Numerical study on the forced convective flow and heat transfer mechanism with macro-patterned hydrophilic-hydrophobic hybrid surfaces

Abstract

Hydrophilic-hydrophobic hybrid surfaces can be used to harmonize the drag and heat transfer. However, the hybrid surfaces are almost microscopic scale and hardly used for forced convection at present. In this study, six macro-patterned hydrophilic-hydrophobic hybrid surfaces (square, diamond, circle, ellipse, triangle, and sector) and a no-slip surface are built. The performances are studied with the k-ε turbulent model by COMSOL, and the mechanism of performance change is analyzed with large eddy simulation (LES). The results show that macro-patterned hybrid surfaces can all reduce the flow drag but have different influences on heat transfer. With the increasing Reynolds number, the drag reduction rate (DR) declines. The largest DRs are 14.57% with the ellipse-patterned at lower Reynolds numbers, and 13.18% with the triangle-patterned at higher Reynolds numbers. For heat transfer capability, although adding hydrophobic parts, the square-patterned and diamond-patterned hybrid surfaces can raise Nusselt numbers. Combined above, the largest goodness factor (φ) enlarged rates are 16.43% (square-patterned) and 16.35% (diamond-patterned). Meanwhile, the influencing mechanism with the macro-patterned hybrid surface concludes four factors: the velocity slip, thermal resistance increases of air cavities, eddies of hydrophilic-hydrophobic interfaces, and the guiding effect of hydrophobic patterns' edges.