Preparation And Building Energy Saving Of Fatty Acids/Diatomite Form-Stable Phase Change Materials

With the development of society,energy crisis increasingly aggravates and energy conservation has been becoming a general trend.Phase change materials can absorb and release thermal energy by phase transformation.While combinbed with the building materials and applied in buildings,it could reduce the indoor temperature fluctuation and improve the living comfort.Thus,more and more attentions about the phase change materials have been focused on the field of building energy conservation.In this paper,a kind of form-stable phase change material(FSPCM)using binary fatty acid eutectic as the phase change material and modified diatomite as the matrix was prepared by vacuum impregnation technology.Thermal properties and structure composition of the fatty acid/diatomite FSPCM was examined in detail.The prepared FSPCM was mixed into the cement mortar to prepare the phange mortar,pahse change test cube and phase change heat exchange clement.And their structural performance,mechanical and thermo-physical properties,and energy-saving effect were also tested and analized.Theory of phase change entergy storage,material science,chemicial technology,heat and mass transfer,test of material properties and structures are used to solve those key questions about prepared of FSPCM,test of atorage/release performance,service performance of phase change building materials,the experiment combine many subjects and technology.Through the research,the goals of FSPCM utilization in building envelope and building energy corservation can be realized and it can provide a new kind of PCM for building energy conservation.The results will provide theoretical evidences for PCM applied in building and increase the diversity and feasilitty.The research results are as follows:(1)Diatomite is chosen as the supporting matrix in the FSPCM and modified by the roasting,acid leaching and roasting plus acid leaching method,respectively.The structural characteristics and composition are investigated by x-ray diffraction(XRD),scanning electron microscopy(SEM)and BET measurement.The results show that the modified diatomite has homogenous pore-size distribution with the most probable pore size ranging from 1-20 nm.Meanwhile,the modified diatomite has integrated structure and moderately rough surface as well.(2)CA and LA is selected as the phase change material and prepared CA-LA binary eutectic.According to the lowest eutectic theory,the mass ratio of CA-LA binary fatty acid eutectic is calculated to be CA:LA=66:44.Melting blending method is adopted to prepare the CA-LA eutectic.Differential scanning calorimetry(DSC)result shows that the phase change temperature of CA-LA is 19.79℃ which is close to the theoretical phase change temperature and the latent heat is 154.16 J/g.Fourier-transform infared(FTIR)spectra indicates that the fatty acid binary eutectic is physical interaction.Thermogravimetric(TG)analysis shows that CA-LA eutectic hardly volatiles and decomposes under 105℃ thus behaves good thermalthermal stability in the low working temperature range.It can be determined that the fatty acid binary eutectic has good thermal storage properties and accords with the requirement of comfortable temperature for living.(3)CA-LA/modified diatomite FSPCM is prepared by vacuum impregnation method and its morphology,structural characteristics,thermo-physical properties are investigated by SEM,XRD,FTIR,thermal cycling test and heat storage/release test.SEM analysis shows that the CA-LA eutectic hase been absorbed into the pores of the modified diatomite.XRD and FTIR results show that there are no chemical reactions between the fatty acid and modified diatomite but combining through simply physical chimeric.Seepage stability experiments conducted on the FSPCM reveal that the mass loss of FSPCM which are dried by single bumping treatment is more than other treatments,but still less than 5wt%.And the sample dried by bumping has higher phase change latent heat and more valuabe in building energy consevation applications.DSC test results show that its phase change temperature and latent heat is 17.68℃ which is close to the CA-LA eutectic and 66.65J/g,respectively.TG tests show that FSPCM has good thermal stability under 105℃ with the mass loss rate of 41.65%.The value is consistent with the DSC analysis on the FSPCM.From the storage/release tests results,the temperature varation curve of the FSPCM during the heating-cooling process has a temperature platformon near 22℃ caused by the phase change of the FSPCM,which proves that the FSPCM can regulate the temperature in some degree.(4)The phase change cement mortars were prepared by stiring at room temperature.SEM results show content of FSPCM has a effect about the stoma numbers of mortar inner.Compression resistance and anti-fold capability of phase change cement mortars gradually decreased with the increasing of FSPCM content.The optimum mixture ratio of phase change cement mortars is 1:0.33:0.17:0.023:0.0015.FTIR tests show that FSPCM and Portland cement mortars are only physical association.The thermal resistance of phase change heatexchange clement is 0.068m2·K/W and the heat transfer coefficient reach 4.59W/(m2·K).The atorage/release curve of phase change experimental box show that pahse change cement mortars have better effect of temperature regulation function when thickness of heatexchange clement is 3cm.