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Thin Heatpipe with Maximum Heat Transfer Rate in Excess of 50 W

1.

INTRODUCTION

As laptop computers and similar data appliances become
progressively thinner and more compact, their CPUs andgraphic memory controller hubs (GMCHs) generate more
and more heat, imposing more severe burdens on heatdissipation and cooling arrangements. Generally, becauseof the limited space for cooling or heat equalization inside
the chassis of such equipment, flattened heatpipes havebeen widely used, but the problem is that as heatpipes
become thinner the heat transfer rate is reduced making it
difficult to cope with smaller, thinner equipment. We havedeveloped a 1-mm thick heatpipe to address the trend tothinner equipment and are pursuing development of heatpipes that satisfy the requirements of the market, but withincreased generation of heat there is a need for thin heatpipes with a larger maximum heat transfer rate.
In this project we have applied our accumulated knowhow and manufacturing technology, and have succeededin overcoming a major difficulty in the past--developmentof a high-performance heatpipe with a heat transfer ratein excess of 50 W and a thickness of only 2 mm. This istwice the thickness of 1-mm heatpipes, but delivers morethan three times the maximum heat transfer rate. In thisway, where the conventional heatpipes dictated the use ofmultiple heatpipes because of low heat transfer rate it ispossible to manage with only one, and the leeway that isprovided with respect to space means that it can beapplied to products in which it was not previously feasible. In the following we describe the structure of the 2mm heatpipe and its performance.

2.

heatpipe, or a sintered metal mass. As can be seen from
Figure 1, however, the walls are comparatively thick sothat any attempt to flatten them to achieve a thinner profile restricts the flow path for the steam and speeds up therate of flow, causing a dispersion limit, in which the working fluid returning to the evaporator section is blown awayby the steam, significantly deteriorating the heat performance.
To address this problem, Furukawa Electric has developed a heatpipe with stronger capillary action that promotes circulation of the working fluid by adopting amesh-type wick and a thin-walled container, as shown in
Figure 2, resulting in the world's thinnest heatpipe at 1mm, capable of the transfer of more than 10 W of heat.
The 2-mm heatpipe developed in this project improveson the structure of the 1-mm heatpipe, with a thin-walled
flattened copper container, in the flat portion of which amesh that provides a steam flow path in itself is closely
bonded. The use of this type of structure facilitatesa) Grooved heatpipe

Grooveb) Sintered heatpipe

STRUCTURE

Heatpipes for use at room temperatures, as in the coolingof laptop computers, normally comprise a container madeof copper, the working fluid, which is water, and a wick toserve as the flow path for the working fluid. Heat is taken
up utilizing the extremely high latent heat of the water acting as the working fluid, steam then moves to the cooling
section, condenses to give up heat, and the condensed
water travels along the wick back to the evaporator section to provide heat transfer. Heatpipes that operate in thisway thus require a means of smoothly returning the working fluid from the condenser to the evaporator section(the wick). In the past, most heatpipes have been of thegrooved type, with grooves cut in the inner surface of theSintered metal mass

Figure 1

Structure of conventional heatpipes.

Metal mesh

Figure 2

Structure of 1-mm-thick heatpipe.

Furukawa Review, No. 32

200785

Thin Heatpipe with Maximum Heat Transfer Rate in Excess of 50 W

smooth transfer of the heat from the heat source to theworking fluid, realizing a heatpipe in which circulation ofthe steam and the working fluid takes place easily.

PERFORMANCE

Figure 3 shows the results of measurement of the maximum heat transfer rate for the 2-mm heatpipe developedin this project. As the figure shows, when the heatpipe
temperature at the heat insulator section is kept at 50°C
and it is operated horizontally, even the input of 50 W produces no sudden temperature rise at the evaporator section, demonstrating that the maximum heat transfer rate isin excess of 50 W. Normally in applications involving heatdissipation and cooling of laptop computers and similarelectronics, the temperature inside the case may often
reach 50°C or more, so that the maximum heat transferrate will doubtless increase further.
And not only 2-mm thicknesses but even flatter configurations have made it possible to manufacture even thinner high-performance heatpipes. With greater flatness,the maximum heat transfer rate tends to be reduced, but
it is still possible to deal with an area of thermal performance that are not covered by existing heatpipes. Figure
4 shows an example of the application of a heatsink using
a heatpipe flattened to 1.5-mm thickness. Bends andsteps can also be formed, and even assuming a case withmultiple heat sources, it is possible to transfer 30 W ofheat.
Figure 5 plots maximum heat transfer rate against heatpipe thickness. In grooved heatpipes, when the maximum
heat transfer rate is large the degree of flattening is small,but as flattening increases the heat transfer rate drops
rapidly. The 1-mm heatpipe, on the other hand, operates
at a thickness unattainable by the grooved type, but its

Temperature（℃）

70

Through development of the high-performance thin-profile heatpipe described here, Furukawa Electric has madeit possible to use heatpipes in a wider range of applications, and has enabled more optimum proposals to bemade. With respect to heatpipes, we are now proceeding
to establish mass production and are scheduled toachieve this by the end of the current year.
For more information, please contact:
Engineering Sec., Thermal and Antenna Solutions
Dept., Electronic Components Div., Electronics andAutomotive Systems Co., Furukawa Electric
TEL: +81-463-24-9873 FAX: +81-463-24-9871

Heatpipe

BendStepCooling section
Evaporator section

Figure 4

Example of application of thin-profile heatpipe

20 W

5030 W40 W

4050 W

123455 W

5Measurement point
T1

CONCLUSION

10 W

6030

4.

T2

T3 = 50℃

Evaporator
sectionHeatpipe

T4T5

Cooling
sectionTotal heatpipe length:

Figure 3205 mm

Evaporator section length:

30 mm

Cooling section length:

100 mmMaximum heat transfer rate of heatpipe.

Maximum heat transfer rate (W)3.

maximum heat transfer rate is not large. Through thedevelopment of this high-performance, thin-profile heatpipe, it has been possible to deal with a thin-profile, highperformance area of thermal performance that could not
be covered by conventional grooved heatpipes or 1-mm
heatpipes.

120

Horizontal operation; working temperature: 50℃

1008060402000

Developed product

Groovedhea tpipe

1-mm
heatpipe

1

Flattened

234Round

567

Heatpipe thickness (mm)Figure 5

Heatpipe performance area.

Furukawa Review, No. 32

200786