Analysis of two-phase pressure drop fluctuations during micro-channel flow boiling

Two-phase pressure drop fluctuations during flow boiling in single micro-channel were experimentally investigated. Degassed FC-72 was tested in micro-channels with a hydraulic diameters of 571 μm, 762 μm and 1454 μm (the aspect ratio (Win/din) is 20, 20 and 10) at liquid mass fluxes of 11.2 kg m−2 s−1, 22.4 kg m−2 s−1 and 44.8 kg m−2 s−1 and heat fluxes of 0–18.31 kW m−2. Flow instabilities were analysed based on the two-phase pressure drop, synchronous visualisation results and thermographic measurements of the channel surface temperature profiles. Low-frequency high-amplitude fluctuation and high-frequency low-amplitude fluctuation are identified, the main causes of which were found to be the periodic reverse and rewetting flow and the vapour slug cluster passage respectively. The analysis based on a non-dimensional parameter K1 helps to better understand the dominant influence on the liquid–vapour interface movement during flow boiling. Effects of heat flux, mass flux and channel hydraulic diameter on the pressure drop fluctuation were discussed. Besides, the coefficient of variation of the pressure drop was calculated to further explore the impact of experimental conditions on the flow boiling instabilities in the high aspect ratio micro-channels.