The effect of such parameters of the cold outlet nozzle of the counter flow vortex tube as the length and widening angle on temperature separation is investigated. Mathematical model of gas dynamics is written with viscosity component. Computational simulation is performed in the OpenFOAM package, using the sonicFoam solver. It is shown that the temperature of the exhaust air decreases along the cold exit nozzle. The presence of the angle of widening of the nozzle affects the amount of cooling, but is not the root cause of the effect. The nonmonotonic dependence of the temperature of the exhaust gas on the length of the cold exit nozzle is demonstrated. When studying the effect on the temperature of the widening angle of a cold-exit nozzle at a fixed length, it was shown that at a fixed volume flow rate, a pronounced non-monotonic dependence is observed, while at a constant pressure drop, there is no non-monotony down to the maximum considered angle.

A model of a counterflow vortex tube has been prepared to study the dependence of the influence of the parameters of cold and hot outlets on the production of cold air. For a fixed geometry of the vortex tube, a simulation is performed with an independent change of the length of the cold outlet nozzle, the angle of the widening of the cold outlet nozzle, and the hot outlet area. In a series of experiments, the pressure of air supplied to the inlet varies in order to take into account the possible effects of computational and model errors. An anomalous increase in the temperature of the outgoing air was observed with a hot outlet area of ~30 cm². Conclusions were drawn about the range of reasonable values of the outlet parameters for the considered configuration of the vortex tube.

This paper studies the hydrodynamic flow in a standard 0.2 ml polypropylene microtube during a polymerase chain reaction by evaluating its discrete numerical representation. The finite volume grid of the microtube is constructed using OpenFOAM toolbox. The dynamics of the flow satisfy the Boussinesq approximation. The feature analysis employs the change of the inclination relative to the neutral position, the interval of which is, for the most part, coarsely divided into segments, significantly refined for the regions of the flow singularity. The flow properties change drastically upon the formation of a double vortex at around 14° as it causes significant reduction of the average flow velocity. In contrast, at substantial inclination angles in both positive and negative directions, the flow velocity reaches its maximum.

In the article, the usability of standard two-parameters models of turbulence for numerical simulation of a vortex tube is discussed. Both k − ε and k − ω turbulence models were checked for subsonic air flows into the vortex tube channel. The main attention was paid to the development of the mesh, the simplicity of the implementation of simulation, and the physical concordance of the model results. Simulations performed by rhoPimpleFoam and sonicFoam solvers using k-ε and k-ω turbulence models gave similar results. The choice was made in favor of the k − ε model.