(366e) Analyzing Reactive Mixing Processes Using Computational Fluid Dynamics and Z-Transform

Computational fluid dynamics (CFD) is used in the chemical industry to analyze the performance of mixing and reactive processes. CFD simulations complement experimental studies by making accessible measurements that are physically difficult to obtain, and they can also be used in lieu of experiments to conduct investigations where there are safety concerns or equipment and capital limitations. The long computational time required to perform good quality CFD simulations of complex systems is often a necessary cost. Motivated by the desire to reduce computational time and enhance the modeling toolset, we have in recent years demonstrated the use of CFD with z-transform, the discrete-time counterpart of the Laplace transform, to provide a powerful, flexible, and time-saving approach for simulating and analyzing the dynamics of mixing processes. Examples that we have illustrated include the open-loop response of a lumped-parameter mixing process, the open-loop response of a distributed-parameter mixing process, the closed-loop response of an unstable mixing process, and the general deconstruction and characterization of mixing processes [AIChE Annual Meeting Papers 2014-354913, 2015-404589, 2016-449915, 2017-486416, and 2018-538613].

In our latest work, we apply the z-transform technique to CFD simulations of reactive mixing unit operations. By postprocessing the CFD simulation data in z-space, we can construct transfer functions for the transported reactive chemical species that are, by design, functionally equivalent to the linear finite-volume discretized equations that comprise the full-scale CFD model. These transfer functions can then be used to generate additional data for analysis with much less computational effort. In this presentation we illustrate this technique using an example of a continuous stirred-tank reactor (CSTR) with a first-order chemical reaction and show that the results obtained using faster z-transform technique are practically identical to the results obtained using fully detailed CFD simulations.