TITLE.PM5

(Ann) #1
FUELS AND COMBUSTION 499

dharm
\M-therm\Th11-1.pm5

i.e., UUPR 21 − = (UUPP 20 − ) + ∆U 0 + (UURR 01 − ) ...(11.14)

Products Reactants
(iii)(ii)(i)
The values of (UURR 01 − ) and (UUPP 20 − ) can be calculated from the following relations :
UURR 01 − = nu uii i
R

∑ () 01 − ...(11.15)


where, ui = Tabulated value of the internal energy for any constituent at the required temperature
T 0 or T 1 in heat unit per mole
ni = Number of moles of the constituent, and


R

∑ = Summation for all the constituents of the reactants denoted by i.


If mass base is used for tabulated values or calculation, then
UURR 01 − = mu uii i
R

∑ () 01 − ...(11.16)


where, ui = Internal energy per unit mass.
The above expression in terms of the specific heats (average values for the required tem-
perature range) may be written as


UURR 01 − = mc Tivi T
R

∑ () 01 − = (T 0 – T 1 ) mcivi
R

∑ ...(11.17)
For products, similar expressions may be written as :
UUPP 20 − = nuii ui
P

∑ () 20 − ... on mole basis


UUPP 20 − = mu uii i
P

∑ () 20 − ... on mass basis


UUPP 20 − = mc Tivi T
P

∑ ()^20 −


= ()TT mcivi
P

20 − ∑ ... in terms of mean specific heats
It may be noted that niCvi = micvi
Analysis for a steady flow or ‘constant pressure’ combustion process :
In such an analysis the changes in enthalpy (H) are important. An analysis carried out as
above will give the following expressions :
HHPR 21 − = (HHPP 20 − ) + ∆H 0 + (HHRR 01 − ) ...(11.18)

Products Reactants

where, ∆H 0 = HHPR 00 − , and is always negative ...(11.19)
[∆H 0 = Enthalpy of combustion at T 0 or the constant pressure heat of combustion at T 0 ]
Expressions for change of enthalpy of reactants and products :
Reactants :
HHRR 01 − = nh hii i
R


∑ () 01 − ... on mole basis ...(11.20)

Free download pdf