Increasing Power Levels Research Articles

Comparative analysis of acoustic calculation methods for throttling devices

Objective. The identification of increased noise levels from ventilation systems during the operation of buildings necessitates complex and costly procedures to detect and eliminate noise sources, conduct dismantling work, install additional silencers, or replace ventilation equipment. Therefore, accurate acoustic calculations are one of the most critical tasks in the design of various facilities. Method. This article presents an analysis of domestic and international methods for determining the noise generated by throttling devices. The accuracy of the calculation results was evaluated by comparing them with data from field tests. Result. A sharp increase in sound power level within the throttling device was observed when the blade angle exceeded 60 degrees, significantly impacting the acoustic environment of the premises and leading to an exceedance of regulated noise levels. Conclusion. The conducted comparative analysis of existing calculation methods revealed that the domestic calculation method provides the required margin for the sound power level of the throttling device across all octave bands. A notable drawback of international calculation methods is the lack of consideration for the acoustic impact of duct fittings and the connection of the duct to the throttle, which underscores the need for further validation of these methods for complex systems.

Interactions of contact force, impedance, and power during repeated atrial arrhythmia ablation after previous atrial fibrillation ablation

BackgroundAcutely effective repeated radiofrequency catheter ablation (RFCA) after previous atrial fibrillation ablation depends on several parameters including local impedance (LI), contact force (CF), and power. ObjectiveWe aimed to investigate the relationship of LI, CF, and power to the LI drop in a repeated atrial RFCA environment. MethodsConsecutive patients undergoing repeated atrial RFCA were studied. High-quality local electrograms were analyzed for morphology changes indicating effective RFCA and associated LI dynamics. The influence of baseline LI, mean CF, and power on the LI drop was analyzed. Investigated power levels included ≤25 W, 30 W, and ≥40 W. ResultsA total of 1390 RFCA points from 48 patients (48% female; median age, 70 years) were analyzed. Of 309 analyzed electrograms, 40.5% showed effective RFCA morphology changes with an elevated median LI drop (effective, 19.7 Ω; partially effective, 14.1 Ω; P < .001). CF showed the highest correlation to the LI drop within high baseline LI and when applying ≥40 W (low baseline LI, R = 0.39; intermediate, R = 0.66; high, R = 0.72). Within low baseline LI regions, CF levels showed a lower correlation to the LI drop (≤25 W, R = 0.30; 30 W, R = 0.35; ≥40 W, R = 0.39). A mean CF ≥10 g resulted in elevated LI drops with higher power compared with lower power within all baseline LI tertiles (P < .001 each). ConclusionWithin high baseline LI regions, CF plays a greater role for the maximum LI drop when higher power is chosen. A mean CF ≥10 g ensures elevated LI drops with increasing power levels.

Cooling of 1 MW Electric Motors through Submerged Oil Impinging Jets for Aeronautical Applications

Electrification of aircraft is a very challenging task as the demand for energy and power is high. While the storage and generation of electrical energy are widely studied due to the limited specific energy and specific power of batteries and fuel cells, electric machines (power electronics and motors) which have years of experience in many industrial fields must be improved when applied to aviation: they generally have a high efficiency but the increase in power levels determines significant thermal loads which, unlike internal combustion engines (ICE), cannot be rejected with the exhaust. There is therefore a need for thermal management systems (TMSs) with the main objective of maintaining operating temperatures below the maximum level required by electric machines. Turboprop aircraft, such as the ATR 72 or the Dash 8-Q400, are commonly used for regional transport and are equipped with two gas turbine engines whose combined power is in the order of 4 MW. Electric and hybrid propulsion systems for these aircraft are being studied by several leading commercial aviation industries and start-ups, and the 1MW motor size seems to be the main option as it could be used in different aircraft configurations, particularly those that exploit distributed electric propulsion. With reference to the topics mentioned above, the present work presents the design of a TMS for a high-power motor/generator whose electrical architecture is known. Once integrated with the electrical part, the TMS must allow a weight/power ratio of 14 kW/kg (or 20 kW/kg at peak power) while maintaining the temperature below the limit temperature with reasonable safety margins. Submerged jet oil is the cooling technique here applied with a focus on diathermic oil. Parameters affecting cooling, like rotor speed and filling factor, are analysed with advanced CFD.

Study of hydraulic turbine flow-induced noise distribution law based on defective runner blade

Abstract In order to analyse flow-induced noise distribution law under the defective runner blade, this paper performs defective treatment on the runner blade according to the HLA855a-LJ-250 hydraulic turbine model. Two kinds of blade models, intact blade and outlet side abrasive blade, are established respectively, and the Realizable k-ε turbulence model and broadband noise source model are used to simulate the hydraulic turbine under rated operating conditions. The simulation results show: 1)Double-row leaf grilles and runner blade are the main dipole flow-induced noise sources; 2)Significant differences in the distribution of the acoustic power levels of the double-row leaf grilles’ characteristic blades and the runners’ characteristic blades under different Schemes; 3)Runner defective blades have less effect on the acoustic power level of spiral case, the rest of the overflow components acoustic power level has a tendency to increase, especially the runner has the greatest impact. The maximum increase in acoustic power level of the runner is almost 17 dB, followed by double-row leaf grilles with an increase of around 8 dB. Therefore, critical attention needs to be paid to the abnormal noise signals of runner and double-row leaf grilles.

Digital non-Foster-inspired electronics for broadband impedance matching

Narrow bandwidths are a general bottleneck for applications relying on passive, linear, subwavelength resonators. In the past decades, several efforts have been devoted to overcoming this challenge, broadening the bandwidth of small resonators by the means of analog non-Foster matching networks for radiators, antennas and metamaterials. However, most non-Foster approaches present challenges in terms of tunability, stability and power limitations. Here, by tuning a subwavelength acoustic transducer with digital non-Foster-inspired electronics, we demonstrate five-fold bandwidth enhancement compared to conventional analog non-Foster matching. Long-distance transmission over airborne acoustic channels, with approximately three orders of magnitude increase in power level, validates the performance of the proposed approach. We also demonstrate convenient reconfigurability of our non-Foster-inspired electronics. This implementation provides a viable solution to enhance the bandwidth of sub-wavelength resonance-based systems, extendable to the electromagnetic domain, and enables the practical implementation of airborne and underwater acoustic radiators.

THE EFFECTS OF LASER MICRO-ENGRAVING VARIABLES ON THE SURFACE CHARACTERISTICS OF THE Ti-6Al-7Nb ALLOY

This investigation aims to analyze the impact of scanning direction, scanning speed, and power level (%) on the surface roughness of Ti-6Al-7Nb alloy specimens subjected to laser micro-engraving. The laser micro-engraving process was carried out by scanning the predetermined geometric configuration six times. Factorial analysis was implemented to determine the impact of system parameters on the surface roughness. Throughout the micro-engraving operations, line spacing, frequency, and pulse width parameters were maintained at a consistent value of 0.03 mm, 100 kHz, and 300 ns, respectively. The optimal conditions for achieving the lowest surface roughness were observed at a scanning speed of 700 mm/s, a power level of 60%, and a scanning direction of 90°. Moreover, in accordance with the experimental parameters employed in this investigation, it was observed that increasing the scanning speed while maintaining a constant power level (%) reduced surface roughness. There was a direct correlation between the increase in power level (%) and a corresponding increase in surface roughness.

Multiphysics simulations of uniaxial compression applied to various rock samples subject to microwave pretreatment

PurposeAmong the various applications involving the use of microwave energy, its growing utility within the mining industry is particularly noteworthy. Conventional grinding processes are often overburdened by energy inefficiencies that are directly related to machine wear, pollution and rising project costs. In this work, we numerically investigate the effects of microwave pretreatment through a series of compression tests as a means to help mitigate these energy inefficiencies.Design/methodology/approachWe investigate the effects of microwave pretreatment on various rock samples, as quantified by uniaxial compression tests. In particular, we assign sample heterogeneity based on a Gaussian statistical distribution and invoke a damage model for elemental tensile and compressive stresses based on the maximum tensile stress and the Mohr–Coulomb theories, respectively. We further couple the electromagnetic, thermal and solid displacement relations using finite element modeling.Findings(1) Increased power intensity during microwave pretreatment results in decreased axial compressive stress. (2) Leveraging statistics to induce variable compressive and tensile strength can greatly facilitate sample heterogeneity and prove necessary for damage modeling. (3) There exists a nonlinear trend to the reduction in smax with increasing power levels, implying an optimum energy output efficiency to create the maximum degradation-power cost relationship.Originality/valuePrevious research in this area has been largely limited to two-dimensional thermo-electric models. The onset of high-performance computing has allowed for the development of high-fidelity, three-dimensional models with coupled equations for electromagnetics, heat transfer and solid mechanics.

Impact of microwave heating on product safety and quality in meatballs

The effects of microwave heating at different processing time and power levels (360 W, 600 W and 900 W) on Salmonella Typhimurium, Escherichia coli O157:H7, Listeria monocytogenes and Staphylococcus aureus in Turkish type meatballs were evaluated. Besides, the changes in the textural and sensorial properties of meatballs were determined to reveal the cooking time and temperatures that would make the product safety without affecting the consumer preferences. In this direction, the experimentally contaminated meatballs were subjected to microwave heating at low, medium and high power levels for different processing times and analysed for the survival of the relevant pathogenic bacteria. The total aerobic bacteria count in meatballs could be reduced approximately 3–4 log CFU/g by medium and high microwave powers, whereas 5–7 log CFU/g inhibition was obtained in meatballs inoculated with pathogens. The increase in power level together with the increasing process time resulted in a decrease in the counts of bacteria and an undesirable effect on the textural and sensorial qualities of meatballs. Microwave heating at medium and high power levels as from 3 min, caused excessive drying and blackening of the product, making it difficult to consume due to crust formation. Consequently, to achieve optimal acceptability of the product by consumers, meatballs should be heated with a microwave power of 600 W and 900 W for 3 min.

The effect of Feminist Therapy-Based Group Counseling program on women's psychological empowerment and internalized sexism.

This study aims to develop and examine the effectiveness of a group counseling program based on feminist therapy to empower women and reduce internalized sexism. The program was designed based on the perspective of consciousness-raising groups, which have an essential place in women's movements. A quasi-experimental design with a pretest-posttest control group was used. The participants of the study were 26 young women, with an average age of 22.50±1.10. Data collection tools included the Internalized Sexism Scale, Woman Psychological Power Scale, and Personal Information Form. Analysis of covariance was used for the data analysis. The results suggested a decrease in internalized sexism levels and an increase in psychological power levels among the participants. These results are important for both mental health and gender studies, and may contribute to future practices and research on psychological and educational interventions to reduce sexism among women.

Cold plasma processing of sesame milk: Changes on physicochemical properties, nutrition, anti-nutritional factors, protein structure and allergenicity

In the recent decade, consumers have preferred plant-based (vegan) foods due to the maintenance of environmental sustainability. However, some of the plant-based foods have a demerit of the presence of anti-nutritional factors and allergenic components. Thus, the current study was aimed at reducing these demerits in sesame milk without spoiling the quality by the use of green, novel, cold plasma technology. This study investigated the effect of a low-pressure plasma (LPP) system's power levels (25, 60 and 120 W) on the physicochemical properties, nutritional changes, anti-nutritional factors, protein structure and allergenicity of sesame milk. No prominent or undesirable changes were observed in the physicochemical properties; conductivity increased with the increase in power level (59.23 mS/cm in control to 61.67 mS/cm at 120 W). The lipoxygenase activity was reduced to 67 % for samples treated at 120 W LPP power. The anti-nutritional factors phytates (25 % reduction from 1.47 mg/g in control to 1.09 mg/g in 120 W) and oxalates (10 % reduction from 39.14 µg/g in control to 35.18 µg/g 120 W) decreased slightly during plasma application. The DSC and FTIR analysis revealed that plasma-induced oxidation changed the secondary protein. However, there was no significant reduction (5 %) in allergenicity during LPP treatment. Though, the plasma application was effective in reducing the enzyme activity and antinutritional factors, no drastic reduction or complete elimination was observed. An increase in power level or exposure time in future could aid in the reduction of allergenicity in sesame milk.

Inactivation of foodborne pathogens in ground pork tenderloin using 915 MHz microwave heating depending on power level

The main purpose of this research was to investigate the effect of power level of 915 MHz microwave heating on the inactivation of foodborne pathogens in ground pork and its bactericidal mechanism. It was demonstrated that the heating rate was proportional to the power level. For instance, the heating rates observed at microwave heating powers of 2, 3, 4, and 5 kW were 1.70, 2.77, 3.35, and 4.03℃/s, respectively. The bactericidal effect of microwave heating also significantly (P < 0.05) increased with increasing power level. In particular, when ground pork was subjected to microwave heating at 5 kW, the reduction level of pathogens was>2 log units higher than at 2 kW. To determine the bactericidal mechanism of microwave heating depending on power level, changes in transmembrane potential and DNA damage were determined using fluorescence. The extent of depolarization in membrane potential of pathogens significantly (P < 0.05) increased as power level increased. There was no significant difference in degree of DNA damage at different power levels. However, the percentage of DNA damage was>86% at all power levels. The transmembrane potential assay indicates that the bacteria exhibited dramatic pore formation on the membrane at 5 kW. Through transmission electron microscopy, the electroporation effect was enhanced as power level increased. Moreover, the quality of ground pork subjected to microwave heating at 2–5 kW was determined by measuring the moisture content, cooking loss, and texture profile.

Active Metasurface Absorber for Intensity- Dependent Surface-Wave Shielding

A novel intensity-dependent metasurface absorber for continuous surface waves is presented, which is composed of electrically tunable unit cells controlled by a centralized active module. PIN diodes are embedded in the unit cells, functioning as rheostats for both the dispersion tuning and dissipation adjustment. The module fulfills the nonlinearity by sensing incoming wave intensities and offers direct-current (DC) signals to control the absorptive array. Owing to the centralized control, the cells operate in good consistency, hence beneficial for a wide frequency band and absorption range. A prototype is fabricated and measured, and its strong intensity-dependent absorption is demonstrated. When the incident power level increases, the absorptance is enhanced gradually from 19.4% to 92.7%. In an instantaneous bandwidth of 12.0%, the absorption can be tuned from 30% to 80% by changing the power. Furthermore, the dynamic range of power and absorption range can be flexibly customized as required, and the nonlinear functions can be promptly turned off if necessary, showing the advantages of the active mechanism. Such results enable the metasurface to be useful in electromagnetic shielding to mitigate the harmful impact of strong surface waves and protect small useful signals.

Stabilization of Olive Oil in Water Emulsion with Dairy Ingredients by Pulsed and Continuous High Intensity Ultrasound.

Application of high intensity ultrasound (HIUS) for stabilization of olive oil in water emulsion with different dairy ingredients including sodium caseinate (NaCS) and whey protein isolate (WPI) was investigated. The emulsions were prepared by homogenization with a probe and then treated with either a second homogenization or HIUS at a different power level (20 and 50%) in pulsed or continuous mode for 2 min. The emulsion activity index (EAI), creaming index (CI), specific surface area (SSA), rheological properties, and droplet size of the samples were determined. The temperature of the sample rose when HIUS was applied in continuous mode and at increasing power level. HIUS treatment increased EAI and SSA of the emulsion and decreased droplet size and CI compared with those of the double-homogenized sample. Among the HIUS treatments, the highest EAI was found in the emulsion with NaCS that was treated at a power level of 50% in continuous mode, and the lowest one was obtained by HIUS applied at a power level of 20% in pulsed mode. SSA, droplet size, and span of the emulsion were not affected by HIUS parameters. Rheological properties of HIUS-treated emulsions were not different from those of the double-homogenized control sample. Continuous HIUS at 20% power level and pulsed HIUS at 50% power level reduced creaming in the emulsion after storage at a similar level. HIUS at a low power level or in pulsed mode can be preferred for heat sensitive materials.

New Converter Solution With a Compact Modular Multilevel Structure Suitable for High-Power Medium-Voltage Wind Turbines

Modern wind turbines with increasing power levels are continuously emerging. These power levels are reaching a point where excessively high currents are obtained if the traditional low-voltage wind-turbine structure is adopted. High currents lead to excessively high losses and the need for bulky and heavy conductors to carry them. A medium-voltage structure should be a more competitive alternative to be adopted in high-power wind turbines. In this article, a new converter solution with a modular multilevel structure suitable for driving modern/future high-power medium-voltage wind turbines is proposed. This converter topology has desirable features common to modular multilevel converters, such as the improved reliability at high voltage levels, and the possibility to synthesize high-power-quality staircase-shape voltages, which leads to low requirements for harmonic and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${dv}/{dt}$</tex-math></inline-formula> filters. Furthermore, the proposed converter presents reduced capacitance and inductance requirements compared with other well-established modular multilevel converter topologies, which should result in a lighter and more compact solution. The proposed solution could potentially allow for the reduction of the overall costs of the supporting structure required to withstand the weight of the wind turbine. Simulation and experimental results are presented in this article to validate the proposed topology.

Ultrasonic Vibration Technology to Improve the Thermal Performance of CPU Water-Cooling Systems: Experimental Investigation

The rapid growth of the electronics industry and the increase in processor power levels requires new techniques to improve the heat transfer rate in their cooling systems. In this study, ultrasonic vibration technology was introduced as an active method to enhance the thermal performance of water-cooling systems. The effects of ultrasonic vibrations at power levels of 30, 60, and 120 watts for different cooling airflow rates were investigated experimentally. The results were validated with available empirical correlations to ensure the accuracy of the measurement systems. The findings indicated that the ultrasonic vibrations enhanced the heat transfer in the liquid-cooling heat exchangers. In addition, the thermal performance of the ultrasonic vibrations was improved by reducing the airflow rate and increasing the ultrasonic power. In addition to the feature of heat transfer improvement, ultrasonic waves are widely used for the cleaning of different types of heat exchangers. Regarding the anti-fouling and anti-accumulation effects of the ultrasonic vibrations, the introduced technology could provide a practical way for developing high-performance nanofluids-based computer cooling systems.

Partial-Power Converter Topology of Type II for Efficient Electric Vehicle Fast Charging

The increasing power levels handled by electric vehicle (EV) dc fast chargers will impose additional challenges to the switching devices in order to cope with the efficiency requirements. A cost-effective alternative to achieve highly efficient power conversion is through the partial-power conversion concept. This article validates the advantages of a step-down Type II partial-power converter (PPC), based on the phase-shifted full-bridge converter, for EV fast chargers. By exploiting the reduced voltage range of an EV battery pack along with the reduced power ratio for a Type II PPC, an extremely efficient charging process can be achieved. The concept is validated with the development of a 7-kW demonstrator, and hence, realistic efficiency measurements are obtained. Results indicate the effectiveness of charging a battery by merely handling 13.32% of the power provided to it, with a peak efficiency of 99.11%.

State-Based peridynamics for thermomechanical modeling of fracture mechanisms in nuclear fuel pellets

This study presents a coupled thermomechanical ordinary state-based peridynamic (OSB-PD) model, including the effects of randomly varying strength parameter and crack gap heat transfer, to investigate the fracture mechanisms in nuclear fuel pellets. The three-dimensional (3D) models of fuel pellets are constructed through irregular non-uniform discretization. The model includes the random variability of the critical stretch of each bond based on normal distribution. The accuracy of the OSB-PD model is validated against the FEM results for the thermomechanical behavior of a fuel pellet without damage. Subsequently, the crack propagation and crack patterns of fuel pellet are studied at different power levels (10 ∼ 40 kW/m). The results show that radial and axial cracks mainly develop during the power rise stage while the circumferential cracks develop during power down stage. These three crack types are verified by comparing with the experimental observations. The number of cracks and fragments of the fuel pellet increases with the increase in power level. Moreover, the fuel pellet can be completely separated at the mid-height cross section when the power level is equal or greater than 25 kW/m.

A computational conjugate heat transfer study of a rectangular minichannel undergoing sinusoidal flow pulsations

The development of current and next generation high performance electronic devices has led to smaller components in more densely packed spaces. The increasing power levels have resulted in ever-increasing heat flux densities which necessitates the evolution of new liquid-based heat exchange technologies. Pulsating flow in single-phase cooling systems is viewed as a potential solution to the problems involving high heat flux densities. A review of published literature indicates a lack of time-resolved and space-resolved links between the hydrodynamic pulsating characteristics and associated heat transfer perturbations. The scope of this work involves the development of a validated three-dimensional conjugate heat transfer computational model to investigate hydrodynamically and thermally fully developed pulsating flows in a heated rectangular minichannel. Simulations were performed for a sinusoidal waveform with a fixed pulsation amplitude for varying pulsation frequencies in the range of 0.02 Hz to 25 Hz, corresponding to Womersley numbers in the range of 0.5 ≤Wo≤ 18.33. Low pulsation frequencies exhibited the well known parabolic profile for the fluctuating hydrodynamic and thermal parameters, i.e., velocity, wall shear, and wall temperature. As a result, the axial pressure gradient, velocity, and wall shear stress profiles were in phase and similar results were obtained for the oscillating wall and bulk fluid temperatures. For the inertia dominated high frequency flows, an increase in axial pressure gradient leads to a phase lag of π/2 when compared with the velocity and wall shear profiles. The shorter time period pulsations exhibit unique attributes in the form of flow reversal effects at local near wall regions. High near wall thermal gradients were observed as a result of stronger viscous effects due to a narrowing thermal boundary layer; consequently the transverse diffusion of heat was ineffective. A phase lag and a subsequent drop in the peak magnitudes existed between the oscillating bulk and wall temperatures for high frequency flows. Fluctuations in near wall heat flux profiles showed a dependency on the imposed pulsation frequencies. For the chosen pulsation profile and frequencies, the overall time averaged thermal performance indicates that pulsating flow performs worse than steady flow for a flow rate amplitude of 1. The highest thermal performance was achieved for Wo=5.1 while maintaining a low friction factor.

Microwave heating and fracturing of granite: Insights from infrared thermal imaging

Microwave heating has been considered as one of the promising rock breaking technologies. However, the non-uniform temperature distribution of microwave treated rocks has not been quantitatively studied and the microwave rock fracturing mechanisms have not been systematically revealed. In this paper, microwave heating tests were implemented using a 6 kW industrial microwave system. The ratio of maximum temperature to average temperature () was studied to characterize the non-uniformity of temperature. The temperature gradient and maximum temperature difference were calculated to quantitatively characterize the thermal stress. Experimental results indicate that the granite fracture temperature threshold is about 200 °C and cracking typically occurs at a minimum temperature gradient of 6 °C/mm. As either power level or irradiation time increases, the thermal gradient and temperature difference increase. For a fixed microwave energy, microwave heating at higher power levels for a shorter duration has a higher and a greater temperature difference and temperature gradient, which explains that the combination of high power and short heating time yields better rock weakening effects.

Effect of vacuum assisted microwave drying on drying behavior of potato cubes

The present study was focused on effect of microwave powers i.e. 160, 320, 480, 640, and 800 W on dryingcharacteristics of potato cube (1.2 c. m. x 1.2 c. m. x 1.2 c. m.). Microwave drying led to reduction in moisturecontent and drying time reduced with the increase in power level. Increase in power level from 20% to100% led to reduction in drying time approximately of 8 min. The drying rate increased with increasingpower level having a minimum value of 0.043% for 160 W power levels to a maximum value of 0.29% for800 W power levels. Increasing the vacuum level further increased the drying rate for each power level. At160 W power level for 100 mmHg vacuum level the maximum reduction in moisture content was 48.668%dry basis, which was increased to a maximum difference in moisture content of 215.75% dry basis at 300mmHg vacuum level or 800 W power level corresponding to a 1/8 time reduced duration of 2.5 min.