about mixture fraction,the 3rd time
 

Hello, everyone. First many thanks for jdc's help. In jdc's last time response (http://www.cfd-online.com/Forum/main.cgi?read=32145), he told me the problem will be in determining Q and Cp. To my understanding, The Q (heat realese per unit mass of fuel)and Cp (special heat capacity)can be assumed constant and can be found in the book about thermodynamic. Am I right? Thanks

Note: following is the detail about my question on mixture fraction and jdc's answer. question-----------------

Hello, everyone, First many thanks for versi and jdc's help. Last time I post a question about mixture fraction. At that time I did not describe the problem clearly, I beg your pardon. I want to simulate a diffusion flame with irrreversible infinite fast chemical approximation. So I think I can get the temperature and mass fraction only from the mixtrue fraction Z;

Z=(f-f_ox)/(f_fu-f_ox), f=s*Y_fu-Y_ox; where Y_fu, Y_ox is mass fraction of the fuel and oxidizer.

In the book "Theoretical and Numerical Combustion" ( edited by Thierry P and Denis V , 2001, R.T. Edwards, Inc. ),I find the formular from Z to calculate temperature (page93). Am I right? Thanks again!

answer of jdc ------------------- Hi Sheng,

Page 93 is indeed giving you relations Z-> T, Fuel, Oxid and Product. Note: this relation also assume that all species and energy are diffusing with the same coefficient (Lewis = 1 for all all species).

The problem will be in determining Q and Cp!

Good luck. Julien

Re: about mixture fraction,the 3rd time
 

Hi Sheng,

You don't need to start a new message each time.

Your method to obtain Q and Cp is indeed the most straightforward. What I was trying to express is:

-> choosing Q and Cp implies choosing the maximum temperature as shown in relation 3.35 p.96.

Therefore, this two parameters are among the most important parameters of the model.

I hoppe this clarify my remark. Good Luck, Julien

Re: about mixture fraction,the 3rd time
 

I would be careful with assuming Cp is constant. With the wide range of temperatures found in combustion problems, the thermodynamic properties show significant real-gas effects. Extensive polynomial fits (so-called NASA polynomials) can be found on various combustion web sites, such as

http://garfield.chem.elte.hu/Burcat/burcat.html

http://www.me.berkeley.edu/gri_mech/

In addition to Cp for a variety of chemical species, there will be information on the heats of formation, from which you can calculate Q.

Re: about mixture fraction,the 3rd time
 

Many Thanks!