Evaporative heat transfer, pressure drop and critical heat flux in a small vertical tube with R-113

Abstract

The local heat transfer coefficient, pressure drop, and critical heat flux have been measured for saturated boiling of R-113 in a round tube with an internal diameter of 0.31 cm, and heated lengths of 12.3 and 24.6 cm. The experiments include vertical, co-current upflow and downflow configurations. A correlation for the local heat transfer coefficient is presented which expresses the Nusselt number as a function of the liquid Reynolds number and boiling number. Pressure drop data for frictional, spatial acceleration and 180° bend losses were successfully correlated by employing slight modifications to commonly accepted two-phase techniques reported in the literature. A new critical heat flux (CHF) correlation, applicable to low reduced pressure conditions, is developed which predicts the vapor quality at dryout in terms of mass velocity, inlet subcooling and heated length. The CHF correlation is accurate to within 5% over the range of conditions covered in the experiment.