Research on two-phase flow instability in parallel rectangular channels

• A model for flow instability in parallel channels with good accuracy was given.
• The power threshold and frequency under different conditions were modeled.
• The effect of asymmetric parameters was studied analytically and systematically.

In the present work, a theoretical model for Density Wave Oscillations flow instability in parallel rectangular channels is built with a lumped mathematical model based on homogenous hypothesis. The parallel channel comprises the entrance section, heating section and riser section and the model consists of the boiling channel model, pressure drop model, parallel channel model and constructive model, while subcooled boiling effect is neglected and the final nonlinear ordinary differential equations are solved by Gear method. The model is validated with experimental data of a single channel with constant pressure drop and that of a twin-channel flow instability experiment. Then the flow instability in twin rectangular channel system is studied under different conditions. The effects of pressure, P, inlet throttling coefficient, kin and exit throttling coefficient, kout are examined through the parameter plane of the subcooling number, Nsub and phase change number, Npch and the frequency of the oscillations, f. Finally, the effects of asymmetric heating and throttling on flow instability are also analyzed.