Heat exchange – With retainer for removable article – Electrical component
Reexamination Certificate
1999-07-23
2001-07-24
Leo, Leonard (Department: 3743)
Heat exchange
With retainer for removable article
Electrical component
C165S185000, C174S016300, C257S722000, C361S690000, C361S703000, C361S704000
Reexamination Certificate
active
06263955
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the cooling of heat-producing electronic components, and more particularly, to a heat exchanger having fluid control elements for deterring the formation of high pressure within the heat exchanger and/or reducing the premature egress of fluid from the heat exchanger caused by the high pressure.
Effective dissipation of heat produced by electronic components is an important concern in optimizing circuitry performance. In addition to optimizing performance, effective heat dissipation also helps to prolong the useful life of those components. Heat dissipation is particularly important in the case of high-power electronic components, such as microprocessors and lasers, which generate a relatively high amount of heat in a relatively small area.
Finding suitable heat exchangers to adequately dissipate the heat generated by these components is a difficult task. These components are typically used in systems housed within a cabinet having a fan mounted in the back. The fan pulls cooling fluid, usually air, across the electrical components mounted within. A suitable heat exchanger should function adequately given this environment. Exotic methods of cooling high-power electronic components, such as forced liquid cooling, are undesirable due to the high cost of implementation and maintenance in these systems. Given their relative simplicity, traditional plate fin heat exchangers are generally preferred from cost and implementation perspectives. These exchangers offer high surface area for heat exchange relative to their size. Nevertheless, often these devices are inadequate to dissipate heat generated from high power electronics, although improvements are being made.
Advances have been made involving the use of narrow channel and micro-channel plate fin heat exchangers to cool electronic components. For example, a patent issued to the applicant, Azar et al., U.S. Pat. No. 5,304,846, discloses a narrow-channeled heat exchanger with certain geometric relations aimed at improving the heat dissipation of the heat exchanger. Specifically, the patent teaches optimal ratios relating the height of the plate fins to the width of the channels. The ratios can be selected to optimize the heat dissipation capabilities of the heat exchanger for a given pressure drop across the heat exchanger.
Although narrow channel heat exchangers significantly improve heat dissipation, they, like all other plate fin designs, suffer from boundary layer formation. The boundary layer consists of hydrodynamic and thermal layers which result from friction or drag between cooling fluid and a plate fin. The layer tends to blanket the plate fin thereby insulating it from the cooler fluid flow. This reduces heat transfer. Additionally, the layer narrows the remaining channel available to fluid flow which further impedes fluid flow thereby compounding the problem. The boundary layer therefore thickens as the fluid progresses down the channel contributing to high pressure within the fin field.
Efforts to reduce boundary layer formation in heat exchangers include irregularities such as protrusions, indentations and louvers along the plate fin surface. These irregularities are intended to disturb the boundary layer to prevent it from building up. From the standpoint of boundary layer disruption, the greatest improvement would be a device having as many irregularities as possible. Unfortunately, however, such as approach leads to practical problems. First, it is difficult, if not impossible, to extrude a plate fin having the desired surface irregularities. Extrusion technique are limited to producing lengthwise ridges (horizontal and vertical) which have limited ability to disrupt the boundary layer. Other manufacturing techniques such as casting and machining also preclude intricate plate fin textures. Perhaps more important though, increasing irregularities, as described above, also decreases the velocity of the passing fluid within the channels formed by the textured plate fins which tends to increase pressure within the fin field.
The applicant has found that high pressure in the fin field leads to inefficient heat transfer and premature egress of fluid from the fin field. Therefore, a need exists for a flat fin heat exchanger that deters high pressure formation, prevents the premature egress of fluid from the fin field caused by the high pressure, and/or minimizes boundary layer formation without increasing pressure. The present invention fulfills this need.
SUMMARY OF THE PRESENT INVENTION
It is therefore the general object of the present invention to provide an improved heat exchanger for dissipating heat from a heat generating component, as well as a method of manufacturing the novel heat exchanger. The heat exchanger comprises a thermally conductive base in thermal communication with the component, a plurality of thermally conductive plate fins affixed to the base wherein the plate fins define a fin field and channels, and fluid control for controlling the flow of fluid within the fin field to minimize the formation of high pressure. Alternatively or in conjunction, the fluid control substantially prevents premature egress of fluid from the top of the fin field caused by the high pressure within the fin field.
It is a further object of the invention to utilize the low pressure created by flow by-pass to vent relatively high pressure fluid within the fin field. To this end, the fluid control comprises fluid communication between a portion of the channels and at least one side of the fin field. The fluid communication enables a portion of fluid within the fin field to be drawn out by the low pressure caused by the flow by-pass. In this way, the formation of high pressure within the fin field is substantially avoided. Suitable fluid communication in this embodiment includes slots, notches, orifices, or perforations through a fin, gaps or spaces along a plate fin, and combinations thereof.
It is even a further object of the invention to provide a novel heat exchanger comprising fluid control having flow guides within the fin field. The flow guides are configured to impart a downward force to a portion of fluid within the fin field to hamper its premature exit out the top. Suitable flow guides include vanes protruding from the plate fins, bars traversing the top of the fin field, and combinations thereof.
In accordance with the invention, these and other objectives are achieved by providing a novel heat exchanger of the present invention. The heat exchanger comprises a plurality of thermally conductive plate fins comprising a vertical profile. Each of the plate fins are vertically affixed to and in thermal communication with the base. The individual fins extend lengthwise across the base from the inlet region to the outlet region. The configuration of the individual fins in conjunction with the layout of the fin field provides for formation of an open region within the fin field. In the embodiments disclosed, the open region may be formed cross-wise within a central region of the fin field or adjacent to the inlet region. The open region functions to reduce friction on fluid passing through the channels of the fin field. Accordingly, this novel configuration provides for a reduction of formation of stagnant fluid flow regions within the fin field.
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Leo Leonard
Lieberman & Brandsdorfer LLC
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