Investigation On The Flow Field And The Acoustic Field Characteristics Of Counter-Flow Vortex Tube

The vortex tube is a device with a simple structure and no mechanical moving parts inside.It also has a unique energy separation effect,separating the compressed gas into cold gas and hot gas through its particular flow field.In recent years,engineering applications of vortex tubes in natural gas dew point control,natural gas liquefaction,and light hydrocarbon recovery have emerged successively at home and abroad.However,there is still a lack of research on the acoustic field characteristics of the vortex tube.Therefore,this paper further studies the formation mechanism of vortex tube flow noise,the relationship between acoustic field characteristics and energy separation effect by changing the structure and working conditions of the countercurrent vortex tube through experiments.At the same time,under the same energy separation effect,the operating conditions of the vortex tube are optimized to reduce the noise.It is of great significance both to study the separation mechanism and to reduce the noise pollution in the industrial application of the vortex tube.The research was carried out using the counter-flow vortex tube with heat pipe lengthdiameter ratio of 9 as the research object by combining experimental measurement and numerical simulation.The vortex tube was tested for orthogonality under different inlet pressures(0.3 MPa,0.4 MPa,0.5 MPa,and 0.6 MPa),different cold mass fraction,and different nozzles(4,5,6).The results show that vortex tubes’ the energy separation characteristics with different nozzle flow channels have the same trend.The temperature drop at the cold end and the temperature rise at the hot end of the vortex tube increase with the increase of the inlet pressure,and the temperature drop at the cold end and the temperature rise at the hot end reach the highest at the cold mass fraction around 0.4 and 0.9 respectively.It is worth mentioning that the 5 nozzles have the strongest energy separation characteristics,and the 4 nozzles have the weakest performance.The acoustic signal is collected by using the acoustic sensor MPA201,and the sound field signal of the vortex tube is processed and analyzed under various working conditions,and the sound field law of the vortex tube is obtained.The acoustic characteristics of the vortex tube were studied by processing and analyzing the signal.The results show that the vortex tube’s acoustic field signal is a broadband signal,and the acoustic energy is mainly concentrated in the frequency range of 4000-5000 Hz.The sound field signal intensity of the vortex tube increases with the increase of inlet pressure.At the same time,the changing trend of the SPL spectrum with frequency under different inlet pressures is almost the same.And when the cold mass fraction is 0.4,the SPL reaches the maximum,and the sound signal gradually weakens with the increase of the cold mass fraction.The overall performance is that the sound field signal of the 5 nozzles vortex tube is the strongest,and when the cold mass fraction is 0.4,it reaches 97 d B.The difference between the three kinds of nozzles is the largest at 0.3 MPa,and gradually decreases with the increase of inlet pressure.The trend of the SPL spectrum changes with frequency becomes gentle.On the premise of the same isothermal effect,it can be found that when the inlet pressure is 0.3 MPa,there is little difference between the three nozzles’ digital acoustic signals.The SPL of 4 nozzles and 6 nozzles are significantly lower than that of5 nozzles under the pressure is 0.6 MPa.When the number of nozzles is the same,the lower inlet pressure should be selected when the temperature effect is satisfied,and the SPL is the lowest.The structure of the vortex tube was simplified,and the three-dimensional geometric model of the vortex tube was established.The software ICEM was used for meshing,and the Reliable k-ε turbulence model was used for steady-state calculation.Based on the same inlet pressure,with the increase of the cold mass fraction,the vortex tube heat pipe’s hightemperature region gradually extends to the vortex chamber in the simulation results of the flow field.The temperature gradient distribution at the hot end is gradually refined concurrently.The LES method was used to calculate the flow field,and the time-varying characteristics of the flow field in the vortex tube were obtained.The formation reason of sound source was accepted by analyzing the aspects of the flow field.The FW-H method was used to simulate the internal sound field,which could not be monitored by experiment,and the characteristics of the internal sound field were obtained.The results can provide a research basis for acoustic field prediction of vortex tube in industrial application.