Hydrophobic surfaces, enabling flow slip past a solid boundary, can potentially be effective for heat transfer enhancement in heat exchanger applications. The scope of the present work is the computational study of forced convection heat transfer in flow past a hydrophobic cylinder, maintained at constant surface temperature. Hydrophobic surfaces are applied in flow control applications, since they enable flow slip past a solid boundary; as a result, they can contribute to flow stabilization. At the same time, hydrophobic surfaces are a potential means for heat transfer enhancement. In the present study, a computational investigation of forced convection heat transfer in cross-flow past a circular hydrophobic cylinder is performed by means of Computational Fluid Dynamics; the effects of hydrophobicity on flow stability and forces are also quantified. Here, low Reynolds number values, Re, are considered, whereas the Prandtl number, Pr, is maintained constant, equal to unity. Hydrophobicity is modelled by means of the Navier model.
For slip conditions applied on the entire cylinder surface, the present results demonstrate that the stabilizing effect of increasing the non-dimensional slip length, b* = b/D, b being the slip length and D the cylinder diameter, is accompanied by a simultaneous enhancement of heat transfer. In particular, the time-averaged mean Nusselt number, Num, is found to be an increasing function of both b* and Re. Further, it is shown that, for the same levels of b*, an equivalent heat transfer rate can be achieved by substantially reducing the extent of the hydrophobic region, in particular by excluding the rear stagnation point region, i.e. at a significantly reduced cost. Overall, the present results illustrate that implementing partial hydrophobicity results in a substantial enhancement of heat transfer rates and a simultaneous (partial or full) suppression of the wake unsteadiness.
