In this article, we present the development of a fuzzy expert system (FES) for fuzzy modeling of the performance of counterflow Ranque-Hilsch vortex tubes for different geometric constructions. Experimental values were obtained from a detailed experimental investigation. With these experimental values, FES models of the Ranque-Hilsch vortex tube behavior were designed using the MATLAB 6.5 fuzzy logic toolbox in Windows XP running on an Intel 3.0-Ghz PC. For this process P, N, , and L/D were chosen as input and Th, Tc, T as output parameters. FES results agree well with experimental data. It was found that the coefficient of multiple determination (R2 value) between the actual and fuzzy predicted data is Th=0.9801, the R2 value for Tc values is 0.9841, and the R2 value for T values is 0.9748.