Design And Experimental Study On Solar Energy System With A Seasonal Storage

Energy is the basis and power of modernization construction,supply and security of the energy is related to the overall situation of China’s modernization.At present,the world political and economic situation is profoundly adjusted,and the relationship between energy supply and demand also changes profoundly.Due to intensified restraint of resources and energy and evident environment problems in our country,the development of resources is just facing a series of challenges,such as adjusting structure,improving energy efficiency and ensuring energy security.As an inexhaustible source of clean energy,solar energy has an important implication for solving the energy and environmental problems.China has become the first power in solar thermal production and application with a near-20-year development.However,the current development of solar thermal heating is still facing a large amount of challenges,for example,lacking in large-scale thermal storage demonstration projects,high cost of land use,huge investment but with poor economy and the complexity of the seasonal heat storage technology etc.are the factors which restrict the development of the system.As the key components of the thermal storage system,the performance of the tank and the insulation material have a great effect on the amount of the available energy of the system,also,their cost also occupies a considerable proportion in the investment of the entire thermal storage system.When the heat storage capacity stays at a low level,the cylindrical water tank is widely used because of its low cost and great heat preservation performance.At present,research on the working process of cylindrical water tank did by the scholars in and out of the country has already been driven to maturity stage.However,as the heat storage capacity reaches to a high level,the cost of cylindrical tanks increases dramatically,and the life and performance of the tank have difficult in meeting the requirements.With higher strength and lighter weight,Rectangular tank,having obvious advantage in higher land utilization rate and lower costs than the cylindrical tank,can be assembled and welded according to actual conditions of constructions sites,which will have broad application prospects in large-scale heat storage.The experimental platform which uses rectangular water tank as the heat storage container undertakes a study on the insulation process and heat storage process of the tank in the method which numerical simulation is combined with experimental analysis under the actual working conditions.The degree thesis main contents as follows: 1.the paper analyzes the application of thermal storage technology and the research status of thermal storage tank,and demonstrates the social and environmental benefits of solar thermal storage system.2.Fixing the heat storage scheme and selecting the system components after the parameters were calculated.3.Establishing the finite element simulation models of rectangular water tank,and the effects of different flow rates on the thermal storage performance of the water tank and the mechanism of the temperature stratification of the tank in the insulation process was researched,also,the experimental results were carried out under the actual working conditions.4.The finite element simulation models of box insulation material was established,and the research on the influence of thickness and structure of insulation material on insulation performance was done.5.Research of the influence of thickness of pipe insulation material on its performance was done.According to the results: 1.When the flow rate of the inlet is less than 0.1m/s,the water tank in heat storage process could form a good temperature stratification,temperature the upper region could reach a high level,also,the useful energy had better quality;2.With the increase of the velocity(higher than 0.1m/s),the depth of the impact of water flow increases,the mixing inside the tank strengthen and the fluid in the tank won’t form a good temperature stratification in the heat storage process.When the flow rate stays between 0.3m/s ~ 0.4m/s,the tank will form a "dead area of low temperature",as the flow rate increases,the tank will form a "low temperature group" instead of the "dead area of low temperature".As the temperature of the water at the inlet increases,the fluid temperature at the outlet rises as well,and the efficiency of solar collectors and plate heat exchangers decreases;3.Under current conditions,the external surface temperature and ambient temperature difference will drop to 3℃ or less when thickness the box insulation material reaches 80 mm,it can ensure a good insulation effect;4.There is a direct transition between the outer circular surface and the plane on the box insulation material.Due to the sudden change of the shape,the heat flux density which has great influence on the thermal insulation performance is high.The convective heat transfer strength can be effectively reduced when the transition is changed to fillet;5.For current system,as the thickness of outer pipe insulation material(rubber insulation cotton)reaches 30 mm,temperature difference between outer surface and ambient temperature is 2.638℃,good insulation efficiency can be achieved 6.within the lifecycle,solar energy storage system which could save standard coal 5922.87 t per ton heat storage capacity,reducing the dioxide,sulfur dioxide,soot and nitrogen oxides emissions were 15.767 t,5.92 kg,5.92 kg and 8.59 kg has good social benefits and ecological benefits.