Patent Application
20120206880
The present invention relates generally to electronics cooling, and more particularly to electronics cooling for high peak thermal output or loss of cooling conditions.
Electronic components typically function optimally at a range of temperatures. Above optimal temperatures, most electronics will degrade more rapidly, and may cease to function altogether. For this reason, electronic components in hot environments or which generate large amounts of heat are commonly cooled via dedicated cooling systems.
Some electronic components, such as motor drives, power conversion units, and electric actuators, often experience uneven duty cycles, wherein peak thermal loads are much higher than median or non-peak thermal loads. In the past, peak load conditions have been determinative in selecting cooling systems for such components. In order to ride through peak thermal load periods which may last on the order of a few minutes or seconds, components have conventionally been over-cooled during normal conditions, requiring larger and more costly cooling systems and/or utilizing a colder or more efficient coolant. This added bulk and weight is undesirable, particularly in aerospace applications where weight is a major concern. Additionally, fluctuations in component temperatures under conventional practices may decrease component operating life. Likewise, if an electronic component must tolerate a loss-of-coolant event, the component is conventionally over-cooled during normal operation, or additional components are added to divide functionality and reduce individual component losses and peak heat fluxes.
The present invention is directed toward a cooling apparatus for high peak load electronics, and an associated method. A thermal spreader is in thermal contact with an electronic component to be cooled, a thermal capacitor, and a cold plate. The cold plate dissipates heat, and the thermal capacitor stores heat in a phase transition during peak loads and reduced coolant events.
Thermal spreader 14 is also in thermal contact with cold plate 16 and thermal capacitor 18. Cold plate 16 may be a conventional heat exchanger, which may dissipate heat into a fluid such as air or a liquid coolant. Thermal capacitor 18 is a phase change thermal capacitor capable of storing large amounts of heat during a phase transition (i.e. melting) of a phase change material, as will be described in greater detail with respect to
During steady state non-peak loads of electronic component 12, heat generated by electronic component 12 will be transmitted through thermal spreader 14 to cold plate 16. Cold plate 16 dissipates heat into the fluid coolant, which carries heat away from cooling assembly 10. During non-peak loads of electronic component 12, therefore, cooling assembly 10 will operate at roughly a steady state temperature. Cold plate 16 is selected to provide sufficient cooling such that this steady state temperature is well below a critical temperature at which electronic component 12 begins to experience deleterious effects from heat. Thermal spreader 14 reduces the temperature of cooling assembly 10 during steady state operation by providing a larger footprint for cooling.
During peak loads of electronic component 12, cold plate 16 may not be capable of dissipating sufficient heat to protect electronic component 12. from excessive temperature excursions. As excess heat builds up, the temperature of cooling assembly 10 will rise until a transition temperature (i.e. melting point) of thermal capacitor 18 is reached. At this transition temperature, phase change material within thermal capacitor 18 (see
In another scenario, loss of coolant fluid at cold plate 16 may impair the heat dissipation capacity of cooling assembly 10. Thermal capacitor 18 allows electronic component 12 to be kept at acceptable temperatures during such loss-of-coolant conditions until all phase change material melts, as described above, thereby allowing cooling assembly 10 to ride through transient loss-of-coolant conditions.
Electronic component 12, thermal spreader 14, cold plate 16, and thermal capacitor 18 are anchored together in an assembled configuration. In the illustrated embodiment, bolts 24 are inserted through bolt slots 26 in electronic component 12, bolt holes 20a in thermal spreader 14, and bolt holes 20b and cold plate 16, while thermal capacitor 18 is secured separately. As bolt 24 is tightened, thermal spreader 14 is anchored atop cold plate 16, and electronic component 12 is anchored atop thermal spreader 14. In alternative embodiments, some or all of the components of cooling assembly 10 may be held together by alternative means, such as by adhesives, soldering, welding or clamping. Bolt holes 20a passes through a boss in thermal spreader 18, so that the working fluid of thermal spreader 18 is not exposed to bolt 24 or to the environment.
Cold plate 16 abuts thermal spreader 14 at a flat surface 28, and may comprise a plurality of fins 30 for increased contact area with a cooling fluid flow F. As fluid flows between and around fins 30, cold plate 16 dissipates heat into the fluid, cooling the entirety of cooling assembly 10. Cold plate 16 is constructed of a thermally conductive material, such as aluminum. Thermal spreader 14 maximizes heat transfer between components, equalizing temperature across cooling assembly 10, and thereby assuring that electronic component 12 will remains relatively cool at all times.
As discussed previously, thermal spreader 14 is in thermal contact with electronic component 12, cold plate 16, and thermal capacitor 18 to equalize temperatures among these components. Thermal interface material 32 may be inserted at interfaces between thermal spreader 14 and electronic component 12, cold plate 16, and thermal capacitor 18, to improve thermal conductivity. Thermal interface material 32 may be, for instance, thermal grease or a thermally conductive pad.
In the pictured embodiment, thermal spreader 14 is a conventional heat pipe plate wherein wicked vapor space 34 carries working fluid 36. Heat applied to any region of thermal spreader 14 causes working fluid in that region to evaporate to vapor. This vapor migrates through vapor space 34 to cooler regions of thermal spreader 14, where it condenses and is absorbed by the wick, releasing heat. Liquid working fluid then flows by capillary forces to replenish fluid evaporated from the hot region. In this way, temperatures are efficiently equalized across thermal spreader 14. In one embodiment, thermal spreader 14 is formed of aluminum and working fluid 36 is methanol. In another embodiment, thermal spreader 14 is formed of copper and working fluid 36 is water. As mentioned with respect to
Thermal capacitor 18 comprises at least one thermally conductive receptacle 22 filled with phase change material 38. Receptacle 22 may be constructed, for instance, of aluminum. Phase change material 38 is a material with a high heat of fusion, which melts and solidifies at a suitable transition temperature. Large amounts of energy can be stored in phase change material 38 at the transition temperature, allowing phase change material 38 it to serve as a heat storage device. Phase change material 38 may be, for example, a low temperature solder, salt, or paraffin-family wax, and is selected to have a transition temperature between the steady state temperature of cooling assembly 10 and the critical temperature of electronic component 12, as noted previously with respect to
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
