ANSYS FLUENT 12.0 Theory Guide - 8.3.3 Using the Non-Premixed Model with Flue Gas Recycle

8.3.3 Using the Non-Premixed Model with Flue Gas Recycle

While most problems you solve using the non-premixed model will involve inlets that contain either pure oxidant or pure fuel ( or 1), you can include an inlet that has an intermediate value of mixture fraction ( ) provided that this inlet represents a completely reacted mixture. Such cases arise when there is flue gas recirculation, as depicted schematically in Figure 8.3.4. Since is a conserved quantity, the mixture fraction at the flue gas recycle inlet can be computed as

$\dot{m}_{\rm fuel} + \dot{m}_{\rm recyc} f_{\rm exit} = (\do... ... fuel} + \dot{m}_{\rm ox} + \dot{m}_{\rm recyc}) f_{\rm exit}$

(8.3-1)

$f_{\rm exit} = \frac{\dot{m}_{\rm fuel}}{\dot{m}_{\rm fuel} + \dot{m}_{\rm ox}}$

(8.3-2)

where $f_{\rm exit}$ is the exit mixture fraction (and the mixture fraction at the flue gas recycle inlet), $\dot{m}_{\rm ox}$ is the mass flow rate of the oxidizer inlet, $\dot{m}_{\rm fuel}$ is the mass flow rate of the fuel inlet, $\dot{m}_{\rm recyc}$ is the mass flow rate of the recycle inlet.

If a secondary stream is included,

$f_{\rm fuel, exit} = \frac{\dot{m}_{\rm fuel}}{\dot{m}_{\rm fuel}\ + \dot{m}_{\rm sec} + \dot{m}_{\rm ox}}$

(8.3-3)

and

$p_{\rm sec, exit} = \frac{\dot{m}_{\rm sec}}{\dot{m}_{\rm sec} + \dot{m}_{\rm ox}}$

(8.3-4)

**Figure 8.3.4:** Using the Non-Premixed Model with Flue Gas Recycle

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