Numerical investigation on slip-flow and heat transfer characteristics in the entrance region of elliptical microchannels

Abstract

This paper concentrates on the numerical investigation of slip-flow and heat transfer characteristics in the entry region of elliptical microchannels under isothermal or isoflux boundary conditions. Slip boundaries caused by rarefaction effect are implemented using user-defined functions. The impacts of Reynolds number (25≤ Re ≤ 1000), Knudsen number (0.01≤ Kn ≤ 0.1), Peclet number (17.5 ≤ Pe ≤ 700) and aspect ratio (0.2≤ ε ≤ 1) on the apparent friction factor Reynolds number product fappRe and local Nusselt number Nu(x) are discussed in detail. The results demonstrate that at the entrance region, fappRe decreases with increasing Re, especially for ε = 0.33, Kn = 0.01 and Re < 500. However, it is independent of Re at fully developed region. At ε = 0.75 and x∗ = 0.0001, when Pe ranges from 17.5 to 350, Nu(x) is decreases by 87 % at the T boundary. The value of Nu(x) for Kn = 0.04 is reduces by 333 when compared with no-slip case at Pe is 17.5. These indicate that heat transfer near the inlet can be effectively enhanced by axial heat conduction. While rarefaction reduces friction losses and weakens the effect of axial heat conduction. Generalized correlations are proposed for fully developed Nu.

Keywords

• Elliptical microchannels
• Entrance region
• Rarefaction effect
• Axial heat conduction