CFD Online Discussion Forums - DPM

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DPM - Solid reaction

Hello world.

I'm trying to simulate a solid reaction inside an ash particle.
Therefore I am using the Discrete Phase Model (DPM).
Nothing special so far, DPM works fine.

Let's consider this:
I want to apply the DPM on a converged simulation of a power plant.
So I am using the DPM without interaction with the continuous phase.
All variables inside the domain are solved, therefore I have the whole zoo of species concentrations at hand.

The most important species to me is oxygen. Why?
Because I want to simulate this reaction:

+ 0.5

$\rightarrow FeO$

Fe and FeO are part of the mineral ash inside the particle.
So I am tempted to define the volume fraction of my particle with two User Defined Scalar:

Code:

P_USER_REAL(p,0) = 1.0

P_USER_REAL(p,1) = 0.0

These two values correspond to 100% Fe and 0% FeO at the beginning of the caluclation.

Typical laws for the propagation of such species are

$\frac{dX}{d \tau} = K (1-X)$

where

and $\tau$ corresponds to the volume fraction of the species and time.

is some coefficient.

Now there is my problem:
The species volume fraction inside the particle are 1 for

and 0 for

.
The application of these numbers to the above law will lead to zero reaction (because 1 - X = 1 - 1 = 0). This can't be right.

The obvious reason? Oxygen!
I think I need to include the oxygen into my considerations.
The reaction will only take place in an oxygen environment.
Remember: The oxygen is part of the allready calculated solution inside the domain.

What I am not sure about is the connection between my definition on the particle itself (the User Defined Scalars) and the oxygen concentration in the domain.

The volume

-concentration of the system containing my particle and oxygen will be less than 1 ...

I'm not sure how to approach this.
How can I tell if stoichiometric conditions apply?
(How do I identify the conditions at all?!)
What happens if there is less/more oxygen than needed?

Hope I made myself clear.
Feel free to answer. Any help is appreciated.

thats an intersting simulation
can you post ur udf codes here
i want to have a look at them

Quote:

Originally Posted by sega (Post 250123)

+ 0.5

$\rightarrow FeO$

Fe and FeO are part of the mineral ash inside the particle.
So I am tempted to define the volume fraction of my particle with two User Defined Scalar:

Code:

P_USER_REAL(p,0) = 1.0

P_USER_REAL(p,1) = 0.0

These two values correspond to 100% Fe and 0% FeO at the beginning of the caluclation.

Typical laws for the propagation of such species are

$\frac{dX}{d \tau} = K (1-X)$

where

and $\tau$ corresponds to the volume fraction of the species and time.

is some coefficient.

Now there is my problem:
The species volume fraction inside the particle are 1 for

and 0 for

Your fomular is similar to the first-order of volatile release in coal combustion. The X doesn't mean the fraction of Fe left in the solid, but means that the Fe yield. On the contrary, (1-X) means Fe left in the solid. Therefore, at the beginning, the 1-X=1, which will let you get largest reaction rate. When the Fe burns up, 1-X=0, the reaction rate will be zero.

Quote:

Originally Posted by sega (Post 250123)

+ 0.5

$\rightarrow FeO$

Fe and FeO are part of the mineral ash inside the particle.
So I am tempted to define the volume fraction of my particle with two User Defined Scalar:

Code:

P_USER_REAL(p,0) = 1.0

P_USER_REAL(p,1) = 0.0

These two values correspond to 100% Fe and 0% FeO at the beginning of the caluclation.

Typical laws for the propagation of such species are

$\frac{dX}{d \tau} = K (1-X)$

where

and $\tau$ corresponds to the volume fraction of the species and time.

is some coefficient.

Now there is my problem:
The species volume fraction inside the particle are 1 for

and 0 for

In my opinion, you'd better correlate the coefficient K with the O2 concentration so as to include the O2 effect.