WO2008109970A2

WO2008109970A2 - Liquid circulation cooling system for electronic devices

Info

Publication number: WO2008109970A2
Application number: PCT/BR2007/000064
Authority: WO
Inventors: Rogério Felipe PIRES; Sandro Luis Vatanabe
Original assignee: Inoveo Pesquisa E Desenvolvimento De Produtos E Projetos De Automação De Sistemas Ltda
Priority date: 2007-03-15
Filing date: 2007-03-15
Publication date: 2008-09-18
Also published as: WO2008109970A3

Abstract

A liquid circulation cooling system for electronic devices comprising pumping means (19), refrigerant liquid cooling means and a heat exchange device (17) in thermal contact with at least one heat-generating electronic device, said heat exchange device (17) comprising a channel through which flows the refrigerating liquid, said channel having a three-dimensional configuration. In a preferred embodiment of the invention, the channel is formed by the gap enclosed by two substantially conical surfaces (41-a, 46) substantially concentric to each other. The walls of the channel may be provided with turbulence inducing elements to enhance the thermal energy transfer to the refrigerating liquid. According to yet another feature of the invention, the efficiency of the thermal energy transfer is enhanced by means of an area increase of the surface in contact with the refrigerant liquid by providing unevenness in said surface. According to a further feature of the invention, said unevenness consists of concave or convex elements provided in said surface. According to another feature of the invention, in preferred embodiments the increase in thermal energy transfer is provided by turbulence- inducing elements provided in the channel through which the refrigerant liquid circulates.

Description

"LIQUID CIRCULATION COOLING SYSTEM FOR ELECTRONIC DEVICES"

Field of the Invention The present invention is directed to a cooling system for electronic devices and, more specifically, a system based on the circulation of a liquid for transferring thermal energy away from the heat-generating semiconductor devices.

Description of the Prior Art

The trend in decreasing the size of semiconductor components leads to smaller electronic devices with the associated concentration of heat, which require more efficient methods of thermal energy management. Typical systems and methods for cooling semiconductor devices include active cooling techniques, such as fans for passing air over a heat sink provided with fins in thermal contact with said device. However, fans require battery power for operation which is problematic for battery operated devices. In addition, such cooling techniques require air flow through the heat sink which must be of a sufficient size to accommodate air flow and cooling. This puts a minimum limit on the size and portability of the electronic device.

Cooling techniques for achieving a more efficient removal of thermal energy employ a cooling medium other than air, such as a liquid, which flows through a heat exchanger attached to the electronic device by means of a pump. Patent document JP 2005016467 discloses a liquid circulation apparatus for an electronic device, such as a microprocessor or equivalent, in which a piezoelectric pump propels the cooling liquid through a constant-section channel embedded in a heat exchanger which is in thermal contact with said electronic device. As shown in Fig. I₅ said heat exchanger comprises two rectangular flat metal plates 11, 12 which enclose a third plate 13 in which a channel 14 is provided. The arrows show the flow direction of the cooling liquid inside said channel, which is propelled by the pump 15. As the cross-section of the channel 14 is substantially uniform throughout its path, the flow is laminar; consequently, the transfer of thermal energy to the cooling liquid is a low- efficiency process. To enhance the removal of heat by the liquid the flow must be increased, so the power consumed by the pump 15 will be higher. In the case of portable equipments, this means a bulkier power pack which limits its portability and handling ease.

Objects of the Invention

In view of the above, it is an object of the present invention to provide a cooling system for electronic equipments which removes the thermal energy generated by semiconductor devices by means of a refrigerant fluid.

It is also an object of the present invention to provide a cooling system in which the efficiency of thermal energy transfer to the refrigerant fluid is higher than in the devices known in the art.

It is another object of the present invention to provide a cooling system with low energy requirements for its operation. It is yet another object of the invention to provide a cooling system which keeps the temperature in the heat exchanger as low as possible, therefore avoiding the deterioration of semiconductor devices such as CCD 's or LED's.

Summary of the Invention

To achieve the foregoing objects and in accordance with a first aspect of the invention, a closed circuit cooling system is provided comprising a pumping device, a refrigerant liquid cooling device and a heat exchanger device in which the surface in contact with the refrigerant liquid is increased by employing a channel with a tri-dimensional configuration

According to another feature of the invention, said channel is substantially conically shaped.

According to yet another feature of the invention, the efficiency of the thermal energy transfer is enhanced by means of an area increase of the surface in contact with the refrigerant liquid by providing unevenness in said surface.

According to a further feature of the invention, said unevenness consists of concave or convex elements provided in said surface.

According to another feature of the invention, in preferred embodiments the increase in thermal energy transfer is provided by turbulence- inducing elements provided in the channel through which the refrigerant liquid circulates.

Brief description of the drawings

The accompanying drawings which are incorporated in and constitute a part of this specification, illustrate a preferred embodiment of the invention and together with the description serve to explain the principles of the invention.

Fig. 1 is a perspective view of a cooling system built according to the previous art.

Fig. 2 is a view of a known system comprising a headband worn by the surgeon, provided with a light source and a camera.

Fig. 3 is a block schematic illustrating the main components of the system in accordance with the present invention.

Fig. 4 is a view of a lighting apparatus employing a LED array mounted on a headband, according to the invention.

Fig. 5 is a side view of the apparatus shown in the previous figure.

Fig. 6 is a perspective view of the light emitting diodes assembly mounted on the heat exchanger device, according to the invention. Fig. 7 shows an exploded view of the heat exchanger device and light emitting diodes assembly, according to the invention.

Fig. 8-a shows an elevation view of the device shown in the previous figure.

Fig. 8-b shows a section through the device, showing the channel through which flows the refrigerating liquid.

Fig. 8-c is a detailed view of the previous figure.

Fig. 9 show the path followed by the refrigerating liquid in the heat exchanging device.

Fig. 10 shows a plan view of the lower element of the heat exchanging device.

Fig. 11 shows a simplified cross-section view of the heat exchanging device.

Fig. 12 shows the turbulence-inducing elements, provided by dimples, applied on the surface of the lower element of the heat exchanging device.

Fig. 13 shows the above-mentioned dimples applied on the inner surface of the upper element of the heat exchanging device. Fig. 14 shows the turbulence-inducing dimples applied on both upper and lower elements of the heat exchanging device.

Detailed Description of the Preferred Embodiments The present disclosure can be better understood by the description of the embodiments given below. However, it is understood that said embodiments are not necessarily limitations to the present disclosure, being included to typify the invention.

Therefore, the invention will be described as applied to the cooling of LED' s (light emitting diodes) employed in a head-mounted apparatus for illuminating a surgical work site, which may include a camera for transmitting a visual image to a remote location for viewing or recording.

A known head-mounted device of the kind mentioned above is the object of US A, 191, 136, whose figure 1 is reproduced in the present specification as Fig. 2. In this drawing, it can be seen that a light source 21 and a camera 22 are mounted on a headband 23 worn by the surgeon 24. The light source 21 is coupled to a remote light source - such as a halogen lamp enclosed in the cabinet 25 - by means of a fiber optic cable 26 which passes over the top of the surgeon's head and down the back of headband 23 to light source 21. It can be seen that the arrangement shown is unwieldy and limits the freedom of movement of the surgeon. Moreover, as is well known, the useful life of the lamp is limited and its efficiency is low. More recent developments in this kind of devices employ light emitting diodes as a source of illumination lighting. As is well known, arrays of semiconductor light sources such as LED's and laser diodes are increasingly being used in lieu of conventional high-pressure light sources, due to several advantages over the latter. For example, such semiconductor light sources are four to five times more efficient than high-intensity light sources. Moreover, they emit lower levels of electromagnetic interference, are more reliable and have more stable outputs over time.

Fig. 4 shows an illumination device 30 worn on a headband 33 which employs an array of LED's 31 for lighting the operating field. This apparatus can also be provided with a compact camera for image recording and transmission purposes, which is not the object of the present disclosure and will not be described henceforth. A lateral view of said headband 31 provided with the illumination device is depicted in Fig. 5. As shown, the illumination device 30 comprises a protective enclosure 34 having an approximately conical shape. Within said enclosure there are mounted the light emitting diodes and the associated heat exchanger device, forming the assembly 35, which is connected to the refrigerating liquid by the flexible tubing 32, which removes the warm liquid from the heat exchanger and brings cold liquid from the cooling device (not shown) into the heat exchange device.

As shown in Fig. 6, the diode array comprises several diodes 31 surface-mounted on an insulating circular base 36, connected to a power supply (not shown) through conducting tracks 37. Said base is juxtaposed to the heat exchanger 38, which is provided with an inlet 39 for cold refrigerating liquid and an outlet 40 for the liquid which has absorbed the heat generated by the light emitting diodes.

The details of the assembly 35, comprising the heat exchanger and the LED mounting array are depicted in the exploded view of Fig. 7. The heat exchanger is made of heat-conducting material, preferentially a metal and more preferentially copper or aluminum, and consists of an upper truncated conical element 41 whose lower edge 42 fits the edge 44 of the disk-like lower portion 45 of the lower element 43. The upper part of said lower element is also a truncated cone 46. As depicted in Fig. 8-b, which shows a cross-section of said assembly 35, said truncated conical part 46 is smaller than the upper conical element. Therefore, when these elements are assembled together, there is provided a gap between the inner conical surface of upper element 41 and the outer conical surface of lower element 43, said gap consisting of a channel 47 through which the refrigerating liquid flows.

As shown in Fig. 7-c and Fig. 7-d, the insulated base 36 in which the LED's 31 are mounted is provided with through-holes 48, positioned coincidently with the bottom surface of LED's 31. Therefore, when the insulated base 36 is brought together with the lower portion 45 of element 43, the knobs 49 which protrude form the lower face of said disk-like lower portion 45 are inserted into said holes 48 and are brought into thermal contact with the bottom surface of the light emitting diodes 31. This situation can be better seen in Fig. 8-b and 8-c. Consequently, the heat generated by the operation of LED's 31 is transmitted through knobs 49 to the main body of the lower element 43 as well as to the upper conical element 41, both of which are in contact with the refrigerating liquid, as will be explained below.

The exploded view of the heat exchanger shows in Fig. 9-a the upper truncated conical element 41 provided in its upper base 50 with inlet 51 and outlet 52 for the refrigerating liquid. The conical portion 46 of the lower element is provided with two channels 53 and 54 aligned with said inlet and said outlet, respectively, as shown in Fig. 9-b. A more detailed view of said channels is depicted in Fig. 10 and Fig. 11, which show, respectively, a plan view of the lower element 43 and a cross section of said lower element along the vertical plane A-A. The direction of the inflow and outflow of the refrigerating liquid is indicated by arrows in Fig. 11, where it can be seen that the incoming cold stream impinges firstly on the upper surface of the disk-like portion 45, which receives the heat generated by the LED's (not shown in these figures).

However, it should be noticed that the refrigerating liquid flow is not restricted to the lower edge of said portion 45. As shown by the arrows in Fig. 9-b, the refrigerating liquid also flows along the whole conical surface of portion 46, as well as along the internal conical surface 41 -a of the upper truncated conical element 41, shown in Fig. 7-a. In other words, the refrigerating liquid flows along the whole section of channel 47 which, as shown in Fig. 8-b, is bound by the inner (lower) surface of said element 41 and the upper surface of said element 46. Therefore, the conical shape of channel 47 provides a much greater contact area with the heat-conducting material of the heat exchanger, due to the fact that this channel is not disposed along a single plan (as is the case with the previous art) but extends in a vertical direction also, resulting in a tri- dimensional hollow body configuration. The increased contact area improves the thermal energy transfer between the heat exchanger and the refrigerating liquid, resulting in a substantially higher efficiency than in the known devices. As a consequence, the device of the invention requires a smaller amount of liquid for its operation, and so, a lower power expenditure for the pumping device.

The thermal energy transfer may be additionally improved by roughening one or more surfaces that bound said channel. The unevenness provided in said surfaces increase the contact area between the channel and the refrigerating liquid, improving the efficiency of the heat transfer. Moreover, such unevenness may also induce turbulence in the flow of the refrigerating liquid, resulting in an additional efficiency in the thermal energy transfer. The unevenness on the surfaces that bound said channel may be provided by concave or convex elements placed on one or more of said surfaces. Convex elements may comprise, among others, ridges, studs, knobs, and so forth while concave elements may be provided by furrows, indentations, and so forth. Fig. 12 shows an embodiment of the invention in which such turbulence inducing means consist of a plurality of dimples 55 provided on the surface of element 43' in contact with the refrigerating liquid. In the embodiment depicted in Fig. 13, the dimples are provided on the inner surface of the upper conical element 41', while Fig. 14 shows dimples applied to both upper 41' and lower 43' elements. Said surface irregularities may easily be obtained through known manufacturing methods, such as die casting, sintering, and so on.

The foregoing description is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obvious modifications or variations are possible in light of the above teachings. Such modifications and variations are within the scope of the invention as defined by the appended set of claims.

Claims

1. A liquid circulation cooling system for electronic devices comprising pumping means, refrigerant liquid cooling means and a heat exchange device in thermal contact with at least one heat-generating electronic device, said heat exchange device comprising a channel through which flows the refrigerant liquid, wherein said channel has a tri-dimensional configuration.

2. A system as claimed in claim 1, wherein said channel is formed by the gap enclosed by two substantially conical surfaces substantially concentric to each other.

3. A system as claimed in claim 2, wherein said gap is substantially uniform at all places of said channel.

4. A system as claimed in claim 1, wherein at least one of the surfaces that bound said channel is treated to increase the area in contact with the refrigerating liquid.

5. A system as claimed in claim 1, wherein at least one of the surfaces that bound said channel is provided with turbulence inducing elements.

6. A system as claimed in claim 5, wherein said turbulence inducing elements are convex elements.

7. A system as claimed in claim 5, wherein said turbulence inducing elements are concave elements.

8. A system as claimed in claim 7, wherein said concave elements consist of dimples on at least one of the surfaces that bound the refrigerating liquid conducting channel.