Experimental and numerical investigation of soot deposition on exhaust heat exchanger tube banks

The exhaust heat exchanger is widely used in waste heat recovery systems (WHR) to recover energy from exhaust gas. However, fouling of the exhaust heat exchanger due to the deposition of soot particles reduces the heat transfer efficiency. In this investigation, a deposition performance experimental system and an improved CFD-based soot deposition prediction model were proposed to investigate the deposition characteristics on tube banks in exhaust heat exchangers. Firstly, the test bench is introduced in detail, and the combination of air heater and soot generator was applied in the test bench to provide the particle flow with specified parameters. Then, considering the effect of thermophoresis, diffusion, inertial impaction, and removal mechanisms, an improved prediction model was proposed. Compared with the traditional two-fluid model (TFM), the thermal-hydraulic performance of exhaust heat exchangers is calculated by CFD software in this model, so it is suitable for all dividing wall type heat exchangers. Afterwards, the influence of particle diameter and tube spacing on the tube bank during the 4 h deposition process was experimentally or numerically investigated. It was found that the comprehensive performance of the tube bank is deteriorated by about 0.45%-1.85% after 4 h of soot deposition. Besides, the deposition amount on the tube bank with smaller tube spacing (1.25D) is lower.