• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.1
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• pp.38-45
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• 2009

Oxy-fuel combustion of pulverized coal is one of the promising new technologies to reduce $CO_2$ and NOx from coal combustion. However, the stability of pulverized coal flame is reduced in the oxy-fuel combustion. This flame stability is concerned with the flame propagation that is affected by surrounding gas and coal characteristics, such as gas temperature, gas composition, coal volatile, coal activation energy and coal size. In this paper, a study on the influence of surrounding gas and coal characteristics on the flame propagation velocity in oxy-fuel combustion of pulverized coal was preformed. One dimensional model was used to calculate the flame propagation velocity of pulverized coal clouds. In this model, the radiation is considered to be the main source of heat exchange, and Monte Carlo method was adopted for accurate calculation of radiation heat flux. It was found that the flame propagation velocity become higher with the decrease of coal activation energy and the increase of coal volatile. Also, according to the increase of gas temperature and $O_2$ concentration, flame propagation velocity increased.

• The Journal of Advanced Prosthodontics
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• v.5 no.2
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• pp.140-146
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• 2013

PURPOSE. The aim of this study was to investigate the destructive effects of biofilm formation and/or biocorrosive activity of 6 different oral microorganisms. MATERIALS AND METHODS. Three different heat polymerized acrylic resins (Ivocap Plus, Lucitone 550, QC 20) were used to prepare three different types of samples. Type "A" samples with "V" type notch was used to measure the fracture strength, "B" type to evaluate the surfaces with scanning electron microscopy and "C" type for quantitative biofilm assay. Development and calculation of biofilm covered surfaces on denture base materials were accomplished by SEM and quantitative biofilm assay. According to normality assumptions ANOVA or Kruskal-Wallis was selected for statistical analysis (${\alpha}$=0.05). RESULTS. Significant differences were obtained among the adhesion potential of 6 different microorganisms and there were significant differences among their adhesion onto 3 different denture base materials. Compared to the control groups after contamination with the microorganisms, the three point bending test values of denture base materials decreased significantly (P<.05); microorganisms diffused at least 52% of the denture base surface. The highest median quantitative biofilm value within all the denture base materials was obtained with P. aeruginosa on Lucitone 550. The type of denture base material did not alter the diffusion potential of the microorganisms significantly (P>.05). CONCLUSION. All the tested microorganisms had destructive effect over the structure and composition of the denture base materials.

• Journal of Hydrogen and New Energy
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• v.21 no.5
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• pp.425-434
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• 2010

Integrated gasification combined cycle (IGCC) is an efficient and environment-friendly power generation system which is capable of burning low-ranked coals and other renewable resources such as biofuels, petcokes and residues. In this study some process modeling on a conceptual entrained flow gasifier was conducted using the ASPEN Plus process simulator. This model is composed of three major steps; initial coal pyrolysis, combustion of volatile components, and gasification of char particles. One of the purposes of this study is to develop an effective and versatile simulation model applicable to numerous configurations of coal gasification systems. Our model does not depend on the hypothesis of chemical equilibrium as it can trace the exact reaction kinetics and incorporate the residence time calculation of solid particles in the reactors. Comparisons with previously reported models and experimental results also showed that the predictions by our model were pretty reasonable in estimating the products and the conditions of gasification processes. Verification of the accuracy of our model was mainly based upon how closely it predicts the syngas composition in the gasifier outlet. Lastly the effects of change oxygen are studied by sensitivity analysis using the developed model.

• School Mathematics
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• v.19 no.4
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• pp.639-661
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• 2017

The purpose of this study is to investigate the relationship between the distance function average speed and the speed function. Particularly, in this study, we investigate the process of constructing the speed function in the distance function (irrational function, exponential function) which is difficult to weaken the argument in the denominator. In this process, students showed various anxieties and expressions about the procedural knowledge that they constructed first. In particular, if student B can not explain all the knowledge he already knows in this process, he showed his reflection on the process of calculating the differential coefficient. This study adds an understanding of the calculation method of students in differential coefficient learning. In addition, it is meaningful that the students who construct procedural knowledge at the time of calculating the differential coefficient have thought about how to provide opportunities to reflect on the procedure they constructed.

• Nuclear Engineering and Technology
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• v.53 no.12
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• pp.4137-4141
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• 2021

As NPPs continue to operate, liquid waste continues to be generated, and containers are needed to store and transport them at low cost and high capacity. To transport and store liquid phase very low-level radioactive waste (VLLW), a container is designed by considering related regulations. The design was constructed based on the existing container design, which easily transports and stores liquid waste. The radiation shielding calculation was performed according to the composition change of barium sulfate (BaSO₄) using the Monte Carlo N-Particle (MCNP) code. High-density polyethylene (HDPE) without mixing the additional BaSO₄, represented the maximum dose of 1.03 mSv/hr (<2 mSv/hr) and 0.048 mSv/hr (<0.1 mSv/hr) at the surface of the inner container and at 2 m away from the surface, respectively, for a 10 Bq/g of ⁶⁰Co source. It was confirmed that the dose from the inner container with the VLLW content satisfied the domestic dose standard both on the surface of the container and 2 m from the surface. Although it satisfies the dose standard without adding BaSO₄, a shielding material, the inner container was designed with BaSO₄ added to increase radiation safety.

• Journal of the Korea Organic Resources Recycling Association
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• v.30 no.4
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• pp.131-139
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• 2022

The aim of this study was to assess the feasibility of a landfill project to reduce greenhouse gas (GHG) from La Chureca Landfill in Managua, Nicaragua ("Project"). The feasibility study involved surveying the status and composition of waste on its way in to the landfill and projecting GHG emissions from the landfill. A projection of the GHG emissions with the IPCC model based on the survey results indicated the period 2006 to 2043 would see mean yearly GHG emissions of 290,147 ton-CO₂/year with model certainty not considered, and 217,610 ton-CO₂/year with model certainty considered. Thus, the result exceeded the corresponding median and mean values of other CDM projects implemented in Central America, even after model uncertainty was considered together with the conservative estimation of carbon capture efficiency. The similar result was produced even with an analysis of sensitivity to error factors. All the findings of the study are expected to be applicable as basic data for deciding about whether & how to proceed with the Project.

• Journal of Ginseng Research
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• v.45 no.2
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• pp.246-253
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• 2021

Background: Ginseng is one of the most valuable herbal supplements. It is challenging to perform quality control of ginseng products due to the diversity of bioactive saponins in their composition. Acid or alkaline hydrolysis is often used for the structural elucidation of these saponins and sugars in their side chains. Complete transformation of the original ginsenosides into their aglycones during the hydrolysis is one of the ways to determine a total saponin group content. The main hurdle of this approach is the formation of various by-products that was reported by many authors. Methods: Separate HPLC assessment of the total protopanaxadiol, protopanaxatriol and ocotillol ginsenoside contents is a viable alternative to the determination of characteristic biomarkers of these saponin groups, such as ginsenoside Rf and pseudoginsenoside F₁₁, which are commonly used for authentication of P. ginseng Meyer and P. quinquefolius L. samples respectively. Moreover, total ginsenoside content is an ideal aggregated parameter for standardization and quality control of ginseng-based medicines, because it can be directly applied for saponin dosage calculation. Results: Different hydrolysis conditions were tested to develop accurate quantification method for the elucidation of total ginsenoside contents in herbal products. Linearity, limits of quantification, limits of detection, accuracy and precision were evaluated for the developed HPLC-MS method. Conclusion: Alkaline hydrolysis results in fewer by-products than sugar elimination in acidic conditions. An equimolar response, as a key parameter for quantification, was established for several major ginsenosides. The developed approach has shown acceptable results in the analysis of several different herbal products.

• Journal of Hydrogen and New Energy
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• v.33 no.6
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• pp.845-855
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• 2022

In response to climate change, the world is continuing efforts to reduce fossil fuels, expand renewable energy, and improve energy efficiency with the goal of achieving carbon neutrality. In particular, R&D is being made on the value chain covering the entire cycle of hydrogen production, storage, transportation, and utilization in order to shift the energy supply system to focus on hydrogen energy. Hydrogen-based energy sources can produce heat and electricity at the same time, so it is possible to utilize heat energy, which can increase overall efficiency. In this study, calculation of the optimal scale for hydrogen-based cogeneration and the composition of heat sources were reviewed. It refers to a method of the optimal heat source size according to the external heat supply and heat storage to be considered. The results of this study can be used as basic data for establishing a hydrogen-based energy supply model in the future.

• Coupled systems mechanics
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• v.12 no.6
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• pp.531-537
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• 2023

Municipal solid waste landfills are unpredictable bioreactors which in cases of mishandling and bad supervision presents numerous risks. The key to municipal waste landfills is to approach them from the point of prevention of the possible consequences, which means using methods of organized waste disposal, and also utilizing landfill gas, as an unavoidable consequence with disposal of municipal solid waste with a high share of biodegradable organic matter. This paper presents an overview about problems of solid municipal waste management, type and composition of waste, and an overview of waste management condition. Further, the problem of landfill and landfill gasses is described with the calculation models of landfill production, as well as the use of the SWM GHG Calculator and LandGEM software on a specific example of gas production for the central zone at Sarajevo landfill "Smiljevici". Main focus of this thesis is the analysis of potentials of greenhouse gas emission reduction measures from the waste management. Overview of the best available techniques in waste management is presented as well as the methodology used for calculations. Scenarios of greenhouse gas emission reduction in waste management were defined so that emissions were calculated using the appropriate model. In the final section of the paper, its description of the problem of collection and utilization the landfill gas at the sanitary landfill "Smiljevici", and implementation of the system for landfill gas collection and solution suggestion for the gasification and exploitation of gas. Energy, environmental and economic benefits can be accomplished by utilizing municipal solid waste as fuel in industry and energy and moreover by utilizing energy generation from landfill gas, which this thesis emphasizes.

• Journal of the Korea Organic Resources Recycling Association
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• v.32 no.1
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• pp.13-19
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• 2024

The objective of this study was to assess the feasibility of a landfill project aimed at reducing greenhouse gas (GHG) from Puerto Cortes Landfill in Honduras ("Project"). The feasibility study involved surveying the status, composition and amount of waste entering the landfill, and projecting GHG emissions from the landfill. A projection of the GHG emissions with the IPCC model and based on the survey results indicated that the period 2027 to 2041 would see a total GHG emission reduction of 506,835 ton-CO₂/year, with a mean yearly GHG emission reduction of 33,789 ton-CO₂, assuming landfill gas collection is implemented, The findings of the study are expected to serve as basic data for deciding about whether and how to proceed with the Project.