180 SUPERHEATED STEAM IN MARINE PRACTICE. 



quire space which can generally be otherwise used to advantage. Then, too, there 

 are heat losses from this type of superheater, as it cannot use all the heat gen- 

 erated in its furnace. 



31. Fig. 2, Plate 90, shows another form of separately fired tubular super- 

 heater, in general resembling a torpedo-boat boiler. This was installed in a num- 

 ber of ships, but the writer has been unable to find the date on which this design 

 first appeared. It was described by Mr. A. F. White before the Institution of Naval 

 Engineers on November 15, 1909. There can be no doubt as to this construction 

 developing high degrees of superheat. 



32. Waste-gas superheaters have appeared in a large variety of forms. Per- 

 haps the two most commonly known in connection with fire-tube boilers are the Wat- 

 kinson and the Foster. Fig. 3, Plate 91, shows a design which was used some time 

 before it was described by Professor Watkinson in his paper previously referred to. 



33. The Foster superheater, Figs. 4 and 5, Plate 91, basically resemble the 

 Watkinson, in that it is a U-shaped pipe with separate saturated and superheated 

 headers. It has been modified in its detail by the following: — 



1st. The introduction of a core, causing the stream to flow in a thin layer be- 

 tween the core and the pipe. 



2d. The outer surface of the pipe is provided with corrugations, for the purpose 

 of protecting the pipe against corrosion, and affording greater heat-absorbing 

 surface. 



3d. Improvement in the means for attaching pipes to the header is provided in 

 this design. 



34. It should be noted that the introduction of the core causes two changes in 

 the steam section in each unit. It would appear that still further improvement is 

 possible in this respect, by making the core continuous through the length of the 

 element. 



35. Fig. 6, Plate 92, illustrates Watkinson's waste-gas superheater of tubular 

 construction. In this design, shown as applied to a single-ended Scotch boiler, part 

 of the gases are conveyed through the back end to a chamber containing the super- 

 heater units, and from this chamber passed to the stack. 



36. Fig. 7, Plate 93, shows the Lovekin "superheater boiler," and is of the 

 waste-gas, cellular construction. It is interesting to note some points of similarity 

 between this and Fig. 6. Both by-pass the gases from the combustion chamber to 

 the superheating surface, Watkinson building the superheater outside the boiler, 

 while Lovekin builds the superheater in the form of boiler tubes which carry the 

 gases and are surrounded by steam. Both forms of construction provide for shut- 

 ting off the gases from the superheating surface, and consequently controlling the 

 degree of superheat, if desired. 



37. Live-gas superheaters were first brought out by Schmidt in 1898, and are 

 illustrated by Fig. 8, Plate 94. This particular design is termed the "fire-tube type," 

 as the superheater unit is introduced into the boiler tube. It is claimed that over 

 a million and a half horse-power of marine engines are being supplied with highly 



