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Research Papers: Alternative Energy Sources

J. Energy Resour. Technol. 2019;141(6):061201-061201-7. doi:10.1115/1.4042404.

With the increasing demand for clean energy, offshore wind power is developing rapidly. But compared to onshore situation, the working environment at sea is very complicated. In order to ensure the stable operation of generators, higher requirements are put forward for the capability of offshore wind power structures to resist wind and waves. This paper proposes a new combined vibration suppressing device, which can be used to suppress the swaying vibration of offshore floating wind generator under waves. The floating wind power station tower was modeled, the wave force and the torsion force of the tower were analyzed, and the fluid structure interaction numerical simulation was carried out. The calculation results demonstrate that the amplitudes of the tower torsion angle have been attenuated by 8%, 11%, and 17% with different vibration suppression devices which are tuned mass damper (TMD), tuned liquid damper (TLD), and a tuned immersed mass and liquid damper. In this case, the new combined device has the best vibration suppression performance. It is validated that compared to the other two single vibration suppression devices, the new combined device has better vibration suppression capacity, and a new way is provided to design the vibration suppression device for offshore floating wind power station.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(6):061202-061202-9. doi:10.1115/1.4042405.

When hydrogen is produced from a biomass or coal gasifier, it is necessary to purify it from syngas streams containing components such as CO, CO2, N2, CH4, and other products. Therefore, a challenge related to hydrogen purification is the development of hydrogen-selective membranes that can operate at elevated temperatures and pressures, provide high fluxes, long operational lifetime, and resistance to poisoning while still maintaining reasonable cost. Palladium-based membranes have been shown to be well suited for these types of high-temperature applications and have been widely utilized for hydrogen separation. Palladium's unique ability to absorb a large quantity of hydrogen can also be applied in various clean energy technologies, like hydrogen fuel cells. In this paper, a fully analytical interatomic embedded atom method (EAM) potential for the Pd-H system has been developed, that is easily extendable to ternary Palladium-based hydride systems, such as Pd-Cu-H and Pd-Ag-H. The new potential has fewer fitting parameters than previously developed EAM Pd-H potentials and is able to accurately predict the cohesive energy, lattice constant, bulk modulus, elastic constants, melting temperature, and the stable Pd-H structures in molecular dynamics (MD) simulations with various hydrogen concentrations. The EAM potential also well predicts the miscibility gap, the segregation of the palladium hydride system into dilute (α), and concentrated (β) phases.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Storage/Systems

J. Energy Resour. Technol. 2019;141(6):061901-061901-10. doi:10.1115/1.4042400.

In this study, the round trip efficiency of a multistage adiabatic compressed air energy storage (A-CAES) system was optimized by differential evolution (DE) algorithm, and decision variables were the pressure ratio of each compressor/expander. The variation of the pressure ratio of each compressor/expander leads to different inlet air temperatures of the heat exchanger. Thus, this optimization method provides more heat energy recovery from compression to increase the inlet air temperature of expanders. Results indicate that the optimization method is effective for the pressure ratio allocation, improving the system efficiency by ∼1% and exergy efficiency of the heat storage process by 5.3% to the maximum compared with an equal pressure ratio distribution A-CAES system. Besides, a uniformity factor of temperature difference (UFTD) of multistage heat exchangers is proposed to analyze the temperature uniformity of the multistage heat exchangers, which indicates that decreasing the UFTD contributes to an increased uniformity of the temperature field and an improvement in heat transfer efficiency. The study is extended onto optimal off-design system configuration and the recommendations are proposed, which provides a guidance for A-CAES system design.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(6):061902-061902-10. doi:10.1115/1.4042403.

The short-cycling operation of a heat pump decreases energy consumption efficiency. Short-cycling operations of ground source heat pump system (GSHP) occur when the ON/OFF control of a heat pump is used in a partial load condition. It is considered effective that GSHP with capacity controls installs to suppress short-cycling operations. However, there is no report on any continuous operations by capacity control GSHP in actual operations. We confirmed that GSHP (water to water) with capacity control operates short-cycling in the residence. Short-cycling operations occurred with a sudden load fluctuation due to opening or closing of the valves. We conducted effective verification experiments of the thermal storage device at the artificial heat load fluctuations condition. When the thermal storage device installed upstream brine circulation line of the heat pump with the capacity control, continuous operations are performed. It was under the condition at the heating heat load of 5 kW is turned ON/OFF every 20 min. In this case, energy consumption efficiency of a heat pump is 13% higher than the efficiency without the thermal storage device.

Commentary by Dr. Valentin Fuster

Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2019;141(6):062001-062001-5. doi:10.1115/1.4042224.

This paper presents a co-simulation platform which combines a building simulation tool with a cyber-physical systems (CPS) approach. Residential buildings have a great potential of energy reduction by controlling home equipment based on usage information. A CPS can eliminate unnecessary energy usage on a small, local scale by autonomously optimizing equipment activity, based on sensor measurements from the home. It can also allow peak shaving from the grid if a collection of homes are connected. However, lack of verification tools limits effective development of CPS products. The present work integrates EnergyPlus, which is a widely adopted building simulation tool, into an open-source development environment for CPS released by the National Institute of Standards and Technology (NIST). The NIST environment utilizes the IEEE high-level architecture (HLA) standard for data exchange and logical timing control to integrate a suite of simulators into a common platform. A simple CPS model, which controls local heating, ventilation, and cooling (HVAC) temperature set-point based on environmental conditions, was tested with the developed co-simulation platform. The proposed platform can be expanded to integrate various simulation tools and various home simulations, thereby allowing for cosimulation of more intricate building energy systems.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(6):062002-062002-10. doi:10.1115/1.4042402.

This paper presents the feasibility and economics of using fuel cell backup power systems in telecommunication cell towers to provide grid services (e.g., ancillary services, demand response (DR)) as well as power for cell towers during emergency conditions. This study evaluates the strategic integration of clean, efficient, and reliable fuel cell systems with the grid for improved economic benefits. The backup systems can potentially enhance capabilities through information exchange with the power grid, which adds value for grid services that depend on location and time. The economic analysis focused on the potential revenue for distributed telecommunications fuel cell backup units to provide value-added power supply. This paper includes case studies on current fuel cell backup power locations and regional grid service programs. The grid service benefits and system configurations for different operation modes provide opportunities for expanding backup fuel cell applications responsive to grid needs. The objective of this work is primarily on how fuel cells can become a significant part of the telecom backup power fleet to reduce system costs, environmental impact, and dependence on fossil fuels, while ensuring continuity of indispensable service for mobile users. The study identifies different fuel cell applications and nano/microgrid approaches for an extensive network of fuel cells as distributed energy resources. The possibilities of various application scenarios extend to fuel cell technologies and microgrids for reliable power supply.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(6):062003-062003-6. doi:10.1115/1.4042451.

Residential energy consumption constitutes a significant portion of the overall energy consumption. There are significant amount of studies that target to reduce this consumption, and these studies mainly create mathematical models to represent and regenerate the energy consumption of individual houses. Most of these models assume that the residential energy consumption can be classified and then predicted based on the household size. As a result, most of the previous studies suggest that the household size can be treated as an independent variable which can be used to predict energy consumption. In this work, we test this hypothesis on a large residential energy consumption dataset that also includes demographic information. Our results show that other variables such as income, geographic location, house type, and personal preferences strongly impact energy consumption and decrease the importance of the household size because the household size can explain only 26.55% of the electricity consumption variation across the houses.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(6):062004-062004-10. doi:10.1115/1.4042406.

In this paper, the performance of a thermochemical battery based on magnesium chloride and ammonia pair with a constant mass flow rate of ammonia gas is studied through a series of experiments using single and multicell configurations. It is shown that a lower mass flow rate lowers the temperature of the reactive complex and increases the duration of the absorption process. However, it was observed that the reaction eventually becomes mass transfer limited which slows the absorption rate to values below those specified by the mass flow controller (MFC). It was shown in the single-cell reactor that a reaction zone starts at the inlet and moves toward the end of the reactor. The mass transfer limited reaction zone movement reduces the absorption rate and temperature in the reaction zone. The overall performance of a multicell thermal battery is also studied to analyze behavior of such reactors as well. It was shown that the controlling the flow rate of ammonia can cause the cells to deviate in absorption rate.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(6):062005-062005-15. doi:10.1115/1.4042407.

This study evaluates the potential aggregate effects of net-zero energy building (NZEB) implementations on the electrical grid in a simulation-based analysis. To estimate the impact of NZEBs on the electrical grid, a simulation-based study of an office building with a grid-tied photovoltaic (PV) power generation system is conducted. This study assumes that net-metering is available for NZEBs such that the excess on-site PV generation can be fed to the electrical grid. The impact of electrical energy storage (EES) within NZEBs on the electrical grid is also considered in this study. Different levels of NZEB adoption are examined: 20%, 50%, and 100% of the U.S. office building stock. Results indicate that significant penetration of NZEBs could potentially affect the current U.S. electricity demand profiles by reducing purchased electricity from the electrical grid and by increasing exported electricity to the electrical grid during peak hours. Annual electricity consumption of simulated office NZEBs in the U.S. climate locations is in the range of around 94–132 kWh/m2 yr. Comparison of hourly electricity demand profiles for the actual U.S. demand versus the calculated net-demand on a national scales indicates that the peak percentage difference of the U.S. net-electricity demand includes about 10.7%, 15.2%, and 9.3% for 100% of the U.S. NZEB stock on representative summer, transition, and winter days, respectively. Using EES within NZEBs, the peak percentage differences are reduced and shifted to the afternoon, including 8.6%, 13.3%, and 6.3% for 100% of the U.S. NZEB stock on each representative day.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(6):062006-062006-9. doi:10.1115/1.4042408.

This paper presents a methodology to predict and optimize performance of an organic Rankine cycle (ORC) using a back propagation neural network (BPNN) for diesel engine waste heat recovery. A test bench of an ORC with a diesel engine is established to collect experimental data. The collected data are used to train and test a BPNN model for performance prediction and optimization. After evaluating different hidden layers, a BPNN model of the ORC system is determined with the consideration of mean squared error (MSE) and correlation coefficient. The effects of key operating parameters on the power output of the ORC system and exhaust temperature at the outlet of the evaporator are evaluated using the proposed model and further discussed. Finally, a multi-objective optimization of the ORC system is conducted for maximizing power output and minimizing exhaust temperature at the outlet of the evaporator based on the proposed BPNN model. The results show that the proposed BPNN model has a high prediction accuracy and the maximum relative error of the power output is less than 5%. It also shows that when the operations are optimized based on the proposed model, the power output of the ORC system can be higher than the experimental results.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(6):062007-062007-8. doi:10.1115/1.4042398.

Intelligent tires can be used in autonomous vehicles to insure the vehicle safety by monitoring the tire and tire-road conditions using sensors embedded on the tire. These sensors and their wireless communication systems need to be powered by energy sources such as batteries or energy harvesters. The deflection of tires during rotation is an available and reliable source of energy for electric power generation using piezoelectric energy harvesters to feed tire self-powered sensors and their wireless communication systems. The aim of this study is to design, analyze, and optimize a rainbow-shaped piezoelectric energy harvester mounted on the inner layer of a pneumatic tire for providing enough power for microelectronics devices required for monitoring intelligent tires. It is shown that the designed piezoelectric energy harvester can generate sufficient voltage, power, and energy required for a tire pressure monitoring system (TPMS) with high data transmission speed or three TPMSs with average data transmission speed. The effect of the vehicle speed on the voltage and electric energy generated by the designed piezoelectric is also studied. The geometry and the circuit load resistance of the piezoelectric energy harvester are optimized in order to increase the energy harvesting efficiency. It is shown that the optimized rainbow piezoelectric energy harvester can reach the highest power generation among all the strain-based energy harvesters that partially cover the inner layer of the tire.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2019;141(6):062008-062008-9. doi:10.1115/1.4042409.

The use of B100 biodiesel for compression ignition engines during the winter poses a challenge due to gelling and plugging of engine filters and fuel lines. The most common method to prevent this issue is blending it with petroleum diesel and many engine manufacturers limit the biodiesel in blends to 20% or less for warrantee purposes; as low as 5% may be set for winter months. In this research, an experimental analysis is performed using a scaled model of the fuel tank with canola oil as a test fluid in the tank. An insulated tank is subjected to an ambient temperature of −20 °C in an icing tunnel facility with air velocity at 10 m/s. The results show that the time for the oil to drop from 20 °C to 5 °C was increased from 18.6 h to 22.5 and 33 h, respectively, when 4 and 12 tubes containing phase change materials (PCM) were inserted in the tank containing 33 l of canola oil. A numerical model was further formulated to predict the transient temperature of the oil and comparison with experimental results showed excellent agreement. Finally, the developed numerical model was used to simulate different designs to investigate the effect of tank filling level, overall heat transfer coefficient, number of PCM modules, and diameter of PCM modules on the tank performance. The results show that B100 can be implemented in diesel engines in cold climates using a passive approach using engine coolant.

Commentary by Dr. Valentin Fuster

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