Analysis of the thermo-hydraulic performance of structured heat transfer surfaces under consideration of particulate fouling using a multiphase Euler-Lagrange approach

Particulate fouling of heat transfer surfaces due to suspended material within the heat exchanger working fluid is still one of the most important problems in heat exchangers. Fouling increases the heat transfer resistance and reduces the effectiveness of heat exchangers which causes higher fuel consumption, maintenance costs and costs due to production loss. Nevertheless, existing fouling models are derived for numerous assumptions and simplifications and are unsuitable for a detailed analysis of fundamental fouling mechanisms. Due to the steadily growing computational resources, the simulation of highly complex processes like particulate fouling using computational fluid dynamics (CFD) becomes more and more important. In contrast to several numerical investigations of heat transfer enhancement methods, CFD studies of structured heat transfer surfaces considering particulate fouling are relatively seldom. Moreover, a extensive analysis of the interaction between local flow structures and fouling deposits using transient, large-scale resolving numerical methods such as LES or hybrid URANS-LES does not exist at this moment. The present study is aimed to fill up this lack of knowledge by introducing a new large-scale resolving multiphase Eulerian-Lagrangian approach into the open source CFD code OpenFOAM which is suitable for CFD studies of heat transfer enhancement methods under consideration of particulate fouling. This method is based on a coupling of the Lagrangian-Particle-Tracking (LPT) and Eulerian approach. Hence, suspended particles are simulated according to their natural behavior by means of LPT as solid spherical particles whereas the carrier phase is simulated using the Eulerian approach. Large Eddy Simulations (LES) are performed for turbulent channel flows combined with a square cavity or spherical dimple (t/D = 0.26, Re = 42000) and foulant particle mass loading ratios up to 0.002 using a dynamic one equation eddy-viscosity turbulence model.