LOW WEIGHT TUBE FIN HEAT SINK

Abstract

The invention provides a lighting device comprising a light source and a heat sink (200). The heat sink (200) is configured to dissipate thermal energy from the light source when in operation. The heat sink comprises a plurality of pin-shaped fins (210) and a support (220), wherein each fin (210) has a fin height (h) relative to the support (220), a bottom part (213) associated with the support (220) and a top part (214), a cross-section having a first width (d1) and a second width (d2) having a ratio d1/d2 selected from the range of 1.2-10, and a first width axis, wherein the first width axes of the pin-shaped fins (210) are arranged parallel, and wherein the pin-shaped fins (210) are hollow over at least part of their fin height (h).

Claims

1-12. (canceled)

13. A heat sink comprising a plurality of pin-shaped fins and a support, wherein each fin has a fin height relative to the support, a bottom part associated with the support and a top part, a cross-section having a first width and a second width having a ratio d1/d2 selected from the range of 1.2-10, and a first width axis, wherein the first width axes of the pin-shaped fins are arranged parallel, and wherein the pin-shaped fins are hollow over at least part of their fin height, wherein each pin-shaped fin comprises a fin wall with the fin wall defining a cavity within the pin-shaped fin having a cavity height, wherein the cavity has a cavity cross-section with a cavity cross-sectional area, wherein over at least part of the cavity height the cavity cross-sectional area reduces in a direction from the top part to the bottom part.

14. A lighting device comprising a light source and a heat sink according to claim 1, wherein the heat sink is configured to dissipate thermal energy from the light source when in operation.

15. The lighting device according to claim 14, wherein the plurality of pin-shaped fins are arranged in an array having one or more pitches selected from the range of 1.2*d1-6*d1.

16. The lighting device according to claim 14, wherein the top parts of the pin-shaped fins are closed.

17. The lighting device according to claim 14, wherein pin-shaped fins have a height in the range of 0.5-100 cm.

18. The lighting device according to claim 14, wherein the heat sink comprises a support structure associated with the top parts of the plurality of pin-shaped fins.

19. The lighting device according to claim 14, wherein the pin-shaped fins are over at least part of their fin height filled with a thermally conductive material.

20. The lighting device according to claim 14, wherein the pin-shaped fins are arranged in a hexagonal array.

21. The lighting device according to claim 14, wherein the lighting device comprises a floodlight.

22. The lighting device according to claim 14, wherein the heat sink is configured to allow during operation of the lighting device an air flow between the pin-shaped fins in a direction parallel to the first width axes.

23. The lighting device according to claim 14, wherein the pin-shaped fins comprise a material selected from the group consisting of aluminum, magnesium, copper, gold, silver, and an alloy comprising one or more of the aforementioned materials.

24. The lighting device according to claim 14, wherein the pin-shaped fins have a cross-sectional shape selected from the group consisting of an oval, a rectangle, and a rhombus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0040] FIGS. 1a-1f schematically depict some aspects and embodiments of the heat sink;

[0041] FIGS. 2a-2b schematically depict some embodiments of a combination of a functional element, such as a light source, and the heat sink; and

[0042] FIGS. 3a-3d schematically depict some arrangement used in an example.

[0043] The drawings are not necessarily on scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] FIG. 1a schematically depicts a heat sink 200 comprising a plurality of pin-shaped fins 210 and a support 220. Both the fins and support may e.g. be of aluminum. The support 220 may especially be a plate-like element. The support may especially have a thickness (or height) in the range of 0.5-50 mm, such as in the range of 2-10 mm. The fins 210 are arranged at one side of the support 220. The other side of the support 220 may be in thermal contact with a functional element (see below).

[0045] Each fin 210 has a fin height h relative to the support 220, such as in the range of 1-100 cm. Further, each fin has a bottom part 213 associated with the support 220 and a top part 214. As is visible for the fins shown in cross-section, the pin-shaped fins 210 are hollow over 100% of their fin height h. Hence, the total height of the heat sink is the thickness or height of the support 220 and the height h of the fins 210.

[0046] Here, a regular array or pattern 1210 is shown. The fins 210 have thus a pitch p. In the schematically depicted embodiment, the arrangement 1210 is hexagonal. Hence, nearest neighbors may differ in distance or pitch depending upon the direction. In a non-hexagonal arrangement, there may be two different pitches between nearest neighbors (see also FIG. 1b).The different pitches are indicated with references p1 and p2. Reference 201 indicates a connector, to associate the fins 210 to the support 220 (see also below). By way of example, the support 220 is drawn flat; however, the support 220 may also be curved and/or include facets (with mutual angles). Reference 215 indicates the fin wall, which is in general relatively thin (compared to the fin height h).

[0047] FIG. 1b schematically depicts an arrangement, here also a non-hexagonal arrangement, in more detail. A number of pitches p can be discerned; especially the pitches p1 and p2 between nearest neighbors are indicated. Further, a pitch approximately orthogonal to the first pitch p1 is indicated with reference p3. In a substantial hexagonal array p1=p2=p3; in non-hexagonal arrays p1 and p2 may be unequal. Note that with such arrangement, air may flow relatively easily through the channels formed by the fins 210. The fins 210 have a cross-section 211 having a first width d1 and a second width d2 having a ratio d1/d2, especially selected from the range of 1.2-10. Further, the fins 210 have a first width axis 212. The first width axes 212 of the pin-shaped fins 210 are arranged parallel (and parallel to the support (not depicted in 1b). Note that also in FIG. 1a these first width axes 212 are mutually parallel (and also parallel to (the plane of) the support 220). In a specific embodiment, d1 is in the range of 8-10 mm, d2 is in the range of 3-6 mm, and the pitches p1 and p2 (and p3) are in the range of 10-20 mm.

[0048] FIG. 1c schematically depict some possible shapes of the (hollow) fins 210. The fins 210 have walls 215 which comprise a thermally conductive material 30 (“fin wall material”), such as aluminum or copper (including alloys of aluminum or copper), etc. As the fins 210 are (over at least part of their height) hollow, a cavity 216 is formed. The cross-section thereof is indicated with reference 217 and the cross-sectional area thereof is indicated with reference 218.

[0049] As shown in FIG. 1d the cross-sectional area 218 of the cavity may vary over the height h of the fin 210. In this schematic embodiment, the cavity or hollowness extends from the top part 214 over about 65% of the height h. The pin-shaped fin 210 may be arranged in a connector 201. This may be a protruding, extending, or indenting or receding structure on or in the support 220 (see also below). The fin 210 may be clamped therein. The connector 201 may also include a soldering or welding connection, or other type of connection between the support 220 and the bottom part 213 of the pin-shaped fin 210.

[0050] FIG. 1e schematically depicts a non-limiting number of options on how, with using connectors 201, the fins 210 may be associated to the support 220. However, other ways to associate the fins to the support 220 may also be possible. The heat sink may be provided as single body or the fins may be soldered or welded to the support, etc.. By way of example, the left fin 210 is open at the top part 214 and from there hollow over 100%, whereas the top part of the others is closed. By way of example, the middle pin-shaped fins 210 is (over at least part of the fin height h) filled with a thermally conductive material 35. Starting from the bottom part, the right fin is hollow over about 90% of its height h.

[0051] To prevent pollution of the tubes they are either (partially) filled with a low density material like foamed poly styrene or a thermal conductive material, but alternatively or additionally the top may especially be closed. A preferred way to realize a closed top is by forging a tube with a closed bottom and placing it upside down on the base plate. The tubes can be press-fit on a die-cast base plate that has features on it to press-fit the tube on to, in order to get a good thermal and mechanical interconnection. Further robustness of the heat sink can be obtained interconnecting the tubes with a kind of network, or wires, bands or rims (embodiments of the herein indicated support structure, see also FIG. 10.

[0052] FIG. 1f schematically depicts an embodiment of the heat sink 200 further comprising (in addition to the support 220) a support structure 240. This support structure 240 is arranged at the top parts 214. Optionally, part of the fins 210 may extend beyond the support structure 240. However, the top parts 214 may also be embedded in the support structure. Optionally the support structure 240 and the support 220 are substantially identical. Hence, they may also include the same type of materials, or identical materials.

[0053] FIG. 2a schematically depicts an embodiment of a device 1000 comprising a heat generating functional element 1010 and the heat sink 200. Here, as example the device 1000 comprises a lighting device 100, and the heat generating functional element 1010 comprises a light source 10. Reference 11 indicates light source light.

[0054] FIG. 2b schematically depicts a floodlight as example of the device 1000, especially the lighting device 100. As indicated above, the weight of the heat sink 200 may be considerable. However, with the present invention this weight may also be considerably reduced compared to prior art heat sinks As shown in FIGS. 2a and 2b, and also the other figures, the heat sink in these embodiments only comprise fins at one side of the support. Further, in FIGS. 2a-2b the support (of the heat sink 200) is configured (at a non-fin side) in physical contact with the functional element 1000.

[0055] FIG. 3a-3d (not to scale!) schematically indicate four situations that were used for doing calculations on the thermal properties of the heat sinks FIG. 3a shows a situation with elliptical pin fins, 30×11 pins, closed top, fin height 100 mm, base thickness 5 mm, fin wall thickness 0.5 mm, substantially hexagonal arrangement with pitch of 17 mm; d3=12.5 mm and d4=20.45 mm. FIG. 3b shows a situation with elliptical pin fins, 34×12 pins, open at the top, fin height 110 mm, base height 4 mm, fin wall thickness 0.8 mm, substantially hexagonal arrangement with a pitch of 15 mm; d3=10.5 mm and d4=17 mm. FIG. 3c shows a situation with circular pin fins, 34×12 pins, closed at the top, fin height 100 mm, base height 5 mm, fin wall thickness 0.5 mm, a substantially hexagonal arrangement with a pitch of 15 mm; d3=8 mm and d4=19 mm. FIG. 3d shows a situation with circular pin fins, 30×11 pins, open top, fin height 110 mm, base height 4 mm, fin wall thickness 0.5 mm, a substantially hexagonal arrangement with a pitch of 17 mm; d3=10.5 mm and d4=22.45 mm. The pitch p herein indicated is the pitch of the row of three fins 210 starting from below left to top right. Pitch p4 indicates another pitch, which may in a hexagonal arrangement be equal to pitch p. The total surface area which is exposed to a flow is 1: 2.6×10.sup.−2 m.sup.2 (3a), 3.1×10.sup.−2 m.sup.2 (3b), 2.9×10.sup.−2 m.sup.2 (3c) and 2.7×10.sup.−2 m.sup.2 (3d).

[0056] As boundary conditions, the following conditions were chosen: [0057] Ambient temperature: 25° C. (298 K); [0058] Aluminum thermal conductivity: 237 W/mK (default value); [0059] Radiation included (Heat sink emissivity=0.9); [0060] Gravity effect included; [0061] Opening for air at 0 Pa relative pressure; [0062] Heat flux attached to the bottom surface of fin base (constant for all cases); [0063] Total heat flux=500 W/85800 mm.sup.2=5827.5 W/m.sup.2.
The Shear Stress Transport (SST) turbulence model was used.

[0064] The results (with reference to FIGS. 3a-3d) are displayed in the table below:

TABLE-US-00001 3a 3b 3c 3d Total Exposed area (m.sup.2) 0.026 0.031 0.029 0.027 Base Area 0.0028 0.0025 0.0025 0.0028 Max Temperature rise (° C.) 68 70 76 77 Power (W) (heat flux*Area) 16.3 14.4 14.4 16.3 Average heat transfer coefficient: 12.8 10.7 8.7 10.9 pins (W/m.sup.2K) Average heat transfer coefficient: 3.8 2.7 2.5 3 Base (W/m.sup.2K) Ave base temperature (° C.) 90 87 96 98 Thermal resistance (K/W) 0.13 0.12 0.14 0.15 Mass flow at inlet (kg/s) 4.8 × 4.1 × 3.3 × 4.1 × 10.sup.−4 10.sup.−4 10.sup.−4 10.sup.−4 Temperature rise of air from 34 35 44 35 ambient (° C.) Width ratio (total model width/ 520/17 520/15 520/15 520/17 section width)

[0065] Then, the thermal resistance of the entire heat sink was evaluated, see below table:

TABLE-US-00002 3a 3b 3c 3d No. of fins 330 408 408 330 One fin area (m2) 2.21E−03 2.41E−03 2.24E−03 2.21E−03 Total fin area (m2) 7.29E−01 9.83E−01 9.12E−01 7.28E−01 Base area (m2) 0.0858 0.0858 0.0858 0.0858 Fin efficiency 0.75 0.82 0.75 0.75 Ave HTC fins (W/m2K) 12.8 10.7 8.7 10.9 Ave HTC base (W/m2K) 3.8 2.7 2.5 3 Thermal resistance 0.14 0.11 0.16 0.16 (K/W)

[0066] The result clearly shows that elliptical pin fins provides better results in terms of maximum temperature and thermal resistance. Further, the flow resistance of the elliptical fins is lower compared to the circular fins. The average heat transfer in the system that may even be further optimized is very high. A higher value could be achieved by optimizing the design more.

[0067] Further, thermal calculations have been done on the straight fins of a heat sink of the size that is required for the floodlight example given above. With some assumptions on the material characteristics and the heat transfer coefficient, the total fin weight is around 11 kg and the thermal resistance from fins to ambient is 0.04 K/W. Similar calculations were done with the tube-fin heat sink, in which the pitch between the tubes was set to a preliminary value of 15 mm, and the tube is elliptical in cross section, with 9 mm maximum diameter and 4.5 mm minimum diameter. The tubes are placed in a hexagonal array. Typically 1320 tubes are needed on the 0.52m×0.495 m base. The thermal resistance (Rth) of the fins to the ambient is expected to be comparable to the straight fin heat sink, about 0.04 K/W, but the fin weight is considerably lower, about 3.6 kg, which is even much lower than 6 kg that is expected for 1 mm fin thickness of the straight fin heat sink.

[0068] With the invention, disadvantages of the prior art that are overcome are amongst others: [0069] the high weight of the finned heat sink; [0070] the low bending and buckling stiffness of general thin walled elements; [0071] the high hydraulic resistance of round or hybrid tubular structures placed in an air flow field.

[0072] Hence, the invention may include a heat sink base (“support”) with rulers, supports, bumps, or holes (“connectors”) to attach arrays of tubes to. The base plate may be flat or curved in 1 direction or curved in 2 directions. The tubes have a low wall thickness that are connected to the base plate by e.g. press fit, screwing, soldering, welding or other connection technologies that guarantee a good thermal connection. Further, the tubes are hollow, and have a non-axisymmetric cross-section. Ovals are the first preference, but other hollow rectangular, hexagonal or other multi-angular profiles that are aligned with the expected air flow direction are also possible. Any longitudinal structure with a non-axisymmetric cross section that offer a high bending stiffness and strength while also offering cooling area which can have addition holes or slits, and that are aligned with the expected air flow direction. For instance, forged (oval) tubes that have a (flat) bottom can be are placed upside down on the heat sink base. Optionally, a low density material to fill the hollow tubular structures preventing pollution and giving additional stiffness to the tubes. Optionally a structure to mechanically interconnect the tubes for robustness, which can be combined with the lids mentioned above.