Liquid Nitrogen Thin-Film Evaporation on Metal Micropillar Arrays

This paper presents an experimental characterization of liquid nitrogen (LN2) thin-film evaporation on additively manufactured and Computer Numerical Control (CNC)-machined metal micropillar arrays. Five different additively manufactured and CNC-machined titanium (Ti-64) and stainless-steel (SS-304) micropillar surfaces with [Formula: see text] heating area were tested at a pressure of 1.38 MPa and a saturation temperature of 110 K. The micropillars had widths of [Formula: see text], [Formula: see text], and [Formula: see text] wall-to-wall spacing and [Formula: see text] height. An optimum micropillar spacing was observed where the heat flux was maximized to [Formula: see text] at approximately [Formula: see text] for the additively manufactured Ti-64 surface owing to the increased mean wicking velocity. A 44.5% decrease in dry-out heat flux was observed for the micropillar surface with the higher thermal conductivity material SS-304 compared to that with Ti-64, which can be attributed to the reduced bubble nucleation time and superheat. A 34% enhancement in dry-out heat flux was observed for the additively manufactured surface compared to the CNC-machined counterpart, which can be attributed to the augmented intrinsic surface roughness. A comparison of the experimental results with the literature model showed that the model overpredicts the dry-out heat flux limit of LN2 thin-film evaporation on both additively and conventionally manufactured metal surfaces.