Research On The Numerical Simulation Method Of Exterior Insulation Defects By Infrared Inspection

Infrared thermography has become a commonly used method in the field of construction quality defects inspection. With the infrared thermal imaging detection technique becoming mature, relevant associations and local quality inspection departments has formulated the corresponding testing standards and technical regulations. And the technology research expands from qualitative analysis to quantitative analysis as well. At present, infrared thermal imaging technique for construction quality is mainly divided into three categories according to different objects:construction defects detection, construction energy conservation detection, damp and leakage detection. Besides, it demonstrates three research directions from the aspect of quantitative analysis:numerical simulation, image post-processing and infrared thermal diagnosis. The main work in this thesis is to numerically simulate and analyse exterior wall heat transfer process with heat preservation deficiency and bonding defects outside the EPS plates thin plaster. Thus theoretical evidences and suggestions are provided for on-site inspection of infrared thermography.Based on instructions of detecting thermotechnical defects of external building envelope and bonding defects of external walls decorative surface by the infrared thermal imaging detection technique in the energy saving detection standards for residential buildings, finite element thermal analysis software called ANSYS is adopted in this paper to build heat transfer model under natural conditions for the two types of defects of exterior walls respectively. Then the dynamic process of heat transfer of external walls is simulated numerically in manifold combinational cases of different defect parameters, orientation of walls, seasons etc. After that the paper analyses the influences of above parameters for temperature distribution of exterior walls’surface. Finally, combined with the practical testing conditions of infrared thermography, the thesis concludes the detectability of infrared thermal imager for defects with different parameters and the optimum detection periods of east, south, west and north walls in different seasons. The results can provide recommendations and the basis for heat preservation deficiency and bonding defects by on-site inspection.The main research contents include the following aspects:(1) By introducing the basic theory of infrared thermal imaging technology and analysing the diabatic process of exterior wall, the detection principle of two exterior insulation defects are drawn. Certain calculated modes of important parameters (solar radiation intensity, daily air temperature, comprehensive temperature) make preparations for subsequent calculation of parameters of numerical simulation.(2) According to the basic principle of finite element and steps of transient thermal analysis by ANSYS. the thesis builds the exterior wall models of heat preservation deficiency outside the EPS plates thin plaster and bond hollowing deficiency respectively, and simulates numerically the diabatic process of the two models. In the thermal analysis of diabatic process of exterior insulation deficiency model, by researching impact of temperature shift before the detection day on the calculation results of the detection day and anlysing characteristics of the temperature distribution on exterior surface, the author put forward requirements of temperature shift before the detection day and change regulations of temperature difference on the exterior surface. In the thermal analysis of diabatic process of bond hollowing in exterior insulation deficiency model, by the comparative analysis between comprehensive outdoor temperature and mean value of exterior surface in normal region, the author draws regular patterns of temperature difference on the exterior surface. Finally, by the comparative calculations analysis of two models, it is concluded that the disparity of temperature difference peak value is caused by diverse defect area and thickness.(3) Verify the feasibility and correctness of the corresponding conclusion of the defect model by using external insulation defect experiment with infrared thermography. Prove that defect area and thickness exert an influence on temperature difference peak of the exterior surface by comparing numerical simulation results of measured data and experimental results. Analyse the the main influence factors of errors between experimental and simulation results. Come to an accordant conclusion with Wenhao Huang’s thesis about the bond hollowing defect experiment of cover layer by numerical simulation analysis of the impact bond hollowing defect size on the temperature difference peak, and demonstrate the feasibility of bond hollowing defect model.(4) To further analyze the impact that defect parameters (depth, thickness, area), orientation of walls and seasons having on the temperature distribution of the exterior surface lacking heat preservation, based on the above heat transfer model, the paper simulate numerically from various combinations of circumstancesdefect parameters (depth, thickness, area), orientation of walls and seasons etc., extracte detectable defect area and determine the optimal detection periods of east, south, west and north walls on the typical day in four seasons. According to defect area and thermal defect ranking, determine the detectability of the infrared thermal imager combining actual shooting conditions, thus provide a basis for on-site detection.(5) Simulate and analyse the influences that defect parameters (depth, thickness, area), orientation of walls and seasons having on the temperature distribution of the exterior surface on the basis of heat transfer model of exterior wall with exterior insulation bonding defects. Imitate temperature field of the exterior surface by the auxiliary means of sprinkler cooling. Compared with the the natural condition, temperature difference of exterior surface rising sharply prove that the method is feasible.(6) Summarize the important conclusions in the former chapter and put forward the deficiency in the research.