Boiling at Subatmospheric Pressures with Enhanced Structures

摘要

Experiments were performed to study the effects of subatmospheric pressures on the boiling of water fromnenhanced structures. The experimentswere conducted at 9.7, 15, and 21 kPa.The boiling enhancement structurewasnintegrated within the evaporator of a compact thermosyphon and had stacked-layer geometry. Each layer of thenporous structure had dimensions of 12:7 u0001 12:7 u0001 1 mm (length u0001 breadth u0001 thickness). Four differentngeometries of the structure were used, each having 1 layer, 2 layers, 4 layers, and 6 layers, respectively. The boilingncurves fromthe enhancement structures were compared with subatmospheric pressure boiling froma plain surface.nSubatmospheric pressure boiling achieved heat fluxes in excess of 100 W=cm2nwith negligible incipient superheat,nwhile keeping boiling surface temperatures below 85u0002nC. Reduced pressures also resulted in reduction of the heatntransfer coefficient with a decrease in saturation pressure. The boiling enhancement structure showed considerablenheat transfer enhancement compared with boiling froma plain surface and also increased the critical heat flux limit.nIncreased height of the structure decreased the heat transfer coefficient and suggested the existence of an optimumnstructure height for a particular saturation pressure.