Dynamics of pressure oscillations in flow boiling and condensation in the minichannel

Abstract

The dynamics of pressure and temperature fluctuations occurring in flow boiling in a minichannel of 1mm diameter, which consists of the heated section and glass condenser have been experimentally investigated and modelled. The amount of vapour in the condenser, the wall temperature of heated channel outlet and pressure drop were simultaneously measured. Data has been analyzed using the Fourier and wavelet methods. The dynamics of pressure and temperature fluctuations has been investigated using the attractor reconstruction, correlation dimension and largest Lyapunov exponent methods. A high speed digital video camera has been used to identify two-phase flow patterns in the glass condenser. The high frequency pressure fluctuations with relatively small amplitude have been observed. It has been found that during those fluctuations the dominant frequency of pressure and temperature fluctuations changes chaotically in time. Such pressure oscillations are accompanied by appearance and disappearance of slug flow in the condenser. It has been shown that dynamics of appearance and disappearance of slug flow has a multifractal character. The model of the oscillations between quasi steady two-phase flow patterns has been presented. It has been shown that the necessary condition for the appearance of chaotic fluctuations of parameters describing the system is the slope of function Δp(G). The qualitative agreement between shapes of return maps obtained in the model and in the experiment has been obtained.