Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
2
3
2010
COUPLED HEAT AND MASS TRANSFER DURING ABSORPTION OF WATER VAPOR INTO LIBR-H2O SOLUTION FAN SHEETS
203-220
Antonio
Acosta-Iborra
Universidad Carlos III de Madrid
N.
Garcia
Department of Thermal and Fluids Engineering, Carlos III University of Madrid, Avda. Universidad 30, 28911 Leganés, Spain
P. A.
Rodriguez
Unidad Asociada de Ingenieria Termicay de Fluidos CSIC-UC3M; Departamento de Ingenieria Termicay de Fluidos, Universidad Carlos III de Madrid, Avda. Universidad, 30, 28911 Leganes, Madrid, Spain
This work characterizes, both numerically and analytically, the heat and mass transfer in a fan-shaped liquid sheet of LiBr−H2O solution that absorbs the surrounding water vapor inside an adiabatic absorber for absorption chillers. A model for the simultaneous heat and mass transfer into the fan-shaped liquid sheet is presented together with the assumptions and simplifications that yield to an affordable problem. The increasing mass flow rate in the sheet due to the absorption of vapor is included in the model, thus resulting in a nonlinear system of equations. The coupled temperature and water mass fraction flow fields in the sheet are numerically solved. Additionally, an approximate analytical solution of the problem is obtained in the form of a series solution. Profiles of normalized temperature and mass fraction in main flow and transverse directions are presented. The radial distribution of local and mean Sherwood number is also evaluated. The results show the existence of temperature and mass fraction regions in the fan sheet which are analogous to the regions present in nonexpanding sheets. Good agreement between the fully nonlinear equations and the analytical approximation is found downstream of the boundary-layer region. Comparison of results for different sheet aperture angles is performed, confirming a significant reduction of the saturation length with the increase of the aperture angle.
RADIAL INJECTION OF A HOT FLUID INTO A COLD POROUS MEDIUM: THE EFFECTS OF LOCAL THERMAL NONEQUILIBRIUM
221-230
D. Andrew S.
Rees
Department of Mechanical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
Andrew P.
Bassom
School of Mathematics and Statistics, University of Western Australia, Crawley, WA 6009, Australia
We consider the manner in which local thermal nonequilibrium effects influence the development of the thermal field when a hot fluid is injected radially into a cold porous medium. A purely forced convection situation is considered, and the evolving thermal fields depend on four non-dimensional parameters, including the Péclet number and the nondimensional interphase heat-transfer coefficient, H. In this primarily numerical study we find that local thermal equilibrium is always attained eventually, but after a time which depends strongly on the value of H. When the Péclet number is large a thermal shock wave is formed within the fluid phase which degrades slowly by imparting heat to the solid phase.
NATURAL CONVECTION FROM AVERTICAL GROUND HEAT EXCHANGER EMBEDDED IN A SEMI-INFINITE POROUS MEDIUM
231-248
Mostafa H.
Sharqawy
Mechanical Engineering Department, KFUPM Box # 1060, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
Hassan M.
Badr
Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
Esmail M. A.
Mokheimer
Mechanical Engineering Department King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia
The heat-transfer process from a vertical ground heat exchanger to the surrounding soil is simulated by natural convection from a vertical cylinder embedded in a semi-infinite porous medium and is investigated numerically. Steady as well as transient behaviors were studied. The governing equations are expressed in the stream function−temperature formulation, and an explicit finite-difference technique was developed to solve the coupled nonlinear equations. Results are presented for a vertical cylinder with uniform heat flux at different Rayleigh numbers and aspect ratios for typical ground heat exchanger conditions. The thermal interaction with the atmosphere represented by Biot number at the ground surface is taken into consideration. The numerical results are used to obtain simple correlations for the average Nusselt number in the transient and steady-state phases, which can be used for simulation as well as sizing of ground heat exchangers.
THERMAL BEHAVIOR OF A SHELL-AND-TUBE HEAT STORAGE UNIT USING TWOPHASE CHANGE MATERIALS
249-268
Hamid Ait
Adine
Cadi Ayyad University, Faculty of Sciences Semlalia, Department of Physics, Fluid Mechanics and Energetic Laboratory, P.O. 2390, Marrakech, 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
A mathematical model, based on the enthalpy method, has been developed to study the thermal behavior and performance of a shell-and-tube heat storage unit employing two phase change materials (PCMs) with different melting temperatures. The shell space is filled with PCMs, and a heat-transfer fluid (HTF) flows by forced convection through the inner tube. This latent heat storage unit (LHSU) can be used for solar heating water applications. Heat is stored by day and it is recovered at night, which reduces the consumption of electricity for heating the water. The proposed model was initially validated with experimental results. Numerical investigations were conducted to examine the effects of the mass flow rate on the thermal performance of the LHSU during both charge (melting) and discharge (solidification). The effects of the HTF inlet temperature and the initial temperature of the PCMs were also investigated for charge and discharge, respectively.
COMPETITION BETWEEN LID-DRIVEN AND NATURAL CONVECTION IN SQUARE CAVITIES INVESTIGATED WITH A LATTICE BOLTZMANN METHOD
269-282
Djamel Eddine
Ameziani
Faculté de Génie Mécanique et de Génie des Procédés, Université des Sciences et de la Technologie Houari Boumediene USTHB, B.P. 32, El-Alia Bab-Ezzouar, 16111 Algiers, Algeria
Y.
Guo
Dalian University of Technology, Dalian 116024, China; University of Paris X-Nanterre, Paris 92410, France
Rachid
Bennacer
L2MGC F-95000, University of Cergy-Pontoise, 95031 Cergy-Pontoise Cedex, Paris, France; ENS-Cachan Dpt GC/LMT/CNRS UMR 8535, 61 Ave. du Président Wilson, 94235 Cachan Cedex, France; Tianjin Key Lab of Refrigeration Technology, Tianjin University of Commerce, 300134
Mohammed
El Ganaoui
Sciences des Procedes Ceramiques et des Traitements de Surface (SPCTS), UMR CNRS 6638, Faculte des Sciences de Limoges 123, av. A. Thomas - 87060 Limoges Cedex
M.
Bouzidi
5LMSSC, CNAM, case 353, 2 rue Conté, 75003 Paris et Univ. Clermont 2, IUT, Av. Atstide Briand, 03100 Montluçon, France
A lattice Boltzmann method is developed to investigate a situation combining natural and forced lid-driven convection in a two-dimensional square cavity over a very wide range of Rayleigh (Ra) and Reynolds (Re) numbers. The features of dynamic and thermal fields are presented for different Ra and Re to explain the role of Richardson number (Ri) in mixed convection. The flow and heat-transfer characteristics are discussed in both cooperation and opposing cases. Within the scope of this study, the predictive formulas are obtained to describe the heat transfer in terms of relationship between the average Nusselt number (Nu) and the controlling parameters. Different from the Lattice Bhatnagar, Gross and Krook approximation (LBGK) approximation, a lattice Boltzmann model is applied in this work.
CLUSTER FLUID DYNAMICS MODEL OF BIOCRYSTAL GROWTH
283-297
Vladimir
Ginkin
State Scientific Center of Russian Federation, Institute for Physics and Power Engineering (IPPE), Russia
Svetlana
Ganina
State Scientific Center of Russian Federation, Institute for Physics and Power Engineering (IPPE), Obninsk, 249033, Russia
A mathematical model was developed and numerical studies performed of the process of crystallization of lysozyme from an aqueous solution of its corresponding protein influenced by the spatial distribution of the precipitating agent’s (NaCl) concentration and the controlling pinpoint action of temperature. The mathematical model describes crystal nucleation and growth depending on the local supersaturation value, and heat and mass transfer within the entire volume of the solution, including the protein crystals. Heat and mass transfer is described by means of the Navier-Stokes equations in the Boussinesq approximation with regard to both thermogravitational and concentration-based convection types.