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Showing papers in "Numerical Heat Transfer Part A-applications in 2010"


Journal ArticleDOI
TL;DR: In this article, numerical simulations of near-critical fluids flowing in uniformly heated straight tubes are carried out, each characterized by a different wall heat flux, and the nearcritical-methane flow condition that exhi...
Abstract: Liquid propellants, which are typically used for regenerative cooling of rocket thrust chambers, can flow in channels at supercritical pressures and in the neighborhood of pseudocritical temperature (near-critical fluid). This could be for instance the case for the envisioned liquid-oxygen/liquid-methane engines with chamber pressures larger than about 50 bar. When the fluid is in such a near-critical condition, deterioration in heat transfer can occur if the heat transfer level is higher than a threshold value. Aiming to improve flow prediction capabilities for the design of such systems, the present study is devoted to numerical simulations of near-critical fluids flowing in uniformly heated straight tubes. After code validation against experimental data of near-critical-hydrogen flow, numerical simulations of near-critical-methane flow in heated tubes are carried out, each characterized by a different wall heat flux. Results are discussed in detail and the near-critical-methane flow condition that exhi...

102 citations


Journal ArticleDOI
TL;DR: In this paper, the porosity of aluminum foams of varying pore sizes was investigated through CT-scanning at 20 micron resolution, and the convective heat transfer results exhibited a dependence on the linear porosity, even though the corresponding volumetric porosity is the same for all the samples considered.
Abstract: Important heat transfer parameters of aluminum foams of varying pore sizes are investigated through CT-scanning at 20 micron resolution. Small sub-samples from the resulting images are processed to generate feature-preserving, finite-volume meshes of high quality. All three foam samples exhibit similar volumetric porosity (in the range ∼91–93%), and thereby a similar thermal conductivity. Effective tortuosity for conduction along the coordinate directions is also calculated. Permeability simulations in the Darcy flow regime with air and water show that the foam permeability is isotropic and is of the order of 10−7 m2. The convective heat transfer results computed for this range of Reynolds numbers exhibit a dependence on the linear porosity, even though the corresponding volumetric porosity is the same for all the samples considered.

97 citations


Journal ArticleDOI
TL;DR: In this paper, a more complex description of braking action was given by the assumption of mutual relation between mating parts of the disc brake system, in which the thermoelasticity theory was applied to the model.
Abstract: This article is concerned with frictional heating phenomenon playing a central role in disc brake (clutch) systems performance. It was of great interest to carry the description of existing numerical solutions of the problem. The level of the calculations was categorized into three problems. The first is a common approach, drawn primarily on the assumption that the heat flow rate generated at the disc/pad interface is a known quantity. Heat generation was substituted by the intensity of heat flux depending on contact pressure, coefficient of friction and evolution of angular velocity, and radius of the disc product. A more complex description of the braking action was given by the assumption of mutual relation between mating parts of the disc brake system. In this case, the thermoelasticity theory was applied to the model. The facts of existing critical speed is established, in which hot spots caused mainly by contact pressure variations frictionally-excited thermoelastic instability phenomenon entered co...

79 citations


Journal ArticleDOI
TL;DR: In this paper, the authors deal with the geometric optimization of a silicon-based microchannel heat sink using a combined numerical optimization and constructal theory to minimize the wall peak temperature subject to various constraints.
Abstract: This study deals with the geometric optimization of a silicon based microchannel heat sink using a combined numerical optimization and constructal theory. The objective is to minimize the wall peak temperature subject to various constraints. The numerical simulations are carried out with fixed volumes ranging from 0.7 mm3 to 0.9 mm3 and pressure drop between 10 kPa to 60 kPa. The effect of pressure drop on the optimized aspect ratio, solid volume fraction, hydraulic diameter, and the minimized peak temperature are reported. Results also show that as the dimensionless pressure drop increases the maximized global thermal conductance also increases.

72 citations


Journal ArticleDOI
TL;DR: In this article, a finite volume model was developed to simulate the transient heat transfer in a protective clothing system, which consists of a fire-resistant fabric, the human skin, and the air gap between the fabric and the skin.
Abstract: A finite volume model was developed to simulate the transient heat transfer in a protective clothing system. The model domain consists of a fire-resistant fabric, the human skin, and the air gap between the fabric and the skin. The model uses a more sophisticated treatment of the air gap compared to previous models: it accounts for transient combined conduction-radiation heat transfer within the air gap and includes the variation in the air gap properties with temperature. Predictions were obtained for the temperature and heat flux distributions in the fabric, skin, and air gap as a function of time, as well as the time to receive skin burn injuries. The numerical model was used to explore the physics of heat transfer in protective clothing, which could potentially be used to improve the performance of this clothing. This study illustrates the dependence of the temporal behavior of the heat fluxes on the specific model assumptions, as well as the associated sensitivity of skin burn predictions to these as...

63 citations


Journal ArticleDOI
TL;DR: A comprehensive survey of the literature in the area of numerical heat transfer (NHT) published between 2000 and 2009 has been conducted by as mentioned in this paper, where the authors conducted a comprehensive survey.
Abstract: A comprehensive survey of the literature in the area of numerical heat transfer (NHT) published between 2000 and 2009 has been conducted Due to the immenseness of the literature volume, the survey

58 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of thermal buoyancy on the upward flow and heat transfer characteristics around a heated/cooled circular cylinder is studied and a two-dimensional finite-volume model is deployed for the analysis.
Abstract: The effect of thermal buoyancy on the upward flow and heat transfer characteristics around a heated/cooled circular cylinder is studied. A two-dimensional finite-volume model is deployed for the analysis. The influence of aiding/opposing buoyancy is studied for the range of parameters −0.5 ≤ Ri ≤ 0.5, 50 ≤ Re ≤ 150, and the blockage ratios of B = 0.02 and 0.25. The flow shows unsteady periodic nature in the chosen range of Reynolds numbers for the forced convective cases (Ri = 0), and the vortex shedding stops completely at some critical values of Richardson numbers.

47 citations


Journal ArticleDOI
TL;DR: In this paper, a penalty finite element method with biquadratic elements is used to solve the non-dimensional governing equations for the triangular cavity involving hot inclined walls and cold top wall.
Abstract: In this article, natural convection in a porous triangular cavity has been analyzed. Bejan's heatlines concept has been used for visualization of heat transfer. Penalty finite-element method with biquadratic elements is used to solve the nondimensional governing equations for the triangular cavity involving hot inclined walls and cold top wall. The numerical solutions are studied in terms of isotherms, streamlines, heatlines, and local and average Nusselt numbers for a wide range of parameters Da (10−5–10−3), Pr (0.015–1000), and Ra (Ra = 103–5 × 105). For low Darcy number (Da = 10−5), the heat transfer occurs due to conduction as the heatlines are smooth and orthogonal to the isotherms. As the Rayleigh number increases, conduction dominant mode changes into convection dominant mode for Da = 10−3, and the critical Rayleigh number corresponding to the on-set of convection is obtained. Distribution of heatlines illustrate that most of the heat transport for a low Darcy number (Da = 10−5) occurs from the top...

47 citations


Journal ArticleDOI
TL;DR: In this paper, an alternate approach is proposed for maintaining uniform temperature via various distributed/discrete heating strategies while maintaining the minimal entropy generation, and finite element simulations are performed for a range of Rayleigh numbers.
Abstract: Uniform temperature distribution is a key parameter in many thermal processing applications. A considerable amount of additional energy is used to enhance the fluid mixing in order to maintain the temperature uniformity, but that affects the overall efficiency of the process. In this article, an alternate approach is proposed for maintaining uniform temperature via various distributed/discrete heating strategies while maintaining the minimal entropy generation. The system of laminar natural convection in differentially and discretely heated square cavities filled with various materials (molten metals, air, aqueous solutions, oils) is considered, and finite element simulations are performed for a range of Rayleigh numbers (Ra = 103–105). Entropy generation is evaluated using finite-element basis sets for the first time in this work, and the derivatives at particular nodes are estimated based on the functions within adjacent elements. Analysis of entropy generation in each case is carried out and a detailed...

42 citations


Journal ArticleDOI
TL;DR: In this paper, an edge-based smoothed finite element method (ES-FEM) in 2D and face based smoothed FEM in 3D were presented to improve the accuracy of the FEM.
Abstract: Hyperthermia treatment is an effective tool of cancer therapy. The main feature of hyperthermia treatment is to use thermal energy to kill the cancer cells without minimum damage to surrounding tissue [1-3]. In such treatment, it is essential to predict the temperature distribution accurately for a given supply of heat at the cancer cells. In this article, an edge-based smoothed finite-element method (ES-FEM) in 2-D and face-based smoothed finite-element method (FS-FEM) in 3-D are presented to improve the accuracy of the finite-element method (FEM) without much change to the FEM setting. In the ES-FEM, the discretized equations are established using the smoothed Galerkin weak form with edge-based smoothing domains. Compared with the FEM that behaves overly-stiff, the ES-FEM model possesses a close-to-exact stiffness. Thus, ES-FEM can provide much more accurate result than the FEM using the same mesh. Numerical examples, including 2-D and 3-D of hyperthermia treatment have been analyzed using ES-FEM and FS...

39 citations


Journal ArticleDOI
TL;DR: In this paper, a numerical study of the Soretic effect on double diffusion in a two-dimensional square cavity filled with a saturated Darcy porous medium is presented, where the horizontal walls of the cavity are subject to different but uniform temperatures and concentrations such that the medium is heated and salted from below.
Abstract: This article presents a numerical study of the Soret effect on double diffusion in a two-dimensional square cavity filled with a saturated Darcy porous medium. The horizontal walls of the cavity are subject to different but uniform temperatures and concentrations such that the medium is heated and salted from below. The left and right vertical walls are adiabatic and impermeable. Combined effects of the buoyancy ratio N (−1.5 < N < 4.4) and the Soret parameter M (−60.5 < M < 155) on the fluid flow and heat and mass transfer characteristics corresponding to monocellular, bicellular, and tricellular modes are studied for R T = 200 and Le = 10. It is found that the thresholds of N marking the transitions towards the oscillatory regime strongly depend on the Soret parameter M. The thermodiffusion phenomenon considerably affects the heat transfer; the Nusselt number increases with M in the case of the tricellular flow, but it goes through a maximum in the case of monocellular and bicellular flows.

Journal ArticleDOI
TL;DR: In this paper, a hybrid scheme based on the Laplace transform, change of variables, and the least squares scheme is proposed to solve the inverse dual-phase-lag bioheat transfer problem in the bilayered spherical tissue.
Abstract: This work attempts to estimate the phase lag times of a tissue based on the dual-phase-lag model from the experimental data. The inverse dual-phase-lag bioheat transfer problem in the bilayered spherical tissue is studied. The difference between two layers in the thermophysical parameters, geometry effects, and measurement errors of the input data make it hard to be solved. To solve the present problem, a hybrid scheme based on the Laplace transform, change of variables, and the least-squares scheme is proposed. In order to evidence the validity and accuracy of the estimated results, the comparison of the history of temperature increase between the calculated results and the experimental data is made for various measurement locations. The effect of measurement location on the estimated results is also investigated.

Journal ArticleDOI
TL;DR: In this paper, a numerical simulation has been carried out on a water curtain used as a radiative shield against a source of thermal radiation, where an Eulerian-Lagrangian code for the dynamics of the mist is combined to a Monte Carlo simulation of the radiative transfer in the air-droplet medium.
Abstract: A numerical simulation has been carried out on a water curtain used as a radiative shield against a source of thermal radiation. An Eulerian-Lagrangian code for the dynamics of the mist is combined to a Monte Carlo simulation of the radiative transfer in the air-droplet medium. Various attenuation efficiencies have been evaluated through comparisons on an academic reference case where multiple injections are generated on a line in order to build a water curtain. The aim of this study is to pinpoint more efficient configurations improving the radiative attenuation in saving the used water amount.

Journal ArticleDOI
TL;DR: In this paper, the fluid flow and heat transfer characteristics around two isothermal square cylinders arranged in a tandem configuration with respect to the incoming flow within an insulated vertical channel at low Reynolds number range were estimated.
Abstract: The fluid flow and heat transfer characteristics around two isothermal square cylinders arranged in a tandem configuration with respect to the incoming flow within an insulated vertical channel at low Reynolds number range (1 ≤ Re ≤ 30) are estimated in this article. Spacing between the cylinders (S) is fixed at four widths of the cylinder dimension (d) and, the blockage parameter (B) is set to 0.25. The buoyancy-aided/opposed convection is examined for the Richardson number (Ri) ranges from −1 to 1 with a fixed Prandtl number (Pr) of 0.7. The transient numerical simulation for this two-dimensional, incompressible, laminar flow and heat transfer problem is carried out by a finite volume code based on the PISO algorithm in a collocated grid system. The results suggest that the flow remains steady for the entire range of parameters chosen in this study. The representative streamlines, vorticity, and isotherm patterns are presented to interpret the flow and thermal transport visualization. Additionally, the ...

Journal ArticleDOI
TL;DR: In this paper, numerical solutions for laminar natural convection heat transfer in a fluid saturated porous enclosure between two isothermal concentric cylinders of rhombic cross-sections were presented.
Abstract: Numerical solutions are presented for laminar natural convection heat transfer in a fluid saturated porous enclosure between two isothermal concentric cylinders of rhombic cross-sections. Simulations are conducted for four values of Raleigh number (Ra = 104, 105, 106, and 107), three values of Darcy number (Da = 10−1, 10−3, and 10−5), three values of porosity (ϵ = 0.3, 0.6, and 0.9), four values of enclosure gap (E g = 0.875, 0.75, 0.5, and 0.25), and two values of Prandtl number (Pr = 0.7 and 5). The results are reported in terms of streamlines, isotherms, mid-height velocity and temperature profiles, and local and average Nusselt number values. The flow strength and convection heat transfer increase with an increase in Ra, Da, E g , and/or ϵ. At low E g values, the flow in the enclosure is weak and convection heat transfer is low even though the total heat transfer is higher than at higher E g values, due to an increase in conduction heat transfer. An increase in Pr is associated with a decrease in the...

Journal ArticleDOI
TL;DR: A design approach is presented to bring adaptability and robustness to multi-scale convective systems through proper orthogonal decomposition-based reduced order thermal modeling, robust design principles, and the compromise decision support problem construct.
Abstract: A design approach is presented to bring adaptability and robustness to multi-scale convective systems. The design method is centered on proper orthogonal decomposition-based reduced order thermal modeling, robust design principles, and the compromise decision support problem construct. The method application for an energy efficient air-cooled data center guarantees safe and robust operation over a 10-year period of increasing power dissipation. The data center traditional design consumes 14–85% more energy than the adaptable design over the 10 years. A robust solution is also found to reduce the variability in the thermal response by 80% compared with an optimal solution.

Journal ArticleDOI
TL;DR: In this article, the Brinkman-Forchheimer-extended Darcy model is used to describe the flow characteristics within a porous medium for different angles of attack with respect to the forced convection.
Abstract: Mixed convection in an obstructed cavity with heated horizontal walls is investigated in this work. Brinkman-Forchheimer-extended Darcy model is utilized to describe the flow characteristics within a porous medium for different angles of attack with respect to the forced convection. Numerical results are obtained for a wide range of Grashof numbers (102–109), Reynolds numbers (102–105), Darcy numbers (10−6–10−1), and aspect ratios (0.25–2). Effects of the pertinent physical parameters are investigated in terms of the flow and temperature fields, as well as Nusselt number distributions. The presented results show that the Darcy number plays a significant role on the flow and thermal fields and the Nusselt number distributions for different flow configurations. For an inclined flow, the vertical velocity component is substantially diminished within a narrow entrance section near the inlet boundary. It is shown that as the aspect ratio increases the thickness of the thermal boundary layer increases, resultin...

Journal ArticleDOI
TL;DR: In this article, wall-resolved and zonal numerical large eddy type simulations are performed for a round jet impinging on a concave hemisphere at Re-=23,000.
Abstract: Wall-resolved and zonal numerical large eddy type simulations are performed for a round jet impinging on a concave hemisphere at Re = 23,000. The zonal method uses a near-wall k–l model and a Hamilton-Jacobi equation to match this to the large eddy simulation zone. To minimize numerical dissipation, a self-adaptive discretization (SDS) scheme is examined. Both second- (n = 2) and sixth- (n = 6) order-based central discretization schemes are tested. The characteristics of the schemes is assessed using two test cases: the development of a subcritical Tollmien-Schlichting (T-S) stability wave in a plane channel and the decay of homogenous, isotropic turbulence (DHIT). It is found, that Smagorinsky LES simulations tend to be too dissipative in the high wave-number region, even with the SDS scheme; hence, the SGS model is omitted. Significant flow feedback is observed for the hemisphere case. Both shear-layer excitation and stabilization is observed. Computed wall pressure coefficients for the zonal NLES metho...

Journal ArticleDOI
TL;DR: In this article, the role of the power-law index n, Reynolds number Re, Prandtl number Pr, and blockage ratio β(=B/H) on the rate of heat transfer from a square cylinder in a channel has been studied over the following ranges of conditions: 0.5 −n −1.8, 60 −Re −160, β −1/4, 1/2, and 0.7 −Pr −50.
Abstract: Forced convection heat transfer characteristics of a long, heated square cylinder blocking the flow of a power-law fluid in a channel is numerically investigated in this study. In particular, the role of the power-law index n, Reynolds number Re, Prandtl number Pr, and blockage ratio β(=B/H) on the rate of heat transfer from a square cylinder in a channel has been studied over the following ranges of conditions: 0.5 ≤ n ≤ 1.8, 60 ≤ Re ≤ 160, β = 1/4, 1/2, and 0.7 ≤ Pr ≤ 50. A semi-explicit finite-volume method is used on a nonuniform collocated grid arrangement. The third-order QUICK and the second-order central difference schemes are used to discretize the convective and diffusive terms, respectively, in the momentum and energy equations. Irrespective of the type of behavior of fluid (different values of n), the average Nusselt number increases as the blockage ratio increases. Similar to the unconfined flow configuration, the average Nusselt number increases monotonically with Reynolds and Prandtl number...

Journal ArticleDOI
TL;DR: In this paper, three-dimensional simulations are performed for the turbulent reactive flow and radiation heat transfer in a walking-beam type slab reheating furnace, and the temperature distributions of the slab and the gas mixture are obtained through a coupled calculation.
Abstract: Three-dimensional simulations are performed for the turbulent reactive flow and radiation heat transfer in a walking-beam type slab reheating furnace. The temperature nonuniformity of the slab, which causes skid marks later during the rolling process, is explored and its improvement is investigated by varying either the distance between two static beams or the height of the skid buttons. The numerical model built takes care of the true geometry and all components of a real furnace. The temperature distributions of the slab and the gas mixture are obtained through a coupled calculation. The investigation shows the skid mark is mainly caused by the radiation shielding effect of the walking-beam system and worsened by the cooling system. The skid mark above the static beam near the furnace wall is more serious than above the other static beam because of poor mixing of fuel and air, and thus less combustion there. To improve the skid mark, the static beams should be moved outward in the soaking zone and the h...

Journal ArticleDOI
TL;DR: In this article, the authors applied the conjugate gradient method with adjoint problem to estimate the bottom wall temperature in the 2D cavity domain by using gas temperature measurements in the flow field.
Abstract: Inverse thermal problem is applied to natural convective flow with radiative heat transfer. The bottom wall temperature in the 2-D cavity domain is estimated by using gas temperature measurements in the flow field. The inverse problem is solved through a minimization of an objective function using the conjugate gradient method with adjoint problem. The effects of functional form of bottom wall temperature profile, the number and the position of measurement points, and the measurement errors are investigated and discussed. The conjugate gradient method is found to work well in estimating the bottom wall temperature, even when natural convection with radiation phenomena is involved.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the flow characteristics of 3D microscale backward-facing step flows with various cross-section aspect ratios compared with those of 2D simplification.
Abstract: The flow in three-dimensional (3-D) microscale backward-facing step is investigated using the direct simulation Monte Carlo method. To ensure the rationality of two-dimensional (2-D) simplification for a 3-D structure, the flow characteristics of the 3-D microscale backward-facing step flows with various cross-section aspect ratios are compared with those of 2-D simplification. When the cross-section aspect ratio of 3-D flow cases is greater than 5, the approaching level of 3-D flows to 2-D simplification is over 98% for the nitrogen flow with inlet Knudsen number (Kn) of 0.04. Moreover, it is found that the approaching level decreases as Kn increases. The dependence between the vortex stability and the cross-section aspect ratio is studied. It is found that the flow separation, recirculation, and reattachment will disappear as the cross-section aspect ratio is less than 1 for flows with inlet Kn of 0.04.

Journal ArticleDOI
TL;DR: In this article, the flow and heat transfer characteristics of oscillating air jets impinging on a flat surface were numerically analyzed and the jet velocity oscillated sinusoidally in time.
Abstract: In this study, the flow and heat transfer characteristics of oscillating air jets impinging on a flat surface were numerically analyzed The jet velocity oscillated sinusoidally in time A computer program, based on the control volume method and SIMPLE algorithm, was developed to numerically analyze the problem Numerical simulations were performed to investigate the effects of the Reynolds number, amplitude, and frequency of the jet oscillation on the flow and heat transfer It was observed that when the jet is oscillated, the Nusselt number moderately increases compared to the Nusselt number of steady jets

Journal ArticleDOI
TL;DR: In this article, a modified discrete ordinate method (MDOM) was used to calculate volumetric radiative information with and without conduction in a concentric spherical enclosure containing a participating medium, and the energy equation of the combined mode transient conduction and radiation heat transfer was formulated and solved using the lattice Boltzmann method.
Abstract: This article deals with the application of the modified discrete ordinate method (MDOM) to calculate volumetric radiative information with and without conduction in a concentric spherical enclosure containing a participating medium. With radiative information known from the MDOM, the energy equation of the combined mode transient conduction and radiation heat transfer is formulated and solved using the lattice Boltzmann method (LBM). Without conduction, for pure radiation case, two benchmark problems, representing nonradiative and radiative equilibrium situations are taken up. In the case of non-radiative equilibrium, an isothermal medium is bounded by cold walls and medium is the source of radiation, while in the case of radiative equilibrium, nonisothermal medium is confined between a hot and a cold wall, and the hot (inner sphere) wall is the radiation source. Depending upon the problem, heat flux, energy flow rate, emissive power, and temperature distributions in the medium are calculated for differen...

Journal ArticleDOI
TL;DR: In this article, the authors used differential quadrature (DQ) technique to analyze heat and fluid flow transport due to natural convection and magnetohydrodynamic (MHD) flows in a square enclosure with a finite length heater.
Abstract: Analysis of heat and fluid flow transport due to natural convection and magnetohydrodynamic (MHD) flows in a square enclosure with a finite length heater has been performed using the differential quadrature (DQ) technique. The heater with constant heat flux is located on the bottom wall of the enclosure and isothermal boundary conditions are applied to the right vertical wall while the remaining walls are adiabatic. The effects of heater length (0.2 ≤ ϵ ≤ 0.8), heater location (0.1 ≤ c/L ≤ 0.9), and direction of magnetic force (0° ≤ φ ≤ 90°) for different values of Grashof (103 ≤ Gr ≤ 106) and Hartmann numbers (0 ≤ Ha ≤ 100) on the heat and fluid flow in the enclosure are studied. According to the results obtained, heat transfer reduces when increasing the Hartmann number. The rate of reduction is higher for high values of Grashof number. The heat transfer rate for the heater closer to the cold wall is considerably higher than the heaters far from the right wall.

Journal ArticleDOI
TL;DR: In this paper, the regeneration behavior of diesel particulate filter is examined by changing such various parameters as exhaust gas temperature and O2 concentration, where NO2 is widely used for continuous regeneration of diesel soot since it can oxidize diesel soots at lower temperatures than the conventional oxidizer O2.
Abstract: A major concern in operating a diesel engine is how to reduce the soot emission from the exhaust gases, as soot has a negative effect on both human health and the environment. More stringent emission regulations make the diesel particulate filter (DPF) an indispensable after-treatment component to reduce diesel soot from exhaust gases. The most important issue in developing an effective DPF, however, is regeneration technology to oxidize the diesel soot trapped in the filter, either periodically or continuously, during regular engine operations. Various methods exist for regenerating diesel soot captured by the filter. Of these, NO2 is widely used for continuous regeneration of diesel soot since it can oxidize diesel soot at lower temperatures than the conventional oxidizer O2 In this work, after introducing governing equations for trapping and regenerating diesel soot in the DPF, regeneration behavior is examined by changing such various parameters as exhaust gas temperature and O2 concentration. Numeric...

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the contribution of water vapor convection to heat transfer through gypsum plasterboard exposed to fire and found that the amount of condensate developing in the pores of the material is low, which allows it to be neglected in engineering calculations.
Abstract: This article investigates the contribution of water vapor convection to heat transfer through gypsum plasterboard exposed to fire. The vapor is generated as a product of the endothermic dehydration reaction in gypsum, and it is then expelled from the material through the pore network by its own pressure, thereby taking part in the heat transfer from the fire-exposed to the cold surface of plasterboard. The gas permeability values of plasterboard core and paper liner are obtained experimentally. The results of simulations are validated against the temperature measurement data obtained for two types of commercial plasterboard tested in the standard fire ISO 834. It is shown that vapor convection plays an essential role in heat transfer through plasterboard during the initial stage of fire. The amount of condensate developing in the pores of the material is found to be low, which allows it to be neglected in engineering calculations.

Journal ArticleDOI
TL;DR: In this article, the authors used the radiation element method (REM) with the lattice Boltzmann method (LBM) to solve a combined mode transient conduction-radiation problem.
Abstract: This article deals with the implementation of the radiation element method (REM) with the lattice Boltzmann method (LBM) to solve a combined mode transient conduction-radiation problem. Radiative information computed using the REM is provided to the LBM solver. The planar conducting-radiating participating medium is contained between diffuse gray boundaries, and the system may contain a volumetric heat generation source. Temperature and heat flux distributions in the medium are studied for different values of parameters such as the extinction coefficient, the scattering albedo, the conduction-radiation parameter, the emissivity of the boundaries, and the heat generation rate. To check the accuracy of the results, the problem is also solved using the finite-volume method (FVM) in conjunction with the LBM. In this case, the data for radiation field are calculated using the FVM. The REM has been found to be compatible with the LBM, and in all the cases, results of the LBM-REM and the LBM-FVM have been found ...

Journal ArticleDOI
TL;DR: In this paper, a parametric study of Prandtl number effects on laminar natural convection heat transfer in a horizontal equilateral triangular cylinder with a coaxial circular cylinder is conducted.
Abstract: A parametric study of Prandtl number effects on laminar natural convection heat transfer in a horizontal equilateral triangular cylinder with a coaxial circular cylinder is conducted. The Prandtl number is varied over a wide range from 10−2 to 105, which corresponds to a variety of working fluids. The governing equations with the Boussinesq approximation for buoyancy are iteratively solved using the finite volume approach. It is shown that the flow patterns and temperature distributions are unique for low-Prandtl-number fluids (Pr ≤ 0.1), and are nearly independent of Prandtl number when Pr ≥ 0.7. In addition, the inclination angle of the triangular enclosure is found to noticeably affect the variations of the local Nusselt number, and to have insignificant influence on the average Nusselt numbers for low Rayleigh numbers when Pr ≥ 0.7.

Journal ArticleDOI
TL;DR: In this article, the effects of one and two baffles in trapezoidal cavities were investigated and the results from several designed case studies were shown in terms of isotherms, streamlines and local and average Nusselt numbers.
Abstract: This article presents an investigation into natural convection in trapezoidal cavities. It examines a cavity whose floor and upper inclined walls are both adiabatic, while the vertical walls are isothermal. For these isothermal walls, we consider two thermal boundary conditions. Under the first condition, the short wall on the left side is heated as the tall one on the right side is cooled. The second condition is the reverse of the first—the short wall is cooled as the tall one is heated. Considering laminar conditions and a two-dimensional system, steady-state computations are carried out to assess the effects of one and two baffles, the baffle's height (H b ), Rayleigh number, 103 ≤ Ra ≤ 106, and three Prandtl number values. To demonstrate the various effects, the results from several designed case studies are shown in terms of isotherms, streamlines, and local and average Nusselt numbers in order. Predictions reveal that the second baffle decreases the cavity's fluid flow and heat transfer. As the hei...