional horizontal channel provided with rectangular heating blocks, periodically mounted on its lower wall, is carried out. The blocks' surface temperature, T H ' , is maintained constant and the former are connected with adiabatic surfaces. The upper wall of the channel is maintained cold at a temperature T C ' H ' . Fluid flow, temperature fields and heat transfer rates are presented for different combinations of the governing parameters which are the Rayleigh number (10 2 ≤Ra≤2x10 6 ), the blocks' spacing (1/4≤C=l ' /H ' ≤1), the blocks' height (1/8≤B=h ' /H ' ≤1/2) and the relative width of the blocks (A=(L ' -l ' )/H ' =1/2). The results obtained in the case of air (Pr = 0.72) show that the flow structure and the heat transfer are significantly influenced by the control parameters. It is found that there are situations where the increase of the blocks' spacing leads to a reduction of heat transfer.

MHD mixed convection flow and heat transfer in an open C-shaped enclosure using water-copper oxide nanofluid

Science.gov (United States)

Armaghani, T.; Esmaeili, H.; Mohammadpoor, Y. A.; Pop, I.

2018-01-01

In this paper, the steady mixed convection flow and heat transfer of water-copper oxide nanofluid in an open C-shaped enclosure is investigated numerically. The enclosure is under constant magnetic field. Effects of Richardson number, magnetic and nanofluid volume fraction parameters are studied and discussed. The nanofluid with a cold temperature of T C and a velocity of u c enters the enclosure from the top right corner and exits from the bottom right corner. The vertical wall of the left side is subjected to a hot and constant temperature T h . Also, other walls are insulated. It is found that the heat transfer is increased via increasing the Hartmann and Reynolds numbers. For low Reynolds numbers, the enhances of the Hartman number leads to a slightly increases of the average Nusselt number, but for high Reynolds numbers, the average Nusselt number gets an ascending trend and the increase in the Hartmann number shows its effect more pronounced. Also, with increase in Ri, the effect of nanofluid on the heat transfer increases. Due to practical impotence, the study of mixed convection heat transfer in enclosures and various shaped of cavities has attracted remarkable attentions in the past few decades. Significant applications of the mixed convection flow can be found in atmospheric flows, solar energy storage, heat exchangers, lubrication technology, drying technologies, cooling of the electronic devices, etc. The present results are original and new for the problem of MHD mixed convection flow and heat transfer in an open C-shaped enclosure using water-copper oxide nanofluid. Comparison of the obtained results with those from the open literature (Mahmoodi et al. [24]) is acceptable.

Natural convection in wavy enclosures with volumetric heat sources

International Nuclear Information System (INIS)

Oztop, H.F.; Varol, Y.; Abu-Nada, E.; Chamkha, A.

2011-01-01

In this paper, the effects of volumetric heat sources on natural convection heat transfer and flow structures in a wavy-walled enclosure are studied numerically. The governing differential equations are solved by an accurate finite-volume method. The vertical walls of enclosure are assumed to be heated differentially whereas the two wavy walls (top and bottom) are kept adiabatic. The effective governing parameters for this problem are the internal and external Rayleigh numbers and the amplitude of wavy walls. It is found that both the function of wavy wall and the ratio of internal Rayleigh number (Ra I ) to external Rayleigh number (Ra E ) affect the heat transfer and fluid flow significantly. The heat transfer is predicted to be a decreasing function of waviness of the top and bottom walls in case of (IRa/ERa)>1 and (IRa/ERa)<1. (authors)

Study of heat exchange in cooling systems of heat-stressed structures

Science.gov (United States)

Vikulin, A. V.; Yaroslavtsev, N. L.; Zemlyanaya, V. A.

2017-01-01

Increasing working parameters of the cycle of gas-turbine engines, complicating design of gas-turbine plants, as well as growing aerodynamic, thermal, static, and dynamic loads, necessitate the development of promising cooling systems for heat-stressed structures. This work is devoted to an experimental study of heat exchange in ducts equipped with systems of inclined and cross walls (fins). It has been found that an increase in the Reynolds number Re from 3000 to 20000 leads to a decrease in the heat exchange, which is characterized by the relative Nusselt number overline{Nu}, by 19-30% at the angle of inclination of the walls φ = 0, 40°, 50°, and 90° if the length of the walls x w is comparable to the spacing b s and by 12-15% at φ = 30° and 90° if x w ≫ b s. If cross walls are used in cooling ducts, the length of the walls x w plays the governing role; an increase in this characteristic from 1.22 × 10-3 to 3.14 × 10-3 m leads to an increase in the intensity of heat exchange by 30-40% and to a decrease in the capacity of the entire system of the walls. It has been shown that, on surfaces with wavy fins, the intensity of heat exchange is closest to that determined in the models under study. For example, values of the Colborne criterion StPr2/3 for ducts equipped with wavy fins and for the models under study differ only slightly (by 2-20% depending on the value of the angle φ). However, the difference for surfaces with short plate fins and ducts equipped with inclined walls is high (30-40%). This is due to the design features of these surfaces and to the severe effect of the inlet portion on heat exchange, since the surfaces are characterized by a higher ratio of the duct length to the hydraulic diameter L/d h at small fin thicknesses ((0.1-0.15) × 10-3 m). The experimental results can be used in developing designs of nozzle and rotor blades of high-temperature gas turbines in gas-turbine engines and plants.

Experiment and Simulation Study on the Amorphous Silicon Photovoltaic Walls

Directory of Open Access Journals (Sweden)

Wenjie Zhang

2014-01-01

Full Text Available Based on comparative study on two amorphous silicon photovoltaic walls (a-Si PV walls, the temperature distribution and the instant power were tested; and with EnergyPlus software, similar models of the walls were built to simulate annual power generation and air conditioning load. On typical sunshine day, the corresponding position temperature of nonventilated PV wall was generally 0.5~1.5°C higher than that of ventilated one, while the power generation was 0.2%~0.4% lower, which was consistent with the simulation results with a difference of 0.41% in annual energy output. As simulation results, in summer, comparing the PV walls with normal wall, the heat per unit area of these two photovoltaic walls was 5.25 kWh/m2 (nonventilated and 0.67 kWh/m2 (ventilated higher, respectively. But in winter the heat loss of nonventilated one was smaller, while ventilated PV wall was similar to normal wall. To annual energy consumption of heating and cooling, the building with ventilated PV wall and normal wall was also similar but slightly better than nonventilated one. Therefore, it is inferred that, at low latitudes, such as Zhuhai, China, air gap ventilation is suitable, while the length to thickness ratio of the air gap needs to be taken into account.

Performance of the PDX neutral beam wall armor

International Nuclear Information System (INIS)

Kugel, H.W.; Eubank, H.P.; Kozub, T.A.; Williams, M.D.

1985-02-01

The PDX wall armor was designed to function as an inner wall thermal armor, a neutral beam diagnostic, and a large area inner toroidal plasma limiter. In this paper we discuss its thermal performance as wall armor during two years of PDX neutral beam heating experiments. During this period it provided sufficient inner wall protection to permit perpendicular heating injections into normal and disruptive plasmas as well as injections in the absence of plasma involving special experiments, calibrations, and tests important for the optimization and development of the PDX neutral beam injection system. Many of the design constraints and performance issues encountered in this work are relevant to the design of larger fusion devices

Atomic weights: no longer constants of nature

Science.gov (United States)

Coplen, Tyler B.; Holden, Norman E.

2011-01-01

Many of us were taught that the standard atomic weights we found in the back of our chemistry textbooks or on the Periodic Table of the Chemical Elements hanging on the wall of our chemistry classroom are constants of nature. This was common knowledge for more than a century and a half, but not anymore. The following text explains how advances in chemical instrumentation and isotopic analysis have changed the way we view atomic weights and why they are no longer constants of nature

Hot wire production of single-wall and multi-wall carbon nanotubes

Science.gov (United States)

Dillon, Anne C.; Mahan, Archie H.; Alleman, Jeffrey L.

2010-10-26

Apparatus (210) for producing a multi-wall carbon nanotube (213) may comprise a process chamber (216), a furnace (217) operatively associated with the process chamber (216), and at least one filament (218) positioned within the process chamber (216). At least one power supply (220) operatively associated with the at least one filament (218) heats the at least one filament (218) to a process temperature. A gaseous carbon precursor material (214) operatively associated with the process chamber (216) provides carbon for forming the multi-wall carbon nanotube (213). A metal catalyst material (224) operatively associated with the process (216) catalyzes the formation of the multi-wall carbon nanotube (213).

Fully developed natural convection heat and mass transfer in a vertical annular porous medium with asymmetric wall temperatures and concentrations

International Nuclear Information System (INIS)

Cheng, C.-Y.

2006-01-01

This work examines the effects of the modified Darcy number, the buoyancy ratio and the inner radius-gap ratio on the fully developed natural convection heat and mass transfer in a vertical annular non-Darcy porous medium with asymmetric wall temperatures and concentrations. The exact solutions for the important characteristics of fluid flow, heat transfer, and mass transfer are derived by using a non-Darcy flow model. The modified Darcy number is related to the flow resistance of the porous matrix. For the free convection heat and mass transfer in an annular duct filled with porous media, increasing the modified Darcy number tends to increase the volume flow rate, total heat rate added to the fluid, and the total species rate added to the fluid. Moreover, an increase in the buoyancy ratio or in the inner radius-gap ratio leads to an increase in the volume flow rate, the total heat rate added to the fluid, and the total species rate added to the fluid

Nusselt correlation to predict heat transfer from an oscillated vertical annular fluid column through a porous domain

Science.gov (United States)

Sayar, Ersin; Sari, Ugurcan

2017-04-01

Experimental evaluation of the heat transfer in oscillating flow under the constant heat flux and constant amplitude fluid displacement conditions is presented for a vertical annular flow through a stainless steel wool porous media. The analysis is carried out for two different heat fluxes and for five different frequencies. The data is acquired from the measurements both in the initial transient period and in the pseudo-steady (cyclic) period by the system. The physical and mathematical behavior of the resulting Nusselt numbers are analyzed, according to data acquired from the experiments and in accordance with the results of the Buckingham Pi theorem. A cycle and space averaged Nusselt number correlation is suggested as a function of kinetic Reynolds number for oscillating flows. The suggested correlation is useful in predicting heat transfer from oscillating flows through highly porous and permeable solid media at low actuation frequencies and at low heat fluxes applied in the wall. The validity of the Nusselt numbers acquired by correlation is discussed using experimental Nusselt numbers for the selected kinetic Reynolds number interval. The present investigation has possible applications in moderate sized wicked heat pipes, solid matrix compact heat exchangers compromising of metallic foams, filtration equipment, and steam generators.

Numerical investigation of nucleate pool boiling heat transfer

Directory of Open Access Journals (Sweden)

Stojanović Andrijana D.

2016-01-01

Full Text Available Multidimensional numerical simulation of the atmospheric saturated pool boiling is performed. The applied modelling and numerical methods enable a full representation of the liquid and vapour two-phase mixture behaviour on the heated surface, with included prediction of the swell level and heated wall temperature field. In this way the integral behaviour of nucleate pool boiling is simulated. The micro conditions of bubble generation at the heated wall surface are modelled by the bubble nucleation site density, the liquid wetting contact angle and the bubble grow time. The bubble nucleation sites are randomly located within zones of equal size, where the number of zones equals the nucleation site density. The conjugate heat transfer from the heated wall to the liquid is taken into account in wetted heated wall areas around bubble nucleation sites. The boiling curve relation between the heat flux and the heated wall surface temperature in excess of the saturation temperature is predicted for the pool boiling conditions reported in the literature and a good agreement is achieved with experimentally measured data. The influence of the nucleation site density on the boiling curve characteristic is confirmed. In addition, the influence of the heat flux intensity on the spatial effects of vapour generation and two-phase flow are shown, such as the increase of the swell level position and the reduced wetting of the heated wall surface by the heat flux increase. [Projekat Ministarstva nauke Republike Srbije, br. TR-33018 i br. OI-174014

Fluid-thermal analysis of aerodynamic heating over spiked blunt body configurations

Science.gov (United States)

Qin, Qihao; Xu, Jinglei; Guo, Shuai

2017-03-01

When flying at hypersonic speeds, the spiked blunt body is constantly subjected to severe aerodynamic heating. To illustrate the thermal response of different configurations and the relevant flow field variation, a loosely-coupled fluid-thermal analysis is performed in this paper. The Mesh-based parallel Code Coupling Interface (MpCCI) is adopted to implement the data exchange between the fluid solver and the thermal solver. The results indicate that increases in spike diameter and length will result in a sharp decline of the wall temperature along the spike, and the overall heat flux is remarkably reduced to less than 300 W/cm2 with the aerodome mounted at the spike tip. Moreover, the presence and evolution of small vortices within the recirculation zone are observed and proved to be induced by the stagnation effect of reattachment points on the spike. In addition, the drag coefficient of the configuration with a doubled spike length presents a maximum drop of 4.59% due to the elevated wall temperature. And the growing difference of the drag coefficient is further increased during the accelerating process.

A small cosmological constant and backreaction of non-finetuned parameters

International Nuclear Information System (INIS)

Krause, Axel

2003-01-01

We include the backreaction on warped geometry induced by non-finetuned parameters in a two domain-wall set-up to obtain an exponentially small Cosmological Constant Λ4. The mechanism to suppress the Cosmological Constant involves one classical fine-tuning as compared to an infinity of finetunings at the quantum level in standard D = 4 field theory. (author)

Condensation on a cooled plane upright wall

International Nuclear Information System (INIS)

Fortier, Andre.

1975-01-01

The vapor condensation along a cooled upright plane wall was studied. The theoretical and experimental results obtained in the simple case, give the essential characteristics of the phenomenon of condensation along a cold wall that keeps the vapor apart from the coolant inside a surface condenser. The phenomenon presents two different appearances according as the wall is wetted or not by the liquid. In the first case a continuous liquid film runs down the wall and a conventional Nusselt calculation gives the film thickness and the heat exchange coefficient between a pure saturated vapor and the cold wall. The calculation is developed in detail and the effect of a vapor flow along the film is discussed as well as that of the presence of a noncondensable gas inside the vapor. In the second case, separated liquid drops are formed on the wall, the phenomenon is called ''dropwise condensation'' and the heat exchange coefficients obtained are much higher than with film condensation. The theoretical aspects of the problem are discussed with some experimental results [fr

Analysis of wall-packed-bed thermal interactions

International Nuclear Information System (INIS)

Gorbis, Z.R.; Tillack, M.S.; Tehranian, F.; Abdou, M.A.

1995-01-01

One of the major issues remaining for ceramic breeder blankets involves uncertainties in heat transfer and thermomechanical interactions within the breeder and multiplier regions. Particle bed forms are considered in many reactor blanket designs for both the breeder and Be multiplier. The effective thermal conductivity of beds and the wall-bed thermal conductance are still not adequately characterized, particularly under the influence of mechanical stresses. The problem is particularly serious for the wall conductance between Be and its cladding, where the uncertainty can be greater than 50%. In this work, we describe a new model for the wall-bed conductance that treats the near-wall region as a finite-width zone. The model includes an estimate of the region porosity based on the number of contact points, and the contact area for smooth surfaces. It solves the heat conduction in a near-wall unit cell. The model is verified with existing data and used to predict the range of wall conductances expected in future simulation experiments and in reactor applications. (orig.)

In-process tool rotational speed variation with constant heat input in friction stir welding of AZ31 sheets with variable thickness

Science.gov (United States)

Buffa, Gianluca; Campanella, Davide; Forcellese, Archimede; Fratini, Livan; Simoncini, Michela

2017-10-01

In the present work, friction stir welding experiments on AZ31 magnesium alloy sheets, characterized by a variable thickness along the welding line, were carried out. The approach adapted during welding consisted in maintaining constant the heat input to the joint. To this purpose, the rotational speed of the pin tool was increased with decreasing thickness and decreased with increasing thickness in order to obtain the same temperatures during welding. The amount by which the rotational speed was changed as a function of the sheet thickness was defined on the basis of the results given by FEM simulations of the FSW process. Finally, the effect of the in-process variation of the tool rotational speed on the mechanical and microstructural properties of FSWed joints was analysed by comparing both the nominal stress vs. nominal strain curves and microstructure of FSWed joints obtained in different process conditions. It was observed that FSW performed by keeping constant the heat input to the joint leads to almost coincident results both in terms of the curve shape, ultimate tensile strength and ultimate elongation values, and microstructure.

First wall fusion blanket temperature variation - slab geometry

International Nuclear Information System (INIS)

Fillo, J.A.

1978-01-01

The first wall of a fusion blanket is approximated by a slab, with the surface facing the plasma subjected to an applied heat flux, while the rear surface is convectively cooled. The relevant parameters affecting the heat transfer during the early phases of heating as well as for large times are established. Analytical solutions for the temperature variation with time and space are derived. Numerical calculations for an aluminum and stainless steel slab are performed for a wall loading of 1 MW(th)/m 2 . Both helium and water cooling are considered. (Auth.)

CONVECTION HEAT TRANSFER IN A CHANNEL OF DIFFERENT CROSS SECTION FILLED WITH POROUS MEDIA

Directory of Open Access Journals (Sweden)

Ahmed A. Mohammad Saleh

2018-05-01

Full Text Available A forced convection heat transfer in ducts (circular, triangular, rectangular cross sections and (1m length with hydraulic diameter (0.1m filled with porous media (glass spheres 12 mm diameter is investigated experimentally at constant heat flux from the wall (1070W/m² with Reynolds number range of (12461-2500. Comparison was made between three ducts for local temperature distribution and local Nusselt number. The experimental results showed the effect of Reynolds number and cross section on the temperature profile and local Nusselt number,also empirical correlations for average Nusselt number and Peclet number were obtained for three ducts.

MHD natural convection in open inclined square cavity with a heated circular cylinder

Science.gov (United States)

Hosain, Sheikh Anwar; Alim, M. A.; Saha, Satrajit Kumar

2017-06-01

MHD natural convection in open cavity becomes very important in many scientific and engineering problems, because of it's application in the design of electronic devices, solar thermal receivers, uncovered flat plate solar collectors having rows of vertical strips, geothermal reservoirs, etc. Several experiments and numerical investigations have been presented for describing the phenomenon of natural convection in open cavity for two decades. MHD natural convection and fluid flow in a two-dimensional open inclined square cavity with a heated circular cylinder was considered. The opposite wall to the opening side of the cavity was first kept to constant heat flux q, at the same time the surrounding fluid interacting with the aperture was maintained to an ambient temperature T∞. The top and bottom wall was kept to low and high temperature respectively. The fluid with different Prandtl numbers. The properties of the fluid are assumed to be constant. As a result a buoyancy force is created inside the cavity due to temperature difference and natural convection is formed inside the cavity. The Computational Fluid Dynamics (CFD) code are used to discretize the solution domain and represent the numerical result to graphical form.. Triangular meshes are used to obtain the solution of the problem. The streamlines and isotherms are produced, heat transfer parameter Nu are obtained. The results are presented in graphical as well as tabular form. The results show that heat flux decreases for increasing inclination of the cavity and the heat flux is a increasing function of Prandtl number Pr and decreasing function of Hartmann number Ha. It is observed that fluid moves counterclockwise around the cylinder in the cavity. Various recirculations are formed around the cylinder. The almost all isotherm lines are concentrated at the right lower corner of the cavity. The object of this work is to develop a Mathematical model regarding the effect of MHD natural convection flow around

A methodology to investigate the contribution of conduction and radiation heat transfer to the effective thermal conductivity of packed graphite pebble beds, including the wall effect

Energy Technology Data Exchange (ETDEWEB)

De Beer, M., E-mail: maritz.db@gmail.com [School of Mechanical and Nuclear Engineering, North-West University, Private Bag X6001, Potchefstroom 2520 (South Africa); Du Toit, C.G., E-mail: Jat.DuToit@nwu.ac.za [School of Mechanical and Nuclear Engineering, North-West University, Private Bag X6001, Potchefstroom 2520 (South Africa); Rousseau, P.G., E-mail: pieter.rousseau@uct.ac.za [Department of Mechanical Engineering, University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa)

2017-04-01

Highlights: • The radiation and conduction components of the effective thermal conductivity are separated. • Near-wall effects have a notable influence on the effective thermal conductivity. • Effective thermal conductivity is a function of the macro temperature gradient. • The effective thermal conductivity profile shows a characteristic trend. • The trend is a result of the interplay between conduction and radiation. - Abstract: The effective thermal conductivity represents the overall heat transfer characteristics of a packed bed of spheres and must be considered in the analysis and design of pebble bed gas-cooled reactors. During depressurized loss of forced cooling conditions the dominant heat transfer mechanisms for the passive removal of decay heat are radiation and conduction. Predicting the value of the effective thermal conductivity is complex since it inter alia depends on the temperature level and temperature gradient through the bed, as well as the pebble packing structure. The effect of the altered packing structure in the wall region must therefore also be considered. Being able to separate the contributions of radiation and conduction allows a better understanding of the underlying phenomena and the characteristics of the resultant effective thermal conductivity. This paper introduces a purpose-designed test facility and accompanying methodology that combines physical measurements with Computational Fluid Dynamics (CFD) simulations to separate the contributions of radiation and conduction heat transfer, including the wall effects. Preliminary results obtained with the methodology offer important insights into the trends observed in the experimental results and provide a better understanding of the interplay between the underlying heat transfer phenomena.

Thermomechanical effects in a laser IFE first wall

International Nuclear Information System (INIS)

Blanchard, James P.; Martin, Carl J.

2005-01-01

Laser fusion chamber walls will experience large, pulsed heat loads at frequencies of several hertz. The heating, consisting of X-rays, neutrons, and ions, occurs over a few microseconds and is deposited volumetrically over the first few microns of the wall. For a reasonable chamber radius, the heating will be such that the surface temperature is a significant fraction of the melt temperature of the wall, and significant plasticity can be expected in ductile wall materials. This paper presents results for the transient temperatures and stresses in a tungsten-coated steel first wall for a laser fusion device. Failure analyses are carried out using both fatigue and fracture mechanics methodologies. The simulations predict that surface cracks are expected in the tungsten, but the cracks will arrest before reaching the substrate if the crack spacing is sufficiently small. In addition, the thermal and stress fields are compared for a laser fusion device with several simulation experiments. It is shown that the simulations can reproduce the peak surface temperatures, but the corresponding spatial distributions of the stress and temperature will be shallower than the reactor case

Natural ventilation in an enclosure induced by a heat source distributed uniformly over a vertical wall

Energy Technology Data Exchange (ETDEWEB)

Chen, Z.D.; Li, Y.; Mahoney, J. [CSIRO Building, Construction and Engineering, Advanced Thermo-Fluids Technologies Lab., Highett, VIC (Australia)

2001-05-01

A simple multi-layer stratification model is suggested for displacement ventilation in a single-zone building driven by a heat source distributed uniformly over a vertical wall. Theoretical expressions are obtained for the stratification interface height and ventilation flow rate and compared with those obtained by an existing model available in the literature. Experiments were also carried out using a recently developed fine-bubble modelling technique. It was shown that the experimental results obtained using the fine-bubble technique are in good agreement with the theoretical predictions. (Author)

Heat transfer in oscillating flows with sudden change in cross section

Science.gov (United States)

Ibrahim, Mounir; Hashim, Waqar; Tew, Roy C.; Dudenhoefer, James E.

1992-01-01

Oscillating fluid flow (zero mean) with heat transfer, between two parallel plates with a sudden change in cross section, was examined computationally. Over 30 different cases were examined; these cases cover wide ranges of Re sub max (187.5 to 30,000), Va (1 to 350), expansion ratio (1:2, 1:4, 1:8, and 1:12) and A sub r (0.68 to 4). Three different geometric cases were considered (asymmetric expansion and/or contraction, symmetric expansion/contraction, and symmetric blunt body). The heat transfer cases were based on constant wall temperature at higher (heating) or lower (cooling) value than the inflow fluid temperature. As a result of the oscillating flow, the fluid undergoes sudden expansion in one half of the cycle and sudden contraction in the other half. Instantaneous friction factors and heat transfer coefficients, for some ranges of Re sub max and Va, deviated substantially from those predicted with steady state correlations.

Heat and salt budgets over the Gulf Stream North Wall during LatMix survey in winter 2012.

Science.gov (United States)

Sanchez-Rios, A.; Shearman, R. K.; D'Asaro, E. A.; Lee, C.; Gula, J.; Klymak, J. M.

2016-02-01

As part of the ONR-sponsored LatMix Experiment, ship-based and glider-based observations following a Lagrangian float are used to examine the evolution of temperature, salinity and density along the Gulf Stream north wall in wintertime. Satellite observations during the survey and the in-situ measurements showed the presence of submesoscale (1) calculated for this regions corroborates the possibility of submesoscale dynamics. Using a heat and salinity budget, we show that surface forcing, entrainment from below and advection by the mean flow velocities are not sufficient to explain the observed rate of change of heat and salinity in the mixed layer. Although confidence estimates prevent an accurate flux divergence calculation, Reynold flux estimates are consistent with a cross-frontal exchange that can reproduce the observed temporal trends.

Experimental study on the heat transfer of MWCNT/water nanofluid flowing in a car radiator

International Nuclear Information System (INIS)

Oliveira, Guilherme Azevedo; Cardenas Contreras, Edwin Martin; Bandarra Filho, Enio Pedone

2017-01-01

This study is concerned with an experimental evaluation of the thermal performance of multi-walled carbon nanotubes (MWCNT) dispersed in distilled water flowing inside an automotive radiator. A two-step method called high-pressure homogenization was used to disperse the MWCNT nanoparticles in water, in concentrations varying between 0.05 and 0.16 wt%. Experiments have been carried out in an experimental set up composed by a wind tunnel that simulates the air flow through a car radiator, and a hot fluid circuit, that circulates the nanofluid inside the radiator. The air flow rate was maintained constant at 0.175 kg/s. The mass flow rate of the hot fluid varied from 30 up to 70 g/s and the inlet temperature was maintained constant at 50, 60, 70 and 80 °C, respectively. The temperature drop and heat transfer rate have been investigated. A slight-decrease on the heat transfer rate, up to 5%, was found for all test conditions. On the other hand as the nanoparticle concentration increased, the heat transfer rate decreased.

Spray-Wall Impingement of Diesel-CNG Dual Fuel Jet using Schlieren Imaging Technique

Directory of Open Access Journals (Sweden)

Ismael Mhadi Abaker

2014-07-01

Full Text Available Natural gas is a low cost fuel with high availability in nature. However, it cannot be used by itself in conventional diesel engines due to its low flame speed and high ignition temperature. The addition of a secondary fuel to enhance the mixture formation and combustion process facilitate its wider use as an alternative fuel. An experimental study was performed to investigate the diesel-CNG dual fuel jet-wall impingement. A constant volume optical chamber was designed to facilitate maximum optical access for the study of the jet-wall impingement at different injection pressures, temperatures and injector-wall distances. The bottom plate of the test rig was made of aluminum (piston material and it was heated up to 500 K at ambient pressure. An injector driver was used to control the single-hole nozzle diesel injector combined with a natural gas injector. The injection timing of both injectors was synchronized with a camera trigger. The jet-wall impingement of diesel and diesel-CNG dual fuel jets was recorded with a high speed camera using Schlieren imaging technique and associated image processing software. The measurements of the jet radial penetration were higher in diesel-CNG dual fuel while the jet height travel along were higher in the case of diesel single fuel.

Transient Resistive Wall Wake for Very Short Bunches

International Nuclear Information System (INIS)

Stupakov, G.; SLAC

2005-01-01

The catch up distance for the resistive wall wake in a round pipe is approximately equal to the square of the pipe radius divided by the bunch length. The standard formulae for this wake are applicable at distances much larger than the catch up distance. In this paper, we calculate the resistive wall wake at distances compared with the catch up distance assuming a constant wall conductivity

Transitional and turbulent boundary layer with heat transfer

Science.gov (United States)

Wu, Xiaohua; Moin, Parviz

2010-08-01

We report on our direct numerical simulation of an incompressible, nominally zero-pressure-gradient flat-plate boundary layer from momentum thickness Reynolds number 80-1950. Heat transfer between the constant-temperature solid surface and the free-stream is also simulated with molecular Prandtl number Pr=1. Skin-friction coefficient and other boundary layer parameters follow the Blasius solutions prior to the onset of turbulent spots. Throughout the entire flat-plate, the ratio of Stanton number and skin-friction St/Cf deviates from the exact Reynolds analogy value of 0.5 by less than 1.5%. Mean velocity and Reynolds stresses agree with experimental data over an extended turbulent region downstream of transition. Normalized rms wall-pressure fluctuation increases gradually with the streamwise growth of the turbulent boundary layer. Wall shear stress fluctuation, τw,rms'+, on the other hand, remains constant at approximately 0.44 over the range, 800spots are tightly packed with numerous hairpin vortices. With the advection and merging of turbulent spots, these young isolated hairpin forests develop into the downstream turbulent region. Isosurfaces of temperature up to Reθ=1900 are found to display well-resolved signatures of hairpin vortices, which indicates the persistence of the hairpin forests.

The Solar Dynamic Buffer Zone (SDBZ) curtain wall: Validation and design of a solar air collector curtain wall

Science.gov (United States)

Richman, Russell Corey

Given the increases in both the environmental and economic costs of energy, there is a need to design and building more sustainable and low-energy building systems now. Curtain wall assemblies show great promise---the spandrel panels within them can be natural solar collectors. By using a Solar Dynamic Buffer Zone (SDBZ) in the spandrel cavity, solar energy can be efficiently gathered using the movement of air. There is a need for a numerical model capable of predicting performance of an SDBZ Curtain Wall system. This research designed, constructed and quantified a prototype SDBZ curtain wall system through by experimental testing in a laboratory environment. The laboratory experiments focussed on three main variables: air flow through the system, incoming radiation and collector surface type. Results from the experimental testing were used to validate a one-dimensional numerical model of the prototype. Results from this research show a SDBZ curtain wall system as an effective means of reducing building heating energy consumption through the preheating of incoming exterior ventilation air during the heating season in cold climates. The numerical model showed good correlation with experimental results at higher operating flows and at lower flows when using an apparent velocity at the heat transfer boundary layer. A seasonal simulation for Toronto, ON predicted energy savings of 205 kWh/m2 with an average seasonal efficiency of 28%. This is considered in the upper range when compared to other solar air collectors. Given the lack of published literature for similar systems, this research acts to introduce a simple, innovative approach to collect solar energy that would otherwise be lost to the exterior using already existing components within a curtain wall. Specifically, the research has provided: results from experiments and simulation, a first generation numerical model, aspects of design and construction of the SDBZ curtain wall and specific directions for further

On the existence of steady flow in a channel with one porous wall or two accelerating walls

Directory of Open Access Journals (Sweden)

Chunqing Lu

1998-11-01

Full Text Available channel either with no-slip at one wall and constant uniform suction or injection through another wall, or with two accelerating walls. The flows are governed by the fourth order nonlinear differential equation $F^{iv}+R(FF'''-F'F''=0$. In the former case, the flow is subject to the boundary conditions $F(-1=F'(-1=F'(1=0$, $F(1=-1$. In the latter case, the boundary conditions are $F(-1=F(1=0$, $F'(-1=-1$, $F'(1 = 1$.

Solar collector wall with active curtain system; Lasikatteinen massiivienen aurinkokeraeaejaeseinae

Energy Technology Data Exchange (ETDEWEB)

Ojanen, T.; Heimonen, I. [VTT Building Technology, Espoo (Finland). Building Physics, Building Services and Fire Technology

1998-12-01

Integration of solar collector into the building envelope structure brings many advantages. The disadvantage of a passive solar collector wall is that its thermal performance can not be controlled, which may cause temporary overheating and low thermal efficiency of the collector. The thermal performance of the collector wall can be improved by using controllable, active collector systems. In this paper a solar collector wall with a controllable curtain between the transparent and absorption layers is investigated. The curtain is made of several low-emissivity foil layers, which ensures low radiation heat transfer through the curtain. The curtain decreases the heat losses out from the collector wall and it improves the U-value of the wall. The curtain is used when the solar radiation intensity to the wall is not high enough or when the wall needs protection against overheating during warm weather conditions. The materials and building components used in the collector wall, except those of the curtain, are ordinary in buildings. The transparent layer can be made by using normal glazing technology and the thermal storage layer can be made out of brick or similar material. The solar energy gains through the glazing can be utilised better than in passive systems, because the curtain provides the wall with high thermal resistance outside the solar radiation periods. The thermal performance of the collector wall was studied experimentally using a Hot-Box apparatus equipped with a solar lamp. Numerical simulations were carried out to study the yearly performance of the collector wall under real climate conditions. The objectives were to determine the thermal performance of the collector wall and to study how to optimise the use of solar radiation in this system. When the curtain with high thermal resistance is used actively, the temperature level of the thermal storage layer in the wall is relatively high also during dark periods and the heat losses out from the storage

Slip-flow and heat transfer of a non-newtonian nanofluid in a microtube.

Science.gov (United States)

Niu, Jun; Fu, Ceji; Tan, Wenchang

2012-01-01

The slip-flow and heat transfer of a non-Newtonian nanofluid in a microtube is theoretically studied. The power-law rheology is adopted to describe the non-Newtonian characteristics of the flow, in which the fluid consistency coefficient and the flow behavior index depend on the nanoparticle volume fraction. The velocity profile, volumetric flow rate and local Nusselt number are calculated for different values of nanoparticle volume fraction and slip length. The results show that the influence of nanoparticle volume fraction on the flow of the nanofluid depends on the pressure gradient, which is quite different from that of the Newtonian nanofluid. Increase of the nanoparticle volume fraction has the effect to impede the flow at a small pressure gradient, but it changes to facilitate the flow when the pressure gradient is large enough. This remarkable phenomenon is observed when the tube radius shrinks to micrometer scale. On the other hand, we find that increase of the slip length always results in larger flow rate of the nanofluid. Furthermore, the heat transfer rate of the nanofluid in the microtube can be enhanced due to the non-Newtonian rheology and slip boundary effects. The thermally fully developed heat transfer rate under constant wall temperature and constant heat flux boundary conditions is also compared.

Thermal Bridge Effects in Walls Separating Rowhouses

DEFF Research Database (Denmark)

Rose, Jørgen

1997-01-01

In this report the thermal bridge effects at internal wall/roof junctions in rowhouses are evaluated. The analysis is performed using a numerical calculation programme, and different solutions are evaluated with respect to extra heat loss and internal surface temperatures.......In this report the thermal bridge effects at internal wall/roof junctions in rowhouses are evaluated. The analysis is performed using a numerical calculation programme, and different solutions are evaluated with respect to extra heat loss and internal surface temperatures....

ORNL facilities for testing first-wall components

International Nuclear Information System (INIS)

Tsai, C.C.; Becraft, W.R.; Gardner, W.L.; Haselton, H.H.; Hoffman, D.J.; Menon, M.M.; Stirling, W.L.

1985-01-01

Future long-impulse magnetic fusion devices will have operating characteristics similar to those described in the design studies of the Tokamak Fusion Core Experiment (TFCX), the Fusion Engineering Device (FED), and the International Tokamak Reactor (INTOR). Their first-wall components (pumped limiters, divertor plates, and rf waveguide launchers with Faraday shields) will be subjected to intense bombardment by energetic particles exhausted from the plasma, including fusion products. These particles are expected to have particle energies of approx.100 eV, particle fluxes of approx.10 18 cm -2 .s -1 , and heat fluxes of approx.1 kW/cm 2 CW to approx.100 kW/cm 2 transient. No components are available to simultaneously handle these particle and heat fluxes, survive the resulting sputtering erosion, and remove exhaust gas without degrading plasma quality. Critical issues for research and development of first-wall components have been identified in the INTOR Activity. Test facilities are needed to qualify candidate materials and develop components. At Oak Ridge National Laboratory (ORNL), existing neutral beam and wave heating test facilities can be modified to simulate first-wall environments with heat fluxes up to 30 kW/cm 2 , particle fluxes of approx.10 18 cm -2 .s -1 , and pulse lengths up to 30 s, within test volumes up to approx.100 L. The characteristics of these test facilities are described, with particular attention to the areas of particle flux, heat flux, particle energy, pulse length, and duty cycle, and the potential applications of these facilities for first-wall component development are discussed

Particle balance under global wall saturation in long-pulse discharges of JT-60U

International Nuclear Information System (INIS)

Nakano, T.; Asakura, N.; Takenaga, H.; Kubo, H.; Shimizu, K.; Kawashima, H.

2007-01-01

During 30s-ELMy H-mode discharges, the wall-pumping rate decreases with a decay constant of several seconds and then becomes constant. During the constant wall-pumping phase, in discharges with a density of 65% of the Greenwald density, the wall-pumping rate is negative, in other words, outgassing. It has been found that this outgassing rate correlates with an increase in the tile temperature around the outer strike point. In discharges with a density of 80% of the Greenwald density, the wall-pumping rate is positive. Unless a high net deposition rate (>60%) of hydrocarbon is assumed, the positive wall-pumping rate cannot be explained only by the co-deposition of deuterium with carbon even if the outgassing rate is assumed to be zero. The vessel deuterium inventory decreases by 1.1 x 10 24 on one experimental day with 17 long discharges. The main chamber wall is suggested as the deuterium source for the decrease of the inventory

Investigation of cascade-type falling liquid-film along first wall of laser-fusion reactor

International Nuclear Information System (INIS)

Kunugi, T.; Nakai, T.; Kawara, Z.; Norimatsu, T.; Kozaki, Y.

2008-01-01

To protect the first wall of an inertia fusion reactor from extremely high heat flux, X-rays, alpha particles and fuel debris caused by a nuclear fusion reaction, a 'cascade-type' falling liquid-film flow is proposed as a 'liquid-wall' concept. The flow visualization experiment to investigate the feasibility of this liquid-wall concept has been conducted. The preliminary numerical simulation results suggest that the current cascade structure design should be improved because less thermal-mixing is expected. The cascade-type structure has, therefore, been redesigned. This new cascade-type first wall consists of a liquid reservoir which has a free-surface to maintain a constant water head in the rear, and connects to a slit composed of two plates, i.e., the first wall is connected to a slit which is partially made up of the first wall to begin with it. The numerical simulations were performed on the new cascade-type first wall and they show the stable liquid-film flow on it. Moreover, the POP (proof-of-principle) flow visualization experiments, which satisfy the Weber number coincident condition, are carried out using water as the working fluid. By comparing the numerical and experimental results, it was found that the liquid-film flow with 3-5 mm thickness could be stably established. According to these results for the new cascade-type first wall concept, it was confirmed that the coolant flow rate and the thickness of the liquid-film could be controlled if the Weber number coincident condition was satisfied

Heating in churches. Heat and moisture transfer simulations for design and climate control; Uppvaermning i kyrkor. Fukt- och vaermetekniska beraekningar foer dimensionering och klimatstyrning