• Proceedings of the Korean Society of Embryo Transfer Conference
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• 1997.10a
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• pp.51-51
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• 1997

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.2094-2099
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• 2004

An experimental study on heat transfer characteristics near the critical pressure has been performed with an internally-heated vertical annular channel cooled by R-134a fluid. Two series of tests have been completed: (a) steady-state critical heat flux (CHF) and (b) heat transfer tests for pressure reduction transients through the critical pressure. In the present experimental range, the steady-state CHF decreases with the increase of the system pressure For a fixed inlet mass flux and subcooling, the CHF falls sharply at about 3.8 MPa and shows a trend toward converging to zero as the pressure approaches the critical point of 4.059 MPa. The CHF phenomenon near the critical pressure does not lead to an abrupt temperature rise of the heated wall because the CHF occurred at remarkably low power levels. In the pressure reduction transient experiments, as soon as the pressure passed through the critical pressure, the wall temperatures rise rapidly up to a very high value due to the occurrence of the departure from nucleate boiling. The wall temperature reaches a maximum at the saturation point of the outlet temperature, then tends to decrease gradually.

• Nuclear Engineering and Technology
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• v.36 no.5
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• pp.403-414
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• 2004

An experimental study of heat transfer characteristics near the critical pressure has been performed with an internally-heated vertical annular channel cooled by R-134a fluid. Two series of tests have been completed: (a) steady-state critical heat flux (CHF) tests, and (b) heat transfer tests for pressure reduction transients through the critical pressure. In the present experimental range, the steady-state CHF decreases with increase of the system pressure for fixed inlet mass flux and subcooling. The CHF falls sharply at about 3.8 MPa and shows a trend towards converging to zero as the pressure approaches the critical point of 4.059 MPa. The CHF phenomenon near the critical pressure does not lead to an abrupt temperature rise of the heated wall, because the CHF occurs at remarkably low power levels. In the pressure reduction transients, as soon as the pressure passes below the critical pressure from the supercritical pressure, the wall temperatures rise rapidly up to very high values due to the departure from nucleate boiling. The wall temperature reaches a maximum at the saturation point of the outlet temperature, and then tends to decrease gradually.

• Membrane Journal
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• v.8 no.3
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• pp.138-147
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• 1998

This paper compared selectivities and mass transfer rates of valuable aromatics (naphthalene group: carbon number 10-12) in the light cycle oil obtained from solvent extraction (SE) with those obtained from liquid membrane permeation (LMP). An aqueous solution of dimethylsulfoxide (DMSO) and an aqueous solution of saporrin and DMSO were used as extraction solvent of SE and the membrane phase of LMP, respectivdy. Selectivities of naphthalene group in reference to n-nonane obtained from SE runs were rapidly increased with decreasing the operating temperature, whereas, those obtained from LMP runs were remained constant throughout the operating temperature. At room temperature, selectivities of naphthalene group obtained from SE were greater than those from SE. Furthermore, mass transfer rates of naphthalene group by SE and LMP were measured in a baffled batch stirred vessel. It was found that the extraction rates of SE were faster by about 280 times than the permeation rates of LMP.

• Nuclear Engineering and Technology
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• v.34 no.4
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• pp.269-285
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• 2002

Water heat transfer experiments were carried out in a uniformly heated annulus with a wide range of pressure conditions. The local heat transfer coefficients for saturated water (low boiling have been measured just before the occurrence of the critical heat flux (CHF) along the length of the heated section. The trends of the measured heat transfer coefficients were quite different from the conventional understanding for the heat transfer of saturated flow boiling. This discrepancy was explained from the nucleate boiling in the liquid film of annular flow under high heat flux conditions. The well-known correlations were compared with the measured heat transfer coefficients. The Shah and Kandlikar correlations gave better prediction than the Chen correlation. However, the modified Chen correlation proposed in the present work showed the best agreement with the present data among correlations examined .

• Journal of Environmental Science International
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• v.32 no.1
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• pp.57-65
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• 2023

The advanced oxidation treatment using persulfate and zero-valent iron (ZVI) has been evaluated as a very effective technology for remediation of soil and groundwater contamination. However, the high rate of the initial reaction of persulfate with ZVI causes over-consumption of an injected persulfate, and the excessively generated active species show a low transfer rate to the target pollutant. In this study, ZVI was modified using selenium with very low reactivity in the water environment with the aim of controlling the persulfate activation rate by controlling the reactivity of ZVI. Selenium-modified ZVI (Se/ZVI) was confirmed to have a selenium coating on the surface through SEM/EDS analysis, and low reductive reactivity to trichlroethylene (TCE) was observed. As a result of inducing the persulfate activation using the synthesized Se/ZVI, the persulfated consumption rate was greatly reduced, and the decomposition rate of the model contaminant, anisole, was also reduced in proportion. However, the final decomposition efficiency was rather increased, which seems to be the result of preventing persulfate over-consumption. This is because the transfer efficiency of the active species (SO4-∙) of persulfate to the target contaminant has been improved. Selenium on the surface of Se/ZVI was not significantly dissolved even under oxidation conditions by persulfate, and most of it was present in the form of Se/ZVI. It was confirmed that the persulfate activation rate could be controlled by controlling the reactivity of ZVI, which could greatly contribute to the improvement of the persulfate oxidation efficiency.

• 한국기계연구소 소보
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• s.14
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• pp.3-15
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• 1985

• Computational Structural Engineering
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• v.21 no.4
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• pp.46-54
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• 2008

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.330-336
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• 2001

Water heat transfer experiments were carried out in a uniformly heated annulus with a wide range of pressure conditions. The local heat transfer coefficients for saturated water flow boiling have been measured just before the occurrence of the critical heat flux (CHF) along the length of the heated section. The trends of the measured heat transfer coefficients were quite different from the conventional understanding for the heat transfer of saturated flow boiling. This discrepancy was explained from the nucleate boiling in the liquid film of annular flow under high heat flux conditions.

• Journal of Welding and Joining
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• v.17 no.1
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• pp.62-70
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• 1999

Since various parameters including the welding conditions and material properties are involved in metal transfer, it is difficult to figure out the effects of each parameter. In this study, dimensional analysis in performed to reduce the number of the parameters and to reveal the effect of each parameter on metal transfer. Dimensionless parameters are derived based on the inertia force and surface tension, and their contributions on metal transfer are estimated by analyzing the calculated results using the volume of fluid (VOF) method. Among several dimensionless parameters, $N_{SE}(=$\mu$_{0}I^{2}/d_{w}${\gamma}$)$ which represents the ratio of the electromagnetic force to surface tension, is found to be appropriate to describe metal transfer and estimate the transition current. Predicted results of transition current and drop size are in reasonably good agreements with available experimental date which show the validity of proposed dimensional analysis.