DESCRIPTION

POLYMERIC MICRO-DISSIPATER, IN PARTICULAR FOR THE THERMAL CONDITIONING OF MECHANICAL AND ELECTRICAL DEVICES

This invention concerns a polymeric micro-heat-sink, in particular for the local thermal conditioning of mechanical and electrical devices.

More precisely, the invention concerns a polymeric micro-heat-sink with the capacity for geometric adaptability and a high dissipation potential per unit volume.

Thermal control is necessary in a large number of industrial applications, from the textile industry to the aerospace industry, mechanical industry and the biomedical industry.

For example, it is known that, during the space missions, the consequences caused by the problems of thermal conditioning of the equipment, of the personnel comfort and of the thermo- mechanical stresses of the structure are of fundamental importance for the successful outcome of the mission. To be underlined also are the importance of size and lightness of the instruments to be used, often characteristics difficult to obtain.

Again, the increase of performance required from the modern electronic circuits of a personal computer has made it so that the power dissipated by the microprocessor has increased: ^this results in its overheating and the consequent reduction in the velocity of the elaboration of the data. For this reason it was necessary to study and develop new systems of cooling that in a few years will substitute the traditional fans that have reached the limit of their performance (for example to adopt a larger fan means an increase in the level of noise while it is working, unpleasant form a comfort point of view). For years in the field of micro-electronics there has been a progressive reduction in the dimensions of the components used: if it was _. not for the foresight of some cooling systems, the working temperatures of the electronic components would have increased enormously, causing numerous and considerable problems.

It was necessary therefore to miniaturize the thermal conditioning system allowing the possibility to thermally condition extremely compact equipment.

Even with the development of diverse technologies in micro-scale with systems in silicone and in metal, we do not have a mouldable and modular system that is adaptable to the geometry of the devices. Given the actual state of the technology, a micro-heat sink that is at the same time flexible, expandable, modular, ultra light and made from the previously mentioned materials, does not exist.

A first step towards new devices was made using polymeric tubes to carry corrosive fluids and that can be bent more easily to adapt to their use in space.

With the need to miniaturize this technology came problems and drawbacks.

In fact, in some works on the subject (J. R. Burns, R. J. J. Jachuck, "Condensation studies using cross- corrugated polymer film compact heat exchanger", 21 (2001) 495-510; L. Zaheed, R. J. J. Jachuck, "Review of polymer compact heat exchanger with special emphasis on a polymer film unit", 24 (2004) 2323-2358), it was found that non microscopic polymers (??) were used for heat sinks. Since polymers are poor conductors they must be designed in a way to maximize the thermal exchange.

In the case of polymeric nano-tubes or micro-tubes, nevertheless, the coefficient of the thermal exchange is proportional to the diameter of the tube and therefore this coefficient result is naturally high.

To explain this in a simple way, we can think that, having the possibility to construct small heat exchangers with polymeric capillaries we can have, at the same time, the possibility to increase the thermal exchange acting on the coefficient of the convective thermal exchange, as defined in the laws that describe the physical thermal exchange:

Q = hSδT,

where h is the coefficient of thermal exchange, S is the surface of exchange and AT is the difference of temperature between the fluid and the surrounding environment.

This coefficient h is in its own way a function of various parameters amongst which the diameter and the typology of the flow. In particular, h is inversely proportional to the diameter and increases with the increase of the turbulence of the flow.

Now, in these polymeric tubes the small diameter greatly increases the coefficient, so in order not to have high levels of leakages of the fluid you must use small quantities. A small quantity in a small conduit does not produce a turbulent motor.

Therefore, to obtain the turbulence, it is written and recorded the use of corrugations of various types (see above mentioned article by J. R. Burns and R. J. J. Jachuck).

The corrugations can be difficult to realize at the level of micro-tubes.

It is also written (patent n° US6892802) about polymeric heat sinks in which the fluid channels are printed on a polymeric plate and all the channels are in straight lines, without adaptability to space and without the possibility to increase the turbulence without corrugations.

The purpose of the present invention is to supply a polymeric micro-heat sink that resolves these problems, surmounts the drawbacks of previous technology and constitutes a valid alternative when a pressure vessel or a compressor are present in order to overcome the pressure drops inside the device.

The object of the present invention is a polymeric heat sink, in particular for the thermal conditioning of mechanical and electrical devices, including: a structure of micro-tubes in which flows the cooling fluid; a system of inlets, distribution and collectors after use of the cooling fluid; the micro-heat sink is characterized by the fact that the micro-tubes are polymeric micro-tubes that narrow and swell in order to present a variable section.

Preferably, according to the invention, the variation of these sections is between 10 and 40% of the average section.

Preferably, according to the invention, the polymeric micro-tubes should have one or more curves.

Preferably, according to the invention, the above mentioned system of inlet, distribution and collector of the cooling fluid includes a single collector to which the polymeric micro-tubes, with at least one curve, are connected both for the inlet and the outlet of the cooling fluid.

Preferably, according to the invention, the polymeric micro-tubes should be made from extruded polymers, the tubes should be glued or have a multi-lumen conduit with various conduits.

Preferably, according to the invention, the polymeric micro-tubes should use a polymer chosen from the following group: fluoropolymers, polyolefin, polyamides, polyesters, polybuntylen-tereftalates, polycarbonates, polyfenilsulfate, thermoplastic elestomers and high quality polymers and for example polyether-ether-ketone.

Preferably, according to the invention, the cooling fluid should be chosen from the following group in the form of gas (dry air, helium, nitrogen, oxygen, argon) or liquids (water, HFC, cooling agents for example, Rl 1, R12, (FREON), R22 (FE-22), R23 (FE-13), Rl 13, Rl 14, R123, R124, R125 (FE-25), R134a, R500, R502, R503, R13B1, HFC-227ea (FM-200, FE-227, RT- 227), Halon 1211 and Halon 1301.

Preferably, according to the invention, the polymeric micro-tubes should be of a composite polymeric matrix material with high thermal conductibility k > 5 W/mK.

Preferably, according to the invention, the micro-heat sink should include also:

a system of sensors to gather and regulate the thermal and fluid dynamics parameters of interest. a system of control, regulation, acquisition and memorization of the parameters of interest.

The invention will now be described in an illustrative but not limitative way, with particular reference to the designs of the figures attached in which: figure 1 shows the first form of realization of the micro-heat sink according to the invention; figure 2 a-f shows different forms of realizations of the micro-tubes used in the micro-heat sink according to the invention; figure 3 shows different forms of realizations of the micro-heat sink according to the invention; figure 4 shows a later compact form of realization of the micro-heat sink according to the invention.

With reference to figure 1, the micro-heat sink 100 according to the invention includes in its particular form of realization: a structure of polymeric micro-tubes, 20, through which the cooling fluid runs; a system of adduction, distribution and collection of the cooling fluid after use (only the collectors 10, 11, are shown, cfr. figure 4); a series of sensors (not shown) for the revelation and regularization of the thermal and fluid technical parameters of interest; a system of control (not shown), regulation, acquisition and memorization of the parameters of interest.

The above mentioned system of inlet, distribution and collector of the cooling fluid in the micro-heat-sink 100 is made up of metal or polymeric collectors 10, 11 and also of accumulated small breathing appliances.

These collectors connect to bundles of 20 polymeric micro-tubes in the shape of a cylinder, a strip or interlaced. This is better illustrated in figure 2a-f.

In figure 2a, in fact, shows a bundle of 20 micro-tubes together and separated in a way to simplify the distribution. In particular, the micro-tubes have been placed one beside the other and then glued together using quick setting glue on the side that will not come into contact with the surface to be cooled. More precisely, the glue is distributed only on the part of the micro-tubes that come from the outlet of the collector to the start of the surface to be cooled: having a very low thermal conductibility, isolate the micro-tubes form the outside environment, in a way that the

increase in temperature of the cooling gas is due to only the thermal exchange in correspondence to the surface to be cooled.

With reference to figure_2b, the micro-tubes are obtained with a multi-lumen extrusion with a cylindrical support, while figure 2c illustrates the same extrusion but with the micro-tubes internally separated by a baffle.

Figure 2d-2f shows the flat extrusion with the micro-tubes in their respective sections, rectangular, circular and circular divided by a baffle.

In accordance with the invention, the above mentioned system of sensors for the revelation of the thermal and fluid parameters of interest are made up of at least one thermocouple, or a thermo resister, or other techniques for the revelation of the temperature and also instruments to measure the pressure and the range placed in correspondence to the key zone of the micro-heat sink.

Also in accordance with the invention, the above mentioned system of control, acquisition and memorization of the parameters of interest include : a prime system of acquisition and control positioned near the micro-heat sink; a secondary system for the memorization and the elaboration of the data revealed; an electronic system of communication between the prime information system and the secondary information system; an electronic system for the transmission of signals arriving from the system of sensors.

In order to permit an easy use of the system of conditioning in accordance with the invention, the above mentioned prime information system includes: equipment for the management of a series of data coming from the system of sensors; equipment for the management of a series of commands directed to the regulation system; equipment for the management of the exchange of data with an external system by way of a cable.

The above mentioned secondary information system is constituted by a personal computer including a monitor, a keyboard and a mouse with a capacity to develop, acquire, record and elaborate the signals to and from the micro-heat sink and the polymeric micro-tubes.

Returning to the part relative to the dissipation, the inlet collectors and the distribution of the cooling fluid have been designed with the aim of obtaining an adequate mounting of the polymeric strip that includes the micro-tubes. By looking at figures 3a and 3d it can be seen that different possibilities exist with regards to the shape of the collectors and the tube bundles as illustrated.

In figure 4 another view in perspective of another preferred form for the realization of the heat sink in accordance with the invention, with a different disposition for the collectors for the adduction and distribution of the cooling fluid.

This figure shows a modular system with a single collector for the thermal control of more devices. The tubes start from the first section 10 of the collector, where it has the inlet 30 for the cooling fluid, and returns to the second section 11 of the collector, where it has the outlet 31 for the cooling fluid. This is possible thanks to the possibility to vary the geometry as you like and to the elasticity of the polymeric tubes.

To all this is added an essential characteristic of the invention, that is that the micro-tubes are formed with a narrowing or swelling along their length. This clever design permits you to get over the problems of turbulence even in the absence of corrugation and with small loads.

In particular, the variation of the section of micro-tubes is between 10 and 40% of the average section.

The realization of a system of this type required the implementation of modern technological solutions: the acquisition and perfection of polymeric materials with adequate thermal, mechanical and chemical characteristics; the realization of polymeric capillaries constituted, for example, by micro-tubes of various sections and forms; the perfecting of a procedure for the mounting of the polymeric micro-tubes; the realization of a system of distribution for the cooling fluid, for example, by collectors of diverse shapes and materials; the realization of a system of sensors for revelation of the temperature constituted, for example, by thermocouples and thermo-resistors; the realization of a system of sensors for revelation of the pressure; the realization of a system to regulate the flow of cooling fluid constituted, for example, by pressure transducers and a system of valves.

The description of a system of micro-heat sink and polymeric micro-tubes for the thermal conditioning of electronic equipment reaches the proposed objectives. In particular: it permits the thermal conditioning of compact equipment of elevated intensity and small dimensions; it permits the installation of this system of thermal conditioning where compactness and light weight are fundamentally important, for example in aerospace applications; it permits the reaching of an elevated thermal efficiency.

The effective advantages deriving from the use of a device such as the present invention are:

obtain systems with an elevated relationship between the exchange surfaces and the volume of the micro-heat sink with polymeric micro-tubes, therefore elevated thermal efficiency. Characteristics that allow you to reach elevated dissipation per unit of volume (up to 50MW/m ³ ), a goal difficult to achieve given its dimensions when compared to conventional systems of thermal control; obtain systems of extreme lightness and compactness of the micro-heat sink with polymeric micro-tubes, thanks to the use of low density materials and the small dimensions of the systems; obtain systems with elevated flexibility and modularity of the micro-heat sink with polymeric micro-tubes which allowing it to be used in areas already compacted with instrumentation, a feat that would be otherwise extremely difficult to achieve; obtain a system with a low rate of loss of cooling fluid, a critical and fundamental element when we move towards miniaturization of a system of thermal conditioning.

To sum up, the advantages characterized by the micro-heat sink with polymeric micro-tubes are: flexibility and modularity; economy; reliable thermal control of the instruments conditioned in this way; the possibility to thermally control zones with integrated instruments; the possibility to obtain a high dissipated thermal flow.

In particular, given the relationship between the surface of exchange and overall volume of this system, the specific thermal power per unit of volume reaches values difficult to reach with equipment of a greater size. This characteristic confers on the micro-heat sink 100 with polymeric micro-tubes in accordance with the invention the possibility to be used, not only in the aerospace field, where compactness, lightness and efficiency are fundamental, but also in other earthly fields (cooling of integrated circuits, of cellular telephones and portable computers, biomedical applications and the conditioning of clothing in extreme environments).

In what has been described above, the preferred forms of realization have been suggested for the variations of the present invention, but it is also intended that the experts in this field can make modifications and changes without going outside of the relative field of protection as defined in the attached declaration.