Novel photonics cooling for next-generation optical telecommunication systems


Unsteady flows are often exploited to enhance heat removal in single-phase cooling systems by disrupting the hydrodynamic and thermal boundary layers, the near-wall gradients and the overall thermal resistance to heat transfer. However, an understanding of the explicit conditions that deliver heat transfer enhancement has yet to be achieved. This owes in part to a high variability in a large parameter space, that contains a variety of flows with complex boundary conditions and geometric dissimilarities, including for example developing flows in short minichannel heat sinks, and pulsating and synthetic jets. Furthermore, heat transfer studies have often chased time- and space-averaged heat transfer enhancement, while convective heat transfer is often unsteady and spatially non-uniform. Hence, the problem should be characterised on a space- and time-dependent basis in order to exploit any potential for heat transfer optimisation.

In a collaboration between the Fluids and Heat Transfer Research Group of Trinity College Dublin and the Thermal Management Research Group of Bell Labs Ireland, Richard Blythman, Tim Persoons, Nick Jeffers, Kevin Nolan and Darina Murray have employed a bottom-up approach to investigate the local time-dependent coupling of the velocity and temperature fields for the simple case of a rectangular channel geometry and fully-developed sinusoidally-pulsating flow using complementary analytical, experimental and numerical techniques. Since the thermal problem is intrinsically dependent on the hydrodynamic problem, the first in a series of articles analyses the decoupled unsteady velocity profile and its derivatives to understand the underlying physical mechanisms that may effect a change in heat transfer. Their research work is published in the International Journal of Heat and Fluid Flow.

The study analyses the velocity profiles and wall shear stresses for a wide range of actuation frequencies (up to Womersley number Wo = 7.0) using particle image velocimetry (PIV) measurements. The experimental data are in excellent agreement with the values predicted by the analytical solution, which is conveniently reorganised in terms of amplitude and phase values. Hence, these measurements constitute the first verification of the analytical theory for a pulsating flow in a rectangular channel geometry. Furthermore, the local instantaneous amplification of wall shear stress with respect to steady flow is presented as a key thermal indicator to be coupled with future wall heat flux measurements. It is found that the local amplitude and phase alterations of the wall shear stress parameters are caused by the evolving interplay of viscous and inertial effects with frequency.

Although more research is needed for this cooling technology to reach full maturity, these new insights may form the basis of a novel adaptive thermal management strategy for next-generation photonics integrated circuits for high-speed telecommunication systems.

Novel photonics cooling for next-generation optical telecommunication systems:. Advances in Engineering

About the author

Richard Blythman received his Bachelor’s degree in Mechanical Engineering from Trinity College Dublin, with his thesis focusing on the fatigue of wind turbine blades due to vortex-induced vibration. In 2013, he was awarded an Irish Research Council scholarship to pursue his Doctorate, under an industrial partnership with the Thermal Management Research Group of Nokia Bell Labs. His research work focused primarily on enhancing and optimising cooling in the next generation of Photonics Integrated Circuits (PICs), although he collaborated with a number of researchers on other projects ranging from triggering localised cooling in microchannels using viscoelastic fluids to measuring simulated heartbeat pulsations with a new wearable sensor technology. He is currently working in product development for a company in the high-performance start-up (HPSU) program of Enterprise Ireland. He also works as a freelance machine learning developer, on projects focusing on predicting stresses in metals using a novel micromagnetic sensor and identifying dangerous rugby tackles from video footage.

Richard is fundamentally interested in the coupling of unsteady heat and fluid flow on a local time-dependent basis. In order to characterise the underlying physical mechanisms, he has developed an analytical model using novel mathematical solutions to the momentum and energy equations in a rectangular channel, and experimentally imaged pulsating flows using the Particle Image Velocimetry (PIV) and Infrared Thermography (IRT) measurement techniques. To date, Richard has authored 7 peer-reviewed journal articles and conference publications, and co-supervised 4 Master’s level students.

Further information at: Linkedin, Researchgate, Googlescholar 

About the author

Dr. ir. Tim Persoons was appointed Assistant Professor in Engineering in the Department of Mechanical & Manufacturing Engineering at TCD in 2013. He has been a visiting Faculty member in the NSF I/UCRC Cooling Technologies Research Center (CTRC) at Purdue University, West Lafayette IN, USA since 2009, and was Visiting Assistant Professor in the Department of Mechanical Engineering, KU Leuven, Belgium during 2009-2010. Tim received his Doctorate in Engineering at KU Leuven in 2006 and his MSc in Mechanical Engineering at KU Leuven in 1999. He was awarded an Irish Research Council (IRC) Postdoctoral Fellowship in 2008, an IRC/Marie Curie INSPIRE International Mobility Fellowship in 2010, and appointed Senior Research Fellow in TCD in 2012. Tim was a co-recipient of the 2013 Hartnett-Irvine Award from the International Centre for Heat and Mass Transfer.

Dr. Persoons’ research activities include multi-scale convective heat transfer in electronics thermal management using unsteady flows, active flow control for sustainable energy technologies, and developing experimental thermal fluid measurement techniques. He is currently supervising 3 PhD students and 4 postdoctoral researchers in TCD, and has graduated 4 PhD students. He has managed research projects totalling over €1.5 Mio from sources including Irish Research Council, Science Foundation Ireland, Enterprise Ireland, FP7 Marie Curie Actions, National Science Foundation, Naughton Foundation, IWT Vlaanderen, Nokia Bell Labs and other industry partners.

Tim has authored over 100 peer-reviewed journal articles, conference publications, keynote and invited lectures. His publications have attracted more than 800 citations (h-index 15). He is a member of the THERMINIC scientific committee, and he has served in editorial roles for Journal of Electronic Packaging (2009-2010) and IEEE Transactions on Components, Packaging and Manufacturing Technology (Special Topics on Data Center Cooling, 2016-2017). He has co-organized several technical-scientific workshops (e.g., THERMINIC-2009, PowerMEMS-2010) and the Workshops on Thermal Management in Telecom Systems and Data Centers (2010, 2012, 2015) in collaboration with CTRC.

More information on Linkedin, Google Scholar, Mendeley, Researchgate .

About the author

Nick Jeffers is a Senior Member of Technical Staff at Nokia Bell Labs. He received a degree in Mechanical Engineering from Trinity College Dublin, Ireland in 2006, and subsequently achieved his PhD from the University of Limerick, Ireland in 2009 in the area of submerged liquid jets for enhanced electronics cooling. He was awarded a post-doctoral research fellowship to continue his research in fluid mechanics and heat transfer at Trinity College Dublin. Nick joined Nokia Bell Labs in 2011 as a Member of Technical Staff and was promoted to Senior Member of Technical Staff in 2014.

He has wide-ranging research interests in the analysis of macro and micro scale mechanical engineering phenomena with particular emphasis on thermal/energy management. Currently he leads multiple high impact projects that he hopes will solve future human challenges. Nick collaborates extensively in the local ecosystem and has supervised 4 completed PhDs and currently supervises 2 PhDs and 2 Post Docs. He has authored and co-authored 16 journal publications, 3 granted patent, 23 patents pending, and 22 peer reviewed conference publications. His work has been recognized by numerous awards and prizes throughout his career.

About the author

Kevin graduated from the University of Limerick with a First Class Honors Degree in Aeronautical Engineering in 2004. Subsequently he undertook a Ph.D in experimental fluid dynamics at the Stokes Institute. Late nights in the Wind Tunnel Lab imbued Kevin with a deep love of photography and image analysis. After completing a Post Doc at the Stokes Institute Kevin was all set to continue begin a Marie Curie in Imperial College London. However Eyjafjallajökull delayed proceedings and he was head hunted to develop optics and software solutions for next generation qPCR at biomedical startup Stokes Bio. After an eventful and productive time at Stokes Bio, which was sold to a large multinational during his time there, Kevin was able to finally jump the pond to London where he spent two years working on extremely large Direct Numerical Simulation (DNS) databases.

Currently he works in Bell Labs Ireland with the Thermal Group. His primary interests are microfluidics, viscoelastic flows and imaging techniques such as Particle Image Velocimetry and Schlieren imaging. He is currently working on sub-critical flow instabilities of viscoelastic flows in microchannels for local heat transfer enhancement. One of his more interesting side projects is the development of a plenoptic Schlieren system. Kevin has published extensively in the Journal of Fluid Mechanics on topics related to structure identification in fluid flows from both experimental and numerical data sets. He is working with students in UL on transition control, in Trinity College on bubble dynamics in two phase flows and his colleagues at Bell Labs on vortex generators and state of the art air movers where his expertise in fluid structure identification is invaluable.

About the author

Professor Darina Murray is a Professor in Mechanical Engineering at Trinity College Dublin. She graduated from University College Dublin with Bachelor’s and Master’s degrees in Mechanical Engineering in 1981 and 1983 respectively. She worked in the electricity supply industry for 2 years before joined the academic staff of Trinity College, where in 1989 she completed her doctorate on the subject of gas-particle heat transfer in cross flow. Professor Murray has led many research projects on topics such as two-phase flow and heat transfer, convective heat transfer measurements, compact heat exchangers, and heat transfer characteristics of exhaust gas sensors, with in excess of €3m funding from Europe, Science Foundation Ireland, Irish Research Council and industry partners such as Nokia Bell Labs.

She is the author of around 160 publications in refereed journals and international conference proceedings. She has served on the scientific committees of 8 international conferences and has refereed papers for 14 international journals. She is the Irish representative on the EU Eurotherm committee, which promotes and fosters European co-operation in thermal sciences and heat transfer. She was made a Fellow of Trinity College in 1996.
The core focus of her research work is the characterisation of convective heat transfer in single and two phase flows, which is core to thermal energy conversion processes as well as to the cooling of electronics systems and manufacturing processes. This is achieved mainly through the use of coupled local and time-resolved heat transfer and fluid flow measurements, using techniques such as hot film anemometry, infrared thermography, high speed imaging and particle image velocimetry. Her current research interests include impinging jet flow and heat transfer, natural convection and heat transfer enhancement in bubbly flows.

More information on Google Scholar, Researchgate 


R. Blythman, T. Persoons, N Jeffers, K.P. Nolan, D.B. Murray. Localised dynamics of laminar pulsatile flow in a rectangular channel. International Journal of Heat and Fluid Flow, Volume 66 (2017), Pages 8–17.


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