GB1568075A

GB1568075A - Infrared cooler

Info

Publication number: GB1568075A
Application number: GB4470376A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-10-27
Filing date: 1976-10-27
Publication date: 1980-05-21

Description

(54) INFRARED COOLER (71) I, GERALD ALTMAN, a citizen of the United States of America, having an address at 41 Westminster Road, Newton Centre, Massachusetts, U.S.A. do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to cooling devices.

Most conventional cooling techniques involve the indiscriminate cooling of relatively large environments even though local cooling of relatively small regions only may be desired. Heat transfer as is well known, involves the phenomena of conduction, convection and radiation. All of these phen omena operate in conventional cooling systems although conventional design is often based primarily on conduction and convection considerations.

The present invention is based on the discovery that improved cooling of a small legion may be achieved by locating the subject region in the path defined by a geometric configuration, in which a small infrared radiation sink and a large infrared radiation condenser, e.g. a converging reflector, are in optical comnaunication.

According to the present invention, there is provided a radiation cooler comprising a relatively large optical condenser for receiving infrared radiation from a subject to be cooled and for redirecting such radiation to a focus region, a relatively small infrared radiation sink located in the focus region, a window which is substantially transparent to infrared radiation for isolating the sink from the atmos where, and a heat exchanger for withdrawing heat from the sink.

Preferably heat is removed from the radiation sink by a thermoelectric heat exchanger, particularly a Peltier effect heat exchanger.

e radiation sink, praticlarly the surface area communicating with the radiation condenser, is operationally electrostatic, i.e. is not a compoint of a closed electrical loop. In other words, the heat sink is electromotively isolated so as to be free of power dissipation that is significant in relation to infrared radiation received from the subject. The cooling configuration of the present invention is the antithesis of irradiating configurations of the prior art in the sense that the present invention predeterminedly locates a "point" radiation sink in adjacence to the focal point of an optical condensing system whereas the prior art predeterminedly locates a "point radiation source in adjacence to the focal point of an optical condensing system.The present invention is believed to take advantage of the scientific principle that the aperture of an optical system assumes the radiance of the object it is imaging when viewed from the image point. The present invention effectively reduces mechanical problems previously inherent in radiation cooling devices. These devices are particularly useful in the maintenance of controlled temperatures for individualized cooling or medical therapy or for scientific or industrial procedures in which convenient mechanical access is precluded, for example, with respect to subject surfaces of irregular shape or minute size.

For a fuller understanding of the present invention, reference is made to the following detailed description, taken in connection with the accompanying drawings, wherein Figure 1 is a perspective view of a radiation cooling device embodying the present invention; Figure 2 is an electrical and mechanical schematic view, partly broken away, of a sub-assembly of the device of Figure 1; Figure 3 is a perspective broken away view of the sub-assembly of Figure 2; Figure 4 is a schematic diagram of a component of the present invention; Figure 5 is a schematic diagram illustrating a first system of the present invention; and Figure 6 is a schematic diagram illustrating a second system of the present invention.

The radiation cooler of Figures 1, 2 and 3 comprises a small radiation sink 20 and a relatively large converging reflector 22. Sink 20 and an object region to be cooled are disposed on the axis of reflector 22 in a geometrical relationship to be described more fully below. As shown, radiation sink 20 is carried by an elongated assemblage 24, which is adjustable along the axis of reflector 22 by screws 26, 28. Screws 26, 28 have unthreaded shank portions, which are rotatable in bearings at the extremities of assemblage 24, and threaded body portions, which are turned in threaded openings in flanges 30, 32 that extend from reflector 22 at diametrically opposite locations with respect to the reflector axis. Along screws 26, 28 are graduations which indicate the distance of radiation sink 20 from reflection 22 along its axis.As shown, reflector 22 is mounted universally on a stand 34 having a stable base 36, an extensible post 38 and a pivotal bearing 40. The reciprocal adjustment of post 38 is fixed by a lockscrew 42 and the angular adjustment of pivot 40 is fixed by a lockscrew 44.

Assemblage 24 includes a series of Peltier effect thermoelectric modules 46, sandwiched between a heat conducting cold plate 48 and a heat conducting hot plate 50. As shown in Figure 2, there are seven thermoelectric modules 46, in the present embodiment, which are distributed in a series along the length of assemblage 24 and which are connected electrically in series and energised by an adjustable power supply 52 through a suitable double lead cord 51. Cold plate 48 is in the form of a copper bar that is registered and in contact with the cold back faces of the series of modules 46. The temperature of cold plate 48 is below the freezing point of water and is adjustable by varying the output of power supply 52. Hot plate 50 is in the form of a copper bar that is registered and in contact with the hot front faces of the series of modules 46.Radiation sink 20 is constituted by a blackened circular region on the back face of cold plate 48 midway between the extremities of assemblage 24.

In one form, radiation sink 20 is composed of a copper compound such as copper oxide or copper sulfide, which is provided by chemical reaction with the face of cold plate 48. In another form, radiation sink 20 is composed of a matt black lacquer, which is provided by painting the back face of cold plate 48. Registered with radiation sink 20 is an infrared radiation transmitting window 53.

In one form, window 53 is in contact with sink 20 and in another form window 53 is slightly spaced from sink 20. In either of these forms, there are air molecules between window 53 and sink 20, the total air volume being sufficiently small so that any water molecules in the total air volume are too few to generate a condensation layer on sink 20 even though its temperature is below the freezing point of water. Surrounding window 53 and enveloping all components of assemblage 24 excepting hot plate 50 is a moisture proof jacket 54 which is composed of an elastomer or elastomeric foam such as polyisobutene or polyurethane. At the upper and lower edges of hot plate 50 are fins 56 for heat dissipation.

The edges of jacket 54 are sealed to hot plate 50 so that all of the components of assemblage 24 are sealed hermetically within the confines of an envelope defined by hot plate 50, jacket 54 and window 53.

Difficulties are encountered in attempting to utilize a large open cooling surface for radiation transfer when its temperature is below freezing because of mechanical problems, particularly difficulties associated with frost prevention. In accordance with the present invention, a geometrically small radiation sink, in which frost and other mechanical problems can be easily controlled, is converted effectively into a geometrically large radiation sink by disposing it on the axis of an infrared optical condenser of relatively large diameter.

The configuration of the reflector, in various modifications is spherical, parabolic, elliptical or aspheric. In Figure 5, for example, a radiation sink 58 isolated from the atmosphere by an infrared transmitting window and a subject region 60 of relatively small area A,, to be cooled, are positioned at conjugate points on the axis 62 of a reflector 64. The configuration is such that a significant proportion of divergent radiation from subject region 60 is converged by reflector 64 toward radiation sink 58. In Figure 6, for example, a radiation sink 66 and a subject region 68 of larger area A2, to be cooled, are positioned respectively at the focal point and at infinity on the axis 70 of a reflector 72. The configuration is such that a significant proportion of parallel radiation from subject region 68 is converged by reflector 72 toward radiation sink 66.

It is preferred that, in terms of cross-sectional area in planes that are normal to the optical axis, the area of the infrared radiation condenser is at least 10 times the area of the radiation sink and most of the exposed surface of the radiation sink, say at least 80%, communicates optically with the infrared radiation condenser. In practice, the ratio of focal length to diameter of the infrared radiation condenser should not exceed 2.0.

In one modification of the illustrated radiation cooler, the converging reflector is a Fresnel reflector. This Fresnel reflector, which is disposed in generally a flat plane, is charac- terized by concentric conoidal facets that correspond to any of the spherical, parabolic, elliptical or aspheric configurations of the reflector of Fig. 1. Window 53 is composed of an infrared transmitting material such as fused quartz, sapphire, magnesium fluoride, mag nesium oxide, calcium fluoride, arsenic trisulfide, zinc sulfide, silicon, zinc selenide, germanium, sodium fluoride, cadmium tell uride or thallium bromide-iodide.It is essen tidal that subject surface 60 or 68 be the only energy source cotmunicating with radiation sink 58 or radiation sink 66. In other words, the uninterrupted thermally conductive path established by the radiation sink and cold plate 48 is electromotively isolated, i.e. it avows electomotive forces that would tend to generate heat by electrical flow in a circuit.

Preferably thermoelectric heat exchange modules 46 incorporate arrays of small thermoelectric elements of the Peltier type, as shown in Figure 4, in which a load 74 to be cooled and a heat sink 76 are separated by a pair of N and P semiconductors 78, 80. One end of each semiconductor 78, 80 is bonded to a common electrical conductor 82. The opposite extremities of semiconductors 78, 80 are bonded to isolated electrical conductors 83, 84. Electrical conductor 82 is attached to load 74 by a thermally conducting, electrically insulating spacer 86. Likewise, electrical conductors 83, 84 are attached to heat sink 76 by a thermally conducting, electrically insulating spacer 90.When direct current is transmitted via leads 91, 92 through electrical conductor 83, N miconductof 78, electrical conductor 82, P semiconductor 80 and electrical conductor 84, cooling of load 74 occurs. The modules 46 provide a heat exchanger that is matched with the thermal path extending from the radiation sink to establish a heat flow of at least 10 Bw/hr(ft2) and, preferably, at least 50 Btu/hr(ft2) when associated with an infrared radiation con denser of one square foot area for medical applications.

In operation, the device of Figures 1, 2 and 3, ordinarily is positioned with respect to a subject surface to be cooled in such a way that its radiation sink is no farther away from the subject surface than a distance equal to twice the diameter of the reflector and such that the optical path from the infrared radiation emitting subject surface via the infrared radiation condenser to the infrared radiation absorbing radiation sink is uninter rupted and unobscured so that heat radiation from the subject surface to the heat sink is continuous. In other words, the device is positioned quite closely to the subject surface in order to achieve the desired heat flow.The infrared radiation of primary interest has a wave length of from 0.8 to 50 microns, particulary in the range of from 4 to 40 microns, i.e. the range associated with the temperature of the human body. Pre ferably, window 53 is composed of a material that is substantially transparent into radiation whose wavelength is the range of 4 to 40 microns.

Certain changes may be made in the present disclosure within the scope of the appended claims, it being intended that all matter contained in the foregoing description or shown in the accompanying drawings be interpreted in an illustrative and not a limiting sense.

WHAT I CLAIM IS:- 1. A radiation cooler comprising a relatively large optical condenser for receiving infrared radiation from a subject to be cooled and for redirecting such radiation to a focus region, a relatively small infrared radiation sink located in the focus region, a window which is substantially transparent to infrared radiation for isolating the sink from the atmosphere, and a heat exchanger for withdrawing heat from the sink.

2. The radiation cooler of claim 1, wherein the heat exchanger is a thermoelectric exchanger and power means are provided for energising the exchanger.

3. The radiation cooler of claim 1, wherein said radiation condenser is a reflector.

4. The radiation cooler of claim 1, wherein said window transmits infrared radiation whose wavelength is substantially in the range of 4 to 40 microns.

5. The radiation cooler of claim 1, 2, 3, or 4, wherein the infrared radiation condenser defines an optical axis and a pair of conjugate surfaces and the radiation sink is disposed on this axis and is located substantially at one of the conjugate surfaces.

6. The radiation cooler of claim 5, wherein radiation sink comprises a blackened body surface and the infrared transmitting window isolates said blackened surface from the atmosphere.

7. The radiation cooler of claim 6, wherein the reflector is spherical.

8. The radiation cooler of claim 6, wherein the reflector is elliptical.

9. The radiation cooler of claim 6, wherein the reflector is aspheric.

10. The radiation cooler of any one of claims 1 to 9, wherein the heat exchanger includes a plurality of thermoelectric modules thermally connected to the radiation sink through a thermal conductor.

11. The radiation cooler of any one of claims 1 to 10, wherein the radiation sink and the infrared radiation transmitting window are separated by an air gap.

12. A radiation cooler substantially as hereinbefore described with reference to Figures 1 to 4 taken with Figure 5 or Figure 6 of the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

tidal that subject surface 60 or 68 be the only energy source cotmunicating with radiation sink 58 or radiation sink 66. In other words, the uninterrupted thermally conductive path established by the radiation sink and cold plate 48 is electromotively isolated, i.e. it avows electomotive forces that would tend to generate heat by electrical flow in a circuit.

Preferably thermoelectric heat exchange modules 46 incorporate arrays of small thermoelectric elements of the Peltier type, as shown in Figure 4, in which a load 74 to be cooled and a heat sink 76 are separated by a pair of N and P semiconductors 78, 80. One end of each semiconductor 78, 80 is bonded to a common electrical conductor 82. The opposite extremities of semiconductors 78, 80 are bonded to isolated electrical conductors 83, 84. Electrical conductor 82 is attached to load 74 by a thermally conducting, electrically insulating spacer 86. Likewise, electrical conductors 83, 84 are attached to heat sink 76 by a thermally conducting, electrically insulating spacer 90.When direct current is transmitted via leads 91, 92 through electrical conductor 83, N miconductof 78, electrical conductor 82, P semiconductor 80 and electrical conductor 84, cooling of load 74 occurs. The modules 46 provide a heat exchanger that is matched with the thermal path extending from the radiation sink to establish a heat flow of at least 10 Bw/hr(ft2) and, preferably, at least 50 Btu/hr(ft2) when associated with an infrared radiation con denser of one square foot area for medical applications.

In operation, the device of Figures 1, 2 and 3, ordinarily is positioned with respect to a subject surface to be cooled in such a way that its radiation sink is no farther away from the subject surface than a distance equal to twice the diameter of the reflector and such that the optical path from the infrared radiation emitting subject surface via the infrared radiation condenser to the infrared radiation absorbing radiation sink is uninter rupted and unobscured so that heat radiation from the subject surface to the heat sink is continuous. In other words, the device is positioned quite closely to the subject surface in order to achieve the desired heat flow.The infrared radiation of primary interest has a wave length of from 0.8 to

50 microns, particulary in the range of from

4 to 40 microns, i.e. the range associated with the temperature of the human body. Pre ferably, window 53 is composed of a material that is substantially transparent into radiation whose wavelength is the range of 4 to 40 microns.

Certain changes may be made in the present disclosure within the scope of the appended claims, it being intended that all matter contained in the foregoing description or shown in the accompanying drawings be interpreted in an illustrative and not a limiting sense.

WHAT I CLAIM IS:- 1. A radiation cooler comprising a relatively large optical condenser for receiving infrared radiation from a subject to be cooled and for redirecting such radiation to a focus region, a relatively small infrared radiation sink located in the focus region, a window which is substantially transparent to infrared radiation for isolating the sink from the atmosphere, and a heat exchanger for withdrawing heat from the sink.
2. The radiation cooler of claim 1, wherein the heat exchanger is a thermoelectric exchanger and power means are provided for energising the exchanger.
3. The radiation cooler of claim 1, wherein said radiation condenser is a reflector.
4. The radiation cooler of claim 1, wherein said window transmits infrared radiation whose wavelength is substantially in the range of 4 to 40 microns.
5. The radiation cooler of claim 1, 2, 3, or 4, wherein the infrared radiation condenser defines an optical axis and a pair of conjugate surfaces and the radiation sink is disposed on this axis and is located substantially at one of the conjugate surfaces.
6. The radiation cooler of claim 5, wherein radiation sink comprises a blackened body surface and the infrared transmitting window isolates said blackened surface from the atmosphere.
7. The radiation cooler of claim 6, wherein the reflector is spherical.
8. The radiation cooler of claim 6, wherein the reflector is elliptical.
9. The radiation cooler of claim 6, wherein the reflector is aspheric.
10. The radiation cooler of any one of claims 1 to 9, wherein the heat exchanger includes a plurality of thermoelectric modules thermally connected to the radiation sink through a thermal conductor.
11. The radiation cooler of any one of claims

1 to 10, wherein the radiation sink and the infrared radiation transmitting window are separated by an air gap.
12. A radiation cooler substantially as hereinbefore described with reference to Figures

1 to 4 taken with Figure 5 or Figure 6 of the accompanying drawing.