Theoretical research on two-phase flow instability in parallel channels under periodic heaving motion condition

A theoretical model for Density Wave Oscillations (DWOs) flow instability in parallel rectangular channels under periodic heaving motion condition is established with a lumped mathematical model based on homogenous hypothesis. The parallel channel comprises of parallel channels, which consists of entrance section, heating section and riser section, and the upper- and lower plenums guaranteeing the isobaric pressure drop condition between channels. The lumped model consists of boiling channel model, pressure drop model, parallel channel model, additional pressure drop model introduced by periodic heaving motion and the constitutive model 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 those of twin-tube-channel and twin-rectangular-channel flow instability experiment under static condition, respectively. Afterwards the flow instability in twin-rectangular channel system is studied under periodic heaving motion condition. The effects of amplitude and frequency of heaving motion are examined through the parameter plane of the subcooling and phase change number and the threshold power for flow instability. The results show that the effect of amplitude on flow instability can be divided into three regions in which thermal hydraulic parameters, heaving motion or both of them together dominant the flow instability; the frequency of heaving motion strongly effects the threshold power when it is identical to that of the DWOs, which can be explained by resonance between the heaving motion and DWOs. And this effect is even stronger when the asymmetric throttling and heating condition is introduced. (C) 2021 Elsevier Ltd. All rights reserved.