Variation And Distribution Of Species Concentration In CA Storage During Reduction Process Of Oxygen

Controlled atmosphere storage(CA storage) has been accepted as the most advanced method of fruits and vegetables storage, which modified the gas component concentration mechanically in cold storage, may keep the quality of fruits and vegetables by reducing their physiological metabolism under the condition of elevated CO2, reduced O2 and low temperature.Obtaining variation and distribution characteristics of O2 and CO2 concentration in controlled atmosphere storage can provide theoretical basis for optimal design of the CA storage. 3D physical and mathematical models were established for gas flow, heat and mass transfer inside a real CA storage for apples in Xian. The specific studies were generalized as follows:(1) The variations of apples’ respiration rate and mass fractions of the velocity-inlet boundary were considered by UDF programs in C language to calculate the apples’ respiration rate changing with the O2 and CO2 concentration in the CA room, and change the mass fractions of the velocity-inlet boundary which should be same with the outlet boundary during the dropping period of O2 concentration in this case.(2) The numerical calculation was done using the program to simulate the process of mass transfer during the dropping period of O2 concentration. The calculation results showed the curves of O2 and CO2 concentration varied with time and distribution law of O2 and CO2 concentration in the CA storage. The simulation results about the reduction of O2 concentration period indicated that the concentration of O2 in gas zone decreases with time as exponential fuction, which was validated by experimental results with an average diference of 0.027.(3) This paper simulated the process after the dropping period of O2 concentration. When the concentration of O2 and CO2 in CA storage reaches the specified values, the concentration of O2 in apple zone is lower than the gas zone, while the concentration of CO2 is contrary to O2. The concentrations of O2 and CO2 in gas zone appear to be relatively uniform, while there is a little gradient in apples zone. For a bigger CA room, we should avoid lower O2 concentration and higher CO2 concentration in the centre of CA storage, which may be harmful to fruits and vegetables.(4) The numerical calculation was done by changing the nitrogen purity and quantity of flow to get the reduction time of O2 concentration in different cases. When the volume fraction of N2 is 96%, the time of rapid O2 reduction process is the least.The results can provide theoretical basis to the reasonable selection for nitrogen generator and nitrogen purity.(5) This paper numerical calculated the dropping period of O2 concentration of yellow peaches in the CA storage on the basis of relative study for yellow peaches respiration rate. As the respiration rate of yellow peaches is higher than apples’, the dropping oxygen time of yellow peaches is shortened obviously and CO2 concentration is higher. We should select reasonable nitrogen generator and management for different fruits and vegetables according to their different properties.The three dimensional physical and mathematical models for gas flow, heat and mass transfer inside the CA storage was established in this paper can be used to get the accurate reduction time of O2 concentration, and provide a valuable reference for choosing reasonable nitrogen generator.