Numerical investigation on ash accumulation characteristics of serrated spiral finned tube heat exchanger in waste heat utilization

Abstract

In this study, a comprehensive loose fouling model is established to investigate the fouling characteristics of fly ash on serrated spiral finned tube heat exchangers. This model considers the energy change during particle collision, the velocity change after particle rebound and slip, and the amplification of fouling time under mixed particle sizes. The results show that the fouling position, morphology, and height obtained by the theoretical model agree well with the experiments. Besides, the serrated spiral fin is the main fouling position due to its high fin ratio and the strong disturbance effect. The 5 μm particles have the highest deposition rate, and fine particles tend to adhere to the second row of finned tubes due to the consumption of initial kinetic energy by the first row. With an increase in fin height by 6 mm, the deposition rate only increases by 1.2 %, while an increase in sawtooth height by 5 mm results in a deposition rate increase of 14.3 %. When the flue gas velocity is less than 7 m/s, finned tubes arranged in a staggered configuration provide the best combination of heat transfer, flow resistance, and anti-ash accumulation performance.