Boiling and Condensation of a Dielectric Liquid in a Closed Enclosure for Electronics Cooling Applications

Abstract

Immersion cooling with a dielectric fluid may provide better cooling while requiring less energy than traditional air and forced convection cooling methods in electronic cooling applications. In a closed immersion cooling system, the fluid (coolant) cycles through the boiling surface and the condenser. In steady state, the boiling and the condensation balance each other. Studying the impact of operating parameters on this balance will guide future designs. In this paper, the vaporization and condensation phenomena have been studied at various operating conditions for an enclosed immersion cooling system, with a 6.35 cm x 6.35 cm porous coated copper surface and cooled by condensation on a cold surface at its top. The filling ratio of the chamber and the flow rate at constant inlet temperature of the water cooling the condensation surface (cold plate) were the studied operating parameters. A two-phase experimental apparatus has been specifically designed to hold coolant (Novec™7000) at an absolute pressure range between 103 kPa to 172 kPa. The experimental procedure followed a rigorous degassing protocol to remove excess air inside the tank (or dissolved in the coolant).At steady-state and the same input heat flux, an increased water flow rate (from 0.2 L/min to 1 L/min) of the condenser led to a lower pressure (35% less), a lower boiling surface temperature (20% less) and a lower thermal resistance (27% less) between the boiling surface and the cooling water inlet. An increase in the filling ratio led to a lower pressure, a similar boiling surface temperature and a similar total thermal resistance. The best overall thermal resistance achieved was (0.128±0.006) °C/W at (12.4±0.6) W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> applied power, heater temperature of (85.5±0.2) °C, cold plate flow rate of (1±0.01) L/min and internal pressure of (165±2) kPa.Since the vaporization and condensation phenomena for a closed immersion cooling systems have not been extensively studied in the literature, the results of this study provide insights into how operating parameters affect the steady-state conditions of the system, to facilitate the design of enclosed immersion cooling systems using a dielectric fluid.