An Experimental Apparatus for Two-phase Cooling of High Heat Flux Application using an Impinging Cold Plate and Dielectric Coolant

Increasing heat transfer rates over smaller area and volumetric footprints are a challenge to electronics cooling. Conventional air-based cooling solutions require larger space for heatsink fins and impose challenges on chassis design. Those challenges of air cooling encourage a shift to a more efficient liquid cooling solution. The more efficient heat transfer performance in a small volume is attributed to high specific heat and latent heat associated with a liquid coolant. In this research, a bench level two-phase experimental setup was built to study the heat transfer and hydraulic performance of a jet impinging cold plate using a dielectric coolant HFE 7000. A copper block heater arrangement was used to mimic a computer chip with a footprint of 1“ × 1” (6.45 cm ² ). Heat transfer performance and pressure drop were compared in single- and two-phase operation at three volumetric flow rates 1.0, 1.25, and 1.75 LPM corresponding to mass fluxes 2005, 2506, and 3509 kg/m ² s respectively. The tests were carried out for heat fluxes ranging from 5 to 70 W/cm ² . It is found that thermal resistance remains unchanged in the single-phase regime at lower heat fluxes but then decreases significantly when boiling occurs at high heat fluxes. At lower heat fluxes and high heat fluxes, thermal resistance decreases with flow rate. However, at moderate heat fluxes (27–58 w/cm ² ), the thermal resistance is independent on flow rate. This behavior is attributed to the dominance of nucleate boiling at moderate heat fluxes. Therefore, thermal performance at moderate heat fluxes depends on cold plate design (nucleate site density) rather than flow rate. Pressure drop decreases slightly (less than 7 %) in single phase regime due to the reduction of viscosity with temperature. When two-phase boiling occurs, pressure drop is observed to rise considerably (over 70 %). A high power of 450 $\mathrm{w}$ was dissipated at operable base temperature (31 to 85°C) and pressure drop (7 to 24 kpa).