EXPERIMENTS ON SUBCOOLED POOL BOILING OF WATER IN MICROGRAVITY (OBSERVATION OF BUBBLE BEHAVIOR AND BURNOUT)

摘要

An experiment on burnout in subcooled pool boiling of water was performed under the microgravity in a parabolic flight by a jet aircraft. A test surface was a thin stainless steel plate heated by the alternative electric current in the microgravity. The liquid subcooling was 10 K, 20 K, 30 K and 40 K. The bubble behavior and the burnout were observed by CCD camera (Figure A-1). At a lower subcooling of water, big bubbles grew on the heating surface but did not detach from the surface (Figure A-1 A). At a higher liquid subcooling, the heating surface was covered entirely with several coalesced bubbles and many fine bubbles were emitted explosively from the surface. The measured burnout heat flux was 200 to 400% higher than the one given by existing theories. In the ground experiment, a cover plate was placed over the heating surface with a small clearance to simulate the attached boiling bubbles over the heating surface. The heating surface was covered entirely with boiling bubbles. Many fine bubbles were observed to be emitted from the surface through coalesced bubbles at a higher liquid subcooling. The burnout heat flux with the cover plate was well agreed with the one in the microgravity (Figure A-2).