Begell House Inc.
Heat Transfer Research
HTR
1064-2285
42
3
2011
Heat Transfer Enhancement in a Narrow Concentric Annulus in Decaying Swirl Flow
199-216
Ali M.
Jawarneh
Department of Mechanical Engineering, The Hashemite University
The characteristics of decaying swirling flows and forced convective heat transfer on the conditions of both laminar and turbulent flow in a narrow concentric annulus were simulated. The governing equations are solved numerically via a finite volume method. A uniform wall temperature at the inner wall and adiabatic conditions at the outer wall are considered as thermal boundary conditions. Solutions for the axial and swirl velocity distributions and the Nusselt number are obtained for different values of the inlet swirl number and the Reynolds number. Simulations show that the inlet swirl number have great influences on the heat transfer characteristics. Under both developing laminar and developed turbulent flow conditions, the increases of the inlet swirl number will enhance the heat transfer. When the inlet swirl number increases it increases the axial velocity near the wall and reduces it at the mid-gap to achieve the conservation of mass due to the existence of secondary flows in the annulus due to centrifugal forces. The increase of the near-wall velocity, in turn, produces larger temperature gradients and a higher heat transfer rate. The swirl velocity profiles decay gradually downstream as a result of friction which leads to damping of the tangential velocity. The swirl has a pronounced effect on the turbulent kinetic energy which is increased evidently with the swirl number. Obviously, a higher turbulence level leads to a considerable improvement in the heat transfer rate. Turbulence level improvement can be attributed to the high velocity gradients. Numerical results show that the turbulent kinetic energy is lower in the mid-gap and higher in the near-wall regions. Moreover, the turbulent structures near the outer wall are more activated than those near the inner wall. The comparison between predicted and experimental data of average Nusselt numbers was found to be in good agreement.
Natural Convection Heat Transfer in Right Triangular Enclosures with a Cold Inclined Wall and a Hot Vertical Wall
217-231
Mostafa
Mahmoodi
Department of Mechanical Engineering, Amirkabir University of Technology, Tehran 15875-4413,
Iran; Department of Mechanical Engineering, University of Kashan, Kashan 87317-53153, Iran
Laminar natural convection fluid flow and heat transfer in right triangular cavities with a varying aspect ratio has been investigated numerically. The vertical wall of triangular cavities is kept at a high temperature, Th, while the inclined wall is kept at a relatively low temperature, Tc, and the base wall is insulated. The nonlinear coupled governing equations have been solved using the finite volume method while the coupling between velocity and pressure fields is done using the SIMPLE algorithm. Calculations were performed for the aspect ratio and the Rayleigh number ranging from 0.25 to 4 and from 104 to 106, respectively. The obtained results show that for all cavity aspect ratios and at all range of Rayleigh number considered a primary clockwise eddy if formed inside the cavity. Moreover it is found that with increase in the aspect ratio, the average Nusselt number of a hot vertical wall increases significantly.
Viscous and Inviscid Solutions of Some Gas Mixture Problems
233-250
Iman
Zahmatkesh
Department of Mechanical Engineering, Islamic Azad University, Mashhad Branch, Mashhad, Iran
Homayoun
Emdad
School of Mechanical Engineering, Shiraz University, Shiraz 71348-51154, Iran
Mohammad M.
Alishahi
School of Mechanical Engineering, Shiraz University, Shiraz 71348-51154, Iran
The aim of the present paper is to simulate some gas mixture problems in the context of a converging-diverging nozzle. A recently proposed multifluid model is utilized for the description of the flow fields. The model consists of separate balance equations for each component species of the system. Thereby, it provides details of the flow fields for each of the constituents separately, which is not available in other continuum descriptions. The new model also computes transport coefficients from some kinetic relations without the requirement of being input externally. Moreover, it automatically describes diffusion processes excluding the use of any coefficients for ordinary, pressure, and thermal diffusion that are generally required in Navier-Stokes computation of gas mixture flows.
During the analysis of the current mixture problems, the viscous as well as the inviscid forms of the multifluid balance equations are solved and the corresponding results are compared with those of the Navier-Stokes and Euler equations.
Numerical Study of Free Convection Heat Transfer in a Square Cavity with a Fin Attached to Its Cold Wall
251-266
Saeid
Jani
Department of Mechanical Engineering, Golpayegan University of Technology, Golpayegan, Iran
Meysam
Amini
Energy Technologies Research Division, Research Institute of Petroleum Industry (RIPI), Tehran, Iran
Mostafa
Mahmoodi
Department of Mechanical Engineering, Amirkabir University of Technology, Tehran 15875-4413,
Iran; Department of Mechanical Engineering, University of Kashan, Kashan 87317-53153, Iran
Fluid flow and natural convection heat transfer in a differentially heated square cavity with a fin attached to its cold wall is investigated numerically. The top and the bottom horizontal walls of the cavity are insulated while the left and right vertical walls of the cavity are maintained at a constant temperature Th and Tc, with Th > Tc, respectively. The governing equations written in terms of the primitive variables are solved numerically using the finite volume method and the SIMPLER algorithm. Using the developed code, a parametric study is performed, and the effects of the Rayleigh number, length of the fin and its position on the flow pattern and heat transfer inside the enclosure are investigated. The results show that for high Rayleigh numbers, a longer fin placing at the middle of the right wall has a more remarkable effect on the flow field and heat transfer inside the cavity.
An Optimal Homotopy Asymptotic Method Solution of Injection of a Newtonian Fluid Through One Side of a Long Vertical Channel
267-283
Saeed
Islam
Department of Mathematics, Abdul Wali Khan University Mardan, 23200 Pakistan
Abdul Majeed
Siddiqui
Department of Mathematics, Pennsylvania State University, York Campus, 1031 Edgecomb Avenue, York, PA 17403, USA
Ishtiaq
Ali
44000, COMSATS Institute of Information Technology, Park Road, Chak Shahzad,
Islamabad, Pakistan.
Manzoor
Ellahi
COMSATS Institute of Information Technology, Park Road, Islamabad, Pakistan
In this paper, the Optimal Homotopy Asymptotic Method is adopted for solving a nonlinear ordinary differential equations arising in the study of injection of a Newtonian fluid through one side of a long vertical channel. It is found that transformation proposed by Wang and Salak (1974) reduces the governing equations into a set of nonlinear ordinary differential equations subject to the relevant boundary conditions. These equations have been solved approximately by using the Optimal Homotopy Asymptotic Method (OHAM) and for assessment it is approximated by the Homotopy Analyses Method. The velocity field and heat transfer on the walls is examined carefully by various Reynolds and Peclet numbers.
Numerical Optimization of Curved Vertical Walls in Natural Convection Flow Fields by the Entropy Generation Minimization Method
285-299
O. Nourani
Zonouz
Mechanical Engineering Department, Marvdasht Islamic Azad University, Fars, Iran
Mehdi
Salmanpour
Department of Mechanical Engineering, Azad Islamic University, Marvdasht Branch, Fars, Iran
In this article, the rate of heat transfer from a curved vertical hot wall in a natural convection flow field was optimized by using the entropy generation minimization method. The continuity, momentum, and energy equations and equations of the second law of thermodynamics are solved iteratively by using the finite difference scheme. The length of the wall is divided into three parts. The curvature induced to the middle part and the curvature radii changed between 0 deg (flat plate) to 45 deg (half circle) in concave and convex shapes. Entropy generation, shear stress, Nusselt number and Bejan number distributions are computed along the wall. It is found in natural convection flow fields. The value of the Bejan number is approximately equal to unity, because of the small value of velocity in natural convection heat transfer; conduction heat transfer dissipation is dominant in entropy generation. The results show that in the convex case the value of entropy generation increases by increasing the curvature radii; but in the concave case the magnitude of entropy generation decreases to approximately 12 deg, after that this value increases.