This document discusses steady flow analysis of reacting mixtures. It defines adiabatic combustion and flame temperature as a combustion process without heat loss or gain, where the maximum temperature achieved is referred to as the adiabatic flame temperature. The maximum temperature occurs during stoichiometric combustion. Excess air is used to control the temperature. Conservation of mass and energy principles are used to calculate the adiabatic flame temperature. The second law of thermodynamics and concept of entropy are also discussed for open systems involving chemical reactions.

1. Steady flow analysis of reacting
mixtures
S.Gunabalan
Associate Professor
Mechanical Engineering Department
Bharathiyar College of Engineering & Technology
Karaikal - 609 609.
e-Mail : gunabalans@yahoo.com
Part - 2

2. Steady flow analysis of reacting
mixtures
Analysis for a steady flow or ‘constant pressure’
combustion process

6. Adiabatic
combustion or Flame temperature
A combustion process without heat loss or gain is adiabatic.
For a combustion process that takes place adiabatically with no shaft
work, the temperature of the products is referred to as the adiabatic
flame temperature.
This is the maximum temperature that can be achieved for given
reactants.
Heat transfer, incomplete combustion, and dissociation all result in
lower temperature.
The maximum adiabatic flame temperature for a given fuel and
oxidizer combination occurs with a stoichiometric mixture
The amount of excess air can be tailored as part of the design to
control the adiabatic flame temperature.

7. Condition for Adiabatic combustion temperature
• reactants enter the combustion process at
25oC (77oF) and 1 atm pressure
• products leaves the process at 1 atm pressure
• combustion is stoichiometric without any
excess air
Excess air will reduce the adiabatic flame
temperature and is often introduced to avoid
flame temperatures exceeding limits sets by the
materials in the combustion system.
http://www.engineeringtoolbox.com/adiabatic-flame-temperature-d_996.html

8. The conservation of mass and conservation of
energy principles is used for the calculation
the energy rate balance on a per
mole of fuel basis,

10. 10
Second Law Analysis of Reacting Systems
Second law for the open system
Taking the positive direction of heat transfer to the system,
the entropy balance relation can be expressed for a steady-flow combustion chamber as
Q
T
S S S S kJ kk
k
gen CV    React Prod  ( / )
Derive an expression for availability in steady state steady flow process (SSSF) involving chemical
reactions ( Apr-2013)
http://ocw.kfupm.edu.sa/ocw_courses/user062/ME204001/Lecture%20Notes/Chapter15.ppt.

11. 11
Second Law Analysis of Reacting Systems
Second law for the open system
Q
T
S S S S kJ kk
k
gen CV    React Prod  ( / )
For an adiabatic, steady-flow process, the entropy
balance relation reduces to
S S Sgen adiabatic,   Prod React 0
The third law of thermodynamics states that the entropy of a
pure crystalline substance at absolute zero temperature is zero.
The third law provides a common base for the entropy of all
substances, and the entropy values relative to this base are
called the absolute entropy.

12. Reference
• Moran, M. J. 2011. Fundamentals of engineering thermodynamics. Wiley,
[Hoboken, N.J.?].
• Rajput, R. K. 2010. Engineering thermodynamics. Jones and Bartlett
Publishers, Sudbury, Mass.
• Nag, P. K. 2002. Basic and applied thermodynamics. Tata McGraw-Hill, New
Delhi.
• http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node1
11.html
• http://www.engineeringtoolbox.com/adiabatic-flame-temperature-
d_996.html
• http://ocw.kfupm.edu.sa/ocw_courses/user062/ME204001/Lecture%20N
otes/Chapter15.ppt.