Investigation of spray cooling schemes for dynamic thermal management

Two-phase spray cooling is considered as one of the most promising thermal management techniques characterized by high heat transfer coefficient (HTC) and critical heat flux (CHF), as well as near-uniform surface temperatures. Normally, spray cooling systems feature steady flow, continuous spray, and are designed to satisfy the maximum expected heat load. However, if the target heat load varies due to operation conditions, such as cold starts and pulsing power cycles, a spray cooling system uses excessive coolant most of the time, and causes low cooling efficiencies because of lower utilization of phase-change heat transfer and higher pumping power. This study aimed to investigate variable and intermittent flow spray cooling characteristics for dynamic thermal management. Variable flow spray cooling scheme requires control of pump input voltage (or speed), and intermittent flow spray cooling scheme requires control of solenoid valve duty cycle and frequency. Tests were conducted on a closed loop system with HFE-7100 at atmospheric pressure and 30°C subcooling, using smooth and enhanced heat transfer surfaces. Results, compared to a baseline performance from steady flow case, indicated that the variable flow spray cooling conditions achieve similar cooling performance at low and moderate heat fluxes, while the intermittent flow spray conditions result in high temperature penalty and much lower CHF.