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June, 1916 satisfactory superheating apparatus. These limitations prevailed, to a great extent, till within 15 or 20 years ago, and, naturally, retarded the growth of the superheater and pre- vented the development of apparatus which could be cheaply constructed, efficiently operated, and easily main- tained at a minimum of cost. Design of Details Another factor, which should not be overlooked, was that engineering practice has been relatively crude in respect to the design of details which were in contact with the steam. Cylin- ders, liners, valves, etc., were, in many instances of a quality of ma- FIG. 2—LOVEKIN “SUPERHEATER BOILER” terial which was not always entirely satisfactory, even for saturated steam. These conditions led to the improve- ment of details, not so much with the idea of adapting them to super- heated steam as of making them reliable under saturated steam opera- tion. Many details, thus improved in the past 20 or 25 years, have been found entirely satisfactory for super- heated steam. Other details have required, with the widespread use of highly superheated steam, still fur- ther improvement. It may be ac- cepted that, at the present time in marine practice, satisfactory serv- ice can be obtained from existing designs of details when they are called upon to be in contact with super- THE MARINE REVIEW heated steam at temperatures up ‘to as high as 625 degrees Fahr. The present tendency with regard to superheating is towards an increas- ing amount. This is true not only in marine practice, but also in loco- motive and stationary engineering. It may be a matter of some surprise, to marine engineers generally, to note what is actually being accomplished with the higher degrees of super- heat. The last decade has witnessed a wonderful advance in the adoption of high degrees of superheat on loco- motives. About 40,000 locomotives throughout the world, of which more than 13,500 are in the United States and Canada, are today operating with temperatures in the steam chest above 600 degrees. Fahr. Some roads in this country are using 700 degrees temperature, while in France a large number of engines are operating daily and with wonderful success, at tem- peratures between 750 degrees and &00 degrees Fahr. Superheat Rapidly Adopted In stationary practice the adoption of superheat has been very rapid, and a large number of plants in the United States use at least 150 de- grees of superheat. In marine prac- tice during the last 15 years, over 1,200 ships have been fitted with superheaters, all using 150 degrees of superheat, the majority of which 199 are .operating with practically 200 degrees of superheat. It is not exag- . geration to state that, at the present time, well over 2,000 steamers use superheated steam, the majority op- erating with what we have classed as “high superheat”. In reality, the adoption of superheated steam is world-wide, and is permeating nearly all branches of steam engineering. Aim in Superheater Design In the development heating apparatus there of points which should of a_ super- are a number be ever pres- ent in the mind of. the designer. Efficiency in design is basic. Upon this success or failure of any appa- ooo00 ecco tH ° ] ° ° ° ° a Ss e00000000 S x 0 000.0 00000000 Sy p000000 9700000 ratus must be eventually determined, and without it a low-priced device is of no value. In a great many instances a high efficiency has been offset by one or more of the three points which will be discussed below. “For efficient superheating,” declares one authority, “the tubes should be small, or, if large, should be fitted either with “cores to form “a ‘thin annulus of steam or with deflecting plates to rotate the steam and throw the heavier and colder particles against the hot tube.” Another fundamental widely accept- ed by designers is for a high velocity of steam past the superheating surface. One writer says: “Rapid relative movement of the heat-delivering and