Laser optical Measurements and numerical Investigations of Macro- and Micromixing in stirred Vessels

Today, increasing energy costs require effective processes, especially in chemical and pharmaceutical industries. Particularly, energy-intensive mixing processes offer high potential for optimization. Despite great efforts of research mixing of liquid-liquid components is not completely predictable. To construct mixing systems, empiricism is used rather than basic knowledge. Local mixing quality is a crucial parameter influencing the economics of such processes. Because of this interaction the interest of investigations concentrates on the measure of local mixing quality in regard to the macroscopic energy inserted mostly by stirrers. In case of a superimposed chemical reaction, complete mixing on molecular scale is required. The prediction of the local composition on molecular scale of a multicomponent system is not possible for complex geometries in mixing processes. A review of available models for mixing processes is given by Baldyga and Bourne (1999). The interaction between stretching, diffusion and reaction at small scales is described by Ottino (1994) in a lamellar model. Muzzio et al. (2003, 2002) extended a one-dimensional model to the complex flow in stirred tanks. Anderson et al. (2002) presented an extended mapping technique for chaotic flows in a journal bearing flow. Gollub et al. (2003) experimentally determined the mixing for a two-dimensional timeperiodic flow exhibiting chaotic mixing. Despite the progress in predicting reactive mixing there is still a need for experiments, visualizing the local distribution of inert and reactive tracers with high spatial and temporal resolution. Laser induced fluorescence has proven to be a suitable measurement technique by Kling and Mewes (2003). The visualization of passive scalars indicates the convective mixing process (Villermaux et al. (1996), Distelhoff and Marquis (2000), Guillard et al. (2000)). In viscous mixing applications stretching and folding occur simultaneously at different rates in each portion of the flow, creating complex, layered structures. A seminal paper concerning the concept of chaotic advection has been published by Aref (1984). Reactive tracers which are pH-sensitive are used for measuring the micromixing indirectly by Bellerose and Rogers (1994) and Hong et al. (2002). In T-shaped micro-mixers the transport phenomena on different scales are investigated by means of pH-sensitive tracers using scanning methods by Hoffman et al. (2006). Van Vliet et al. (2000) used also a laser scanning method for investigating three dimensional concentration fields.