An improved model to calculate the length of the mixing chamber of the ejector was proposed on the basis of the Fano flow model, and a method to optimize the structures of the mixing chamber and diffuser of the ejector was put forward. The accuracy of the model was verified by comparing the theoretical results calculated using the model to experimental data reported in literature. Variations in the length of the mixing chamber L m and length of the diffuser L d with respect to variations in the outlet temperature of the ejector T c , outlet pressure of the ejector p c , and the expansion ratio of the pressure of the primary flow to that of the secondary flow p g /p e were investigated. Moreover, variations in L m and L d with respect to variations in the ratio of the diameter of the throat of the motive nozzle to the diameter of the mixing chamber d g0 /d c3 and ratio of the outlet diameter of the diffuser to the diameter of the mixing chamber d c /d c3 were investigated. The distribution of flow fields in the ejector was simulated. Increasing L m and d c3 reduced T c and p c . Moreover, reducing p g /p e or d g0 /d c3 reduced T c and p c . The length of the mixed section L m2 , which was determined on the basis of the Fano flow model, increased as p g increased and decreased as d c3 increased. The mixing length L m1 , which was considered the primary flow expansion, showed the opposite trend with that of L m2 . Moreover, L d increased as p g /p e and d c /d c3 increased. When the value of d c was 1.8 to 2.0 times as high as that of d c3 , the semi-cone angle of the diffuser ranged between 6°and 12°. At a constant d c /d c3 , decreasing T c and p c increased L d .
KEYWORDSMixing chamber; length; Fano flow; diffuser; diameter ratio; expansion ratio; optimization method Nomenclature A cross-sectional area (m 2 ) c p specific heat at a constant pressure (kJ/kg•K) D diameter (m) f coefficient of friction k adiabatic index L length (m)