Study On Boiling Pressure Drop And Instability Of Flow In Fine Channel Of Phase Separation Structure Under Electric Field

With the rapid development of modern science and technology,traditional heat transfer devices are increasingly unable to meet the heat dissipation requirements of highly integrated device systems,and smaller microchannels are more likely to produce larger flow resistance in the thermal process of phase transformation.In this paper,a PTFE film is set locally in the inlet and outlet section of the countercurrent parallel micro-channel.The PTFE film only allows the gas phase to pass through but prohibits the liquid phase to pass through.Periodic pressure switch is used to provide the pressure difference required for the gas phase transfer,which makes the gas phase transfer between the two channels with different flow directions and reduces the flow resistance of working medium in the channel.In this paper,the boiling pressure drop and instability of flow in the micro-channel of phase separation structure under the action of electric field are studied.The main research contents are as follows:(1)Study on two-phase pressure drop characteristics of micro-channel with different number of exhaust holes.The influence of seven reversing cycles(60 s,80 s,100 s,120 s,140s,160 s and 180 s)on the pressure drop of PSS-3 channel with more exhaust holes,PSS-2channel with fewer exhaust holes and PSS-1 channel without exhaust holes was studied.The results show that the total pressure drop of the two phases is small when the reversing period is 120 s.Based on the reversing period,the pressure drop of the three structural channels is studied when the heat flux ranges from 76.61 k W/m~2 to 150.70 k W/m~2 under different inlet subcooling degrees.The results show that the two-phase pressure drop of PSS-3 and PSS-2channels with phase separation structure is smaller than that of PSS-1 channel without phase separation structure under the same working condition.(2)Study on two-phase pressure drop characteristics of micro-channel in phase separation structure under electric field.Under the condition that other working conditions remain unchanged,the pressure drop characteristics of three micro-channels with different structures under the action of 0 V,400 V,800 V,1200 V and 1600 V were studied,and the visualized observation results of bubble behavior and flow pattern transformation process in the channels were combined with the high-speed camera.COMSOL software is used to simulate the electric field distribution in the micro-channel with limited bubbles,and the mechanism of electric field affecting pressure drop is discussed.The results show that the pressure drop increases,the number of bubbles increases,and the aspect ratio of confined bubbles decreases.However,the existence of phase separation structure makes the confined bubble smaller in the channel,and the effect of electric field strengthening is improved,especially in the case of high heat flux,and the pressure drop is smaller than that of no phase separation structure.(3)Study on flow instability in micro-channel of phase separation structure with or without electric field.It is found that the electric field increases the fluctuation of the pressure drop,while the phase separation structure can reduce the fluctuation of the pressure drop under the same working condition.By comparing the frequency domain characteristics of the three structures under different voltages,it is found that the frequency corresponding to the second main frequency is larger at high voltage than that at low voltage,and the ps S-3 has the highest frequency corresponding to the second main frequency at the same voltage.In addition,by comparing the slope of negative slope area of ps S-1 and PSS-3 channel pressure drop flow curves under different voltages,it can be seen that the probability of Ledinegg instability is slightly higher under the action of electric field,while the phase separation structure can slow down the probability of Ledinegg instability.