Ultrasonic Humidification Atomization Characteristics And Humidity Control Of Fruit And Vegetable Fresh-keeping Transportation

China is a big country of fruit and vegetable production and consumption in the world.In recent years,with the rapid growth of people’s demand for high-quality fruits and vegetables,it has brought new opportunities and requirements for the development of cold chain logistics technology in China.Air-controlled fresh-keeping transportation technology is an advanced and efficient technology for fruit and vegetable preservation.The technology can restrain respiration of fruits and vegetables by controlling gas composition,temperature,relative humidity and so on,thus prolonging the transportation cycle of fruit and vegetable fresh-keeping.In view of the problems and shortcomings of ultrasonic humidification in fruit and vegetable storage transportation at present,this paper combines experimental research with numerical simulation.The characteristics of particle size distribution of ultrasonic humidified water mist and the relative humidity distribution in fruit and vegetable storage container were studied.The main research work is as follows:(1)the research on the particle size distribution of ultrasonic humidified water mist is based on the way of keeping fresh fruits and vegetables by ultrasonic humidification.A highspeed camera was used to study the influence of the distance between the diaphragm of different ultrasonic humidifying atomizer head and the liquid level of humidifying tank on the humidifying effect.The experiment platform of ultrasonic humidifying water mist particle size distribution based on laser particle sizer was set up.The influence rule of ultrasonic humidifying water mist volume middle diameter and particle size percentage with different factors was analyzed,and the water level of different humidifying water tank was obtained,and the water level of different humidified water tank was obtained,and the water level of different humidifying water tank was obtained.The influence of the number of ultrasonic humidifying atomizer and the velocity of water mist transportation on the particle size distribution.(2)Experimental study on accuracy and Distribution uniformity of Ultrasonic humidification Control;set up an experimental platform for controlling ultrasonic humidification in fruit and vegetable fresh-keeping transport chamber,and studied the number of different ultrasonic humidifying fogging heads and the number of filter mesh.The influence of wind speed and inlet width on the distribution of relative humidity is studied.The variation coefficient and absolute overshoot are obtained.The results show that the number of filter mesh,the number of ultrasonic humidifying fog head,the number of filter mesh,the number of ultrasonic humidifying atomizer,and so on,vary with different factors.The wind speed and inlet width had no significant effect on the uniformity of relative humidity(sig.> 0.05),but the number of filter mesh had a significant effect on the control accuracy of ultrasonic humidification(sig.< 0.05).The optimum combination of relative humidity uniformity in fruit and vegetable fresh-keeping transport chamber is the number of filter mesh 500,the number of ultrasonic humidifying and atomizing head is 8,the wind speed of return air duct 8 m / s,the width of air inlet 80 mm.The optimum combination with high precision of ultrasonic humidification control for fruit and vegetable fresh-keeping transport chamber is the number of filter mesh 500,the number of ultrasonic humidifying and atomizing head is 12,the wind speed of return air duct 12m/s and the width of air inlet 80 mm.(3)the physical model of ultrasonic humidifying device based on the carriage of freshkeeping fruits and vegetables was set up by optimizing the body and ultrasonic humidification device of fruit and vegetable fresh-keeping transport compartment.The distribution of water fog and relative humidity on the surface of fruits and vegetables during ultrasonic humidification were studied.ICEM CFD was used to divide the grid,based on Fluent software and combined with porous media model,the distribution of water mist and the distribution of relative humidity on the surface of fruits and vegetables were studied.At the same time,the physical and respiratory characteristics of the test material and the heat transfer characteristics on the wall of the chamber were added.The SIMPLE algorithm was used to study the outlet angle and height of the ultrasonic humidified water mist.The influence of relative humidity monitoring sensor position and stacking layer number of fruits and vegetables on the distribution of relative humidity on the surface of the cargo was studied.The optimum parameters of the transportation chamber and ultrasonic humidification device for fruit and vegetable preservation were obtained.The above research can provide reference for improving the uniformity and accuracy of ultrasonic humidification in fruit and vegetable transportation chamber,thus improving the storage quality of fruits and vegetables.