Low-temperature energy conversion using a phase-change acoustic heat engine

Meir, Avishai; Offner, Avshalom; Ramon, Guy Z.

doi:10.1016/j.apenergy.2018.09.124

Cited by 26 publications

(10 citation statements)

References 22 publications

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“…However, it appears that due to insufficient internal circulation of the finite volume of water in these closed systems, these oscillations could not maintain a limit cycle and naturally shut down shortly after the stability limit was exceeded. A similar standing-wave system with an air-water vapour gas mixture was recently reported by Meir, Offner & Ramon (2018), who demonstrated the first stable operation of a thermoacoustic engine with phase change. This engine was aligned vertically such that condensed water dripped back to the stack by gravity, creating a self-contained water circulation mechanism and successfully maintaining a stable limit cycle.…”

Section: Introductionsupporting

confidence: 57%

“…As a result, a limit cycle was maintained with a hybrid stack consisting of 'dry' and 'wet' sections, each producing acoustic power through different heat transfer mechanisms. Meir et al (2018) measured not only a dramatic decrease in the onset and limit cycle temperature differences (compared with the reference case of dry air as working gas), but also a significant increase in the produced pressure amplitude. While these studies have laid the foundations and illustrated the potential of this form of thermoacoustics, a systematic investigation of the physical mechanisms involved has yet to be performed.…”

Section: Introductionmentioning

confidence: 87%

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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: Introductionsupporting

confidence: 57%

Section: Introductionmentioning

confidence: 87%

Acoustic oscillations driven by boundary mass exchange

et al. 2019

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“…As a result, the thermoacoustic conversion can be enhanced. This effect has been demonstrated in recent studies of phase-change (or wet) thermoacoustic engines and refrigerators [7][8][9][10][11][12][13][14]. Furthermore, it has been predicted that the phase-change thermoacoustic conversion has the potential to increase the energy density of classical thermoacoustic devices by up to one order of magnitude, with an efficiency above 40% of Carnot limit, especially when working under small temperature differences [9,10].…”

Section: Motivation and Significancementioning

confidence: 85%

“…However, after being studied for more than four decades, the room for further improving the performance through traditional pathways, such as improving acoustics, is becoming increasingly narrow, as clearly seen in travelling-wave devices where the achieved acoustic field is becoming close to ideal (i.e., near travelling-wave phase and large acoustic impedance) [3,4]. A promising approach for a breakthrough that significantly improves the performance of thermoacoustic systems is the use of phase-change thermoacoustic conversion [5][6][7][8][9][10]. In phasechange thermoacoustic devices, the working fluid is a mixture consisting of an ''inert'' gas and a ''reactive'' component, which undergoes periodical evaporation and condensation during the oscillation.…”

Section: Motivation and Significancementioning

confidence: 99%

PC-TAS: A design environment for phase-change and classical thermoacoustic systems

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Blanc²,

Vardi-Chouchana³

et al. 2022

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“…More recently, Boroujerdi et al [17] had analytically investigated the influences of stack and thermoacoustic heat engine dimensions as well as charging pressure on both onset temperature and oscillating frequency under different working gases. Furthermore, Meir et al [18] had experimentally and analytically demonstrated that mass transfer can significantly lower the temperature gradient required to achieve acoustic onset in phase-change thermoacoustic heat engines.…”

Section: Introductionmentioning

confidence: 99%