Preparation Of Al₂O₃/Na₂SO₄·10H₂O Composite Phase Change Heat Storage Material

The heat source of the greenhouse mainly depends on the heat supply of the wall in winter night,while the traditional wall materials mostly use environmental resources materials such as rock and red brick.Na₂SO₄·10H₂O has a large heat storage capacity and the phase change temperature is close to the required temperature for the growth of crops.It is suitable to be used as the phase change heat storage substrate of greenhouse walls.However,the problems of supercooling degree and phase stratification are the main factors restricting its wide application.To some extent,inorganic porous materials can not only effectively reduce the degree of undercooling,but also completely solve the problems of phase stratification and liquid phase leakage.But,the porous materials sold in the market are not only low in output but also expensive.Therefore,this study explores the recycling of solid waste aluminum dross residue.The acid leaching and alkaline purification are used to prepare high-purity Al（OH）₃precursors,and agricultural waste straw powder is used as a sacrificial template to prepare porous Al₂O₃.The phase change materials were modified with borax as nucleating agent,KCl as phase change temperature regulator,and homemade porous Al₂O₃ was used as phase change support material.The porous alumina matrix composite shaped phase change heat storage material was prepared by vacuum physical adsorption method,and the experimental parameters were optimized by three-factor five-level orthogonal combination test method,and the optimal experimental process was selected to provide experimental basis for the application of greenhouse wall.The main research contents and conclusions are as follows:（1）Preparation of porous Al₂O₃ from solid waste.First,the high-purity Al（OH）₃precursor was prepared from aluminum ash residue of industrial solid waste by acid extraction（H₂SO₄）and alkali purification（Na OH）.Secondly,porous Al₂O₃ was prepared by roasting agricultural waste straw powder as sacrificial template.After experimental research:The H₂SO₄ of 1.6mol/L,5 h and heating temperature of 80℃are the best condition for the test,the maximum leaching rate of aluminum element is 70.7%;High-purity 99.4 wt%Al（OH）₃ precursor can be prepared by Na OH and water purification process.the prepared Al₂O₃ has a specific surface area of 261.22 m²/g,a pore volume of 0.34 cm³/g,and an average pore size of 52.64 nm by.roasting process.（2）Study on modification of Na₂SO₄·10H₂O.Na₂SO₄·10H₂O was used as the raw material to adjust the cooling rate,and borax,KCl and Al₂O₃ were added to modify it.It was found that the cooling rate,borax,KCl and Al₂O₃ had a significant influence on the actual crystallization temperature,phase transition temperature and supercooling degree of Na₂SO₄·10H₂O.In addition,the addition of porous Al₂O₃ can produce a secondary phase transition,which can effectively reduce the subcooling degree and phase transition temperature and increase the heat release and heat release time.（3）Preparation of composite shaped phase change materials.Based on the results of single factor experiment,using vacuum physical adsorption of composite prepared by the finalize the design phase change materials,with phase change temperature,degree of supercooling and phase change latent heat value as test index,three factors five levels orthogonal combination experiment analysis of optimization:primary and secondary order of factors influencing the value of phase change latent heat and cooling rate,alumina and borax content;The optimal optimization parameters were 0.94℃/min cooling rate,2.86 wt%borax and 29.89 wt%alumina,and the results obtained from the empirical test were basically consistent with the optimization results.