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A multivariable linear investigation of two-phase flow instabilities in parallel boiling channels under high pressure. (English) Zbl 1144.76474

Summary: This paper presents experimental results as well as an analytical model of density-wave instability in parallel boiling channels under high pressure. The experiments have been performed on a high-pressure steam-water loop. Different types of two-phase flow instabilities have been observed, including density-wave (DWO), pressure drop, thermal and second density-wave (2nd DWO) oscillations. The 2nd DWO appears at a very low exit steam quality (approx. <0.1) and in the positive portion of the \(\Delta \)P-G curves with both channel flow rates oscillating in phase. The DWO can appear at pressures up to 192 bar and disappears above 207 bar. A multivariable linear model is developed to analyse the system stability in the frequency domain by means of multivariable control system theory. The multichannel boiling system is expressed by transfer matrix models which include feedback on the two-phase pressure drop and external loop pressure drop. A computer program, DENSITY-PARA, is coded for the stability analysis of a parallel boiling channel system with or without cross-connection. Using this model, the effect of the main parameters on the system stability can be analysed conveniently.

MSC:

76Txx Multiphase and multicomponent flows
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