Capillary Wicking and Heat Transfer during Boiling of HFE-7100 on Black Silicon Surfaces with Different Morphologies

Abstract

The paper presents the results of an experimental study on the effect of the morphology of a hemi-wicking black silicon surface on capillary wicking and heat transfer characteristics during pool boiling of HFE-7100. The investigated homogeneous and hybrid silicon surfaces were fabricated using low-temperature plasma-chemical etching. It was shown that the modified silicon surfaces enhance liquid wicking, with taller homogeneous needle-like microstructures promoting more efficient liquid spreading. Hybrid surfaces (combining low and high needle-like microstructures) exhibit significantly higher values of the Wi number (characterizing capillary wicking) compared to homogeneous ones. Heat transfer experiments were carried out on the most efficient (in terms of capillary wicking) homogeneous and hybrid black silicon surfaces. Unlike in the case of water boiling, the expected increase in critical heat flux (CHF) was not achieved for HFE-7100 on black silicon surfaces due to the partial or complete loss of hydrophilicity during boiling. Instead, the experiments revealed a noticeable enhancement of the heat transfer coefficient (HTC) on both homogeneous and hybrid surfaces, which can be attributed exclusively to the effect of microstructuring rather than capillary wicking.