The Numerical Simulation Of CaSO₄ Fouling Process On Heat Transfer Surface

Fouling deposition is ubiquitous phenomenon in operation process of heat exchangers, which produces additional heat resistance, having a serious influence on the performance of the heat exchanger, and giving rise to a huge waste of energy and economic losses. There are many different kinds of foul, and the formation mechanism is complex. In order to have a more in-depth understanding of fouling deposition process, the crystallization fouling process on heat transfer surface was simulated and analyzed based on the computational fluid dynamics method by taking CaSO4 supersaturated solution as an example.Firstly, this paper stated fouling model from fouling deposition model and removal model, give the calculation methods of the foul layer thickness and fouling resistance, and a method for surface temperature determining to have better understand the depositional mechanism, and provide the basis for the numerical simulation. Then the classical methods of numerical simulation "virtual fouling" was introduced, and a new method "no virtual fouling" was come up with to improve its shortcomings.Secondly, the method "virtual fouling" was used to simulate the fouling process of CaSO4 supersaturated solution in rectangular channel under constant heat flux condition. The results were compared with the experimental data to verify the correctness of the model. The temporal variations of deposition mass rate, removal mass rate, fouling thickness, and fouling resistance on the heated surface were analyzed, and the temperature distribution within the foul layer was studied. Then the influence of these parameters on fouling process were analyzed such as heat flux density, fluid inlet temperature, inlet velocity and fluid concentration.Finally, the method of "no virtual fouling" was used to simulate the fouling process in the rectangular channel, and the temperature and velocity distribution in flow domain during the fouling process were obtained. Then this method was applied to simulate the crystallization fouling process in convergent-divergent tube under constant heat flux, and the temperature and velocity distribution were analyzed.