Proton Exchange Membrane Fuel Cell (PEMFC) has advantages that other energy sources don’t have, and recently, it has been spotlighted in many industries such as transportation and power generation. However, although much research has been conducted on PEMFC, studies on operating conditions of bipolar plates in cells have been insufficient. Most of the studies that have been conducted so far are obtained by setting a few points on the edge or the latter line of the bipolar plate when acquiring data such as the operating temperature or relative humidity of the cell, so the research is extremely limited. In order to maximize the performance of PEMFC and preserve its durability, it is very important to control operating temperature and humidity optimally. Typically, water contents inside membrane electrolyte is determined by externally delivered water vapor and electrically reacted water vapor. Since water vapor is delivered and exhausted through bipolar plate, the vapor concentration in the bipolar plate is a clue to understand operating characteristics of PEMFC. Even though vapor concentration is a key to improve the performance, it is very difficult to measure direct distribution on the membrane electrode assembly. Therefore, this study attempted to observe the behavior of vapor flow inside the bipolar plate. By mounting several sensors in the flow path of the bipolar plate, it is possible to measure the temperature and humidity field data in the flow path, so that it is possible to observe the actual operating environment in the stack under various operating conditions and to establish a control strategy. Especially, this approach not only makes it possible to analyze the static water content in a steady state where no change in load occurs, but also enables dynamic observation of transient characteristics in the flow path when the current density changes. Several temperature and humidity sensors were installed on the bipolar plates of the cathode and anode respectively, and reliability and performance evaluations were performed through experiments. Reliability was evaluated by setting up a relatively accurate comparison sensor among the existing sensors that were not used in this study, and analyzed the effects of flow disturbance in the flow path by comparing with the polarization curve in the general cell. After the sensor calibration, an experiment was performed to obtain temperature and humidity data as the current density changed. As a result, it was possible to quantitatively analyze the water content delivered from the outside or generated inside the stack.

The energy harvesting performance of a flapping airfoil is studied through discrete vortex model. Results are obtained for a thin flat airfoil that undergoes a sinusoidal flapping motion for reduced frequencies of k = fC/U ∞ = 0.06–0.16 where f is the heaving frequency of the foil, C is the chord length and U ∞ is the freestream velocity. The airfoil pitches about the mid-chord and the heaving and pitching amplitudes of the airfoil are h 0 = 0.5C and θ 0 = 70° respectively, as these numbers have been shown to give optimal energy harvesting results for a rigid airfoil. The study applies a panel-based discrete vortex model that incorporates a leading edge suction parameter criterion to understand the flow behavior around the airfoil. The leading edge suction parameter is found from 2D CFD simulations (Navier-Stokes equations solved in Fluent) for all K values. A correlation between the critical leading edge suction parameter and reduced frequency is found from the identified critical LESP values. An empirical trailing edge separation correction is also applied to the transient force results since flow separation at the trailing edge is anticipated. The parameters of interest from the model are transient distributions of force, power output, and overall efficiency. Model results are then validated against 2D CFD simulations. The effect of reduced frequency on power production and overall efficiency is finally studied to identify the optimal reduced frequency for energy harvesting applications.

In this paper, the stochastic optimization of a horizontal-axis composite wind turbine blade is performed. Wind energy has become widely popular in recent decades as an alternative source of energy and many studies have been devoted to finding an optimal wind turbine blade using deterministic optimization. However, the actual responses of the wind turbine blade such as power generation are affected by the stochastic nature of wind, uncertainties in material properties and modeling parameters, and so on. This can have an undesirable impact on the performance and reliability of blades, which demands the consideration of uncertainties during optimization. To this end, a surrogate-based stochastic optimization of a wind turbine blade considering the influence of randomness in wind speed on power generation was studied. A slight gain in average power over the baseline blade was obtained and it demonstrated the promise of the presented framework for the design of wind turbine blades.

The behavior of Cross-linked Polymers in finite deformations is often characterized by nonlinear behaviour. In this paper, we propose to embed an artificial neural network (ANN) within a micro-mechanical platform and thus to enforce certain physical restrictions of an amorphous network such as directional dependency and history-dependency of the constitutive behavior of rubber-like materials during loading and unloading. Accordingly, a strain energy density function is assumed for a set of chains in each direction based on ANN and trained with experimental data set. Summation of the energies provided by ANNs in different directions can determine the strain energy density function of the matrix. Stress-strain relation is derived from strain energy density function. Polyconvexity is enforced to assure minimized potential energy, a global solution for an optimization problem, and thermodynamic consistency that show the model cannot generate energy. The model is validated against multiple sets of experimental data, e.g. uniaxial, shear, and biaxial deformation available in the literature. This model captures not only the loading and unloading paths but also the inelastic response of these materials, such as the Mullins effect and permanent set. The model can be generalized to other materials and other inelastic effects as well.

Nowadays, more significant effort is needed to improve power generation efficiency to respond to environmental concerns. Several innovative technological options are under development and, among them, the integration of different energy systems is one remarkable opportunity. In this work, a combination of three different thermodynamic cycles has been proposed and studied: an Inverted Brayton cycle (IBC) is used to exploit the exhaust gas enthalpy of a Brayton-Joule cycle and a Steam Power Plant is bottomed to the Inverted Brayton Cycle, in order to recover the high thermal power wasted in its cooling section. In other words, a quite conventional natural gas combined cycle power plant is repowered introducing the Inverted Brayton Cycle to exploit the gas thermal power between the gas turbine and the heat recovery steam generator. In this integration, each parameter has a strong influence on the overall performance of the system: pressure ratio of the gas cycle, sub-atmospheric pressure of the inverted one, turbines inlet and outlet temperatures and heat recovery grade in the bottom steam section have been investigated in order to optimize the working conditions and find a best operating point. A post combustion opportunity was also considered, exploring for the best position to place it along the gases path and to get the maximum additional power through the repowering intervention.

According to executive order 18-01 and 20-01 signed by the Washington State Governor, all newly constructed public buildings and facilities shall be designed to be net-zero energy capable. To respond to the governor’s order, the Washington State Department of Transportation (WSDOT) has asked for the design of a system that can use biowaste that accumulates at their safety rest stop areas to generate electricity to power the facilities. The goal of this project seeks to assist WSDOT by designing, building, and testing the capability of a small-scale methane energy generator that can be scaled to fit the needs of any rest area. There are a small number of methane generators in existence [1.]. However, they are not designed to satisfy the needs of net-zero energy facilities and safety rest areas. In this work, a net-zero methane generation system is presented to show how it can convert biowaste into methane for electricity at rest areas. The model is composed of two tanks to store the biomaterial, a filtration system to remove hydrogen sulfide (H 2 S) and carbon dioxide (CO 2 ), a generator that runs on methane gas, and a photovoltaic system that powers temperature sensing devices. Through testing, it was shown that this system could generate energy through the use of bovine waste. Further improvements are needed to increase methane production and make operation more efficient. Future testing on human waste from a safety rest area will also be necessary before proving that the system can meet energy generation requirements.

The life cycle assessment (LCA) of a middle-class household of 5 members in Guayaquil, Ecuador was performed in order to identify the life cycle stages and activities with higher environmental burdens. LCA is a quantitative tool for assessing the environmental performance of products or systems during its life span, through the compilation and further evaluation of the inputs, outputs, and potential environmental impacts. The life cycle of the house included a 50-year lifespan house divided into three stages: pre-occupation, occupation, and post-occupation stage. The type of house chosen for the analysis represents the current trend of urban growth and planning of the city, which is pointing towards residential zones and housing plans far away from central areas. The notion of household metabolism is associated with the occupation stage. Household metabolism refers to all flows of matter and energy related to anthropogenic activities conducted on a household, which is a socio-economic entity that consists of people living together occupying a dwelling or part of it. Households are key entities of the anthroposphere because the sum of all private households is the process on which all other processes depend on and serve directly or indirectly. The total energy use and emissions for which the sum of households is responsible reflects the importance of considering its influence when assessing the environmental impact of dwellings. Five energy case scenarios were analyzed. These included different energy mixes and the use of inductive cookers as an alternative to those that use liquefied petroleum gas (LPG), which are the most used in Ecuador. The influence of the energy production structure of the country on the environmental impact of the household is supported by the results. A higher share of hydroelectricity in the energy mix, compared with the share of thermal electricity, presented lower environmental impacts in most categories. Public policies that encourage a shift towards a cleaner electricity production technology may decrease the overall environmental impact of households and buildings. The occupation stage entails the highest contribution to all impact categories, e.g. 88% of global warming potential (GWP), followed by the pre-occupation stage, contributing 10% of GWP. Food consumption has not been considered in reviewed studies, although it represents the highest environmental burden within the occupation stage of the house, followed by electricity, and gas use: 43, 27, and 20% of GWP respectively. The results support the importance of including household metabolism in LCA studies due to the high environmental burden associated with it, and the influence of the electricity production structure of the country on the life cycle impact of households.

Capturing the tidal energy is one of the ways of tapping natural and renewable energy which do not involve the cost of working fluid/ fuel. The present work focuses on some of the feasibility aspects of setting up of major tidal power plants along the seacoast. Besides, the present study synergizes on methods of estimating the power-producing capacities in regions along the seacoast. Estimation of power-producing capacities, calendar month-wise, and lunar month-wise gave handy information. Also, the estimation of power-producing capacities of different regions along a location gave clarity on the probable regions of interest for producing power simultaneously. A comparison of the estimates with the details of the literature authenticated the study. A discussion of producing more tidal power in specific locations gave insights into the aspects that may have been ignored in the literature. Geographic restrictions along the local seacoast like identifying the security-sensitive regions rationalized the estimating procedures. The paper includes a discussion of various factors that address the feasibility concerns. The study supposedly helps space exploration too.

It is known that high temperatures adversely affect the performance of gas turbines, but the effect of the combination of atmospheric conditions (temperature and relative humidity -RH- ) on the operation of this type of system is unknown. In this work the effects of atmospheric conditions on the energy and exergy indicators of a power plant with gas turbine were studied. The indicators studied were the mass flow, the specific work consumed by the compressor, specific work produced by the turbine, the combustion gas temperature, the NO concentration, the net output power, the thermal efficiency, the heat rate, the specific consumption of fuel, the destruction of exergy and exergy efficiency. Among the results, it is noted that for each degree celsius that reduces the temperature of the air at the compressor inlet at constant relative humidity on average, the mass flow of dry air increases by 0.27 kg/s, the specific work consumed by the compressors decreases by 0.45%, the output power increases by 1.17% and the thermal efficiency increases by 0.8%, the exergy destruction increases by 0.72% and the exergy efficiency increases by 0.81%. In addition, humidity changes relative to high temperatures are detected more significantly than at low temperatures. The power plant studied is installed in Cartagena, Colombia and since it is not operating in the design environmental conditions (15 °C and 60% relative humidity) it experiences a loss of output power of 6140 kW and a drop in thermal efficiency of 5.12 %. These results allow considering the implementation of air cooling technologies at the compressor inlet to compensate for the loss of power at atmospheric air conditions.

Thermoelectric materials are defined as materials which can convert heat into electrical energy. Thermoelectric materials are often used for applications such as power generation or refrigeration. Because of the applications for thermoelectric materials, it is important to understand the electrical-to-thermal coupling behavior of such materials. The thermoelectric materials simulated are 2D film configurations of Tin Selenide (SnSe). Using the derivations for non-equilibrium electron-phonon dynamics as well as obtaining the phonon dispersions, second-order and third-order elastic constants, the thermoelectric properties can be calculated. For the purposes of this paper, the correlation of thermoelectric properties such as thermopwer, thermal conductivitty, and thermoelectric figure of merit with parameters such as the characteristic length of the 2D material as well as the applied voltages of 0 V/m, 10,000 V/m, and 20,000 V/m over the 2D material. Furthermore, an analysis on the effect of strain on the thermoelectric properties of SnSe is conducted.

This work describes the design and construction of a four-stage traveling-wave thermo-acoustic system for electricity generation. The thermo-acoustic conversion consists of using a sound-wave for the transfer of heat from a low to high-temperature medium or the use of heat energy to generate a sound wave. Both the absence of moving parts and the simplicity of thermo-acoustic systems make the technology sustainable for converting low-grade waste heat into acoustic power. Many existing studies have pointed out the acoustic-to-electric potential of thermo-acoustic systems. Hence in this work, a thermo-acoustic system has been developed. The traveling-wave system has a total length of 3 560 mm. The distance between each thermo-acoustic engine is 640 mm. Each engine stage had four cartridge heaters used to generate the heat required. A commercial loudspeaker was used to convert sound into electricity. The minimum temperature difference necessary to induce a voltage at the terminals of the loudspeaker was approximately 200°C. The four-stage traveling-wave system generated the highest output voltage of 4.218 V.

Thermoelectric generator technology can be utilized as a renewable energy source and has untapped potential. Thermoelectric generators (TEGs) have been used by industry experts to make some thermodynamic processes slightly more efficient. However, TEGs can be operated in a manner that allows for greater energy production at a higher efficiency and in a stand-alone setting. This paper presents design and analysis of an innovative portable water-cooled thermoelectric generator apparatus. The apparatus can create clean energy using optimal heat transfer through the device. To reduce the amount of power lost to internal heat resistance, the device is cooled by a large body of water. Solar irradiation is the primary heat source for the TEGs and is absorbed using copper foil and high emissive paint. The temperature differential predicted during device operation was modeled using ANSYS. The ANSYS heat transfer model revealed that heat absorption and subsequent transfer to a body of water was possible without exceeding the operating parameters of the TEGs. Experimental results revealed that a 120°C temperature difference across the TEGs produced 12.5 V of electricity. Analysis of the water-cooled TEG prototype performance revealed that power production is possible, and the design has numerous applications.

In comparison to fossil fuels, solar energy is a more sustainable option due to its high availability and less environmental impact. Improving the efficiency of solar farms has been a primary concern of solar energy research. Many studies focus on the control of the tilt angle of solar modules to maximize their solar radiation reception and energy generation. However, an increase in solar radiation is accompanied by an increase in module temperature, which is known to be a significant parameter that reduces the power generation efficiency. Wind is another influential factor that helps Photovoltaic systems maintain a low operating temperature by enhancing the rate of heat transfer. Therefore, solar radiation and wind behavior are both critical parameters that must be considered to optimize solar panel performance. In this paper, the effect of wind conditions on solar panel performance will be examined. The solar panel energy output model will be built by empirically considering the irradiation, ambient temperature, wind speed, and wind direction. The published weather data and energy output data for the year 2017–2018 have been collected from Antelope Valley Solar Ranch, located in Lancaster, California. Four models have been proposed and the results indicate that the model which incorporates the wind conditions has the highest accuracy in approximating the energy production of solar farms. Among the factors that affect the temperature of solar panels and further the efficiency of solar panels including solar irradiation, convection, conduction, wind plays a major role in convective heat transfer. Based on this model, the potential improvement of energy generation via introducing a horizontal installation angle and adjusting this angle monthly according to the wind conditions is further analyzed. These results will help designers improve the design of solar farms by taking into consideration the local weather conditions.

The recent awareness on the environmental issues related to global warming is leading to the search for always more efficient energy conversion systems and, mainly, with very low carbon dioxide emissions. In fact, they are strictly related to the combustion reaction of fossil fuels which is the main process of the actual power generation technology. In this regard, fuel cells are energy conversion systems which are characterized by higher efficiency and near-zero CO 2 emissions. Their novel integration with conventional power plants participates to the concept of the decarbonization of the economy. In this work, the integration of two high temperature fuel cells (HTFC) with a gas turbine power plant has been proposed and investigated, thanks to the combination of a physical model of the fuel cells and a numerical one of the components involved in the gas turbine cycle. In the layout studied, fresh air is compressed, pre-heated and used in a Solid Oxide Fuel Cell (SOFC), where the high operating temperature and the exothermic process give exhaust gases at very high temperatures, suitable for an expansion in a turbine. After the expansion, the gases are rich of CO 2 and, so, they can be sent to the cathode side of a Molten Carbonate Fuel Cell (MCFC). Hence, the so-defined integrated plant is composed by three power units: a turbine, a SOFC and a MCFC; operating pressure, fuel need, oxygen and carbon dioxide utilizations in the fuel cells are parameterized in order to optimize the whole plant and find additional room of energy exploitation. Moreover, the MCFC acts as an active device for carbon separation, introducing further environmental benefits.

The manuscript presents a novel power electronics sliding mode control design for photovoltaic energy conversion systems. In order to maximize the power generation from solar panels, P&O maximum power point tracking algorithm is applied. The purposed first and high-order sliding mode control techniques are developed to overcome the irradiance and load fluctuation challenge, and to optimize the power conversion efficiency. Compared with the first-order method, the higher-order sliding mode approach can significantly reduce the chattering effect in the Buck-Boost converter. The output of the DC-DC converter is then fed into a voltage-oriented control based SVPWM inverter for three-phase AC power generation. Computer simulation studies have shown the effectiveness and robustness of the proposed power electronics control approach for solar energy systems.

Wind farm energy production optimization has received significant attention in recent years. Much of this effort had been focused on optimizing positions of wind turbines within a wind farm domain during the design and planning stage. Optimization of wind turbine positions can reduce wake interactions of upstream turbines. In addition to optimizing turbine positions to reduce wake interactions, prior studies have shown that optimizing yaw and pitch angles can improve energy production as upstream wakes yaw away from downstream turbines. However, yaw angle optimization at the wind farm level has been difficult due to lack of low-fidelity wake model for simulating yawed wakes. Recently, an analytical wake model capable of simulating yawed turbine wakes had been developed, which enable wind farm-scale yaw optimization. In this work, a binary quadratic programming model problem formulation has been developed to optimize yaw angles of wind farms. Yaw optimization of two position-optimized layouts available in the literature were performed to study the potential of yaw optimization. In particular, we set out to understand how layout and wind farm density affect yaw optimization potential. An optimized layout of 39 turbines with 40m rotor diameter in a 2km by 2km domain was used in this study. For this wind farm, yawing optimization only improved power production by ∼1.5% under favorable wind directions. However, as wind farm power density increases by increasing rotor diameter to 60m and 80m, power production improved by ∼5% and ∼10% respectively, under favorable wind directions. Finally, another yaw optimization was performed on an optimized layout with 48 turbines of 82m rotor diameter in a 4km by 4km domain using the proposed model formulation. Under favorable wind directions, yaw angle optimization improved performance by ∼4%. The results show that yaw optimization can improve power production in the same order of magnitude as layout optimization, and that it should be considered in addition and/or in tandem to layout optimization.

Renewable energy sources and related conversion technologies are considered as the main solution for resolving the current issues related to global warming and environmental protection. Salinity gradient energy (SGE) is a source of renewable energy which can be defined as the Gibbs Energy of mixing when two solutions with different salinities mix together. The difference in the salinity of salt solutions is the main driving force of energy production by the SGE conversion technologies. One of the main conversion technologies of SGE is reverse electrodialysis (RED). In this technology the gradient between the concentrated and diluted salt solutions, the ions with a negative charge (anion) and positive charge (cation) pass through selective ion exchange membranes known as anion exchange membrane and cation exchange membrane. The driving force for diffusion of the ions is a function of the concentration gradient. The chemical potential of the salt solution is a function of the concentration of the salt solution and plays an important role in the Gibbs energy of mixing. The chemical potential of the salt solution is a thermodynamic property which is a function of the concentration and activity coefficient of the salt solution. The activity coefficient of the salt solution is a unique parameter which depends on the ionic strength of the solution and the type of ions in the salt solution. The salts with higher activity coefficient have a higher potential to be used in the SGE conversion process due to higher released Gibbs Energy during the mixing process. In this paper the thermodynamic model presented by Bromley [1], is used to calculate activity coefficient of 20 salts at different concentrations (0.01–6 molal). Two dimensionless parameters, Φ and Ψ, are defined as the ratio of activity coefficient and concentration between the concentrated and diluted solutions in 6 and 0.5 molal respectively. Using the dimensionless parameters, the theoretical open circuit voltage (OCV) of salt solutions in a RED cell is calculated. The salts are screened and ranked based on the activity coefficients and the theoretical open circuit voltage (OCV). The best salts are selected for use in a RED cell based on the activity coefficients and theoretical OCV. These alts could have potential for developing SGE storage systems in combination with renewable energy devices.

Free Piston Stirling Engine is an external combustion engine, which can use diversified energy resources, such as solar energy, nuclear energy, geothermal energy, biomass, industrial waste heat etc. and is suitable for the remote area power generation due to the advantage of robustness, durability, reliability, and high efficiency. In this work, a Free Piston Stirling Engine has been designed based on the numerical simulation results and previous experimental experience. Direct Metal Laser Sintering method has been adopted for the manufacturing of the key components including the displacer cap, displacer body, piston housing, cold heat exchanger, and regenerator. One dimension analysis using Sage software has been conducted. The designed engine has a power output of 65W with the hot and cold end temperature is 650°C and 80°C respectively, and charge pressure is 1.35 MPa. Finite Element Method has been used to analyze the structural stress of the engine, which is operated at the high temperature and high pressure, to determine if it is able to tolerate the operating condition designed by the Sage according to the Section VIII Division 2 of the ASME Boiler and Pressure Vessel ( BPV ) Code. In addition, Computational Fluid Dynamics (CFD) method has been used to investigate the flow distribution in heat exchangers (heat acceptor, regenerator, and heat rejecter), as the heat exchanger performance affect the engine performance greatly. Considering the large mesh number, a quarter of the heat exchangers have been investigated, in order to reduce the mesh numbers and accelerate the calculation speed.

Large Eddy Simulation (LES) turbulence and multiphase Volume of Fluid (VOF) model are employed to predict the spatial and temporal characteristics of the turbulent flow structures near micro-hydrokinetic turbine operating in the proximity of a free surface. The turbine power performance and the free surface dynamics, and its interaction with the turbine are characterized by examining the results of both single-phase and multiphase flow simulations. Simulations are conducted at the turbine’s best efficiency point at a tip speed ratio of 1.86 with the rotation rate of 150 rpm and the free stream water velocity of 2.25 m/s. The multiphase flow simulation is carried out at Froude number of 1.06. The results indicate slight interaction between the deformed free surface and the turbine wake structures. Acceleration in the flow velocity is observed near the free surface due to the physical confinement. The results indicate that turbine power generation is reduced by about 2.0%, and the thrust coefficient is reduced by 1.60%. It is demonstrated that the turbine performance at this Froude number is hardly influenced by the presence of the free surface.

Wettability alteration has significant applications in microfluidics, energy production and process engineering. Surfactants have been widely used for wettability alteration on surfaces. More recently, electrowetting (EW) has emerged as a powerful microfluidic technique to dynamically alter wettability. EW relies on the application of an electrical potential difference across a dielectric layer on which the fluid rests. This work analyzes the extent of wettability enhancement of water droplets on a hydrophobic surface (in air) via the use of surfactants and EW. Nine surfactants were chosen from the categories of anionic, cationic and zwitterionic surfactants. The critical micelle concentration (CMC) of these surfactants, and the wettability of surfactant-infused water droplets was measured at post and pre-CMC concentrations. Next, experiments were conducted to quantify the wettability enhancement of water droplets (with surfactants) via EW. Many interesting insights on the interplay between surfactants and electric fields are uncovered in this work. As expected, adding surfactants enhances wettability up to the CMC. EW can further enhance wettability of surfactant solutions and further reduce the contact angle by as much as 30°. Interestingly, it is seen that the influence of EW in enabling CA reduction is reduced by the addition of surfactants at pre-CMC levels. Conversely, surfactants strengthen the influence of EW at higher concentrations. It is noted that the extent of wettability alteration via EW is limited by the phenomena of contact angle saturation, wherein the contact angle saturates beyond a certain voltage. Interestingly, it is seen that at post CMC concentrations, the saturation contact angles are independent of surfactant concentrations.