Design And Experimental Study On The CO₂ Cold Storage Refrigeration System

As we all known,cold storage as an important part of the cold chain logistics and with the cold chain logistics rapidly development in recent years,the rapid growth of the total domestic storage capacity is more obvious.At the same time,with the international community increasing attention on energy-saving emission reduction and environmental protection,which accelerate the progress of the phase-out of freon refrigerant,so natural refrigerants and other low-GWP alternative technology has become the main study direction in the refrigeration and air conditioning industry recently.So far,the cold storage refrigeration system is still dominated by ammonia refrigeration system and the technology is relatively mature.However,as a result of several major domestic accidents occuring,people now re-focus on carbon dioxide.Taking into account the excellent physical properties of carbon dioxide at low temperatures.,the development of new carbon dioxide refrigeration technology has become the research hotspot in the refrigeration industry.At present,domestic and foreign applications of CO₂ in cryogenic refrigeration systems are mostly cascade system,two-stage booster system and secondary system.Development of a simple,high-efficiency CO₂ refrigeration system has become a research trend with respect to these systems.Someone propose a kind of CO₂ cold storage refrigeration system considering the characteristics of the soil temperature is constant,in which CO₂ is the sole refrigerant of the system.The condenser adopts the GSHP technology to exchange heat,that is,the CO₂ exhaust directly make heat exchange with the underground soil to achieve the better condensation.The evaporator adopts the top row tube technology,reducing the power consumption and mechanical heat.The system take full advantage of the high pressure of CO₂,so that the system operation successfully in the subcritical cycle.The CO₂ cold storage refrigeration system has been applied in one cold storage project for the first time and successfully running all the way.In this paper,the system is analyzed theoretically,and then the design analysis is carried out in combination with the refrigeration system of the cold storage project.Finally,the stability of the refrigeration system,the energy consumption of the refrigeration system,the uniformity and the fluctuation of the cold storage temperature are measured respectively in the field.Firstly,the refrigeration system of the cold storage is simplified,and then the cycle characteristic of the simplified system is analyzed theoretically.It is found that when the refrigeration system has a certain working condition,the theoretical refrigeration coefficient is related to the evaporator outlet superheat and the intermediate saturation temperature?or intermediate saturation pressure?.Finally,the thermodynamic calculation model of the cold storage system is established and analyzed by means of mathematical software MATLAB.The results show that under the steady condition,the intermediate saturation temperature and the evaporator outlet superheat degree have little impact on the theoretical COP.Secondly,in this paper,the design of the actual refrigeration system is analyzed in detail.Then,under the given design conditions,the main refrigeration equipments and the important auxiliary equipments of the CO₂ refrigeration system are calculated for the analysis.Finally,the main parameters of the pressure and temperature of the refrigeration system are monitored and measured.The results show that the refrigeration system has good running stability.Secondly,the energy consumption of the refrigeration system is measured in the field.The data show that the average energy consumption per hour of the refrigeration system is only 53.83 k W·h,that is the annual power consumption per cubic meter is only 6.2k W·h.Finally,during the normal operation of the cold storage,the field temperature monitoring and measurement has been carried out for one week.After data processing,it is found that the maximum temperature fluctuation in the storage is only 0.6?,the overall average is 0.3?,The average of the nonuniformity is only 0.15?.These good data show that the cold storage has good temperature uniformity and smaller temperature fluctuation.