Radial Heat Flux Limits in Potassium Heat Pipes: An Experimental and Analytical Investigation.

摘要

A radial flux limit of 147 W/cm(sup 2) at the wetted inner tube wall has been demonstrated with a Nb-1%Zr/K heat pipe, a flux 5 times greater than the previously accepted safe design level of 25-30 W/cm(sup 2). The wick structure was an annular gap type fabricated from 100 (times) 100 mesh Nb-1%Zr screen. Rigorous fabrication and cleaning procedures are believed to be critical to good wetting, resulting in significantly reduced active nucleation site size and a higher boiling limit. The procedure used to clean this heat pipe included acid wash, Freon-TF degrease, ethanol wash, high-vacuum firing, and operation as a lithium heat pipe. A heat pipe boiling limit model, based on the active nucleation site radius, is described. An active nucleation site radius of 6 (times) 10(sup -6) m (2.4 (times) 10(sup -4) in) correlates the radial flux boiling limit measured in these tests. 4 refs., 2 figs.