Enhancing the RIM process with pulsation technology: CFD study
Multi-scale and/or multi-disciplinary approach to process-product innovation
CFD & Multiscale Modelling in Chemical Engineering (T3-4P)
Keywords: RIM, chaotic mixing, T-jet mixer, oscillation and pulsation
Enhancing the RIM process with pulsation technology: CFD study
Ertugrul Erkoç1, Ricardo J. Santos1, Madalena Dias1,2, José Carlos B. Lopes1,2*
1Labaratory of Separation and Reaction Engineering, Chemical Engineering Department, Faculdade de Engenharia da Universidade do Porto, Portugal.
2Fluidinova-Engenharia de Fluidos S.A., Portugal
* Corresponding author
T type mixers, where two opposed jet streams impinge each other in a confined mixing chamber have a wide range of applications, mainly for the production of polyurethanes in Reaction Injection Molding, RIM, as well as in micro-mixers applications. The flow regime inside the chamber can be oscillatory or self-sustainable chaotic. In self-sustainable chaotic flow regimes, the jet streams engulf each other in evolving vortices throughout the mixing chamber; and in oscillatory flow regimes both streams flow segregated throughout the mixing chamber due to the low amplitude of flow oscillation, which is not sufficient to break the segregation plane between the streams. In self-sustainable chaotic flow regimes the vortices formation is associated with strong jets oscillations (Teixera et al. 2005) that present frequencies around typical values, while the oscillatory flow regimes present low amplitude oscillations with very well defined frequency. Erkoç et al. (2006) reported the usage of dynamic measurements of static differential pressure signal between the two impinging jets for the determination of oscillations typical frequencies for both flow regimes.
The flow field structures occurring at self-sustainable chaotic flow regimes are the main mixing mechanisms in the RIM process, as shown in Santos et al. (2005). On the other hand, the efficiency of mixing in such type of processes is crucial for the quality of the product as shown from the polymerization works of Kolodziej et al. (1982 and 1986), and thus the importance of maintaining a self sustainable chaotic flow regime in the mixing chamber. Although the first studies of Malguarnera and Suh (1977) reported that to establish a self-sustainable chaotic flow regime, the Reynolds number has to be above a certain value and the momentum ratio of the jets has to be equal to one, Erkoç et. al. (2006) showed that even when these conditions are satisfied, the continuous operation of RIM at self-sustainable chaotic regime is not assured, as for the same conditions, both oscillatory or self sustainable chaotic regime can be observed.
Besides the natural oscillation of the flow at chaotic regime, the use of force pulsations of the feeding streams can enhance mixing (Ni, et al., 2003). If the natural/non-forced frequencies of oscillation of the flow are known, the process of forcing mixing can be enhanced in various ways: by increasing the amplitude of the natural frequency; by inducing multiple frequencies, which break the typical flow field structures; or at least aid/forcing the natural system oscillations through pulsation in order to prevent transient situations where convective mixing patterns may not occur under short periods.
Once the typical frequency values are known for a sustainable chaotic regime for certain conditions, in this study, the enhancement of mixing by maintaining a self-sustainable chaotic flow regime by pulsation will be shown by 2D CFD simulation for three different cases where either both of the jets are pulsed in phase and out phase, or only one jet is pulsed with a typical frequency. The effect of pulsation will be assessed from frequency analysis of the flow field dynamic simulations, since Santos (2003) clearly established the connection between typical flow frequencies and mixing mechanisms and scales.
1. Erkoç, E., Santos, R.J., Nunes, M.I. and Lopes, J.C.B., Mixing Dynamics Control in RIM Machines, 19th International Symposium of Chemical Reaction Engineering, Potsdam, Germany, (2006)
2. Lopes, J.C.B., Santos, R.J., Teixeira, A.M. and Costa, M.R.P.F.N., Production Process of Plastic Parts by Reaction Injection Moulding, and Related Head Device, World Intellectual Property Organization, WO 2005/097477 (2005)
3. Kolodziej, P., Macosko, C.W. and Ranz, W.E., The Influence of Impingement Mixing on Striation Thickness Distribution and Properties in Fast Polyurethane Polymerisation, Polymer Engineering and Science, 22, 388-392 (1982)
4. Kolodziej, P., Yang, W.P., Macosko, C.W. and Wellinghoff, S.T., Impingement Mixing and its Effect on the Microstructure of RIM Polyurethanes, Journal of Polymer Science, 25, 2359-2377 (1986)
5. Malguarnera, S.C. and Suh, N.P., Liquid Injection Molding I. An Investigation of Impingement Mixing, Polymer Engineering and Science, 17, 111-115 (1977)
6. Ni, X., Mackley, M.R., Harvey, A.P., Stonestreet, P., Baird, M.H.I. and Rama Rao, N.V., Mixing Through Oscillations and Pulsations - A Guide to Achieving Process Enhancemnets in the Chemical and Process Industries, Transactions Institution of Chemical Engineers, 81, 373-383 (2003)
7. Santos, R.J., Mixing Mechanims in Reaction Injection Moulding - RIM. An LDA/PIV Experimental Study and CFD Simulation, PhD Thesis, Universidade do Porto (2003)
8. Santos, R.J., Teixeira, A.M. and Lopes, J.C.B., Study of Mixing and Chemical Reaction in RIM, Chemical Engineering Science, 60, 2381-2398 (2005)
9. Teixeira, A.M., Santos, R.J., Costa, M.R.P.F.N. and Lopes, J.C.B., Hydrodynamics of the Mixing Head in RIM: LDA Flow-Field Characterisation, AIChE Journal, 51, 1608-1619 (2005)
See the full pdf manuscript of the abstract.
Presented Tuesday 18, 13:30 to 15:00, in session CFD & Mutliscale Modelling in Chemical Engineering (T3-4P).
