Macroscopic and microscopic
Microscopic, temperature T
Considered at molecular level
Without taking events at molecular level , Macroscopic
System and control volume
energy
Volume ,V
rgy
ene
Closed system : no mass interaction, only energy
Open system: ma
isotherm
Entropy
Two reversible adiabatic can not intersect each other
A
p
C C
v
RA
B
AB and CB are two reversible adiabatic and they intersect at B.
AC is a reversible isotherm. Through AC we can transfer heat to the cycle ABC which is
A close cyclic pro
Maximum work or available energy from a system
Initially a body of mass m, is at temp T, what is the maximum work that
can be obtained out of it if the environment is at which is lower than
the body temperature T.
;
w
For max work output,
;
If the system
Digital Thermodynamics
Smart Refrigerators will be able to tell you
if it is consuming too much power or needs
defrosting or you are opening it too often.
For this the microprocessors in it must
incorporate digital thermodynamics.
Property Charts
pV=nRT,
Heat and Work Devices
Heat Exchangers, Pumps
(Compressors), Turbines and Nozzles
Boiler
High Pressure Steam when directed at a
Turbine produces electricity. This HP Steam is
produced from a Boiler which is supplied with
water at High pressure. It has to
Absolute thermodynamic temp scale
T1
Q1
Engine
Q2
Q2
Engine
For any heat engine. For a reversible cycle =
So,
Third law of thermodynamics.
Absolute zero on Kelvin scale
Can not be reached without violating
Q1
2nd law of thermodynamics
W1=Q1-Q2
Engine
T2
W
Entropy
Entropy is a property besides Pressure,
Temperature and Volume which is used to
define engineering processes that occur.
Property Charts
H, U And S.
Are the usual dependent and independent
variables used in property charts. Though P, V
and T are
Second Law
For A Cycle
Kelvin Planck
Let a substance undergoes heat and work interactions
and completes a cycle. Say It takes is Q from a hotter
object and it does work.
It cannot go back to
initial state until it rejects some heat Q1 to an object
colder
Second law of thermodynamics
Similarity between heat and work: both are energy, but the difference between them is:
Work can be completely converted to heat but heat can not be completely converted to
Work in a closed cycle or cyclic process.
Limitation o
Properties of Pure substances
Air as a mixture of gases is pure. Water and its vapor in a tank is pure, but air and water
vapor in the liquid form in a tank is not pure .
Acetone
5
10
Acetone
250
225
175
150
180C
1100 kPa
125
3
10
3000 kPa
200
4
10
130C
T
System and Control Volume
In Thermodynamics the devices such
as heat engines and refrigerators are
systems with an input and an output.
Work
WORK: The IC Engine, in an automobile drives the vehicle by
consuming a fuel, petrol in most cases. The input is
Tutorial -3 (unsteady flow process)
1. Two kg of water at 500 kPa, 20C is heated in a constant pressure process (SSSF)
to 1700C. Find the best estimate for the heat transfer. (6.15) Ans: 12849 kJ
2. A mixing chamber with heat transfer receives 2 kg/s of R
First law applied to flow process
For any system and process the first law can be written as:
E = all forms of energy stored in the system= KE + PE+ U
This form of equation is only suitable for closed process. But for open process
it is better to use the
Area-moment theorem is semi-graphical method.
Consider a beam as shown below. Two points A and B are considered.
Portion of the Elastic curve AB
From the relation
d
B
d2 y M
=
d x 2 EI
we get
M
( dy )= EI dx
dx
(1)
B
M
d dy = EI dx=
dx A
A
( )
= area und