Research On The Control Of Constant Temperature And Humidity System And The Precooling Of Vegetables And Fruits

China produces a large amount of fruits and vegetables every year. However, no complete cold chain has been founded for fruits and vegetables in china due to the unadvanced technology. There is no precooling for fruits and vegetables in many occasions, which brings a great economic loss and decrease of the quality. It's a significative mission to develop appropriate equipment or system for cooling and precooling of fruits and vegetables.This thesis has studied a new type of cold store, which can provide constant temperature and humidity. The main work contained to establish an appropriate control strategy, to write the control programme and to ascertain the parameters of PID controller via theoretic and experimental method. First step is to deduce the structure of the control model, and then make out the unknown parameters of the model by step response diagram, which has been widely used in control engineering. Then calculate the parameters of the every PID controller based on some experiential formulae. Through experiments, found that the change of the integral effect was too rapid, and the theoretic value of the PID parameter could not keep the temperature of the cold store to a target value. This thesis analysis the fluctuation of the temperature. Then, a method was been introduced in this thesis to improve the integral control effect. Finally, the right value of the control parameters and the suited control method were made out. The control effect satisfied the control targets and the energy consumption is more lower.Also this thesis there's some experiment research in precooling of vegetables and fruits. Analyzed some important influencing factors of precooling, such as velocity, humidity and temperature of the air. Find some rules of the infection.