Gareth J. Bennett, John Mahon, Darina Murray, Tim Persoons, Ian Davis, Heat Transfer Enhancement In Ducts Due To Acoustic Excitation, 7th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics (ExHFT-7), Kraków, Poland, 28/06 - 03/07, 2009, 2009, 10
The thermoacoustic effect that results from the interaction of a sound wave in a
compressible fluid in contact with solid boundaries is known to be capable of removing heat from
power dissipating systems. In this paper the standing wave acoustic field that is generated in an open
ended duct, a section of which is heated, and how it interacts with the aerodynamic flow field is
examined by an experimental study. Specifically, the effect the fluctuating acoustic pressure and
associated particle velocity have on the internal fluid dynamics is investigated. The ultimate goal is
to fully understand and optimize the interaction mechanisms in order to enhance the overall convective
heat transfer from a heated duct to internal flow. An experimental rig which has been designed and
built allows the fundamental fluid dynamic, acoustic and heat transfer mechanisms to be studied.
The rig consists of a circular duct with a central copper isothermally heated section which is
instrumented with thermocouples, a heat flux sensor, microphones and a cross-wire probe. The
cross wire is used to measure both time varying temperature and velocity at a high frequency and
spatial resolution and a calibration procedure which allows the sensor to measure fluctuating
velocity at elevated temperatures is reported. Results from the current investigation demonstrate
how convective heat transfer from the heated duct section to the internal flow is enhanced due to
acoustic excitation. In this preliminary, investigative study, it is suggested that two different heat
transfer mechanisms are identified: one associated with the increased turbulent mixing due to the
added particle velocity; the second associated with acoustic streaming. The results show significant
increases in flow temperature and heat transfer coefficients for free and forced convection regimes.
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