Maximum Pressure Amplitude Research Articles

Impacts of impeller blade number on centrifugal pump performance under critical cavitation conditions

The number of impeller blades is a significant geometric parameter that considerably impacts centrifugal pump performance. A transient numerical analysis of a centrifugal pump is conducted to examine the influence of the variable impeller blade number on pump performance under critical cavitation conditions. Six different impellers with 3, 5, 7, 8, 9, and 11 blades are examined numerically at a rotational speed of 2900 r/min when other impeller parameters remain unchanged. Fields of interior flow and properties of centrifugal pumps are studied concerning static pressure, velocity magnitude, and vapor volume fraction using ANSYS Fluent to perform the numerical simulation. The results show that numerical analysis can accurately predict centrifugal pump internal flow. The current results match experimental and numerical data for the NPSH, with a 4.65% discrepancy. Blade numbers affect the flow field and pressure amplitude, especially at the outlet region. As blade numbers increase, pressure increases, and the impeller with 11-blade has the maximum pressure amplitude. The impeller with a seven-blade achieved its highest efficiency level, exhibiting a 0.48% improvement under non-cavitation conditions and a 1.4% improvement under critical cavitation conditions compared to the original model. Furthermore, the cavity size on an individual blade of a model with three-blade is more extensive compared to other models. In addition, the impeller with a nine-blade exhibits the lowest value of the vapor volume percentage. This research analyses the influence of different blade numbers on the performance of centrifugal pumps while operating under critical cavitation conditions. It aims to provide novel insights into the flow characteristics associated with such circumstances.

Experimental investigation on the mode transition characteristics of a phase-change thermofluidic oscillator with external loads

Phase-change thermofluidic oscillator has drawn significant attention thanks to its low operating temperature, which is beneficial for recovering low-grade heat. The vapor–liquid coupling oscillation in the thermofluidic oscillator leads to complex non-linear mode transition phenomenon that affects the steady operation. In this work, the mode transition characteristics of a thermofluidic oscillator with external loads (i.e., a needle valve and a load reservoir) are experimentally investigated through bifurcation analysis. A low-order van der Pol model is employed to examine the effect of acoustic resistance on mode transition. Experimental results demonstrate that modifying the valve opening and load volume under a constant temperature difference can trigger bifurcation, resulting in high-frequency limit cycle, low-frequency limit cycle and quasi-periodic modes. The non-linear features of each mode are revealed through phase space and Poincaré section, with Neimark-Sacker bifurcation, second bifurcation and inverse Neimark-Sacker bifurcation observed. Steady-state performance of oscillator is then characterized under different oscillation modes. The maximum pressure amplitudes measured are 11.54 kPa during the high-frequency oscillation and 1.35 kPa during the low-frequency oscillation, while the maximum displacement amplitudes obtained are 45.5 mm during the high-frequency oscillation and 91.4 mm during the low-frequency oscillation. The oscillation modes can be adjusted by external load to maximize output performance. This study offers comprehensive guidelines for constructing phase-change thermofluidic oscillators.

Extending the operational range of Francis turbines: A case study of a 200 MW prototype

Francis turbines are now widely used to support the integration of renewable and intermittent energy sources such as solar and wind power. Consequently, these turbines often operate away from their best efficiency point (BEP). Such operations cause detrimental pressure fluctuations in the runner and draft tube, leading to early fatigue failures. To address these harmful flow conditions and extend the operating range of Francis turbines, a mitigation system was developed and tested on a large-scale, high-head 200 MW Francis turbine. The system consists of four circular rods placed in the draft tube with variable radial protrusion lengths, adjustable using linear actuators. Pressure, accelerometer, and vibration sensors installed on the turbine allowed quantification of the rod system performance. The results demonstrate the system’s capability to reduce pressure pulsations by up to 80 % in terms of maximum pressure amplitude and 100 % in terms of fatigue cycle in both low and high-frequency ranges, up to ten times the runner frequency, based on pressure analysis. The optimal rod protrusion ranges from 5 to 20 % of the runner outlet diameter function of the operating load. The impact of the rods’ protrusion on the turbine structure appears negligible from the accelerometer measurements performed on the draft tube and spiral casing. The hydraulic efficiency is reduced by up to 1 %. These findings are significant across a wide range of part-load operations, from 40 % to 60 % load, indicating the potential to extend the operational range of existing Francis turbines. The research presented here is a novel attempt to enhance the existing Francis turbines with a new degree of freedom using protruding rods.

A Flexural Ultrasonic Transducer for Inducing Acoustic Cavitation on Material Surfaces

Abstract Purpose This paper proposes a flexural ultrasonic transducer specifically designed for surface treatment of materials with delicate surfaces such as skin by acoustic cavitation at low frequencies. The goal of this preliminary study is to assess the resonance frequencies and the output sound pressure of the proposed transducer and confirm generation of acoustic cavitation on the surface of an artificial skin phantom. Methods A transducer prototype was designed based on structural-acoustic simulation and fabricated. The proposed design employs a concave-shaped acoustic resonator with a spherical cavity, which is driven by flexural vibration of a piezoelectric ceramic disk actuator. The transducer prototype has compact dimensions of 15 mm in diameter and 8 mm in axial length, working at frequencies around flexural vibration modes of the piezoelectric disk with a thickness of 1 mm. Results The maximum sound pressure amplitude reached 125 kPa with an input voltage amplitude of 10 V at the second resonance frequency of 167 kHz, where the third axisymmetric eigenmode was excited. Despite enhancing the maximum pressure, the sound pressure outside the resonator attenuates because the near-field distance of the irradiated sound wave is smaller than the height of the resonator. This implies that the proposed method provides the cavitation effect on material surfaces, possibly minimizing the side effect of ultrasound irradiation on the underlying structure. Cavitation generation on a urethane gel surface was directly observed by using a high-speed video camera. Conclusion We confirmed that acoustic cavitation was generated and propelled to the target surface. It concludes that ultrasound irradiation using the proposed ultrasonic transducer could be a promising alternative for effective and safe ultrasound treatment of material surfaces.

Effect of temporal increase in equivalence ratio on combustion instability of a lean-premixed swirling hydrogen flame

The effect of temporal increase in the equivalence ratio on the combustion instability of a lean-premixed low-swirl hydrogen jet flame in a low-swirl combustor (LSC) is investigated in detail using a high-fidelity Large-Eddy Simulation (LES). The equivalence ratio is linearly increased from 0.3 to 0.5 over a duration of 0.4 s. The results show that the pressure oscillation amplitude in the combustor increases significantly when the equivalence ratio at the combustor inlet (ERCI) exceeds 0.42, and the maximum pressure amplitude and the combustion instability mode exhibit trends consistent with those in a previous experiment and numerical simulation conducted with the same LSC setup at a fixed equivalence ratio of 0.39. Temporal variations in the equivalence ratio and consequently the temperature inside the combustor cause the drastic amplification of pressure oscillation (when the ERCI exceeds 0.42) whose amplitude is larger than that at the fixed equivalence ratio (= 0.39). Prior to the onset of this exceptionally strong combustion instability, a transient irregular oscillation phenomenon comprising instantaneous changes in the pressure oscillation frequency is observed. While the pressure oscillations in the combustor and in the injector channel are in phase after the onset of strong combustion instability, they are in opposite phases during the occurrence of the irregular oscillation phenomenon prior to the onset of strong combustion instability. This irregular oscillation phenomenon predicted by the LES may play a crucial role in the mechanism of transition from stable combustion to combustion instability.

Biaxial Excitation and Reception Method Applied to Ultrasound Imaging.

The biaxial method consists of the utilization of orthogonal electric fields in single-element piezoceramics both in transmission and reception. This study demonstrates the application of the biaxial method to broadband transducers. We developed a three-element biaxial transducer array to demonstrate the feasibility of biaxial method in imaging applications. Finite element analysis was used to model the response of a single transducer element. An electric characterization was performed at each transducer element to determine their driving frequency. Each transducer was driven at 6.25 MHz and tested in different phases to determine the phase that produced the maximum pressure amplitude and shortest pulsewidth. Both simulations and experimental results showed that the acoustic pressure and half-pulsewidth followed a sinusoidal response as a function of the difference in phase applied to the lateral electrodes, as it has been described in our previous work. An imaging test was performed by placing a 0.36-mm diameter nylon wire 20 mm away from the transducer while driving and receiving each element with different combinations of conventional and biaxial driving. By applying a biaxial rephasing at the receiving electrodes during the data analysis, we obtained a maximum reduction in the axial resolution from 4.6 to 1.3 mm and signal-to-noise ratio (SNR) improvements from 15.2 to 24.4 dB, when compared to conventional driving.

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.

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.

Effect of Blending Dimethyl Carbonate and Ethanol with Gasoline on Combustion Characteristics

We investigated the effects of blending dimethyl carbonate (DMC) and ethanol with commercial gasoline on combustion characteristics. Our experimental approach involved using a rapid compression and expansion machine (RCEM) to achieve elevated temperatures and pressures. The fuels containing different volumes of oxygenated hydrocarbons were burned at equivalence ratios of 1.0 or 0.7, an initial temperature of 340 K, and initial pressures of 0.10 or 0.05 MPa. To simulate knocking phenomena, we installed a rectangular channel in the combustion chamber of the RCEM and measured the pressure history inside the chamber. By analyzing the pressure history resulting from the end-gas autoignition, we evaluated the combustion duration and maximum pressure amplitude. Blending both oxygenated fuels with gasoline effectively reduced the maximum-pressure amplitude in the end-gas autoignition, with ethanol exhibiting a more pronounced suppression effect compared to DMC in the same volumetric mixing ratio. At an initial pressure of 0.10 MPa, the combustion durations of DMC/gasoline blends showed non-linear behavior, being shorter than those of pure gasoline and DMC and comparable to those of the ethanol/gasoline blends. However, the blending effect of DMC on combustion durations was greatly mitigated when the initial pressure was reduced to 0.05 MPa. Conversely, the combustion durations for ethanol/gasoline blends showed a nearly monotonic reduction with an increase in the ethanol blending ratio at both initial pressures of 0.10 and 0.05 MPa. Finally, we discussed the differential impact of the blending effect of oxygenated hydrocarbons on combustion characteristics.

Optimizing transducer aperture subdivision for aberration correction during transabdominal histotripsy

This study investigated the effect of transducer aperture subdivision on aberration correction performance for transabdominal histotripsy. A transducer aperture and geometric curvature similar to clinical histotripsy devices (750 kHz, 20 × 16 cm width, 14 cm radius of curvature) was subdivided into 64, 256, and 1024 elements (10.7λ, 5.3λ, 2.6λ). For each of the three designs, optimal space filling (100%) equal area polygons with a pseudo-random arrangement of elements was used following the technique described by Rosnitskiy. 3D acoustic path maps were constructed from abdominal CTs of 3 de-identified human subjects and assigned acoustic properties from literature. For each transducer, acoustic transmission was simulated using k-Wave at 3 target locations in the liver of each subject with and without implementing ideal aberration correction. Across all subjects and targets (n = 9), AC increased the maximum focal pressure amplitude by 26% (0%-59%) on average for 64 elements, 38% (5%-84%) for 256 elements, and 42% (7%–92%) for 1024 elements. These results suggest 5.3λ elements may near an optimal subdivision for transabdominal histotripsy aberration correction when taking into account the cost of transducer and driving system fabrication. Acoustic simulations can save fabrication time and costs when optimizing device design.

Study of pressure wave dynamics in a channel with a spherical bubble cluster

The features of wave propagation in a bubbly liquid are associated with the combined interaction of nonlinear, dispersive, and dissipative effects. In a liquid with bubbles, the properties of a practically incompressible liquid, which is a carrier phase, change dramatically with a small volume (and even more so, mass) addition of gas (bubbles), which is a dispersed phase. The peculiarity of bubbly liquids is due to their high static compressibility while maintaining a high density close to that of the liquid, which in turn leads to a low equilibrium speed of sound. In this paper, we study two-dimensional axisymmetric wave perturbations in a channel with water containing a spherical cluster filled with a water-air bubble mixture and located at one of the end boundaries. Based on the results of numerical calculations, the dependence of the maximum pressure amplitude formed in the channel on the geometrical parameters of the cluster is analyzed. It has been established that the presence of a near-end bubble cluster can significantly both increase and decrease the effect of the wave signal incident on the wall, depending on the size of the cluster and its characteristics.

Acoustophoretic trapping of particles by bubbles in microfluidics

We present in this paper a simple method to produce strategic acoustic particle capture sites in microfluidic channels in a controlled way. Air bubbles are intermittently injected into a micro-capillary with rectangular cross section during a flow motion of liquid suspensions containing micron-sized particles or particles to create bubble-defined “micro-gaps” with size close to 200 µm and spheroidal geometry. The establishment of a 3D standing acoustic wave inside the capillary at a frequency close to 1 MHz produces different radiation forces on solid particles and bubbles, and acoustic streaming around the bubble. While the sample flows, part of the particles collect along the acoustic pressure node established near the central axis and continue circulating aligned through the capillary until reaching the end, where are released enriched. Meanwhile, the bubble travels very fast toward positions of maximum pressure amplitude beside the channel wall, driven by Bjerkness forces, and attach to it, remaining immovable during the acoustic actuation. Some particles adhere to its membrane trapped by the acoustic streaming generated around the oscillating bubble. Changes of frequency were applied to analyze the influence of this parameter on the bubble dynamics, which shows a complete stability once attached to the channel wall. Only increasing the flow motion induces the bubble displacements. Once reached the open air at the end of the capillary, the bubble disappears releasing the trapped particles separated from their initial host suspension with a purity degree. The device presents a very simple geometry and a low-cost fabrication.

Energy Dissipation and Chemical Yield of an Ultrasound Driven Single Bubble

A detailed parameter study is made of chemically active spherical bubbles. The calculations apply an up-to-date chemical mechanism for pure oxygen initial content, taking into account pressure dependency, duplication of chemical reactions, and proper third-body efficiency coefficients. The chemical yield is defined as the amount of substance at the maximum bubble radius, and the dissipated power is approached in a relatively new method. The parameter study focuses on finding the parameter combinations where maximum yield and maximum energy efficiency arise for various chemical species (O3, OH radical, H2 and H2O2). Results show that the locations of maximum yield and efficiency points differ significantly, depending on the chemical species. Usually, neither chemical yield nor efficiency values arise at maximum pressure amplitude and minimum driving frequency (as one would presumably expect).

PS-BPC03-7: ARE OSCILLOMETRIC WAVEFORMS DIFFERENT IN PREGNANCY?

Objective: Hypertensive disorders of pregnancy are leading causes of maternal and perinatal morbidity and mortality. Automated blood pressure (BP) measurements are being used in clinical practice; however, understanding of how oscillometric waveform vary between pregnant and non-pregnant individuals remains low. Design and Methods: Pregnant individuals over 20 weeks gestational age and healthy, non-pregnant women were recruited. Healthy, non-pregnant women (HNP) were matched to healthy pregnant women (HP), and pregnant women with a hypertensive disorder of pregnancy (HDP) by age (± 10 years), arm circumference (± 6 cm), and BMI at the time of BP measurement (± 13 kg/m2). There were seven individuals in each group for a total of 21 participants. BP measurements were done per the International Organization for Standardization (ISO) protocol using a custom-built oscillometric device as the test device and 2-observer mercury auscultation as the reference measurement. Four pairs of auscultatory measurements and four oscillometric measurements were obtained for each participant. Baseline demographics, auscultatory BP and BP derived from slope-based and fixed ratio algorithms were determined. Oscillometric waveform and envelope features were compared among groups. Results: In HNP, HP, and HDP groups respectively: mean age was 31.3 ± 4.8; 32.1 ± 3.6; 32.0 ± 4.4 years; arm circumference 31.9 ± 3.3; 32.3 ± 4.9; 34.0 ± 3.3 cm; BMI 26.8 ± 3.8; 32.0 ± 7.2; 32.4 ± 3.7 kg/m2; mean auscultatory BP (systolic/diastolic) 103.3 ± 11.1/66.5 ± 7.4; 110.6 ± 4.0/56.9 ± 6.5; 132.6 ± 19.0/83.9 ± 13.3 mmHg. HDP had significantly higher auscultatory systolic (P < 0.05) and diastolic (p < 0.01) BP than the other groups. The pregnant groups (HP, HDP) had significantly higher heart rate (p < 0.01); higher pulses (p < 0.05) in the oscillometric waveform (OMV); lower average width in the pulses (p < 0.01); higher pressure amplitude at which the OMW peaks (p < 0.05) with longer time to reach this maximum pressure amplitude (p < 0.05); greater area under the curve (p < 0.01). Compared to HNP, the HDP showed significantly skewed OMW to the right (p < 0.01); greater spread in the OMW envelope (p < 0.05) and lesser random variation in the OMW envelope (p < 0.01). A typical OMV with the 3 groups superimposed is demonstrated in Figure 1. Conclusion: Significant differences in the oscillometric waveform morphology and parameters were found in pregnancy and in hypertensive disorders of pregnancy compared to healthy controls. These results suggest that pregnancy-specific algorithms may be required to optimize accuracy for oscillometric BP measurement.

Criteria of thermochemical conditions of steam gas explosions in dynamic accident modes at nuclear power units with WWER reactors

The main lessons of the major accident at the Fukushima-Daiichi NPP in 2011 for the nuclear power industry identify the need to model, analyze and develop emergency measures for relatively unlikely events with catastrophic environmental consequences, taking into account multiple failures of safety systems. Steam-gas explosions became one of the main causes of the catastrophic environmental consequences of the Chernobyl and Fukushima accidents. Criteria and conditions for the occurrence of steam-gas explosions in dynamic emergency modes in the "tight" reactor circuit of nuclear power reactor units (NPP) with water-water reactors (WWER) with failures of safety systems valves and emergency steam gas removal are determined by the rate of change of thermodynamic and physico-chemical parameters. A method for determining the criteria and conditions for the occurrence of steam-gas explosions in dynamic accident modes with a "tight" reactor circuit and failure of safety valves for modeling the initial emergency events – seismic effects, falling of massive objects, etc. is presented. The conditions for the occurrence of hydrogen explosions are determined by the maximum rate of increase in the temperature of fuel oil shells, and the conditions for steam explosions are determined by the maximum rate of pressure increase as a result of the intensification of vaporization processes. The criteria for the occurrence of steam explosions in dynamic emergency modes are determined by the maximum pressure amplitude and the propagation speed of acoustic disturbances in the steam volume. And the criteria for hydrogen detonation in dynamic emergency modes are determined by the maximum amplitude of the increase in the temperature of the fuel shells and the average flow rate of the coolant in the active zone of the reactor.

Piezoelectric Harvesting of Fluid Kinetic Energy Based on Flow-Induced Oscillation

Flow-induced oscillations widely exist in pipelines, fluid machinery, aerospace, and large-span flexible engineering structures. An inherent energy conversion mechanism can be developed for fluid kinetic energy utilization or acoustic energy harvesting. Fluid-resonant acoustic oscillation is featured by stability, easy operation, and a simple mechanical structure. Acoustic oscillation has high intensity and a mono-frequency, which is beneficial for energy harvesting. A simple cavity with appropriate structural dimensions that can induce fluid-resonant oscillations is set and combined with piezoelectric technology to generate electric power. The energy conversion mechanism is studied numerically and experimentally. The effects of flow velocity on the acoustic frequency, the pressure amplitude, and the output voltage of piezoelectric transducer are analyzed. A stable standing wave acoustic field can be generated in the cavity in a certain range of flow velocity. The results show that the higher intensity acoustic field occurs in the first acoustic mode and the first hydraulic mode and can be obtained in the range of flow velocity 27.1–51.1 m/s when the cavity length is 190 mm. A standing wave acoustic field occurs with a frequency of 490 Hz and a maximum pressure amplitude of 15.34 kPa. The open circuit output voltage can reach 0.286 V using a preliminary transducer. The device designed based on this method has a simple structure and no moving parts. It can harvest the fluid kinetic energy that widely exists in pipelines, engineering facilities, air flow forming around transportation tools, and the natural environment. Its energy output can be provided for the self-powered supply system of low-power sensor nodes in wireless sensor networks.

Noncontact rotation of a small object using ultrasound standing wave and traveling wave

In an acoustic standing wave generated in the air between a vibrator and a reflector, a small object is levitated near the nodal positions of the sound pressure where the acoustic radiation force and the gravity are balanced. By controlling the sound field spatially and temporally, the object can be transported without contact. In this report, we experimentally investigated the non-contact high-speed rotation of a small object using ultrasound, which can be applied to measurement techniques of the physical properties of liquids. The experimental system consists of a vibrating disc with four bolt-clamped Langevin-type transducers and a reflector, and an acoustic standing wave is generated between them. The effects of the tilt angle of the reflector with respect to the vibrator on the rotation speed of the object and the acoustic field were investigated. When the tilt angle was around 1.2°, the object was trapped in the air at 31.5 kHz by the standing-wave component in the vertical direction and rotated by the traveling-wave component propagating in the horizontal direction. The maximum sound pressure amplitude and the rotation speed of the object were changed with the tilt angle, and a larger sound pressure amplitude gave a larger rotation speed.

Numerical and Experimental Study on the Effect of Rotor–Stator Distance on Rotor–Stator Interaction Strength within Mixed-Flow Centrifugal Pumps

In this article, the influence of rotor–stator distance on the pump performance and rotor–stator interaction strength within mixed-flow centrifugal pump was investigated based on numerical calculation and test verification. Firstly, the performances of mixed-flow centrifugal pumps with two different rotor–stator distances were obtained and compared with the numerical results, which confirms the high accuracy of the numerical simulation. Next, the performances of mixed-flow centrifugal pumps with five different rotor–stator distances were compared and analyzed. It was found that the hydraulic performance of the mixed-flow centrifugal pump varies slightly as the rotor–stator distance increases. The mean values of the standard deviation of the head and efficiency of the mixed-flow centrifugal pump at each rotor–stator distance under full flow conditions are only 0.16 m and 0.11%, respectively. Then, the strengths of the rotor–stator interaction with different rotor–stator distances were analyzed. It was found that the strengths of the shock interaction, the wake interaction, and the potential interaction were all reduced with increasing rotor–stator distance. Moreover, when the rotor–stator distance is 1.5 mm, the pressure distribution in the circumferential direction of the rotor–stator interference zone shows obvious unstable characteristics: the pressure change amplitude is significantly greater than the other rotor–stator distance of the pressure change amplitude, the maximum and minimum pressure amplitude difference being 56.9 kPa, and with the increase in the rotor–stator distance, the maximum and minimum pressure amplitude difference gradually decreases, with an average value of 32.3 kPa. These findings could provide useful insight into prospects for the improvement of the operational stability of mixed-flow centrifugal pumps, and the results of this study can be extended to all centrifugal pumps using diffusers in the form of vanes as the pressure chamber, which has strong practical application and theoretical value.

Meteorological parameters and hospitalizations of patients with sickle cell anemia: a 20-year retrospective study in Campinas, São Paulo, Brazil

ABSTRACT To investigate the influence of climate on hospitalizations of sickle cell anemia (SCA) adults and children, we analyzed the health and meteorological parameters from a metropolis (1999-2018). 1462 hospitalizations were coded for SCA patients in crisis (M:F = 715:747) and 1354 hospitalizations for SCA patients without crisis (M:F = 698:656) [age = 22.9 vs 15.2 years and duration of hospitalization (DoH) = 5.7 vs 4.4 days, respectively,]. More hospitalizations were for adults than children in crisis, and for children than adults without crisis. More children and adults were hospitalized in winter andspring than in summer and autumn Hospitalizations correlated positively with humidity (lag −5), maximum pressure (lag −2), mean pressure (lag −2), and thermal amplitude (lag −2), and negatively with maximum temperature (lag −3). DoH positively correlated with minimum temperature (lag −4). Understanding these complex associations would induce attitudinal/behavioral modifications among patients and their caregivers.

Effects of phase aberration on transabdominal focusing for a large aperture, low f-number histotripsy transducer

Objective. Soft tissue phase aberration may be particularly severe for histotripsy due to large aperture and low f-number transducer geometries. This study investigated how phase aberration from human abdominal tissue affects focusing of a large, strongly curved histotripsy transducer. Approach. A computational model (k-Wave) was experimentally validated with ex vivo porcine abdominal tissue and used to simulate focusing a histotripsy transducer (radius: 14.2 cm, f-number: 0.62, central frequency f c: 750 kHz) through the human abdomen. Abdominal computed tomography images from 10 human subjects were segmented to create three-dimensional acoustic property maps. Simulations were performed focusing at 3 target locations in the liver of each subject with ideal phase correction, without phase correction, and after separately matching the sound speed of water and fat to non-fat soft tissue. Main results. Experimental validation in porcine abdominal tissue showed that simulated and measured arrival time differences agreed well (average error, ∼0.10 acoustic cycles at f c). In simulations with human tissue, aberration created arrival time differences of 0.65 μs (∼0.5 cycles) at the target and shifted the focus from the target by 6.8 mm (6.4 mm pre-focally along depth direction), on average. Ideal phase correction increased maximum pressure amplitude by 95%, on average. Matching the sound speed of water and fat to non-fat soft tissue decreased the average pre-focal shift by 3.6 and 0.5 mm and increased pressure amplitude by 2% and 69%, respectively. Significance. Soft tissue phase aberration of large aperture, low f-number histotripsy transducers is substantial despite low therapeutic frequencies. Phase correction could potentially recover substantial pressure amplitude for transabdominal histotripsy. Additionally, different heterogeneity sources distinctly affect focusing quality. The water path strongly affects the focal shift, while irregular tissue boundaries (e.g. fat) dominate pressure loss.