EXPERIMENTAL AND NUMERICAL ANALYSIS OF R744 EJECTORS OPERATED IN PART LOAD

摘要

This paper presents an experimental and a numerical investigation of R744 ejectors. For different operatingrnconditions, several experimental tests were carried out. The experimental results show a strong correlationrnbetween the mass entrainment ratio and pressure lift. The achieved ejector efficiencies reach from 22% to 33%rnfor the pressure lifts between 3.5 bar and 9 bar. The experimental data was used to validate the numericalrnsimulations. For a detailed investigation, three cases were chosen. To perform the simulations, thernhomogeneous equilibrium model (HEM) and the k-ε RNG turbulence model were used. The contour plots ofrnMach number, turbulent kinetic energy and pressure as well as plots along the flow path reveal the flow patternrndetails. The approach of a sectional and cumulative increase in entropy rate was used to investigate local andrnglobal flow irreversibilities. The results show that the diffuser section contributes little to the overall increasernin entropy rate with values from 10.12% up to 28.73% and that the diverging part of the motive nozzlerncontributes a considerable amount more with values from 33.3% up to 37.77%. It can be concluded thatrnchanges in turbulence along the mixer and diffuser are the main reason for the different efficiencies.