Experimental Study On Internal Flow Field Of Vortex Tube Based On LDV

The vortex tube is a simple thermal device that separates compressed gas into hot and cold streams.Due to its advantages,such as no moving parts,no maintenance,small size and light weight,The vortex tube has benn widely used in many applications,such as refrigeration,heating,gas separation,air dehumidification,natural gas liquefaction.Due to the complex flow structure in the vortex tube,the reason for its energy separation has not been consistently reached.Clear velocity distribution and flow structure within the vortex tube are essential to explain this phenomenon.Many researchers carried out visualization experiments.In early studies,they observed the flow in the vortex tube by injecting dye and carbon powder into the vortex tube,but the results were not ideal.Some use rotatable pitot tube to extend into the vortex tube for velocity measurement,but this kind of invasive measurement will cause interference to the flow field of the vortex tube,and the operation conditions are relatively simple.Compared with the visualization study of the vortex tube mentioned above,the two-dimensional laser Doppler velocimetry technology has a high measurement accuracy,and the laser non-invasive measurement can avoid the interference of the flow field.Therefore,two-dimensional LDV velocity measurement system is used to test the flow field of the vortex tube in this paper.Firstly,transparent vortex tubes of diameter 30 mm are designed for the visualization experiment.The software parameters of LDV in the experiment are set up and the measurement errors in the experiment are analyzed.Then,the inlet pressure of the vortex tube is fixed at 0.1bar,and the tangential velocity,axial velocity and radial velocity distribution of the vortex tube with a length of 360 mm,600mm,900 mm and 1200 mm are obtained under four cold mass fraction conditions(0.2,0.4,0.6,0.8).The experimental results show that the tangential velocity in the vortex tube shows the Rankine vortex distribution,the mean axial velocity distribution present good axial symmetry,the radial velocity value is close to zero,and the overall distribution is irregular.According to the axial velocity distribution,the reverse flow boundary and stagnation point in the vortex tube are plotted.Increasing the cold mass fraction results in an expansion of the reverse flow boundary.Next,the energy separation performance curves of four vortex tubes are obtained through experiments,a deterioration in the energy separation performance due to an excessively short or long tube was revealed,The stagnation point is not a basic flow structure in a vortex tube;on the contrary,it possibly occurs in during suboptimal performance.Finally,based on the study of vortex tube velocity distribution,according to the energy separation performance of vortex tube,two new heating systems applied to LNG vaporization station are proposed,and the energy conservation of these two systems is analyzed and calculated.Analysis and calculation to acquire the two system energy saving ratio can reach more than 59.47% and 90%,compared with the traditional LNG vaporization heat system both systems have good energy saving and environmental protection.