Study On The Mechanism And Numerical Simulation Of Two-phase Flow In The Ejector

With the popularization of the refrigeration cycle either in the daily life or in the industrial production, the disadvantages of the traditional refrigeration cycles have been more and more prominence. Since the earlier refrigeration cycles consume large energy and make the pollution severe, the investigation of the new-fashioned cycles becomes the keystone. The ejector expansion refrigeration cycle has gained much attention because of its ability to utilize low-temperature thermal energy resources, and its simple structure and reliable operation.The study of gas-liquid ejector, which is used in the ejector expansion refrigeration cycle, is carried out. A numerical simulation is employed to discuss the mechanisms and the characteristics of the two-phase flow field in the mixing section emphatically. The following are the main contents:1. Based on the theoretical analysis of the gas-liquid ejector, the mathematical and the physical models of the two-phase flow in the mixing section are established especially. Cooperating with the achievement of Peter Menegay, a CFD code is programmed to simulate the mixing section of the ejector. The parabolic two-phase flow conservation equations are presented using HFC-134A as the refrigerant. Also described is the IPSA algorithm, important in modeling non-equilibrium effects. Other features of the code, such as two-dimension Prandtl's mixing length turbulence model and wall function approximation, are also discussed. Discretization of the equations by the control volume method is described. And the Thomas algorithm is employed to compute iteratively for the simulation.2. Post processing of the calculated results is carried out by the Visual Basic program and Microsoft Excel. The contours and graphs of the pressure, velocity and quality are obtained to analyze the mechanisms of the two-phase flow in the mixing section. The flow field shows that the interaction between the fluids, including mass and momentum transfer, occurs primarily at the beginning of the mixing section. There is the 'mixing boundary layer' in the motive flow because of the evident non-equilibrium between the subcooled motive flow and the superheated suction flow. In the downstream where the mixing boundary layer is vanished, the flow becomes steady and the condition of the two-phase flow remains unchanged. Along with the whole mixing process, there is always the refrigerant liquid's evaporation occurring.