Design Of Mobile Differential Pressure Frecooling And Variable Temperature Storage Device And Study On Precooling Effect

China is a big country of fruit and vegetable production and consumption.The output of fruits and vegetables ranks first in the world,more than half of the world's total output.With the continuous development of China's economic level,people's requirements for material living standards are rapidly improving,especially the demand for fresh fruits and vegetables is also rapidly increasing.The huge output and demand determine the huge demand for cold chain logistics and cold chain-related equipment of agricultural products circulation.Precooling is the first step of cold chain logistics of agricultural products,an important link to solve the"first kilometer"of cold chain logistics of fruits and vegetables,and an effective measure to reduce the circulation rot rate of perishable fruits and vegetables.Among them,pressure-difference precooling is a kind of precooling method with wide application range and fast precooling speed in fruit and vegetables precooling.This paper designed and developed a mobile differential pressure precooling device which integrated differential pressure precooling and variable temperature storage for fruits and vegetables after picking,and carried out air distribution simulation analysis and experimental research on the effect of precooling and variable temperature storage.The research contents are as follows.(1)Design and develop a mobile differential pressure pre-cooling and variable temperature storage device,which is actually applied to pre-cooling in fruit and vegetable producing areas.The outer size of the box body is 2959mm×2418mm×2018mm,and the inner size is 2290mm×2154mm×1864mm.The device takes the thickness of 75mm polyurethane insulation board as the enclosure structure of the pressure differential precooling device.The outer surface is made of color steel plate,and the inner surface is made of stainless steel.The device is designed as a mobile pressure-difference precooling device for fruits and vegetables,which is mainly composed of pressure-difference precooling device,constant temperature refrigeration for fresh-keeping and variable temperature storage.According to the design structure and function,the precooling capacity,pressure difference precooling load calculation and refrigeration system design of the device were carried out.The maximum single precooling capacity of the calculated device was 318.5kg.(2)According to the structure of the designed device storehouse,the compressor,condenser,evaporator,throttling device of the refrigeration system and other auxiliary refrigeration equipment such as pressure difference fan inside the storehouse,condensing fan outside the storehouse,high pressure liquid reservoir,drying filter,gas-liquid separator are selected.The compressor of the device selects frequency conversion compressor,which can accurately control the temperature according to the change of load in the warehouse.The refrigerant is environmental friendly refrigerant R410A,with the maximum cooling capacity of 13.76kW.The circulating air volume in the warehouse is 8000m~3/h,and the total pressure of the differential pressure fan in the warehouse is 400Pa.(3)The ICEM-CFD pre-processing software was used to divide the space in the device warehouse into three-dimensional structured grids.The precooling area was regarded as a porous medium.Fluent software was used for numerical calculation to simulate the air distribution of the air circulation in the warehouse,and the wind speed uniformity around the precooling area and the middle return air channel was analyzed with focus.It is found that the wind speed in the precooling area and the return air channel decreases with the increase of the distance from the return air outlet.When the wind speed in the return air passage is at the return air outlet,the maximum wind speed is 10.1m/s,and when the distance from the return air outlet is 0.7m,the minimum wind speed is 1.2m/s.In the precooling area,the velocity cloud map of the device in the height direction of Y=50mm,Y=450mm,Y=950mm and Y=1350mm was taken,and the average precooling wind speed was 1.24m/s,the highest wind speed was 2.1m/s,and the lowest wind speed was 0.55m/s.(4)Taking Yantai large cherry as the research object,the device was used to carry out differential pressure precooling experiment on 151.5 kg cherry,and to conduct experimental research on the effect of variable temperature storage after precooling,and to analyze the change rule of cherry rot rate,sugar content,hardness and other parameters under variable temperature storage mode.The experimental results showed that the cherry center temperature decreased from 25.9?to 3?after 37min precooling.In the variable temperature storage mode,the cherries can achieve a loss-free storage period of about 20?23 days,during which the sugar content and hardness change little,so the original flavor of cherries can be better maintained.The change rate of sugar content and hardness within 35 days is not more than 19%and 18%,and the loss rate can be guaranteed within 37 days is not more than 16%.