Active tuning of acoustic oscillations in a thermoacoustic power generator G. Poignand, C. Olivier, G. Penelet, P. Lotton Laboratoire d'Acoustique de l'Université du Maine, UMR CNRS 6613 Avenue Olivier Messiaen, 72085 LE MANS Cedex 9, France 1
Thermoacoustic engines Thermoacoustic engines : autonomous oscillators, heat input Qh acoustic power Wac Onset of a self sustained acoustic wave (at the frequency of the most unstable mode) controlled by linear effects Saturation controlled by nonlinear effects: acoustic power dissipation or temperature/acoustic field modification Qc Qh Wac 2
Thermoacoustic engines Thermoacoustic engines : autonomous oscillators, heat input Qh acoustic power Wac Onset of a self sustained acoustic wave (at the frequency of the most unstable mode) controlled by linear effects Saturation controlled by nonlinear effects: acoustic power dissipation or temperature/acoustic field modification Problem : nonlinear effects = complicated processes, not fully described Gedeon streaming minor losses Thermoacoustic heat pump Rayleigh streaming nonlinear propagation 3
Thermoacoustic engines Thermoacoustic engines : autonomous oscillators, heat input Qh acoustic power Wac Onset of a self sustained acoustic wave (at the frequency of the most unstable mode) controlled by linear effects Above threshold, saturation controlled by nonlinear effects: acoustic power dissipation or temperature/acoustic field modification Problem : nonlinear effects = complicated Common solution : use of passive elements processes, not fully described (semi-empirically designed) Gedeon streaming membrane minor losses jet pump Rayleigh streaming tapered tube nonlinear propagation shaped resonator 4
Thermoacoustic engines Thermoacoustic engines : autonomous oscillators, heat input Qh acoustic power Wac Onset of a self sustained acoustic wave (at the frequency of the most unstable mode) controlled by linear effects Saturation controlled by nonlinear effects: acoustic power dissipation or temperature/acoustic field modification New approach : active control method to Problem : nonlinear effects = complicated processes, not fully described control the acoustic field → external forcing of the self sustained wave Gedeon streaming minor losses Rayleigh streaming nonlinear propagation Auxiliary source 5
Thermoacoustic engines Thermoacoustic engines : autonomous oscillators, heat input Qh acoustic power Wac Onset of a self sustained acoustic wave (at the frequency of the most unstable mode) controlled by linear effects Saturation controlled by nonlinear effects: acoustic power dissipation or temperature/acoustic field modification New approach : active control method Problem : nonlinear effects = complicated processes, not fully described → external forcing of the self sustained wave to control the acoustic field Gedeon streaming Microphone G minor losses Rayleigh streaming φ nonlinear propagation Auxiliary source Auxiliaire source 6
Active tuning of acoustic oscillations in a thermo- acoustic power generator 1. Experimental setup 2. Experimental results 2.1 External auxiliary source 1 2.2 Internal auxiliary source Microphone G φ Microphone G Auxiliary source φ Auxiliary source [1] C. Olivier, G. Penelet, G. Poignand and P. Lotton . « Active control of thermoacoustic amplification in a thermo-acousto- 7 electric engine », Journal of Applied Physics, vol. 115 [17], 2014.
Thermoacoustic power generator Thermoacoustic core: 1.12 m Ambiant heat exchanger electrodynamic loudspeaker Regenerator Monacor SPH 170C Hot heat exchanger Thermal buffer tube Ambiant heat exchanger 1.73 m 0.25 m designed with Delta-Ec [W.C. Ward, G.W. Swift & J.P. Clark, J. Acoust. Soc. Am., 123(5) (2008)] Fluid : air Frequency: 40 Hz Static pressure : 5 Bars Onset condition: Qh = 60 W, ΔT = 401 K Ambient temperature : 295 K η max = 1 %, Pel max = 1W Low efficiency: engine = study model (modular, limited budget, low efficiency alternator) but designed to work closed to its maximum value. 8
Travelling wave thermoacoustic engine part Hot heat exchanger Cold heat exchanger Regenerator Ceramic stack with two ribbon Copper block with 2 mm Stainless steel wire mesh diameter drilled holes. Porosity: 69 % heaters Water circulates around the Hydraulic radius: 20 μm Length: 1.5 cm block. Length: 2.3 cm Qh max = 235 W (Rribbon = 4.7 Ω) Porosity: 69 % Length: 1.5 cm 9
Active control method Electro-acoustic feedback loop microphone G audio amplifier electrical power generated, W el dissipated in a resistor heat input , Qh φ phase-shifter electric power supplied, Wls additional power produced Input parameters: heat input Qh , gain G and the phase φ Measured parameters: W el W el (G=0) + ∆ W el Efficiency without auxiliary source η Ø = and with active control : η = Qh Qh+Wls Temperature difference without auxiliary source ΔT Ø and with active control ΔT η < η Ø ? Objective : play on input parameters (Qh, G, φ) Δ W el > Wls ? 10
Active tuning of acoustic oscillations in a thermo- acoustic power generator 1. Experimental setup 2. Experimental results 2.1 External auxiliary source 1 2.2 Internal auxiliary source Microphone G φ Microphone G Auxiliary source φ Auxiliary source [1] C. Olivier, G. Penelet, G. Poignand and P. Lotton . « Active control of thermoacoustic amplification in a thermo-acousto- 11 electric engine », Journal of Applied Physics, vol. 115 [17], 2014.
Efficiency η versus φ for different G Qh = 70 W, G = 0 ( - ),20 (+), 30 (*), 32 (o) or 100( ◊ ), without active control (--) with the phase φ : - η varies optimal phase φ opt - acoustic wave death when the gain G ↗ : - η ↗ and ΔT ↘ nonlinear interaction ? 12
Wls and Wel versus G for φ = φ opt Qh = 70 W (o), without active control (--) ∆Wel (o) additional power produced Wls ( • ) power supllied to AC source For low Qh : - η increases with the gain G - configurations for which ∆ W el > W LS W el (G=0)+∆ W el NB: η = Qh+Wls 13
Wls and Wel versus G for φ = φ opt Qh = 140 W ( ), without active control (--) ∆Wel ( ) additional power produced Wls ( ) power supllied to AC source NB: η = For higher Qh : - efficiency improvement saturates - configurations for which ∆ W el > W LS W el (G=0)+∆ W el NB: η = Qh+Wls 14
Active tuning of acoustic oscillations in a thermo- acoustic power generator 1. Experimental setup 2. Experimental results 2.1 External auxiliary source 1 2.2 Internal auxiliary source Microphone G φ Microphone G Auxiliary source φ Auxiliary source [1] C. Olivier, G. Penelet, G. Poignand and P. Lotton . « Active control of thermoacoustic amplification in a thermo-acousto- 15 electric engine », Journal of Applied Physics, vol. 115 [17], 2014.
Efficiency η versus φ for different G Qh = 70 W, G = 0 ( - ), 10 (-), 40 ( ◊ ◊ ), 70 ( + ) , 135 ( ) or 190( o ), without active control (--) Same results than for the first configuration : - optimal phase φ opt (varies with the gain) - acoustic wave death for high G : - η > η Ø , ΔT > ΔT Ø 16
Wls and Wel versus G for φ = φ opt Qh = 70 W (o), 100W ( ), without active control (..) ∆Wel ( ,o) additional power produced Wls ( , • ) power supllied to AC source efficiency improvement saturates configurations for which ∆ W el > W LS W el (G=0)+∆ W el NB: η = Qh+Wls 17
Hysteresis behaviour Method : 1. Search onset condition, Qh ↗ 2. Above onset : Efficiency measurement when Qh ↗ and then Qh 3. Search offset condition Steady-state measurements φ = φ opt , G = 0 ( - ) without active control (..) For G = 0, ΔT onset > ΔT Ø onset and η < η Ø 18
Hysteresis behaviour φ = φ opt , G = 0 ( - ), 40 ( ◊ ◊ ) without active control (..) For G = 0, ΔT onset > ΔT Ø onset and η < η Ø For G ≠ 0, hysteresis behaviour: ΔT offset < ΔT onset , system works for Qh < Qh onset 19
Hysteresis behaviour Qh = 70 W, G = 0 ( - ), 40 ( ◊ φ = φ opt , G = 0 ( - ), 40 ( ◊ ◊ ◊ ), 70 ( + ) , 135 ( ) or 190( o ), ), 70 ( + ) , 135 ( ) without active control (..) without active control (..) For G = 0, ΔT onset > ΔT Ø onset and η < η Ø For G ≠ 0, hysteresis behaviour: ΔT offset < ΔT onset , system works for Qh < Qh onset With the gain G , ΔT offset ↘, ΔT onset < ΔT Ø onset , η > η Ø 20
Conclusions Active control Active control works : Efficiency improvement: efficiency η higher than the one without active control η Ø Lower onset temperature: onset temperature ΔT onset lower than the one without active control ΔT Ø onset hysteresis behaviour : offset temperature ΔT offset lower than onset temperature ΔT onset But why ? simplified model to get better comprehension 21
Perspectives Active control with two phase-tuned sources: already performed on an annular thermoacoustic engine [1] [1] C. Desjouy, G. Penelet, and P. Lotton «Active control of thermoacoustic amplification in an annular engine», Journal of Applied Physics, vol. 108, n° 11, 2010. Active control applied on a high power thermoacoustic engine (currently being built) 0.90 m Fluid : helium Static pressure : 22 Bars Heat input : 1000 W Efficiency (theoretical): 20 % alternator: Electric power: 200 W 0.34 m Qdrive 1S 132D 22
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