Microfluidic devices for heat transfer

Details Microfluidic devices for heat transfer Microfluidic devices for heat transfer

2001-09-28

2002-12-31

Chervinsky, Boris (Department: 2835)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S698000, C361S704000, C361S707000, C361S718000, C361S719000, C257S714000, C174S015100, C165S080400

Reexamination Certificate

active

06501654

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an apparatus and method for accomplishing heat transfer using microfluidic systems, such as may be useful for transferring heat to and from electronic devices and components thereof, including but not limited to computers, analytical instruments, lasers, other similar electronic instruments and apparatuses.
BACKGROUND OF THE INVENTION
At the outset, it should be noted that although the invention is described with reference to electronic equipment, particularly computers, the invention can be used in practically any application requiring heat transfer.
Many electrically-powered systems include environments having heat-producing elements contained within substantially enclosed areas. For example, within a typical computer system, the heat generated internally by certain components (such as integrated circuit (IC) devices, power supplies, motors, and transformers) may be substantial. This heat must be dissipated at a rate sufficient to maintain critical system components at acceptable temperatures in order to prevent premature component or system failure.
While small increases in operating temperature may not be immediately detrimental to the operation of electronic components, long-term operation at elevated temperature levels may adversely impact their longevity and reliability. This is particularly true for relatively sensitive integrated circuit or data storage devices, such as central processing units (CPUs) or disk drives, respectively, which may suffer disproportionate reductions in longevity with incremental increases in operating temperature. Moreover, the operating speed and reliability of many electronic systems suffers as the operating temperatures of their components rise. Additionally, mechanical effects resulting from wide variations in temperature and high peak temperatures may eventually induce component failures.
A conventional approach for providing heat transfer in computer systems is to cool the air inside a computer enclosure using a fan, which draws cold outside air into the enclosure. Because temperature-sensitive components such as ICs and disk drives typically act as significant heat sources, however, often this conventional approach is not sufficient to maintain air within the computer chassis at a temperature sufficiently below the maximum allowable temperature for these components, since each component may not dissipate heat effectively enough to maintain its temperature within acceptable limits. Additional localized (e.g. forced) cooling of these components often must be used to increase the rate of heat transfer.
Moreover, rising processor speeds and higher capacity circuits cause even greater thermal loads, thus requiring even more cooling air flow through enclosures to dissipate the attendant heat. In the past, conventional design wisdom has dictated that this increased cooling air flow be achieved by increasing the size and/or number of cooling fans within the housing. This, of course leads to several well-known and heretofore unavoidable problems, limitations and advantages such as: increased cost and complexity of the overall electronic apparatus; diminished space within the housing for additional operating components such as printed circuit boards, drives, etc.; increased operating fan and air movement noise; increased interference from electromagnetic radiation; and increased power consumption.
Specifically, as system electronics become more powerful, absent substantially increased cooling flow these electronic components can dissipate so much heat that they can create localized “hot spots” within an enclosure that make it very difficult to maintain thermal compliance for all of the electronics. Making matters worse, consumers have become more sensitive to noise and continue to demand quieter computers and electronic devices. This demand from consumers contradicts the need to increase air flow through the system to maintain thermal compliance. Efforts to improve thermal compliance issues have met with little success due to the rapid increase of electronic component power dissipation. Safety agencies limit the area that can be vented from a computer housing due to potential fire hazards. Thus, in the past, as electronic power dissipation has increased with the rise in processor speeds, so has cooling fan speed and size. Elevated fan speeds have resulted in decreased fan life, and the noise created by this approach has resulted in consumer complaints.
One approach for enhancing heat removal from localized areas or individual components such as ICs uses heat sinks, typically composed of a series of metal fins, that may be attached to component, preferably in close physical contact. Use of a heat sink permits (1) a larger heat transfer area to be used, and (2) heat to be drawn away from the component to another area. For example, a heat sink contacting an integrated circuit may project directly into a stream of cooling air such as may be provided by fans mounted on the walls of the case or on top of the heat sink. A forced flow of cooling air absorbs the heat from the heat sink and the resulting warmed air is blown outside the computer case.
A passive heat sink coupled with a fan, however, is often insufficient to provide adequate local cooling. The heat sink is typically placed next to a fan positioned to blow air out of the enclosure. Since air typically enters the enclosure case from a side opposite the fan, the air is usually pre-heated by other components within the system before reaching the heat sink to a level higher than the ambient air temperature. This can lower the cooling efficiency to such a point that the desired component (e.g., an integrated circuit) coupled to the heat sink may not get an appropriate amount of cooling. Since the desired component may not be totally cooled, the excess heat is typically dissipated throughout the enclosure causing the temperature of the enclosure to rise. In such systems the temperature of the enclosure may be up to 10 degrees Celsius higher than the ambient air temperature.
Moreover, certain electrical components used to increase computing speeds and characterized by particularly high power dissipation have required larger and larger heat sinks to keep the air flow requirements to reasonable levels. These heat sinks have grown to very large sizes in the past several years in order to keep fan speeds to a minimum. Many recent heat sink designs have exceeded the dimensional limits of the socket to which the electrical device is connected. This has caused problems for factories producing the systems, the designers of the system boards, and the end users. It has also caused difficulties for consumers seeking to upgrade their systems. For example, most modern microprocessors are designed to fit into a socket having an integral handle (e.g., a zif socket). To permit a processor to be inserted into, removed from, and locked within such a socket, the handle must be free to rotate up and down. Most heat sinks associated with these processors have exceeded the dimensional limits of the socket, thus causing the handle to be inaccessible. As a result, removing the processor becomes an onerous task once the heat sink is installed.
Another traditional approach to satisfying ever-increasing heat dissipation requirements has been to dramatically increase the size of an air inlet to an enclosure. Such inlets are commonly placed along the front plastic bezel of an enclosure. Increasing the size of an air inlet helps to increase air flow, but only to a certain degree since there is a limit as to how much the front side vents can be enlarged. Industrial designers generally desire to keep such inlets from becoming an eyesore for the consumer, and the visible vent area on a front bezel hampers the industrial designer's ability to provide a clean design that is aesthetically pleasing. Additionally, safety agencies refuse to approve or “list” enclosures having air inlets sized so large as to permit a user's finger to enter the device.
Therefore, there exists a g

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