Study On Thermal Insulation Of Silica Aerogels Wall Based On Heat Capacity And Thermal Resistance Network Model

Silica aerogel insulation materials have great development prospects in the field of building energy conservation owning to their ultra-low thermal conductivity,fire-resistant noncombustible and other properties.In this paper,SiO2 aerogel/glass fiber composites were prepared by sol-gel method and ambient pressure drying technology.The micro structure,thermal conductivity,compressive strength and hydrophobic angle of the SiO2 aerogel/glass fiber composites were tested,respectively.The test results are compared with the molded polystyrene,extruded polystyrene,polyurethane foam,and the glass fiber.The building model box experiment was used to test the thermal insulation performance of five kinds of thermal insulation materials,such as molded polystyrene board,extruded polystyrene board,polyurethane foam board,and glass fiber,under the ascending temperature conditions,and experimental data,such as the internal and external surface temperature and the internal air temperature of the box,were obtained.The experimental results showed that the thermal insulation effect of SiO2 aerogel/glass fiber composites is better than the other four thermal insulation materials when the material thickness is the same.Based on the thermoelectricity analogy theory,a 3R2 C heat flow network model for the composites wall was established.The test box experimental data was used to verify the accuracy and feasibility of the model.The results showed that the simulation results of the 3R2 C heat flow network model was consistent with the experimental results,and the error is within 5%.Compared with numerical models,the computation time of the 3R2 C heat flow network model is approximately 0.6% of the computation time of the fluid simulation software,and the computational efficiency was significantly improved.The model was used to research and analyze the effect of the internal and external thermal insulation methods on the thermal insulation performance of the test box under heating conditions and cooling conditions.As a result,it was found that the indoor air temperature of the silica aerogels box,EPS box,XPS box,PU box and glass fiber box was 30.9°C,33.7°C,33.2°C,32.6°C and 33.5°C,respectively,when using external insulation and the temperature was calculated under the heating conditions for 3 hours.And the indoor air temperature of the five test boxes were nearly 35°C while using internal insulation at the same time.The indoor air temperature of the silica aerogels box,EPS box,XPS box,PU box and glass fiber box were 1.2°C,-3.0°C,-1.9°C,-1.3°C and-2.7°C,respectively,when using the external thermal insulation and the temperature was calculated under the heating conditions for 3 hours.And the indoor air temperature of the five test boxes had reached-5.0°C while using internal insulation at the same time.Taking Guangzhou as a typical city in the hot summer and warm winter climate zone,considering the different orientations,different insulation methods(external insulation,internal insulation and sandwich insulation)and different insulation materials(silica aerogel composites and EPS),the thermal characteristics of SiO2 aerogel/fiber composite materials applied in actual building walls were studied by using conventional building wall construction,and compared with the molded polystyrene insulation wall.The results showed that compared with traditional insulation materials,SiO2 aerogels/glass fiber composites have great potential for energy saving in building wall insulation systems.