Transient analysis of cryogenic cooling performance for high-power semiconductor lasers using flash-evaporation spray

Abstract

• Transient phase-change heat transfer analysis was performed in cryogenic regimes. • A heat flux estimation method that considers an imposed heat flux was proposed. • The moderate spurt duration (Δ t = 30 s) produced preferable cooling performance. • Small-orifice-diameter nozzle has low cooling rate but high thermal efficiency. Focusing on the cryogenic cooling for the high-power semiconductor lasers to improve their output performance, this work conducted an experimental investigation on analyzing the transient cooling performance using a single-pulsed flash-evaporation spray with the environmental cryogen R32. A heat flux calculation methodology that considers an imposed heat flux as a boundary condition, was first developed to assist the transient heat transfer analysis. The results provided further insight into phase-change heat transfer on the hot surface from high-temperature to cryogenic regimes through coupling the heat transfer measurements with observations of hydrodynamic liquid film formation and development. The moderate spurt duration (Δ t = 30 s) that produced a large temperature drop (109.5 °C) and high time-averaged cooling rate (24.1 W/cm 2 ) was preferable. The significant losses in droplets’ momentum and mass contributed to the fast decrease in cooling effect as nozzle-to-surface distance ( Z ) increased. Specifically, shortening Z from 50 to 10 mm not only increased the maximum surface heat flux from 19.6 to 73.6 W/cm 2 , but also broadened the temperature region with high heat flux. The nozzle with a smaller orifice diameter (0.5 mm) produced a lower cooling rate. Whereas surprisingly, its lower flow rate resulted in the lesser coolant accumulation and splashing on the hot surface, which elevated its thermal efficiency. The low spray thermal efficiencies (≤16.2%) in the present work attribute to the low liquid utilization and coverage area across the hot spot surface under the spray impact.