Technical Field

The invention relates to a heat sink comprising a container for accommodating a cooling fluid.

Background

Using heat sinks for cooling electronical components are widely known and used in many areas such as in the telecommunication industry. The most common type of heat sinks is made of aluminum (Al) or aluminum alloys. Another common material in heat sinks is copper. The material thermal properties and the size is limiting the cooling capacity of the heat sink. Other factors important for the cooling capacity of the heat sink are the surrounding air temperature and air speed.

Many cooling scenarios in the telecom industry do not have evenly distributed heat loads. In this case, heat spreading and utilizing the available heat sink volume is crucial. Most heatsinks are made of solid and uniform material. Aluminum and copper have thermal and mechanical properties that make them suitable for different types of heat sinks. Copper has high thermal conductivity and is a very good material in some cooling applications. Copper can be suitable for small indoor heat sink applications but the cost and weight are high. This makes copper less suitable for large heat sinks. Aluminum has a lower thermal conductivity, but its cost, weight and mechanical properties are better than copper. Aluminum heat sinks however have a lower thermal conductivity than copper. The maximum conductivity of aluminum is approximately 200 W/mK. This property limits its ability to spread heat in the heat sink and limits the cooling capacity. In some cases, heat sinks made of graphite are used but the cost is high and conductivity is limited to < 1000 W/mK. Also, the mechanical properties for e.g. strength, corrosion of graphite are not optimal for telecom equipment.

Furthermore, some heat sinks are cooled by natural cooling, i.e. heat is transferred to the surrounding air by convection and the air moves, driven by density difference in hot and cold air. In forced cooling applications a fan transports the heated air from the heat sink. Heat sinks of different material; heat load and geometry can be optimized by optimizing distance and thickness of the cooling fins. There are also manufacturing limitations as to how the cooling fins can be organized and concerning their individual geometry. Summary

An objective of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

Another objective of embodiments of the invention is to provide a solution having improved cooling capacity compared to conventional solution.

The above and further objectives are solved by the subject matter of the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned and other objectives are achieved with a heat sink for cooling electronical heat sources, the heat sink comprising one or more cooling modules, each cooling module comprising: a cooling wall having a back side comprising attachment means for attaching an electronical heat source at the back side of the wall, and a front side arranged opposite to the back side; a container arranged at the front side of the cooling wall adjacent to and in thermal contact with the electronical heat source for accommodating a cooling fluid; and a cooling fin arranged at the front side of the cooling wall, wherein the cooling fin comprises internal channels connected to the container and wherein the channels are configured for receiving the cooling fluid in gas form from the container and returning the cooling fluid in liquid form to the container, in operation, thereby circulating the cooling fluid in the cooling module.

The back side and the front side may also be denoted back surface or back plane and front surface or front plane. Hence, the back side and the front side may in examples be defined by extension planes.

An advantage of the heat sink according to the first aspect is that the container will keep the cooling fluid in liquid form close to the heat sources while allowing the cooling fin to be mainly gas-filled. This will allow the cooling fluid to move freely inside the common volume in gas or liquid form driven by the difference in temperature in different parts of the heat sink. Another effect of having the container is that the cooling fin may almost solely be used for condensation since the cooling fin is mainly occupied by gas. This is in contrast to conventional solutions where the cooling fin will always be partially filled with liquid and hence not contributing to the condensation of the cooling fluid. The thermal property of the heat sink according to the first aspect such as heat transfer ability, i.e. the ability for heat to spread in the material, is therefore improved compared to conventional solutions. The improved thermal performance compared to the traditional heat sink can further be used to reduce the volume and the weight of the heat sink. This is very attractive for telecommunication operators and hence an important competitive factor.

In an implementation form of a heat sink according to the first aspect, the channels are connected to the container by means of an inlet part for receiving the cooling fluid in gas form from an opening of the container, and an outlet part for returning the cooling fluid in liquid form to the opening of the container.

An advantage with this implementation form is that dedicated parts are provided for receiving the cooling fluid and for returning the cooling fluid.

In an implementation form of a heat sink according to the first aspect, the inlet part extends substantially along an extension plane of the cooling wall.

An advantage with this implementation form is that the cooling fluid in gas form can raise upwards in the heat sink.

In an implementation form of a heat sink according to the first aspect, the outlet part extends outwards from an extension plane of the cooling wall in an angle in relation to the extension plane of the cooling wall.

An advantage with this implementation form is that the gravitational force is used for returning the cooling fluid into the container.

In an implementation form of a heat sink according to the first aspect, the angle is between horizontal and opposite vertical, in operation.

An advantage with this implementation form is that the angle may be used as a design parameter for adapting the heat sink to different applications.

In an implementation form of a heat sink according to the first aspect, the cooling fin comprises a solid base arranged at a lower part of the cooling wall, and wherein the channels are arranged above the solid base. An advantage with this implementation form is that the cooling performance of the heat sink is further improved as the solid base act as a large cooling element in the heat sink thereby increasing the circulation of the cooling fluid in the heat sink.

In an implementation form of a heat sink according to the first aspect, a top part of the solid base forms a bottom part of the outlet part.

An advantage with this implementation form is that the guiding of the cooling fluid in liquid form back to the container is improved.

In an implementation form of a heat sink according to the first aspect, the container is arranged between the front side of the cooling wall and the solid base.

An advantage with this implementation form is that the cooling performance of the heat sink is further improved.

In an implementation form of a heat sink according to the first aspect, the container is arranged at the lower part of the cooling wall at the front side of the cooling wall opposite to the electronical heat source.

In an implementation form of a heat sink according to the first aspect, the heat sink comprises two or more cooling modules attached to each other.

An advantage with this implementation form is that a modular cooling system may be provided.

In an implementation form of a heat sink according to the first aspect, the two or more cooling modules are interconnected with each other thereby allowing the cooling fluid to circulate between the two or more cooling modules.

An advantage with this implementation form that if the heat load is different between the two cooling modules, the interconnection means that the heat load can be shared between the two cooling modules for improved cooling in the whole heat sink.

In an implementation form of a heat sink according to the first aspect, the two or more cooling modules are interconnected with each other by means of a conduit coupling openings of the containers of the respective two or more cooling modules. An advantage with this implementation form is that the conduit act as an overflow conduit such that surplus condensate (in liquid form) in the upper cooling module can travel down to the lower cooling module. However, also cooling fluid in gas form can travel up from the lower cooling module to the upper cooling module. The conduit therefore has a double function thus improving the cooling properties of the heat sink.

In an implementation form of a heat sink according to the first aspect, the two or more cooling modules are interconnected by means of a coupling channel interconnecting the channels of the respective two or more cooling modules.

An advantage with this implementation form is that the cooling fluid in gas form more easily can travel between the two cooling modules.

In an implementation form of a heat sink according to the first aspect, the two or more cooling modules comprise a same number of channels or different number of channels.

An advantage with this implementation form is that a flexibility is provided when designing heat sinks.

In an implementation form of a heat sink according to the first aspect, the two or more cooling modules comprise a same channel configuration or different channel configurations.

An advantage with this implementation form is that a flexibility is provided when designing heat sinks.

According to a second aspect of the invention, the above mentioned and other objectives are achieved with an arrangement comprising one or more cooling modules according to any one of the preceding implementation forms and one or more electronical heat sources attached at the cooling modules.

Further applications and advantages of the embodiments of the invention will be apparent from the following detailed description.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain different embodiments of the invention, in which: - Fig. 1 and 2 show a heat sink seen in two different views according to an embodiment of the invention;

- Fig. 3 and 4 show a heat sink seen in two different views according to a further embodiment of the invention;

- Fig. 5 and 6 show heat sinks with different channel configurations according to embodiments of the invention;

- Fig. 7 shows a heat sink comprising two cooling modules vertically attached to each other according to an embodiment of the invention;

- Fig. 8 shows a heat sink comprising two cooling modules vertically attached to each other according to an embodiment of the invention;

- Fig. 9 shows a heat sink comprising two cooling modules horizontally attached to each other according to an embodiment of the invention;

- Fig. 10 and 11 show two interconnected cooling modules in two different views according to an embodiment of the invention;

- Fig. 12 shows a heat sink comprising three cooling modules according to an embodiment of the invention; and

- Fig. 13 shows an arrangement in a base station according to an embodiment of the invention.

Detailed Description

Increasing cooling capacity by introducing a forced air solution, e.g. using a fan, is not recommended for telecom equipment that are installed in towers, masts rooftops, etc. The fan solution requires maintenance to ensure that the fan function over a long time period. This can cause large cost and reliability problems in telecom equipment. Therefore, often passive - maintenance free cooling solutions are preferred.

There are some existing technologies that can be introduce in heat sinks to improve heat spreading. For example, heat pipes, vapor chamber and thermo siphons. These solutions use a cooling fluid that evaporates in a hot area close to a heat source and condenses in another cooler part of the heat sink. Some cooling fluids, like water have suitable physical properties, i.e. latent heat, viscosity and density, and in such two-phase system, i.e. condensation - evaporation, heat can be spread very efficiently in the heat sink. Incorporating such a two- phase system locally in a heat sink can be very efficient for single electrical components.

Two-phase cooling components attached - or built into a heat sinks can often move heat from one area or position in the heat sink to another area but not connect to every part of the heat sink. The volume in where the cooling fluid can circulate is limited to a single cooling fin, a single heat pipe, or a single heat sink base plate. Single cooling fins with integrated two-phase system exists, base plate with integrated two-phase system is also available but no solutions can connect all parts of the heat sink, base plate and cooling fins, into single two-phase system.

An objective of embodiments of the invention is therefore to increase the heat transfer ability of heat sinks so that heat can be spread more efficient in heat sinks while also keeping the amount of cooling fluid low. By introducing a container accommodating the cooling fluid the amount of cooling fluid needed in the heat sink is reduced compared to conventional heat sinks. The different parts of the present heat sink may be connected by a common internal closed volume. Therefore, two-phase cycling can take place in the closed volume and distribute the heat more efficiently in the heat sink.

Fig. 1 and 2 show a heat sink for cooling electronical heat sources seen in two different views according to an embodiment of the invention. The heat sink is seen in a cross-sectional side view in Fig. 1 and in a cross-sectional view from behind in Fig. 2. Generally, the heat sink 100 comprises one or more cooling modules but only one cooling module 200 is shown in Fig. 1 and 2. In the following disclosure embodiments comprising a plurality of modules will be presented more in detail.

With reference to Fig. 1 and 2, each cooling module 200 comprises a cooling wall 202 having a back side 204 comprising attachment means 212 for attaching at least one electronical heat source 300 at the back side 204 of the wall 202. The cooling wall 202 further has a front side 206 arranged opposite to the back side 204. Each cooling module 200 also comprises a container 208 arranged at the front side 206 of the cooling wall 202 adjacent to the electronical heat source 300 and in thermal contact with the electronical heat source 300 for accommodating a cooling fluid. A cooling fin 210 is arranged at the front side 206 of the cooling wall 202, and the cooling fin 210 comprises internal channels 214 which are connected to the container 208. The channels 214 in operation are configured for receiving the cooling fluid in gas form from the container 208 and returning the cooling fluid in liquid form to the container 208, thereby circulating the cooling fluid in the cooling module 200.

The back side of the cooling wall 202 may be attached/connected to the electronical heat source, such as electrical components on a PCB. The front side of the cooling wall 202 opposite to the backside may be in direct contact with the cooling fluid. The attachment means 212 may e.g. be mechanical fastening means such as screws and bolts or adhesives such as thermal glue. Examples of electronical heat sources 300 are application specific integrated circuit (ASIC) and field programmable gate array (FPGA).

The cooling fluid is illustrated with arrows in the Figs., in which a black arrow illustrates the cooling fluid in liquid form and a white arrow illustrates the cooling fluid in gas form. Also, the cooling fluid in liquid form in the container 208 is illustrated in the Figs. Hence, when the electronical heat source 300 is active, i.e. when in operation, heat is generated by the electronical heat source 300. The heat will be transferred from the electronical heat source 300 via the cooling wall 202 to the cooling fluid accommodated in the container 208. Thereby, a part of the cooling fluid will convert to gas form which will travel in the internal channels of the cooling module 200. When the gas is cooled enough in the internal channels the cooling fluid will convert back from gas form to liquid form and due to gravity be guided down back into the container 208. In this way the cooling fluid will circulate in the heat sink between the container 208 and the internal channels 214 of the cooling fin 210 and thereby cooling the electronical heat source 300.

In other words, the cooling fluid is heated up by heat load, evaporates and rises up and out into the cooling fin, connecting the cooling wall with the outer plate of the cooling fin 210 since the cooling fin 210 has internal channels for the gas/liquid flow in the heat sink 100. As the vaporized gas reaches colder areas in the cooling fin, the gas will condensate back to liquid form and be transported by gravity back to the container 208 of the heat sink 100. The internal volume for two-phase circulation in the cooling fin 210 is connected to the volume of the container 208. This means that the condensed and evaporated cooling fluid can move to any part of the heat sink ^' s internal volume. This results in very good heat spreading in the heat sink 100.

In embodiments of the invention and as shown in Fig. 1 , the channels 214 of the cooling fin 210 are connected to the container 208 by means of an inlet part 216 for receiving the cooling fluid in gas form from an opening 228 of the container 208, and also a separate outlet part 218 for returning the cooling fluid in liquid form to the opening 228 of the container 208. As also shown in Fig. 1 , the inlet part 216 may extend substantially along an extension plane P of the cooling wall 202. In operation the extension plane P may be substantially vertical. Thereby, the gas may move upwards from the container 208 into the channels 214 of the cooling fin 210.

As further illustrated in Fig. 1 the outlet part 216 extends outwards from an extension plane P of the cooling wall 202 in an angle a in relation to the extension plane P of the cooling wall 202 in operation. Mentioned angle a may be between horizontal (H) and opposite vertical (OV), in operation. Vertical may herein mean in parallel with the gravitational force acting on the heat sink 100 and the volume of the container 208. This means that the angle a is between 0 to 90 degrees.

As also shown in Fig. 1 and 2, the container 208 is arranged at the lower part 222 of the cooling wall 202 at the front side 206 of the cooling wall 202 opposite to the electronical heat source 300. Thereby, as much heat as possible can be transferred from the electronical heat source 300 to the cooling liquid in the container 208.

The volume of the container 208 and hence the dimension of the container 208 may be adapted to the application. For example, the lateral size of the container 208 may depend on the heat load and the cooling fluid used in the heat sink 100. For example, some cooling fluid needs larger cross section area for performing well. Further, the vertical size of the container may depend on the heat load and the heat load size of the heat sink 100. The level of the cooling fluid in the container 208 may ideally be above the level of the heat load.

Fig. 3 and 4 show a heat sink 100 seen in two different views according to a further embodiment of the invention. The main difference compared to the heat sink 100 in Fig. 1 and 2 is that the cooling fin 210 in this embodiment comprises a solid base 220 arranged at a lower part 222 of the cooling wall 202 which means that the channels 214 in this case are arranged above the solid base 220 in an opposite vertical direction in the cooling module 200. The solid base 220 may be formed from the same material as the other parts of the heat sink, such as the cooling fan 210 and the channels 214. The solid base 220 may form a large cooling area hence improving the circulation in the heat sink 100 and therefore also the cooling capacity.

As may also be noted from Fig. 3, a top part of the solid base 220 forms a bottom part of the outlet part 218 so that the cooling fluid in liquid form can flow at the top part of the solid base 220 down into the container 208. In this respect, the container 208 may be arranged between the front side 206 of the cooling wall 202 and the solid base 220 as shown in Fig. 3.

Fig. 5 and 6 show two heat sinks with different channel configurations according to embodiments of the invention. The internal channels in Fig. 5 extend substantially in the horizontal plane whilst the channels in Fig. 6 extend in the vertical plane. It is to be noted that embodiments of the invention are not limited to the shown channel configurations. For example, the channels may have different shapes and dimension and extend in different planes as long as the cooling fluid is well guided in the channels so as to circulate in the heat sink 100. A rule of thumb may be that the channel configurations should be so designed that vaporized cooling fluid can condensate in an enough rate in the cooling channels.

It is further noted that the angle a of the heat sink 100 in Fig. 5 and 6 is less steep than the angle a in Fig. 1 and 3. The present heat sink 100 has been tested with good performance in angles a between almost 0 to 30 degrees to horizontal. The heat sink 100 itself may e.g. be tilted from -20 to +20 degrees in operation with good cooling performance. This means that the heat sink 100 is suitable to be mounted in telecommunication masts and the like.

Fig. 7 shows a heat sink comprising two cooling modules 200a, 200b attached to each other according to an embodiment of the invention. The two cooling modules 200a, 200b are in this case attached to each other in the vertical plane, hence a first cooling module 200a is arranged atop of a second cooling module 200b in a stack. The cooling modules 200a, 200b are not interconnected which means that two cooling modules 200a, 200b form separate closed loops for the circulation of the cooling fluid as illustrated with the arrows in Fig. 7. Moreover, the second cooling module 200b at the bottom of the heat sink 100 also comprises a solid base 220 as previously described. The first cooling module 200a arranged atop of the second cooling module 200b does however not have a solid base on its own. The first cooling module 200a may however have a solid base. It may further be noted that the two cooling modules 200a, 200b in Fig. 7 comprise the same number of channels and the same channel configuration. However, this may not always be the case as shown in Fig. 8.

Fig. 8 shows a heat sink comprising two cooling modules 200a, 200b according to a further embodiment of the invention where the two cooling modules 200a, 200b comprise different number of channels but the same channel configurations. Hence, it should be realized that the cooling modules of the heat sink 100 may have the same number of channels or different number of channels and/or the same channel configuration or different channel configurations. This implies that any combinations are possible within the scope of the invention. The number of channels and channel configuration may depend on the heat source(s) attached to the particular cooling module. For example, due to the heat generated by the heat source(s). In this respect it may be noted that different electronical heat sources may generate different heat levels and have different operating heat limits.

Fig. 9 shows an embodiment in cross-sectional view seen from behind when two cooling modules 200a, 200b are attached to each other in the horizontal plane, i.e. side by side in a row. The cooling modules 200a, 200b may be in thermal contact with each other or be in thermal isolation from each other. Thermal isolation may be achieved using plastic parts or any other thermally isolating materials attached between the cooling modules 200a, 200b. On the other hand, for thermal contact between the cooling modules 200a, 200b any material having good thermal conductivity may be employed.

Fig. 10 and 11 show two cooling modules 200a, 200b in a cross-sectional side view and in a cross-sectional view from behind, respectively, according to an embodiment of the invention. The two cooling modules 200a, 200b are interconnected with each other thereby allowing the cooling fluid to circulate between the two or more cooling modules 200a, 200b, i.e. the two cooling modules 200a, 200b does not form separate closed loops but instead one common loop in which the cooling fluid can circulate.

Different means and methods may be employed for the interconnection of the two cooling modules 200a, 200b and in the non-limiting disclosed example, the two or more cooling modules 200a, 200b are interconnected with each other by means of a conduit 224 coupling the openings 228a, 228b of the containers 208a, 208b of the respective two or more cooling modules 200a, 200b. The conduit 224 may be considered to act as an overflow pipe ensuring that the cooling fluid is not trapped in one of the cooling modules for improved cooling in the whole heat sink 100. The cooling fluid can therefore, in operation, travel upwards in the conduit from the bottom module 200b in gas form to the upper module 200a. At the same time the cooling fluid may also, in operation, travel downwards in liquid form from the upper module 200a to the bottom module 200b. The corresponding liquid connection, i.e. the conduit 224, where the liquid runs down to the below container 208b is most suited in the base. Its enterance may be located in a position as to not drain the above container 208a too much since this may effect the circulaiton of the cooling fluid in the heat sink 100.

Moreover, as also illustrated in Fig. 10 for improved circulation the two cooling modules 200a, 200b may further be interconnected by means of a coupling channel 226 interconnecting the channels 214a, 214b of the respective two or more cooling modules 200a, 200b. The coupling channel 226 is mainly for gas connection allowing gas circulation between the two cooling modules 200a, 200b. It may be envisaged that the conduit 224 will be used by the liquid to run down in the heat sink 100 and the coupling channel 226 will be used by the gas to rise up in the heat sink 100. They are however not exclusive to the mentioned use and gas and liquid may both use the conduit 224 and the coupling channel 226 partially. It may however be important that at least the liquid can run down in the heat sink 100, since too much gas can never rise due to natural physics. Most condensate may spread out in the cooling fin, and due to angle a the condensate may not find its way to the coupling channel 226. In contrast gas will move towards the coldest regions of the heat sink 100 which is the cooling fin and not to the conduit 224. The cooling fin is often where cold gas has condensated, liquid has a much higher density than gas so there will be an under-pressure and new gas needs to compensate for this. Once gas is in the cooling fin it may or may not condensate before it reaches the coupling channel 226. If the gas has not condensated the gas will continue to rise through the coupling channel 226.

A purpose of interconnecting the cooling modules may be that heat load is very uneven between the cooling modules and therefore the heat load may be spread to a larger area for improved cooling in the whole heat sink 100.

The dimensions and design of the conduit 224 and the coupling channel 226 depends on the cooling application. An interesting parameter in this respect may be the flow area through the conduit 224 and the coupling channel 226. It is envisaged that these parameters may be tuned so as to fulfil the requirements of the specific application. The flow area is also an interesting parameter to consider when designing the internal channels 214. In this respect the flow area may be considered for a single channel, a subsection of channels or for all channels of the cooling fin 210.

Fig. 12 shows a heat sink comprising three cooling modules 200a, 200b, 200c according to an embodiment of the invention. Generally, the heat sink 100 disclosed herein may have any number of cooling modules attached to each other in the vertical plane and/or in the horizontal plane. In the exemplary case it may be noted that the three cooling modules 200a, 200b, 200c are stacked on each other in the vertical plane and each cooling module comprises its own electronical heat source(s) attached on the back side. Further, it is only the bottom cooling module 200c, in this particular example, that comprises a solid base 200 and each module forms its own closed loop, i.e. the cooling modules 200a, 200b, 200c are not interconnected with each other. However, in not shown embodiments a heat sink comprising a plurality of cooling modules, some or all cooling modules may be interconnected with each other and some or all cooling modules may comprise its own solid base.

The geometry and size of the heat sink 100 according to embodiments of the invention can vary depending on the application. Several parameters may be considered to optimize the geometries of the heat sink 100 for a given application. Non-limiting examples of parameters can be heat sink height and width, number of cooling fins, cooling fin width and length, cooling fin spacing in different directions, cooling fin angle relative to the cooling wall i.e. angle a, cooling fin- and liquid channel number and dimensions, filling level of cooling fluid, etc. Different cooling fluids can be considered as well as materials in heat sink parts. Non-limiting examples are R1233zd, acetone, ammonia, and water. It may be noted that the combination of cooling fluid and material of the heat sink is important. For example, the combination of water and aluminum has low performance since this combination will produce non condensable gas inside the container and channels which will reduce heat transfer ability. A good combination may be aluminum and R1233zd, and also copper and water.

The manufacturing methods for producing the present heat sink 100 includes but is not limited to die casting, sheet metal punching and stamping, extrusion, or any other suitable method. The joining of different heat sink parts may be sealed and handle internal over pressure. The joining method may e.g. be brazing and soldering.

Fig. 13 shows an arrangement 300 comprising one or more cooling modules according to any one of the preceding claims and one or more electronical heat sources attached at the cooling modules. The arrangement 300 may e.g. be part of a base station for cooling electrical components such as antennas, antenna arrays, remote radio units (RRUs) and massive multiple input multiple output (MIMO) devices.

It has been shown in studies that the amount of cooling fluid needed in the present heat sink can be reduced by 60% - 75% compared to conventional heat sinks. Further, the cooling capacity is also improved compared to conventional heat sinks. For example, the temperatures of typical components in a typical radio base station application could decrease significantly, approx. 10-20 degC.

Finally, it should be understood that the invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.