82

MODERN STEAM PRACTICE.

Fig. 42.—TubulärSuperheater

plates are not carried to the ends of the superheaters, an openingbeing left at these points; thus between the inner and outershells cellular compartments are formed, the steamcoming in at the bottom of one cell travels upwards,and then descends into another compartment, and soon according to the number of compartments, until itis finally carried away by the steam-pipe, the heatedgases in this arrangement acting on the inside tube,the outside shell, and the lower end-plate, all of whichare contained within the bottom part of the funnel.

Again, we have a vertical superheater of the cylindri-cal dass, but instead of one large tube passing throughit, a series of small tubes are securely rivetted to theend-plates, thus forming a multitubular superheater;again, time is required, so it is necessary to placedivision plates, rivetted to the sides and one end, having an open-ing at the other end, thus the steam being admitted at the toppasses downwards, flowing all round the small tubes, and thenupwards in the other compartments according to the number ofdivision plates fitted, until it passes into the steam-pipe to thecylinder. Sometimes the multitubular type has the tubes lyinghorizontally, and division plates so disposed that the steam fromthe boiler enters at the bottom, passing through the small tubes,then returning, and finally passing through the top rows, thus thesteam goes three times through, from the point where it entersthe superheater, at the bottom, to that point at the top on theopposite side where it is taken away by the steam-pipe. In planthis arrangement has the tubes at the central part, the tube-platesbeing inclosed with a circular shell, and the tubes arranged invertical rows. At the middle and sides there is space left so thatthe heated gases are not so much obstructed as when passingbetween the tubes; this makes a very effective arrangement, andmay be reckoned a good example where time is required.

Many examples of tubulär superheaters have been fitted directlyon the tube-plate, some arrangements having the tubes merely a con-tinuation of the tubes in the boiler, the pitch of the tubes in the super-heater being identical. With this plan time is sacrificed and surfaceadopted; however, in some cases the tubes are laid the long way ofthe smoke-box, having boxes at each end, one end in communi-cation with the steam-space in the boiler, and the other with that of