WO2015034397A1

WO2015034397A1 - Evaporative cooling system for led module

Info

Publication number: WO2015034397A1
Application number: PCT/RU2014/000628
Authority: WO
Inventors: Евгений Анатольевич ЧИННОВ; Олег Александрович КАБОВ
Priority date: 2013-09-05
Filing date: 2014-08-22
Publication date: 2015-03-12
Also published as: RU2013140942A; RU2551137C2; EA201600127A1; EA029368B1

Abstract

The invention relates to radioelectronics, and specifically to the cooling of the heat-emitting components of electronic equipment. The aim of the invention is to, in a highly effective manner, remove heat from each semiconductor LED assembled into a module, with a minimum heat transfer resistance value and with a minimum impact of uncondensed impurities. Said aim is achieved in that an evaporative cooling system for an LED module is composed of a base made of a highly thermally-conducting material on which LEDs are installed, a microporous structure which is adjacent to the thermally-conducting base and which is located between the thermally-conducting base and a radiator, said radiator having channels which are positioned below the LEDs and which are perpendicular, relative to the plane in which the LEDs are installed, in such a way that portions of the thermally-conducting base which are adjacent to the ends of the channels form, in maximum proximity to p-n junctions of the LEDs, an intensifying heat-exchange surface made of a porous material, wherein each channel is blocked, by a funnel having a steam conduit, in such a way that the upper portion of the funnel is adjacent to the intensifying surface.

Description

LED EVAPORATOR COOLING SYSTEM

MODULE

The invention relates to electronics, in particular to the cooling of fuel elements of electronic equipment, LED systems.

Known flat heat pipe [US3613778, 10.19.1971, B64G1 / 50; B64G1 / 58; F28D 15/02], filled with a porous metal wick or mesh in the steam channel.

The thickness of the wick helps to increase the heat transfer capacity of the heat pipe. However, with an increase in the thickness of the wick, its thermal resistance in the radial direction increases, which prevents the growth of the heat transfer ability of the pipe as a whole and reduces the permissible maximum heat flux density in the evaporator.

A device for cooling electronic components is known [US4975803, 04/04/1990, H05 7/20], which has a sandwich construction and consists of a plurality of plates enclosed in a metal body (parallelepiped) parallel to the plane of installation of electronic components and made of a porous material with diagonal microchannels, moreover, the microchannels of adjacent plates have opposite directions. The porous core with microchannels is filled with a liquid coolant. Heat is transferred to the end parts of the case where the radiator is located.

In this design, heat removal mainly to the end part does not provide effective heat transfer to the radiator. Effective thermal conductivity of a liquid-saturated porous material in the direction perpendicular to the plane of installation of electronic components are significantly smaller than in the direction parallel to the plane of installation of electronic components.

A known device is a thermosiphon [RU2373473, 07/16/2008, H05K7 / 20], which can significantly increase the efficiency of heat transfer from the heated part to the cooled area by intensifying heat transfer during condensation under conditions of high air content in the system. The thermosiphon contains a housing, a lower chamber filled with liquid, a funnel with a steam line, a steam generator in the lower chamber and a condenser in the upper chamber, and a valve is installed in the lower chamber to vent some of the air out.

A thermosiphon without a funnel with a pipeline for the movement of steam can work normally only if air is pumped out of the system and the liquid is thoroughly degassed.

Closest to the technical nature of the claimed system is a cooling device for the heat-generating components of the module of electronic equipment [RU2403692, 04/29/2009, N05K1 / 00, N05K7 / 20], consisting of a heat-sink base, printed circuit boards and electrical components installed on them. The heat sink base is made of microporous material with microchannels and filled with liquid coolant. Microchannels are located in the heat sink in two orthogonal directions parallel to the plane of the printed circuit board. Heat is transferred to the end of the heat sink base.

However, heat removal mainly to the end part of the heat sink base does not provide effective heat transfer to the radiator adjacent to the plane of the printed circuit board.

Almost all known heat pipes and thermosiphons for effective operation require preliminary pumping of air and maintaining high tightness, which leads to a decrease in the reliability of devices and their high cost [Handbook of heat exchangers. M. Energoatomizdat, 1987, Dan P., Ray D. Heat pipes. M. Energy, 1979, 272 s, Pioro I.L., Antonenko V.A., Pioro L.S. Efficient heat exchangers with two-phase thermosiphons. Kiev. Naukova Dumka, 1991, 246 p.]. The presence of even a slight air admixture in the inner part of heat pipes or thermosiphons leads to a sharp decrease in the heat transfer coefficient during condensation of the working fluid.

Thus, the main problem of all heat pipes is non-condensed impurities (air or gas) that accumulate in the condensation zone, which leads to a decrease in condensation and, consequently, to a decrease in the efficiency of their work.

An object of the present invention is to provide highly efficient heat removal from each of the semiconductor LEDs assembled in a module with a minimum value of heat transfer resistance and a minimum effect of non-condensed impurities.

The problem is solved by combining known elements, namely, a well-known feature of electronic component cooling devices, a heat-removing base of a porous material with channels filled with liquid coolant [RU2403692, 04/29/2009, Н05К1 / 00, Н05К7 / 20], and a known thermosiphon construction element , funnels with a steam line, [RU2373473, 07/16/2008, H05K7 / 20], leading to the achievement by the object of a new result.

The problem is solved in that in the evaporative cooling system of the LED module, consisting of a base with LEDs mounted on it, to which is adjacent a layer of microporous material filled with liquid coolant with channels, according to the invention, the base is made of highly heat-conducting material, the microporous structure adjacent to the heat-conducting base is in volume, s limited to a heat-conducting base and a radiator, the surface of which is covered with a thin layer of non-porous heat-conducting material. In the microporous structure, under the LEDs, perpendicular to the plane of their installation, there are channels, and they are located so that the parts of the heat-conducting base adjacent to the ends of the channels form, in the maximum proximity to the p-η junctions of the LEDs, an intensifying heat transfer surface made of a porous material, the pore size of which smaller pore sizes of the microporous structure and decrease towards the center of the LED. Each channel is blocked by a funnel with a steam line so that the funnel is adjacent to the intensifying surface with the upper part, and the heat-transfer intensifying surface.

In FIG. 1 schematically depicts an evaporative cooling system for an LED module, where: 1 - a heat-conducting base; 2 - LEDs; 3 - microporous structure; 4 - channels; 5 - radiator, 6 - intensifying surface; 7 - steam line; 8 - funnel.

The evaporative cooling system of the LED module consists of a heat-conducting base 1, on which LEDs 2 are installed, a microporous structure 3, filling the volume between the heat-conducting base 1 and the radiator 5, in which channels 4 are located under the LEDs perpendicular to the plane of their installation, each of which is blocked by a funnel for 8 s steam line 7.

Between the heat-conducting base 1 and the ends of the channels 4 in the maximum proximity to the p-η transitions of the LEDs there is an intensifying heat exchange surface 6 (a surface that intensifies boiling and evaporation). The intensifying heat transfer surface 6 is made of a porous material, and the pore sizes are smaller than the pore sizes of the microporous structure 3 and are reduced towards the center of the heat-emitting diode to create the necessary capillary pressure, which is especially important at high heat fluxes.

The funnel 8 with its upper part adjoins the intensifying heat transfer surface, and its lower part is a steam pipe 7 ending near the end of the channel in the cooling zone.

The surface of the radiator 5 is covered with a thin layer of non-porous heat-conducting material.

During the operation of the evaporative cooling system of the LED module, the LEDs emit heat (heating zone), which is transmitted to the ends of the channels. In order to ensure the transfer of heat emitted by the LEDs to the cooling zone (surface of the radiator), the microporous structure 3 with channels 4, located in the volume limited by the heat-conducting base 1 and the radiator 5, is filled with a liquid heat carrier, for example water, and the microporous structure 3 is saturated with a heat carrier in the liquid phase, and in channels 4, the coolant is in the vapor phase. The coolant transfers heat from the LED heating zone to the cooling zone due to the latent heat of vaporization. The heat entering the heating zone from the LEDs causes evaporation of the coolant. On an intensifying surface, boiling begins at significantly lower superheat temperatures, and the heat transfer coefficient is much higher than on a smooth surface.

When the coolant boils on the intensifying surface, the vapor is collected in a funnel (evaporation zone). In the evaporation zone, an excess vapor saturation pressure is created, which is spent on accelerating the steam and overcoming the friction force of the steam flow on the surface of the steam pipe. As a result, the pressure along the length of the steam line from the evaporation zone drops. In the middle section of the channel, the pressure stabilizes (adiabatic section). AT In the cooling zone, pressure is restored to almost the pressure in the evaporation zone.

The resulting pressure difference causes the steam to move through the steam line from the heating zone to the cooling zone, where the steam condenses, giving off the latent heat of vaporization. Steam moving along the steam line displaces non-condensed impurities (air or gas) and propagates in the channel, forcing the non-condensed impurities into the middle region of the channel. Thus, most of the non-condensed impurities accumulate in the middle part of the channel, and not in the cooling zone, and does not affect the efficiency of condensation.

As a result of constant evaporation, the amount of liquid in the heating zone decreases, and the liquid-vapor phase interface moves inside the microporous structure, which causes the appearance of capillary pressure here. This capillary pressure causes condensed liquid in the cooling zone to return back to the heating zone. Thus, heat is continuously transferred from the heating zone to the cooling zone.

An additional capillary pressure arises due to the fact that the pore size of the intensifying heat transfer surface is significantly smaller than the pore size of the filler of microporous material and even decreases towards the center of the heat-emitting LED, which is especially important at high heat fluxes. When pores are dried in the central part of the intensifying surface, the capillary pressure increases, providing a more intensive supply of fluid to the vicinity of the LED and, accordingly, higher values of the removed heat fluxes.

Thus, the provision of highly efficient heat removal from semiconductor LEDs with a minimum value of heat transfer resistance and a minimum effect of non-condensed impurities is achieved due to: b 1. The high value of effective thermal conductivity along the channels (heat pipes), which is more than two orders of magnitude higher than the thermal conductivity of modern printed circuit boards;

2. intense boiling and evaporation of the liquid on the intensified surface near the p-η transition of the LEDs;

3. displacement of non-condensed impurities in the middle region of the channel due to the presence in the channel of a funnel with a steam line.

The proposed design requires a one-time filling with liquid and is less sensitive to variations in the initial volume of liquid, in contrast to heat pipes known from the art, which require filling with a precisely defined volume of liquid while evacuating.

The performance of the proposed design of the evaporative cooling system of the LED module is confirmed by experimental data and performed estimates and calculations.

Claims

CLAIM

1. The evaporative cooling system of the LED module, consisting of a base with LEDs mounted on it, adjoins a layer of microporous material filled with liquid coolant with channels, characterized in that the base is made of highly heat-conducting material, the microporous structure adjacent to the heat-conducting base is limited a heat-conducting base and a radiator, the surface of which is covered with a thin layer of non-porous heat-conducting material, in microporous steel A channel is arranged under the LEDs perpendicular to the LED installation plane so that the parts of the heat-conducting base adjacent to the ends of the channels form an intensifying heat exchange surface in the maximum proximity to the p-η transitions of the LEDs, while each channel is blocked by a funnel with a steam pipe so that the funnel is adjacent to the upper part to intensifying surface.

2. The evaporative cooling system of the LED module according to claim 1, characterized in that the intensifying heat transfer surface is made of a porous material whose pore sizes are smaller than the pore sizes of the microporous structure and decrease towards the center of the LED.