Experimental study on defrosting of ultra-low temperature circular microtube bundles under forced convection conditions

Frost formation on the micro-tube bundle surface in the precooling system of combined-cycle engines is a critical issue that requires urgent resolution. Cryogenic coolants are typically selected as the cooling medium due to the demanding performance requirements of precoolers. The frost formation characteristics on the precooler surface are influenced by its ultra-low temperature (below -100 ℃) conditions. These characteristics differ considerably from those observed on common low temperature surfaces. Moreover, due to the compact design requirements of precoolers, traditional defrosting methods are no longer applicable. Therefore, it is necessary to develop new defrosting strategies tailored to the operating conditions of precoolers. This study experimentally investigates the influence of anhydrous ethanol on frost growth on micro-tube bundles under ultra-low temperature forced convection conditions. The differences in frost suppression under various states of anhydrous ethanol are examined. Under ultrasonic atomization of anhydrous ethanol, the reduction in frost layer thickness is studied at different ethanol injection ratios. The influence of varying humid air parameters on frost inhibition by anhydrous ethanol is also evaluated. While differing from conventional defrosting methods, its effectiveness in inhibiting frost formation enables its application as a defrosting technique under specific operating conditions. The results indicate that, under ultra-low temperature forced convection, ethanol vapor more effectively suppresses frost formation on micro-tube bundles compared to liquid ethanol droplets. Furthermore, under fixed experimental conditions, an optimal ethanol injection ratio exists that maximizes the reduction in frost layer thickness. The study also demonstrates that variations in humid air temperature, velocity, and absolute humidity considerably influence the frost suppression performance of anhydrous ethanol. The findings of this study can serve as a reference and provide guidance for theoretical defrosting research on precoolers.