Research On The Performance Of R134a Gas-liquid Two-phase Ejector

Gas-liquid two-phase ejector is one boost device that pumps low-pressure fluids with high-pressure steam and raises pressure after shock wave process.It doesn’t need extra energy supply in running process.The ejector has advantage of simple structure,stable performance and without leakage.It has replaced the high energy consumption pump which applied on low temperature ORC(Organic Rankine Cycle)gradually.Effectively increase of energy efficiency can be realized.The complex phenomena of phase change and shock wave in the mixing chamber greatly affect the performance of the ejector.The one-dimensional ejector model which has been established is rarely considered the phenomena and its prediction does not match with the actual.Therefore,works of the thesis are as follow.1、A one-dimensional model is established that has considered in the phase change and shock phenomena in the mixing process.The working fluid R134a which is environment friendly and lower-boiling has been selected.The iterative algorithm is used to calculate the outlet pressure and injection coefficient of the gas-liquid two-phase ejector.Computation program based on MATLAB platform has been compiled.REFPROP software has been used to calculate the thermal properties of R134a.2.The effect of the inlet parameters and mixing chamber geometry on pressure improvement and injection coefficient,mixing chamber resistance are analyzed.In order to analyze the shock intensity of the throat of mixing chamber,the change of pressure after shock is introduced and the variation trend of the parameter in different working conditions is analyzed.The study found that the outlet pressure is raised by about 0.04MPa and 0.08MPa respectively,the entrainment ratio is decreased by 6 and 3.6 respectively when the inlet steam pressure is increased by 2.5MPa.The outlet pressure is decreased by about 0.1MPa,the entrainment ratio is increased by 5.1 and 3.0 respectively when the inlet steam temperature is increased by 35K.The outlet pressure is raised by about 2.63MPa and 2.73MPa respectively,the entrainment ratio is decreased by 22 and 22.26 respectively when the inlet liquid pressure is increased by 0.3MPa.The outlet pressure is decreased by about 1.78MPa and 186MPa respectively,the entrainment ratio is increased by 5.1 and 3.0 respectively when the inlet liquid temperature is increased by 23K.This means that the inlet steam parameters have little effect and the inlet liquid parameters have great effect on the performance of the ejector.In order to optimize the performance of the ejector,selection of suitable inlet steam pressure and temperature,higher inlet liquid pressure and lower inlet liquid temperature is suggested in the two-phase ejector designing and operating according to the study.3.A thermodynamic model of R134a ORC(Organic Rankine Cycle)system is established according to the performance of R134a gas-liquid ejector.The effect of R134a gas-liquid ejector inlet liquid parameters on thermal efficiency and irreversible efficiency of the system is studied.The system thermal efficiency is raised by 2.0%and 1.78%respectively,the system irreversible efficiency is decreased by 22 and 22.26 respectively when the inlet liquid pressure is increased by 0.2MPa.The improvement of the inlet liquid pressure can increase the system thermal efficiency and operation stability.But it can also lower the system irreversible efficiency.Due to the limitation of R134a gas-liquid ejector performance,the optimization of the system performance by the way of adjusting the ejector inlet liquid pressure is limited for single-stage ejector ORC system.The study provides theoretical guidance for the design and operation of gas-liquid two-phase ejector and ORC system.