Effect Of Ultrasonic Frequency Research Articles

Effect of ultrasonic frequency on mass transfer of acoustic cavitation bubble

Mass transfer of acoustic cavitation bubble is numerically investigated focusing on ultrasonic frequency. In the present simulation, transport of chemical specie from an acoustic cavitation bubble after rapid bubble compression is modeled. The simulation results indicate that the bubble oscillation is more nonlinear, and the oscillation amplitude becomes larger with sound pressure amplitude, ultrasonic frequency, and bubble size. Under the condition of strong nonlinear bubble oscillations, the bubble shape becomes non-spherical. The mass transfer of chemical specie becomes smaller with sound pressure amplitude at 20 kHz ultrasound due to shell effect and area effect, although it becomes larger with pressure amplitude at higher ultrasonic frequency because the concentration of chemical specie in the bubble becomes high near the periphery of bubble due to hysteresis effect, which becomes remarkable especially at higher ultrasonic frequency because time for the bubble compression becomes too short for chemical specie to diffuse at higher ultrasonic frequency.

Enhancing solubility of polymer-loaded febuxostat through ultrasound-assisted microfluidic antisolvent nanoprecipitation: Optimization using Box-Behnken design

Febuxostat (FEB) nanoparticles with the use of poloxamer 407 were prepared using ultrasound assisted microfluidic nanoprecipitation method to enhance febuxostat's solubility and bioavailability. The optimization for this purpose was conducted using the Box Behnken design (BBD) approach. Four factors and three level BBD was used to study the interactive and individual effect of ultrasonic frequency (X1), amplitude (X2), Ultrasound assisted microfluidic reactor (USMR) temperature (X3), and micromixer confluence angle (X4) on selected two responses. Particle size (Y1) and encapsulation efficiency (% EE) (Y2) were the desired responses. The formulated FEB nanoparticles were analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM). The minimum nanoparticle size, 7.156 nm with 0.22 polydispersity index (PDI) was attained for FEB-loaded polymer nano-sized particles. To investigate the drug release rate (% DR), fast-dissolving tablets of raw FEB and optimized FEB formulation were prepared. A 1.25-fold improvement in FEB solubility rate was experimentally achieved compared to raw FEB. No chemical interaction between the drug and polymer was observed using FTIR. Optimized FEB formulation showed a 92.94 % release rate of the drug in 90 min with 91.70 % EE.

Study of poly allyl diglycol carbonate Kinetics treatment induced by ultrasonic frequency plasma

This research reveals the possibility of altering the structural, surface, fluorescence, and optical characteristics of CR-39 polymer detector by the effect of Ultrasonic frequency (UF) plasma argon gas. The samples were exposed to the plasma at different times ranging from 20 min to 100 min. Fourier Transform Infrared (FTIR) Spectroscopy, contact angle goniometer, surface roughness tester, photoluminescence spectroscopy, and UV/Vis Spectroscopy have been applied to analyze alterations of CR-39 polymeric films to understand the mechanisms of produced alterations by plasma treatment. The obtained FTIR spectra demonstrated that the plasma treatment-related changes in the absorption bands are associated with the treatment time, leading to two critical processes, degradation, and crosslinking. In comparison to the untreated surface, the surface wettability results showed that the liquids' contact angle decreased after treatment with a UF plasma source. This modification in the treated surface denotes an increase in polar groups there, which causes the surface to change to a hydrophilic state. The surface roughness of the samples following plasma treatment showed that UF plasma significantly changed the surface morphology of the CR-39 films. After plasma exposure, considerable emission bands were produced, and the photoemission spectra of the treated film showed a fluorescence response. As the exposure time increased, more fluorescence peaks were formed due to the increase in defects. The UV/Vis spectra showed that the modified films' absorption edges were moved toward lower photon energies. This resulted in a smaller optical energy gap, which led to an expansion of the carbon cluster. Additionally, the untreated sample's transmittance dropped from 92% to 47% for the treated film. In contrast to untreated films, a change in optical characteristics was seen in treated films.

Bubble oscillations at low frequency ultrasound for biological applications

Bubbles oscillating in the presence of ultrasound is commonly employed in biomedical applications for drug delivery, ultrasound enhanced thrombolysis, and the transport and manipulation of cells. This is possible because bubbles tend to interact with the ultrasound to undergo periodic shape changes known as shape-mode oscillation, concomitant with the generation of liquid agitation or streaming. This phenomenon is examined both experimentally and theoretically on a single bubble at a frequency of (45 ± 1) kHz. Effects of ultrasonic frequency and power on the flowfield were explored. Experiments revealed different trends in the development of liquid streaming velocities at different acoustic forcing conditions (5.53, 6.80 and 7.02 Vpp), with lowest (0.5 mm/s) and highest (1.1 mm/s) values of time-averaged mean streaming velocity occurring at 6.80 Vpp and 7.02 Vpp, respectively. Simulations captured the simultaneous evolution of bubble-shapes that helped create flow vortices in the liquid surrounding the bubble. These vortices collectively responsible in generating signature patterns in the liquid for a dominant shape-mode of the bubble, and could also generate localised shear stresses for practical application. The velocity and pressure profiles in the liquid around the bubble confirmed the connection of the applied and reflected soundwaves in driving this phenomenon.

Effect of ultrasonic frequency on the structural and functional properties of pea protein isolation.

Pea protein, as a by-product of peas (Pisum sativum L.), is rich in a variety of essential amino acids that can meet the body's protein needs and is a valuable source of protein. Since the function of pea protein is closely related to its structure, pea protein has been subjected to different modifications in recent years to improve its application in food and to develop new products. The effects of sonication frequency (primary and secondary time) on pea protein isolate's (PPI's) structural and functional properties were investigated. Sodium dodecyl sulfate polyacrylamide gel electrophoresis demonstrated that different sonication frequencies at the same power (600 W) treatment had no effect on PPI's molecular weight. Fourier-transform infrared spectroscopy revealed that treatment at different sonication frequencies caused secondary structural changes in PPI. The particle size distribution, foaming, stability, surface hydrophobicity, emulsification, and oxidation resistance of PPI were improved after primary and secondary sonication, but secondary sonication was not more effective than primary sonication for an extended period of time. Overall, ultrasound is able to improve the structural and functional properties of pea proteins within a suitable range. It provides a theoretical basis for elucidating the modification of the structure and function of plant proteins by ultrasound and lays the foundation for the development of plant proteins in food applications as well as development. © 2023 Society of Chemical Industry.

Effect of Ultrasonic Frequency on Structure and Corrosion Properties of Coating Formed on Magnesium Alloy via Plasma Electrolytic Oxidation.

This study explores the application of ultrasonic vibration during plasma electrolytic oxidation (PEO) to enhance the corrosion resistance of magnesium (Mg) alloy. To this end, three different ultrasonic frequencies of 0, 40, and 135 kHz were utilized during PEO. In the presence of ultrasonic waves, the formation of a uniform and dense oxide layer on Mg alloys is facilitated. This is achieved through plasma softening, acoustic streaming, and improved mass transport for successful deposition and continuous reforming of the oxide layer. The oxide layer exhibits superior protective properties against corrosive environments due to the increase in compactness. Increasing ultrasonic frequency from 40 to 135 kHz, however, suppresses the optimum growth of the oxide layer due to the occurrence of super-soft plasma swarms, which results in a low coating thickness. The integration of ultrasonic vibration with PEO presents a promising avenue for practical implementation in industries seeking to enhance the corrosion protection of Mg alloys, manipulating microstructures and composition.

High-efficiency degradation catalytic performance of a novel Angelica sinensis polysaccharide-silver nanomaterial for dyes by ultrasonic cavitation.

Currently, the polluted wastewater discharged by industry accounts for the major part of polluted bodies of water. As one of the industrial wastewaters, dye wastewater is characterized by high toxicity, wide pollution, and difficulty in decolorization degradation. In this paper, a novel composite nanomaterial catalyst of silver was prepared by using Angelica sinensis polysaccharide (ASP) as a reducing and stabilizing agent. And the optimum reaction conditions explored are VAgNO3=5mL (300mM) and vASP=7% (w/v) for 6h at 90°C. In addition, the ASP-Ag nanocatalyst was characterized by several techniques. The results demonstrated that ASP-Ag nanoparticles were successfully synthesized. Degradation rate, which provides a numerical visualization of the percentage reduction in pollutant concentration. With the wrapping of ASP, the ultrasonic catalytic degradation rates of different organic dyes including rhodamine B (RB), methylene blue (MB), and methyl orange (MO) were from 88.2%, 88.7%, and 85.2% to 96.1%, 95.2% and 93.5% at room temperature, respectively. After the experiments, when cdyes=10mg/L, the highest degradation rate can be observed under cAPS-AgNPs=10mg/L with the most powerful cavitation frequency f=59kHz. The effect of ultrasonic frequency on the acoustic pressure distribution in the reactor was investigated by using COMSOL Multiphysis@ software to propose the mechanism of ultrasonic degradation and the mechanism was confirmed by OH radical trapping experiments. It indicates that OH produced by the ultrasonic cavitation effect plays a determinant role in the degradation. And then, the intermediate products of the dye degradation process were analyzed by gas chromatography and mass spectrometry (GC-MS), and the possible degradation processes of dyes were proposed. The resulting products of degradation are SO42-, NH4+, NO3-, N2, CO2 and H2O. Finally, the recycling degradation experiments showed that catalyst maintains a high degradation rate within reusing 5 cycles. Thus, this catalyst is highly efficient and recyclable.

Tensile fracture test of nanocomposite ceramics under ultrasonic vibration based on nonlocal theory

Based on non-local theory, the dispersion characteristics of ultrasonic vibration in Specimen tension are analyzed, and the effects of ultrasonic frequency and amplitude on the wave dispersion are obtained through theoretical analysis. Tensile tests were carried out using an ultrasonic vibration system and specimens, and the test process as well as test parts were observed and analyzed. The influence of the ultrasonic vibration on fracture properties and the change of grain micro-organization under different loading conditions were verified by experiments. The introduction of ultrasonic vibration changes the internal stress of the ceramic fracture, affects the hardness of the workpiece, and also leads to the scattering of particles, which leads to the aggravation of ultrasonic attenuation and phase velocity dispersion. SEM and XRD analyses showed that with the increase in ultrasonic frequency and amplitude，the trans -granular fracture was more obvious, the micro-cracks and dimples increased, and micro-pores increased in size and number. The tensile stress produced by ultrasonic vibration will induce the transformation from T-phase ZrO2 particles to M-phase ZrO2 particles and absorb strain, which greatly improves the plastic mechanical properties of nanocomposite ceramics. Due to the inherent phase transformation toughening mechanism, the material improves the plastic mechanical properties under the ultrasound excitation, and it is easier to achieve ductile domain processing.

Characterization of sonicated gluten protein and subsequent rheological properties of model dough and noodles.

The present study aimed to investigate the effects of the thermo-mechanical and rheological properties of a wheat gluten-sonicated model dough and noodles, as well as the effects of ultrasonic frequency (20, 28, 40, 68 and 80 kHz) on the functional properties and structural features of gluten. Water absorption, stability and developmental time, and viscoelastic behavior of gluten-sonicated model dough were all found to be improved. Water absorption, tensile resistance and stretching distance of noodles increased markedly, whereas cooking loss decreased. Ultrasonication at different frequencies also significantly affected gluten structure, including its surface hydrophobicity, micro-network structure, and secondary and tertiary structures. These alterations then caused changes in its functional characteristics. Compared to untreated gluten, sonicated gluten exhibited significantly increased oil and water capacities (8.75-15.26% and 100.65-127.71% higher than the untreated gluten, respectively), foaming and emulsifying properties, and increased solubility (63.46-98.83% higher than control). In addition, these findings indicated that 40 kHz was the likely resonance frequency of the cavitation bubble in the gluten solution. However, sodium dodecyl sulfate-polyacrylamide gel electrophoresis electropherograms revealed that such treatments did not affect the molecular weight of gluten, which was also consistent with its unchanged disulfide bond content. The present study clarified the impact of frequency on the properties of gluten and model dough. The best frequency for modification of gluten was 40 kHz. Collectively, these findings suggest that ultrasonic technology has the potential for use in modifying wheat gluten and commercial noodle processing. © 2022 Society of Chemical Industry.

Effect of ultrasonic far-infrared synergistic drying on the characteristics and qualities of wolfberry (Lycium barbarum L.)

This study investigated the effects of ultrasonic frequency, ultrasonic power, irradiation height and temperature on the drying characteristics, quality and microstructure of wolfberry by ultrasonic-assisted far-infrared drying. By fitting five commonly used thin-layer drying mathematical models, it was found that the coefficient of determination (R2) of the Weibull model was 0.99400–0.99825, the root mean square error (RMSE) was 1.2162 × 10-4–4.5209 × 10-4, and the reduced chi-square (χ2) was 0.00207–0.00663, which was the best fit. Under the application of ultrasound, the average drying rate of wolfberry increased. Compared with natural drying, the polysaccharide content increased by 33.2 % at 250 mm irradiation height, and the total phenol content increased by 44.9 % at 40 kHz ultrasonic frequency. The antioxidant activity was the strongest, and the total flavonoids content was the highest (2.594 mg/g) at 24 W ultrasonic power. By comparing the microstructure of wolfberry under different drying methods, such as a fresh sample, natural drying, hot air drying, and ultrasonic-assisted drying, we found that the ultrasonic assistance increased the number of micropores on the surface of wolfberry, reduced the damage to epidermal cells, reduced the mass transfer resistance of the drying process and accelerated the drying process. This study shows that ultrasonic-assisted far-infrared drying technology played a significant role in the heat and mass transfer of wolfberry drying, and had great potential in the commercial processing of wolfberry.

Numerical study of the synergistic effect of cavitation and micro-abrasive particles

In ultrasonic-assisted machining, the synergistic effect of the cavitation effect and micro-abrasive particles plays a crucial role. Studies have focused on the investigation of the micro-abrasive particles, cavitation micro-jets, and cavitation shock waves either individually or in pairs. To investigate the synergy of shock waves and micro-jets generated by cavitation with micro-abrasive particles in ultrasonic-assisted machining, the continuous control equations of a cavitation bubble, shock wave, micro-jet, and micro-abrasive particle influenced by the dimensionless amount (R/R0), a particle size-velocity–pressure model of the micro-abrasive particle was established. The effects of ultrasonic frequency, sound pressure amplitude, and changes in particle size on micro-abrasive particle velocity and pressure were numerically simulated. At an ultrasonic frequency of 20 kHz and ultrasonic sound pressure of 0.1125 MPa, a smooth spherical SiO2 micro-abrasive particle (size = 5 µm) was obtained, with a maximum velocity of 190.3–209.4 m/s and pressure of 79.69–89.41 MPa. The results show that in the range of 5–50 μm, smaller particle sizes of the micro-abrasive particles led to greater velocity and pressure. The shock waves, micro-jets, and micro-abrasive particles were all positively affected by the dimensionless amount (R/R0) of cavitation bubble collapse, the larger the dimensionless quantity, the faster their velocity and the higher their pressure.

Pengaruh frekuensi ultrasonik terhadap mortalitas serangga perusak kayu Dinoderus minutus Fabricius (Coleoptera: Bostrichidae)

Dinoderus minutus Fabricius (Coleoptera: Bostrichidae) merupakan hama utama perusak kayu dan bambu, dan menjadikannya sebagai relung ekologi. Pengendalian kumbang tersebut masih bergantung pada insektisida sintetik yang dapat memicu resistensi. Penelitian ini menjadi uji pendahuluan penggunaan frekuensi ultrasonik sebagai agen pengendalian D. minutus. Penelitian bertujuan untuk mempelajari pengaruh frekuensi ultrasonik terhadap mortalitas D. minutus. Metode yang digunakan adalah pemaparan frekuensi ultrasonik terhadap imago D. minutus selama 7 hari dan 14 hari di dalam ruangan dengan suhu udara 28 °C hingga 29 °C dan kelembaban udara 70% hingga 81%. Hasil penelitian menunjukan bahwa perlakuan frekuensi ultrasonik menghasilkan mortalitas sebesar 80,00% dengan durasi paparan 14 hari. Hasil menunjukkan bahwa frekuensi ultrasonik dengan waktu paparan yang tepat dapat digunakan sebagai bentuk pengendalian D. minutus.

Identification of the Effect of Ultrasonic Friction Reduction in Metal-Elastomer Contacts Using a Two-Control-Loop Tribometer

Pneumatic cylinders are widely used in highly dynamic processes, such as handling and conveying tasks. They must work both reliably and accurately. The positioning accuracy suffers from the stick-slip effect due to strong adhesive forces during the seal contact and the associated high breakaway forces. To achieve smooth motion of the piston rod and increased position accuracy despite highly variable position dynamics, sliding friction and breakaway force must be reduced. This contribution presents a specially designed linear tribometer that has two types of control. Velocity control allows the investigation of sliding friction mechanisms. Friction force control allows investigation of the breakaway force. Due to its bearing type, the nearly disturbance-free detection of stick-slip transients and the dynamic contact behavior of the sliding friction force was possible. The reduction of the friction force was achieved by a superposition of the piston rod’s movement by longitudinal ultrasonic vibrations. This led to significant reductions in friction forces at the rubber/metal interface. In addition, the effects of ultrasonic frequency and vibration amplitude on the friction reduction were investigated. With regard to the breakaway force, significant success was achieved by the excitation. The force control made it possible to identify the characteristic movement of the sealing ring during a breakaway process.

Mechanism of low-frequency and high-frequency ultrasound-induced inactivation of soy trypsin inhibitors

In this study, the effect of ultrasonic frequency and power on the inactivation of soy trypsin inhibitors (TIs) was investigated to explore the ultrasound-induced inactivation mechanism. It was observed that 20 kHz and 355 kHz ultrasound have better inactivation efficiency than 1056 kHz. First-order rate constants for the inactivation process were obtained, which increased with increasing ultrasonic power at both 20 kHz and 355 kHz. For 20 kHz ultrasound, the formation of TI aggregates resulting from the physical effects of acoustic cavitation decreased the interactions between the active sites of TIs and trypsin, thus reducing the TI activity. For 355 kHz ultrasound, most of the methionine in the TIs was oxidised within 5 mins, resulting in a faster reduction of TI activity. Subsequent aggregation of TIs resulted in further TI inactivation. SDS-PAGE showed that neither disulphide bonds nor CC coupling were involved in the formation of aggregates.

Investigating the Effects of Ultrasonic Frequency and Membrane Technology on Biodiesel Production from Chicken Waste

In this study, the experiments were carried out under different operating conditions to evaluate the effect of ultrasound waves on biodiesel production from chicken feet oil. A two-step esterification–transesterification mechanism was employed to improve the biodiesel quality. The continuous (methanol-to-oil molar ratio and KOH catalyst amount) and discrete (frequencies, 25 and 45 kHz) variables were investigated using the experimental design method. The five-level three-factor response surface method (RSM) was assisted to optimize the biodiesel synthesis variables. Applying RSM based on the central composite design (CCD), a polynomial equation was fitted to the experimental data with the aid of Design-Expert software. The model accuracy was checked by analysis of variance (ANOVA). The results showed the highest yield of 89.74% could be achieved by using an M/O molar ratio of 12, a KOH concentration of 1 wt%, and an ultrasound frequency of 45 kHz. Finally, a mathematical model of biodiesel production in a membrane system was developed. The reaction rate constant was calculated as a function of ultrasonic frequency. Compared with the conventional method, the membrane system has significantly improved chicken feet biodiesel production’s reaction rate. The membrane is more effective at higher frequencies than at lower ones.

Ultrasound frequency effect on soybean protein: Acoustic field simulation, extraction rate and structure

This study endeavored to develop a method to evaluate the effect of ultrasound frequency on soybean protein extraction. In the ultrasonic frequencies range from 20 to 52 kHz, 28, 35, and 45 kHz were predicted to be the resonance frequencies in the ultrasound-assisted extraction (UAE) process of soybean protein by simulating the acoustic field distribution. The absolute sound pressure and the relative standard deviation could be well-coordinated via frequency regulation. The extraction experiment of soybean protein showed that the extraction rate was improved significantly (p < 0.05) with the aid of ultrasound. The extraction effect was optimal at 28 kHz and the extraction rate was improved to 73.35 g/100 g from 46.09 g/100 g of control under the same condition. The structure of the extracted protein was analyzed by the spectrum to further explore the mechanism of the effect of ultrasonic frequency. Spectral analysis showed that 20, 28, and 35 kHz had a significant influence on the structure of protein molecules. Therefore, acoustic field simulation can be used as one effective method for selecting ultrasonic frequency, which could help to optimize equipment and improve efficiency.

Simultaneously enhanced strength and ductility of TIG welds in Inconel 718 super-alloy via ultrasonic pulse current

Abstract This paper presents a novel self-induced ultrasonic arc welding (U-TIG) with high-efficient, which improves tensile strength and ductility of TIG welds in Inconel 718 super-alloy simultaneously. The effects of ultrasonic frequencies on arc shape, weld forming and weld penetration characteristics were systematically studied by high-speed camera and optical microscope. The characteristics of grains and precipitated phases in the weld metal were quantitatively analyzed by backscattered electron microscope, electron backscatter diffraction. The evolution models of grains refinement and reduction-dispersion with Laves phase were constructed based on molecular dynamics model and numerical simulation. The evolution diagrams of microstructures in tensile stretching revealed the mechanism of enhancing strength and ductility. Ultrasonic pulse current not only reduces and refines Laves phase, respectively by 81.8% and 52.2%, but refines grains (almost 33%) with higher orientation. The excellent distribution of the finest grains and Laves phase with dispersion is corresponding to ultrasonic frequency nearly 80 kHz, which benefits ductility enhancement of welds from 311% to 410%. Grains refinement leads to the increasing of grains boundary length and zigzag, meanwhile, the morphology of Laves phase changes from long-strip shape to refined pebble one, which is responsible for tensile strength improvement, closing to base metal of 92%.

Effect of ultrasonic frequency and power on the sonodynamic therapy activity of cationic Zn(II) phthalocyanines

We report on the sonodynamic activity of cationic phthalocyanines (Pcs) and the effect of the variation of two parameters: ultrasound frequency and power (Par I (1 MHz, 1 W cm−2), Par II (1 MHz, 2 W cm−2), Par III (3 MHz, 1 W cm−2) and Par IV (3 MHz, 2 W cm−2)) on the efficiency of their reactive oxygen species generation and cancer eradication in vitro thereof. Where Par stands for the various combinations of these parameters. Four Pcs were investigated with substituents bearing diethylamine, ortho- and para-pyridine and morpholine groups. Overall, the para-pyridine and morpholine Pcs showed substantial sono-activity in the various ultrasound parameters with Par I and IV generally showing better singlet oxygen and hydroxyl radicals generation confirmed by electron paramagnetic resonance spectroscopy. In some cases, very high hydroxyl radicals' generation was observed at Par II. Furthermore, the fragmentation of the Pcs after Par II treatments was confirmed using UV–vis and magnetic circular dichroism spectroscopy. The reactive species generation efficacy decreased at Par III for all samples. Ultrasound assisted cytotoxicity of the Pcs was confirmed in vitro using the human (Michigan Cancer Foundation-7) breast cancer cell line.

Sonochemical effect and pore structure tuning of silica xerogel by ultrasonic irradiation of semi-solid hydrogel

Silica xerogels were prepared by the sol-gel method under ultrasonic irradiation, using tetraethylorthosilicate (TEOS) as the starting material. Hexamethyldisiloxane (HMDSO) was used as the hydrophobizing agent. When preparing silica xerogel, it is necessary to perform aging and hydrophobization to suppress shrinkage during ambient pressure drying, however, such treatments are time-consuming. In this study, the semi-solid hydrogel was irradiated with ultrasonic for the first time in order to accelerate aging and hydrophobic treatment, and the effect of ultrasonic frequency on structure was investigated. Firstly, ultrasonic irradiation was performed at frequencies of 100 kHz and 500 kHz, followed by hydrophobic treatment at a frequency of 500 kHz, in order to promote aging. The results identify optimum conditions for ultrasonic irradiation to promote aging and hydrophobization reactions, and it was found to be possible to prepare silica xerogels in less than 1/5 of the conventional time. The silica xerogels had a low density and the shrinkage was suppressed. In this study, it was found that ultrasonic irradiation of semi-solid hydrogel was very effective for promoting the reaction.

Effect of Ultrasonic Frequency on Thickener Performance

Gravity thickening is an important aspect to solve numerous environmental and safety problems that were created by tailings discharging at low solid concentrations. Furthermore, in order to efficiently facilitate the separation of released water and solid sediments, a continuous thickening system with ultrasonic equipment has been used to investigate the thickening performance of copper‐mine tailings under different ultrasonic frequencies (16 kHz, 20 kHz, 22 kHz, 25 kHz, and 28 kHz). After freeze‐drying treatment, the underflow samples are imaged using the scanning electron microscope (SEM); then, the structure of floc or aggregates in the SEM images is quantifiably analyzed using the software of Image J. Results show that the underflow concentration increases as the ultrasonic frequency increases and decreases afterwards. A linear logarithmic function can explain the relationship between underflow concentration and run time at a certain ultrasonic. The underflow concentration is maximized at 64.47 wt. % when the ultrasonic frequency is 22 kHz. Based on the analysis on the microstructure of underflow samples, the minimum pore average size and pore average fraction are obtained when the ultrasonic frequency is 22 kHz, implying that 22 kHz is the optimum ultrasonic frequency combining the results of the underflow concentration.