Design And Study On The Solar Air Heating System With Phase Change Materials Energy Storage In Greenhorse

The main purpose of the greenhouse is to provide suitable conditions for the crop inseasons when the conditions are not suitable for plant growth. The temperature has the mostobvious effect on crop. In northern China, the temperature is very low and the temperaturedifference between day and night is larger in early spring, late autumn and winter. Thetemperature in the greenhouse, especially the nighttime temperature in the case of non-heatedis very difficult to ensure the normal growth of crops. The high heating energy consumption,operating cost in cold seasons is the main problem to China's greenhouse production. Thehigh cost limits the improvement of the greenhouse production efficiency greatly. In recentyears, with the rapid development of China's greenhouse, the energy consumption of thegreenhouse production is also increasing. In China, greenhouse is mostly used in ruralagricultural production as an important means to enhance farmers' income. But the energyshortage in China is particularly serious in rural areas, which greatly limits the role of thegreenhouse to increase efficiency in agricultural production. To improve the greenhouseapplication value in agricultural production, it is necessary to reduce the cost of production ofthe greenhouse. The most economical and effective way is to store excess heat in the daytimeand release at night to ensure the growth of crops.Combined phase change heat storage materials and solar air heater, this article designeda solar air heater-phase change heat storage device and test its performance. This articleselected Na₂HPO₄12H₂O as the main phase change heat storage Material, and improved theperformance of its phase transition for using in the. Then this experiment designed the solarcollectors, and combined phase change heat storage materials and solar collectors. Throughthe experimental study, results show that:(1) When using Na₂HPO₄12H₂O as the phase change thermal storage material,Na₂SiO₃9H₂O and graphite are suitable nucleating agent. And Na₂SiO₃9H₂O can increasethe viscosity while graphite can enhance the thermal conductivity. While adding3%Na₂SiO₃9H₂O and3%graphite into Na₂HPO₄12H₂O at the same time, the composite system has aphase transition temperature of33.5°C, and the undercooling can be reduced to0°C. It is a good solution to undercooling phenomenon of Na₂HPO₄12H₂O. Though the stability test ofNa₂HPO₄12H₂O+3%Na₂SiO₃9H₂O+3%graphite, the results show that, thecomposite system has a phase transition temperature of33.4°C, and the undercooling is0°C. Its phase transition time is27min. The composite system has good stability and goodapplication prospects in the phase change thermal storage field. Though the DSC test ofNa₂HPO₄12H₂O+3%Na₂SiO₃9H₂O+3%graphite, the results show that, the phasetransition temperature is34.02°C, and the latent heat is179.3J/g. The system has suitablephase transition temperature and lager latent heat. It is a good phase change thermal storagematerials.. Though the repeatability test of Na₂HPO₄12H₂O+Na₂SiO₃9H₂O+graphite,the results show that the system is reproducible, stable performance, and has good applicationprospects in the phase change thermal storage field.(2) The solar collectors-heat storage device is composed by the shell, the insulatinglayer, the transparent cover plate, and the heat storage material. The shell is made of wood,which size is160cm×120cm×34cm (LWH), thickness2cm. The board insulation layer ispolystyrene. The underside thickness of the insulation board is4cm, and the surroundingthickness of the insulation board is2cm. The cover is made of two layers of plastic, betweenwhich is air layer. The Lighting area is150cm×120cm, and the distance between two layersis2cm. is made of aluminum, which takes the form of black shutters. The size of the absorberplate is150cm×110cm. The part of phase change material is composed by a number ofregenerative cells, which are filled with Na₂HPO₄12H₂O+Na₂SiO₃9H₂O+graphite. Thedevice has air inlet and air outlet with a diameter of15cm, which control the flow of air inthe heat storage devices, and air exchange with the Environment. The test result shows that,the collector without has an efficiency of55.3%. The collector-regenerative device with heatstorage material has a regenerative efficiency of43%.