# How to input enthalpy of formation for a reaction?

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• Last Post 04 March 2019
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sooraj546 posted this 04 March 2019

 Sir,Problem explanation:I have few reactions happening. I wanted to define constant heat of formation/consumption of each reaction/enthalpy for each reaction. I have used specific heat UDF to define the cp for each material there h is a pointer to calculate enthalpy rt. so far i haven't changed it to any value as i need to input for a particular reaction not for each species. I know the heat of reaction is defined in Fluent as the sum over the components of formation enthalpy multiplied with the birth /decay rate of particular species#include "udf.h"
DEFINE_SPECIFIC_HEAT(my_user_cp, T, Tref, h, yi)
{
real cp=2000.;
*h = cp*(T-Tref);
return cp;
}Final intention:If we define a reaction under species transport and give its reaction rate through UDF then fluent will automatically calculated the heat of formation/consumption rt as cp*ΔT for ideal gas....................................... so whats the solution for this?I need to input a heat source term as (rate of each reaction *ΔH*...etc)W/m3. I already have calculated data as constant ΔH values for each reaction. So if i add a source term for heat source it will be conceptually wrong rt........as it will considered itself and i am adding it as well.WHATS THE SOLUTION FOR THIS

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abenhadj posted this 04 March 2019

Check energy source term due to reaction from theory guide. It dépens on the formation enthalpy of each component and it's reaction rate.

Best regards,

Amine

sooraj546 posted this 04 March 2019

sir i have checked it....................but i want to input constant enthalpy of reaction not species.........................as i have mentioned earlier..........is there any way

abenhadj posted this 04 March 2019

How does it look? The only way here will be via a source Term UDF and does not make a sense here.

Best regards,

Amine

sooraj546 posted this 04 March 2019

i actually asked about this elaborately in last post but you said no need to add source term .................it calculates automatically etc.......

abenhadj posted this 04 March 2019

Please mark the real answer as the answer which really helped you.

Best regards,

Amine

abenhadj posted this 04 March 2019

Yes no need it is done automatically. But if you want to do something different you require source terms,

Best regards,

Amine

sooraj546 posted this 04 March 2019

so that what i am asking so it will calculate automatically and if i add a source term then a summation of both will be there rt................which is wrong? i want just from the source term only..............

sooraj546 posted this 04 March 2019

so if i give h=0 in udf below and add the my required source term with will it work ...........................?         So finally in total only my source term will be there

#include "udf.h"
DEFINE_SPECIFIC_HEAT(my_user_cp, T, Tref, h, yi)
{
real cp=2000.;
*h = cp*(T-Tref);
return cp;
}

abenhadj posted this 04 March 2019

No. Specific Heat UDF is to adjust specific heat.

Again you need to be thorough in your description.

Best regards,

Amine

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