Preparation Of Hydrated Salt Composite Phase Change Materials And Application In Buildings Energy Savings

By using the latent heat storage characteristics of phase change energy storage materials and combining them with building envelopes,it is possible to suppress indoor temperature fluctuations by increasing the thermal inertia of building envelopes and achieve the purpose of building energy conservation.Hydrated inorganic salts have the advantages of high latent heat value,low price,and non-toxicity,and have great potential in the field of building energy conservation.However,problems such as supercooling,high phase transition temperature,and liquid leakage often limit their application in engineering.In this thesis,disodium hydrogen phosphate dodecahydrate（DHPD）is taken as the research object.First,50nmCu is added as a heterogeneous nucleating agent to suppress its supercooling,and then it is mixed with sodium carbonate decahydrate（SCD）to reduce the phase transition temperature.It is compounded with expanded vermiculite（EVM）to solve the problem of liquid leakage,and the composite phase change material is prepared into a phase change energy storage board and applied to the building roof.Concluded as follow:（1）Doped with 50nmCu to prepare modified DHPD,the mass fraction is 1.2%,and the subcooling degree is 0.8℃,compared with pure DHPD,it is reduced by 93%,the heat storage time is reduced by 35%,the phase transition temperature is 35.1℃,and the latent heat of phase transition is 253J·g^-1.In order to illustrate the excellent characteristics of 50nmCu as a heterogeneous nucleating agent and heat transfer agent,compared with 10umCu and 1mmCu doped with the same mass fraction,and through SEM and contact angle tests,it was concluded that 50nmCu has the advantages of high specific surface area and surface energy.Promote the formation of DHPD crystal nuclei on its surface,thereby reducing the degree of subcooling.The 50nmCu heat conductive agent has a small particle size and is relatively densely distributed in DHPD,forming a good heat transfer network.The solid and liquid conductivity are the largest,which are 27%and 19.6%higher than those of pure DHPD,respectively.（2）In order to reduce the phase transition temperature of the modified DHPD and make it applicable to building envelopes,CCH,SD,and SCD were selected and incorporated into the modified DHP for theoretical analysis.It was concluded that SCD is most suitable for preparing eutectic hydrated salts.When the eutectic mixing point is reached,the mass ratio is 43.52:56.48,the phase transition temperature is27.16℃,and the latent heat of phase transition is 255.15J·g^-1.At the same time,DSC test verified that the eutectic hydrate salt was formed when the mass ratio was 43.52:56.48.At this time,the latent heat of phase transition was 233J·g^-1,and the phase transition temperature was 26.8℃,which was almost equal to the theoretical value of27.13℃.This method is used to guide the preparation of eutectic hydrated salts with high reliability.（3）In the preparation of eutectic hydrated salt/EVM composite phase change material,an adsorption capacity theory is proposed to calculate the theoretical adsorption amount of eutectic hydrated salt,and the experiment is guided according to the theoretical value.The results show that the calculated value（60%）is almost consistent with the experimental value（62%）,indicating that the calculation method is reliable.The phase transition temperature is 25.7℃,and the latent heat of the phase transition becomes 134.2J·g^-1.After 500 thermal cycles,the latent heat value of the eutectic hydrate salt/EVM is 106.6J·g^-1,indicating that the prepared phase change energy storage material Good thermal stability is a feasible building energy storage material.（4）Phase change energy storage plates and EVM plates were prepared from eutectic hydrated salt/EVM composite phase change materials and EVM,respectively,for phase change rooms and reference rooms.The thermal characteristics of phase change rooms and reference rooms were tested for two consecutive days,and The method is combined with numerical analysis.The results show that compared with the reference room,the phase change room can suppress temperature fluctuations during the period of strong irradiance（10:00¹6:00）,and the peak temperature decreases by 2.7℃and 2.8℃,respectively,and its peak value The temperature appeared later than the reference room.The phase change room TLL values are reduced by 5%and 4.3%,and the energy saving ratesηare 15%and 20.5%,respectively.This shows that the experimental room can suppress indoor temperature fluctuations,can keep the indoor temperature in a more comfortable interval,and achieve building energy saving.The optimized space volume is 0.012m³,and the TLL value is basically maintained at 6%,and the energy saving rateηreaches 28%,which provides theoretical and experimental references for its application in building envelopes.