Simulation of ejector for vacuum generation

Abstract

Supersonic ejectors are used in a wide range of applications such as compression of refrigerants in cooling systems, pumping of volatile fluids, or vacuum generation. The objective of the present paper is to mesh and simulate, in an OpenFOAM environment with an open access implicit density-based solver HiSA, the physics of the vacuum ejector, and, later, compare the results with experimental measurements. In order to achieve this a 2D axisymmetric mesh made by hexahedral cells has been created. Steady solutions have been obtained, with prescribed total pressure in primary and secondary inlets. Secondary total pressure ranges from 1 to around 0.2 bar in which the secondary flow is zero. Numerical results are compared with experimental measurement, with two flowmeter sizes for small flow rate accuracy. Two regimes are encountered. In supercritic regime the secondary is chocked and sonic flow is reached in the second nozzle. In subcritic regime, the secondary flow is subsonic. The agreement is good, although simulation tends to slightly overestimate flow rate for large values region.