Mechanical Energy Conversion Efficiency Research Articles

Effect of scandium concentration on the performances of cantilever based AlN unimorph piezoelectric energy harvester with silicon nitride substrate

Microelectromechanical systems (MEMS) offer its ability to sense, control and actuate on sub-micron scale and exhibit its effect on macro scale. To implement any specific MEMS system, small, efficient and long-lifespan micro power sources are required. Piezoelectric energy harvester (PEH) along with radioactive source is one of the most promising approaches to harness electrical energy at micro to millimeter range. In this report, a scandium (Sc) doped Aluminium Nitride (AlN) unimorph piezoelectric energy harvester has been demonstrated. Unimorph piezoelectric layer is built on Silicon Nitride (Si3N4) substrate platform that act as cantilever beam and that can be vibrated by inbuilt radioactive system. In particular, Si3N4 as cantilever material and the impact of Sc doping concentration on electrical and mechanical properties of AlN piezoelectric thin film materials have been studied in MATLAB simulation platform. Results obtained from numerical study suggests that the proposed energy harvester model composed of AlScN unimorph piezoelectric (with 10% Sc doping concentration, Sc-10%) layer and Si3N4 cantilever can yield a maximum power output of ~ 19.33 μW and overall mechanical energy conversion efficiency of ~ 91.07%. These are the maximum output power and mechanical energy conversion efficiency numerically obtained from Sc doped AlN piezoelectric energy harvester systems to the best of our knowledge.

Fast dynamics and low power losses of high-speed solenoid valve based on optimized pre-excitation control algorithm

Aiming at the requirements of high precision and reliability of digital hydraulic systems, high-speed solenoid valve (HSSV) needs to satisfy both fast dynamics and low power losses. In this paper, the dynamic performance and power losses of HSSV are studied by combining the coupling relationship between multi-physical fields, and based on the analysis conclusion, a control algorithm for HSSV is optimized based on pre-excitation control algorithm (PECA) to effectively speed up the switching behavior and reduce power losses. The theoretical and experimental results indicate that increasing the pre-opening voltage (POV) and reducing the pre-closing voltage (PCV) can shorten the switching delay time. However, the copper loss increases with the POV, resulting in a lower mechanical energy conversion efficiency. On the other hand, enlarging the opening voltage (OV) and closing voltage (CV) can speed up the switching process of HSSV, but it causes a significant increase in iron and copper losses. The dynamic performance and power losses of the HSSV are dimensionless mapped and the parameter group (POV = 3.6 V, OV = 14 V, PCV = 2.25 V, CV = −24 V) with optimum and well-balanced behaviors is selected with bubble scatter analysis and variation coefficient. The time required for HSSV to open and close was 1.21 ms and 1.71 ms, respectively, and the final temperature rising is optimized at 40.9 ℃. Therefore, the optimized PECA meets the expected requirements.

A Double-Electrode-Layer Wind-Driven Triboelectric Nanogenerator with Low Frictional Resistance and High Mechanical Energy Conversion Efficiency of 10.3%

As a new technology for harvesting distributed energy, the triboelectric nanogenerator (TENG) has been widely used in harvesting wind energy. However, the wind-driven TENG (WD-TENG) faces the problems of high frictional resistance and low mechanical energy conversion efficiency. Here, based on optimizing the structure of the wind turbine, a rotational double-electrode-layer WD-TENG (DEL-WD-TENG) is developed. When the rotational speed is less than 400 round per minute (rpm), the dielectric triboelectric layer rubs with the inner electrode layer under its gravity; when the rotational speed is higher than 400 rpm, the dielectric triboelectric layer rubs with the outer electrode layer under the centrifugal force. The double-electrode-layer structure avoids the energy loss caused by other forces except gravity, centrifugal, and electrostatic adsorption, which improves the mechanical energy conversion efficiency and prolongs the working life of the DEL-WD-TENG. The conversion efficiency from mechanical energy to electricity of the DEL-WD-TENG can reach 10.3%. After 7 million cycles, the transferred charge of the DEL-WD-TENG is reduced by about 5.0%, and the mass loss of dielectric triboelectric layer is only 5.6%. The DEL-WD-TENG with low frictional resistance and high energy conversion efficiency has important application prospects in wind energy harvesting and self-powered sensing systems.

A State-of-the-Art Self-Cleaning System Using Thermomechanical Effect in Shape Memory Alloy for Smart Photovoltaic Applications

This research aims to present a state-of-the-art cleaning technology solution that effectively overcomes the dust accumulation issue for conventional photovoltaic systems. Although continuous innovations and advanced developments within renewable energy technologies have shown steady improvements over the past years, the dust accumulation issue remains one of the main factors hindering their efficiency and degradation rate. By harvesting abundant solar thermal energy, the presented self-cleaning system uses a unique thermomechanical property of Shape Memory Alloys to operate a solar-based thermomechanical actuator. Therefore, this study carries out different numerical and experimental validation tests to highlight the promising practicability of the developed self-cleaning system from thermal and mechanical perspectives. The results showed that the system has a life expectancy of over 20 years, which is closely equivalent to the life expectancy of conventional photovoltaic modules while operating under actual weather conditions in Dammam city. Additionally, the thermal to mechanical energy conversion efficiency reached 19.15% while providing average cleaning effectiveness of about 95%. The presented outcomes of this study add to the body of knowledge an innovative methodology for a unique solar-based self-cleaning system aimed toward smart and modern photovoltaic applications.

Interface Engineering for Efficient Raindrop Solar Cell.

A raindrop solar cell can work either on rainy days to collect mechanical energy of the raindrops or on sunny days to harvest solar energy, which achieves high energy conversion efficiency in various energy environments. However, the low efficiency of raindrop energy harvesting is a dominating barrier to the raindrop solar cells in practical applications. In this work, a MoO3/top electrode-based triboelectric nanogenerator (MT-TENG) with high rain droplet energy conversion efficiency, integrated with a perovskite solar cell through shared electrodes, has been proposed. The interface electrons between the triboelectric layer and electrode can be blocked by the MoO3 layer with high permittivity and wide bandgap, and the MoO3-based TENG (M-TENG) therefore increases the surface charge density. Thus, the top electrode structure in the solid-liquid interface can greatly increase the output charge by 101.1 times in total. By adjusting the water droplet parameters of tap water to simulate the actual application scenario, the raindrop output power and mechanical energy conversion efficiency can reach 0.68 mW and 12.49%, respectively. In addition, due to the high transmittance of the MT-TENG, the perovskite solar cell can still sustain a high photovoltaic power conversion efficiency of 19.38%. By virtue of the shared electrode circuit design, the raindrop solar cell can continue to purvey electric power on rainy and sunny days, and it only takes about 175 s to charge a 2.2 μF capacitor to 5 V.

A one-structure-layer PDMS/Mxenes based stretchable triboelectric nanogenerator for simultaneously harvesting mechanical and light energy

Triboelectric nanogenerator (TENG) has attracted enormous interests since it is able to efficiently convert various energies into electrical energy and drive low-power personal electronic sensors. However, TENG is usually restricted to harvest mechanical energy, and the realization of TENG with the ability to harvest light energy is rarely reported. In this work, a multifunctional stretchable TENG using polydimethylsiloxane/Mxenes composites as triboelectric layer is demonstrated, which is able to simultaneously harvest mechanical and light energy. Beneficial from the highly electronegative surface and intense surface plasmon excitations property of Mxenes, our TENGs exhibit high mechanical energy conversion efficiency and excellent light response property. Compared to the device without illumination, the open-circuit voltage and short-circuit current with light illumination increased from 145 to 453 V, and 27 to 131 μA, respectively, and the instantaneous light power conversion efficiency achieved 19.6%. Meanwhile, our TENGs are demonstrated to detect sound instructions and wind speed, which can inspect frequency, amplitude, and speed in various environments. Furthermore, TENG actuated color-tunable LED matrix is fabricated to develop an environmental interaction visualization system. This work greatly expands the functionality of TENG in energy harvesting, and provides a universal strategy for simultaneously harvesting mechanical and light energy in a one-structure-layer-based TENG.

Experimental study on pressurization characteristics of a water droplet entrapped in molten LBE pool

In a postulated Steam Generator Tube Rupture (SGTR) accident of pool-type Lead-cooled Fast Reactor (LFR), highly-pressurized water from the secondary circuit will be discharged into the primary vessel containing low-pressure molten lead-based alloy (commonly pure lead or low-melting-point Lead-Bismuth Eutectic (LBE)). One of the dangers of such accident is the formation of a multiphase flow structure consisting of water droplets inside the molten metal pool, which could result in energetic Coolant-Coolant Interaction (CCI). In this study, to ascertain the pressurization characteristics underlying the CCI process, a series of experiments is conducted through releasing water lump of different volumes and shapes within a molten LBE pool based on the PMCI (Pressurization characteristics in Melt-Coolant Interaction) experimental facility at the Sun Yat-sen University. To obtain comprehensive understandings, a variety of experimental parameters are employed such as the temperature (subcooling), volume and geometry of water lump along with the temperature and depth of the molten LBE pool. After detailed analyses, it is verified that within the thermal interaction zone, there is the possibility for the steam explosion to occur that generally produces more violent pressure buildup. For the non-explosion cases, all our experimental parameters except the water subcooling are observed to have remarkable impact on the pressurization characteristics. Due to the restraining role of steam bubbles generated at the LBE-water interface, for given thermal condition (i.e. melt & water temperature) and LBE-pool depth, increasing water volume is confirmed to result in limited pressurization. Instead of LBE static pressure, the effect of pool depth on pressurization is supposed to be primarily caused by the varied easiness of the molten LBE penetration through the vapor interface. Regardless of steam explosion, the calculated mechanical energy conversion efficiency for present CCI experiments is found to be varied over a narrow scope of 2.5–5.5%. Current experiments provide a great amount of favorable database and insight for enhanced understanding on the mechanisms of SGTR accident as well as for the improved validations of LFR safety analysis codes in China.

Electrode selection rules for enhancing the performance of triboelectric nanogenerators and the role of few-layers graphene

The development of portable and wearable electronics requiring only few tens of microwatts to operate fosters the search for low power energy sources. Moreover, the fast-growing demand for new sustainable energy has raised the interest in energy harvesters able to convert mechanical energy into electrical power. Triboelectric nanogenerators (TENGs) can provide such green power supply. Recent developments in TENGs technology show that they can be used in different applications ranging from wearable self-powered sensors to wind and sea wave energy harvesting. In spite of the wide number of TENGs developed so far, an in depth understanding of their working principle is still missing. In this work, we highlight the fundamental role played by the interface between the triboelectric material and the electrode collector in contributing to the TENG's power generation. We show that by simply replacing the 'standard' gold electrodes with flexible few layer graphene electrodes in TENGs operating in vertical contact mode, a 26-fold increase in power density is achieved. Here, we elucidate the main mechanism at the base of such boost in power output, describing guidelines for the combination of electrode and triboelectric materials to optimize the mechanical energy conversion efficiency in TENGs.

Metal-Free Catalyst with Large Carbon Defects for Efficient Direct Overall Water Splitting in Air at Room Pressure.

Hydrogen can be used as a conventional clean energy resource, only by obtaining it in a cheap, simple, and feasible way. From the perspective of solar energy utilization, photocatalytic water splitting is essentially limited by high electric energy and intermittent solar energy. Here, we demonstrate that the carbon defects could decompose water directly by using low-value mechanical energy in the daily environment without using the sacrificial agent. The prepared metal-free carbon catalyst (OPC-900) with rich graphene topological defects shows several redox states in acetonitrile, which can accumulate redox equivalents and respond for overall water splitting in air at room pressure. Under stirring or light conditions, charges can be created and accumulated on the catalyst surface and split water into H2 and O2 in low conductivity medium. The mechanical energy conversion efficiency of stirring in ultrapure water is 7.01%. Our work combines visible light with low-value mechanical energy for widespread decomposition of water to produce hydrogen in air under normal pressure.

A comparative study on local fuel-coolant interactions in a liquid pool with different interaction modes

From the past analyses of Core Disruptive Accidents (CDA) for sodium-cooled fast reactors, it has been recognized that with the assumption of very pessimistic conditions, a large-scale molten-fuel pool, which contains sufficient amount of fuel to achieve the prompt criticality by fuel compaction, might be formed. Due to the potential entrapment of liquid sodium into the fuel pool, local Fuel-Coolant Interaction (FCI) in the pool is considered to be one of the various initial factors resulting in such compactive fluid motions. To ascertain the mechanisms underlying this interaction more reliably, in our earlier publication a number of simulated experiments was carried out by releasing a given amount of liquid water into a molten pool (comprised of a low-melting-point alloy) using the PMCI (Pressurization characteristics in Melt-Coolant Interaction) facility recently developed at the Sun Yat-sen University. In this work, motivated to acquire more enhanced understanding, the effect of interaction mode on local FCIs is further investigated by adding new experimental data within the Melt-Injection (MI) mode. From detailed analyses, it is found that except the existence of a similar impact of melt temperature, much difference in the influence of other experimental parameters such as the liquid volume delivered, water subcooling along with the pool depth is observed. In addition, the performed analyses in this work also confirm that compared to previous Coolant-Injection (CI) mode, the mechanical energy conversion efficiency is much lower within the MI-mode condition. This work provides a large palette of beneficial experimental data and evidence for the better understanding of CDAs and improved verifications of fast reactor safety accident analysis codes in China.

Performance of high‐power thomson coil actuator excited by a current pulse train

This paper uses FEA simulations to investigate the behaviour of a high-speed, high-power Thomson coil (TC) actuator suitable for HVDC protection applications, when excited by a double discharge. The influence of the resulting pulse train on the amplitude of observed armature vibration is investigated. The significance of the pulse train on the device electrical to mechanical energy conversion efficiency is assessed and compared with the efficiency obtained using the conventional single discharge approach.

3D printing individualized triboelectric nanogenerator with macro-pattern

Triboelectric nanogenerator (TENG) is one of the most attractive candidates for providing a green energy source capable of satisfying the world's energy consumption. 3D printing is a promising route to satisfy the demands of various self-powered devices with individualized design in practical applications such as signal processing, precisely tuning circuits, active sensor networks, remote controls, and flexible electronics. This work reports an approach of fused deposition modeling (FDM), one of 3D printing methods, which enables the creation of optimized digital designs for TENG devices for the purpose of efficiently harvesting ambient vibration energy. To obtain satisfying output power and high mechanical energy conversion efficiency, various positive and negative polymers were chosen as friction layers, such as polylactic acid (PLA), nylon (PA), a mixture of polypropylene and polyethylene (PP/PE), and poly(ethylene terephthalateco-1,4-cylclohexylenedimethylene terephthalate) (PETG). By increasing the vibrational frequency from 5 Hz to 20 Hz, the output voltage of the TENG device increased from 50 V to 241 V in a TENG device using nylon (PA) and a mixture of polypropylene and polyethylene (PP/PE). The TENG device had a 0° contact angle between the two films, which also had some macroscopic patterns on their surfaces. Simultaneously, a decrease in the filling rate (from 100% to 20%) and thickness (from 0.4 to 0.2 mm) resulted in an increase in the output voltage from 57 V to 176 V and from 50 V to 241 V, respectively. To better understand the effects of the printing parameters on the output performance, we studied the factors of the filling rate, thickness, contact angle and the width of the zigzag pattern. From these results, we conclude that 3D printing based on the FDM strategy to fabricate TENG outstandingly improves the output performance by decreasing the effective Young's modulus. Additionally, the peak of the current reaches 1.52 mA in ultrashort time. The triboelectrification efficiency in this vertical contact-separation mode reaches 63.9%. Our concept of 3D printing based on FDM will stimulate further fundamental work in fabricating approaches to harvesting environmental energy.

Regenerative Shock Absorber Using a Two-Leg Motion Conversion Mechanism

This paper presents the development of a novel regenerative shock absorber sized for a passenger car suspension system. The shock absorber includes a simple and highly efficient motion converter called a two-leg mechanism , a planetary gearhead, and a brushless three-phase rotary machine. The design and analysis of the regenerative shock absorber are presented by considering the dynamics and efficiency of the electromechanical device. The performance of the regenerative damper is evaluated under sinusoidal excitation inputs for typical amplitudes and frequencies in a vehicular suspension system. Experimental results show that a damping coefficient of $1720$ N $\cdot$ s/m can be achieved by controlling the external loads. Furthermore, a mechanical energy conversion efficiency between 0.71 and 0.84 is achieved, which is considerably higher than other mechanisms reported in the literature, such as ball screw, rack-and-pinion, and linear mechanisms.

Study on a Piezohydraulic Motor for Maximal Energy Efficiency

A piezohydraulic linear motor driven by a piezostack diaphragm pump is presented and studied. The diaphragm of pump chamber consists of a membrane and rigid disk, instead of a single piston or membrane. An analytical model is established to evaluate piezohydraulic motor performance in terms of velocity, pushing force, mechanical energy conversion efficiency (MEE), and electromechanical energy conversion efficiency (EMEE). The involved effect factors of motor performance are radius ratio (rigid-disk radius to chamber radius), area ratio (pump-chamber area to cylinder-piston area), force ratio (external load to blocked force of piezostack), and step ratio (cylinder-piston stroke to free displacement of piezostack). Analytical results show that there are optimal structural parameters (radius ratio and area ratio) for property parameters (force ratio, step ratio, MEE, and EMEE) to obtain maximal values. Considering the achievable peak MEE and EMEE, the design method was introduced for different purpose of applications. A piezohydraulic motor was fabricated and tested to examine the influence of radius ratio on performance of the piezohydraulic motor. The experimental results show that both the motor velocity and driving force can be enhanced with optimizing radius ratio.

Wind power plant resilience

A wind energy system transforms the kinetic energy of wind into mechanical or electrical energy that can be harnessed for practical use. Mechanical energy is most commonly used for pumping water in rural or remote locations. Electrical energy is obtained by connecting wind turbine with the electricity generator. The performance of the wind power plant depends on the wind kinetic energy. It depends on the number of design parameter of the wind turbine. For the wind power plant the wind kinetic energy conversion depends on the average wind velocity, mechanical energy conversion into electricity, and electricity transmission. Resilience of the wind power plant is the capacity of the system to withstand changes of the following parameters: wind velocity, mechanical energy conversion into electricity, electricity transmission efficiency and electricity cost. Resilience index comprise following indicators: change in wind velocity, change in mechanical energy conversion efficiency, change in conversion factor, change in transmission efficiency, and change in electricity cost. The demonstration of the resilience index monitoring is presented by using following indicators, namely: average wind velocity, power production, efficiency of electricity production, and power-frequency change. In evaluation of the resilience index of wind power plants special attention is devoted to the determination of the resilience index for situation with priority given to individual indicators.

Energy Storage and Transportation Based on Sulfuric Acid Decomposition and Synthesis Processes

A chemical energy storage and transportation system is conceived based on sulfuric acid decomposition and synthesis processes using hot oxygen as a vector. A thermodynamic assessment is carried out to determine the thermal performance of the process; it is found that the energy storage density is about 0.58 GJ/m3 for 365 cycles per year operation, the overall thermal energy storage efficiency is about 62 percent, the energy transportation efficiency is about 29 percent, and the thermal to mechanical energy conversion efficiency is about 25 percent.