Experimental Study On Steam Injection Quasi-two-stage Compression Refrigeration System

In the vapor compression refrigeration cycle,after the refrigerant is determined,the evaporation pressure and the condensing pressure of the system are determined by the evaporation temperature and the condensing temperature,respectively.The evaporation temperature is determined by the function of the system,and the condensing temperature is limited by the ambient medium.When the evaporation temperature decreases,the compression ratio of the compressor increases,because the clearance volume of the compressor exists,therefore,based on the relevant theoretical formula,as the compression ratio increases,the compressor clearance volume decreases,when the compression ratio is increased to a certain value,the clearance volume is reduced to zero,then the compressor will no longer inhale,and the cooling capacity drop to zero.Since the ejector increases the pressure of the ejected fluid without consuming mechanical energy directly,it was introduced into the single-stage vapor compression refrigeration system in this thesis,and the steam jet Quasi-two-stage compression refrigeration system experimental platform was built,and the performance of system was studied.The ejector utilizes the exhaust of the compressor as the power,and ejects the refrigerant at the outlet of evaporator,and sends it into the compressor suction port after increasing the pressure,which not only reduces the compression ratio to get lower evaporation temperature,but also does not generate excess power consumption.The ejector is an important part of the steam ejector quasi-two-stage compression refrigeration system.In this paper,the basic size of the ejector was calculated by the dynamic function method.The influence of the change of the parameters of the inlet and outlet of the ejector on the ejector coefficient and system performance was investigated.In addition,the mathematical model of compressor,evaporator,condenser,expansion valve and gas ejector was established,and the relevant calculation program was compiled by MATLAB language,and the performance of the system was simulated theoretically.The experimental platform was built,and it can achieve two kinds of circulation through the valve switch,including single-stage steam compression refrigeration cycle and steam jet quasi-two-stage compression refrigeration cycle.The change of cooling capacity and system performance under different operating conditions were studied experimentally.In this paper,the experimental study of steam ejector quasi-two-stage refrigeration system and single-stage steam compression refrigeration system shows that the steam jet quasi-two-stage refrigeration system can obtain lower evaporation temperature than single-stage steam compression refrigeration system,and the performance coefficient of the steam jet quasi-two-stage refrigeration system performance is better than single-stage steam compression refrigeration system in low evaporation temperature.The experiment data shows that when the evaporation temperature down to-22.57?(Tk=303.15K),the COP of steam ejection quasi-two-stage refrigeration system is superior to the single-stage vapor compression refrigeration system.When the evaporation temperature down to-31.43 ?(Tk=308.15K),the single-stage steam compression refrigeration system will no longer produce cooling capacity.With the increase of compression ratio,the compressor volume coefficient becomes zero,the compressor suction amount becomes zero,although the refrigeration system is still running,the cooling capacity has changed to zero.In this paper,the system with ejector can achieve the minimum evaporation temperature of-36.52?.The experimental investigation of gas ejector was carried out to investigate the influence of the change of inlet and outlet parameters on ejector coefficient,system performance and cooling capacity.Firstly,the influence of the fluid pressure at the ejector outlet on the injection coefficient,system performance and cooling capacity was analyzed.The experimental data shows: with the increase of outlet mixed fluid pressure,the injection coefficient decreases gradually,and the refrigerating capacity of the system decreases,but the system COP has a quadratic curve relationship with the variation of mixed fluid pressure at the outlet,when the inlet fluid pressure of the ejector is 880 KPa and the outlet pressure of mixed fluid is 220KPa~240KPa,the system COP is better.Then the influence of working fluid on injection coefficient and system performance was analyzed.The experimental data shows: when the pressure of the working fluid increases gradually,the injection coefficient,the system COP and the refrigerating capacity all increase first and then decrease.Under the experimental conditions in this paper,when the working fluid pressure is 900KPa~930KPa,the system COP is better.In addition,the relationship between ejector pressure and injection coefficient,system COP and cooling capacity was analyzed.The experimental data shows: When the pressure of the injected fluid increases,the injection coefficient shows an upward trend,and the cooling capacity presents the same trend,but the system COP and the injection fluid pressure present quadratic curve relations,when the pressure of injection fluid is 130KPa~150KPa,the system COP is better.