A Junction Block Incorporating a Micro Heat-Pipeby Yoshiaki Sawaki *, Masami Takase *, Masami Tanabe *, Teruo Nakao *2,
Isao Kinoshita *2, Tadashi Ikezawa *3, Ken'ichi Namba *4 and Masahiro Suzuki *5

Recent progress in automotive technologies has been remarkable and has been

ABSTRACT accompanied by a steady proliferation in electric circuitry and auxiliary equipment,

leading to a growing need for electrical devices for the vehicle.
Junction boxes are generally the means used to simplify increasingly complex circuitry but thestrong trend in recent years to incorporate more circuits and components has brought about aheightened need for more compact, higher-density designs.
In addition the heat generated by relays, fuses and other components has become a major issue,
and for the first time a micro heat-pipe has been used to address the problem of heat from automotive electrical equipment. Further development work is expected to make this a priority technology
for Furukawa Electric.

1.

INTRODUCTION

More than 20 years have already passed since a junction
block was developed to simplify the complicated car electric circuits of a wire harness, and nevertheless the junction block has been used until now with its structure remaining almost unchanged. The rising temperature in theblock has always been a problem, and the various methods required for the preventive measures have become
the main cause of the increase in cost. This excessive risein temperature not only causes such troubles as degrading or malfunction of parts due to overheating but also, atworst, might eventually cause a fire in the car. Although
the temperature rise problem of the junction block, which
is one of the most important safety parts, was expected tobe solved as soon as possible, no drastic preventive measures have been found until now.
The micro heat-pipe mounted to the junction block is
expected to give a drastic solution to the rising temperature problem.
Following are the advantages of the micro heat-pipe:1)(1) Simple structure and simple operating principle,
trouble-free,* Design Sec., Block Engineering Dept., Electric Appliance Div., Automotive Products Gr.
* 2 Testing Sec., Block Engineering Dept., Electric Appliance Div., Automotive Products Gr.
* 3 Design Sec., Block Engineering Dept., Ohmi Electric
Wire & Cable Inc.,* 4 Thermal Management Development Team, Yokohama
Research Lab.
* 5 Production Engineering Sec., µ HP Team, Electronic
Products Div.

(2) Excellent isothermal property and high heat transfer
performance,(3) Low heat resistance and good thermal response,(4) Operating by non-motive force (by temperature difference only) and noise-free,(5) Excellent workability and free in mounting shape, and(6) Very compact, occupies a small amount of space.
Thus, the mounting of the micro heat-pipe to the junction block is deemed to provide many advantages. However, this was the first time to employ the micro heat-pipe
to a car under a severe environment, and various problems were thought to arise. The authors introduce hereunder the micro heat-pipe, which they started to develop
several years ago and succeeded in putting into practicaluse in a new model car that was launched into mass-production in January, 1998.

2.

ON MICRO HEAT-PIPE

2.1 Construction and Working Principle
The heat-pipe is generally defined as a heat transfer device which is a closed vacuum vessel containing a small
amount of a volatile medium called operating liquid enclosed in a wick having capillary force to circulate themedium and performs heat transfer by the medium which
repeats evaporation and condensation continuously2). The
micro heat-pipe is the generic name of heat-pipes for micro device heat radiation, and heat-pipes of 3 mm, 4 mm
and 6 mm in diameter are currently put into practical use.
A heat-pipe of 3 mm in diameter is adopted in this experiment.

19

Radiated toopen air(water etc.)
Tair
Heat radiationfrom micro heatpipe throughTc,wallheat radiatingplate etc.

Condensation(Latent heat
liberation)

Maximum heat transfer amount (W.m)

Figure 1

TairTj

Tc,wallTh, wallrc

Heat
generatedfrom heatingparts etc.
Tj

rh

Tv
Heat resistant circuit

Heat absorption
through heatTh, wall collecting plateetc. to micro
heat-pipe

Operating liquid
circulation(Capillary force)
Tv
Heat transfer(Vapor flow)

Evaporation(Latent heatabsorption)

Working principle of micro heat-pipe

Predicted value
Experimental value
Conditions of micro
heat-pipe sample
26
Number of groups :50˚CEvaporating temperature :Total length of items to be
200 mmmeasured :Length of evaporating section : 50 mm
50 mm
Length of insulating section :Length of condensation section : 100 mm(Horizontal)

Inclination (˚)

Figure 2

Maximum transferable heat of micro heat-pipe

A micro heat-pipe is made of pure copper and its inside
is kept highly depressurized. Figure 1 shows the working
principle which illustrates that heat transfer is performedby circulation of pure water i.e. the operating liquid which
repeats evaporation and condensation.
2.2 Maximum Heat Transfer AmountFigure 2 shows a comparative graph of the calculated value
and measured value of the maximum heat transfer amountfor a micro heat-pipe3). It is understood from the graph thatthe maximum heat transfer amount increases as the tilt of
the pipe increases while the heat transfer amount per micro heat-pipe is approximately 9 W when the pipe is held
horizontally(at zero inclination).
2.3 Long-Term Reliability
For employment of a micro heat-pipe as a car device, notonly its performance but also its long-term reliability under
diverse environmental conditions is essential. The standard for manufacturing the micro heat-pipes developed by
Furukawa are based on manufacturing methods inclusiveof various special types of processes to improve the longterm reliability. They have established the reliability of over
60 years under the same definite operating condition4).
The 60-year reliability can be said " to be enough" in termsof a car's life.
2.4 Problems in Employment to Car
2.4.1 Breakage by Freezing
A micro heat-pipe which uses pure water as its operating

20

liquid may break by freeze-expansion when the temperature goes below 0°C. Since micro heat-pipes used in cars
are longer in length than those used generally (such as apersonal computer), more operating liquid is required. The
temperature inside a car engine room is lowered to theoutside air temperature when the car is parked, this temperature drop becomes serious especially in winter. Therefore, the authors have taken up this problem as one of theessential issues which requires countermeasures in viewof quality assurance.
2.4.2 Heat Collecting/Radiating Structure
We have already studied the micro heat-pipe to give it acertain heat transfer performance as a heat transfer device. However, the structure for heat collection to micro
heat-pipe and that for heat radiation from micro heat-pipe
are important points for efficient heat transfer, and it isalso necessary to consider a structure bearable even under the severe environmental conditions as well as amounting structure to the junction block. Hence, the authors have taken up the problem as their technical task fora solution.

3.

APPLICATION OF JUNCTION BLOCK,USING MICRO HEAT-PIPE

3.1 Background and Objective of Development
The automation of a car wire harness manufacturing process is behind the times, however the improvement of productivity and reduction of fraction defective have always
been important tasks. Besides, in the case where a large
number of circuits are used, the enlargement of diameterin the wire harness as a trunk line and the increase inweight are inevitable, resulting in lower production anddeterioration in quality at the car manufacturer plant. In
particular, a car model which has been developed at thistime has a large number of circuits and the manufacturer
was keenly in need of the quality improvement of a wire
harness, capable of making production easier than before.
At this time, various measures have been taken to decrease, as much as possible, the number of splice joints
and complicated branches in a wire harness that are thecauses of lower production. Also, as our goal of this development, simplification of a wire harness was set by accumulating circuits into junction blocks. The application of
the micro heat-pipe to the junction block is a step for realization of the optimum form of a wire harness. Thus, thedevelopment has been proceeded mainly to solve the problems as cited in 2.4 above.
3.2 Major Development Items (1)3.2.1 Measures against Breakage by Freezing
It was found in the freeze-breakage test of a micro heatpipe that it was not broken, even though its length elongated to a certain extent, unless it was tilted at an angle ofover 15 degrees from the horizontal. It is extremely hard,
however, to manage and keep the angle of heat-pipe al-

Furukawa Review, No. 18. 1999

Plastic sleeve

No measures taken(for reference)

Micro heat-pipe

Aluminumblock

Plastic
sleeve* All the micro heat-pipes used have 200 mm length* Conditions of sample such as dimensions etc. are omitted.
(Tests conducted on several types of samples.)* Test conducted on several types of samples for anti-freezing
measures other than the above. (Details are omitted.)

Figure 3

Test samples for prevention of breakage by freezing

ways level, especially in the conditions of parking lots.
Moreover, it is impossible to always ensure the performance of a unit junction block as a spare part and also
keep it safe in the event of car accidents. At this time, various types of samples have been made as shown in Figure 3 and the verification tests by heat cycles have been
carried out.
3.2.2 Method, Conditions and Standards for Evaluation
Under the test of heat cycle, the samples were held in a
vertical position in evaluating conditions where the temperature was repeatedly changed from -14°C to +10°C /one cycle (30min). We set a standard value for the test ofevaluation. This was obtained from the formula shown
below, on the basis that the frequency of freezing for a
day was once, winter season for a year was three months,
the period of guarantee was 10 years.
Once(frequency) × 3(months) × 30(days) × 10(years)= 900 = around 1000 cycles
3.2.3

Test Results and Measures against FreezeBreakage
Table 1 shows the results of the evaluation test. Only analuminum block cleared the evaluation standard of 1,000
cycles, and the other blocks were broken due to the expansion by freezing around the end of the micro heatpipe. Since the aluminum block is expensive and requires
ample space, the development was carried out using acopper sleeve, and the optimum dimensions such as the
thickness and length of the sleeve were determined according to the evaluation in various aspects.
3.2.4

Appropriate Operating Liquid Volume for MicroHeat-Pipe
As our development of the micro heat-pipe progressed,
the length to be used was determined as 316 mm. It was
revealed, however, that this size did not protect the micro
heat-pipe against breakage by freezing even using a copper sleeve, since the size of the heat-pipe required moreamount of internal operating liquid not to lower the maximum heat transfer. It was also found that, with a 316 mm
micro heat-pipe length and with such an operating liquidvolume so as not to decrease the maximum heat transfer

Table 1

Evaluation test results for prevention of breakage
by freezing using partial samples

Aluminum block

Plastic sleeve

Measures not taken(for reference)

Cleared 1,000 cycles

Broken at around 200
cyclesBroken at only several
cycles. No change in appear- . No change in appear- . The part slightly
ance
above the end of theance. Adhered to aluminum . Adhered to plastic
micro heat-pipe wassleeve due to the ex- broken due to the exblock due to the expansion of the micro
pansion of the micro
pansionheat-pipe
heat-pipe. Good in post-test op- . Broken at sleeveerationJudgement* The micro heat pipe used is 200 mm in length.

Maximum heat transfer
amount (W.m)

Aluminum block

Sample conditions
Number of groups:
26
Vapor temperature:
50˚C
Total length of sample: 316 mm
Shape:
Bent product
Inclination: Heat collecting side 0˚Heat radiating side 30˚Operating liquid amount (%)

Figure 4

Relationship between working fluid volume andmaximum transferable heatamount (the amount will be referred to hereafter as V), a
breakage took place at the bottom end of the micro heatpipe even though the sleeve length was elongated for enlarging its protective portion. It finally became necessary
to determine the amount of operating liquid to establish
the measures by a copper sleeve against freeze-breakage.
A sample of a micro heat-pipe was made, having its
length of 316 mm and the before said appropriate operating liquid amount V was decreased to 40-80%, and a heat
cycle test was conducted to verify the operating liquidamount.
The result of the test revealed that in the case where a
316 mm long micro heat-pipe was held in a vertical position for a long period of time, the threshold value with which
the measure against freeze-breakage to be effective was
60% of V or less. In this consequence, it was decided thatthe operating liquid amount for the micro heat-pipe to be
used in the junction block should be 40-60% of V (a marginal range was set, taking the yield into consideration).
3.2.5

Change in Maximum Heat Transfer Amount vs.
Change in Operating Liquid Volume
Since the decrease in operating liquid, as measuresagainst breakage by freezing, directly affects the heat transfer performance, the maximum heat transfer amount wasmeasured in the specification of a new product. Figure 4
shows the relationship between the operating liquid amount21

and the maximum heat transfer amount.
As the result of measurement, it was found that the
maximum heat transfer amount of the sample having theoperating liquid amount of 40-60% of V was about 4-6 W
when the micro heat-pipe was mounted to a car. The heattransfer performance of the sample was lowered as compared to the performance in standard operating liquidamount, however this is the only solution for the freezebreakage problem which directly affects the total qualityof the micro heat-pipe at the moment, it was therefore decided to proceed with the development in this specification.
Table 2

3.3 Major Development Items (2)3.3.1 Investigation of Heat Collecting / Radiating Structure
Regarding the pipe positioning, we studied a wire connected type relay block, integrated bus bar type junction
block and other various block units. In the present development, the mounting structures for each relay block andjunction block were investigated and the differences in theeffects between them were confirmed.
First, the heat collecting structure and heat radiating
structure for each type of blocks were examined and theevaluation of the effect was carried out using model

Optimum structures of heat collecting and heat radiating sections(1) Structure of heat collecting section
Relay block type

Direct insertion

Contact terminal

Junction block typeHeat collecting
plate
Heat collecting
plate

Potting

Direct insertion

Potting resin is filled Same as for relay
around housing
block typeHeat collecting plate

PottingHeat collecting plate Same as for relay
block type

Structure views(Images)Arranging heatcollecting plate over Outer wall of
the junction blockhousingHeat-pipe
Heat collectability
Reliability
Possibility of
establishment
Ease in assembly
Cost
Total judgement(2) Structure of heat radiating section
ClosedBuilt-inHeat-pipe

Structure views(Images)

Air cooling
Natural air cooling

Heat-pipe

Mounting to car body

Water cooling
Fin

Fin

Washing tank

Terminal locked by
screw

Tank

Terminal

Fixed bycaulking

Block

Fixed by bracket

BracketFixinghole oncar body

Heat-pipe
Block
Heat radiatability
Reliability
Possibility of
establishment
Ease in assembly
Ease in mounting
to a car
Cost
Total judgement

22

Furukawa Review, No. 18. 1999

Table 3
Micro heat-pipe

Comparison of the effect of micro heat-pipe in theblock
Relay block type

Items

Loweredtemperature

Lowering
rate

Loweredtemperature

Lowering
rate

Maximum effect

3.7˚C

5.0 %

8.9˚C

21.9 %

Minimum effect

0.3˚C

0.6 %

4.3˚C

10.7 %

Average effect

1.6˚C

2.8 %

6.6˚C

17.1 %

Micro ISO relay housing

Bracket mounting part

* The lengths of micro heat-pipes used are about 250 mm for relay
block type and about 150 mm for junction block type, dependingon the structure difference in blocks* Covers are omitted

Figure 5

Prototype of relay block for evaluation of assembly
into car structure

Iron bracket

Mounting bolt
holesBus-bar, insulation
plate composite

Micro heat-pipe
Lower case

* Covers are omitted

Figure 6

Prototype of junction block for evaluation ofassembly into car structuresamples. As shown in Table 2, in the relay block type, thedirect insertion method was desirable; in the junction block
type, fixing the micro heat-pipe to a heat collecting plate
was desirable for heat collecting. For the heat radiating
structure, fixing the micro heat-pipe directly to a car bodyby bracketing was the most effective.
3.3.2

heat-pipe is made to contact with and fixed to the heatcollecting plate by clamping the micro heat-pipe fixing portion with this plate's curled hook portion.

Upper caseHeat collecting
plate

Heat-pipe
fixing pad

Junction block type

Consideration of Mounting Structure to Car by
Block Types
After consideration on the automotive block applicationsof the above confirmed heat collecting / radiating structures, the mounting structure was investigated using existing blocks of several different types.
(1) Mounting structure of a relay block type
A partly remodeled relay block having a general structure was used as a sample. As shown in Figure 5, theheat collecting section is inserted directly between the terminals on the contact side of the micro ISO relay, and theheat radiating section is extended to a bracket portion sothat contact is made with the iron plate of the car body bytightening the bracket.
(2) Mounting structure of a junction block type
A partly remodeled junction block having a general structure was used as a sample. As shown in Figure 6, a heatcollecting plate is used for the heat collecting section andthe heat radiating section is extended to another iron platebracket and tightened by this bracket so that contact ismade with the iron plate of the car body. Then the micro

3.3.3 Result of Evaluation on Effect Comparison
Table 3 summarizes the test result of comparison among
the samples. In the relay block type, the temperature lowering effect of a maximum of 3.7°C (5.0%) and an average of 1.6°C (2.8%) was observed. This effect was limited
only to the vicinity of the micro heat-pipe and less effectwas observed at a distant place. The fact-- that the temperature lowering effect is less for comparatively high heattransfer performance of the micro heat-pipe-- may be dueto the lowering of heat collecting efficiency by such a structure where resin and air layers exist between the micro
heat-pipe and heat source.
While in the junction block type, a significant temperature lowering effect of a maximum of 8.9°C (21.9%) andan average of 6.6°C (17.1%) was observed. Besides, thiseffect was observed all over the block as compared to therelay block type, from which it may be concluded that theheat collecting plate worked effectively.
It can be said that the junction block type, which uses aheat collecting plate, is superior to the relay block type formaking the micro heat-pipe work effectively. It was, therefore, decided thereafter to proceed with the developmentof the junction block type.
3.4

Thermal Simulation and Calculation of Heating
Value
In the design of the junction block-- in order to estimate
the number of micro heat-pipes required, the temperaturerise distribution and the effect of the micro heat-pipe wereconfirmed by thermal simulation. This was carried out inthe case where specified circuits and parts were assembled within the dimensions of a junction block designated by car manufacturers. Since the internal structure
and other details were not specified, the simulation test
was conducted using a simplified model. It was hard toanalyze the complicated internal structure using limited
data, and the simulation was not able to give the same
results as shown in 3.3.3 where the effect was checked.
Car manufacturers also express a strong request for theestablishment of the thermal simulation technology. It is,therefore, necessary to immediately develop software
which enables the analysis precisely even with limited23

parameters during the initial period of development, andthis is deemed as an important future task.
The number of micro heat-pipes required was estimatedby the heating value calculation of the junction block.
From equation (1), the total heating value of a new heatpipe is estimated to be about 23 W.

QALL = QR + QF + QB + QC ------------------------- (1)Where, QALL is a total heating value, QR is the relay
heating value, QF is the fuse heating value, QB is thebus bar heating value and QC is the connection heating value.
Next from equation (2), the junction block internal temperature rise is estimated to be about 50°C.

The heat radiating plate was mounted to a fixed bracket
portion of a car body, and by fixing the junction block theheat radiation plate came in contact with a car body. For
the fixing of the heat radiating plate to the pipe, a part of
the heat radiating plate was curled and caulked and thenfixed by soldering.
Hereunder are given the principal advantages of the junction block incorporating the micro heat-pipe which has beendeveloped at this time.
(1) The world's first mounting of a micro heat-pipe to thejunction block has realized a compact and high density
assembly of many circuits and parts into the block andcontributed to the simplification in the wire harness ofthe power source system in the car.

QALL = 1.78Seq × ∆Tm1.25 ---------------------------- (2)Seq = St + Ss + Sb /2 ---------------------------------(3)Where, ∆Tm in equation (2) is the junction block internal temperature rise, St in equation (3) is the upperarea, Ss is the side area and Sb is the bottom area ofa junction block respectively5)~6).
The junction block standard temperature rise designatedby the car manufacturer (to be mentioned hereafter) is
below 40°C, and the heat transfer amount of a micro heatpipe required is estimated to be approximately 4.5 W fromequation (4).

QX = QALL ( ∆Tm - Tk ) / ∆Tm ------------------------ (4)Where, Qx is the heat transfer amount required and
Tk is the junction block standard temperature rise designated by the car manufacturer.
Comparing the results with the data on the maximum
heat transfer amount cited in 3.2.5, the heat transfer may
seem to be a little insufficient; however, the number of micro heat-pipes required for the junction block was decided
at one, taking into consideration the temperature lowering
effect due to the thermal equalization work by the heatcollecting plate.

* Lower cover is omitted

Figure 7

Appearance of developed product* Covers are omitted

Upper case

3.5 Structure of Junction Block with Micro Heat-Pipe
Figure 7 shows an outside view of the new product developed at this time, i.e., the junction block to which a micro
heat-pipe is applied (a lower cover is not illustrated). It was
designed according to the results of the previous consideration. Figure 8 shows a rough illustration of the component parts excluding covers; Figure 9, the structure of aheat collecting section; Figure 10, the structure of a heatradiating section.
For freeze-breakage prevention, copper sleeves were
soldered at both ends of the micro heat-pipe and a bending process was done to the pipe considering the heattransfer efficiency when it is mounted to a junction block,so that the heat radiating section is directed upward.
The heat collecting plate was layered at the top of aone-pieced circuit layer composite in the junction block.
The micro heat-pipe was fixed by caulking to a curled partof the heat collecting plate and a TOX process (generally
a thin plate jointing method by deep drawing using punchand die) was made at the curled spot.

24

Zero layer insulation plate
Copper sleeve

Micro heat-pipe
Heat collecting plate

Heat radiatingplate
Bus-bar, insulation
plates composite
Metal collar

Lower case

Figure 8

Components of developed productFurukawa Review, No. 18. 1999

(2) The heat collecting plate, which is also used as agrounding bus-bar, reduces the joints of several relay
coil circuits. The micro heat-pipe connected to the heatcollecting plate and the heat radiating plate functions
as the grounding bus-bar, thus the multi-functional property of the micro heat-pipe has increased its value.
(3) With the consideration that heat generally moves upward in the junction block, the heat collecting plate andthe pipe are placed on top of the layered circuits toimprove heat collecting efficiency.
(4) Owing to the measures taken against freeze-breakage of the micro heat-pipe, the long-term reliability wasenhanced by taking into consideration the quality, notonly during the mounting period to an actual car, butalso during the storage period as a supplemental part.
(5) Making the heat radiating plate come in contact with
the iron body plate of a car, heat can be dissipatedfrom the junction block directly to a car, thus enhancing
heat radiating efficiency.
(6) The high-temperature, high-strength solder, excellingin an anti-crack property, was used on the micro heatpipe fixing part and sleeve fixing part of the heat radiating plate which protrudes outside of the junction block.
It improves resiliency against the environment as well
as reliability in the electrical and thermal connection.
3.6

Method, Conditions and Standards of Evaluation
as a Junction Block
Based on the method, conditions and standards of evaluation on the junction block specified by the car manufacHeat collecting
plate
Caulked part of
micro heat-pipe

turer, various evaluation tests have been conducted including tests on initial characteristics, durability etc. Confirmation has been made for the performance and the effect of the micro heat-pipe.
Here, criteria for evaluation in the temperature rise test
will be described which is of the utmost importance among
various evaluation tests. The critical temperature rise of
below 40°C is decided on the basis of stress relief performance of a brass terminal against temperature. The heatresistant limit temperature at which the electric brass terminal can maintain its performance is 120°C, and the engine room temperature is 80°C in general. Thus the limit
temperature rise is calculated, 120°C minus 80°C equals
to 40°C.
3.7

Results of Various Evaluations and Effect of MicroHeat-Pipe
It was confirmed that the junction block developed thistime finally cleared all the criteria for evaluation designatedby the car manufacturers and no problems exist with regard to mounting it to a commercial car.
The verification was carried out on the effect of the micro heat-pipe incorporated into junction block by conducting the temperature rise test on both the junction blocks,
with and without the micro heat-pipe. Figure 11 shows thetest result.
The effect of the micro heat-pipe covered the entire junction block by the heat collecting plate, and the lowering oftemperature was observed by a maximum of 9.4°C (19.7%)
and an average of 3.5°C (6.8%). The effect was conspicuous particularly in the proximity of its mounting portion
where relays are concentrated. This is due to the effective
and synergetic action of both collecting local heat by the
micro heat-pipe and the heat equalizing by the heat collecting plate over the entire junction block.

Micro heat-pipe

To heatcollecting
plate
Mounting
bolt holeHeat radiating
plate

Temperature measuring position

Heat radiating
plate
Case bracket
fixing section

Heat-pipe

Terminal

Caulked part of sleeve
Caulked part of
micro heat-pipe

Heat collecting
plate

Copper sleeve

Effect (%)

Bus-barView from case bracket side
(Side not visible after assembling to case)

Product, measures
taken

Fuse
receptacle

Heat collecting structure of developed product

Relay
receptacle2

Figure 9

Relay
receptacle1

Micro heat-pipe

Product, measures
not taken

Temperature lowering
rate (%)

To heatradiatingplate

Temperaturerise (˚C)

TOX-processed
section* Figure shows only representative temperature measuring
positions where temperature lowering effects were remarkable* For J/B without measures, ordinary copper pipe was used inplace of heat-pipe* At the heat radiating plate, J/B with measures shows higher
temperatures due to the effect of micro heat-pipe

Soldered part

Figure 10 Heat radiating structure of developed productFigure 11 Validation test results of micro heat-pipe indeveloped product

25

4.

CONCLUSION

In this development, the followings are confirmed: the performance of the micro heat-pipe incorporated into junction block (in a car under various environmental conditions), applicability of a micro heat-pipe to a car( under asevere environmental conditions), and its effect to temperature (rising and lowering). It was revealed that themeasure using the micro heat-pipe was superior to others
and was able to contribute to the solution for many technical problems.
However, in this development, there still remain several
points to be reviewed in the future:(1) Establishment of a thermal simulation method(2) Further improvement of heat collecting / radiating efficiency and the structure of the micro heat-pipe(3) Measures against freeze-breakage by operating liquid amount which maximum heat transfer volume does
not decrease(4) Further cost reduction(5) Search for and investigation of heat radiating technology other than by application of a micro heat-pipe
The solution of these problems will lead to the establishment of a technology superior to those of competitors
and the advancement in technical development in the future is eagerly required.

26

REFERENCES

1) "Micro Heat Pipe Technical Data", The Furukawa Electric Co.,
Ltd.,1-3. (in Japanese)
2) "Heat Pipe", Furukawa Electric News, 10, (1989), 6. (in Japanese)
3) K. Sato et al.: "Micro Heat Pipe", Furukawa Electric Review,
No.88, (1991), 4-5. (in Japanese)
4) J. Kitanoya, et al.: "MPU Heat Radiator for Lap-Top PCs Using Micro Heat Pipe", Furukawa Electric Review, No.97,(1995), 64-65. (in Japanese)5) Ito et al: "Design of Thermal Countermeasures for Electronic
Equipment", Nikkan Kogyo Shimbun, (1982), 99. (in Japanese)6) Ishizuka et al.: Proceedings of Mechanical Engineers Societyof Japan, 50-460, 13, (1984), 3193. (in Japanese)
Manuscript received on July 10, 1998.

Furukawa Review, No. 18. 1999