Experimental Study On Steam Ejector Refrigeration System Driven By Low Temperature Heat Source

The ejector refrigeration system uses industrial waste heat or solar energy to cool,is a potential way of refrigeration.The system has simple structure,no motion parts,low initial and operating cost,long service life,is an environment-friendly refrigeration system.The working conditions and the ejector structure have an important influence on the system performance.This paper focuses on its impact on the "imaginary throat" of the ejector to discuss the impact on the system performance.This paper establishes the analytical model of ejector refrigeration system and ejector design model.The influence of several common refrigerants(R152a、R134a、R123、R236fa、R141b and R-718(water))on the system performance are compared from physical properties,environmental protection,safety and economy,and choose water as the refrigerant of this experiment.This paper presents the structural design of the ejector.The design conditions in this article are: working fluid temperature is 70℃,ejection fluid temperature is 15 ℃,condensation temperature is 28 ℃;a movable nozzle ejector with is designed,which the nozzle throat diameter is set to 6.4mm and the mixing chamber diameter is set to 20 mm.And it is verified by two-dimensional numerical simulation by the numerical simulation software FLUENT.In this paper,a movable nozzle ejector refrigeration system experiment platform with water as the refrigerant is built.The main experimental devices are introduced in the article: generator,evaporator,condenser,constant temperature heat source,accumulator,liquid circulating pump,etc.,as well as data acquisition equipment(temperature sensor,pressure sensor and vortex flowmeter)and supporting software.The effects of different condensing pressures,different occurrence temperatures,different evaporating temperature conditions and different nozzle position(NXP)on the system performance are studied.The experimental results with the design results and the numerical simulation results is compared.The comparison results show that the error range of the entrainment ratio and the critical pressure of the ejector are both within 10%,indicating that the model is effective.Error may come from idealization of design and simulation process,error of data acquisition equipment and influence of processing process.The experimental results show that:(1)The effective area and position of the "hypothetical throat" in the ejector are affected by the generator temperature and the evaporator temperature,resulting in an impact on the performance of the system.(2)Both higher generator temperature and higher evaporator temperature will cause the ejector to have a higher critical pressure.The high-pressure fluid has higher energy,which increases the momentum of the mixed fluid,thereby increasing the critical back pressure of the ejector.(3)The COP,cooling capacity and entrainment ratio of the system will first increase and then decrease with the increase of the generator temperature,and increase with the increase of the evaporator temperature.(4)Different nozzle position also affect the effective area and position of the "hypothetical throat",thereby affecting system performance.There is an optimal nozzle position for a fixed-structure ejector.The results of this paper can provide theoretical reference for the structural design of ejector and the operating conditions of ejector refrigeration system.