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Fan apparatus and electrical equipment including such apparatusFan apparatus and electrical equipment including such apparatus description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070286744, Fan apparatus and electrical equipment including such apparatus. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001]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 [0002]Fans are used to provide air movement and are particularly useful in cooling applications. [0003]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. [0004]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 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. [0005]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. [0006]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. [0007]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. [0008]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 [0009]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. [0010]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. [0011]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. [0012]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. [0013]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. [0014]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. [0015]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. [0016]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. [0017]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. [0018]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. [0019]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 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. [0020]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. [0021]Having two heat-dissipative members for heat transfer allows the bearing cooling system to effectively be independent of orientation of the fan. Continue reading about Fan apparatus and electrical equipment including such apparatus... 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