Mixed Convection in a Vertical Parallel Plate Microchannel

2006 ◽  
Vol 129 (2) ◽  
pp. 162-166 ◽  
Author(s):  
Mete Avcı ◽  
Orhan Aydın
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Newtonian Fluid ◽  
Wall Temperature ◽  
Parallel Plate ◽  
Temperature Jump ◽  
Velocity Slip ◽  
Convection Parameter

In this study, fully developed mixed convective heat transfer of a Newtonian fluid in an open-ended vertical parallel plate microchannel is analytically investigated by taking the velocity slip and the temperature jump at the wall into account. The effects of the mixed convection parameter, Gr/Re, the Knudsen number, Kn, and the ratio of wall temperature difference, rT, on the microchannel hydrodynamic and thermal behaviors are determined. Finally, a Nu=f(Gr∕Re,Kn,rT) expression is developed.

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.

Mixed Convection in a Vertical Microannulus Between Two Concentric Microtubes

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Mete Avcı ◽  
Orhan Aydın
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Mixed Convection ◽  
Convective Heat Transfer ◽  
Temperature Jump ◽  
Slip Flow ◽  
Velocity Slip ◽  
Slip Flow Regime ◽  
Convection Parameter ◽  
Rarefaction Effects

In this study, fully developed mixed convective heat transfer of a Newtonian fluid in a vertical microannulus between two concentric microtubes is analytically investigated by taking the velocity slip and the temperature jump at the wall into account. The effects of the mixed convection parameter Gr/Re, the Knudsen number Kn, and the aspect ratio r* on the microchannel hydrodynamic and thermal behaviors are determined. Finally, a Nu=f(Gr∕Re,Kn,r*) expression is developed. It is disclosed that increasing Gr/Re enhances heat transfer while rarefaction effects considered by the velocity slip and the temperature jump in the slip flow regime decreases it.

scholarly journals Gas Microflows in the Slip Flow Regime: A Critical Review on Convective Heat Transfer

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Stéphane Colin
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Flow Regime ◽  
Convective Heat ◽  
Temperature Jump ◽  
Numerical Models ◽  
Slip Flow ◽  
Velocity Slip ◽  
Constant Wall Temperature ◽  
Slip Flow Regime

Accurate modeling of gas microvection is crucial for a lot of MEMS applications (microheat exchangers, pressure gauges, fluidic microactuators for active control of aerodynamic flows, mass flow and temperature microsensors, micropumps, and microsystems for mixing or separation for local gas analysis, mass spectrometers, vacuum, and dosing valves…). Gas flows in microsystems are often in the slip flow regime, characterized by a moderate rarefaction with a Knudsen number of the order of 10−2–10−1. In this regime, velocity slip and temperature jump at the walls play a major role in heat transfer. This paper presents a state of the art review on convective heat transfer in microchannels, focusing on rarefaction effects in the slip flow regime. Analytical and numerical models are compared for various microchannel geometries and heat transfer conditions (constant heat flux or constant wall temperature). The validity of simplifying assumptions is detailed and the role played by the kind of velocity slip and temperature jump boundary conditions is shown. The influence of specific effects, such as viscous dissipation, axial conduction and variable fluid properties is also discussed.

Numerical Study of Convective Heat Transfer of Multiple Internal Isolated Blocks in an Enclosure

Solar Energy ◽  
2005 ◽  
Author(s):  
Xutao Zhang ◽  
Jianing Zhao ◽  
Fusheng Gao ◽  
Jun Gao ◽  
Songling Wang
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Convective Heat Transfer ◽  
Forced Convection ◽  
Convective Heat ◽  
Numerical Study ◽  
Thermal Design ◽  
Square Enclosure ◽  
Forced Convective Heat Transfer ◽  
Low Reynolds

The treatment of Convective Heat Transfer Coefficients (CHTCs) in an enclosure has a significant impact on the thermal design of electronic appliance, especially the CHTCs in an enclosure with internal isolated blocks. The CHTCs of the isolated blocks for pure natural convection are usually used, while it may not be applicable to any practice. Combined convective heat transfer, even forced convective heat transfer, is sometime more applicable in reality. In our present work, first of all, validation of the turbulence model for CFD simulation of natural convective flows in a square enclosure is performed. The values of CHTCs for vertical walls obtained by using a low Reynolds k-ε model agree well with the existed correlations. The simulation also indicates that the distance from the first grid to the wall has a significant impact on the CHTCs. Using this low Reynolds k-ε model, computer simulations of natural and forced convective heat transfer within a square enclosure containing ten isolated blocks are performed. For both the natural and forced convection, the dimensionless Nusselt numbers are derived by the obtained results. For the case of mixed convection, the CHTCs are established by blending those for natural and forced convection using the Churchill-Usagi approach, which is a general expression combines the asymptotic solutions of independent CHTCs into the mixed convection by using a Churchill-Usagi blending coefficient.

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