Slip boundary conditions

In this study, the laminar nanofluid flow in the microchannel with a discontinuous-boundary condition was investigated. Considering the slip condition, heat transfer and entropy generation were studied. Different layouts with the discontinuous-boundary condition (i.e. layouts A, B and C) were introduced and compared with the basic microchannel (microchannel with the continuousboundary condition). Reynolds number and non-slip coefficient parameters on the effect of using discontinuous-boundary condition were discussed. The results revealed that the application of discontinuous-boundary condition affects the heat transfer as well as entropy generation so that the effects are more pronounced at higher Reynold number. By applying discontinuous-boundary condition, the heat transfer through the layouts of A, B and C was 34, 45 and 53% higher than the base microchannel. Simultaneously, the entropy generation through the layouts of A, B and C intensified by 31, 39 and 46%, respectively. The results proved that the applying slip condition has two positive effects as well as a negative effect. It enhanced the heat transfer and diminished the viscose entropy generation, but on the other hand, it intensified the thermal entropy generation.

Considering the influence of wall slip on fluid flow is important for many engineering topics involving liquid-solid interfacial phenomena, such as flow through porous media, liquid coatings and lubrication. Boundary slip can act as a method to reduce friction in lubricated contacts. Furthermore, surface texturing can also play a positive role to enhance the film thickness. Therefore, combination of these two methods can be beneficial in order to improve the tribological performance of lubricated contacts. Although, in recent years the study of frictional behaviour of surface with boundary slip is getting more attention, the combination of these two methods of surfaces properties modification is interesting to investigate. For the no-slip boundary condition, the first layer of fluid molecules has the same velocity as the contacting solid surface and this condition has been widely applied in the field of fluid mechanics. In lubricated contacts with boundary slip, the first layer of the lubricant molecules move with a different velocity from that of the solid surface. In this article, the frictional behaviour of boundary slip in parallel sliding lubricated contacts for textured surfaces is investigated. This study shows that boundary slip has a significant influence on the film thickness in case of textured surfaces. Furthermore, it is possible to increase the film thickness, and enhance the frictional behaviour by modifying the boundary slip parameters.

Abstract. In this paper we investigate the Navier Stokes flow equations of micro-polar fluids by peristaltic pumping through the cylindrical tube. Taking into account the slip boundary conditions at the wall and using the suitable change of variables, we transform these equations into the ordinary differential equations for which we apply the Adomian decomposition method. Doing so we obtain the stream function, the axial velocity, the micro-polar vector and the pressure. 1.

Motivation: Nano-and Microfluidics "Microflows & Nanoflows" Karniadakis (2005) • Control and manipulation of fluids at submicron scales • The behavior of fluids at the microscale is different from 'macrofluidic' behavior (low Re, high S/V ratio)

This paper compares the optimal geometry of a rectangular microchannel heat sink (MCHS) for different channel wall surfaces, namely, conventional (uncoated and smooth), hydrophobic, and superhydrophobic. For this purpose, the three-dimensional Navier-Stokes and energy equations with the slip boundary conditions are numerically solved using the finite volume method. Shape optimization is then carried out based on the response surface methodology and the desirability function approach. The optimal channel width ratio (β) and the number of channels (N), that yield the lowest thermal resistance of the heat sink for a fixed pumping power (Ω), are reported. The results show that as the wall hydrophobicity increases, the optimal β decreases, whereas the optimal N increases. For instance, the optimal N increases from 80 for an MCHS with hydrophobic walls to 140 for its counterpart with superhydrophobic walls. This trend is attributed to the strengthening effect of interfacial slip as channel width shrinks. It is also found that the overall thermal resistance of hydrophobic and superhydrophobic MCHS is reduced by 5 and 20%, respectively, compared with that of conventional one. The results also show that the beneficial effect of increasing wall hydrophobicity on the thermal performance weakens with an increase in Ω, and almost vanishes for Ω > 2 Watts.