The present invention relates generally to heat sinks for cooling electronic equipment such as a remote radio unit (RRU) and more specifically to such heat sinks that obtains the cooling effect by natural convection.

BACKGROUND ART

The distributed base station has obvious advantages like easy installation, operation and maintenance compared to the traditional base station. At the same time, operators want high output power, light weight, small size, etc., which result in higher heat density of a RRU, the main module of distributed base station. RRU heat consumption is now raised from 200W to currently 300W, and RRU cooling becomes more and more important and challenging. A RRU is cooled by employing a heat sink and exploiting natural convection. A prior art RRU heat sink is shown in figure 1 and consists mostly of straight fins, which are optimized based on the internal heat consumption, heat sink height and their temperature to enhance the total cooling capacity and to get lower temperature in the unit. The current optimization methods mentioned above cannot further improve the cooling capacity, and some new design or technology must be applied to enhance cooling. One standard method to raise RRU cooling capacity is to enlarge the HS volume as shown in figure 2. Increased HS volume implies higher fins and increased HS surface area, which is crucial to the heat dissipation. Another prior art to RRU cooling capacity is to apply fan cooling as shown in figure 3. An independent fan tray is fixed on the top of RRU, and the RRU cooling capacity is raised since the main heat transfer mechanism is changed from natural convection to forced convection.

There are a number of problems with prior art heat sinks. Thus, in order to raise the RRU cooling capacity, one prior art solution is as mentioned above to increase the cooling area, which will lead to increased volume and weight of the RRU. The increase in volume does not meet the operator objectives to reduce the overall appearance of the site. The increase in weight would result in higher requirements for installation on a tower or a pole, and it would result in higher cost. This prior art is not easily accepted by operators.

Another prior art solution is to add an independent fan tray. However, the independent fan cannot effectively reduce the RRU volume, and the independent fan tray would give a new RRU appearance and volume, and in addition, it does not meet the operator requirement for simple and uniform appearance. Furthermore fan trays require maintenance, which is difficult and costly when the RRU is fixed on a wall, a tower or some other high location. Hence, this prior art solution is also difficult to accept by operators . In the traditional heat sink with straight fins, the air flows through the air channel formed between the fins due to buoyancy forces, and the air is heated continuously as it flows from the bottom to the top. As a result, the air temperature is higher at the upper half of the RRU, and the cooling capacity of the fins in that area is hence reduced .

DISCLOSURE OF THE INVENTION

On this background, it is an object of the invention to provide a heat sink that overcomes or at least relieves the problems of the prior art. In the enhanced heat sink structure according to the present invention the length of the air channels formed between adjacent fins is reduced, whereby the self- heating effect is reduced. According to the invention there is thus archived a higher cooling capacity for the same heat sink volume.

According to the invention there is provided a heat sink comprising a plurality of fins arranged such that channels are formed between adjacent fins, wherein the channels comprise an air inflow and an air outflow. The heat sink according to the invention comprises at least two groups of fins arranged such that the air inflow of the channels of a first of these groups is located differently from the air outflow of the channels of the remaining of these groups. Thereby, hot air from the outflow of groups of channels located below the first group of channels is prevented from entering the channels of the first group of channels. It should be noted that in the present context the term "air inflow" refers to the or those locations or areas where air enters the heat sink structure from the surroundings and similarly that the term "air outflow" refers to the or those locations or areas where air leaves the heat sink structure and flows out into the surroundings. Such locations or areas are in the detailed description of the invention indicated by arrows, but it is understood that these indications are only exemplary and show some specific locations of inflow to the structure and outflow from the structure. Further, as the flow of hot air in the channels in the present context is driven by an upwardly directed buoyancy force it is understood that throughout this specification, the "first" group of fins or channels refers to the group located in the direction of air flow caused by the buoyancy force of the hot air. Thus, for instance, in the two embodiments shown in figures 4 and 5, respectively, the respective longitudinal axes Y extends in an upward direction relative to ground.

According to an embodiment of the invention, the at least two groups of fins are arranged such that the longitudinal direction of the fins of the first group extends at an angle a relative to the longitudinal direction of the fins of the second group, where a ≠ 0 degrees .

Further objects, features, advantages and properties of the enhanced heat sink according to the present invention will become apparent from the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed portion of the description, the invention will be explained in more detail with reference to the exemplary embodiments shown in the drawings, in which : Figure 1 is a first example of a prior art heat sink;

Figure 2 is a second example of a prior art heat sink, in which the cooling effect is enhance by increasing the height of the fins and increasing the cooling area of the heat sink;

Figure 3 is a third example of a prior art heat sink in which increased cooling capacity is obtained by the provision of fans changing the heat transfer mechanism from natural convection to forced convection;

Figure 4 is a schematic representation of a heat fin structure according to a first embodiment of the present invention; and

Figure 5 is a schematic representation of a heat fin structure according to a second embodiment of the invention .

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to figure 1 there is shown a prior art heat sink 1 comprising a section of fins 2 of relatively short height. When the cooling capacity of this prior art heat sink is found to be insufficient, the height of the fins may be increased as shown in the prior art heat sink according to figure 2, thereby increasing the cooling area of each fin.

An alternative to obtaining increased cooling efficiency by increasing the height of the fins is shown in figure 3, in which fan cooling is applied. One or more cooling fans 4 are placed on top of the RRU and the cooling capacity is raised since the main heat transfer mechanism is changed from natural convection (in figure 1 and 2) to forced convection. With reference to figure 4 there is shown a schematic representation of a heat fin structure according to a first embodiment of the present invention. According to this embodiment the heat sink is divided into three groups 5, 6 and 7: the upper group 5 where the fins 8 are vertical (as seen in the figure) , the group 6 to the lower-left where the fins 9 are diagonal pointing the upper left, and the group 7 to the lower-right where the fins 10 are diagonal pointing towards the upper right. In the vicinity of the air volume indicated as Air inflowl and Air inflow2 air flows from the front of the heat sink 1 into the channels 11 formed by adjacent fins 8, and continue along the vertical fins 8 where the air finally flow upward, and out of the volume of the heat sink at the Air outflowl and Air outflow2.

Furthermore, air flows into the lower left group 6 of the heat sink from the front part near Air inflow3 and the bottom part near Air inflow4. The inclined fins 9 ensure that the heated air is let out of the heat sink volume directly (Air outflow3 and Air outflow4) without heating the upper parts of the heat sink.

In the lower right group 7 of the heat sink, a symmetric behavior is observed.

The air channels 11, 12 and 13 in the three groups 5, 6 and 7, respectively, are independent of each other, so the air-flows in the three groups are accordingly decoupled .

The heat sink according to this embodiment of the invention is thus divided into three groups, and the air channels and airflow in the three groups are independent of each other, and the effect of temperature series is reduced. The temperature of the air in channels of upper part is decreased, and the total cooling capacity of the HS is raised approximately by 10%.

The fins 9 in the second group 6 are in this embodiment inclined at an angle β relative to the longitudinal axis Y through the fins 8 of the first group 5. The fins 10 in the third group 7 are inclined at an angle a relative to the longitudinal axis Y. In the shown embodiment, the angles a and b are substantially equal, but it is understood that this may generally not be the case, and that also a-symmetrical designs of the heat sink according to the invention may be envisage and fall within the scope of the present specification. Similarly, the heat sink according to the invention may not be symmetrical about the Y-axis as shown in figure 4.

The basic concept of the present invention can be implemented by various other embodiments than the one shown in figure 4. Thus, an alternative embodiment is shown in figure 5. In this embodiment the heat sink 1 is divided into two groups: an upper group 14, in which the fins 16 are vertical (as seen in the figure), and a lower group 15, in which the fins 18 are running diagonally towards the upper right of the heat sink at an angle γ relative to the axis Y. Alternatively, the fins 18 in lower group 15 can run diagonally toward the upper left of the heat sink.

In the upper group 14, Air inflowl and Air inflow2 provides air into the channels 17 from the front of the heat sink, while the vertical fins 16 lead the air upward, and the hot air flows out through Air outflowl and 2.

In the lower group 15, air flows through the channels 19 in the lower group 15 through Air inflow3 from the left of the heat sink and Air inflow4 from bottom of the heat sink. The inclined fins 18 ensure that the heated air from the lower part of the heat sink is lead out of the heat sink volume without reducing the cooling capacity of the upper part.

The air channels 17 and 19 in the two groups 14 and 15 respectively are independent of each other, whereby the air flow in the two sections become independent on each other.

Although the teaching of this application has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the teaching of this application.

The term "comprising" as used in the claims does not exclude other elements or steps. The term "a" or "an" as used in the claims does not exclude a plurality. The single processor or other unit may fulfill the functions of several means recited in the claims.