A vortex tube is a device which separates the incoming compressed gas into two streams, one having a lower temperature and other having a higher temperature than the incoming air. Experimental study on the vortex tubes of different inner diameter was reported here with air as the working medium. With an increase in inlet pressure, the temperature separation and cooling capacity had increased. The maximum temperature separation was obtained at a cold mass fraction of 0.2 and maximum cooling capacity was obtained for a cold mass fraction of 0.6 for all tubes. The curvature of pipe had different effects on different inner diameter vortex tubes. The vortex tubes having smaller inner diameter had better cooling capacity than larger inner diameter tubes for similar inlet mass flow rate and similar inlet pressure. © 2019 Begell House Inc. All rights reserved.