Research On Performance Optimization Of Indirect Cooling Refrigeration System

Due to a series of problems existing in refrigerant,many cold warehouses have been replaced by indirect cooling refrigeration systems which rely on refrigerant carrier for cooling capacity transfer.The heat transfer efficiency of indirect cooling refrigeration system is often lower than that of direct expansion refrigeration system because of the larger temperature difference.Aiming at this problem,this paper focuses on the performance optimization of indirect cooling refrigeration system.In the experiment,four new types of mixed secondary refrigerant(ZhongFu1,ZhongFu3,LengKuZhuanYong and ShouGuang)were used,and the main performances of these four secondary refrigerants were compared and analyzed,and the influence of different types of secondary refrigerants on the refrigerating capacity of indirect cooling refrigeration system was tested.In the early stage of the work is completed,the shell and tube heat exchanger for indirect cooling system and air cooler both heat exchange equipment has established the mathematical model,has carried on the simulation using the MATLAB software,through the shell and tube heat exchanger and cooling fan of simulation has been done and indirect cooling system heat transfer coefficient and heat transfer temperature difference between the total performance trend along with the change of working condition.On the basis of the experiment also test the performance parameters of indirect cooling refrigeration system with the warehouse temperature,the change of the secondary refrigerant flow,cooling fan frequency,under the condition that the frequency of the cooling fan is constant at 30 Hz,the flow rate of refrigerant carrier changes,the flow rate of refrigerant carrier is constant at 2950L/h,and the frequency of the cooling fan changes,The cooling time required to reduce the storage temperature from 15℃ to-20℃ by three kinds of secondary refrigerant were selected for the test refrigeration system.Meanwhile,the influence of different frequency of the cooling fan and the flow rate of the secondary refrigerant on the refrigeration efficiency of the indirect cooling refrigeration system was compared.The influence of the frequency of each cooler,the flow rate of each secondary refrigerant and the temperature of each warehouse on the total heat transfer temperature difference,refrigerating capacity,energy consumption and COP of the indirect cooling system was compared at the frequency of the cooling fan(20Hz,30 Hz,40Hz,50Hz),the flow rate of secondary refrigerant(1000L/h,1500L/h,2000L/h,2950L/h),and the temperature of the warehouse(-5℃,-8℃,-11℃,-14℃,-17℃,-20℃).The experimental measurement results and MATLAB simulation results are compared and analyzed based on the total heat transfer temperature difference of the system.The main results are as follows:(1)Through the performance test of four new types of mixed secondary refrigerant of ZhongFu1,ZhongFu3,LengKuZhuanYong and ShouGuangmodel,it is found that ZhongFu3 has the best comprehensive performance,with the lowest freezing point and viscosity.At-30 ℃,the kinemastic viscosity is only 9.756 mm/s,and the weight is612 g.Moreover,under the same working conditions,the cooling time of ZhongFu3 secondary refrigerant connected to the cooling system was the shortest,only 3.7 hours.(2)Through to simulate the evaporator and the cooler,The heat transfer coefficient of the evaporator and cooler will increase with the increase of the temperature of the cold storage room,the increase of the flow of secondary refrigerant and the increase of the frequency of the cooling fan,The heat transfer temperature difference of evaporator and cooler will decrease with the increase of the flow of refrigerant,the decrease of the frequency of the cooling fan and the decrease of the temperature in the warehouse.Moreover,the total heat transfer temperature difference of the system reaches the minimum when the frequency of the cooling fan is 50 Hz,the secondary refrigerant flow rate is 2950L/h.(3)When the cold storage temperature increases,the cooling capacity,total power consumption and COP of the indirect cooling refrigeration system will all increase to different degrees.The storage temperature has more influence on the refrigerating capacity of the system than the secondary refrigerant flux.At the reservoir temperature of-20℃,the maximum refrigerant carrier flow of 2950L/h,the cooling capacity is only 2.47 kW,but at the minimum secondary refrigerant flow of 1000L/h at the reservoir temperature of-5℃,the cooling capacity is still 4.32 kW,the difference between the two is 1.85 kW.In addition,the COP of indirect cooling system can be improved more effectively by increasing the flow rate of secondary refrigerant at high cold storage temperature.(4)The experiment found that when the secondary refrigerant flow increased,the cooling capacity,total power consumption and COP of the indirect cooling refrigeration system all increased accordingly,and the time spent when the cold storage decreased to the same temperature became shorter.When the flow of secondary refrigerant is maximum,the cooling time of the system can be effectively reduced by 3.7 hours.However,as the secondary refrigerant flow continued to increase,the increase amplitude of refrigerant capacity,total power consumption and COP began to decrease,and the increase a mplitude of refrigerant capacity decreased by 0.9% respectively at the secondary refrigerant flow rate of 2950L/h compared with that at the secondary refrigerant flow rate of 2000L/h.(5)When the frequency of the cooling fan increases from 20 Hz to 50 Hz,the cooling capacity,total power consumption and COP of the indirect cooling system will increase and then decrease,increase,increase and then decrease,respectively.The cooling capacity and COP of the system will reach the maximum value at 30 Hz and the minimum value at 50 Hz.And the maximum cooling capacity and COP difference between the two frequencies is 2.81 kw,0.24.(6)As the temperature in the warehouse rises,the refrigerating capacity of ZhongFu3,ZhongFu1 and LengKuZhuanYong secondary refrigerant is increasing.And at a certain temperature in the warehouse,the cooling capacity of the three secondary refrigerant has a trend of rising with the increase of the cooling capacity of the refrigerant flow,of which the cooling capacity of LengKuZhuanYong secondary refrigerant is the smallest,ZhongFu3 cooling capacity is the largest,thedifference in cooling capacity is 0.96 kW.(7)The temperature difference between the indirect cooling system measured by the experiment and the indirect cooling system calculated by the simulation was compared and analyzed,and it was found that the variation trend of the two with the research parameters was exactly the same,and the error was only within 15%,which proved the accuracy of the model.