CO_2 is a promising alternative to hazardous, ozone-depleting and global-warming refrigerants. It is more suitable to the ejector refrigeration cycle than to the vapor compression cycle. However, shock waves significantly reduce the efficiency of the ejector nozzle and, therefore, they must be investigated to improve the efficiencies of the nozzle and the ejector and the coefficient of performance of the ejector refrigeration cycle. This paper elucidates the types of Shockwaves in two-phase flow of CO_2 in converging-diverging nozzles and their relationship to inlet conditions and two-phase thermodynamic states. Shock waves in supersonic liquid-vapor flows with low and medium quality through the diverging sections of the nozzles were investigated. Strong-and thin-equilibrium shock waves were calculated and considered as the ideal limiting case of actual shock waves. Pseudo-shock waves and dispersed shock waves were obtained from the experiment. Both were weaker than the equilibrium shock waves and indicated relaxation phenomena. Based on a theoretical model, the pseudo-shock waves had long relaxation times. The large liquid droplets formed could not be easily decelerated by the vapor. Conversely, the dispersed shock waves had short relaxation times. The small liquid droplets formed could be easily decelerated by the vapor, but the deceleration was less rapid than that in the equilibrium shock waves.
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