These local centers of combustion arc* due to the excess air supply.
In proportion as they cool, the gases drop lower and lower, uni-
formly heating all of the tubes, which for this reason work in a
The Cleveland iron tube air* heater, which is not so widely
known, likewise works upon the (Iwvndrnft principle, (Fig- 70).
The disappearance of the numerous typos of iron tube air
heaters and the survival of the Bcwege.x and Cleveland designs
supplies a very good example of the importance of giving the cor-
rect direction to the circulation of the gases in furnaces.
VI. STEAM BOILERS
The constructors of steam boilers very rarely consider the
rational distribution of the hot, gases. Those defects are particu-
larly frequent in the most recently designed types of water-tube
boilers, an well as in the older designs. The lack of knowledge
of the laws governing the flow of the heated, gases explains the
t d I
numerous and complicated forms of baffling of all. kinds, aB well
as the use of special dampers to force the hot gases to bathe the
heating surface of the boiler and its tubes regularly and com-
(Note, by Englwh trantttatfir. -The* ahHolute neglect and dinregard of tho
most elementary laws of phynicn is not corifinod to tho circulation of the
heated gawK, hut, is gronnly violated in the water ctintulution an well.)
In reality it is not necessary to have any baffling nor walls.
The hot gases have a natural tendency to flow in such a way that
the entire heating surface of tho boiler will be bathed by thorn
in a very uniform and regular manner. Without going into details,