Abstract The effect of vortex generator parameters (Cold orifice angle, Cold orifice diameter and Nozzle area) on vortex tube performance is investigated experimentally. Vortex tube is connected to a natural gas pipeline with constant pressure of 4 bars. To improve vortex tube efficiency, six generators with different cold orifice angle, five generators with different cold orifice diameter and three generators with different nozzle area are studied for each experiment part. Results show variation of nozzle area has no effect on optimum cold mass fraction while cold mass angle and cold mass diameter move this point. Increment in cold orifice diameter increases optimum cold mass fraction and decreases cold temperature. As the angle of cold orifice increases, more mass flow passes through cold outlet and optimum cold mass fraction also increases. The expansion of the gas in the diffuser type cold orifice is investigated as the dominating reason for the different vortex tube performance. These mentioned designing parameters of vortex generator affect the flow pattern and efficiency of vortex tube as a consequence. For cold orifice angle of 4.1°, cold orifice ratio of 0.64 and nozzle area ratio of 0.14, highest efficiency is achieved.