The power industry is rapidly changing as demand for eco-friendly and stable power supply increases along with global greenhouse gas emission regulations. Small-capacity renewable power sources ...represented by photovoltaics and wind are continuously increasing as a form of microgrid to supply electric power to a community or island. As a result, microgrids based on renewable resources have come into wide usage around small areas or islands in Korea. In particular, the microgrid development policy of Korea is focused on electric power quality, as well as expansion in renewable energy supply for reducing greenhouse gas emissions. From 2009, the government began to develop independent carbon-free microgrids with photovoltaic and wind powers instead of traditional power diesel generators for small islands. The goal of this paper is to investigate a feasible economic microgrid topology for implementing the carbon-free island (CFI) under an acceptable level of reliability. First, we derive three scenarios of power systems including photovoltaics, wind, battery, and fuel cells. Next, we assess economic feasibility on top of the power supply reliability of the scenarios. Then, we perform a sensitivity test to suggest economic conditions for achieving the CFI goals. Finally, we present carbon-free-based microgrid models considering the CFI policy of Korea.
Herein, we propose an unsupervised learning architecture under coupled consistency conditions to estimate the depth, ego-motion, and optical flow. Previously invented learning techniques in computer ...vision adopted a large amount of the ground truth dataset for network training. A ground truth dataset, including depth and optical flow collected from the real world, requires tremendous effort in pre-processing due to the exposure to noise artifacts. In this paper, we propose a framework that trains networks while using a different type of data with combined losses that are derived from a coupled consistency structure. The core concept is composed of two parts. First, we compare the optical flows, which are estimated from both the depth plus ego-motion and flow estimation network. Subsequently, to prevent the effects of the artifacts of the occluded regions in the estimated optical flow, we compute flow local consistency along the forward-backward directions. Second, synthesis consistency enables the exploration of the geometric correlation between the spatial and temporal domains in a stereo video. We perform extensive experiments on the depth, ego-motion, and optical flow estimation on the Karlsruhe Institute of Technology and Toyota Technological Institute (KITTI) dataset. We verify that the flow local consistency loss improves the optical flow accuracy in terms of the occluded regions. Furthermore, we also show that the view-synthesis-based photometric loss enhances the depth and ego-motion accuracy via scene projection. The experimental results exhibit the competitive performance of the estimated depth and the optical flow; moreover, the induced ego-motion is comparable to that obtained from other unsupervised methods.
Direct measurement of the adhesion energy of monolayer graphene as-grown on metal substrates is important to better understand its bonding mechanism and control the mechanical release of the graphene ...from the substrates, but it has not been reported yet. We report the adhesion energy of large-area monolayer graphene synthesized on copper measured by double cantilever beam fracture mechanics testing. The adhesion energy of 0.72 ± 0.07 J m–2 was found. Knowing the directly measured value, we further demonstrate the etching-free renewable transfer process of monolayer graphene that utilizes the repetition of the mechanical delamination followed by the regrowth of monolayer graphene on a copper substrate.
For the chemical vapor deposition (CVD) of graphene, the grain growth of the catalyst metal and thereby surface roughening are unavoidable during the high temperature annealing for the graphene ...synthesis. Considering that nanoscale wrinkles and poor uniformity of synthesized graphene originate from the roughened metal surface, improving surface flatness of metal thin films is one of the key factors to synthesize high quality graphene. Here, we introduce a new method for graphene synthesis for fewer wrinkle formation on a catalyst metal. The method utilizes a reduced graphene oxide (rGO) interfacial layer between the metal film and the wafer substrate. The rGO interlayer releases the residual stress of the metal thin film and thereby suppresses stress-induced metal grain growth. This technique makes it possible to use much thinner nickel films, leading to a dramatic suppression of RMS roughness (∼3 nm) of the metal surface even after high temperature annealing. It also endows excellent control of the graphene thickness due to the reduced amount of total carbon in the thin nickel film. The synthesized graphene layer having negligible amount of wrinkles exhibits excellent thickness uniformity (91% coverage of monolayer) and very high carrier mobility of ∼15 000 cm2/V·s.
We demonstrate that the use of a monolayer graphene as a gate electrode on top of a high-κ gate dielectric eliminates mechanical-stress-induced-gate dielectric degradation, resulting in a quantum ...leap of gate dielectric reliability. The high work function of hole-doped graphene also helps reduce the quantum mechanical tunneling current from the gate electrode. This concept is applied to nonvolatile Flash memory devices, whose performance is critically affected by the quality of the gate dielectric. Charge-trap flash (CTF) memory with a graphene gate electrode shows superior data retention and program/erase performance that current CTF devices cannot achieve. The findings of this study can lead to new applications of graphene, not only for Flash memory devices but also for other high-performance and mass-producible electronic devices based on MOS structure which is the mainstream of the electronic device industry.
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•Process design and optimization of ammonia decomposition are successfully performed.•9% of fuel ammonia can decompose 91% of feed ammonia.•Ammonia combustor has optimum efficiency of ...59% at 1500 K.•Ammonia combustion is suitable at fuel-rich region with an equivalence ratio of 1.07.•30% recirculated flue gas reduces NOx from 339 to 0.51 ppm.
Ammonia is an important commodity for both direct and indirect applications. It can be used directly as a carbon-free fuel source as well as for the purpose of renewable hydrogen storage and transport. In this study, hydrogen production from ammonia decomposition in a multi catalytic packed bed reactor with an intermediate heating system is reported using Aspen Plus V.12. The process simulation model results have been validated through experimental data for commercially available Ru/Al2O3 catalyst and Temkin-Phyzev reaction kinetics. The results exhibit that ammonia decomposition is a highly endothermic reaction, therefore requires significant heat energy. The decomposition parameters such as temperature and pressure are optimized for large-scale ammonia decomposition. For the ammonia combustion, thermal efficiency, fuel-saving, and product yield are analyzed and optimum values are found to be 59%, 22% and 77% for each parameter, respectively. During the pure ammonia combustion, NOX emissions are a major issue. To monitor the NOX emissions, parameters such as equivalence ratio, temperature and pressure are analyzed to witness the optimum operating conditions. To improve the flame quality such as laminar velocity, minimum ignition temperature, and adiabatic flame temperature of the ammonia combustion, waste hydrogen stream from the pressure swing adsorption (PSA) unit is blended with the fuel ammonia. The blending of hydrogen with fuel ammonia resulted in higher NOX emissions, which can be reduced by recirculation of 30% of the flue gas with air–fuel stream.
In this paper, a device utilizing the hollow cathode discharge is demonstrated to diagnose the possibility of improving luminous efficacy of a microplasma device. A series of experiments is conducted ...by measuring luminous efficacy, which is an important factor in display devices, in accordance with specifications of the cylindrical hollow and gas pressure. The proposed structure has two electrodes, and one of them contained a cylindrical hole and is called a hollow electrode. The hollow electrode works as either a cathode or an anode alternately due to the ac operating conditions. When the hollow electrode operated as a cathode, the luminous efficacy is higher than that of the anode case, and this tendency is observed consistently throughout all experiments. Moreover, from the measurement results on the tendency of luminous efficacy in terms of hole specifications, different aspects of luminous efficacy are obtained, depending on whether the variation is in the diameter or in the depth. In case of the diameter, the luminous efficacy is improved when p middot D (i.e., the product of the gas pressure and the diameter of the cylindrical hole) is less than one Torr ldr cm. In the case of the depth, the maximum value of luminous efficacy exists at the certain p middot d (i.e., the product of the gas pressure and the depth of the cylindrical hole).
Hydrogen is one of the potential candidates to replace fossil fuels to meet net zero emissions target. This study reports a detailed techno-economic and environmental assessment of hydrogen ...production through ammonia decomposition. The case study is based on a multiple catalytic packed bed reactor with intermediate heating system. Aspen plus® and MATLAB® were linked to evaluate economic and environmental impact of the process. The process parameter like furnace temperature, flue gas recirculation, ammonia decomposition temperature, market ammonia supply pressure, ammonia decomposition pressure, hydrogen purification unit's pressure and equivalence ratio, and economic parameters of capital expenditure (CAPEX) and operating expenditure (OPEX) were considered. The overall thermal efficiency of the developed process is found to be 79%. The levelized cost of hydrogen (LCOH) is estimated and found to be 6.05 USD/kg of H2 based on CAPEX and OPEX. A major contribution of up to 62.2% to LCOH comes from the price of feed Ammonia. Based on 25-year plant life with 10% discounted rate the plant is economically viable, with a return on investment of 23.7%, in a payback period of 3.58 years. Global warming potential of the process is also carried out.
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•Techno-economic and environmental assessment on ammonia decomposition was carried out.•Overall thermal efficiency of H2 production from NH3 decomposition process is 79%.•LCOH of H2 production from NH3 decomposition process is 6.05 USD/kg of H2.•Ammonia price alone contributes up to 62.2% of LCOH.•GWP analysis of H2 production from NH3 decomposition process is 0.66 kg of CO2/kg of H2.
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•Experimental and simulated solubilities of CO2 in MDEA/AMP/H2O determined.•Liquid phase non-ideality was evaluated using the electrolyte–NRTL model.•Aspen Plus - MATLAB linking ...algorithm for data driven thermodynamic modelling.•Evaluation of ionic behavior based on a subset of ranked electrolyte pairs.•Biogas upgrading process analysis using LSA, GSA, and MOO.
Data driven thermodynamic models has a great potential to add value to the accuracy of simulation processes. In this study experimental data driven e-NRTL activity coefficient model is used to evaluate the behavior of MEA/AMP and MDEA/AMP aqueous systems for biogas upgrading. The vapor liquid equilibrium (VLE) experimental data is used for regression of the electrolyte pair parameters of e-NRTL activity coefficient model, which were then used to design the process for biogas upgrading by using Aspen Plus in combination with MATLAB. Experiments have been carried out for CO2 solubility as a function of CO2 partial pressure (PCO2) at different amine blending ratios such as 9/21/70, 15/15/70, and 21/9/70 (w/w/w percent) for each MEA/AMP/H2O and MDEA/AMP/H2O systems at a wide temperature range of 323.15–383.15 K. The importance of regressed parameters was confirmed through global sensitivity analysis (GSA) using Monte Carlo simulation. The local sensitivity analysis (LSA) and GSA for biogas upgrading process based on data driven thermodynamic modeling have been carried out in terms of the biomethane purity, reboiler heat duty, and methane slip. Finally, the optimal process parameters were found through multi-objective optimization (MOO) for developed biogas upgrading process.
In this paper, the characteristics of microdischarge phenomena in a plasma device with an auxiliary electrode located on the center of the coplanar gap were investigated. The microdischarge showed ...three discharge modes in accordance with the auxiliary pulse voltages, and its luminous efficacy was improved when it operated in the efficient mode. To understand the mechanisms of that improvement of efficiency, a wall-charge measurement system was proposed and applied to measure the wall-charge behavior, which is a key for the diagnosis of discharge characteristics. For the efficient mode, measurement of wall-charge behavior indicated the presence of the three high efficiency factors, namely, long-gap discharge, current reduction, and priming effect. For the inefficient mode, however, the measured wall-charge behavior indicated that strong short-gap discharges were generated between sustain and auxiliary electrodes, and then, the high efficient factors were not observed. Additionally, in order to operate the device in the efficient mode, the tendency of the mode transition was investigated in terms of panel specifications, such as barrier rib height and coplanar gap. The results indicate that the transition voltage between the efficient and inefficient modes increased when the barrier rib height increased, and it showed the tendency resembling the Paschen curve with various coplanar gaps.
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