VOID FRACTION CHARACTERISTICS OF ONE-COMPONENT GAS-LIQUID TWO-PHASE FLOW IN SMALL DIAMETER TUBES

Abstract

When designing a two-phase flow loop system for space structures, it is necessary to understand the effect of surface tension on the gas-liquid two-phase flow behaviors. In this paper, the effect of the tube diameter on the void fraction characteristics of vertical upward one-component gas-liquid two-phase flows in small diameter (inner diameter = 4.0, 2.0, 1.1, and 0.5 mm) circular tubes is discussed. FC-72 was used as the working fluid. The void fraction was measured by a capacitance method and the flow behaviors were observed simultaneously using a high-speed camera. The transition boundaries of the observed flow pattern agreed well with the Mishima and Ishii model, except in the case of the 0.5 mm tube. The gas volumetric flux at the transition from slug to annular flow for the 0.5 mm tube was higher than that obtained by the previous model. For the annular flow, the average void fractions were overestimated by the homogeneous model and Cioncolini and Thome model due to the high slip ratio. In the correlation based on the drift-flux model, the distribution parameter for the annular and churn flows in each tube agreed well with the Zuber annular flow model and the Ishii churn flow model, respectively. The drift velocities were overestimated by these models, except in the case of the 4.0 mm tube. The disturbance wave frequency for annular flow increased when the tube diameter was decreased to 1.1 mm; however, for the 0.5 mm tube the frequency decreased due to enhancement of the surface tension effect.