• Clean Technology
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• v.28 no.3
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• pp.238-248
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• 2022

The world is striving to transition to a carbon-neutral society. It is expected that using hydrogen instead of hydrocarbon fuel will contribute to this carbon neutrality. However, there is a need for combustion technology that controls the increased NOx emissions caused by hydrogen co-firing. Flameless combustion is one of the alternative technologies that resolves this problem. In this study, a numerical analysis was performed using the 1D opposed-flow diffusion flame model of Chemkin to analyze the characteristics of flameless combustion and the chemical reaction of methane-hydrogen fuel according to its hydrogen content and flue gas recirculation rate. In methane combustion, as the recirculation rate (K_v) increased, the temperature and heat release rate decreased due to an increase in inert gases. Also, increasing K_v from 2 to 3 achieved flameless combustion in which there was no endothermic region of heat release and the region of maximum heat release rate merged into one. In H₂ 100% at K_v 3, flameless combustion was achieved in terms of heat release, but it was difficult to determine whether flameless combustion was achieved in terms of flame structure. However, since the NOx formation of hydrogen flameless combustion was predicted to be similar to that of methane flameless combustion, complex considerations of flame structure, heat release, and NOx formation are needed to define hydrogen flameless combustion.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.2
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• pp.169-177
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• 2023

Phase stability diagrams were constructed for magnesium alanate (Mg(AlH₄)₂) nanoparticles to investigate the reversible hydrogen storage reaction by using density functional theory. Our findings indicate that bulk Mg(AlH₄)₂ shows favorable hydrogen release, but unfavorable hydrogen uptake (adsorption) reactions. However, for Mg(AlH₄)₂ nanoparticles, it was observed that hydrogen release and recharge can be achieved by controlling the particle size and temperature. Furthermore, by predicting the decomposition phase diagram of Mg(AlH₄)₂ nanoparticles with varying hydrogen partial pressure, it was discovered that reversible dehydrogenation reactions can occur even in relatively large nanoparticles by controlling the hydrogen partial pressure.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.6
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• pp.609-619
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• 2014

In the present study, the frequency of the undesired accident was estimated for a quantitative risk assessment of a large-scale hydrogen liquefaction plant. As a representative example, the hydrogen liquefaction plant located in Ingolstadt, Germany was chosen. From the analysis of the liquefaction process and operating conditions, it was found that a $LH_2$ storage tank was one of the most dangerous facilities. Based on the accident scenarios, frequencies of possible accidents were quantitatively evaluated by using both fault tree analysis and event tree analysis. The overall expected frequency of the loss containment of hydrogen from the $LH_2$ storage tank was $6.83{\times}10^{-1}$times/yr (once per 1.5 years). It showed that only 0.1% of the hydrogen release from the $LH_2$ storage tank occurred instantaneously. Also, the incident outcome frequencies were calculated by multiplying the expected frequencies with the conditional probabilities resulting from the event tree diagram for hydrogen release. The results showed that most of the incident outcomes were dominated by fire, which was 71.8% of the entire accident outcome. The rest of the accident (about 27.7%) might have no effect to the population.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.5
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• pp.616-624
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• 2011

Hydrogen storage and release of Fe/Zr/Mo mixed oxide mediums were investigated by hydrogen reduction and water splitting oxidation($Fe_3O_4+4H_2{\rightleftharpoons}3Fe+4H_2O$). As the results of TPR/O, Mo was an additive to enhance the reactivity of water splitting oxidation as well as the stability of the medium. On the other hand, it seemed that $ZrO_2$ additive provided the passway for the diffusion of gaseous chemicals on the medium in repeated redox cycles. Among the Fe/Zr/Mo mediums, a FeZrMo-7 medium (Fe/Zr/Mo=80/13/7mol%) exhibited the best performance with good durability during five repeated redox cycles. The amount of hydrogen evolved on the medium was maintained at ca. 10.7mmol-$H_2$/g-medium corresponding to the hydrogen storage amount of ca. 2.2wt%.

• Transactions of the Korean hydrogen and new energy society
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• v.13 no.1
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• pp.90-99
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• 2002

In order to utilize hydrogen energy in a large-scale in the future, development of effective hydrogen storage method is essentially required as well as that of efficient hydrogen production method. The hydrogen storage method using metal hydrides has been holding the spotlight as a safer and higher-density hydrogen storage method than conventional hydrogen storage methods such as liquid hydrogen or compressed hydrogen storage method. However when metals react with hydrogen to store hydrogen as metal hydrides, they undergo exothermic reactions, while metal hydrides evolve hydrogen by endothermic reaction. Therefore, hydrogen storage tank should have such structure that it can absorb or release reaction heat rapidly and efficiently. In this study, a review on the improvement of the heat release and absorption structure in the hydrogen storage tank was conducted, and as a result, a new type of hydrogen storage tank with the structure of vertical-type wall was designed and manufactured. Experimental results showed that this new type of tank could be used as an efficient hydrogen storage tank because its structure is simpler and manufacture is easier than cup-type hydrogen storage tank with the structure of packed horizontal cup.

• Nuclear Engineering and Technology
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• v.47 no.1
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• pp.1-10
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• 2015

After the Fukushima Daiichi nuclear power plant (NPP) accident, new regulatory requirements were enforced in July 2013 and a backfit was required for all existing nuclear power plants. It is required to take measures to prevent severe accidents and mitigate their radiological consequences. The Regulatory Standard and Research Department, Secretariat of Nuclear Regulation Authority (S/NRA/R) has been conducting numerical studies and experimental studies on relevant severe accident phenomena and countermeasures. This article highlights fission product (FP) release and hydrogen risk as two major areas. Relevant activities in the S/NRA/R are briefly introduced, as follows: 1. For FP release: Identifying the source terms and leak mechanisms is a key issue from the viewpoint of understanding the progression of accident phenomena and planning effective countermeasures that take into account vulnerabilities of containment under severe accident conditions. To resolve these issues, the activities focus on wet well venting, pool scrubbing, iodine chemistry (in-vessel and ex-vessel), containment failure mode, and treatment of radioactive liquid effluent. 2. For hydrogen risk: because of three incidents of hydrogen explosion in reactor buildings, a comprehensive reinforcement of the hydrogen risk management has been a high priority topic. Therefore, the activities in evaluation methods focus on hydrogen generation, hydrogen distribution, and hydrogen combustion.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.6
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• pp.487-494
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• 2013

In this study, solutions for a liquid pool spreading model with continuous and instantaneous release are discussed based on the model used in the FERC's report. The effects of the release time on the liquid pool volume and radius are investigated for the continuous release. For the continuous release with the frictional resistance force in the liquid pool spreading model, the vaporization time decreases as the release time increases. On the other hand, for the continuous release without the frictional resistance force in the liquid pool spreading model, the vaporization time increases as the release time increases. These phenomena are deeply related to the pool radius. In addition, the effects of the initial pool radius for the instantaneous release in the liquid pool spreading model are discussed. For the case with the frictional resistance force in the liquid pool spreading model, as reducing release time in the model with the frictional resistance force for the continuous release, the solution for a continuous release approaches to that for an instantaneous release. On the contrary to this, the pool volume and radius for the instantaneous release without the frictional resistance force are totally different from those for the continuous release without the frictional resistance force.

• The Korea Journal of Herbology
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• v.28 no.4
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• pp.57-62
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• 2013

Objectives : Lonicerae Japonicae Flos (LJF) has been shown anti-oxidant, anti-inflammatory, anti-viral, anti-rheumatoid properties. However, it is still largely unknown whether LJF inhibits skin injury against oxidative stress in human keratinocyte, HaCaT cells. The purpose of this study was to evaluate the protective effects of LJF against hydrogen peroxide($H_2O_2$)-induced oxidative stress in human keratinocytes, HaCaT cells. Methods : To evaluate out the protective effects of LJF on oxidative injury in HaCaT cells, an oxidative stress model of HaCaT cells was established under a suitable concentration (500 ${\mu}M$) hydrogen peroxide. HaCaT keratinocyte cells were pre-treated with LJF (0.1, 0.25 or 0.5 mg/ml), and then stimulated with $H_2O_2$. Then, the cells were harvested to measure the cell viability, DNA damage, and release of reactive oxygen species (ROS). Results : LJF (0.1, 0.25 or 0.5 mg/ml) itself did not show any significant toxicity in HaCaT cells. The treatment of $H_2O_2$ caused the oxidative stress, leading to the cell death, and DNA injury. However, pretreatment with LJF reduced cell death, and DNA injury. The stimulation of $H_2O_2$ on HaCaT cells resulted in excessive release of ROS, which is the main factor of oxidative stress. The excessive release of ROS was inhibited by LJF treatment significantly. Conclusions : These results could suggest that LJF exhibited the protective effects of HaCaT cells against $H_2O_2$-induced oxidative stress by inhibiting ROS release. It could be explained that LJF inhibit skin damages against oxidative stress. Thus, LJF would be useful for the development of drug or cosmetics treating skin troubles.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.2
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• pp.161-172
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• 2014

Hydrogen, which can be produced from abundant and widely distributed renewable energy resources, seems to be a promising candidate for solving the concerns for improving energy security, urban air pollution, and reducing greenhouse gas emissions. The two primary motivating factors for hydrogen economy are fossil fuel supply limitations and concerns about global warming. But the safety issues associated with hydrogen economy need to be investigated and fully understood before being considered as a future energy source. Limited operating experience with hydrogen energy systems in consumer environments is recognised as a significant barrier to the implementation of hydrogen economy. To prevent unnecessary restrictions on emerging codes, standards and local regulations, safety policies based on real hazards should be developed. This article studies briefly the direct impact-distances from hazard events such as hydrogen release and jet fire, and damage levels from hydrogen gas explosion in a confined space. Based on the direct impact-distances indicated in the accident scenarios and consumer environments in Korea, the safety policies, which are related to hydrogen filling station, hydrogen fuel cell car, portable fuel cell, domestic fuel cells, and hydrogen town, are suggested to implement hydrogen economy. To apply the safety policies and overcome the disadvantages of prescriptive risk management, which is setting guidance in great detail to management well known risk but is not covering unidentified risk, hybrid risk management model is also proposed.

• The Korean Journal of Physiology
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• v.29 no.1
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• pp.1-11
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• 1995

Alveolar macrophages play a pivotal role in the pathogenesis of silicosis since the macrophages may release a wide variety of toxic and inflammatory mediators as well as mitogenic growth factors. In the present study, the effects of in vitro exposure to silica on release of various mediator such as reactive oxygen species, platelet activating factor(PAF), and interleukin-1 (IL-1) by alveolar macrophages were examined. First, hydrogen peroxide release from alveolar macrophages was monitored by measuring the change in fluorescence of scopoletin in the absence or presence of graded concentration of silica. Significantly enhanced release of hydrogen peroxide was observed at 0.5 mg/ml and above. A maximal enhancement of 10 fold above control was observed at 5 mg/ml silica. Similarly, in vitro exposure to silica also significantly stimulated the generation of chemiluminescence from alveolar macrophages at 0.5 mg/ml and above with n maximal enhancement of 8 fold at 5 mg/ml silica. Second, PAF release from alveolar macrophages after 30 min incubation at $37^{\circ}C$ in absence or presence of zymosan and silica was determined by measuring $^{3}H-serotonin$ release ability of the conditioned macrophage supernates from platelets. 5 mg/ml zymosan as a positive control fur the PAF assay increased PAF release by 19 % of total serotonin release. Furthermore, silica also resulted in significant enhancement of the PAF release compared with that in unstimulated (control) cells, i.e., $17.7{\pm}5.8%$ and $24.0{\pm}4.9%$ of total serotonin release at 5 mg/ml and 10 mg/ml silica, respectively, which represents the release of nanomole levels of PAF. Lastly, IL-1 production by alveolar macrophages was analysed following their stimulation with lipopolysaccharide (LPS) and silica by their capacity to stimulate thymocyte proliferation. $10\;{\mu}g/ml$ LPS resulted in an 11 fold increase in IL-1 production. In comparison, $50\;{\mu}g/ml$ silica resulted in a 4 fold increase in IL-1 release. These data indicate that in vitro exposure of alveolar macrophages to silica activates the release of various bioactive mediators such as reactive oxygen species, PAF and IL-1 which thus contribute to amplification of inflammatory reactions and regulation of fibrotic responses by the lung after inhalation of silica.