# Understand a CEL expression

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 February 26, 2018, 16:11 Understand a CEL expression #1 New Member   ofer d Join Date: Dec 2017 Posts: 2 Rep Power: 0 Hello, I am trying to understand how this fire combustion expression works: if(x<20[m]*0.04689*t^2/20000[s^2],0.02 [kg m^-3 s^-1],0 [kg m^-3 s^-1]) So far i only understood that alpha*t^2=Q is the fire growth rate, (not sure why we divide by Q?) And that 0.02 is mass burn rate over a fire domain of 20mX2mX0.5m. How does the if condition works? Thanks

 February 26, 2018, 16:45 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,728 Rep Power: 143 In english, the expression says: If node x location is less than 20 metres*0.04689*time (in seconds)^2/20000[seconds^2] (so a quadratic in time in x direction), then return 0.02 kg/m^3 per second (so that sounds like some mass per unit volume being generated), otherwise do nothing. Read the CFX reference guide for more details on the if statement. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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