Heat exchange – With retainer for removable article – Electrical component
Reexamination Certificate
1999-12-16
2004-05-04
Atkinson, Christopher (Department: 3743)
Heat exchange
With retainer for removable article
Electrical component
C165S080400, C165S185000, C361S700000, C257S714000
Reexamination Certificate
active
06729383
ABSTRACT:
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
BACKGROUND OF THE INVENTION
The present invention relates to methods and apparatuses for cooling electronic components and other objects, more particularly to such methods and apparatuses involving removal, absorption and/or dissipation of heat.
A “heat sink” (alternatively spelled “heatsink”) is a device used for removing, absorbing and/or dissipating heat from a thermal system. Generally speaking, conventional heat sinks are founded on well known physical principles pertaining to heat transference. Heat transference concerns the transfer of heat (thermal energy) via conduction, convection, radiation or some combination thereof. In general, heat transfer involves the movement of heat from one body (solid, liquid, gas or some combination thereof) to another body (solid, liquid, gas or some combination thereof).
The term “conduction” (or “heat conduction” or “thermal conduction”) refers to the transmission of heat via (through) a medium, without movement of the medium itself, and normally from a region of higher temperature to a region of lower temperature. “Convection” (or “heat convection” or “thermal convection”) is distinguishable from conduction and refers to the transport of heat by a moving fluid which is in contact with a heated body. According to convection, heat is transferred, by movement of the fluid itself, from one part of a fluid to another part of the fluid. “Radiation” (or “heat radiation” or “thermal radiation”) refers to the emission and propagation of waves or particles of heat. The three heat transference mechanisms (conduction, convection and radiation) can be described by the relationships briefly discussed immediately hereinbelow.
Conductive heat transfer, which is based upon the ability of a solid material to conduct heat therethrough, is expressed by the equation q=kA&Dgr;T/l, wherein: q=the rate of heat transfer (typically expressed in watts) from a higher temperature region to a lower temperature region which is in contact with the higher temperature region; k=the conduction coefficient or conductivity (w/m-c), which is a characteristic of the material composition; A=the surface area (m
2
) of the material perpendicular to the direction of heat flow; &Dgr;T=the temperature difference (° C.), e.g., the amount of temperature drop between the higher temperature region and the lower temperature region; and l=length (m) of the thermal path through which the heat is to flow (e.g., material thickness).
Convective heat transfer, which is based upon the ability of a replenishable fluid (e.g., air or water) to absorb heat energy through intimate contact with a higher temperature solid surface, is expressed by the equation q=hA&Dgr;T, wherein: h=the fluid convection coefficient (w/m
2
−° C.), wherein h is determined by factors including the fluid's composition, temperature, velocity and turbulence; and, A=the surface area (m
2
) which is in contact with the fluid.
Radiative heat transfer, which is based upon the ability of a solid material to emit or absorb energy waves or particles from a solid surface to fluid molecules or to different temperature solid surfaces, is expressed by the equation q=A&egr;{haeck over (o)}(T
s
4
−T
∞
4
), wherein: &egr;=the dimensionless emissivity coefficient of a solid surface, characteristic of the material surface; {haeck over (o)}=the Stefan-Boltzmann constant; A=the surface area (m
2
) which radiates heat; T
s
=absolute temperature of the surface (K); and, T∞=absolute temperature of the surrounding environment (K).
It is theoretically understood that, regardless of the heat transfer mechanism, heat transfer rate q can be increased by increasing one or more factors on the right side of the equation—viz., the heat transfer coefficient (k, h or E), and/or the (surface or cross-sectional) area A and/or the temperature reduction &Dgr;T—and/or by reducing the path length l.
In current practical contexts, heat sinks generally are designed with a view toward furthering the conductive properties of the heat sink by augmenting or optimizing the conduction coefficient k, the surface area A and the path length l. Conduction coefficient k depends on the materiality of the heat sink. In this regard, according to conventional practice, a heat sink structure is made of a thermally conductive solid material, thereby maximizing the conduction coefficient k characteristic of the heat sink. In addition, the heat sink structure tends to be rendered large (e.g., bulky or voluminous), especially the portion thereof which contacts the to-be-cooled body, thereby maximizing the cross-sectional area A or minimizing the path length l which are design characteristic of the heat sink.
Generally speaking, the materials conventionally used in the industry for heat sink manufacture are characterized by high heat conductivity and low weight. These materials are usually a metal or metal alloy. The most common materials used in the manufacture of heat sinks are aluminum and copper. These materials are often coated with nickel or another finish to prevent corrosion. Metal alloy materials are also finding their way into the mainstream of heat sink design, provided they have a high thermal conductivity and a low weight.
All conventional heat sinks which have been observed, including those which are commercially available, effectuate some form of conductive heat transfer, and are primarily dependent thereon or governed thereby. Conventional heat sinks mainly rely on heat conduction through a solid-on-solid contacting interface between the tobe-cooled object and the heat sink device. These conventional devices are typically fabricated from a high heat-conducting material, generally a metallic material.
Many conventional heat sinks feature various arrangements and configurations of protrusive structuring (e.g., pins, fins, pins-and-fins, mazes, etc.) which are intended to increase the heat sink's size parameters (cross-sectional area A), thereby increasing the amount of conductive heat transfer surface (i.e., the amount of conductive heat dissipation/removal). The protrusive structuring is rendered to be thermally conductive and to increase the overall heat transfer coefficient the heat sink.
Some of these conventional devices implement cooling fluid flow (e.g., water or air) which passes through the heat sink's protrusive structure or structures, or which otherwise contacts solid material of the heat sink. In all such known applications, the heat sink is adapted to first being thermally conductive, and the fluid is adapted to then being thermally convective with respect to heat which has previously been thermally conducted by the heat sink.
Typically in conventional practice, a sizable mass (e.g., a block) of a thermally conductive solid substance (e.g., a metallic material) is placed in direct contact with the high temperature body. Nevertheless, heat sink applications involving a high power density (i.e., high heat flux, or high heat dissipation over a small surface area) do not ideally lend themselves to a cooling methodology wherein a thermally conductive material directly contacts a body which operates at a high power density. Some of the potential detriment stems from the normal circumstance that the thermally conductive material is metallic.
Metals are characterized by the presence of relatively free electrons, and hence are characterized by high thermal conductivity as well as high electrical conductivity. There exists a relation between the thermal conductivity of a metal to its electrical conductivity; pursuant to the Wiedemann-Franz law, for instance, the ratio of the thermal conductivity of any pure metal to its electrical conductivity is about the same at the same given temperature.
Cannell Michael J.
Cooley Roger
Garman Richard W.
Green Geoffrey
Harrison Peter N.
Atkinson Christopher
Kaiser Howard
The United States of America as represented by the Secretary of
LandOfFree
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