JP2015201415A - heat dissipation structure for LED cooling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED light bulb that can ensure a heat dissipation amount below a permissible temperature of an LED element.SOLUTION: An LED element 1 is cooled by using heat dissipation from a surface that transmits light through a wall that transmits visible light, as well as radiates light well with a different wavelength, in particular, far-infrared light contributing heat dissipation. Although this heat radiation structure has a ball shell shaped heat pipe, in which saturated liquid and steam is confined, a heat absorption part 6 has a small area in an edge portion of the ball shell, whereas a heat dissipation part is a ball shell surface and has a much larger area compared to the hear absorption part 6. Heat is absorbed at the heat absorption part 6 by evaporation of a working fluid, condensed at an internal surface of an outer shell 5 exposed to the outside, and dissipated from an external surface thereof by heat emission and heat transfer by convection. Because the heat is transferred to the surface of the outer shell 5 having a large area from the LED element 1 by the same principle with the heat pipe, the temperature of the surface of the outer shell 5 rises up to a temperature close to that of the LED element, thus ensuring a heat dissipation amount below a permissible temperature of the LED element.

Description

The present invention relates to an LED lighting device using an LED (light emitting diode) as a light source.

LEDs have high energy savings and are promising as a light source for new lighting fixtures. However, LED elements that can be used for lighting have low heat resistance and generate heat at a high volume density, so it is necessary to devise heat dissipation to ensure the life of the elements.

In conventional bulb-shaped LEDs, except for those that use forced convection by a fan, the heat generated in the element is dissipated, so as in Patent Document 1, a metal heat dissipating surface is provided on the bottom of the bulb (on the base side) From there, natural convection, thermal radiation, or both are often used. The heat-dissipating surface is often made of lightweight aluminum or its alloy with high thermal conductivity. A method of transporting heat to a light-transmitting outer shell surface using a heat pipe has been proposed in Patent Document 2, but this patent only assumes the shape of a conventional tube as the shape of the heat pipe itself. Therefore, no proposal has been presented for the efficient diffusion of heat over the entire spherical outer shell surface proposed by this patent.

JP 2008-243780 A Special table 2012-519350 gazette

A light bulb may have poor heat dissipation depending on its usage conditions. For example, it has been widely practiced to install a light bulb in a ceiling cavity. In this case, since hot air stays around the bulb, it is difficult to expect heat dissipation by natural convection, which may lead to overheating of the LED element. Even when trying to use the radiation from the bottom of the bulb, the heat radiation from the wall warmed by the hot air staying on the radiation surface and by the heat conduction through the base part reduces the net heat dissipation. There is a risk of overheating of the device. Under such adverse conditions, overheating shortens the life of LED bulbs, making it impossible to utilize the energy-saving properties of LED bulbs.

It is effective to use heat radiation from the light bulb surface (surface through which illumination light passes) as a cooling method for LED light bulbs regardless of the installation location. The purpose of the light bulb is to deliver light to the object to be illuminated. Therefore, when using heat radiation from the surface of the light bulb that allows light to pass through, the heat radiation assumed at the time of design is not affected by the installation method. It is secured and does not choose the installation location. Using a heat pipe with a condensing surface that is the entire surface of a sphere that is ordinarily used to scatter light and give off a soft impression, the heat generated by the LED is placed there. Guidance and heat radiation using heat radiation from the outer shell and natural convection.

Heat radiation from the outer shell surface of the bulb, especially thermal radiation, reaches the object to be illuminated in the same way as visible light used as lighting. Therefore, the influence of the surface warmed by the heat radiation of the bulb is extremely small, and the attitude and location of the bulb Cooling capacity can be secured without choosing. This cooling method is possible because the resin normally used as the outer surface of LED bulbs transmits visible light well, but emits far infrared rays that contribute to radiant heat transfer. As a result, there are no restrictions on the location and orientation of the light bulb, and anyone can easily use LED light bulbs under conditions that satisfy the design life.

Cross section Cross section

As illustrated in FIG. 1, an LED element (1) is arranged, and heat is guided to a spherical heat pipe along a thermally conductive substrate (2) that conducts heat generation to the surroundings. This heat pipe is not tubular, but the working fluid is contained in a space sandwiched between two partial spherical shells, outer shell (5) and inner shell (3), and a thin circular plate (6) at the end. Liquid and steam are enclosed. The ring plate (6) is brought into close contact with the substrate, and the heat generated by the LED is absorbed as evaporation heat on the inner surface of the ring plate of the spherical heat pipe. The generated steam condenses inside the outer shell, which is maintained at the lowest temperature, and circulates through the wick (4) installed inside the outer shell to the heat sink.

The shape of the spherical heat pipe is not limited to the spherical shell shape. The space between the curved surfaces where the curvature changes and the spacing is almost constant can form a heat pipe, and the space between flat plates can form a heat pipe. In addition, the distance between two curved surfaces / planes may change. In addition, there may be a straight tube type or a donut shape often found in fluorescent lamps.

The wick can be composed of cloth (woven of twisted yarn) or woven single fibers, and can be formed by cutting fine grooves in the outer shell material, or by making irregularities. Is also possible. Grooves can be cut in various ways, such as cutting, grinding, etching and embossing. If the outer shell is made of glass, ground glass can also be used. As the wick material, a resin or glass having a high visible light transmittance is effective, but it can be a material conventionally used as a wick of a heat pipe such as a metal.

The second method is a method using two heat pipes in series as illustrated in FIG. The heat generated by the LED element (1) is transported to the center of the outer shell (5) using the first heat pipe (7) of the conventional type along the symmetry axis of the bulb. Heat is further transported to the outer shell using a second spherical shell-shaped heat pipe with the inner surface of the outer shell (5) as the condensation surface. The second heat pipe with the outer shell surface as the condensation surface has a generally hemispherical outer shell (5) and a generally hemispherical inner shell (3) that separates the flow path for steam and liquid. A wick (4) is attached to the inner surface of the shell. The liquid condensed on this surface permeates the wick and circulates to the evaporation part (the heated part, the tip of the heat pipe (7)). In the case of a wick made of fiber, the wick is supported so that it almost touches the inside of the outer shell.

The third method is similar to the second method, but uses a heat pipe in which a space for continuous transport of heat transporting liquid and steam forms a space. The wick (4) is installed along the inner surface of the outer shell, extends through the center of the tube on the central axis of the bulb to the area where the LED element (1) absorbs heat, and circulates the condensate.

The fourth method is similar to the third method, except that the wick (4) is placed on the surface of the inner shell, which extends along the tube wall of the tube on the central axis of the bulb, and the LED element ( Reach the heat absorption area of 1) and circulate the condensate. This method improves the flow of condensate near the endothermic part and the flow of evaporated vapor compared to the third method. Because the outer shell absorbs part of the radiation from the inner shell to the surroundings, the amount of heat released due to the same temperature difference is reduced, but heat dissipation is possible.

For Examples 1 to 4, it is possible to divide the spherical heat pipe with a simple wall along the steam flow.

Compared to Examples 1 to 4, the spherical heat pipe can be divided into a plurality of heat pipes in a direction perpendicular to the steam flow. In this case, a method of diffusing heat to a surface of the outer shell through a thick transparent material corresponding to the outer shell after the heat is diffused by a heat pipe having a circular shape or a cross section close thereto, which is assumed in Patent Document 2, is included in the present invention. Not included, limited to the case where the majority of the heat transferred to the outer shell surface condenses on the outer surface of the outer shell and the inner surface of the outer shell at almost regular intervals.

In a light bulb with a limited installation direction, such as when the shape of the outer shell surface is a candle flame, it is sufficient that the condensate flows to the evaporation part (heat absorption part) by gravity, and there is also a heat pipe (heat siphon) without a wick. possible.

Claims (4)

Made of the same material as the outer shell (5) (the outer surface that usually scatters light in LED bulbs) made of a material with high visible light transmission and high emissivity for far-infrared rays with a wavelength of 4 μm to 30 μm A heat pipe with a space where the working fluid / steam flows between the inner shells (3) (unlike conventional heat pipes, the cross-sectional area through which the working fluid / steam flows varies greatly, so it is not a pipe-like shape. A heat dissipation structure that diffuses the heat generated by the LED element (1) to the outer shell surface by the same principle as a pipe) and dissipates the heat to the surroundings by heat radiation and convective heat transfer from there. The transmission region is not limited to visible light, but can include ultraviolet and near infrared regions.
The shape of the outer shell surface includes a sphere that has been used in incandescent bulbs and a shape close to that, and a flat surface that has hardly been used in incandescent bulbs. It can also be a fluorescent tube straight tube or donut tube, or similar shell surface. The shape of the space where the working fluid / steam flows includes a single space, and a simple wall that is divided into multiple spaces in parallel (by walls along the steam flow).
In the wick (4) that circulates the condensate, synthetic resin fibers or natural fibers with low visible light absorption are used, or fine grooves or irregularities are formed on the inner surface of the outer shell. Wick includes not only the inside of the outer shell but also the outside of the inner shell, or both, and also the one that does not install the wick in anticipation of gravity circulation (heat siphon). Heat is transferred from the heat absorbing part to the final heat radiating part by a heat pipe, and the area of the final heat radiating part is much larger than the area of the heat absorbing part. A heat-dissipating structure with a structure in which the area of the part with almost constant spacing occupies the majority of the heat-dissipating surface. That is, the space in which the spherical shell-shaped hydraulic fluid / vapor flows according to claim 1 is divided into parallel heat pipes having a rectangular or close cross section in a direction perpendicular to the fluid flow. The sectional shape of the divided heat pipes includes trapezoidal, triangular, semicircular, or a shape close to that of the wide heat dissipation part. It has the final heat dissipating part described in claims 1 and 2 and another heat pipe combined in series to transport heat to the heat absorbing part. This includes heat pipes that are combined in series and divided into parallel heat pipes. In addition, it includes those with LEDs installed on the surface of the heat pipe. The situation and heat flow according to claim 1, 2, 3 wherein the spherical shell surface is used as a heat absorbing part, and the edge of the spherical shell or a part corresponding thereto is brought into thermal contact with a low-temperature heat source. Reversed endothermic structure.

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