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A thimble tube boiler is a form of steam boiler, usually provided as an auxiliary boiler or heat-recovery boiler. They are vertical in orientation and would be considered a form of water-tube boiler. == Description == The characteristic feature of this boiler are its 'thimble tubes'. These are short horizontal water tubes, closed at one end and tapered. They are thus similar to the field-tube boiler, which also uses single-ended closed tubes, but with important differences. The field-tube boiler uses downward-pointing vertical tubes and these also have an internal tube. This extra tube segregates the flow into a central cold downcomer and an upwelling outer flow of heated water and boiling steam. In the thimble tube, there is no such segregation and so boiling is a random process with flow back and forth along the tube. The thimble tube boiler was developed after experiments by Thomas Clarkson and is still firmly associated with the Clarkson firm as a maker. Other makers also produced them in smaller quantities. Niven of Newcastle upon Tyne were granted a patent in 1935, some decades after Clarkson began manufacture, for a relatively small improvement. As boiling is random, the boiler is limited in both its evaporative capacity and also its maximum furnace temperature. However the boiler can offer a large heating area in a small volume, costs comparatively little to construct relative to this area and is also accessible for cleaning. Accordingly the boiler was not generally used as a primary steam power generator but typically as a donkey boiler supporting secondary or hotel services, particularly on-board ships. The boilers were also mostly used as heat-recovery boilers, from the exhausts of large marine diesel engines, as these operated at a lower temperature than a direct-fired boiler. Some were equipped as composite boilers, heated by exhaust gases when under way or with oil-firing when in port. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Thimble tube boiler」の詳細全文を読む スポンサード リンク
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