Study On Mixing And Detecting Of Gas Proportion In MAP System

With the steady development and perfection of Modified atmosphere packaging (MAP) technique, excellent functions and features of fresh-keeping were reflected clearly. MAP technique can adjust various gas proportions to adapt requirements of all kinds of products packaging, prolong preservation period and shief life of food, and truly keep its primary color, original smell, and superiority of the food nutritional labeling to process food. Therefore, it is most important for the food modified atmosphere package to ensure that the gas component in the original package is high accuracy. Based on the existing equipment of modified atmosphere packaging, MAP system was researched and designed, which is important practical significance to solve our problem of modified atmosphere packaging of food.Firstly, proportional gas mixer and gas on-line analyzer were analysised and designed. The mixing principle of gas mixer was analysised. Structure of of diaphragm Gas proportional regulator valve was designed. Mathematical model of regulator valve's gas flow and pressure was built using fluid mechanics. The simulation analysis of flowrate-pressure drop characteristic curve was done using MATLAB. Structure of the mixing chamber was designed in order to control gases flow ratio by changing the inlet valve body diameter. The principle of O2 Sensor and CO2 Sensor of CMV-2 are analyzed, which provide a theoretical basis to ensure the quality of MAP in proportional gas on-line detection system. That CMV-2 and DQB-700N vacuum packaging machine matched gas circuit system and cycling of valve control mechanism were designed.Secondly, with regard to the backward state of technology and applications of MAP in our country, an intelligent MAP system based on the reliable measurement and control of the gas concentration in the packaging was proposed which includes Mix9001 ME gas mixer, CMV-2 gas analyzer, DQB-700N vacuum packaging machine and PLC controller in order to achieve gases blending proportion in container and gas-filled package. In this system, gas analyzer was used for detecting gas proportion and PLC was used for controlling gas mixer and vacuum packaging device. This proposed system not only obviates the traditional vacuum chamber and reduced packaging costs, but also reduces gas consumption and raises working efficiency with gases blending proportion and gas-filled package automatically.Finally, the MAP system was used to research rice fresh-keeping by modified atmosphere, to examine control precision of several gases blending proportion for safer use and the effect of modified atmosphere packaging. The experiment results indicate that the system accuracy of gases blending proportion is 1.28 %, the gas replacement rate is 97.701%. Considering the rice water, fatty acids, reducing sugars, viscosity and gas costs and other factors, the choice of gas mixture which gas volume ratio of CO2 and N2 is 6:4 can achieve the purpose of delaying the aging of rice. And its fresh-keeping effect is twice as much air packaging for the 120 days in storage.