Mixed Convection in Ducts With Asymmetric Wall Heat Fluxes

1987 ◽  
Vol 109 (4) ◽  
pp. 947-951 ◽  
Author(s):  
Win Aung ◽  
G. Worku
Keyword(s):  
Mixed Convection ◽  
Parallel Plate ◽  
Numerical Study ◽  
Vertical Channel ◽  
Quantitative Information ◽  
Heat Fluxes ◽  
Forced Flow ◽  
Uniform Wall ◽  
Laminar Convection ◽  
Asymmetric Heating

Results are presented of a numerical study dealing with combined free and forced laminar convection in a parallel plate vertical channel with asymmetric wall heating at uniform heat fluxes (UHF). The forced flow at the inlet is assumed to be spatially uniform and directed vertically upward. Quantitative information is provided pertaining to the effects of buoyancy and asymmetric heating on the hydrodynamic and thermal parameters. For values of Gr/Re up to 500 no flow reversal is predicted, in contrast to the case of uniform wall temperatures (UWT) recently reported. Other fundamental differences between UHF and UWT also are indicated.

Mixed Convection in a Vertical Parallel Plate Microchannel With Asymmetric Wall Heat Fluxes

2006 ◽  
Vol 129 (8) ◽  
pp. 1091-1095 ◽  
Author(s):  
Mete Avcı ◽  
Orhan Aydın
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mixed Convection ◽  
Convective Heat Transfer ◽  
Parallel Plate ◽  
Temperature Jump ◽  
Velocity Slip ◽  
Heat Fluxes ◽  
Limiting Case ◽  
Convection Parameter

In this study, exact analytical results are presented for fully developed mixed convective heat transfer of a Newtonian fluid in an open-ended vertical parallel plate microchannel with asymmetric wall heating at uniform heat fluxes. The velocity slip and the temperature jump at the wall are included in the formulation. The effects of the modified mixed convection parameter, Grq∕Re, the Knudsen number, Kn, and the ratio of wall heat flux, rq=q1∕q2, on the microchannel hydrodynamic and thermal behaviors are determined. Finally, a Nu=f(Grq∕Re,Kn,rq) expression is developed. For, the limiting case of Kn=0, the results are found to be in an excellent agreement with those in the existing literature.

Numerical Study on Mixed Convection in Porous Media in a Channel With an Open Cavity Below

2010 ◽  
Author(s):  
Bernardo Buonomo ◽  
Oronzio Manca ◽  
Paolo Mesolella ◽  
Sergio Nardini
Keyword(s):  
Mixed Convection ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Vertical Wall ◽  
Open Cavity ◽  
Temperature Fields ◽  
Forced Flow ◽  
Heated Wall ◽  
Local Thermal Equilibrium ◽  
Uniform Heat Flux

A numerical analysis of mixed convection in gas saturated metal foam in a horizontal channel with an open cavity heated at uniform heat flux on a vertical wall is studied numerically. Non-local thermal equilibrium and Brinkman-Forchheimer-extended Darcy model are assumed. Boussinesq approximation with constant thermophysical proprieties are considered. Results are carried out for an aluminium foam with 10 PPI and ε = 0.909, the fluid is air and for the assisting case. Results, for different Peclet and Rayleigh numbers, are given in terms of solid and fluid wall temperatures and local Nusselt numbers and stream function and temperature fields. Results show that diffusive effect determined lower temperature values inside the solid and the fluid temperatures are higher in all considered cases. The interaction between the forced flow in the channel and the buoyancy due to the heated wall determines different thermal and fluid dynamic behaviors.

A Numerical Study of Developing Buoyancy-Assisted Mixed Convection With Spatially Periodic Wall Heating

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Chris D. Dritselis
Keyword(s):  
Mixed Convection ◽  
Richardson Number ◽  
Numerical Study ◽  
Heat Fluxes ◽  
Computational Time ◽  
Convection Flow ◽  
Parabolic Model ◽  
Flow Modification ◽  
Elliptic Model ◽  
Spatially Periodic

The validity of a parabolic model for simulating the developing buoyancy-assisted mixed convection flow in a vertical channel with spatially periodic wall temperature is verified by a full elliptic model of the momentum and energy equations. A detailed assessment of the effects of the grid resolution, the Richardson number, the Reynolds number, and the preheating zone is presented through extensive comparisons of the velocity and temperature fields and spatial variations of pressure and local heat fluxes at the walls yielded by both models. The parabolic model is capable of reproducing the flow modification into a pattern consisting of a recirculating zone with increasing Richardson number, capturing adequately the main trends of the flow and heat transfer results. For certain combinations of the relevant nondimensional parameters, the solutions of the parabolic model agree reasonably well with those of the elliptic model from a quantitative point of view. In all the cases examined here, the computational time needed by the parabolic model is significantly smaller than that of the elliptic model.

scholarly journals Effects of Reynolds and Prandtl Number on Mixed Convection in an Octagonal Channel with a Heat-Generating Hollow Cylinder

2012 ◽  
Vol 4 (2) ◽  
pp. 337 ◽  
Author(s):  
S. Parvin ◽  
R. Nasrin
Keyword(s):  
Heat Transfer ◽  
Finite Element Method ◽  
Finite Element ◽  
Prandtl Number ◽  
Mixed Convection ◽  
Hollow Cylinder ◽  
Numerical Study ◽  
Vertical Channel ◽  
Fluid Temperature ◽  
Element Method

A numerical study has been executed to analyze the effects of Reynolds and Prandtl number on mixed convective flow and heat transfer characteristics inside an octagonal vertical channel in presence of a heat-generating hollow circular cylinder placed at the centre. All the walls of the octagon are considered to be adiabatic. Galerkin weighted residual finite element method is used to solve the governing equations of mass, momentum and energy. Results are presented in terms of streamlines, isotherms, the average Nusselt number and the maximum fluid temperature for different combinations of controlling parameters namely, Reynolds number, Prandtl number and Richardson number. The results indicate that the flow and thermal fields as well as the heat transfer rate and the maximum fluid temperature in the octagonal channel depend significantly on the mentioned parameters.Keywords: Heat-generation; Hollow cylinder; Octagonal channel; Mixed convection; Finite element method.© 2012 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi: http://dx.doi.org/10.3329/jsr.v4i2.8142   J. Sci. Res. 4 (2), 337-348 (2012)

Convective Cooling of a PCB Like Surface With Mixed Heating Conditions in a Vertical Channel

2006 ◽  
Vol 129 (2) ◽  
pp. 129-143 ◽  
Author(s):  
Vipin Yadav ◽  
Keshav Kant
Keyword(s):  
Heat Flux ◽  
Nusselt Number ◽  
Printed Circuit Boards ◽  
Empirical Relation ◽  
Load Condition ◽  
Vertical Channel ◽  
Heat Fluxes ◽  
Experimental Investigations ◽  
Uniform Heat Flux ◽  
Uniform Wall

Printed circuit boards (PCBs) with uniform surface temperature and uniform wall heat flux are ideal to study. However, in reality, the heating conditions existing on the PCB surfaces are much different from the ideal ones. Present attempts have been made to study different combinations of uniform heat flux (UHF) and uniform wall temperature (UWT) heating conditions on a single surface and to develop more realistic relationships between various flow and thermal parameters for evaluating the local and averaged Nusselt number. Both the numerical and experimental investigations were undertaken to study partial and mixed UHF and UWT heating conditions on a buoyancy assisted convection cooling of simulated PCB forming one wall of the vertical channel while, the other wall was kept insulated. The current work considers moderate to high flow Reynolds number (14.1×103≤Re≤2.35×105) in the channel and range of heat fluxes near that occurring in electronic cooling applications using air as a coolant (0.0<q≤5.0W∕cm2). Data for heat flux and Nusselt number occurring at various locations of the plate surface under different heating conditions are presented to analyze variation patterns; and an empirical relation is put forward which is capable of predicting Nu under the heating conditions mentioned. The empirical expression obtained can be used for getting an optimized layout of the PCBs inside the equipment cabinet, thus resulting in better design for more reliable and safe operation under potentially harsh environment and/or maximum load condition.

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