Performance of a miniature ejector for application in a nitrogen Joule-Thomson cycle: Experimental and numerical analysis

The performance of Joule-Thomson (JT) cryocoolers can be improved by introducing ejectors. Ejectors with various geometric features have been proposed and investigated for cryogenic cooling in earlier studies, but only limited research is done on ejectors with a nozzle throat diameter less than 1 mm. In this paper, we present a miniature ejector with a nozzle throat diameter of 162 μm that was measured using X-ray computed tomography. When the ejector was operated with nitrogen gas at 295 K with a primary inlet pressure of 80 bar, a secondary inlet pressure of 0.5 bar and an outlet pressure of 1.2 bar, the primary and the secondary mass-flow rates were 394 mg/s and 83 mg/s, respectively. The measured primary mass-flow rate was quite close to the value predicted by a dynamic model, whereas the measured secondary mass-flow rate was lower than the predicted value, which was mainly caused by a non-axisymmetric machining defect of the nozzle that was assumed to be axisymmetric in the dynamic model. Besides, the effects of operating pressures and nozzle position on the ejector performance were analyzed. The study demonstrates the applicability of a miniature ejector in a JT cooling cycle.