Simulation of a Non-Newtonian Dense Granular Suspension in a Microfluidic Contraction

Paper in proceeding, 2013

The success of a solder paste jet printer is based on an uninterrupted flow of fluid, specifically dense fluid suspensions, through a series of ducts inside the printing head. It is well known that the flow of dense suspensions is prone to jamming and sedimentation effects, both of which could entail detrimental failure modes in the printing heads. A thorough understanding of the fluid dynamics of suspensions as they flow through ducts and connections is of utmost importance. The purpose of this study is to propose a novel simulation framework and to show that it captures the main effects such as mass flow and partial jamming in a cylindrical duct test configuration. The granular suspension is a generic solder paste with solder particles immersed in a flux. The simulations are performed in the multi-phase flow solver IBOFlow. A two fluid model is used for the granular suspension and the discretization is done an Euler-Euler framework. The averaged momentum equations from Enwald et al. (1996) are solved together with the common continuity equation generating a shared pressure field. Explicit constitutive equations for the interfacial momentum transfer and particle pressure are employed. To capture the shear thinning effects of the non-Newtonian suspensions the standard Carreau rheology model is used. To study how the fluid flow affects the local volume fraction and partial jamming in the duct, simulations are performed for different applied pressure drops ranging from one to five bars. For both particle pressure models, the resulting mean bulk velocities are compared with experiments with good agreement, and partial jamming is observed. Hence, it is concluded that the proposed framework is suitable to model and simulate the granular suspension in a micro fluid contraction.