SIMULATION OF SHOCK WAVES IN SUPERSONIC FLOW OF CO_2 THROUGH A CONVERGING-DIVERGING NOZZLE OF TRANSCRITICAL EJECTOR REFRIGERATION SYSTEM

摘要

Shock waves in nonequilibrium liquid-vapor flow in a converging-diverging nozzle were simulated andrncompared to the experimental results in previous studies of the authors. Additional findings from simulationrnin the present study were found to be in agreement with the experimental results.rnIn the simulation, flow of uniformly dispersed droplets and vapor was assumed. Momentum and thermalrnrelaxation phenomena were incorporated in the derived equations. Simulation results using the equations forrnsupersonic two-phase flow of CO_2 in converging-diverging nozzles intended for a research on therntranscritical ejector refrigeration system are presented.rnIn a first previous study by the authors, shock waves along the diverging sections of relatively long nozzlesrnwere investigated in a blowdown device. Inlet conditions near the critical point were selected, wherein thernpressure range was 8–9 MPa and the obtained temperature range was 25–41℃. Correspondingly, backrnpressures ranged from 1.2 to 4.2 Mpa. In a second study by the authors, the expansion valve of the vaporrncompression refrigerator used was replaced by a relatively short converging-diverging nozzle to isolate thernnozzle and to easily investigate its inlet and outlet states. The inlet conditions used were 9–11 Mpa at 37–rn55℃. To determine different intensities of shock waves, the widest possible back-pressure range obtainedrnwas 3.6–5.9 Mpa.rnRelaxation phenomena, weak pseudo-shock waves and dispersed shock waves were obtained from thernsimulation. Weak pseudo-shock waves occurred in liquid-dominated two-phase flow, while dispersed shockrnwaves occurred in vapor-dominated flow. It was simulated and verified in this study that shock wavesrnintensify with increasing divergence angle given the same inlet condition, and with increasing supercriticalrninlet entropy given the same nozzle. The results are in agreement with the experiment and similar simulationrnresults in the previous studies.