Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
7
4
2015
THERMOPHORESIS EFFECT ON THE FREE CONVECTIVE FLOW IN A DIFFERENTIALLY HEATED SQUARE CAVITY
283-291
Serban R.
Pop
Faculty of Science and Engineering, Computer Science, University of Chester, Chester, United
Kingdom
Teodor
Grosan
Faculty of Mathematics and Computer Science, Babes-Bolyai University, 400084 Cluj-Napoca,
Romania
A numerical analysis is made for thermophoretic transport of small particles through the convective flow in a differentially heated square cavity. The governing gas-particle partial differential equations are solved numerically for some values of the considered parameters to investigate their influence on the flow, heat, and mass transfer patterns. It is found that the effect of thermophoresis can be quite significant in appropriate situations.
NUMERICAL INVESTIGATION OF HEAT TRANSFER DURING SOLIDIFICATION IN A RECTANGULAR ENCLOSURE WITH INTERNALLY HORIZONTAL PARTIAL FINS
293-312
Laila
Khatra
Cadi Ayyad University, Faculty of Sciences Semlalia, Department of Physics, Fluid Mechanics
and Energetic Laboratory (affiliated to CNRST, URAC 27), Marrakesh, Morocco
Hamid
El Qarnia
Cadi Ayyad University, Faculty of Sciences Semlalia, Department of Physics, Fluid Mechanics
and Energetic Laboratory (affiliated to CNRST, URAC 27), Marrakesh, Morocco
Mohammed
El Ganaoui
University of Lorraine, LERMAB/IUT Longwy, Institut Carnot, Nancy, France
El Khadir
Lakhal
Automatic, Environmental and Transfer Process Laboratory (Affiliate to CNRST, URAC 28)
Marrakesh, Morocco
The paper aims to investigate numerically the thermal and flow characteristics of an internally finned rectangular
enclosure during the solidification process of a superheated phase change material (PCM). This work is motivated by the need to intensify heat transfer and accelerate the discharge process in latent heat storage units. A mathematical model is developed and a fixed-grid enthalpy formulation is adopted for modeling the solidification process coupling with convection-conduction heat transfer. The finite volume method was used for discretization. The obtained numerical results are compared with experimental and numerical ones found in the literature and reasonable agreement is obtained.
Numerical investigations were carried out to evaluate the effects of the aspect ratios of the rectangular enclosure, A, and fins, Af , on the heat transfer enhancement, by keeping the mass of the PCM and fins constant. Solutions are obtained for aspect ratios A (ranging from 3 to 8) and Af (ranging from 2.69 to 13.89). A comparative study of finned and unfinned enclosures shows clearly that introducing fins weakens the undesirable natural convection, improves the nondimensional rate of heat extraction, and assures rapid solidification. Results indicate that for an aspect ratio A = 4 and in the range of the aspect ratio Af explored in this study, the nondimensional solidification time is reduced by 17.74%. The results also reveal that for a fin aspect ratio of Af = 5, the nondimensional solidification time is reduced by 49.48% when the aspect ratio of the enclosure, A, varies from 3 to 8.
RADIATIVE HEAT TRANSFER FROM SUPERSONIC FLOW WITH SUSPENDED POLYDISPERSE PARTICLES TO A BLUNT BODY: EFFECT OF COLLISIONS BETWEEN PARTICLES
313-325
Dmitry L.
Reviznikov
Moscow Aviation Institute, Volokolamskoe Shosse 4, 125993 Moscow, Russia; Dorodnicyn Computing Centre, Federal Research Center "Computer Science and Control" of Russian Academy of Sciences, 44, b. 2, Vavilov st., Moscow, 119333, Russia
Andrey V.
Sposobin
Moscow Aviation Institute, Volokolamskoe Shosse 4, 125993 Moscow, Russia
Leonid A.
Dombrovsky
Joint Institute for High Temperatures, 17A Krasnokazarmennaya Str., Moscow,
111116, Russia; Tyumen State University, 6 Volodarsky Str., Tyumen, 625003, Russia
This study is motivated mainly by the interest in thermal conditions in the experimental testing of composite materials used in design of rocket engines. Therefore, a model problem with parameters typical of engineering problems of this type is considered. At the same time, the computational methods and qualitative results are expected to be also applicable to some reentry problems. This particular numerical analysis is focused on the effects of collisions between alumina particles and realistic size distribution of alumina particles on both the flow field of particles and radiative heat transfer to the front surface of the blunt body. The computational method used in the heterogeneous flow field calculations takes into
account the collisions between the particles. The approximate models examined by the authors for the radiative transfer in recent publications are also employed in the present paper. The computational study of the problem showed that the effect of collisions between the particles is significant for both the flow field of particles behind the shock wave and the radiative heat transfer. It is also interesting that an equivalent average radius of particles in approximate monodisperse calculations is quite different in the cases of a relatively cold and hot surface of the body. A physical explanation of this result is given.
COUPLED HEAT AND MASS TRANSFER WITH ONE SUBLIMATION MOVING INTERFACE AND FREEZING ZONE
327-337
S. K.
Singh
Department of Mathematics, NIT, Patna, India
Tadkeshwart N.
Mishra
DST-CIMS, Faculty of Science, BHU, Varanasi
Kabindra Nath
Rai
Department of Mathematical Sciences, Indian Institute of Technology (BHU), Varanasi- 22005, Uttar Pradesh, India; DST-CIMS, Banaras Hindu University,Varanasi-22005, Uttar Pradesh, India
The present work discusses coupled heat and mass transfer during freeze-drying of a wet substance where sublimation
and freezing occur concurrently. The formulation is based upon the Luikov system and the fact that in the wetted region, heat and mass transfer is due to temperature and concentration gradients; in the frozen region, heat transfer is due to temperature gradients; and in the dried region, vapor flow results from both moisture and pressure gradients. An exact solution of the problem is obtained and effects of several parameters on freezing and sublimation have been observed and discussed in detail. The whole analysis is presented in dimensionless form. Numerical examples of particular interest have been studied and discussed in detail.
ON ULTIMATE REGIME OF RAYLEIGH-BENARD CONVECTION
339-344
Igor B.
Palymskiy
Siberian State University of Telecommunications and Information Sciences, 630102,
Novosibirsk, Russia
Turbulent convection of liquid in a vertical narrow channel is simulated numerically for the case of heating from below. The liquid is assumed to be viscous and incompressible, the horizontal boundaries flat, isothermal, and free from shear stress, and the vertical boundaries adiabatic rather than isothermal. The Boussinesq approach without any semiempirical
relationships (DNS) has been used, and the flow is considered to be two-dimensional and nonstationary. A special pseudo-spectral method with enough resolution and Prandtl number equal to 10 is used to investigate the asymptotic regime of convection at high Rayleigh number (ultimate regime). By means of a direct numerical simulation of convection in a two-dimensional narrow channel, with the channel height divided by its width, being of order 10, this regime may be derived with a relatively low Rayleigh number value of order 2×109. Nusselt and Reynolds numbers in the new asymptotic regime derived are linear functions of Rayleigh number, Nu~Ra and Re~Ra. The linear law derived for Nusselt and Reynolds numbers appears to be additional to the conventional root law.
A SIMULATION OF COMPRESSIBLE BOUNDARY−LAYER FLOW WITH HEAT TRANSFER AND PRESSURE GRADIENT
345-352
Mohammad Reza
Mohaghegh
Department of Mechanical Engineering, University of Torbat Heydarieh, Torbat Heydarieh, Iran
In this paper, numerical solution of similarity equations for compressible laminar boundary-layer flow considering heat transfer and arbitrary pressure gradient has been undertaken. These equations have been solved with the assumption of a small difference in viscosity, adopting a Prandtl number of 1 for a Falkner-Skan type compressible flow. Since similarity equations of momentum and energy of the flow are coupled and dependent on each other, they have to be solved simultaneously. The numerical technique applied in this work is a fourth-order Runge-Kutta method for ordinary differential equations. Also, a shooting method is used for the governing boundary conditions which have to be solved iteratively to reach convergence. Obtained results show that for favorable (negative), pressure gradient, there is no separation in the flow either for the hot wall or for the cold one. It also supports the fact that unfavorable (positive) pressure gradient is a necessity for separation. However, there is a difference between the two obtained face angles that
cause separation in these two face conditions. As heat transfer in the boundary layer from the wall to the fluid causes a discontinuity in the velocity profile and will increase the tendency of backflow, this angle is less for a hot wall compared to the cold one. Also, the problem has been simulated using the FluentTM code and the numerical results are compared by the results of Fluent, to validate each other.
HIGH-ORDER SPHERICAL HARMONICS METHOD FOR RADIATIVE TRANSFER IN SPHERICALLY SYMMETRIC PROBLEMS
353-371
Guillaume Lambou
Ymeli
Laboratoire de Mecanique et de Modelisation des Systemes Physiques (L2MSP), Department of Physics/Faculty of Science, University of Dschang, Cameroon, P.O. Box 67 Dschang, Cameroon
Herve Thierry
Kamdem Tagne
University of Dschang
A matrix formulation of the spherical harmonics method to predict radiative transfer in participating layer and layered media within spherical geometry is presented. This formulation combines forward finite-difference spatial discretization and the conjugate gradient squared methods to solve the resulting partial differential equations of radiative intensity moments. Henceforth, a high-order spherical harmonics solution has been obtained without difficulty. Comparisons with other methods are carried out for boundary radiative fluxes, transmittance, and reflectance associated with radiative heat transfer through homogeneous/inhomogeneous, isotropic/anisotropic participating spherical layer and layered media. The comparisons show excellent agreement between exact and very high-order spherical harmonics predictions. It was found that a high order of the PN approximation is necessary to produce accurate results at the inner boundary of hollow spherically symmetric media, while low- or moderate-order of the PN approximation is sufficient to obtained accurate results at the outer boundary of both hollow and solid spherically symmetric media.
BOOK REVIEW OF TEXT BOOK: THERMAL ENERGY SYSTEMS, DESIGN AND ANALYSIS
373-374
Brian E.
Milton
Emeritus Professor, School of Mechanical and Manufacturing Engineering The University of New South Wales Sydney, NSW 2052 Australia