Specific acoustic impedance measurements of an air-filled thermoacoustic prime mover

Arnott, W. P.; Bass, Henry E.; Raspet, Richard

doi:10.1121/1.404167

Cited by 9 publications

(2 citation statements)

References 6 publications

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“…We now examine different gas mixture compositions and how their properties affect the temperature difference required for onset. The inert gas in the mixtures is either air or helium, two commonly used gases in thermoacoustic systems (Arnott, Bass & Raspet 1992;Swift 1992). The reactive gases selected for this comparison are water, ethanol and methanol, all used as condensable vapours that undergo Curves are plotted against: (a) the Womersley number, τ ν ≡ h(ω/ν) 1/2 , where the stack cold-side temperature is T c = 20 • C, and (b) the averaged concentration of the reactive gas in the stack, C m , for τ ν = 2.5. evaporation/condensation.…”

Section: Effects Of Mixture Compositionmentioning

confidence: 99%

Acoustic oscillations driven by boundary mass exchange

et al. 2019

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Thermoacoustic instability – self-sustained pressure oscillations triggered by temperature gradients – has become an increasingly studied topic in the context of energy conversion. Generally, the process relies on conductive heat transfer between a solid and the fluid in which the generated pressure oscillations are sustained. In the present study, the thermoacoustic theory is extended to include mass transfer; specifically, the working fluid is modified so as to incorporate a ‘reactive’ gas, able to exchange phase with a solid/liquid boundary through a sorption process (or through evaporation/condensation), such that most heat is transferred in the form of latent heat rather than through conduction. A set of differential equations is derived, accounting for phase-exchange heat and mass transfer, and de-coupled via a small-amplitude asymptotic expansion. These equations are solved and subsequently manipulated into the form of a wave equation, representing the small perturbation on the pressure field, and used to derive expressions for the time-averaged, second-order heat and mass fluxes. A stability analysis is performed on the wave equation, from which the marginal stability curve is calculated in terms of the temperature difference, $\unicode[STIX]{x0394}T_{onset}$, required for initiation of self-sustained oscillations. Calculated stability curves are compared with published experimental results, showing good agreement. Effects of gas mixture composition are studied, indicating that a lower heat capacity of the inert component, combined with a low boiling temperature and high latent heat of the reactive component substantially lower $\unicode[STIX]{x0394}T_{onset}$. Furthermore, an increase in the average mole fraction of the reactive gas, $C_{m}$ strongly affects onset conditions, leading to $\unicode[STIX]{x0394}T_{onset}\sim 5\,^{\circ }\text{C}$ at the highest value of $C_{m}$ achievable under atmospheric pressure. An analysis of the system limit cycle is performed for a wide range of parameters, indicating a systematic decrease in the temperature difference capable of sustaining the limit cycle, as well as a significant distortion of the acoustic wave form as the phase-exchange mechanism becomes dominant. These findings, combined, reveal the underlying mechanisms by which a phase-exchange engine may produce more acoustic power than its counterpart ‘classical’ thermoacoustic system, while its temperature difference is substantially lower.

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Section: Effects Of Mixture Compositionmentioning

confidence: 99%

Acoustic oscillations driven by boundary mass exchange

et al. 2019

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“…In a subsequent paper, Arnott et al measured the changes in impedance of a thermoacoustic stack as the temperature gradient was varied. 8 Significant, measurable changes in the impedance occurred for a 20-K change in temperature across a 4.0-cm-long porous stack.…”

Section: Introductionmentioning

confidence: 99%

Estimation of temperature gradient effects on the normalized surface impedance of soils

Raspet

Sabatier

Arnott

1997

The Journal of the Acoustical Society of America

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Ground impedance measurements are used for sound propagation predictions and to determine soil properties. Solar heating of the ground leads to significant temperature swings and gradients in the near surface soil. The equations of thermoacoustics are applied to estimate the magnitude of the temperature effects on the impedance and develop an approximate equation for the adjustment of measured impedance. Ambient temperature effects are shown to be significant; temperature gradient effects in soils are negligible. The theory is applicable to noise control applications where larger gradients may occur in sound absorbing materials.

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Experimental Verification of Stability Characteristics for Thermal Acoustic Oscillations in a Liquid Helium System

Timmerhaus

1994

Advances in Cryogenic Engineering

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Specific acoustic impedance measurements of an air-filled thermoacoustic prime mover

Cited by 9 publications

References 6 publications

Acoustic oscillations driven by boundary mass exchange

Acoustic oscillations driven by boundary mass exchange

Estimation of temperature gradient effects on the normalized surface impedance of soils

Experimental Verification of Stability Characteristics for Thermal Acoustic Oscillations in a Liquid Helium System

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