Begell House Inc.
Heat Transfer Research
HTR
1064-2285
49
6
2018
NUMERICAL SIMULATION OF COOLING A 2D SQUARE BLOCK CONSIDERING PHASE TRANSFORMATION AND CHANGES IN THERMODYNAMIC PROPERTIES
483-490
Jae Ryong
Lee
Korea Atomic Energy Research Institute, 1045 Daedeok-daero, Yuseong-gu, 305-353, South Korea
Il Seouk
Park
School of Mechanical Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu,
702-701, South Korea
During a cooling process, a high-temperature steel usually in austenite phase undergoes a phase transformation to ferrite and bainite. Due to the phase transformation, the material changes its metallurgical structure and hence its mechanical characteristics, including the strength and toughness. In addition, the phase transformation causes a related exothermic reaction and changes the thermodynamic properties. Therefore, the cooling process and its relevant phase transformation should be treated together by coupling them. In this study, the cooling process of a two-dimensional square steel block is investigated numerically by considering the phase transformation from austenite to ferrite. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation (Avrami, 1939) was adopted for the phase transformation analysis. The cooling results with and without consideration of the phase transformation eff ect are compared.
NATURAL CONVECTION IN TRANSIENT MHD DISSIPATIVE FLOW PAST A SUDDENLY STARTED INFINITE VERTICAL POROUS PLATE: A FINITE DIFFERENCE APPROACH
491-508
Nazibuddin
Ahmed
Department of Mathematics, Gauhati University, Guwahati-781014, Assam, India
M.
Dutta
Department of Applied Sciences, Institute of Science and Technology, Gauhati University,
Guwahati-781014, Assam, India
An attempt has been made to perform a finite difference analysis to study the effects of the magnetic field, thermal radiation, Reynolds number, chemical reaction, and of dissipating heat on the MHD transient dissipative flow past a suddenly started infinite vertical porous plate with ramped wall temperature. An implicit finite difference method of Crank–Nicolson type is adopted to solve the resultant system of dimensionless coupled nonlinear differential equations governing the flow. It is seen
that our observation and that of some already published work are consistent as regards the behavior of the magnetic field
and chemical reaction on the flow although the flow geometries of the two works are not the same.
NUMERICAL STUDY OF A SOLAR GREENHOUSE DRYER WITH A PHASE-CHANGE MATERIAL AS AN ENERGY STORAGE MEDIUM
509-528
Orawan
Aumporn
Laboratoire de Mathématiques et PhySique (LAMPS), Université de Perpignan Via Domitia
52, Avenue Paul Alduy, F-66860 Perpignan cedex, France
Belkacem
Zeghmati
Laboratoire de Mathématiques et PhySique (LAMPS), Université de Perpignan Via Domitia
52, Avenue Paul Alduy, F-66860 Perpignan cedex, France
Xavier
Chesneau
Laboratoire de Mathématiques et PhySique (LAMPS), Université de Perpignan Via Domitia
52, Avenue Paul Alduy, F-66860 Perpignan cedex, France
Serm
Janjai
Solar Energy Research Laboratory (SERL), Department of Physics, Faculty of Science, Silpakorn University, Nakhon Pathom 73000, Thailand
A numerical study of the thermal behavior of a solar greenhouse dryer with a thermal energy storage unit is presented. The solar greenhouse dryer consists of a gothic metallic arch structure covered with a polycarbonate film on a metallic plate floor. The products to be dried (100 kg of banana Musa ABB CV. Kluai "Namwa") are located as a thin layer on four metallic grids. The thermal energy storage unit, disposed under the greenhouse floor, is composed of a layer of phase-change materials (PCM) placed between the metal plate and a concrete slab. Paraffin wax was used as PCM in thermal energy storage with a melting temperature of 28°C. Transfer equations are derived by considering energy balance for different components of the greenhouse dryer. The enthalpy method and heat conduction equation have been used for calculating the PCM layer and concrete slab, respectively. Equations are solved numerically by an implicit finite difference scheme and homemade software. Parametric studies of the greenhouse dryer coupled to the thermal energy storage unit illustrate the effects of drying air volume flow rate on the greenhouse temperature, drying duration, as well as the efficiency of the solar dryer and energy storage unit. Our results allowed us to conclude that under the climatic conditions of Nakorn Pathom (Thailand) the thermal storage unit improves the greenhouse solar dryer efficiency. For instance, for the drying air volume flow rate ranging from 0.05 to 0.2 m3·s-1, this efficiency varies between 12% and 38% with a thermal storage unit and between 8% and 28% without a storage unit.
HOMOTOPY STUDY OF ENTROPY GENERATION IN MAGNETIZED MICROPOLAR FLOW IN A VERTICAL PARALLEL PLATE CHANNEL WITH BUOYANCY EFFECT
529-553
Srinivas
Jangili
Department of Mathematics, National Institute of Technology Meghalaya, Shillong, 793003, India
O. Anwar
Bég
Fluid Mechanics, Nanosystems and Propulsion, Aeronautical and Mechanical Engineering,
School of Computing, Science and Engineering, Newton Building, University of Salford,
Manchester M54WT, United Kingdom
The paper presents the results of an analytical investigation into the buoyancy force effects on the entropy generation in magnetohydrodynamic non-Newtonian flow due to constant pressure gradient in a vertical parallel plate channel. The length of the channel plates is assumed to be infinite and uniform, and they are held at different temperatures. The Eringen thermomicropolar material model is used to simulate the rheological flow in the channel. The resulting governing equations are then solved under physically viable boundary conditions at the channel walls, using the Homotopy Analysis Method (HAM). The variations of emerging non-Newtonian and thermophysical parameters, i.e., couple stress parameter (between 1 and 10), Eringen micropolar parameter (0 ≤ c < 1), Reynolds number (between 1 and 5), Grashof number (between 0.1 and 5), Hartmann number (between 0.5 and 2), Brinkman number (between 0.1 and 0.5), and viscous dissipation parameter
(between 0 and 1) are considered. The prescribed ranges of the parameters are physically representative of the real
non-Newtonian magnetohydrodynamic thermal systems employing micropolar fluids. The computations show that an increasing
magnetic field effect reduces the entropy production at the channel walls, whereas the converse behavior is observed
for the increasing couple stress parameter, Reynolds number, Grashof number, and the viscous dissipation parameter. The
increasing micropolarity parameter and Hartmann number effectively decrease the entropy generation production.
INVESTIGATION OF HEAT FLUX DISTRIBUTION IN LARGE-SCALE POOL FIRES UNDERNEATH THE FUEL SURFACE USING A FIRE DYNAMIC SIMULATOR
555-567
Song
He
School of Resources and Environmental Engineering, Wuhan University of Technology, Luoshi Road 122, Wuhan, 430070, P.R. China
Qian
Li
School of Resources and Environmental Engineering, Wuhan University of Technology, Luoshi
Road 122, Wuhan, 430070, P.R. China
Hui
Yang
State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230027, P. R. China
Huaming
Dai
School of Resources and Environmental Engineering, Wuhan University of Technology, Luoshi Road 122, Wuhan, 430070, P.R. China
Xianfeng
Chen
School of Resources and Environmental Engineering, Wuhan University of Technology, Luoshi Road 122, Wuhan, 430070, P.R. China
In our study, with the help of a fire dynamic simulator (FDS), full-scale oil tank fires are simulated, and the horizontal and vertical heat flux distributions underneath the fuel surface were studied. The horizontal heat flux distribution always has a peak underneath the fuel surface, and the peak gradually shift s to the edge of the tank with increase in the height. The effect of the grid resolution and the number of solid angles (NSA) on the fire environment was discussed and an appropriate grid size and NSA were chosen.
THE FALKNER–SKAN FLOW WITH VARIABLE VISCOSITY AND NONLINEAR ROSSELAND THERMAL RADIATION
569-582
Asterios
Pantokratoras
School of Engineering, Democritus University of Thrace, 67100 Xanthi, Greece
Tiegang
Fang
Department of Mechanical and Aerospace Engineering, North Carolina State University, 911 Oval Drive–Campus Box 7910, Raleigh, NC 27695, USA
A steady laminar boundary-layer flow over a wedge in the presence of nonlinear Rosseland radiation is investigated. The fluid viscosity is considered variable and assumed to be a function of temperature. Similar governing equations are obtained using a suitable transformation and solved by the Runge–Kutt a method. The problem is governed by Prandtl number, surface temperature parameter, viscosity parameter, exponent parameter, and radiation parameter, and the influence of these parameters on the results is presented in tables and figures. A new radiation parameter is introduced which leads to an asymptotic state not found until now.