PubMed Health⌕ Search

Biomedical subjects

GW Swift

Publications and source records attributed to GW Swift.

6 recordsLinked to original sources
PubMed2000

Thermoacoustic separation of a He-Ar mixture

We report observation of a new mixture-separation process: an insonified mixture of helium and argon in a narrow duct spatially separates along the acoustic-propagation axis. We measure mole-fraction differences across the ends of the duct as large as 7%. We measure initial separation flux densities as high as 10(-3) M2 c, where M is the acoustic Mach number and c is the sound speed. This initial separation flux, as a function of both the amplitudes and the relative phasing of the pressure and velocity oscillations in the duct, agrees well with a recent theory involving oscillating thermal diffusion in the acoustic boundary layer.

Journal Article↗
PubMed2000

A thermoacoustic-Stirling heat engine: detailed study

A new type of thermoacoustic engine based on traveling waves and ideally reversible heat transfer is described. Measurements and analysis of its performance are presented. This new engine outperforms previous thermoacoustic engines, which are based on standing waves and intrinsically irreversible heat transfer, by more than 50%. At its most efficient operating point, it delivers 710 W of acoustic power to its resonator with a thermal efficiency of 0.30, corresponding to 41% of the Carnot efficiency. At its most powerful operating point, it delivers 890 W to its resonator with a thermal efficiency of 0.22. The efficiency of this engine can be degraded by two types of acoustic streaming. These are suppressed by appropriate tapering of crucial surfaces in the engine and by using additional nonlinearity to induce an opposing time-averaged pressure difference. Data are presented which show the nearly complete elimination of the streaming convective heat loads. Analysis of these and other irreversibilities show which components of the engine require further research to achieve higher efficiency. Additionally, these data show that the dynamics and acoustic power flows are well understood, but the details of the streaming suppression and associated heat convection are only qualitatively understood.

Journal Article↗
PubMed2000

The Huygens entrainment phenomenon and thermoacoustic engines

The earliest known reference to the mode-locking, or entrainment, of two maintained oscillators is Christiaan Huygens' description of two pendulum clocks "falling into synchrony" when hung on the same wall. We describe an analogous phenomenon in acoustics-the mode-locking of two thermoacoustic engines which have their cases rigidly welded together, but which are otherwise uncoupled. This "mass-coupling" might compete with acoustic coupling when the latter is used to enforce antiphase mode-locking in such engines, for vibration cancellation. A simple theory relating the phase difference between the engines in the locked state to the corresponding ratio of their pressure amplitudes is in excellent agreement with theory and numerical simulations. The theory's prediction relating the phase difference to the engines' natural frequency difference is qualitatively confirmed by experiment, despite larger experimental uncertainties. The mass coupling is relatively weak compared to the aforementioned acoustic coupling, and in general occurs in antiphase, so we conclude that mass coupling will not interfere with vibration cancellation by acoustic coupling in most circumstances.

Journal Article↗