Hybrid Heat Transfer Augmentation from Oscillating Cylinder with Partial Superhydrophobic Janus Surfaces

Abstract

Flow over an oscillating cylinder has been the subject of various studies as well as its heat transfer characteristics due to the lock-in phenomenon which occurs as a result of multiple frequencies being present in the system. The motivation was to investigate the effect of superhydrophobicity on heat transfer and wake dynamics of partially superhydrophobic oscillating cylinder. Applying the slip condition causes the drag and root-mean-square lift coefficients to reduce by 46 and 75% in comparison to the no-slip case, respectively. It also augments the average Nusselt number by 55% accompanied by a 21% increase of the natural shedding frequency compared to the no-slip cylinder. Considering the reduction of force coefficients, it is shown that the application of slip over a 135° segment of the surface is an optimum case, resulting in 47% and 85% decrease of the drag and root-mean-square lift coefficients, respectively. Application of slip over the surface of the cylinder also causes the average Nusselt number to become nearly 6 times greater than the no-slip oscillating cylinder at the lock-in condition. Further analysis based on thermal performance index (TPI) proves that a high value of TPI = 6 can be reached for the superhydrophobic cylinder.