Preparation And Properties Of Inorganic Hydrated Salt Composite Phase Change Energy Storage Concrete

With the continuous development of science and technology and the growing demand for energy in human society,the energy crisis and environmental pollution issues have become increasingly prominent.People have paid more and more attention to the efficient use of energy.Inorganic hydrated salt phase change materials can efficiently absorb or release heat through phase changes,greatly improve energy storage performance,and have the advantages of low cost,constant phase change temperature,safety and environmental protection,but their problems of supercooling and phase separation limit their widespread application.In this paper,disodium hydrogen phosphate dodecahydrate phase change material is used as the main body,and various modification methods are explored and an inorganic hydrated salt composite phase change energy storage concrete is prepared.Firstly,the modified effect of expanded graphite on disodium hydrogen phosphate dodecahydrate was tested,which can greatly improve the thermal conductivity and reduce the undercooling of the material.However,the addition of nucleating agent and the cost of expanded graphite are not suitable for large-scale application to concrete in.A colloidal disodium hydrogen phosphate dodecanoate-decanoic acid composite phase change material was prepared by the sol-gel method,and its thermal properties were comprehensively evaluated.The composite phase change material was added to C30 concrete.Phase change energy storage concrete slab.The heat storage performance of the concrete slab was tested and the strength of the phase change concrete block was tested.The following conclusions were reached:(1)A composite phase change energy storage material was prepared by adding porous reticulated expanded graphite and sodium silicate nonahydrate to disodium hydrogen phosphate dodecahydrate.The structural observation and thermal performance tests were performed on the composite materials.The experimental results show that the addition of 4% by mass of expanded graphite can reduce the supercooling of DHPD from 14.3 ° C to 5.9 ° C.When the expanded graphite is added by more than 6% by mass It can eliminate the phase separation of DHPD,and expanded graphite can greatly improve the thermal conductivity of composite phase change materials.The preferred composition ratio of the composite phase change energy storage material is 90% Na2HPO4 · 12 H2 O + 6% EG + 4% Na2 Si O3· 9 H2 O.At this time,the phase change latent heat of the composite material is 220.6J / g,and the phase change temperature is 33.6℃.The thermal conductivity is 2.4W / m·K,and the supercooling degree is 1.5℃ Compared with pure DHPD,the supercooling degree is reduced by 89.5%,and the thermal conductivity is increased by 3.4 times.After 300 cycles of cold and hot cycling of the composite,its thermal properties such as phase change latent heat,thermal conductivity,and supercooling are stable.However,it is necessary to add nucleating agent and the cost of expanded graphite is not suitable for large-scale application in concrete.(2)A colloidal disodium hydrogen phosphate dodecanoate-Capric acid composite phase change material was prepared by the sol-gel method.First,the ratio of the eutectic mixture of the composite material was theoretically predicted.By analyzing the DSC curve and the eutectic twophase diagram,it was found that close to a binary eutectic mixture was formed when the DHPD ratio CA in the composite phase change material was 7: 3.The experiment found that the colloidal state disappeared when the mass ratio of Capric acid in the composite material was greater than 40wt%,and the reason why the mixture was colloidal was speculated.The chemical reaction of the composite material did not occur through FTIR and XRD testing but physical mixing.The phase change temperature of the disodium hydrogen phosphate-decanoic acid composite phase change material tested is 33.8 ℃,the supercooling degree is 0.9 ℃,the latent heat value of the phase change is 168.8J / g,and the thermal conductivity is 0.468 W / m·K under the solid state of 15 ℃,0.532 W / m·K in 50℃ liquid state.The test results also show that the disodium hydrogen phosphate dodecahydrate-decanoic acid composite material has a 94.8% reduction in supercooling compared to pure disodium hydrogen phosphate dodecahydrate,and its thermal conductivity in solid state is increased by 1.96 times compared to pure decanate,Its thermal conductivity in liquid state is increased by 2.37 times,and it has a higher latent heat of phase change.The measured results are compared with the theoretical predicted values,and the predicted lowest eutectic ratio is close to the actual value,and the phase change latent heat and the phase change temperature differ greatly.Finally,after 300 cycles of cooling and heating,the phase change latent heat value,supercooling degree,phase change temperature,and colloidal morphology of the composite phase change material are stable,and no phase separation occurs.(3)The use of expanded graphite composite phase change material will absorb the water required to prepare concrete,and compared with the cost and process difficulty,finally selected disodium hydrogen phosphate dodecahydrate-decanoic acid as the main phase change material.Compared with ordinary C30 concrete slabs,phase change energy storage concrete slabs have found that the temperature change rate of phase change energy storage slabs is lower under the same heating and cooling conditions,and there is a heat release platform near the phase transition temperature of composite materials,indicating that composites are added.Experimental tests on concrete slabs incorporating composite phase change materials of different mass ratios have similar energy storage effects.With the addition of 5% mass fraction of phase change materials,the strength of concrete decreases by 24.9% and continues to increase to 10% For a phase change material with a mass fraction,the concrete strength will suddenly drop by 60.2%.Through comprehensive evaluation of the energy storage performance and mechanical strength,the final mass ratio of the composite phase change material is 5% of the total mass of the concrete.