Study On Environmental Information Perception And Mutual Feedback Regulation Mechanism Of Fresh-keeping Transport Of Fruits And Vegetables

Preservation and transportation of fruits and vegetables is an indispensable part of the cold chain logistics system of agricultural products.At home and abroad,the mainly existing preservation and transportation equipment is nitrogen-regulating refrigerated transport,which is generally characterized by high cost and extensive regulation.The introduction of liquid nitrogen filling and air conditioning system,as well as the development of the research on the mechanisms of environmental information perception in the preservation and transportation of fruits and vegetables and mutual feedback regulation not only have scientific and theoretical significance,but also are worthy of application and promotion.Focusing on regulatory and influencing factors in fruit and vegetable preservation,and mechanisms of information perception of environmental parameters and mutual feedback regulation,this study investigated control parameter optimization,sensor packaging,data fusion,fault diagnosis,remote monitoring,prototype development and experiments of air conditioning,ventilation and humidification device,details are as follows:(1)Analysis of regulatory and influencing factors in fruit and vegetable preservationCombined with the physical properties of liquid nitrogen,a liquid nitrogen vaporization device was designed and a vaporization model was established to analyze the correlation factors for the vaporization effect of liquid nitrogen.In addition,a liquid nitrogen filling and air conditioning test platform was constructed for liquid nitrogen filling test,which demonstrated that fin spacing had a significant influence on temperature and oxygen volume fraction,with larger fin spacing positively correlated with lower oxygen reduction rate and cooling rate and more homogeneous temperature and humidity fields.Moreover,fin spacing had no obvious effect on relative humidity which presented an overall trend of first decreasing and then increasing.Further,ventilation velocity significantly affected oxygen volume fraction and temperature;to be more specific,higher ventilation velocity was positively correlated with lower oxygen reduction rate and higher cooling rate,and relative humidity and temperature were corresponding to each other with good homogeneity in temperature field while poor homogeneity in humidity field.However,no significant effects of environmental temperature were found on oxygen volume fraction,temperature or relative humidity;and lower environmental temperature was positively related to poorer homogeneity of temperature and humidity fields.By changing the length,width and height of the air duct,an orthogonal test for the homogeneity in the distribution of fresh-keeping environment when refrigeration and humidification was designed.Results showed that when the dimension parameters of the air duct(length × width × height)were designed as 1,500 mm × 500 mm × 60 mm,the combination evaluation for the homogeneity of temperature and humidity fields in carriages revealed the highest score.By changing the ventilation velocity in the air duct,outlet area and position,a numerical simulation was carried out to investigate the change rules of air and cargo temperature in containers.Results presented that increasing the ventilation velocity in the air duct and enlarging outlet area could promote air cooling in containers and enhance the homogeneity of the temperature distribution on the surface of cargo.An ultrasonic humidification efficiency test platform was designed to analyze the working characteristics of humidification oscillators.Results revealed that larger height from humidification oscillators to the water level in a tank is correlated with the trend of first increasing and then decreasing of humidification efficiency.Additionally,the larger number of humidification oscillators was positively related to lower humidification efficiency of single humidification oscillator.Moreover,larger spacing between humidification oscillators could increase overall humidification efficiency,but the increasing trend was gradually reduced.Further,humidification oscillators distributed in a “line” were superior to in a “square”.Increasing tank temperature had a significantly promoting effect on humidification efficiency.(2)Research on mechanisms of preservation environmental information perception and mutual feedback regulationThe mechanisms of preservation environmental information perception of fruits and vegetables were investigated,which demonstrated that single-point sensor package had a significant impact on the data monitoring of temperature and relative humidity in containers,while had no obvious effect on the data monitoring of oxygen volume fraction.Through monitoring data fusion by applying a wireless network,dynamically updating the data fusion values of environmental parameters,constructing a self-learning information perception-prediction model based on stored data,and dynamically adjusting sleep time of wireless sensor,multi-point sensor effectively increased the regulation accuracy of environmental parameters of fruit and vegetable preservation,and reduced energy consumption in the system.A fault self-diagnosis system for the regulation of fruit and vegetable fresh-keeping environment based on current feedback factors was designed;a knowledge base of expert system for electrical equipment parameters was generated according to experimental data;an equipment fault self-diagnosis strategy was proposed;intelligent decision-making for system faults was realized;and relevant experiments were carried out.Mean response time of fault identification was 1.84s;the rate of fault identification exceeded 96%;and mean correction time of fault recovery was 1.92 s.A remote mutual feedback system for fruit and vegetable preservation environment based on a mobile network platform was designed;the real-time communication for the equipment and remote handheld terminal of preservation and transportation was achieved;and the remote monitoring and early warning of preservation environmental parameters,equipment working status and faults was finished.(3)Design and realization of an intelligent control system for fruit and vegetable preservationA centralized control system for air-conditioning and fresh-keeping environment of fruits and vegetables was designed;data acquisition,wave filtering,calculation,controlling,feedback,man-machine conversation and real-time monitoring were achieved by using the automatic control method with double limit values and a priority of temperature.A distributed control system for air-conditioning and fresh-keeping transport vehicle of fruits and vegetables based on CAN bus was designed;a parallel task design scheme for the control system of fresh-keeping environment was put forward;a test platform composed of 1 main controller node and 4 communication nodes was constructed;and a communication test of the CAN bus was carried out.Results demonstrated that data packet loss rate was lower than 0.004%,error rate was 0%,system operation was stable,and reliability was high.(4)Development and test of air-conditioning and fresh-keeping containerA air-conditioning and fresh-keeping container was designed and trial-produced,with a nitrogen filing and oxygen reduction rate of 0.31%/min,a cooling rate of 1.0?/min,a humidification rate of 3.0%/min,and a duration of comprehensive regulation from fresh-keeping environment to target environment of 260 min.By using the distributed control system based on CAN bus,integrated fault diagnosis and remote monitoring,which were cooperated with friendly human-computer interaction interface,parameters of preservation environment and equipment working status in containers were real-time collected,equipment working was comprehensively regulated,intelligent control and real-time feedback of fruit and vegetable preservation were realized,and the quality of stored and transported fruits and vegetables was guaranteed.