| With the continuous increase of apple production in China,the task of storage and preservation of fruits and vegetables after harvest is aggravated.The evaporator is one of the most important components in the cold storage system,and its operating performance determines the distribution of environmental temperature,relative humidity,and wind speed during the storage of fruits and vegetables,then affect the fruit and vegetable preservation effect and the energy consumption of cold storage operation.The use of top-row tubes in cooling equipment inside the warehouse has the advantages of low energy consumption and low consumption of fruits and vegetables.Therefore,it is of great practical and economic significance to study the heat transfer characteristics and the factors which could affect the cooling effects of the cold storage.Taking the cold storage as the research object,a three-dimensional steady-state heat transfer numerical model for the cold storage environment under natural convection conditions is established based on a discrete coordinate radiation model(DO model).The influence of the double-finned tubes emissivity,the tubes bundle spacing,the fin height and the different arrangement orientation of the three-finned tubes to the heat transfer efficiency of the tubes and the distribution of air temperature and velocity of the cold storage were studied,The main research contents are as follows:(1)Established a mathematical model for the heat transfer and flow in an empty space of double-finned tubes,and the air distribution characteristics in the cold storage under the combined effects of natural convection and radiation heat transfer were studied,which proved a reference for reasonable stack height and distance to the wall.(2)The mathematical and physical models of the cold storage of double-finned rows of pipes in a full state of goods were established.The influence of the outersurface emissivity of the pipes,the spacing of the bundles to the heat transfer performance of the pipe row,the distribution of airflow in the cold storage,and the product were studied.The results shows that the greater the surfaces emissivity of tubes,the better the heat transfer effect of the cooling tubes.The heat exchange capacity and radiation heat transfer per unit area of the tubes reached the maximum for the cold storage when the emissivity of the double-finned tubes is 0.9 and the tube bundle spacing is 180 mm.What’s more,the lower the ambient temperature in the cold storage,the better cooling effects of fruits and vegetables in the stack area is better.(3)On the premise of the above research results,studied the cooling effect and heat transfer performance of the double-finned tubes with different fin heights.The results shows that the height of the pipe is not as high as possible.The pipe has the highest heat transfer intensity per unit when the height of the fins is 30 mm for the cold storage studied in this paper,the utilization ratio of the pipe area is also the highest,which improves its economic efficiency.(4)The ambient temperature and velocity distribution in the storage with two different layout forms were studied when the cooling unite are three-finned tubes,the arrangement of tube bundles was analyzed on the effects of radiation heat exchange between three-finned tubes and surrounding solid medium,the natural convection intensity between hot and cold air,and the air distribution within the cold storage.The results show that the highest temperature of the three-finned tubes is 274.7 K when it is arranged in the forward direction,which is 0.4 K lower than that in the reversed arrangement.At the same time,through comparative analysis,the heat transfer efficiency of the double-finned tubes in this paper is greater than the three-finned tubes,and the temperature in the cargo area is much lower than the three-finned tube. |
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