Vortex tube (VT) is a simple mechanical device which splits compressed gas of room temperature into cold and hot streams. It can produce cold stream down to around -30℃ and hot stream up to around 130℃. However, the detail of its mechanism of energy separation is still unclear. One of the most important parameters of energy separation is the tangential velocity of the working gas at the exit of the tangential nozzle, which is installed in a vortex chamber. In this research, we measured

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... re of cold stream using thermocouple probe, then calculated the tangential velocity at the exit of the tangential nozzle and isentropic efficiency. The results indicate that the tangential velocity and the isentropic efficiency increase as the cold fraction decrease, and reach maximum values at the inlet pressure of 0.3 to 0.5MPa and cold fraction less than 0.34.