Effect of thermal boundary conditions on forced convection under LTNE model with no-slip porous-fluid interface condition

Natural convection inside a rectangular cavity with different temperature boundary conditions on the cold top plate was studied using a Mach-Zehnder interferometer for θ = 15, 45, and 60 deg to the horizontal. At θ = 60 deg coupling with external forced convection and non-coupled heat transfer from a cavity with an isothermal top plate was studied. In all experiments the bottom hot plate was isothermal. The Rayleigh number Ra was varied from subcritical to 6×105 and the cavity aspect ratio ARx, from 6.68 to 33.4. The Reynolds number of the external forced flow Redh was constant and approximately equal to 5.8×104. It was found that for Ra ≲ 3×104 the differing thermal boundary conditions at the top plate did not affect the local or average heat transfer rates from the cavity. For Ra ≳ 3×104 coupling at the top plate compared to the non-coupled case resulted not only in a reduction in the variation of the local heat transfer rates at the cold plate, but also in a significant reduction in the variation of the average transfer rates from hot and cold plates of the cavity. Forced convection at the top plate as compared to natural convection resulted only in a small reduction in the heat transfer coefficient at the cold plate. Correlation equations for coupled and noncoupled average heat transfer rates are presented.

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Azimuthally inhomogeneous thermal boundary conditions in turbulent forced convection pipe flow for low to medium Prandtl numbers

International Journal of Heat and Fluid Flow ◽

10.1016/j.ijheatfluidflow.2019.05.003 ◽

2019 ◽

Vol 77 ◽

pp. 352-358

Author(s):

Steffen Straub ◽

Pourya Forooghi ◽

Luca Marocco ◽

Thomas Wetzel ◽

Bettina Frohnapfel

Keyword(s):

Boundary Conditions ◽

Forced Convection ◽

Pipe Flow ◽

Thermal Boundary Conditions ◽

Prandtl Numbers

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Thermal Boundary Conditions and Some Solutions for Laminar Duct Flow Forced Convection

Journal of Heat Transfer ◽

10.1115/1.3450158 ◽

1974 ◽

Vol 96 (2) ◽

pp. 159-165 ◽

Cited By ~ 76

Author(s):

R. K. Shah ◽

A. L. London

Keyword(s):

Laminar Flow ◽

Boundary Conditions ◽

Forced Convection ◽

Heat Exchangers ◽

Duct Flow ◽

General Classification ◽

Compact Heat Exchangers ◽

Thermal Boundary Conditions

The importance of laminar flow forced convection theoretical solutions for the design of compact heat exchangers has been well realized. Many of these theoretical solutions published in the literature are difficult to interpret by a designer, because thermal boundary conditions used in the analysis are generally not defined clearly and consistently. The objective of this paper is to clarify this situation by a systemized presentation. Starting with a general classification, nine specific thermal boundary conditions are categorized for singly connected ducts. At the end, the most useful fully developed laminar flow solutions for some important duct geometries are summarized for the designer.

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