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e
CFA - Tours 2006
Acoustique
&
Techniques n° 45
evidence in the electronic packaging community that thermal
management – with its focus on system reliability – is evolving
to include energy management issues.
With reference to energy processing, point-of-source thermal
management technologies open avenues for greater efficiency.
By reducing thermal resistance from source to sink, higher
sink temperatures are possible, potentially reducing the
cost associated with removing heat to
the ultimate energy sink – the ambient,
external air. Moreover, the recovery of
energy may even be feasible. Although it
is not anticipated that sink temperatures
would ever be sufficiently high to facilitate
efficient thermodynamic engines, it may
be possible to harness waste energy from
an electronic system in order to drive
the cooling scheme associated with the
system. Solbrekken et al [19] illustrated this
approach for implementation in portable
electronics, using a thermoelectric cell to
drive a cooling fan.
Portable systems are notably constrained
in terms of available space, and it would
appear that energy recovery in larger
scale, fixed electronic systems – in data
centres, for example – could offer large
cost savings. In this regard, point-of-source
thermal management technologies, by
facilitating higher sink temperatures,
may play a key role. For conventional
air cooling, the waste energy stream is
approximately 10-15°C above ambient:
a thermal management solution with low
thermal resistance which increased this
temperature differential to 70°C would
improve the thermodynamic (Carnot)
efficiency from <5% to ~20%, which is
possibly sufficient to contribute to running
a cooling scheme.
Challenges for the Acoustics
Community
Thermal management solutions which
involve active element such as fans and
pumps can generate appreciable levels
of noise. Many applications are subject
to stringent noise regulations – typically,
sound power maxima of 4.5-4.8B and
5.0-5.5B, declared in accordance with
ISO 9296, are stipulated for electronic
equipment with fans in idle and operational
modes respectively. As the power density
of electronic systems increases, it will
become necessary to deploy ever more
aggressive cooling solutions – with higher
speed fans, for example, or multiple fans –
which will generate greater levels of noise.
At present, it is generally the responsibility
of thermal designers to manage acoustic
noise – a task which is typically achieved
through extensive testing of prototypes. It
is evident that there is rich scope for acousticians to contribute
to the application area of thermal management. In this regard,
three challenges can be identified :
Minimisation of acoustic noise
In contemporary electronic systems, the main sources
of acoustic noise are cooling fans and, to a lesser extent,
Fig. 6 : Comparison of heat transfer and hydrodynamic results with literature
Thermal Management of Electronic Systems: Emerging Technologies and Acoustic Challenges
Gestion thermique des systèmes électroniques : Technologies naissantes et défis acoustiques