Teaching Nonideal Reactors with CFD Tools
Abstract
In this paper, a computational fluid dynamics (CFD) code (Fluent) was used to illustrate important concepts regarding residence time distribution (RTD) theory. The case study adopted considers isothermal laminar flow through 2-D reservoirs of different geometries (various length/height, L/H, ratios), and a tracer step input is simulated for RTD determination. From the steady-state solution, quasi-stagnant zones are easily identified, particularly for high flow rates (or, more rigorously, high Reynolds numbers) and for low L/H ratios. In some cases, the fraction of dead volumes amounts to values as high as 7 0%. For high L/H ratios, one approaches the theoretical RTD for laminar flow between parallel plates. Transient simulations are also very useful because they allow "visualization" of the evolution of tracer concentration fronts, which animation is available on our web site. The RTD obtained allows students to predict a reactor's performance, either in steady-state or transient regime. Such information can also be obtained directly from Fluent by simulating the injection of a reactive feed stream. The use of a commercially available CFD tool is illustrated to be advantageous, as it allows students to easily visualize and understand the involved concepts, namely flow pattern and behavior/diagnosis of nonideal reactors.