多孔二氧化钛强化的相变材料储热机理研究

Investigation of the thermal storage mechanism of porous TiO_(2) enhanced phase change materials

相变材料在热能存储技术中的应用往往受到形状不稳定、低导热等限制。基于钛酸四丁酯的水解反应,通过一步法原位合成了基于二氧化钛的新型定型相变材料。相变材料的定型过程无须任何固化剂和有机溶剂,且无任何污染排放。此外,定型相变材料表现出理想的形状稳定性和防泄漏性能,并具有较高潜热(115 J/g)。进一步研究发现未完全干燥的样品(SP)出现异常的双峰相变行为。以干燥时间为变量,通过对SP进行质量损失测试、组分分析等研究后发现,SP中残留的非石蜡液相物质和二氧化钛的协同效应促进了(110+111)晶体结构的生长,从而增大了结晶过程中石蜡的平均晶面间距,进一步导致被封装的石蜡结晶过程中(110+111)晶面与020晶面比例失衡,最终在差示扫描量热法(DSC)曲线中出现异常的双峰相变现象。

The application of phase change materials in thermal energy storage technology is often limited by unstable shape and low thermal conductivity.In the present work,a novel phase change materials for in situ encapsulation of titanium dioxide were synthesized by a one-step method based on the hydrolysis reaction of tetrabutyl titanate.The encapsulation process of phase change materials does not require any curing agents or organic solvents and does not emit any pollutants.Moreover,the material exhibits excellent shape stability and leak resistance,and has a high latent heat(115 J/g).Further study revealed anomalous bimodal phase change behavior in the incompletely dried samples.Taking the drying time as a variable,it was found that the synergistic effect of the residual nonparaffinic liquid phase material and titanium dioxide in the sample promoted the growth of(110+111)crystal structure,which increased the average crystallite spacing of the paraffin waxes during the crystallization process,and further led to an imbalance of the(110+111)crystallite to 020 crystallite ratio during the crystallization process of encapsulated paraffin waxes.This further leads to an imbalance in the ratio of the(110+111)crystal face and the 020 crystal face during the crystallization process of the encapsulated paraffin wax,and eventually an abnormal bimodal phase transition phenomenon appears in the differential scanning calorimetry(DSC)curve.