Inasmuch as one of the first problems to be attacked will be the
determination of the length of travel and the time required to complete
combustion in a flame in which the lines of stream flow are nearly
parallel, great care was taken to make the inner surfaces of the tunnel
smooth, and all corners and hollows are rounded out in the direction of
travel of the gases.
Provision is made, by large peep-holes in the sides, and by smaller
sampling holes in the top, for observing the fuel bed at several points
and also the flame at 5-ft. intervals along the tunnel. Temperatures and
gas samples are taken simultaneously at a number of points through these
holes, so as to determine, if possible, the progress of combustion
(Fig. 1, Plate XVIII).
About twenty thermo-couples are embedded in the walls, roof, and floor,
some within 1 in. of the inside edge of the tunnel walls, and some in
the red pressed brick near the outer surface, the object of which is to
procure data on heat conduction through well-built brick walls[16] (Fig.
2, Plate XVIII).
In order to minimize the leakage of air through the brickwork, the
furnace and tunnel are kept as nearly as possible at atmospheric
pressure by the combined use of pressure and exhausting fans.
Nevertheless, the leakage is determined periodically as accurately as
possible.
At first a number of tests were run to calibrate the apparatus as a
whole, all these preliminary tests being made on cheap, carefully
inspected, uniform screenings from the same seam of the same mine near
Pittsburg. Later tests will be run with other coals of various volatile
contents and various distillation properties.
It is anticipated that the progress of the tests may suggest changes in
the construction or operation of this chamber. It is especially
contemplated that the section of the chamber may be narrowed down by
laying sand in the bottom and fire-brick thereon; also that baffle walls
may be built into various portions of it, and that cooling surfaces with
baffling may be introduced. In addition to variations in the tests, due
to changes in construction in the combustion chamber, there will be
variations in the fuels tested. Especial effort will be made to procure
fuels ranging in volatile content from 15 to 27 and to 40%, and those
high in tar and heavy hydro-carbons. It is also proposed to vary the
conditions of testing by burning at high rates, such as at 15, 20, and
30 lb. per ft. of grate surface, and even higher. Records will be kept
of the weight of coal fired and of each firing, of the weight of ash,
etc.; samples of coal and of ash will be taken for chemical and physical
analysis, as well as samples of the gas, and other essential data. These
records will be studied in detail.
[Illustration: Fig. 17.