1. Unit No:01
Thermodynamics
Prof. Yash B. Parikh
M.Tech (Computer Integrated Manufacturing)
B.E.(Mechanical Engineering)
Assistant Professor
Department of Mechanical Engineering
2. Enthalpy
2
The word enthalpy is based on the Greek
word enthalpos, which means to put heat into.
It comes from the Classical Greek prefix en-,
meaning to put into, and the verb thalpein, meaning
"to heat".
Enthalpy is a measure of the total energy of
a thermodynamic system.
It’s a thermodynamic quantity, equal to the internal
energy of a system plus the product of its volume
and pressure.
“Enthalpy” is the amount of energy in a system
capable of doing mechanical work.
It’s denoted by “H”.
It’s an extensive property.
3. Enthalpy
3
The equation is,
H = U + p . V
H is the enthalpy of the system.
U is the internal energy of the system.
p is the pressure at the boundary of the system and
its environment.
V is the volume of the system.
For unit mass of gas, equation becomes
h = u + p . V
Where, h is specific enthalpy
u is specific internal energy
4. Enthalpy as a function of T
4
Since, u = Cv . T and p . v = RT,
h = u + p . v
h = Cv . T + RT
h = (Cv + R) T
h = Cp . T
Since Cp is const for gas, it implies that h is the
function of temperature T only.
5. Example 1
5
In a certain thermodynamic process of an ideal gas,
the volume changes from 0.2 m3 to 0.5 m3 , while
pressure changes as per p = 150 [ (V/100) + 1 ] ,
where p is in N/m2 and V is in m3 . Find work done by
gas in kJ.
DEC 2010 5 Marks
6. Example 2
6
A certain gas occupies a space of 0.3 m3 at a
pressure of 2 bar and a temperature of 77 degree
centigrade. It is heated at constant volume, until
pressure is 7 bar.
Determine :
a) temp at the end of the process
b) mass of the gas
c) change in internal energy
d) change in enthalpy
DEC 2011 6 Marks
