# Help needed

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 January 26, 2012, 05:18 Help needed #1 Senior Member   Shashwat Join Date: Nov 2011 Posts: 107 Rep Power: 5 Dear all I am new to CFX. I am doing the tutorial 12 flow in a catalytic converter. I have a question in "creating porous domain" As in the tutorial They have introduced Basic setting > fluid and particle definition>Fluid 1>Material> Air Ideal gas My question is 1. Why do they put "Air Ideal gas" instead of porous material honeycomb ceramic material? Thank you Regards Shashwat

 January 26, 2012, 07:07 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,941 Rep Power: 85 The material they define is the fluid. You do not define a material for the cat converter, instead you merely define resistance coefficients.

 January 27, 2012, 03:10 help needed #3 Senior Member   Shashwat Join Date: Nov 2011 Posts: 107 Rep Power: 5 Dear friend I am new to CFX. I am doing the tutorial 12 flow in a catalytic converter. I have a question in "setting initial values" in the catalytic housing How come they set the initial velocity -2.8m/s.? why is not zero along the Z direction? As far as my knowledge is concerned, -ve sign indicates that the flow is in the opposite direction. How did they calculate the initial velocity? Please clarify Thank you Regards Shashwat

 January 27, 2012, 03:41 #4 Senior Member   Christoph Join Date: May 2011 Location: Germany Posts: 182 Rep Power: 9 Do you also read the Tutorial!? That may help 12.6.6. Setting Initial Values A sensible guess for the initial velocity is the expected velocity through the catalyst housing. You can assume incompressible flow and apply conservation of mass to obtain an approximate velocity of 2.8 [m s^-1] through the housing based on the following known information: The inlet velocity: 25 [m s^-1] The cross sectional area of the inlet and housing, which can be determined using the function calculator in CFD-Post: 0.001913 m^2 and 0.024039 m^2 respectively The porosity of the honeycomb structure: 70%

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