Critical Flashing Flows in Nozzles With Subcooled Inlet Conditions

Abstract

Examination of a large number of experiments dealing with flashing flows in converging and converging-diverging nozzles reveals that knowledge of the flashing inception point is the key to the prediction of critical flow rates. An extension of the static flashing inception correlation of Jones [16] and Alamgir and Lienhard [17] to flowing systems has allowed the determination of the location of flashing inception in nozzle flows with subcooled inlet conditions. It is shown that in all the experiments examined with subcooled inlet regardless of the degree of inlet subcooling, flashing inception invariably occurred very close to the throat. A correlation is given to predict flashing inception in both pipes and nozzles which matches all data available, but is lacking verification in intermediate nozzle geometries where turbulence may be important. A consequence of this behavior is that the critical mass flux may be correlated to the pressure difference between the nozzle inlet and flashing inception, through a single phase liquid discharge coefficient and an accurate prediction of the flashing inception pressure at the throat. Comparison with the available experiments indicate that the predicted mass fluxes are within 5 percent of the measurements.

Investigation on the choking flow characteristics in electronic expansion valves

“…Owing to the effect of the metastable state phenomenon, it has been generally found that models based on assumptions of homogeneous equilibrium under-predict the critical discharge rate. Among the models [10,12,13] which calculate the flashing critical mass flux in nozzles, N. Abuaf's [13] model gives the satisfied accuracy. In this model, the pressure undershoot at the flashing inception location can be calculated by the following equation…”

“…Superheated liquid in rapid depressurizing flashing flow has been founds by many investigators [11][12][13][14][15]. Owing to the effect of the metastable state phenomenon, it has been generally found that models based on assumptions of homogeneous equilibrium under-predict the critical discharge rate.…”

“…According to Abuaf's [13] results, flashing inception point is located at the minimal area plane (throat). • The refrigerant immediately downstream the evaporation wave is in homogenous and thermal equilibrium.…”

“…Schrock [11], O.C. Jones Jr. [12], N. Abuaf [13], A.A. Kornahauser [14], G.S. Harrell [15], K. Akagawa et al [16], M.M.…”

“…In this paper, N. Abuaf's [13] model for two-phase flow convergent-divergent nozzle is employed to predict the choking mass flow rate and the refrigerant's metastable state immediately upstream the evaporation wave, and Wadle's [18] abrupt diffuser model is employed to predict the pressure recovery downstream the shock wave. Together with the evaporation wave theory, the choking flow characteristics of EEVs are investigated.…”