Images processing and flow measurement applied to the thermographic analysis of heat-losses in boilers' isolation

This paper suggests a methodology to calculate the thermic flow through waterwall-boiler's home isolated walls, using thermic images. The procedure is based on the provided information by a thermogram and is helped with: the thermogram's range, knowing the camera's FOV, surface's emmisivity and characteristic length, object-to-camera distance, environmental temperature, and the calibration curve that relates grey-levels with temperatures. A software tool to upload and process the information mentioned above was developed. This tool uses a steady-stable unidimentional model of heat transfer to figure the thermic flow; and to calculate the surface's average natural convection coefficient h _c uses heuristic correlations developed for common geometries. To test the technique functioning, the information given by the software tool was compared to the data given by the heat flow meter. In laboratory tests this comparison showed a 6% error range of relative error. The final validation was made on a waterwall-boiler's home isolated walls and the highest error obtained was close to 15%. Regardless the calibration curve was found under laboratory conditions and the empiric correlations to calculate h _c are for isometric surfaces, the methodology presented a good performance. This then is a first step to quantify the global heat losses on waterwall-boiler's home isolated walls.