The Local and Average Heat Transfer Characteristic of Confined Jet Array Impingement Boiling of Aqueous Ethylene Glycol Solutions

摘要

Liquid Jet impingement cooling is deemed as one of the most promising high heat flux cooling technologies. Compared with single phase cooling, two-phase cooling has advantages of more uniform heating surface temperature, lower pressure drop and less mass flow rate. In this paper, a closed-loop experimental setup is built to study confined jet array impingement boiling of 43% mass concentration aqueous ethylene glycol solution. The rectangular heating surface made of thin metal film is 20 mm × 40 mm and with the thickness of 0.03 mm. The in-line jet array has the jet orifice diameter d=1 mm, the dimensionless jet-to-target spacing H/d=1, and the dimensionless jet-to-jet spacing S/d=5. The experiments are performed at atmospheric pressure to explore the effects of jet impingement velocity and liquid subcooling. The tested jet velocity is 0.2, 0.31 and 0.5 m/s respectively, while the inlet subcooling is ranged from 36℃ to 96℃. The results showed that wall temperature and even heat transfer mode at different locations of the heating surface are quite different, with the lowest temperature on the heating surface directly under the jets and the highest temperature on the heating surface under the center of four jets where the nucleation boiling incepts earliest and the critical heat flux (CHF) occurs. Increasing subcooling and jet velocity can delay the onset of nucleate boiling and enhance the critical heat flux dramatically. Wall temperature overshooting phenomenon can only be found on the heating surface under the center of four jets when the jet velocity is low and sub-cooling is high.