Refrigeration – Processes – Circulating external gas
Reexamination Certificate
2000-12-21
2002-12-10
Doerrler, William C. (Department: 3744)
Refrigeration
Processes
Circulating external gas
C062S271000
Reexamination Certificate
active
06490874
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates, in general, to the removal of moisture from within an electronics enclosure, and in particular to a method and apparatus employing a single heat pump to dehumidify and thermally condition the air within an electronics enclosure.
2. Description of Related Art
Electronic devices, which are cooled to below ambient temperatures and which operate in an environment in which water vapor is present, are subject to condensation problems which may cause corrosion and short circuits. It is therefore desirable to remove water vapor from the environment in which electronic devices operate. While corrosion and short circuiting may be caused by water vapor within the environment surrounding the electronic devices regardless of the device or environment temperatures, the problems intensify for devices operating at lower temperatures, as water vapor may begin to condense on the cooled surfaces of the electronic devices.
As is known, CMOS circuit performance may be improved by reducing the temperatures at which the circuits operate, i.e. the chip junction temperature. As the chip junction temperature decreases, however, the outer surface temperature of the chip package also decreases. The package outer surface includes the electrical interconnections between the package and the next level of assembly, such as a board: the temperature of these interconnections also decreases as chip junction temperature decreases. Heat transfer through these electrical interconnections, therefore, decreases board temperatures. As chip junction temperatures decrease further, eventually the temperature of one or more portions of these exposed surfaces (package outer surface, interconnections, and board) falls below the dew point temperature of the ambient atmosphere surrounding the components. At this point, condensation forms on the module and board surfaces, including electrical interconnections, unless preventive actions are taken. Therefore, dehumidification is highly desirable for environments containing electronic devices operating at temperatures below ambient dew point.
Two basic approaches have been taken to eliminate condensation on cold module surfaces: maintain the external module surfaces at temperatures above room ambient dew point, or condition the atmosphere within the enclosure such that its dew point is lower than the electronic components' external surface temperatures.
The first method, maintaining module surface temperatures above dew point, may be accomplished by providing sufficient insulation around each module, such that the external surface temperature of the insulation remains above room ambient dew point. This approach is discussed in a United States patent application entitled “Inflatable Sealing System for Low Temperature Electronic Module,” Ellsworth et al., Ser. No. 09/360,727, having a filing date of Jul. 27, 1999, assigned to the same assignee as the present application and hereby incorporated herein by reference in its entirety, and which is not admitted to be prior art with respect to the present invention by its mention in this Background Section. As the chip temperature decreases, however, more insulation is required around each module to maintain external surface temperatures above the dew point. At some point, as chip temperatures are decreased far below dew point, it may also be necessary to provide auxiliary heaters at the external surfaces of the insulation in order to maintain the module insulation surface temperature above the dew point.
The second method, lowering the dew point of air within the enclosure below the external surface temperature of the cooled modules, prevents condensation without requiring insulation around the modules. This approach is discussed in a United States patent application entitled “Sub-Dew Point Cooling of Electronic Systems,” Chu et al., Ser. No. 09/281,135, having a filing date of Mar. 29, 1999, assigned to the same assignee as the present application and hereby incorporated herein by reference in its entirety, and which is not admitted to be prior art with respect to the present invention by its mention in this Background Section. In order to lower the dew point temperature of the ambient atmosphere within the enclosure, some method should be employed to remove moisture from the atmosphere within the enclosure, preferably providing the ability to further remove the moisture from within the enclosure itself. Further, in order to decrease the burden on the moisture removal device, it may be desirable in some applications to provide an enclosure that is at least somewhat sealed against entry of ambient air. While sealing the enclosure may not be required in all applications, a well sealed enclosure requires less frequent (i.e. lower duty cycle) operation of the moisture removal device than would be required in a poorly sealed enclosure.
Depending upon the specific application and the moisture removal method used, the enclosure air temperature may be lowered as a byproduct of the moisture removal process. The temperature reduction may be caused by reduced heat transfer between enclosure air and ambient air, as a result of partially sealing the enclosure against ingress of ambient air. Heat transfer from ambient air to enclosure air tends to mitigate the effect of heat transfer from the enclosure air to the cooled surfaces within the enclosure. Alternatively, the temperature reduction may be caused by the use of a cold heat exchanger to dehumidify the enclosure air. For some applications, the presence of other mitigating factors may maintain the enclosure air temperature within acceptable limits. For other applications, however, continued system operation may result in enclosure air temperatures below room ambient dew point, eventually causing the temperature of the enclosure outer surface to drop below room ambient dew point, resulting in the formation of condensation on the enclosure outer surface.
In such applications, two methods have been employed in the art to prevent condensation from forming on the external surfaces of the enclosure. One method involves insulating the enclosure, such that the external surface remains above ambient dew point. A second method involves the use of an auxiliary heater to heat the enclosure air.
For the foregoing reasons, there is a need for methods and devices capable of preventing the formation of condensation on the cooled surfaces of electronic components, without insulating the electronic components or the enclosure. There is, therefore, a need for methods and devices capable of removing water vapor from the atmosphere within an electronics enclosure and further from the enclosure itself, without lowering the temperature of the atmosphere within the enclosure.
SUMMARY OF THE INVENTION
The present invention is directed to a method and apparatus for conditioning the air within an electronics enclosure, without external condensation, and without the need to insulate the enclosure or to provide an auxiliary heat source. Toward this end, a recuperative environmental conditioning unit is proposed which dehumidifies the air within the enclosure by causing the air to pass over a heat exchanger in thermal contact with the cold element of a heat pump, and reheats the air prior to returning it to the enclosure by causing the air to pass over a heat exchanger in thermal contact with the hot element of the same heat pump. In this way, moisture is removed from the air within the enclosure, eliminating the need for insulation around the electronic components. Since the dehumidified air is warmed prior to returning to the enclosure, the enclosure temperature remains above the room ambient dew point temperature, eliminating the need to insulate the enclosure. Further, since the air is heated by the hot element of the heat pump, no auxiliary heat sources are required. By using the same heat pump to cool and heat the enclosure air, the heat extracted during cooling is recouped. Finally, the conduit forms a sump or collection area, from which the con
Chu Richard C.
Ellsworth, Jr. Michael J.
Simons Robert E.
Doerrler William C.
Shulman Mark
Wojnicki, Jr. Andrew J.
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