Design And System Control Of Mobile Vacuum Pre-Cooling Equipment Based On CFD

Pre-cooling is the first link of the storage of fresh fruits and vegetables.It can not only be used to reduce the energy consumption,but also be used to cool the fruit and vegetables during the subsequent transport.At the same time,the heat from postharvest and breathing can be removed to prolong the preservation period,ensure the quality,safety and taste of fruits and vegetables.Due to the development of pre cooling being inadequate in China,the loss rate of fruits and vegetables circulation is up to nearly 20%.While the pre-cooling has been as the essential part in the cold chain,and the loss is just down to 5%.So that,it is the urgent problem to be solved in our country.Vacuum pre-cooling,air pre-cooling(the pressure pre-cooling,cold storage pre-cooling)and water pre-cooling are the three main ways to pre-cool.Compared to other ways,vacuum pre-cooling has the advantages of pre-cooling fast and evenly.But it has weightlessness rate and is only applied to large surface area and small volume of fruits and vegetables,such as Chinese cabbage,cabbage,mushroom and so on.Water pre-cooling is relatively fast.It is applied to fruits and vegetables with high water resistance,such as litchi,pear,apple etc.During the pre-cooling,most of fruits and vegetables are stacked in the pre-cooling room,while it has the disadvantage of pre-cooling unevenly.Temperature is the key factor in the pre-cooling effect to directly affect the loss rate in the subsequent cold chain.The faster cooling fruits and vegetables down to the proper storage temperature,the lower loss level.Therefore,the pre-cooling equipment can be as far as possible placed in or close the fruit and vegetable production area.However,due to the limitations of space and resources,there is a lot of distance from pre-cooling equipments to production area.And the pre-cooling of the distance is often ignored.In order to overcome the shortcomings of vacuum pre-cooling,it combines with cold water pre-cooling in this paper using the principle of improving the evaporation rate of water in the negative pressure to design the pre-cooling equipment.In view of the above problems of limitation of time,ways and space and pre-cooling unevenly,it proposes the mobile vacuum pre-cooling equipment with cold water,which can save the time and space,combines the advantages of the two pre-cooling ways and using the distance from the refrigerating room or pre-cooling room.In this paper,according to the purpose of pre cooling fruit and vegetables,the following tasks:(1)Designing a mobile fruit and vegetable pre-cooling equipment combines with the advantages of vacuum pre cooling and cold water pre-cooling,based on the medium truck.It changes the traditional stack way of fruit and vegetable,instead of using five chain conveyor mesh belt transmission of fruits and vegetables.The contact with the outside is full,which can increase the heat dissipation area to pre-cool evenly.(2)Using the CFD software to simulate analysis on pre-cooling equipment to go in quest of the best condition of pre-cooling and selecting different conditions of the cold water temperature(1?,3?,5?),cold water velocity(0.5m/s,1.5m/s,2.5m/s)and the cold water pipe switch ways(all layers opened,the odd layers opened,the even numbers layers opened)as three factors and three levels orthogonal experiment method and take the smallest temperature as the study objectives to make simulation experiment.According to the simulation analysis results and data,it can be obtained that when the cold water temperature is at 3?,cooling speed at 0.5m/s,choosing the odd layer open,the temperature difference in pre-cooling room is smallest.(3)Designing the control system of fruits and vegetables pre-cooling equipment,the distribution of temperature sensor,photoelectric sensor,pressure sensor and the humidity sensor.According to the signal collection of the pre-cooling system and the judgment of pre-cooling state,stopping and starting of vacuum pump,the cooling chamber chain wheel and cold water spray can be achieved automatically.The man-machine interactive function is realized by touch screen and the pre cooling state of the detection system is implemented.