7/28/2019 Use of Shell and Tube Type Marine Condensers in a Refrigeration System

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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 coo lant passes through the tubes with refrigerant condensing on the o utside.

Condenser tubes provide heat transfer surfaces in which heat from the hot refrigerant on the o utsides of the tubes passes through the w alls of the tubes to the coo ling water inside. Sea water is the usual cooling medium for shell and tube condensers, but fresh water from central coolingsystems 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 largenumber of short circuits may be used, to keep pressure drop to a minimum. Water velocity is restricted to prevent erosion o f the tubes, usuallybeing kept below 2 .5 m/s.

Marine condensers are very susceptible to co rrosion and much research has been done to lengthen their useful life. With halogenatedhydrocarbon 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 (amm onia) tends to corrode these m aterials however, and it has been found necessary to use stainless steel or even bimetallictubes and clad tube plates, with ferrous metal being in contact with the refrigerant, and non-ferrous with the sea water. The use of sacrificialanodes in the water ends o f the condensers is co mmon and so metimes a short length of ungalvanized pipe is fitted between the condenser andthe galvanized steel pipe system.

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

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1 20-07-2011 21:53