Applications of Computational Thermal Simulationin Product Designby Mamoru Shimada *Computational simulation has become an indispensable tool for research anddevelopment. In the past it was often seen as little more than a substitute forexperiment, but there are times when it yields information that is difficult to obtain directly fromexperiments. With progress in software and hardware it has recently become a simple matter toundertake large-scale computations.
Furukawa Electric makes use of computational simulation in any number of fields. The range
in which thermal and fluid dynamics simulations are used is very wide, from the developmentof heat-dissipating devices and various modules to the design of equipment and cases. Here
we propose to introduce examples of applications of thermal and fluid dynamics simulation to avariety of products.

ABSTRACT1.

INTRODUCTION

Computational simulation is being used in all sorts offields: scholarly research, weather forecasting and architectural and structural design for a start, and everythingfrom finance and the military to regional development.
The use of simulation is not limited to specialized disciplines, but as evidenced by the terms “computer-aided
engineering (CAE)”, it has become a familiar design tool,
indispensable to new product development for manufacturing industries. And behind this lies the higher speedsof computers and advances in software.
Simulation software as a design tool has been in existence for several decades, and has long been used in
its own ways. But these earlier versions of simulation
software needed supercomputers or workstations to run.
Their application was also limited to comparatively smallscale models and their operation required highly trained
specialists, so that they could not really called a highproductivity tool.
The last few years, however, have seen a dramaticincrease in the number-crunching power of the personal
computer (PC), delivering performance that was previously available only from mainframes at dramatically decreasing cost. Thus it is increasingly common for simulations
to be run on PCs. And with higher PC computing performance, the software, by adoption of the GUI, has becomemuch easier to use, with vast proliferation of function andimprovements in computing efficiency.
* Ecology and Energy Lab., R&D Div.

This rapid progress in both hardware and software hastransformed computational simulation from an arcane
activity that was the preserve of the specialist to a convenient tool, easily mastered by any ordinary researcheror technician. Another major change was that it became
easy and cheap to simulate large-scale models. In thepast the problems of limitations imposed by computer
hardware and the excessive time required for computation meant that a large-scale model of complex configuration could not be simulated as is. This required a varietyof time-consuming expedients, such as simplification of
the model.
Nowadays, however, with the upgrading of computer
performance, it has become possible, given just the CAD
drawings, to apply computational simulation with virtually
no further adjustments. Finally let us draw attention to thepreviously unimaginable wealth of expressive power thatcomes from the visualization enabled by software. Thismeans that far from being restricted to a means of replacing experiment, it has become a powerful tool for making
presentations of great persuasive power.

2.

ADVANTAGES OF SIMULATION

Among the advantages of using simulation the two thatare most generally appreciated may well be:1) It reduces the number of experiments and prototypes, thereby lowering development costs; and
2) It enables estimation of results that would be difficult
to confirm experimentally.
For these reasons simulation is particularly useful inFurukawa Review, No. 27

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Applications of Computational Thermal Simulation in Product Designcases in which model changes occur frequently and life
cycles are short, so that product development must be
carried out quickly, or in cases in which the object to bemeasured is so small or the cost of measurement so prohibitive that conducting experiments is difficult.
But despite the advances that have been made in simulation, it will be difficult to totally eliminate prototyping andexperimentation. Although advances in computational
technique have resulted in improved accuracy, there
are still fields in which accuracy remains inadequate.
Furthermore simulation still requires a certain amount ofmodeling based on human thought. Specifically, since
the parameters required for calculation must be enteredbased on human decision-making, errors of humanjudgment will still occur. Sometimes a factor that was
discarded in the modeling process may manifest itself
in unexpected ways in the actual product, giving rise toresults that are significantly different from the simulation.
It is therefore essential that the measured and calculated
results be constantly compared with each other to confirm accuracy.
Then, in addition to the two advantages of simulation
mentioned above, we may consider the following:3) Whenever design changes are made, simulation permits model changes and computations to be implemented in a short time. Design can thus be revisedover and over, raising the degree of completeness ofthe design.
4) Radical designs, which in the past could not be seriously considered because of limitations on the timerequired, can be placed on the agenda for examination.
5) In experiments, data can only be obtained on a limited number of measurement points, but with simulation, physical values for the total computation domain
can be calculated at one time using a one-time calculation. Thus the data obtained is abundant and it ispossible to acquire data for any desired point. In thisway feeding the results of the simulation back into thedesign can elicit new ideas.
We believe that if the characteristics of simulation thathave been shown here are accurately appreciated, theadvantages that simulation offers as a development tool
can be maximized.
Furukawa Electric also actively uses computational simulation, and besides establishing a specialized organization for undertaking sophisticated analysis, we are applying it broadly in the development workplace and design
workplace, in forms that are closely related to productdevelopment.
Taking a look at the areas in which simulation is used,
we find an extremely wide variety—thermal and fluid
dynamics analysis, as well as structural design, electromagnetic field analysis, acoustics and vibration analysis,
optical design, analysis of chemical reactions and processes, design of molecular materials, and so on. In thispaper we have chosen products that are thermal-related
in the broad sense, and present examples in which simulation is used in close integration with their development.

3.

THERMAL-RELATED PRODUCTS FROMFURUKAWA ELECTRIC

Although we blithely use the phrase thermal-related products there are a variety of types, from those that actively
utilize and control heat (power generating equipment,
for example) to products for which a compromise solution has to be reached for heat that is generated as an
unavoidable consequence. Generally speaking, it would
seem that the cases of the latter type, in which unwanted
heat has to be disposed of in some manner, are much
more common, and to respond to these needs, Furukawa
Electric has developed a wide range of heat-dissipating
devices such as heatpipes and heatsinks. Photo 1 showssome typical micro heatpipes, and Photo 2 shows a typical heatsink using heatpipes.

Photo 1

Photo 2

Typical micro heatpipes.

Typical heatpipe-heatsink.

Next are modular products incorporating cooling components such as heatpipes or Peltier devices, or heaters
or other heating components, exemplified by temperature
control type optical modules and case cooling devices.
There are also products like reflow ovens, which actively
make use of heat.
Finally, as examples of products that require measures
to deal with heat that has unavoidably been generated
we may mention communications equipment, cases andoptical transmission devices incorporating highly exothermic devices or modules.

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Applications of Computational Thermal Simulation in Product Design

Heat dissipating devices are developed based on
detailed thermal design in order to obtain the desired
thermal performance. Not only that, thermal design isbecoming indispensable even for modular components,
equipment and packages that are more compact or more
exothermic. Accordingly full design consideration using
thermal and fluid dynamics analysis is being given in thedevelopment process.
Table 1

Thermal management problems in various types of
products.

Type of product

Thermal management problem

Thermal resistance reduction; Downsizing;
Heat-dissipating device
Height reduction; Noise reduction
Power consumption reduction; Temperaturestabilization; Downsizing; Output power
Modular productenhancement; Enlargement of working temperature range
Power consumption reduction; Downsizing;
Equipment and units
Noise reduction; Elimination of heat spot

Table 1 summarizes the objectives for which thermal
design is being done for each of the types of products
described above. We can see that the efficient dissipationof unwanted heat to control temperature is the problem
common to all these products, but there are also developmental problems that differ according to the type of
product. The accuracy required of the simulation also differs according to the type of product.
In this paper we have selected a number of examples
to illustrate the advantages of thermal simulation: fromamong heat-dissipating products, a heatsink for a desktop PC and a heatsink for an optical amplifier; fromamong modular devices, a laser diode module; and as
an example of equipment and units, optical transmission
equipment.

4.

APPLICATIONS TO HEAT-DISSIPATINGDEVICESHeat-dissipating components that Furukawa Electric hasbrought to commercial production are many and varied, including heatpipes, power plates, vapor-chamber,
Crimped fin ®, heat transfer sheets, coated aluminum
sheets for heat dissipation, metal core circuit boards,
and so on. Of these the most representative is the heatpipe. The heatpipe is a phase change heat transport
device, and because of its outstanding heat-equalizing
properties and high reliability it is used in a wide range ofapplications, from cooling power semiconductors to heatdissipation for small electronic devices. Notebook PCs
are particularly impacted by advances both in smaller
size and in greater CPU heat generation. Thus the needfor heatpipes is increasing most rapidly in products formobile applications 2). In future, it is anticipated that usage
in desktop PCs will increase 3). Since heatpipes are fundamentally heat-equalizing devices, they are generally usedin the form of heatpipe-heatsinks, joined to heat-dissipating fins.
Photo 3 shows a typical Crimped fin® heatsink for cooling the CPU of a desktop PC. Desktop PCs are subject to

Photo 3

Crimped fin® heatsink for desktop PC.

fewer restrictions on power consumption and space thannotebook PCs, with the result that CPU heat generation indesktops is increasing at a faster pace than in notebooks.
In the past CPU heatsinks have been of the aluminum
extrusion type or the soldered type. At present, however,with the quantity of heat generated reaching near 100 W,
it is becoming difficult to satisfy specifications for thermal
resistance with the conventional heatsinks. The Crimped
fins, which Furukawa Electric has recently developed tocope with higher heat generation, constitute a Crimped
fin heatsink in which the fin base and fins are joined bycrimping, achieving a low level of heat resistance that wasdifficult in conventional heatsinks.
Figure 1 shows simulated temperature contours for a
Crimped fin heatsink for a desktop computer. Features of
the Crimped fin heatsink include fins of a slim profile difficult to achieve with the extruded heatsink, and greater
ease in achieving high-density fin arrangement. Anotherfeature is the freedom with which the shape and materials
used for the base and fins can be designed. Accordingly
the aim in this project was to make adjustments tothe shape of the base, thereby achieving compatibility between lighter weight and heat-dissipating properties.
Simulation was also applied in discovering the optimum
base design.
Figure 2 shows the airflow between the fins and fin temperature contours for a Crimped fin heatpipe-heatsink.
We consider that when base width was too great the
airflow from the fan was obstructed by the base and was

Figure 1

Simulated temperature contours for Crimped finheatsink.

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Applications of Computational Thermal Simulation in Product Design

Figure 3
Figure 2

Airflow and fin temperature contours for a Crimped
fin heatpipe-heatsink.

diverted to the outside, so that inadequate air flowed
between the fins and heat resistance increased. When,on the other hand, the base width was too little, the heatfrom the heat source was not adequately transmitted tothe tips of the fins, fin resistance was reduced, and theheat-dissipating characteristics were degraded. We wereable to realize a design in which, by setting the basewidth at an optimum value, the airflow from the fan wasdischarged between the fins unimpeded by the base, sothat heat was adequately transmitted to the tips of the
fins.

Simulated temperature contours for HP-HS in Photo 4.

modular products incorporating heat-dissipating devices.
Here we would like to introduce an example of the useof thermal simulation in designing a laser diode module
used in a wave-division multiplexing (WDM) system, atype of device used in optical fiber communications.
WDM is a method for achieving high-speed transmission by sending optical signals of different wavelengths
simultaneously over a single optical fiber, and at present
is the method in general use on trunk lines and otherlong-haul transmission paths. In order to avoid interference by signals of adjacent wavelength, the carriers
used require the severest wavelength stability. Since thewavelength emitted by the laser diode, which acts as thelight source, is temperature-dependent, a thermoelectriccooler (TEC) must be built into the module to provide
temperature control.
Figure 4 is a schematic showing a laser diode module, in which the diode chip, together with a thermistor,
is mounted on a TEC module for temperature control. In
some cases components may also be mounted to monitor the wavelength of the light emitted by the diode chip.

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Photo 4

Typical heatpipe-heatsink for optical fiber Raman
amplifier.

Photo 4 shows a typical heatpipe-heatsink for an optical fiber Raman amplifier. Figure 3 shows the simulated
temperature contours for the HP-HS for a Raman amplifier shown in Photo 4. By making use of a heatpipe in thisway, we were able to realize a heatsink with a slimmer
profile that in the past, and at the same time cope with
devices generating large amounts of heat.

5.

APPLICATIONS TO MODULARPRODUCTS

Thermal simulation is useful not only in developing heatdissipating devices themselves, but also in designing

Figure 4

Schematic of laser diode module.

Figure 5 shows the result of a simulation of the dependence of TEC power consumption on LD module casetemperature. The heavy dependence of power consumption on case temperature is due to the fact that as casetemperature increases the load on the TEC becomes
greater, resulting in a dramatic increase in TEC power
consumption. Also, if the case temperature exceeds agiven value, it becomes impossible to control diode chiptemperature.
Next, Figure 6 shows the result of a simulation of thedependence of diode chip temperature on case temperature. The fact that chip temperature is dependent oncase temperature despite the use of temperature con-

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Applications of Computational Thermal Simulation in Product Design

tribution inside the case of an optical communication
unit. Accurately measuring this kind of airflow distribution inside equipment with an electronic circuit board ofcomplex configuration and a complicated arrangement ofheatsinks is well nigh impossible, but simulation makes itchild's play to grasp in a moment the flow of air inside theequipment.

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Simulated dependence of TEC power consumption
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Simulated dependence of diode chip temperature oncase temperature.

trol is because of the temperature difference between
the thermistor that measures temperature and the othercomponents. The thermistor itself is always kept at a set
temperature, but the other components are in fact influenced by the ambient temperature. In practical terms it isextremely difficult to measure experimentally the temperatures of components inside such a small module. By contrast the use of thermal simulation makes it easy to calculate the temperature at each part of the module. Also,
when the design is changed, it is possible to examine
quickly and at low cost the way in which the temperatureof each part has changed.

6.

APPLICATIONS TO EQUIPMENTDESIGN

Furukawa Electric offers a range of equipment for telecommunication, including routers, fiber-optic transmission devices, and so on. Every time a model change ismade on such equipment, size becomes smaller andperformance higher, so that devices emitting more andmore heat must be mounted at greater and greater density, requiring countermeasures that become ever moredifficult.
Figure 7 shows an example of simulated airflow dis-

Simulated airflow distribution in opticalcommunication unit.

If the airflow inside the equipment can be understood,
countermeasures can be taken, such as disposing hot
devices where airflow is favorable, selecting the appropriate fans and fins to use, or providing channeling vanes
to control the flow of air. If it were desired to study device
placement by experimenting on actual objects, it would
be necessary to go to the trouble of fabricating circuitboards, and this would take a large amount of time andmoney. But with simulation, changes in device placement
would need only minor corrections of the model, and awide variety of layouts could be tried in a short time.

7.

CONCLUSION

Furukawa Electric has made wide use of computational
simulation in developing its products, and simulation has
already taken its place with experimentation as an indispensable technique. In this report we have introduced
examples of the use of thermal and fluid dynamics simulation of a variety of products in the area of heat.
The advantages of simulation are becoming widely
understood in Furukawa Electric's corporate culture. We
intend to further promote information sharing and technological interchange among different departments, thereby
dealing with the important task of simulation in the development workplace.

REFERENCES
1) Y. Suzuki et al.: Furukawa Electric Review, 106 (2000) 1. (inJapanese)2) M. Ohmi et al.: Furukawa Electric Review, 108 (2001) 11. (inJapanese)
3) T. Shimura et al.: Proc 13th IHPC, 2 (2004) 244.
4) M. Shimada et al.: Heatpipe Technology 20 (2001) 17. (in Japanese)

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