Theoretical And Experimental Investigations Into Energy Separation Effect Of Vortex Tubes

The vortex tube is a new device which separates standard compressed air into hot and cold air streams simultaneously. Due to the compactness and lack of moving parts, simple structure, convenient operation, reliable run as well as free maintenance and so on, the vortex tube has been found increased use in commercial application, such as heating, cooling, cleaning, drying gases and separating gas mixtures, which is highly reliable, and is easy to regulate and to obtain energy flows with parameters that vary within very wide limits. The vortex tube has extraordinary widespread prospect in the applications of scientific researches and industrial domain. In spite of the potential usefulness and simple geometry of the vortex tube, its real physical processes and energy separation effect are far from being fully understood. Since the invention of the vortex tube, the vortex tube and theoretical value of coherent energy separation as well as its potential applications have been being focused by more and more experts.Relational expressions among inlet temperature, cold and hot exit temperature, cooling effect, heating effect as well as cold air fraction were obtained. The entropy model of energy separation process was also derived by usage of thermodynamic first law and thermodynamic second law. Physical mechanism of energy separation effect inside the vortex tube was disclosed through analyzing turbulent total energy equation of compressed air under the conditions of cylindrical coordinate. The results show that energy separation effect caused by compressible swirl air inside the vortex tube is mainly due to radial heat flux, viscous shear work in the axial and tangential direction.The influences of the numbers of nozzle, the diameter of separation orifice, the length of vortex tube, the taper of regulating valve on the maximum refrigerating effect of the vortex tube were investigated associated with the method of orthogonal optimum design. As a result, the optimum geometrical parameters of the vortex tube were obtained. Systematic experiments were conducted to investigate the influences of the tangential inlet pressure and the cold air fraction on the cooling effect, specific refrigerating output and refrigerating efficiency of the optimum vortex tube. Empirical equation is presented based on the experimental data. For the vortex tube used in these experiments, the given empirical equation provides excellent correlativity with the experimental data.Under the constant inlet pressure, the cooling effect, the specific refrigerating output and the refrigerating efficiency as a function of the following geometrical parameters was studied: the numbers of nozzle, the diameter of the separation orifice, the length of the vortex tube and the taper of regulating valve. The dimensionless entropy generation and exergy efficiency was analyzed based on the experimental data. The results demonstrate that the extent of irreversible loss within the vortex tube is extreme large.The programs of measuring flow field and temperature field were designed. The distribution of total pressure, static pressure, total velocity, tangential velocity, axial velocity and temperature at different axial and radial location were acquired. The influences of inlet pressure and cold air fraction on the distributions of various flow parameters along the radial direction were also investigated. The results show that the usage of three-hole probe and bare thermocouples can meet the experimental requirements very well. The flow flied and the temperature profiles from experiments are shown to agree accurately with the previous studies, which provide a credible means for further study on the physical mechanisms of the energy separation effect inside the vortex tube.The technique of Computational Fluid Dynamics (CFD) was adopted to simulate the flow field and heat transfer of three-dimensional compressed air with strong swirl within the vortex tube considering the flow's movement characteristic inside the tube. Based on the numerical results, the skeleton map of three-dimensional flow field was depicted distinctly and the temperature distributions were also acquired. In order to validate the numerical results, comparisons between the numerical predictions and the experimental results were conducted and satisfactory agreements were observed. A non-dimensional strategy was adopted to compare velocity, temperature distributions along the radial direction at a given axial location with the experimental data from previous studies, so the accuracy of the numerical results was further validated. Real essential phenomena of energy separation effect inside the vortex tube can be disclosed by the method of numerical simulation which was validated by the experimental results.