Value Of Load Resistance Research Articles

Experimental and theoretical assessment of the effects of electrical load variation on the operability of a small-scale Organic Rankine Cycle (ORC)-based unit equipped with a hermetic scroll expander

Scroll expanders are widely adopted in small-scale Organic-Rankine-Cycles-(ORCs)-units integrated with renewable energy sources for low power residential Combined Heat and Power Production (CHP). These expanders are often connected to variable direct loads without the possibility to impose its speed externally. Despite the effect of electric load variation on expander speed is known, a minor attention is focused on its impact on the plant operability and regulation. To fill this gap, a wide experimental analysis is carried out on a solar micro-cogenerative ORC-based power unit equipped with a 1 kW hermetic scroll expander connected with a variable electric load. The experimental behaviour of the ORC-unit was assessed for different values of load resistance (from 20 Ω up to 80 Ω). Results show that properly acting on the load resistance the ORC-power unit can be improved up to 50 % in terms of efficiency and power production. Moreover, if the expander is properly designed its self-regulatory capability allows to achieve similar performance of an equivalent speed-controlled expander tested on the same plant. Finally, a new theoretical model reproducing the impact of main operating quantities on expander behaviour was developed and experimentally validated paving the way to a novel model-based control approach.

Thermoelectric Energy Harvesting from the Roof and Attics of a Building

Globally people are faced with difficulties in environmental pollution, increasing power costs, and global warming. As such researchers are focusing on enhancing energy-harvesting using thermoelectric generators for power generation to lessen the difficulties. Through the Seebeck effect, thermoelectric generators (TEGs) have proven their ability to convert thermal energy into electric power. Given the unique benefits they present, thermoelectric generators have arisen in the recent decade as a possible alternative to other green power generation technologies. A thermoelectric generator (TEG) is a solid-state device that converts thermal energy into electrical energy. TEG consists of elements of p and n-type semiconductors, connected thermally in parallel and electrically in series. In this paper, one hundred and ninety-two thermoelectric generators connected in series and parallel were used to investigate the thermal energy potential at the roof and attic area for domestic application for 20 days from the falling solar radiation on a residential prototype in Bashar, Wase Local government area of Plateau State. A theoretical analysis was used in determining the average output power (P) due to the delta T across the thermoelectric generator module junction. The load resistance value of the thermoelectric generator configuration was evaluated. The results show that the TEG generated power output ranging from 217 mW to 1.99 W throughout the day, 5.97 mW to 13.8 mW in the morning, and 6.8 mW to 36.9 mW in the evening. Furthermore, The finding also reveals that the attic side has the capacity to store thermal energy, which can be harnessed owing to the fast heat transfer to the surroundings during the convection process. In conclusion, solar irradiance has a major impact on the system.

An integrated alkali metal thermoelectric converter with sodium hydroxide thermoelectric water splitter and organic Rankine cycle for efficient power and hydrogen production

This study proposes the integration of the NaOH thermochemical water splitting cycle with both an alkali metal thermoelectric converter and an organic Rankine cycle. The objective of the proposed model is to enhance the overall efficiency by utilizing the waste heat generated by the NaOH thermochemical water splitting process and redirecting the heat from the alkali metal thermoelectric converter using bypass when hydrogen demand is low.Performance parameters such as system efficiency, system power, hydrogen production, AMTEC power production, and ORC power production were examined in the study. The results indicated an increase in power and hydrogen production with higher hot-end temperatures, along with an overall reduction in system efficiency for low values of load resistance. The system achieved a maximum efficiency of 53.37%.The system efficiency reached its peak at an AMTEC hot end temperature of 1173 °C, achieving 53.37 % efficiency at an RL value of 1.01 O. When the system operates at its maximum AMTEC power production, the AMTEC modules supply 12.81 kW, while the ORC generates 5.57 kW, and the hydrogen compressor consumes 0.13 kW. The total electrical power generation is 18.38 kW. The findings also indicate that the utilization of the bypass led to a reduction in hydrogen production while increasing the power output of the organic Rankine cycle.

FEA Comparison of the Mechanical Behavior of Three Dental Crown Materials: Enamel, Ceramic, and Zirconia.

The restoration of endodontically treated teeth is one of the main challenges of restorative dentistry. The structure of the tooth is a complex assembly in which the materials that make it up, enamel and dentin, have very different mechanical behaviors. Therefore, finding alternative replacement materials for dental crowns in the area of restorative care isa highly significant challenge, since materials such as ceramic and zirconia have very different stress load resistance values. The aim of this study is to assess which material, either ceramic or zirconia, optimizes the behavior of a restored tooth under various typical clinical conditions and the masticatory load. A finite element analysis (FEA) framework is developed for this purpose. The 3D model of the restored tooth is input into the FEA software (Ansys Workbench R23)and meshed into tetrahedral elements. The presence of masticatory forces is considered: in particular, vertical, 45° inclined, and horizontal resultant forces of 280 N are applied on five contact points of the occlusal surface. The numerical results show that the maximum stress developed in the restored tooth including a ceramic crown and subject to axial load is about 39.381 MPa, which is rather close to the 62.32 MPa stress computed for the natural tooth; stresses of about 18 MPa are localized at the roots of both crown materials. In the case of the zirconia crown, the stresses are much higher than those in the ceramic crown, except for the 45° load direction, while, for the horizontal loads, the stress peak in the zirconia crown is almost three times as large as its counterpart in the ceramic crown (i.e., 163.24 MPa vs. 56.114 MPa, respectively). Therefore, the zirconia crown exhibits higher stresses than enamel and ceramic that could increase in the case of parafunctions, such as bruxism. The clinician's choice between the two materials should be evaluated based on the patient's medical condition.

APPLICATION OF BAYESIAN REGULARIZATION FOR IMPROVING THE QUALITY OF ELECTRICAL ENERGY IN THE ELECTRICAL SUPPLY SYSTEM

The possibility of using neural networks in the field of the energy coefficients correction of a power supply system with uneven load in phases is being studied. This need is justified by the fact, that the calculation of the necessary parameters of the symmetry-compensating device was previously based on the Nelder – Mead search optimization method. Search optimization performing is computationally expensive, takes long computation times, and may calculate anomalous values. The article develops the idea of using technology for predicting the parameters of a symmetry-compensating device, based on neural network modeling using Bayesian regularization. For a given set of initial data, the best selected configuration turned out to be a neural network of two layers, implemented in the MATLAB package using the machine learning tool Neural Network Toolbox. The network input parameters are a set of tuples, consisting of load values in each of the three phases of the power supply system, which are resistive-inductive in nature. There are six input quantities in total (load resistance and inductance values in each of the three phases) and all their values are different, which causes current asymmetry in the network and reactive power. The target matrix is formed from tuples, consisting of three values, which are the parameters of the symmetrical compensating device, calculated by the optimization method, in such a way as to compensate reactive power and to balance currents in the network. The number of data tuples, required to train a neural network was determined empirically. During the experiments, the optimal number of neurons in the neural network was also revealed. The use of the generated neural network to calculate the parameters of the symmetry-compensating device determined approximate solutions is comparable in accuracy to the values, found by optimization methods. With the help of the generated neural system, adequate quasi-solutions for calculating the parameters of the symmetry-compensating device were determined, which, in case of calculation, using the optimization method, led to anomalous values, that didn’t optimize the energy coefficients of the power supply system to the required extent. Also, such neuropredictions protect the system from receiving excessive high parameters of symmetry compensating device, which can be obtained with an optimization approach.

Parametric optimisation of a dual cantilever flutter for electromagnetic wind energy harvesting

This paper investigates the parametric optimisation of dual cantilever flutter (DCF) beams for electromagnetic wind energy harvesting application. When two cantilever beams are placed side by side facing the direction of the wind flow, both beams would oscillate in an anti-phase motion once the critical flutter speed has been achieved. This arrangement is known as the DCF and it represents an ideal situation for energy harvesting through electromagnetic induction due to its anti-phase motion. Experimental results showed that the optimum load resistance value for the device is equivalent to a single-degree-of-freedom vibration energy harvester for low electromagnetic coupling case, despite the difference in the type of oscillations. Further analysis showed that there among the two possible arrangements for the magnets one arrangement results in a 51.5% larger magnetic flux density. It was seen that reducing the length of the electromagnetic DCF by 41.2% can increase the power output of the device by approximately six times, although the critical flutter speed also increased by 125.0%. Finally, some suggestions were provided on how to further improve the device.

Derivation of generalized thermoelectric energy equations and the study of thermoelectric irreversible processes based on energy, exergy, and entransy analysis

AbstractThermoelectric (TE) generation is becoming a valuable and promising research direction. Many researchers have carried out system analysis and performance optimization of thermoelectric technologies based on the generalized thermoelectric energy balance equations. However, it is assumed that TE legs have no heat exchange with the ambient except at the junctions of the hot and cold ends where heat flows in and out. Based on basic thermoelectric effects and fundamental theories of heat transfer, a detailed derivation of the revised generalized thermoelectric energy equations considering convective heat transfer between TE legs and the ambient has been carried out. Irreversible heat transfer processes have been analyzed by employing energy analysis based on the first law of thermodynamics and exergy analysis based on the second law of thermodynamics. The results show that convective heat transfer leads to a decrease in both energy and exergy efficiencies: the rate and magnitude of the decrease in exergy efficiency are greater than those of the decrease in energy efficiency. The exergy efficiency is relatively high despite the low energy efficiency in operation, revealing the features and advantages of thermoelectric generators (TEGs) in low‐grade energy utilization. For TEG efficient operation, the load resistance value should match the system's internal resistance, or at least be greater than that, to avoid a sharp drop in power output and efficiencies. In an attempt at theoretical analysis, the concept of entransy was first introduced into thermoelectric analysis, yielding two concise relational equations which reflect the intrinsic link between Carnot cycle efficiency, energy efficiency, exergy efficiency, and entransy flow transfer efficiency. The entransy analysis based on the index of entransy flow transfer efficiency, together with energy analysis and exergy analysis, may be a novel and valuable guideline for the operation and optimization of TEGs, which needs to be further investigated.

Contact-electrification enabled water-resistant triboelectric nanogenerators as demonstrator educational appliances

Triboelectric nanogenerators (TENG) work on the principle of tribo and contact electrification, which is a common phenomenon observed in daily life. TENGs are moving closer to commercialization, particularly for small scale energy harvesting and self-powered sensing. The toys and games industry has attracted a large audience recently with the introduction of digital toys. In this paper we embedded TENGs to power up a toy and operate during its specific application. We have modified two potential electronic demonstrator applications using TENG for lobster toy (LT-TENG) and stress ball (SB-TENG) device. The LT-TENG device generates a maximum electrical response of 60 V/2 µA, with a power of 55 µW and power density of 0.065 µW m−2 at a load resistance value of 10 MΩ. Similarly, the SB-TENG device made of aluminum and PDMS as the triboelectric layers generates a maximum electrical output response of 800 V and 4 µA peak to peak current with an instantaneous power of 6 mW and a power density of 3.5 mW m−2 respectively at a load resistance of 10 MΩ. In addition, the layers of the TENGs are packed with polyethylene to maintain the performance of the nanogenerator under harsh environmental conditions, especially with humid environments. The water resistance studies proved that the packed SB-TENG is impervious to water. The LT-TENG device is accompanied by four LEDs, and the device lights up upon actuating the handle. The SB is connected with the measuring instrument to record the quantity of force at which the SB is pressed. The adopted approach paves the way to convert these traditional toys into battery-free electronic designs and its commercialization.

Comparative performance of nonlinear energy harvesters through strongly coupled fluid-structure-electrical interactive models

Micro power generators (MPGs) can harvest electrical power from ambient energy resources in natural environments to operate small-scale electronic devices. Such systems exploit structural vibrations due to cross-flow instabilities through fluid–structure interactions (FSI). Due to attractive features of piezoelectric transducers, we utilize them for vibration-to-electricity conversion in this work. We develop strongly coupled FSI-based computational models to handle large-amplitude structural motions in which unsteady forces exerted by fluid flows on structures, their dynamical responses, and harvested power are directly computed. Our mathematical model for incompressible flows over moving bodies relies on arbitrary Lagrangian–Eulerian (ALE) formulation. Our in-house FSI solver primarily works using radial basis interpolation technique for grid morphing. Using broad ranges of fluidic, structural, and electrical parameters, we investigate the power generation performance of two types of MPGs, working through vortex-induced vibrations of a circular cylinder and a fluttering NACA-0012 airfoil, under different excitation conditions. Optimum values of load resistance are found to maximize the harvested power. Furthermore, our findings support the linear analysis, which provides insights into the possible instabilities in the electro-mechanical system. Another salient feature of this research work is the inclusion of cubic nonlinear stiffness in the energy harvesting models.

Driving Strategy Based on Artificial Neuron Device for Array Circuits

Over the past many years, array circuits, as an important part of electronic systems, show a wide range of application scenarios. However, the pursuit of high-density array circuits will certainly lead to a steep increase in the area of the array driving circuit. In this article, we present a switching array circuit with an artificial neuron, where the neuron acts as a discrete control center for the array circuit, which can effectively reduce the area of the array driving circuit by 75%. In this work, we found that the value of load resistance can affect the switching of individual devices and control the branch threshold voltage range, thus affecting the information processing capability of the branch. This new paradigm of optimized array circuit driving strategy can be used to tune the set and reset threshold voltage of neurons, while processing and outputting information by using this type of configuration. This work provides a potential platform for promoting the development of electronic devices and future high-density array circuits.

Energy Harvesting from Ambient Vibration at Low Force/Acceleration Input

Background: Ambient vibration is a promising source to provide low-power electronic devices with energy. The piezoelectric direct effect is widely used to generate energy from mechanical stress. Generating sufficient power in milliwatts is often obtained with input acceleration greater than 1g (9.81 m/s2) Aim: In this work, the author demonstrated that low acceleration (between 0.1g and 0.9 g) vibration sources can be utilized to generate a satisfactory level of electric power. Method: A low pre-stress was introduced by fixing the piezo structure to the shaker using adhesive tape. the driving force which was less than 0.06 N. The harvester was tested at a vibration frequency of 173 Hz. Result: The maximum power of 1.5 mW was achieved when the harvester resistance matches the load resistance value. At maximum harvested power, the efficiency was found to be 1.6. Conclusion: The results indicated that prestreseed piezoceramics is good candidate for vibration energy harvesting.

Modeling the performance of contact-separation triboelectric nanogenerators

Triboelectric nanogenerators (TENGs) are a promising and attractive energy harvesting technology because they are environmentally friendly and low cost. Here, the performance of dielectric-dielectric TENGs operating in the contact-separation mode was studied using time-dependent finite-element numerical simulations. To evaluate the TENG performance, the open-circuit voltage, short-circuit current and optimum resistance were obtained. The results are in agreement with the available physical models for the short-circuit current, with the current increasing (decreasing) with the TENG's area (material's thickness). Contrarily to established models, the open-circuit voltage varied with the area and material's thickness and reasons for such disagreement are given. A better understanding on the effect of high load resistance values is also provided due to their impact on charge flow in the TENG cycle (transient state) and performance. This work shows that finite-element simulations are a viable tool to provide a deeper understanding and new paths to optimize contact-separation TENGs.

Simulation of Load Behavior Based on Perturb-Observation Method in Non-Isolated Boost Converter for Maximum Power Point Tracking of Thermoelectric Generators

The efficiency of thermoelectric generators (TEGs) is quite low. To operate the TEGs at the maximum power point (MPP), the internal resistance of the connected load and the TEG must be equal. This is not always possible. For this, converters containing the maximum power point tracking (MPPT) algorithm tracking MPP are placed between the TEG and the load. These converters cannot perform MPPT on every connected load value. The aim of this study is to investigate at which load values MPPT can be performed in non-isolated boost converters by using perturb & observation (P&O) method. For this purpose, a 50 W converter was designed with a 45.76 W TEG in MATLAB/Simulink environment. Load resistance value has been increased starting from the minimum value up to 5.84 ohm being the internal resistance value of the TEG. For this case, the amount of error in MPPT was large up to the internal resistance value of the TEG. In other words, the P&O algorithm could not perform MPPT. When the load resistance value started from 5.84 ohms and increased to larger values, MPPT could be performed by means of the non-isolated boost converter with the P&O algorithm.

Optimization of Magnetically Coupled Resonant Wireless Power Transfer Based on Improved Whale Optimization Algorithm

This study aimed to address the optimization of magnetically coupled resonant wireless power transfer. An equivalent circuit for the wireless power transfer was established and the factors affecting the transmission efficiency were analyzed. To optimize the system, an improved whale optimization algorithm (WOA) was proposed and applied to optimize the optimal matching values of resonant frequency and load resistance. Performance of the improved WOA was tested using different test functions, and the optimized parameters were applied to the transmission efficiency test of the wireless power transfer system. Experiments demonstrated that the improved WOA effectively optimized the transmission efficiency and achieved good application results in the intelligent transfer system.

Evaluation of the Influence of the Load Resistance on Power and Efficiency in the Square and Circular Periodic WPT Systems

We are currently seeing an increasing number of devices that support wireless power transfer (WPT) technology. In order to avoid early prototyping and carry out a series of experimental analyses, it was possible to use numerical methods at the design stage to estimate the potential power transfer and efficiency of the system. The purpose of this study is to present a method of analysis for a periodic wireless power transfer system, using periodically arranged planar coils with field and circuit models. A three-dimensional numerical model of a multi-segment charging system with periodic boundary conditions was solved with the finite element method (FEM). An equivalent circuit model of the periodic WPT system was proposed, and the required lumped parameters were obtained using analytical formulas. Mathematical formulas were supplemented with the analysis of several geometric variants, taking into account different sizes of transmitting and receiving coils, as well as different numbers of turns. Both proposed methods of analysis allowed for the determination of load resistance values at which the variants of WPT systems considered in the research had maximum efficiency. The ranges of load resistance values in which the efficiency of the system exceeded 50% were indicated. The results obtained are very helpful in the proper selection of the load resistance, without the need for multiple tests and their resulting multiple measurements. The results also showed that the proposed circuit model was able to achieve similar accuracy as the numerical model, and the complexity of the model and analysis was significantly reduced. The obtained results will allow the design of WPT systems with appropriate selections of load resistance to achieve maximum efficiency.

Piezoelectric Energy Harvesting Gyroscopes: Comparative Modeling and Effectiveness

Given its versatility in drawing power from many sources in the natural world, piezoelectric energy harvesting (PEH) has become increasingly popular. However, its energy harvesting capacities could be enhanced further. Here, a mathematical model that accurately simulates the dynamic behavior and energy harvested can facilitate further improvements in the performance of piezoelectric devices. One of the goals of this study is to create a dependable reduced-order model of a multi-purpose gyroscope. This model will make it possible to compute the harvested voltage and electrical power in a semi-analytical manner. The harvested voltage is often modeled as an average value across the whole electrode surface in piezoelectric devices. We propose a model which provides practical insights toward optimizing the performance of the system by considering a spatially varying electric field across the electrode surface length. Our framework allows investigation of the limits of applicability of the modeling assumptions across a range of load resistances. The differential quadrature method (DQM) provides the basis for the suggested numerical solution. The model is also employed to examine energy harvesting under various resistance loads. The newly developed spatially varying model is evaluated for open- and closed-circuit conditions and is proved to be accurate for various values of load resistance that have not previously been considered. The results show that using a spatially varying model is more versatile when modeling the performance of the piezoelectric multifunctional energy harvester. The performance may be accurately captured by the model for load resistances ranging between 103 Ω and 108 Ω. At optimum load resistance and near 65 KHz, the maximum power output predicted by the spatially varying (SV) model is 1.3 mV, 1.5 mV for the open-circuit (OC) model, and 2.1 mV for the closed circuit (CE) model. At a high-load resistance, the SV and OC models all predict the maximum power output to be 1.9 mV while the CE model predicted the maximum voltage to be 3 mV.

Soliton wave parameter estimation with the help of artificial neural network by using the experimental data carried out on the nonlinear transmission line

In this study, an artificial neural network (ANN) model is generated, which is used to estimate the output parameters of soliton waves produced as a result of nonlinear transmission lines (NLTLs). Three different output parameters are acquired as a consequence of the experiments carried out utilizing the five various input parameters that are set in the ANN-based study. Input parameters for NLTL designs with 116 different experiments; inductor (L), input voltage (Vi) value, number of nodes (n), capacitance (C(V)) and load resistance (RLoad) values. Output parameters values, which are maximum voltage (Vmax), center frequency (fcenter), and voltage modulation depth (VMD). Input and output data; 70 % is set aside for training, 15 % for validation and the remaining 15 % for testing. Training, validation, and testing steps are repeated for the output parameters, in which case more than 99 % correlation is found as a result of each operation. An absolute percentage error value is found for each output parameter. Moreover, Mean absolute percentage error (MAPE) is calculated for these output datasets. The data set is tested for the experimental studies carried out in the literature, and it is observed that there is a compliance of over 99 % for this situation.

FPGA-Based Frequency Tracking Strategy with High-Accuracy for Wireless Power Transmission Systems

Aiming at the problem of the unavoidable phase-tracking error of the wireless power transfer (WPT) system caused by dead time, MOSFET drive and other factors, this paper proposes a frequency-tracking method with high accuracy based on a Field-Programmable Gate Array (FPGA) to track the current and voltage phase differences on the transmitting side. Compared with fixed-phase systems, the proposed method accurately controls the phase difference between voltage and current. It detects the phase difference in real time and adjusts the phase compensation angle dynamically to ensure that the system always operates under the optimal zero-voltage switching (ZVS) state, which reduces system loss. Experiments under operating conditions of varying transmission distances and load resistance values are carried out on a prototype. The experimental results show that the proposed method achieves a desired phase difference of 11.5° under the conditions of varying transmission distances and load resistance values, which meets the expectation of a phase difference between 10.5° and 13° to achieve ZVS. Within the range of over-coupling conditions, the output power and transmission efficiency of the WPT system are more significantly improved than those of the fixed-frequency system, which verifies the feasibility of the proposed method.

Investigation on a Shutdown Control Strategy with Residual Oxygen Rapid Elimination for Proton Exchange Membrane Fuel Cell System

During the shutdown process of the fuel cell system for vehicles, the air entering the anode chamber can form the hydrogen/air interface, accelerating the carbon corrosion of the catalytic layer. According to optimized control strategies, the carbon corrosion of fuel cells can be reduced. Nowadays, the main control strategies include gas purging and the consumption of residual oxygen in the stack by the auxiliary load. However, the oxygen in the fuel cell stack cannot be fully consumed or can cause the single-cell voltage to rise to 0.8 V with an inappropriate discharge current drop rate and auxiliary load resistance value, thus affecting the protective effect of the shutdown strategy. In this work, a shutdown strategy of the fuel cell system is studied. After the experiment, the optimized value of the discharge current drop rate and the auxiliary load resistance were obtained. With the resistance value of 50 Ω and the current drop rate of 7 A/s, the shutdown time of the fuel cell system is 13.5 s and the time of single-cell voltage above 0.82 V in the fuel cell stack is 0.1 s. Thus, the optimized shutdown strategy can reduce the shutdown time.

Performance analysis of thermoelectric power-generation system with natural convection cooling

Nowadays, high-performance electronic devices release large amounts of heat throughout their operation. Thermoelectric passive cooling systems can offer a cost-efficient and straightforward solution for the thermal management of such devices based on a passive heatsink and a thermoelectric generator (TEG). TEG can transform a part of the heat generated by the electronic chip into electricity for the power supply of microelectronic systems. The thermoelectric system investigated here contains a 12 W Positive Temperature Coefficient (PTC) heating element placed on a 4 × 4 cm2 aluminium plate, a commercial SP1848-27145 TEG device and a finned plate heatsink recycled from a desktop PC. Two types of tests were performed here. An energy efficiency test was initiated at different load resistance values RL between 1 and 40 Ω by directly connecting TEG output to a direct current (DC) electronic load. The second test was developed for electrical power generation at 3.3 V–5 V by integrating a DC–DC boost converter between the TEG output and the electronic load set at RL of 600–900 Ω. It was registered a maximum energy conversion efficiency of 1.17 % for RL=2Ω, close to the internal resistance value of the TEG module. The second test revealed the generation of output electrical powers with minimum values of 15–17.5 mW at a temperature difference between TEG plates of about 20 K.