Short Notes: Refrigeration and Air-Conditioning | Short Notes for Mechanical Engineering PDF Download

 Page 1


Refrigeration and Air-Conditioning 
Refrigeration Cycle: Refrigeration is the process in which heat is removed from a 
body enclosed space so that its temperature is reduced and then maintained at the 
temperature below the surrounding temperature. The working substance which is 
used to produce refrigeration is known as refrigerant.
Heat Pump: Heat pump is used to remove heat from a body at lower temperature 
and transfer this heat to a body having high temperature on the expense of external 
work supplied.
Coefficient of Performance;
Desired effect
COP = -------------------
Woifc input
Here, the desired effect is to give heat to higher temperature body.
c o p - -
Qh
w
Q h - Q
( COP ) =
1
1- I l
Th
L
.COP=
-T
L
Page 2


Refrigeration and Air-Conditioning 
Refrigeration Cycle: Refrigeration is the process in which heat is removed from a 
body enclosed space so that its temperature is reduced and then maintained at the 
temperature below the surrounding temperature. The working substance which is 
used to produce refrigeration is known as refrigerant.
Heat Pump: Heat pump is used to remove heat from a body at lower temperature 
and transfer this heat to a body having high temperature on the expense of external 
work supplied.
Coefficient of Performance;
Desired effect
COP = -------------------
Woifc input
Here, the desired effect is to give heat to higher temperature body.
c o p - -
Qh
w
Q h - Q
( COP ) =
1
1- I l
Th
L
.COP=
-T
L
where, TH = high temperature,
Tl = lower temperature
Refrigerator: Working principle of refrigerator is same as heat pump, but its aim to 
keep cool the body whose temperature is below atmospheric temperature.
_ Desired effect 
Woric input 
Q
c o p = —
\v
COP = — —
Qh- Q l
Tl
t h- t l
f c ° P ) R =
Where, TH and TL are higher and lower temperature respectively.
(CO P)p = (C O P )r + 1
Principle o! refrigerator
where, QL= heat at lower temperature,
Qh = heat at higher temperature
Unit of Refrigeration: It has standard unit of TR (Ton or Refrigeration). 1 TR (one 
ton of refrigeration) means capacity to freeze one ton of water from and at 0°C in 
24 h.
1TR = 211 kJ min 
= 3.517 k\V 
= 200 BTHU mill
Key Points
• A refrigerator is a device operating in a cycle, maintains a body at a 
temperature of the surroundings.
• There is performance parameter in a refrigerator cycle, called the coefficient 
of performance.
• Heat pump is a device which operating in a cycle, maintains a body at a 
temperature higher than the temperature of the surroundings.
Reversed Carnot Cycle: When the processes of Carnot cycle is reversed, then it is 
called reversed Carnot cycle.
Page 3


Refrigeration and Air-Conditioning 
Refrigeration Cycle: Refrigeration is the process in which heat is removed from a 
body enclosed space so that its temperature is reduced and then maintained at the 
temperature below the surrounding temperature. The working substance which is 
used to produce refrigeration is known as refrigerant.
Heat Pump: Heat pump is used to remove heat from a body at lower temperature 
and transfer this heat to a body having high temperature on the expense of external 
work supplied.
Coefficient of Performance;
Desired effect
COP = -------------------
Woifc input
Here, the desired effect is to give heat to higher temperature body.
c o p - -
Qh
w
Q h - Q
( COP ) =
1
1- I l
Th
L
.COP=
-T
L
where, TH = high temperature,
Tl = lower temperature
Refrigerator: Working principle of refrigerator is same as heat pump, but its aim to 
keep cool the body whose temperature is below atmospheric temperature.
_ Desired effect 
Woric input 
Q
c o p = —
\v
COP = — —
Qh- Q l
Tl
t h- t l
f c ° P ) R =
Where, TH and TL are higher and lower temperature respectively.
(CO P)p = (C O P )r + 1
Principle o! refrigerator
where, QL= heat at lower temperature,
Qh = heat at higher temperature
Unit of Refrigeration: It has standard unit of TR (Ton or Refrigeration). 1 TR (one 
ton of refrigeration) means capacity to freeze one ton of water from and at 0°C in 
24 h.
1TR = 211 kJ min 
= 3.517 k\V 
= 200 BTHU mill
Key Points
• A refrigerator is a device operating in a cycle, maintains a body at a 
temperature of the surroundings.
• There is performance parameter in a refrigerator cycle, called the coefficient 
of performance.
• Heat pump is a device which operating in a cycle, maintains a body at a 
temperature higher than the temperature of the surroundings.
Reversed Carnot Cycle: When the processes of Carnot cycle is reversed, then it is 
called reversed Carnot cycle.
isotfw m al 
comports von 
i
Reversed Carrvol cycle 
or \ p V coordinate
A diaba tic 
, compression
tV 'C b C V 'T T V c . 
e*p«ir*< > n
Reversed Carnot cycle 
on r s coordinate
Heat absoifced 
Work input
Jd
1
O )
1
Jr*
y
1
y
S4 = S;
7, (SA- S ,) - T 2(S2- S : )i (7i - r, )(S4 - s , )
Si = S:
7,
COP = — *
7 - r ,
Where T2 and 7 > are the temperature at section 2 and 1 respectively and Si, S2, S3 
and S4 are the entropy at 1, 2, 3 and 4 respectively.
Air Refrigeration System: In air refrigeration, Bell Coleman cycle is used which 
works on reversed Brayton cycle while Brayton cycle is used for gas turbine.
COP of reversed Brayton cycle,
Refrigeration effect
COP =
\V
(R p )
Heat absorbed by air in cold chamba-
« a c p(Tt - r 4)
ma CF(X2- T i )- m a Cp (7 ,- T J 
(T - T a)
COP =
(r; - r ; ) - a ; - r 4)
Let pressure ratio is rp, then
Page 4


Refrigeration and Air-Conditioning 
Refrigeration Cycle: Refrigeration is the process in which heat is removed from a 
body enclosed space so that its temperature is reduced and then maintained at the 
temperature below the surrounding temperature. The working substance which is 
used to produce refrigeration is known as refrigerant.
Heat Pump: Heat pump is used to remove heat from a body at lower temperature 
and transfer this heat to a body having high temperature on the expense of external 
work supplied.
Coefficient of Performance;
Desired effect
COP = -------------------
Woifc input
Here, the desired effect is to give heat to higher temperature body.
c o p - -
Qh
w
Q h - Q
( COP ) =
1
1- I l
Th
L
.COP=
-T
L
where, TH = high temperature,
Tl = lower temperature
Refrigerator: Working principle of refrigerator is same as heat pump, but its aim to 
keep cool the body whose temperature is below atmospheric temperature.
_ Desired effect 
Woric input 
Q
c o p = —
\v
COP = — —
Qh- Q l
Tl
t h- t l
f c ° P ) R =
Where, TH and TL are higher and lower temperature respectively.
(CO P)p = (C O P )r + 1
Principle o! refrigerator
where, QL= heat at lower temperature,
Qh = heat at higher temperature
Unit of Refrigeration: It has standard unit of TR (Ton or Refrigeration). 1 TR (one 
ton of refrigeration) means capacity to freeze one ton of water from and at 0°C in 
24 h.
1TR = 211 kJ min 
= 3.517 k\V 
= 200 BTHU mill
Key Points
• A refrigerator is a device operating in a cycle, maintains a body at a 
temperature of the surroundings.
• There is performance parameter in a refrigerator cycle, called the coefficient 
of performance.
• Heat pump is a device which operating in a cycle, maintains a body at a 
temperature higher than the temperature of the surroundings.
Reversed Carnot Cycle: When the processes of Carnot cycle is reversed, then it is 
called reversed Carnot cycle.
isotfw m al 
comports von 
i
Reversed Carrvol cycle 
or \ p V coordinate
A diaba tic 
, compression
tV 'C b C V 'T T V c . 
e*p«ir*< > n
Reversed Carnot cycle 
on r s coordinate
Heat absoifced 
Work input
Jd
1
O )
1
Jr*
y
1
y
S4 = S;
7, (SA- S ,) - T 2(S2- S : )i (7i - r, )(S4 - s , )
Si = S:
7,
COP = — *
7 - r ,
Where T2 and 7 > are the temperature at section 2 and 1 respectively and Si, S2, S3 
and S4 are the entropy at 1, 2, 3 and 4 respectively.
Air Refrigeration System: In air refrigeration, Bell Coleman cycle is used which 
works on reversed Brayton cycle while Brayton cycle is used for gas turbine.
COP of reversed Brayton cycle,
Refrigeration effect
COP =
\V
(R p )
Heat absorbed by air in cold chamba-
« a c p(Tt - r 4)
ma CF(X2- T i )- m a Cp (7 ,- T J 
(T - T a)
COP =
(r; - r ; ) - a ; - r 4)
Let pressure ratio is rp, then
r = £ l = A
9 Pi P* *
COP — ^ ^
t C l
1
K "
r , - ? ; t. - tx
J i T*
c o p - 1 ,
7 - 1
Y
( r , ) - l
Where, y = index, rp = pressure ratio
Vapour Compression refrigeration System: In this system, refrigerant (like NH3 R- 
12, R-11 etc) changes its phase from liquid to vapour and vice-versa. When liquid 
changes into vapour, it produces refrigerating effect by absorbing latent heat from 
cold chamber. This process is known as evaporation.
Expansion
Vapour compression refrigeration system
1 -»2 -» compression process (Isentropic)
2 -? 3 -? condensation process (At constant pressure)
3 -? 4 -? expansion process (Isenthalpic process)
4 1 evaporation process (At constant pressure)
COP =
Refrigeration effect
Work done by compressor
COP =
hj- h,
h, - h[
Where hi, h2 and hA are the enthalpy at section 1, 2 and 4 respectively. 
Key Points
• COP of refrigerator working between two fixed temperature TL and TH (TH > Ti) 
will have fixed COP.
• A reversible heat engine can work like a refrigerator or a heat pump.
• Vapour compression refrigeration cycle
Page 5


Refrigeration and Air-Conditioning 
Refrigeration Cycle: Refrigeration is the process in which heat is removed from a 
body enclosed space so that its temperature is reduced and then maintained at the 
temperature below the surrounding temperature. The working substance which is 
used to produce refrigeration is known as refrigerant.
Heat Pump: Heat pump is used to remove heat from a body at lower temperature 
and transfer this heat to a body having high temperature on the expense of external 
work supplied.
Coefficient of Performance;
Desired effect
COP = -------------------
Woifc input
Here, the desired effect is to give heat to higher temperature body.
c o p - -
Qh
w
Q h - Q
( COP ) =
1
1- I l
Th
L
.COP=
-T
L
where, TH = high temperature,
Tl = lower temperature
Refrigerator: Working principle of refrigerator is same as heat pump, but its aim to 
keep cool the body whose temperature is below atmospheric temperature.
_ Desired effect 
Woric input 
Q
c o p = —
\v
COP = — —
Qh- Q l
Tl
t h- t l
f c ° P ) R =
Where, TH and TL are higher and lower temperature respectively.
(CO P)p = (C O P )r + 1
Principle o! refrigerator
where, QL= heat at lower temperature,
Qh = heat at higher temperature
Unit of Refrigeration: It has standard unit of TR (Ton or Refrigeration). 1 TR (one 
ton of refrigeration) means capacity to freeze one ton of water from and at 0°C in 
24 h.
1TR = 211 kJ min 
= 3.517 k\V 
= 200 BTHU mill
Key Points
• A refrigerator is a device operating in a cycle, maintains a body at a 
temperature of the surroundings.
• There is performance parameter in a refrigerator cycle, called the coefficient 
of performance.
• Heat pump is a device which operating in a cycle, maintains a body at a 
temperature higher than the temperature of the surroundings.
Reversed Carnot Cycle: When the processes of Carnot cycle is reversed, then it is 
called reversed Carnot cycle.
isotfw m al 
comports von 
i
Reversed Carrvol cycle 
or \ p V coordinate
A diaba tic 
, compression
tV 'C b C V 'T T V c . 
e*p«ir*< > n
Reversed Carnot cycle 
on r s coordinate
Heat absoifced 
Work input
Jd
1
O )
1
Jr*
y
1
y
S4 = S;
7, (SA- S ,) - T 2(S2- S : )i (7i - r, )(S4 - s , )
Si = S:
7,
COP = — *
7 - r ,
Where T2 and 7 > are the temperature at section 2 and 1 respectively and Si, S2, S3 
and S4 are the entropy at 1, 2, 3 and 4 respectively.
Air Refrigeration System: In air refrigeration, Bell Coleman cycle is used which 
works on reversed Brayton cycle while Brayton cycle is used for gas turbine.
COP of reversed Brayton cycle,
Refrigeration effect
COP =
\V
(R p )
Heat absorbed by air in cold chamba-
« a c p(Tt - r 4)
ma CF(X2- T i )- m a Cp (7 ,- T J 
(T - T a)
COP =
(r; - r ; ) - a ; - r 4)
Let pressure ratio is rp, then
r = £ l = A
9 Pi P* *
COP — ^ ^
t C l
1
K "
r , - ? ; t. - tx
J i T*
c o p - 1 ,
7 - 1
Y
( r , ) - l
Where, y = index, rp = pressure ratio
Vapour Compression refrigeration System: In this system, refrigerant (like NH3 R- 
12, R-11 etc) changes its phase from liquid to vapour and vice-versa. When liquid 
changes into vapour, it produces refrigerating effect by absorbing latent heat from 
cold chamber. This process is known as evaporation.
Expansion
Vapour compression refrigeration system
1 -»2 -» compression process (Isentropic)
2 -? 3 -? condensation process (At constant pressure)
3 -? 4 -? expansion process (Isenthalpic process)
4 1 evaporation process (At constant pressure)
COP =
Refrigeration effect
Work done by compressor
COP =
hj- h,
h, - h[
Where hi, h2 and hA are the enthalpy at section 1, 2 and 4 respectively. 
Key Points
• COP of refrigerator working between two fixed temperature TL and TH (TH > Ti) 
will have fixed COP.
• A reversible heat engine can work like a refrigerator or a heat pump.
• Vapour compression refrigeration cycle
h - - - +
• Entropy
S, - S, + CD In ^
* ¦ ' r,
^ 2 = h2+Cp (T2-T2)
• For isentropic process, S 2 = SyS3 = S 4
Compressor: A compressor is used in refrigerator to increase the pressure of gas. 
To compress the refrigerant we use reciprocating compressor generally in the 
vapour compression refrigeration system,
p V curve
Stroke volume
V. = - d l * * * L 
¦ 4
where, d = diameter of compressor
L = stroke length
Volume flow rate of refrigerant
V— n . —dlLn N 
4
Where, N = rotational speed 
H v = volumetric efficiency 
n = number of cylinders
Actual volume compressed
Stroke volume
„ V .H - V .- V ,
* ¦ ------- %-------
where, Vc = clearance volume 
c = clearance ratio
V , V V
~ ~ V 3