Farzad Shiri - M.Sc. Student, Mechanical Engineering Department, Islamic Azad University, Mashhad Branch,Mashhad, Iran
Seyed Mahmoud Abolhassan Alavi - Assistant Professor, Mechanical Engineering Department, Islamic Azad University, Mashhad Branch, Mashhad, Iran

The purpose of this paper is to investigate the effect of using a convergent hot tube on vortex tube refrigeration capacity. The computational fluiddynamics (CFD) model used here is a threedimensional 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 simulated in order to analyze the performance of the vortex tube.The results showed that as the angle converges from the cylindrical model (β=0°), the cold temperature separation improves at cold mass fractions greater than about 0.3, but increasing the angle more than 2° impairs the cold temperature separation compared with the cylindrical model because of the development of a secondary circulation in the vortex tube. Validation of a previous experimental study that used a cylindrical vortex tube has also been carried out in this research.

Vortex tube; Convergent hot tube; Numerical simulation; Energy separation