• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.602-611
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• 2001

Experiments on the condensation heat transfer characteristics inside a smooth and a microfin tube with R410A/R22 are performed in this study. The test tubes 7/9.52 mm in outside diameters and 3m in length are used. Varying the mass flux of the refrigerant and the condensation temperatures, the average heat transfer coefficients and pressure drop are investigated. Most flows in this study are in the annular and/or wavy flow regime. It is shown that the heat transfer is enhanced and the pressure drops are larger in the microfin tube than the smooth tube. From the heat transfer enhancement coefficients and the pressure drops, it is found that the high heat transfer enhancement factors are obtained in the range of small mass flux while the penalty factors are almost equal. Experiments results show that average heat transfer coefficients of R410A is larger than that of R22 and pressure drop of R410A is less than R22.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.7
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• pp.667-673
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• 2000

In order to understand the laminar flow heat transfer enhancement by the swirl flow, the effects of heat transfer in a circular pipe with a twisted tape insert were investigated experimentally. In the present study, the uniform heat flux condition was considered. The laminar heat transfer correlations were developed using the least-square-fit from the surface temperature distribution of an electrically-heated pipe and flow property data. Average Nusselt number correlations with the twisted tape insert were expressed as a function of swirl parameter, Reynolds number and Prandtl number. In the case of the twisted ratio y = 6.05, the mean Nusselt number increased approximately 500% and the friction factor increased approximately 300%, compared to the case of the empty pipe, respectively.

• Journal of the Korean Society of Industry Convergence
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• v.4 no.4
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• pp.395-401
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• 2001

The characteristics of heat transfer and pressure drop through tubes has been investigated experimentally for a compound heat transfer enhancement. The test tubes were spirally indented tubes with wire coil inserts which had a various combinations of pitch and helix angles. Pure water was used as working fluids for the experiments, Heat transfer coefficients and friction factors of the test tubes were evaluated from the values of measured temperatures, flow rates and pressure drops. An performance evaluation was performed to find an optimal combination of spirally indented tubes with wire coil inserts. When the helix angle of wire coil insert are $71^{\circ}-72^{\circ}$, the best heat transfer enhancement was shown. The friction factor was 9 - 13 times higher than those in smooth tubes, and the heat transfer was enhanced a maximum of 500%.

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.2
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• pp.36-43
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• 2001

In order to understand the laminar heat transfer enhancement by swirl flow, the effects of heat transfer in a circular pipe with twisted inserts are investigated experimentally. In the present study, a uniform heat flux condition is considered. Laminar heat transfer correlations are developed using least square fit method from surface temperature distributions of an electrically-heated pipe and flow properties. Average Nusselt number correlations with twisted inserts are expressed as a function of swirl parameter, Reynolds number and prand시 number. When the twisted ratio is 6.50, mean Nusselt number and friction factor increase by approximately 500% and 300%, respectively, compared with the values for a pipe without inserts.

• Journal of Audiology & Otology
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• v.25 no.4
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• pp.230-234
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• 2021

Otosclerosis, a hereditary disorder characterized by disordered resorption and deposition of bone, results in progressive hearing loss. Osteogenesis imperfecta (OI) is a genetic disorder characterized by recurrent fractures, blue sclera, and varying degrees of hearing impairment; and is a known risk factor for otosclerosis. After adolescence, the risk of fracture decreases, reducing the need for follow-up in OI. However, otosclerosis is a progressive disorder. In this report, we discuss two cases of familial otosclerosis with different clinical features. We hypothesize that the difference in hearing level correlates with the difference in computed tomography findings. The mother, whose case was considered severe, was prescribed hearing aids, while the daughter, who had normal hearing level, was regularly followed up.

• Korean Journal of Audiology
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• v.25 no.4
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• pp.230-234
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• 2021

Otosclerosis, a hereditary disorder characterized by disordered resorption and deposition of bone, results in progressive hearing loss. Osteogenesis imperfecta (OI) is a genetic disorder characterized by recurrent fractures, blue sclera, and varying degrees of hearing impairment; and is a known risk factor for otosclerosis. After adolescence, the risk of fracture decreases, reducing the need for follow-up in OI. However, otosclerosis is a progressive disorder. In this report, we discuss two cases of familial otosclerosis with different clinical features. We hypothesize that the difference in hearing level correlates with the difference in computed tomography findings. The mother, whose case was considered severe, was prescribed hearing aids, while the daughter, who had normal hearing level, was regularly followed up.

• Journal of Family Resource Management and Policy Review
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• v.14 no.2
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• pp.109-126
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• 2010

This study set out to investigate if work-family conflict and work-family enhancement would have mediating effects on the impact of gender role attitudes of women from double income households on their satisfaction of work and marriage. A structural modelof gender role attitudes was set as the independent variable, work-family conflict and work-family enhancement as the mediating variables, and work satisfaction and marriage satisfaction as the dependent variables. The subjects consisted of 2,713 married women from double income households and information was obtained from the first year data of the Korean Longitudinal Survey of Women and Families (KLoWF) collected by the Korean Women's Development Institute (KWDI). Using SPSS 15.0 software, descriptive statistics were gathered, and frequency and factor analyses were conducted. AMOS 7.0 software was used to analyze both the measurement model and the structural model. The results indicate that work-family conflict and work-family enhancement had partial mediating effects on the impacts of gender role attitudes on work and marriage satisfaction among women from double income households. Notably, work-family enhancement had a greater effect than work-family conflict, which suggests that the elements of work-family enhancement, which are the positive aspects of work on family and family on work, should be promoted. It is, however, also important to make efforts to resolve work-family conflict by increasing the satisfaction level of work and marriage among women from double income households.

• Journal of electromagnetic engineering and science
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• v.10 no.3
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• pp.86-91
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• 2010

In this paper, a double-layered frequency selective surface(FSS) superstrate was built and tested. The unit cell of the proposed FSS consists of a ring slot and a dipole-shaped structure and shows a complementary frequency response. Each unit cell is printed on two sides of a substrate. By using these double-layered structures, the first resonant frequency of the pass-band can be lowered. As a result, the size of the unit cell is minimized and the spacing between the other cells is reduced. The proposed FSS-dipole composite antenna is designed for the gain enhancement of wide-band code division multiple access(WCDMA) frequency bands(1.92~2.17 GHz) with a low quality factor(Q=0.17). To verify the gain enhancement performance of the FSS, an FSS-dipole composite antenna was created. Although the FSS layer enhances the gain of the primary radiation source of the dipole antenna, the FSS-dipole complex antenna cannot show a uniform gain over the entire desired frequency band. The experimental results show a gain enhancement of 3 dBi with an FSS superstrate in the WCDMA frequency band.

• Journal of Welding and Joining
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• v.33 no.4
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• pp.50-56
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• 2015

In general, discontinuity of metallurgical and structural points of weld zone could decline the fatigue strength. For the lightweight trend, the AHSS application in automotive chassis is in-progress. However, there are few research reports on AHSS welds fatigue strength in especially automotive chassis parts. Therefore, in this study, we evaluated the effects of the factors affecting the AHSS welding fatigue strength. As the result, the stress concentration of weld bead is the most important factor for welding fatigue strength. For the enhancement of welding fatigue strength, we focused on reducing the stress concentration of the welding beads. So, we applied and proved the plasma welding process and GTAW (Gas Tungsten Arc Welding) dressing method. It was verified by uniaxial fatigue specimen, fatigue performance increased from 40 to 60% by applying TIG dressing method compared to the conventional GMAW (Gas Metal Arc Welding). These results could be recommended the enhancement of fatigue performance of AHSS.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.14 no.2
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• pp.8-14
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• 2018

A boiling heat transfer is used in various industry such as power generation systems, heat exchangers, air-conditioning and refrigerations. In the boiling heat transfer system, the critical heat flux (CHF) is the important factor, and it indicated safety of the system. It has kept up studies on the CHF enhancement. Recently, it is reported the CHF enhancement, when working fluid used the nanofluid with excellent thermal properties. Therefore, in this study, we investigated the influence of nano particles coated surface for heat transfer enhancement in pure water, oxidized multi-wall carbon nanotube nanofluid (OMWCNT), and oxidized graphene nanofluid (OGraphene). Nanoparticles were coated for 120 sec on the surface, and we measured the CHF at the flow velocities of 0.5, 1.0, and 1.5 m/sec, respectively. As the results, both of the OMWCNT and OGraphene nanofluids increased up to about 34.0 and 40.0%.