# Need help:about energy equation in CFX

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 June 14, 2009, 22:45 Need help:about energy equation in CFX #1 New Member   Stein Join Date: Apr 2009 Location: Shanghai in China Posts: 11 Rep Power: 10 Sponsored Links In CFX,two kinds of energy equation has been provided,i.e.Thermal energy equation and Total enthapy equation.SO ,my question is about two equations as follows? Firstly:In theory ,two equations are equal,but why CFX provides these two options.What conditions can these two equations be used. Secondly:In CFX_help documentation,only total enthapy equation for muti-component condition has been presented and described .So,does it mean only total enegy equation can be applied for muti-component,but Thermal energy eqaution not. Thirdly.If I use Thermal energy equation to simulate combustion ,is there any reaction heat source term in this equation.Or,I wonder if combustion model is activated ,CFX will add heat source term to the equqtion automaticly? Finnally.I hope someone can give me detalied explanation about the difference between these two equation and If I use total enthapy equation to simulate combustion ,is it all right?

 June 15, 2009, 02:32 #2 Senior Member     George Join Date: Mar 2009 Location: Birmingham, UK Posts: 257 Rep Power: 11 the two energy models are not the same and nowhere in the documentation is saying that check the combustor totorial to learn how to setup combustion. if the reactions you want are not in the standard libary you need to provide cfx with kinetic data in an nutshel use total energy if you have high speed flows or phase change __________________ Top 4 tips 1. Knowledge is everything and Ignorance is dangerous. 2. Understand your limitations and try to eliminate them. 3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window. 4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials

 June 15, 2009, 09:34 #3 New Member   Stein Join Date: Apr 2009 Location: Shanghai in China Posts: 11 Rep Power: 10 In theory,energy equation has a few representation styles,i.e.temperture as variable,thermal energy ,static ehthalpy ,or total enthalpy as variable and so on. Also, these styles can be transformed to each other,so they are actual equal in theory.But when they present in CFD,they become not the same,and should be used in certain condition,why? Particularly, in CFX ,only total enthalpy equation has been derived and described in multi-component part of HELP documentation,does it mean thermal energy cant be used to modeling multi-component flow? And combustion actually can be treated as multicomponent reaction flow.So,the total enthalpy equation should be used to combustion modeling,isn't it? At last ,I wanna know if thermal energy equation is used to model combution,is there reaction heat source term in thermal energy eqaution or just a eqaution without source term like total enthalpy eqaution.

 June 24, 2009, 20:44 #4 New Member   Stein Join Date: Apr 2009 Location: Shanghai in China Posts: 11 Rep Power: 10 Someone help me answer this question ,Thank you

July 2, 2009, 22:31
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 Originally Posted by Stein Someone help me answer this question ,Thank you

The thermal energyeqn is just the total energy equation minus the mechanical energy eqn.

The reaction heat release is included. Why would they not be?

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