Dimensional analysis and performance laws for organic vapor flow turbomachinery

Abstract

Non-dimensional groups of variables are obtained for describing turbomachinery performance working with non-perfect gases. The dimensional analysis follows the Rayleigh method and Buckingham-Π theorem. It employs the bulk modulus, the specific gas constant, and the derivative of the compressibility factor regarding pressure at constant entropy. Following a classical analysis from Traupel, this new similarity number is a valuable measure of the non-perfectness of a gas. As an outcome of the present study, it is found that the compressibility factor is not a primary similarity number for non-perfect gas flows. Still, its derivative is part of such a dimensionless number. At least two new similarity numbers are required for describing non-perfect compressible gas flows in addition to the conventional perfect gas similarity numbers. As a limit case of the dimensional analysis, the well-known similarity numbers for a perfect gas result with the isentropic exponent similarity. The theoretical analysis is applied to flow applications utilizing the closed-loop organic vapor wind tunnel test facility CLOWT at Muenster. These applications cover the experimental investigation of the flow of an organic vapor past a circular cylinder and a centrifugal organic vapor compressor's performance. The results of the test cases support the main findings of the dimensional analysis.