Acoustic Input Power Research Articles

Investigation on a two-stage pulse tube cooler at liquid hydrogen temperature using independent displacer phase shifter

Phase shifter plays an important role in affecting cooling performance of pulse tube cooler (PTC). Warm displacer has been considered a very promising phase shifter due to phase shifting ability and work recovery. Independent displacer phase shifter (IDPS) for two stage PTC is purposed in this paper. Based on a two stage PTC, IDPS and a stepped displacer phase shifter (SDPS) have been comparatively investigated. Firstly, the phase shifting mechanism of two type displacers was studied. Numerical simulation was then conducted to investigated the effect of spring stiffness, moving mass and mechanical damper, and the optimal parameters of SDPS and IDPS were obtained. A cooling power of 1.8 W at 20 K was obtained with 220 W acoustic power input using IDPS, which is 16.9 % higher than that of SDPS. Next, Axial distributions of the phase difference and acoustic power were presented and discussed. In addition, exergy losses in each component were compared. IDPS presented the potential of achieving a higher cooling efficiency at lower temperature stage.

Vortex ultrasound catheter for cerebral intravenous sonothrombolysis

One treatment challenge for cerebral venous sinus thrombosis (CVST) is to achieve recanalization within a short period of time (e.g., 30 min) for significant clinical outcomes. Ultrasound-mediated thrombolysis (sonothrombolysis) presents a promising treatment for venous embolism. In this paper, a miniature vortex ultrasound transducer with frequency of 1.8 MHz was developed for sonothrombolysis. A composite transducer with 2-by-2 sub-aperture piezoelectric elements was assembled into a 9-French catheter to generate a physical helical wavefront. The prototyped vortex ultrasound catheter was characterized by measuring the acoustic pressure amplitude and phases, followed by in-vitro- sonothrombolysis tests. It was found that a vortex ultrasound field can be successfully generated by the prototype. The vortex lytic rate was increased by more than 50% compared with the nonvortex lysis with the same acoustic power input. A long (∼7.5 cm), completely occluded in-vitro- 3D model of acute CVST was fully recanalized within 8 min. The unprecedented sonothrombolysis rate was likely attributed to the vortex ultrasound-induced shear stress, which can effectively disrupt acute blood clots. Furthermore, no vessel wall damage over ex-vivo bovine veins was found after the vortex sonothrombolysis treatment.

Experimental study of acoustic agglomeration coupled with water droplets on eliminating cable fire smoke

Acoustic agglomeration to eliminate fire smoke is one of the most promising technologies at this stage, and we effectively solve technical stumbling blocks such as narrow acoustic frequency range, sound pressure level injury, and long agglomeration time using acoustic waves coupled with water droplets. According to the mechanism and experimental research, acoustic waves coupled with water droplets technology can broaden the optimal agglomeration frequency range, reduce the influence of acoustic power, and effectively improve agglomeration efficiency. Water droplets with a concentration of 40 g/m 3 were added at the acoustic frequency of 1.5 kHz and the acoustic power of 10 W to achieve the safe escape threshold for personnel within 30 s of working while reducing the damage to the human ear caused by the high sound pressure level. • A new method to eliminate fire smoke is proposed. • The addition of water droplets can expand the range of agglomeration frequencies. • 50% reduction in required agglomeration time. • The addition of water droplets can reduce the acoustic power input. • Reduces damage to the human ear from high sound pressure levels.

Influence of frequency and pressure on entropy production characteristics of regenerator at 20 K pulse tube cryocooler

Highly sensitive very long band infrared detectors present the need for 2-stage pulse tube cryocoolers in the 20 K temperature region. The entropy production is closely related to the operating frequency and operating pressure of the cryocoolers, which limits the performance of cryocoolers. The entropy production characteristics with operating frequency at 35∼45 Hz and the operating pressure at 2.4∼3.2 MPa of a two-stage pulse tube cryocooler working at 20 K are studied. Active phase regulation is used to reduce the effect of impedance caused by pressure and frequency in the regenerator. The entropy production characteristics, acoustic power, and axial distribution of energy flow of the cold finger at different operating frequencies and operating pressures are compared theoretically. The results show that at a constant input acoustic power and an operating pressure of 2.8 MPa, the cooling capacity increases and the pre-cooling capacity decreases as the operating frequency decreases. At the operating frequency of 40 Hz, the secondary cooling capacity and the required pre-cooling capacity increased with the increase of operating pressure. Further, an experimental test platform is built to verify the simulation. Experimental phenomena are analyzed and interpreted in terms of the average temperature and impedance characteristics along the axial of the finger. This study provides a reference for the optimization of the entropy production and performance improvement of the regenerator of pulse tube cryocooler, especially the thermally coupled pulse tubes cryocooler working at the liquid hydrogen temperature for high-sensitivity infrared detection.

Development of a 20K two-stage Stirling type pulse tube cryocooler with pre-cooling inside second-stage pulse tube

Cryocoolers working in the liquid hydrogen temperature are important for applications such as cryo-pump, superconductor cooling and cryogenic electronics. This paper analyzes and compares the 20K gas-coupled two-stage Stirling type pulse tube cryocooler with and without pre-cooling. The pre-cooling uses some of the cooling power generated by the first stage cold head to pre-cool the middle of the second stage pulse tube. Given the same input acoustic power, the simulation results show that the cooling capacity of the second stage increase from 0.64 W to 2 W@20 K while the first stage available cooling capacity decrease from 5.84 W to 3 W@77 K when the pre-cooling is used. Meanwhile, the cryocooler relative Carnot Efficiency in terms of acoustic power increases from 10.3% to 14.6%.

A multi-frequency sonochemical reactor utilizing a cylindrically focused acoustic wavefield for improved sonochemical efficiency

Sonochemistry involves several steps. First, an acoustic wave must be generated with sufficient energy to nucleate cavitation. This cavitation event must then be energetic enough to produce radicals through the sonolysis of the gas or vapor molecules in the bubble. Finally, these radical species must survive long enough to react with other chemical species to yield the desired product. The sonochemical efficiency (SE) is thus defined as the ratio of the product yield to the input acoustic power. Here, we put forward a novel approach to enhancing the SE by designing a multi-frequency (0.25 to 1MHz) sonochemical reactor that reflects a cylindrically spreading acoustic wave 180°. The reflected wave converges to cylindrically shaped high-intensity “hot zone” positioned along the axis of the reaction vessel. At modest power input, we detected noise with a passive cavitation detector in air-saturated water, suggesting the direct nucleation of cavitation. Using the Weissler reaction to determine the production of hydroxyl radicals, we determined the SE of our sonochemical reactor at various operation conditions. We also compared these values to conventional bath, horn, and plate sonochemical reactors. The comparison suggested that our reactor design had a better sonochemical efficiency for the Weissler reaction.

Acoustically Driven Sorption Heat Pump

Recent years have seen a dramatic rise in global cooling demand, driven by economic growth and climate change, and resulting in an increasing share of the total electric power consumption. Meanwhile, the ubiquitous vapor-compression air conditioners use refrigerants, which contribute greatly to global emission of greenhouse gases. In order to reduce the strain on electric grids, heat-driven technologies must be developed. Here, an acoustic driven sorption cooling device is examined experimentally and theoretically. The device can potentially utilize heat or electricity as a power input, uses environmentally benign working fluids, and offers simple, reliable construction with little to no moving parts. The results demonstrate the sorption-mediated, time-averaged heat-transfer mechanism, driven by the acoustic field. An unoptimized, proof-of-concept device is operated using a mixture of atmospheric air and either water or methanol, with cordierite and zeolite sorbents. The device is able to achieve temperature differentials $>30{\phantom{\rule{0.1em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. Moreover, a coefficient of performance of approximately 3 (based on the acoustic power input) is achieved at a temperature difference of $10{\phantom{\rule{0.1em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. Theoretical calculations provide an outlook on the operation of such technology, compared with existing cooling technologies, demonstrating its potential for achieving high efficiencies. Finally, prospects for further development are discussed.

Numerical study on a heat-driven piston-coupled multi-stage thermoacoustic-Stirling cooler

This work investigates a novel heat-driven multi-stage thermoacoustic cooler that can satisfy cooling requirements in the applications of natural gas liquefaction and high-temperature superconductivity. The proposed system consists of a compressor, multiple thermoacoustic units (engines and coolers) coupled by piston-cylinder assemblies. The acoustic power input by the compressor is successively multiplied in the thermoacoustic engine units, and the amplified acoustic power is then consumed to produce cooling power in the thermoacoustic cooler units. The proposed system overcomes the limitations of the traditional thermoacoustic systems owing to high efficiency, compact size, and ease of control. Analyses are first performed to explore the influence of the number of stages. The design method of the pistons is presented based on acoustic impedance matching principle.Based on the optimized system, simulations are then conducted to investigate the axial distribution of the key parameters, which can explain the reason for improved thermodynamic performance. At heating and cooling temperatures of 873 K and 130 K, the system achieves a cooling power of 2.1 kW and a thermal-to-cooling relative Carnot efficiency of 23%. This represents significant increases by over 60% in efficiency and 80% in cooling capacity when compared to existing systems. Simulations further demonstrate how controlling the input acoustic power and frequency via the compressor enables control of the system under various conditions. Further discussions are made considering a potential combined cooling and power system, indicating an overall thermal-cooling-electricity efficiency of 34% without any external electric power required for the compressor.

Calculating the Effect of Ribs on the Focus Quality of a Therapeutic Spherical Random Phased Array.

The overlaying rib cage is a major hindrance in treating liver tumors with high intensity focused ultrasound (HIFU). The problems caused are overheating of the ribs due to its high ultrasonic absorption capability and degradation of the ultrasound intensity distribution in the target plane. In this work, a correction method based on binarized apodization and geometric ray tracing approach was employed to avoid heating the ribs. A detailed calculation of the intensity distribution in the focus plane was undertaken to quantify and avoid the effect on HIFU beam generated by a 1-MHz 256-element random phased array after the ultrasonic beam passes through the rib cage. Focusing through the ribs was simulated for 18 different idealized ribs-array configurations and 10 anatomically correct ribs-array configurations, to show the effect of width of the ribs, intercostal spacing and the relative position of ribs and array on the quality of focus, and to identify the positions that are more effective for HIFU applications in the presence of ribs. Acoustic simulations showed that for a single focus without beam steering and for the same total acoustic power, the peak intensity at the target varies from a minimum of 211 W/cm2 to a maximum of 293 W/cm2 for a nominal acoustic input power of 15 W, whereas the side lobe level varies from 0.07 Ipeak to 0.28 Ipeak and the separation between the main lobe and side lobes varies from 2.5 mm to 6.3 mm, depending on the relative positioning of the array and ribs and the beam alignment. An increase in the side lobe level was observed by increasing the distance between the array and the ribs. The parameters of focus splitting and the deterioration of focus quality caused by the ultrasonic propagation through the ribs were quantified in various possible different clinical scenarios. In addition to idealized rib topology, anatomical realistic ribs were used to determine the focus quality of the HIFU beam when the beam is steered both in axial and transverse directions and when the transducer is positioned at different depths from the rib cage.

KIERUNKI ROZWOJU I BADAŃ TERMOAKUSTYCZNYCH URZĄDZEŃ CHŁODNICZYCH Z FALĄ STOJĄCĄ

Chłodzenie termoakustyczne to perspektywiczna technologia, która wykorzystuje energię fali akustycznej do transportu ciepła z ośrodka o niskiej do ośrodka o wysokiej temperaturze. Do głównych zalet tej technologii zalicza się dużą niezawodność, prostą konstrukcję urządzeń, a przede wszystkim brak szkodliwych dla środowiska czynników chłodniczych. Z drugiej strony wadą tej technologii jest relatywnie niska sprawność w porównaniu do współczesnych rozwiązań konwencjonalnych. Głównie z tej przyczyny urządzenia termoakustyczne wciąż pozostają w fazie szerokich badań mających na celu poprawę ich wydajności. W artykule tym przedstawiono kierunki obecnie prowadzanych prac. Uwagę zwrócono zwłaszcza na badania eksperymentalne z zakresu wyboru optymalnych parametrów konstrukcyjnych i eksploatacyjnych termoakustycznych urządzeń chłodniczych z falą stojącą. Omówiono również budowę oraz podstawową zasadę działania takich urządzeń.

Theoretical modeling and experimental verifications of the single-compressor-driven three-stage Stirling-type pulse tube cryocooler

This paper establishes a theoretical model of the single-compressor-driven (SCD) three-stage Stirling-type pulse tube cryocooler (SPTC) and conducts experimental verifications. The main differences between the SCD type and the multi-compressor-driven (MCD) crycooler are analyzed, such as the distribution of the input acoustic power in each stage and the optimization of the operating parameters, in which both advantages and difficulties of the former are stressed. The effects of the dynamic temperatures are considered to improve the accuracy of the simulation at very low temperatures, and a specific simulation example aiming at 10 K is given in which quantitative analyses are provided. A SCD three-stage SPTC is developed based on the theoretical analyses and with a total input acoustic power of 371.58 W, which reaches a no-load temperature of 8.82 K and can simultaneously achieve the cooling capacities of 2.4 Wat 70 K, 0.17 W at 25 K, and 0.05 W at 10 K. The performance of the SCD three-stage SPTC is slightly poorer than that of its MCD counterpart developed in the same laboratory, but the advantages of lightweight and compactness make the former more attractive to practical applications.

Theoretical and experimental study of a gas-coupled two-stage pulse tube cooler with stepped warm displacer as the phase shifter

A compact and high efficiency cooler working at liquid hydrogen temperature has many important applications such as cooling superconductors and mid-infrared sensors. This paper presents a two-stage gas-coupled pulse tube cooler system with a completely co-axial configuration. A stepped warm displacer, working as the phase shifter for both stages, has been studied theoretically and experimentally in this paper. Comparisons with the traditional phase shifter (double inlet) are also made. Compared with the double inlet type, the stepped warm displacer has the advantages of recovering the expansion work from the pulse tube hot end (especially from the first stage) and easily realizing an appropriate phase relationship between the pressure wave and volume flow rate at the pulse tube hot end. Experiments are then carried out to investigate the performance. The pressure ratio at the compression space is maintained at 1.37, for the double inlet type, the system obtains 1.1 W cooling power at 20 K with 390 W acoustic power input and the relative Carnot efficiency is only 3.85%; while for the stepped warm displacer type, the system obtains 1.06 W cooling power at 20 K with only 224 W acoustic power input and the relative Carnot efficiency can reach 6.5%.

Analysis of a displacer-coupled multi-stage thermoacoustic-Stirling engine

A new thermoacoustic-Stirling engine is introduced, composed of a compressor, regenerative assemblies, displacers and an alternator. The regenerative assemblies are coupled to displacers to successively multiply the acoustic power input by the compressor. The amplified acoustic power is converted into electric power in the alternator. This new configuration overcomes the limitations of traditional thermoacoustic or Stirling engines, including losses in long resonant tubes, response hysteresis and current inversion. The design method of the displacers and alternators is presented. Numerical simulations are carried out to investigate the characteristics of this system. Results show that the overall efficiency of this system could reach 47% with heating temperature of 900 K. Changing alternator load is the most plausible factor in piston or displacer exceeding the displacement limit. These parts can be effectively protected as long as the voltage of the compressor can be instantaneously adjusted. The working frequency, charging pressure and mechanical resistance do not substantially influence the efficiency and power capacity, when varied within a limited range. This allows the proposed engine to work stably when these parameters deviate from the design.

Performance analysis of the thermoacoustic refrigerator with the standing wave and air as a working fluid

Thermoacoustic refrigerator is a new and emerging technology capable of transporting heat from a low-temperature source to a high-temperature source by utilizing the acoustic power input. These devices, operating without hazardous refrigerants and owning no moving components, show advantages of high reliability and environmental friendliness. However, simple to fabricate, the designing of thermoacoustic refrigerators is very challenging. This paper illustrates the impact of significant factors on the performance of the thermoacoustic refrigerator which was measured in terms of the temperature difference generated across the stack ends. The experimental device driven by a commercial loudspeaker and air at atmospheric pressure as a working fluid was examined under various resonator length and operating frequencies. The results indicate that appropriate resonator’s length and operating frequency lead to an increase in the temperature difference created across the stack. The maximum values were achieved for operating frequency equalled to 200 and 300 Hz whereas resonator length corresponded to the half-length of the acoustic wave for these frequencies. The results of experiment also confirm that relationship between these parameters is strongly affected by the stack spacing, which in this research was equalled to 0.4 mm.

Numerical and experimental study of an annular pulse tube used in the pulse tube cooler

Multi-stage pulse tube coolers normally use a U-type configuration. For compactness, it is attractive to build a completely co-axial multi-stage pulse tube cooler. In this way, an annular shape pulse tube is inevitable. Although there are a few reports about previous annular pulse tubes, a detailed study and comparison with a circular pulse tube is lacking. In this paper, a numeric model based on CFD software is carried out to compare the annular pulse tube and circular pulse tube used in a single stage in-line type pulse tube cooler with about 10 W of cooling power at 77 K. The length and cross sectional area of the two pulse tubes are kept the same. Simulation results show that the enthalpy flow in the annular pulse tube is lower by 1.6 W (about 11% of the enthalpy flow) compared to that in circular pulse tube. Flow and temperature distribution characteristics are also analyzed in detail. Experiments are then conducted for comparison with an in-line type pulse tube cooler. With the same acoustic power input, the pulse tube cooler with a circular pulse tube obtains 7.88 W of cooling power at 77 K, while using an annular pulse tube leads to a cooling power of 7.01 W, a decrease of 0.9 W (11.4%) on the cooling performance. The study sets the basis for building a completely co-axial two-stage pulse tube cooler.

Investigation on a Three-Stage Stirling-Type Pulse Tube Cryocooler for Cooling the Low-T $_c$ SQUID

This paper presents the design and performance improvement of a three-stage Stirling-type pulse tube cryocooler (SPTC) aimed to achieve effective cooling at 4.2 K for the low- T $_c$ superconducting quantum interference device (SQUID). The system integration of the three-stage SPTC and the low- T $_c$ SQUID is described, and the cryocooler is arranged with the thermally coupled configuration. A developed electrical circuit analogy model is proposed to analyze the internal operating mechanisms of the three-stage SPTC. In addition, a three-stage thermally coupled SPTC is simulated and fabricated. The performance of each stage is tested individually. The first-stage SPTC can achieve 15.67 W at 80 K. A no-load cooling temperature of 17.4 K can be obtained by the two-stage SPTC with a total input acoustic power of 424.0 W. Under the precooling of the first two stages of SPTC, the simulated results indicate that the third-stage SPTC can acquire 6.35 mW at 4.2 K when the input acoustic power is 49.5 W, and the displacement of the cold end turns out to be 1.45 μm from peak to peak.

Cochlear Outer-Hair-Cell Power Generation and Viscous Fluid Loss.

Since the discovery of otoacoustic emissions and outer hair cell (OHC) motility, the fundamental question of whether the cochlea produces mechanical power remains controversial. In the present work, direct calculations are performed on power loss due to fluid viscosity and power generated by the OHCs. A three-dimensional box model of the mouse cochlea is used with a feed-forward/feed-backward approximation representing the organ of Corti cytoarchitecture. The model is fit to in vivo basilar membrane motion with one free parameter for the OHCs. The calculations predict that the total power output from the three rows of OHCs can be over three orders of magnitude greater than the acoustic input power at 10 dB sound pressure level (SPL). While previous work shows that the power gain, or the negative damping, diminishes with intensity, we show explicitly based on our model that OHC power output increases and saturates with SPL. The total OHC power output is about 2 pW at 80 dB SPL, with a maximum of about 10 fW per OHC.

Acoustic separation of milk fat globules—Principles in large scale processing

The acoustic manipulation of particulates in standing wave fields is a well-established technique, with the fundamental theory describing the acoustic radiation forces first reported in 1934 by King. To date, there are few demonstrations of the technique on a volume-scale relevant to industrial application, due to difficulties in scaling the acoustic radiation forces over large distances. Other issues such as the onset of acoustic streaming with high acoustic power input may also impact upon the effectiveness of separation in large systems by disrupting the collection of particulates in the pressure nodal/antinodal regions. In recent work, we have demonstrated the capability of ultrasonic standing waves applied in a liter-scale vessel to concentrate and/or remove fat globules from whole milk with volume throughputs up to 30 L/h. By tuning parameters according to acoustic fundamentals, the technique can be used to specifically select milk fat globules of different sizes in the collected fractions. We report key design and operation principles at large scale using milk as a model system, which has potential to be applied to particulate fluids of biomedical relevance such as blood and lipids.

Ultrasonic processing for recovery of chicken erythrocyte hemoglobin

Hemoglobin from chicken blood has been shown to be a good substitute for synthetic polymeric flocculants. One stage of processing the blood entails lysis of the cells to release the hemoglobin; in the present study, the use of ultrasonic processing at this stage is investigated. Washed chicken blood cells are suspended in buffer and run continuously through a chamber attached to an ultrasonic probe. Calorimetry is used to measure acoustic power input to the liquid. Ultrasonic cell lysis is tested using chamber residence times of 75–300ms, and the equipment's entire range of power inputs. The hemoglobin release kinetic parameters are determined and it is shown that above a particular level, increasing power input can actually result in a decreased rate constant. Ultrasonic processing can damage proteins, so reduction of hemoglobin's flocculant activity is considered. Using a sensitive assay involving suspensions of kaolin clay, no effect of ultrasonic processing on hemoglobin flocculant activity is detected. Although the conversion of electrical power to acoustic power is inefficient, the electric power required to release greater than 90% of the hemoglobin is shown to be minimal.

The effects of liquid height/volume, initial concentration of reactant and acoustic power on sonochemical oxidation

Even though much knowledge on acoustic cavitation and its application has been accumulated over the past decades, further research is still required to develop industrial uses of acoustic cavitation. It is because the available information is mainly based on small-scale sonoreactors and the design and optimization of sonoreactors for large-scale applications have not been widely studied. In this study, the effects of liquid height/volume, initial concentration of the reactant and input acoustic power on sonochemical oxidation reactions including iodide ion oxidation, As(III) oxidation, and hydrogen peroxide generation were investigated using a 291kHz sonoreactor with various liquid height/volumes (50, 100, 200, 300, 500, and 1000mL) and input powers (23, 40, and 82W). As the liquid height/volume and the input power changed, the power density varied from 23 to 1640W/L and the maximum cavitation yields of triiodide ion for 23, 40, and 82W were observed at 0.05, 0.1, and 0.2/0.3L, respectively. It was found that low power was more effective for the small volume and the large volume required high power level and the moderate power density, approximately 400W/L, was suggested for the sonochemical oxidation of iodide ion in the 291kHz sonoreactor in this study. Similar results were observed in the generation of hydrogen peroxide and the sonochemical oxidation of As(III) to As(V). It was also revealed that KI dosimetry could be applicable for the estimation of the sonochemical reactions of non-volatile compounds such as As(III).