| During the operation of the refrigeration system,the precondition of determining the comprehensive heat transfer performance of the evaporator is the gas-liquid two-phase refrigerant is distributed in the equal dry and flow by diverter after throttling.Shunt are usually designed according to the standard conditions,when the system deviate from the design conditions,The difference of pressure drop in the cooling fan coil is increased,It is easy to cause the uniform shunt capacity of the shunt to be greatly reduced or even lost,resulting in uneven fluid flow in the evaporator.Firstly,this paper optimizes the allocation mechanism of a new type of shunt,and put forward the new shunt performance testing methods,analysis the feasibility of the new shunt,and in the current situation for energy conservation,reducing the enterprise cost cause far-reaching significance.Secondly,the critical flow theory is introduced,the mathematical model of two-phase critical flow is established,and the size of the critical nozzle is selected and calculated based on the critical flow theory,and a new type of shunt is designed.Thirdly,the CFD simulation of the splitter with the premixed segment and the nozzle is carried out to draw the following conclusions:When the volume rate of liquid was adjusted to 70%,by the mixture of the swirl vane and the rectifying action of the rectifier,when reaching the nozzle,the air and liquid mixture was basically even.The flow pattern of each nozzle inlet of the shunt is basically the same,which achieves the function of flow setting and basically realizes the distribution in the equal dry and flow of diverter.Fourthly,five shunts of Venturi shunt,Germany CAL shunt,Gas-liquid separating shunt,shunt with nozzle and shunt with premixed and nozzle will be connected to cooling fan test system,in this paper,The data were collected and processed at 0℃,-4℃,-8℃,-12℃,-16℃,-20℃,and-18℃under seven working conditions,seven kinds of working conditions at the data is collected and processed to get the inhomogeneity of the five shunts,The overheat is equally divided,correspondence the cooling capacity of the cooling fan,the heat transfer coefficient,the pressure drop of the shunt,the pressure drop of the cooling fan,and the total pressure drop,and draw a graph for comparison,the main conclusions drawn from experimental study and data analysis are as follows:(1)the experimental results show that,with the decrease of the library temperature,the inhomogeneity of the shunt is also reduced,and the closer to the nozzle design conditions,When close to set conditions(evaporation temperature 25℃,the temperature in the library-18℃or so),the distribution of the nozzle effect is best,non-homogeneous is only 0.78%,It is indicated that the diverter with premixed segment and nozzle has small difference with superheat of each other,and basically has reached the homogeneous donor of each branch.In the same working condition,the inhomogeneity of the shunt with the premixed and nozzle is the lowest,followed by the shunt with nozzle,the gas-liquid separating shunt,the CAL shunt,the venturi shunt.(2)with the loss of the library temperature,degree of superheat presents the downward trend,within the scope of the working condition of the whole,The minimum superheat is the shunt with premixed section and the nozzle,So its refrigerating capacity is also the largest,Its refrigeration capacity is 10.9%higher than that of the gas liquid separation distributor at 0℃.Under the same working condition,shunt with nozzle,the vapor-liquid separation shunt,the CAL type shunt and the Venturi type shunt corresponding to the superheat of the evaporator is the next,When the working condition is low,At-8℃below,shunts of CAL,the vapor-liquid separator and the critical nozzle type are corresponding with the average superheat of evaporators are near lower than 3℃,It shows that the air cooler has sufficient liquid supply and the evaporator area has been fully utilized.(3)When the temperature is 0℃,the shunt with premixed and nozzle has a biggest refrigerating capacity in 8.65kW.The second is the nozzle type shunt,and it’s refrigerating capacity is 8.65kW.The shunt with premixed section and critical nozzle than single nozzle type shunt,gas liquid separate shunt,Germany CAL shunt,Venturi shunt at the refrigerating capacity of the corresponding air cooler were increased by 3.0%,10.9%,20.1%and 25.4%in the temperature of 0℃respectively.The refrigerating capacity of the shunt with premixed section and critical nozzle is 6.0kW,and the shunt with premixed section and critical nozzle than single nozzle type shunt,gas liquid separate shunt,Germany CAL shunt,Venturi shunt at the refrigerating capacity of the corresponding evaporator were increased by 3.2%,9.2%,16.3%and 22.7%in the temperature of-18℃.Under the same experimental condition,the cooling capacity of the premixed segment and nozzle type diverter is the most.(4)With the decrease of cold storage temperature,the heat transfer coefficient of the cooling fan decreases.From 0℃to-20℃,corresponding With premixed section and critical nozzle,nozzle type,gas liquid separate,Germany CAL,and Venturi type of five shunt which the heat transfer coefficient is from 39.0 W/(m~2·K),37.8 W/(m2·K),36.2W/(m~2·K),33.2 W/(m~2·K),31.9 W/(m~2·K),to 30.2 W/(m~2·K),29.6 W/(m~2·K),29.1W/(m~2·K),27.7 W/(m~2·K),27.6 W/(m~2·K)respectively.The heat transfer coefficient were decrease by 29.1%,21.8%,19.7%,16.5%and 13.5%respectively.The percentage of premixed segment and nozzle drop is the largest.In the same working condition,the heat transfer coefficient corresponding to the premixed segment and nozzle type diverter is the largest.,and when the temperature is 0℃,respectively than the nozzle type,gas liquid separate,CAL,Venturi type shunt of the heat transfer coefficient were increased by 3.2%,7.7%,17.5%and 22.3%.The heat transfer coefficient is 31.8 W/(m~2·K)in cold storage temperature.The diverter designed in this paper improves the evaporation pressure of the cooling fan,the cooling capacity and the coefficient of heat transfer are of great significance to optimizing the overall performance of the refrigeration system.The experimental results show that the shunt can reduce the heat transfer temperature to a certain extent,reduce the irreversible loss of the cold fan,and have a very good heat transfer performance to the cold fan.The great improvement is of far-reaching significance for energy saving and reducing the operation cost of the enterprise under the current situation. |
