Performance and flow characteristics of nozzles for initially subcooled hot water (influence of turbulence and decompression rate)

Abstract The purpose of this study was to improve the performance characteristics of a convergentdivergent nozzle for flashing expansion of initially subcooled hot water. The slip between the vapor and liquid along the divergent passage and the maximum nonequilibrium pressure drop at the nozzle throat (this is related to the thermal nonequilibrium) cause a decline in the nozzle efficiency. To decrease the maximum pressure drop, a nozzle with thin wires just upstream of the throat and a nozzle with a smaller convergent angle were manufactured and tested. Initially subcooled hot water at an inlet pressure of 0.47 MPa and inlet temperatures of 409.9 to 421.8 K (inlet subcoolings of 0.9–12.9 K) were used with the nozzle back pressures ranging from 5 to 101.3 kPa. The following results were attained: (1) the maximum nonequilibrium pressure drop at the throat decreased and the thrust coefficient increased by 10%; (2) the thrust coefficient was found to be independent of the inlet subcooling and exit stream-expansion ratio; (3) a correlation between the ratio of the exit pressure to the inlet pressure and the appropriate exit stream-expansion ratio was obtained empirically; and (4) the critical flow rate was found to be lower than that for an ordinary convergent-divergent nozzle.

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