Pressure Amplitude Research Articles

Investigation on flame propagation and end-gas auto-ignition of ammonia/hydrogen in a full-field-visualized rapid compression machine

Ammonia-hydrogen engine has attracted much attention due to its carbon-free nature. Given that ammonia has high knock resistance (indicated by its high research octane number of nearly 130), researchers are trying to increase the compression ratio (CR) to improve engines’ thermal efficiency. However, knocking cycles can still be detected in ammonia-hydrogen engines under elevated thermodynamic conditions. To further explore the ammonia-hydrogen knocking process, this study conducted a series of spark-ignition combustion experiments focusing on flame propagation and end-gas auto-ignition in a full-field-visualized rapid compression machine. Four ammonia-hydrogen blended fuels with hydrogen energy fractions of 0 % (H0), 10 % (H10), 20 % (H20), and 100 % (H100) were comparatively tested under the thermodynamic conditions of 30 bar and 750–985 K. The experimental results showed that the flame speed of H0, H10, and H20 is around 3–6 m/s under test conditions, much lower than that of H100, which exceeds 37 m/s at 30 bar/750 K. Strong end-gas auto-ignitions with maximum pressure amplitudes of 77 bar and 101 bar were recorded for H0 at 30 bar/985 K and H10 at 30 bar/915 K, respectively. The two auto-ignition events both exhibited detonation characteristics by clear wavefronts with speeds reaching up to 1620 m/s (H0) and 1812 m/s (H10). Based on the experimental results, simulations were carried out to analyze the chemical process during the end-gas auto-ignition. The simulated results showed that for H0 at 30 bar/985 K, the NO-, NO2-, and H2NO-related reactions contributed most to heat production, which improved the end-gas reactivity and promoted the occurrence of auto-ignition. For H10 at 30 bar/915 K, the H + O2 (+M) = HO2 (+M) became the most exothermic reaction, indicating the hydrogen addition significantly promoted the ammonia's end-gas auto-ignition. Additionally, the detonation events observed in this study can be well classified in the ε -ξdiagram.

NUMERICAL THREE-DIMENSIONAL MODEL OF ULTRASONIC COAGULATION OF AEROSOL PARTICLES IN VORTEX ACOUSTIC STREAMING

Separation of highly dispersed systems with huge liquid-gas or liquid-solid interfaces is relevant for practical tasks of gas purification from the most highly dispersed and difficult-to-detect dispersed fraction PM2.5, and separation of nanoparticles (including their small agglomerates) in fine chemical technology processes. One of the most effective ways to separate highly dispersed systems with a large interface surface is to combine each of the closed subsurfaces (surfaces of individual dispersed particles) under the influence of hydrodynamic effects in the gas phase, arising both near the interface surfaces and at a considerable distance from them, due to the superposition of ultrasonic vibrations. Since the efficiency of ultrasonic coagulation decreases with a large distance between closed subsurfaces from each other in PM2.5 aerosol and the small size of these surfaces, it is necessary to create conditions for the emergence of new nonlinear effects that contribute to the local compaction of the dispersed fraction. In a resonant and significantly inhomogeneous ultrasonic field (with a scale of inhomogeneity on the order of the wavelength), vortex acoustic flows arise, which, due to inertial forces, locally compact the dispersed phase in the form of an increase in the concentration of aerosol particles. A numerical model of ultrasonic coagulation of PM2.5 aerosol particles in three-dimensional (3D) vortex acoustic streaming is proposed in this paper. The model is designed to identify the possibility of increasing the efficiency of ultrasonic coagulation in 3D streaming by virtue of the following mechanisms: (1) local increase in concentration caused by the inertial transfer of particles to the periphery of 3D vortices in the gas phase; (2) increase in the frequency of particle collisions due to 3D turbulent disturbances in ultrasonic fields; and (3) increase in productivity and ensuring uninterrupted implementation of the process in a flow mode owing to transfer of particles between the streamlines of the main vortices initiated by ultrasonic vibrations. The listed mechanisms for increasing the efficiency of coagulation in 3D streaming are taken into consideration by introducing two stream functions, considering turbulent chaotic disturbances of the flow resulting in dispersion of particle velocities. It was possible to establish based on numerical analysis of the model using the example of PM2.5 that laminar vortex flows begin to influence at sound pressure level from 160-165 dB, and turbulent disturbances make an additional contribution in the range of sound pressure levels from 140-170 dB. At the same time, as a result of 3D turbulent disturbances, the efficiency of coagulation reaches almost 100% at a sound pressure level 5 dB lower than with laminar flows (sound pressure amplitude, 3 times lower).

Investigation of Two-Way Fluid-Structure Interaction of Blood Flow at Different Temperature using CFD

At this work, fluid-structure interaction was used to biomechanical challenges relating to blood flow in artery bifurcation to investigate potential solutions. The purpose of this study was to evaluate the influence that artery geometry has under constant flow, pulsatile flow, and varied blood temperatures. In this study, the flow of blood through the artery was simulated using a non-Newtonian fluid model, and the finite element technique was utilized to analyse the data. For the purpose of analysing the differences between pulsatile flow and steady flow, a user-defined function, or UDF, was developed as part of the suggested input velocity model. In order to accurately estimate the pressure distribution, velocity flow, wall shear stress, and wall deformation, a simulation called ANSYS 17.2 is used to model the fluid-structure interaction that occurs when blood flow is superimposed on an arterial wall. According to the findings, the pressure amplitude steadily increases in the artery zone for high temperatures, demonstrating that the projected pressure is 15% greater than it was when the temperature was low. This is in contrast to the low temperature, for which the predicted pressure was 15% lower. In addition, the area close to the apex has the highest levels of shear stress, which then drop down precipitously farther along the wall until they reach an almost constant level. In general, the location of maximum total deformation is shown at peak systole for the artery when the temperature is high. This is the location where the pressure is high, particularly at the artery bifurcation, and where there is a maximum wall deformation of 0.447 mm. In addition, this is the location where the maximum total deformation occurs. These findings are of great use in the design of arterial bifurcation as well as the assessment of recurrent mechanical loads, both of which contribute to the prediction of life.

Influence of MHz-order acoustic waves on bacterial suspensions

The development of alternative techniques to efficiently inactivate bacterial suspensions is crucial to prevent transmission of waterborne illness, particularly when commonly used techniques such as heating, filtration, chlorination, or ultraviolet treatment are not practical or feasible. We examine the effect of MHz-order acoustic wave irradiation in the form of surface acoustic waves (SAWs) on Gram-positive (Escherichia coli) and Gram-negative (Brevibacillus borstelensis and Staphylococcus aureus) bacteria suspended in water droplets. A significant increase in the relative bacterial load reduction of colony-forming units (up to 74%) can be achieved by either increasing (1) the excitation power, or, (2) the acoustic treatment duration, which we attributed to the effect of the acoustic radiation force exerted on the bacteria. Consequently, by increasing the maximum pressure amplitude via a hybrid modulation scheme involving a combination of amplitude and pulse-width modulation, we observe that the bacterial inactivation efficiency can be further increased by approximately 14%. By combining this scalable acoustic-based bacterial inactivation platform with plasma-activated water, a 100% reduction in E. coli is observed in less than 10 mins, therefore demonstrating the potential of the synergistic effects of MHz-order acoustic irradiation and plasma-activated water as an efficient strategy for water decontamination.

Experimental study on high-frequency subharmonic scattering characteristics of ultrasound contrast agent microbubbles under low ambient pressure

Correlation between nonlinear subharmonic scattering of ultrasound contrast agent microbubbles and ambient pressure is expected to be used for local brain tissue pressure monitoring. Although high-frequency ultrasound has achieved high-resolution imaging of intracranial microvessels, the research on high-frequency subharmonic scattering characteristics of microbubbles is insufficient at present, which restricts the research progress of estimating local brain tissue pressure based on high-frequency subharmonic scattering of microbubbles. Therefore, under the excitation of 10 MHz high-frequency ultrasound, the effects of different acoustic pressures and ambient pressures on the high-frequency subharmonic scattering characteristics of three different ultrasound contrast agents including SonoVue, Sonazoid and Huashengxian were investigated in this in vitro study. Results showed that the subharmonic scattering amplitudes of the three microbubbles increased with the increase of ambient pressure at the peak negative acoustic pressures of 696, 766 and 817 kPa, and there was a favorable linear correlation between subharmonic amplitude and ambient pressure. Under the above three acoustic pressures, the highest correlation coefficient of SonoVue was 0.948 ( P = 0.03), the highest sensitivity of pressure measurement was 0.248 dB/mm Hg and the minimum root mean square error (RMSE) was 2.64 mm Hg. Sonazoid's highest correlation coefficient was 0.982 ( P < 0.01), the highest sensitivity of pressure measurement was 0.052 dB/mm Hg and the minimum RMSE was 1.51 mm Hg. The highest correlation coefficient of Huashengxian was 0.969 ( P = 0.02), the highest sensitivity of pressure measurement was 0.098 dB/mm Hg and the minimum RMSE was 2.00 mm Hg. The above in vitro experimental results indicate that by selecting ultrasound contrast agent microbubbles and optimizing acoustic pressure, the correlation between high-frequency subharmonic scattering of microbubbles and ambient pressure can be improved, the sensitivity of pressure measurement can be upgraded, and the measurement error can be reduced to meet the clinical demand for local brain tissue pressure measurement, which provided an important experimental basis for subsequent research in vivo.

An Ultrasensitive Laser-Induced Graphene Electrode-Based Triboelectric Sensor Utilizing Trapped Air as Effective Dielectric Layer.

Air, a widely recognized dielectric material, is employed as a dielectric layer in this study. We present a triboelectric sensor with a laser-induced graphene (LIG) electrode and an air-trapped pad using silicone rubber (SR). A very thin device with a thickness of 1 mm and an effective gap for contact-separation between the films of silicone rubber and polyimide (PI) of 0.6 mm makes the device extremely highly sensitive for very low amplitudes of pressure. The fabrication of LIG as an electrode material on the surface of PI is the key reason for the fabrication of the thin sensor. In this study, we showed that the fabricated air-trapped padded sensor (ATPS) has the capability to generate an output voltage of ~32 V, a short-circuit current of 1.2 µA, and attain a maximum power density of 139.8 mW m-2. The performance of the ATPS was compared with a replicated device having a hole on the pad, allowing air to pass through during contact-separation. The observed degradation in the electrical output suggests that the trapped air in the pad plays a crucial role in enhancing the output voltage. Therefore, the ATPS emerges as an ultra-sensitive sensor for healthcare sensing applications.

Corneal retardation time as an ocular hypertension disease indicator

Objective. A detailed analysis of the corneal retardation time τ as a highly related parameter to the intraocular pressure (IOP), and its plausible role as an indicator of ocular hypertension disease. Approach. A simple theoretical expression for τ is derived within the corneal viscoelastic model of Kelvin-Voigt with 3 elements. This retardation time can be easily calculated from the well-known signal and pressure amplitudes of non-contact tonometers like the Ocular Response Analyzer (ORA). Then, a population-based study was performed where 100 subjects aged from 18 to 30 were analyzed (within this group, about 10% had an elevated IOP with more than 21 mmHg). Main results. A clear relationship between the corneal retardation time and the corneal-compensated intraocular pressure (IOPcc) was found, underlying the risk for ocular hypertensive (OHT) subjects with lower τ values to develop hypertension illnesses (due to the inability of poorly viscoelastic corneas to absorb IOP fluctuations, resulting in probable optic nerve damage). Significance. Our results might provide an useful tool to systematically discern which OHT patients (and even those with normal IOP values) are more likely to suffer glaucoma progression and, consequently, ensure an early diagnosis.

Shape manipulation of a rotating liquid liner imploded by arrays of pneumatic pistons: Experimental and numerical study

Shaping the inner surface of a rotating, imploding liquid metal liner as it compresses a magnetised plasma target is an important aspect of the Magnetised Target Fusion (MTF) scheme pursued by General Fusion. Reduced-order modelling has shown that the liner's inner surface shape can be manipulated during the implosion by spatially varying the amplitude and timing of pressure applied at the liner's outer surface. A sub-scale apparatus was constructed to investigate this concept, using water as the liner material. A simplified axisymmetric model of this apparatus was also developed using OpenFOAM software. Experimental pressure and rotational speed were used as inputs to numerical simulations. Very good agreement between numerical and experimental liner trajectories was obtained for a wide range of implosion parameters. Data analysis confirmed an initially cylindrical inner liner surface can be shaped and the shaped surface remains symmetrical to radial compression ratios of at least 7:1, despite driving the implosion using pneumatic piston arrays. Furthermore, experiments demonstrated suppression of Rayleigh-Taylor instability for shaped implosions by using liner rotation. This is significant, as literature only confirms this suppression for cylindrical implosions. These results increase confidence in simplified numerical modelling as a predictive tool for designing MTF machines.

Characterization of a Novel Additive Manufacturing Micromix Nozzle Burning Methane to Hydrogen

Abstract As the energy landscape transitions to low/zero-carbon fuels, gas turbine manufacturers are targeting fuel flexible operation with natural gas, syngas, and hydrogen-enriched mixtures. Having a single geometry that can support the different fuel blends requested by clients can accelerate the transition to cleaner energy generation and mitigate the environmental impact of gas turbines. Toward this goal, micromix combustion technology has received significant interest, and when coupled with additive manufacturing, novel injector geometries with unique configurations may be capable of stabilizing premixed, partially-premixed, and diffusion flames using fuel mixtures ranging from pure methane to pure hydrogen. In this work, a preliminary investigation of this micromix concept is performed in the Atmospheric Combustion Rig at the National Research Council (NRC) Canada. Flame stability maps are obtained for fuel lean mixtures of H2/CH4 ranging from 0/100, 70/30, 90/10, to 100/0%, by volume. Multiple flame shapes are observed depending on the fuel mixture and combustion mode selected. Particle image velocimetry (PIV), OH, and acetone planar laser-induced fluorescence (PLIF), and acoustic measurements provide additional insights into the combustion process of these novel burners to better understand the stability mechanisms. The quality of the fuel–air mixing from the premixed and micromix injectors is assessed using acetone as a tracer for the fuel, while simultaneous OH-PLIF measurements provide an indication of the postflame regions in the flow. Acoustic measurements complete the current dataset and provide combustion dynamics maps measuring the normalized pressure amplitudes and identifying the dominant frequencies. The preliminary characterization of this additive manufacturing (AM) micromix nozzle shows promising fuel flexibility with wide stability margins and low combustion dynamics for this single nozzle burner.

A multi-layered corrugated resonator acoustic metamaterial with excellent low-frequency broadband sound absorption performance

How to design acoustic metamaterials with excellent low frequency broadband sound absorption and mechanical properties is a concern and bottleneck in the field of structural vibration and noise control. Based on the principle of Helmholtz resonator and lightweight multi-functional sandwich structure, we propose a multi-layered corrugated resonator acoustic metamaterial (MLCRAM) and fabricate a sample using 3D printing technology. Through theoretical and simulated studies of the MLCRAM model, it is presumed that the MLCRAM has excellent sound absorption performance in the frequency range of 500 to 1000 Hz, which is mainly attributed to the parallel combination of resonant cavities. Then the experimental test of the sample is also carried out to verify the reliability of both theoretical and simulated methods. By analyzing the complex frequency plane, the influence of coupling effects between resonant cavities on the sound absorption properties of the MLCRAM. Subsequently, the overall sound absorption mechanism of the MLCRAM is further analyzed in terms of sound velocity, sound pressure amplitude, and power dissipation density. It has been demonstrated that MLCRAM exhibits excellent low-frequency broadband sound absorption performance, providing a reference for the design of novel acoustic metamaterials.

Transcranial Ultrasonic Focusing by a Phased Array Based on Micro-CT Images.

In this paper, we utilize micro-computed tomography (micro-CT) to obtain micro-CT images with a resolution of 60 μm and establish a micro-CT model based on the k-wave toolbox, which can visualize the microstructures in trabecular bone, including pores and bone layers. The transcranial ultrasound phased array focusing field characteristics in the micro-CT model are investigated. The ultrasonic waves are multiply scattered in skull and time delays calculations from the transducer to the focusing point are difficult. For this reason, we adopt the pulse compression method and the linear frequency modulation Barker code to compute the time delay and implement phased array focusing in the micro-CT model. It is shown by the simulation results that ultrasonic loss is mainly caused by scattering from the microstructures of the trabecular bone. The ratio of main and side lobes of the cross-correlation calculation is improved by 5.53 dB using the pulse compression method. The focusing quality and the calculation accuracy of time delay are improved. Meanwhile, the beamwidth at the focal point and the sound pressure amplitude decrease with the increase in the signal frequency. Focusing at different depths indicates that the beamwidth broadens with the increase in the focusing depth, and beam deflection focusing maintains good consistency in the focusing effect at a distance of 9 mm from the focal point. This indicates that the phased-array method has good focusing results and focus tunability in deep cranial brain. In addition, the sound pressure at the focal point can be increased by 8.2% through amplitude regulation, thereby enhancing focusing efficiency. The preliminary experiment verification is conducted with an ex vivo skull. It is shown by the experimental results that the phased array focusing method using pulse compression to calculate the time delay can significantly improve the sound field focusing effect and is a very effective transcranial ultrasound focusing method.

Void formation and suppression in CFRP laminate using newly designed ultrasonic vibration assisted RTM technique

This study introduces an ultrasonic vibration assisted resin transfer molding (RTM) technique as an innovative approach to address the inherent challenges associated with traditional methods for producing CFRP laminates. It investigates the mechanism of void formation in CFRP composites under ultrasonic vibration using 3D X-ray microscopy. Numerical calculations and simulation analyses are also employed to validate the impact of ultrasonic vibration on mechanical properties of CFRP. The findings indicate that ultrasonic vibration results in CFRP laminates with more uniform thickness, leading to a substantial increase in fiber volume fraction up to ∼16 %. Concurrently, there are significant improvements in flexural strength (∼20 %) and fracture energy (∼90 %). Ultrasonic vibration also effectively reduces CFRP porosity by at least 25 %, resulting in a more consistent distribution of voids, primarily consisting of small circular voids. This porosity reduction is attributed to the cavitation effect and enhancing wettability, consequently improving the mechanical properties of CFRP. Moreover, simulations and numerical calculations demonstrate the significant occurrence of cavitation effect within the resin under specific process conditions. The intensity of cavitation is influenced by factors such as the initial bubble radius, acoustic pressure amplitude, and static pressure of the resin. The ultrasonic-assisted RTM process is proved as a promising method for producing CFRP laminates with superior properties.

Study on the splashing behavior of high-speed railway ballast in ice and snow environment: Analysis of the influence of the train speed, ice mass and striking position

The snow flight in severe cold regions has occurred on many high-speed railway lines in China, directly impacting the safety of high-speed railway operations. However, the research on this problem has not been carried out systematically at present, and the establishment of the theoretical simulation model remains blank. In this paper, the DEM-MBD-CFD coupling analysis method is used to build a refined simulation model of snow flight on high-speed train-ballasted track, which reproduces the actual scenes of three typical cases where the snow flight hits the train body and verifies the reliability of the model with field test results. The results show that the wind pressure amplitude at the center of the ballast bed is the largest, the bottom of the rail is the second largest, and the shoulder of the ballast is the smallest. After the ballast particles fly away from the ballast bed, the main power source is the negative pressure generated by the train’s airflow field. The number of flying ballast particles and the impact force on the train floor grow with the increase of train speed. When the train speed increases to 400 km/h, the average impact force increases to 12.76 kN, which is approximately 8.7 times the impact force at 250 km/h. With the increase of ice mass, the impact stress first increases rapidly and then slowly. When the ice mass is 7 kg, the impact stress has exceeded the yield strength of the train body, seriously affecting the safety of the operation. Many prevention measures, such as reducing the operation speed, implementing ice and snow removal, installing anti-splash coating and grille, and optimizing the structure design, can be taken to reduce the damage of snow flight.

Comparative Study of Histotripsy Pulse Parameters Used to Inactivate Escherichia coli in Suspension.

Bacterial loads can be effectively reduced using cavitation-mediated focused ultrasound, or histotripsy. In this study, gram-negative bacteria (Escherichia coli) in suspension were used as model bacteria to evaluate the effectiveness of two regimens of histotripsy treatments: cavitation histotripsy (CH) and boiling histotripsy (BH). Ten-milliliter volumes of Escherichia coli were treated at different negative focal pressure amplitudes and over time periods up to 40 min. Cavitation activity was characterized with coaxial passive cavitation detection (PCD) and synchronized plane wave B-mode imaging. CH treatments exhibited a threshold behavior that was consistent with PCD metrics of cavitation. Above the threshold, bacterial inactivation followed a monotonically increasing log-linear relationship that indicated an exponential inactivation rate. BH exhibited no threshold, but instead followed a different monotonically increasing inactivation rate. Inactivation rates were larger for BH at or below the CH threshold, and larger for CH substantially above the threshold. CH studies performed at different pulse lengths at the same duty cycle had similar inactivation rates, suggesting that at any given pressure amplitude, the "on time" was the most important variable for inactivating E. coli. The maximum inactivation was produced by CH at the highest pressure amplitudes used, leading to a log reduction >4.2 for a 40 min treatment. The results of this study suggest that both CH and BH can be used to inactivate E. coli in suspension, with the optimal regimen depending on the attainable peak negative focal pressure at the target.

Radial and translational motions of a gas bubble in a Gaussian standing wave field

Acoustic waves with a finite beam width are widely used in acoustic manipulation and cavitation applications. In view of this, radial oscillation and translational motion of a gas bubble in a Gaussian standing wave field are studied in this work. Dynamic differential equations for the bubble are derived with the axial and transverse motions coupled with each other. A comprehensive numerical study is also carried out in the parameter space of the driving frequency, pressure amplitude, initial coordinate, off-axial distance and beam waist. The results demonstrate that the nonlinear radial oscillation can be intensified by a higher pressure amplitude and a smaller off-axial distance. Whether the driving frequency is much lower than the resonance frequency determines not only the final equilibrium position but also the direction of translational motion for the gas bubble. With the widening of the Gaussian standing wave, the radial oscillation will be weakened and the translational motion will be slowed down due to reduction of the pressure gradient regardless of the driving frequency. The results obtained in this study is of interest for an understanding of the bubble dynamics in non-plane acoustic wave fields.

Biotransport in human phonation: Porous vocal fold tissue and fluid–structure interaction

Human phonation involves the flow-induced vibrations of the vocal folds (VFs) that result from the interaction with airflow through the larynx. Most voice dysfunctions correspond with the fluid–structure interaction (FSI) features as well as the local changes in perfusion within the VF tissue. This study aims to develop a multiphysics computational framework to simulate the interstitial fluid flow dynamics in vibrating VFs using a biphasic description of the tissue and FSI methodology. The integration of FSI and a permeable VF model presents a novel approach to capture phonation physics' complexity and investigate VF tissue's porous nature. The glottal airflow is modeled by the unsteady, incompressible Navier–Stokes equations, and the Brinkman equation is employed to simulate the flow through the saturated porous medium of the VFs. The computational model provides a prediction of tissue deformation metrics and pulsatile glottal flow, in addition to the interstitial fluid velocity and flow circulation within the porous structure. Furthermore, the model is used to characterize the effects of variation in subglottal lung pressure and VF permeability coefficient by conducting parametric studies. Subsequent investigations to quantify the relationships between these input variables, flow perfusion, pore pressure, and vibration amplitude are presented. A linear relationship is found between the vibration amplitude, pore pressure, and filtration flow with subglottal pressure, whereas a nonlinear dependence between the filtration velocity and VF permeability coefficient is detected. The outcomes highlight the importance of poroelasticity in phonation models.

Numerical and experimental investigations on shape optimization of submerged floating tunnels with a discrete adjoint method

The shape of the tube in submerged floating tunnels (SFTs) plays a critical role in determining their performance and safety in marine environments. In this study, a gradient optimization procedure based on the discrete adjoint method is performed to minimize the drag force under uniform currents action. The free form deformation approach is employed to parameterize the design variables. The physical mechanisms of the optimization process are revealed via unsteady numerical simulations and experimental tests. Moreover, the hydrodynamic performance of the tube with the optimal shapes subjected to a wave–current combination is also evaluated. The results show that the drag coefficient is significantly reduced through optimization by reducing the pressure amplitude in the negative-pressure area. Additionally, the lift oscillation is also suppressed to delay structural fatigue, owing to the strength reduction and increased distance of the wake vortex. The experimental analysis indicates the advantage of the optimal shape in reducing the loads under wave–current actions, accompanied by changes in the frequency distribution of the force and vortex structure. The elliptical shape of the SFT's tube provides significant advantages in drag reduction at high Reynold number. Suggestions on the shape design of the section of SFT are given according to different types of constraints.

Acceleration mechanism of abrasive particle in ultrasonic polishing under synergistic physical vibration and cavitation: Numerical study

Ultrasonic technology is widely applied in the engineering ceramic polishing processes without the limitation of material properties and ideally integrated into computer numerical control system. Ultrasonic-induced cavitation and mechanical vibration effect could accelerate the motion of solid abrasives. The individual behaviors of microjet/shockwave of ultrasonic cavitation in gases and liquids, and micro-abrasives with simple harmonic vibrations in solids and liquids has been extensively studied. To conduct a systematic and integrated study of abrasives behavior in the polishing contact region involving abrasive, surround-workpiece wall, ultrasonic physical vibration, and ultrasonic cavitation impact, a novel model integrating the free abrasive motion velocity and fixed abrasive indentation depth under multi-scale contact was proposed according to Hertzian contact theory, Greenwood-Williamson model, indentation deformation theory, the basic equations of cavitation bubble dynamics, cavitation impact control equations, and Newton's law of motion equation. The effects of ultrasonic amplitude, ultrasonic frequency, preloading force and particle size on the proposed model were investigated by theoretical analysis and numerical simulations. Ultrasonic physical vibration mainly influences the dynamic gap and further influence the number of different abrasives. Furthermore, the indentation depth of fixed abrasive depends mainly on the abrasive geometry. As the contact gap and abrasive size decrease, the indentation depth gradually decreases. Under the synergistic effect of cavitation-induced shock wave and microjet, the velocity of free abrasive in this paper is generally 0–150 m/s, and the kinetic energy of free abrasive increases roughly linearly with increasing frequency and approximately as a quadratic function with increasing particle size. Increasing the preloading force leads to a reduction in the abrasive kinetic energy. Besides, the kinetic energy induced by the shock wave has a cliff-like increment at an amplitude of 0.7–0.8 μm. It is revealed that the abrasive kinetic energy is suppressed by the cavitation bubble expansion and collapse at smaller ultrasonic pressure amplitude and surround-wall distance. This research provides a theoretical reference for the modeling of potential defects and material removal on the workpiece surface caused by abrasive motion during polishing, and reduces the trial cost for parameter optimization in actual polishing processing.

Suspending droplets beyond the Rayleigh limit: The interplay of acoustic and gravity forces

In this work, we experimentally investigate the suspension behavior of droplets subjected to standing acoustic waves. We focus on the droplet sizes beyond the Rayleigh limit, i.e., when the droplet size is comparable to the wavelength of the acoustic wave. We show that an acoustic field can disrupt the uniform motion of aqueous droplets in oil and cause them to either suspend or settle, depending on the interplay between acoustic and gravity forces. Remarkably, in contrast to droplets within the Rayleigh limit, the critical acoustic power or minimum pressure amplitude required to suspend droplets beyond the Rayleigh limit is dependent on the droplet size. As the droplet size increases, the critical acoustic power increases significantly. Building upon this understanding, a novel sorting method is proposed based on critical acoustic power.

Thermal optimization of inter-stage heat exchangers distribution in a three-stage cascading pulse tube cooler

The cascading pulse tube cooler (CPTC) with a transmission tube has the advantages of high efficiency by energy recovery and high reliability by introducing no extra moving parts to the system and can provide cooling capacity at different cooling temperatures. The efficiency of CPTC still needs further improvement to meet the requirement of superconducting cooling and other applications. As there are 3 heat exchangers (HXs) in each stage of CPTC, it’s essential to analyze the losses inside the HXs and optimize the distribution of HXs in CPTC. In this paper, the numerical simulation is conducted to analyze the temperature distribution and pressure drop of different arrangements of hot-end HX (HHXs) and transmission tubes. Simulation results show that the acoustic loss decreases from 10.36 W to 5.17 W when first stage HHX (HHX I) is eliminated from the original CPTC for the same working condition. Experimental tests of a three-stage CPTC are carried out to verify the optimal distribution of the HHXs, the cooling capacity of the three-stage CPTC increases from 249.6 W (original) to 273.5 W (optimized) at 233 K with an input power of 500 W, and the efficiency is improved by 9.46 %. Moreover, the efficiency of the three-stage CPTC with the optimized distribution of the HHXs is improved by 50.7 % at 233 K when compared with the single-stage PTC. The pressure amplitude at the inlet of each stage also increases. The results verify the optimization method for the distribution of IHXs and further confirm that CPTC improves the efficiency of PTC.