Performance Characteristics of Convergent-Divergent Nozzles for Subcooled Hot Water (3rd Report,Effect of Induced Turbulence on Nozzle Performance)

A thin wire is installed just upstream of the throat in a convergent-divergent nozzle in order to decrease pressure undershoot(that is,the degree of the thermal nonequilibrium)at the throat. To study the effect of the wire diameter(0.3 to 1.5mm)on the nozzle performance,experiments have been carried out using initially subcooled hot water under inlet pressures of 0.47,0.62 and 0.77MPa,and inlet subcoolings of 6,12, and 19 K. The one-dimensional void fraction is measured. Moreover,the measured pressure profiles and void fractions are compared with those calculated using the code "MINI-TRAC". The results are summarized as follows:(1)The greater the inlet subcooling or the lower the inlet pressure,the greater the improvement (using the method of a wire installation)of the nozzle performance. (2)The difference of the wire diameter has little effect on the nozzle performance. The pressure profiles for the nozzle with the wire agree with those calculated from the code "MINI-TRAC". (3)The one-dimensional void fraction profile can be obtained using real-time neutron rasiography and image processing