Study On Modification And Application Of Phase Change Energy Storage Materials With Disodium Hydrogen Phosphate Dodecahydrate

The traditional greenhouse in China has the problem of low energy efficiency.The excess heat in the day cannot be stored,and the heat loss at night is serious,resulting in the mismatch between the supply and demand of heat in space and time.Phase change energy storage material can realize the function of energy storage with temperature increase in the daytime and heat release after cooling at night,however,the application of phase change energy storage material is limited due to its defects such as supercooling,phase separation and leakage.The properties of disodium hydrogen phosphate dodecahydrate as phase change material were studied,and the modification of the matrix material was studied by adding different additives,and the purpose is to prepare composite energy storage materials which can be used in greenhouse through modification research.The melting and crystallization of disodium hydrogen phosphate dodecahydrate were analyzed by means of melting curve,cooling curve and XRD.The products formed by cooling are different at different temperatures,and Na2HPO4·12H2O was produced by cooling at 40? and 45?,and Na2HPO4·7H2O was produced at 50?.The experiment shows that disodium hydrogen phosphate dodecahydrate will lose water to form Na2HPO4·7H2O and its solution at 45?,while Na2HPO4·7H2O will continue to lose water to form a solution when the temperature is higher than 50?,and the loss of water is reversible.The melting process of disodium hydrogen phosphate dodecahydrate is divided into two stages:physical melting and chemical dehydration.Before water loss,the closer to the critical state of dehydration,the greater the supercooling degree is,and the maximum temperature can reach 25.5?.Solution and precipitation were formed after water loss.5mL,10ml and 15ml water were added to each 10g sample to dissolve the precipitation,and the subcooling degree of the obtained solution was tested,which was 9.8?,13.1? and 14.4?,respectively.The lower the concentration of the solution,the greater the subcooling degree.Four different nucleating agents,sodium silicate,diatomite,aluminum nitride and bentonite,were used as nucleating agents and their effects on the properties of matrix materials were studied.The subcooling degree of the samples with sodium silicate 9 added was 4.5°c,5.5°c and 7.5°c,and the latent heat values of phase transition were 151 J/g,147J/g and 187.7J/g,respectively.The supercooling degree of the sample with diatomite added was 9.8?,4.7? and 4.3?,and the latent heat value of phase transition was 157.7j/g,175.7j/g and 198.5J/g,respectively.With the increase of the amount of aluminum nitride nanometer,the subcooling degree of the sample tended to increase,and the latent heat value of phase transition decreased.When the addition amount was 1%,the subcooling degree could be reduced to 3.4?,and the latent heat value could be up to 220.9J/g.The addition of bentonite will not reduce the subcooling degree and the latent heat value of the sample will be reduced.Composite phase change energy storage materials were prepared with sodium hydrated carbonate as temperature regulator at different ratios of 1:1,1:2,1:3 and 1:4.The phase transition temperature was measured by the step-cooling curve at 21.2 ?,24.8 ?,26.4? and 29.3?,respectively.When the mixing ratio is 1:2,the composite prepared has a phase change temperature of 24.8?,which is suitable for application in greenhouse,but there is still a supercooling degree of 3.1?.On the basis of 1:2 mixing of sodium carbonate hydrate and disodium hydrogen phosphate dodecahydrate,1%aluminum nitride nanometer was added,through test and characterization,the phase change heat absorption temperature of the composite was around 25?,and the supercooling degree was reduced to 1.6?.Aiming at the problem that composite material and wall are easy to leak,the application device is designed.The composite phase change energy storage material is packaged separately by material pipe,and then the material pipe is integrated into the heat storage box.The fan is used to realize the heat exchange of hot and cold air,so as to realize the purpose of temperature regulation of the greenhouse.