Theoretical analysis for accelerated two-phase flow, (1)

Accelerated two-phase flow occurs when the gas-phase volumetric flow increases due to pressure reduction along the flow and boiling resulting from the pressure reduction or external heating. This study aims at indicating the hydrodynamic and thermodynamic analyses of the condition change of accelerated two-phase flow, considering the frictions between phases and on tube wall and the influence of the resulting increase of entropy, and at the same time, examining the propriety of calculation, comparing the numerical calculation with the experimental results. First, the investigations heretofore are reviewed, and the fundamental equations are shown. Further, the auxiliary relative equations are derived for heat capacity contributing to the pressure loss due to the friction on tube wall in two-phase flow, the pressure loss based on the friction between phases, the phase transfer quantity of each phase in pressure reduction process and the increase of entropy. Using the above equations, the simultaneous differential equations for analyzing the flow when liquid flows into a low pressure space as two-phase critical flow through a constant section channel from a high pressure tank are obtained, and numerically analyzed by Runge-Kutta-Gill method. The results are described on the identification of critical flow generation, and the changes of pressure, quality, void rate, flow velocity and others along a channel. The pressure change and critical flow rate measured in the experiments on steam-water two-phase flow agreed well with the calculated values, especially excellently at the part where pressure changed rapidly in the vicinity of channel outlet. (Wakatsuki, Y.)