Study On The Performance Of Composite Phase Change Materials Based On Solar Heat Storage Tank

Economic and social development is inseparable from energy,China's energy resources are rich,but with low per capita resources capacity,saving energy,is a realistic choice to alleviate resource constraints in China.As a kind of energy,solar energy has unique advantages in energy development.The solar radiation has the advantages of high energy,widely distributed,and does not produce waste and harmful substances when used with energy,but also has the disadvantages of low energy density,low conversion efficiency,seasonality and intermittence.Therefore,efficient heat storage method has become the main measure to improve the utilization efficiency of solar energy.Phase change heat storage technology is the use of phase change materials to phase change in a certain temperature range,release the energy by reverse phase change when the heat supply is insufficient.Phase change heat storage technology can solve the imbalance of energy supply in time and space,and increase the energy utilization efficiency.This article combines phase change materials and carbon fiber to prepare composite phase change materials and use in solar heat storage tank.During the daytime when the solar heating hot water through the heat exchange tube,composite phase change materials absorb quantity of heat in the form of latent heat,then the cold water absorb this part of heat at night to and can be use for life.This paper select static acid which with high phase change latent heat as phase change materials,carbon fiber which with high thermal conductivity as adding material to enhance heat transfer,add ethyl cellulose to solve settleability of carbon fiber in liquid static acid.Prepare composite phase change materials by melt blending method,doing SEM analysis,XRD analysis,DSC analysis,thermal constant and thermal stability analysis for it.The results showed that carbon fiber/static acid composite phase change materials had good chemical compatibility and no other substance were created after mixing.Carbon fiber can effectively improve the thermal conductivity of static acid.With the addition of carbon fiber,the phase change temperature and latent heat of the composite phase change materials decreased.Carbon fiber/static acid composite phase change materials has good thermal stability,carbon fiber still evenly distributed in the static acid after 200 times of melting and solidification cycle.Meanwhile,compared with before cycle,the phase change temperature of composite phase change materials is basically unchanged,and the latent heat is decreased.Considered the test results of composite phase changematerials with different mass ratios,composite phase change materials has appropriate phase change temperature,phase change latent heat and thermal conductivity when the carbon fiber content is 7.5%,at this time the phase change temperature of composite phase change materials is 67.7?,the latent heat is 192.6 J/g.Therefore,7.5% carbon fiber/static acid composite phase change materials was selected as the heat storage material of the phase change heat storage water tank.Carbon fiber/static acid composite phase change materials was applied to the solar energy storage tank,and established the phase change energy storage experiment system to study the heat storage/heat release characteristics of the composite phase change materials.The results showed that in the process of heat storage(heat release),the distance closer to the copper tube,the higher(lower)the temperature is,and the faster the melting(solidification)is.In the initial stage of heat storage(heat release),the temperature rise(temperature drop)is relatively fast,and tend to be gentle with the passage of time.In the process of heat release,the temperature difference between inlet and outlet of cold water gradually decreases in phase change energy storage tank.ICEM CFD software was used to build a phase change energy storage tank model,and was simulated by Fluent software to explore the change law of temperature of composite phase change materials and outlet water.The results showed that in the process of phase change heat storage,when it is carried out for about 8hours,the temperature of the whole energy storage tank reaches 90?.In the process of heat storage(heat release),the temperature of the composite phase change materials in the lower part of the phase change energy storage tank is higher(lower)than that in the upper part,and the melting(solidification)interface keeps advancing upward.In the initial stage of phase change heat release process,the outlet water temperature drops rapidly,then tend to be gentle.The higher the inlet cold water temperature is,the higher the outlet water temperature is.When the process of phase change heat release is carried out for 2 hours,the inlet cold water temperature is 25?,the outlet water temperature is 35.8 ?,indicating that the composite phase change materials applied to the phase change energy storage tank has a certain effect.