Convective heat transfer for a gaseous slip flow in micropipe and parallel-plate microchannel with uniform wall heat flux: effect of axial heat conduction

Microscale fluid dynamics has received intensive interest due to the emergence of microelectromechanical systems technology. When the mean free path of the gas is comparable to the channel’s characteristic dimension, the continuum assumption is no longer valid and velocity slip and temperature jump may occur at the duct walls. Slip flow heat transfer in annular microchannels has been examined. The effects of velocity slip and temperature jump on the hydrodynamically and thermally fully developed heat transfer characteristics for laminar flow have been studied analytically. The analysis is carried out for both uniform wall heat flux on one wall, adiabatic on the other wall, and uniform wall heat flux on both walls. The results indicate that the slip flow Nusselt numbers are lower than those for continuum flow and decrease with an increase in Knudsen number for most practical engineering applications. The effects of Knudsen number, radius ratio, and heat flux ratio on heat transfer characteristics are discussed, respectively.

Download Full-text

Influence of Short Helical Tape on Local Convective Heat Transfer and Thermal Performance Characteristics in Turbulent Decaying Swirl Flow

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.2380 ◽

2010 ◽

Vol 8 (1) ◽

Cited By ~ 1

Author(s):

Smith Eiamsa-ard ◽

Vichan Kongkaitpaiboon ◽

Khwanchit Wongcharee

Keyword(s):

Heat Transfer ◽

Convective Heat Transfer ◽

Convective Heat ◽

Thermal Performance ◽

Swirl Flow ◽

Transfer Rates ◽

Friction Factors ◽

Plain Tube ◽

Uniform Wall ◽

Uniform Wall Heat Flux

This paper reports the experimental investigation of local convective heat transfer enhancement, flow friction and thermal performance factor behaviors in the tube fitted with the short helical tapes (SHTs) acting as decaying swirl flow generators. The tapes with three different helical tape angles (? = 90°, 135° and 180°) and three different channel numbers (N = 2, 3 and 4 channels) were tested under the uniform wall heat flux condition. The performance of each tape is compared with the performance of the plain tube subject to the same pumping power. The experimental results show that the heat transfer rates and friction factors of the tube with SHTs are respectively in range of 1.15 to 1.9 and 1.49 to 2.31 times of those in the plain, corresponding to thermal performances between 0.98 and 1.46. The correlations for Nusselt number (Nu) as a function of Reynolds number (Re), Prandtl number (Pr), helical tape angle (?) and the number of channel (N) are also developed.

Download Full-text

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

Journal of Heat Transfer ◽

10.1115/1.2737483 ◽

2006 ◽

Vol 129 (8) ◽

pp. 1091-1095 ◽

Cited By ~ 33

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.

Download Full-text

Effects of Creep Flow and Viscous Dissipation in the Slip Regime for Isoflux Rectangular Microchannels

Volume 11: Micro and Nano Systems, Parts A and B ◽

10.1115/imece2007-42619 ◽

2007 ◽

Cited By ~ 2

Author(s):

Jennifer van Rij ◽

Tim Ameel ◽

Todd Harman

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Pressure Drop ◽

Convective Heat Transfer ◽

Viscous Dissipation ◽

Convective Heat ◽

Numerical Algorithm ◽

Slip Flow ◽

Creep Flow ◽

Nusselt Numbers

The effects of rarefaction on convective heat transfer and pressure drop characteristics are numerically evaluated for uniform wall heat flux rectangular microchannels. Results are obtained by numerically solving the momentum and energy equations with both first- and second-order slip velocity and temperature jump boundary conditions. The resulting velocity and temperature fields are then evaluated to obtain the microchannel Poiseuille and Nusselt numbers. In addition to the effects of rarefaction, the effects of aspect ratio, thermal creep flow, and viscous dissipation are investigated for locally fully developed Poiseuille and Nusselt numbers. The constant wall heat flux results obtained in this study are compared to constant wall temperature results obtained previously, using the same numerical algorithm, at various aspect ratios including the limiting case of parallel plate microchannels. In addition to supplying previously unreported data on slip flow convective heat transfer and pressure drop characteristics, these results verify the numerical algorithm for more complex future slip flow analyses.

Download Full-text