Numerical study on the performances of steam-jet vacuum pump at different operating conditions

A mathematic model based on realizable k-ɛ turbulence model for transonic flow was proposed to investigate the mixing flow behaviours of primary and secondary fluids in steam-jet vacuum pump and the affections to the pumping performances. The simulation was carried out to predict the static pressure distribution among mixing chamber wall by a commercial computational fluid dynamics (CFD) code FLUENT 6.2. Close agreements between the predicted results and experimental data validated the present theoretical model. Using the present approach, the velocity vectors and Mach number profiles in mixing chamber at different back pressures and the secondary fluid pathlines and mass flux profiles at different suction pressures were predicted. It is found that there are swirls separated from secondary fluid near the wall and the velocity of secondary fluid was fallen down obviously when the back pressure was bigger than critical back pressure. The above two factors lead to the entrainment ratio (Em) reduced rapidly. It is also found that the mass flux increased with the increasing of suction pressures and made the entrainment ratios increased. The prediction results show that the pressure ratio (K) is a dominant position in affecting the pump's performances.