A series of heat-transmission tests undertaken two years ago, is being
continued on the ground floor of Building No. 21, on modified apparatus
reconstructed in the light of the earlier experiments by Mr. W. T. Ray.
The purpose of the tests on this apparatus has been to determine some of
the laws controlling the rate of transmission of heat from a hot gas to
a liquid and _vice versa_, the two being on the opposite sides of a
metal tube.
It appears that four factors determine the rate of heat impartation from
the gas to any small area of the metal[17]:
[Footnote 17: The assumption is made that a metal tube free from scale
will remain almost as cool as the water; actual measurements with
thermo-couples have indicated the correctness of this assumption in
the majority of cases.]
(1).--The temperature difference between the body of the gas and the
metal;
(2).--The weight of the gas per cubic foot, which is proportional to
the number of molecules in any unit of volume;
(3).--The bodily velocity of the motion of the gas parallel to any
small area under consideration; and (probably),
(4).--The specific heat of the gas at constant pressure.
The apparatus consists of an electric resistance furnace containing
coils of nickel wire, a small (interchangeable) multi-tubular boiler,
and a steam-jet apparatus for reducing the air pressure at the exit end,
so as to cause a flow of air through the boiler. A surface condenser was
attached to the boiler’s steam outlet, the condensed steam being weighed
as a check on the feed-water measurements. A number of thermometers and
thermo-couples were used to obtain atmospheric-air temperature,
temperatures of the air entering and leaving the boilers, and feed-water
temperature.
The apparatus is now being reconstructed with appliances for measuring
the quantity of air entering the furnace, and an automatic
electric-furnace temperature regulator.
[Illustration: PLATE XIX.
Fig. 1.--Gas Producer, Economizer, and Wet Scrubber.