Experimental investigation of liquid jet impingement heat transfer at superhydrophobic surfaces

This paper presents an experimental exploration of thermal transport due to a water jet impinging on post patterned superhydrophobic surfaces and provides the first experimental data for this problem. The surface is heated to temperatures much lower than the saturation value. Results are obtained for a smooth hydrophobic surface and superhydrophobic surfaces with varying microfeature pitch (w = 8, 16, and 24 mu m) and cavity fraction (Fc = 0.56 and 0.85) and are compared to results derived from a previously published analytical model. The jet Reynolds number varied from 1.1 x 104 to 1.7 x 104 and the nominal surface heat flux varied from 2.5 x 104 to 4.9 x 104 W/m2. Results obtained for all superhydrophobic surfaces show a significant decrease in the local and average Nusselt numbers (up to 30 % reduction) compared to impingement on a smooth surface. Further, the reduction is a strong function of the surface post and cavity geometric parameters. The effective temperature jump length is determined for all scenarios considered, representing the first experimental measurements of temperature jump length for heat transfer at superhydrophobic surfaces. Functional relationships showing how the average Nusselt number and the non -dimensional temperature jump length depend on the superhydrophobic surface parameters are also presented.