Study On Refrigerant Leakage And Diffusion Characteristics Of Ammonia Carbon Dioxide Cascade Cold Storage

With China’s acceptance of the Kigali amendment,the new national standard stipulates that "halogenated hydrocarbons and their mixtures should not be directly evaporated in the cold room for refrigeration in large and medium-sized cold storage and large and medium-sized refrigeration systems".In practical engineering practice,ammonia carbon dioxide cascade refrigeration system has been more and more widely used,and the development situation is very good.However,ammonia has certain risks,and carbon dioxide is not a toxic gas.However,when the concentration of carbon dioxide in the air in the environment is high to a certain extent,it will also endanger human life,health and safety.Therefore,it is necessary to study the leakage and diffusion characteristics of these two refrigerants in ammonia carbon dioxide cascade cold storage.Firstly,this paper introduces the research status of ammonia carbon dioxide cascade refrigeration system at home and abroad in recent years;Secondly,the theoretical analysis of refrigerant leakage and diffusion is carried out,and the physical and chemical properties of ammonia and carbon dioxide and the calculation method of leakage are summarized;Thirdly,the mathematical model of ammonia and carbon dioxide leakage and diffusion is established.According to the physical model of a refrigeration room of ammonia carbon dioxide cascade cold storage,the grid is divided,and the ammonia leakage and diffusion simulation,carbon dioxide leakage and diffusion simulation and simultaneous leakage and diffusion simulation of ammonia and carbon dioxide in the room are carried out.The concentration distribution of ammonia and carbon dioxide is analyzed;After the leakage and diffusion of ammonia and carbon dioxide,the accident ventilation simulation is carried out under the placement of various accident fans,so as to obtain the concentration distribution of ammonia and carbon dioxide under various conditions;Finally,taking an ammonia carbon dioxide cascade cold storage as the research object,the ammonia gas detector and carbon dioxide gas detector are used to detect the leakage point of the refrigeration room,so as to explore the diffusion distribution of the refrigerant in the refrigeration room after the refrigerant leakage in the refrigeration room under normal conditions.The results show that after the leakage of ammonia from the leakage hole,under the action of pressure difference,the ammonia is pushed to spray far away.After reaching the wall,it collides and diffuses around.With the accumulation of time,the ammonia concentration in the machine room increases continuously,and the ammonia accumulation speed in the upper part is faster;After the leakage of carbon dioxide gas from the leakage hole,it will spray rapidly to a distance,and it is obviously affected by gravity.The diffusion will tend to sink,and a higher concentration will be accumulated at the bottom with the passage of time;If economic factors are not considered,when refrigerant leakage occurs in the machine room,the ventilation effect of opening four accident fans on the top and side walls of the machine room is ideal,and relevant suggestions are put forward;In case of leakage in the machine room under normal conditions,the pressure of carbon dioxide in the machine room is much higher than that of ammonia,so that the concentration of leaked carbon dioxide will be higher than that of ammonia.This paper has certain guiding significance for the safe operation of ammonia and carbon dioxide cascade cold storage refrigeration system.