CHAPTER13 



CONDENSERS AND OTHER HEAT EXCHANGERS 



This chapter deals with the major pieces of 

 heat transfer apparatus found in the condensate 

 and feed system of the conventional steam turbine 

 propulsion plant. Heat exchangers discussed 

 here include the main condenser, the air ejector 

 condenser, the gland exhaust condenser, the vent 

 condenser, the deaerating feedtank, and the aux- 

 iliary condenser. The arrangement of piping that 

 connects these units is discussed in chapter 9 of 

 this text. 



MAIN CONDENSER 



The main condenser is the heat exchanger in 

 which exhaust steam from the propulsion tur- 

 bines is condensed as it comes in contact with 

 tubes through which cool sea water is flowing. 

 The main condenser is the heat receiver of the 

 thermodynamic cycle— that is, it is the low tem- 

 perature heat sink to which some heat must be 

 rejected. The main condenser is also the means 

 by which feed water is recovered and returned 

 to the feed system. If we imagine a shipboard 

 propulsion plant in which there is no main con- 

 denser and the turbines exhaust to atmosphere, 

 and if we consider the vast quantities of fresh 

 water that would be required to support even one 

 boiler generating 150,000 pounds of steam per 

 hour, it is immediately apparent that the main 

 condenser serves a vital function in recovering 

 feed water. 



The main condenser is maintained under a 

 vacuum of approximately 25 to 28.5 inches of 

 mercury. The designed vacuum varies accord- 

 ing to the design of the turbine installation and 

 according to such operational factors as the load 

 on the condenser, the temperature of the outside 

 sea water, and the tightness of the condenser. The 

 designed full-power vacuum for any particular 

 turbine installation may be obtained from the 

 machinery specifications for the plant. Some 



turbines are designed for a full-power exhaust 

 vacuum of 27.5 inches of mercury when the cir- 

 culating water injection temperature is 75° F; 

 others are designed for a full-power exhaust 

 vacuum of 25 inches of mercury with a circulat- 

 ing water injection temperature of 75° F. 



It is often said that an engine can do a greater 

 amount of useful work if it exhausts to a low 

 pressure space than if it exhausts against a high 

 pressure. This statement is undeniably true, but 

 for the condensing steam power plant it may be 

 somewhat misleading because of its emphasis on 

 pressure. The pressure is important because it 

 determines the temperature at which the steam 

 condenses. As noted in chapter 8 of this text, an 

 increase in the temperature difference between 

 the source (boiler) and the receiver (condenser) 

 increases the thermodynamic efficiency of the 

 cycle. By maintaining the condenser under vac- 

 uum, we lower the condensing temperature, in- 

 crease the temperature difference between 

 source and receiver, and increase the thermody- 

 namic efficiency of the cycle. 



Given a tight condenser and an adequate sup- 

 ply of cooling water, the basic cause of the vac- 

 uum in the condenser is the condensation of the 

 steam. This is true because the specific volume 

 of steam is enormously greater than the specific 

 volume of water. Since the condenser is filled 

 with air when the plant is cold, and since some 

 air finds its way into the condenser during the 

 course of plant operation, the condensation of 

 steam is not sufficient to establish the initial vac- 

 uum nor to maintain the required vacuum under 

 all conditions. In modern shipboard steam plants, 

 air ejectors are used to remove air and other 

 noncondensable gases from the condenser. The 

 condensation of steam is thus the major cause 

 of the vacuum, but the air ejectors are required 

 to help establish the initial vacuum and then to 

 assist in maintaining vacuum while the plant is 

 operating. 



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