# Simulations of reactive flows in COMSOL

Submitted by Burgess on Mon, 10/10/2022 - 18:34

Original Title: Simulating Reacting Flows in COMSOL In recent versions of COMSOL Multiphysics ®, we have added several new multiphysics interfaces, decomposed the basic physics interfaces into separate interfaces, and predefined the coupling between multiphysics fields in the "Multiphysics" node of the model tree. This update perfectly combines the flexibility of the basic physical field interface with the convenience of predefined multi-physical field coupling. Study of fluid flow and reactions in gases and liquids The Chemical Reaction Engineering, CFD, and Plasma modules contain various forms of equations to describe the transport of chemicals in concentrated solutions, including Maxwell-Stefan equations and mixed-average models. For a concentrated solution, the model equation must take into account the interaction between all substances in the solution, while the model for a dilute solution involves only the interaction between the solute and the solvent. The above two descriptions are illustrated in the schematic below. Dilute solution (left) and concentrated solution (right). Dilute solution mainly includes solute and solvent, as well as the interaction between different solvents. A concentrate solution contains all that interaction between the substances. The velocity field of a concentrated solution is defined as the sum of the fluxes of each species I,rotovap distillation, accompanied by the interactions of the species: Expand the full text (1) Where n is the flux in kg/ (m m ² 2; s) and ρ is the density in kg/m m ² 3;. For a dilute solution, the velocity field depends on the velocity of the solvent: (2) From the above figure and equation (1), we can see that the mass transfer and fluid flow in the concentrated solution are tightly coupled. Use the new "reactive flow" multiphysics interface in COMSOL Multiphysics ® In previous versions of COMSOL Multiphysics, the Reaction Flow interface was a stand-alone multiphysics interface with its own domain settings and boundary conditions,decarboxylation after extraction, specifically designed to handle flow coupling and the transfer and reaction of chemicals. Because all settings are predefined, the interface is easy to use. However, on the other hand, such predefined physical field interfaces lose some flexibility to some extent. Suppose that when you want to make more drastic changes to the dense mass transfer equation and the flow equation separately, the predefined multiphysics interfaces are not adequate for this, and you must define the problem by adding both types of physics interfaces separately, and then manually create the multiphysics coupling. When using the new Reactive Flow interface for strong solution problems, jacketed glass reactor ,cbd crystallization equipment, you can change the transport equation and fluid flow settings separately to handle such tightly coupled problems. The coupling itself is defined in the Multiphysics node. Many operations can be performed with this capability, such as changing from laminar to turbulent flow, or changing the transport model from the Maxwell-Stefan equation to a mixed-average model. Let's take a look at how this can be implemented in the model tree and in the "multi-physics" node setup. As shown in the screenshot below, all the regular nodes in this basic physical interface allow the user to modify them at any time after the couplings are predefined in the "Multi-Physical" node. The predefined coupling controls the mass flux and agrees with the continuity equation of the flow when the mass flux of all substances is summed. In this way, the two sets of equations are fully coupled in both directions. Model tree with the Reactive Flow multiphysics node enabled. Not only can we choose the physical field interfaces to be coupled, but we can also change the flow model to include turbulent reacting flows. Compared with the previous multi-physical field interface, this method has greater flexibility while retaining ease of use. Another advantage of the new Reactive Flow multiphysics interface is in the Research node. By solving the fluid flow equations, we can obtain a more accurate initial guess of the total flux. In Step 2, we have only solved the mass transfer problem, where the velocity field is calculated from the previous fluid flow equations.