Investigating the effect of water nano-droplets injection into the convergent-divergent nozzle inlet on the wet steam flow using entropy generation analysis

Abstract

In many industrial pieces of equipment, such as ejectors, thermo-compressors, supersonic separators, etc., in which the condensation phenomenon occurs spontaneously, steam enters the nozzle in a saturated condition. Liquid droplets are likely to be present in the saturated vapor. In the present paper, the effect of the existence of a number (9 cases) of liquid droplets (with a fixed size of 20 nm in all cases) on the saturation steam has been studied. The results demonstrate that with the increase in the number of droplets at the nozzle inlet; pressure, temperature, liquid mass fraction, mass-generated rate and entropy increase in the convergent part. However, the growth of droplets and Mach number decrease. Furthermore, due to steam condensation and latent heat transfers to steam, the degree of supercooling, the supersaturation ratio and the flow rate at the nozzle inlet are decreased, the intensity of condensation shock is reduced, and shock occurs with delays. With an increase in the number of droplets, condensation shock and the nucleation phenomenon will not occur. The amount of entropy production decreases with the surge in the number of droplets at first, and then begins to increase. The results demonstrate that in the presence of 3 × 10+14 droplets, compared to the absence of water droplets at the nozzle inlet, generated entropy, liquid mass fraction and the mass flow rate will decrease by 9.4%, 12.5%, and 1.7%, respectively.