Thermal modeling of single-phase and two-phase 2D-chip cooling using microchannels

Microprocessor are seeing an exponential rise in switching speeds and transistor densities, which are leading to significantly higher heat fluxes. Two-phase schemes utilizing boiling are becoming very popular over the past few years due to their ability to tackle much higher heat dissipation challenges in comparison to single-phase schemes. In this paper, we investigate thermal performance and pressure drop for microchannels in single-phase flows and two-phase boiling flows. Microchannel configurations with three different hydraulic diameters were investigated: 909 μm, 191 μm, and 95 μm. Three different working fluids were compared: water is used for the single-phase study, R2345fa and HFE7000 for the two-phase study. As expected, increase in hydraulic diameter, decreases the pressure drop and increases the thermal resistance for a fixed flow rate. Two-phase flows show higher pressure drop and lower thermal resistance in comparison to single-phase flows. Two factors contribute to lower resistances in two-phase flow; lower convective resistance due to high heat transfer, and negative advection resistances due to high pressure drop. Some two-phase test cases predict sub-atmospheric exit pressures, making those inlet conditions impractical in real two-phase flow loop designs. To avoid sub-atmospheric pressure predictions in two-phase flow, the total thermal resistance should be calculated based on the exit temperature of the fluid. Using this, decrease in hydraulic diameter of the microchannel from 191 μm to 95 μm, shows increase in the total thermal resistance due to increased pressure drop impact on mean fluid temperature.