Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
2
4
2010
COMBINED HEAT AND MASS TRANSFER WITH PHASE CHANGE IN A VERTICAL CHANNEL
299-310
Mohamed Aboudou
Kassim
Fluid Mechanics and Energetic Laboratory, CNRST Associate Unit URAC27, Cadi Ayyad University, Morocco
Brahim
Benhamou
Fluid Mechanics and Energetic Laboratory, CNRST Associate Unit URAC27,Cadi Ayyad University, Morocco
Souad
Harmand
Thermique Ecoulement Mécanique MatériauxMise en Forme Production - TEMPO - Université de Valenciennes et du Hainaut Cambrésis, BP 59313 Valenciennes CEDEX 9, France
The objective of this study is to investigate numerically the effects of mixed convection heat and mass transfer with phase change in a vertical parallel-plate channel. One of the plates is wetted by a thin liquid water film and maintained at a constant temperature, while the other is dry and thermally insulated. The mathematical model is solved numerically by the finite volume method. Buoyancy forces' effects on heat and mass transfer and hydrodynamic field are studied. The results show that these forces have an important effect on the flow field as well as on heat and mass transfer characteristics. Indeed, they act in the opposite direction of the upward flow and induce a flow reversal near the isothermal plate. Heat and mass transfers are diminished by buoyancy forces, which slow down the flow.
RANS SIMULATION OF EFFECT OF EVAPORATING DROPLETS ON A TURBULENT HEAT TRANSFER IN A MIST FLOW IN A SUDDEN PIPE EXPANSION
311-321
Viktor I.
Terekhov
Kutateladze Institute of Thermophysics, Laboratory of Thermal and Gas Dynamics, Russian Academy of Sciences, Siberian Branch, 630090,1, Acad. Lavrent'ev Avenue, Novosibirsk, Russia; Novosibirsk State Technical University, K. Markx av., 20, Novosibirsk, 630073, Russia
Maksim A.
Pakhomov
Kutateladze Institute of Thermophysics, Laboratory of Thermal and Gas Dynamics, Russian Academy of Sciences, Siberian Branch, Lavrent'ev Avenue, 1, 630090, Novosibirsk, Russia
A mathematical model of the two-phase mist flow past a sudden pipe expansion using the Eulerian/Eulerian approach was developed in the case of water and ethanol droplets. The effect of mass concentration of droplets and their size on the structure of the separation flow region and on the heat transfer were analyzed in detal. The results obtained are compared with previously experimental and numerical data for two-phase flows developing down stream of sudden pipe expansion.
EFFECTS OF HEAT SOURCE/SINK AND RADIATIVE HEAT TRANSFER ON HYDROMAGNETIC NATURAL CONVECTIVE FLOW THROUGH A VERTICAL CHANNEL
323-332
Ajay Kumar
Singh
Department of Mathematics, C. L. Jain College, Firozabad-283 203, India
Effects of heat source and radiative heat transfer on unsteady hydromagnetic natural convective laminar flow of an incompressible homogeneous, electrical conducting, viscous fluid through a porous medium in a vertical channel consisting of semi-infinite parallel walls is studied. The fluid flows under the influence of uniform magnetic field applied normal to the flow. Using the Laplace transform technique, the solutions for velocity and temperature fields are obtained. Expressions for skin friction and rate of heat transfer are also derived. The effects of material parameters on temperature distribution, velocity field, skin friction, and rate of heat transfer are discussed for symmetrical cooling of the channel walls. The effects of material parameters on velocity are shown graphically, while those of skin friction and heat transfer rate are presented in tabular form and a corresponding discussion is made. The model finds applications in nuclear heat transfer processes, metallurgy, and energy systems.
HIGH ACCURACY NUMERICAL APPROACH FOR NON-SIMILAR MIXED CONVECTION BOUNDARY LAYER FLOW OVER A HORIZONTAL PLATE
333-339
K.
Venkatasubbaiah
Department of Mechanical Engineering, Indian Institute of Technology Hyderabad, Hyderabad, 502205, India
The mixed convection boundary layer flow over a heated horizontal plate is studied using high accuracy numerical method. Present analysis is valid when the buoyancy force effects are small compared to forced convection effects. The mixed convection boundary layer equations are given with the buoyancy term represented by Boussinesq approximation. The non-similar mixed convection boundary layer equations are solved directly using direct integration method with out any approximation for non-similar terms. Numerical results are reported for assisting and opposing mixed convection flows for air. Reported results show that both the local Nusselt number and local friction factor values are increasing with increase in buoyancy parameter for assisting mixed convection flows and decreases with increasing buoyancy parameter for opposing mixed convection flows. Reported results reveal that both the local Nusselt number and the local friction factor values are high compared to local similarity and localnon-similarity methods for assisting mixed convection flows and less compared to local similarity and localnon-similarity methods for opposing mixed convection flows. Reported results show that velocity and temperature profiles in the boundary layer are exactly matches compared to local similarity method for low value of buoyancy parameter (ξ). For assisting mixed convection flows, the significant buoyancy effects are encountered for ξ ≥ 0.05 and the velocity exhibit an over shoot beyond the free stream velocity for high values of ξ. For opposing mixed convection flows, the effect of buoyancy is to reduce the velocity compared to pure forced convection. The thickness of thermal boundary layer decreases with increasing buoyancy parameter for assisting mixed convection flows and increases with increasing buoyancy parameter for opposing mixed convection flows. Present study provides an accurate numerical approach to solve non-similar mixed convection boundary flows.
DEPRESSURIZATION EFFECTS ON THE THERMAL FIELDS AND HEAT TRANSFER DURING HEMI-SPHERICAL BUBBLE GROWTH ON A HEATED SURFACE
341-358
Anthony J.
Robinson
Department of Mechanical and Manufacturing Engineering, Parsons Building, Trinity College, Dublin, Ireland; and Department of Mechanical Engineering, McMaster University, Hamilton, Ontario, Canada
A numerical simulation has been carried out which predicts the growth and wall heat-transfer characteristics of a bubble atop a heated flat surface in an otherwise quiescent pool of liquid. In accordance with the experimental conditions and observations of Merte et al. (1995), the simulations are carried out on a constant heat flux surface in microgravity, and the bubble maintains a hemispherical shape with no contribution of a microlayer. The model, computational technique, and interface tracking methodology provide very high spatial and temporal resolution. This is true for the micrometer-sized nucleus in metastable equilibrium with its surrounding liquid at the end of the measured waiting time, through the surface tension, transition, and heat transfer controlled growth domains where the bubble expands to macro-sized. The simulations indicate that the rapid depressurization of the vapor bubble as it expands occurs in conjunction with a like drop in the vapor temperature. This establishes a substantial temperature gradient and subsequent evaporative cooling effect of the heater surface near the moving triple interface. The influence of bulk liquid advection and transient conduction is discussed in relation to the bubble dynamics.
THERMAL-FLUID MODELING OF A VISI-COOLER
359-370
S. Joseph
Sekhar
St.Xavier's Catholic College of Engineering, India
Dhasan Mohan
Lal
R&AC Division, Department of Mechanical Engineering, College of Engineering, Guindy, Anna University, Chennai − 600 025, India
The steady state thermofluid behavior of a visi-cooler has been mathematically modeled using a distributed parameter technique for R-12 and R-134a/R-290/R-600a mixtures. The pressure drop in condenser and evaporator tubes, pressure-volume diagram, temperature glide, compressor power, and per day energy consumption for various operating conditions have been extracted. Experiments also have been conducted for both the refrigerants for similar operating conditions. The simulation revealed that a mixture of R-134a, R-290, and R-600a with mass percentage of 91%, 4.068%, and
4.932%, respectively, is more efficient than R-12 in all performance aspects. The deviation of experimental results from the simulated values is observed to be within ±12%. The experiments also showed that the percentage reduction in the per day energy consumption with the mixture is between 10.8% and 19.6% for the tested conditions.
ESTIMATION OF THE ABLATIVE PARAMETERS IN ABLATIVE COMPOSITES USING NONLINEAR PARAMETER ESTIMATION METHODS
371-379
A.
Hakkaki-Fard
Department of Mechanical Engineering, University of Tehran, Tehran, Iran
Farshad
Kowsary
Department of Mechanical Engineering, University College of Engineering, University of Tehran, Tehran 515-14395, Iran
Alireza
Pourshaghaghy
Islamic Azad University ,Qazvin Branch, Qazvin, Iran
M.
Sefidgar
Department o fMechanical Engineering, University of Tehran, Tehran, Iran
In this article, nine ablative parameters of ablative composites are estimated using nonlinear inverse methods. The mathematical model of the ablative composite when exposed to a thermally harsh condition has been developed on the basis of the decomposition of the resin and formation of the char layer at a critical temperature. Three zones of virgin material, pyrolysis zone, and char layer along with two moving boundary surfaces are incorporated into the thermal model. The Levenberg-Marquardt method is used for estimating the unknown properties. Considering the nonlinear behavior of the inverse problem and the insulating behavior of the composite, the convergence of the solution method is acceptable and the estimated parameters are reliable.
VISCOUS DISSIPATION EFFECTS ON HEAT TRANSFER FOR OSCILLATING FLOW IN A PIPE PARTIALLY FILLED WITH A POROUS MEDIUM
381-395
D.
Dhahri
Laboratoire d’Etudesdes Systèmes Thermiques et Energétiques, Ecole Nationale d’Ingénieurs de Monastir, Rue Ibn Eljazzar, 5019 Monastir, Tunisia
Khalifa
Slimi
ISTLS
Sassi Ben
Nasrallah
Laboratoire d'Études des Systèmes Thermiques et Énergétiques, Ecole Nationale d'Ingénieurs
de Monastir, Monastir 5019 Tunisie
A numerical study is reported here to investigate a laminar incompressible oscillating flow and heat transfer into a finite length pipe of circular crss section partially filled with an annular lining of porous medium. The porous substrate is attached to the wall, which is heated with uniform temperature. The flow in the porous materialis described by the Brinkman-Lapwood-Forchheimer extended Darcy model with variable porosity. The model for the energy transport is based on the local thermal equilibrium assumption, between the fluid and the solid phases, and takes into account the viscous dissipation effects. The control volume-based finite element method (CVFEM) is used for solving the governing differential equations system with an unequal order velocity-pressure interpolation. A comprehensive analysis of the influence of the Darcy number, the Womersly number, the thermal conductivity ratio, the heat capacity ratio, the porous layer thickness, and the Eckert number is presented and discussed throughout the article.