Preparation Of Metal Organic Framework UiO-66-NH₂ And Its Effect On Heat Transfer And Thermal Storage Properties Of Lauric Acid And Sodium Sulfate Decahydrate

Under the background of"carbon peak"and"carbon neutral",substantial energy saving and carbon reduction in buildings have become the inevitable trend of modern building development.Renewable energy sources such as solar energy and wind energy,as zero-carbon energy,are the main energy sources to achieve significant energy saving and carbon reduction in buildings.However,these renewable energy sources are intermittent and highly volatile,which makes the efficient use of renewable energy inseparable from energy storage.Phase change thermal energy storage with high energy storage density,constant phase change temperature and stable performance is considered as a key technology for buildings to achieve energy saving and carbon reduction by using renewable energy.In order to improve the heat transfer and thermal storage performance of phase change thermal storage materials,this paper investigates the heat transfer and thermal storage performance of phase change thermal storage materials by preparing metal organic framework materials（MOFs）and exploring the effect of metal organic framework material UiO-66-NH₂ on the heat transfer and thermal storage performance of lauric acid（LA）and sodium sulfate decahydrate（Na₂SO₄·10H₂O）by adding MOFs to phase change thermal storage materials.In this thesis,the metal organic framework material UiO-66-NH₂ was first ready by the solvothermal technique,and its chemical composition and microscopic morphology were investigated by Fourier remodel infrared spectrum analysis（FT-IR）,X-ray diffraction（XRD）,and scanning electron microscopy（SEM）.The specific surface area,pore size and thermal stability of the UiO-66-NH₂ were investigated by specific surface area and pore size tests and thermogravimetric analysis.On this basis,taking organic phase change material lauric acid and inorganic phase change material crystalline hydrated salt Na₂SO₄·10H₂O as matrix,a series of composite phase change thermal storage materials were prepared by adding UiO-66-NH₂ to the phase change system.The effect of metal organic framework material UiO-66-NH₂ on the thermal storage performance of phase change thermal storage materials was investigated.FT-IR,XRD and SEM were wont to study the chemical composition and microscopic morphology.The consequences of UiO-66-NH₂ on the melting point,latent heat,specific heat and thermal conductivity of the phase change thermal storage materials were investigated by DSC and Laser flashing method,the heat transfer effect of UiO-66-NH₂ on the phase change process of the phase change thermal storage material was investigated by calculating the average heat transfer rate,and thermal stability by thermogravimetric analysis.The most studies area unit as follows.（1）The metal organic framework material UiO-66-NH₂ was prepared by solvothermal method with simple operating equipment.The chemical composition and microscopic morphology of UiO-66-NH₂ are consistent with the standard samples in the literature,which proves that the synthesis of UiO-66-NH₂ is successful,as characterized by FT-IR,XRD and SEM tests.By analyzing the N₂ adsorption and desorption isotherms obtained from the specific surface area and pore size analyzer,it is known that the adsorption type of UiO-66-NH₂ is microporous adsorption,and the specific surface area of the prepared UiO-66-NH₂ is as high NH₂ has high specific surface area and well-developed microporous structure.The skeleton of UiO-66-NH₂ collapses only when the temperature of UiO-66-NH₂ exceeds 600°C,which indicates its excellent thermal stability,as obtained by thermal weight loss test analysis.（2）UiO-66-NH₂ was added to phase change thermal storage material LA by melt blending method to prepare LA@UiO-66-NH₂ composite phase change thermal storage materials.The results of FT-IR,XRD and SEM show that the addition of UiO-66-NH₂ will not change the chemical structure and composition of LA,but it can increase the solid specific heat and liquid specific heat of LA.DSC test results showed that the addition of UiO-66-NH₂ had little effect on the melting point and phase transformation latent heat of LA.UiO-66-NH₂ had the highest specific heat in the solid state at 1.0 wt.%addition and in the liquid state at 0.2 wt.%,which were 20.3%and 21.5%higher than LA,respectively.The results of thermal conductivity test and average heat transfer rate calculation showed that the addition of UiO-66-NH₂ could increase the thermal conductivity and average heat transfer rate of LA.It was found that the solid-state thermal conductivity of LA increased by 10.50%and 6.30%with the addition of 0.6wt.%and 1.0 wt.%of UiO-66-NH₂,respectively.After adding UiO-66-NH₂ in different proportion,the heat transfer rate of LA@UiO-66-NH₂ phase change material increases.When the addition proportion is 0.6wt.%,the average heat transfer rate of LA@UiO-66-NH₂composite phase change material is the highest,which is 39.42%higher than that of pure LA.The addition of UiO-66-NH₂ promoted the endothermic process of LA.（3）The Na₂SO₄·10H₂O@UiO-66-NH₂ composite phase change material was prepared by adding UiO-66-NH₂ to the phase change thermal storage material Na₂SO₄·10H₂O by melt blending.The results of FT-IR,XRD and SEM show that the addition of UiO-66-NH₂ will not change the chemical structure and composition of Na₂SO₄·10H₂O.However,it is found that after adding low mass fraction of UiO-66-NH₂,the melting point of the composite phase change thermal storage material is higher than that of pure Na₂SO₄·10H₂O.The melting point of the sample with the addition ratio of 0.2wt.%is the highest,which is 17.03%higher than that of Na₂SO₄·10H₂O.The addition of different proportions of UiO-66-NH₂ has different effects on the phase transition latent heat of Na₂SO₄·10H₂O.The latent heat of the composite phase change thermal storage material with addition ratios of 0.4 wt.%,0.6 wt.%,and 0.8 wt.%was increased by 5.9%,3.4%,and 4.7%compared to pure Na₂SO₄·10H₂O,while the latent heat of the composite phase change thermal storage material with addition ratios of 0.2 wt.%and 1.0wt.%was reduced by 4.2%and 1.6%.The addition of different ratios of UiO-66-NH₂ had different effects on the specific heat of Na₂SO₄·10H₂O.The highest solid and liquid specific heats of the composite phase change thermal storage materials were obtained at the addition ratio of 0.4 wt.%,which were 120.0%and 132.9%higher than that of Na₂SO₄·10H₂O,respectively.The addition of UiO-66-NH₂ increased the decomposition temperature of Na₂SO₄·10H₂O and reduced the mass loss of Na₂SO₄·10H₂O.When the addition ratio is 0.8wt.%,the maximum decomposition temperature of the composite material is 113.2°C,which is5.6°C above that of pure Na₂SO₄·10H₂O.When the addition ratio is 1.0 wt.%,the minimum low mass fraction UiO-66-NH₂ decreased the average heat transfer rate of solid-liquid phase change of composite phase change thermal storage materials.When the addition ratio was 1.0wt.%,the average heat transfer rate of Na₂SO₄·10H₂O@UiO-66-NH₂ composite phase change thermal storage materials was the lowest,which was 23.59%lower than that of Na₂SO₄·10H₂O.UiO-66-NH₂ hinders the endothermic process of Na₂SO₄·10H₂O.