Experimental Study On Hygrothermal Performance Of Inorganic Fiber And Organic Closed-Cell Insulation

Thermal insulation is one of the most effective methods to reduce the heating and cooling loss through building envelopes.Optimizing the thermal performance of thermal insulation is the foundational work of improving the thermal performance of building envelope systems and plays an important role in reducing energy consumption of buildings.Based on the experimental study of hygrothermal performance of thermal insulation,this paper proposes a novel test method and visual identifications of moisture transport paths to investigate the moisture transport mechanism and its impact on the heat transfer procedure.The work of this thesis help provide a set of reference data,as well as an analysis method,to accurately predict the thermal performance of building envelope systems.To improve the shortcoming that exists in current test method,which is "sampling before testing" during the measurement of the hygrothermal performance in thermal insulation,this study proposes a simultaneous test method by considering variations of heat and moisture transfer in the same time period to obtain more accurate hygrothermal properties.The entire specimen is divided into metering region and sampling region for thermal conductivity measurement and moisture content measurement respectively.The simultaneous variation of hygrothermal properties can be obtained by calculating the mapping relationship between these two regions.Based on the measuring principle of the method,an experimental facility is constructed accordingly.After the systematic calibration,the temperature regulation range of the testing system is 278K~323K,±0.2K;the humidity regulation range is 15%~100%,±2%;and the accuracy of the thermal conductivity measurement is 5%.Based on this testing system,the measurements of two types of thermal insulation are conducted.Results indicate that for fibrous insulation aerogel blanket,the moisture content increases rapidly under high temperature and humidity gradient.After 23 and 16 days testing,the thermal conductivity of these two samples are around 3 times and 3.3 times of the initial value,with the moisture content of 29.0% and 32.1%.Moisture ingress may detach aerogel particles from fibers and lead to irreversible damage to the aerogel blanket.For close-cell thermal insulation phenolic,after 28 days testing,the moisture content increases rapidly to 90.9% due to the capillary channels among the closed cells.The thermal conductivity of the sample shows a rapid increase during initial stage and then reach a stable level,which is 1.3 times of the initial value.For the visual identification of moisture transport paths,NaCl tracer-scanning electron microscopy,stereomicroscope and atomic force microscope are utilized to identify the transport paths based on liquid water;and magnetic resonance imaging technology is utilized to identify the transport path based on liquid water and water vapor.Results indicate that for close-cell thermal insulation phenolic,the through-pinhole on the cell walls and the capillary channel among closed cells are the main channels of moisture ingression,which have a great influence on the thermal properties.The damaged cells on the surface are also one of the main reasons for the increase of moisture content in the samples.