Void fraction characteristics of adiabatic one-component vertically upward two-phase flows in circular and non-circular small diameter tubes

摘要

Evaporating and condensing heat transfer and pressure loss characteristics strongly depend oninterfacial structure of gas-liquid two-phase flows. Cross-sectional average void fraction is importantparameter on the one-dimensional analysis. Recently, since channel diameter becomes smaller, theeffect of surface tension on the flow behaviors would become stronger. This study deals with voidfraction characteristics of adiabatic two-phase flows using FC-72 as the working fluid. Crosssectionalaverage void fraction was measured by capacitance sensor. Circular, square and triangulartubes with the hydraulic diameter of 2 mm were used. Vertically upward flow was selected to evaluatefor axially symmetric phase distribution. From the results, it was confirmed that for the square andtriangular tube, void fraction became lower than the circular tube because liquid was accumulatedin the corner by surface tension. Although the lower void fraction leads to larger slip velocity, thegas-liquid interface of liquid film became smoother.