Thermal properties of heat exchanger fouling

The heat transfer capabilities of industrial heat exchangers are reduced by the build-up of insulating deposits (fouling) on their surfaces. This has an adverse environmental impact due to the necessary increase in energy consumption and the subsequent depletion of nonrenewable fuel sources. Studies of the microstructure of material obtained from heat exchanger surfaces in pulverised coal combustion plants, highlight their geometrical self-similarity over a range of length scales. We will discuss a methodology for estimating the thermal properties of these materials which utilises these self-similarity properties using fractal analysis and renormalisation. The self-similar microstructure of the fouling materials is captivated by a family of random fractals called shuffled Sierpinski carpets (SSC). The thermal conductivity of the SSC can then be predicted both from its box counting fractal dimension and via a generalised real space renormalisation method. This latter approach also affords an analysis of the percolation threshold of two phase fractal media.