Numerical Simulation Of Growth Characteristics Of Micro-particlate Fouling In Tubes

Urban sewage as an important clean cold and heat source,the waste heat recovery from it can not only improve the utilization of energy,but also protect the environment and save costs,so that human beings can achieve the goal of energy conservation and emission reduction better and faster.However,there is a lack of theoretical guidance in the design of sewage source heat pump.Designers often use fouling factors to consider the existence of fouling,which will produce additional costs and affect the pump efficiency.In this paper,the growth characteristics of silica particle fouling in sewage pipes is studied by numerical simulation,and the correlation formula of the deposition rate of silica particle fouling is deduced,which provides theoretical basis for the design of sewage source heat pump systems.Firstly,this study developed an Eulerian-Eulerian model for predicting the particle deposition rate on heat-exchanger surface based on four deposition mechanisms(Brownian and Eddy diffusion,gravity,turbophoresis,and thermophoretic),and the numerical simulation model was validated by four different cases.Meanwhile,the applicability of five turbulence models in particle fouling prediction was discussed,and RNG k-ε turbulence model was selected for this study.Secondly,the particle fouling model was used to simulate the growth process of silica particle fouling under different conditions,and The effects of fluid velocity,particle concentration,temperature and particle size on the fouling growth characteristics were investigated.The simulation results show that with the increase of velocity,the deposition rates of turbophoresis,Brownian and Eddy diffusion increase,while the deposition rates of gravity and thermophoretic decrease,Among them,the change of turbophoresis deposition rate is the largest,while the other three changes are very small,which leads to the increase of total deposition rate.With the increase of particle concentration,the deposition rate caused by the four deposition mechanisms increased linearly,so the total deposition rate increases,resulting in the increase of fouling thermal resistance.Temperature has little effect on the deposition of particle,with the increase of inlet temperature or wall temperature,the deposition rate of gravity,turbophoresis,Brownian and Eddy diffusion increase,the absolute value of thermophoretic deposition rate decreases with the increase of inlet temperature,while increases with the increase of wall temperature.When the particle diameter increases,the gravity deposition rate,turbophoresis deposition rate and the absolute value of thermophoretic deposition rate increase,while Brownian and Eddy diffusion deposition rate has a small reduction,so the total deposition rate increases.Lastly,based on the simulation data,the correlation between particle fouling deposition rate and flow rate,temperature,concentration,particle size is deduced by using the dimensionless analysis method,and the calculation value of the correlation is compared with the simulation value.The comparison results show that the correlation can better calculate the particle fouling deposition rate.