We have received from M. Menges (of the Hague) a most interesting
description of an apparatus on which he has been at work for some time
past, with the object of generating electricity by the direct conversion
of heat, or, as it might be more accurately described, by a more direct
conversion than that of an ordinary dynamo. M. Menges' apparatus
depends, like that of Edison, upon the fact that the magnetic metals
lose their magnetic permeability at a certain temperature.
It differs greatly, however, from its predecessor in important points,
especially in the fact that it does not require the aid of any external
source of motive power.
In Edison's pyromagnetic dynamo it will be remembered that it is
necessary to provide some small amount of motive power from an
extraneous source in order to revolve the shield by which the heat is
alternately directed on one half or the other of the armature cores. M.
Menges' apparatus is, on the contrary, wholly automatic.
We proceed to give a free translation of the description furnished us by
the inventor.
In attempting to employ the thermo-magnetic properties of iron or nickel
in the construction of machines for the generation of electricity upon
an industrial scale, we are met with the difficulty that the heating and
cooling of large masses of metal not only involves great loss of heat,
but also requires much time. Hence, to obtain a useful effect of any
importance, it would appear necessary to employ machines of dimensions
altogether impracticable. By the device and method of construction now
to be explained this difficulty has, however, been completely overcome.
The action of a magnetic pole diminishes so rapidly with the increase of
distance that it may suffice to remove the armature to a distance
relatively small compared with its own dimensions, or with those of the
magnet, in order to reduce the action to a negligible value. But if the
magnet, N S, and the armature, A, being at a certain distance, we bring
between them a piece of iron or nickel, d, then the magnetic force
upon A is immediately and very considerably increased. In modern
language, the resistance of the magnetic circuit has been reduced by the
introduction of a better magnetic conductor, and the number of lines of
force passing through A is proportionately increased. The mass of the
piece, d, may, moreover, be relatively small compared with that of N S
and A. If d be again withdrawn, the magnetic resistance is increased,
and the lines through A are again a minimum.
Now, it is evident that we can also obtain the same effect by
sufficiently heating and cooling the intermediate piece, d; and again,
with a broad field we can alter the distribution of the lines at will by
heating or cooling one side of this piece or the other. For this reason
we will call the piece d the _thermo-magnetic distributor_, or, briefly,
the distributor.
We will now describe the manner in which this principle has been
realized in the practical construction of both a thermo-magnetic
generator and motor.
[Illustration: Fig. 1.]
Fig. 1 shows an elevation and part section of one of the arrangements
employed. Fig. 2 is a plan of the same machine (in the latter the ring,
_a a_, appearing on a higher plane than it actually occupies).
[Illustration: Fig. 2.]
N S is an electro-magnet, _a a_ the armature, wound as a Gramme ring,
and fixed to a frame with four arms, which can turn freely upon a pivot
midway between the poles. The cross arms of the frame are attached at 1,
2, 3, 4, Fig. 2. Between the magnets and the armature is placed the
distributor, _d d_, where it occupies an annular space open above and
below. Both the magnets and the armature are coated on the sides facing
the distributor with mica or some other non-conductor of heat and
electricity. The distributor is attached to and supported by the cross
arms, so that it turns with the armature.
The distributor is composed of a ribbon of iron or nickel, bent into a
continuous zigzag. This form has the advantage of presenting, in the
cool part of the distributor, an almost direct road for the lines of
force between the poles and the armature, thus diminishing the magnetic
resistance as far as possible. At the same time the Foucault currents
are minimized. To the same end it is useful to slit the ribbon, as in
Fig. 3. This also facilitates the folding into zigzags.
[Illustration: Fig. 3.]
The distributor is heated at two opposite points on a diameter by the
burners, _b b_, above which are the chimneys, _e e_. The cooling of the
alternate section is aided by the circulation of cold air, which is
effected by means of the draught in the chimneys, _e e_. At the points
of lowest temperature a jet of air or water is maintained. The cross
arms are insulated with mica or asbestos at the points where they extend
from the armature to the distributor.
It will now be evident that while the distributor is entirely cool, many
of the lines of force pass from N to S without entering the armature
core; but if heat is applied at the points 1 and 2 in the figure, so as
to increase the magnetic resistance at these points, then a great
portion of the lines will leave the distributor, and pass through the
armature core. Under these conditions, so long as heat is applied at two
points equidistant from N and S, we might, if we so pleased, cause the
armature to be rotated by an external source of power, and we should
then have an E.M.F. generated in the armature coils--that is to say, the
machine would work as an ordinary dynamo, and the power expended in
driving the armature would be proportionate to the output.
Suppose next that the points of heating, and with them the alternate
points of cooling 90 deg. apart, are shifted round about 45 deg., so
that the two hot regions are no longer symmetrically situated in respect
to each pole of the field. The distribution of the magnetization has
therefore become unsymmetrical, and the iron core is no longer in
equilibrium in the magnetic field. We have, in fact, the conditions of
Schwedoff's experiment upon a larger scale, and if the forces are
sufficient to overcome the frictional resistance, a rotation of the ring
ensues in the endeavor to restore equilibrium. The regions of heating
and cooling being fixed in space, this rotation is continuous so long as
the difference of temperature is maintained. The ring in rotating
carries with it the armature coils, and of course an E.M.F. is generated
in the same way as if the motive power came from an external source. In
this respect the machine therefore resembles a motor generator, and the
rotation is entirely automatic.
The armature coils are connected with a commutator in the usual way, and
the field may, of course, be excited either in shunt or in series. M.
Menges says that the residual magnetization is sufficient in his machine
to start the rotation by itself.
When the machine is to be used as a motor, it is evident that the
windings on the armature core need only be sufficient to supply current
to excite the field, or by the use of permanent magnets they may be
dispensed with altogether.
M. Menges has further designed a large number of variations on the
original type, varying the arrangement of the several parts, and
employing armatures and fields of many different types, such as are
already in use for dynamos.
In Fig. 4 a machine is represented in which the field is external to the
armature.
[Illustration: Fig. 4.]
In Fig. 5 we have a thermo-magnetic generator, which corresponds to the
disk machine in dynamos. Similar parts are indicated by the same letters
in each of these figures, so that no further detailed description is
necessary.
[Illustration: Fig. 5.]
In another modification M. Menges proposes to rotate the burners and
leave the armature and distributor at rest. But in this case it is
evident that the E.M.F. produced would be much less, because the
magnetization of the core would only undergo a variation of intensity,
and would nowhere be reversed, except, perhaps, just in front of the
poles. In machines modeled on the Brush type it is evident that the
distributor need not be continuous.
Enough has, however, been said to indicate the extent of the field upon
which the principle may be applied.--_The Electrician._
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