Air Infiltration Characteristics Of Cold Storage During Door Opening And Closing Process Based On Dynamic Mesh Model

In recent years,with the rapid development of China's cold storage industry,the total amount of cold storage has continued to grow,and therefore the problem of energy consumption in cold storage is highlighted.Cold storage door,as an important part of the cold storage buildings,would cause a large amount of outdoor hot air to enter the cold storage due to the frequent goods putting in and out,thus affecting the storage quality of the stored goods.Therefore,it is particularly important to study the main factors affecting the cold air infiltration of the cold storage door,optimize the cold storage building design,and reduce the overall energy consumption level of the cold storage.This paper takes an apple air-controlled cold storage in Xi'an as the research object,a three-dimensional unsteady numerical calculation model for gas flow and heat transfer in cold storage is established.The dynamic mesh model in Fluent is adopted to realize the opening and closing process of the cold storage door in order to study the intrusion of hot air and the impact on the storage environment of the goods in cold storage.The influence of cold storage door type,the difference of cold storage temperature,the door open time and air curtain device are analyzed on hot air intrusion.The details are as follows:By changing the type of cold storage door,the seepage characteristics of the sliding door and the rolling door were studied.In the 20s opening and closing process,the total seepage volume of the sliding door and the rolling door are 20.47m~3 and 17.12m~3, respectively,accounting for 2.6%and 2.2%of the total cold storage volume,thus the total seepage volume of the rolling door is 16.4%smaller than the sliding door.In both cases,the temperature rise in the cold storage is 0.38?and 0.32?,respectively,which indicates that the influence of the height of the door on the rate of seepage is greater than the width of the door.The rolling door has a better performance on reduce the seepage of the door.By changing ambient temperatures,the influence of temperature difference on the seepage of the cold storage door was studied.As the temperature difference between the inside and outside of the cold storage increases,the difference in thermal pressure between the inside and outside of the cold storage increases at the same height.In the case of temperature difference between 10?,15?and 20?,the door seepage rate is1.03 m~3/s,1.4 m~3/s and 1.68 m~3/s,respectively.The results show that increasing the temperature difference will significantly increase the air infiltration rate of the door.When the temperature difference is doubled,the additional load caused by air infiltration increases by 2.44 times.By extending the open time of the cold storage door,the changes of the temperature field and the air-controlled atmosphere in the cold storage are studied.When the door opening time is extended from 20s to 60s,the average temperature rise of the cold storage reaches 1.5?or more,and the temperature rise in the upper part of the cold storage exceeds 3?,which is far beyond the fluctuation range allowed by the cold storage specification.The concentration of oxygen and carbon dioxide was changed from 3%to 4.78%and 2.71%,respectively.The change of gas concentration will enhance the respiration of fruits and vegetables,which is not conducive to the long-term storage of fruits and vegetables.In order to maintain the atmosphere of the cold storage,the nitrogen generator should be turned on in time.By installing an air curtain device on the original cold storage model,the sealing performance of the air curtain device is studied during the opening and closing of the cold storage door.In the 0-2 s of the door opening time,since the air curtain jet has not yet reached the cold storage ground,its function to isolate the inside environment of the cold storage has not been established,and the air infiltration rate of the door has not changed at this time.Starting from 3s,as the air curtain jet reaches the cold storage ground,the sealing effect of the air curtain is demonstrated,and the air curtain efficiency is gradually increased from 60%to 73%.Compared with the door without air curtain,the air infiltration rate with air curtain is reduced from 1.4 m~3/s to 0.4m~3/s.During the 20s door opening and closing process,the average temperature rise in the cold storage is 0.12?,which is 68.4%lower.