Qpedia continues its review of technologies developed for electronics cooling applications. We are presenting selected patents that were awarded to developers around the world to address cooling challenges. After reading the series, you will be more aware of both the historic developments and the latest breakthroughs in both product design and applications.
We are specifically focusing on patented technologies to show the breadth of development in thermal management product sectors. Please note that there are many patents within these areas. Limited by article space, we are presenting a small number to offer a representation of the entire field. You are encouraged to do your own patent investigation.
Further, if you have been awarded a patent and would like to have it included in these reviews, please send us your patent number or patent application.
In this issue our spotlight is on spray cooling for electronics thermal management.
There are several US patents in this area of technology, and those presented here are among the more recent. These patents show some of the salient features that are the focus of different inventors.
Full Coverage Spray and Drainage System and Method for Orientation-Independent Removal of High Heat Flux
US 8550372 B2 – Timothy A. Shedd and Adam G. Pautsch
A cooling system and method that significantly improves spray evaporative cooling by using arrays of slot or plane sprays to create coverage of the entire heated surface to be cooled without allowing interaction between plumes that are spraying from the nozzles. The sprays are directed at an angle to the surface to take advantage of the high droplet momentum possessed by the spray to direct a flow of coolant fluid across the surface toward desired draining points, thereby enabling drainage regardless of the orientation of the unit.
The present invention provides a spray cooling system and method that significantly improves spray evaporative cooling by creating a directed momentum flow of cooling fluid across a surface to be cooled. In accordance with the present invention, a spray of cooling fluid is directed directly onto the surface of a work piece to be cooled at an angle with respect to the work piece surface so as to create a flow of cooling fluid in a substantially single direction along the work piece surface. The spray of cooling fluid preferably may be delivered via a plurality of generally fan shaped sprays. The sprays are positioned and aligned to create cooling fluid coverage of the entire heated surface to be cooled without allowing interaction between the spray plumes in a manner that may cause areas of cooling fluid stagnation on the surface.
A full coverage spray and drainage system in accordance with the present invention may be implemented in an otherwise conventional spray cooling system including a reservoir of an appropriate cooling fluid (e.g., Fluorinert-72 for the cooling of electronic circuitry, preferably saturated with a non-condensable inert gas, such as nitrogen), a pump for delivering the cooling fluid under pressure from the reservoir to a spray chamber to be sprayed therein from nozzles onto the work piece to be cooled, and appropriate filtering, metering, and control systems. Cooling fluid is returned from the spray chamber to the coolant reservoir via a drainage point or points in the spray chamber.
In accordance with the present invention, the drainage point or points in the spray chamber may be positioned with respect to the coolant spray such that the flow of cooling fluid directed in a substantially single direction along the work piece surface also is directed toward the drainage point or points. Thus, the cooling fluid momentum directs the fluid toward the drainage point, thereby assuring proper drainage of the cooling fluid despite changes in the orientation of the cooling system.
Directly Injected Forced Convection Cooling for Electronics
Electronic circuitry includes a circuit board and at least one component mounted on the circuit board, with the at least one component generating heat while in use. The circuit board includes one or more apertures aligned with one or more respective components, and the electronic circuitry is configured to provide, while in use, a path for coolant fluid to flow through each aperture and past the respective component.
By providing at least one aperture aligned with a component that generates heat in use, improved cooling of the electronic circuitry may be provided, as cooling effects can more efficiently be targeted at those parts of the circuitry that generate or dissipate heat.
Each aperture may be, but is not necessarily positioned at that point or within that region of the circuit board that is a minimum distance from the component or a respective one of the components.
The central axis of each aperture may be, but is not necessarily, perpendicular to the plane of the circuit board and at least one component. Preferably each aperture is arranged such that a straight line extending out of the aperture along the central axis of the aperture would pass through the component with which the aperture is aligned. Preferably each aperture is arranged such that, in use, coolant fluid exits the aperture towards the component with which the aperture is aligned.
The coolant fluid may be liquid or gas. The coolant fluid may be water. The coolant fluid may comprise a dielectric fluid, for example poly-alpha-olefin (PAO), or an inert gas, for instance nitrogen. Preferably the coolant fluid is air. In some circumstances, the coolant fluid may be supplied from a pressurized source, for instance a pressurized gas cylinder.
The position of each aperture may be such that, in use, coolant fluid passing through the aperture approaches the surface of the component with which the aperture is aligned from a perpendicular direction.
Thereby a jet impingement effect may be provided such that, preferably, the coolant fluid breaks through a respective thermal boundary layer next to the or each at least one heat generating component. Such thermal boundary layers are stable layers of air or other fluid which may build up next to the or each component and which exhibit a temperature gradient away from the component. The presence of such thermal boundary layers can reduce convective cooling effects.
Narrow Gap Spray Cooling in a Globally Cooled Enclosure
Electronic circuit boards are arranged as respective parallel pairs defining a narrow gap there between. One or more such pairs of boards are supported within a hermitically sealable housing and cooled by way of spraying an atomized liquid coolant from a plurality of nozzles into each narrow gap. Transfer of heat from the circuit boards results in vaporization of at least some of the atomized liquid within the narrow gap. The housing further serves to guide a circulation of vapors out of each narrow gap, back toward the nozzles, and back into each narrow gap. A heat exchanger exhausts heat from the housing and overall system, wherein vapor is condensed back to liquid phase during contact and heat transfer therewith. Condensed liquid is collected and re-pressurized for delivery back to the nozzles such that a sustained cooling operation is performed.
One embodiment provides for a system, including a first entity and a second entity that are respectively disposed such that they define a narrow gap between them. The system also includes at least one nozzle, wherein the nozzle is configured to spray an atomized liquid so that a flow of the atomized liquid and a vapor is induced through the narrow gap. The system also includes a heat exchanger that is configured to condense some of the vapor to liquid, the condensed vapor defining a condensate. The system further includes a housing configured to guide a circulation of at least some of the vapor, which is flowing out of the narrow gap, away from the heat exchanger and into proximity with the at least one nozzle.
Another embodiment provides for a system, the system comprising a housing configured to selectively open-ably enclose a plurality of electronic circuit boards. The system further includes a plurality of electronic circuit boards supported in the housing, wherein at least some of the electronic circuit boards are arranged to define respective pairs of boards. At least one pair of boards defines a narrow gap there between. The system also includes at least one nozzle associated with each narrow gap, each nozzle being configured to spray an atomized liquid into the narrow gap defined by the associated pair of boards. The housing is also configured to guide a circulation of a vapor exiting each narrow gap into proximity with the at least one nozzle associated with the at least one narrow gap.
Still another embodiment provides an apparatus. The apparatus includes a nozzle configured to spray an atomized liquid in a generally conical distribution pattern. The apparatus further includes a re-shaper that is configured to reform the spray of atomized liquid into a generally planar distribution pattern.
Enhanced Spray Cooling Technique for Wedge Cooling
US 8729752 B2 – Balwinder Singh Birdi, Simon Waddell and William Scherzinger
The present invention relates to apparatus and methods for heat removal and, more particularly, apparatus and methods for spray cooling a wedge of a generator rotor.
In generators, electromagnetic losses occur in the magnetic iron and the copper. These losses result in production of heat which must be removed to maintain overall temperature below that allowable for the copper coating and the insulation used in the construction of the generators. The rotor core, which is made of magnetic iron, can be conduction cooled by flowing fluid through the rotor shaft. However, the removal of heat from copper is better managed if oil is passed through the hollow wedges. Due to lower thermal resistance, the flow of fluid in the vicinity of copper is much more effective in removing heat from the copper and in keeping the overall temperature below the allowable limit. This is done with conduction mode of heat removal.
Since the heat transfer coefficient (HTC) depends upon the velocity of the fluid, the removal of heat is not very efficient, and a very high flow is needed to create a reasonable HTC for conduction cooling. Further, because the rotor is a rotating component, having a large amount of fluid at a radius away from the rotor shaft is not desirable, especially for high powered larger diameter and high-speed machines.
In one aspect of the present invention, a spray cooling manifold comprises a manifold ferrule adapted to circumscribe a shaft of a rotating machine; a manifold pipe having a bend of about 90 degrees having a first end attached to the manifold ferrule and a second, opposite end; a cooling fluid channel running from an inside surface of the manifold ferrule to the second, opposite end of the manifold pipe; and a pipe extending from the second, opposite end of the manifold pipe, the pipe adapted to extend into a wedge of the rotating machine, the pipe having a plurality of holes formed there along.
In another aspect of the present invention, a rotating machine rotor comprises a shaft; a plurality of coils disposed on the shaft; a plurality of wedges disposed between the coils; bands securing the wedges on the rotor; and a manifold comprising a manifold ferrule adapted to circumscribe the shaft; a plurality of manifold pipes, each having a bend of about 90 degrees, each having a first end attached to the manifold ferrule and a second, opposite end attached to a wedge pipe extending into the wedges; a cooling fluid channel running from an inside surface of the manifold ferrule to the wedge pipe; and a plurality of holes disposed along the wedge pipe.
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