Liquid slip and heat transfer in rotating rectangular microchannels

Although the no-slip boundary condition has been extensively used in conventional fluid flow problems, the recent experimental results show that liquid slip can occur in micro-sized channels with hydrophobic or superhydrophobic surfaces. By exploring the liquid slip phenomena, it is possible to reduce the hydrodynamic resistance inside a microchannel. In this article, we will study the water slip phenomena in rotating microchannels. The rotating microchannel is an essential part of centrifugal microfluidic platform, which has emerged as an advanced technique in biomedical applications and chemical separations. We have numerically investigated the flow and heat transfer inside a straight rectangular microchannel subjected to orthogonal rotation and slip boundary conditions at the channel walls. A pressure based finite volume technique in a staggered grid was applied to solve the steady incompressible Navier-Stokes and energy equations. A grid independence study was performed and the code was validated against benchmark problems. The numerical results showed that, for an orthogonally rotating microchannel, different slip velocities were induced at the left and right walls whereas identical slip velocities were produced in the bottom and top walls. In the fully developed region, the effect of secondary flow increased with the rotation but decreased with the slip length. A reduction of about 28.5-36% in hydrodynamic resistance was observed using a slip length of 10 μm for channel aspect ratio α (=width/height) = 1.0 − 20.0. Correlations for friction relation (fRe) as a function of slip length (λ) and rotational Reynolds number (Reω) was proposed. The combined effect of slip length and rotation on convective heat transfer parameters was also studied. It was found that, the liquid slip can increase or decrease the Nusselt number depending on the secondary flow effect and the aspect ratio of the microchannel.