Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
2
2
2010
INVERSE SOLUTION TO STEADY TWO-DIMENSIONAL HEAT CONDUCTION IN PLANE WALLS
103-110
mohamed
mosaad
Professor
An analytical technique is developed for solving the inverse problem of steady heat conduction in a two-dimensional flat plate. In the problem, the temperature and heat flux on one of the plate boundaries are known functions of the space variable. Explicit closed-form expressions are derived for calculating the two-dimensional distributions of temperature and heat flux in the solid plate for arbitrary over-specified boundary temperature and heat flux profiles. The solution does not require knowledge of the thermal conditions on the other plate boundaries. The effect of uniform heat generation inside the plate is exactly modeled in the general solution. Test problems of known exact solutions are used to examine the validity of the proposed analytical technique.
INFLUENCE OF DUST ON THE HEAT TRANSFER IN A FIXED BED REACTOR
111-123
Hans
Haering
University of Technology Dresden
B.
Weiss
Siemens VAI Metals Technologies GmbH & Co., Turmstrasse 44, P.O. Box 4, A-4031 Linz, Austria
Franz
Winter
Institute of Chemical Engineering, Christian Doppler Laboratory for Chemical Engineering at High Temperatures Vienna University of Technology, Getreidemarkt 9/166, A-1060 Vienna, Austria
R.
Lange
Institute of Process Engineering and Environmental Technology, Dresden University of Technology, Miinchner Platz 3, D-01062 Dresden, Germany
Georg
Aichinger
Siemens VAI Metals Technologies GmbH & Co, Turmstrasse 44, P. O. Box 4, A-4031 Linz, Austria
J.
Wurm
Siemens VAI Metals Technologies GmbH & Co, Turmstrasse 44, P. O. Box 4, A-4031 Linz, Austria
This investigation focuses on the influence of dust on heat transfer in a fixed bed reactor. Industrial application shows that the heat transfer with dust is significantly smaller than without dust. To determine the reason for this effect, a laboratory-scale fixed bed reactor was built and transient temperature profiles measured at different positions in the fixed bed. In the experimental study, a three-phase system (solid, solid, gas) including dust is compared with a two-phase system (solid, gas) for three different bed materials, such as mono- and polydisperse solid iron spheres, direct reduced iron ore, and char particles. The measured data were evaluated by using a modified two-phase model with separate heat balances for a pseudohomogenous solid and a gas phase which were solved by analytical approximation and a numerical method using a commercial program, Aspen Custom Modeler. For determination of the heat-transfer coefficients, parameter estimation was done using the internal program Nelder Mead algorithm. The results were compared with established correlations and data from literature and show significant influence of dust on the heat-transfer rates due to channeling effects caused by local dust accumulation. Due to particle size distribution and different specific surfaces, the reduction of the gas-solid heat-transfer coefficient for char and direct reduced iron ore is less pronounced than for mono- and polydisperse solid iron spheres. The heat-transfer coefficient decreases to 6% in comparison with the results without dust.
COMBINED BUOYANCY EFFECTS OF THERMAL AND MASS DIFFUSION ON LAMINAR CONVECTION IN A VERTICAL ISOTHERMAL CHANNEL
125-138
Othmane
Oulaid
LMFE, Physics Department, Faculty of Sciences Semlalia, PO Box : 2390, Marrakech 40 001, Morocco; and THERMAUS, Département de génie mécanique, Université de Sherbrooke, Sherbrooke J1K 2R1, Québec, Canada
Brahim
Benhamou
Fluid Mechanics and Energetic Laboratory, CNRST Associate Unit URAC27,Cadi Ayyad University, Morocco
Nicolas
Galanis
THERMAUS, Département de génie mécanique, Université de Sherbrooke, Sherbrooke J1K 2R1, Quèbec, Canada
This paper reports on a numerical study of laminar mixed convection flow associated with mass transfer and phase change in a vertical parallel-plate channel. The plates are wetted by thin liquid water films and maintained at a constant temperature lower than that of the air entering the channel. The solution of the governing equations is based on the finite volume method with the well-known SIMPLER algorithm for handling the velocity-pressure coupling. Numerical results show that buoyancy forces have an important effect on the hydrodynamic field, as well as on the heat- and mass-transfer characteristics. These forces induce a flow reversal. Additionally, heat transfer associated with phase change (i.e., latent heat transfer) is more important compared to sensible heat transfer.
THE BOUNDARY DESIGN OF A TWO-DIMENSIONAL CAVITY WITH FREE CONVECTION BY THE CONJUGATE GRADIENT METHOD
139-149
H.
Ajam
Mechanical Engineering Department, The University of Sistan & Baluchestan, 98135-161, Zahedan, Iran
An inverse analysis is employed to estimate the unknown temperature distribution over the heater surface of a square cavity with natural convection from the knowledge of desired temperature and heat flux distributions over a given design surface. The direct problem of natural convection in a square cavity is solved by the finite volume method. The conjugate gradient method is used for minimization of an objective function, which is expressed by the sum of square residuals between estimated and desired temperatures over the design surface. The performance and accuracy of the present method for solving inverse convection heat-transfer problems is evaluated by comparing the results with a benchmark problem and a numerical experiment.
COMPUTING COUPLED DENSITY-DRIVEN FLUID FLOW AND HEAT FLUX IN POROUS MEDIA
151-163
Antonio Soto
Meca
Department of Applied Physics, ETSII, Campus Muralla del Mar, UPCT, Cartagena 30203, Spain
Francisco
Alhama
Applied Physics Department, Universidad Politécnica de Cartagena 30202, España
The problem of unsteady, coupled density-driven fluid flow and heat transport in a 2-D domain is numerically simulated for the first time using a network model whose design is based on the network simulation method. The problem is formulated according to the stream function and temperature variables, which have inherent advantages. The proposed model, which is formed of two separated networks, one for the fluid flow and one for the heat flux, is very simple since each network contains very few electrical devices, one for each of the terms of the finite-difference differential equations derived from the mathematical model. Time remains as a continuous variable in the model. Coupled and nonlinear terms are also implemented by simple devices which are programmed by software. Three different devices are required to implement the whole network, so that very few programming rules are needed for the design. The model is run on a circuit simulation code which provides the results both in graphic or tabulated form, without any other mathematical manipulation by the user. As a sample application, the Elder short-heated problem is solved and the solutions compared with those of other authors. Computing times are of the order of seconds for grids of 800 volume elements.
LES VERSUS RANS MODELING OF TURBULENT JET FLOW IN A COAXIAL MIXER
165-182
Andrei
Chorny
Turbulence Laboratory, A. V. Luikov Heat & Mass Transfer Institute, P. Brovka Str. 15, Minsk, 220072, Belarus
Johann
Turnow
Chair of Modeling and Simulation, Department of Mechanical Engineering and Marine Technology,
University of Rostock, Albert-Einstein-Str. 2, 18055 Rostock, Germany
Nikolai
Kornev
Chair of Modeling and Simulation, Department of Mechanical Engineering and Marine Technology,
University of Rostock, Albert-Einstein-Str. 2, 18055 Rostock, Germany
Egon
Hassel
Institute for Technical Thermodynamics Faculty of Mechanical Engineering and Marine Technology University of Rostock Albert-Einstein-Str. 2, D-18059 Rostock, Germany
The present work compares the results on large eddy simulation (LES) and Reynolds averaged Navier-Stokes (RANS) modeling of turbulent jet and coflow mixing of incompressible fluid (Schmidt number Sc ≈ 1000) in a coaxial mixer representing a cylindrical channel with a diameter D placed coaxially to a tube with an inner diameter d. Two different mixing regimes can be observed: (1) with a recirculation zone to develop just behind the tube at D/d > 1 + Q and (2) without a recirculation zone at D/d > 1 + Q. Here D/d is the diameter ratio and Q is the coflow-to-jet flowrate ratio. Turbulent transfer of inert passive admixture is considered to verify LES and RANS mixing models by comparing our numerical results and the available experimental data. For turbulent mixing to be described, the conservative scalar theory is adopted to calculate the averaged mixture fraction and its variance. The chemical source term in the transfer equation for reagent concentration is closed by the eddy dissipation concept and the presumed β-PDF of mixture fraction. LES is performed by invoking two subgrid scale (SGS) models: a dynamic variant of the Smagorinsky model proposed by Germano et al. (1991) and a dynamic mixed model extended to scalar fields. These models are adopted to study turbulent mixing with a fast chemical neutralization reaction. Complete analysis is made of the numerical results obtained.
NUMERICAL SIMULATIONS OF THERMO-VISCOUS FINGERING INSTABILITY IN POROUS MEDIA
183-201
M. N.
Islam
Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, Alberta T2N 1N4, Canada
Jalel
Azaiez
Department of Chemical and Petroleum Engineering, Schulich School of Engineering, University of Calgary, Calgary, Alberta, Canada T2N1N4
Brij
Maini
Numerical simulations using a pseudo-spectral method based on the Hartley transform are conducted to examine the viscous fingering instability of miscible flow displacements involving heat transfer between the fluids. The flow geometry consists of a rectilinear homogeneous porous media where the fluids and the media are assumed in thermal equilibrium. The physical model is represented using a continuity equation, Darcy's law, and volume-averaged forms of the convection-diffusion equation for mass and energy balance. The dependence of the fluids viscosities on both temperature and concentration is represented by two dimensionless parameters; the solutal viscosity ratio; βC, and the thermal viscosity ratio; βT. In particular, the study analyzed the effects of varying important parameters such as the Lewis number, the thermal lag coefficient, and the thermal mobility ratio on the dynamics of the flow. The development of new finger structures is analyzed by examining contours of the concentration and characterizing them qualitatively through a spectral analysis of the average concentration and an analysis of the variations of the mixing length and the relative contact area. It is found that diffusion of heat and its redistribution between the fluid and solid phases have a strong effect on the growth of the fingers. Furthermore, close and intricate interactions between the fluid and thermal fronts affect the subsequent development of instability, even when the two fronts are separated, with the thermal front lagging behind the fluid one.