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Simultaneous test and visual identification of heat and moisture transport in several types of thermal insulation

Guo, Haijin, Cai, Shanshan, Li, Kun, Liu, Zhongming, Xia, Lizhi, Xiong, Jiazhuang
Energy 2020 v.197 pp. 117137
aerogels, cooling, foams, heat transfer, insulating materials, liquids, magnetic resonance imaging, moisture diffusivity, permeability, scanning electron microscopy, thermal conductivity, water content
The utilization of thermal insulation is one of the most effective methods to reduce the heating and cooling loss through building envelopes. However, moisture ingress driven by the pressure gradient across the insulation may lead to a variation of the effective thermal conductivity, which highly deteriorates the thermal performance of building envelopes. In order to investigate moisture transport mechanism and its impact on the heat transfer procedure, a novel simultaneous test method based on the modified guarded hot box is proposed to investigate the variations of the moisture content and the effective thermal conductivity of thermal insulation, besides, several possible visual identification methods are applied to analyze the moisture transport paths. Based on the proposed methods, both aerogel blanket and organic foam are investigated on the variations of hygrothermal properties. Results indicate that compared to the foam insulation, the moisture content has a greater impact on aerogel blankets with the thermal conductivity increase to 3 times of the initial values. Both scanning electron microscopy (SEM) combined with crystal tracer and magnetic resonance imaging (MRI) are utilized to identify the moisture transport paths of phenolic and polyisocyanurate foams. Pinholes and capillary channels are two main paths for liquid permeation into phenolic.