DE8804742U1 - Heat sink with inserted filler piece for cooling an electrical component with a liquid cooling medium - Google Patents

Description

• ti «« »♦

> i I 1 t < ·

Siemens AG

Heat sink with inserted filler piece Cooling of an electrical component with a liquid cooling medium

The innovation relates to a heat sink for electrical components, in particular for power transistors, through which a liquid cooling medium flows to dissipate the waste heat transferred to the heat sink, and which has a heat-conducting carrier for the electrical component, through which a channel for the cooling medium to flow passes.

In an electrical component, e.g. a power transistor or thyristor, a liquid cooling medium is often used to dissipate the waste heat given off to a heat sink. The problem here is usually to ensure sufficient thermal conductivity in the transition between the heat sink and the liquid cooling medium flowing through it. The reason for this is that the liquid cooling medium partially "sticks" to the inner surfaces of the flow channels. This creates a so-called "boundary layer" of stationary cooling medium, which is not involved in the flow of the remaining cooling medium through the center of the flow channel. This boundary layer covers the inner walls of the heat sink flow channels like an insulator and hinders the heat transfer between the heat sink and the cooling medium. The heat-insulating effect of this boundary layer is particularly pronounced when oil is used as the cooling medium, since oil has a high heat storage capacity but poor thermal conductivity. In addition, the boundary layer thickness is particularly large due to the high oil viscosity.

To increase the thermal conductivity of such liquid-flow heat sinks, it is known to increase the length

Mie 2 Bih / 05.04.1988

M 63 H 6 EN

of the resulting flow channel passing through the heat sink, e.g. by using several parallel flow channels. However, such an increase in the overall transition area between the heat sink and the cooling medium available for heat transfer can generally only be achieved by significantly increasing the dimensions or by increasing the design and manufacturing effort of the heat sink. In particular in electrical systems in power electronics, where a large number of preferably identical electrical components, e.g. in a power converter, have to be cooled, it is particularly important for

For reasons of space requirements, it is undesirable if the external dimensions ( d of the heat sink) exceed those of the associated individual component, e.g. a so-called "disk cell". In addition, liquid cooling is preferred due to its greater heat transport capacity compared to air cooling, especially where a particularly compact design of the respective electrical system is desired and necessary.
20

In order to increase the thermal conductivity, it is also known to increase the flow rate of the liquid coolant. In addition to the actual increase in the coolant flow rate, this measure also reduces the thickness of the insulating boundary layers. In practice, however, there are usually strict limits to increasing the flow rate, as this requires a strongly exponentially increasing pump power requirement. However, in mobile electrical systems in particular, e.g. in aircraft, the degrees of freedom available for designing the coolant pumps are very limited, particularly in terms of energy requirements and size.

The innovation is based on the task of specifying a liquid-flow heat sink with the most compact possible external design and simple internal design.

4 4 with mid

, 4 a . 4 4 , , .4

■ 4 · · i I)M ij ti 4

, 4 .44 4 < 4 ·

G 31&Iacgr; 6 DE

maximum thermal conductivity in the transition area between the heat sink and the cooling medium can be achieved without having to increase the flow rate of the cooling medium.

P The problem is solved by a heat-conducting filler piece which is inserted into the flow channel to increase the thermal conductivity of the transition between the cooling body and the cooling medium and is connected to the inner wall in a heat-conducting manner. lö Particularly advantageous designs of such a filler piece and further embodiments of the innovation are specified in the subclaims.

The innovation is further explained in more detail using the following figures, which show:

FIG Ia-Ic the structure of a liquid-flow heat sink

in plan view» side and front view,

FIG 2 a filler piece in the form of a helical spiral with an approximately rectangular cross-section, FIG 3 a filler piece in the form of a helical spiral

with a parabolic cross-section,

FIG 4 Filler pieces in the form of a pipe packing consisting of pipe pieces,

FIG 5 Filler pieces in the form of a tube packing consisting of tube pieces with a core pin in the centre,

FIG 6 a filler piece in the form of one of a plurality of

Balls consisting of ball packing,

FIG 7 Filler pieces in the form of a milled piece with groove-shaped flow channels on the top,

FIG 8 Filler pieces in the form of a barrel piece with groove-shaped flow channels on the top and an additional core hole in the center,

FIG 9 Filler pieces in the form of a corrugated, right-left spring piece,

■ · ■

■ «I

G 3 \ h 6 EN

4
FIG 10 Filler pieces in the form of a longitudinal piece with

an approximately rectangular cross-section, and FIG 11 filler pieces in the form of a longitudinal piece with a parabolic cross-section.

\

Figures 1a, 1b and 1c show an example of a possible embodiment of a liquid-flow heat sink for an electrical component in a top, side and front view. The essential element of this heat sink is a heat sink carrier 2 with a diameter L, which is cylindrical in the example in FIG. 1. The object to be cooled is brought into heat-conducting contact with this carrier, in particular via its support surface F. Its external dimensions, determined by the diameter L, advantageously correspond approximately to the dimensions of the object to be cooled. The heat sink carrier 2 is preferably penetrated by a single, in particular straight-running flow channel 3 with a diameter D for the liquid cooling medium. Connection pipes 1 are used to feed in and out the cooling medium, and are advantageously provided at the ends with external threads 4 for connecting further cooling medium hoses. The embodiment of a heat sink shown in FIG 1 is characterized by a particularly simple external structure, which is particularly due to the flow channel 3 that runs straight through the heat sink carrier 2.

According to the innovation, a heat-conducting filler is preferably inserted into the part of the flow channel 3 located inside the heat sink carrier 2 and connected to its inner wall in a heat-conducting manner. This has the particularly advantageous effect of significantly increasing the surface available for this heat transfer in the area of the heat sink in which the majority of the heat energy is transferred to the liquid cooling medium, and thus the thermal conductivity of the entire heat sink.

Furthermore, the boundary layer that otherwise evenly covers the entire flow channel" | Inner sides 3 in the area

88 G3 H 6 EN

of the filler piece is disturbed. In the filler piece itself, shorter and thinner boundary layers are formed compared to the previous boundary layer. This achieves a particularly advantageous reduction in the temperature gradients within the cooling medium on the downstream side of the filler piece in the flow channel cross-section. The heat-insulating influence of the boundary layers is therefore particularly advantageously reduced by the innovation, especially in the center of the heat transfer between the heat sink and the cooling medium, by inserting the filler piece, in particular in the part of the flow channel 3 located directly in the core of the heat-conducting carrier 2.

The thermal conductivity-increasing effect of the filler can be further increased by increasing the flow speed of the cooling medium as it passes through the filler due to its cross-sectional design. This further reduces the thickness of the boundary layers inside the filler and thus their heat-insulating effect. In a further embodiment of the innovation, the formation of short, thin boundary layers and the internal mixing of the cooling medium can be particularly advantageously further promoted by the filler being designed in sections and the resulting partial fillers being inserted into the flow channel at a distance from one another. Finally, it is particularly advantageous if the partial fillers are also inserted into the flow channel axially rotated relative to one another. This ensures that the cooling medium no longer flows through the heat sink carrier in continuous, straight paths running parallel to the flow channel wall.

Rather, the flow direction dGs cooling medium \

by the twisted partial filling pieces, sometimes redirected several times. j This additional internal mixing of the cooling medium also contributes to a further reduction in the heat transfer resistance between the heat sink, filling piece and cooling medium. Based on in ;

the particularly advantageous embodiments shown in Figures 2 to 9 of heat-conducting fillers If the innovation

· I

&bull; I 1

&bull; 1 1

88 G 3 1 4 6 EN

further explained in more detail. The upper part of each figure shows a cross-section and the lower part shows a top view of the respective filling piece.

FIG 2 shows a filler piece S1 which has the shape of a helical spiral with an approximately rectangular cross-sectional area. This is in heat-conducting connection with the inner wall of the flow channel 3 by means of the transition points 5 on the long sides. In the embodiment shown in FIG 2, this spiral extends exactly over the full length L of the part of the flow channel 3 located in the heat sink carrier 2. A filler piece of this type has the particular advantage that the flow speed of the cooling medium is slightly increased due to the slight reduction in the flow cross-section. On the other hand, however, the heat transfer resistance between the heat sink and the cooling medium is significantly reduced due to the additional surface available within the spiral. Furthermore, a particularly small boundary layer thickness can be expected due to the flow of the cooling medium on the curved surfaces of the spiral.

The further embodiment S2 of a spiral-shaped filler piece shown in FIG. 3 is particularly characterized by a parabolic cross ^- section area. In this case, the edge areas near the contact surfaces 6 to the inner wall of the flow channel are "thickened", while the cross-sectional profile in the center of the flow channel "tapers". This particularly advantageously reduces the heat transfer resistance between the heat sink and the spiral-shaped filler piece S2 at the contact surfaces 6.

Another advantageous filler piece is shown in FIG 4. It consists of a large number of individual pipe pieces 7, which are clamped in particular via a single pipe piece 8 serving as a core pipe in the flow channel 3 to form a pipe packing RS1. This filler piece is also characterized by a

t * &igr; *

4 11 It ■ ·

&bull; II 1 1 I *

&bull; 111 > » * ·

&bull; II t . II - 11 « 9 i 111·

G 3 14 6 EN

relatively low flow resistance. Due to the large number of individual pipe sections 7, the surface area increase in relation to the length of the filler piece is particularly large in the case of such a filler piece RS1. In addition, this type of filler piece is particularly suitable for being designed in the form of several, preferably short, partial filler pieces. In the top view of the flow channel section of length L shown in the lower part of FIG 4, for example, three such partial pipe packings RS11, RS12 and RS13 are used. In this way, particularly short boundary layer lengths are achieved within the individual partial filler piece, which in turn increases the thickness and thus the heat-insulating effect of the respective boundary layer.

) is reduced. According to one of the already explained further embodiments of the innovation, in the embodiment of FIG 4 these partial filling pieces are already both axially rotated in the flow channel direction and inserted into the flow channel 3 at a distance 9 from each other. Since this diverts the coolant flow in the areas 9 between the partial filling pieces RS11, RS12 and RS13, which is indicated by arrows in FIG 4, a better internal mixing of the cooling medium results on the downstream side of each partial filling piece and thus a reduction in the temperature gradients within the cooling medium as seen in the flow channel cross-section. In another embodiment not shown, the partial filling pieces can also be used without

) spacing directly one after the other in the flow channel if the wall thicknesses of the individual pipe sections 7 are small compared to the inner diameter of the pipe sections.

FIG. 5 shows a further advantageous embodiment of a filler piece designed as a tube packing RS2. In contrast to the embodiment of the TIG 4, this has a solid core pin 11 in the center. This makes it particularly advantageous to increase the contact force of the tube pieces 7 on the inner wall of the flow channel 3, and thus the thermal conductivity between the cooling body carrier and the filler piece RS2 at the contact surfaces.

«II »&igr;&iacgr;»

* (■ I it**

&bull; r t * Il <*

I « · 1 I C I 4 . 4* <

6 31 &eeacgr; g DE

are connected to one another in a heat-conducting manner to form a ball packing KP. This is characterized by a particularly strong enlargement

10 can be improved« Here too, the filler piece can be designed to be particularly advantageously divided. The top view in Fig. 5 shows the two partial filler pieces R521 and RS22 as an example, which are axially rotated relative to one another in the manner already described and inserted into the flow channel at a distance from one another*

FIG 6 shows another advantageous filler piece. It consists of a large number of heat-conducting balls, which, while maintaining flow gaps,

ßeruhg the heat transfer between heat sink or filling

piece and cooling medium available surface. In |

In a particularly advantageous embodiment, this filler piece KP is made of sintered material, whereby particularly good \

Heat-conducting transitions between the individual balls of this ball pack can be achieved through sintering.

The further embodiment of a filler piece FRS1 shown in FIG. 7 consists of a cylinder in whose surface groove-shaped flow channels SK are milled. The webs 12 of such a "milled piece" FRS1 thus formed enable a particularly good heat-conducting transition due to the large contact surfaces 15 with the inner wall of the flow channel. This filler piece is also particularly suitable for being filled in parts ^. The top view in FIG. 7 shows, as an example, the two partial fillers FRSI1 and FR512, which are axially rotated in relation to one another in a known manner and inserted into the flow channel at a distance from one another.

In a further embodiment FRS2 of a milled piece shown in FIG 8, an additional core hole 14 is provided in the center of the filler piece to further increase the surface area and reduce flow resistance. Here too, it is particularly advantageous if this is designed in a split manner. The

4 . i II t /

til &igr; Il '

4 · · IIIIII AS I I · &bull; I ' · 1

88 G 3 H 6

! 9

Top view in FlG 8 shows the three parts as an example.

filling pieces FRS21, FRS22 and FRS23, which are axially rotated relative to one another in the manner already described and are inserted into the flow channel 3 at a distance of ν-ε. 5

FIG 9 shows another advantageous filler piece, which is designed in the form of a corrugated, ring-shaped spring piece FDS. The outer sides of the spring piece form particularly good conductive contact surfaces 13 with the inner wall of the StrÖ-

Iu iüiykanales 3, Wahlu uj.6 Because the inner surfaces of the filler piece contribute to the enlargement of the surface area of the filler piece. Due to the extremely slight reduction in the flow cross-section caused by such a filler piece, it is not absolutely necessary, according to the plan view in FIG. 9 , to insert partial filler pieces FDS1, FDS2 and FDS3 at a distance from one another in the flow channel 3. Rather, these partial spring pieces can be inserted directly one after the other into the flow channel 3 and preferably fill its entire length L in the heat sink carrier. This makes it possible to achieve a particularly high increase in surface area between the heat sink or the partial filler pieces and the cooling medium without a significant increase in the flow resistance.

The upper part of FIG. 9 shows a cross-section of an example of a first partial filler FDS1 and a dashed line shows a second partial filler FDS2 located behind it in the direction of flow and axially rotated. Due to such "gap placement" of partial fillers, the innovation achieves in the manner already described that, for example, the front sides of the spring inner regions 16 of the second partial filler FDS2 are not located in the "flow shadow" of the boundary layers on the spring inner regions 16 of the first partial filler FDS1. The front side of this second partial filler FDS2 facing the flow can thus be directly flowed against for the most part by the cooling medium in a particularly advantageous manner.

The « > I I · *

It 111 111

« ti· H

&bull; > t III ■II al ··

G 3 H 6 EN

, ) 10

FIG. 10 shows a further advantageous filler piece in the form of a plate-shaped, straight longitudinal piece QS1 with an approximately rectangular cross-sectional area. It is inserted into the flow channel 3 in the direction of flow of the cooling medium and is in heat-conducting connection with its inner sides via the contact surfaces 17. This increases the surface available for heat transfer to the cooling medium 24 in a particularly simple manner. In addition, only a relatively thin, visibly gliding boundary layer of cooling medium is to be expected on the longitudinal piece itself due to its short length. In comparison to the filler piece S1 with the shape of a helical spiral according to FIG. 2, such a filler piece is characterized by a particularly low flow resistance. This filler piece is also particularly suitable for being designed in sections. The top view in FIG. 10 shows, as an example, three axially rotated relative to one another in a known manner and spaced 9 from one another. Partial filler pieces QSIl ₁ , QS12 and QS13 inserted into the flow channel 3. Due to the low flow resistance of each of these partial longitudinal pieces, they can be inserted into the flow channel directly one after the other without any spacing, as is the case with the example of the partial spring pieces FDSl, FDS2, FDS3 as shown in FIG 9.

Finally, FIG 11 shows a further embodiment QS2 of the longitudinal piece serving as a filler piece. In accordance with the filler piece S2 with the shape of a helical spiral S2 according to FIG, the cross-sectional area here also runs parabolically, with the edge areas near the contact surfaces 18 to the inner wall of the flow channel being "thickened", while the cross-sectional profile "tapers" in the center of the flow channel.

16 Protection claims
11 figures

Claims (1)

"° 88 G 3 H 6 EN Protection claims 1. Heat sink for electrical components, in particular for power transistors, through which a liquid cooling medium flows to dissipate the heat loss transferred to the heat sink, with a) a heat-conducting carrier (2) for the electrical component element, which is penetrated by a channel (3) for the flow of the cooling medium,
marked by b) a heat-conducting filler piece (S1,S2 _} RS1,RS2,KP,FRS1,FRS2, FDS,QS1,QS2), which is inserted into the flow channel (3) to increase the thermal conductivity of the transition between the heat sink and the cooling medium and is connected in a heat-conducting manner to its inner wall (FIGS. 1 to 9). I
f.
|; 2. Heat sink according to claim 1, characterized by a ball packing (KP) as a filler piece, in which heat-conducting balls are connected to one another in a heat-conducting manner while maintaining flow gaps (FIG 6). 3. Cooling body according to claim 2, characterized in that the balls of the ball packing (KP) are connected to one another by sintering. 25
&igr; 4. Cooling body according to claim 1, characterized by a helical spiral (S1,S2) as a filler piece (FIG 2,3). 5. Cooling body according to claim 4, characterized in that the cross-sectional area of the spiral (S2) in the center of the flow channel is smaller than at the transition points (6) to the flow channel inner wall (FIG 3). 6. Cooling body according to claim 1, characterized by a tube packing (RSl, RS2) as a filling piece, in which heat-conducting tube pieces (7) are arranged in particular while maintaining HM · 1 I 4 « · * <l »β · t 88 G 3 H 6 OE of flow gaps are connected to each other in a heat-conducting manner (FIG 4 and 5). 7. Cooling body according to claim 6, characterized by a core pin (11) in the center of the tube packing (RS2) to increase the pressure of the tube pieces (7) among each other (FIG 5). 8. Cooling body according to claim 1, characterized by a milled piece (FRS1, FRS2) as a filler piece with groove-shaped flow channels (SK) on the upper side (FIGS. 7 and 8). 9. Cooling body according to claim 8, characterized by a core bore (14) in the center of the milled piece (FRS2) (FIG 8). 10. Heat sink according to claim 1, characterized by a corrugated, annular spring piece (FDS) as a filler piece (FIG 9). 11. Cooling body according to claim 1, characterized by a straight, plate-shaped longitudinal piece (QSl) as a filler piece (FIG 10). 12. Cooling body according to claim 11, characterized in that the cross-sectional area of the longitudinal piece (QS2) in the center of the flow channel is smaller than at the transition points (18) to the flow channel inner wall (FIG. 11). 13. Cooling body according to one of claims 4 to 12, characterized in that the filler pieces are divided (FIGS. 4, 5, 7, 8 and 9). I I I 11« *· ·» ■ < I I 1 > t I < <* · 88 e 3 &iacgr; if 6 DE ^f13 IA ₄ Cooling body according to claim 13, characterized in that the parts (FiSIi, RSl2, Rl3, RS21, RS22 _t etc.) are inserted into the flow channel (3) at a distance (9) from one another (F ^- IG 4, 5, 7 and 8). 5 15. Cooling body according to claim 13 or 14, characterized in that the partial filling pieces are inserted into the flow channel (3) in an axially rotated manner one below the other. 16. Heat sink according to one of the preceding claims, characterized by oil as the cooling medium.