Study On Phase Change Heat Transfer Behind Shock Waves Based On Piston Diaphragmless Shock Tube

In nature,phase transition phenomena such as condensation or evaporation behind the shock wave sometimes occur.Under low temperature conditions,the sound velocity of the gas will decrease and the Mach number of the gas will be increased,which will make it easier to form a shock wave.The phase change phenomenon behind the shock wave will bring a series of safety problems to the machine,which will corrode the blade surface,cause vibration,and even damage the body of the machine.Therefore,the research on the phase change heat transfer behind the shock wave has extremely engineering application value and scientific research value.In this paper,the traditional diaphragm shock tube is improved,and a piston diaphragmless shock tube is designed.The continuous movement of two pistons is used to replace the membrane rupture process of the diaphragm shock tube.The shock tube does not need to break the membrane to generate shock waves during the process of generating shock waves.It prevents the membrane fragments generated when the membrane ruptures from contaminating the shock tube.It avoids the replacement of the diaphragm and the shock tube being opened,which will not cause water vapor to flow into the observation section of the shock tube.It reduces the error in the experiment of phase change heat transfer behind the shock wave.Keeping the shock tube tightly closed during the experiment and vacuuming at any time can effectively improve the efficiency of the experiment.A cooling device is installed above the observation section of the shock tube.Heat insulation device is installed on the outside.Make it possible to carry out low temperature experiments in the temperature range of 180K-240 K.And record experimental data through piezoelectric sensors and temperature sensors.In this paper,the experimental values obtained are compared with the theoretical values obtained through the calculation of the Rankine-Hugoniot equation to verify the characteristics of the shock tube.After obtaining good characteristics verification,nitrogen is used as the driving gas and HFC-134 a gas is used as the driven gas to study the phase change heat transfer behind the shock wave.Due to the installation of cooling devices and adiabatic devices,the driven gas with a high boiling point will be condensed behind the shock wave,and there will be liquid film on the wall of the shock wave tube.A shock wave visualization system and an optical interference system are designed,and the two systems can work synchronously.The thickness of the condensate film that changes with time is measured by an optical interference method based on multiple reflections of the He-Ne laser beam.The signal of the laser interference system is recorded by an oscilloscope,and then the data of the liquid film thickness is calculated based on the captured information.Furthermore,physical quantities such as heat flux and temperature of the liquid film generated behind the shock wave are calculated.Synchronous shock wave images can be obtained to observe the state of the shock wave at different points in time.The results show that the piston-type filmless shock tube has good performance.The experimental value obtained is in good agreement with the value of the Rankine-Hugoniot curve.Combined with the shock wave visualization image,it is judged that this shock tube can provide reliable data for the phase change heat transfer experiment behind the shock wave.Through the shock wave visualization system,the shape of each stage of the shock wave and the bifurcation phenomenon of the reflected shock wave can be observed.Through the He-Ne laser beam optical interference system,it is found that a liquid film is formed on the inner wall of the shock tube behind both the incident shock wave and the reflected shock wave under certain conditions.And the growth rate of the liquid film behind the reflected shock wave is less than the growth rate of the liquid film behind the incident shock wave.