EP2041859A2

EP2041859A2 - Fan apparatus and electrical equipment including such apparatus

Info

Publication number: EP2041859A2
Application number: EP07809402A
Authority: EP
Inventors: Marc Scott Hodes; Alan Michael Lyons; Alan O'loughlin
Original assignee: Lucent Technologies Inc
Current assignee: Nokia of America Corp
Priority date: 2006-06-12
Filing date: 2007-06-08
Publication date: 2009-04-01
Also published as: US20070286744A1; KR20090011011A; WO2007146128A2; WO2007146128A3; CN101467336A

Abstract

A fan includes a plurality of blades 9 carried by a hub housing 10 mounted on a rotatable motor shaft 6. The shaft 6 includes a heat pipe 11 to transfer heat from the motor bearings 7 and 8 to a heat dissipative plate 15. The fan is particularly useful for cooling electrical and electronic equipment housed within a cabinet, such as, for example, in a telecommunications arrangement.

Description

Hodes 15-34-4 - 1 -

FAN APPARATUS AND ELECTRICAL EQUIPMENT INCLUDING SUCH

APPARATUS

FIELD OF THE INVENTION

The present invention relates to fan apparatus, and particularly, but not exclusively, to fan apparatus used to provide cooling for electrical and electronic equipment such as, for example, telecommunications equipment.

BACKGROUND OF THE INVENTION

Fans are used to provide air movement and are particularly useful in cooling applications.

Typically, a fan has one or more blades arranged about a fan hub which is mounted on a motor-driven rotatable shaft. The life and reliability of a fan is dependent on the motor bearing in which the shaft is mounted. Bearing life, in turn, is dependent upon several variables, including the construction materials, machining tolerances, lubricant formulation and operating temperature. Temperature is the most critical of these variables, as the bearing failure rate is an exponential function of operating temperature. The bearing lubricant may become irreversibly degraded and lose its effectiveness if the temperature becomes too great. Mechanical failure may also occur because of thermal expansion and its effect on tolerances.

The fan motor bearing may be cooled by providing openings in the fan hub. This permits air to be conducted through the motor, thereby allowing a source of relatively cool air to dissipate heat generated by the motor and bearing. Most fans incorporate these openings. The effectiveness of this technique is limited, however, for several reasons. As the fan becomes smaller, the available area for ventilation is reduced, thereby reducing the cooling effectiveness. In larger fans, the volume of windings is very large and thus the ability to draw sufficient amounts of air is reduced. Also, in some applications, the ambient air temperature at the bearing is itself appreciably high, lessening its effectiveness in providing cooling. This can be a particular.problem, for example, where the fan is used to cool high-powered electrical equipment, such as typically employed in telecommunication systems and housed Hodes 15-34-4 - 2 -

within essentially closed cabinets. The total heat load and heat density generated by telecommunications equipment are both projected to rise rapidly in future as designs evolve. As a result, the exhaust air temperature ejected from equipment cabinets is increasing with new designs, leading to higher fan failure rates and limiting the effectiveness of convective air-cooling technologies.

For certain types of fans, air-cooling of the hub is not possible. The windings of fans designed for harsh environments are sealed in a protective polymer encapsulant. This encapsulation precludes the use of air-cooling and, indeed, serves as a thermal insulator. Heat generated by the bearings and motor is trapped at the bearing, thus causing the bearing to operate at a higher temperature compared to unencapsulated fans.

Another approach to improving bearing reliability is to use an enhanced lubricant formulation. Although this approach has proven to be useful, the addition of more effective cooling for the bearings would extend the usefulness of these enhanced lubricant formulations.

Failure of a fan in some cases might require reduced power operation of the item being cooled. In other cases, fan failure may necessitate complete shutdown of equipment. This is particularly undesirable, for example, where the equipment is included in a telecommunication station located at a site remote from service personnel.

If there is failure of one fan in a group of several working together, the remaining ones may need to be operated at a higher speed to compensate, increasing noise levels and reducing their lifetimes.

BRIEF SUMMARY OF THE INVENTION The present invention relates to fan apparatus comprising at least one blade carried by a shaft which is rotatably mounted in a motor bearing arrangement. The shaft comprises a heat pipe having an evaporator section and a condenser section, the condenser section being more distant from the motor bearing arrangement than the evaporator section. Hodes 15-34-4 - 3 -

The inventors have realized that a different mechanism may be used to cool the bearing compared to prior art techniques. Instead of relying on air convection cooling, a conductive cooling pathway is provided between the bearing and the ambient air by the heat pipe. Thus, the impact of waste heat generated from electrical losses in the motor is reduced. This contrasts with prior art techniques that are aimed at reducing friction within the bearing or altering ambient temperature.

A heat pipe is a structure that includes a small amount of liquid, which conveniently is water, within a sealed envelope. Vapor and liquid exist within the heat pipe in an equilibrium state. When the evaporator section is heated, vapor pressure increases in that region as evaporation takes place. The vapor at the higher pressure is transported along the heat pipe to the condenser section. As the temperature here is lower because it is more distant from the bearing than the evaporator section, the vapor condenses and gives up its latent heat of vaporization. The liquid then returns to the evaporator section, the heat pipe operating in a continuous cycle. Heat generated in the bearing is conducted directly into the evaporator section of the heat pipe. The heat is then transported rapidly down to the condenser section of the heat pipe, by the action described above, where it is dissipated.

As there are no moving parts, the use of a heat pipe offers good reliability. Also, because the liquid operates at a low pressure and is only present as a small quantity, there is low risk of leakage. Although water is convenient as a working fluid, other substances, for example, methanol, could be used instead.

Return of condensed liquid to the evaporator section may take place under the influence of gravity alone. In other embodiments, a wicking material is used to provide a return path via capillary action. For example, the wicking material may be a sintered, porous structure coating the inside of the heat pipe. If the pore size is small enough, capillary forces can be sufficiently great so as to permit the heat pipe to operate in any orientation, which is particularly advantageous. Capillary action may also be achieved using grooved structures, meshes, or fiber, for example, or other configurations with small dimensions. Hodes 15-34-4 - 4 -

Lowering the temperature of the bearing by including a heat pipe increases the life and reliability of the fan. Bearing life may thus be extended without altering the material composition, or mechanical tolerances, of the bearing or lubricant.

In contrast to conventional fan designs having air vents for cooling the fan motor, the ability to cool the bearing using the invention is not limited by small fan hub size, or by the volume of windings. Elimination of air vents is also advantageous as it reduces the noise generated by running the fan motor.

Furthermore, the present invention may be used with a design in which motor windings are potted in a polymeric encapsulant, improving reliability of fan motors in harsh environments. The bearing of a fan with an encapsulated motor is cooled equally well as that of a fan with an unencapsulated motor.

By employing the invention, better thermal management of the bearing may allow the use of higher viscosity lubricant materials with better tribological properties, such as improved lifetime. Thus, using the invention to obtain improved bearing cooling can have a synergistic affect on lubricant selection to yet further increase fan life.

In one embodiment of the invention, the shaft is substantially wholly constituted by the heat pipe. In another embodiment, the heat pipe forms a part of the shaft. The heat pipe may be of steel, copper, nickel, aluminum or any other suitable material. The heat pipe may comprise a cylinder of circular cross-section, but other configurations and cross-sectional geometries may be used providing the performance of the shaft is not unacceptably compromised.

To enhance heat transfer from the condenser section into the ambient air, in one embodiment, the condenser section of the heat pipe is in thermal contact with a heat-dissipative member. The heat-dissipative member may be, for example, of a thermally conductive material arranged in a flat, finned, curved, or other configuration having good heat dissipation properties. The increased surface area it provides improves the overall heat transfer coefficient between the condenser section of the heat pipe and the ambient air. The heat-dissipative member, in one embodiment, is located such that it extends beyond the hub housing. The shape and placement of the Hodes 15-34-4 - 5 -

member is chosen to minimize obstruction to the overall fan flow stream while maximizing heat transfer to the air. The heat-dissipative member may be shaped to reduce airflow noise by directing air more effectively either towards or away from the blade. The heat-dissipative member may be mounted such that it interacts with upstream airflow, or it could be mounted downstream, or heat-dissipative members may be positioned both upstream and downstream of the airflow. In one embodiment, the material of the fan blade is chosen so that the blade, or blades, act as a heat dissipative member in addition to moving the air. For example, the fan blade may be made of aluminum, which has a relatively high thermal conductivity and low density. Other materials may also have the necessary thermal and structural properties to perform both functions. In other embodiments, the fan blades may be of relatively poor thermal conductivity but no separate heat dissipative member is included because the fan apparatus performs sufficiently well without such additions. Having two heat-dissipative members for heat transfer allows the bearing cooling system to effectively be independent of orientation of the fan.

Both push and pull systems are used to cool electronic equipment shelves. In a push system, the fan or fans are mounted at the air inlet. Thus ambient air is forced into the shelf, flows over the circuit packs, and the heated air exits through a top or back mounted exhaust panel. One advantage of a push system is that the shelf is maintained under positive pressure relative to the ambient, thus reducing the opportunity for entrained undesirable contaminants, for example, dust, to become deposited on the circuit packs. The fans in push systems are exposed to cooler ambient air temperatures. In a pull-through arrangement, the fans are mounted at the system exhaust.

This configuration can result in more uniform airflow over the packs and has other advantages. The air is heated by the electronic equipment first before passing over the fan, and the temperature of the rack of equipment is lower than the temperature of the air flowing over the fan. However, the higher ambient temperatures result in shorter fan lifetimes. Hodes 15-34-4 - 6 -

In one embodiment of the invention, in a pull-through system, the condenser section of the heat pipe is mechanically and thermally connected to a support structure by which the fan is mounted on an equipment rack. Thus the motor bearing temperature may be maintained closer to the ambient air temperature of the room, rather than the higher temperature of the air exhausted from the high-powered electronics cabinet.

In another embodiment of the invention, the shaft is rotatably supported in a mounting remote from the motor bearing. This improves mechanical stability of the shaft. The mounting may be another bearing or a bushing, for example. The mounting may be such that it also permits thermal connection of the condenser section of the heat pipe to a support structure, insuring the efficient transfer of heat from the condenser section to the support structure. This conductive mechanism is thermally efficient because of the lower temperature and higher surface area of the cabinet, and to the relatively lower conductive thermal resistance between shaft and the cabinet, relative to convective thermal resistance between the plate and the air.

By mounting the condenser portion of the heat pipe to the equipment rack, the temperature of the motor bearing arrangement may be reduced and thus its life significantly extended.

BRIEF DESCRIPTION OF THE DRAWINGS Some embodiments of the present invention will now be described by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 schematically illustrates in cross-section fan apparatus in accordance with the invention;

Figure 2 schematically illustrates in cross-section a heat pipe included in the apparatus of Figure 1;

Figure 3 schematically illustrates another embodiment of the invention; Figure 4; schematically illustrates a further embodiment of the invention in which encapsulant protects the motor;

Figure 5 schematically illustrates telecommunications apparatus including a fan tray; Hodes 15-34-4 - 7 -

Figure 6 shows in greater detail part of the apparatus shown in Figure 5; and Figure 7 schematically illustrates another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to Figure 1, fan apparatus 1 includes an external-rotor motor 2, having rotor laminations 3, stator laminations 4 and stator windings 5 arranged to rotationally drive a motor shaft 6 about the axis X-X. The shaft 6 is mounted in a bearing arrangement, consisting of first and second motor bearings 7 and 8 respectively. The fan apparatus 1 includes an impeller having a plurality of blades 9. The blades 9 are mounted on a hub housing 10, which is carried by the shaft 6, such that, when the motor 2 drives the shaft 6, the blades 9 rotate to move ambient air in the direction shown by the arrow.

The shaft 6 almost wholly consists of a heat pipe 11, which is shown in greater detail in Figure 2. The heat pipe 11 comprises a hollow steel tube with its inner surface carrying a sintered wicking structure 12. A small quantity of water, sufficient to saturate the wicking structure 12, is also contained within the tube. The heat pipe 11 has an evaporator section 13, which is located in the region of the first and second bearings 7 and 8, and a condenser section 14. The condenser section 14 is extensive in the direction of the front of the motor 2, where the blades 9 are located.

Heat generated at the bearing arrangement 7, 8 causes water to vaporize at the evaporator section 13. Vapor travels along the heat pipe 11 to the condenser section

14, which is cooler than the evaporator section 13. The vapor condenses and returns to the evaporator section 13 via the wicking structure 12. This mechanism causes heat to be transferred away from the first and second bearings 7 and 8, so that they are maintained at a lower temperature than would be the case if no heat pipe were included.

In this embodiment, a heat-dissipative member, configured as a plate 15, is joined to the heat pipe 11 at the condenser end of the shaft 6. This increases the available surface area by which heat transfers from the condenser section 14 into the ambient air. However, although advantageous, inclusion of a plate or other means Hodes 15-34-4 - 8 -

additional to the heat pipe to enhance heat transfer is not essential to benefit from the invention.

In another embodiment, the shaft 6 is only partly constituted by heat pipe. For example, one bearing of a bearing arrangement might tend to reach a higher temperature than another bearing, or bearings, included in the arrangement, in which case, only the bearing which runs hotter may require cooling. In another embodiment, the bearing arrangement may include only a single bearing.

In another embodiment, not illustrated, the heat pipe is extensive from the motor in the opposite direction to that shown in Figure 1. In this embodiment, the evaporator section is located at the bearing arrangement, as in the assembly shown in Figure 1, and the condenser section is extensive at the rear of the fan assembly 1, on the other side of the motor 2 to the blades 9. A heat-dissipative member, such as the plate 15 shown in Figure 1, may also be used in such an alternative embodiment. With reference to Figure 3, in which similar parts to those in Figure 1 are given the same reference signs, the shaft 6 is substantially wholly constituted by a heat pipe 16, which extends from the bearing arrangement 7, 8 to beyond the hub housing 10 in one direction and beyond the motor 2 in the other direction. The part of the heat pipe 16 near the bearings 7 and 8 acts as an evaporator section 17 and the two extremities are condenser sections 18 and 19, both of which act together with the evaporator section 17 to provide heat transfer in opposite directions away from the bearings 7 and 8 as shown by the arrows. Heat-dissipative members 20 and 21 are fixed to the heat pipe 16 at either end. In other embodiments, either one, or both, of the heat-dissipative members 20 and 21 are omitted.

In another embodiment having two condenser sections, the heat pipe has two corresponding evaporator sections, each being associated with a respective condenser section, and there is no continuous path between them. In this case, the heat pipe functions as two discrete components.

With reference to Figure 4, a fan apparatus 1 includes encapsulation material 21 around the windings. The blades 9 are of aluminum and no separate heat- Hodes 15-34-4 - 9 -

dissipative member is included in this embodiment, the blades 9 having good thermal conductivity.

With reference to Figure 5, a telecommunications apparatus includes a cabinet 22 housing electronic equipment 23 racked on shelves 24. A fan tray 25, on which is mounted a plurality of fans 26, is located at the top of the cabinet 22. Each of the fans 26 includes a heat pipe in accordance with one of the previously described embodiments. The fans 26 operate to draw air over the electronic equipment 23 in a pull-through system.

One of the fans is shown in greater detail in Figure 6. It includes a heat pipe 27, which is extensive from the motor bearing arrangement 28 to the rear of the motor 29 where it is thermally connected via an additional bearing 30, or a bushing, to the cabinet wall 31. This gives additional mechanical security as well as providing a path for cooling. A mounting bracket 32 provides the main structural support for the fan. Operation of the fans may be further enhanced by applying active cooling to the cabinet housing. For example, a refrigeration panel 33 may be included.

In another embodiment, a fan tray may be included at the base of the cabinet, as shown in a broken line at 34 in Figure 5, in a push-through system, in addition to, or instead of, the pull-through system.

Figure 7 illustrates another embodiment of the invention that is similar to that shown in Figure 1 except that in this case, a heat-dissipative member 35 located in front of the hub 10 is shaped so as to deflect airflow and thus reduce noise.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. AU changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

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1. Fan apparatus comprising at least one blade carried by a shaft which is rotatably mounted in a motor bearing arrangement, the shaft comprising a heat pipe having an evaporator section and a condenser section, and the condenser section being more distant from the motor bearing arrangement than the evaporator section.

2. Fan apparatus as claimed in claim 1 and including a heat-dissipative member which is in thermal contact with the condenser section of the heat pipe.

3. Fan apparatus as claimed in claim 2 and wherein the heat-dissipative member is said at least one blade.

4. Fan apparatus as claimed in claim 2 and wherein the heat-dissipative member is a substantially planar thermally conductive plate.

5. Fan apparatus as claimed in claim 2 and wherein the heat-dissipative member is configured to direct airflow so as to reduce the airflow noise level compared to the noise level if the member were absent.

6. Fan apparatus as claimed in claim 1 and wherein the heat pipe is extensive on both sides of the motor bearing arrangement and includes two condenser sections, each being more distant from the motor bearing arrangement than an associated evaporator section.

7. Fan apparatus as claimed in claim 6 and wherein the heat pipe comprises a single evaporator section located between the two condenser sections. Hodes 15-34-4 - 11 -

8. Fan apparatus as claimed in any preceding claim and including a heat sink, the, or at least one, condenser section being thermally connected to the heat sink, and the heat sink being actively cooled.

9. Fan apparatus as claimed in any preceding claim and including a fan tray and a plurality of fans mounted in said fan tray, at least one fan of said plurality comprising at least one blade carried by a shaft which is rotatably mounted in a motor bearing arrangement, the shaft comprising a heat pipe having an evaporator section and a condenser section, and the condenser section being more distant from the motor bearing arrangement than the evaporator section.

10. Electrical apparatus comprising electrical equipment, a cabinet which houses said equipment, and at least one fan, said fan including at least one blade carried by a shaft which is rotatably mounted in a motor bearing arrangement, the shaft comprising: a heat pipe having an evaporator section and a condenser section, and the condenser section being more distant from the motor bearing arrangement than the evaporator section.