Begell House Inc.
Heat Transfer Research
HTR
1064-2285
40
8
2009
Incremental Heat Conduction Versus Mass Reduction in Large Corrugated Walls Derived from a Large Plane Wall
717-727
Justin E.
Robbins
Department of Mechanical Engineering, The University of Vermont, Burlington, VT 05405, USA
Antonio
Campo
Department of Mechanical Engineering, The University of Vermont, Burlington, VT 05405, USA
A conventional large plane wall of thickness H is equivalent to a cluster of stackable square modules of side H with a hot left side, a cold right side, and insulated top and bottom sides (or planes of symmetry). When the two vertical sides of a primary square module are bent inward symmetrically, various kinds of scalloped modules (inscribed in the square module) could be formed depending upon the levels of curvature. Correspondingly, a collection of large corrugated walls can be built consisting of stackable scalloped modules. The heat conduction across any secondary scalloped module is intrinsically two-dimensional, in contrast to the heat conduction across a primary square module that is one-dimensional. As a "proof-of-concept", the governing heat conduction equation in two dimensions is solved numerically with the Finite Element Method under the COMSOL platform for three pre-selected derived modules with different degrees of scallopness. The heat conduction enhancement of the three scalloped modules is contrasted against the basic square module, taking into account concurrently the beneficial mass reduction.
Approximate Solution of Mixed-Convection Boundary-Layer Flow Adjacent to a Vertical Surface Embedded in a Stable Stratified Medium
729-745
Davood
Ganji (D.D. Ganji)
Babol University
A.
Asgharian
Department of Mechanical Engineering, Babol University of Technology, P. O. Box 484, Babol, Iran
N. Sedaghati
Zadeh
Department of Mechanical Engineering, Babol University of Technology, P. O. Box 484, Babol, Iran
In this paper, the analytic solution of the steady mixed-convection boundary-layer flow through a stable stratified medium adjacent to a vertical surface is obtained using the newly developed analytic method, namely the homotopy analysis method (HAM). The velocity outside the boundary layer and the surface temperature are assumed to vary linearly from the leading edge of the surface. It is found that dual solutions exist, and the thermal stratification delays the boundary layer separation.
The analytic results are compared with the numerical solution (NS) and the comparison demonstrates that there is good agreement between the numerical solution and the HAM solution. Moreover, the convergence of the obtained HAM solution is discussed explicitly. The obtained analytic solution is valid for all values of the dimension-less parameters λ and Pr as is shown below.
Novel Hybrid Finite-Difference Thermal Lattice Boltzmann Models for Convective Flows
747-775
Ahmad Reza
Rahmati
Department of Mechanical Engineering, University of Kashan, Kashan, Iran
Mahmud
Ashrafizaadeh
Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, Iran
Ebrahim
Shirani
Foolad Institute of Technology, Fooladshahr, Isfahan, 8491663763, Iran
In this article, two Hybrid Thermal Lattice Boltzmann (HTLB) methods are proposed to simulate thermally driven flows. In these methods, the velocity field is solved by a Fractional Volumetric Multi Relaxation Time Lattice Boltzmann (FV-MRT-LB) scheme and an En-tropic Lattice Boltzmann (ELB) method, while the advection-diffusion equation for temperature is solved separately by a finite difference technique. In order to demonstrate the ability of the FV-MRT-LB and ELB methods for simulation of isothermal flows, a two-dimensional cavity-driven flow has been simulated at different Reynolds numbers. Then two classical cases of buoyancy-induced flows, i.e., a differentially heated cavity flow and a Rayleigh-Be′nard convective flow, have been studied numerically at different Rayleigh numbers with a Prandtl number of 0.71. The numerical results show that both HT-FV-MRT-LB and HT-ELB methods can produce accurate results.
Development and Power Performance Test of a Small Three-Blade Horizontal-Axis Wind Turbine
777-792
K. R.
Ajao
Department of Mechanical Engineering, University of Ilorin, Ilorin, Nigeria
Isaac Kayode
Adegun
Department of Mechanical Engineering, University of Ilorin, Ilorin, Nigeria
The parameterization, installation, and testing of a locally developed three-blade horizontal-axis wind turbine were carried out. The turbine blades were fabricated from Mansonia Altissima wood because of its availability, good strength, and resistance to both fatigue and soaking, with a rotor swept area of 3.65 m2 and the blade angle of attack was experimentally determined to be 7°. The turbine was installed on the roof top of the University of Ilorin, Faculty of Engineering Central Workshop Building at a hub height of 14.9 m from the ground level while the turbine generator was sourced locally. The direct current (d.c.) power output of the test turbine was measured at the battery bank terminal by a Power Analyzer and a direct current (d.c.) to alternating current (a.c.) inverter converts the d.c. power output to a.c. power and was measured by a digital wattmeter. An anemometer with a data logger installed on a meteorological tower (MET) measured the wind speed and direction over the test period. The cut-in wind speed, that is, the speed at which the wind turbine starts to produce power was determined to be 3.5 m/sec. One minutes averages of wind speed and power output was used to determine the power curve for the wind turbine. Measured power increase consistently with increased wind speed and the power curve obtained compared fairly well with standard power curves.
Validity of Solid-Liquid Bubble Interface Modeling in Partial Nucleate Boiling
793-804
M-ed El Hocine
Benhamza
Laboratoire d'Analyses Industrielles et Génie des Matériaux, Guelma University
Fella
Chouarfa
Laboratoire d'Analyses Industrielles et Génie des Matériaux, Guelma University, Guelma 24000, P.O. Box 401, Algeria
In this study, an identification of various models of partial nucleate boiling heat transfer is carried out in order to recognize the dependence between dominant physical parameters. There is a multitude of correlations for modeling nucleate boiling heat transfer phenomena, so the main goal of this analysis is to determine the validity of each model and at the same time to identify the more dominating nucleate boiling heat transfer physical phenomenon. This is done by comparing different models with a vast range of reliable experimental data. Comparison between various correlations and experimental data shows that the Sakashita and Kumada model gives the best results in nucleate boiling heat transfer. Results also show that the most dominating physical phenomenon in the zones of partially isolated bubbles is transient conduction, taking place mainly under the bubbles. This is in contrast with the majority of the models which consider convection as the most important mode in nucleate boiling heat transfer. An increase in the nucleation-site density leads to a decrease in the size of activation cavities as well as in a detachment diameter of vapor bubbles. The selected model can also be extrapolated and used in the case of fully developed bubble zones.
Natural Convection in a Cavity with Orthogonal Heat-Generating Baffles of Different Lengths
805-819
S.
Saravanan
UGC-DRS Center for Fluid Dynamics, Department of Mathematics, Bharathiar University, Coimbatore 641 046, Tamil Nadu, India
A. K.
Abdul Hakeem
UGC-DRS Center for Fluid Dynamics, Department of Mathematics, Bharathiar University, Coimbatore 641 046, INDIA
Prem Kumar
Kandaswamy
UGC-DRS Center for Fluid Dynamics, Department of Mathematics, Bharathiar University, Coimbatore-641046, Tamil Nadu, India; Department of Mechanical Engineering, Yonsei University, Seoul, South Korea
Natural convection in a closed square cavity induced by two mutually orthogonal heat-generating baffles is considered. A numerical investigation is made to understand the effect of baffle dimensions on the resulting heat transfer characteristics. The coupled nonlinear governing equations were solved by the finite difference method using the Alternating Direction Implicit technique and the Successive Over-Relaxation method. The results obtained indicate that the flow and temperature fields strongly depend on the dimensions of heat-generating baffles. It is found that when both baffles are mounted inside the cavity an increase in the length of any of the baffle results in a proportionate increase in the overall heat transfer rate. But no significant changes in the overall heat transfer rate occur for different positions of the baffles. When the vertical baffles is mounted on the cavity wall it extracts heat energy from the cavity and behaves like a cold wall for an increase in its length. The study provides additional basic design information during fabrication in microelectronics industry.
The Application of the Adomian Decomposition Method to Nonlinear Equations Arising in Heat Transfer and Boundary Layer
821-834
Davood
Ganji (D.D. Ganji)
Babol University
H.
Nateghi
Department of Mechanical and Electrical Engineering, Babol University of Technology, PO Box 484, Babol 47144, Iran
M.
Abaspour
Department of Mechanical and Electrical Engineering, Babol University of Technology, PO Box 484, Babol 47144, Iran
O.
Rasouli
Department of Mechanical and Electrical Engineering, Babol University of Technology, PO Box 484, Babol 47144, Iran
Many researchers have been interested in application of mathematical methods to find analytical solutions of nonlinear equations and, for this purpose, new methods have been developed. Since most of temperature distribution problems are strongly nonlinear due to heat transfer and a boundary layer, an analytical solution of them is confronted with some difficulty. In this paper, some nonlinear second-order equations are studied by the Adomian decomposition method. After introducing the Adomian decomposition method and the way of obtaining the Adomian polynomial, we solved the nonlinear heat conduction and convection equations. Finally, the problems are depicted at various iterations and comparing our results with the numerical solutions illustrated their excellent accuracy.
Author Index, Vol. 40
835-837
Tables of Contents, Vol. 40
839-843