Comparison of Deionized Water and FC-72 in Pool and Jet Impingement Boiling Thermal Management

Abstract

High heat fluxes and stringent constraints on surface temperature and its uniformity during thermal management of electrical and electronic components often necessitate use of boiling heat transfer. This paper compares the pool and jet impingement boiling heat transfer characteristics of deionized water and FC-72 at an equivalent fluid saturation temperature of 57°C and for identical experimental conditions. To lower the saturation temperature of water down to 57°C, experiments with water are performed at a reduced absolute system pressure of 0.176 bar. Despite the reduction in pressure, pool boiling critical heat flux with deionized water is found to be 3.6 times larger than with FC-72. Furthermore, jet impingement is seen to enhance boiling heat transport more significantly for water than for FC-72. Consequently, heat transfer coefficients during jet impingement boiling are as much as 3.9 times larger for water compared to FC-72 at identical Reynolds numbers and surface temperatures. The heat transfer advantage of using water is mainly associated with the superior thermophysical properties of this fluid. However, in addition to the large fluid saturation temperature at atmospheric conditions, direct cooling of electronics is frequently not possible using water due to the incompatibility of the fluid with electrical components. To assess the practical utility of subatmospheric deionized water through indirect cooling of electronics, a 1-D heat sink analysis is performed on a multichip module geometry. The overall thermal resistance of the heat sink using water is determined to be around two times lower than that of direct cooling of FC-72 on a silicon substrate. Under saturation condition of the working fluids, dissipation of heat fluxes in excess of ~45 W/cm2 with the multichip module using water is constrained by the chip surface temperature limit.