Turbulence inducing heat pipe for improved heat transfer rates

Details Turbulence inducing heat pipe for improved heat transfer rates Turbulence inducing heat pipe for improved heat transfer rates

2002-08-27

2003-06-03

Bennett, Henry (Department: 3743)

Heat exchange

Intermediate fluent heat exchange material receiving and...

Liquid fluent heat exchange material

C165S104220, C165S104260, C165S104330, C361S700000, C174S015200

Reexamination Certificate

active

06571863

ABSTRACT:

BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a heat pipe for transferring heat from a heat source to a heat dissipater. More specifically, a looped heat pipe for transferring heat by regulating the direction of fluid flow and introducing turbulence into the fluid flow to increase heat transfer rates from the heat source to the heat pipe and from the heat pipe to the heat dissipater is disclosed.
2. Description of the Prior Art
The dissipation of heat generated by modern electronic components has become a major concern for designers of many modern devices. Approaches to the problem vary from passive heat sinks to external liquid refrigeration systems. One common solution to the problem is to transfer heat away from the heat source, via a heat pipe or other device of similar functionality, to a location where it can be dissipated more readily.
FIG. 1
illustrates the concept of a simple prior art heat pipe comprising a hollow tube. Enclosed in the upright tube is a working fluid, often a freon derivative. Here the term “upright” means a combination of a vertical disposition and having the heat source at or near the bottom of the tube and the cooling region at or near the top of the tube. When heat is applied to a heat absorbing region of the heat pipe, the working fluid absorbs the heat through vaporization and expands toward the heat dissipating region where the working fluid releases the latent heat through condensation, and due to gravity, falls back to the heat absorption region completing the cycle.
FIG. 2
demonstrates a slightly more complicated version of a prior art heat pipe. The heat pipe shown in
FIG. 2
is oriented in less than an upright position so that gravity no longer exerts a great enough force on the re-condensed working fluid to adequately return it to the heat absorption region for recycling. In this case, some kind of wick-like structure
25
lines the walls of the tube, drawing the re-condensed working fluid back to the heating region via capillary action.
There additionally are looped variations of the basic types of heat pipes as shown in
FIG. 3. A
conventional looped heat pipe
32
also comprises a working fluid, a heat absorbing region
35
, a heat dissipating region
34
, an expansion pipe
37
, and a return pipe
39
. As before, heat is absorbed in the heat absorbing region by the working fluid through vaporization. The vaporized working fluid flows up through the expansion pipe
37
into the heat dissipating region
34
where the working fluid condenses, releasing latent heat due to cooler temperatures present in the heat dissipating region
34
. The return pipe
39
conventionally comprises a wick-like structure to return the condensed working fluid from the heat dissipating region
34
to the heat absorbing region
35
through capillary action. The main purpose of providing a separate expansion pipe
37
and return pipe
39
is to reduce the inhibiting forces acting between the vaporized working fluid and the returning condensed working fluid trying to flow in two opposite directions in the same pipe.
Although a closed loop, the capillary action caused by the wicks in the return pipe
39
is still necessary to cause the various working fluid states to circulate properly. Additionally, wicks have the disadvantage of usually requiring a wire mesh to support them and perhaps more critically, have limitations as to length in their ability to furnish adequate capillary action for the proper functionality of the heat pipe
32
.
Wick-less looped heat pipes are disclosed in U.S. Pat. No. 2,518,621, U.S. Pat. No. 3,929,305, and U.S. Pat. No. 4,921,041. Of particular interest is U.S. Pat. No. 4,921,041 where the wick-like structures have effectively been replaced by a plurality of check valves, each check valve restricting working fluid flow to a single direction resulting in proper circulation. The check valves propel and amplify expansion forces generated during working fluid vaporization to force circulation in the direction controlled by the check valves.
However, any fluid flowing within the confines of a pipe conforms to a series of well establish physical laws. Please refer to
FIG. 4
showing a portion of a pipe
50
filled with a fluid flowing through the pipe from left to right. As fluids flow, they exhibit viscous tendencies, that is, the fluid molecules tend to stick to any nearby solid surface as well as to other fluid molecules nearby. As a result, not all of the fluid within the pipe flows at the same rate but conceptually form telescoping tubes of fluid with the cross-sectional center moving faster than the cross-sectional edges. In
FIG. 4
, the arrows
52
-
58
represent possible relative velocities of the laminar flowing fluid at differing locations within the pipe. This uniform laminar flow reduces the heat transferring ability of the fluid because the cooler portions of the fluid, those near the wall such as
52
, do not readily mix with the warmest portions of the flow,
58
in the center. The fluid near arrow
58
is never in contact with the cooling wall of the pipe
50
and any heat dissipation from the fluid designated by the arrow
58
must migrate across the arrows
56
,
54
, and
52
before being released from the system. Additionally, the difference in temperatures between adjacent arrows is smaller than the difference between
52
and the cooling wall of the pipe
50
further inhibiting the transfer of heat.
While the “041” patent successfully eliminates wick-like structures from heat pipe construction, it fails to address one of the most critical functions of a heat pipe, that of transferring the latent heat out of the vaporized working fluid as efficiently as possible while in the heat dissipating region. Conventional check valves permit the fluid in the center of the pipe to flow more easily than the fluid near the circumference of the heat pipe, further inhibiting the transfer of heat as described in the previous paragraph.
It is obvious that the more efficiently the heat is removed from the vaporized working fluid, the more efficient the heat pipe becomes. What is needed is a heat pipe design which not only eliminates the length limitations imposed by wick-like structures, but a heat pipe design that transfers the latent heat out of the vaporized working fluid more effectively, therefore dissipating heat more effectively and resulting in a more efficient heat pipe.
SUMMARY OF INVENTION
It is therefore a primary objective of the claimed invention to improve heat transfer rates in a wick-less heat pipe by improving fluid flow. Another objective of the claimed invention is to provide a heat pipe with an increased ability to operate properly in unconventional orientations relative to a heat source.
Briefly summarized, the claimed invention includes a tube of suitable length to form a sealed, closed loop. The tube additionally has a first surface adapted to contact at least a portion of a heat source to function as a heat absorbing region and a second surface adapted to contact at least a portion of a heat dissipater to function as a heat dissipating region. The tube encases a low viscosity working fluid for transferring heat from the heat absorbing region to the heat dissipating region. At least one radially segmented disk is in the tube to act as a one-way flow regulator to restrict the flow of the working fluid around the interior of closed loop of the tube to a single direction from an upstream side of the radially segmented disk to a downstream side of the radially segmented disk.
The radially segmented disk has an outer edge of each segment hinged to a thin-walled, pipe shaped spacing ring. The hinges allow the segments to pivot from a closed orientation to an open orientation or from the open orientation to the closed orientation. The closed orientation forms a substantially planar, fluid blocking structure for preventing a flow of the working fluid toward the upstream direction through the radially segmented disk. The open orientation has the segments pivoted in a downstream

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