COLD STORAGE FOR APPLES AND PEARS 



19 



CONDENSER 



The condenser has one purpose. It must permit the passage of 

 heat from the compressed ammonia to the cooling water (or air in an 

 atmospheric condenser) and do so at as low an ammonia temperature 

 as possible. It must transfer all the heat that has been taken up in 

 the evaporator as well as that added by the work of the compressor. 

 The passage of heat into the cooling water is facilitated by a large 

 area of cooling surface, by a large quantity of cooling water, by a low 

 water temperature, and by high velocity of the water and ammonia 

 passing the surface. A high ammonia temperature also increases the 

 quantity of heat transferred to the cooling water, but it is the function 

 of the condenser to receive and discharge the ammonia at as low a tem- 

 perature as possible. The 

 design of the condenser 

 and its operation should be 

 such as to remove the re- 

 quired quantity of heat 

 without excessive ammo- 

 nia temperatures. 



In operation the effec- 

 tiveness of the condenser 

 may be judged by the 

 head pressure indicated 

 on the gage. If the head 

 pressure goes too high, 

 the effects on the system 

 are that less heat is re- 

 moved from the cold 

 rooms and more power is 

 required to operate the 

 compressor. The effect of 

 various high head pres- 

 sures on poAver require- 

 ments at various suction 

 pressures may be seen in 

 the accompanying chart 

 (fig. 2). For example, 

 when operating at a 25- 

 pound suction pressure, and a head pressure of 120 pounds, about 1.0 

 horsepower is required to remove 288,000 B. t. u. per day (1 ton of re- 

 frigeration) ; whereas, at a head pressure of 195 pounds, about 1.5 

 horsepower is required for removing heat at the same rate. That is, 

 the power cost is about 50 percent higher at a 195- than at a 120-pound 

 pressure. At the same time, a high head pressure results in reducing 

 the heat that the system can handle. This is illustrated in figure 3. 



If the head pressure is too high when the plant is running to capacity, 

 it may be because the condenser is too small, there is not enough cooh 

 ing water, the cooling water is too warm, noncondensable gases are 

 present, or the condenser tubes are dirty. The water used in the con- 

 denser usually contains impurities that corrode the pipes and form 



200 



to 



b 

 a. 



§ 



CO 



CO 



8 12 



100 



80 



A 

 A 



A 





/ 





A 



f 



£ 









A 



A 



$ 







/ 





/? 





/ / 



/ 



A 





^Xj> 



/ 







V 



r 



10 15 20 25 30 35 



Suction pressure (pounds persq.rn.) 



Figure 2. — Effect of condensing and suction 

 pressures upon power requirements of a typi- 

 cal ammonia compressor. 



