Energy thermodynamic cycles

en

1. THERMODYNAMIC CYCLES
HEAT ENGINES&HEAT PUMPS
EFFICIENCY AND COEFFICIENT OF PERFORMANCE
PRESENTED BY:SUJI.S.K

2. THERMODYNAMIC CYCLES

A thermodynamic cycle is a series of
thermodynamic processes transferring heat
and work, while varying pressure, temperature
and other state variables, eventually returning
a system to its initial state

3. A minimum of 3 such processes are required to
construct a cycle.
All processes need not have work interactions (eg:
isochoric)
All processes need not involve heat interactions
either (eg: adiabatic process).

4. “When a system undergoes a thermodynamic
cycle then the net heat supplied to the system
from the surroundings is equal to the net
work done by the system on its surroundings”
ΣQsupplied-ΣQrejected= Wnet
The efficiency of the cycle is defined as
η= Wnet/ΣQsuppied

5. Carnot Cycle

It consists of two isotherms and two
adiabatics

6. Carnot Cycle (contd..)
•Carnot cycle is the one with which all other cycles are
compared.
•η= W
net
/ΣQ
supplied

= ΣQsupplied-ΣQrejected/ΣQsupplied
=Q41-Q32/Q41 =(T1-T2)/T1
Carnot efficiency of (T1-T2)/T1 is the best we can get for
any cycle operating between two fixed temperatures.

7. OTTO CYCLE
It consists of two isochores and two adiabatics

8. OTTO CYCLE(contd..)
There is no heat interaction during 1-2 and 3-4
•Heat is added during constant volume heating (2-3)
Q23= Cv(T3-T2)
•Heat is rejected during constant volume cooling(4-1)
Q14= Cv(T4-T1)
•η = W
net
/ΣQ
supplied

= ΣQsupplied-ΣQrejected/ΣQsupplied
=(Q23-Q14)/Q23= 1 -[(T4-T1) / (T3-T2)]

9. Diesel Cycle
Diesel cycle consists of two isoentropic, one
isochoric and one isobaric process

10. Diesel cycle(contd..)
Q
23
=mCp(T3-T2)
Q
14
=mCv(T4-T1)
η = W
net
/ΣQ
supplied
= ΣQsupplied-ΣQrejected/ΣQsupplied
=(Q23-Q14)/Q23
= 1 –(1/γ)[(T4-T1) / (T3-T2)]

11. Brayton Cycle
The fuel can be Natural gas or synthetic fuel
gas.
It consists of two isoentropic and two isobaric
processes

13. Reversible Cycle
•A cycle consisting of all reversible processes is a
reversible cycle. Even one of the processes is
irreversible, the cycle ceases to be reversible.
Otto, Carnot and Brayton cycles are all reversible.

14. •A reversible cycle with clockwise processes
produces work with a given heat input and are
known as power cycles. The same while
operating with counter clockwise processes will
reject the same heat with the same work as input
and are known as heat pump cycles .

15. HEAT ENGINE
•A device which produces work by
transferring heat from a warmer to a
cooler body is called a heat pump.

16. Carnot Engine
•Carnot engine has one Q +ve process and one Q
-veprocess. This engine has a single heat source at T1and a
single sink at T2. If Q +ve> Q -ve; W will be +ve. It is a heat
engine

17. Heat pump
•A device which transfers heat from a cooler to
a warmer body (by receiving energy) is called
a heat pump.
•A refrigerator is a special case of heat pump.
•Just as efficiency for a heat engine, for a heat
pump the coefficient of performance (COP) is
a measure of how well it isdoing the job.

18. Carnot Cycle for a Refrigerator/heat
Pump
»TH=T1, TC=T2

19. Heat Pump (contd…)
•In a heat pump the entity of interest is Q1.
COP
HP
= Q
1
/W
•In a refrigerator the entity of interest is Q2.
COP
R = Q
2/W
•NOTE: η, COP
HPCOP
R are all positive numbers,
•The highest COP
HP
obtainable will be T1/(T1-T2)
and highest COP
R
obtainable will be T2/(T1-T2)

20. •An irreversible engine can’t produce more
work than a reversible one.
•An irreversible heat pump will always
need more work than a reversible heat
pump.
•An irreversible expansion will produce less
work than a reversible expansion
•An irreversible compression will need
more work than a reversible compression