International Journal of Heat and Mass Transfer, Vol.42, No.13, 2439-2454, 1999
Elimination of boiling incipience temperature drop in highly wetting fluids using spherical contact with a flat surface
This work examines the effectiveness of the zero-angle cavities created by curved contact with a flat surface in promoting vapor embryo capture, low temperature boiling incipience. and reduction or elimination of the incipience temperature overshoot with highly wetting liquids. Using FC-72 as a test liquid, both single and multiple spherical point contacts on a flat heater in both horizontal and vertical orientations are examined. The effects of contact force, material conductivity, and fluid flow obstruction as well as overall boiling behavior resulting from the surface contact are addressed. Boiling incipience behavior, for contact forces between 4.45 and 26.7 N, showed independence of force for all contact materials. Multiple contact points of insulative material with conductive tips showed the greatest improvement, virtually eliminating the temperature excursion often associated with incipience while still allowing sufficient liquid access to the boiling surface such that the critical heat flux was within only 6% of that for a bare surface. Because such features are large, it is unlikely that prolonged boiling or submersion would significantly degrade the boiling enhancement effects, as is the case with the small features resulting from surface roughening techniques.