NICK JEFFERS BA. BAI.
PhD Research Postgraduate (2006-2009)

e: nick.jeffers@ul.ie

t: +353-61-202471

Nick Jeffers graduated from the Trinity College Dublin in 2006 with a first class honours degree in Mechanical Engineering. He has been awarded a postgraduate scholarship to study at Stokes, funded under Enterprise Ireland's Industry-Led Research Programme in Power Electronics.

PhD Project Title: An Investigation of Microscale Heat Transfer Phenomena

Background: Thermal control of electronic systems is imperative in order to ensure specified levels of performance and reliability. The choice of cooling technique depends on a range of factors: heat dissipation; heat flux; ambient temperature; maximum component temperatures; space and weight restrictions; acoustic noise limitations; maintenance requirements; and cost. For systems with moderate heat dissipation, fan-driven forced convection air cooling is the technology most commonly deployed in practice. Conventional forced air cooling offers a number of advantages: readily available cooling medium; ease of implementation and packaging; low cost; and relatively low maintenance requirements. There are a number of disadvantages, however – convective heat transfer coefficients only of order 102 W/m2°C; space requirements for airflow and heat sinks; acoustic noise generation; and the limited reliability of fans. Although there has been recent discussion about extending the limits of air cooling, it is clear that the adaptation of liquid cooling is imminent for many high power applications due to increasing heat flux levels at die, package and substrate.

The objective of the research project is to design and optimise primary and secondary heat exchangers for the liquid cooling of electronic systems. A range of primary heat exchangers will be considered: a card-level cold plate for multiple component cooling; a substrate-level cooler for mounting to Printed Circuit Boards (PCBs); and microchannel structures for package-level cooling. For the secondary heat exchanger, an aluminium chassis is proposed, with micro-scale channels for liquid-side transfer, and the application of a fan-sink for energy transfer to ambient. Established analytical techniques for heat exchanger design will be employed, in conjunction with the application of simulation (Fluent and Flotherm) to determine the heat transfer, hydrodynamic and aerodynamic characteristics of the elements of the exchangers. A range of test vehicles will be fabricated and instrumented for the measurement of pressure drop and heat transfer characteristics. These characteristics will then be expressed in terms of entropy generation rate – the common currency of lost work – in order to facilitate thermodynamic optimisation. The anticipated outcome of the research will be an optimised heat exchange system for the liquid cooling of electronics, with a fundamental understanding of its operation.

Publications to date

Jeffers, N., Punch, J. and Walsh, E., 2007, “An Experimental Characterisation of Miniature Scale Cold Plates for Electronics Cooling Applications”, submitted to the ASME-JSME Thermal Engineering and Summer Heat Transfer Conference, HT2007-321537, Vancouver, BC, Canada, July 8-12.