Numerical Simulation on Soot Particle Deposition Distribution Characteristics of Tube Heat Exchangers

An exhaust heat exchanger is an important part of the waste heat recovery system of an internal combustion engine. However, the particulate matter in the diesel engine exhaust will be deposited on the surface of the heat exchanger. As fouling grows, the deposition surface is gradually covered by the fouling layer with low thermal conductivity. This phenomenon will reduce heat transfer efficiency, increase equipment operation costs and maintenance costs, and bring uncertainty to the heat exchanger design. At present, research on the deposition of soot particles from internal combustion engine mostly focuses on the change in the total number of particles deposited on the heat exchanger. Studies on the deposition distribution of the soot particles on the heat exchange surface are relatively scarce. This research can directly reflect the area where in the particle deposition is concentrated, which consequently guides the structure optimization of a heat exchanger. A numerical model is developed to explore the deposition distribution of soot particles in a tubular heat exchanger considering particle adhesion and rebound behavior based on the discrete phase model of the software FLUENT, extended by user-defined functions(UDFs). The particle deposition distribution for different flow rates and particle diameters is examined. The influence of longitudinal pipe spacing on the particle deposition ratio is also explored. Results show that compared with the first two rows of tubes, the third row has the highest deposition ratio(57.8%) because of the fully formed wake region. The particle deposits accumulate primarily in the stagnation region of the first row of tubes and the wake region of each tube. In other words, the particle deposition occurs mainly in areas with low particle velocity and a high probability of collision with heat exchange surfaces. Considering the deposition and heat transfer performance, a tube-spacing value of 1.75 is recommended at different flow rates. © 2021, Editorial Board of Journal of Tianjin University(Science and Technology). All right reserved.