Preparation And Properties Of Phase Change Wallboard Composite Energy Storage Materials

In this thesis,we design and build a phase change thermal storage wall panel system containing heat collection,heat storage,and heat dissipation functions by selecting suitable phase change thermal storage materials and performance improvement for the nighttime heating demand of agricultural greenhouses,and based on the information of solar irradiation in Jinan area throughout the year.The system uses the collected and stored solar energy for heating at night to solve the problem of mismatch between supply and demand in solar energy utilization in time and the environmental pollution caused by fossil energy heating.According to the screening principle of phase change materials and practical application requirements,disodium hydrogen phosphate dodecahydrate was selected as phase change heat storage material for wallboard preparation,and 2wt%Al₂O₃ nucleating agent,2wt%CMC thickening agent,and 0.2wt%PVP dispersant were added to prepare the DHPD-CAP composite system.The heat storage performance of the composite system was tested and analyzed by heating and cooling cycle experiments combined with SEM,XRD,FT-IR,TG,and DSC.The results show that the supercooling degree of the DHPD-CAP composite system decreases to4.0?,and the phase separation of the composite system is improved obviously.The latent heat of phase transformation is 175.71J/g,which is 10%higher than that of pure DHPD.Further adding 0.25wt%,0.5wt%,0.75wt%,1wt%,and 1.25wt%MWCNTs thermal conductivity enhancers to the DHPD-CAP composite system to prepare the DHPD-CAP/MWCNT composite.The heat storage performance of the composite system was tested and analyzed by heating and cooling cycle experiments combined with SEM,XRD,FT-IR,TG,and DSC.The results show that compared with DHPD-CAP,the supercooling degree of DHPD-CAP/MWCNT composites is further reduced to 0.8?,and there is almost no supercooling phenomenon.The phase separation of the composites was further improved.With the increase of the mass fraction of MWCNTs,the latent heat of phase change of the composites increased first and then decreased.When the amount of MWCNTs was 1wt%,the latent heat of phase change of the composites was the largest,which was 217.57J/g,and the latent heat of phase change was 36.19%higher than that of pure DHPD.In addition,the heat transfer performance of DHPD-CAP/MWCNT composites was improved after the addition of MWCNTs,and the heat storage and release time of DHPD-CAP/MWCNT composites were reduced by 11.74%and 16.51%,respectively,compared with pure DHPD.Finally,the thermal cycling stability of the DHPD-CAP/MWCNT₄composite was tested and analyzed.The experimental results show that the stability of the composite phase change material is good,and the step cooling curves of the composite phase change material coincide after 50 thermal cycles.After 50 thermal cycles,the melting temperature of DHPD-CAP/MWCNT₄ composite phase change material is 35.40?,and the latent heat of phase change is 214.65 J/g,which has almost no attenuation compared with the first cycle(217.57 J/g).The designed DHPD composite phase change material can meet the application demand of energy storage wall panels in agricultural greenhouses.Based on the above phase change material research,this thesis designed the structure of phase change heat storage wall panel and determined the encapsulation method of phase change material as double-layer composite tubular encapsulation;then designed and improved the structure of phase change wall panel and built the integrated wall panel of heat collection,heat storage,and heat dissipation,from back to front,the heat insulation layer,rear ventilation layer,phase change heat storage layer,front ventilation layer,and glass layer,and the size of phase change wall panel was 250mm×2200mm×1000mm.Then 12 groups of phase change wall panels(250mm×2200mm×1000mm)were connected to has been built a phase change wall panel system with a thickness of 250mm,a height of 2200mm,and a width of 12000mm by combining with the actual situation of an agricultural greenhouse.The operation results of the phase change thermal storage wall panel system show that:(1)Under typical overcast weather conditions,there is no obvious rising and falling trend of indoor temperature,temperature between phase change materials,the surface temperature of heat-absorbing layer,lower vent temperature and upper vent temperature,the highest temperature between phase change materials in a day is 8.5?,and the lowest indoor temperature in a day is6.8?,and the phase change thermal storage wall panel system does not perform heat collection,heat storage,and heat dissipation.(2)Under typical cloudy weather conditions,the indoor temperature,the temperature between phase change materials,the surface temperature of the heat-absorbing layer,the temperature of the lower vent,and the temperature of the upper vent all have obvious rising and falling trends,the maximum temperature between phase change materials in one day is 34.0?,and the temperature curve at the highest point is only maintained for a short time,only some phase change materials have undergone phase change,the lowest temperature of the indoor in one day was 5.6°C.The phase change heat storage wall panel system performed heat collection and partial heat storage during the day and heat dissipation during the night.(3)Under typical sunny weather conditions,the outdoor temperature,indoor temperature,surface temperature of the heat-absorbing layer,lower vent temperature,and upper vent temperature all had obvious rising and falling trends,and the temperature between the phase change materials was maintained between 34.0?and 36.2?during the day,and the indoor temperature was kept above 15.7?throughout the day.The heat dissipation was carried out.The above results show that the phase change material and phase change thermal storage wall panel prepared in this thesis have good solar energy thermal storage capacity and greenhouse room temperature regulation capacity,which can significantly improve the temperature environment required by crops.