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 TM 55-1905-220-14-8
4-29. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).
PHYSICAL PROPERTIES OF SATURATED REFRIGERANT-12* (Continued)
PRESSURE
DENSITY
HEAT CONTENT ABOVE -40
F
Temp.
LBS. PER SQ. IN
LBS. PER CU.FT.
B.T.U. PER LB.
Temp
Deg. F.
Absolute
Gauge
Liquid
Vapor
Liquid
Latent Total of Vapor Deg. F.
Col.1
Col.2
Col.3
Col.4
Col.5
Col.6
Col.7
Col.8
Col.9
120
171.8
157.1
76.02
4.167
36.16
53.99
90.15
120
122
176.2
161.5
75.72
4.288
36.66
53.62
90.28
122
124
180.8
166.1
75.40
4.413
37.16
53.24
90.40
124
126
185.4
170.7
75.10
4.541
37.67
52.85
90.52
126
128
190.1
175.4
74.78
4.673
38.18
52.46
90.64
128
130
194.9
180.2
74.46
4.808
38.69
52.07
90.76
130
132
199.8
185.1
74.13
4.948
39.19
51.67
90.86
132
134
204.8
190.1
73.81
5.094
39.70
51.26
90.96
134
136
209.9
195.2
73.46
5.247
40.21
50.85
91.06
136
138
215.0
200.3
73.10
5.405
40.72
50.43
91.15
138
140
220.2
205.5
72.73
5.571
41.24
50.00
91.24
140
+Inches of Mercury Vacuum.
*Reproduced from Circular No. 12 of the American Society of Refrigerating Engineers.
(2) Cycle of Operation.
(a) The cycle of operation of a refrigeration system comprises four distinct functions:
1 The absorption of heat by the evaporation of liquid refrigerant under low pressure.
2 Forcing the heat contained in the resulting gas to a higher temperature level by compression.
3 The rejection of heat by the condensation and liquefaction of the compressed refrigerant vapor.
4 The reduction of pressure within the evaporator so that the liquid refrigerant may be evaporated and
the cycle repeated.
(b) The refrigeration cycle can be traced from any point in the system. Therefore, referring to the
following figure, let us start with the liquid refrigerant entering the evaporator (cooling coils). The refrigerant is
supplied to the cooling coils by an automatic throttling device called the expansion valve, which is actuated by
both pressure and temperature. The refrigerant as supplied to the inlet side of the expansion valve is in a liquid
state and under high pressure. The expansion valve is one of the division points between the "high side" and
the "low side" of the system.
4-858
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