WO2012130536A1

WO2012130536A1 - A heat sink device and lighting apparatus having the heat sink device

Info

Publication number: WO2012130536A1
Application number: PCT/EP2012/053173
Authority: WO
Inventors: YingJun CHENG; Yu Mao
Original assignee: Osram Ag
Priority date: 2011-03-25
Filing date: 2012-02-24
Publication date: 2012-10-04
Also published as: CN102691997A; CN102691997B

Abstract

The present invention relates to a heat sink device for lighting apparatus, comprising a cylindrical matrix (1) and a plurality of fins (2) extending radially outwardly on an outer surface of the matrix (1), wherein an accommodating cavity (3) is formed in the matrix (1) for accommodating components of the lighting apparatus, and wherein each of the fins (2) is at least formed with a bending portion (4) extending in a direction of the adjacent fins (2) on at least a portion of an end of the fins away from the matrix (1). The heat sink device designed according to the present invention does not prominently increase the volume of the fins while increasing the thermal dissipation surface area; moreover, the convective heat transfer coefficient of each fin is optimized with the special design of the heat sink device. In addition, the present invention also relates to lighting apparatus having the heat sink of such type.

Description

A Heat Sink Device and Lighting Apparatus Having the Heat

Sink Device

Technical Field

The present invention relates to a heat sink device and lighting apparatus having the heat sink device of such type.

Background Art LED retrofit lamps of the types such as MR16, PAR38, A60 and GX53 are seethingly finding the way of replacing other traditional lighting apparatus such as incandescent and fluores^¬ cent lamps because they can offer the benefits of energy sav^¬ ing, small size and long lifetime. With the technology devel- opment, LED package itself can reach high efficiency, such as 1401m/W for cold white and 901m/W for warm white and they are supposed to have a long lifetime as to 50,000 hours, but when the LED is integrated into a retrofit lamp together with an LED driver, a thermal management device and an optical compo- nent, the efficiency and lifetime of the retrofit lamp are highly dependent upon how to design the driver, heat sink device and optical component. Some of the electrical power con^¬ sumed in the LED converts to heat rather than light. Accord^¬ ing to statistics of U.S. Department of Energy, 75% to 85% of energy used to drive the LED is converted to heat, and the heat must be conducted from the LED die to the underlying PCB and heat sink device. If the heat cannot be conducted timely, the LED' s light output performance will be reduced and a color shift will be produced in the short term, and the life- time of the LED will be shortened in the long term. And the performance of the heat sink device directly affects the LED lighting device. A good heat sink device design should be ca^¬ pable of providing favorable local air flow conditions, good radiation between surfaces, low material cost and simpler and easier manufacturing. In order to obtain favorable thermal dissipation performance, most heat sink devices are designed to have an increased thermal dissipation surface area by using a larger number of fins within the form factor limitation. For example, Chinese Patent application No . CN200940816Y discloses a heat sink de- vice for an LED spot lamp including a reflecting mirror, a lampshade and a cylindrical heat spreader. A number of fins are set outside of the spreader. A cavity is formed in the center of the spreader. In order to produce good heat conduc^¬ tion effect, the fins surround the cavity, and the cavity is filled with heat conducting material.

The fins of the heat sink device disclosed above are designed for the purpose of better thermal dissipation through convection or high surface emissivity is preferred for better ra^¬ diation. Therefore, these heat sink devices achieve the above object via increased thermal dissipation surface area of the fins and using painted surface. In addition, the fin of such type is manufactured in most cases with a die casting process because of the complicated structure. The disadvantages thereof are quite obvious: firstly, a heat transfer coeffi- cient of an aluminum alloy used in the die casting process is not high; and secondly, the increased surface area of the heat sink device is not necessarily followed by prominently improved thermal dissipation capability, because the thermal dissipation capability of the heat sink device depends upon not only the surface area of the heat sink device but also the convective heat transfer coefficient on each surface, and this coefficient relates to physical properties of a fluid performing convection, physical situation in which the convection occurs and geometric size of the fins. In addition, though the painted surface has good surface emissivity, it will also bring about additional conductive thermal resis- tance since most painted materials are poor at heat conduc^¬ tion capability. Therefore, most of the coloring materials have poor thermal conduction ability. Further, the mould in the die casting process is also relatively costly.

Summary of the Invention Therefore, the object of the present invention lies in pro^¬ viding a heat sink device for lighting apparatus. The heat sink device has a relatively small volume while being capable of providing favorable thermal dissipation capability, and also, the heat sink device in the present invention has a relatively high surface emissivity. In addition, the cost for manufacturing the heat sink device according to the present invention is quite low.

The object of the present invention is implemented as follow. The heat sink device comprises a cylindrical matrix and a plurality of fins extending radially outwardly on the outer surface of the matrix, an accommodating cavity is formed in the matrix for accommodating components of lighting apparatus, wherein each fin is at least formed with a bending portion extending in a direction of adjacent fins on at least a portion of an end of the fin away from the matrix. With such solution, the thermal dissipation surface of the fins is prominently increased, while the basic profile and size of the heat sink device remain unchanged.

Preferably, the number of the finsare optimized using the

AT— 8 7?⁰'⁶³ W⁰-¹ 7^"-°-⁶¹ 7¹-0.32 I

formula ^- -^{6XK n l} J , wherein N is the number of the fins; R is the radius of the heat sink device whose cross section is circular; H is the height of the heat sink device; L is the length from the matrix to the ends of the fins away from the matrix; and T is the thickness of the fins. With this formula, it is calculated whether a compli^¬ cated fin design really helps thermal dissipation performance. An optimal thermal dissipation performance is obtained by adjusting the fin thickness and fin number, size and shape of the bending portion, etc. Of course, the bending portion should be optimized in design, which needs to take into consideration of the increasing of the surface area of the fins and the convective heat transfer coefficient of each fin. When designing the bending portion, on one hand, the surface area of the fins is increased with the bending portion so as to implement quick heat exchange when conducting convection; and on the other hand, the shape and size of the bending portion should be taken into consid^¬ eration so as to optimize the convective heat transfer coef^¬ ficient. The convection thermal resistance R_th=l/ (h*A) of the surface of fins exposed to the convective ambient can be known according to Newton heat convection law, wherein h is the convective heat transfer coefficient and A is the surface area of the fins. Thus, it is not only the surface area of the fins but also the convective heat transfer coefficient that affect the convective thermal resistance.

Preferably, the bending portion extends at least beyond half of the gap between two adjacent fins. With this solution, the area of the thermal dissipation surface is increased as much as possible, and the convective condition will not be nega- tively affected at the same time.

Further preferably, the bending portion extends tangently in a direction of adjacent fin. In such manner, the surface area of the fins is increased, and the profile and size of the heat sink device remain unchanged.

It is provided according to a preferred solution of the pre- sent invention that the fins, bending portions and matrix are manufactured in one piece from aluminum with extruding process. The extruded aluminum (with a thermal conductivity around 210W/m/k) is better at conducting heat compared with the die casting alloy (with a thermal conductivity around 120 W/m/k) . In addition, the cost of the heat sink device manufactured from aluminum with the extruding process is much lower and easier for manufacturing.

Preferably, the matrix, fins and bending portions are ano- dized or etched, whereby better surface emissivity and better thermal dissipation performance are obtained.

It is provided according to a preferred solution of the pre^¬ sent invention that the accommodating cavity is divided by a separator into a first accommodating cavity for accommodating an electronic driver of the lighting apparatus and a second accommodating cavity for accommodating LEDs and optical components of the lighting apparatus. Thus, the heat dissipated by the electronic driver will not affect the LEDs so as to prolong the service life of the LED.

Preferably, the separator and the matrix are formed in one piece so as to further simplify the manufacturing process.

It is provided according to the present invention that the fins are designed to be two-dimensional. The two-dimensional fins are more advantageous, for instance, for the fluid of air to flow between the fins, so as to be favorable to im- proving the heat exchange capability of the heat sink device in convection and improving the performance of the heat sink device .

The other object of the present invention lies in providing lighting apparatus having the heat sink device of the type above .

Brief Description of the Drawings

The drawings constitute a portion of the Description for fur^¬ ther understanding of the present invention. These drawings illustrate the embodiments of the present invention and ex^¬ plain the principle of the present invention together with the Description. In the drawings, the same element is repre^¬ sented by the same reference sign, wherein

Fig. 1 is a schematic diagram of a heat sink device for an MR16-type LED retrofit lamp;

Fig. 2 is a schematic diagram of the heat sink device for the MR16-type LED retrofit lamp observed from another angle;

Fig. 3 is a schematic diagram of the heat sink device for the MR16-type LED retrofit lamp observed from the bottom; Fig. 4 is a schematic diagram of a heat sink device for a

GX53-type LED retrofit lamp;

Fig. 5 is a schematic diagram of the heat sink device for the

GX53-type LED retrofit lamp observed from another angle;

Fig. 6 is a schematic diagram of a heat sink device for an A60-type LED retrofit lamp; Fig. 7 is a schematic diagram of the heat sink device for the A60-type LED retrofit lamp observed from another angle;

Fig. 8 and Fig. 9 are charts of measured results and simula^¬ tion results of heat sink device surface temperatures and solder joint temperatures of die at different driving cur^¬ rents for an MR16-type LED retrofit lamp and for a GX53-type LED retrofit lamp, respectively; and

Fig. 10 to Fig. 12 are charts of relationships between solder joint temperatures and different fin numbers and thicknesses of heat sink devices for an MR16-type LED retrofit lamp, a GX53-type LED retrofit lamp and an A60-type LED retrofit lamp, respectively.

Detailed Description of the Embodiments

Fig. 1 shows a heat sink device according to the present in- vention, specifically designed as the heat sink device for an MR16-type retrofit lamp. This heat sink device has a cylin^¬ drical matrix 1 and a plurality of fins 2 extending radially outwardly on an outer surface of the matrix 1. These fins 2 are designed to be two-dimensional. The matrix 1 has a cylin- drical accommodating cavity 3 that is divided by a separator 5 into a first accommodating cavity 3a and a second accommo^¬ dating cavity 3b (see Fig. 2), wherein the first accommodat^¬ ing cavity 3a is used for accommodating an electronic driver of lighting apparatus and the second accommodating cavity 3b is used for accommodating LEDs and optical components such as reflector and lens of the lighting apparatus. In addition, it can be seen from Fig. 1 that each fin 2 gradually gets widened in a direction away from the matrix 1, starting from an opening rim of the first accommodating cavity 3a, so as to form an arc-shaped end trend. Moreover, a bending portion 4 extending in a direction of the adjacent fins 2 is formed on at least a portion of the end. The bending portion 4 extends at least beyond half of a gap between two adjacent fins 2. In the present embodiment, the bending portion 4 just extends to a position of half of the gap between two adjacent fins 2, and the bending portions 4 extend tangently in a direction of the adjacent fins 2. What's more, the end of the fin 2 is not entirely formed with the bending portion 4, which effectively avoids influence of the bending portion to convection. In the present embodiment, all of the matrix 1, the fins 2, the bending portions 4 and the separator 5 are manufactured in one piece from aluminum with an extruding process.

Fig. 2 is a schematic diagram of the heat sink device for the MR16-type LED retrofit lamp observed from another angle. The second accompanying cavity 3b can be seen from this angle.

Fig. 3 is a schematic diagram of the heat sink device for the MR16-type LED retrofit lamp observed from the bottom, wherein R is radius of the heat sink device whose cross section is circular; H is height of the heat sink device; L is length from the matrix 1 to ends of the fins 2 away from the matrix 1; and T is thickness of the fins 2. In conjunction with the height H of the heat sink device shown in Fig. 1, the number N of the fins may be calculated according to the formula

N = | L5.8xR^0'63xH⁰¹xL-^0'61xr-^a32 J|. C„ert.ai.nl-y, thi.s f,ormula can be applied to not only the heat sink device for the MR16-type

LED retrofit lamp but also the heat sink device for retrofit lamps of other types.

Fig. 4 is a schematic diagram of a heat sink device for a GX53-type LED retrofit lamp. This heat sink device differs from that shown in Fig. 1 in shapes of the first accommodat ing cavity 3a and the fins 2 and setting condition of the bending portions 4 on the fins 2. In the heat sink device for the GX53-type LED retrofit lamp, accommodating grooves 3c are further formed at both ends of the first accommodating cavity 3a and also provided in the matrix 1, so as to be adapted to a shape of an electronic driver of the GX53-type LED retrofit lamp. Moreover, it can be further seen from Fig. 3 that the two-dimensional fins 2 extend radially outwardly on an outer surface of the matrix 1, and an end of the fin 2 away from the matrix 1 is provided parallel with a surface of the ma- trix 1. Besides, the bending portions 4 are formed on entire ends of the fins 2.

Fig. 5 is a schematic diagram of the heat sink device for the GX53-type LED retrofit lamp observed from another angle. The second accompanying cavity 3b likewise can be seen from this angle.

Fig. 6 is a schematic diagram of a heat sink device for an A60-type LED retrofit lamp. This heat sink device merely dif^¬ fers from that shown in Fig. 1 in the shape of the fin 2. The fin 2 in the heat sink device for the A60-type LED retrofit lamp likewise gradually gets widened in a direction away from the matrix 1, starting from an opening rim of the first accommodating cavity 3a, so as to form a wavy end trend.

Similarly, Fig. 7 is a schematic diagram of the heat sink de^¬ vice for the A60-type LED retrofit lamp observed from another angle. The second accompanying cavity 3b can be seen there^¬ from.

Fig. 8 and Fig. 9 are charts of measured results and simula^¬ tion results of heat sink device surface temperatures and solder joint temperatures of die at different driving cur- rents for an MR16-type LED retrofit lamp and for a GX53-type LED retrofit lamp, respectively. It can be seen from the two charts that the simulation results very well at a low LED power condition, while a temperature obtained in the simula^¬ tion is 1-3°C lower than a measured temperature at a high LED power condition. But a relative error for a simulation model within 5% is generally acceptable.

Fig. 10 to Fig. 12 are charts of relationships between solder joint temperatures and different fin numbers and thicknesses of heat sink devices for an MR16-type LED retrofit lamp, a GX53-type LED retrofit lamp and an A60-type LED retrofit lamp, respectively. In the solutions of the present inven^¬ tion, the relationships between the solder joint temperatures and different fin numbers and thicknesses of the heat sink devices for the MR16-type LED retrofit lamp, the GX53-type LED retrofit lamp and the A60-type LED retrofit lamp are ana^¬ lyzed based on validation CFD simulation models. The three charts show a same trend, i.e. for a small fin number, the fin thickness has little effect on the solder joint tempera^¬ ture, while for a big fin number, a smaller fin thickness re- suits in a lower weld leg temperature and indicates a better thermal dissipation capability. For a fixed fin thickness, there is an optimal fin number for a lowest solder joint tem^¬ perature. If 0.8mm is considered as a minimum fin thickness according to manufacturing and mechanical strength limita- tion, the optimal fin numbers for the MR16-type, the GX53- type and the A60-type LED retrofit lamps are 16, 18 and 18, respectively .

The above is merely preferred embodiments of the present in^¬ vention but not to limit the present invention. For the per- son skilled in the art, the present invention may have vari^¬ ous alterations and changes. Any alterations, equivalent sub^¬ stitutions, improvements, within the spirit and principle of the present invention, should be covered in the protection scope of the present invention.

1 matrix

2 fin

3 accommodating cavity 3a first accommodating cavity

3b second accommodating cavity

3c accommodating groove

4 bending portion

5 separator R radius of the heat sink device whose cross section is circular

H height of the heat sink device

L length from the matrix to ends of the fins away from the matrix T thickness of the fins

Claims

1. A heat sink device for lighting apparatus, comprising a cylindrical matrix (1) and a plurality of fins (2) extending radially outwardly on an outer surface of the matrix (1), wherein an accommodating cavity (3) is formed in the matrix (1) for accommodating components of the lighting apparatus, and wherein each of the fins (2) is at least formed with a bending portion (4) extending in a direction of the fins (2) that are adjacent on at least a portion of an end thereof away from the matrix (1) .

2. The heat sink device according to claim 1, wherein a number of the fins (2) are optimized using formula as follow

N = | L5.8xR^0'63xH⁰¹xL-^0'61xr-^a32 J|, wherei.n _MΝ i.s the num,ber of. t. ,he fins (2); R is radius of the heat sink device whose cross section is circular; H is height of the heat sink device; L is length from the matrix (1) to ends of the fins (2) away from the matrix (1) ; and T is thickness of the fins (2) .

3. The heat sink device according to claim 1 or 2, wherein the bending portion (4) extends at least beyond half of a gap between two of the fins (2) that are adjacent.

4. The heat sink device according to claim 1 or 2, wherein the bending portion (4) extends tangently in a direction of the fins (2) that are adjacent.

5. The heat sink device according to claim 1 or 2, wherein the fins (2), the bending portions (4) and the matrix (1) are manufactured in one piece.

6. The heat sink device according to claim 1 or 2, wherein the fins (2), the bending portions (4) and the matrix (1) are manufactured from aluminum.

7. The heat sink device according to claim 1 or 2, wherein the fins (2), the bending portions (4) and the matrix (1) are manufactured with an extruding process.

8. The heat sink device according to claim 1 or 2, wherein the matrix (1), the fins (2) and the bending portions (4) are anodized or etched.

9. The heat sink device according to claim 1 or 2, wherein the accommodating cavity (3) is divided by a separator (5) into a first accommodating cavity (3a) for accommodating an electronic driver of the lighting apparatus and a second ac^¬ commodating cavity (3b) for accommodating LEDs and optical components of the lighting apparatus.

10. The heat sink device according to claim 8, wherein the separator (5) and the matrix (1) are formed in one piece.

11. The heat sink device according to claim 1 or 2, wherein the fins (2) are designed to be two-dimensional.

12. Lighting apparatus comprising the heat sink device ac^¬ cording to any one of claims 1 to 11.