Research On Ultra-Low Temperature Cold Chain Transportation Monitoring System Based On Dry Ice

In recent years,using vans to transport heat insulation box using dry ice as refrigerant has become the main mode of ultra-low temperature cold chain transportation.Due to the lack of the research results that can guide the setting of the best temperature measurement points and CO2 gas concentration measurement points of the ultra-low temperature cold chain transportation monitoring system,the setting of measurement points is unreasonable,which often leads to temperature measurement deviation,and the unmeasured high concentration CO2 gas distribution area poses a great threat to people’s lives.In view of the above problems,in this paper,the combination of simulation and experiment is used to find the best measurement points,and the ultra-low temperature cold chain transportation monitoring system is designed.The main research work of this paper includes the following contents:Firstly,the factors affecting the temperature distribution of dry ice insulation box are analyzed,and the aluminum alloy frame is used to fix the container to reduce the influence of the change of container posture on the temperature measurement results.Based on the above arrangement,the temperature field near the container is divided into two stages: stable and unstable.This paper mainly studies the temperature field in the unstable stage when the container is exposed to the CO2 gas.According to the three-dimensional quasi steady state assumption,the prediction model of temperature field of dry ice insulation box is constructed.According to the simulation results,it is determined that the best temperature measurement point of the dry ice insulation box is on the center of the top surface of the container.Secondly,the factors affecting the CO2 gas concentration distribution in the van environment are analyzed,and the influence of the placement style of dry ice insulation box in the van on the CO2 gas concentration distribution is compared and verified,and the uniform and single-layer placement style is adopted,which can reduce the growth rate of CO2 gas concentration at the height of a man.Build the prediction model of CO2 concentration distribution in the van environment.Based on the analysis of existing studies,the CO2 concentration distribution in the closed van when it reaches equilibrium is set as the initial condition for the simulation experiment.The simulation results show that when the car door is opened,the CO2 concentration on the ground around the insulation box decreases the slowest that it is selected as the best measurement point.Then,the hardware and software of the ultra-low temperature cold chain transportation monitoring system are designed.The main control circuit,temperature measurement circuit,CO2 gas concentration measurement circuit and power management circuit are designed with Easy EDA.The hardware is designed with functions of high-precision temperature measurement,stable power monitoring and CO2 gas concentration measurement.The Android application program is designed based on Uni-app to realize the function of reliable data transmission and provide visual interface for users.Spring and Hibernate are used to realize database management,HTTP/HTTPS is used to realize the communication between host computer and database,and provides historical data management.Finally,the above research is verified by experiments.The effectiveness of the simulation of the temperature prediction model is verified in the temperature field distribution experiment of the dry ice insulation box.The results show that the temperature curve of the test point has the same characteristics as the simulation results,and the values are close to each other.By a series of experiments,the rationality of the hardware design is verified.The results show that the layout of the hardware components of the logger is reasonable,and the heat of the heating elements has no effect on the communication chip;The error of temperature measuring circuit is within the allowable range under different temperature measuring conditions;There is no overcharge or over discharge,the constant current in the constant current charging stage is 400 m A,the charging temperature is under 60℃,and the full power consumption of 2000 m Ah lithium battery with deep discharge is 6 hours;The average current of standby mode is 232 u A,the average current of data measurement mode is5.1m A,and the average current of data transfer mode is 43.2m A.The rationality of the system design is verified in the simulation environment experiment.The results show that all indexes of the logger are normal in the process of completing a 1.5h simulated transportation,which proves that it has high practicability.