Since, cooling is the main use of vortex tube, the exited heat from the hot outlet of vortex tube can be assumed as the wasted energy when it is used as a cooling device. So, this paper tries to reduce the hot and cold temperatures at exhausts in order to increase the vortex tube cooling power. In this paper, a new method is studied which uses the shell heat transfer mechanism to affect the flow pattern inside the vortex tube. This research tries to clarify the flow pattern inside the vortex tube applying a fixed negative heat flux on the wall of the vortex tube. The results indicate that a part of main tube (around 23%) can be introduced as the effective cooling length.

Purpose – The purpose of this paper is to investigate the effect of convergent nozzles on the thermal separation inside a vortex tube, using a three-dimensional (3D) computational fluid dynamics (CFD) model as predicting tool. Design/methodology/approach – The 3D finite volume formulation with the standard k-ε turbulence model has been used to carry out all the computations. Six different nozzles for convergence angle have been utilized β=0, 2, 4, 6, 8 and 10°. All other geometrical parameters were considered fixed at the experimental condition, i.e. main tube and chamber sizes and 294.2 K of gas temperature at inlets. Findings – The numerical results present that there is an optimum convergence angle for obtaining the highest efficiency and β=2° is the optimal candidate under the simulations. It can be pointed that, some numerical data are validated by the available experimental results which show good agreement. Practical implications – It is a useful and simple design of nozzle injectors to achieve the maximum cooling capacity. Originality/value – In the work with assuming the advantages of using convergent nozzles on the energy separation and their considerable role on the creation of maximum cooling capacity of machine, the shape of nozzles was concentrated. This research believes that choosing an appropriate convergence angle is one of the important physical parameters. So far, an effective investigation toward the optimization of convergent nozzles has not been done but the importance of this subject can be regarded as an interesting research theme; so that the machine would operate in the way that the maximum cooling effect or the maximum refrigeration capacity is provided.

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The purpose of this paper is to investigate the effect of using a convergent hot tube on the vortex tube refrigeration capacity. The computational fluid dynamics (CFD) model used is a three-dimensional steady compressible model that utilizes the k-ɛ turbulence model. In this numerical research, different convergence angles of the hot tube (β=0°, 0.5°, 0.88°, 1°, 1.5°, and 2°) have been considered to analyze the vortex tube performance. The results showed that as the angle converges from the cylindrical model (β=0°), the cold temperature separation improves at the cold mass fractions greater than about 0.3, but increasing the angle more than 2° impairs the cold temperature separations compared to the cylindrical model, because of the secondary circulation development inside the vortex tube. Also, a successful validation has been carried out between some available experimental results and the present numerical model (for cylindrical vortex tube) IntroductionThe vortex tube is a simple device, without any moving parts, that separates a pressurized flow of air (or any inlet gas) into hot and cold streams. Compressed air enters tangentially into the vortex chamber, where it splits into two lower pressure streams, the peripheral and the inner vortexes. The hot stream rotates near the outer radiuses (near the wall) while the cold stream flows at the center of the tube. The hot outer layers of the compressed gas escape through the conical valve side at the end of the tube. The remaining gas returns in an inner vortex and leaves through the cold exit orifice located at the other end of the tube near the inlets. This behavior is schematically illustrated in Figure 1. There are various explanations for this behavior happened in the vortex tubes. One explanation is that, owing to centrifugal force, the outer air is under higher pressure than the inner air. So, the temperature of the outer layers is higher than that of the inner layers. Another explanation is that as both vortices have the same angular velocity and direction, the inner vortex loses angular momentum.