This document discusses refrigeration systems and their components. It describes the Carnot cycle and how it applies to refrigerators and heat pumps. The vapor compression cycle is explained in detail, including the functions of the compressor, condenser, expansion valve, and evaporator. Factors that affect system performance are outlined. Various refrigeration system configurations are presented, such as multipressure and cascade systems.

1. REFRIGERATION SYSTEM
By: Engr. Yuri G. Melliza

2. Refrigeration : Is that area of
engineering that deals with the different
mechanism involved in maintaining a
temperature of a space or material below
that of the immediate surroundings.
Uses of Refrigeration:
1. Ice making
2. Cold Storage
3. Air conditioning
4. Food preservation
5. Other industrial processes that uses refrigeration

3. Carnot Cycle:
A. Carnot Engine
Processes:
1 to 2 - Heat Addition (T = C)
2 to 3 - Expansion (S = C)
3 to 4 - Heat Rejection (T = C)
4 to 1 - Compression (S = C)
T
S
1 2
34
TH
TL
QA
QR

4. Heat Added (T = C)
QA = TH(S2 - S1) → 1
S2 - S1 = S3 – S4 = ∆S
QA = TH ∆S → 2
Heat Rejected (T = C)
QR = TL(S3 – S4) → 3
S2 - S1 = S3 – S4 = ∆S
QR = TL ∆S → 4
Net Work
W = ΣQ ; W = QA - QR
W = ∆S (TH – TL) → 4
Where:
TH – high temperature, °K
TL – low temperature, °K

5. Thermal Efficiency
100%x
Q
W
e
A
=
100%x
Q
Q-Q
e
A
RA
=
100%x
Q
Q
e
A
R






−= 1
100%x
T
T-T
e
H
LH






=
100%x
T
T
e
H
L






−= 1
→ 5
→ 6
→ 7
→ 9
→ 8

6. B. Carnot Refrigerator
Processes
1 to 2 - Compression (S =
C)
2 to 3 - Heat Rejection (T =
C)
3 to 4 - Expansion (S = C)
4 to 1 - Heat Addition (T =
C)TH
T
TL
S
1
23
4
QA
QR

7. Heat Added (T = C)
QA = TL(S1 – S4) → 10
S2 – S3 = S1 – S4 = ∆S
QA = TL ∆S → 11
Heat Rejected (T = C)
QR = TH(S2 – S3) → 12
S2 – S3 = S1 – S4 = ∆S
QR = TH ∆S → 13
Net Work
W = ΣQ ; W = QR - QA
W = ∆S (TH – TL) → 14

8. Coefficient of Performance: It is the ratio of
the refrigerating capacity to the net cycle
work.
W
Q
COP A
=
Q-Q
Q
COP
AR
A
=
T-T
T
COP
LH
L
=
→ 15
→ 16
→ 17

9. C. Carnot Heat Pump: A heat pump uses the
same components as the refrigerator but its main
purpose is to reject heat at high thermal energy
level.
Heat Added (T = C)
QA = TL(S1 – S4) → 20
S2 – S3 = S1 – S4 = ∆S
QA = TL ∆S → 21
Heat Rejected (T = C)
QR = TH(S2 – S3) → 22
S2 – S3 = S1 – S4 = ∆S
QR = TH ∆S → 23

10. Performance
Factor
Net Work
W = ΣQ ; W = QR - QA
W = ∆S (TH – TL) → 24
W
Q
PF R
=
Q-Q
Q
PF
AR
R
=
T-T
T
PF
LH
H
=
1COPPF +=
→ 25
→ 26
→ 27
→ 28

11. Vapor Compression
Cycle
Processes:
1 to 2 - Compression (S = C)
2 to 3 - Heat Rejection (P = C)
3 to 4 - Expansion (h = C)
4 to 1 - Heat Addition (P = C)
Basic Components:
1. Gas Compressor
2. Condenser
3. Expansion Valve
4. Evaporator

12. Schematic Diagram
Evaporator
Condenser
4 1
23
QA (Heat
Added)
QR (Heat Rejected)
W (Work)
Compressor
Expansion
Valve

13. Ph and TS Diagram
1
23
4
S = C
P
h
1
2
3
4
h = C
T
S

14. Compressor
W = m(h2 – h1) KW
For Isentropic Compression (PVk
= C)
k
1k
1
2
1
2
P
P
T
T
−






=








−





−
=
−
1
P
P
1k
kmRT1
W
k
1k
1
2
P1V1’ = mRT1

15. Where:
m – mass flow rate in kg/sec
V1’ – volume flow rate in m3
/sec
P1 – suction pressure in KPa
P2 – discharge pressure in KPa
T1 – suction temp. in °K
T2 – discharge temp. in °K

16. 100%x
P
P
c-c1η
100%x
V
V
η
k
1k
1
2
v
D
1'
v
















+=
=
−
Volumetric Efficiency:

17. Where:
V1’ - volume flow rate measured at intake,m3
/sec
VD -displacement volume, m3
/sec
Displacement Volume:
a. For Single acting
m3/sec
4(60)
Nn'LD
=V
2
D
π
b. For Double acting (without considering piston
rod)
m3/sec
4(60)
Nn'LD2
=V
2
D
π

18. c. For Double acting (considering piston rod)
[ ] m3/secd-2D
4(60)
LNn'
=V 22
D
π
Piston Speed:
PS = 2LN m/min
Where:
L - length of stroke, m
D - diameter of bore, m
d - piston rod diameter, m
N - no. of RPM
n’ no. of cylinders

19. Compressor
Efficiencies:
100%x
WorkIndicated
WorkIdeal
cn
=η
a. Compression Efficiency
100%x
WorkShaftorBrake
WorkIndicated
m
=η
b. Mechanical Efficiency
100%x
WorkShaftorBrake
WorkIdeal
c
mcnc
=η
ηηη =
c. Compressor Efficiency

20. Condenser:
QR = m(h2 – h3) KJ/sec
For an air cooled condenser
QR = m(h2 – h3) = mCPa(ta2 – ta1) KJ/sec
For water cooled condenser
QR = m(h2 – h3) = mwCPw(tw2 – tw1) KJ/sec
Where:
a – refers to air
w – refers to water
1 – inlet condition
2 – exit condtition
Cpa = 1.0045 KJ/kg-°C
CPw = 4.187 KJ/kg- -°C

21. Expansion Valve:
h3 = h4
%100x
h
hh
x
fg4
f44
4
−
=
Where: x - quality
Evaporator:
QA = m(h1 – h4) KJ/sec or KW
QA = 60 m(h1 – h4) KJ/min
1 TR = 211 KJ/min
TR – tons of refrigeration

22. Coefficient of Performance
W
Q
COP A
=
where
QA – refrigerating effect or
Refrigerating capacity, KW
W – compressor work, KW

23. Wet compression
1
1
2
2
33
4
4
P
h S
T

24. Subcooling the refrigerant
1
1
2
2
3
3
4
4
P
h S
T

25. Superheating the suction vapor
1
1
2
2
33
4
4
P
h S
T

26. Effects of Operating Conditions
Effects of Increasing the vaporizing temperature:
a. The refrigerating effect per unit mass
increases.
b. The mass flow rate per ton decreases
c. The volume flow rate per ton decreases.
d. The COP increases.
e. The work per ton decreases.
f. The heat rejected at the condenser per
ton decreases.

27. Effects of Increasing the condensing temperature:
a. The refrigerating effect per unit mass
decreases.
b. The mass flow rate per ton increases
c. The volume flow rate per ton increases.
d. The COP decreases.
e. The work per ton increases.
f. The heat rejected at the condenser per
ton increases.

28. Effects of superheating the suction vapor
A. When superheating produces useful cooling:
a. The refrigerating effect per unit mass
increases.
b. The mass flow rate per ton decreases
c. The volume flow rate per ton decreases.
d. The COP increases.
e. The work per ton decreases.
B. When superheating occurs without useful
cooling:
a. The refrigerating effect per unit mass
remains the same.
b. The mass flow rate per ton remains the same.
c. The volume flow rate per ton increases.
d. The COP decreases.

29. e. The work per ton decreases.
f. The heat rejected at the condenser per
ton increases.
Effects of subcooling the liquid:
a. The refrigerating effect per unit mass
increases.
b. The mass flow rate per ton decreases
c. The volume flow rate per ton decreases.
d. The COP increases.
e. The work per ton decreases.
f. The heat rejected at the condenser per
ton decreases.

30. Liquid – Suction Heat Exchanger
The function of the heat exchanger are:
1. To ensure that no liquid enter the compressor
2. To subcool the liquid from the condenser to
prevent bubbles of vapor from impeding the
flow of refrigerant through the expansion valve.

31. Actual vapor compression cycle:
As the refrigerant flows through the system
there will be pressure drops in the condenser,
evaporator and piping. Heat loses or heat gains will
occur depending on the temperature difference
between the refrigerant and the surroundings.
Compression will be polytropic with friction and heat
transfer instead of isentropic.

32. Condenser
Compressor
Evaporator
Heat exchanger

33. Multipressure System
A multipressure system is a refrigeration system that
has two or more low-side pressure. The low-side
Pressure is the pressure of the refrigerant between
the expansion valve and the intake of the compressor.
Removal of Flash gas:
The flash gas that develops during the throttling
process between the condenser and evaporator was
removed and recompressed before complete expansion.
With flash gas removal a savings in power requirement
will occur.

34. Intercooling
Intercooling between two stages of compression redu-
ces the work of compression per kg of vapor. Intercoo-
ling in a refrigeration system can be accomplished with
a watercooled heat exchanger or by using refrigerant.
The watercooled intercooler may be satisfactory for two
stage air compression, but for refrigerant compression
The water is not cold enough. The alternate method
uses liquid refrigerant from the condenser to do the
intercooling. Discharge gas from the low stage com-
pressor bubbles through the liquid in the intercooler.
Refrigerant leaves the intercooler as saturated vapor
at the intercooler pressure.

35. Two evaporators and one compressor
1
23
4 5 6
7 8
compressor
Pressure-reducing
valve
condenser
HP evaporator
LP evaporator

36. condenser
evaporator
Flash tank and
Intercooler
LP compressor
HP compressor
Two compressors and one evaporator

37. condenser
LP evaporator
Flash tank and
Intercooler
LP compressor
HP evaporator
Two compressors and two evaporators
HP compressor

38. Optimum Intercooler or Inter-stage pressure
41i PPP =
Where:
Pi – optimum interstage or intercooler pressure
in KPa
P1 – suction pressure of LP compressor, KPa
P4 – discharge pressure of HP compressor, KPa

39. Cascade
System
Condenser
Cascade
Condenser
Evaporator
HP Compressor
LP Compressor
A. Closed cascade condenser

40. Condenser
Cascade
Condenser
Evaporator
HP Compressor
LP Compressor
B. Direct Contact type cascade condenser

41. Air Cycle Refrigeration
A. Closed or Dense - Air System
Cooler
Expander Compressor
Refrigerator

42. Cooler
Expander Compressor
Refrigerator
B. Open - Air System
P
V
1
23
4
T
S
1
2
3
4

43. Compressor Work:
111
k
1k
1
21
C
mRTVP
1
P
P
1k
kmRT
W
=








−





−
=
−
Cooler:
)T(TmCQ 32pR −=
Expander:
333
k
1k
3
43
E
mRTVP
1
P
P
1k
kmRT
W
=








−





−
=
−

44. Refrigerator:
)T(TmCQ 41pA −=
Network
W = Wc – WE
W = QR - QA

45. PRODUCT LOAD
Product Load – is the total amount of heat removed from a
product in a refrigerated space.
m m m
t1 t2tf
Q1 Q
2
Q
3
Q = Q1 + Q2 + Q3 + Q4
CP1 CP2

46. Where:
Q1 – sensible heat in cooling the product
from t1 to tf
Q2 – latent heat of fusion (freezing) of the
product at tf
Q3 – sensible heat in cooling further the
product from tf to the final
temperature t2
Q4 – heat losses or other heat gains from
the products
Q1 = mCP1(t1 – tf) KJ/hr

47. Q2 = m(hL) KJ/hr
Q3 = mCP2(tf – t2)
Q4 = Q – (Q1 + Q2 + Q3)
Where:
m – mass of product, kg/hr
Cp1 – specific heat of product below
freezing, KJ/kg-C or KJ/kg-K
Cp2 - specific heat of product above
freezing, KJ/kg- °C or KJ/kg- °K
t1 – initial temperature, °C
tf – freezing point temperature, °C
t2 – final temperature, °C
hL – latent heat of freezing, KJ/kg