Standing Wave Systems Research Articles

The effect of operating conditions on heat transfer for parallel plate heat exchangers of thermoacoustic standing wave systems

Thermoacoustic systems represent a promising technology for clean cooling and/or power generation. However, understanding of the behavior of oscillatory flow inside the system under high drive ratio operating conditions, at elevated mean pressures, range of frequencies, and high flow amplitudes, remains limited and poses challenges for designing efficient systems with minimal losses. This paper presents a numerical investigation into the flow and heat transfer characteristics across a coupled cold and hot parallel-plate heat exchanger operating under standing-wave type oscillatory flow conditions. The models were developed for various conditions, spanning frequencies from 13 Hz to 100 Hz and mean pressures between 1 and 20 bar, using both nitrogen and helium as working fluids. The study reveals significant phenomena such as heat accumulation and annular effects in both temperature and velocity/vorticity fields. These findings were discussed in the context of their impact on the heat transfer performance of the heat exchanger. Specifically, the emergence of vortices was examined in relation to mean pressure, alongside jet-like velocity profiles and natural convection effects. Furthermore, the paper includes a comparative analysis between the heat transfer model employed in this study and previous works, aiming to validate the findings. This research enhances the understanding of fluid dynamics and heat transfer phenomena within heat exchangers of thermoacoustic devices, thereby contributing to advancements in future design improvements.

Source Properties and Resonance Characteristics of the Tsunami Generated by the 2021 M 8.2 Alaska Earthquake

AbstractA tsunami was triggered in the North Pacific Ocean by the 2021 Alaska earthquake (M 8.2) on July 29. We studied the source properties and resonance characteristics of the tsunami event using observed records from offshore tsunameters and coastal tide gauges as well as numerical simulation. Spectral analyses were conducted on records at tsunameters and tide gauges. We reconstructed the tsunami source spectrum by calculating the ratio of tsunami spectra to the background spectra of these stations. Based on the source spectrum, we estimated the source size of the 2021 Alaska earthquake to be 332 km (length) 256 km (width), which was generally consistent with the source model proposed by the United States Geological Survey using seismological approaches. In addition, we also performed spectral analyses of the tsunami wavefield in a region of interest, including the Aleutian Islands and the Alaska Peninsula. Standing wave systems were found south of the Alaska Peninsula and the Aleutian Islands. The Aleutian Islands prevent the propagation of tsunami oscillations. Only a small portion of energy propagates through the archipelago from the main part of the Pacific Ocean to the Bering Sea.

Optimization of Ultrasonic Acoustic Standing Wave Systems

Ultrasonic acoustic standing wave systems find use in many industrial applications, such as sonochemical reactions, atomization of liquids, ultrasonic cleaning, and spray dry. In most applications, highest possible sound pressure levels are needed to achieve optimum results. Until now, the atomization of liquids is limited to fluids with low viscosity, as systems generating sufficient sound pressure for atomizing fluids with higher viscosities are often not marketable due to their low throughput or high costs. For the production of polymer or metal powders or the dispensing of adhesives, highest sound pressures should be achieved with systems in suitable size, with good efficiency and at low cost but without contamination of sonotrodes and reflectors by the dispersed media. An alternative to the use of more powerful transducers is increasing the intensity of the acoustic standing wave field by optimizing the boundary conditions of the acoustic field. In most existing standing wave systems a part of the radiating sound waves does not contribute to the process, as the waves spread into the wrong direction or wipe themselves out due to interference. In order to obtain maximum sound pressure amplitudes in the standing wave field, all waves should be trapped between the sonotrode and the reflector. In addition, the resonance condition should be met for all radiated waves. These conditions can be fulfilled by optimizing the shapes of sonotrode and resonator as well as the distance between them. This contribution reports on a model, which is able to simulate the sound field between a transducer surface and a reflector. Using a linear finite-element model, the boundary conditions of the standing wave system are optimized. Sound pressure levels of the standing wave field are calculated for different shapes of reflectors and boundary conditions like the distance between the transducer and the reflector. The simulation results are validated by sound-field measurements via refracto-vibrometry and a microphone. Finally, optimization guidelines for the generation of high-intensity acoustic standing wave fields are shown and verified by measurements.

Generation of functional hepatocyte 3D discoids in an acoustofluidic bioreactor.

Ultrasonic standing wave systems have previously been used for the generation of 3D constructs for a range of cell types. In the present study, we cultured cells from the human hepatoma Huh7 cell line in a Bulk Acoustic Wave field and studied their viability, their functions, and their response to the anti-cancer drug, 5 Fluorouracil (5FU). We found that cells grown in the acoustofluidic bioreactor (AFB) expressed no reduction in viability up to 6 h of exposure compared to those cultured in a conventional 2D system. In addition, constructs created in the AFB and subsequently cultured outside of it had improved functionality including higher albumin and urea production than 2D or pellet cultures. The viability of Huh7 cells grown in the ultrasound field to 5FU anti-cancer drug was comparable to that of cells cultured in the 2D system, showing rapid diffusion into the aggregate core. We have shown that AFB formed 3D cell constructs have improved functionality over the conventional 2D monolayer and could be a promising model for anti-cancer drug testing.

Resonance control of acoustic focusing systems through an environmental reference table and impedance spectroscopy.

Acoustic standing waves can precisely focus flowing particles or cells into tightly positioned streams for interrogation or downstream separations. The efficiency of an acoustic standing wave device is dependent upon operating at a resonance frequency. Small changes in a system’s temperature and sample salinity can shift the device’s resonance condition, leading to poor focusing. Practical implementation of an acoustic standing wave system requires an automated resonance control system to adjust the standing wave frequency in response to environmental changes. Here we have developed a rigorous approach for quantifying the optimal acoustic focusing frequency at any given environmental condition. We have demonstrated our approach across a wide range of temperature and salinity conditions to provide a robust characterization of how the optimal acoustic focusing resonance frequency shifts across these conditions. To generalize these results, two microfluidic bulk acoustic standing wave systems (a steel capillary and an etched silicon wafer) were examined. Models of these temperature and salinity effects suggest that it is the speed of sound within the liquid sample that dominates the resonance frequency shift. Using these results, a simple reference table can be generated to predict the optimal resonance condition as a function of temperature and salinity. Additionally, we show that there is a local impedance minimum associated with the optimal system resonance. The integration of the environmental results for coarse frequency tuning followed by a local impedance characterization for fine frequency adjustments, yields a highly accurate method of resonance control. Such an approach works across a wide range of environmental conditions, is easy to automate, and could have a significant impact across a wide range of microfluidic acoustic standing wave systems.

Tidal stream resource characterisation in progressive versus standing wave systems

Characterisations of the tidal stream resource and its variability over various timescales are crucial for the development of the tidal stream energy industry. To date, no research has compared resource sensitivity in standing wave (when peak currents occur midway between high and low water) and progressive wave (where peak currents occur at high and low water) tidal systems. Here, we compare the flow regimes of standing wave versus progressive wave systems and the associated variations in tidal stream power with applications to device deployment options (floating-platform turbines versus bottom-mounted turbines). We use a validated 3D numerical model (ROMS) of a globally-significant tidal energy shelf sea region (Irish Sea), to test the hypotheses that the influence on potential extractable energy, and suitability for different devices, may be markedly different between these contrasting systems. Power density was also calculated and compared for floating versus bottom-mounted devices using in-situ current data (ADCPs) obtained from a standing wave site and a progressive wave site. We show that progressive wave systems are characterised by velocity-asymmetry over a tidal cycle (i.e. stronger peak flows at high water than at low water), leading to power-asymmetry. Such power asymmetry was shown to have more of an effect on floating device technology, where an assumed turbine depth tracks the sea surface, in contrast to bottom-mounted technology, where the hub height is fixed at a certain position above the sea bed. Shallow, high-flow regions where tidal range is large contained up to 2.5% more power density from bottom-mounted compared with floating turbines; however, there were areas where floating devices were exposed to higher mean currents over a tidal cycle. Standing wave systems, where flow asymmetry is minimised, did not particularly favour either technology. The results highlight the requirement for detailed resource assessments to consider the vertical plane, and are applicable to all potential tidal stream energy sites.

Cavitation and non-cavitation regime for large-scale ultrasonic standing wave particle separation systems – In situ gentle cavitation threshold determination and free radical related oxidation

We here suggest a novel and straightforward approach for liter-scale ultrasound particle manipulation standing wave systems to guide system design in terms of frequency and acoustic power for operating in either cavitation or non-cavitation regimes for ultrasound standing wave systems, using the sonochemiluminescent chemical luminol. We show that this method offers a simple way of in situ determination of the cavitation threshold for selected separation vessel geometry. Since the pressure field is system specific the cavitation threshold is system specific (for the threshold parameter range). In this study we discuss cavitation effects and also measure one implication of cavitation for the application of milk fat separation, the degree of milk fat lipid oxidation by headspace volatile measurements. For the evaluated vessel, 2MHz as opposed to 1MHz operation enabled operation in non-cavitation or low cavitation conditions as measured by the luminol intensity threshold method. In all cases the lipid oxidation derived volatiles were below the human sensory detection level. Ultrasound treatment did not significantly influence the oxidative changes in milk for either 1MHz (dose of 46kJ/L and 464kJ/L) or 2MHz (dose of 37kJ/L and 373kJ/L) operation.

Enhanced creaming of milk fat globules in milk emulsions by the application of ultrasound and detection by means of optical methods

The effects of application of ultrasonic waves to recombined milk emulsions (3.5% fat, 7% total solids) and raw milk on fat destabilization and creaming were examined. Coarse and fine recombined emulsions ( D[4, 3] = 9.3 μm and 2.7 μm, respectively) and raw milk ( D[4, 3] = 4.9 μm) were subjected to ultrasound for 5 min at 35 °C and 400 kHz or 1.6 MHz (using a single transducer) or 400 kHz (where the emulsion was sandwiched between two transducers). Creaming, as calculated from Turbiscan measurements, was more evident in the coarse recombined emulsion and raw milk compared to that of the recombined fine emulsion. Micrographs confirmed that there was flocculation and coalescence in creamed layer of emulsion. Coalescence was confirmed by particle size measurement. These results imply that ultrasound has potential to pre-dispose fat particles in milk emulsions to creaming in standing wave systems and in systems with inhomogeneous sound distributions.

Oscillatory soil response and liquefaction in an unsaturated layered seabed

AbstractThe subject of wave‐induced soil response in a real seabed has attracted the attention of geotechnical and coastal engineers over the last three decades, for which several basic theories have been developed. However, the evaluation of soil liquefaction has not been attempted theoretically in a seabed with multiple sub‐layers, in which homogeneity in soil properties can be assumed within each layer. In this study, a semi‐analytical approach is presented for obtaining solutions for the pore pressure and effective stresses in a non‐cohesive layered seabed of finite thickness subject to a system of three‐dimensional waves. Based on the numerical results for a layered seabed, influences of soil characteristics (relative layer thickness, permeability ratio and shear modulus) on seabed responses are described. Special attention is given to the effect of placing a coarser material as a top layer for protecting an underlayer of finer sediment. Although only a three‐layered seabed is explicitly solved in this study, the procedure outlined can readily be extended to a multi‐layered soil system. The three‐dimensional solutions can also be applied to the two‐dimensional progressive or standing wave systems.

Experimental study of a thermoacoustic termination of a traveling-wave tube

Much of the recent experimental work in thermoacoustics has concentrated on standing wave systems. A recent analysis of traveling-wave thermoacoustics [J. Acoust. Soc. Am. 94, 2232–2239 (1993)] prompted an experimental study. The measurements presented herein confirm theoretical predictions that the work done on a traveling wave is thermoacoustic in nature and not due to a Stirling cycle. Experimental response curves are given for two different terminations and compared to theory. The thermoacoustic effect provides a modest change in the reflected and transmitted amplitudes.

The proton enigma

It is suggested that the proton and neutron magnetic moments can be calculated by a theory involving a standing wave systems centered on the proton. (AIP)

Nonlocal structures: Bilocal photon

As a starting point, it is postulated that all particles and fields are built from a single primitive field, which must then be a massless fermion with a σ spin of one-half. Two helicities are embodied in a τ spin of one-half. The vacuum is an open Fermi sea whose height is a wave number κ. Elementary particles are structures having the form of standing-wave systems floating on the vacuum sea, with the height κ providing both the scale of inner structural size and the mass unit for the elementary particle mass spectrum. A bilocal photon starts with a function describing two primitive quanta with parallel σ spin and opposite τ spin. A centroid-time wave equation then couples-in an infinite set of orthogonal functions. The introduction of an operatorQλ permits the reduction of the infinite secular determinant to a finite six-by-six determinant. Solutions (for the infinite expansion) are obtained describing photons with right-handed and left-handed polarizations. Superpositions of these give linearly polarized photons. Electric and magnetic field vectors, satisfying the vacuum Maxwell equations, are obtained from a bilocal Hertz vector given by п= (2/κ3c)(∂/∂tr)∇rΨ(1,2), where Ψ(1,2) is the bilocal wave function, and tr and r are the relative time and relative position variables.

Analysis of resonance standing-wave measurements

Linear and nonlinear numerical techniques for fitting measurements on resonant standing-wave systems to theoretical resonance formulas are described. The fits are correct for background and enable the normal-mode frequencies and widths to be precisely determined.

Determination du profil spectral d'une raie en emission stimulee a partir de phenomenes d'ondes stationnaires de duree faible (30 nanosecondes)

A wave-train of finite length emitted by a ruby laser, produces standing wave systems in a Fabry-Pérot cavity. The Fourier transform of its modulation function yields an approach to the shape of the spectral distribution. Results are given for various energies of the optical pump, from the threshold, showing the evolution of the spectrum.

Production and Detection of Solitary Macroscopic Quantized Vortices in Helium II

Ultrasonic cavitation was induced in liquid helium using plane and cylindrical standing-wave systems resonant at 89 and 53 kc/sec, respectively. The threshold voltage for cavitation noise was measured at different rotation rates of a shaft, with and without an attached paddle, rotating in the vicinity of the sound field. Below the $\ensuremath{\lambda}$ point the threshold was found to be lowered sharply at a critical rotation rate ${\ensuremath{\omega}}_{c}$. The experiments were repeated with five different shaft sizes, and ${\ensuremath{\omega}}_{c}$ was found to be inversely proportional to ${r}^{2}$, where $r$ is the radius of the shaft. The constant of proportionality was found to be $\frac{\ensuremath{\hbar}}{m}$, where $m$ is the mass of one helium atom. Further, smaller threshold reductions were observed at rotation rates of $2{\ensuremath{\omega}}_{c}$, with the largest shaft sizes. These results are consistent with the theory of quantized vortex formation and appear to indicate that such vortices play a role in the cavitation nucleation process.

Large signal bunching of electron beams by standing-wave and traveling-wave systems

Large signal bunching processes in the presence of space charge are studied by extending techniques used to compute multi-cavity klystron bunching. Bunching capability of traveling-wave and standing-wave systems is examined by using an assumed spatial and time distribution of electric field, and interesting high degrees of bunching are predicted.

METHODS AND MEANS FOR DETERMINING THE NATURAL MODES OF VIBRATION OF MECHANICAL STRUCTURES

Cyclic strains in vibrating mechanical structures often lead to failures because of the resulting fatigue of the material. Both theory and practice indicate that the breaks or other types of failure occur at a node of one of the numerous natural modes of vibration of the structure. These natural modes of vibration can be determined theoretically if the structure is simple and the parts are of geometrical form but usually the problem is too complicated for exact solution and the best that can be hoped for from theory is a rough approximation of the resonant frequencies and a still rougher approximation of the location of the nodes of the vibrating system. The present paper describes a simple method and means for experimentally determining the several natural resonant frequencies of any mechanical system and the location of the nodes of their respective standing wave systems. Its effectiveness is demonstrated by analyzing three modes of vibration of a ship's propeller.