Numerical Simulation Of Fouling Process On Heat Transfer Surface

Fouling results in tremendous loss to design and operation of heat exchangers and becomes of a major unsolved problem in the heat transfer field, had received widespread attention to the fouling mechanism research. The goal of this thesis would be to simulate the fouling process of heat transfer surface using the numerical heat transfer, the main jobs were as follow:Unstructured collocated finite volume method for Navier-Stokes equations was developed, the pressure-velocity coupling was treated using SIMPLE algorithm and explicit correction step technique was applied to speed the convergence rate, some benchmarked problems for numerical heat transfer such as lid-driven cavity flow, natural convection flow of square cavity and flow around cylinder were simulated to testify the program.According to CaSO4 fouling formation mechanism, a new model was proposed for CaSO4 fouling which took into account the effect of both crystallization and particulate fouling, the suspended particulates in solution was calculated based on the nucleation rate equation. Considering the influence of fouling deposition on flow passage and heat transfer resistance, in view of the fouling formation on bottom heat transfer surface of a rectangular flow channel, the modified mean velocity and realistic heat flux method was suggested, the calculation steps for numerical simulation of fouling formation was concluded.CaSO4 fouling process when its supersaturated solution flow through rectangular flow passage was unsteady simulated, therein forced convection heat transfer was calculated using SIMPLE program and fouling process using fouling model. First, without considering particulate fouling, simulated crystallization growth, obtained the realistic heat flux distribution, wall temperature, fouling/solution interface temperature and deposition rate, then calculated fouling resistance, the results were coincident with the published experimental date. Then the particulate fouling model was introduced, simulated the real CaSO4 fouling process under the combined particulate-crystallization mechanism, the proposed composite model predicted the mean fouling resistance for considering particulate fouling to be 2.44-5.84 times that of without considering, the result showed that the fouling layer in the downstream was thicker than that of upstream, and fouling curves exhibit an asymptotic trends. The influence of velocity, fouling/solution interface temperature and supersaturation on the fouling behavior was investigated, the fouling rate increased as velocity increases when the surface temperature keeps constant, while it decreased as velocity increased when heat flux was unchanged, and the fouling rate increased as surface temperature and supersaturation increases.