A Numerical and Experimental Performance Assessment of a Single-Phase Supersonic Ejector

This paper proposes an integrated numerical–experimental study of a fixed geometry ejector designed for a cooling system activated by waste heat. Ejector operation is analyzed for cases of imposed input and output sets of conditions in terms of pressures and/or temperatures. Experiments with constant primary conditions and secondary temperature were conducted in a range of outlet pressures for model validation purposes. A parametric analysis was then performed for constant pressure and temperature conditions at both inputs (primary and secondary) by varying the outlet pressure. For each test case, performance in terms of entrainment ratio, local parameters distributions (P, M, τ) and the internal flow structure were analyzed in an attempt to establish a link between the external constraints, the flow structure, the operation stability and performance within the range of cooling applications. The ranges of operating conditions investigated were P p = 4.77 bar, T p = 83 °C and, respectively, 1.7 ≤ P c ≤ 2.4 bar, 12.5 °C ≤ T e ≤ 16.5 °C, at saturation. Experimental entrainment ratio, ER exp in the range of 0.12–0.22 was numerically simulated within ± 10%. It was shown that both the ejector operation and the internal flow configurations were sensitive to backpressure. More particularly, an optimal backpressure exists to which corresponds an on-design conditions with maximized entrainment ratio and a shock-wave train located at the end of the mixing chamber. A backpressure increase sets the ejector in off design. This mode of operation is characterized by a shift of the shock train toward the inlets, a disturbance of the flow configuration, a diminution of the entrainment ratio and a deterioration of the operation stability. On the other hand, a backpressure decrease does not affect the ejector stability of operation at its maximum entrainment ratio for the prevailing conditions.