Chapter IS-CONDENSERS AND OTHER HEAT EXCHANGERS 



When the temperature of the outside sea 

 water is relatively high, the condenser tubes are 

 relatively warm and heat transfer is retarded. 

 For this reason, a ship operating in warm trop- 

 ical waters cannot develop as high a vacuum in 

 the condenser as the same ship could develop 

 when operating in colder waters. 



Two basic rules that apply to the operation 

 of single-pass main condensers should be kept 

 in mind. The first is that the OVERBOARD TEM- 

 PERATURE should be about 10° higher than the 

 INJECTION TEMPERATURE. The second rule 

 is that the condensate discharge temperature 

 should be within a few degrees of the temperature 

 corresponding to the vacuum in the condenser. 

 The accompanying chart lists vacuums (based on 

 a 30. 00- inch barometer) and corresponding tem- 

 peratures. 



Inches of Mercury 



Corresponding 

 Temperature (°F) 



29.6 53 



29.4 64 



29.2 72 



29.0 79 



28.8 85 



28.6 90 



28.4 94 



28.2 98 



28.0 101 



27.8 104 



27.6 107 



A main condenser is shown in cutaway view 

 in figure 13-1. A slightly different main con- 

 denser is shown in outline drawing in figure 13-2. 

 The operating principles of the two condensers 

 are identical except for minor details. 



In any main condenser, there are two separate 

 circuits. The first is the vapor-condensate 

 circuit in which the exhaust steam enters the con- 

 denser at the top of the shell and is condensed as 

 it comes in contact with the outer surfaces of the 

 condenser tubes. The condensate then falls to the 

 bottom of the condenser, drains into a space 

 called the hot well , and is removed by the con- 

 densate pump. Air and other noncondensable 

 gases that enter with the exhaust steam or that 

 otherwise find their way into the condenser are 

 drawn off by the air ejector through the air 

 ejector suction opening in the shell of the con- 

 denser, above the condensate level. 



The second circuit is the circulating water 

 circuit. During normal ahead operation, a scoop 



injection system^ provides automatic flow of sea 

 water through the condenser. The scoop, which 

 is open to the sea, directs the sea water into the 

 injection piping; from there, the water flows into 

 an inlet water chest, flows once through the tubes, 

 goes into a discharge water chest, and then goes 

 overboard through a main overboard sea chest. 

 A main circulating pump provides positive cir- 

 culation of sea water through the condenser at 

 times when the scoop injection system is not ef- 

 fective—when the ship is stopped, backing down, 

 or moving ahead at very low speeds. 



All main condensers that have scoop injec- 

 tion are of the straight-tube, single-pass type. 

 A main condenser may contain from 2000 

 to 10,000 copper-nickel alloy tubes. The length 

 of the tubes and the number of tubes depend upon 

 the size of the condenser; and this, in turn, de- 

 pends upon the capacity requirements. The tube 

 ends are expanded into a tube sheet at the inlet 

 end and expanded or packed into a tube sheet at 

 the outlet end. The tube sheets serve as parti- 

 tions between the vapor-condensate circuit and 

 the circulating water (sea water) circuit. 



Various methods of construction are used to 

 provide for relative expansion and contraction of 

 the shell and the tubes in main condensers. Pack- 

 ing the tubes at the outlet end sometimes makes 

 sufficient provision for expansion and contrac- 

 tion. Where the tubes are expanded into each tube 

 sheet, the shell may have an expansion joint. Ex- 

 pansion joints are also provided in the scoop in- 

 jection line and in the overboard discharge line. 

 Additional means such as flexible support feet 

 or lubricated sliding feet are provided to com- 

 pensate for expansion and contraction differen- 

 tials between the shell and the condenser sup- 

 porting structure. 



As shown in figure 13-3, a central steam lane 

 extends from the top of the condenser all the way 

 through the tube bundle, down to the hot well. The 

 exhaust steam which reaches the hot well through 

 this steam lane tends to be drawn under the tube 

 bundle toward the sides of the condenser shell, 

 in the general direction of the air cooling sec- 

 tions, thus sweeping out any air which would 

 otherwise tend to collect in the hot well. Part of 

 the steam which is drawn through the hot well 



^ A major advantage of scoop injection is that it pro- 

 vides a flow of cooling water at a rate which is con- 

 trolled by the speed of the ship and hence is automat- 

 ically correct for various conditions. Scoop injection 

 is standard for naval combatant ships and for many 

 of the newer auxiliary ships. 



349 



