(281c) Microscale Fluid Flow Visualization in CIJR and MIVM and CFD Model Validation Using Confocal μ-LIF

The process of producing nanoparticles via precipitation requires supersaturation due to rapid mixing effect at the smallest scale. This effect can be achieved in microscale reactors such as confined impinging jet reactor (CIJR) and multi-inlet vortex mixer (MIVM) at high Reynolds numbers where strong turbulence can be observed. With the help of computational fluid dynamics (CFD), ?experimentless? design of such reactors can be possibly realized. Previously, the CFD model, DQMOM-IEM, developed by the Fox group at Iowa State University has been compared not only with the conversion of 2,2-dimethoxypropane (DMP) that was obtained experimentally by the Prud'homme group at Princeton University [1,2], but also with the microscale particle image velocimetry (μ-PIV) results [3,4]. The model predicted both the conversion of DMP and the velocity field accurately.

First, in order to extend the validation and to get an intuitive understanding of the mixing, the pH indicator phenolphthalein is employed to visualize the impinging jets. One stream of CIJR contains NaOH and phenolphthalein and the other HCl and phenolphthalein (two streams for each solution in MIVM). The fluid turns fuchsia once these two streams come into contact, which illustrates the molecular scale mixing. Since previous experiments were done for Re_j = 600 and 1000 (defined as the inlet Reynolds number), where the flow is turbulent, both of them are also chosen in this work for comparison. Qualitatively, these experimental results give satisfactory agreement with simulations.

Next, the concentration field is measured using the microscale laser induced fluorescence (μ-LIF). Up till this point, only passive scalar mixing is accomplished with confocal technology since it has the advantage of optical sectioning which makes the LIF measurement more accurate. The fluorescent dye rhodamine 6G is used as the passive scalar and the flow is turbulent. The mixture-fraction mean and variance obtained from the micromixing model are compared to that from μ-LIF. Correspondingly, the large-scale segregation (LSS) and small-scale segregation (SSS) are analyzed.

[1] Y. Liu and R. O. Fox. CFD Predictions for Chemical Processing in a Confined Impinging-Jets Reactor. AIChE Journal. 2006(52):731?744.

[2] Y. Liu, C. Cheng, Y. Liu, R. K. Prud'homme and R. O. Fox. Mixing in a Multi-Inlet Vortex Mixer (MIVM) for Flash Nano-precipitation. Chemical Engineering Science. 2008(63):2829?2842.

[3] Y. Liu, M. G. Olsen and R. O. Fox. Turbulence in a Microscale Planar Confined Impinging-Jets Reactor. Lab on a Chip. 2009(9):1110?1118.

[4] J. C. Cheng, M. G. Olsen and R. O. Fox. Investigation of Fluid Dynamics in a Multi-Inlet Vortex Reactor by Computational Fluid Dynamics & Microscopic Particle Image Velocimetry. Applied Physics Letter. (In Press)