• Bulletin of the Korean Chemical Society
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• v.28 no.12
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• pp.2454-2458
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• 2007

Exploring the basic concepts for the design of CO2-philic molecules is important due to the possibility for “green” chemistry in supercritical CO2 as substitute solvent systems. The Lewis acid-base interactions and C?H…O weak hydrogen bonding were suggested as two key factors for the solubility of CO2-philic molecules. We have performed high level quantum mechanical calculations for the van der Waals complexes of CO2 with trimethylphosphate and trimethylphosphine oxide, which have long been used for metal extractants in supercritical CO2 fluid. Structures and energies were calculated using the MP2/6-31+G(d) and recently developed multilevel methods. These studies indicate that the Lewis acid-base interactions have larger impact on the stability of structure than the C?H…O weak hydrogen bonding. The weak hydrogen bonds in trimethylphosphine oxide have an important role to the large supercritical CO2 solubility when a metal is bound to the oxygen atom of the P=O group. Trimethylphosphate has many Lewis acid-base interaction sites so that it can be dissolved into supercritical CO2 easily even when it has metal ion on the oxygen atom of the P=O group, which is indispensable for a good extractant.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.1
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• pp.96-104
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• 2020

A model combustor has been designed and fabricated for studying the combustion characteristics of oxygen (O₂)/hydrogen (H₂) flames under supercritical conditions. The combustor is designed to allow combustion experiments up to 60 bar, the supercritical pressure condition of O₂ and H₂. Injectors can be replaced to study various types of flames and the combustion chamber is designed to visualize flames by installing optical windows. Through the preliminary tests, including a high-pressure (up to 60 bar) test using air and combustion tests for coaxial jet flames of liquid oxygen (LO₂)/gaseous hydrogen (GH₂) at elevated pressure, the reliability of the combustor has been demonstrated.

• Journal of ILASS-Korea
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• v.15 no.4
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• pp.182-188
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• 2010

Significant real fluid behaviors including rapid property changes take place where high pressure combustion devices such as rocket engines. The flamelet model is the reliable approach to account for the real fluid effects. In the present study, the flamelet equations are extended to treat the general fluids over transcritical and supercritical states. The real fluid flamelet model is carried out for the gaseous hydrogen and cryogenic liquid oxygen flames at the wide range of thermodynamic conditions. Based on numerical results, the precise discussions are made for effects of real fluid, pressure, and differential diffusion on the local flame structure.

• Transactions of the Korean hydrogen and new energy society
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• v.26 no.1
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• pp.8-14
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• 2015

In this study, the model biomass was used for hydrogen production by supercritical water gasification (SCWG). Model biomasses were glycerol, glycine, lignin and cellulose. The feed concentration was set to 1 wt%. Experiments were conducted in a reactor at $440^{\circ}C$ and above 26.3 MPa for 30 min. The effects of catalysts such as alkali metal salt ($K_2CO_3$ and $Na_2CO_3$) and transition metal salts ($Ni(NO_3)_2$, $Fe(NO_3)_3$ and $Mn(NO_3)_2$) on the gasification were systematically investigated. No tar or coke was observed in all experiments. The results showed that the gasification efficiency increased with various catalysts. For the cellulose and glycerol, all catalysts were effective for the promoted $H_2$ production compared with no catalyst. The significant decrease of $H_2$ production compared with no catalyst was observed with $Na_2CO_3$ and $Fe(NO_3)_3$ for glycine and lignin. respectively. The highest H2 production, 1.24 mmol was obtained for glycerol-SCWG with $Mn(NO_3)_2$. Conclusively, the addition of $Mn(NO_3)_2$ enhanced all model biomass gasification efficiency and increased the hydrogen production promoting the supercritical water reaction.

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.4
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• pp.297-302
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• 2019

In this paper, the power generation efficiency increase has been studied for a Rankine cycle using both supercritical carbon dioxide as a working fluid and LNG as a coolant with PRO/II with PROVISION release 10.0 from Aveva company. Peng-Robinson equation of the state model with Twu's alpha function was selected for the modeling of the power generation cycle using LNG cold heat. Power generation efficiency was increased from 24.82% to 57.76% when using LNG as a coolant for supercritical carbon dioxide power generation cycle.

• Korean Chemical Engineering Research
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• v.47 no.3
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• pp.281-286
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• 2009

Bitumen extraction and sulfur removal from Athabasca oil sand were conducted using water in sub- and supercritical condition. Bitumen yield in micro reactor was investigated in the pressure range of 15~30 MPa, the temperature of 360 and $380^{\circ}C$ and water density $0.074{\sim}0.61g/cm^3$ for 0~120 min. Bitumen yield increased with reaction pressure irrespective of temperature and dramatically increased in especially supercritical region due to hydrogen formed from water gas shift reaction. Total amount of gas product decreased with reaction pressure but the portion of sulfur and hydrogen increased a little with increasing pressure to 25 and 30 MPa. It is seen that supercritical condition was favourable to the hydrogen formation and sulfur removal. Bitumen yield and sulfur removal from original oil sand reached a maximum 22% and 40% respectively in supercritical condition(the reaction time of 60 min at $380^{\circ}C$ and 25 or 30 MPa).

• Progress in Superconductivity and Cryogenics
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• v.24 no.3
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• pp.62-67
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• 2022

Liquid hydrogen (LH₂) has a higher density than gaseous hydrogen, so it has high transport efficiency and can be stored at relatively low pressure. In order to use efficient bulk hydrogen in the industry, research for the LH₂ supply system is needed. In the high-pressure hydrogen station based on LH₂ currently being developed in Korea, a heat exchanger is used to heat up supercritical hydrogen at 700 bar and 60 K, which is pressurized by a cryogenic high-pressure pump, to gas hydrogen at 700 bar and 300 K. Accordingly, the heat exchanger used in the hydrogen station should consider the design of high-pressure tubes, miniaturization, and freezing prevention. A helical heat exchanger generates secondary flow due to the curvature characteristics of a curved tube and can be miniaturized compared to a straight one on the same heat transfer length. This paper evaluates the heat transfer performance through parametric study on the distance between coils, guide effect, and anti-icing design of helical heat exchanger. The helical heat exchanger has better heat transfer performance than the straight tube exchanger due to the influence of the secondary flow. When the distance between the coils is uniform, the heat transfer is enhanced. The guide between coils increases the heat transfer performance by increasing the heat transfer length of the shell side fluid. The freezing is observed around the inlet of distribution tube wall, and to solve this problem, an anti-icing structure and a modified operating condition are suggested.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.3
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• pp.21-29
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• 2013

Turbulent flow and thermal fields of gaseous hydrogen/liquid oxygen flames at supercritical pressure are investigated by turbulence models. The modified Soave-Redlich-Kwong (SRK) EOS is implemented into the flamelet model to realize real-fluid combustions. For supercritical fluid flows, the modified pressure-velocity-density coupling are introduced. Based on the algorithm, the relative performance of six convection schemes and the predictions of four turbulence models are compared. The selected turbulence models are needed to be modified to consider various characteristics of real-fluid combustions.

• Journal of ILASS-Korea
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• v.15 no.4
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• pp.189-194
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• 2010

This study has been mainly motivated to numerically model the transcritical mixing and reacting flow processes encountered in the liquid propellant rocket engines. In the present approach, turbulence is represented by the extended k-$\varepsilon$ turbulence model. To account for the real fluid effects, the propellant mixture properties are calculated by using SRK (Souve-Redlich-Kwong) equation of state model. In order to realistically represent the turbulence-chemistry interaction in the turbulent non-premixed flames, the flamelet approach based on the real fluid flamelet library has been adopted. Based on numerical results, the detailed discussions are made for the real fluid effects and the precise structure of the transcritical cryogenic liquid nitrogen jet and gaseous hydrogen/liquid oxygen coaxial jet flame.

• Journal of computational fluids engineering
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• v.12 no.4
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• pp.74-84
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• 2007

The flowfield characteristics in a straight rectangular channel have been investigated through a numerical model to analyze the regenerative cooling system that is used in rocket engine cooling. The supercritical hydrogen coolant introduces strong property variations that have a major influence on the developing flow and heat transfer characteristics. Of particular interest is the improved understanding of the physical characteristics of such flows through parametric studies. The approach used is a numerical solution of the full Navier-Stokes equations in the three dimensional form including the arbitrary equation of state and property variations. The present study compares constant and variable property solutions for both laminar and turbulent flow. For laminar flow, the variation of aspect ratio is examined, while for turbulent flow, the effects of variation of channel length and Reynolds number are discussed.