Hydrothermal performance analysis of various surface roughness configurations in trapezoidal microchannels at slip flow regime

2020 ◽  
Vol 28 (6) ◽  
pp. 1522-1532 ◽  
Author(s):  
Davood Toghraie ◽  
Ramin Mashayekhi ◽  
Mohammadreza Niknejadi ◽  
Hossein Arasteh
Keyword(s):  
Surface Roughness ◽  
Performance Analysis ◽  
Flow Regime ◽  
Slip Flow ◽  
Slip Flow Regime

Roughness Effect on the Heat Transfer Coefficient for Gaseous Flow in Microchannels

2010 ◽  
Author(s):  
Metin B. Turgay ◽  
Almila G. Yazicioglu ◽  
Sadik Kakac
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Nusselt Number ◽  
Flow Regime ◽  
Viscous Dissipation ◽  
Slip Flow ◽  
Roughness Height ◽  
Working Fluid ◽  
Axial Conduction ◽  
Slip Flow Regime

Effects of surface roughness, axial conduction, viscous dissipation, and rarefaction on heat transfer in a two–dimensional parallel plate microchannel with constant wall temperature are investigated numerically. Roughness is simulated by adding equilateral triangular obstructions with various heights on one of the plates. Air, with constant thermophysical properties, is chosen as the working fluid, and laminar, single-phase, developing flow in the slip flow regime at steady state is analyzed. Governing equations are solved by finite element method with tangential slip velocity and temperature jump boundary conditions to observe the rarefaction effect in the microchannel. Viscous dissipation effect is analyzed by changing the Brinkman number, and the axial conduction effect is analyzed by neglecting and including the corresponding term in the energy equation separately. Then, the effect of surface roughness on the Nusselt number is observed by comparing with the corresponding smooth channel results. It is found that Nusselt number decreases in the continuum case with the presence of surface roughness, while it increases with increasing roughness height in the slip flow regime, which is also more pronounced at low-rarefied flows (i.e., around Kn = 0.02). Moreover, the presence of axial conduction and viscous dissipation has increasing effects on heat transfer with increasing roughness height. Even in low velocity flows, roughness increases Nusselt number up to 33% when viscous dissipation is considered.

Averaged Reynolds Equation Extended to Gas Lubrication Possessing Surface Roughness in the Slip Flow Regime: Approximate Method and Confirmation Experiments

1989 ◽  
Vol 111 (3) ◽  
pp. 495-503 ◽  
Author(s):  
Y. Mitsuya ◽  
T. Ohkubo ◽  
H. Ota
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Approximate Method ◽  
Flow Regime ◽  
Reynolds Equation ◽  
Slip Flow ◽  
Roughness Effects ◽  
Gas Lubrication ◽  
Slip Flow Regime ◽  
Average Film Thickness

The average film thickness theory is extended to gas lubrication possessing surface roughness in the slip flow regime. A simplified averaged Reynolds equation is derived and its applicability is confirmed through comparing with experiments. This averaging equation makes use of the mixed average film thickness defined as Havem = αHm + (1 − α)Hmˆ, where m = 1, 2 and 3; α indicates the mixing ratio; and H¯ and Hˆ denote the arithmetically and harmonically averaged film thicknesses. The experiments were performed using computer flying heads having precisely photolithography-fabricated longitudinal, transverse or checkered pattern roughnesses under submicron spacing conditions. From the excellent agreement obtained between the calculated and experimental results, it can be concluded that the assumption that velocity slippage occurs along the surface even if roughnes is present is justified, and that the approximate method is applicable for determining the surface roughness effects in the slip flow regime.

scholarly journals Thermal diffusion and chemical reaction effects on unsteady flow past a vertical porous plate with heat source dependent in slip flow regime

2016 ◽  
Vol 13 (1) ◽  
pp. 51-62 ◽  
Author(s):  
Narasu Siva Kumar ◽  
Rushi Kumar ◽  
A. G. Vijaya Kumar
Keyword(s):  
Fluid Flow ◽  
Heat Source ◽  
Flow Regime ◽  
Thermal Diffusion ◽  
Chemical Reaction ◽  
Slip Flow ◽  
Porous Plate ◽  
Stream Velocity ◽  
Vertical Porous Plate ◽  
Slip Flow Regime

The present study investigates an analytical solution of free convective unsteady fluid flow in presence of thermal diffusion and chemical reaction effects past a vertical porous plate with heat source dependent in slip flow regime. The plate is assumed to move with a constant velocity in the direction of fluid flow, while free stream velocity is assumed to follow exponentially increasing small perturbation law. The velocity, temperature and concentration profiles are presented graphically for different values of the parameters entering into the problem. Finally the effects of pertinent parameters on the skin friction coefficient, Nusselt number and Sherwood numbers distributions are derived and have shown through graphs and tables by using perturbation technique.

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