THERMOACOUSTICS Optimisation of the Feedback Loop of the Thermoacoustic Travelling wave Engine David Wee Shuon Tzern Yousif Abdalla Abakr David Hann Paul Riley

The Simplest form of a Travelling Wave Thermoacoustic Engine Regenerator Linear Alternator Tuning Stub Feed Back Loop Limiting amplitude occurs when the amplification of the regenerator is equivalent to the power absorbed by the system Total Power Absorbed = Power absorbed by Linear Alternator + System Losses

Thermoacoustic Engine SCORE -StoveTM Thermoacoustic Engine REQUIREMENT Efficiency Compact INFLUENCING PARAMETER Elbow Bends An understanding of the Acoustic Transmission through bends is required in order to optimise the system

MICROPHONE Decomposition Method Decomposition Transfer Function Scattering Matrix Technique

MICROPHONE Experimental Setup Optimum Travelling wave Load

MICROPHONE Experimental Setup Investigated Bends

Reynolds Number vs. Transmission Loss [%] Legend r = hydraulic cross sectional radius (m) R = Radius of curvature of elbow(m) u = RMS particle velocity (ms-1) c = Speed of sound (ms-1) ω = angular frequency (s-1) ν = kinematic viscousity (m2s-1) Legend r = hydraulic radius (m) R = radius of curvature of elbow(m) u = RMS particle velocity (ms-1) c = speed of sound (ms-1) ω = angular frequency (s-1) ρ = density (kg/m3) ν = kinematic viscousity (m2s-1)

Dean Number vs. Transmission Power Loss [%] Linear Loss Region Non-Linear Loss Region

PIV Experimental Setup PIV=Particle Image Velocimetry

PIV Experimental Setup

PIV Experimental Setup

Dean Number vs. Transmission Power Loss [%] Linear Loss Region Non-Linear Loss Region

Dean Number vs. Transmission Power Loss [%] Linear Loss Region Non-Linear Loss Region At Higher operating Amplitude such as that of the Engine, Losses may go up to 10% or more

CONCLUSIONS A monotonic relationship has been found between the Percentage Acoustic Transmission Loss and the Acoustic Dean Number. A critical Dean Number (≈1) above which the transmission losses increase significantly has been identified. Particle Image Velocimetry is being used to investigate the transition to nonlinearity by consideration of the flow field. Once verified this would prove an important breakthrough in the design of future feedback resonator loop for thermoacoustic systems by providing new information about the additional losses at the elbow bends.

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