**1. Introduction**

Modeling of chemical reactors attempts to solve both conservation (mass, energy, and momentum) and chemical kinetics equations [1]. The complexity of the mathematics involved can be drastically reduced by considering that convection dominates the diffusion, by assuming a unidimensional scenario or by simplifying the momentum transport equations [2]. Nevertheless, these assumptions may oversimplify the mathematical model by neglecting mixing problems. Mixing plays a fundamental role in reaction engineering. For instance, the

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kinetics, the molecular weight, and the composition of polymers can be altered due to local concentration gradients as a consequence of bad mixing [3].

In this study, a batch chemical reactor is analyzed. This type of reactor is defined as a closed and spatially uniform system where the chemical species are transformed only as a function of time. The transformation of chemical species can be quantified by following any physico‐ chemical property associated with either reagents or products. During free radical polymeri‐ zations, the viscosity of the medium increases dramatically while products are formed [4]. The kinetics of polymerization can be followed from the change of viscosity.

Rapid computational development has made the numerical analysis of phenomena associated with stirred tanks easier [5]. For example, through CFD, Patel [6] studied the mixing process on a continuous stirred tank reactor and how the thermal polymerization of styrene is affected.

Computational analysis in stirred reactors has to consider at least two models: one for turbulence and the other for stirring. The turbulence model describes the random and chaotic movement of a fluid [7], while the stirring model describes the displacement of the fluid as a consequence of the local movement of mechanical parts.

The study of batch reactors with a tracer is the basis for understanding flow behavior [8]. Tracer evolution curves allow to identify regions with turbulence, dead zones, recirculation cycles, closed circuits, or even to determine the mixing time of the reactor [9, 10].

In this work, a tracer test was used to validate a mathematical model. The mixing process was analyzed by using both the experimental and simulated behavior of the tracer. The experi‐ mental kinetics of polymerization was obtained by a multiparametric nonlinear regression of viscosity-time data.
