Spray cooling with ammonium hydroxide

An experimental study was conducted to investigate the performance characteristics of spray cooling with ammonium hydroxide (NH4OH) binary mixture for high heat flux removal. Two mixtures, having ammonia mass fractions of 0.3 and 0.5, were selected to represent practical operation conditions near atmospheric pressure and room temperature. Experimental setup involved a closed loop system with a vapor atomized spray nozzle and a 1-cm2 heater sample that simulated a high heat flux source. Tests were performed with gradually increasing heat fluxes of up to 800 W/cm2 and maintaining surface temperatures below ∼75 °C at varying liquid and vapor flow rates. Results indicated that the heat transfer coefficient (HTC) values from NH4OH mixtures can be lower than those from pure water and pure ammonia. The data suggested that boiling depression, due to mass diffusion resistance at liquid vapor interface, could greatly affect the overall spray cooling performance, especially when the binary mixtures comprise components with widely different boiling points. The study therefore provides performance characteristics, as well as some fundamental insights, for a potential spray cooling scheme suitable for low temperature, low pressure operations in various applications including thermal management of aerospace electronics and electro-optics.