Patent Application
20060179849
1. Field
The following invention disclosure is generally concerned with: solid state heat transfer systems and specifically concerned with highly efficient Peltier effect semiconductor cooling systems.
2. Prior Art
Peltier effect heat transfer systems have enjoyed considerable success in various applications. They are clean, simple with no moving parts, long lasting, easy to use, reliable, among other things. In brief alternating ‘P’ type and ‘N’ type doped semiconductor elements are connected together to form a serial electronic circuit and a parallel thermal circuit. At each PN junction, electrons are driven from the conduction band of the ‘N’ material, into lower energy levels of the conduction band in the ‘P’ materials. This is necessarily accompanied by localized heating in the junctions and/or connector as the energy difference becomes converted to heat. Conversely, when electrons pass from a ‘P’ type material into a ‘N’ type material, the electrons are promoted to higher energy levels and absorb energy; i.e. cooling occurs in these types of junctions. When these devices are arranged such that heating occurs in one location and cooling in another, the result is a heat transfer system having wonderful characteristics.
In some high performance systems known in the art, a first stage Peltier cooler is coupled to a second stage cooler. The first stage may have a small surface area ‘cold side’ and a ‘hot side’ (of similar size) coupled to a large ‘cold side’ of the second stage. The thermal load of the second stage is higher than the first and it is advantageous to deploy that second stage in a configuration of increased surface area, that is increased surface area in comparison to the first stage. This can be seen in many versions of systems presented by experts in the literature. In particular,
While Peltier type, all-electronic, heat transfer systems are quite well known, these are generally deployed with geometries necessary to support the primary characteristics associated with a large plurality of semiconductor elements simultaneously arranged in a serial electronic circuit and a parallel thermal circuit. Most typically, a plurality of roughly cubic, alternately doped semiconductor elements is distributed over a planar region to yield an opposing ‘cold side’ and ‘hot side’; i.e. the parallel thermal circuit. This is a well known standard arrangement.
It is notable that the terms ‘hot side’ and ‘cold side’ are quite standard in the industry. These terms come from the fact that physical construction constraints tend to demand that many thin semiconductor elements are laid about in a planar region and are typically sandwiched between buffer substrates on either side to form a thin planer device in which one side cools while the other heats. Although alternative arrangements are possible, it is nearly invariable that Peltier cooling systems are configured this way.
In Fritz et al, U.S. Pat. No. 5,515,238 a system is presented with reduced spacing between semiconductor elements thereby improving its performance. However, these systems adopt similar architecture as their predecessors and have area ratios, hot side/cold side which are quite close or equal to one.
One notable exception is taught by Douglas Hoffman in a vapor compression cycle refrigeration system of U.S. Pat. No. 5,361,587. Because Hoffman deploys his thermoelectric cooler as a gas condenser, it is quite inconvenient to bring gas into contact with a planar surface. So, Hoffman arranges his doped semiconductor elements about the outside surface of a cylinder in which gas can be made to flow. He improves the surface area of the heated portion by adding cooling fins to increase the heat transfer to passing air.
Another important new development in related arts includes the disclosure of US Patent Application Publication numbered: 2004/0120156 A1 of Jun. 24, 2004. These inventions relate to combinations of Peltier cooling systems with LED devices to effect a high performance/high power light source. The suggested devices are brilliant systems having great potential to provide exceptional lighting performance features. However, they are constructed upon “out-of-the-plane” technologies well know in Peltier system arrangements. Further, they do not provide asymmetrical cool/hot areas which yield advantage to point type heat sources such as the LEDs being cooled with the device.
While systems and inventions of the art are designed to achieve particular goals and objectives, some of those being no less than remarkable, these inventions have limitations which prevent their use in new ways now possible. Inventions of the art are not used and cannot be used to realize the advantages and objectives of the inventions taught herefollowing.
Comes now, Abramov, V. S.; Sushkov, V. P.; Polistanskiy, Y. G.; Shishov, A. V.; and Scherbakov, N. V., with inventions of heat transfer systems including semiconductor devices for highly localized cooling. It is a primary function of these systems to provide efficient heat management to improve the performance and lifetime of a device otherwise susceptible to damage from heat energy.
Point Source
A first distinguishing factor can be found in the fact that these systems are designed for point heat sources. Cold portions of these systems are arranged as a small circular ‘point’. As such, they are particularly suitable for small single element semiconductor heat sources such as lasers and light emitting diodes. Thermal electric coolers of the art are almost exclusively designed to couple with large area planar heat sources. As such systems of the art typically have a large area cold plane.
Another primary distinguishing feature of inventions presented herein relates to asymmetric hot and cold areas. Systems first taught here include a cold area having a size much smaller than the size of the hot area. As such, a greater capacity to dissipate heat is realized. In these systems, ‘cold sides’ of the art are translated to a small circular area in these systems. A cold area is made far smaller than the warm area to which it is connected. As such, the heat transfer power, is ‘focused’ to a small point and concentrated. This supports cooling of devices which are heat point sources. These arrangements provide a leveraged advantage; as heat dissipation depends upon the area over which heat may be transferred.
When the hot area is large in comparison to the cold area, an advantage is realized whereby the cold area is far more effectively cooled than when the areas are similar as commonly found with systems known in the art. Typically, the cold side and hot side of a Peltier cooler are each separated from ambient temperature by approximately the same temperature difference. When the cold area is much smaller than the hot area, an asymmetric temperature difference is realized. The cold area is considerably colder than ambient temperature when compared to the amount by which the hot area is hotter than ambient temperature. Such asymmetric temperature difference favors heat transfer system objectives in preferred versions as will be more clear in view of the full disclosure herefollowing.
These systems are further distinct from those in the art as they are build into a single plane architecture. In best versions, a cold area, a hot area, and Peltier heat transfer elements all lie in the same plane. By comparison, the art only contains those having parallel planes separated and space from one-another in an orthogonal direction. Here, a circular cold area lies concentric with a annular hot area of far greater size. These are coupled together via Peltier element arranged in a radial fashion. Accordingly, present inventions include radically different thermal circuits of rather distinct geometry. While still maintaining a serial electric circuit, a radial distribution of semiconductor components forms concentric areas in a single plane which correspond to a ‘hot side’ and a ‘cold side’ known in common Peltier devices. In best versions, a ‘cold area’ lies concentric with and interior to a ‘hot area’; both lying substantially in the same plane. A flat planar arrangement is advantageous as it cooperates well with the two dimensional architecture of electronic circuit boards. Peltier heat transfer systems of these inventions can be considered two dimensional devices in striking comparison to the more typically three dimensional systems having significant extent along a normal axis with respect to the planes in which they are built.
In most general terms, heat transfer systems of these inventions are defined as being comprised of: one or more semiconductor pair of at least one ‘P’ type and one ‘N’ type element, each element having a cold end and a hot end, further having an active area thermally coupled to the cold ends and a heat dump thermally coupled to the hot ends, whereby the heat dump is appreciably larger in area than the active area. Thus, these systems benefit from an efficient heat spreading scheme where heat from a very small area (source) is distributed to comparatively very large areas via Peltier effect semiconductor elements.
It is a primary object of these inventions to provide electronic heat transfer systems.
It is an object of these inventions to provide heat transfer systems having an improved area ratio with respect to hot and colds ‘sides’.
It is a further object to provide systems compatible and cooperative with the planar nature of circuit board topology.
It is an object of these inventions to provide heat transfer systems most suitable for point source heat generating elements.
A better understanding can be had with reference to detailed description of preferred embodiments and with reference to appended drawings. Embodiments presented are particular ways to realize these inventions and are not inclusive of all ways possible. Therefore, there may exist embodiments that do not deviate from the spirit and scope of this disclosure as set forth by appended claims, but do not appear here as specific examples. It will be appreciated that a great plurality of alternative versions are possible.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims and drawings where:
Throughout this disclosure, reference is made to some terms which may or may not be exactly defined in popular dictionaries as they are defined here. To provide a more precise disclosure, the following terms are presented with a view to clarity so that the true breadth and scope may be more readily appreciated. Although every attempt is made to be precise and thorough, it is a necessary condition that not all meanings associated with each term can be completely set forth. Accordingly, each term is intended to also include its common meaning which may be derived from general usage within the pertinent arts or by dictionary meaning. Where the presented definition is in conflict with a dictionary or arts definition, one must use the context of use and liberal discretion to arrive at an intended meaning. One will be well advised to error on the side of attaching broader meanings to terms used in order to fully appreciate the depth of the teaching and to understand all the intended variations.
Semiconductor element—a semiconductor element is a bulk material typically formed as a crystal which may be doped with an impurity (or impurities) to form a lattice which supports transmission of electrical currents.
Semiconductor element pair—a semiconductor element pair includes one ‘P’ type doped semiconductor element and one ‘N’ type doped semiconductor element in a similar crystal both in composition and geometry.
Heat source—is a device which generates heat and enjoys improved performance when cooled by a heat transfer system.
Heat dump—a heat dump is a thermal body into which heat may be transmitted and passed from a heat transfer system.
‘Hot area’—a hot area of these heat transfer systems roughly corresponds to the ‘hot side’ of a common Peltier cooler except that its geometry is not a ‘side’ but rather an area of typically circular section.
‘Cold area’—a cold area of these heat transfer systems roughly corresponds to the ‘cold side’ of a common Peltier cooler except that its geometry is not a ‘side’ but rather an area of typically circular section.
Active area—an active area includes the junction between a heat source and a cold area of a heat transfer system.
While ‘hot area’ and ‘cold area’ are used extensively throughout this disclosure, it will be understood by experts that reversal of the current will reverse the heating/cooling action at each, thus hot areas become cold areas and visa-versa. Cooling at the center is suggested throughout for consistency but lost of generalization is not intended by this nomenclature and reversal is fully anticipated for point source heating or temperature stabilization applications.
In accordance with each of preferred embodiments of these inventions, there is provided apparatus for heat transfer. It will be appreciated that each of the embodiments described include an apparatus and the apparatus of one preferred embodiment may be different than the apparatus of another embodiment.
Systems described herefollowing are primarily distinctive and characterized by the following features: 1) the ‘cold side’ is fashioned as a point or very small circular area; 2) the system is embodied in a substantially planar scheme having a radial pattern; and 3) the hot/cold area ratio is high or greater that about 1.2. These features can only be realized via the very unique and new geometries which will become apparent in the following presentation.
The cooled portion of these special heat transfer devices can be very small indeed. The geometric nature of the devices permits a ‘cold area’ which approximates a point. All the cooling action is focused into a very small portion at the center of a radially symmetric configuration. As such, these systems are most appropriate for use in conjunction with systems which demand heat control at a point as opposed to the cooling in a planar section commonly found in art.
The geometric nature of these systems are further distinct in that their components are built in a common plane quite unlike their better known cousins. That is, the cold area, the hot area, and the transfer elements (Peltier elements) are all in approximately the same plane; by ‘approximately in the same plane’ it is meant that the aspect ratio of these devices may be about 5 or greater. The hot and cold areas may be coplanar and are generally concentric. In the art, systems are built in the orthogonal direction with respect to a first cooling plane, a second heating plane and the space therebeween which is necessarily not zero or thin. Because of this new arrangement, these systems can be supported in normal circuit board construction and deployment. These systems can be built integrally therewith other electronics on a single circuit board; the Peltier elements being inserted or soldered alongside resistors, capacitors, ICs, et cetera. Peltier coolers of the arts are added to circuit boards into space reserved for them and their hosted device is added to a coupling at the cooling plane. They are not formed integrally with the common circuit board components. A major distinction of these systems is immediately obvious in consideration of the fact that the hot and cold areas (along with circuit traces, active area, et cetera) are coplanar.
Finally, one may consider the ratio of area sizes—the cold area with respect to the warm area. A most effective heat transfer system distributes or dissipates heat into a heat dump. The larger the heat dump, the more effective it may sink heat. The geometric nature of these systems and their unusual configurations permit very high ratio of hot area to cold area which improves the effectiveness of the system task at hand: heat transfer. These systems couple to a virtual point; while common Peltier systems couple to a large 2 dimensional flat area.
In addition to the core heat transfer systems, these inventions also include heat transfer systems in combination with special high performance electronic devices and specially configured heat sinks. These systems interface with special heat generation devices such as a high performance semiconductor lasers or light emitting diodes for example; heat point sources. That is, these sources are considerably small and may highly localized heat generation mechanisms. In this regard, they cooperate very well with the radial geometry suggested throughout this presentation. One might consider the heat transfer systems presented here an efficient bridge between a high performance heat point source and a spatially distributed heat dump. Further, these systems are primarily built in a single plane raising their compatibility with circuit board technologies. They may be fabricated in automated systems supporting common circuit board manufacture; a considerable advantage.
The cold area configured as a small circular area is ideally suited to accommodate therein a single element high performance electronic device, for example a Quantum Cascade Laser, which benefits greatly from operation at reduced temperatures. Similarly, high output light emitting diodes, LEDs, can have higher light output when they are aggressively cooled by active devices such as the heat transfer systems taught here. As the LED is virtually a point source, its geometry cooperates with the cold area of these heat transfer systems. Other devices which will enjoy benefits particular to these systems also include detector systems—in particular infrared detectors which have greatly reduced noise when operated in a cooled state. Thus, these inventions include radially configured Peltier cooling systems in conjunction with a point, single element electronic heat source; either semiconductor lasers, light emitting diodes, and photodetectors by way of example.
In addition, it is not merely a cooling function in which these devices are well suited, but rather temperature stabilization at a point. Since these heat transfer systems are particularly powerful at finite and small areas, electronic devices having that property and which benefit from temperature stabilization, will find greatly improved performance when used together. The high area ratio further magnifies the ability of these systems to quickly respond to temperature changes and correct them in stabilization schemes. In contrast, a planar Peltier system has a far higher thermal momentum at the cold side and cannot quickly respond to need for a temperature adjustment.
Systems of these inventions also include the combination of heat transfer systems with heat sinks particularly configured for proper interface with such heat transfer systems having a particular geometric characteristic. That is, heat sink systems arranged with an annular interface which may be thermally coupled to the hot area of the heat transfer system. The hot area is the structure which permits output (heat) from the heat transfer system and thus, heat sinks which effective cooperate with these heat transfer systems are particular in their geometric construction as they will permit such interface. Examples are presented herefollowing of a cooling fin arrangement. One will also appreciate that other heat sinks having an annular receiving interface provide particular advantage to these heat transfer systems and are accordingly part of the combinations claimed here.
These inventions will be most clearly understood in view of examples including those which have reference to drawings appended hereto. In a most basic first illustrative example a heat transfer system with asymmetric heating/cooling areas is presented in
In preferred versions, each element of the thermocouple is arranged in the shape of a pie-wedge portion. That is, a pseudo-triangular shape with its apex missing (see diagram). The tip of the apex is omitted in order that the centermost area is left empty. In some arrangements, this is required as this is the location into which the heat load is placed and connectors and Peltier elements might otherwise interfere with normal operation of this device.
The semiconductor elements may be semiconductor crystals formed in accordance with common semiconductor growing schemes. They are doped in accordance with designs whereby alternating elements are comprised of ‘N’ and ‘P’ type semiconductor material. In some versions, crystals may be first grown, then cut to preferred shapes, and cut with preferred crystalline orientation, then assembled into the designs taught here. This is particularly the case when it becomes desirable to manipulate the crystalline axis direction with respect to the device geometries. Thus these thermocouple elements may be formed separately and later soldered into place in the wheel framework device. Alternatively, the Peltier elements may be grown directly on a substrate. A two step process would permit all of the ‘P’ type elements to be grown at once. In a separate step, all of the ‘N’-type elements could be grown together.
Sometimes herein, we refer to the centermost region of a disk shaped device as the ‘active area’. Into the center we typically place a heat source and more specifically, a heat source having a geometric approximation of a point source. A laser for example, or other high power electronic device which produces significant heat but benefits from being cooled, is thermally coupled to the active area whereby the cooling effect brought by the heat transfer system is enjoyed by the high performance device.
Similarly, the ‘hot area’ at the system periphery is preferably coupled to a heat sink sometimes herein called a “heat dump”. In simple versions, the surrounding air is sufficient to carry away heat from the hot area and the hot area operates as a radiator. In some versions having high thermal loads, a cooling fin arrangement can aid in increasing further the area from which heat is spread. A cooling fin heat sink can be prepared for effective thermal coupling to the specially shaped annular hot area.
One can appreciate more fully the details of some preferred arrangements of these systems in view of a cross section diagram. While
Accordingly,
One will more fully appreciate the advantages of such arrangements in view of the diagram presented as
The electronic relationships between elements of these systems is better understood with reference to
It is instructive to consider the repeat element of the systems described in the previous figures.
While most preferred versions include pie-wedge shaped Peltier elements, it is possible to provide a similar advantage with more common cylindrically shaped Peltier elements in the special geometric arrangement presented as
While the reader will surely now firmly appreciate the advantage realized in these systems which have a very large hot area in comparison to the cold area, it is never-the-less instructive to refer back to the systems commonly found as state of the art. In prior art systems depicted in
It is difficult, if not impossible, to get an area ratio as great as one gets naturally in the new systems presented in this disclosure. Further, the construction of the systems in the art tend to be built in a direction orthogonal with respect to the working plane (i.e. circuit board) of the overall electronic layout, a significant disadvantage in many arrangements. Contrarily, systems of these inventions remain planar and the hot/cold area ratio may be increased without practical limit without increasing the thickness of the system. This is due to the fact that the cold area, hot area and semiconductor elements therebetween all lie in the substantially the same plane.
While the entire heat transfer device is now easily understood as a stand alone unit, one gains further appreciation when considering the interface between the device and those exterior systems to which it is designed to be coupled. While most of the preceding disclosure is directed to heat transfer systems as stand-alone systems, it is also important to consider how it relates and interfaces with components used in conjunction with these heat transfer systems. For example, the physical structure and geometries of heat sources and heat sinks which are appropriate for use with these devices is worthy of some detailed discussion. Both the heat source and heat sink and their intrinsic characteristics and interfaces in view of the proposed system configurations imply unique relationships and behaviors which are not found in systems previously known. As it is a fundamental function of these devices to remove heat from a source and deposit that heat at a sink, we consider here a few possibilities for the heat sink component. Typically, heat is emitted into a surrounding environment. Many electronic systems simply use a fan to blow air about; these air currents carrying heat away from hot components. Where air currents must cool devices which generate significant heat in relation to their size, then sometime a heat sink includes a cooling fin arrangement to increase the surface area. A material of high thermal conduction exposes a great surface area to air currents and provides efficient heat transfer from an heated area to the surrounding environment. Accordingly, these systems sometimes enjoy use of a cooling fin arrangement; and in certain cases particular cooling fin arrangements. The interface between these heat transfer systems and a cooling fin set is the hot area. A cooling fin set can be configured to form a thermal coupling to the hot area of systems presented in previous graphs. This can be more fully understood in view of the exploded view diagram of
The examples above are directed to specific embodiments which illustrate preferred versions of devices and methods of these inventions. In the interests of completeness, a more general description of devices and the elements of which they are comprised as well as methods and the steps of which they are comprised is presented herefollowing.
One will now fully appreciate how Peltier effect semiconductor heat transfer systems may be configured to support construction on planar substrates having high hot:cold area ratios. Although the present inventions have been described in considerable detail with clear and concise language and with reference to certain preferred versions thereof including best modes anticipated by the inventors, other versions are possible. Therefore, the spirit and scope of the invention should not be limited by the description of the preferred versions contained therein, but rather by the claims appended hereto.
