• Journal of Mechanical Science and Technology
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• v.14 no.5
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• pp.537-546
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• 2000

The heat transfer characteristics of refrigerant-oil mixture for horizontal in-tube evaporator have been investigated experimentally. A smooth copper tube and a micro-fin tube with nominal 9.5 mm outer diameter and 1500 mm length were tested. For the pure refrigerant flow, the dependence of the axial heat transfer coefficient on quality was weak in the smooth tube, but in the micro-fin tube, the coefficients were 3 to 10 times greater as quality increases. Oil addition to pure refrigerant in the smooth tube altered the flow pattern dramatically at low mass fluxes, with a resultant enhancement of the wetting area by vigorous foaming. The heat transfer coefficients of the mixture for low and medium qualities were increased at low mass fluxes. In the micro-fin tube, however, the addition of oil deteriorates the local heat transfer performance for most of the quality range, except for low quality. The micro-fin tube consequently loses its advantage of high heat transfer performance for an oil fraction of 5%. Results are presented as plots of local heat transfer coefficient versus quality.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.57-64
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• 2000

The present work investigates the heat transfer characteristics for laminar fully developed forced convection in an internally finned tube with axially uniform heat flux and peripherally uniform temperature through analytical models of convection in a porous medium. Using the Brinkman-extended Darcy flow model and the two equation model fur heat transfer, analytical solutions fur fluid flow and heat transfer are obtained and compared with the exact solution for fluid flow and the numerical solutions for conjugate heat transfer to validate the porous medium approach. Using the analytical solutions, parameters of engineering importance are identified and their effects on fluid flow and heat transfer are studied. Also, the expression fur total thermal resistance is derived from the analytical solutions and minimized in order to optimize the thermal performance of the internally finned tubes.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.501-501
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• 2012

A 2.45 GHz electron cyclotron resonance (ECR) plasma source with a belt magnet assembly configuration (BMC) was developed for hyperthermal neutral beam (HNB) generation. A plasma source for high flux HNB generation should be satisfied with the requirements: low pressure operation, high density, and thin plasma. The ECR plasma source with BMC achieved high density at low operation pressure due to electron confinement enhancement caused by high mirror ratio and drifts in toroidal direction. The 2.45 GHz microwave launcher had a circularly bended WR340 waveguide with slits. The microwave E-field profile induced by the microwave launcher was studied in this paper. The E-field profile was a cups field perpendicular to B-filed at ECR zone. The optimized E-field profile and B-field were found for effective ECR heating.

• Analytical Science and Technology
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• v.16 no.5
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• pp.426-429
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• 2003

Neutron induced prompt gamma-ray spectroscopy (NIPS) system equipped with a $^{252}Cf$ neutron source and a n-type coaxial HPGe detector was installed for the quantitative analysis of aqueous samples in KAERI, Korea. Since the thermal neutron flux for the $^{252}Cf$ neutron source is relatively low compared to that for the reactor, the use of a thermal neutron reflector in the NIPS system may lead to improved results. The enhancement by using various reflectors was carried out by comparing the Cl peak with or without a cadmium plate between sample and the $^{252}Cf$ source. The use of pyrolitic graphite as a reflector provided a good result.

• Journal of ILASS-Korea
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• v.14 no.4
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• pp.178-183
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• 2009

Spray cooling heat transfer was experimentally investigated for water sprays impacting on mico-fins structured surfaces in the single phase and nucleate boiling regions. The heat transfer surfaces consist of cubic fins and triangular grooved fins. The spray produced using full cone spray nozzles, and experiments were made under the test condition of $Q=4.92{\times}10^{-6}{\sim}15.83{\times}10^{-6}\;m^3/s$, $T_f=35{\sim}55^{\circ}C$. From the experimental results, it was found that cubic fins surface had the largest heat flux enhancement relative to the smooth surface.

• Nuclear Engineering and Technology
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• v.43 no.3
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• pp.217-242
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• 2011

A variety of Generation III/III+ water-cooled reactor designs featuring enhanced safety and improved economics are being proposed by nuclear power industries around the world in efforts to solve the future energy supply shortfall. Thermal-hydraulics is recognized as a key scientific subject in the development of innovative reactor systems. Phase change by boiling and condensation in the reverse process is a highly efficient heat transport mechanism that accommodates large heat fluxes with relatively small driving temperature differences. This mode of heat transfer is encountered in a wide spectrum of nuclear systems,and thus it is necessary to determine the thermal limit of water-cooled nuclear energy conversion in terms of economic and safety. Such applications are being advanced with the introduction of new technologies such as nanotechnology. Here, we investigated newly-introduced nanotechnologies relevant to boiling and condensation in general engineering applications. We also evaluated the potential linkage between such new advancements and nuclear applications in terms of advanced nuclear thermal-hydraulics.

• Journal of the Korean institute of surface engineering
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• v.25 no.6
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• pp.299-308
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• 1992

Titanium nitride(TiN) has been synthesized by nitrogen ion irradiation onto the Ti thin film deposited on STD11 and SKH9 tool materials. The effect of irradiation flux and substrate temperature on the formation behavior and mechanical properaties of TiN were investigated through X-ray diffraction analysis, hardness and pin-on-disc wear testings. Nitrogen ion irradiation onto arc evaporated Ti thin film produced TiN of < 200> orientation at elevated temperature and thereby enhancing surface microhardness by 50% at maximum. Wear resistance was also improved by nitrogen irradiation at most process conditions. The enhancement of wear resistance appeared to be more effective for the nitrogen irradiated conditions at room temperature than at elevated temperature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1267-1276
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• 1998

Falling-film evaporation experiments with aqueous lithium bromide (LiBr) solution were performed to investigate the heat transfer characteristics of enhanced copper tubes. Enhanced tubes (a knurled tube, a spirally grooved tube, and a tube coated with $20{\mu}m$ aluminum particles) and a bare tube were selected as test specimens. Averaged evaporation fluxes of water were obtained from horizontal tubes with various film Reynolds numbers, system pressures, LiBr concentrations and degrees of wall superheat. The enhanced performance of steam generation was compared between tubes with varying parameters. The knurled tube geometry showed the most excellent performance among the tubes tested. The specified enhanced tubes were more useful for generating steam on a low grade heat source such as waste heat.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.229-234
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• 2007

Microscale heat transfer and microfluidics have become increasingly important to overcome some very complex engineering challenges. The use of very small passages to gain heat transfer enhancement is a well documented method for achieving high heat flux dissipation. As the passage size is decreased, the heat transfer performance increases but the pressure drop increases sharply when the passage size is reduced. In this study, the performance evaluation of micro plated heat exchangers under the counter flows with straight, V-shaped and Y-shaped channel are carried out.

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.4
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• pp.163-168
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• 2007

The feature of six existing condensation heat transfer correlations for microfin tubes were evaluated with the consideration of vapor quality, mass flux, geometries, and various refrigerants. The Kosky and Staub [15] and the Jaster and Kosky [16] correlations for smooth tube were used for the evaluation of the heat transfer enhancement factor (EF). For the prediction of zeotropic mixtures, most correlations show discrepancy with previous measurements. The Yu and Koyama [4] and the Shikazono et al. [8] correlations do not consider spiral angle effect. The Han and Lee [10] correlation shows fin height growth deteriorates heat transfer. Experimental verification to develop reliable condensation heat transfer correlation for microfin tubes is still needed with the consideration of geometrical effects and working conditions.