Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
3
5
2011
EFFECTS OF BUOYANCY ON THE PERFORMANCE OF A VERTICAL DOUBLE-PIPE HEAT EXCHANGER
345-357
10.1615/ComputThermalScien.2011003483
Ionut
Voicu
Universite de Caen, LUSAC-EA 4253, rue Luis Aragon, BP 78, 50130, Cherbourg-Octeville, France
Nicolas
Galanis
THERMAUS, Département de génie mécanique, Université de Sherbrooke, Sherbrooke J1K 2R1, Quèbec, Canada
Thierry
Mare
INSA de Rennes, LGCGM, IUT Saint Malo, France
mixed convection
parallel flow
aiding/opposing buoyancy
variable properties
numerical study
CFD simulations of heat transfer between two fluids in a parallel-flow vertical double-pipe heat exchanger, taking into consideration conduction in the walls, viscous dissipation, variable fluid properties, and axial diffusion in the fluids, illustrate the effects of buoyancy on the velocity and temperature profiles as well as on the Nusselt numbers and friction coefficients. In particular, the results show that flow reversal occurs at different positions depending on the flow direction. In the developing region, the fluid bulk temperatures, the wall temperature, and the local Nusselt numbers for both fluids depend on the flow direction. For the conditions under consideration, the Nusselt number for the fully developed flow in the inner pipe lies between the corresponding forced convection values for the constant heat flux and constant temperature conditions, while the one in the annulus is smaller than both these forced convection values. It is established that the flow and thermal fields in the inner cylinder and the annulus cannot be predicted correctly by studying each one separately since the thermal condition at the solid wall separating the two fluids depends on flow characteristics such as the Richardson number in the inner tube.
NUMERICAL STUDY OF STRUCTURES OF LAMINAR OPPOSED FLOW PREMIXED METHANE-HYDROGEN-AIR FLAMES AT LOW STRAIN RATE
359-373
10.1615/ComputThermalScien.2011003468
Deshpande
Shrikrishna
Department of Mechanical Engineering, Indian Institute of Technology Madras, India
R.
Sreenivasan
Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, India 600036
Vasudevan R.
Raghavan
Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, India
600036
opposed flow flame
hydrogen-methane mixture
flame structure
detailed chemical kinetics
optically thin radiation model
Numerical investigation of laminar counterflow premixed methane-hydrogen-air flames at a low strain rate is presented. Simulations are carried out with a numerical model incorporated with C2 chemical mechanism having 25 species and 121 reaction steps, and with an optically thin radiation submodel. The numerical model is validated using the experimental data reported in the literature in terms of temperature and species concentrations in flames from opposed flow premixed methane-air and hydrogen-air streams. Parametric studies are performed for opposed flowing methane-hydrogen and air mixtures. A premixed methane-hydrogen and air with a rich mixture equivalence ratio (1.75) flows from the top duct, and one having a lean mixture equivalence ratio (0.25) flows from the bottom duct. The volumetric fraction of hydrogen in the fuel mixture has been varied from 20 to 80%. The strain rate used in the present study is kept constant at 50 s-1. Variation of velocity, temperature, species concentrations, and net reaction rates of oxygen, methane and hydrogen along the axis for various cases are presented and discussed in detail. Double flame zones are observed for all the cases. The addition of hydrogen to the rich side stream is seen to be effective in modifying the extents of both reaction zones. The reaction rate of methane is seen to be enhanced with the addition of hydrogen.
SHAPE IDENTIFICATION OF FROST FORMATION AROUNDA REFRIGERATION TUBE VIA THE INVERSE HEAT CONDUCTION APPROACH
375-387
10.1615/ComputThermalScien.2011003612
Hamid
Fazeli
School of Mechanical, Industrial and Manufacturing Engineering, Oregon State University,
Corvallis, OR, USA
M.
Mirzaei
Department of Aerospace Engineering, K.N. Toosi University of Technology, Tehran, Iran
inverse heat transfer
shape identification problem
conjugate gradient method
frost formation
In this paper, the shape identification method in the inverse heat conduction problems is applied to estimate the shape of frost on a refrigeration tube. The inverse algorithm consists of direct and inverse analysis, and a gradient-based optimization method. The direct analysis used a finite element method in an unstructured grid system to solve the direct heat conduction problem. The inverse analysis is based on recording temperature data on the surface of a refrigeration tube that calculates the objective function. The employed gradient-based optimization method is constructed using the adjoint, sensitivity, and conjugate gradient method (Powell-Beal’s version), which is used to calculate the gradient of the objective function and step size, and minimize the objective function, respectively. The effects of different Biot numbers on the refrigeration tube, shape scales, noisy temperature data, number of sensors, and different grid sizes are investigated. The results show that this proposed inverse algorithm is more efficient in the prediction of frost formation.
THERMOCAPILLARY CONVECTION IN A FREE LIQUID LAYER IN THE PRESENCE OF AN ADJACENT GAS FLOW
389-396
10.1615/ComputThermalScien.2011003644
Olga N.
Goncharova
Department of Differential Equations, Altai State University, 61, st Lenina, Barnaul, 656049, Russia; Institute of Computational Modeling of the Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russia; Heat Transfer International Research Institute, Universite Libre de Bruxelles, Bruxelles, Belgium
Yulia O.
Kabova
Institute of Thermophysics, Russian Academy of Sciences, Novosibirsk 630090, Russia; Centre of Smart Interfaces, Technische Universitaet Darmstadt, 64287 Darmstadt, Germany
Oleg A.
Kabov
Kutateladze Institute of Thermophysics of the Siberian Branch of the Russian Academy of Sciences, 1, Acad. Lavrentyev Ave., Novosibirsk, 630090, Russia; Novosibirsk State University, 2, Pirogova str., Novosibirsk, 630090, Russia; Novosibirsk State Technical University, 20 Prospect K. Marksa, Novosibirsk, 630073, Russia
convection
cocurrent gas flow
free boundary
exact solutions
The nonstationary motions of a free heat-conducting liquid layer under conditions of weightlessness are investigated analytically and numerically. To describe the dynamics of a layer with free boundaries subjected to nonhomogeneous heating and to the action of an external gas phase, a special class of the solutions of the Navier-Stokes equations is used. The 2D solutions are characterized by a linear dependence of the longitudinal component of velocity on the longitudinal coordinate. The results allow demonstrating a behavior of free liquid films and to control the mechanisms of the layer deformations at the normal and anomalous thermocapillary effects.
NUMERICAL STUDY OF A VARIABLE POROSITY POROUS LAYER IN A CHANNEL WITH INSULATED WALLS
397-405
10.1615/ComputThermalScien.2011002683
Arman
Hasanpour
Babol University of Technology, Noshirvani university technology
Mousa
Farhadi
Faculty of Mechanical Engineering, Noshirvani University of Technology, Babol, Islamic Republic of Iran
Kurosh
Sedighi
Babol University of Technology, Faculty of Mechanical Engineering, Babol, Iran
porous media
lattice Boltzmann method
variable porosity
flow stabilization
A numerical investigation of flow and heat transfer in a horizontal channel partially filled with a porous screen with nonuniform inlet has been performed by the lattice Boltzmann method. The flow in the porous layer has been simulated by the Brinkman-Forchheimer model. Numerical solutions have been obtained for variable porosity models, and the effects of Darcy number and porosity have been studied in detail. The inlet flow has two different velocities and temperatures even as the walls are adiabatic. It is found that the flow stabilization depends on the Darcy number. Also, the results show that the stabilization of the flow field and heat transfer depends on the number. The distribution of the stream field becomes more stable by decreasing Darcy number. Moreover, temperature distribution is more homogeneous at a lower Darcy number and porosity value. Results illustrate that the effect of the variable porosity is significant only in the region of the solid boundary. In addition, the difference between the constant and variable porosity models is decreased by Darcy number reduction.
NATURAL CONVECTION IN A HORIZONTAL ANNULAR POROUS CAVITY SATURATED BY A BINARY MIXTURE
407-417
10.1615/ComputThermalScien.2011003541
Alloui
Zineddine
Departement de Genie Mecanique, Faculte de Technologie, Universite Mustapha Ben Boulaid Batna, Algerie; Laboratoire d'Innovation en Construction, Eco-Conception et Genie Sismique, LICEGS, Universite Mustapha Ben Boulaid, Batna, Algerie
Patrick
Vasseur
Ecole Polytechnique, Université de Montréal, C.P. 6079, Succ. "Centre ville", Montréal,
Québec H3C 3A7, Canada
natural convection
annular cavity
porous media
thermodiffusion
Soret effect
The Darcy model with the Boussinesq approximation is used to study natural convection in a horizontal annular porous layer filled with a binary fluid under the influence of the Soret effect. Both the inner and the outer cylinders are kept at constant temperature with the inner surface higher than that of the outer. The governing parameters for the problem are the Rayleigh number Ra, the Lewis number Le, the buoyancy ratio φ, the radius ratio of the cavity R, and the normalized porosity ε. Two main convective modes are studied, namely, single- and double-cell convection in each half of the enclosure. Numerical solutions of the full governing equations are obtained for a wide range of the governing parameters. The existence of dual solutions for a range of the buoyancy ratio φ that depends on the other governing parameters has been demonstrated. Also, oscillating flows are obtained on increasing or decreasing φ beyond critical values.
PROPAGATION OF SELF-SUSTAINED EVAPORATION FRONTS AT STEP-WISE HEAT GENERATION AND CRISIS PHENOMENA AT POOL BOILING
419-426
10.1615/ComputThermalScien.2011004011
Aleksandr N.
Pavlenko
Kutateladze Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences,
Novosibirsk, Russia
Vladimir Egorovich
Zhukov
Kutateladze Institute of Thermophysics, Russian Academy of Sciences, 1, Academician Lavrentiev Avenue, Novosibirsk 630090, Russia
Irina P.
Starodubtseva
Institute of Thermophysics, Russian Academy of Sciences, Novosibirsk 630090, Russia
boiling incipience
transitional processes
crisis phenomena
nano-fluids
This work deals with the investigation results of transitional processes and crisis phenomena on boiling at step-wise heat release under the conditions of free convection. It is shown that the structure formation due to small-scale quickly growing perturbations at the evaporation front leads to a significant increase in the average velocity of the vapor cavity propagation. The effect of the addition of nano-sized particles of SiO2 into the liquid on the velocity of the self-sustained evaporation front is shown. A numerical model of the temperature disturbance evolution with unsteady heat flux pulsations in the front of the boiling regime change was implemented. It was found that the heat flux pulsations in front of the film boiling site increases the average rate of their propagation, especially at low frequencies.
UNSTEADY NATURAL CONVECTION OF NANOFLUIDS IN AN ENCLOSURE HAVING FINITE THICKNESS WALLS
427-443
10.1615/ComputThermalScien.2011004105
Genii V.
Kuznetsov
National Research Tomsk Polytechnic University, Institute of Power Engineering, Tomsk,
634050, Russia
Mikhail A.
Sheremet
Professor, Head of the Department (Department of Theoretical Mechanics), Tomsk State University,
Tomsk, Russian Federation
numerical simulation
nanofluids
conjugate heat transfer
natural convection
enclosure
Numerical simulation of conjugate natural convection in an enclosure filled with Al2O3/water nanofluid has been carried out. The Navier-Stokes and energy equations in dimensionless variables such as "stream function-vorticity-temperature" have been solved numerically. Special attention was paid to the effects of the Rayleigh number Raf = 104, 105, and 106, dimensionless time 0 < τ < 1000, solid wall thickness, and the thermal conductivity ratio on both local and integral parameters. Detailed results including streamlines, temperature, and vorticity profiles in terms of the key parameters have been obtained. Features of the thermo-hydrodynamic fields due to the presence of the nanoparticles have been determined.