The condenser receives the high-pressure, high-temperature refrigerant vapor from the compressor. In the condenser, the refrigerant vapor flows around tubes through which seawater is flowing. As the vapor gives up its superheat (sensible heat) to the seawater, the temperature of the vapor drops to the condensing point. The refrigerant then changes to a liquid and is sub-cooled slightly below its condensing point. This is done at the existing pressure to ensure that the liquid refrigerant will not flash into vapor.

A water-cooled condenser for an R-12 refrigeration system is shown in figure 16-11. Circulating water is obtained through a branch connection from the fire main or by an individual pump taking suction from the sea. The purge connection, shown in figure 16-11, is on the refrigerant side. It removes air and other noncondensable gases that are lighter than the R-12 vapor.

Figure 16-11.-Cutaway view of a water-cooled condenser for an R-12 refrigeration system.

Most condensers used for shipboard refrigera-tion plants are of the water-cooled type. However, some small units have air-cooled condensers. Air-cooled condensers consist of tubing with external fins to increase the heat transfer surface. Most air-cooled condensers have fans to ensure positive circulation of air around the condenser tubes.