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Salinity gradient power generation based on nanochannels has drawn much attention for its green and sustainable advantages. However, previous studies have tended to focus on regularly shaped nanochannels, while rough and irregular surfaces are naturally formed during the preparation of nanochannels (similar to sinusoidal nanochannels). In this paper, a model of salinity gradient energy conversion in sinusoidal nanochannels is established. The impacts of the geometrical parameter dimensions of the sinusoidal channel (including initial phase, channel length, average radius, amplitude, and angular frequency) on the power generation performance under different salinity gradients are systematically investigated. The results show that the sinusoidal nanochannel has better salinity gradient power generation performance than cylindrical nanochannel. It obtains the best power generation performance when the initial phase is zero. Besides, increasing the nanochannel length facilitates ion selectivity and energy conversion efficiency. At high concentration difference, decreasing the average radius or increasing the amplitude help increase the maximum output power and enhance the energy conversion efficiency. The maximum output power of about 1.27 pW and energy conversion efficiency of about 32.8% were obtained by optimizing the sinusoidal channel amplitudes. It is also found that increasing the angular frequency is favorable to improving energy conversion performance at the high concentration difference. These results provide helpful information for designing and optimizing salinity gradient energy conversion systems. [ABSTRACT FROM AUTHOR]

Energy conversion efficiency and operation bandwidth are two main concerns in piezoelectric energy harvesting in low-frequency vibration environments. This paper presents a compact two-degree-of-freedom nonlinear piezoelectric energy harvester (2DOF NPEH) with a stopper. The proposed harvester consists of an elastic beam, a piezoelectric beam with tip mass, a pair of repulsive magnets, and a mechanical stopper. A bistable configuration is established through magnetic interaction. This study investigates the generating characteristics of the 2DOF NPEH under frequency-sweep excitation, utilizing a rigid stopper (RS) and different elastic stoppers (ESs). The experimental results indicate that the implementation of a mechanical stopper in a NPEH contributes to widening the operation bandwidth and enhancing the peak voltage. As the stiffness of the stopper increases, the bandwidth gradually shrinks while the peak voltage increases. The optimal energy conversion efficiency depends on the stiffness of the ES, and it occurs when the wire diameter of the spring is 1.2 mm. Compared with the 2DOF NPEH without a stopper, the utilization of a RS results in a 13.85-fold increase in the bandwidth of the generator at the first resonance. Moreover, the maximum absolute voltage is 12.82 times and 3.47 times the output voltage of the 2DOF NPEH at the first and second resonance, respectively. This work offers valuable insights into the design and optimization of piezoelectric energy harvesters in practical applications. [ABSTRACT FROM AUTHOR]

Coalescence-induced self-propelled droplet jumping has attracted extensive attention because of its huge potential for enhancing dropwise condensation heat transfer, anti-icing, and self-cleaning. Most previous studies focus on binary droplet jumping, with little research on the more complex and realistic multi-droplet jumping. As a result, the effect of the droplet arrangement on the multi-droplet jumping phenomenon remains unclear. In this paper, the self-propelled jumping of three droplets with different arrangements (two droplets are fixed, and the location of the third one is changed) is numerically simulated, and energy conversion efficiency is studied. Based on two different forming mechanisms, region I (the coalescence between the lateral droplets forms the central liquid bridge) and region II (the changed interface curvature of central droplets turns into the central liquid bridge under surface tension) are defined in three-droplet arrangements. The liquid bridges exhibit different dynamic behaviors in two particular regions, even the jumping velocity is determined by the moving synchronicity of liquid bridges in each region. The critical distribution angle that leads to the overall nonmonotonic change of jumping velocities ranges between 110° and 120° (0.02 ≤ Oh ≤ 0.16). Compared with the symmetry of the droplet configuration, the geometry of the droplet arrangement plays a dominate role in the nonmonotonic change. The maximum energy conversion efficiency is just over 6.5% and the minimum is just under 3%. The findings of this study not only reveal how the arrangement affects ternary droplet jumping and explain the phenomenon that cannot be explained before, but deepens our understanding of multi-droplet jumping as well. [ABSTRACT FROM AUTHOR]

Coalescence-induced droplet jumping on superhydrophobic surfaces has attracted significant attention in recent years. In this paper, by using a three-dimensional multiphase lattice Boltzmann model, we numerically investigated the droplet jumping on V-shaped groove superhydrophobic surfaces induced by the coalescence between two droplets located in the asymmetric V-shaped groove. First, it is found that the self-jumping process gradually becomes inefficient when the groove angle decreased, which is caused by the increasing viscous dissipation with the decrease in the groove angle. In order to overcome the weakness of the V-shaped superhydrophobic surface and enhance the droplet jumping performance, an improved V-shaped superhydrophobic surface with a triangular prism was conceived. Numerical results showed that the normalized jumping velocity and the energy conversion efficiency of the V-shaped superhydrophobic surface with a triangular prism can be increased by up to 80% and 210%, respectively, in comparison with those of the surface without the triangular prism. The jumping enhancement mainly arises from the combined effect of the redirection of the expanding liquid bridge by the V-shaped sidewalls, as well as the earlier and sufficient impact of the liquid bridge on the triangular prism in the groove. Moreover, using the improved V-shaped superhydrophobic surface, a guided jumping can be achieved due to the reaction forces exerted by the V-shaped sidewalls and the triangular prism, and the jumping angle can be more accurately predicted based on the groove angle. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT), which transfers energy without a physical link, has recently received significant research interest. Due to the advantages of small dimension, low operation frequency, and low transmission loss, magnetoelectric WPT (ME-WPT) has been shown to be a promising technology for internet of things (IoT) and implantable medical device (IMD) applications. However, ME-WPT requires a direct-current (DC) magnetic bias for optimal performance and prior arts have implemented large electromagnets, Helmholtz coils, or externally positioned magnet bias systems, which increase the system dimension. Furthermore, the highest energy conversion efficiency (ECE) reported by prior ME-WPT studies is 0.62%, which needs to be improved. In this paper, we present an ME-WPT system with a novel miniaturized ME-WPT receiver and a spiral coil based transmitter. Four DC magnets are integrated onto the ME-WPT receiver to significantly reduce its dimension while providing a DC magnetic bias of 190 Oe for optimal performance. Electrochemical polarization characterizations are introduced to analyze the performance of the WPT receiver, which reveal that a maximum output power of 4.096 mW is obtained. A record ECE of 2.64% is reported, the highest among all ME-WPTs to date. The output power is improved by at least 49.3 times compared with the ME-WPT without integrated DC magnets. The influence of the input voltage and the distance between transmitter/receiver on the performance of the ME-WPT system is studied, which shows that the output power increases as the distance decreases and the input voltage increases. The proposed ME-WPT system with integrated DC magnets has potential applications in IoT and IMDs. [ABSTRACT FROM AUTHOR]

The energy conversion efficiency (the ratio of the maximum jumping kinetic energy to the maximum surface energy released from droplet coalescence) is an essential indicator of the self-propelled jumping of droplets, which determines its value for applications in various fields. In the practical condensation process, the initial states of the multidroplets with different sizes and distributions have a significant effect on the energy conversion efficiency, but the mechanism behind this effect remains unclear. This paper reveals the effect of the initial states of droplets on the energy conversion efficiency of multidroplet jumping (mainly three droplets) from the perspective of energy conversion and the internal flow of the merged droplets. Different initial states will lead to different flow directions of the liquid microclusters inside the merged droplets. The consistency between the flow direction and the jumping direction will affect the energy conversion efficiency. To characterize this effect quantitatively, we construct a machine learning model based on a convolutional neural network to predict the energy conversion efficiency of multidroplet jumping with different initial distribution angles and radius ratios. The input of the neural network is the images of the initial state of the droplets, and the output is the energy conversion efficiency. After training, the neural network can predict the energy conversion efficiency of multidroplet jumping with an arbitrary initial state. [ABSTRACT FROM AUTHOR]

Current studies reveal the expectation that photovoltaic (PV) energy conversion will become the front-runner technology to stem against the extent of global warming by the middle of this century. In 2019, the passivated emitter and rear cell (PERC) design has taken over the majority of global photovoltaic solar cell production. The objective of this paper is to review the fundamental physics of the underlying cell architecture, its development over the past few decades to an industry main stream product, as well as an in-depth characterization of current cells and the future potential of the device structure. The early development of PERCs was set by an intriguing series of improvements starting in 1989 and resulting in a long-standing energy conversion efficiency record of 25.0% set up in 1999. It took a decade of intense technological development to implement this structure as an upgrade to existing production lines and another decade to increase the efficiency of industrially manufactured cells to over 22%. Our analysis of state-of-the-art large-area screen-printed PERCs is based on the pilot-line technology in the Photovoltaic Technology Evaluation Center at the Fraunhofer ISE, which is assumed to be representative of current state-of-the art cell processing. The main recent cell efficiency improvements have been achieved thanks to fine line metallization taking advantage of the high quality emitter formation and passivation and to improvements in material quality. In order to enhance the energy yield of the PV modules, innovations in interconnection technology like multibusbar and shingling technology as well as bifaciality are supported by PERC developments. Over the years, ongoing improvements have been made in the understanding of PERCs by analytical and numerical modeling of these devices. We show a study based on 3D numerical modeling and an extrapolation of the PERC device structure and technology to achieve an efficiency of 26%. This result surpasses earlier investigations due to the combination of technology components, as further improved front contact and emitter design as well as rear passivation and mirrors. We expect that PERCs can also play a strong role at the bottom of multijunction solar cells and will defend a strong position in global PV production beyond the end of the now starting decade. [ABSTRACT FROM AUTHOR]

Proof mass can adjust the natural frequency of a cantilevered energy harvester to fit the vibration source frequency and, hence, improve energy efficiency. In this paper, a cantilevered energy harvesting model including a proof mass is presented based on the flexoelectric theory. The electromechanical coupling responses at steady state are obtained for harmonic excitations and then reduced to single-mode expressions for modal excitations. The flexoelectric coupling coefficient, which represents conversion of energy, is investigated. The numerical results reveal that the flexoelectric coupling coefficient can be improved by adjusting the proof mass to make the vibration frequency of the microbeam adapt to that of the ambient vibration source. The adjusting strategies have also been formulated. In addition, the flexoelectric coupling coefficient increases with the decrease in the thickness of the microbeam. As expected, the flexoelectric coupling coefficient can further be enhanced when the beam thickness reaches nanometer scale. For the beam thickness h = 0.3 μm, the current output decreases and the voltage output increases with the increase in the electrical load resistance. When the electrical load resistance is around 100 MΩ, the power output arrives at its maximum. The resonance frequency shifts from 34 693 Hz to 35 350 Hz with the increase in the load resistance from short- to open-circuit conditions, and the flexoelectric coupling coefficient for this thickness lever is kr ≈ 0.19. [ABSTRACT FROM AUTHOR]

The photoelectric power conversion efficiency of polymer solar cells is till now, compared to conventional inorganic solar cells, still relatively low with maximum values ranging from 7% to 8%. This essentially relates to the existence of exciton and charge carrier loss phenomena, reducing the performance of polymer solar cells significantly. In this paper we introduce a new computer simulation technique, which permits to explore the causes of the occurrence of such phenomena at the nanoscale and to design new photovoltaic materials with optimized opto-electronic properties. Our approach consists in coupling a mesoscopic field-theoretic method with a suitable dynamic Monte Carlo algorithm, to model the elementary photovoltaic processes. Using this algorithm, we investigate the influence of structural characteristics and different device conditions on the exciton generation and charge transport efficiencies in case of a novel nanostructured polymer blend. More specifically, we find that the disjunction of continuous percolation paths leads to the creation of dead ends, resulting in charge carrier losses through charge recombination. Moreover, we observe that defects are characterized by a low exciton dissociation efficiency due to a high charge accumulation, counteracting the charge generation process. From these observations, we conclude that both the charge carrier loss and the exciton loss phenomena lead to a dramatic decrease in the internal quantum efficiency. Finally, by analyzing the photovoltaic behavior of the nanostructures under different circuit conditions, we demonstrate that charge injection significantly determines the impact of the defects on the solar cell performance. [ABSTRACT FROM AUTHOR]

The energy balance of the black liquor gasification (BLG) system, which is the core part in the Pulp-Syngas-Heat and Electricity combined cycle system, was analysed in this paper. Based on existing engineering parameters, we compared the energy consumption, conversion efficiency and energy cost of the BLG system under the different process conditions, in particular the air separation and concentration sections. Comparative analysis of these critical processes would facilitate the optimization of energy conversion efficiency and energy cost, as well as ascertain the influence of electricity and heat price on them. Results showed the drive combination of mechanical vapour recompression concentrating black liquor and electric driven preparation of oxygen (MVR-Motor) had the highest energy conversion efficiency of 73.18% but maximal energy cost. The drive combination of multi-effect evaporation concentrating black liquor and back pressure steam turbine preparation of oxygen (MEE-BPST) had the lowest energy cost, despite its energy conversion efficiency a little lower than MVR-Motor. For the drive combination of MVR-Motor, BLG system can get 224.32 kgce net energy output per 1000 kg straw pulp. Selection of reasonable process technology would promote the commercialization of BLG and the links to paper industry, biomass energy industry, and chemical industry, which benefits the control of black liquor pollution. [ABSTRACT FROM AUTHOR]

The terahertz surface wave oscillator (SWO) faces the problem of the low energy conversion efficiency due to the fact that working mode is the surface wave but the output mode is the volume wave, and it is very difficult to extract the terahertz wave efficiently. In the meantime, the possibility of the RF breakdown increases as a result of the intense electric field on the surface of slow wave structures (SWSs). To overcome these problems, the field distribution in the SWSs of the 0.147 THz relativistic SWO is analyzed in this paper, and the results indicate that the electric field distribution in the SWSs is similar to that in spoof surface plasmon polaritons (SSPPs). In order to improve the energy conversion efficiency of the SWO, we propose to adopt the circular SSPP coupler with tapered gratings at the end of the uniform SWSs, which is implemented to smoothly bridge the surface wave and guided wave. Second, the SWO with the coupler is simulated using particle-in-cell code UNIPIC. The simulation results indicate that the output terahertz power enhances 52% after the SSPP coupler is used. More importantly, the numerical results demonstrate that the intensity of the electric field decreases 25% on the corrugation surface of the SWSs, so the RF breakdown can be avoided in the terahertz relativistic SWO. [ABSTRACT FROM AUTHOR]

Faster consumption of hydrocarbon fuel in the transport sector is posing global threat of depletion of fossil fuel reserves. Studies are being extensively done to search for an alternative energy source and/or to find out appropriate energy conversion system. Among various alternatives, the use of compressed atmospheric air in air turbine is an attractive option provided the atmospheric air is compressed by natural sources such as sun energy, wind energy, etc. It has the capability to produce shaft work with almost zero pollution in the environment. This paper details the mathematical modeling of a small capacity compressed air driven multivane air turbine. The effect of having different vane angles and inlet pressure on shaft work output has been studied and analyzed here. The study shows that the flow work has significant contribution in total work output and varies from 1.5% to 16.3% at different pressures, 2–6 bars, and injection angles, 30°–60°. The total shaft work is found to be maximum at vane angle θ=36° (ten vanes) when injection angle is kept at 60°, and it reduces at vane angle θ=45° (eight vanes) when injection angle is kept at 45° and further goes down at vane angle θ=60° (six vanes) when injection angle is 30°, if injection pressure is maintained at 6 bars and speed of rotation at 2500 rpm. [ABSTRACT FROM AUTHOR]