Master of Science
Chemical and Biochemical Engineering
The key to controlling the quality of liquid dispersion coated films lies in the particle distribution in the flow field. The control of particle dispersion in the film can also empower the optimization of the process operation. Therefore, a numerical simulation of a solid-liquid suspension in the dip coating (free withdrawal) process using the finite element method for the fluid flow has been developed. The neutrally buoyant suspension is considered as a Newtonian fluid with a concentration-dependent viscosity. A continuum constitutive equation is employed based on the diffusive flux model in twodimensional flow. The main purpose of this study is used to assess the shear-induced migration phenomenon in free-surface of concentrated suspension and the effects of the coating bath walls near the substrate to explore the particle distribution in the flow field. Other parameters studied include particle concentration, particle radius, and withdrawal speed. The simulation results show a highly nonuniform distribution of particles in the coating film and recirculation regions. The suspension flow model predicts regions of low and high particle concentration compared to the average concentration. Higher concentration region presents at the middle and outer part of the coating film, varied depending on the parameter. Lower concentration region presents at the moving substrate region. Certainly, the nonuniform shear flow and the shape of the interface induces particle migration in concentrated suspension in the dip coating process.
Moghadasi, Mahdieh, "Investigation and Modeling of the Dip Coating for Dispersions with Near Wall Effects" (2019). Electronic Thesis and Dissertation Repository. 6040.