Air-water Two-phase Flow Pattern And Identification In Pebble-bed Porous Channel

In the research of new-concept reactor, debris bed cooling, and chemical industry, gas-liquid two-phase flow in porous media are involved. Theoretical analysis and experimental study on gas-liquid two phase flow in porous media channel were investigated in this paper. The study was conducted under normal temperature and pressure with the gas-liquid two-phase mixture as working fluid. The test section adopts the method of filling round glass balls Including the diameter of 8mm, 5mm and 3mm in the Plexiglas's tube to structure porous media channel.Firstly, in order to overcome the difficulties of observing gas-liquid two-phase flow-pattern in porous media channel, the method of refractive index compensation is used to carry out the flow pattern visualization study. Observed five flow patterns including bubbly flow, string-like flow, liquid column pulse flow, foam pulse flow and annular pulse flow, and depicted the flow pattern map.Secondly, analyzed the pressure fluctuation characteristics of different flow patterns in the time-frequency. Time-domain analysis shows that the pressure fluctuation signals of different flow patterns have different amplitudes and periodicities. Frequency domain analysis shows that with the continuous changes in flow pattern, the signal frequency of pressure fluctuations has an obvious regularity.In the aspects of resistance characteristics, homogeneous flow model was adopted to study the resistance characteristics of gas-liquid two-phase flow in porous media. Discussed the effects that porosity, filling ball's diameter, and Reynolds number of gas-liquid to the pressure drop, and proposed a new correlation of the pressure drop calculation, the relationship applies to various size of filling the ball.The flow-resistance characteristics associate with the flow patterns, This paper attempts to achieve the flow-pattern identification by analyzing the resistance characteristics. The results show that the coefficient of resistance is tied up with flow patterns closely, and the changing trend of the resistance coefficient can objectively reflect the different flow patterns. Based on the analysis of variation of the resistance coefficient, the flow pattern-transition lines and flow-pattern discriminates were given.