A numerical investigation of conjugate convection with surface radiation from horizontal channels with protruding heat sources has been carried out. The flow is assumed to be steady, laminar, incompressible, hydrodynamically and thermally developing. Air is considered as the working fluid. The geometric parameters such as spacing between the channel walls, size of the protruding heat sources, thickness of the substrate and the spacing between the heat sources are fixed. Results are presented to show the effect of parameters such as ReS, GrS*, kp/kf, ks/kf, εp and εs on the fluid flow and heat transfer. A correlation for the non-dimensional maximum temperature is also developed using the method of asymptotic expansions. © 2006.

C. Balaji

Department of Mechanical Engineering

Correlation methods

Heat radiation

Hydrodynamics

Incompressible flow

Laminar flow

Mixed convection

Numerical analysis

CONJUGATE MIXED CONVECTION

Horizontal channel

PROTRUDING HEAT SOURCES

SURFACE RADIATIONS

Channel flow

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IIT Madras

International Journal of Heat and Mass Transfer

Mixed convection is seen in high power devices where natural convection alone is not enough. At high temperatures radiation also contributes considerably. This work is concerned with the effect of surface radiation on mixed convection and conjugate convection in a channel with discrete heat sources. Flow is laminar and the parameters considered for this study are thermal conductivity of PCB (printed circuit board), Reynolds number, position of heat sources and emissivity of surface (emissivity of the inner surfaces of the channel are kept constant while those of the heat sources is varied). Constant fluid properties with Pr = 0.707 with Boussinesq approximation is considered. All numerical simulation has been done using FLUENT. The Reynolds number ranges from 115 to 690 (corresponding to air inlet velocity 0.25 to 1.5m/sec) and emissivity ranges from 0.1 to 0.9. Temperatures of heat sources decrease with increase in velocity, thermal conductivity of PCB and the emissivity. © Published under licence by IOP Publishing Ltd.

Fulltext

Journal of Physics: Conference Series

Conjugate mixed convection with discrete heat sources in a rectangular channel with surface radiation

In this article, the results of a numerical investigation of conjugate mixed convection from a vertical channel with discrete protruding heat sources mounted on the right side wall of a vertical channel have been presented. The flow is considered to be laminar, two-dimensional, hydrodynamically, and thermally developing. All geometric parameters such as the size of the protruding heat sources and the spacing between the protruding heat sources, the spacing between the channel walls, and the thickness of the channel walls are fixed. The parameters such as Reynolds number (ReS), modified Grashof number (Gr*S), ratio of thermal conductivity of heat sources and thermal conductivity of fluid (kp/kf), ratio of thermal conductivity of channel walls and thermal conductivity of fluid (ks/kf), emissivity of heat sources (εp), and emissivity of channel walls (εs) are varied to understand the flow and heat transfer characteristics. A correlation for the nondimensional maximum temperature has also been developed for this configuration using the method of asymptotic expansion method. Copyright © Taylor &amp; Francis Group, LLC.

Numerical Heat Transfer; Part A: Applications

Conjugate mixed convection with surface radiation from a vertical channel with protruding heat sources

In this article, numerical study of combined natural convection and radiation heat loss from a modified cavity receiver of a solar dish collector using asymptotic computational fluid dynamics approach is presented. The natural convection and radiation heat losses are estimated for different angle of inclinations ranging from 0 (aperture facing sideways) to 90 (aperture facing downward). The numerical results are presented to show the effect of parameters such as Grashof number, angle of inclination, emissivity, temperature ratio, and diameter ratio on convection and radiation heat losses. Separate Nusselt number correlations for natural convection heat loss and combined convective and radiative heat loss are given using the method of asymptotic expansions. The heat loss model is comparable with well-known models. It is observed that the present heat loss model follows the same trend as that of the other heat loss models.

Heat Transfer Engineering

Investigation of convection and radiation heat losses from modified cavity receiver of solar parabolic dish using asymptotic computational fluid dynamics

This paper reports the results of an experimental investigation of transient, turbulent mixed convection in a vertical channel in which one of the walls is heated and the other is adiabatic. The goal is to simultaneously estimate the constants in a Nusselt number correlation whose form is assumed a priori by synergistically marrying the experimental results with repeated numerical calculations that assume guess values of the constants. The convective heat transfer coefficient "h" is replaced by the Nusselt number (Nu) which is then assumed to have a form Nu = a (1+RiD)b ReDc where a, b and c are the constants to be evaluated. From the experimentally obtained temperature time history and the simulated temperature time history, based on some guess values of a, b, and c, one can define the objective function or the residue as the sum of the square of the difference between experimentally obtained and simulated temperatures. Using Bayesian inference driven by the Markov chain Monte Carlo method, one, more or all of the constants a, b and c are retrieved together with the uncertainty involved in these estimates. Additionally, the estimated parameters are compared with experimental benchmarks. © 2010 by ASME.

2010 14th International Heat Transfer Conference, IHTC 14

A correlation for Nusselt number under turbulent mixed convection using transient heat transfer experiments

Natural convection in a fluid saturated porous medium has been numerically investigated using a generalized non-Darcy approach. The governing equations are solved by using Finite Volume approach. First order upwind scheme is employed for convective formulation and SIMPLE algorithm for pressure velocity coupling. Numerical results are presented to study the influence of parameters such as Rayleigh number (106 ≤Ra ≤108), Darcy number (10-5 ≤ Da ≤ 10-2), porosity (0.4 ≤ ε ≤ 0.9) and Prandtl number (0.01 ≤ Pr ≤ 10) on the flow behavior and heat transfer. By combining the method of matched asymptotic expansions with computational fluid dynamics (CFD), so called asymptotic computational fluid dynamics (ACFD) technique has been employed to generate correlation for average Nusselt number. The technique is found to be an attractive option for generating correlation and also in the analysis of natural convection in porous medium over a fairly wide range of parameters with fewer simulations for numerical solutions. © 2007 Springer-Verlag.

Heat and Mass Transfer/Waerme- und Stoffuebertragung

Non-Darcy buoyancy driven flows in a fluid saturated porous medium: The use of asymptotic computational fluid dynamics (ACFD) approach

A numerical investigation is carried out to study fluid flow and heat transfer characteristics of conjugate mixed convection from a two dimensional horizontal channel with four protruding heat sources mounted on one of the finite thick channel walls. The flow is assumed as laminar, hydrodynamically and thermally developing. Water and FC70 are the fluids under consideration. The geometric parameters such as spacing between the channel walls (S), size of protruding heat sources (L h×t h), thickness of substrate (t) and spacing between heat sources (b) are fixed. Results are presented to show the effect of parameters such as Re S , Gr S * , Pr, k p/k f and k s/k f on fluid flow and heat transfer characteristics. Using the method of asymptotic expansions, correlations are also presented for the maximum temperature of heat source. © Springer-Verlag 2004.

Mixed convection heat transfer from a horizontal channel with protruding heat sources

In this work, the possibility of combining the method of matched asymptotic expansions with Computational Fluid Dynamics (CFD), a technique called ACFD, has been explored, for a new class of problems that involve interaction of radiation with convection. A specific problem of natural convection with surface radiation from an open cavity has been considered to demonstrate the efficacy of the ACFD approach. The work clearly demonstrates the adequacy of the approach and it appears to be an attractive option in the analysis of such multi-mode problems in heat transfer. © 2003 Elsevier Science Ltd.

International Communications in Heat and Mass Transfer

The use of ACFD approach problems involving surface radiation and free convection

This paper reports the results of a numerical study of the fundamental problem of combined mode heat transfer in a vertical slot. The paper is a sequel to the work of the authors on problems of interaction of natural convection with radiation and conduction in closed and open cavities. The present paper considers the intractions between all three modes of heat transfer and, hence, represents the most general case of interaction. The slot simulates a typical intermediate fin in a fin array or a typical section in an extruded heat sink commonly employed in practice. A detailed parametric study has led to useful correlations. The nature and extent of the coupling between the various modes of heat transfer are also elucidated. © 1995 Elsevier Science Inc.

Journal	International Journal of Heat and Mass Transfer
ISSN	00179310
Open Access	No