An improved Front-Tracking technique for the simulation of mass transfer in dense bubbly flows. (2nd October 2016)

• Record Type: Journal Article
• Authors: Roghair, I.; Van Sint Annaland, M.; Kuipers, J.A.M.
• Is Part Of: Chemical engineering science. Volume 152(2016)
• Page Start: 351
• Page End: 369
• Publication Date: 2016-10-02
• Subjects: Numerical modeling -- Front tracking -- Bubbly flows -- Bubble swarms -- Mass transfer; Chemical engineering -- Periodicals; Génie chimique -- Périodiques; Chemical engineering; Periodicals; Electronic journals; 660
• DOI: 10.1016/j.ces.2016.06.026
• Languages: English
• ISSNs: 0009-2509

Abstract

Abstract: Direct numerical simulation results of mass transfer in dense bubble swarms using a Front-Tracking (FT) model will be presented, where the effect of the gas hold-up has been investigated. The FT method is particularly suited for bubble swarm simulations, since bubbles do not coalesce artificially, but traditional FT techniques often suffer from artificial volume loss of the bubbles. For this reason, a specialized remeshing technique is presented to counteract any occurring volume defects, while keeping all physical undulations on the bubble surfaces unharmed. For the simulation of gas-to-liquid mass transfer, a species transport equation (convection–diffusion–reaction) was coupled to the FT hydrodynamics solver, which was solved on a superimposed refined mesh for higher accuracy. The velocity components have been interpolated to the refined grid using a higher-order solenoidal method. Enforcement of the Dirichlet condition for the concentration at the gas–liquid interface is achieved with an immersed boundary method, enabling the description of gas to liquid mass transfer. Careful validation of the newly implemented model shows satisfactory results. The liquid side mass transfer coefficient in dense bubble swarms, with gas fractions between 4% and 40%, has been investigated using the new model. The simulations have been performed in a 3D domain with periodic boundaries, mimicking an infinite swarm of bubbles. The results indicate that the liquid-side mass transfer coefficient rises only slightly with increasing gas fraction. Abstract : Graphical abstract: Abstract : Highlights: A procedure that enforces volume conservation of dispersed elements for Front-Tracking models was outlined. A mass transfer model, based on convection–diffusion–reaction, was coupled to the Front-Tracking hydrodynamic model. The mass transfer model can be solved on a refined mesh, for which a solenoidal velocity interpolation is outlined. Mass transfer in dense bubble swarms is simulated, for gas fractions up to 40%, showing a small increase in mass transfer coefficient as a function of the gas hold-up.