Multi-mode heat transfer using a thermal heat pipe valve

An electronic device has a heat pipe containing a heat transfer fluid. The heat pipe has a first section and a second section. Inside the heat pipe is a valve disposed between the first section and second section of the heat pipe. The valve has an actuator that is used to regulate the flow of the heat transfer fluid between the first section and the second section of the heat pipe in response to a changed state detected by a sensor.

FIELD OF THE INVENTION 
This invention relates to a heat transfer system. More specifically, it 
relates to a multi-mode heat transfer system having a valve disposed 
between two sections of a heat pipe for use in electronic devices. 
BACKGROUND OF THE INVENTION 
The trend in the design of electronic devices, such as notebook computers 
or personal data assistants, is to provide as small a package as 
functionally possible while at the same time providing for comfortable 
cool and lightweight operation. Additionally, market forces also require 
that electronic devices, such as notebook computers, deliver the same 
computational horsepower as their desktop equivalents in order to justify 
their cost. However, to achieve this faster performance, integrated 
circuits (ICs), especially the central processing unit (CPU), the graphics 
controller, and the memory devices all require more power, which create 
more heat in the device. The combination of this additional heat and a 
smaller package creates additional stress on the internal components, 
causing the electronic devices to quit working or literally become too hot 
to handle. 
Another problem, especially with notebooks, is that peripheral modules such 
as floppy, CD-ROM, Zip and DVD drives and PC cards not only take up space, 
they create more heat. Also, many of these peripheral modules are 
sensitive to heat generated from the other components in the electronic 
device and may prematurely fail to operate if these temperature sensitive 
modules become too hot. 
Several different techniques have been developed to deal with the excess 
heat generated in an electronic device. By slowing the CPU clock rate 
down, the heat generated by the CPU decreases; however, the user's desire 
for desktop performance can not be met. By creating a docking station to 
hold various peripherals that are not used when the electronic device is 
mobile, more space becomes available in the electronic device for 
additional heat transfer structures. However, the electronic device in a 
docking environment usually causes the user to change their expectations 
of use such that the user wants full performance with an external monitor 
and keyboard as well as access to a network such as the Internet. In this 
situation, usually the electronic device's cover or lid is closed, or the 
electronic device is enclosed by the docking station, and in both cases 
the heat transfer properties of the electronic device change. What is 
required for future electronic devices is an optimal way to keep them cool 
in whatever operating mode the user decides to use. 
SUMMARY OF THE DISCLOSURE 
An electronic device has a heat pipe containing a heat transfer fluid. The 
heat pipe has a first section and a second section. Inside the heat pipe 
is a valve disposed between the first section and second section of the 
heat pipe. The valve has an actuator that is used to regulate the flow of 
the heat transfer fluid between the first section and the second section 
of the heat pipe in response to a changed state detected by a sensor.

DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATIVE EMBODIMENTS 
FIG. 1 is a schematic illustration of a heat transfer system 10 for an 
electronic device 12, such as a notebook computer or personal data 
assistant (PDA), comprised of at least one heat producing component 40 
which is attached to a second heat pipe section 180 which carries heat 
from the component 40 to a heat sink area 50. A heat pipe is a passive 
hermetically sealed closed container which contains a wick or other 
capillary structure, contained within the inner walls of the container, 
soaked with a small amount of vaporizable fluid, preferably water or 
another liquid that has been depressurized to reduce the boiling point of 
the fluid to a temperature less than the maximum operating temperature of 
the heat producing component 40, i.e. 90.degree. C. Unless specifically 
called out, the term fluid used in this specification encompasses the 
fluid within the heat pipe in either a liquid or vapor state. In the 
preferred embodiment, the heat producing component 40 applies heat to one 
end of the heat pipe causing the water or other liquid to vaporize (boil) 
and thus absorb energy, then this vapor travels to the cool end of the 
heat pipe and condenses. In the process of condensation, the fluid 
releases the heat (the energy previously absorbed) to the exterior of the 
heat pipe. The fluid returns to the warm portion of the pipe via the wick 
or other capillary structure and the process is repeated. As the vapor 
pressure drop between the evaporator and condenser is very small, the heat 
pipe maintains an essentially constant temperature along the length of the 
heat pipe. With the proper design, the heat pipe can transfer large 
amounts of heat without temperature losses. 
Heat sink area 50 is designed to radiate heat freely into the air away from 
the electronic device 12. Optionally, to improve the rate of heat 
transfer, a fan 60 may be combined with heat sink area 50. The fan 60 is 
controlled by logic circuit 80 to operate depending on the states of 
several factors, as will be discussed in more detail later. Exemplary 
factors are: sensing when the component 40 is too hot; sensing that 
ambient air inside the electronic device 12 is too hot; sensing that the 
electronic device 12 is being used in different modes (such as docking); 
sensing that the lid of the electronic device 12 has been closed; sensing 
that a new temperature sensitive module has been inserted into the 
electronic device 12; and detecting that a component, such as an 
integrated circuit (IC), has changed to a new mode of operation (i.e., a 
CPU speedup or a change of the graphic controller display mode). Those 
skilled in the art will appreciate that other states that affect the 
thermal performance of the electronic device 12 could be used to provide 
input to logic circuit 80 and still fall with the spirit and scope of the 
invention. 
There may be times during operation of the electronic device 12, such as in 
a notebook computer, when nominal heat dissipation is required and fan 
operation is not desired due to the noise created or the power consumed by 
the fan. In these instances, a heat spreader 30 is coupled to component 40 
through a first heat pipe section 170 and is placed under the keyboard, 
palmrest or other exposed surface area to allow heat to be released out of 
the electronic device 12. However, this heat spreader 30 often spreads 
heat to temperature sensitive modules or other peripheral devices, which 
may affect their performance. In addition, when the lid or cover is closed 
over the exposed surface area, it may be necessary for the heat spreader 
30 to stop functioning, as the heat it is dissipating cannot leave the 
electronic device 12 and the excess heat builds up inside the electronic 
device 12 causing the temperature sensitive modules to fail. Thus, the 
heat spreader 30 restricts the temperature that the heat producing 
component 40 can operate. If the heat spreader 30 can be disconnected from 
the heat sink area 50 and fan 60 circuit, the heat producing component 40 
can be operated at higher temperatures that are within its specification 
without affecting the components near the heat spreader 30. 
The invention addresses this problem by creating a magnetic valve 20, which 
is disposed between the second heat pipe section 180, and the first heat 
pipe section 170. The second heat pipe section 180 is further coupled to 
component 40 and heat sink area 50 and first heat pipe section 170 is 
further coupled to heat spreader 30. This magnetic valve 20 is 
electronically controlled by a driver 70 that is driven by a logic circuit 
80 which combines a number of decision variables from temperature control 
circuit 90, dock control circuit 100, and miscellaneous control circuit 
110. Temperature sensor(s) 120 provide temperature state(s) to temperature 
control circuit 90 in the form of different levels, which in turn impels 
the magnetic valve 20. Dock detection circuit 130 provide docking states 
to dock control circuit 100 in the form of different levels which impels 
the magnetic valve accordingly to deal with different dock situations. 
Several miscellaneous sensors or switches such as lid switch 140, module 
detect 150, or IC mode detect 160, among others, can be input into a 
miscellaneous control circuit 110 in the form of different levels. The 
different levels correspond to respective changed states, which determine 
when to impel magnetic valve 20. 
Also shown is a dock device 64, such as a docking station, which has an 
additional fan 62 which can be used to couple additional airflow across 
heat sink area 50, which is exposed when docked, depending on the power 
load of the electronic device 12 and the amount of heat detected in heat 
system 10. 
FIG. 2 illustrates the preferred embodiment's cross section of magnetic 
valve 20 and its coupling to a second heat pipe section 180 and a first 
heat pipe section 170. The magnetic valve 20 is comprised of a shell 22, 
which allows magnetic penetration through it, such as copper tubing that 
also provides excellent heat conduction. Surrounding the shell 22 is a 
coil 230 of wire which is wound preferably in a voice coil configuration 
to permit an electric current flowing through it to generate a magnetic 
field. The magnetic field may also be provided by an external magnetic 
material or other magnetic field producing device. When using a coil 230, 
the magnetic field can be enhanced or prevented from radiating far from 
magnetic valve 20, by using an optional field concentrator 220, preferably 
a ferrous shield. Inside of magnetic valve 20 is placed an actuator 250, 
which may be either magnetically attractive, such as a ferrite core, or 
magnetically polarized, such as a permanent magnet. A spring 240 is used 
to position the actuator 250, which is shown in FIG. 2 in a `normally 
open` position. Actuator 250 has a hollow center or grooves on its 
peripheral surface to allow fluid in the magnetic valve 20 to pass by the 
valve. A first wick 200 allows fluid to move through first heat pipe 
section 170. A second screen 260 provides support for the spring 240 and 
is perforated with at least one aperture to allow fluid and optionally, a 
second wick 190 from second heat pipe section 180 to flow into the 
magnetic valve 20. When coil 230 is not activated the spring 240 retracts 
actuator 250 from a first screen 210 which has at least one aperture 
designed to allow fluid to flow when actuator 250 is not in contact with 
it. When coil 230 is activated, the magnetic field generated by the 
electronic current flowing through coil 230 impels actuator 250 to contact 
first screen 210 and thus block off the at least one aperture to prevent 
fluid from flowing from second heat pipe section 180 to first heat pipe 
section 170. Although the fluid flow in the heat pipe is restricted from 
flowing to the first heat pipe section 170, a small amount of heat might 
be transmitted through the metal shell. Another embodiment envisions that 
an insulator is placed between the valve and metal shell of the first heat 
pipe section 170 to reduce this heat leakage. Another embodiment to reduce 
heat leakage is to have first screen 210 made of an heat insulating 
material. 
Although first wick 200 and second wick 190 are shown as being placed in 
the center of the heat pipe, other architectures for providing a wick or 
capillary force are known to those skilled in the art and could be used in 
place of that shown in the drawings and still fall within the spirit and 
scope of the invention. 
It should be noted that actuator 250 and spring 240 should be oriented such 
that the spring 240 is in contact with the second screen 260, which 
contacts that heat pipe section attached to heat producing component 40. 
This selection of valve orientation prevents pressure built up in the heat 
pipe fluid from heat generated by heat producing component 40 from 
counteracting the spring compression force of spring 240 when closed and 
thereby cause a fluid leak in magnetic valve 20. 
FIG. 3A illustrates a view of the cross-section AA perspective of FIG. 2 of 
first screen 210. Aperture 212 provides openings for fluid flow and target 
214 provides a stop. 
FIG. 3B illustrates the cross-sectional view from the BB perspective of 
actuator 250, showing actuator aperture 252, which allows fluid flow 
through the actuator. 
FIG. 3C illustrates the cross-sectional view from the CC perspective of 
FIG. 2 of the second screen 260. Second screen 260 has aperture 262 and 
center aperture 264 that allows second wick 190 to enter the magnetic 
valve 20. 
Those skilled in the art will appreciate that other aperture shapes are 
possible for the screens and actuator and still meet the spirit and scope 
of the invention. 
FIG. 4 illustrates a first alternative embodiment of a normally closed 
valve 20 in which spring 242 is long enough to force actuator 250 up 
against first screen 210, effectively blocking the flow of fluid through 
the apertures in first screen 210. The coil 230 and field concentrator 220 
are shifted over the spring 242 such that when coil 230 is activated, the 
magnetic field generated impels actuator 250 toward second screen 260 
thereby compressing spring 242 and allowing fluid to flow through first 
screen 210. 
FIG. 5 illustrates a second alternative embodiment of valve 20 in which an 
actuator 258 is shaped to fit into the aperture of first screen 210 such 
that the amount of displacement of the actuator 258 from first screen 210 
is proportional to the amount of electric current in coil 230 and the 
displacement of the actuator 258 controls the volume of fluid flow through 
first screen 210. This approach allows a controlled varied fluid flow that 
further refines the amount of heat transferred to first heat pipe section 
170. An opening 252 in actuator 258 provides a fluid path through actuator 
258. Optionally, to maintain tight control of fluid seepage around 
actuator 258, a lubricating film 254, preferably a Teflon lubricant like 
polytetrafluoroethylene (PTFE), is applied on the outside of actuator 258. 
Wick 190 can be placed in actuator 258 to help control the fluid flow from 
the second heat pipe section 180. 
FIG. 6 illustrates a third alternative embodiment of the invention in which 
actuator 259 is comprised of a magnetic material and a second screen 262 
is comprised of a magnetically attractive material such as iron. In this 
instance, there is no need for a spring as actuator 259 returns to an open 
position upon deactivation of the magnetic field from coil 230, due to the 
actuator's magnetic attraction to second screen 262. A lubricating film 
254, preferably PTFE, allows the actuator 259 to smoothly slide back and 
forth within the shell 22. Coil 230 and field concentrator 220 (if used) 
are positioned over first screen 210 to draw and impel actuator 259 
towards first screen 210 when coil 230 is energized with electrical 
current to create a magnetic field. 
FIG. 7 illustrates a fourth alternative embodiment of the invention in 
which the actuator is comprised of either a magnetic material or 
magnetically attractive material. Two coils, a first coil 230A and a 
second coil 230B are used to each attract actuator 250, such that by 
activating either the first coil 230A or the second coil 230B, the valve 
is closed or opened, respectively. It is also envisioned in another 
embodiment that once the valve is closed by having first coil 230A 
activated and impelling actuator 250 to abut against first screen 210 and 
after a sufficient time for the vapor pressure in second heat pipe section 
180 to build up, the electric current in first coil 230A can be reduced or 
shut-off and the valve held closed by the pressure in second heat pipe 
section 180. This reduction or shut-off of current into first coil 230A 
allows for reduced power consumption. As second heat pipe section 180 
cools, either due to reduced power from heat producing component 40 or due 
to the effectiveness of fan 60 or dock fan 62 and heat sink area 50, the 
pressure on actuator 250 is reduced and vapor flows into the first heat 
pipe section 170. As the heat spreader 30 then warms, logic circuit 80 
detects when to re-activate first coil 230A to close the heat pipe valve. 
The magnetic fields in first coil 230A and second coil 230B are optionally 
enhanced with a first field concentrator 220A and second field 
concentrator 220B, respectively. In another embodiment, it is envisioned 
that first coil 230A and second coil 230B are used to sense the location 
of actuator 250 before determining which coil to activate to impel 
actuator 250 to an open or closed position. This sensing is performed by 
detecting the change in inductance of the respective coil, which can be 
accomplished by various techniques known to those skilled in the art. By 
determining the position of actuator 250, if the electronic device 12 is 
jarred or moved, the valve could move out of position, be detected, and 
returned back to its proper state. It is also envisioned that the 
energizing current into the coils can optionally be pulsed to a higher 
level to overcome either initial friction or magnetic forces and then 
reduced to maintain the valve in an open or closed position. This variable 
pulsed energizing current technique allows for smaller coils thus reducing 
cost and saving space. 
FIG. 8 is a flow chart representing an exemplary embodiment of logic 
circuit 80 for an electronic device, such as a notebook computer, where 
the heat spreader is used as the primary heat dissipation and the heat 
sink area and fan used when either the heat spreader is overloaded or the 
electronic device is being used in a mode where the use of the heat 
spreader is undesirable, such as when the cover is closed. Start block 400 
defines the initial state of the logic circuit 80, where a valve is 
initially open to allow the heat spreader to operate and the fan is off to 
conserve power. Logic circuit 80 checks miscellaneous control circuit 110 
to determine if the lid is closed in decision block 410. If the lid is 
closed the logic proceeds to decision block 470 because the heat spreader 
will be unable to dissipate heat readily from the electronic device. 
Otherwise, logic circuit 80 checks dock control circuit 100 in decision 
block 420 to see if the electronic device 12 is docked. If docked, the 
electronic device receives power from an AC outlet and the fan can be used 
without regard to power dissipated from the fan so the logic proceeds to 
decision block 470. Otherwise, logic circuit 80 checks miscellaneous 
control circuit 110 in decision block 430 to see if a temperature 
sensitive module, like a battery or a peripheral such as a floppy drive, 
CD-ROM or DVD player, is installed in the electronic device. When a 
temperature sensitive module is installed, the heat spreader may cause it 
to become too warm so the logic proceeds to decision block 470. Otherwise, 
logic circuit 80 checks to see if the CPU (the heat producing component 40 
in this example) is running in a high power mode in decision block 440. If 
so, the logic proceeds to decision block 470 because in this example the 
heat spreader will be unable to handle dissipating the heat from the CPU. 
Otherwise, logic circuit 80 checks temperature control circuit 90 to see 
if the heat spreader 30 has reached its maximum operating temperature in 
decision block 450. If it has (perhaps from a combination of other factors 
such as graphics mode, memory operation, or PC cards), then the logic 
proceeds to decision block 490. Otherwise, the magnetic valve 20 is opened 
in block 460 to allow heat flow from component 40 (here represented as a 
CPU) to the heat spreader 30 and the logic begins checking at block 410 
again. 
Decision block 470 compares the ambient temperature in the electronic 
device to a preset temperature limit. If the preset temperature limit has 
been reached, block 490 enables the fan 60 to turn on and cool heat sink 
area 50 and block 490 closes the magnetic valve 20 and the logic proceeds 
back to start block 400. Otherwise, if the ambient temperature is O.K., 
the fan 60 is turned off in block 480 before proceeding back to the start 
block 400. 
Those skilled in the art will appreciate that other logic implementations 
exist other than that shown in the exemplary embodiment to control the 
magnetic valve 20 and fan 60 and still fall within the scope and spirit of 
the invention. For example, alternative embodiments have been contemplated 
where different subsets of the decision blocks 410-440 are present. 
Indeed, one of these alternate embodiments eliminates all of the decision 
blocks 410-440 and 470-480, with start block 400 connected directly to 
block 450 and having block 490 only closing the valve.