Begell House Inc.
Heat Transfer Research
HTR
1064-2285
41
2
2010
Natural Convective Heat and Fluid Flow in a Two-Dimensional Enclosure with an Isoflux Partition Utilizing Different Fluids
107-127
Biju T.
Kuzhiveli
Mechanical Engineering Department, National Institute of Technology, Kozhikode, Kerala-673601, India
ANILKUMAR
S.H
SCT COLLEGE OF ENGG.
Steady natural convective flow and heat transfer in a two-dimensional enclosure with a centrally placed isoflux thin partition utilizing different fluids are investigated for a range of Rayleigh numbers, partition heights, and aspect ratios. The enclosure has two vertical isothermal walls and two horizontal adiabatic walls. The present study is based on a similar configuration with an isoflux thin partition symmetrically embedded at the bottom wall. The governing equations are modeled by a stream function-vorticity formulation and are solved numerically by the finite-difference approach. The Rayleigh number ranges from 103 to 106 . The study includes computations for enclosures at various partition heights ranging from 0.2 to 0.7, aspect ratio from 0.5 to 2, and isoflux values ranging from 0.5 to 2. The fluids used are air, fluorocarbon liquid (FC 77), and ethylene glycol. A comprehensive comparison with previously published numerical and experimental results showed an excellent agreement. The results are presented for different fluids in the form of streamlines and isotherm plots. Variation of the local Nusselt number over the isoflux partition and isothermal wall provides a valuable insight into the physical processes. A numerical correlation is proposed for the heat and fluid flow studies in a wide range of thermal and geometric parameters.
Modes of Heat Transfer in the Leidenfrost Effect
129-135
Rabi I.
Rabady
Electrical Engineering Department, Jordan University of Science and Technology P.O. Box 3030, Irbid 22110-Jordan
Heat transfer in the suspended liquid droplet on a surface of the hot base, which is known as the Leidenfrost effect, was widely mistaken to be credited mainly to conduction. The investigator proposed and proved experimentally that radiation is the prime mode responsible for heat transfer; this was achieved by a well isolated experiment that accounts for most of the noisy effects that are associated with the occurrence of the investigated effect. The investigator reports on observing that the Leidenfrost effect may occur even when the temperature of the hot base is below the boiling point, which proves the assumption. This new finding should significantly contribute to better understanding of the nature of the Leidenfrost phenomenon.
Numerical Study of Buoyancy-Opposed Wall Jet Flow
137-153
A.
Abdel-Fattah
Department of Mechanical Power Engineering, Faculty of Engineering Menoufiya University, Shebin El-Kom
This paper describes a numerical study of the flow and thermal fields for an opposed wall jet. The hot water is injected from a plane jet down one wall of a vertical passage of a rectangular cross section into cooled water which moves slowly upward. The flow is assumed to be two-dimensional, steady, incompressible, and turbulent. The finite volume scheme is used to solve the continuity equation, momentum equations, energy equation, and k−ε model equations. The flow characteristics were studied by varying the Richardson number (0.0 ≤ Ri ≤ 0.052) and the ratio of background velocity to jet velocity (0.05 ≤ R ≤ 0.15). The results showed that the buoyancy limited the downward penetration of the jet and its lateral spread when the Richardson number increased. The shear layer formed at the interface between the two flow streams, and it became more concentrated at higher values of the Richardson number. In this region, the intensity of the turbulence became stronger and the turbulent shear stress had a minimum value. When the velocity ratio increased, the penetration of jet decreases, its lateral spreading becomes less. Also the temperature difference decreases with the velocity ratio increase. The numerical results give a good agreement with the experiment data of [1].
Highly Nonlinear Temperature-Dependent Fin Analysis by Variational Iteration Method
155-165
F.
Fouladi
Department of Mechanical Engineering, Babol University of Technology, Babol, Iran
E.
Hosseinzadeh
Division of Thermal Energy, Technical University of Denmark, Lyngby, Denmark
Amin
Barari
Aalborg University
Ganji
Domairry
Department of Mechanical Engineering, Babol University of Technology, Babol, Iran
In this research, the variational iteration method as an approximate analytical method is utilized to overcome some inherent limitations arising as uncontrollability to the nonzero endpoint boundary conditions and is used to solve some examples in the field of heat transfer. The available exact solutions for the linear equations and the numerical solutions for the nonlinear ones are good bases to demonstrate the accuracy and efficiency of the proposed method. With the help of the method one can simply analyze the thermal characteristics of a straight rectangular fin for all possible types of heat transfer because of the explicit outputs as the successive approximate solutions.
The Effect of Suspended Particles on Marginal Stability of Magnetized Ferrofluid with Internal Angular Momentum
167-186
Sunil
Kumar
NIT Hamirpur (H.P.)
Prakash
Chand
Department of Applied Sciences, Jawahar Lal Nehru Government Engineering College, Sunder Nagar, H.P. -174 401, India
Amit
Mahajan
Department of Applied Sciences, National Institute of Technology, Hamirpur, 177 005, India; Department of Mathematics and Statistics, University of Windsor, Windsor, Ontario, N9B3P4, Canada
This paper deals with the theoretical investigation of the effect of dust particles on the marginal stability of a ferrofluid layer with internal angular momentum heated from below subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained using a linear stability analysis theory and normal mode analysis method. For the case of stationary convection, the effect of various parameters like dust particles, magnetization, coupling parameter, spin diffusion parameter, and heat conduction parameter has been analyzed. The critical magnetic thermal Rayleigh number for the onset of instability is also determined numerically for sufficiently large values of the magnetic parameter M1 and results are depicted graphically. It is observed that the critical magnetic thermal Rayleigh number is reduced because the heat capacity of clean fluid is supplemented by that of dust particles. The principle of exchange of stabilities is found to hold true for the ferrofluid with internal angular momentum in the absence of dust particles, coupling parameter, and microinertia. The oscillatory modes are introduced due to the presence of dust particles, coupling parameter, and microinertia, which were nonexistent in their absence. The sufficient conditions for the nonexistence of overstability are also obtained.
Flow Diverter Optimum Angle to Enhance Free Convection Heat Transfer from a Vertical Array of Isothermal Tubes
187-205
Mehdi
Ashjaee
Department of Mechanical Engineering, University of Tehran, Tehran, Iran
Siamak
Farahmand
Faculty of Mechanical Engineering, University of Tehran, Tehran, Iran
Ehsan
Chavoshi
Faculty of Mechanical Engineering, University of Tehran, Tehran, Iran
Tooraj
Yousefi
Mechanical Engineering Department, Razi University, Kermanshah, Iran
Effect of a flow diverter inclination angle on free-convection heat transfer from a vertical array of five isothermal horizontal tubes has been investigated experimentally using a Mach-Zehnder interferometer. Four fiberglass flow diverters with the width of a 3-cylinder diameter are placed parallel and midway between the tubes at an inclination angle of 30°, 45°, and 60°. The tubes vertical spacing (centre-to-centre) is kept constant to a 3-cylinder diameter. The experiments are carried out for various Rayleigh numbers based on the cylinder diameter in the range of 103 to 2.5 × 103 . Also the flow diverters of a 45° inclination angle which are made of copper are used in the experiments to study the effect of diverters' thermal conductivity on heat transfer from the array. Up to a maximum of 30% increase in heat transfer from the array is observed with a fiberglass flow diverter at an angle of 45°. Also a 10% decrease in the Nusselt number is occurred for the copper diverters with respect to fiberglass ones. The enhancement in heat transfer decreases as the flow diverter angle deviates from 45° for all Rayleigh numbers.