The mass balance is nonlinear:

,

where

is the concentration of product

(

),

is the reactant feed concentration (mol),

and

are the pre-exponential factors for the forward and reverse reactions (1/s),

and

are the activation energies for the forward and reverse reactions (cal/mol),

is residence time (s),

is the ideal gas constant (J/[mol K]), and

is temperature of the CSTR (K).

The energy balance is linear and has two terms that correspond to (1) the energy needed to change the feed temperature to the reactor temperature, and (2) the energy removed or added by heat transfer to a cooling/heating fluid, which is at a constant temperature of 310 K.

=

,

where

is the volumetric flow rate (

),

is the density of the bulk fluid (

),

is the mass heat capacity of the feed (cal/[kg K]),

and

are the temperatures of the feed and coolant (K),

is the heat transfer coefficient (

),

is the heat transfer area (

), and

is the heat of reaction (cal/mol).

As the feed temperature increases from a low value, the reactor temperature increases until the reactor reaches a temperature above which three steady-state solutions are possible. The upper and lower solutions are stable, and the middle solution is unstable. The operating conditions of the reactor depend on how the reactor is started up. As the feed temperature increases further, a temperature is reached above which only one solution is possible, and this has a high conversion.

Varying the heat transfer coefficient changes both the slope and intercept of the energy balance line, and this can change the number of steady-state solutions. Increasing the pre-exponential factor for the reverse reaction changes the mass balance curve, and the maximum conversion decreases as the equilibrium conversion become less than one.

The screencast video at [1] shows how to use this Demonstration.