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Conclusion
Power dissipation data clearly points toward increasing thermal loads for
telecommunication and information technology systems. This rise is occurring
because the drive toward higher system throughput with decreased cabinet footprint
is stronger than the drive toward reduced power consumption. As these heat loads
rise, there will be a corresponding increase in acoustic noise emission. The
design trend data indicates that noise emission is likely to rise by 1-2 bels
(10-20 dB) over the next five-to-ten yeaqs.
Given the proliferation of desktop workstations, it is also
important to note that fans in these systems control the background noise levels
in many office environments. While people have grown accustomed to this added
noise, the negative effects of fan noise will likely become more apparent as
hands-free desktop conferencing becomes more widespread. Very little noise research
has been done on small cooling fans since they are low-margin commodity items.
However, it is clear that the conventional techniques will
soon be inadequate. While active control may seem at first to be a promising
solution, there are several technical and financial problems that may be impossible
hurdles [11]. So, new approaches to noise reduction will probably come from
radical changes in cabinet design unless a concerted effort is made to initiate
research on the basic understanding of the noise generation mechanisms in small
air-moving devices [12].
The above discussion assumes that systems will continue to be predominantly
cooled using forced-convection. Despite the fact that other thermal management
technologies exist, forced-air cooling will remain the predominant technique because
it is relatively cheap, highly reliable and designers are well versed in its use.
However, given the dissipation trends in chip design, it is clear that hybrid
designs that couple forced convection system cooling with "local" cooling
of high dissipation chips will become more common. It may be that local cooling
technologies such as spray cooling, jet impingement, heat pipes, thermoelectric
cooling, and liquid cooling may finally see more widespread use.
Acknowledgments
Many people within Lucent and other organizations have been kind enough to
provide assistance during the preparation of this paper. The author is grateful
for their input and cooperation.
D.A. Quinlan
Bell Laboratories
Lucent Technologies Inc.
101 Crawfords Corner Way, Rm 1H-511
Holmdel, NJ 07733-3030, USA
Tel.: 732-332-5386
Fax: 732-949-8797
Email:
dbq@lucent.com
References
1 G.C. Maling, "Historical developments in the control of noise generated
by small air-moving devices,"
Noise Control Engineering Journal 42(5),
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3 ETSI ETS 300 753, "Equipment Engineering (EE): Acoustic noise
emitted by telecommunications equipment."
4 Statskontoret Technical Standard 26:2, "Noise of computer and business
equipment."
5 U.S. Occupational Safety and Health Administration (O.S.H.A.) 29 CFR
1910.95 (CFR=Code of Federal Regulations).
6 C.J.M. Lasance, "The need for a change in thermal design
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12 D. Quinlan and P. Bent, "High frequency noise generation
in small axial flow fans," Journal of Sound and Vibration (in press -
1998)
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