U.S. patent number 3,681,929 [Application Number 05/095,728] was granted by the patent office on 1972-08-08 for thermoelectric device.
Invention is credited to Hans Schering.
United States Patent |
3,681,929 |
Schering |
August 8, 1972 |
THERMOELECTRIC DEVICE
Abstract
Thermoelectric device includes at least one Peltier block formed
of a plurality of n and p-conductive semiconductor legs and
metallic bridge members interconnecting the legs at opposite warm
and cold sides of the Peltier block, heat exchanger means located
respectively at the warm and the cold sides of the Peltier block
and having a surface disposed adjacent a surface of the bridge
members located at the warm and the cold sides respectively of the
Peltier block, and an intermediate layer of solid insulating
material and deformable medium for improving heat transfer
sandwiched between the surfaces at the warm and the cold sides
respectively of the Peltier block, the insulating material being in
the form of crystalline particles having a grain diameter exceeding
the sum of the roughness depths of the surfaces between which the
respective intermediate layer is sandwiched.
Inventors: |
Schering; Hans (1000 Berlin 20,
DT) |
Family
ID: |
5754028 |
Appl.
No.: |
05/095,728 |
Filed: |
December 7, 1970 |
Foreign Application Priority Data
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Dec 10, 1969 [DT] |
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P 19 63 023.0 |
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Current U.S.
Class: |
62/3.2; 136/204;
136/203 |
Current CPC
Class: |
F25B
21/02 (20130101); H01L 35/32 (20130101); F25B
2321/023 (20130101) |
Current International
Class: |
F25B
21/02 (20060101); H01L 35/32 (20060101); F25b
027/00 () |
Field of
Search: |
;136/203,204 ;62/3 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wye; William J.
Claims
I claim:
1. Thermoelectric device comprising at least one Peltier block
formed of a plurality of n and p-conductive semiconductor legs and
metallic bridge members interconnecting said legs at opposite warm
and cold sides of said Peltier block, heat exchanger means located
respectively at said warm and said cold sides of said Peltier block
and having a surface disposed adjacent a surface of the bridge
members located at said warm and said cold sides respectively of
said Peltier block, and an intermediate layer of solid insulating
material and deformable medium for improving heat transfer
sandwiched between said surfaces at said warm and said cold sides
respectively of said Peltier block, said insulating material being
in the form of crystalline particles having a grain diameter
exceeding the sum of the roughness depths of the surfaces between
which the respective intermediate layer is sandwiched, and a
carrier medium mixed with said crystalline particles, said carrier
medium being in liquid state at least when initially applied to
said surfaces of said bridge members and both of said heat
exchanger means.
2. Thermoelectric device according to claim 1, wherein said
crystalline particles are formed of at least one metal oxide.
3. Thermoelectric device according to claim 2, wherein said metal
oxide is selected from the group consisting of berryllium oxide,
aluminum oxide and quartz.
4. Thermoelectric device according to claim 1, wherein said
crystalline particles are formed of silicon carbide.
5. Thermoelectric device according to claim 1, wherein said
crystalline particles comprise a multiplicity of substantially
spherically shaped granules.
6. Thermoelectric device according to claim 1, wherein said carrier
medium in said liquid state thereof has a viscosity of greater than
100 centistoke.
7. Thermoelectric device according to claim 1, wherein said carrier
medium consists at least partly of silicone oil.
8. Thermoelectric device according to claim 1, wherein said carrier
medium is formed at least partly of a hardening plastic
material.
9. Thermoelectric device according to claim 8, wherein said plastic
material is a synthetic resin having a base of ricinus oil.
Description
My invention relates to thermoelectric device having at least one
Peltier block formed of a plurality of n and p-conductive
semiconductor legs and metallic bridge members interconnecting the
legs at opposite warm and cold sides respectively of the Peltier
block, and having a surface disposed adjacent a surface of the
bridge members located at the warm and cold sides respectively of
the Peltier block, and an intermediate layer of solid insulating
material and deformable medium for improving heat transfer,
sandwiched between the surfaces at the warm and the cold sides
respectively of the Peltier block.
As a general rule, Peltier blocks are constructed so that the n and
p-conductive semiconductor legs are traversed in a meandering
manner by electrical current. The metallic bridge members between
the semiconductor legs of the Peltier block are provided with
respective opposite surfaces, on of which is located at the cold
and the other at the warm side of the Peltier block. Both sides of
the Peltier block are usually provided with heat exchanger devices
in order to dissipate heat produced at the warm side thereof to the
surroundings or to a cooling medium and in order to absorb heat
from the surroundings at the cold side of the Peltier block or to
cool a warm medium thereat.
Since the metallic bridge members at one side of the Peltier block
have different potentials from one another, electrical insulation
is required to be located between them and the heat exchanger
element adjacent thereto, so as to prevent a short circuit through
the metallic heat exchanger element. However, such electrical
insulation causes temperature drop between the respective sides of
the Peltier block and the respective surface of the heat exchanger
elements located adjacent thereto. This is undesirable from the
standpoint of optimum utility of the temperature difference that is
available between the Peltier block and the respective heat
exchanger elements.
It has been known to dispose heat exchanger element foils such as
mica foil or foils of plastic material, for example, between the
Peltier blocks and the respective heat exchanger elements, the
foils being of solid insulating material which electrically
insulates the metallic bridge members from the respective surfaces
of the heat exchanger element. To improve heat transfer, auxiliary
pasty or soft masses can be applied between the Peltier block on
the one hand and the heat exchanger element on the other hand for
filling in unevenesses and roughness depths of the surfaces.
Even when great care is taken, it is possible to damage the
electrically insulating foil, i.e. to rupture or tear the mica or
plastic material foil, during the manufacture of the thermoelectric
device, rendering the thermoelectric device unserviceable.
With respect to other known embodiments of the thermoelectric
device wherein a mechanically stable or reliable connection between
the Peltier blocks and the heat exchanger elements is provided, the
aforedescribed heretofore known type of assembly has the advantage
that the connecting bridge members, on the one hand, and the heat
exchanger elements, on the other hand, can be selected without
being concerned with the different coefficients or expansions of
the material thereof, but only with the electrical and thermal
conductivity thereof. It is especially desired that the surfaces be
movable relative to one another so that the metallic bridge members
and the semiconductor legs rigidly connected thereto, are not
additionally stressed mechanically.
It is accordingly an object of the invention, to provide
thermoelectric device which avoids the disadvantages of the greater
number of heretofore known types of thermoelectric devices and
which is an improvement over the last mentioned advantageous type
of thermoelectric device.
With the foregoing and other objects in view, I provide in
accordance with my invention, thermoelectric device comprising at
least one Peltier block formed of a plurality of n and p-conductive
semiconductor legs and metallic bridge members interconnecting the
legs at opposite warm and cold sides of the Peltier block, heat
exchanger means located respectively at the warm and the cold sides
of the Peltier block and having a surface disposed adjacent a
surface of the bridge members located at the warm and the cold
sides respectively of the Peltier block, and an intermediate layer
of solid insulating material and deformable medium for improving
heat transfer sandwiched between the surfaces at the warm and the
cold sides respectively of the Peltier block, the insulating
material being in the form of crystalline particles having a grain
diameter exceeding the sum of the roughness depths of the surfaces
between which the respective intermediate layer is sandwiched.
Due to the stated dimensions of the crystalline particles, a
minimum spacing between the surfaces to be electrically insulated
is established. The advantages of good heat transfer and high
mechanical stability are provided by the crystalline structure of
the insulating material. In accordance with a further feature of
the invention, metallic oxides, such as berryllium oxide, aluminum
oxide and quartz, having desirable coefficients of
thermoconductivity have sufficiently high electrically insulating
characteristics are suitably employed as the crystalline
particles.
The properties of thermal conductivity between the surfaces of the
device of the invention, is increased to the 10th power when the
crystalline particles are formed of silicon carbide. Silicon
carbide in itself is an electrical conductor; however, by suitable
pre-treatment or when stored for a very long time, an oxide skin or
layer is formed on the silicon carbide crystals and has the
necessary electrical insulation properties.
In accordance with another feature of the invention, the
crystalline particles consist of a multiplicity of substantially
spherically shaped grains. The advantage thereof is that the
desired flow characteristic between the surfaces which are to be
thermally conductively connected, is increased.
In accordance with yet another feature of the invention, in order
to increase the coefficient of heat transfer from the Peltier block
to the heat exchanger, at least part of the crystalline particles
is impressed into the surfaces that are being thermally
connected.
In accordance with still another feature of the invention and in
order to provide a simplified handling of the particulate material
when applied to the surfaces that are to be thermally conductively
connected, the particulate material is mixed with a carrier medium
which is liquid at least when it is applied to the surfaces. Other
added features of the invention are that the carrier medium has an
effective viscosity of greater than 100 centistoke when applied to
the surfaces, and may be formed at least partly of silicone
oil.
In accordance with an additional feature of the invention, the
carrier medium for the particulate material is formed of at least
one hardenable plastic material which is elastically yieldable and
affords equalization of the varying expansion between the heat
exchanger and the Peltier block. In accordance with another, more
specific feature of the invention, the hardenable plastic material
is, for example, artificial resins based on castor oil or ricinus
oil-isocyanate(known in the art by the trademark Desmodur).
Other features which are considered as characteristic for the
invention are set forth in the appended claims.
Although the invention is illustrated and described herein as
embodied in thermoelectric device, it is nevertheless not intended
to be limited to the details shown, since various modifications and
structural changes may be made therein without departing from the
spirit of the invention and within the scope and range of
equivalents of the claims.
The construction and method of operation of the invention, however,
together with additional objects and advantages thereof, will be
best understood from the following description of specific
embodiments when read in connection with the accompanying drawing,
in which:
FIG. 1 is an elevational view of there thermoelectric device of my
invention, showing schematically a Peltier block located between
two heat exchanger elements; and
FIG. 2 is a much enlarged fragmentary sectional view of FIG. 1
enclosed within the circle Z thereof.
Referring now to the drawing and more particularly to FIG. 1
thereof, there is shown therein a thermoelectric device in
accordance with my invention, which is formed with a Peltier block
1 having a cold side 2 and a warm side 3, both sides being
connected to heart exchanger elements 4. Ordinarily, the
connections between the heat exchanger elements 4 and the Peltier
block 1 are effected by non-illustrated clamping members which
press the engagement surfaces 5 of the respective heat exchanger
elements 4 against the warm and cold sides 2 and 3 of the Peltier
block 1. The heat exchanger elements 4 are provided with fins or
ribs 6 through which an air current is passed for suitable warming
or cooling the ribs or fins, as the case may be.
The Peltier block 1 is formed of a multiplicity of n and
p-conductive semiconductor legs and metallic bridge members
coordinated therewith, (only part of the one of the legs 1' and
part of one bridge member 1" being shown in FIG. 2). The Peltier
block is not shown in detail in the drawing, since such devices are
well-known in the art. The semiconductor legs are connected
electrically in series so that an electric current traverses the
semiconductor legs and the connecting metallic bridge members in a
meandering or tortuous path. The metallic bridge members are
formed, for example, of copper, while the metallic heat exchanger
elements 4 are formed of aluminum, for example. Insulation 7 formed
of crystalline particulate material is disposed or sandwiched
between the surfaces 5 of heat exchanger elements 4 of the adjacent
surfaces of the respective bridge members at the warm or cold side
of the Peltier block 1. The grain size or diameter a of the
particles of the insulating material 7 exceeds the sum of the
roughness depths b and b' of the surfaces 3 and 5 respectively. In
the embodiment of FIG. 2, the particulate material 7 is at least
partly pressed into the surfaces 3 and 5 that are being connected
together. To facilitate handling, the particulate material is mixed
with a carrier medium 8 having good heat conductive properties. The
particulate material 7 which is formed, for example, of beryllium
oxide, aluminum oxide, quartz or silicon carbide, is provided with
as spherical a shape as possible in order to improve the flow
properties of the intermediate layer sandwiched between the
respective heat exchanger elements 4 of the Peltier block 1. River
sand, for example, has this spherical shape. The spherical shape
can be produced, however, by polishing or grinding in a ball mill,
for example.
The carrier medium 8 is advantageously in liquid state at least
when applied to the surfaces 3 and 5 that are to be connected
together. The liquid carrier medium 8 advantageously has a
viscosity of greater than 100 centistoke. Naturally, it is possible
to produce a grain medium at least partly of silicone oil.
In certain cases, it is advantageous for the carrier medium to be
formed of an elastic, yieldable and expandable plastic material
which hardens after being applied to the surfaces 3 and 5, such as,
for example, an artificial resin having a base of castor oil or
ricinus oil -- isocyanate. In order to improve further the thermal
conductivity between the Peltier block and the heat exchanger
elements, it may be advantageous to employ additional relatively
smaller electrically insulating particles whose quantity and size
is determined so that they fill the voids located between the
particles of crystalline insulating material 7.
* * * * *