• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.66-73
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• 2020

In the hydrogen compression cycle, which is currently being developed, hydrogen is compressed to a very high pressure using a compressor, and then stored and used in a high-pressure vessel. This shows that an increase in the temperature of hydrogen in the vessel due to a pressure rise during the filling process and the pressure fatigue due to the repeated cycle may cause problems in the reliability of the vessel. In this paper, for the entire processes in a 50 MPa hydrogen compression system, theoretical and numerical methods were conducted to analyze the following: the temperature increase of hydrogen in the vessel and the time required to reach thermal equilibrium with the surroundings, the change in temperature of hydrogen passing through the pressure reducing valve, and the required capacity of the heat exchanger for cooling the vessel. The results will be useful for the design and construction of hydrogen compression systems, such as hydrogen charging stations.

• Journal of Environmental Science International
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• v.5 no.3
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• pp.387-398
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• 1996

Granular sludge formation and it's activity change are the most important factors in achieving successful start-up and operation of UASB reactor. Nevertheless, the detailed mechanism is still unknown. On the basic of the experiments in laboratory-scale UASB reactor, the effect of hydrogen partial pressure on sludge granulation was evaluated. Size distribution method and specific metabolic activity of the sludge with the operation time were used as a means for estimating the degree of the sludge granulation. At the constant hydrogen loading, the granulation increased as starvation periods in hydrogen supply increased, resulting in high organic removal efficiency. It was evidient that hydrogen play very important role in granulation and sludge granulation was achieved through mutual symbiosis between hydrogen utilizing bacteria and hydrogen producing bacteria under the hydrogen dificient conditions. Key words : granular sludge, UASB reactor, hydrogen partial pressure.

• Journal of the Korean Society of Combustion
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• v.18 no.3
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• pp.31-37
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• 2013

Numerical simulations are conducted to investigate the feature of spontaneous ignition of hydrogen within a certain length of downstream tube released by the failure of pressure boundaries of various geometric assumption. The results show that the ignition feature can be varied with the shape of pressure boundary. The ignition at the contact region are developed at the spherical pressure boundaries due to multi-dimensional shock interactions, whereas the local ignition is developed in limited area such as boundary layer at the planar pressure boundary conditions. The spontaneous ignition inside the tube can be generated from the reaction region of only boundary layer regardless of existence of the reaction of core region.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.787-790
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• 2009

There are several types of compressors which are appropriate for hydrogen gas station. Metal diaphragm type of hydrogen compressor is the one of them, a use in which satisfies the requirements of maintaining gas purity and producing high pressure over 700 bar. The objective of this study is to investigate an characteristics of compression as bulk modulus of oil varies. Three cases of bulk modulus ranging from $2{\times}10^9$, $4.52{\times}10^9$ and $7{\times}10^9$ were studied through FSI (Fluid Structure Interaction) analysis. Gas pressure, oil pressure and deflection degree of diaphragm were analysed during a certain period of compression process. Highest pressure and deflection were found in the condition of high bulk modulus of $7{\times}10^9$.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.3
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• pp.307-315
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• 2023

The physical and chemical changes exhibited by high density polyethylene (HDPE) after treatment with hydrogen at a pressure of 90 MPa followed by rapid release of the hydrogen were studied. X-ray diffraction, differential scanning calorimetry, thermo gravimetric analysis, and attenuated total reflectance (ATR)-fourier transform infrared (FTIR) were used for this purpose. As a result, it was found that the degree of crystallinity of HDPE decreased after hydrogen pressure treatment, while the average thickness of lamellae that constitute the crystals and the melting temperature of the crystalline region actually increased. The decomposition temperature also increased by about 3℃. In addition, it was found that the hydrogen bonding network between -OH groups in the HDPE sample was strengthened and partial chain scission occurred. These cut chains were found to be terminated by oxidative degradation such as cross-linking between chains, -C=O, -C-O, and -CHO, or by the formation of -CH₃ at the chain ends, as confirmed by ATR-FTIR.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.4 no.2
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• pp.1-6
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• 2008

Very High Temperature Gas Cooled Reactor (VHTR) has been selected as a high energy heat source for nuclear hydrogen generation. The VHTR can produce hydrogen from heat and water by using a thermo-chemical process or from heat, water, and natural gas by steam reformer technology. A co-axial double-tube primary hot gas duct (HGD) is a key component connecting the reactor pressure vessel and the intermediate heat exchanger (IHX) for the VHTR. In this study, a preliminary design analysis for the primary HGD of the nuclear hydrogen system was carried out. These preliminary design activities include a determination of the size, a strength evaluation and an appropriate material selection. The determination of the size was undertaken based on various engineering concepts, such as a constant flow velocity model, a constant flow rate model, a constant hydraulic head model, and finally a heat balanced model.

• International Journal of Air-Conditioning and Refrigeration
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• v.6
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• pp.124-135
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• 1998

A thermodynamic cycle analysis is performed for refrigerator-precooled Linde-Hampson hydrogen liquefiers, including catalysts for the ortho-to-para conversion. Three different configurations of the liquefying system, depending upon the method of the o-p conversion, are selected for the analysis. After some simplifying and justifiable assumptions are made, a general analysis program to predict the liquid yield and the figure of merit (FOM) is developed with incorporating the commercial computer code for the thermodynamic properties of hydrogen. The discussion is focused on the effect of the two primary design parameters - the precooling temperature and the high pressure of the cycle. When the precooling temperature is in a range between 45 and 60 K, the optimal high pressure for the maximal liquid yield is found to be about 100 to 140 bar, regardless of the ortho-to-para conversion. However, the FOM can be maximized at slightly lower high pressures, 75 to 130 bar. It is concluded that the good performance of the precooling refrigerator is significant in the liquefiers, because at low precooling temperatures high values of the liquid yield and the FOM can be achieved without compression of gas to a very high pressure.

• Journal of the Korea Safety Management & Science
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• v.16 no.4
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• pp.167-173
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• 2014

Hydrogen energy is expanding in range for civil use together with development of pollution-free power sources recently, and it is judged that the use of hydrogen will increase more as a part of carbon dioxide reduction measures according to the Climatic Change Convention. Especially, it is thought that the securement of safety of the used dispenser will be the biggest obstacle in the use of high-pressure hydrogen because the hydrogen station is operated in a high pressure. This study found risks in the process and problems on operation by making use of HAZOP(6 kinds), a qualitative safety evaluation technique, and FMEA(5 kinds), a fault mode effect analysis, for the hydrogen charging system at a hydrogen gas station, derived 6 risk factors from HAZOP and 5 risk factors from FMEA, and prepared measures for it.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2977-2983
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• 2008

The combustion characteristics of a partially premixed flame in a dump combustor were studied to determine the effects of hydrogen enrichment in propane. Bluff-body was used for flame stabilization. Fuel mixtures containing a hydrogen mole fraction ranging from 0.1 to 0.5 were burnt at ambient pressure within a quartz chamber. Tests were carried out keeping the total reactant flow rate by adjusting the fuel and air flow rates. The fluctuations of pressure were measured by piezoelectric pressure sensor. The instantaneous flame structure and OH chemiluminescence images were described by High-speed Intensified Charged Coupled Device (HICCD) camera and Intensified Charged Coupled Device (ICCD) camera. The present results show that hydrogen enrichment in fuel changed the location of primary reaction zone from inner recirculation zone to turbulent shear layer and pressure signal. The reason is that chemical aspects take precedence over flow aspects in the hydrogen-enriched flame.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.7
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• pp.28-33
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• 2022

In this study, we analyze the flow characteristics according to the internal shape of a 700bar hydrogen charging gun for hydrogen electric vehicles. When charging hydrogen, it receives a high-pressure charging pressure. At this time, we analyze the flow characteristics according to the shape of the nozzle and find the shape of the nozzle that minimizes energy loss. Ultimately, the optimal design of the nozzle was obtained by comparing the pressure difference between the inlet pressure and outlet pressure under a fixed mass flow condition.