| With the wide application of cold storage,the defrosting and frosting of the evaporator of the cold storage has also received extensive attention.At present,the energy waste caused by the inability to defrost in time and incomplete defrosting has been very serious.Because the inside of the cold storage is in a low temperature and high humidity environment for a long time,the temperature on the evaporator fins is easily lower than the dew point temperature of the water vapor in the humid air under the same pressure,and a frost layer is easy to form.The frosting situation will become more and more serious.If defrosting is not performed in time at this time,the performance of the refrigeration system will be greatly affected.Therefore,researching the appropriate defrosting control method is an important part of researching refrigeration system.The main purpose of this paper is to use Raspberry Pi to accomplish the collection and storage of temperature and humidity data,image data,storage temperature data and other data and remote web page display during the experiment of the evaporator of the cold storage,and to optimize the defrosting of the small refrigerator through experimental analysis and data processing.control process.This paper firstly investigates the background of defrosting methods and related defrosting control methods,clarifies the research ideas and contents of this paper,and then analyzes the growth mechanism of frost layer and the factors affecting frost formation,and controls the air pressure difference.The defrosting method and the frost layer image control defrosting method are introduced in detail.After that,the Raspberry Pi and other equipment were selected as the main equipment for data acquisition,data storage,image acquisition,image processing,and web page display in this experiment.In order to complete the corresponding functions,the operating environment and related function libraries of related programs are installed and built on the Raspberry Pi and personal PC.Then use the Python language to write the main programs on the Raspberry Pi 4B to realize the functions of temperature and humidity data acquisition,image acquisition,image processing,data storage,and web page display.The temperature and humidity data of the frost layer on the surface of the fins,the storage temperature data,the frost layer image,etc.,and the frost layer image data,etc.,collected by the Raspberry Pi during the frosting and defrosting process of the evaporator are compared and analyzed.Through the written program,the evaporator frost layer image is subjected to threshold processing,mean hash comparison and other processing processes,and the frost layer image defrosting coefficient S is introduced to reflect the melting degree of the evaporator frost layer.The larger the defrosting coefficient S,the more frost,the more completely the layer melts,the smaller the more the frosting.And the air pressure difference-outlet temperature defrosting control method is tested under the working conditions of-12℃ and-18℃.The results found that although the defrosting time is short and the fluctuation of the storage temperature is small,the defrosting coefficient at the end of defrosting is not very high.By observing the frost layer image at the end of defrosting,it is found that the evaporator remains at the end of defrosting.Part of the frost layer,that is,the phenomenon of "incomplete defrosting" appears,indicating that the outlet temperature is not suitable as the end point of defrosting,and it needs to be optimized.After that,three groups of feasibility experiments were carried out to use the frost layer image defrosting coefficient S instead of air pressure difference and outlet temperature as the starting and ending points of defrosting,and it was found that when the frost layer image defrosting coefficient S was 0.28,it was suitable as the start of defrosting.point,when the defrost coefficient S is 0.87,it is suitable as the end point of defrosting.Then,experiments were carried out on the small cold storage using defrosting coefficient-defrosting coefficient to control the defrosting method,and the experimental results were obtained and the two defrosting control methods were compared and analyzed.Finally,it is found that the defrosting coefficient-defrosting coefficient control defrosting method based on Raspberry Pi is more complete and thorough,and will not affect the subsequent cooling process.It is a better defrosting control method,and the cost of the whole monitoring system is relatively low,stable operation,can be used in the defrosting process of cold storage. |
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