3. Heat Engine
The concept of the second
law of thermodynamics
applied to heat engine is
equally applicable on the
internal combustion
engines used in our cars,
motorcycles, ships,
airplanes, etc.
4. Heat Engine
A heat engine takes in some fluid accross a cycle
process where (1) the heat is absorbed from one high
temperature source, increasing energy in machine; (2
) change partly energies in this goes to mechanical
effort; and (3) discarding residuary energy as a heat
goes to low temperature source.
1 2 W Q Q 1 2 Q Q Q
5. Cooler Engine
The basic principle of a
cooler engine is flowing
heat from the cool
reservoir T2 to the hot
reservoir T1 by exerting
external effort on the
system. This principle is
opposite to that of in
aheat engine.
6. The magnitude of external work needed in a cooler engine
is formulated as follows
W = Q1 – Q2
Q1 = heat absorbed from low temperature
Q2 = heat given at high temperature
If the process happening in the cooler engine is reversible,
then it is called an (ideal cooler) where the following
equation applies
2
Q
Cooler Engine
2
T
1
1
T
Q
7. Cooler Engine
examples of cooler engine are:
refrigerator and air conditioner
In a refrigerator, what functions as the cool reservoir is the
refrigerator’s interior (place to store foods) and what functions as
the hot reservoir is the external air around the refrigerator. The
external work used to transfer heat from the refrigerator’s inside
to the outside air is obtained from the electric current running in
the system.
In an air conditioner, what functions as the cool reservoir is the
inside of the air conditioner, while what function as the hot
reservoir is the air outside the ac machine.
8. Cooler Engine
If the performance of a heat engine is shown by the
efficiency of the engine, the performance of a cooler
engine is shown by its coefficient of performance.
Coefficient of performance is defined as the ratio of
values of the heat in the cool reservoir to the work
applied in the system. In equation form, the coefficient
of performance is written as follows:
T
2
CP
1 2
Q
2 2
1 2
T T
Q Q
Q
W
9. Steam Engine
The other application of thermodynamic
second law is the steam engine in a train. Heat
produced through the coal combustion is
changed into mechanical energy that can
move the train’s wheels. The principle of a
Steam engine is the same with the heat
engine.
11. Exercise
◦ Mention the application of the 2nd law of thermodynamics
◦ Explain the difference of basic principle among the heat engine and
the cooler engine!
◦ Which is object that functions as the cool reservoir and the hot
reservoir in the refrigerator and in the air conditioner?
