CHAPTER 19 



REFRIGERATION AND AIR CONDITIONING PLANTS 



Refrigeration equipment is used aboard ship 

 for a number of purposes, including the refrig- 

 eration of ship's stores, the refrigeration of 

 cargo, the cooling of water, and the conditioning 

 of air for certain spaces. The distinction be- 

 tween refrigeration and air conditioning should 

 be noted. Refrigeration is only a coolingprocess; 

 air conditioning is a process of treating air so as 

 to simultaneously control its temperature, hu- 

 midity, cleanliness, and distribution to meet the 

 requirements of the conditioned spaces. 



REFRIGERATION 



The purpose of refrigeration is to cool 

 spaces, objects, or materials and to maintain 

 them at temperatures below the temperature of 

 the surrounding atmosphere. In order to produce 

 a refrigeration effect, it is merely necessary to 

 expose the material to be cooled to a colder 

 object or environment and allow heat to flow in 

 its "natural" direction— that is, from the warm- 

 er material to the colder material. For example, 

 a pan of hot water placed on a cake of ice will be 

 cooled by the flow of heat from the hot water to 

 the ice. We can maintain this refrigeration effect 

 as long as the ice lasts. But no matter how much 

 ice we have, we cannot produce a refrigeration 

 effect any greater than the cooling of the water 

 to 32° F. We cannot, for example, cause the water 

 to freeze by this method, since freezing would 

 require the removal of the latent heat of fusion 

 from the water after it had been cooled to 32° F; 

 and for thisprocess we would need a temperature 

 difference that does not exist when both the water 

 and the ice are at 32 F. When the purpose of re- 

 frigeration is theproductionof ice or the mainte- 

 nance of temperatures lower than 32 F at atmos- 

 pheric pressure, it is obvious that ice is not a 

 suitable refrigerant. 



Refrigeration is a process involving the flow 

 of heat, and is therefore a thermodynamic 

 process. From previous discussion in this text, 

 we may surmise that a closed cycle^ would be 

 most practicable for a large-scale refrigeration 

 system. When we try to visualize such a cycle, 

 however, it may appear at first glance that the 

 cycle will have to run backwards. Thus far in 

 this text, we have been primarily concerned with 

 a closed cycle in which thermal energy (in the 

 form of heat) is converted into mechanical 

 energy (in the form of work). Now, instead of 

 wanting to convert heat into work, we want to 

 remove heat from a body and we want to con- 

 tinue to remove heat from this body even after 

 its temperature has been lowered below that of 

 its surroundings, in order to maintain the body 

 at its lowered temperature. In other words, we 

 want to extract heat from a cold body and dis- 

 charge it to a warm area. 



The question is: How can this be done, since 

 we know from the secondlaw of thermodynamics 

 that heat cannot, of itself, flow from a colder body 

 or region to a warmer one? It is entirely pos- 

 sible to extract heat from a body at a low tem- 

 perature and discharge it to a body or region at 

 a higher temperature, provided a suitable expen- 

 diture of energy is made to accomplish this. The 

 energy supplied to the refrigeration cycle for 

 this purpose is in the form of work (mechanical 

 energy) done on the working fluid (refrigerant) 



Thermodynamic cycles are discussed in chapter 8 of 

 this text. A closed cycle is one in which the working 

 fluid never leaves the system except through accidental 

 leakage. Instead, the working fluid undergoes a series 

 of processes which are of such a nature that the fluid 

 is returned periodically to its initial state and is then 

 used again. 



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