Liquid Nitrogen Spray Cooling of a Simulated Electronic Chip

Abstract

Evaporative spray cooling with liquid nitrogen is investigated as a candidate method for thermal management of electronic assemblies utilizing High Temperature Super-Conducting (HTSC) materials. A heated copper surface simulating an electronic chip is cooled in two configurations: spraying vertically upwards onto the heated surface (normal impingement), and spraying across the heated surface in a confined channel (narrow gap). For both cases, heat transfer is characterized for a range of supply pressures and liquid inlet temperatures. For the normal impingement study, three full cone nozzles were tested at variable spacing from the heated surface. For the narrow gap study, one fan-spray atomizer was tested with a fixed gap height of 1 mm. The results indicated that heat transfer rates do not vary considerably over a wide range of operating conditions. Heat flux up to 75 W/cm² was obtained at a surface temperature below 83 K. Two distinct regions of heat transfer are observed: a forced-convection dominated region at low superheat, followed by a thin film evaporation region where heat transfer coefficients rise sharply with increasing surface temperature. In general, heat transfer is roughly an order of magnitude improved over pool boiling. The results have favorable implications for thermal management of advanced cryoelectronic packages.