How to use variable value in CEL expression correctly.

Goenitz · September 16, 2019, 10:36

Hi all,

I am doing a catalyst reaction simulation in a 20 x 3.1 x1 mm geometry (x,y,z).

Catalyst start at 8mm from inlet and last till 12mm. To calculate pressure of methane, in a mixture name MSR, I am using these expression.

MSR.CH4.molf*pabs
areaAve(MSR.CH4.molf)@Catalyst*pabs

The first expression I guess taking bulk value of methane in 3D domain of catalyst region like 4x3.1x1mm whereas 2nd expression is taking avg value of methane at surface name 'Catalyst' (4x1 mm).

Problem is I think both expressions are not valid as reaction only take place at catalyst surface and not in bulk 3D domain. Also, as methane reacts with oxidant so its value decreases so taking avg of the value is not good assumption.

P.S
1. both expression give different results (5% difference).
2. Though i apply the expression as source at Catalyst surface (so expression is applicable to surface only) but it calculates the value of bulk CH4 mole fraction in 3D if I use first expression, I think.

Goenitz · September 16, 2019, 10:43

In other words I want to use local methane mole fraction at Catalyst which is varying as reaction is proceeding.

Opaque · September 16, 2019, 11:44

The first expression is what you want.

The local value for each variable in the expression at the evaluation location, say face, element, point, etc.

September 16, 2019, 10:36	How to use variable value in CEL expression correctly.	#1
Goenitz Member Abdullah Arslan Join Date: Apr 2019 Posts: 94 Rep Power: 7	Hi all, I am doing a catalyst reaction simulation in a 20 x 3.1 x1 mm geometry (x,y,z). Catalyst start at 8mm from inlet and last till 12mm. To calculate pressure of methane, in a mixture name MSR, I am using these expression. MSR.CH4.molfpabs areaAve(MSR.CH4.molf)@Catalystpabs The first expression I guess taking bulk value of methane in 3D domain of catalyst region like 4x3.1x1mm whereas 2nd expression is taking avg value of methane at surface name 'Catalyst' (4x1 mm). Problem is I think both expressions are not valid as reaction only take place at catalyst surface and not in bulk 3D domain. Also, as methane reacts with oxidant so its value decreases so taking avg of the value is not good assumption. P.S 1. both expression give different results (5% difference). 2. Though i apply the expression as source at Catalyst surface (so expression is applicable to surface only) but it calculates the value of bulk CH4 mole fraction in 3D if I use first expression, I think. Last edited by Goenitz; September 16, 2019 at 10:37. Reason: addition

September 16, 2019, 11:44		#3
Opaque Senior Member Join Date: Jun 2009 Posts: 1,880 Rep Power: 33	The first expression is what you want. The local value for each variable in the expression at the evaluation location, say face, element, point, etc. Goenitz likes this.

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September 16, 2019, 10:43		#2
Goenitz Member Abdullah Arslan Join Date: Apr 2019 Posts: 94 Rep Power: 7	In other words I want to use local methane mole fraction at Catalyst which is varying as reaction is proceeding.