Improvements in Thermo-electric Elements and Piles.
Year: 1888

page_text: Date of Application, 14th Jan., 1888
Specification Accepted, 17th Feb., 1888
Improvements in Thermo-electric Elements and Piles.
We, ROBERT JACOB GÜLCHER of No. 118 Kurfurstendamm Berlin in the German
Empire, Engineer, and the firm of JULIUS PINTSCH of Nos. 72 & 73 Andreasstrasse
Berlin in the Germany Empire Engineers do hereby declare the nature of this inven-
tion and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statement :—
This invention relates to that description of thermo-electric elements in which a
direct conversion of heat into electricity is effected according to known thermo-electric
principles, and it has for its object, on the one hand, to increase the useful effect of
these elements, and on the other hand to adopt such arrangements as will afford
advantages in their practical construction.
These conditions are in the first instance complied with by making the thermo-
electric bars of which the elements or piles are composed, not, as heretofore, of solid
bodies but of hollow bodies, and so arranged that only their smallest base surfaces are
used for heating, while all the other surfaces are used for cooling the elements. By
this means not only is the electro-motive force produced greater for one and the same
expenditure of heat and the same mass of thermo-electric material, but also, as proved
by experiment the proportion of the length of the thermo-electric bars to their outer
diameter which is necessary for producing the greatest useful effect, is more favourable
than heretofore. Thus while, for instance, with a solid cylindrical bar of a certain
alloy the greatest electro-motive force was obtained when the length of the bar was
from 8 to 10 times greater than the diameter, the requisite proportion between length
and diameter for producing the greatest effect was reduced to from 0.9 to 1.0 when
the bar was made hollow, while retaining the saine outer diameter. And with this
construction the electro-motive force of the hollow cylinder was even greater than with
the solid bar of 8 to 10 times the length.
By means of this considerable reduction in the necessary length of the thermo-
electric bars, not only is a great saving in thermo-electric material effected but the
still greater advantage is attained that the electrical resistance of the thermo-electric
elements is considerably decreased, so that by the use of hollow bodies in place of solid
bars (with the same quantity of heat) not only a higher electro-motive force, but also
a stronger current is obtained.
The simplest form of hollow body which is suitable for the purposes of the present
invention is the above mentioned hollow cylinder shewn at Figure 1 of the accompanying

page_text: drawings. With this form only the annular surface a is heated, while the other
surfaces b c d serve for radiating the heat and consequently for cooling the element.
The annular surfaces a and c form the two poles of the element.
The hollow bodies may however receive other forms suitable for the said purpose;
they may, for example, be formed as hollow parallelopipeds of square, rectangular,
triangular or other polygonal cross-section, or as hollow cones or frustrums, pyramids,
and the like. The essential feature of the present invention is the same in either case,
namely that of forming the element as a hollow body. The cause has not as yet been
fully explained, but it is a fact determined by long continued experiments, that
even without a continual increase of the section through which the current
passes (as with cones, pyramids &c.) The proportion between the length and the
outer diameter of the thermo-electric bars requisite for producing the greatest effect,
is a much more favourable one than heretofore when these bars are made of hollow
bodies.
The total amount of cooling surface plays only a subordinate part in this phenomenon,
as is shewn by the above mentioned example.
We will now describe the different modifications of the above described improved
construction of thermo-electric elements by the use of hollow bodies, as also the
combinations of these with known and new arrangements for practically carrying out
the invention.
In the first place, the inner space of the hollow body may he utilised by the
introduction therein of a solid bar, also of thermo-electric material, as shewn
in Figure 2. The surfaces a a to be heated are connected by a metal piece a¹,
which serves both for conveying the heat to these surfaces, as also for the conducting
connection thereof.
The action of such a compound element can, however, as is shewn by what has been
before stated, be considerably increased if in place of introducing a solid bar, a second
hollow body is introduced into the first one. The form of such inner hollow body may
be similar to that of the outer one or it may be different therefrom. The inner hollow
body may also be either of the same material as the outer one, or it may be of a
different thermo-electric material, as shewn at Figure 3. The two hollow bodies
are in this case supposed to be connected in series, but they may also be arranged in
parallel.
When the two hollow bodies are of different material, they may of course also be
either of the same or of a different form.
3
Figure 3 shews by way of example the combination of two hollow cylinders,
Figure 4 shews the combination of a hollow frustrum of a cone with a hollow
cylinder.
The action of such a combined element may also be further increased by providing
the inner hollow body with air holes! somewhat below the edge of the outer hollow
body, as shewn at Figure 4. In each pair of elements there is then produced a con-
tinuous circulation of air that assists the cooling thereof, the air entering the interior
of the larger hollow body and passing through the air holes into the interior of the
inner body, from the end of which it again escapes into the atmosphere, as indicated
by the arrows.
This circulation of air, and its beneficial action is increased if the outer open end
of the inner body is provided with a chimney or air flue C Figure 5.
These latter may be made of suitable material, but they must be so formed that in
building up several elements to form a pile or battery the current of warm air rising
up from the chimneys does not come in contact with the elements above it, or their
chimneys. For this purpose it is advantageous to arrange the chimneys at a sufficient
inclination W from the vertical as shewn at Figure 5.
A still better action is produced if the chimneys or air flues C of each pair of
elements are led, insulated from each other, to the heating space common to all in such
manner that this space is quite isolated from the outer air and is only fed with warmed
air from the chimneys in a similar manner to the regenerative heating and lighting
apparatus.

page_text: Figure 6 shews a diagram of such an arrangement with a thermo column composed
of several clements.
A A are the outer and B B the inner hollow bodies of the elements. CC are the
insulated air flues which conduct the warmed air into the common heating chamber
where it effects the combustion of the gases issuing from the Bunsen burner E. The
arrows indicate the direction of the air currents. The several elements are insulated
from each other and from the heating chamber and can be arranged either in parallel
or in series.
The combustion gases rising in the combustion chamber draw the air required for
the combustion from the flue C, whereby, on the one hand, the circulation of the air
and consequently the cooling of the elements is increased and on the other hand the
combustible gases are fed with warmed air, whereby an increased heat is produced in
the combustion chamber.
Thus both an increased cooling and an increased heating of the elements is effected
resulting in an increased production of electro-motive force.
In addition to the herein before stated advantages that arise from the use of hollow
bodies and their combinations to thermo-electric elements, and which have the effect of
producing a comparatively high electro-motive force with a small internal resistance of
the elements, other important advantages may be attained thereby, which with the
simplest possible construction, result in the best possible utilisation of the source of
heat, and consequently also a very considerable saving of fuel.
Although an apparatus constructed according to the arrangement shewn in Figure 6
already acts more economically than the thermo-columns heretofore used, for the
above stated reasons, yet the loss of heat with such an apparatus is still considerable.
The common heating chamber absorbs for the heating of its walls, from which the
heat is transmitted to the elements, a considerable amount of heat. Furthermore, a large
quantity of heat escapes upwards from the heating chamber and is entirely lost; and
lastly the heating apparatus itself (i.e. at Figure 6 the Bunsen burner E) absorbs con-
siderable heat without utilising such heat for the production of electricity.
These considerable losses of heat are entirely obviated if the elements formed of
hollow bodies are so arranged that they can themselves be made to serve as their own
heating apparatus. This is effected in the first instance if the inner hollow body of
each pair of elements is used for the conduction of the combustible gases, and if the
ends of both the hollow bodies that have to be heated are provided with one or more
openings communicating with the inner hollow body, through which the gases can
issue and can enter into combustion immediately at the ends of the hollow bodies that
have to be heated. Thus if for example as shewn at Figure 7; such a pair of
elements is arranged vertically with the heated ends downwards, the interior of the
inner body B being connected with the gas supply pipe, and the gas issuing from a small
hole in the bottom be ignited, it will, in burning, apply itself in circular form to the
cominon connecting plate a' (as on account of its lower specific gravity it will tend
to rise on issuing) coming all round in contact with the air and thus producing
perfect combustion, that is, producing a blue smokeless flame as with a Bunsen
burner.
The heat thus produced is by this arrangement almost entirely absorbed by the end
of the pair of elements to be heated, and it is sufficient to provide the plate a' with a
disc F of Mica Asbestos or other bad conductor of heat, of a larger diameter than the
end of the outer body A, in order to protect the upper part of the latter from the
radiated heat of the flame and the current of hot air rising up therefrom.
The gas passing down through the inner body B also has a cooling effect upon the
upper part thereof.
The same result is obtained if a similar pair of elements is placed in an inverted
vertical position as at Figure 8, a plate a² being fixed at a certain distance from the
upper end. By this means the issuing gas is spread out and in that case also burns
with a blue flame, which will be in contact with the surface of the plate a¹ so as to
heat the same, as however by this arrangement the heat given off to the plate a will
be lost it will be evident that it would be of advantage to replace that plate by a

page_text: second pair of elements having its heated end a² downwards as at Figure 9, thus
leaving a space between the two in which the flame burns, so that this serves to heat
the two pairs of elements simultaneously, thus effecting a still greater economy of
fuel.
The upper pair of elements are, as before, provided with a disc F of Mica for
protecting the upper part from the heat.
The inner upper body B may be provided with lateral holes 1, for effecting air
circulation, as previously described.
It will be evident that instead of supplying the gas through the lower inner
elements, it may be made to pass down through the upper ones, as at Figure 7, but
the arrangement shewn at Figure 9 would appear to be the most practical.
Figure 9 also shows the arrangement for combining several pairs of elements to a
pile or battery. J is a hollow stand which is connected by a nozzle with the gas
supply, and from which the gas passes into the several lower inner hollow bodies B
fixed thereon, the corresponding set of upper elements being carried by a standard H
having radial arms C.
The combination of two hollow thermo-electric bodies arranged one within the
other may lastly also be arranged with much advantage for forming their own heating
apparatus in such manner, that instead of heating their surfaces from the outside, they
are heated from the inside.
Figures 10, 11 and 12 shew respectively a vertical section, a plan, and a cross
section at G. H. Figure 10, of such an arrangement.
The inner hollow body B serves to conduct the combustible gas, but it is not
connected directly with the heating plate a¹ but by means of a metal piece C brazed
into the same, of star shaped section, in such manner that a space of a certain size is
formed, between the plate a and the end surface of the body B. By this means there
are formed within the edge of the body B several small openings o Figure 12. The
metal piece C serves at the same time both for effecting the electrical connection
between the two hollow bodies and for transmitting the heat to the body B. The
outer hollow body A is bulged out at its base in order to afford the flame sufficient
room within it, and it is provided with openings (preferably slits) s¹ through which
the combustion gases escape. The bars t, formed between these slits are made to
increase considerably in transverse section towards the base surface in order that the
bars t, may effectually take up the heat and conduct it to the base a.
Pairs of elements thus arranged are preferably fixed vertically upon a gas chamber
common to all, in a manner similar to the lower pairs of elements at Figure 9. The
gas passes, in this arrangement up the body B and through the openings o where it
enters into combustion inside the body A, with the air supply rising up through the
latter; a flame of annular shape giving no smoke will again result, heating the plate al
to a high degree. The heat of the combustion gases issuing through the slits s will in
great measure be taken up by the bars t, which conduct it, as above stated, to the
base a.
It will be readily understood that this arrangement will give a greater useful
effect than those previously described, not only because the heat is utilized to the
greatest extent, but also because by the combustion of the gas within the body A and
the issue of the combustion gases through the slits s, a strong current of air from
outside towards and up through the body A is produced, whereby the lower open end
of the latter is effectually cooled and consequently the difference of temperature
between the two ends and the resulting electromotive force will be increased. The
cooling of the body B is effected, as in the previous arrangements by the current of
gas flowing through it.
With this arrangement however a special device for igniting the gas jet inside the
element is required. This consists simply of a two-way cock common to all the
elements combined in the battery, arranged so that in one position it permits more gas
to flow through than is required for actuating the elements.
When the cock is in this position the gas issues through the slits s and is ignited
outside so that it burns over the element with a blue flame. After a few minutes
the elements will have attained the degree of heat at which the above mentioned

page_text: circulation of air is sufficiently strong to feed an internal flame with sufficient air to effect
perfect combustion. The flame will then shift from the outside through the slits s to
the inside where it will burn within the edge of the body B. The cock is then
turned into its second position so as to supply the elements with only the amount of
gas requisite for their proper action.
It is to be understood that the pairs of elements are suitably insulated from each
other and from the other parts of the apparatus, and that they may be connected
either in series or in parallel. In the diagram at Figure 9 they are shown connected
in series.
The pairs of elements may be made of any size, according to the strength of current
required, and any number of them may be combined in one apparatus according to
the electro-motive force required. It is advantageous to arrange the pairs of elements
in concentric circles. Several such apparatus may also be combined together.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. In thermo-electric elements and piles, constructing the elements of hollow bodies
of thermo-electric material, such as cylinders, cones, and the like, such bodies being
so arranged that only the smallest base surface thereof serve for receiving heat, while
all the other surfaces serve for cooling the element.
2. The combination of a hollow thermo-electric body such as is referred to in the
preceding claim with a second solid or hollow thermo-electric body arranged within
the first named one.
3. In combined thermo-electric elements such as are referred to in the preceding
claim, forming lateral air holes in the inner hollow body, somewhat below the edge
of the outer one, for producing a circulation of air that will assist in the cooling of
the elements.
4. In combination with the arrangement of thermo-electric elements referred to in
the preceding clain, the use of chimnies or air channels, such as C Figure 5 of the
drawings, for accelerating the circulation of air.
5. In the construction of thermo-electric apparatus referred to in the preceding
claim, arranging the chimnies or air channels so as to lead into the heating chamber
common to all, in order to accelerate the circulation of the air through the elements
so as to increase the cooling thereof, and on the other hand to feed the combustible
gases with warm air whereby the heat of the combustion chamber will be increased.
6. The arrangement of the two hollow therino-electric bodies combined, one within
the other referred to in the second Claim, in such manner as to serve simultaneously
as a heating apparatus therefor, the inner hollow body serving as conduit for the
combustible gas, which issues therefrom through one or more openings at the end to
be heated of the elements and enters into combustion either outside both elements, or
within the outer one.
7. Arranging two pairs of elements such as are referred to in the second Claim
with their heated ends opposite each other that the one such pair serves as heating
apparatus as set forth in the preceding claim, while the combustion of the gas issuing
therefrom serves to heat both pairs of elements.
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