Improvements in Multitubular Air Heating Apparatus.
Year: 1895

page_text: Date of Application, 21st Sept., 1895-Accepted, 26th Oct., 1895
COMPLETE SPECIFICATION.
Improvements in Multitubular Air Heating Apparatus.
I, SAMUEL CLELAND DAVIDSON of Sirocco Engineering Works, Belfast,
Ireland, Merchant, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
This invention has reference to multitubular air heating apparatus in which the
tubes are heated by live or exhaust steam passing through them.
In apparatus of this type, where the tubes through which the steam passes are
arranged to conduct the steam as a vertical flow and return current from an inlet
chamber in the base of one end of an enclosing compartment to an exhaust chamber
in the base of the other end, the tubes are generally made of a U-shape, but in
such arrangements the elbows or bends of the outer rows of the U-shaped tubes
must be carried over those of the inner rows whereby when several of these rows
of tubes are employed the outer tubes are so much longer than the inner ones that
they exhibit to the steam an equivalently greater amount of cooling and friction
surface, and the various rows are therefore of relatively unequal efficiency in
transmitting the heat from the steam passing through to the air passing over
them. The object of the hereinafter described invention is to have the tubes so
arranged that while any number of rows of tubes for the flow and return current
of the steam can be employed that may be desirable, all the flow and all the return
tubes shall be of equal length, and in order to provide for the difference of
expansion between the flow and return tubes (due to the average temperature of
the flow tubes being considerably higher than that of the return) the flow tubes
are so arranged in a separate group from the return tubes that the expansion of
the former which is greater than the latter owing to the temperature being higher,
can take place independently of the tubes in the return group, so that the greater
expansion of the flow tubes shall not put any detrimental strain on the jointing of
either the flow or return tubes in the perforations of the steam receptacles with
which they are connected.
The improved multitubular air heating apparatus is constructed in two distinctly
separate sections or groups of perfectly straight tubes, securely fitted at both ends
into corresponding perforations in a pair of metal plates which form covers to
trough-shaped chambers or boxes, to which said plates are so secured that these
chambers or boxes form steam chests at both ends of each group of tubes. One
of these steam chests thus formed is preferably employed as the base of its group
of tubes, and for brevity of description I hereinafter refer to same as the lower
steam chest and to the steam chest at the opposite end of same group of tubes as
the upper steam chest. One of the groups of tubes is for flow of the steam
current, and the other group for the return.
The two groups of tubes are placed side by side and the upper steam chests
connected by a pipe of sufficiently large diameter to let the steam freely pass
from the upper steam chest of the one group of tubes to that of the other, and in
order to keep the lower steam chests, with respect to the upper ones, a corre-
sponding distance apart, they are connected by distance bolts. The lower steam
chest of the flow group is suitably arranged to connect with the exhaust steam
pipe from an engine or with a pipe direct from a boiler for the supply of live
steam. The lower steam chest of the return group has the exhaust pipe for
carrying away the uncondensed steam so placed that it also acts as a drain pipe

page_text: '
water; and into this pipe another drain pipe of smaller diameter
is connected from the lower steam chest of the flow group for relieving it also of
condensed water.
The two groups of flow and return pipes are then enclosed in a casing of sheet
iron or other suitable material, and the air to be heated is driven or drawn over
and amongst the tubes by means of a fan or other air propelling apparatus, and I
preferably place the return group of tubes next to the cold air inlet and the flow
group next the hot air outlet from the casing.
The exhaust or live steam, or partly both, on being admitted to the lower steam
chest of the flow group of tubes rises through these tubes to the upper steam chest,
from which it passes through the connecting pipe to the upper steam chest of the
return group and then down through these tubes to the lower steam chest where
the drain and exhaust pipe freely conducts away the remaining steam and with it
the water of condensation.
The accompanying drawings more fully explain the improvements :-
Figure 1 is a longitudinal section of the apparatus on the line XX of Figure 3;
Figure 2 is a cross section on the line Y Y of Figure 3; Figure 3 is a sectional
plan on the line Z Z of Figure 1.
The heating apparatus is divided into two separate sections or groups of tubes,
A representing those for the flow current of the steam and B those for the return.
C is the lower steam chest forming the base of the section or group of tubes A
and into which the exhaust or live steam is admitted by the pipe A¹. The lower
ends of the tubes A pass through and are expanded into a plate D which also
forms a cover for and is bolted to the lower steam chest C. The tubes A also pass
through and are expanded at their upper ends into a plate E which forms the
bottom of the upper steam chest F the top cover of which is formed by the
sheet G. Attached to the sheet G is a pipe H leading to and connecting with
the upper steam chest K of the section or group of tubes B. L is the top cover of
the steam chest K to which the pipe H is also attached. M is the perforated plate
forming the bottom of the chest K and into which the, upper ends of the tubes B
are expanded. N is the perforated plate forming the top cover of the lower steam
chest through which the lower ends of the tubes B pass and into which they are
expanded. P is a small drain pipe for the water condensed in the flow tubes A
and collecting in the lower steam chest C, to drain away into the exhaust and drain
pipe R by which the water and uncondensed steam is carried away from the lower
steam chest O. S is the sheet-iron casing surrounding the tube sections A and B.
T is the inlet for the cold air and U the outlet for the heated air to which outlet
may be attached pipes or other conduits for leading the heated air wherever same
may be required. The lower steam chests C and Ŏ are kept their proper distance
apart by the distance bolts V.
The working of the apparatus is as follows:-
Steam, either exhaust from an engine, or live from a boiler, or partly both, is
admitted to the lower steam chest C by the pipe A¹ and flows up through the
tubes A into the upper steam chest F passing from thence through the pipe H to
the upper steam chest K, then down it through the tubes B into the lower steam
chest finally passing away by the drain and exhaust pipe R. The tubes in the
group A from receiving the first flow of the steam will of course be hotter than
those in the group B and their relative longitudinal expansion will be equivalently
greater, but as the flow and return tubes are all of an equal length, and as the
steam is subjected to a mixing together in the upper steam chests after leaving the
flow group of tubes and before entering the return group, all the tubes in each
group have practically an equal expansion from being at about an equal average
temperature and are therefore about equal in heat transmitting efficiency.
As the pipe H which connects the upper steam chests F and K and the distance
bolts which connect the lower steam chests C and O do not form a rigidly hard
connection between them, but allow of a slight movement of the one group
independently of the other the extra expansion of the flow group A can thus

page_text: take place without in any way detrimentally affecting the jointing of the tubes in
either group; the arrangement of the tubes in two groups of short straight lengths
also combines with the above advantages a highly effective shape of casing for
bringing the air into contact with the hot tubes.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what I
claim is :-
1. The improved apparatus for heating air comprising a group or series of tubes
of equal length for the inflow of the heating steam and a separate group or series
of tubes of equal length for the outflow of the steam the tubes of each group
being inserted at both ends into a steam receiving chamber, so that the steam
has a free passage through the tubes of each group from one end chamber to the
other, and a steam conduit pipe to convey the steam from the second chamber of
the inflow group of tubes to the first chamber of the outflow group of tubes,
substantially as hereinbefore described and as illustrated in the accompanying
drawings.
2. In multitubular air heating apparatus, a separate group or series of tubes of
equal length for the inflow of the heating steam and a separate group or series of
tubes of equal length for the outflow of the steam the two groups being so arranged
that the expansion of the tubes of the one group can take place independently of
the tubes of the other group, substantially as herein before described.
3. The general combination of parts constituting the improved air heating
apparatus substantially as described and as illustrated in the accompanying
drawings.
Th
100g
J. C. MEWBURN & ELLIS,
55 and 56 Chancery Lane, London, Chartered Patent Agents.