Comparison of three radiative formulations for radiative and convective heat transfer interactions in three dimensional turbulent boundary layers

Abstract Heat transfer from relatively short vertical isothermal cylinders in a horizontal forced fluid flow has been considered. The flow conditions are such that the buoyancy forces resulting from the temperature differences in the flow are in general significant despite of the presence of a horizontal forced flow of air, that is, mixed convective flow exists. Because the cylinders are short and the buoyancy forces act normal to the forced flow, three-dimensional flow exists. The experiments were performed in a low velocity, open jet wind tunnel. The study involved the experimental determination of the mean heat transfer coefficient and a comparison of the results with a previous numerical analysis. Mean heat transfer rates were determined using the ‘lumped capacity’ method. The mean Nusselt number has the Reynolds number, Grashof number and the height to diameter ratio of the cylinders as parameters. The results have been used to determine the conditions under which the flow departs from purely forced convection and enters the mixed convection regime, i.e., determining the conditions for which the buoyancy effects should be included in convective heat transfer calculations for short cylinders.

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Effect of Edge Conditions on Natural Convective Heat Transfer From a Narrow Vertical Flat Plate With a Uniform Surface Heat Flux

Volume 8: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A and B ◽

10.1115/imece2007-42712 ◽

2007 ◽

Cited By ~ 1

Author(s):

Patrick H. Oosthuizen ◽

Jane T. Paul

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Convective Heat Transfer ◽

Convective Heat ◽

Surface Heat Flux ◽

Three Dimensional ◽

Surface Heat ◽

Heated Plate ◽

Two Dimensional ◽

Adiabatic Surface

Two-dimensional natural convective heat transfer from vertical plates has been extensively studied. However, when the width of the plate is relatively small compared to its height, the heat transfer rate can be greater than that predicted by these two-dimensional flow results. Because situations that can be approximately modelled as narrow vertical plates occur in a number of practical situations, there exists a need to be able to predict heat transfer rates from such narrow plates. Attention has here been given to a plate with a uniform surface heat flux. The magnitude of the edge effects will, in general, depend on the boundary conditions existing near the edge of the plate. To examine this effect, two situations have been considered. In one, the heated plate is imbedded in a large plane adiabatic surface, the surfaces of the heated plane and the adiabatic surface being in the same plane while in the second there are plane adiabatic surfaces above and below the heated plate but the edge of the plate is directly exposed to the surrounding fluid. The flow has been assumed to be steady and laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. It has also been assumed that the flow is symmetrical about the vertical centre-plane of the plate. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in terms of dimensionless variables. Results have only been obtained for a Prandtl number of 0.7. A wide range of the other governing parameters have been considered for both edge situations and the conditions under which three dimensional flow effects can be neglected have been deduced.

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Pressure Drop and Convective Heat Transfer in Different SiSiC Structures Fabricated by Indirect Additive Manufacturing

Journal of Heat Transfer ◽

10.1115/1.4045732 ◽

2020 ◽

Vol 142 (3) ◽

Cited By ~ 2

Author(s):

Ehsan Rezaei ◽

Maurizio Barbato ◽

Sandro Gianella ◽

Alberto Ortona ◽

Sophia Haussener

Keyword(s):

Heat Transfer ◽

Additive Manufacturing ◽

Convective Heat Transfer ◽

Convective Heat ◽

Three Dimensional ◽

Ceramic Foam ◽

Transfer Coefficients ◽

Pressure Drops ◽

Surface Areas ◽

Averaged Model

Abstract The microstructure of porous materials has a significant effect on their transport properties. Engineered cellular ceramics can be designed to exhibit properties at will, thanks to the advances in additive manufacturing. We investigated the heat and mass transport characteristics of SiSiC lattices produced by three-dimensional (3D) printing and replication, with three different morphologies: rotated cube (RC), Weaire–Phelan (WPh), and tetrakaidecahedron (TK) lattices, and a commercially available ceramic foam. The pressure gradients were measured experimentally for various velocities. The convective heat transfer coefficients were determined through a steady-state experimental technique in combination with numerical analysis. The numerical model was a volume-averaged model based on a local thermal nonequilibrium (LTNE) assumption of the two homogeneous phases. The results showed that for TK and WPh structures, undesirable manufacturing anomalies (specifically window clogging) led to unexpectedly higher pressure drops across the samples and increased thermal dispersion. Compared to the TK and WPh structures the manufactured RC lattice and the random foam had lower heat transfer rates but also lower pressure drops. These lower values for the RC lattice and foam are also a result of their lower specific surface areas.

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Three-Dimensional Flow Effects on Convective Heat Transfer From a Window Covered by a Simple Plane Blind With No Top Covering

Heat Transfer, Volume 1 ◽

10.1115/imece2006-16054 ◽

2006 ◽

Author(s):

Patrick H. Oosthuizen

Keyword(s):

Heat Transfer ◽

Convective Heat Transfer ◽

Convective Heat ◽

Vertical Wall ◽

Three Dimensional ◽

Approximate Model ◽

Conductive Heat ◽

Three Dimensional Flow ◽

Dimensional Flow ◽

Flow Effects

Most studies of convective heat transfer in window-blind systems assume that the flow over the window-blind arrangement is two-dimensional. In some cases, however, three-dimensional flow effects can become important. The present study was undertaken to determine how significant such effects can be for the particular case of a window covered by a simple plane blind. Only convective heat transfer has been considered. The situation considered is only an approximate model of the real window-blind situation. The window is represented by a rectangular vertical isothermal wall section embedded in a large vertical adiabatic plane wall surface and exposed to a large surrounding "room" in which the temperature is lower than the window temperature. The plane blind is represented by a thin vertical wall having the same size as the "window" which offers no resistance to heat transfer across it and in which conductive heat transfer is negligible. The gaps between the blind and the window at the sides and at the top of the window-blind system are assumed to be open. The flow has been assumed to be laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces. The solution has been obtained by numerically solving the three-dimensional governing equations written in dimensionless form. The effects of the dimensionless governing variables on the window Nusselt number have been numerically examined.

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