Study On Preparation Of Multiple Composite Phase Change Materials And The Applications In Building Energy Saving

Application study of phase change materials and phase change energy storage technologies in the field of building energy saving is an effective way to achieve low energy consumption as well as create the condition for solar, wind and low-cost clean energy applications in heating and air-conditioning systems. In practical applications, however, phase change energy storage building materials present the problems of durability ascribed to thermal cycling that produce leakage with which the effect of heat storage is reduced; problems of the higher price of phase change materials and encapsulate technology for which exorbitantly high cost of unit thermal energy storage be brought about; and the problems of making energy storage body more lightweight and smaller in the context of considerable heat storage. These three problems restrict the desired effect in the process of phase change energy storage utilized in building materials.In this paper, based on the comprehensive research status at home and abroad, aim at the problems of phase change materials in practical application, cheap resources of paraffin used as phase change raw materials is combined with common building materials. Around five aspects: multiple composition of paraffin phase change materials, choosing of porous matrix absorbing materials, encapsulation and form-stable of composite phase change materials, preparation of phase change energy storage building materials and situation applications, the main study are process as follows:1. Several paraffin phase change materials are composited according to ternary eutectic theory system, through both temperature-time cooling curve test and DSC thermal performance test, the best ratio of 3# paraffin to n-tetradecane to solid paraffin is 1:2:7, the phase change temperature and enthalpy are 24.14 ℃ and 159 J/g. Thermal performance is significantly better than that of solid-liquid binary complex system.2. Expanded perlite and vitrified microsphere are chosen as carriers for adsorption, the adsorption of paraffin in vacuum is about 3~4 times than that in natural for the same time, and the adsorption capacity of vitrified microsphere is greater than expanded perlite, the scanning electron microscope(SEM) shows that the PCM can fill the pore structure. Taking styrene-acrylic emulsion and EVA emulsion as encapsulate materials, the encapsulate effect of styrene-acrylic emulsion is better through leaking rate test The mass lose rate of paraffin/vitrified microsphere form-stable phase change materials is far less than paraffin/ vitrified microsphere which is encapsulated by styrene-acrylic,the mass loss rate is only 4.42% after 30 thermal cycling. So paraffin/ vitrified microsphere form-stable phase change materials which is encapsulated by styrene-acrylic emulsion is chosen to prepare phase change energy storage mortar. The compressive strength of paraffin/vitrified microsphere phase change energy storage mortar is 5.35 MPa and the strength loss is 10.85%, when compared with the blank sample, the thermal conductivity decreased to 76.83%. The phase change temperature range is 22~26℃ which is consistent with the prepared ternary composite phase change material. The specific heat capacity is about 2 times of the ordinary mortar. Conclusion is phase change composite material can improve the insulation performance of mortar.3. Select out shale ceramsite of 15~20mm and 5~10mm diameter, the adsorption capacity of which in nature for 24 h is only 15.2% and vacuum adsorption paraffin for 2h can reach 2 times of that in natural for 24 h. The minimum leakage rate of paraffin/ ceramsite form-stable phase change materials is 2.8% after 30 thermal cycling when encapsulated by epoxy resin, so it can effectively prevent the leakage problem of phase change material of ceramsite in thermal cycling. The phase change temperature range of encapsulated paraffin/ ceramsite phase change concrete is 25~29℃,the thermal conductivity is 0.2156 W / m·K, the compressive strength is 14.0MPa, the loss rate of the compressive strength after 30 thermal cycling is 21.07%.4. Through establishment of the physical model to simulate the use of phase change building materials in the roof structure. As the phase change mortar plate is used for external insulation layer, the internal temperature of housing model taken 60 min to raise from 20.1℃ to 29.6℃, which is about 1.5 times of the ordinary mortar, and the temperature is lower than the internal of model after the same time. While the phase change mortar plate used for ceiling layer, the same temperature range is about 2 times of that used for exterior insulation layer, and the internal temperature of housing model decreases 3.4 ℃ compared with it for exterior insulation layer, the temperature control effect is better. Through ANSYS Workbench software, the situation of which phase change mortar plate used for ceiling layer is simulated, the results show that: when 40 ℃ constant heat source applied to the external environment, the temperature in process of heat flow from roof layer to interior dropped to 22.15℃ and the heat flow from 24267 W / m2 down to 2696.8~5393.1 W / m2, which suggests that phase change mortar can absorb heat into their own latent, then reduce heat flow and room temperature, and consistent with the physical simulation test results.