Boiling heat transfer in small channel for development of ultrafine cryoprobe

Boiling heat transfer experiment to develop an ultrafine cryoprobe was conducted. The flow passage of the experimental apparatus simulated the structure of the ultrafine cryoprobe which is the co-axial double tube. The effects of the difference from the structure on the boiling phenomena were evaluated. Water under the low pressure condition was used as working fluid. A glass tube was used for the outer tube to visualize the phenomena and its inner diameter was 1.2 mm. The emission of small bubbles from the inner tube in the glass tube was observed. Furthermore, the temperature measurement with the heat flux supplied on the needle surface was conducted. The relationship between the needle surface temperature and the heat flux clarified that the needle surface temperature of smaller inner tube becomes lower. This fact indicates that the pressure drop of the inner tube or the state of water at the exit of the inner tube is important for the ultrafine cryoprobe.