Experimental Study on Heat Transfer Characteristics of Hollowing Defect Areas on Building Facade

Infrared detection is more and more widely used in the field of non-destructive testing of buildings to detect whether there is a defect on the surface of the building facade. In many cases, it is necessary to obtain more information about the defect, such as the depth of the defect, so as to evaluate the severity of the defect and repair. The theoretical formula of hollowing defect depths was derived in this paper based on the heat transfer characteristics of the intact and defective areas on the building facade, and the influence of defects with different shapes, sizes and cavity thicknesses on the temperature distribution of the building facade was summarized quantitatively. Firstly, the theoretical formula of the hollowing defect depth and the factors affecting the distribution of the temperature gradient on the building facade excited by external thermal source was derived and restricted by the boundary condition. Secondly, three sets of physical building facade models that contained hollowing defects with different shapes, sizes and cavity thicknesses were fabricated and designed, and the experimental platform was built. The infrared thermograms and the temperature characteristic curves of the hollowing defect in a natural light environment were obtained and fitted according to the temperature differences of the defective area, while analyzing the influence of the size, shape and cavity thicknesses on surface temperature distribution. Finally, the theoretical formula of the defect depth that is applicable to the building façade was validated through the experimental simulation of 14 forms of hollowing. The experimental results demonstrated that the revised formula of defect depth is consistent with the actual defect depth, and the three-dimensional positioning of the hollow drum defect of the building facade can be effectively carried out and combined with the defect size taken from the obtained infrared thermal image.