Nucleate Pool Boiling of Water in Normal and Reduced Gravity Environments

A NASA Learjet was used to produce a low-gravity environment for two series of nucleate pool boiling experiments. Surface-temperature and heat-flux measurements and high-speed microphotography of bubble phenomena were made on 18 prepared boiling surfaces. The surfaces were polished copper disks, 25.4 mm and 19.1 mm in diameter, with variable artificial nucleation site densities from 0.2 to 32 sites/cm². Both 1-g and low-g data were obtained for comparison. In every case, the boiling heat-transfer coefficient increased significantly to a new steady value for the duration of the low-gravity period. Rapid movement of the surfaces of the large vapor masses that were observed is indicative of considerable turbulent liquid motion, apparently induced by the bubble growth and coalescence. In no case was a decreased heat-transfer coefficient observed, which would be indicative of film boiling.