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DOI 10.21662
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Privalov L.Yu., Mikhaylenko C.I. The impact of an additional inlet point on the hot outlet side on the vortex tube productivity. Multiphase Systems. 14 (2019) 3. 176–183 (in Russian).
2019. Vol. 14. Issue 3, Pp. 176–183
URL: http://mfs.uimech.org/mfs2019.3.024,en
DOI: 10.21662/mfs2019.3.024
The impact of an additional inlet point on the hot outlet side on the vortex tube productivity
Privalov L.Yu.∗, Mikhaylenko C.I.∗∗
∗Ufa State Aviation Technical University, Ufa, Russia
∗∗Mavlyutov Institute of Mechanics, UFRC of RAS, Ufa, Russia

Abstract

Based on numerical simulation, the production of cold and hot air on a modified countercurrent vortex tube is studied. A feature of the modification under study is an additional air inlet area along the axis of the pipe from the hot outlet side. An additional point of blowing air is designed to redistribute the gas flows at the cold and hot outlets. Computational experiments were performed in the OpenFOAM software package using the sonicFoam solver based on the k−ε turbulence model under the assumption of an ideal gas. The dependence of the flow rate and temperature at the cold and hot outlets for different lengths of the main channel of the vortex tube was studied. For all considered pipe lengths, finite-volume grids were prepared in which the rectangular shape of the cells was preferably observed and their excessive stretching was avoided. To speed up the simulations, MPI technology was used; spatial decomposition of the original mesh was performed by decomposePar utility into equal parts along the pipe. This approach allowed us to reduce the computation time by approximately 3.5 times when running on six processes. The results of parallel modeling were combined with the reconstructPar utility and further processed by a Python program written using the vtk library. Thus, average values of the main physical characteristics by time and space at the cold and hot outlets were obtained. Results are discussed that demonstrate the effect of the vortex tube length on temperature and air flow at the respective outputs. The behavior of its main characteristics, non-standard for a vortex tube, is shown, an assumption is made about the reason for this behavior: the collision of very fast flows makes instability. Preliminary conclusions are made about choosing the effective length of the vortex tube with an additional air inlet channel at which the ratio of air temperature at the hot and cold outlets is the largest.

Keywords

Ranque–Hilsch effect,
vortex tube,
turbulence,
OpenFOAM

Article outline

The article considers a vortex tube, supplemented by another air inlet channel. The additional inlet is oriented along the axis of the main channel and is located in its center on the side of the hot diaphragm. The objective of this design is to redistribute the swirling air flows in order to provide the biggest output of cold air.

The mathematical model of the processes under consideration is written on the basis of the equations of continuity, momenta and energy for the case of viscous compressible flow. The system of equations is supplemented by the equation of state of an ideal gas and equations for the kinetic energy of turbulence and the dissipation rate of turbulence. Thus, the turbulent flows inside the vortex tube are described by the k—ε turbulence model.

Computational simulation is performed in the OpenFOAM software using the sonicFoam solver. The choice of a solver is dictated by the fact that transonic flows with shock waves can be realized in the channel of a vortex tube and, especially, in the diaphragm of cold air. In preparing the finite-difference grid, much attention is paid to preserving the orthogonality and uniformity of the sizes of the final volumes. The significant size of the finite difference grid is dictated by the choice of parallel computations using MPI. This approach allows us to accelerate calculations up to 3.5 times with the involvement of 6 processes.

The results show that the additional air inlet channel has a noticeable effect on the redistribution of flows in the vortex tube. However, this effect should be taken into account only for “short” pipes with a main channel length L < 50 cm. The explanation for this effect, apparently, lies in the formation of a soft “piston” directed towards the cold diaphragm in the center of the channel. In general, this is a positive property that can be used to achieve a greater yield of cold air in practice.

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