heat of combustion

841911 · July 11, 2020, 01:29

Hi,
i have e reaction for Propane and heat of combustion is 24.2 MJ/kg.
I don't know how to set 24.2 MJ/k in CFX?
Can you hlp me?
Tnx

aero_head · December 24, 2020, 23:48

Hello Mohsen,

Please check out this thread, I believe it goes over what you are asking:
change heat of combustion

In sum, ANSYS CFX does not use the heat of combustion, or heat of fuel explicitly anywhere in the combustion model. It uses thermodynamic properties of the material. The ANSYS CFX implementation of the energy equation does not use any split of the enthalpy material definition.

For these properties (and you can consult a Thermodynamics book),

Sample reaction: A * Propane + B * O2 + C * N2 --> D * CO2 + E * H2O + F * N2

heat of combustion formula as a function of the enthalpies defined as:

h_material = h_material_ref + Cp_material (T - T_ref)

Once you work out the heat of combustion, it should be a function of the reference enthalpy of your type Propane and the adiabatic flame temperature for the value you have.

Gerry Kan · December 25, 2020, 12:01

Dear Mohsen:

The 24.2 figure you posted is some kind of heating value (as an aside for hydrocarbons it should be closer to 50 MJ/kg fuel, you should check it again).

That said, you don't specify heat of reaction in a reaction. What you need are the (temperature dependent) heats of formation for each of the species involved in your reaction mechanism, as part of their thermophysical properties. The energy released will be summed up across all species according to your mechanism and local thermodynamic state.

Hope that helps, Gerry.

July 11, 2020, 01:29	heat of combustion	#1
841911 New Member mohsen Join Date: Jul 2020 Posts: 8 Rep Power: 5	Hi, i have e reaction for Propane and heat of combustion is 24.2 MJ/kg. I don't know how to set 24.2 MJ/k in CFX? Can you hlp me? Tnx

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Error - Solar absorber - Solar Thermal Radiation	MichaelK	CFX	12	September 1, 2016 05:15
Heat Release vs. Apparent Heat Release // Comparison with GT Power	MFGT	CONVERGE	10	August 17, 2016 02:38
Which type of heat transfer's model AVL-Fire use in internal combustion engines?	amin_u50	AVL FIRE	0	May 13, 2014 12:02
Constant velocity of the material	Sas	CFX	15	July 13, 2010 08:56
Combustion with heat transfer and cooling	KamilSobczak	FLUENT	0	June 16, 2010 09:28

December 24, 2020, 23:48		#2
aero_head Senior Member Kira Join Date: Nov 2020 Location: Canada Posts: 435 Rep Power: 8	Hello Mohsen, Please check out this thread, I believe it goes over what you are asking: change heat of combustion In sum, ANSYS CFX does not use the heat of combustion, or heat of fuel explicitly anywhere in the combustion model. It uses thermodynamic properties of the material. The ANSYS CFX implementation of the energy equation does not use any split of the enthalpy material definition. For these properties (and you can consult a Thermodynamics book), Sample reaction: A * Propane + B * O2 + C * N2 --> D * CO2 + E * H2O + F * N2 heat of combustion formula as a function of the enthalpies defined as: h_material = h_material_ref + Cp_material (T - T_ref) Once you work out the heat of combustion, it should be a function of the reference enthalpy of your type Propane and the adiabatic flame temperature for the value you have.

December 25, 2020, 12:01		#3
Gerry Kan Senior Member Gerry Kan Join Date: May 2016 Posts: 347 Rep Power: 10	Dear Mohsen: The 24.2 figure you posted is some kind of heating value (as an aside for hydrocarbons it should be closer to 50 MJ/kg fuel, you should check it again). That said, you don't specify heat of reaction in a reaction. What you need are the (temperature dependent) heats of formation for each of the species involved in your reaction mechanism, as part of their thermophysical properties. The energy released will be summed up across all species according to your mechanism and local thermodynamic state. Hope that helps, Gerry.