The Numerical And Experimental Study Of Gas-Liquid Two-Phase Ejector

Gas-liquid two-phase ejector is a device without moving parts, in which steam is used to drive cold liquid from a pressure lower than the primary steam to a pressure higher than the primary steam. Gas-liquid two-phase ejector has been applied in many fields, especially for the circulating pump in bi-ejector system and emergency water injection in steam generators of nuclear reactors. The aim of the gas-liquid two-phase ejector is to obtain a higher discharge pressure. The performance of two phase ejector is influenced by several geometrical factors (e.g. the throat sectional area of the primary flow nozzle, the primary nozzle position, the throat sectional area of mixing chamber) and the operational condition(e.g. primary pressure, driving fluid pressure). Mixing chamber, where the primary steam and the driving fluid come into contact, involves complicated mass, momentum and energy exchange.Based on the theoretical study of gas-liquid two-phase ejector, an experimental study was described in order to show the performance of ejector. Furthermore, a numerical simulation was accomplished to discuss the two-phase flow mechanisms and the flow characteristics of the two-phase flow in the mixing chamber. The main contents are the following:(1) On the basis of the mathematical analysis of gas-liquid two-phase ejector, a new-style gas-liquid two-phase ejector model has been presented. According to the model, the design procedure of the ejector using R141b as refrigerant is presented. By calculation, the main dimensions of the two phase ejector such as the throat sectional area of the primary flow nozzle and mixing chamber have been defined. A calculation program written in Visual basic is finished in order to evaluate the primary pressure, driving fluid temperature and flow on the performance of the ejector.(2) In the two-phase ejector's mixing chamber, there exists a complicated mass, momentum and energy exchange between gas phase and liquid phase. Based on the defined flow pattern, this paper discussed the flow field distribution of the two phase flow. This paper presented a new model of the two phase flow and solved the model in finite difference scheme. Simulate computation demonstrated the radical direction distributions of the pressure, velocity and void fraction in the mixer. Furthermore, the numerical simulation calculated the axial direction distributions of velocity. And it further verified the mixing mechanism of the gas-liquid flow.(3) With the gas-liquid two-phase ejector as the core, a new laboratory bench to verify the performance of ejector has been designed and built. For the sake of testing the mechanisms of the mixing chamber and condensing shock wave,16 pressure holes were evenly arranged along the mixing chamber and diffuser in 4 rows. The equipment devices (generator, storage tanks, circulation pump and condenser) and testing gauges (pressure transducer, temperature sensor and pressure gages) have been selected. Then the ejector, equipment devices, testing gauges and pipelines were arranged according to the system diagram, thus the gas-liquid two-phase ejector equipment table has been built. Based on the former study on the performance of two-phase ejector, primary pressure, driving fluid flow rate, ejector pressure, the primary nozzle position and the angle of the primary nozzle have been tested.