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Assessment of Retrofitting Measures for a Large Historic Research Facility Using a Building Energy Simulation Model
Young Tae Chae, Young M. Lee, David Longinott
November 28, 2018 (v1)
Keywords: energy conservation measures (ECMs), historic research facility, system retrofitting, whole building energy simulation
A calibrated building simulation model was developed to assess the energy performance of a large historic research building. The complexity of space functions and operational conditions with limited availability of energy meters makes it hard to understand the end-used energy consumption in detail and to identify appropriate retrofitting options for reducing energy consumption and greenhouse gas (GHG) emissions. An energy simulation model was developed to study the energy usage patterns not only at a building level, but also of the internal thermal zones, and system operations. The model was validated using site measurements of energy usage and a detailed audit of the internal load conditions, system operation, and space programs to minimize the discrepancy between the documented status and actual operational conditions. Based on the results of the calibrated model and end-used energy consumption, the study proposed potential energy conservation measures (ECMs) for the building envelop... [more]
Streamer Propagation and Breakdown in a Very Small Point-Insulating Plate Gap in Mineral Oil and Ester Liquids at Positive Lightning Impulse Voltage
Pawel Rozga
November 28, 2018 (v1)
Subject: Other
Keywords: breakdown, lightning impulse, mineral oil, natural ester, streamer propagation, synthetic ester
This article presents the results of comparative studies on streamer propagation and breakdown in a point-insulating plate electrode system in mineral oil and two ester liquids. The studies were performed for a 10-mm gap and a positive standard lightning impulse. The work was focused on the comparison of light waveforms registered using the photomultiplier technique. The results indicated that both esters demonstrate a lower resistance against the appearance of fast energetic streamers than mineral oil. The reason for such a conclusion is that the number of lightning impulses supplied to the electrode system for which the above-mentioned fast streamers appeared at a given voltage level was always higher in the case of ester liquids than mineral oil. In terms of breakdown, the esters tested were assessed as more susceptible to the appearance of breakdown in the investigated electrode system. The number of breakdowns recorded in the case of esters was always greater than the correspondin... [more]
Interdependencies between Biofuel, Fuel and Food Prices: The Case of the Brazilian Ethanol Market
Deborah Bentivoglio, Adele Finco, Mirian Rumenos Piedade Bacchi
November 28, 2018 (v1)
Subject: Energy Policy
Keywords: Ethanol, Gasoline, granger causality, prices, sugar, Vector Error Correction Model (VECM)
Brazil is currently the world’s largest sugar producer and exporter, as well as the world’s largest producer and consumer of sugarcane ethanol as a transportation fuel. The growth of this market originates from a combination of government policies and technological change, in both the sugarcane ethanol processing sector and the manufacture of flex-fuel vehicles. In recent years however, ethanol production has been questioned due to its possible impact on food prices. The present paper aims to explore the impact of Brazilian ethanol prices on sugar and gasoline prices. The relationships between a times series of these prices are investigated using a Vector Error Correction Model (VECM), supported by Granger Causality tests. In addition, Impulse Response Functions (IRFs) and Forecast Error Variance Decompositions (FEVD) are computed in order to investigate the dynamic interrelationships within these series. Our results suggest that ethanol prices are affected by both food and fuel prices... [more]
Scheduling of Electricity Storage for Peak Shaving with Minimal Device Wear
Thijs van der Klauw, Johann L. Hurink, Gerard J. M. Smit
November 28, 2018 (v1)
Keywords: device aging, electrical energy storage, mixed integer linear program (MILP), peak shaving, polynomial time optimal algorithm
In this work, we investigate scheduling problems for electrical energy storage systems and formulate an algorithm that finds an optimal solution with minimal charging cycles in the case of a single device. For the considered problems, the storage system is used to reduce the peaks of the production and consumption within (part of) the electricity distribution grid, while minimizing device wear. The presented mathematical model of the storage systems captures the general characteristic of electrical energy storage devices while omitting the details of the specific technology used to store the energy. In this way, the model can be applied to a wide range of settings. Within the model, the wear of the storage devices is modeled by either: (1) the total energy throughput; or (2) the number of switches between charging and discharging, the so-called charging cycles. For the first case, where the energy throughput determines the device wear, a linear programming formulation is given. For the... [more]
Energy Converter with Inside Two, Three, and Five Connected H₂/Air Swirling Combustor Chambers: Solar and Combustion Mode Investigations
Angelo Minotti
November 28, 2018 (v1)
Keywords: Computational Fluid Dynamics, detailed chemistry, fluid-structure interaction, hydrogen-air combustion, meso-combustor, whirl flow
This work reports the performance of an energy converter characterized by an emitting parallelepiped element with inside two, three, or five swirling connected combustion chambers. In particular, the idea is to adopt the heat released by H₂/air combustion, occurring in the connected swirling chambers, to heat up the emitting surfaces of the thermally-conductive emitting parallelepiped brick. The final goal consists in obtaining the highest emitting surface temperature and the highest power delivered to the ambient environment, with the simultaneous fulfillment of four design constraints: dimension of the emitting surface fixed to 30 × 30 mm², solar mode thermal efficiency greater than 20%, emitting surface peak temperature T > 1000 K, and its relative ∆T < 100 K in the combustion mode operation. The connected swirling meso-combustion chambers, inside the converter, differ only in their diameters. Combustion simulations are carried out adopting 500 W of injected chemical power, stoichio... [more]
Market Equilibrium and Impact of Market Mechanism Parameters on the Electricity Price in Yunnan’s Electricity Market
Chuntian Cheng, Fu Chen, Gang Li, Qiyu Tu
November 28, 2018 (v1)
Keywords: Cournot model, electricity price, market equilibrium, market mechanism parameter
In this paper, a two-dimensional Cournot model is proposed to study generation companies’ (GENCO’s) strategic quantity-setting behaviors in the newly established Yunnan’s electricity market. A hybrid pricing mechanism is introduced to Yunnan’s electricity market with the aim to stimulate electricity demand. Market equilibrium is obtained by iteratively solving each GENCO’s profit maximization problem and finding their optimal bidding outputs. As the market mechanism is a key element of the electricity market, impacts of different market mechanism parameters on electricity price and power generation in market equilibrium state should be fully assessed. Therefore, based on the proposed model, we precisely explore the impacts on market equilibrium of varying parameters such as the number of GENCOs, the quantity of ex-ante obligatory-use electricity contracts (EOECs) and the elasticity of demand. Numerical analysis results of Yunnan’s electricity market show that these parameters have nota... [more]
Optimal Scheduling of Energy Storage System for Self-Sustainable Base Station Operation Considering Battery Wear-Out Cost
Yohwan Choi, Hongseok Kim
November 28, 2018 (v1)
Keywords: battery wear-out cost, demand response (DR), dynamic programming (DP), energy storage system (ESS), optimal scheduling, peak shift, photovoltaic (PV), sustainable base station (BS)
A self-sustainable base station (BS) where renewable resources and energy storage system (ESS) are interoperably utilized as power sources is a promising approach to save energy and operational cost in communication networks. However, high battery price and low utilization of ESS intended for uninterruptible power supply (UPS) necessitates active utilization of ESS. This paper proposes a multi-functional framework of ESS using dynamic programming (DP) for realizing a sustainable BS. We develop an optimal charging and discharging scheduling algorithm considering a detailed battery wear-out model to minimize operational cost as well as to prolong battery lifetime. Our approach significantly reduces total cost compared to the conventional method that does not consider battery wear-out. Extensive experiments for several scenarios exhibit that total cost is reduced by up to 70.6% while battery wear-out is also reduced by 53.6%. The virtue of the proposed framework is its wide applicability... [more]
A Novel Protection Method for Single Line-to-Ground Faults in Ungrounded Low-Inertia Microgrids
Liuming Jing, Dae-Hee Son, Sang-Hee Kang, Soon-Ryul Nam
November 28, 2018 (v1)
Subject: Other
Keywords: distributed energy resources, microgrid protection, single line-to-ground (SLG) fault, ungrounded low-inertia microgrid
This paper proposes a novel protection method for single line-to-ground (SLG) faults in ungrounded low-inertia microgrids. The proposed method includes microgrid interface protection and unit protection. The microgrid interface protection is based on the difference between the zero-sequence voltage angle and the zero-sequence current angle at the microgrid interconnection transformer for fast selection of the faulty feeder. The microgrid unit protection is based on a comparison of the three zero-sequence current phase directions at each junction point of load or distributed energy resources. Methods are also included to locate the minimum fault section. The fault section location technology operates according to the coordination of microgrid unit protection. The proposed method responds to SLG faults that may occur in both the grid and the microgrid. Simulations of an ungrounded low-inertia microgrid with a relay model were carried out using Power System Computer Aided Design (PSCAD)/E... [more]
Combining Unsteady Blade Pressure Measurements and a Free-Wake Vortex Model to Investigate the Cycle-to-Cycle Variations in Wind Turbine Aerodynamic Blade Loads in Yaw
Moutaz Elgammi, Tonio Sant
November 28, 2018 (v1)
Subject: Other
Keywords: dynamic stall, free-wake vortex model, NREL Phase VI rotor, unsteady angle of attack, wind turbine aerodynamics, yawed rotor
Prediction of the unsteady aerodynamic flow phenomenon on wind turbines is challenging and still subject to considerable uncertainty. Under yawed rotor conditions, the wind turbine blades are subjected to unsteady flow conditions as a result of the blade advancing and retreating effect and the development of a skewed vortical wake created downstream of the rotor plane. Blade surface pressure measurements conducted on the NREL Phase VI rotor in yawed conditions have shown that dynamic stall causes the wind turbine blades to experience significant cycle-to-cycle variations in aerodynamic loading. These effects were observed even though the rotor was subjected to a fixed speed and a uniform and steady wind flow. This phenomenon is not normally predicted by existing dynamic stall models integrated in wind turbine design codes. This paper couples blade pressure measurements from the NREL Phase VI rotor to a free-wake vortex model to derive the angle of attack time series at the different bl... [more]
Analysis and Solution for Operations of Overcurrent Relay in Wind Power System
Yeonho Ok, Jaewon Lee, Jaeho Choi
November 28, 2018 (v1)
Keywords: coordination of protection relay, malfunction of protection relay, overcurrent relay, wind power system, wind speed
Wind power systems are being integrated increasingly into the power grid because of their large capacity and easy access to the transmission grid. The reliability of wind power plants is very important and the elimination of protective relay’s malfunctions is essential to the mitigation of power quality problems due to the frequent starts and stops of high capacity wind generators. In this study, the problem of frequent false operations of the protective relays are analyzed using real data as line voltages, line currents, and wind speed. A new re-coordination of the overcurrent relay (OCR) based on the wind speed is proposed to avoid frequent operations of relays and tested for a grid-connected wind farm. This study verifies that the false actions by the OCRs that are not accompanied by actual electrical faults in the power grid or wind power system can be solved by the appropriate re-coordination of the OCR.
New Scheme for Seamless Operation for Stand-Alone Power Systems
Hyun-Jun Kim, Yoon-Seok Lee, Byung-Moon Han, Young-Doo Yoon
November 28, 2018 (v1)
Keywords: battery energy storage system (BESS), current control, engine generator (EG), phase-locked loop (PLL), photo voltaic (PV) panels, seamless operation, voltage control
On remote islands photovoltaic (PV) panels with battery energy storage systems (BESSs) supply electric power to customers in parallel operation with engine generators (EGs) to reduce fuel consumption and environmental burden. A BESS operates in voltage control mode when it supplies power to loads alone, while it operates in current control mode when it supplies power to loads in parallel with the EG. This paper proposes a smooth mode change of the BESS from current control to voltage control by using initial value at the output of integral part in the voltage controller, and a smooth mode change from voltage control to current control by tracking the EG output voltage to the BESS output voltage using a phase-locked loop (PLL). The feasibility of the proposed scheme was verified through computer simulations and experiments with a scaled prototype.
Application of a Heat Flux Sensor in Wind Power Electronics
Elvira Baygildina, Liudmila Smirnova, Kirill Murashko, Raimo Juntunen, Andrey Mityakov, Mikko Kuisma, Olli Pyrhönen, Pasi Peltoniemi, Katja Hynynen, Vladimir Mityakov, Sergey Sapozhnikov
November 28, 2018 (v1)
Keywords: heat flux sensor, measurement, power electronics, reliability, wind turbine
This paper proposes and investigates the application of the gradient heat flux sensor (GHFS) for measuring the local heat flux in power electronics. Thanks to its thinness, the sensor can be placed between the semiconductor module and the heat sink. The GHFS has high sensitivity and yields direct measurements without an interruption to the normal power device operation, which makes it attractive for power electronics applications. The development of systems for monitoring thermal loading and methods for online detection of degradation and failure of power electronic devices is a topical and crucial task. However, online condition monitoring (CM) methods, which include heat flux sensors, have received little research attention so far. In the current research, an insulated-gate bipolar transistor (IGBT) module-based test setup with the GHFS implemented on the base plate of one of the IGBTs is introduced. The heat flux experiments and the IGBT power losses obtained by simulations show sim... [more]
A Stackelberg Game Theoretic Analysis of Incentive Effects under Perceived Risk for China’s Straw-Based Power Plant Supply Chain
Lingling Wang, Tsunemi Watanabe
November 28, 2018 (v1)
Keywords: biomass power plant, perceived risk, stackelberg game theory, Supply Chain
The rapid expansion of the biomass power generation industry has resulted in the conversion of substantial agricultural waste (crop straw) into energy feedstock, thereby increasing the income of farmers and promoting the development of rural areas. However, the promising industry faces financial deficits because of difficulties in collecting straw from farmers. To determine strategies for overcoming the biomass supply problem, we apply Stackelberg game theory in modeling the Chinese biomass supply chain and design incentive scenarios under stakeholder risk perception. We illustrate the proposed methodology through an empirical case study on China and demonstrate the effects of incentives on farmers and middlemen. Results show that with incentives, straw quantity and stakeholder profit are expected to increase. Incentives exert a particularly remarkable effect on farmers, with such inducements producing the highest social welfare. Moreover, perceived risk dramatically affects stakeholde... [more]
Study of the Injection Control Strategies of a Compression Ignition Free Piston Engine Linear Generator in a One-Stroke Starting Process
Huihua Feng, Yuyao Guo, Yu Song, Chendong Guo, Zhengxing Zuo
November 28, 2018 (v1)
Keywords: free piston engine, injection control strategies, linear motor
For a compression ignition (CI) free piston engine linear generator (FPLG), injection timing is one of the most important parameters that affect its performance, especially for the one-stroke starting operation mode. In this paper, two injection control strategies are proposed using piston position and velocity signals. It was found experimentally that the injection timing’s influence on the compression ratio, the peak in-cylinder gas pressure and the indicated work (IW) is different from that of traditional reciprocating CI engines. The maximum IW of the ignition starting cylinder, say left cylinder (LC) and the right cylinder (RC) are 132.7 J and 138.1 J, respectively. The thermal-dynamic model for simulating the working processes of the FPLG are built and verified by experimental results. The numerical simulation results show that the running instability and imbalance between LC and RC are the obvious characters when adopting the injection strategy of the velocity feedback. These co... [more]
Managing Climate Policy Information Facilitating Knowledge Transfer to Policy Makers
Charikleia Karakosta, Alexandros Flamos
November 28, 2018 (v1)
Keywords: architectural knowledge retrieval, climate change, international and European climate policy, knowledge transfer, ontology, resource description framework
In the challenging context of intense negotiations and radical developments in the field of climate policy, informing stakeholders about opportunities and pathways and about scientific insights and warnings is important to help create positive dynamics. Policy makers need digestible information to design good policies, and understand their options and the possible impacts of these options. They need access to well-structured knowledge, as well as appropriate techniques to manage information and data. However, available information is often difficult to access, not in the right format and of limited use to stakeholders. The range of knowledge needs identified has to be effectively addressed by providing interested parties with suitable, to-the-point information, covering the identified gaps. This is the main aim of this article that proposes the design and development of a climate policy database, which contains all the resources that can cover the identified knowledge gaps. The resourc... [more]
Sliding Mode Variable Structure Control of a Bearingless Induction Motor Based on a Novel Reaching Law
Zebin Yang, Ling Wan, Xiaodong Sun, Fangli Li, Lin Chen
November 28, 2018 (v1)
Keywords: adaptive variable-rated reaching law, adaptive variable-rated sliding mode controller (ASMC), Bearingless Induction Motor (BIM), chattering, robustness
In order to improve the performance of the Bearingless Induction Motor (BIM) under large disturbances (such as parameter variations and load disturbances), an adaptive variable-rated sliding mode controller (ASMC) is designed to obtain better performance of the speed regulation system. Firstly, the L 1 norm of state variables is applied to the conventional exponential reaching law and an adaptive variable-rated exponential reaching law is proposed to reduce system chattering and improve bad convergence performance of the sliding mode variable structure. Secondly, an integral sliding-mode hyper plane is produced according to the speed error in speed regulation system of BIM. Current signal is extracted by the combination of the sliding-mode hyper plane, the electromagnetic torque and the equation of motion. Finally, the feedback speed can adjust operating state adaptively according to speed error and make system chattering-free moving. The simulation and experiment results sho... [more]
Metamaterial Absorber Comprised of Butt-Facing U-Shaped Nanoengineered Gold Metasurface
Masih Ghasemi, Pankaj Kumar Choudhury
November 28, 2018 (v1)
Subject: Materials
Keywords: complex optical mediums, metamaterial absorbers, nanostructured mediums, plasmonic resonators
The paper reports spectral features of the absorbed electromagnetic (EM) waves in a new kind of multilayered plasmonic metamaterial thin film comprised of homogenous layers of copper and silicon as the bottom and the middle sections (of the thin film), respectively, and the inhomogeneous U-shaped nanoengineered gold layer as the top. Each unit cell of the top metasurface consists of one upside and one downside U-shaped (butt-facing) structure. The absorbance of EM waves is simulated in the wavelength range of 200−1500 nm under different incidence angles considering the wave as being transmitted from the metasurface side. The low-order TE and TM modes are taken into account for the estimation of wave absorbance under varying metasurfaces as well as silicon layer thicknesses. It has been found that the nanoengineered gold layer causes higher confinement of power in silicon, which can be further controlled by suitably adjusting its thickness. Further, the increased thickness of metasurfac... [more]
NMOS-Based Integrated Modular Bypass for Use in Solar Systems (NIMBUS): Intelligent Bypass for Reducing Partial Shading Power Loss in Solar Panel Applications
Pieter Bauwens, Jan Doutreloigne
November 28, 2018 (v1)
Keywords: diode bypass, partial shading, photovoltaic power, power loss, smart bypass
NMOS-based Integrated Modular Bypass for Use in Solar systems (NIMBUS) is designed as a replacement for the traditional bypass diode, used in common solar panels. Because of the series connection between the individual solar cells, the power output of a photovoltaic (PV) panel will drop disproportionally under partial shading. Currently, this is solved by dividing the PV panel into substrings, each with a diode bypass placed in parallel. This allows an alternative current path. However, the diodes still have a significant voltage drop (about 350 mV), and due to the fairly large currents in a panel, the diodes are dissipating power that we would rather see at the output of the panel. The NIMBUS chip, being a low-voltage-drop switch, aims to replace these diodes and, thus, reduce that power loss. NIMBUS is a smart bypass: a completely stand-alone system that detects the failing of one or more cells and activates when necessary. It is designed for a 100-mV voltage drop under a 5-A load cu... [more]
Thermo-Economic and Heat Transfer Optimization of Working-Fluid Mixtures in a Low-Temperature Organic Rankine Cycle System
Oyeniyi A. Oyewunmi, Christos N. Markides
November 28, 2018 (v1)
Keywords: heat transfer coefficients, low-grade heat, low-pressure expanders, multi-objective optimization, ORC capital costs, organic Rankine cycles (ORC), thermo-economic analysis, working-fluid mixtures
In the present paper, we consider the employment of working-fluid mixtures in organic Rankine cycle (ORC) systems with respect to thermodynamic and heat-transfer performance, component sizing and capital costs. The selected working-fluid mixtures promise reduced exergy losses due to their non-isothermal phase-change behaviour, and thus improved cycle efficiencies and power outputs over their respective pure-fluid components. A multi-objective cost-power optimization of a specific low-temperature ORC system (operating with geothermal water at 98 °C) reveals that the use of working-fluid-mixtures does indeed show a thermodynamic improvement over the pure-fluids. At the same time, heat transfer and cost analyses, however, suggest that it also requires larger evaporators, condensers and expanders; thus, the resulting ORC systems are also associated with higher costs. In particular, 50% n-pentane + 50% n-hexane and 60% R-245fa + 40% R-227ea mixtures lead to the thermodynamically optimal cyc... [more]
A Parameter Identification Method for Dynamics of Lithium Iron Phosphate Batteries Based on Step-Change Current Curves and Constant Current Curves
Zhichao He, Geng Yang, Languang Lu
November 28, 2018 (v1)
Keywords: constant current curves, decouple, parameter identification, step-change current curves
Parameterization of battery dynamics based on terminal operating data is a main concern in engineering applications of batteries. The key technology is designing an adequate test procedure and a data processing procedure to excite different inner dynamics and then estimate the parameters of a corresponding equivalent circuit model (ECM). This paper proposes a parameter identification method that utilizes the terminal voltage curves (TVC) under step-change current conditions and constant current conditions. With this method, I-V characteristics of battery’s Ohmic resistance, mass diffusion process, thermal process and SOC varying process are decoupled and parametric functions of an ECM are obtained. Experimental results show that the method is easy to be implemented and modeling accuracy is sufficient for applications.
Empirical Operational Energy Analysis of Downtown High-Rise vs. Suburban Low-Rise Lifestyles: A Chicago Case Study
Peng Du, Antony Wood, Brent Stephens
November 28, 2018 (v1)
Subject: Energy Policy
Keywords: Chicago, high-rise, infrastructure, life style, low-rise, operational energy, transportation
It is widely accepted that the concentration of people living in high-density city centers offers greater operational energy efficiency and lower greenhouse gas emissions than lower-density expanded suburbs. The prevailing assumption is that lower-density suburbs are dominated by larger low-rise buildings that have higher building energy use requirements and greater per-person automobile travel requirements than high-density city centers dominated by medium- and high-rise buildings located in close proximity to a variety of public transit systems. However, very few studies to date have utilized empirical data at an individual household scale to evaluate differences in the operational energy (OE) footprints for both building and transportation energy end-uses between high-rise urban and low-rise suburban households. Therefore, this work collects empirical data on building and transportation OE consumption by individuals and households living in two economically similar groups: existing... [more]
The Influence of Environmental Constraints on the Water Value
Ignacio Guisández, Juan I. Pérez-Díaz, José R. Wilhelmi
November 28, 2018 (v1)
Subject: Energy Policy
Keywords: maximum ramping rates, minimum environmental flows, mixed integer linear programming, stochastic dynamic programming, water value
The establishment of more severe hydrological environmental constraints, usually as seasonal minimum flows (ϕ) and maximum ramping rates (ρ), on hydropower operation is a growing trend. This paper presents a study on the influence of ϕ and ρ on the water values (WV) of a real hydropower plant that participates in the Spanish day-ahead electricity market. For this purpose, a master-slave algorithm, based on stochastic dynamic programming (SDP) and deterministic mixed integer linear programming (DMILP), is used on a real hydropower plant. The master module, based on SDP, has a yearly planning period with weekly time steps and considers three state variables: stored water volume in the reservoir at the beginning of each week; weekly water inflow; and average weekly energy price. The slave module, based on DMILP, has a weekly planning period with hourly time steps and considers many features of the hydropower plant operation, such as: start-up costs, evaporation, wear and tear costs, etc.... [more]
Wind Turbine Driving a PM Synchronous Generator Using Novel Recurrent Chebyshev Neural Network Control with the Ideal Learning Rate
Chih-Hong Lin
November 28, 2018 (v1)
Keywords: discrete-type Lyapunov function, permanent magnet synchronous generator, recurrent Chebyshev neural network, wind turbine
A permanent magnet (PM) synchronous generator system driven by wind turbine (WT), connected with smart grid via AC-DC converter and DC-AC converter, are controlled by the novel recurrent Chebyshev neural network (NN) and amended particle swarm optimization (PSO) to regulate output power and output voltage in two power converters in this study. Because a PM synchronous generator system driven by WT is an unknown non-linear and time-varying dynamic system, the on-line training novel recurrent Chebyshev NN control system is developed to regulate DC voltage of the AC-DC converter and AC voltage of the DC-AC converter connected with smart grid. Furthermore, the variable learning rate of the novel recurrent Chebyshev NN is regulated according to discrete-type Lyapunov function for improving the control performance and enhancing convergent speed. Finally, some experimental results are shown to verify the effectiveness of the proposed control method for a WT driving a PM synchronous generator... [more]
Optimization of Internal Cooling Fins for Metal Hydride Reactors
Vamsi Krishna Kukkapalli, Sunwoo Kim
November 28, 2018 (v1)
Keywords: exothermic hydriding reaction, finned surface, hydrogen storage, metal hydride reactor
Metal hydride alloys are considered as a promising alternative to conventional hydrogen storage cylinders and mechanical hydrogen compressors. Compared to storing in a classic gas tank, metal hydride alloys can store hydrogen at nearly room pressure and use less volume to store the same amount of hydrogen. However, this hydrogen storage method necessitates an effective way to reject the heat released from the exothermic hydriding reaction. In this paper, a finned conductive insert is adopted to improve the heat transfer in the cylindrical reactor. The fins collect the heat that is volumetrically generated in LaNi₅ metal hydride alloys and deliver it to the channel located in the center, through which a refrigerant flows. A multiple-physics modeling is performed to analyze the transient heat and mass transfer during the hydrogen absorption process. Fin design is made to identify the optimum shape of the finned insert for the best heat rejection. For the shape optimization, use of a pred... [more]
Optimal Operation of Network-Connected Combined Heat and Powers for Customer Profit Maximization
Da Xie, Yupu Lu, Junbo Sun, Chenghong Gu, Jilai Yu
November 28, 2018 (v1)
Keywords: bidirectional energy flow, combined heat and power (CHP), discrete optimization, profit model, real-time price
Network-connected combined heat and powers (CHPs), owned by a community, can export surplus heat and electricity to corresponding heat and electric networks after community loads are satisfied. This paper proposes a new optimization model for network-connected CHP operation. Both CHPs’ overall efficiency and heat to electricity ratio (HTER) are assumed to vary with loading levels. Based on different energy flow scenarios where heat and electricity are exported to the network from the community or imported, four profit models are established accordingly. They reflect the different relationships between CHP energy supply and community load demand across time. A discrete optimization model is then developed to maximize the profit for the community. The models are derived from the intervals determined by the daily operation modes of CHP and real-time buying and selling prices of heat, electricity and natural gas. By demonstrating the proposed models on a 1 MW network-connected CHP, results... [more]
Showing records 26 to 50 of 370. [First] Page: 1 2 3 4 5 6 Last