Boiling at Subatmospheric Pressures with Enhanced Structures

摘要

Experiments were performed to study the effects of subatmospheric pressures on the boiling of water from enhanced structures. The experiments were conducted at 9.7,15, and 21 kPa. The boiling enhancement structure was integrated within the evaporator of a compact thermosyphon and had stacked-layer geometry. Each layer of the porous structure had dimensions of 12.7 × 12.7 × 1 mm (length × breadth × thickness). Four different geometries of the structure were used, each having 1 layer, 2 layers, 4 layers, and 6 layers, respectively. The boiling curves from the enhancement structures were compared with subatmospheric pressure boiling from a plain surface. Subatmospheric pressure boiling achieved heat fluxes in excess of 100 W/cm~2 with negligible incipient superheat, while keeping boiling surface temperatures below 85℃. Reduced pressures also resulted in reduction of the heat transfer coefficient with a decrease in saturation pressure. The boiling enhancement structure showed considerable heat transfer enhancement compared with boiling from a plain surface and also increased the critical heat flux limit. Increased height of the structure decreased the heat transfer coefficient and suggested the existence of an optimum structure height for a particular saturation pressure.