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HEAT TRANSFER ENHANCEMENT DUE TO ACOUSTIC EXCITATION
Presented by Ross Tuite
Supervisors: Dr. Gareth BennettProf. Darina Murray
Introduction and Background
SituationEuropean electronics industry – €45bn, 177,000 jobs
Transistor density doubling every two years
Introduction and Background
SituationEuropean electronics industry – €45bn, 177,000 jobs
Transistor density doubling every two years
ProblemHeating exceeds Cooling Heat Transfer Bottleneck
Fans required to remove heat Added noise
Introduction and Background
SituationEuropean electronics industry – €45bn, 177,000 jobs
Transistor density doubling every two years
ProblemHeating exceeds Cooling Heat Transfer Bottleneck
Fans required to remove heat Added noise
SolutionConstructive use of fan noise
Heat transfer enhancement using thermo-acoustic effect
Thermo-acoustic Effect
Classical ApproachPhase-lock sound wave with thermal input (Rijke tube)Generation of high-amplitude sound energy
Thermo-acoustic Effect
Classical ApproachPhase-lock sound wave with thermal input (Rijke tube)Generation of high-amplitude sound energy
Current ApproachSuperposition of acoustic field on turbulent flow
Increased mixing in the flow increased heat transfer
Thermo-acoustic Effect
Classical ApproachPhase-lock sound wave with thermal input (Rijke tube)Generation of high-amplitude sound energy
Current ApproachSuperposition of acoustic field on turbulent flow
Increased mixing in the flow increased heat transferTwo Mechanisms Observed:Added particle velocity (acoustic fluctuations) and mixing
Thermo-acoustic Effect
Classical ApproachPhase-lock sound wave with thermal input (Rijke tube)Generation of high-amplitude sound energy
Current ApproachSuperposition of acoustic field on turbulent flow
Increased mixing in the flow increased heat transferTwo Mechanisms Observed:Added particle velocity (acoustic fluctuations) and mixingAcoustic streaming at high amplitudes
Acoustic StreamingMean Velocity Fluctuating Velocity
• Increased local mean and fluctuating velocity
• Increased velocity = increased heat transfer
Investigation and Main Aims
Novel Approach:• Examine physics of process• Understand and optimise effect
Investigation and Main Aims
Novel Approach:• Examine physics of process• Understand and optimise effectNovel testing conditions:• Turbulent flow• Low acoustic amplitude• Open-ended duct
Rig and Set-upSchematic of Rig Hydrodynamic/ Acoustic Fields
Acoustic Theory
Introduction of Standing Waves
63Hz and 167Hz:Maximum pressure, zero velocity
113Hz and 223Hz:Zero pressuremaximum velocity
Rig and Set-up
Upper Duct Section
Lower Duct Section
Cross-Wire and Hot-Film Anemometry
Cross-Wire Hot-Film / Thermocouple
Flow temperature/ velocity Surface temperature/ heat flux
Rig and Set-up
PMMA duct held vertically between fan and speaker1. Flow temperature (Tm) – Cold-wire2. Surface temperature (Ts) – Thermocouple3. Surface Heat Flux (q’’) – Hot-filmAll measurements taken along same planeHeat transfer at surface:
Newton’s Law of cooling
Experimental Procedure
Cross-wire Measurements Stepper Motor
• Axial mid-point• 15 Temperature and
velocity measurements• Four resonant
frequencies at each point
Temperature ResultsFree Convection Forced Convection
Acoustic Amplitude: 91dB
Ts =
80°
C
Ts =
61.
4°C
Velocity ResultsMean Velocity Fluctuating Velocity
Flow Velocity: 2 m/s
Heat Flux ResultsFree Convection Forced Convection
Surface Temperature ResultsFree Convection Forced Convection
Phase 1 2 3 4 5 6 7
Frequency (Hz) - 63Hz 113Hz - 167Hz 223Hz -
Conclusion
• Heat transfer enhancement for turbulent flow• Added particle velocity at low amplitude• Acoustic oscillations increase mixing• Signs of acoustic streaming
Further Study
• Removal of Speaker• Heat Transfer Enhancement using fan BPF
(noisier fan)• Evanescent waves below cut-off frequency• Cooling effect without acoustic penalty• Possible small-scale applications
Questions?
