Experimental results with a variable geometry ejector using R600a as working fluid

• An experimental study with a variable geometry ejector with isobutane is presented.
• The influence of the spindle position on the ejector performance is assessed.
• The critical condenser pressures are determined.
• The existence of an optimal spindle position was experimentally verified.
• The performance improvements compared to a fixed geometry ejector are demonstrated.

Experimental results with the first laboratory scale variable geometry ejector (VGE) using isobutane (R600a) are presented. Two geometrical factors, the area ratio and the nozzle exit position, can be actively controlled. The control of the area ratio is achieved by a movable spindle installed in the primary nozzle. The influence of the spindle position (SP) and condenser pressure on ejector performance are studied. The results indicate very good ejector performance for a generator and evaporator temperature of 83 °C and 9 °C, respectively. COP varied between 0.4 and 0.8, depending on operating conditions. The existence of an optimal SP, depending on the back pressure, is identified. A comparison of the benefit of applying the variable geometry design over a fixed geometry configuration is assessed. For example, for a condenser pressure of 3 bar, an 80% increase in the COP was obtained when compared to the performance of a fixed geometry ejector.