Improvements in Thermo-electric Batteries.
Year: 1891

page_text: Date of Application, 6th June, 1891-Accepted, 11th July, 1891
[Communicated from abroad by ROBERT JACOB GÜLCHER and the firm of JULIUS
PINTSCH, both of Berlin, Germany.]
Improvements in Thermo-electric Batteries.
I, CHARLES DENTON ABEL of 28 Southampton Buildings Chancery Lane in
the County of London, Consulting Engineer and Patent Agent 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 for its object to produce a greater useful effect than has
heretofore been attainable in the direct conversion of heat into electricity by means
of thermo electric batterics or piles.
This object is attained in the first instance by reducing the internal resistance of
the separate rows of thermo electric elements arranged round a heating chamber,
or themselves forming such heating chamber, in the same proportion as the electro-
motive force decreases with the temperature in those parts of the heating chamber
where the elements are more and more distant from the source of heat.
If all the elements of a thermo electric pile be made of the same dimensions and
of the same material, the internal resistances of the separate rows of elements
which are built up to form the pile must all be equal, or nearly so. But as these
rows of elements are situated at varying distances from the source of heat, and the
temperature of the heating chamber decreases gradually from a certain point, the
electromotive force of the rows must also gradually diminish, the greater their
distance from the source of heat.
Now, if the rows of elements be connected with each other in series (for their
connection in parallel is in any case excluded on account of the unequal electro-
motive forces), their electromotive forces will of course run together.
But with each added row the internal resistance increases to an equal extent,
while the added electromotive forces become gradually smaller.
E:
As the total useful effect of the pile is equal to the square of the electromotive
force thereof, divided by its quadruple resistance it follows that the useful
effect of the pile can only be increased by the increase of the number of rows of
elements up to a certain distance from the source of heat, and must begin to decrease
again on the rows of elements being extended beyond that point, because the
internal resistance of the pile increases disproportionately.
It may indeed be
shown by a simple calculation that, commencing from a certain distance, the useful
effect of the entire pile will be even smaller than that of the first row of elements,
so that eventually by the increase of the number of rows of elements, the useful
effect of the pile will be decreased instead of increased.
If however care be taken that in every row the proportion of the internal resistance
to the electromotive force which such row generates in its particular position shall
remain constant, a very different result is obtained.
Thus if, for example the electromotive force in the first row of elements be equal
to E, and the internal resistance equal to R, and if the electromotive force in the
second row be only the internal resistance should only be with a row whose
E
2'
R
R
2
E
the resistance should be and so on. If now
3
3'
electromotive force is equal to
these rows be connected together in series, the useful effect will continually increase
with every added row, even though, at the most distant rows where the temperature

page_text: of the heating chamber is comparatively low, such increase may be very small
and the case cannot occur in which the useful effect of the pile becomes decreased
by an increase in the number of rows of clements; on the contrary, with every
addition there will be some increase. By this means the heat of the heating chamber
will be utilised to the greatest possible extent. The practical carrying out of this
condition of construction presents no great difficulties. After having determined
the necessary dimensions and number of the elements of the first row nearest to
the source of heat, according to the special object in view, the said condition may
be carried out in respect of the following rows by either varying the sections of
the elements while retaining the same number, such as, for example by making the
elements correspondingly higher, or by decreasing the length of the elements to a
corresponding extent. Lastly the condition can also be fulfilled by employing for
the more distant rows of elements where the temperature has sufficiently decreased,
such an alloy of a more fusible nature which produces a comparatively higher
electromotive force than that produced by the metals or alloys of higher melting
point, used in the first rows, and which permits of decreasing the number of clements
in a row, and consequently its internal resistance to a corresponding extent.
Secondly, the useful effect of a thermo-electric pile is increased according to this
invention by connecting the two electrodes of each element at the ends to be licated
by means of an intermediate contact piece of good conducting metal, instead of by
soldering, in such manner that the end of the one electrode is heated considerably
more than the end of the other. This is effected by suitably extending the inter-
mediate contact piece and only subjecting one end thereof directly to the temperature
of the heating chamber, while the other end is insulated by means of suitable bad
conductors of heat from the high temperature of the heating chamber, and only
receives that smaller amount of heat which is transmitted from the first named end
by the body of the intermediate contact piece. With that end of the intermediate
contact piece which is subject to the high temperature is connected the positive
electrode, consisting of a refractory metal such as nickel, while the negative
electrode, generally consisting of an easily fusible alloy, such as antimony and zinc,
is connected to the other end.
If, as was generally done heretofore, the ends of the electrodes that are to be
heated are connected together by solder or by a short intermediate contact piece
so that, on heating the connected part, they each receive an equal or nearly equal
degree of heat, then only such temperatures of the source of heat can be employed
directly for the production of electricity, as are below the melting point of the
easily fused negative electrodes. Higher temperatures must therefore be first
correspondingly reduced by suitable means, such as by a fire clay wall placed in
front of the ends of the elements, &c., before the heat reaches the elements. This
produces a considerable loss of energy which is obviated by the present improved
construction, as with this, the higher temperatures can be utilised without detriment
to the easily fusible electrodes.
By this means alone the useful effect of a thermo-electric battery is already
considerably increased.
But the useful effect is still further increased by the fact that with the new
arrangement the easily fusible electrode need only be made about half as long as
such elements have heretofore been made.
Experiments in this respect have shown that, after having once determined the
proper dimensions of the extended intermediate contact for the high temperatures,
this intermediate contact may be made of the same length also for the lower
temperatures without-in comparison to the old arrangement-decreasing the electro
motive force of the separate elements. In consequence hereof the internal resistance
of a pile made of such elements will only be about half as great as it would
otherwise be, if the elements were constructed according to existing arrangements:
Consequently such a pile yields, with equal electromotive force, an intensity of
current nearly double that heretofore obtained under otherwise the same
conditions.

page_text: If to this be added the gain in electrical energy by the direct utilisation of the
high temperatures of the source of heat, then a pile consisting of elements arranged
according to the present invention will give a useful effect more than double that
obtainable from thermo-electric piles of existing construction. In this the further
increase of useful effect obtained by the first described improvement has been quite
left out of consideration.
On the accompanying drawing Figure 1 shews a vertical section of a thermo-
electric battery constructed according to the conditions of the present invention;
aa is the heating chamber, round which are arranged the wheel shaped rows of
elements 3 &c., which in the example given are placed one above the other.
The points of connection c c of the separate clements themselves form the inner
wall of the heating chamber.
"
The separate elements, as also the rows of elements are insulated from each
other in a suitable manner by means of layers e of material that is at the same
time a bad conductor of heat, such as a mixture of fossil meal and asbestos. The
cooling of the soldered parts d d is effected by copper bands soldered thereto,
which are connected by wires to hoops of insulating material 9 9 such as ebonite,
paraffined wood &c.
The proportion between the internal resistance and the electromotive force is
rendered constant in each row of elements by making the separate elements of
equal size only so far as the temperature of the heating chamber is about at the
same height, such as from to ; from the point where the temperature begins
to decrease, the sections of the elements are made to gradually increase, being for
this purpose increased in height, while the other dimensions remain the same
(1 to 7,10).
The heating chamber a a is heated by means of a Bunsen burner I of hollow
cylindrical form, which imparts to the chamber a constant high temperature over a
tolerably extended surface, such as from to . It will be readily understood that
the thermo-electric pile could also be otherwise heated, such as by a petroleum
burner, or by a coke fire.
g
The rows of elements rest in the present instance upon a suitable stand fixed
together with the burner i kupon a base plate o. Over the rings of the top row
of elements is placed a conical hood h h of sheet iron with a central outlet which
can be connected in any convenient manner with a chimney, in order to expose the
cooling bands to a strong current of air. The hood is provided with lugs
through which and through corresponding lugs on the bottoni stand pass screw
bolts for securing the parts firmly together.
Figure 2 shews a sectional plan of a single row of elements. ce are the con-
necting pieces or intermediate contacts to be heated, which are made of a good
conductor of heat, such as copper. On one side thereof the positive electrodes pp
of sheet nickel are brazed, while the negative electrodes bb of an alloy such as
antimony and zinc, are cast into hollows of the said contacts. The separate
elements, which are placed closely side by side at their connecting parts è c, are
insulated from each other by thin strips of mica 77. The remaining free space
between the elements is filled with a bad conductor of heat e e, with which the
elements are also covered at top and bottom. There are two copper cooling
bands connected to each element, whereby an effective cooling of the outer
soldered points d d is produced. g is the ring of vulcanite or other material to
which the outer ends of the cooling bands are attached.
The drawing shews all the elements connected in series; they may however,
according to circumstances, be all or partly connected in parallel. The mode of
connecting the elements in the one row however determines the mode of connection
of the other rows in the same pile. The rows themselves must, for the grounds
already stated, always be connected in series. Several rows of elements could be
combined together to groups of equal electromotive force, and these groups may
then be connected in parallel. The elements are shewn in the drawing as being
formed of massive bar shaped electrodes, these may however of course have various

page_text: other forms, for example they may be hollow bodies constructed as described in
the Specification to Patent No. 623 of 1888.
Figures 3 and 4 shew two of the new elements with the extended intermediate
contacts C. bare the negative electrodes of easily fusible metal which are cast
around the coned or dovetailed plugs c, of the intermediate contacts. The positive
electrodes consist, for example, of strips of sheet nickel pp, and they are connected
with the ends of the intermediate contacts either by brazing them on as at
Figure 3, or by casting them in as at Figure 4. Only the ends of c c connected to
the positive electrodes are directly subjected to the temperature of the source of
heat, while the ends el connected to the negative electrodes only transmit such
heat to the latter as is conducted from e to 'through the intermediate contact.
For this purpose the elements may be, for example, arranged in the same manner
as shewn at Figure 2, the entire free space both between the extended intermediate
contacts as also between the electrodes being filled with an insulating bad conductor
of heat.
By suitably proportioning the extended intermediate contact a considerable
difference of temperature may be maintained between the two points c and c¹ so
that if for example the positive electrode p has a temperature of say 500° C. and
above, the negative electrode at only receives a heat of say 300° C. which
temperature is below the melting point of the alloy employed.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I claim :-
1. In thermo-electric batteries or piles, so constructing the rows of elements
arranged round a common heating chamber or themselves forming such chamber,
that the internal resistance of the separate rows of elements is reduced in the same
proportion as the electromotive force decreases with the decrease of temperature in
those parts of the heating chamber which are more distant from the source of heat,
whereby the proportion between the internal resistance and the electro-motive
force is made constant throughout all the rows of elements, substantially as
described.
2. The connection of the ends to be heated of the two electrodes forming a
thermo-electric element by means of a suitably extended intermediate contact piece
of good conducting metal replacing the usual soldered joint, such elements being so
arranged that the end of the one clectrode is heated to a greater extent than the
end of the other electrode, only the end of the intermediate contact piece which is
connected to the refractory electrode being directly heated while the other end
only receives heat by conduction, substantially as described.
Dated this 6th day of June 1891.
ABEL & IMRAY,
Agents for the Applicant.