Theoretical And Experimental Study On Hot Liquid Defrosting In Cold Frame

Cold frame is the basic establishment for developing cold-storage industry.It is also the building for storing goods under low temperature.With the rapid development of national economy and advance of people's standard of living,the require of cold frame is at a high pitch. Evaporator frosting can affect the capability of cold frame.How to defrost effectively is a serious problem.A new defrosting method,hot liquid defrosting,is introduced in this paper.The refrigeration system has five main parts:compressor,condenser,expanding valve, refrigeration evaporator and defrosting evaporator.Their mathematic models are established respectively.Moreover,the mathematic model of hot liquid defrosting refrigeration system is established.It can be computed with MATLAB programme and the rule of capability variety of refrigeration system during defrosting is analysed.The experiment plan is designed and the experiment set is rectified on the basis of former one.Experiment of cold leaking is carried out to fit a thrice power multinomial about temperature difference with leaking cold.The multinomial can be used to compute different leaking cold with different temperature difference.The time of defrosting which is ascertained by experiment is 15 minutes.The research on hot liquid defrosting affecting the capability of cold frame is carried out under different work condition.The results are as follows:1.The temperature difference is about 5℃during hot liquid defrosting.2.Hot liquid defrosting can get large degrees of supercooling.It avails to enhance the refrigeration capacity during the process of defrosting.3.The temperature of evaporator is always below 30℃during the process of defrosting.Compared with hot gas defrosting,it is less effect on efficiency of fin of heat-exchanger.The experimental result has some deviation because of the differences between stimulant cold frame condition and actual cold frame.Otherwise,the system switches manually.Switching time can't accord with the demand of engineering.How to improve auto-control system should be settled in the future.