Improvements in Electric Steam Generators and Heaters.
Year: 1891

page_text: Date of Application, 11th Aug., 1891-Accepted, 3rd Oct., 1891
COMPLETE SPECIFICATION.
Improvements in Electric Steam Generators and Heaters.
I, WILLIS MITCHELL, of Malden, in the County of Middlesex, and State of
Massachusetts, United States of North America, Electrician, do hereby declare
the nature of my invention for IMPROVEMENTS IN ELECTRIC STEAM
GENERATORS AND HEATERS, to be particularly described and ascertained in and
by the following statement :-
The object of this invention is to generate steam by electricity more quickly and
cheaply than in the electric steam generators and heaters heretofore employed and
in such volume as to answer the purposes of an ordinary engine boiler. To this
end I employ the construction and combination of parts hereinafter set forth and
claimed.
In the accompanying drawings,
Figure 1 represents a transverse section of a steam generator embodying my.
invention;
Figure 2 represents a longitudinal vertical section of the same, with slight
modifications ;
Figure 3 represents a detail view of the heating cylinder with its outer covering
removed, so as to expose the exterior wire; and
Figure 4 represents a detail view of said heating cylinder, covered, and of the
outlet pipe shown in Figure 1, the two being slightly separated.
Figure 5 represents a further detail view of said heating cylinder to a larger
scale.
then
A designates the boiler or steam generator casing, which is of the ordinary
cylindrical form; B, a reservoir for water arranged in the upper part of the
interior space of said boiler or steam generator; and C, an electric heating device,
consisting of concentric hollow cylinders e preferably of asbestos, on all of which
except the outer one the heating wire D is wound. In winding, the coils or spirals
are prevented from touching each other, every wire being in the space of ten or
twelve, more or less. The method of putting together the electric heating device
is to wind the wire after the fashion above stated on the innermost cylinder
to slip over said cylinder, and the wire thus wound, the second cylinder; then to
wind said wire back on the latter and so to continue until the last cylinder or
covering layer is reached. This acts as a jacket for all. The ends of the wire
extend out from one end of the heating device and form part of an electric circuit.
The spirals or coils of said wire do not fill the spaces between the cylinders or
layers c, which are mainly reserved for the water that is to be heated. The ends
of said heating device are closed; but communication is made between reservoir B
and the spaces between layers c by an inlet pipe E, Figure 1, having several
branches, e, or several independent pipes E, Fig. 2, and an outlet pipe F.
The said inlet pipes extend down from one end of reservoir B and enter inde-
pendently the said spaces between cylinders c, one pipe going to each space as
shown, above the centre of the cylindrical heating device, or the branches e of the
downwardly extending pipe E, Figure 1, likewise enter said spaces. From the
other end of said heating device, branch pipes f extend in like manner, but from
the lower part of each space, to the main outlet pipe F aforesaid. This leads up
to the other end of reservoir B.
The circuit of the water is from one end of said reservoir, through pipes E and e
or E', to each of said spaces; and then through these latter and out by way of
branch pipes and main pipe F to the other end of said reservoir. The circuit of
the electric current in the wire is into the heating device near the centre, thence
around the cylinders c successively, except the exterior one, and finally out again,

page_text: a generator and outside conductors completing it; or it may be reversed, entering
at the outside of the heater and escaping near the centre. The wire is preferably
coated with insulating material, though this is not necessary, if care be taken in
winding.
The heating action is not wholly due to the resistance of the wire; for I have
discovered that when wound at such intervals as stated a very great calorific effect
may be produced in the enclosed spaces without greatly heating the wire itself.
This action I am not able to explain, it being one of those subtle and mysterious'
electrical phenomena, perhaps allied in nature to induction, of which, except by
their results, we as yet know very little. In the present instance, these results are
undoubted, recurring constantly in practice. I am able to handle the wire spirals
without burning my fingers when the heat at the end of the enclosed spaces would
be simply unendurable.
Of course, the wire may be wound in this way on a single cylinder or layer or
core instead of winding it successively on a series of such cylinders as stated. In
that case, the heating device would not be so well suited to the particular use here
specified; but either a heating cylinder of one layer thus prepared or one of several
layers, as above described and shown, may be made use of wherever calorific action
is needed.
Having thus described my invention, what I claim as new and desire to secure by
letters patent is :
1st. In a steam generator, the combination of a water reservoir with a heating
device consisting of a series of layers alternating with water-spaces, a wire forming.
part of an electric circuit and wound on said layers within said spaces, and inlet
and outlet pipes connecting said heating device and reservoir, substantially as and
for the purpose set forth.
2nd. In combination with reservoir B, the concentric, hollow layers having
water spaces between them which are closed at the ends, the wire D wound on said
layers within said spaces and forming part of an electric circuit, the inlet pipes E
extending from one end of said reservoir independently to said spaces at one end
of the heating device, and the outlet pipe having branches whereby the water
passes from the other end of said heating device to the said reservoir, substantially
as set forth.
3rd. A heating device consisting of a core or successive layers and a wire, wound
thereon, forming part of an electric circuit, the winding being such that each wire
coil or spiral is separated considerably from the others and is located in a space
about ten times its own width, more or less, according to the service required, in
order that said wire may generate a heat in excess of the heat of resistance,
substantially as set forth."
In presence of
ROBERT W. SCOTT.
P. R. TRIPP..
WILLIS MITCHELL.