11.1. Honeycomb Monolith Reactor Calculations

The Honeycomb Monolith Reactor is a special case of a general plug-flow reactor, where user input parameters describing the honeycomb geometry are used to automatically calculate the available surface area for gas-surface reactions. In the Ansys Chemkin User Interface, the Honeycomb Monolith Reactor is represented as a separate reactor icon.

When this reactor model is chosen, Ansys Chemkin provides a special parameter-entry panel that allow users to specify parameters that describe the honeycomb monolith and catalyst loading conditions. These parameters are then automatically converted into corresponding plug-flow parameters by the Chemkin Interface utilities. Table 11.1: Honeycomb Monolith Reactor Parameters shows the parameters with the default units that are entered by the user on the Honeycomb Monolith Reactor Panel tabs.

Table 11.1: Honeycomb Monolith Reactor Parameters

Parameter

Default Units

Cells Per Square Inch,

1/in2

Cell Wall Thickness,

mil or 1/1000 in

Diameter,

cm

Length,

cm

Cell Size, or the width of the individual cell channel for a square channel

cm

Metal Surface Area,

cm2 /g catalyst

Metal Weight,

g catalyst

Metal Dispersion,

%

Pressure Gradient,

dyne/cm3


Using this information, Ansys Chemkin performs the following conversions behind the scenes, to set up the PFR model using honeycomb monolith parameters:

  1. Calculates the internal surface area of the PFR, , where is the active internal surface area per unit length of the plug-flow reactor (cm2 /cm):

    (11–14)

  2. Calculates the external heat transfer area per unit length (cm2 /cm), :

    (11–15)

  3. Calculate the cross sectional flow area (cm2), :

    (11–16)

    (11–17)

  4. Set up a pressure profile to represent the user-specified pressure drop. In this case we assume a linear profile from the beginning of the channel to the end of the channel, with the starting point set at the reference pressure specified in the main reactor panel, and the ending pressure set as:

    (11–18)

When a user chooses units different from the default, the units conversion will be performed automatically, as with other Ansys Chemkin parameters.

Once these parameters have been calculated, the simulation proceeds as described for the general Plug-flow Reactor.