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The lack of plant-side energy storage analysis to support nuclear power plants (NPP), has setup this research endeavor to understand the characteristics and role of specific storage technologies and the integration to an NPP. The paper provides a qualitative review of a wide range of configurations for integrating the energy storage system (ESS) to an operating NPP with pressurized water reactor (PWR). The role of ESS technologies most suitable for large-scale storage are evaluated, including thermal energy storage, compressed gas energy storage, and liquid air energy storage. The methods of integration to the NPP steam cycle are introduced and categorized as electrical, mechanical, and thermal, with a review on developments in the integration of ESS with an operating PWR. By adopting simplified off-design modeling for the steam turbines and heat exchangers, the results show the performance of the PWR steam cycle changes with respect to steam bypass rate for thermal and mechanical storage integration options. Analysis of the integrated system characteristics of proposed concepts for three different ESS suggests that certain storage technologies could support steady operation of an NPP. After having reviewed what have been accomplished through the years, the research team presents a list of possible future works.

Organic light-emitting diode (OLED) microdisplays have attracted much attention as displays for small form factor augmented reality (AR) devices. To realize glass-like thin and wide field of view (FoV) AR devices, we designed a display module with a high aspect ratio microdisplay and a thin optical component. For the high aspect ratio microdisplay, we developed the color OLED microdisplay with a 32:9 aspect ratio and a 0.8-inch diagonal ∼2,490-ppi CMOS backplane. To express color and reduce optical crosstalk, we fabricated the color filter (C/F) patterning directly on the white OLED. We also developed a pin mirror lens with 11 pin mirrors to improve the optical efficiency and quality with a thin lens. By combining the microdisplay with LetinAR’s pin mirror lens, we successfully demonstrated an AR device with a wide horizontal FoV of 46° but with a small form factor 4 mm lens.

Objectives:In this study, a adjusted sewage & wastewater treatment capacity-required area estimation methodology was proposed through various data analysis for the required area of domestic sewage & wastewater treatment, the occupancy ratio of each sub-facility, and the treatment processing method. In addition, the reduction rate of the required area according to the application of the adjustment methodology presented in this study was evaluated quantitatively by comparing the actual area with the expected area.Methods:Statistical analysis was performed by collecting 654 data of more than 500 m3/day of treatment capacity in domestic sewage & wastewater treatment facilities. The 33 sewage & wastewater treatment facilities constructed by the LH sample groups were divided into functional areas and analyzed for occupancy rates by each facility.Results and Discussion:A capacity-required area regression model was developed for the collected each samples. As a result, the distributions of the regression model were divided into two clusters according to the analysis sample differences. It was analyzed that the estimated required area using the local government sample group was estimated to be relatively higher than the LH sample group. In this study, a adjusted capacity-required area model based on regression model derived from LH sample was proposed by considering green site ratio and treatment processing methods in sewage & wastewater treatment plant. The results are as follows: A = 15.638×Q0.7414×α×β (α: conversion factor for green site ratio, β: conversion factor for treatment processing method). Conclusions:Recently, the wastewater treatment facilities have been in decentralization and small scale, and the introduction of the advanced treatment method that requires a relatively small area such as MBR or SBR has been accelerating. Consequently, it could be expected that the methodology proposed in this study will save about 50~60% of the required area for wastewater treatment facilities.

Co-combustion of bunker-C oil and bio-heavy oil for power generation provides a strategic way for mitigating the environmental burdens (climate change) due to the intrinsic carbon neutrality of bio-heavy oil. Prior to the co-combustion process, the high content of Na and K in heavy oil should be removed for the operational safety. Given that the washing process has been currently practiced for metal removal, it is desirable to develop the chemical-free washing process. Note that H2SO4 was commonly used during the washing process. To this end, this study laid great emphasis on the possible use of CO2 for the washing process. To increase the removal efficiency of Na and K, this study particularly employed micro-/nano-sized CO2 bubbles. To access the in-depth insights, a computational fluid dynamics (CFD) simulation was conducted prior to a lab-scale experimental work. The CFD simulation suggests that CO2 bubbling expedited the mixability during the washing process. Also, the CFD simulation suggested that the CO2 bubbling effects could be enhanced because the high viscosity of bio-heavy oil cancelled out the buoyancy force. A lab-scale experimental work was also in good agreement with the CFD simulation. In the presence of CO2 bubbles, 80% of Na and K was removed when the volumetric ratio of water and bio-heavy oil was 8. Even under the volumetric ratio condition of 0.125, the metal removal efficiency was not substantially reduced. Thus, all experimental findings signify that metal removal by micro-/nano-sized CO2 bubbling should be done by a cascade system.

From the very first time that graphene was used as a transparent electrode for OLED applications, the emergence of active-matrix (AM)-graphene OLED displays has been envisioned. Realizing this expectation, however, turned out to be difficult. Two obstacles are the growth and transfer of a large-area graphene film and the patterning of a graphene film into pixels. To solve these problems, a process of patterning a graphene film without surface contamination was developed. The fabrication of OLED panels by the patterned graphene anode on Gen 2(370 × 470 mm)-sized and flexible substrates was successfully demonstrated. In this work, oxide TFT arrays were combined as a switching backplane, and a pixelated graphene OLED was used as an emissive layer, to realize AM-graphene OLED displays. To explore the technical feasibility of flexible AM-graphene OLED displays, the aforementioned components were formed on a flexible substrate. For commercial-level production, all the processes that were used were chosen to be compatible with the conventional display processes.

Microdisplay is a key technology for realizing augmented reality (AR) and mixed reality (MR) devices, which have attracted much attention of late. Even though the operating voltage in the tandem structure is higher than that in the single structure, 2-stack tandem OLED exhibited 20,000 cd/m2 at 9 V, which is compatible with CMOS circuit driving. Due to its top-emitting geometry with a tandem structure, the OLED device with a well-controlled thickness exhibited a white spectrum with (0.26, 0.26) color coordinates. The pixel density of the fabricated microdisplay panel with a white tandem OLED was about 2350 pixels per inch, and the active area of the panel was 0.7 inch diagonally. The resolution of the panel was 1280 × 1024, corresponding to SXGA, and the maximal luminance was 3,000 cd/m2.

Biochar is widely used for various environmental remediation strategies such as soil amendment because of its intrinsic carbon negativity and porosity. Biochar is a charcoal-like material produced via pyrolysis of biomass. To determine an effective method for modification of the porosity and morphology of biochar and establishment of a more sustainable pyrolysis platform for biomass valorization, this study used CO2 as a reactive gas medium in the biomass pyrolysis process. This study placed emphasis on elucidating the role of CO2 in the production of biochar from different types of biomass, such as cellulose, xylan, lignin, grass, and oak wood. The surface area and porosity of biochar were strongly related to the type of biomass. Under comparable pyrolysis conditions, the surface area of biochar decreased in the following order: cellulose > xylan > lignin ∼ oak wood > grass. The use of CO2 as the gas medium in biomass pyrolysis affected the surface area and porosity of biochar samples derived from biomass feedstock. For instance, the surface area and total pore volume of the oak-wood-derived biochar produced in the CO2 environment were twice those produced in the N2 environment. Given that the increases in the biochar surface area and porosity were attributed to the enhanced release of volatile organic compounds (VOCs) from biomass, CO2 may have enhanced VOC release (removal) during pyrolysis. Therefore, the use of CO2 in a pyrolysis platform is expected to be a strategic approach for biomass valorization.

This paper is primarily a case study on transesterification of avocado oil for the synthesis of biodiesel. Many operational parameters and components were studied in an attempt to identify the optimal process for non-catalytic transesterification, and dimethyl carbonate (DMC), an acyl acceptor was identified as key to one very efficient methodology. Non-catalytic transesterification experiments using DMC and/or methanol (MeOH) were conducted under varied temperatures and varied amounts of silica loading. The maximum yield of fatty acid methyl esters (FAMEs) of 92.96% was shown to be achievable at 380 °C. The miscibility of avocado oil and DMC was seen to be a key factor in providing a strategic means for delaying thermal cracking of FAMEs. Lastly, this study reported that the optimal mass ratio of silica to oil was over 8 at 380 °C.

Supercritical CO2 (S-CO2) has the potential to be used as the working fluid in a power cycle since S-CO2 shows a density value high as its liquid phase while the viscosity value remains closer to its gaseous phase. Thus, it requires much less work to compress due to its low compressibility as well as relatively small flow resistance. However, the S-CO2 leakage flow from turbo-machinery via seal becomes one of the important issues since not only it influences the cycle efficiency due to parasitic loss but also it is important for evaluating the system safety under various operating conditions. In this paper, the gap effect, which is studied by changing the diameter of an orifice, cavity length effect, and the number of tooth effect in a simulated labyrinth seal geometry nozzle are presented. Experimental results under various conditions including not only single phase flow but also two phase flow conditions are presented.

To achieve the more sustainable thermolytic energy conversion platform for biomass, this study particularly employed CO2 as reactive gas medium. Thus, this study laid great emphasis on elucidating the mechanistic role of CO2 during the thermolysis of biomass. As a case study, sawdust was used as the carbon substrate in this study. Lab-scale pyrolysis of sawdust in the CO2 environment revealed that the homogenous reactions between volatile organic carbons (VOCs) from the thermolysis of sawdust and CO2. In detail, two mechanistic pathways arising from CO2 were identified. First, CO2 played a role for an oxygen-donor and reacted with VOCs, thereby resulting in CO formation. Second, CO2 expedite thermal cracking of VOCs. In an effort to enhance the identified mechanistic role of CO2, industrial waste, namely red mud, was mixed with sawdust to fabricate the Fe-carbon composite, and the Fe-carbon composite was further used as a catalyst. In the presence of the Fe-carbon composite, the identified mechanistic roles of CO2 were further reinforced.

This study demonstrates that CO2 enhances the production of a syngas component and also hinders the formation of benzene derivatives and polycyclic aromatic hydrocarbons (PAHs) during the pyrolysis of sewage sludge. A thermogravimetric analysis and two lab-scale pyrolysis setups (single-stage and two-stage) were used to understand the role of CO2 in the pyrolysis of sewage sludge. The use of CO2 enhanced the thermal cracking of volatile species formed during the pyrolysis, resulting in the enhanced production of carbon monoxide (CO) at temperatures higher than 550 °C. In addition, less tar (e.g., 20% in N2; 17% in CO2) and more gas product (39% in N2; 44% in CO2) were formed in the presence of CO2 after the pyrolysis of sewage sludge, indicating that the use of CO2 shifts pyrolytic carbon distribution from tar to pyrolysis gas. In addition to the decrease in tar, the PAH content in the tar was also decreased, meaning that CO2 suppresses the formation of benzene derivatives and PAHs during pyrolysis. Solid residues formed following the pyrolysis (in the presence of N2 and CO2) were also characterized, which showed that Ca, K, and Mg are effectively immobilized in the solid product. These residues can potentially be used for soil amendment. This study suggests that utilizing CO2 increases the thermal efficiency of sewage sludge pyrolysis and suppresses the formation of harmful chemical species such as PAHs. A pyrolysis process operated using CO2 would be an effective treatment method for byproducts of municipal and industrial wastewater treatment processing (e.g., sewage sludge).

Here in this study, the thermolysis of aquatic biopolymer (i.e., chitin) was mainly investigated as a strategic means for reinforcing the insecure supply chains of terrestrial biomass. To maximize carbon utilization in the carbon substrate and establish a sustainable pyrolysis platform, this study particularly employed CO2 as reactive gas medium. To this end, this study laid great emphasis on elucidating the mechanistic role of CO2 in pyrolysis of chitin. For the fundamental study, the thermolysis of chitin in CO2 in reference to the case in N2 was characterized thermo-gravimetrically. A series of the TGA tests signified that the homogeneous reactions between solid-state chitin and CO2 should be excluded. However, a lab-scale pyrolysis of chitin in CO2 demonstrated that CO2 enhanced thermal cracking of the volatile hydrocarbon species from the thermolysis of chitin. In parallel, CO2 reacted with the volatile hydrocarbon species to form CO. To justify such genuine mechanistic roles of CO2, two-stage pyrolysis of chitin was conducted, and all experimental findings strongly supported the genuine mechanistic roles of CO2.

Pyrolysis of defatted Euglena gracilis was investigated in this study to maximize energy recovery from algal biomass after lipid extraction. Prior to pyrolysis of defatted E. gracilis, the growth rate of E. gracilis was monitored to determine its potential as an initial carbonaceous feedstock for pyrolysis. This study revealed that the cell density of E. gracilis linearly increased for the first 5 days, during which the cell density reached 6.06 ± 0.82 g L−1, demonstrating that defatted E. gracilis is a promising feedstock for pyrolysis. To increase the thermal efficiency of defatted E. gracilis pyrolysis, CO2 was employed as a reactive gas medium. CO levels were increased by 45% following pyrolysis of defatted E. gracilis in a CO2 environment compared to in an N2 environment. Considering that CO is a highly combustible permanent gas, the use of CO2 in pyrolysis may result in the production of more fuel-range gaseous chemicals. Additionally, CO2 utilization increased the gaseous product yield compared to N2-pyrolysis for treating the defatted algal biomass while decreasing tar yield.

Operation with reduced number of operators is considered as an important operational mode to improve economics of a nuclear power plant (NPP) in the future and it will be more important for the small modular reactors (SMRs). To control NPPs efficiently and safely with a reduced number of operators, an intelligent operation system can be very useful. However, reduced number of operators will result in larger consequence in human error due to simultaneous multi-unit failures are now more probable than the conventional operational mode. Thus, to decrease the probability of human error occurrence for the reduced number of operators, the development of an autonomous operation system with certain level of intelligence is inevitable. The prediction capability of system’s behavior as well as understanding the root cause for the current situation should be an essential function of the designed autonomous operation system. The authors propose to use the current system thermal–hydraulic (STH) analysis code platform to develop such intelligence. As a demonstration of the suggested method, the authors used the STH code to track the accident initiator of both large pressurized water reactor (PWR) and SMR. The discussions on how this method can be useful for future NPP operation and how generic differences in system design actually influence the system behavior are presented.

Up to date, despite the massive generation of crude oil sludge (COS), the technical completeness for disposing COS has not been fully achieved. Considering its harmfulness and the high content of hydrocarbon species, establishing an environmentally benign platform for the simultaneous waste disposal and energy recovery will be greatly important. To this end, this study mainly focuses on pyrolysis of COS. To develop the more sustainable pyrolytic platform for COS, this study particularly employed carbon dioxide (CO2) as reactive gas medium. To chase the thermolytic behaviors of COS in the presence of CO2, a series of the TGA tests of COS was conducted, and the TGA tests confirmed that CO2 did not change the thermolytic behaviors, such as onset and end temperature for the thermolysis of COS. Nevertheless, CO2 greatly influenced the pyrogenic products via the heterogeneous reactions (i.e., volatilized hydrocarbons and CO2). In detail, CO2 expedited the thermal cracking and dehydrogenation of volatilized hydrocarbons evolved from COS, thereby resulting in the enhanced generation of H2, CH4, C2H6, C2H4, and C2H2. Despite the fact that the enhanced thermal cracking and dehydrogenation generally enhances the aromaticity in pyrolytic oil, the enhanced generation of CO was observed only from pyrolysis of COS in CO2, of which enhanced generation of CO effectively decreased the aromaticity by restricting the formation of benzene derivatives.

For the valorization of biomass and steel slag, co-pyrolysis of rice straw and steel slag was carried out as a case study. To achieve the more sustainable pyrolytic platform, carbon dioxide (CO2) was employed as reactive medium. Therefore, this study laid great emphasis on chasing the mechanistic roles of CO2 in the thermolysis of the mixture (rice straw + steel slag) at the fundamental level. This study experimentally validated that CO2 reacted with thermally induced hydrocarbon species from rice straw via the gas phase reactions. Such reactions resulted in CO formation at temperatures ≥ 480 °C, of which the reaction kinetics was catalytically accelerated when steel slag was co-pyrolyzed with rice straw. Note that steel slag contained the significant amount of metals and alkaline compounds. However, co-pyrolysis of rice straw and acid-washed slag revealed that the enhanced reaction kinetics resulting in CO formation at temperatures ≥ 480 °C was imparted from alkaline compounds such as CaCO3. Also, this study showed that CO2 effectively suppressed dehydrogenation during the thermolysis of rice straw. Such mechanistic roles of CO2 played a pivotal role to shift carbon distribution from pyrolytic oil to pyrolytic gas. The different thermal degradation routes triggered by CO2 led to the morphologic change to carbon-slag composite. In detail, the surface area of carbon-slag composite was enlarged in the CO2 atmosphere. To impart the desirable functionality, the surplus amount of CO formed from CO2 was re-used to transform iron oxides in the composite into zero-valent iron (Fe0). Porosity and zero-valent iron in carbon-slag composite increased the As(V) sorptive capability, of which the removal efficiency reached up to 99.3% at pH 6.9.

In this study, condensation heat transfer and multi-phase pressure drop of CO2 near the critical point are investigated occurring in a Printed Circuit Heat Exchanger (PCHE) for a supercritical CO2 power cycle application in mind. Homogeneous Equilibrium Model (HEM) approach is used to evaluate and develop appropriate heat transfer and pressure drop correlations. The experiment was performed with the CO2 test facility called SCO2PE (Supercritical CO2 Pressurizing Experiment) in KAIST. The heat transfer and pressure drop test was conducted with the PCHE in the facility. Existing correlations were compared to the test data and a new set of correlations was necessary to be developed. A new set of correlations is newly suggested in this paper which captures physical characteristics reasonably well.

We investigated the optical reflectance, surface roughness, and sheet resistance of aluminum (Al)/titanium nitride (TiN), titanium (Ti), and tungsten (W) layers on Si substrates, which are available in the CMOS foundry, for organic light-emitting diode (OLED) microdisplays. The devices with different metal anode layers exhibited different hole-injection properties and OLED performances, owing to the different optical and electrical properties of metal anode layers. Based on the OLED characteristics, the Al/TiN layer was selected as an anode layer for OLED microdisplays. A green monochromatic OLED microdisplay panel was designed and implemented using the 0.11-μm CMOS process. The density of pixels was ~2 351 pixels per inch and the panel's active area was 0.7 in in diagonal. The resolution of the panel was 1 280 × 3 × 1 024, corresponding to SXGA. The panel was successfully operated, and the maximal luminance was ~460 cd/m2.

Air pollution sensors based on organic transistors have attracted much interest recently; however, the devices suffer from low responsivity and slow response and recovery rates for gas analytes. These shortcomings are attributed to the low charge-carrier mobility of organic semiconductors and to a structural limitation resulting from the use of a thick and continuous active layer. In the present work, we investigated the material properties of a multiscale porous zeolitic imidazolate framework, [Zn(2-methylimidazole)2]n (ZIF-8), and examined its potential as an analyte channel material inserted at an organic-transistor active layer. A series of carbonized zeolitic imidazolate frameworks (ZIFs) were prepared by thermal conversion of ZIF-8 and also studied for comparison. The microstructures, morphologies, and optical/electrical characteristics of polythiophene/ZIF-8 hybrid films were systematically investigated. Organic-transistor-type nitrogen dioxide sensors based on the polythiophene/ZIF-8 hybrid films showed substantially improved sensing properties, including responsivity, response rate, and recovery rate. The electrical conductivity of the carbonized ZIF-8s enhanced the field-effect mobility of the organic transistors; however, the sensing performance was not improved, because of the closed pore structures resulting from the carbonization. These results provide invaluable information and useful insights into the design of transistor-type gas sensors based on organic semiconductor/metal-organic framework hybrid films.

A supercritical CO2 (S-CO2)-cooled Brayton cycle is under development for distributed power applications for remote regions. In order to successfully develop it, issues of controlling shaft levitation with bearings have to be solved. From several studies, magnetic bearings have been suggested for reliable levitation performance with reduced cost and complexity. However, several studies on magnetic bearing show that instability issues under high-pressure fluid and high-speed operating conditions may exist. The purpose of this research is to provide background for understanding the instability of magnetic bearings under S-CO2 conditions and propose functional requirements of the magnetic bearing. Thus, the rotating shaft with magnetic bearings operating under high pressure fluid was first analyzed. To test the theory, a magnetic bearing test rig was constructed. By comparing experimental data to the analysis results, the analysis results were verified. Therefore, the analysis results can be used for predicting instability in the future and can contribute to the development of better magnetic bearing controllers.

Rubrene-based electrochemiluminescence (r-ECL) cells with two different solvent systems is prepared, one in a co-solvent system with a mixture of 1,2-dichlorobenzene and propylene carbonate (DCB : PC, v/v 3 : 1) and another in a single solvent system of tetrahydrofuran (THF), as the medium to form a liquid-electrolyte (L-El). By simply changing the solvent systems, from the co-solvent DCB : PC (v/v 3 : 1) to the single solvent THF, with the same amount of electrochemiluminescent rubrene (5 mM) and Li-based salt, a dramatically enhanced brightness of over 30 cd m−2 is observed for the r-ECL cell in L-ElTHF which is approximately 7-times higher than the brightness of 5 cd m−2 observed for the r-ECL in L-ElDCB:PC(v/v 3:1).

Due to small footprint and high efficiency, a Supercritical CO2 (S-CO2) power cycle is considered to be one of the promising next-generation power cycles. Although S-CO2 is reported as a powerful cleaning agent, the performance of a power system operating with S-CO2 will also inevitably degrade over time. Previous researchers have shown that turbomachinery deterioration could be a major subject regarding the system performance degradation. Nevertheless, no quantitative evaluation has yet been made so far. In this study, the impact of the performance degradation of the S-CO2 turbomachinery on the overall performance of the system is analyzed quantitatively. The concept of Health Parameter is used to simulate turbomachinery degradation. To quantify the impact, an S-CO2 direct-cycle small modular reactor is selected as a target system. A transient analysis platform is built using a nuclear system safety analysis code and the deep neural network (DNN)-based S-CO2 turbomachinery off-design performance model. System dynamics are evaluated for primary frequency control ability and secondary load-following capability. Results show that the control problems during the transient state can occur when the output fluctuations are large and the performance degradation is severe. It has been confirmed that even control failures of the PID controllers can occur. Therefore, the performance degradation of turbomachinery must be monitored and considered, for an operation strategy for S-CO2 systems.

The ability to image pressure distribution over complex three-dimensional surfaces would significantly augment the potential applications of electronic skin. However, existing methods show poor spatial and temporal fidelity due to their limited pixel density, low sensitivity, or low conformability. Here, we report an ultraflexible and transparent electroluminescent skin that autonomously displays super-resolution images of pressure distribution in real time. The device comprises a transparent pressure-sensing film with a solution-processable cellulose/nanowire nanohybrid network featuring ultrahigh sensor sensitivity (>5000 kPa−1) and a fast response time (1000 dpi) pressure imaging without the need for pixel structures. Our approach provides a new framework for visualizing accurate stimulus distribution with potential applications in skin prosthesis, robotics, and advanced human-machine interfaces., Electronic skin that spatially maps pressure distribution through imaging shows limited performance despite improvements to data acquisition. Here, the authors report ultraflexible, transparent electroluminescent skin capable of high-resolution imaging of pressure distribution over 3D surfaces.

A methodology is developed for thermal-hydraulic analysis and design of a breed-and-burn molten salt reactor (BBMSR). By using separate fuel and coolant molten salts, the BBMSR is proposed to overcome key materials limitations of traditional breed-and-burn and molten salt reactor designs. The BBMSR fuel concept includes an inner wall that divides the ascending and descending flows of naturally convecting fuel salt. A finite-difference model (FDM) is developed to iteratively solve for the temperature and velocity distributions in both sections of the concentric fuel. The FDM is used to perform parametric studies of the effect of fuel geometry and heat generation rate on the heat transfer performance of the fuel. The FDM is then integrated into a design search algorithm that identifies the operational limits for a given BBMSR fuel geometry, within a set of defined constraints. A range of thermal-hydraulic fuel design options are evaluated, and trade-off studies are performed to identify the most promising fuel design space for competitive power production and neutronic efficiency in the BBMSR.

The enhancement of the luminance of organic light-emitting diode (OLED) panels with various areas (2.25–6084 mm2) using a microlens array (MLA) film was investigated. The luminance enhancement was dependent on the viewing angle, and the largest enhancement (64%) was observed in the normal direction while 60 and 18% enhancements were observed at 60 and 30°, which led to lower enhancement (38%) of the total luminous flux compared with the luminance enhancement (64%) in the normal direction. The luminance enhancement with the MLA film also depended on the panel area, and the smaller panels showed lower luminance enhancement than the larger ones. As for the small panels, the straying light beyond the panel areas significantly affected the luminance of the panels, and over 60% luminance enhancement was observed in the normal direction for the large panels (2500 and 6084 mm2) with the MLA film while only 48 and 58% luminance enhancements were observed at the small panels (2.25 and 70 mm2).

Presented is a flexible dual-mode display operable in reflective and emissive mode according to ambient light for optimal visibility on a nonplanar surface. Flexible-backplane-embedding organic light-emitting diodes (OLEDs), thin-film transistors (TFTs), and control electrodes for liquid crystal (LC) shutter are realized by the laser lift-off (LLO) method and the newly developed polyimide (PI) delamination technique. A novel color-filterless LC shutter with color dyes is merged with this flexible backplane for operation in reflective mode. This work opens up a promising approach to building displays that are adaptive to the surrounding environment for better usability.

After the Fukushima accident, the importance of an emergency power supply for a nuclear power plant has been emphasized more. In order to maximize the performance of the existing emergency power source in operating nuclear power plants, adding a waste heat recovery system for the emergency power source is suggested for the first time in this study. In order to explore the possibility of the idea, a comparison of six supercritical carbon dioxide (S-CO2) power cycle layouts recovering waste heat from a 7.2 MW alternate alternating current diesel generator (AAC DG) is first presented. The diesel engine can supply two heat sources to the waste heat recovery system: one from exhaust gas and the other from scavenged air. Moreover, a sensitivity study of the cycles for different design parameters is performed, and the thermodynamic performances of the various cycles were evaluated. The main components, including turbomachinery and heat exchangers, are designed with in-house codes which have been validated with experiment data. Based on the designed cycle and components, the bottoming S-CO2 cycle performance under part load operating condition of AAC DG is analyzed by using a quasi-steady state cycle analysis method. It was found that a partial heating cycle has relatively higher net produced work while enjoying the benefit of a simple layout and smaller number of components. This study also revealed that further waste heat can be recovered by adjusting the flow split merging point of the partial heating cycle.

In many countries, the uncontrolled generation of large amounts of food waste has resulted in severe environmental issues. Among various treatment methods that have been proposed, anaerobic digestion to produce biogas from food waste is a proven and environmentally friendly route for simultaneous food waste treatment and energy recovery. In this study, we suggest an effective methane fermentation of food waste by mixing wood chips with feedstock to minimize the sludge generation in the process. The food waste generated in an apartment complex in the Republic of Korea was used as biogas feedstock. The use of wood chips in the process increased the production of methane and hydrogen. At the food waste to wood chip ratio of 0.5, 20 ml g−1 of methane and 13.9 ml g−1 of hydrogen were produced for 15 days at 35°C. The results of this study suggest the successful application of wood chips to the anaerobic digestion of food waste for producing biogas.

A new structure for a switchable mirror device based on reversible electrodeposition is proposed. This device does not contain Cu ions in the electrolyte and adapts a counter electrode. The feasibility of the device was evaluated with a WO3 film, which is a well-known electrochromic material, as a counter electrode. Even in the absence of Cu ions, the WO3 film facilitates a clean erase feature in the device. Furthermore, using a pre-deposited Ag film as a working electrode, Ag deposition can be driven at a substantially lower voltage than that in conventional devices. Moreover the deposition current decreases with the progress of Ag deposition, and stops after completion of the deposition process. The results clearly indicate that the tri-bromine ion, which makes the self-erasing circulation, is not generated during Ag deposition process. The new switchable mirror shows excellent bistability and size scale-up is possible because it does not consume continuous current in the mirror state. By appling the proposed technology, a switchable mirror device with a 7 cm × 9 cm active area was successfully fabricated.

Co-pyrolysis of chicken manure and biomass was investigated in this study. The pyrolysis of individual samples was characterized by thermogravimetric analysis (TGA) under N2 and CO2 atmospheres. This demonstrated that the impact of CO2 content on the physical aspects of pyrolysis such as onset and end temperatures, and residual mass was negligible. However, a high CaCO3 content (17 wt%) in chicken manure catalyzed the Boudouard reaction. Despite its negligible physical influence, CO2 evidently affected the co-pyrolysis of chicken manure and biomass chemically. It expedited the thermal cracking of hydrocarbons from the co-pyrolysis of chicken manure and biomass. Moreover, between 550 and 660 °C, CO2 reacted with condensable hydrocarbons, effectively improving CO generation. This observation suggested that CO2 acted as both carbon scavenger and oxygen donor in the co-pyrolysis of chicken manure and biomass, a driving force for shifting carbon distribution between pyrogenic products. For example, pyrolytic oil was transformed into syngas, especially CO, offering an innovative means to modify compositions of pyrolytic products. These effects were not observed in the presence of CaCO3 and/or CaO.

Nuclear power plants should be capable of contributing safely and flexibly to the electrical grid stability. This research deliberates the feasibility of a new innovative concept of a passive and autonomous frequency control operation (PAFO) in soluble-boron-free (SBF) pressurized water reactors (PWRs). The new concept eliminates any required active control in the reactor core for attaining primary and secondary frequency control operational modes in PWRs. In particular, control rods and soluble-boron are not utilized in a PAFO. Meanwhile, the reactor power maneuvering is achieved entirely by the passive reactor feedback to the coolant temperature change. This approach is motivated by the strongly negative coolant temperature coefficient available in an SBF coolant system. In order to ascertain judiciously the practical viability of the proposed concept, numerical simulations of passive primary and secondary frequency operations are performed using a lumped PWR system model solved by an in-house FORTRAN-95 computer code. The various simulation parameters are obtained from 3D Monte Carlo simulations of an SBF 450 MWt PWR by using Serpent-2 code with ENDF/B-7.1 data library. The numerical simulations are carried out at the beginning, middle and end of the fuel cycle to emphasize the effect of fuel burnup on the proposed PAFO. Moreover, sensitivity analyses on xenon worth and nominal fuel temperature are performed to deliberate their impacts in tailoring the reactor performance. Because the reactor power matches well with the power demand with a small variation in coolant temperature during the frequency control, we conclude that there is promising potential for the proposed PAFO concept.

In this study, we introduce a low-cost, efficient, porous catalytic material produced from chicken manure by pyrolysis (i.e., chicken manure biochar) for converting waste cooking oil into fatty acid methyl esters (FAME, i.e., biodiesel) via transesterification. Chicken manure can be pyrolysed at different temperatures (350, 450, 550, and 660 °C), and the properties of the resulting biochar are dependent on the temperature at which the biochar is made. The biochar in our study contained a large amount of inorganic compounds (mostly CaCO3) that expedite the catalytic activity during the transesterification of waste cooking oil. Compared to SiO2, the chicken manure biochar lowered the transesterification reaction temperature at which the highest FAME yield (95%) was achieved (350 °C). However, despite the catalytic effect of CaCO3 in the chicken manure biochar, undesirable thermal cracking of FAME occurred. To avoid this, the mass ratio of silica to chicken manure biochar was optimised. The optimal mass ratio of silica to chicken manure biochar was found to be less than 0.8. This study suggests an environmentally benign biodiesel production process that recycles organic waste such as chicken manure.

Supercritical CO2 (S-CO2) power cycles have received much attention due to their desired advantages in various applications. Due to the substantial difference in specific heat of S-CO2 at different pressure, unique characteristics inside heat exchangers, especially in the recuperator, are observed and affect the cycle design. In this research, the problem of inner pinch occurring inside the S-CO2 recuperator is identified and resolved by suggesting a new framework for the definition of heat exchanger effectiveness using the point of zero inner pinch. The design methodology of S-CO2 cycles is improved using this definition by developing a module to calculate the zero inner pinch using artificial neural network (ANN) to undergo a learning process. As a result, the computation time required for cycle analysis is reduced by an order of 10 3 in the case of simple recuperated Brayton cycle, under the accuracy of 10 - 7 error bound. As the readers gain the access to the developed module for calculating the zero inner pinch, the procedure for S-CO2 cycle optimization will become far more manageable for researchers, and as a result, this result can allow the conceptualization of even further complex layouts in S-CO2 cycle research.

This study emphasizes the control of benzene derivatives and polycyclic aromatic hydrocarbons (PAHs) in thermolysis of polyvinyl chloride (PVC) using CO2. To this end, the generation of benzenes and PAHs from the thermolysis of PVC in N2 was characterized and all experimental findings from the thermolysis of PVC in N2 were used as the reference value to configure the role of CO2 in the thermolysis of PVC. The formation of hydrogen chloride (HCl) followed by the subsequent dechlorination in the thermolysis of PVC in N2 resulted in the high yield of charring compounds, providing a favorable condition for forming benzene derivatives and PAHs. However, the thermal degradation of PVC in CO2 showed the genuine thermal degradation patterns. For instance, despite the presence of the source for oxygen, the formation of CO at temperatures higher than 600 °C was observed in the thermolysis of PVC in CO2, suggesting that some unknown reactions between hydrocarbons from the thermolysis of PVC and CO2 are initiated to form CO. In addition to these unknown reactions, the enhanced thermal cracking induced by CO2 was observed. Two identified roles of CO2 during the thermolysis of CO2 was only limited at temperatures higher than 600 °C. However, despite no precise description for the mechanistic role of CO2 at this stage of study, the formation of benzene derivatives and PAHs was effectively controlled in the presence of CO2 at temperatures higher than 480 °C. Thus, these empirical findings in this study are necessary to further be investigated in the future, which offers a great venue offering a new means for modifying and/or controlling the harmful chemical species.

Adjoint sensitivity based optimization methodology for a supercritical CO2 (S-CO2) cycle is developed in this paper. The adjoint sensitivity analysis method (adjoint method) is a way to analyze sensitivity very quickly. By using the developed methodology, the optimal state variation due to the change of cycle parameters is analyzed. The S-CO2 recompression Brayton cycle is used for an example case for the demonstration of the proposed method. The independence of time consumption for the developed adjoint sensitivity analysis method to the number of optimized variables is demonstrated. For the test case, the developed algorithm shows the ability to make the design parameters converge with a precision of 10−6 by more than ten times faster for calculating the sensitivity than conventional optimization methods. Validation of the obtained optimal point is also included in the paper. For the validation, a response surface analysis is performed to visualize the pathway during the iteration for optimization. It is very challenging to carry out the optimization having the same precision using a brute force algorithm or a probability-based optimization algorithm since the number of variables to be optimized is substantial for this type of a problem. The smoothness of an optimal cycle efficiency variation is observed in every case.

In this study, we explored the mechanistic features of CO2 in the thermolysis of PVC to modify the pyrogenic products. The mechanistic roles of CO2 in the thermolysis of PVC were varied with the pyrolytic temperature. For example, CO2 participated in unknown reactions to form CO at temperatures higher than 600 °C, where CO2 played a key role as an oxygen donor (new finding). This new thermal behavior induced by CO2 could be a new way to shift carbon from pyrolytic oil to syngas (i.e., H2 and CO) without using catalysts. This identified reaction that formed CO was noticeably enhanced in the presence of CaCO3 by up to 12 times, which was proportional to the loading of CaCO3. The stepwise thermal degradation mechanisms for PVC (i.e., dehydrogenation followed by dechlorination) provided favorable conditions for forming benzene derivatives and PAHs in pyrolytic oil. In the temperature range from 480 to 600 °C, CO2 played a key role in restricting the formation of benzene derivatives, which subsequently lowered the formation of PAHs by blocking the pathway for the gas-phase addition reactions. At the current stage of this study, the operational parameters such as the exact amount of CO2, space velocity for CO2, and other parameters for the thermolysis of PVC were fully optimized. However, all the experimental findings marginally described the possible utilization of CO2 for modifying pyrogenic products, which can be applied in various fields such as air pollutant controls (APCs) and energy applications. As such, further studies need to be conducted in the near future.

With increasing demand for transparent conducting electrodes, graphene has attracted considerable attention, owing to its high electrical conductivity, high transmittance, low reflectance, flexibility, and tunable work function. Two faces of single-layer graphene are indistinguishable in its nature, and this idea has not been doubted even in multilayered graphene (MLG) because it is difficult to separately characterize the front (first-born) and the rear face (last-born) of MLG by using conventional analysis tools, such as Raman and ultraviolet spectroscopy, scanning probe microscopy, and sheet resistance. In this paper, we report the striking difference of the emission pattern and performance of transparent organic light-emitting diodes (OLEDs) depending on the adopted face of MLG and show the resolved chemical and physical states of both faces by using depth-selected absorption spectroscopy. Our results strongly support that the interface property between two different materials rules over the bulk property in the driving performance of OLEDs.

To meet the energy requirement for a remote and isolated region, a concept of supercritical CO 2 (S-CO 2 ) cooled micro modular reactor (MMR) has been developed, which is easy to transport by fully modularizing the nuclear power system. From the previous work, only the on-design performances of MMR were presented. However, since the nuclear system needs to meet high safety standard, the design can be finalized only after the evaluation of the nuclear system response under multiple transient conditions. Such transient conditions may include part load operation and postulated accidents. The system response can be evaluated only with a high fidelity computer simulation, since it is almost impossible to construct a nuclear facility to test at such conditions. The simulation is performed to guarantee its autonomous operability and safety. Unfortunately, a system analysis computer code available for the S-CO 2 cycle analysis is yet to be developed for the MMR safety evaluation. Description of a S-CO 2 system analysis code platform is first presented in this paper. After that, the developed code is validated with experimental data. The steady state of MMR is first modeled with the code, which is followed by simulations of part load operation and postulated accidents of MMR. All simulation results show that the current design of MMR has the ability to maintain its safety and structural integrity even under extreme conditions to protect the public from radiation hazard at all times.

Here in this study, the genuine role of CO2 in co-pyrolysis of swine manure and coal was mainly investigated to increase the thermal efficiency of the thermo-chemical process. The TGA test of swine manure and coal revealed that the CO2 co-feeding impact on any reactions (≤740 °C) between CO2 and the sample surface (i.e., heterogeneous reaction) should be excluded. A batch-type co-pyrolysis revealed two genuine CO2 co-feeding impacts on co-pyrolysis of swine manure and coal. First, CO2 can be an additional source for C and O through a plausible reaction between pyrolytic oil and CO2, which led to the enhanced generation of CO by the conversion of volatile organic carbons (VOCs) evolved from thermal deconstruction of pyrolytic substrate. Second, CO2 expedite the thermal cracking of VOCs, which also resulted in the more generation of H2 and CH4. Two genuine roles of CO2 in co-pyrolysis of swine manure and coal occurred independently. All experimental findings will be directly applicable to the gasification process since pyrolysis is an intermediate step for the gasification.

This paper presents the neutronics and transient studies of a supercritical CO2-cooled micro modular reactor (MMR). The suggested MMR is an extremely compact, integrated, and truck-transportable reactor with 36.2 MWth power and a 20-year lifetime without refueling. A salient feature of the MMR is that all the components including the generator are contained in a small reactor vessel. For a minimum volume and maximum lifetime of the MMR core, a fast neutron spectrum is utilized. To improve the fuel-coolant compatibility and to maximize the fuel volume fraction, UC fuel is considered. A unique replaceable fixed absorber (RFA) is also introduced in order to maintain the excess reactivity at less than 1 dollar during the whole operational period. A drum-type reactivity control system is adopted in the MMR as the primary control system to prevent a control rod ejection accident and a single absorber rod located at the core center is used as the secondary ultimate shutdown system. The neutronics analysis is performed by using the continuous energy Monte Carlo code Serpent with the ENDF/B-VII.1 library. In addition, an unprotected loss of flow (ULOF) accident is simulated by the system analysis code GAMMA+ to show the passive safety of the MMR system.

As the share of renewable energy will be increasing, there is a growing interest in flexible power sources and energy storage systems due to the intermittent nature of renewable energy. We propose the Energy Storage System (ESS) integrated Nuclear Power Plant (NPP) as a solution. The system operates on load-following by branching the mass flow from the steam cycle to the ESS without changing the reactor thermal output. However, the merging point can be different for heat storing ESS and work storing ESS because the outlet conditions of the ESS vary depending on the type of ESS. In this study, the merging points are categorized into two types, feedwater heater and condenser. At each merging point, cycle optimization is performed while increasing the branch flow into ESS. The optimization goal is to maintain the feedwater temperature at the inlet of a steam generator. The power output and energy delivered to the ESS according to the merging point are estimated. From this study, it was found that when 25% of the inlet mass flow rate to the low-pressure turbine is diverted to ESS, the overall output of the steam cycle is decreased by 44.17% for the heat conversion ESS and 49.95% for the work conversion ESS.

Recently, oxy-combustion cycles with CO2 dilution have been of interest to eliminate NOx emission and to facilitate CO2 capture. Theoretically, they are operated in an overall stoichiometric condition. In addition, high pressure is preferred not only for better thermal efficiency but also for easier CO2 capture and storage. In this study, a triple-coaxial-tube was selected as the simplest conceptual design for an oxy-combustion burner at elevated pressure. Flame stabilization, soot emissions, and combustion efficiencies were investigated in relation to variation of the tube size, CO2 dilution ratio, and pressure. As a result, a jet Reynolds number and CO2 diffusion could explain the flame stabilization limits. Soot emission could be reduced at atmospheric pressure when the fuel-tube tip was moved into the middle oxidant tube, which also improved the combustion efficiency. Nevertheless, serious soot emissions recurred at excessive fuel flow rates and at elevated pressures. In such conditions, a lifted flame detached from the fuel-tube tip could be employed by increasing the flow rate or enhancing the CO2 dilution, and the soot emission was reduced again without losing combustion efficiency. Finally, the flame-stabilization mechanisms of the attached flame and of the lifted flame were discussed and optimized designs and operating conditions were proposed for less soot emission and better combustion efficiency at higher pressures.

The four different geometries of a reactor vessel auxiliary cooling system (RVACS) are designed to investigate how the heat removal capability changes by the geometries. Each geometry has different heat transfer characteristics regarding airflow and the presence of an air separator and an insulation material. The heat removal performance is evaluated with the reactor vessel (RV) temperature, the RV wall emissivity, and the airflow gap. For the same RVACS volume, 600 °C RV temperature, and 6-cm gap, the heat removal capability varies from 240.8 kW to 308.5 kW, depending on the geometry. The wall emissivity is less effective for Geometry 2, which has a large cavity volume and a small heat transfer area compared to the other geometries. The highest heat removal performance was obtained using Geometry 3 because cold air flows in from the bottom of the RVACS, improving both radiative and convective heat transfer. Reducing the gap size by 3 cm results in only 80.0 kW of heat removal capability for Geometry 1, and the heat removal dramatically decreases to 0.2 kW at an RV temperature of 800 °C. A sufficient RVACS gap size of at least 6 cm with a 0.6-m diameter intake pipe is required to provide adequate natural circulation and eventually enhance the heat removal capability.

A Supercritical CO2 (S-CO2) power cycle is one of the next generation power conversion cycles, which has many advantages originate from unique fluid’s characteristics near the critical point. Recently, a concept of small modular nuclear reactor (SMR) coupled with an S-CO2 power cycle is proposed to target aggressively expanding SMR market. However, many components of S-CO2 power cycle were designed with the experiences from the conventional fluids such as air and water. In this paper, in order to harness the full potential of the S-CO2 power cycle by utilizing the fluid properties further, an S-CO2 compressor with different characteristics from air compressor is evaluated in the viewpoint of system level. The analyzed compressor has a larger backswept angle in the impeller than the conventional compressor and this can be done due to the unique properties of S-CO2. A 10 MW scale SMR is selected to demonstrate the compressor’s effect on the system performance and control. As a result, S-CO2 cycle with larger backswept angle compressor can be regulated by inventory control in a wider load variation because the system has low surging mass flow rate. Thus, the system with larger backswept angle compressor has 5.6% wider part-load performance range with inventory control alone than the system with conventional compressor.

In this paper, a thermodynamic study of newly suggested supercritical carbon dioxide (s-CO2) cycle layouts using an isothermal compressor is presented. The isothermal compressor is conceptually defined using the ‘infinitesimal approach’ in attempt to resolve the ambiguity in its performance framework. As part of preliminary investigation, the isothermal compressor is demonstrated thermodynamically, and the calculations highlight that it reduces the compression work significantly under s-CO2 power cycle operating conditions over other representative working fluids. The in-house code is modified to allow the analysis of three s-CO2 cycle layouts, simple recuperated Brayton cycle, recompression Brayton cycle, and partial heating Brayton cycle, adopting the isothermal compressor. The cycle performance is evaluated through a sensitivity analysis of cycle design parameters, pressure ratio and flow split ratio. When the machinery is applied, the cycle net efficiency of the simple recuperated cycle and the recompression cycle is improved by 0.5% point and 1–3% points, respectively. Moreover, the partial heating cycle layout, known for its outstanding performance in waste heat recovery applications as a bottoming cycle, produces 15–18% more net work when using an isothermal compressor, compared to the reference cycle. Overall, the use of the isothermal compressor not only improves the general cycle performance, but also provides another degree of freedom for cycle design optimization of s-CO2 cycles.

Although the number of meshes and their distribution are important parameters that affect both computation resources and the accuracy of the numerical results, meshing of most of all computational problems still depends highly on the users’ experiences. In this paper, a deterministic adjoint-based method of optimizing mesh distribution is proposed. The developed method is applied to a nuclear power plant safety analysis. The mesh optimization was performed with 1D steady state cylindrical nuclear fuel problem first. Radial and axial mesh distributions are optimized respectively. With no surprise, the optimized mesh system performs superior than the same number of uniformly meshed system. However, it was unexpected that the optimized mesh retains generality and therefore, the optimized mesh system can be still the best mesh system for given number of meshes under different condition or even during transient analysis. The authors applied the optimized mesh distribution to nuclear system safety analysis. A large pressurized water reactor cold leg guillotine break (LBLOCA) scenario was analyzed and the consequence of different mesh systems is investigated and discussed. From this preliminary study the usefulness and implication of the adjoint based mesh optimization method for the nuclear safety analysis is uncovered.

To establish a green platform for biodiesel production, this study mainly investigates pseudo-catalytic (non-catalytic) transesterification of olive oil. To this end, biochar from agricultural waste (maize residue) and dimethyl carbonate (DMC) as an acyl acceptor were used for pseudo-catalytic transesterification reaction. Reaction parameters (temperature and molar ratio of DMC to olive oil) were also optimized. The biodiesel yield reached up to 95.4% under the optimal operational conditions (380 °C and molar ratio of DMC to olive oil (36:1)). The new sustainable environmentally benign biodiesel production introduced in this study is greener and faster than conventional transesterification reactions.

This study systematically investigates simultaneous genuine roles of CO2 in pyrolysis process by comparing the susceptibility of pyrolysis of various biomass feedstocks (spent coffee ground, oak wood, corn stover, macroalgae, microalgae, cellulose, hemicellulose, and lignin) to CO2: 1) the enhanced thermal cracking of volatile organic carbons (VOCs) evolved from the thermal decomposition of biomass and 2) the direct reaction between VOCs and CO2. The identified roles of CO2 led to the enhanced generation of CO and the subsequent reduction of condensable tar. Even though the influence of CO2 on pyrolysis of various biomass and coal was universal, it exhibited a different magnitude due to the different susceptibility to CO2. This study also reports that the susceptibility to CO2 was contingent on the lignin content in biomass.