Condensation of Nitrogen Gas on Metal Micro-Pillar Arrays

In this study, engineered micro-pillar surfaces were employed to demonstrate the condensation of nitrogen gas for a cryogenic heat pipe. To re-capture water vapor during thermal excavation, UTEP Aerospace Center team is developing an engineered additively manufactured cryogenic heat pipe to absorb heat from the incoming vapor and collect ice on the evaporator section of the heat pipe. The absorbed heat from the sublimated water vapor will evaporate the liquid nitrogen inside the heat pipe that requires to be condensed at the engineered condenser by rejecting heat to the atmosphere. The aim of this work is to characterize the condensation heat transfer performance of additively manufactured micropillar arrays. High pressure (similar to 1.38 MPa) saturated nitrogen gas (similar to 110 K) was condensed on the vertically aligned 1 cm x 1 cm micro pillar arrays of both additively manufactured titanium (Ti64) micro-pillar test surface and conventional CNC machined SS 304 micro-pillar surfaces. Both additively manufactured and conventional CNC machined micro-pillars have width of 400 mu m, wall-to-wall spacing of 500 mu m, and height of 600 mu m. A heat flux of similar to 41 W/cm(2) was achieved at a degree of sub-cooling of similar to 17 K during the film condensation for the additively manufactured Ti-64 surface. A maximum heat flux of similar to 22 W/cm(2) was achieved at a degree of sub-cooling of similar to 18 K for the CNC machined SS-304 sample.