COMSOL 6.4 - Reactions

Reactions

Use the node to account for the consumption or production of species through chemical reactions. Define the rate expressions as required.

Domain Selection

From the list, choose the domains on which to define rate expression or expressions that govern the source term in the transport equations.

Several reaction nodes can be used to account for different reactions in different parts for the modeling geometry.

Reaction Rates

The list shows all the Chemistry interfaces that are coupled to the current mass transport interface. The coupling conditions for the Chemistry interfaces are:

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Active

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(under the section) is cleared

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(under the section) set to the current mass transport interface

The reaction rates can be taken from a coupled Chemistry interface automatically or by specifying a rate expression Ri (SI unit: mol/(m3·s)) for species i:

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With a interface selected, the species mass sources will be set to the corresponding reaction rates in the according to the table. In the case of partial coupling, the mass sources for the uncoupled species will be set to 0.

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. Enter a value or expression in the field. Note that if you have the Chemistry interface available, provided with the Chemical Reaction Engineering Module, the reaction rate expressions can be generated automatically and picked up from the lists. For an example, see the application Fine Chemical Production in a Plate Reactor as linked below.

Reacting Volume

This section is only available when the Mass Transport in Porous Media property is available and selected. See www.comsol.com/products/specifications/ for more details on availability.

When specifying reaction rates for a species in porous media, the specified reaction rate may have the basis of the total volume, the pore volume, or in the case of using the volume of a particular phase (applicable when modeling an unsaturated porous medium).

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For , the reaction expressions, in mol/(m3·s), are specified per unit volume of the model domain (multiplied by unity).

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For , the reaction expressions, in mol/(m3·s), are specified per unit volume of total pore space. The reaction expressions will be multiplied by the domain porosity, εp. (εp equals unity for nonporous domains).

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For , the reaction expressions, in mol/(m3·s), are specified per unit volume of liquid in the pore space. The expressions will be multiplied by the liquid volume fraction θl. (θl equals the porosity (εp) on Porous Medium domains).

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For , the reaction expressions, in mol/(m3·s), are multiplied by the gas volume fraction θg = εp − θl. θg equals 0 for Porous Medium domains.

Heat Source

The heat source will be defined as reaction heat from whole Chemistry if the list is set to a coupled chemistry interface, otherwise it is defined as the specified value (SI unit: W/m3).