Kim D.-K.,GFTEK Corporation |
Oh Y.-J.,GFTEK Corporation |
Kim S.-H.,ITC Corporation |
Hong K.-J.,Gwangju University |
And 3 more authors.
Transactions on Electrical and Electronic Materials | Year: 2013
In this paper, silicon solar cells are analyzed regarding power conversion efficiency by changed capacitance in the depletion region. For the capacitance control in the depletion region of silicon solar cell was applied for 10, 20, 40, 80, 160 and 320 Hz frequency band character and alternating current(AC) voltage with square wave of 0.2~1.4 V. Academically, symmetry formation of positive and negative change of the p-n junction is similar to the physical effect of capacitance. According to the experiment result, because input of square wave with alternating current(AC) voltage could be observed to changed capacitance effect by indirectly method through non-linear power conversion (Voltage- Current) output. In addition, when input alternating current(AC) voltage in the silicon solar cell, changed capacitance of depletion region with the forward bias condition and reverse bias condition gave a direct effect to the charge mobility. © 2013 KIEEME. All rights reserved.
Park S.-Y.,KAIST |
Kim J.,KAIST |
Choi I.-W.,KAIST |
Chang D.,KAIST |
And 3 more authors.
Society of Petroleum Engineers - International Petroleum Technology Conference 2013, IPTC 2013: Challenging Technology and Economic Limits to Meet the Global Energy Demand | Year: 2013
Offshore flowlines transporting hydrocarbons have to be operated very carefully to avoid the formation of gas hydrates as they are considered one of the largest concerns for flow assurance engineers. The oil and gas industry is generally relying on chemical injection for hydrate inhibition; however hydrate blockages can occur in many different places of offshore production system due to unexpected circumstances. Once hydrate blockage formed considerable efforts are required to dissociate the hydrate via deprcssurization. Because residual hydrate structures known as gas hydrate precursors will be present in the aqueous phase after dissociation, the risk of hydrate re-formation becomes extremely high. Although the KHIs are becoming popular in many fields as hydrate inhibitors are considered not effective to inhibit the hydrate formation in the presence of residual hydrate structures, so that the use of KHIs for shut-in and restart operations is not recommended. In this study, new experimental procedures composed of three stages are designed to simulate the dissociation of hydrate blockages and transportation of well fluids experiencing hydrate formation. The obtained experimental results have shown that gas hydrates are rapidly re-formed when the temperature of dissociated water falls into the hydrate formation region. With an injection of KHIs before transporting the well fluids, the subcooling increased significantly indicating the possible use of KHIs for transporting the well fluids after dissociation of hydrate blockage. Moreover, the inhibition performance of KHIs is also investigated with two different gases to study the effect of gas composition. This study is confirmed that KHIs are possible candidate to prevent the hydrate re-formation in well fluids experiencing hydrate formation if the KHI is carefully evaluated. Copyright © (2013) by the Society of Petroleum Engineers.
News Article | January 4, 2016
« Ford expands SYNC with Apple CarPlay, Android Auto, 4G LTE and new apps | Main | UK awards $10M to cut NOx from nearly 450 buses with SCR retrofits » Researchers from the Korea Advanced Institute of Science and Technology (KAIST), with colleagues from the Korea Institute of Energy Research (KIER), Qatar University and major battery manufacturer LG Chem have developed a technique for the delicately controlled prelithiation of SiO anodes for high-performance Li-ion batteries. The result, paired with a an emerging nickel-rich layered cathode, Li[Ni Co Al ]O is high Columbic efficiencies (CE) and a full cell energy density 1.5-times as high as that of a graphite-LiCoO cell in terms of the active material weight. A paper on their work is published in the ACS journal Nano Letters. Although silicon is a very attractive anode material because of its higher energy density, its huge volume change over repeated charge−discharge cycles impairs the cycle life through pulverization of active particles, film delamination, and unstable solid−electrolyte interphase (SEI) formation. As an alternative approach to avoid the known drawbacks, silicon monoxide (SiO , x ≈ 1) phase has been recently adopted because its SiO (y near 2) background matrix can buffer the volume expansion of inner Si nanodomains. On the basis of this structural advantage, some SiO electrodes demonstrated very stable cycling performance. Nonetheless, most of these phases suffer from inferior performance in a crucial parameter, namely initial Coulombic efficiency (ICE). This shortcoming originates primarily from Li ion trapping in the matrix and SEI layer formation during the first lithiation. Hence, in an overall performance viewpoint, while facilitating the long-term cycling performance, the background matrix, in turn, sacrifices the ICE. The compromised ICE would impose a great hurdle in constructing full-cells in practical applications because poor ICE necessitates an excess amount of cathode active material solely for the first cycle, leading to a lessened total energy density. For reference, current commercial LIBs involving graphite anodes usually have ICEs higher than 85% at low C-rates (∼0.1C). Attaining the optimal degree of lithiation is very critical for stable full-cell operations, the team noted. Insufficient lithiation leaves Li trapping sites and does not improve the ICE enough, but overlithiation removes the possibility of accepting Li ions during the actual alloying reaction in the first charge. To hit the sweet spot, the team prelithiated the pristine electrode via an electrical short with Li metal foil in the presence of an optimized circuit resistance while simultaneously monitoring the voltage between both electrodes. The procedure is compatible with the existing roll-to-roll manufacturing line and could be immediately applicable to the current state-of-the-art LIB anodes containing SiO , they concluded.
Ju H.,Gwangju Institute of Science and Technology |
Eom J.,Gwangju Institute of Science and Technology |
Lee J.K.,Institute for Research In Catalysis |
Choi H.,Korea Institute of Energy Research |
And 4 more authors.
Electrochimica Acta | Year: 2014
We have investigated the comparable performance of raw and ash-free coal in the operation of a direct carbon fuel cell (DCFC). The various structural and morphological analyses using SEM, TEM, EDX, XPS, XRD, and TGA are carried out to study the distinct physicochemical properties of coals. Due to contained volatile organic compounds, raw coal generates about a two-fold higher fuel cell performance compare to ash-free coal below a reaction temperature of 750 C. However, over a cell temperature of 900 C, both of them reach a similar power density of 170 mW cm-2. In the long-term operation of a DCFC, we observe a distinctly more durable power performance using ash-free coal than that of raw coal. © 2013 Elsevier Ltd. All rights reserved.
Chung M.-S.,KIER |
Jung Y.-G.,KIER |
ASME 2012 11th Biennial Conference on Engineering Systems Design and Analysis, ESDA 2012 | Year: 2012
Numerical test and eigenvalue analysis for a two-phase channel flows for energy conversion systems like fuel cells or water electrolysers with flow regime transitions are performed by using the well-posed system of equation that takes into account the pressure jump at the phasic interface. The interfacial pressure jump terms derived from the definition of surface tension which is based on the surface physics make the conventional two-fluid model hyperbolic without any additive terms, i.e., virtual mass or artificial viscosity terms. The four-equation system has three sets of eigenvalues; each of them has an analytical form of real eigenvalues relevant to the sonic speeds with phasic velocities of three typical flow regimes such as dispersed, slug, and separated flows. Further, the eigenvalues for the flow transition regions can also be obtained numerically for smooth calculation of flow regime transitions. The sonic speeds agree well not only with the earlier experimental data but also with those of an analytical model. Owing to the hyperbolicity of this model, we can adopt an upwind method, which is one of the well-known Godunov type upwind methods. A typical example of two-phase flows shows that the present model can simulate the phase separation caused by density difference of two-phase fluids. Copyright © 2012 by ASME.
Scott J.,CH2M |
Pontee N.,CH2M |
McGrath T.,Wildfowl and Wetlands Trust |
Cox R.,UK Environment Agency |
Coastal Management: Changing Coast, Changing Climate, Changing Minds - Proceedings of the International Conference | Year: 2015
The Steart Coastal Management Project is one of the largest managed realignment and habitat creation projects ever carried out in the UK. As compensation for disappearing habitat elsewhere in the Severn Estuary the Environment Agency (EA) has transformed 477 hectares of the Steart Peninsula into wildlife rich habitats whilst improving the flood defences and providing greatly improved provision for public access and community involvement. This complex scheme has faced and overcome numerous challenges including: community engagement, which turned opposition into support; development of a mosaic of habitat types; the design and construction of earthworks, which worked within the constraints of the site; the complete replacement of an extensive water management network; and the construction of a breach and exit channel. This paper outlines the key aspects of the project and documents the lessons that were learnt during the planning, design and construction phases of the project. Background The extensive mudflats and saltmarsh of the Severn Estuary are under threat due to coastal squeeze. In the UK, the combined effect of sea level rise and existing flood defences are causing approximately 100ha of saltmarsh to be lost annually (Environment Agency, 1999). The Steart scheme was undertaken to provide compensatory habitat to replace the habitat being lost whilst also improving flood defences to the local area. The scheme involved the construction of new improved set back defences, an artificial creek network, a new water management network, and breaching the existing defences. The Steart Peninsula is located on the north Somerset coast in Bridgwater Bay at the confluence of the River Parrett and the Bristol Channel (Figure 1). The Stolford to Steart Sea Defences Pre-Feasibility Report (Environment Agency, 1998) and the Shoreline Management Plan (Halcrow, 2010) for the area identified that it was a suitable location to create new intertidal habitat in the Severn Estuary and Bristol Channel area. Prior to the scheme being undertaken the peninsula was characterised by low lying ground which had been reclaimed in historical times for farming through the construction of embankments.
Beamish S.,Kier |
El-Belbol S.,Structures Delivery |
Proceedings of the Institution of Civil Engineers: Forensic Engineering | Year: 2016
Cathodic protection has been applied to reinforced concrete structures in the UK as a reinforcement corrosion protection technique since the 1980s. It is now well established in the toolbox of repair techniques available for chloride-contaminated reinforced concrete structures. Cathodic protection is an ‘active’ technique and includes an ongoing operation and performance-monitoring commitment. The technique works by introducing an anode through which a small direct current is applied to protect the reinforcement. Monitoring is required to ensure that the current is maintained at the correct level to maintain the reinforcement adequately. This paper provides a brief history of the use of cathodic protection on reinforced concrete in the UK, including the trials and subsequent wholesale use of the technique on the Midland Links motorway viaducts. Also described are the operating and performance-monitoring requirements for cathodic protection systems, including the sensors and monitoring and control equipment used. The paper also discusses the use of monitoring data in the management of cathodic protection systems, and the structures to which they are applied, to predict future performance and life, allowing future maintenance interventions to be planned and providing best value for structure owners. © 2016, Thomas Telford Services Ltd. All Rights Reserved.
Jeong J.H.,University of Ulsan |
Jung D.W.,University of Ulsan |
Lim O.T.,University of Ulsan |
Pyo Y.D.,KIER |
International Journal of Automotive Technology | Year: 2014
This work experimentally investigates how the dwell time between pilot injection and main injection influences combustion and emissions characteristics (NOx, CO, THC and smoke) in a single-cylinder DI diesel engine. The experiments were conducted using two fuel injection systems according to the fuel type, diesel or dimethyl ether (DME), due to the different fuel characteristics. The injection strategy is accomplished by varying the dwell time (10°CA, 16°CA and 22°CA) between injections at five main injection timings (−4°CA aTDC, −2°CA aTDC, 0°CA aTDC, 2°CA aTDC and 4°CA aTDC). Results from pilot-main injection conditions are compared with those shown in single injection conditions to better demonstrate the potential of pilot injection. It was found that pilot injection is highly effective for lowering heat-release rates with smooth pressure traces regardless of the fuel type. Pilot injection also offers high potential to maintain or increase the BMEP; even the combustion-timing is retarded to suppress the NOx emission formation. Overall, NOx emission formation was suppressed more by the combustion phasing retard effect, and not the pilot injection effect considered in this study. Comparison of the emissions for different fuel types shows that CO and HC emissions have low values below 100 ppm for DME operation in both single injection and pilot-main injection. However, NOx emission is slightly higher in the earlier main injection timings (−4°CA aTDC, −2°CA aTDC) than diesel injections. Pilot injection was found to be more effective with DME for reducing the amount of NOx emission with combustion retardation, which indicates a level of NOx emission similar to that of diesel. Although the diesel pilot-main injection conditions show higher smoke emission than single-injection condition, DME has little smoke emission regardless of injection strategy. © 2014, The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg.
Woo Y.,KIER |
International Journal of Automotive Technology | Year: 2014
Free piston engine generators which utilize a free piston engine and a linear generator are under investigation by a number of research groups around the world. Free piston engines give power output in a more efficient way when compared to conventional crankshaft engines, because the former do not have a crank mechanism which brings about additional mechanical loss. However, for the reliable and stable operation of the free piston engine generators, it is required to have a viable control system to address the uncertainty of piston motion. In this paper, most of the successful free piston engine generator developments were reviewed and a recent experimental result on a prototype free piston system was also presented with regard to engine performance with different mixture preparation strategies. © 2014 The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg.
Chung M.-S.,KIER |
Jung Y.-G.,KIER |
ASME 2011 5th International Conference on Energy Sustainability, ES 2011 | Year: 2011
Numerical test and eigenvalue analysis for a two-phase channel flows for energy conversion systems like fuel cells or water electrolysers with flow regime transitions are performed by using the well-posed system of equation that takes into account the pressure jump at the phasic interface. The interfacial pressure jump terms derived from the definition of surface tension which is based on the surface physics make the conventional two-fluid model hyperbolic without any additive terms, i.e., virtual mass or artificial viscosity terms. The four-equation system has three sets of eigenvalues; each of them has an analytical form of real eigenvalues relevant to the sonic speeds with phasic velocities of three typical flow regimes such as dispersed, slug, and separated flows. Further, the eigenvalues for the flow transition regions can also be obtained numerically for smooth calculation of flow regime transitions. The sonic speeds agree well not only with the earlier experimental data but also with those of an analytical model. Owing to the hyperbolicity of this model, we can adopt an upwind method, which is one of the well-known Godunov type upwind methods. A typical example of two-phase flows shows that the present model can simulate the phase separation caused by density difference of two-phase fluids. Copyright © 2011 by ASME.