Chapter 19. -REFRIGERATION AND AIR CONDITIONING PLANTS 



The refrigerant leaves the evaporator as a 

 low pressure superheated vapor, having ab- 

 sorbed heat and thus cooled the space. The 

 remainder of the cycle is concerned withdispos- 

 ing of this heat and getting the refrigerant back 

 into a liquid state so that it can again vaporize 

 in the evaporator and thus again absorb heat. 



The low pressure superheated vapor is drawn 

 out of the evaporator to the suction side of the 

 compressor. The compressor is the unit which 

 keeps the refrigerant circulating through the 

 system. In the compressor cylinders, the re- 

 frigerant is compressed from a low pressure 

 vapor to a high pressure vapor, and its tem- 

 perature rises accordingly. 



The high pressure R-12 vapor is discharged 

 from the compressor to the condenser. Here the 

 refrigerant condenses, giving up its superheat, 

 its latent heat of vaporization, and its heat of 

 compression to the cooling sea water which 

 flows through the condenser tubes. The refrig- 

 erant, still at high pressure, is now a liquid 

 again. 



From the condenser, the refrigerant flows 

 into a receiver, which serves as a storage place 

 for the liquid refrigerant. From the receiver, 

 the refrigerant goes to the thermostatic expan- 

 sion valve and the cycle begins again. 



From this brief summary of an R-12 vapor- 

 compression refrigeration system, it may be 

 seen that the cycle is indeed one in which heat 

 is "pumped uphill" as a result of the arrange- 

 ments which cause the refrigerant to go through 

 successive phases of expansion, evaporation, 

 compression, and condensation. 



Major Components 



The major components of a shipboard R-12 

 refrigeration plant are shown diagrammatically 

 in figure 19-2. The primary parts of the system 

 are the thermostatic expansion valve, the evapo- 

 rator, the compressor, the condenser, and the 

 receiver. Additional equipment required to com- 

 plete the plant includes piping, pressure gages, 

 thermometers, various types of control switches 

 and control valves, strainers, relief valves, sight 

 flow indicators, dehydrators, and charging con- 

 nections. Figure 19-3 shows most of the compo- 

 nents on the high pressure side of an R-12 

 system, as actually installed aboard ship. 



In the following discussion of the major com- 

 ponents of an R-12 system, we will treat the 

 system as though it had only one evaporator, 

 one compressor, and one condenser. As may be 



seen from figure 19-2, however, a shipboard 

 refrigeration system may (and, indeed, usually 

 does) include more than one evaporator and may 

 include additional compressor and condenser 

 units to provide operational flexibility and to 

 protect against loss of refrigerating capacity. 



THERMOSTATIC EXPANSION VALVE .-The 

 thermostatic expansion valve, shown in figure 

 19-4, is essentially a reducing valve between the 

 high pressure side and the low pressure side of 

 the system. The valve is designed to proportion 

 the rate at which the refrigerant enters the cool- 

 ing coil to the rate of evaporation of the liquid 

 refrigerant in the coil; the amount depends, of 

 course, on the amount of heat being removed 

 from the refrigerated space. 



A thermal bulb for the thermostatic expan- 

 sion valve is clamped to the cooling coil, near 

 the outlet. The bulb contains R-12. Control tub- 

 ing connects the bulb with the area above the 

 diaphragm in the thermostatic expansion valve. 

 When the temperature at the bulb rises, the R-12 

 expands and transmits a pressure to the dia- 

 phragm; this causes the diaphragm to be moved 

 downward, thus opening the valve and allowing 

 more refrigerant to enter the cooling coil. 

 When the temperature at the bulb falls, the 

 pressure above the diaphragm is decreased 

 and the valve tends to close. Thus the tem- 

 perature near the evaporator outlet controls 

 the operation of the thermostatic expansion 

 valve. 



EVAPORATOR.— The evaporator consists of 

 a coil of copper tubing installed in the space to 

 be refrigerated. Figure 19-5 shows some of this 

 tubing. The liquid R-12 enters the tubing at a 

 very much reduced pressure and the boiling 

 point is therefore very much lowered. In pass- 

 ing through the expansion valve, going from the 

 high pressure side of the system to the low 

 pressure side, some of the refrigerant boils and 

 vaporizes because of the reduced pressure and 

 some of the remaining liquid refrigerant is 

 thereby cooled to its boiling point. Then, as the 

 refrigerant passes through the evaporator, the 

 heat flowing to the evaporator from the sur- 

 rounding air causes the rest of the liquid re- 

 frigerant to boil and vaporize. 



After the refrigerant has absorbed its latent 

 heat of vaporization and all the liquid has been 

 vaporized, the refrigerant continues to absorb 

 heat until it has acquired about 10° F of super- 

 heat. The amount of superheat is determined by 

 the amount of liquid refrigerant admitted to the 



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