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UDF for Cp of mixtures

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Old   December 23, 2018, 14:34
Default UDF for Cp of mixtures
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Anshuman Sinha
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I am doing a combustion analysis of Carbon monoxide gas, here I have defined my mixture template as Carbon di-oxide , Carbon monoxide and oxygen.

I have defined the cp of individual species as udf given below :

Code:
#include "udf.h"
DEFINE_SPECIFIC_HEAT(my_user_cp_o2, T) 
{ 
	real cp;
	real x= T;

	
		cp = 1000* ( -2e-15*(pow(x,4.) ) + 3e-11*(pow(x,3.)) - 1e-07*(pow(x,2.) ) + 0.0004*x + 0.8287 );

	return cp; 
}

DEFINE_SPECIFIC_HEAT(my_user_cp_co2, T) 
{ 
	real cp;
	real x= T;


		cp = 1000*(-7e-15*(pow(x,4.) )+ 1e-10*(pow(x,3.) )- 5e-07*(pow(x,2.) )+ 0.001*x + 0.5775 );

	return cp; 
}

DEFINE_SPECIFIC_HEAT(my_user_cp, T) 
{ 
	real cp;
	real x= T;

		cp = 1000*(-3e-16*(pow(x,4.) )+ 9e-12*(pow(x,3.) )- 8e-08*(pow(x,2.) )+ 0.0003*x + 0.9586) ;

	return cp; 
}
the result say invalid cp value for temp = -607.9 K


I have set the individual cp's for CO,CO2 and O2 through the udf in the materials section under mixture materials.

Now in the cp of mixture ( when we click edit on mixture template). I know I have to define cp wrt. composition like y[co2]*cp[co2]+y[o2]*cp[o2] + ...
But how will it be done ?

Will law of mixing do it for me ? or shall I write a new udf for it ? If new udf is to be written then how ?


Why am I getting an error for temp = -602K, as temp less than 0K is not possible.
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