基于有机绝热材料微结构的热湿传递机理及保冷性能研究

The application of high performance thermal insulation is one of the most efficient ways to limit heat loss to the ambient and is of great importance to reduce total energy consumption for refrigeration and cryogenic systems. It also plays a significant role on the service lifetime of refrigeration system and the ambient air quality. The meso-structure characteristics of materials are key factors to reduce heat gain and moisture intrusion from ambient to the insulation systems. However, the impacts of meso-structure characteristics on the insulation properties are difficult to be quantified which limit the accuracy of simulation models used for performance prediction. According to the framework of multi-scale method, this project aims to further study the impacts of meso-structure on the insulation performance and optimize the meso-structure for improvements on the thermal performance and the moisture resistance of organic thermal insulation. In this project, the applicant proposed a novel method by combining 1H-NMR technique and NaCl tracing to reveal the mechanism of moisture transport in the commonly used organic thermal insulation. Fractal-LBM method will be considered to simulate the heat and moisture transfer in meso-scale and the effective transport coefficients, such as thermal conductivity and diffusivity, will be inversely determined from the meso-scaled models. According to multi-variable optimization method, these coefficients will further correlate with main meso-structure parameters, which will be identified from sensitivity analysis. These meso-scaled effective coefficients provide a possible and effective way to connect the heat and mass transfer in multi scales (from meso to REV) so that the meso-structure characteristics will be fully considered in the model for better accuracy. The significance of this project can be summarized as follows: by considering multi-scale mechanism in the analysis of heat and mass transfer, the accuracy of the model will be effectively improved and it will solve the “bottleneck” problem that commonly exist in current models. The mechanism of heat and moisture transfer in the closed-cell insulation will be revealed in the meso-scale and the impacts of main structural parameters on the overall performance of thermal insulation will be studied in order to provide some optimal structures on the improvement of organic thermal insulation materials with low heat gain and moisture intrusion.

应用高性能的绝热材料是降低制冷低温系统能耗最有效的措施之一，对系统寿命及环境空气品质也存在重要影响。材料的微结构是影响保冷性能的关键因素，也是限制预测模型精度的难点问题。本项目基于跨尺度的建模框架和方法，对有机绝热材料保冷性能的提升进行研究和优化。项目创新性的提出联合运用核磁共振氢谱技术与示踪测试方法探索湿分在闭孔有机绝热保冷材料中的输运机理，辨识湿分在复杂多孔体中的传输路径与分布形态，通过分形-格子玻尔兹曼方法对导热及扩散等宏观输运现象进行介观表述，并通过全参数辨识与多变量寻优的方法实现等效输运系数的微结构表征，实现跨尺度模型的高精度与高效求解。本项目以跨尺度的方式将机理研究与应用对象紧密结合从而突破热湿耦合模型精度受限的“瓶颈”问题，阐明有机绝热材料内热湿输运过程的新机理和微结构对保冷性能的影响机制，提出以微结构调控优化保冷性能的新途径，为制冷系统的节能运行提供保障。

应用高性能的绝热材料是降低制冷低温系统能耗最有效的措施之一，对系统寿命及环境空气品质也存在重要影响。材料的微结构是影响保冷性能的关键因素，也是限制预测模型精度的难点问题。本项目基于跨尺度分析方法，对有机绝热材料保冷性能的提升进行研究和优化，为材料结构改进提供理论依据。.项目研究阶段的主要研究成果及其科学意义如下：（1）首次对有机闭孔绝热材料中的湿分输运路径进行可视化辨识，联合运用核磁共振氢谱技术与示踪测试方法明确两类有机闭孔绝热材料中的湿分传输途径：酚醛的湿分输运路径包括发泡不均匀而形成的骨架裂缝、泡壁针孔结构以及破损结构，PIR的湿分输运路径则主要为破损的泡腔，以及可能存在的少量骨架间孔道。（2）首次提出热湿同步测试技术，通过实验明确酚醛和PIR的热湿特性，结合实验现象从孔道结构、表面化学特性等机理上解释其热湿变化规律：酚醛在处于热湿环境的初期更易形成内部液桥增强传热，后期湿分多存于冷表面，使导热系数呈现先快速增长后稳定的趋势，质量含湿量为90.9%时样本导热系数为初始值的1.29倍；PIR则由于表面泡孔中气体的影响，以及内部热湿传递优先路径形成的较慢，导热系数呈现先增长后减少再缓慢增加的趋势，质量含湿量为30.7%时样本导热系数为初始值的1.31倍。（3）首次将细微观结构特征与多孔绝热材料的热湿传递相关输运系数联系，并通过算法实现不同尺度间的交互，构建跨尺度热湿传递模型，分析孔隙率、闭开孔体积比、偏移比、孔径、接触角等结构因素对热湿输运系数及传热传湿过程的影响程度与规律；研究发现，孔隙率仍为影响热湿传递过程的主要因素，随着孔隙率的增加，其他结构参数的影响程度逐渐增强，影响幅度可达25%以上，但在低孔隙率、低饱和度条件下，闭开孔体积比、偏移比和接触角将改变孔隙内的液相分布方式，而对热湿传递初始阶段的影响较大，接触角相较于其他因素其影响较小。基于主要细微结构参数的影响机制，以酚醛样本为例，提出优化其热湿特性的结构方案。