Performance Characteristics of Divergent-Convergent Nozzles for Subcooled Hot Water

Abstract

The purpose of this study is to obtain basic information for the design of a convergent-divergent nozzle for flashing expansion of initially subcooled water. The conical-type nozzles had a sharp-edged throat of 3.5 mm diameter. Nozzles with different divergent angles and different exit stream-expansion ratios were tested. Initially subcooled water samples at an inlet pressure of 0.47 MPa and inlet temperatures of 409.7 to 421.5 K (inlet subcoolings of 13 to 1.2 K) were used in the range of nozzle back pressures of 10 to 160 kPa. As a result, (1) The values of the thrust coefficient are discussed in relation to the subcooling, back pressure, nozzle divergent angle, and exit stream-expansion ratio ; (2) A method to determine the optimum exit stream-expansion ratio for a given pressure ratio is proposed ; and (3) The relationship between the critical mass flow rate and the critical pressure ratio is discussed based on the experiments.