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Showing records 76 to 100 of 111. [First] Page: 1 2 3 4 5 Last
Dopamine Incorporated Forward Osmosis Membranes with High Structural Stability and Chlorine Resistance
Yi Wang, Zhendong Fang, Chaoxin Xie, Shuaifei Zhao, Derrick Ng, Zongli Xie
April 8, 2019 (v1)
Subject: Materials
Keywords: chlorine resistance, dopamine, forward osmosis, interfacial polymerization, structural stability, thin-film composite
The degradation and detachment of the polyamide (PA) layer for the conventional thin-film composite (TFC) membranes due to chemical disinfectants cleaning with chlorine and material difference of PA layer and substrate are two major bottlenecks of forward osmosis (FO) technology. In this study, a new type of FO membranes was first prepared by controlling dopamine (DA) as the sole amine in the aqueous phase and the reaction with trimesoyl chloride (TMC) as the acyl chloride during interfacial polymerization (IP) process. The influence of membrane synthesis parameters such as monomer concentration, pH of the aqueous phase, IP reaction time and IP temperature were systematically investigated. The optimized membrane showed both improved structure stability and chlorine resistance, more so than the conventional TFC membrane. In general, novel DA/TMC TFC membranes could be an effective strategy to synthesize high-performance FO membranes with excellent structural stability and chlorine resis... [more]
Analysis of Overlying Strata Movement and Disaster-Causing Effects of Coal Mining Face under the Action of Hard Thick Magmatic Rock
Quanlin Wu, Quansen Wu, Yanchao Xue, Peng Kong, Bin Gong
April 8, 2019 (v1)
Subject: Other
Keywords: bed separation, disaster-causing mechanism, fracture, hard and thick magmatic rocks, orthogonal ratio test, similar simulation
When the hard and thick key strata are located above the working face, the bed separation structure is easy to be formed after mining because of the high strength and integrity of the hard and thick key strata and the initial breaking step is large. After the hard, thick strata are broken, the overburden will be largely collapsed and unstable in a large area and the dynamic disaster is easily induced. In this study, considering the fundamental deformation and failure effect of coal seam, the development law of the bed separation and the fractures under hard and thick magmatic rocks and the mechanism of breaking induced disaster of hard and thick magmatic rocks are studied by similar simulation tests. The results of the study are as follows: (1) The similar material ratio of coal seam is obtained by low-strength orthogonal ratio test of similar materials of coal seam, that is, cement:sand:water:activated carbon:coal = 6:6:7:1.1:79.9. (2) The magmatic rocks play a role in shielding the d... [more]
Quantitative Estimates of Nonlinear Flow Characteristics of Deformable Rough-Walled Rock Fractures with Various Lithologies
Qian Yin, Lixin He, Hongwen Jing, Dong Zhu
April 8, 2019 (v1)
Keywords: confining pressure, critical Reynolds number, lithology, nonlinear flow, rough-walled fractures, transmissivity
The existence of surface roughness, various contact conditions and the occurrence of flow nonlinearity make the flow process in natural rock fractures more complicated. To evaluate the fluid flow regimes in deformable rough-walled rock fractures, a great many hydromechanical tests were conducted on nine real fractures artificially produced from a wide range of lithological diversity. For fractures with a certain JRC (fracture roughness coefficient) value, the confining pressure varied from 5 to 20 MPa, and the hydraulic pressure was increased from 0.4 to 6.0 MPa. The experimental results display that (i) regression analyses of the raw experimental data indicate that the Forchheimer’s law provides a perfect description for flow process through the fractures. The coefficients of viscous and inertial pressure drops undergo a growth of 2⁻3 orders of magnitude with an increase in the confining pressure; (ii) the hydraulic aperture decreases by approximately 87.41⁻92.81% as the confining pre... [more]
On-Line Optimal Input Design Increases the Efficiency and Accuracy of the Modelling of an Inducible Synthetic Promoter
Lucia Bandiera, Zhaozheng Hou, Varun B. Kothamachu, Eva Balsa-Canto, Peter S. Swain, Filippo Menolascina
April 8, 2019 (v1)
Keywords: model calibration, model-based optimal experimental design, optimal inputs, synthetic biology, system identification
Synthetic biology seeks to design biological parts and circuits that implement new functions in cells. Major accomplishments have been reported in this field, yet predicting a priori the in vivo behaviour of synthetic gene circuits is major a challenge. Mathematical models offer a means to address this bottleneck. However, in biology, modelling is perceived as an expensive, time-consuming task. Indeed, the quality of predictions depends on the accuracy of parameters, which are traditionally inferred from poorly informative data. How much can parameter accuracy be improved by using model-based optimal experimental design (MBOED)? To tackle this question, we considered an inducible promoter in the yeast S. cerevisiae. Using in vivo data, we re-fit a dynamic model for this component and then compared the performance of standard (e.g., step inputs) and optimally designed experiments for parameter inference. We found that MBOED improves the quality of model calibration by ∼60%. Results furt... [more]
Diffusion in Nanoporous Materials: Novel Insights by Combining MAS and PFG NMR
Jörg Kärger, Dieter Freude, Jürgen Haase
April 8, 2019 (v1)
Keywords: Adsorption, diffusion, hierarchical host materials, MAS, NMR, PFG
Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) allows recording of molecular diffusion paths (notably, the probability distribution of molecular displacements over typically micrometers, covered during an observation time of typically milliseconds) and has thus proven to serve as a most versatile means for the in-depth study of mass transfer in complex materials. This is particularly true with nanoporous host materials, where PFG NMR enabled the first direct measurement of intracrystalline diffusivities of guest molecules. Spatial resolution, i.e., the minimum diffusion path length experimentally observable, is limited by the time interval over which the pulsed field gradients may be applied. In “conventional„ PFG NMR measurements, this time interval is determined by a characteristic quantity of the host-guest system under study, the so-called transverse nuclear magnetic relaxation time. This leads, notably when considering systems with low molecular mobilities, to severe... [more]
A Numerical Study of Stress Distribution and Fracture Development above a Protective Coal Seam in Longwall Mining
Chunlei Zhang, Lei Yu, Ruimin Feng, Yong Zhang, Guojun Zhang
April 8, 2019 (v1)
Keywords: gas drainage, gob behaviors, longwall mining, permeability, stress relief
Coal and gas outbursts are serious safety concerns in the Chinese coal industry. Mining of the upper or lower protective coal seams has been widely used to minimize this problem. This paper presents new findings from longwall mining-induced fractures, stress distribution changes in roof strata, strata movement and gas flow dynamics after the lower protective coal seam is extracted in a deep underground coal mine in Jincheng, China. Two Flac3D models with varying gob loading characteristics as a function of face advance were analyzed to assess the effect of gob behavior on stress relief in the protected coal seam. The gob behavior in the models is incorporated by applying variable force to the floor and roof behind the longwall face to simulate gob loading characteristics in the field. The influence of mining height on the stress-relief in protected coal seam is also incorporated. The stress relief coefficient and relief angle were introduced as two essential parameters to evaluate the... [more]
Simulation and Test Bed of a Low-Power Digital Excitation System for Industry 4.0
Jun-Ho Huh, Hoon-Gi Lee
April 8, 2019 (v1)
Keywords: computer architecture, digital excitation system, Industry 4.0, low power, operating system, Simulation, smart grid, Test Bed
Since modeling and simulation are the two most effective tools that can be used in the design or analysis process, they play a vital role in developing such system. In many cases, they are the only possible means of making a safe engineering decision for a new concept of process for a large-scale system. Elsewhere, they are used as a critical element in the analysis of energy systems or to suggest a method of developing a novel and effective energy system model. Thus, in this study, simulations and test bed experiment were carried out to assess a low-power digital excitation system in order to validate its effectiveness. The excitation systems currently used by most of the power stations in the Republic of Korea were installed during the 1970s or 1980s. Unfortunately, it is difficult to seek technical assistance for them as they depend on foreign technologies, requiring a large sum to be paid when requesting one or more engineers to be dispatched. As such, technical updates have always... [more]
Challenges in Nanofluidics—Beyond Navier⁻Stokes at the Molecular Scale
Peter J. Daivis, Billy D. Todd
April 8, 2019 (v1)
Keywords: hydrodynamics, molecular dynamics, nanofluidics, non-local constitutive equations, slip, spin-coupling
The fluid dynamics of macroscopic and microscopic systems is well developed and has been extensively validated. Its extraordinary success makes it tempting to apply Navier⁻Stokes fluid dynamics without modification to systems of ever decreasing dimensions as studies of nanofluidics become more prevalent. However, this can result in serious error. In this paper, we discuss several ways in which nanoconfined fluid flow differs from macroscopic flow. We give particular attention to several topics that have recently received attention in the literature: slip, spin angular momentum coupling, nonlocal stress response and density inhomogeneity. In principle, all of these effects can now be accurately modelled using validated theories. Although the basic principles are now fairly well understood, much work remains to be done in their application.
Supported Ionic Liquid Membranes for Separation of Lignin Aqueous Solutions
Ricardo Abejón, Javier Rabadán, Silvia Lanza, Azucena Abejón, Aurora Garea, Angel Irabien
April 8, 2019 (v1)
Subject: Materials
Keywords: glucose, lignin, separation, supported ionic liquid membranes, xylose
Lignin valorization is a key aspect to design sustainable management systems for lignocellulosic biomass. The successful implementation of bio-refineries requires high value added applications for the chemicals derived from lignin. Without effective separation processes, the achievement of this purpose is difficult. Supported ionic liquid membranes can play a relevant role in the separation and purification of lignocellulosic components. This work investigated different supported ionic liquid membranes for selective transport of two different types of technical lignins (Kraft lignin and lignosulphonate) and monosaccharides (xylose and glucose) in aqueous solution. Although five different membrane supports and nine ionic liquids were tested, only the system composed by [BMIM][DBP] as an ionic liquid and polytetrafluoroethylene (PTFE) as a membrane support allowed the selective transport of the tested solutes. The results obtained with this selective membrane demonstrated that lignins we... [more]
Simulation and Analysis of Oleic Acid Pretreatment for Microwave-Assisted Biodiesel Production
Weiquan Ma, Tao Hong, Tian Xie, Fengxia Wang, Bin Luo, Jie Zhou, Yang Yang, Huacheng Zhu, Kama Huang
April 8, 2019 (v1)
Keywords: biodiesel, coupling, microwave heating, multiphysics calculation, oleic acid
Oleic acid needs to be heated when it is utilized for biodiesel production, but, as a low-loss solution, oleic acid is difficult to heat by microwave. An efficient heating method for oleic acid is designed. A high loss material porous media is placed in a quartz tube, and a microwave directly heats the porous medium of the high loss material. The oleic acid flows through the pores of porous media so that the oleic acid exchanges heat during this process and rapid heating of oleic acid is achieved. A coupling model, based on the finite element method, is used to analyze the microwave heating process. The multiphysics model is based on a single mode cavity operating at 2450 MHz. An elaborate experimental system is developed to validate the multiphysics model through temperature measurements carried out for different flow velocities of oleic acid and different microwave power levels. The computational results are in good agreement with the experimental data. Based on the validated model,... [more]
Agent-Based Modeling of Immune Response to Study the Effects of Regulatory T Cells in Type 1 Diabetes
Qian Xu, Mustafa Cagdas Ozturk, Ali Cinar
April 8, 2019 (v1)
Subject: Biosystems
Keywords: agent-based modeling, CD4+ T cells, CD8+ T cells, dendritic cells, regulatory T cells, Type 1 Diabetes, α cells
Regulatory T cells (Tregs) have an important role in self-tolerance. Understanding the functions of Tregs is important for preventing or slowing the progress of Type 1 Diabetes. We use a two-dimensional (2D) agent-based model to simulate immune response in mice and test the effects of Tregs in tissue protection. We compared the immune response with and without Tregs, and also tested the effects of Tregs from different sources or with different functions. The results show that Tregs can inhibit the proliferation of effector T cells by inhibiting antigens presenting via dendritic cells (DCs). Although the number and function of Tregs affect the inhibition, a small number of Tregs compared to CD4⁺ T cells can effectively protect islets in pancreatic tissue. Finally, we added Tregs to the system in the middle phase of the immune response. The simulation results show that Tregs can inhibit the production of effector CD8⁺ T cells and maintain a good environment for β cell regeneration.
Facile Fabrication of Recyclable, Superhydrophobic, and Oleophilic Sorbent from Waste Cigarette Filters for the Sequestration of Oil Pollutants from an Aqueous Environment
Augustine O. Ifelebuegu, Egetadobobari E. Lale, Fredrick U. Mbanaso, Stephen C. Theophilus
April 8, 2019 (v1)
Keywords: Adsorption, cigarette filters, hydrophobicity, oil/water separation, recyclability
The oil industry is plagued with regular incidences of spills into the environment, causing environmental damage to flora and fauna, especially in marine environments where spills easily travel long distances from their sources. This study was carried out to investigate a simple two-step process for the conversion of waste cigarette filters into a superhydrophobic and oleophilic sorbent for application in oil/water separation and spill clean-up. Ultrasonically cleaned filters were surface modified by chemical vapour deposition using methyltrichlorosilane. The results show that the functionalised waste filters achieved superhydrophobic properties with a water contact angle of 154 ± 3.5°, adsorbing 16 to 26 times their weights in various oils, which is a better oil sorption performance than those of commercially available non-woven polypropylene adsorbents. Also, the sorption capacity did not significantly deteriorate after 20 cycles of reuse, with up to 75% sorption capacity retained. T... [more]
Valorization of Shale Gas Condensate to Liquid Hydrocarbons through Catalytic Dehydrogenation and Oligomerization
Taufik Ridha, Yiru Li, Emre Gençer, Jeffrey J. Siirola, Jeffrey T. Miller, Fabio H. Ribeiro, Rakesh Agrawal
April 8, 2019 (v1)
Keywords: process synthesis and design, shale gas condensate, shale gas condensate-to-heavier liquids, Technoeconomic Analysis
The recent shale gas boom has transformed the energy landscape of the United States. Compared to natural gas, shale resources contain a substantial amount of condensate and natural gas liquids (NGLs). Many shale basin regions located in remote areas are lacking the infrastructure to distribute the extracted NGLs to other regions—particularly the Gulf Coast, a major gas processing region. Here we present a shale gas transformation process that converts NGLs in shale resources into liquid hydrocarbons, which are easier to transport from these remote basins than NGL or its constituents. This process involves catalytic dehydrogenation followed by catalytic oligomerization. Thermodynamic process analysis shows that this process has the potential to be more energy efficient than existing NGL-to-liquid fuel (NTL) technologies. In addition, our estimated payback period for this process is within the average lifetime of shale gas wells. The proposed process holds the promise to be an energy eff... [more]
A Systems and Treatment Perspective of Models of Influenza Virus-Induced Host Responses
Ericka Mochan, Emily E. Ackerman, Jason E. Shoemaker
April 8, 2019 (v1)
Subject: Biosystems
Keywords: influenza A virus, interferon pre-stimulation, mathematical modeling, sensitivity analysis, systems biology
Severe influenza infections are often characterized as having unique host responses (e.g., early, severe hypercytokinemia). Neuraminidase inhibitors can be effective in controlling the severe symptoms of influenza but are often not administered until late in the infection. Several studies suggest that immune modulation may offer protection to high risk groups. Here, we review the current state of mathematical models of influenza-induced host responses. Selecting three models with conserved immune response components, we determine if the immune system components which most affect virus replication when perturbed are conserved across the models. We also test each model’s response to a pre-induction of interferon before the virus is administered. We find that each model emphasizes the importance of controlling the infected cell population to control viral replication. Moreover, our work shows that the structure of current models does not allow for significant responses to increased interf... [more]
Photocatalytic Inactivation of Enterobacter cloacae and Escherichia coli Using Titanium Dioxide Supported on Two Substrates
Yelitza Aguas, Margarita Hincapié, Camilo Sánchez, Liliana Botero, Pilar Fernández-Ibañez
April 8, 2019 (v1)
Subject: Biosystems
Keywords: Enterobacter cloacae, Escherichia coli, heterogeneous photocatalysis, solar disinfection, supported TiO2
The antibacterial photocatalytic activity of TiO₂ supported over two types of substrates, borosilicate glass tubes (TiO₂/SiO₂-borosilicate glass tubes (BGT)) and low-density polyethylene pellets (TiO₂-LDPE pellets), which were placed in a compound parabolic collectors (CPC) reactor, was evaluated against Enterobacter cloacae and Escherichia coli under sunlight. Three solar photocatalytic systems were assessed, suspended TiO₂, TiO₂/SiO₂-BGT and TiO₂-LDPE pellets, at three initial bacterial concentrations, 1 × 10⁵; 1 × 10³; 1 × 10¹ CFU/mL of E. coli and total bacteria (E. cloacae and E. coli). The solar photo-inactivation of E. coli was achieved after two hours with 7.2 kJ/L of UV-A, while total bacteria required four hours and 16.5 kJ/L of UV-A. Inactivation order of E. coli was determined, as follows, suspended TiO₂/sunlight (50 mg/L) > TiO₂-LDPE pellets/sunlight (52 mg/L) > TiO₂/SiO₂-BGT/sunlight (59 mg/L), the best E. coli. inactivation rate was obtained with TiO₂-LDPE pellets/sunlig... [more]
Identifiability and Reconstruction of Biochemical Reaction Networks from Population Snapshot Data
Eugenio Cinquemani
April 8, 2019 (v1)
Keywords: flow-cytometry, moment equations, regulatory networks, reporter gene systems, statistical inference
Inference of biochemical network models from experimental data is a crucial problem in systems and synthetic biology that includes parameter calibration but also identification of unknown interactions. Stochastic modelling from single-cell data is known to improve identifiability of reaction network parameters for specific systems. However, general results are lacking, and the advantage over deterministic, population-average approaches has not been explored for network reconstruction. In this work, we study identifiability and propose new reconstruction methods for biochemical interaction networks. Focusing on population-snapshot data and networks with reaction rates affine in the state, for parameter estimation, we derive general methods to test structural identifiability and demonstrate them in connection with practical identifiability for a reporter gene in silico case study. In the same framework, we next develop a two-step approach to the reconstruction of unknown networks of inte... [more]
Improving Flexibility and Energy Efficiency of Post-Combustion CO₂ Capture Plants Using Economic Model Predictive Control
Benjamin Decardi-Nelson, Su Liu, Jinfeng Liu
April 8, 2019 (v1)
Keywords: Energy Efficiency, optimal control, post-combustion CO2 capture, time-varying operation
To reduce CO 2 emissions from power plants, electricity companies have diversified their generation sources. Fossil fuels, however, still remain an integral energy generation source as they are more reliable compared to the renewable energy sources. This diversification as well as changing electricity demand could hinder effective economical operation of an amine-based post-combustion CO 2 capture (PCC) plant attached to the power plant to reduce CO 2 emissions. This is as a result of large fluctuations in the flue gas flow rate and unavailability of steam from the power plant. To tackle this problem, efficient control algorithms are necessary. In this work, tracking and economic model predictive controllers are applied to a PCC plant and their economic performance is compared under different scenarios. The results show that economic model predictive control has a potential to improve the economic performance and energy efficiency of the amine-based PCC process up... [more]
Finding the Signal in the Noise: Determining North America’s best path forward for sustainable energy
Thomas A Adams II
March 31, 2019 (v2)
Keywords: Calcium Looping, Carbon Dioxide Capture, Chemical Looping, Life Cycle Analysis, Meta-Study, Oxyfuels, Postcombustion Capture, Solid Oxide Fuel Cells, Technoeconomic Analysis
One of the largest engineering challenges of our time is finding technical solutions that permit the use of our energy resources in a sustainable way. In order to achieve meaningful and positive change, new energy systems must adhere to the triple bottom line of sustainability. This means that new technical solutions must be economically, socio-politically, and environmentally sustainable, such that they can be rapidly adopted and accepted. The engineering literature is full of a great many technical proposals for new energy systems, but it turns out to be quite hard to objectively look at them all, see through the hype, and decide which are the best and most promising technologies in which to invest our research and development dollars. In this talk, I will present a case study with the results of our recent meta-study covering over 100 candidate electricity generation systems with carbon dioxide capture, in order to determine which are the most promising classes of technologies. I wi... [more]
Optimization of Reducing Sugar Production from Manihot glaziovii Starch Using Response Surface Methodology
Abdi Hanra Sebayang, Masjuki Haji Hassan, Hwai Chyuan Ong, Surya Dharma, Arridina Susan Silitonga, Fitranto Kusumo, Teuku Meurah Indra Mahlia, Aditiya Harjon Bahar
March 26, 2019 (v1)
Subject: Biosystems
Keywords: alternative fuel, bioethanol, Fermentation, hydrolysis, Manihot glaziovii (M. glaziovii), Optimization
Bioethanol is known as a viable alternative fuel to solve both energy and environmental crises. This study used response surface methodology based on the Box-Behnken experimental design to obtain the optimum conditions for and quality of bioethanol production. Enzymatic hydrolysis optimization was performed with selected hydrolysis parameters, including substrate loading, stroke speed, α-amylase concentration and amyloglucosidase concentration. From the experiment, the resulting optimum conditions are 23.88% (w/v) substrate loading, 109.43 U/g α-amylase concentration, 65.44 U/mL amyloglucosidase concentration and 74.87 rpm stroke speed, which yielded 196.23 g/L reducing sugar. The fermentation process was also carried out, with a production value of 0.45 g ethanol/g reducing sugar, which is equivalent to 88.61% of ethanol yield after fermentation by using Saccharomyces cerevisiae (S. cerevisiae). The physical and chemical properties of the produced ethanol are within the specifications... [more]
Prognosis of the Remaining Useful Life of Bearings in a Wind Turbine Gearbox
Wei Teng, Xiaolong Zhang, Yibing Liu, Andrew Kusiak, Zhiyong Ma
March 26, 2019 (v1)
Keywords: bearing in gearbox, prognostic, remaining useful life (RUL), wind turbine
Predicting the remaining useful life (RUL) of critical subassemblies can provide an advanced maintenance strategy for wind turbines installed in remote regions. This paper proposes a novel prognostic approach to predict the RUL of bearings in a wind turbine gearbox. An artificial neural network (NN) is used to train data-driven models and to predict short-term tendencies of feature series. By combining the predicted and training features, a polynomial curve reflecting the long-term degradation process of bearings is fitted. Through solving the intersection between the fitted curve and the pre-defined threshold, the RUL can be deduced. The presented approach is validated by an operating wind turbine with a faulty bearing in the gearbox.
Lobatto-Milstein Numerical Method in Application of Uncertainty Investment of Solar Power Projects
Mahmoud A. Eissa, Boping Tian
March 26, 2019 (v1)
Keywords: Egypt, numerical simulation, real option, Renewable and Sustainable Energy, stochastic differential equation
Recently, there has been a growing interest in the production of electricity from renewable energy sources (RES). The RES investment is characterized by uncertainty, which is long-term, costly and depends on feed-in tariff and support schemes. In this paper, we address the real option valuation (ROV) of a solar power plant investment. The real option framework is investigated. This framework considers the renewable certificate price and, further, the cost of delay between establishing and operating the solar power plant. The optimal time of launching the project and assessing the value of the deferred option are discussed. The new three-stage numerical methods are constructed, the Lobatto3C-Milstein (L3CM) methods. The numerical methods are integrated with the concept of Black⁻Scholes option pricing theory and applied in option valuation for solar energy investment with uncertainty. The numerical results of the L3CM, finite difference and Monte Carlo methods are compared to show the ef... [more]
Analysis on Filling Ratio and Shield Supporting Pressure for Overburden Movement Control in Coal Mining with Compacted Backfilling
Yanli Huang, Junmeng Li, Tianqi Song, Guoqiang Kong, Meng Li
March 26, 2019 (v1)
Keywords: coal mining with compacted backfilling (CMCB), elastic-thin-plate mechanical model, filling ratio, numerical simulation, overburden movement, shield supporting pressure
Since the weight of overburden is sustained by both the backfill body and the unmined solid coal in coal mining with compacted backfilling (CMCB) panels, the stress and deformation characteristics of the surrounding rocks in coal mining are radically changed. The overburden movement control mechanism by coordinating with backfill body and shield in CMCB was studied systematically in this paper. Based on the analysis of deformational and structural characteristics of surrounding rock in CMCB panels, the methods of theoretical analysis, numerical simulation and engineering test are employed. The results show that the fracture of the main roof is mainly controlled by the filling ratio φ and is non-correlated to the shield supporting pressure p. However, p has a significant control effect on the deflection of roof within the shield canopy length, and adversely affects the filling ratio. With the increase of the filling ratio of the gob, the maximum sagging of the immediate and the main roo... [more]
Experimental Study on Specific Heat of Concrete at High Temperatures and Its Influence on Thermal Energy Storage
Jianwen Pan, Renxin Zou, Feng Jin
March 26, 2019 (v1)
Subject: Materials
Keywords: concrete, high temperature, specific heat, thermal energy storage
Using concrete as a thermal energy storage (TES) material is a promising option for large-scale solar-thermal resource development and utilization. Specific heat is one of the most important characteristics for TES performance. In this paper, the half-open dynamic method based on the mixing principle is proposed and applied to measure concrete-specific heat at temperatures up to 600 °C. Measurement of the specific heat of corundum ceramic (99% Al₂O₃) is first performed, and the test results illustrate the accuracy and efficiency of the proposed test method. Furthermore, concrete-specific heat tests are carried out at high temperatures. It found that the specific heat increases as the temperature rises, especially, linearly in the range of 300⁻600 °C, in which the concrete TES module is expected to be in operation. Finally, the effect of concrete-specific heat changes with temperature on its TES capacity is investigated, demonstrating that specific heat is of great significance for conc... [more]
Power Control of Low Frequency AC Transmission Systems Using Cycloconverters with Virtual Synchronous Generator Control
Achara Pichetjamroen, Toshifumi Ise
March 26, 2019 (v1)
Keywords: cycloconverters, low frequency AC transmission system (LFAC), multi-terminal, power control, virtual synchronous generator (VSG)
This paper is focused on the application of a multi-terminal line-commutated converter-type low frequency AC transmission system (MTLF) using a cycloconverter by applying a new power control scheme for multi-terminal operation. With the virtual synchronous generator (VSG) control scheme, the transmitting power among the multi-terminal system can be accomplished without a communication link for frequency synchronization in each terminal. The details of the proposed control scheme are explained in order to understand the advantages of this method. The configuration of a two-phase low frequency AC transmission system (LFAC) is adopted to examine with the proposed control scheme. Simulation results are provided to illustrate the proposed control scheme with respect to the LFAC system’s performance.
Bioenergy from Low-Intensity Agricultural Systems: An Energy Efficiency Analysis
Oludunsin Arodudu, Katharina Helming, Hubert Wiggering, Alexey Voinov
March 26, 2019 (v1)
Subject: Biosystems
Keywords: bioenergy, biofuel, Energy Efficiency, EROEI, high-intensity industrialized agricultural production systems, low-intensity eco-agricultural production systems, NEG
In light of possible future restrictions on the use of fossil fuel, due to climate change obligations and continuous depletion of global fossil fuel reserves, the search for alternative renewable energy sources is expected to be an issue of great concern for policy stakeholders. This study assessed the feasibility of bioenergy production under relatively low-intensity conservative, eco-agricultural settings (as opposed to those produced under high-intensity, fossil fuel based industrialized agriculture). Estimates of the net energy gain (NEG) and the energy return on energy invested (EROEI) obtained from a life cycle inventory of the energy inputs and outputs involved reveal that the energy efficiency of bioenergy produced in low-intensity eco-agricultural systems could be as much as much as 448.5⁻488.3 GJ·ha−1 of NEG and an EROEI of 5.4⁻5.9 for maize ethanol production systems, and as much as 155.0⁻283.9 GJ·ha−1 of NEG and an EROEI of 14.7⁻22.4 for maize biogas production systems. Thi... [more]
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