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Use of marine condensers in a refrigeration system

Shell and tube type marine condensers : Marine condensers are generally of the shell and tube type, designed for high pressures. There may a few coil-in-casing or other types still in use. The coolant passes through the tubes with refrigerant condensing on the outside.



Condenser tubes provide heat transfer surfaces in which heat from the hot refrigerant on the outsides of the tubes passes through the walls of the tubes to the cooling water inside. Sea water is the usual cooling medium for shell and tube condensers, but fresh water from central cooling systems is increasingly being used. The refrigerant vapour is cooled first to saturation point, then to the liquid state.

The design of condensers is largely dictated by the quantity and cost of the circulating water, and, where water is plentiful as at sea, a large number of short circuits may be used, to keep pressure drop to a minimum. Water velocity is restricted to prevent erosion of the tubes, usually being kept below 2.5 m/s.

condensers

Fig:Condensers

Marine condensers are very susceptible to corrosion and much research has been done to lengthen their useful life. With halogenated hydrocarbon refrigerants, the use of aluminium brass or cupro-nickel tubes and brass tube plates is acceptable and has reduced the rate of corrosion on the sea-water side.

Refrigerant 717 (ammonia) tends to corrode these materials however, and it has been found necessary to use stainless steel or even bimetallic tubes and clad tube plates, with ferrous metal being in contact with the refrigerant, and non-ferrous with the sea water. The use of sacrificial anodes in the water ends of the condensers is common and sometimes a short length of ungalvanized pipe is fitted between the condenser and the galvanized steel pipe system.

The use of fresh water from a central cooling system closed circuit, avoids the problem of sea-water corrosion.





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