Numerical Simulation Of Environment In Container Type Fruit And Vegetable Air-conditioned Box

Controlled atmosphere preservation technology makes fruits and vegetables to achieve the effect of controlled atmosphere preservation by changing the ratio of gas components(mainly CO₂and O₂)in the storage environment,in which the establishment and use of controlled atmosphere storage is the initial use of controlled atmosphere preservation technology.With the renewal and progress of technology,box controlled atmosphere preservation has been developed on the basis of air conditioning storage.compared with air conditioning storage,the biggest advantage of air conditioning box lies in"mobility",flexible and simple operation and management,and can realize long distance,cross-regional and off-season sales of fruits and vegetables.In this paper,the liquid seal decompression apple atmosphere regulation is taken as the research object,and its three-dimensional unstable numerical simulation model is simplified and established.The changes and distribution characteristics of gas components in the environment during apple storage,the variation of respiration rate and the replacement scheme after gas component concentration overshoot are studied by using CFD simulation software.The research contents and results are mainly divided into the following parts:(1)According to the design size of the liquid seal decompression air conditioning box,the fruit and vegetable storage chamber is simplified as a closed rectangular cavity,the physical model is established,the gas area and the cargo area are reasonably analyzed and assumed,the non-steady mass transfer control equation is established,the main control parameters of the porous media in the apple cargo area are determined,and the UDF program is compiled by using the respiratory action rate formula and the respiratory heat formula.The results showed that the respiration of apple cargo area changed with the concentration of CO₂and O₂.(2)The changes and distribution characteristics of CO₂and O₂gas components during 6 days of apple storage were simulated.It was found that the concentrations of CO₂and O₂in the box basically met the requirements of controlled atmosphere environment after 6 days of storage.The"inhomogeneity coefficient"was introduced to quantitatively evaluate the concentration distribution of gas components.At t=12h,the respiration of apple began to stabilize,and the distribution of CO₂and O₂began to be homogenized.At the end of storage time(t=96h),the heterogeneous coefficient of gas components was close to 0,which could be seen to be basically uniform distribution.By comparing the simulation analysis data with the calculation results of the empirical formula,it is found that the maximum error is 3.98%and the average error is 2.66%.The error range is small,which indicates that the simulation results can be used to guide the management of daily air conditioning control of air conditioning box.(3)Under the condition of the same storage temperature and humidity,the distribution of gas component concentration in ordinary freezer was studied,and the curves of CO₂and O₂concentration were fitted.It was found that the respiratory effect of ordinary freezer was greater than that of air conditioning box2.The inhomogeneity coefficient of gas composition distribution was calculated.It was found that the inhomogeneity coefficient of cargo area and gas showed a decreasing trend during storage.On the 4th day,the inhomogeneity coefficients of cargo area and gas area were 3.28E-05 and 1.38E-05,respectively.Based on the empirical formula of respiratory action rate,the average respiratory rate of 4-day storage period was calculated to be 4.02×10mol/(kg·h).The results showed that the average change rate was 61.08%,which indicated that the respiration effect of general cooling tank was 61.08%more than that of air-conditioning box during this period of storage.(4)The replacement scheme of gas component overshoot in gas conditioning box was studied,and the gas exchange speed was selected as v=1.5m/s,1.8m/s,2.0m/s and 3.0m/s to study the replacement speed.Compared with the change of gas component concentration of each replacement velocity,the optimum replacement speed was determined.After the replacement velocity is determined,the optimum replacement time is 35min by analyzing the concentration change of CO₂and O₂gas components in the box.The distribution uniformity of gas components in the box after replacement was studied.The non-uniformity coefficient of cargo area and gas area is calculated,and it is found that the distribution uniformity is good.Introduction of respiratory gas emission efficiency This concept quantitatively evaluates the replacement effect.It is found that the highest exhaust efficiency of respiratory gas is 10 at 35min,which further indicates that the time node is the best ventilation time.