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Tham khảo tài liệu 'intro to marine engineering 2 2011 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | ì 40 Auxiliaries Frame plate Carrier bar Pressure plate Support post Figure 7.5 Plate-type heat exchanger a construction b operation With shell and tube coolers the end covers are removed to give access to the tubes for cleaning. Special tools are usually provided by the cooler manufacturer for cleaning the tubes. The end covers can also be cleaned. Tube leakage can result from corrosion. This can be checked for or identified by having the shell side of the cooler circulated while the Auxiliaries 141 cooling water is shut off and the end covers removed. Any seepage into the tubes will indicate the leak. It is also possible to introduce fluorescent dyes into the shell-side liquid any seepage will show under an ultraviolet light as a bright green glow. Leaking tubes can be temporarily plugged at each end or removed and replaced with a new tube. Plate-type coolers which develop leaks present a more difficult problem. The plates must be visually examined to detect the faulty point. The joints between the plates can present problems in service or on assembly of the cooler after maintenance. Where coolers are out of use for a long period such as during surveys or major overhauls they should be drained on the sea water side flushed through or washed with fresh water and left to dry until required for service. Heaters Heaters such as those used for heavy oil are shell and tube type units similar in construction to coolers. The heating medium in most cases is condensing steam. Distillation systems Distillation is the production of pure water from sea water by evaporation and re-condensing. Distilled water is produced as a result of evaporating sea water either by a boiling or a flash process. This evaporation enables the reduction of the 32000 parts per million of dissolved solids in sea water down to the one or two present in distilled water. The machine used is called an evaporator although the word distiller is also used. Boiling process Sea water is boiled using energy
