Thin Film Evaporation of Liquid Nitrogen on Additively Manufactured Micro-Structured Surfaces for Lunar Ice Collection

Abstract

This work presents the experimental characterization of thin film evaporation heat transfer of an engineered heat pipe on additively manufactured micro-pillar arrays using saturated liquid nitrogen as the working fluid. Three engineered micro-pillar arrays of 400 400 μm square pillar width, 500 μm, 600 μm and 700 μm wall-to-wall spacing and 600 μm pillar height were fabricated using advanced 3D printing method from titanium alloy (Ti-64). The test articles were provided with primary and secondary reservoirs, and overflow drain port to ensure enough liquid supply to the test surfaces and capillary driven thin film evaporation heat transfer tests. The test samples measure 3 cm × 4 cm with active heating area of 1 cm × 1 cm micro pillar arrays. G-10 insulated custom-built copper heater block was used to provide the joule heating to the test surfaces. The cryogenic thin film evaporation experiments were performed using a custom-built high pressure (up to 3 MPa) stainless steel test chamber. The tests were performed at 1.38 MPa pressure where the chamber was pressurized using cold gaseous nitrogen (GN2), and corresponding saturation temperature of 110 K. A maximum dry-out heat flux of ~ 91 W/cm2 was achieved at a wall-superheat of ~ 11 K for the Ti-64 micro-pillar arrays of 400 μm square pillar width, 500 μm wall-to-wall spacing and 600 μm pillar height during thin film evaporation of saturated liquid nitrogen. This work aims to develop an engineered cryogenic heat pipe for lunar ice collection.