Numerical performance comparison of different tube cross-sections for heat recovery from particle-laden exhaust gas streams

Abstract

Heat recovery from exhaust gas streams is applicable to a wide variety of industries. However, high heat transfer resistance of gases and the presence of entrained particulate matter that readily fouls limits industry uptake of current heat recovery technology. Improvements to standard heat exchanger designs are needed. In this study Computational Fluid Dynamics (CFD) is used to investigate the effect of ten different tube cross-sections on heat transfer resistance, gas flow resistance and foulability. The average wall shear stress around the shape is used to predict foulability and an estimated asymptotic fouling resistance is used to calculate an equivalent fouled Coulburn j factor, jf. CFD results show the best tube for exhaust heat recovery is an elliptical tube closely followed by the flattened round tube. The ellipse shape produced fouled Coulburn j factor, jf values, expressed as a ratio of tube bank friction factor f, over 100% higher than that of standard round tube. A flattened round tube is also promising, given enough spacing between the tubes, and may be the practical economic optimum.