Validation of a 2D CFD Model for Hydrodynamics' Studies in CIJ Mixers

Abstract

A 2D model of a confined impinging jets mixer having the same geometry of the mixing chamber of a Reaction Injection Moulding, RIM, machine is introduced for the flow field simulation in a Computational Fluid Dynamics, CFD, code. From the CFD simulations the flow field structures and dynamics are clearly established. In addition, the numerical parameters affecting the 2D model simulations are studied, setting for each parameter a validity range. The 2D model is validated and used in the study of some operational parameters: the Reynolds number, the Froude number and the momentum ratio between the opposed jets. The validation of the CFD simulations is also made by comparison with experimental results. The limitations of the 2D model, for simulating the actual 3D flow field, are assessed; from the 2D/3D comparison, it is clearly shown that the introduced model can predict the main flow field features.

On the 2D nature of flow dynamics in opposed jets mixers

“…This Reynolds number of 150 for 3D geometries is closely related in terms of flow regimes with the 2D case where Re = 300. On the comparison of 2D and 3D transition Reynolds numbers in opposed jets mixers see Santos et al…”

“…27 The flow in opposed jets is mainly affected by the dynamics in the plane of the jets, a plane defined by jets' axis and mixing chamber's axis. As a consequence, the flow in CIJs has been extensively studied from 2D physical models that were validated and compared with actual 3D physics in previous works of Santos et al 28,29 The first opposed-jets mixers were cylindrical with two opposed round jets 30 a geometry typically referred to as CIJs mixers/reactors. The first studies on CIJs were focused in the mixing process for Reaction Injection Moulding (RIM) processes, where CIJs typically have chamber diameter 1 cm and diameter of the injectors from 1 to 3 mm.…”

“…This Reynolds number of 150 for 3D geometries is closely related in terms of flow regimes with the 2D case where Re 5 300. On the comparison of 2D and 3D transition Reynolds numbers in opposed jets mixers see Santos et al 28 In Figure 4, isosurfaces of the z vorticity component are used to show the overall rotation of the flow in the CIJ. The imaging of 3D flows is quite complex, and so only some information on the 3D flow can be obtained from Figure 4.…”

“…In the 3D CIJs the opposed jets impinge each other and after the fluid spreads radially from the impingement point, while in the 2D CIJs the jets bend toward the outlet before contacting and so there is no deceleration of the jets upon impinging each other. 28 The radial spreading of the jets in the 3D CIJs causes the flow dynamics to dissipate at a distance D from the impingement point, after which point the flow is fully developed with a parabolic velocity profile. In the 2D CIJs the fact that the flow is constrained in one dimension hinders dissipation mechanisms promoting a dynamic evolution of vortices throughout the mixing chamber at least up to the outlet of simulated domain, 4.5 D. So, the 3D CIJs have a faster reduction of scales when the jets impinge, but the flow dynamics dissipates in a shorter region of the mixing chamber.…”

A study on the micromixing performance in microreactors for polymer solutions

“…All experiments were performed at room temperature (RT: 296 ± 2 K). It is worth noting that the Reynolds number and the momentum ratio ( R M ) of two solutions have been claimed as two of the main factors affecting the mixing performance in mixers or reactors in Reaction Injection Modeling (RIM) . Thus, experimental conditions were adjusted to assure relevant requirements ( R M = 1 and Q 1 /Q 2 = 1).…”