| Due to energy problems,various industries are promoting energy conservation and emission reduction.China has included "carbon peaking and carbon neutrality" in the 14th Five-Year Plan.In order to achieve "carbon peak,carbon neutral",all industries must save energy and reduce emissions.Cold storage is a vital part of the cold chain.Cold storage is used for cryogenic storage of goods.During the operation of the cold storage,the quality of the goods in the cold storage will be affected by the hot air intruding from the outside.The entry and exit of people and the loading and unloading of goods cause the door to be opened for a long time or frequently,causing the intrusion of hot air.The intrusion of hot air will cause violent heat and mass exchange at the door of the cold storage.The contact of hot and cold air will produce a lot of mist,which affects the safety of people entering and leaving.During the operation of cold storage,the cooling load caused by air infiltration at the door accounts for more than half of the total cooling load.By installing an air curtain at the door of the cold storage,the exchange of hot and cold air can be isolated and the infiltration of air at the door of the cold storage can be reduced.The air curtain is a device composed of fans,air ducts,and air handling equipment.The air curtain can form an invisible curtain.This paper takes the experimental cold storage of No.3 laboratory building of Tianjin University of Commerce as the research object.The air infiltration at the cold storage door and the performance of the air curtain were analyzed using CFD.The designed cold storage temperature is -18℃,the outdoor environment temperature is 25℃,the external dimension model of the cold storage is 7.25m×5.4m×3.1m,and the size of the cold storage door is 2.3m×2.2m.Standard k-epsilon equations and governing equations are utilized for numerical simulations.Analyze structural factors of horizontal circulating air curtains,such as nozzle width,jet velocity,jet angle,etc.The performance of double-layer air curtain and single-layer air curtain is compared and analyzed.The main conclusions of this study are as follows:（1）Due to the effect of thermal pressure at the door of the cold storage,the cold air and the ambient hot air exfiltrate and infiltrate to the outside and the inside of the cold storage,respectively.There is a neutralizing surface with zero residual pressure at the cold storage door.There is no infiltration and exfiltration of air on the neutralizing surface.The experimental data is verified by the numerical simulation model,which proves the accuracy of the numerical simulation results;（2）As the width of the nozzle increases,the air curtain becomes more and more effective in isolating the air.When the nozzle width is 0.05 m,0.10 m,0.15 m and 0.20 m,the efficiency of the air curtain is 39.240%,40.011%,43.052% and 43.103%,respectively;（3）With the increase of the air curtain jet velocity from 8m/s to 12m/s,the performance trend curve of the air curtain first increases and then decreases.The trend curve proves that the air curtain jet velocity is not proportional to the air curtain efficiency.There is an optimal air curtain jet velocity.Different air curtain nozzle widths have different optimal jet velocity,which makes the air curtain insulation effect the best.When the nozzle width is 0.05 m,0.10 m,0.15 m,0.20 m,the optimal jet velocity are 10m/s,10m/s,9m/s,8m/s,and the air curtain performance are 39.240%,40.011%,43.789 %,45.042%;（4）Outward deflection of the air curtain jet can properly improve the performance of the air curtain.The optimal deflection angle of the air curtain changes with the change of the air curtain jet velocity.When the air curtain jet velocity is 9m/s.The best air curtain efficiency is 39.813%.At this time,the corresponding optimal jet angle is 5°.When the air curtain jet velocity is 10m/s.The best air curtain efficiency is 41.198%.At this time,the corresponding optimal jet angle is 10°.When the air curtain jet velocity is 11m/s.The best air curtain efficiency is 41.528%.At this time,the corresponding optimal jet angle is 5°;（5）By changing the jet temperature can effectively reduce the rise of temperature inside the cold storage.When the cold storage door was opened and the air curtain was operated for 30 s.The average temperature rise in the reservoir when the jet temperature was 25℃,10℃,0℃,-10℃,and-18℃ were 12.57℃,11.04℃,9.93℃,8.78℃,and7.79℃,respectively;（6）Compared to single-layer air curtain,double-layer air curtain is more effective in isolating the environment inside and outside the cold storage.The double-layer air curtain has 9.31% and 8.35% less air infiltration than the single-layer spout width of 0.05 m and the single-layer spout width of 0.10 m.The efficiency of the double-layer air curtain is 44.898%. |
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