Relationship between physical parameters of supercritical fluids and normal shock characteristics

Abstract

Physical parameters of supercritical fluids change drastically near the critical region, which makes it difficult to predict and analyze the supercritical fluid flow parameters behind the normal shock wave. In this paper, in combination with supercritical fluid physical parameters database, we employed an iterative algorithm to solve the flow parameters behind normal shock by deriving shock equations. The change of normal shock parameters of six supercritical fluids with inflow state was studied by the controlled variable method and a correlation analysis. The results show that when the inflow Mach number is fixed, the normal shock parameters, such as density ratio and pressure ratio, change rapidly in the Widom zone as a result of the dramatic changes of the physical parameters. When the inflow state is the same, the normal shock pressure ratio of NH3 is the highest, whereas that of C8H24O2Si3 and C10H22 are pretty low. The normal shock intensity of supercritical fluid is better reflected by the pressure ratio rather than Mach number. According to the correlation analysis, the compressibility factor and the sound speed of inflow are the main physical factors that affect the normal shock density ratio and pressure ratio, respectively. Based on the main physical factors, empirical equations for predicting the change trend of normal shock pressure ratio and density ratio are obtained.