ANALYTICAL STUDY OF CRITICAL HEAT-FLUX IN 2 PHASE THERMOSIPHON (RELATIONSHIP BETWEEN MAXIMUM FALLING LIQUID RATE AND CRITICAL HEAT-FLUX)

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 coun tercurrent annular flow. The CHF point on the thermosyphon is proved t o 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 whi ch an envelope line generated from momentum equation and its partial d erivative, intersects the mass balance line. The CHF calculated from t he maximum liquid rate, is found to be in fairly good agreement with t he existing CHF data in a closed thermosyphon and the CHF data measure d for open thermosyphon. Normal operation of the thermosyphon cannot b e obtained at any liquid of water, R113, and R22 for a small tube diam eter of less than 2 mm within a wide range of L/D=4.8 to 960 and densi ty ratio of rho(L)/rho(G)=6.17 to 1602.