Analytical Study of Critical Heat Flux in Two Phase Thermosyphon : Relationship between Maximum Falling Liquid Rate and Critical Heat Flux

Abstract

An analytical study has been done of critical heat flux of a two-phase thermosyphon, in which a liquid film and a vapor flow exist in a countercurrent annular flow. The CHF point on the thermosyphon is proved to correspond to a maximum falling liquid rate fed to the thermosyphon, which can be determined from three equations of momentum, its partial derivative with void fraction, and mass balance in the thermosyphon. This maximum point, furthermore, becomes identical to the point at which an envelope line generated from momentum equation and its partial derivative, intersects the mass balance line. The CHF calculated from the maximum liquid rate, is found to be in fairly good agreement with the existing CHF data in a closed thermosyphon and the CHF data measured for open themosyphon. Normal operation of the thermosyphon cannot be obtained at any liquid of water, R113, and R22 for a small tube diameter of less than 2 mm within a wide range of L/D-4.8 to 960 and density ratio of ρι/ρG=6.17 to 1602.