Active flow control for cold-start performance enhancement of a pump-assisted, capillary-driven, two-phase cooling loop

This paper discusses active flow control schemes for the cold-start performance enhancement of a pump-assisted, capillary-driven, two-phase cooling loop. A Proportional-Integral (PI) control algorithm was used to regulate the boiling condition (from pool boiling to thin-film boiling) in the evaporator and back pressure in the system during cold-start at low heat input. The active flow control improved the thermal resistance at low heat inputs by 50% compared to the baseline case using constant flow rate, while realizing a total pumping power savings of 56%. Temperature overshoot and its associated large temperature fluctuations occurring at cold-start were also investigated. A separate PI control algorithm was used to mitigate temperature overshoot and achieve a more stable start-up with smaller temperature fluctuations. A constant evaporator surface temperature of 60 °C with a variation of ±8 °C during start-up was accomplished. Evaporator thermal resistances as low as 0.10 cm2-K/W were also observed.