Power Absorption Efficiency Research Articles

The combined effect of active packaging and relative phase sweeping on microwave heating performance in a dual-port solid-state system

The combined effect of active shielding packaging and relative phase sweeping on heating performance in a dual-port solid-state microwave heating process was evaluated. Four types of heating strategies that combine two factors (passive and active packaging and fixed and sweeping relative phase) were used in heating a tray of 300 g gellan gel sample for 3 min. The temperature distributions at the top and middle layers of the heated samples were collected and analyzed for heating uniformity index (HUI) and power absorption efficiency (PAE). The results showed that both active shielding package and relative phase sweeping can individually improve the HUI while maintaining high PAE. The packaging factor and relative phase factor showed a significant interaction effect (p = 0.0021) in influencing HUI but not PAE, highlighting the necessity of considering both factors (packaging and relative phase) when optimizing the microwave heating uniformity. The combination of active packaging and sweeping relative phase is a robust heating strategy that delivers the best heating performance that is significantly better than or similar to other combinations of packaging and relative phase strategies.

A Numerical Study of the Performance of Point Absorber Wave Energy Converters

Free-floating and submerged wave energy converters (SWECs) are regarded as promising technologies for renewable energy production. These converters rely on a heave-motion buoy to capture the kinetic energy of ocean waves and convert it into electrical energy through power conversion systems. To better understand the impact of various factors on power generation and efficiency, the effects of different buoy shapes (rectangular, circular cylinder, and trapezoidal fin), submergence depths (0, 0.1, and 0.2 m), wave heights (0.04, 0.06, and 0.1 m), and spring stiffness (50 and 100 N/m) were investigated. A 2D numerical wave tank with a buoy was simulated, and the results were validated against experimental data. Information on vorticity, vertical displacement, power absorption, and efficiency are provided. The findings indicate that the buoy shape and wave height significantly affect power absorption and efficiency. Additionally, this study reveals that increasing submergence leads to higher power absorption and lower conversion efficiency.

LSTM RNN-based excitation force prediction for the real-time control of wave energy converters

Wave energy is a type of abundant and dense renewable energy. Wave force prediction is a critical technology that influences power absorption efficiency in the real-time control of wave energy converter (WEC). Could wave elevation be used to predict wave excitation force directly by training artificial neural network? This method results in rapid and suitable prediction for real-time control. A long short-term memory recurrent neural network (LSTM RNN) algorithm is introduced to identify characteristics of wave excitation forces based on wave elevations. In this method, the wave elevations in front of the structure are measured to obtain sufficient time to actuate the control manipulation. A total of 180 regular wave and 12 irregular wave tests are conducted, and the LSTM RNN model is trained based on the experimental results. The performance of the LSTM algorithm is verified. According to the regular cases in the study, the LSTM prediction can identify high-order harmonic loads, and the anti-noise capability of the LSTM algorithm can filter random noises from the measure signals. In the irregular cases, the LSTM RNN algorithm performs effectively to predict the wave force excited on the structure using wave elevations measured by wave probes. The best combinations of the test setting parameters are determined to guide experimental tests and WEC prototypes.

Impedance matching design of capacitively coupled plasma with fluid and external circuit coupled model

AbstractThis paper establishes a fully self‐consistent coupled model of fluid and external circuits. The Kirchhoff equation, the charge conservation equation, and Poisson equation are coupled via boundary conditions and integrated into the fluid model for iterative parameter solution. On the basis of this model, we investigate the influence of impedance matching on single‐frequency capacitively coupled plasma characteristics under different parameters and topological structures. The findings suggest that after several iterations the matching parameters converge. Using different initial circuit parameters, the adjustable capacitance and inductance are eventually adjusted to approximately equal values, resulting in the same optimal matching state, whereas diverse discharge parameters led to different outcomes. Under fixed parameters for two topologies, the power absorption efficiency increases, and the reflection coefficient approaches zero, and the best matching is found. This model can be extended to different fluid programs to investigate the impact of complex external circuits with impedance matching network on plasma discharge while simultaneously seeking best impedance matching.

CFD and radiation field modeling of the NETmix milli-photocatalytic reactor: Evaluation of illumination systems composed of LEDs with distinct view angles

The coupling of ray tracing and computational fluid dynamics simulations was explored for the NETmix milli-photoreactor. Three LEDs plates composed of 15 inline LEDs were simulated and the LEDs-to-reactor distance varied. The radiation field obtained through ray tracing was incorporated into CFD simulations to elucidate the impact of LEDs light distribution patterns on the reactor performance. The employed LEDs emitted the same amount of power with the same light spectrum in all cases. The evaluated LEDs present a 48∘, 63∘ and 120∘ view angle. The impact of the distinct radiation fields on the photocatalytic oxidation of the n-decane over a thin TiO2 catalyst film was elucidated. Power absorption efficiency, homogeneity index, global illumination efficiency and the pollutant conversion were evaluated for each of the proposed illumination systems. The registered irradiance values varied from 154 W m−2 to 331 W m−2 with homogeneity indexes between 28.4% and 73.1%. Simulations have shown the dependency of the photocatalytic process on the homogeneity of the radiation field and how LED source selection is an important step in the modeling of photoreactors. The characteristics of the LEDs lamps had a significant impact on the pollutant degradation results.

Parametric analysis of a two-body floating-point absorber wave energy converter

In the evolution of floating-point absorber wave energy conversion systems, multiple-body systems are gaining more attention than single-body systems. Meanwhile, the design and operation factors affecting the performance of multiple-body systems are much greater than those of single-body systems. However, no systematic study has yet been presented. In this article, a theoretical model is proposed by using a coupled oscillator system consisting of a damper-spring system to represent a two-body system (the floating body and the reacting body). Dimensionless expressions for the motion response and wave power absorption efficiency are derived. With the newly developed model, we prove that an appropriately tuned two-body system can obtain a limiting power absorption width of L/2π (L is the incident wavelength) as much as a single-body system. The generic case of a two-body system is presented with numerical simulations as an example. The results show that increasing the damping coefficient can reduce the wave frequency at which the peak of power absorption efficiency occurs. Increasing stiffness can make the wave frequencies for high power absorption efficiency move to a higher frequency region and can also make the spectrum bandwidth for high power absorption efficiency become narrower. Further, we show that the two-body system can absorb more wave energy at low wave frequencies than the single-body system.

Performance of two vertically submerged piezoelectric plate wave energy converters in presence of a non-flat flexible barrier

Wave energy converters together with flexible breakwaters not only provide shelter to the energy devices against wave attacks but also offer improved performance, longer survivability and lower costs. Thus, in the present work we are interested to investigate the interaction of linear water waves with an array of three thin vertical plates, comprising of two plate wave energy converters and one flexible breakwater, submerged in water of finite depth in a two dimensional space. The plate in the middle of the setup is a flexible plate of variable thickness, and on either side of it are piezoelectric plate wave energy converters with constant thickness. The problem is solved by converting the associated boundary value problem into a system of coupled integral equations. A modified form of the energy balance equation is derived, which results due to the presence of the two piezoelectric plates. We investigate how the structural properties of the piezoelectric plates like their submergence depths, plate lengths, distance from the breakwater and different edge conditions can affect the wave attenuation and wave power absorption efficiency. Further, it is also examined how the presence of the non-uniform flexible plate with different flexibility and lengths can improve the performance of the system. It is analysed that shorter sized piezoelectric plate wave energy converters in the presence of non-flat flexible plate offer higher wave power absorption efficiency at lower frequencies.

Power performance of an asymmetric wave energy converter near a partial reflection wall

Wave power absorption of a heaving-body wave energy converter (HBWEC) can be improved by making the device highly asymmetric and deploying it near a coastal wall, harbour pier, or breakwater. However, the coupling between the geometric asymmetry of the HBWEC and the partial reflecting boundaries of the various walls and the consequential influence on the power performance of the HBWEC are unclear. This research aims to fill this gap. A semi-analytical model based on the linear potential flow theory is proposed to deal with an HBWEC with an arbitrary bottom shape and a partial reflection wall. The degree of asymmetry (DoA) of the HBWEC and the reflection rate of the wall are mathematically defined. Results show that the wall increases the power performance of an HBWEC by increasing the reflected wave energy through an increase in the reflection rate. Practically, an HBWEC should have a larger DoA to make it more immune to the change of the reflection rate and therefore more adaptable to different situations. These findings could offer recommendations for the design and deployment of an HBWEC according to the properties of the wall, improving wave power absorption efficiency and avoiding unnecessary costs due to improper design.

Generation of all-fiber third-order orbital angular momentum modes based on femtosecond laser processing of long-period grating

The generation of orbital angular momentum (OAM) modes is very important, for they have a variety of applications such as in optical tweezers, quantum optics, and optical communication systems. Particularly, how can high-order OAM modes be generated efficiently in fibers with the advantage of low cost and compatible with fiber system? The Traditional method for first order to third order OAM is based on long period fiber grating (LPFG) fabricated by carbon dioxide laser. However, high power and large focused spot of carbon dioxide laser are unfavorable for stable and repeatable generation of higher-order OAM, which needs the LPFG with small grating pitch. In order to solve this problem, a third-order OAM mode converter based on femtosecond microfabrication is proposed and fabricated for the first time. With the advantage of 4.4 μm focused spot size near the core, lower power and lower heat absorption efficiency, this method can be more stable and promising. Therefore, we first carry out the mode filed analysis and simulate the intensity and phase profiles of the superposed mode field in LP odd-even mode on different scales and phases patterns to obtain OAM mode. Second, we use the coupled-mode theory to analyze and simulate the transmission spectrum of LPFG, which guides the setting of the grating parameters such as the grating pitch, the depth of modulation and the length of the grating. By experimental verification, an asymmetric modulated long-period fiber grating with a pitch setting to 194 μm is fabricated on a six-mode fiber. The fundamental mode can be converted into the third-order angular linear polarization mode LP<sub>31</sub> mode with 98% mode conversion efficiency near 1550 nm, and further converted into the OAM<sub>±3</sub> modes by superposition of the odd and even LP<sub>31</sub> mode with ±π/2 phase difference. At the same time, this fiber grating can also generate LP<sub>12</sub> mode with 90% mode conversion efficiency near 1325 nm. Then we can take the same approach to transform LP<sub>12</sub> mode into OAM modes with angular first-order as well as radial second-order. The experimental result is consistent with the simulation result. Thus, this scheme provides an idea for generating the high-order OAM modes in all-fiber systems by using only one grating with high repeatability.

A numerical study on float design for wave energy converter

In the present work, a computational fluid dynamic simulation has been performed to investigate the movement of free-floating objects in wavy water. The movement of objects of different shapes, namely rectangular, trapezoidal, and hemisphere, has been simulated using the volume of the fluid model, and a satisfactory match between the simulated data and experimental results has been obtained. It is observed that the nature of vortices influences the movement of different shapes of the same mass. The rectangular shape has more vertical displacement as compared to the other two shapes. With the increase in characteristic dimension, power absorption efficiency increases and become constant, indicating a critical value of characteristic dimension for a given wave condition. On the other hand, with an increase in wave height, power absorption increases, but efficiency decreases. Trapezoidal shape with fin found to be optimum float shape.

Design and analysis of the bulbous-bottomed oscillating resonant buoys for an optimal point absorber wave energy converter

This study proposes innovative bulbous-bottomed buoy designs for an optimal oscillating-body wave energy converter (WEC). The effects of buoy shapes and the shape-influenced hydrodynamic coefficients on the motion and power absorption efficiency of a single-body heaving WEC are investigated. The frequency-domain analyses and spectral modeling were performed in ANSYS AQWA considering regular and irregular waves for optimal and sub-optimal power take-off (PTO). The wave climate data was obtained for ShiDao station China, and the middle frequency of the wave range with the highest probability of occurrence was selected as standard natural frequency, which was achieved by equalizing the diameter, mass, and volume of all the buoys. The bulbous-bottomed buoys could achieve 28.1% higher absorption efficiencies than the non-bulbous shapes. The buoy with the most expansive bulbous bottom of 1.6m height (SB-3) is the most optimal buoy with the highest power absorption and efficiency in both optimal and suboptimal PTO modes, with a maximum of 16.8% and 21.5% increase in response amplitude operator (RAO) and power absorption, correspondingly, relative to non-bulbous cylindrical-hemispherical (C-HS) buoy. The experimental validation of the simulated RAO and power of the 1:12.5 scale model of the SB-3 revealed 28% and 27.18% greater values, respectively, compared to C-HS, justifying that the SB-3 buoy could be a better choice for designing an oscillating-body WEC in all waves. By increasing the bulbous bottom width by 90% and fillet height by 100%, the performance of the bulbous buoys was enhanced by 12.2%.

Best impedance matching seeking of single-frequency capacitively coupled plasmas by numerical simulations

Impedance matching can maximize the absorbed power transferred to the plasma load and minimize the reflected power, making it critical and indispensable for capacitively coupled plasmas (CCPs). The external circuit usually interacts with the plasma nonlinearly, so the global simulation of the external circuit and plasma and the matching design is very challenging. In this work, an a priori model was proposed to match the plasma impedance and the external circuit impedance for single-frequency CCPs. By calculating the plasma impedance and the matching network, the matching parameters were iteratively updated to find the best matching parameters. By adjusting the capacitance and the inductance of the circuit by numerical simulations, the reflection coefficient can be significantly reduced. At the same time, the plasma power absorption efficiency will be significantly improved. The universality of the method was demonstrated by choosing different initial circuit, discharge, and plasma parameters. The proposed method provides an effective matching design reference for CCPs.

Landing Performance Study for Four Wheels Twin Tandem Landing Gear Based on Drop Test

The drop tests of a twin tandem landing gear with different filling parameters are carried out in two different landing attitudes (level and tail-down). The overload coefficient and power absorption efficiency are obtained. Curves of dynamic oscillation and pressure change for the pitch damper are obtained. The results show that twin tandem landing gear has a good ability to absorb the work of landing impact. Under landing weight, the vertical overload coefficients during level landing and tail-down landing are 1.14 and 1.07, respectively, when the corresponding efficiencies of its buffer system are 80.9% and 83.3%. During tail-down landing, the work absorbed by the pitch damper accounts for only 14.9% of the maximum pitching kinetic energy of the trolley. When the orifice diameter of the pitch damper keeps the same, its peak axial load does not change significantly with the change of its initial pressure. When the initial pressure of the pitch damper keeps the same, the decrease of its orifice diameter is beneficial to the vibration attenuation of the trolley. The smaller recoil channel may lead to a significant increase in the peak pressure of the pitch damper, which should be a consideration in its design.

Development of a complementary-frequency strategy to improve microwave heating of gellan gel in a solid-state system

As a helpful step towards the future development of a solid-state microwave system that can dynamically control microwave source parameters to deliver better heating performance, a complementary-frequency heating strategy has been developed and will be discussed here. The proposed complementary-frequency heating strategy is based on potential microwave heating uniformity enhancement through microwave frequency shifting during heating has shown promise to improve the microwave heating performance. The average temperature and heating uniformity results of this strategy were compared to conventional heating strategies like Fixed-Frequency and Sweeping-Frequency strategies. Typically, the Complementary-Frequency strategy could selectively use specific frequencies in the microwave heating process. These frequencies could be identified based on their associated complementary temperature profile of the top surface of the food product collected by a thermal imaging camera and sequenced in a specific order dictated by a predefined algorithm. The results indicated that both the Sweeping-Frequency and the Complementary-Frequency strategies could uniformly heat food products more than the Fixed-Frequency strategy. Meanwhile, the Complementary-Frequency strategy can trade-off microwave power absorption efficiency and heating uniformity to deliver a higher heating rate than the Sweeping-Frequency strategy does. • Complementary heating patterns were utilized to develop the frequency-shifting strategy. • The Complementary-Frequency strategy can be developed to balance efficiency and uniformity. • The Complementary-Frequency strategy could improve the microwave heating performance.

Design of Large-Scale Microwave Cavity for Uniform and Efficient Plastic Heating.

To reduce carbon emissions during heating in the manufacturing processes, microwave technology has attracted significant attention. Microwaves have considerable advantages over traditional heating methods, including more rapid heating, lower thermal damage, and eco-friendly processes. To apply microwaves to the manufacturing process, uniform and efficient heating is required. We analyzed the effect of various design parameters for uniform and efficient heating by changing the cavity heights, application of the reflector, and number and positions of waveguides. We conducted a numerical simulation and verified the findings by experiments. The results showed that a slight change in the cavity height altered the electromagnetic field distribution and heating parameters, such as the coefficient of variance and power absorption efficiency. With reflectors installed, 66% of cases exhibited better comprehensive evaluation coefficient (CEC) with consideration of uniform heating and power absorption. The spherical reflector showed 81% of cases, better than those of the ordinary model without a reflector. Furthermore, when double waveguides were installed, the average coefficient of variance (COV) was improved by 22%, and power absorption efficiency was increased by 53% compared to the single waveguide case. When the power applied to the waveguides was doubled, the average COV values improved by 18%. This large-scale analysis will be helpful in applying microwaves to actual industrial sites.

Self-consistent simulation of the impedance matching network for single frequency capacitively coupled plasma

Matching networks are of vital importance for capacitively coupled plasmas (CCPs) to maximize the power transferred to the plasma discharge. The nonlinear interaction between the external circuit and plasma has to be considered to design suitable matching networks. To study the effect of the matching circuit, we coupled particle in cell/MC(Monte Carlo) model and nonlinear circuit equations based on Kirchhoff’s laws, in a fully nonlinear and self-consistent way. The single-frequency capacitively coupled discharge with ‘L’-Type matching networks are simulated. Fully self-consistently results of circuit and plasma parameters are presented and then power absorbed by the plasma and efficiency are calculated. With the tune of the matching network, the efficiency can reach 28.7%, leading to higher potential as well as higher electron density at fixed source voltage. Besides, only very small components of the third harmonics are found in the plasma voltage and current while surface charge densities have multiple harmonics on account of the strong plasma nonlinearity. Finally, the effects of matching capacitors on discharge are analyzed, results show that smaller and of 500–1000 pF may be a proper choice for better matching, resulting in higher voltage across the CCP, and thus higher electron density and power absorption efficiency are obtained.

Energy utilization and heating uniformity of multiple specimens heated in a domestic microwave oven

To improve the energy utilization and quality of multiple specimens heated in a domestic microwave oven, we developed a theoretical model that considered the electromagnetic, heat, mass and momentum fields and phase change. Specimens with different distances, volumes and shapes were compared and discussed. The state parameter distribution uniformity and concentrative degree were described by the coefficient of variation (COVE, COVT, COVM and COVP), the microwave focusing degree (MFD) and thermal runaway. The energy utilization efficiency was quantified by the specific power absorption efficiency (SPAE). Microwave focusing, hot spots, and dry and wet spots occurred during the process and were influenced by the electric field distribution, mass and heat transfer and certain geometries. When the distance between the two specimens was approximately one wavelength (in free space), the energy utilization was higher, but the uniformity was worse. The SPAE of the specimens with larger volumes was lower due to energy attenuation, which gave rise to a lower average temperature, lower phase change rate, higher average moisture content and better moisture distribution uniformity. The distribution uniformity of the electric field and temperature of the cylindrical specimens were the best.

Performance of a plate‐wave energy converter integrated in a floating breakwater

A plate-wave energy converter (pWEC) moored in front of a floating stationary breakwater is considered. The pWEC is composed of a submerged flexible plate with piezoelectric layers bonded to both faces of it. Hence the elastic motion of the plate excited by water waves can be transformed into useful electricity due to the piezoelectric effect. To evaluate the performance of the breakwater-attached pWEC in terms of wave power absorption and wave attenuation, a hydroelastic model based on linear potential flow theory and the eigenfunction matching method is developed with the electromechanical and the hydrodynamic problems of the pWEC coupled together. The pWEC can be either simply supported or clamped at the edge. A multi-parameter analysis is carried out with the employment of the present model. Effects of the width, submergence and edge types of the plate, together with the scales of the breakwater, including its width and draft, on wave power absorption and wave attenuation, are examined. As the pWEC moves towards a deeper position, the main peaks of the frequency response of the wave power absorption efficiency become lower and narrower. In contrast, its effect on wave attenuation is limited.

Heating of biomass in microwave household oven - A numerical study

To improve the efficiency of biomass heating by microwaves, this paper studied numerically the heating of wood, sugar cane bagasse, orange peel and palm oil in microwave domestic oven. The study focused in the evaluation of power absorption capability of the biomasses in cylindrical and sphere shapes. The Maxwell equations were employed to calculate the microwave electromagnetic field distribution in the microwave cavity and in the samples, coupled to heat equation. Quantitatively, the power absorption capability and temperature distribution uniformity were, respectively, described by power absorption efficiency (PAE) (0.07 < PAE < 0.87) and the coefficient of variation (COV), varying between 0.01 and 0.14. Two dimensional plots of temperature evolution as function of time was used to determine the locations of the resonating peaks as function of peak number. The rate of heating efficiency was evaluated using the degree of thermal runaway ΔT (1K<ΔT<102K) and evolution of average temperature T¯ (298K<T¯<343K) and their relationship with the energy absorbed by the samples and COV, respectively. The comprehensive evaluation coefficient (CEC), that describes the usability of a specific sample in industry, varied between 1 and 14, was calculated for the biomasses and shapes.

Planar Dual Polarized Metasurface Array for Microwave Energy Harvesting

The design of a dual polarized metasurface collector based on the metamaterial full absorption concept for electromagnetic energy harvesting is introduced. Unlike previous metamaterial absorber designs, here the power absorbed is mostly dissipated across a resistive load rather than within the dielectric substrate. This is achieved by channeling the absorbed power to an optimal resistive load through a via hole. The simulation results show that a power absorption efficiency of 98% is achieved at an operating frequency of 2 GHz for a single unit cell. A super unit cell consisting of four cells with alternating vias was also designed to produce a dual polarized metasurface. The simulation results yielded a radiation to AC efficiency of around 98% for each polarization.