Begell House Inc.
Heat Transfer Research
HTR
1064-2285
44
7
2013
EXPERIMENTAL INVESTIGATION OF OPPOSING MIXED CONVECTION HEAT TRANSFER IN A VERTICAL FLAT CHANNEL IN THE TRANSITION REGION. 1. ANALYSIS OF LOCAL HEAT TRANSFER
589-602
Robertas
Poskas
Lithuanian Energy institute; Kaunas Univerity of Technology, Kaunas, Lithuania
Arunas
Sirvydas
Lithuanian Energy Institute, Branduolinës inþinerijos problemø laboratorija, Breslaujos str. 3, LT-44403 Kaunas
Jokubas
Kolesnikovas
Lithuanian Energy Institute, Branduolinës inzinerijos problemø laboratorija, Breslaujos str. 3, LT-44403 Kaunas, Lithuania
Raimondas
Kilda
Lithuanian Energy Institute, Branduolinës inzinerijos problemø laboratorija, Breslaujos str. 3, LT-44403 Kaunas, Lithuania
In this paper, the results of experimental investigation into the local opposing mixed convection heat transfer in a vertical flat channel in the transition region are presented. Variation of the local heat transfer rate at different air pressures (0.1−0.4 MPa), i.e., in the case of different buoyancy effects, was analyzed. The analysis of the results revealed a significant increase in the heat transfer rate on increase in the buoyancy effect at a certain value of x/de. This is related to the change in the flow regime, i.e., formation or disappearance of vortices. Moreover, it was determined
that in the case of vortical flow, the heat transfer rate is significantly higher than in the case of turbulent flow, and the transition to turbulent flow occurs at higher Re numbers. Therefore, the results obtained change the concept of the transition from laminar to turbulent
flow under a significant buoyancy effect.
UNSTEADY MHD MIXED CONVECTION STAGNATIONâ€POINT FLOW IN A MICROPOLAR FLUID ON A VERTICAL SURFACE IN A POROUS MEDIUM WITH SORET AND DUFOUR EFFECTS
603-620
Aurang
Zaib
Department of Mathematical Sciences, Federal Urdu University of Arts, Science and
Technology, Gulshan-e-Iqbal Karachi-75300, Pakistan
Abdul Rahman M.
Kasim
Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia JB, 81310 Skudai, Johor, Malaysia
N. F.
Mohammad
Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia JB, 81310 Skudai, Johor, Malaysia
Sharidan
Shafie
Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia
81310 UTM Johor Bahru, Johor, Malaysia
The problem of an unsteady MHD mixed convection flow with heat and mass transfer in a micropolar fluid near the forward stagnation point in a porous medium with Soret and Dufour effects has been investigated. The self-similarity transformation is used to transform the governing
equations and then to solve them numerically using an implicit finite difference scheme. In this study, we consider both assisting and opposing flows. The profiles of velocity, microrotation, temperature, and concentration, as well as the skin friction, and the rate of heat and mass transfer are determined and presented graphically for physical parameters. The results show that the magnetic parameter decreases the reduced skin friction and reduced heat and mass transfer for the assisting flow while the opposite trend is observed for the case of opposing flow. It is also found that the buoyancy parameter decreases the thermal and concentration boundary layer thickness for an assisting flow and increases for an opposing one.
EFFECT OF RECTANGULAR AND TRIANGULAR THIN ADIABATIC FINS ON MIXED CONVECTION IN A SQUARE CAVITY WITH TWO VENTILATION PORTS
621-643
Fatih
Selimefendigil
Mechanical Engineering Department, Celal Bayar University, Manisa, 45140, Turkey
In the present work, a square enclosure with two ventilation ports in the presence of adiabatic differently shaped fins placed on the bottom wall of the cavity are numerically analyzed for the mixed convection case in the range of Richardson numbers from 1 to 120 at the Reynolds number equal to 300. The walls of the cavity are kept at a constant temperature, and two different fin shapes (a rectangular and a triangular one) are considered. The effect of the fin height and Richardson number on the heat transfer and fluid flow characteristics is analyzed numerically. The results are presented in terms of streamlines, isotherm plots and averaged Nusselt number
plots. It is observed that the length of a fin has a considerable effect on the thermal performance of the system. The shape of a fin affects the flow field and heat transfer characteristics only at a short fin length.
STUDY OF CONVECTIVE HEAT TRANSFER IN A SQUARE CAVITY FILLED WITH A VISCOPLASTIC FLUID BY TAKING INTO ACCOUNT VISCOUS DISSIPATION
645-663
Nabila
Labsi
Laboratoire des Phenomenes de Transfert, Faculte de Genie Mecanique et de Genie des Procedes, Universite des Sciences et de la Technologie Houari Boumediene BP, 32 El Alia, 16111 Bab Ezzouar, Algiers, Algeria
Youb Khaled
Benkahla
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
Abdelkader
Boutra
Laboratoire des Phenomenes de Transfert, Faculte de Genie Mecanique et de Genie des Procedes, Universite des Sciences et de la Technologie Houari Boumediene BP, 32 El Alia, 16111 Bab Ezzouar, Algiers, Algeria
The present work is devoted to the numerical study of forced, natural and mixed convective heat transfer inside a square cavity filled with a non-Newtonian viscoplastic fluid described by the Bingham rheological model. The upper and bottom walls of the enclosure are thermally insulated, while the remaining walls are mobile and differentially heated. In order to solve the general
coupled equations, a code based on the finite volume method is used and has been validated after comparison of the present results with those from the literature.
Viscous dissipation effects on hydrodynamic and thermal properties are analyzed for various values of the Richardson number. The results show that the Richardson number affects the hydrodynamic characteristics as well as heat transfer in a cavity filled with a viscoplastic fluid and leads to a flow structure modification different from that obtained for a Newtonian fluid. The same observation is done concerning the effect of the Brinkman number. Indeed, it has been noted that neglecting the viscous dissipation results in a significant underestimation of heat transfer in an enclosure, especially in the case of natural heat transfer convection.
TRIPLE TUBE AMMONIA EVAPORATOR DESIGN FOR DOMESTIC ABSORPTION REFRIGERATORS
665-686
Ahmed Mohammed
Adham
Erbil Polytechnic University
Normah
Mohd-Ghazali
Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor Barhru, Malaysia
Mikdam M.
Saleh
Power Engineering Department, College of Engineering, University of Baghdad, Alâ€Jadriya, Baghdad, Iraq
Robiah
Ahmad
UTM Razak School of Engineering and Advanced Technology, Universiti Teknologi Malaysia International campus, 54100 Jalan Semarak, Kuala Lumpur, Malaysia
A usable concept for an ammonia evaporator in an absorption refrigerator based on a triple tube design is considered. The differential equations that describe the energy transfer between the ammonia refrigerant and the ammonia hydrogen gas mixture are utilized to simulate the thermal and hydrodynamic performances and hence to determine the operation of evaporator. This simulation
procedure is used to determine the geometrical parameters of the evaporator, subject to certain optimization criteria that were incorporated in a cost function. The final design of the evaporator, which is based on 100 W of cooling power at −6.7 °C, has a length of 1.523 m and triple tube diameters of 28.5, 22.2, and 15.8 mm. The evaporator's design is such that only a single penetration through the refrigerator's wall is necessary, which greatly simplifies the construction and reduces its cost.