Numerical evaluation of a variable geometry ejector for cooling applications

It is known that one of the most important geometrical factors influencing ejector performance is the area ratio between the nozzle and constant area section (rA). Its optimal value depends strongly on the operating conditions. Any change in the upstream and downstream pressures (temperatures) would require a different ejector to provide optimal performance. In the present work, a new feature, a spindle in the primary nozzle is suggested to achieve the highest entrainment ratio and critical back pressure with a single ejector for different operating conditions. The theoretical analysis was carried out with a CFD model using FLUENT for a 5 kW rated capacity steam ejector. Operating conditions were selected in a range that would be suitable for an air-conditioning application using evacuated tube solar collectors as heat source. For comparison, different ejectors with rA in the range of 14 to 25 were also simulated. The results indicated that the effect of the spindle position was similar to the effect of changing the area ratio. It was found that by changing the spindle position, the effective nozzle area can be adjusted and an optimal rA can be adjusted with a single ejector.