Experimental Study On Pressure Oscillation Characteristics Of Chugging Of Steam Direct Contact Condensation In A T-type Microchannel

According to the fluctuation characteristics of the vapor-liquid interface,steam direct contact condensation can be divided into many flow patterns,and chugging is one of the typical flow patterns,which has the characteristics of periodic suction and discharge of supercooled water.This flow pattern is accompanied by the instantaneous violent fluctuation of the vapor-liquid interface and the resulting pressure oscillation,which has been a hot issue in recent decades.In view of the adverse impact of pressure oscillation induced by chugging on system safety,the research content of chugging generally focuses on restraining its pressure oscillation in macro scale,especially in nuclear power and other fields.However,from another perspective,scholars have proposed to solve the heat dissipation of high heat flux electronic devices by using the characteristics of chugging under micro-scale conditions in recent years.A prototype has been preliminarily developed at the level of MEMS.However,the closely related pressure oscillation characteristics and their influencing factors need to be further studied.It can be seen that in-depth discussion on the fluctuation characteristics and pressure oscillation characteristics of chugging two-phase interface in the micro channel has important scientific and engineering significance for the design and research and development of new high heat flux electrical device heat sink.Firstly,based on the original test-bed,this paper redesigns and modifies the condensation pressure oscillation measurement system.Then,the visual experiment of chugging in the micro channel and the research on condensation pressure oscillation are carried out,the chugging flow pattern is further refined,the corresponding pressure signal is obtained,the pressure spectrum analysis is carried out,and the internal relationship between flow pattern and condensation pressure oscillation characteristics is clarified.According to the fluctuation characteristics of the vapor-liquid interface,it can be divided into internal chugging and external chugging.The external chugging can be further divided into rough surface chugging and smooth surface chugging.For internal chugging,the whole process of steam condensation is completed in the vertical branch pipe and does not reach the main pipe;In the process of rough surface chugging,steam forms bubbles and breaks in the horizontal main pipe;for smooth surface bubble chugging it is also found formed bubbles in the horizontal main pipe,but there was no rupture.The pressure oscillations of the above different flow patterns are analyzed in time domain and frequency spectrum,which lays a foundation for flow pattern identification from the characteristics of pressure oscillations.In addition,it is found that the pressure concentration area within 1 second increases with the increase of steam mass flow rate.The pressure oscillation intensity(standard deviation)increases with the increase of steam mass flow,but the pressure oscillation intensity does not change obviously under different subcooled water flow.The kurtosis coefficient first decreases with the increase of steam mass flow,and then tends to be stable.It is found that it is less affected by the change of cold water mass flow,but more affected by the change of steam mass flow.With the increase of steam mass flow,the first dominant frequency of pressure oscillation roughly decreases first and then increases,while the amplitude corresponding to the first dominant frequency roughly increases first and then decreases.With the increase of subcooled water mass flow,the first dominant frequency of pressure oscillation basically shows an increasing law.This study further improved the cognition of chugging in the micro channel,clarified the fluctuation characteristics of the two-phase interface,analyzed the inducing mechanism of condensation pressure oscillation,and analyzed the influence law of different steamwater flow on chugging.It is expected that the research results will have a certain reference value for the engineering application of chugging in microchannels.