Development Of Multivariate Modified Atmosphere Packaging Machine Of Gas Automatic Mixed

Modified Atmosphere Packaging(MAP)is a packaging technology that forms an ideal gas environment in food packaging,which inhibits the growth and reproduction of bacteria and molds that cause food corruption,reduces the respiratory intensity of fruits and vegetables,delays the aging of fruits and vegetables,and thus extends the shelf life of food.The MAP machine is an important equipment to realize this technology.The quality of the modified atmosphere packaging machine affects the effect of food preservation.In this paper,the research status of the MAP machine were summarized,the process route of MAP machine was analyzed,the overall design scheme of the multivariate MAP machine of gas automatic mixed machine was proposed,the working principle and motion law of each actuator were designed,mainly including heat sealing cutting mechanism,film pulling mechanism and gas displacement system.The heat seal cutting mechanism mainly completed the selection of temperature controller and the logic design of cylinder limit;The film pulling mechanism had completed the film pulling path design and shaft selection;The method of gas replacement was determined as pumping and charging simultaneously.The gas replacement device was the core device that ensured the gas replacement rate.The existing MAP machines usually have the problem of low gas replacement rate,mainly due to design defects in the configuration.However,currently there is a lack of theoretical and effective technical methods for the design of gas displacement devices,relying heavily on the experience of designers.In this paper,the computer fluid dynamics technology was used to design the gas displacement device with FLUENT and other computer fluid mechanics software;An analytical model was designed for the gas replacement device,flow field analysis and numerical simulation of the gas replacement process was conducted;The effects of different inlet angles and the placement of fruit and vegetable models on gas displacement were researched;The simulation results showed that the flow field stability was high when the inlet angle was 45°,and the 99%gas displacement rate could be achieved at 1.0 s,which was the optimal configuration.The simulation results of fruits and vegetables model showed that the placement of fruits and vegetables had a significant impact on the gas flow field,reaching the target concentration at 1.2 s,which could meet the requirements of gas displacement.A gas displacement device was designed based on flow field simulation results and gas displacement rate.The gas mixing system of the MAP machine affects the gas proportioning accuracy and determines whether the whole machine can reach the target gas atmosphere rate.In this paper,different mixing systems were studied,including pressure mixing system,volume mixing system,time mixing system,throttling mixing system and mass flow mixing system.The working principle,structure and characteristics of the above five air mixing modes were summarized.The Comprehensive evaluation assessment of fuzzy mathematics was adopted to select mass flow mixing system as designed equipment gas mixing method,and the mass flow controller(MFC)as the core was adopted.The principle and classification of MFC was expounded,the control principle of thermal MFC was researched.A basic calculation model between gas mass flow and electric power was obtained through King’s law,and the simplified calculation model between gas mass flow and voltage value under the temperature compensation circuit was found.A gas mixing system based on MFC was built,including MFC,gas mixing tank and each group of solenoid valves,and the mixing accuracy of the system was measured.The results revealed that the average relative deviation of CO2 and O2 was 1%and 0.62%respectively,which met the overall design requirements.The control system of the modified atmosphere packaging machine was designed.The whole machine was controlled by PLC.The control principle and logic of each mechanism were analyzed.The PLC hardware control system and its control program was designed.In order to verify the rationality of the design of the modified atmosphere packaging machine,a three-dimensional model of the whole machine was designed,and a prototype machine was made for test.The accuracy of gas regulation,gas replacement rate and the performance and production capacity of the packaging machine were taken as experimental indexes.The prototype test results indicated that theoretical replacement time of the prototype was 1.3 s.The average relative deviation of CO2 and O2 adjustment accuracy was 1.17%and 1.40%,respectively.The entire machine operated smoothly,with coordinated movement of all actuators,without air leakage and jamming,which meant that the designed equipment met the overall design requirements of the complete machine.