• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.1
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• pp.45-50
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• 2012

The plate fin and tube type of heat exchanger is widely used in air conditioner, and the heat exchanger is assembled by the mechanical expansion of copper tubes and fastening the aluminum fin. The objective of the present study is to investigate how the mechanical expansion of copper tube affects on the heat transfer performance of a plate fin and tube type heat exchanger. This study has been performed by experimental and numerical methods. The numerical and experimental results show that the tube expansion ratio has a influence on the heat transfer performance. Within the tested expansion ratio, the contact pressure shows the peak value and it decreases as the expansion ratio increases. Air-side heat transfer coefficient increases until the expansion ratio reaches 1.23, and then decreases with the similar pattern to the contact pressure. Also, contact heat transfer coefficient shows the maximum when the contact pressure is highest as well as the air-side heat transfer coefficient.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.12
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• pp.996-1003
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• 2002

Heat transfer characteristics were investigated for the falling film flowing down the outside of an electrically heated vertical tube. Water was used for the falling film, and its Reynolds number was varied in the range of 70～500. Because water is heated and evaporated as it flows down, both sensible and latent heat transfer should be considered. The effect of the surrounding air movement was investigated by changing the direction of the air injection; without air injection, parallel-flow, and counter-flow. For all cases, sensible teat transfer rate was almost linearly increased with the increasing film flow rate. It was found that the film heat transfer coefficient was hardly influenced by the parallel air flow. However, the counter-flow of air reduced the heat transfer coefficient, which might be caused by the uneven distribution or flooding of the film. At high heat flux, a sudden change of the film heat transfer coefficient was detected as the film flow rate reached the transition value. It is supposed that this phenomenon was caused by the change in the film flow pattern.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.4
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• pp.570-577
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• 2000

Local heat transfer characteristics inside a hard disk driver(HDD) are investigated in this study. The investigation is considered between disks co-rotating in a cylindrical enclosure. The gap spacing, rotating speed and head-arm positions are mainly considered to understand the flow and heat transfer in the co-rotating disks. The naphthalene sublimation technique is used to determine local heat/mass transfer coefficients on the rotating disk. Flow patterns inside the co-rotating disks are investigated using a Laser Doppler Anemometer (LDA) and also analyzed numerically. The results show that the heat transfer coefficients on the disk changed little with the gap spacing between disks. Heat transfer rates in the outer region increases with increasing rotating Renolds number, but the values normalized by that on a free rotating disk give a similar pattern for the tested cases. The head-arm inserted between the rotating disks destroys the inner region resulting in enhancement of heat transfer in that region.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.7
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• pp.862-872
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• 1997

Ice formation in a horizontal circular cylinder has been studied numerically. From the numerical analysis results, it was found that there were three types of freezing pattern and that freezing phenomenon was affected largely by density inversion and cooling rate. The type of freezing pattern largely depends on the secondary flow which is generated by density inversion. When supercooling energy is released before the development of the secondary flow, the annular ice layer grows. If the energy is released when the secondary flow is considerably developed and the supercooled region is removed to the upper half part of the cylinder, an asymmetric ice layer grows. And if the energy is released after perfect development of the secondary flow, instantaneous dendritic ice formation over the full region occurs. Furthermore, this secondary flow was found to have an effect on heat transfer characteristics. The heat transfer rate becomes small at the instant when the secondary flow is generated, but becomes large with the development of the flow. It's concluded that for the facilitation of heat transfer it is desirable to keep water in liquid phase until the secondary flow is perfectly developed. This study gave an instruction of performance improvement of capsule type ice storage tank.

• Speech Sciences
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• v.15 no.1
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• pp.25-36
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• 2008

Language transfer means that the speaker's first language or previously acquired language influences on the production of the target language. This study aims at examining if there is native language influence on the production of English intonation by Korean speakers. The pitch accent patterns and the values of duration, F0, and intensity of the stressed vowel of the word with emphatic accent in the sentence produced by Korean speakers are compared to those of American English speakers. The results show that when the word receives emphatic accent in the sentence, American English speakers put H* accent on the stressed syllable of the word, but Korean speakers mostly assign high pitch on the last syllable of the word and have LH tonal pattern despite the fact that primary stress does not come on the last syllable within a word. In addition, comparison of the values of duration, F0, and intensity of the stressed vowel of the word with emphatic accent to those of the word with unmarked neutral accent shows that Korean speakers do not realize the intonation of the accented word appropriately because the values decrease even though the word has emphatic accent. This study finds out that there are differences in the production of English intonation of the word with emphatic accent between native speakers of English and Korean speakers, and that there is negative transfer of Korean intonation pattern to the production of English intonation by Korean speakers.

• Phonetics and Speech Sciences
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• v.8 no.4
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• pp.71-78
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• 2016

The purpose of this study is to investigate the effect of Japanese(L1) on the production of Korean accentual phrases(L2). Korean and Japanese have a similar prosodic structure. But different from Korean, Japanese is a pitch accent language. So each word has its own pitch accent. And pitch accents are maintained in the sentence intonation. This difference will have a negative influence on the production of Korean sentence intonation. For this study 4 Korean natives speakers and 10 advanced Japanese learners of Korean participated in the production test. The material analysed constituted 11 Korean sentences, six of which contain formally identical Sino-Korean and Sino-Japanese words. The results show that the initial pitch pattern of Korean accentual phrases was affected by Japanese pitch accent types and this interference was greater for formally identical Sino-Korean and Sino-Japanese words. But besides initial tones of accentual phrase, some positive interference was observed in the internal tonal pattern of accentual phrase. In the phonetic realization, the internal pitch range and initial pitch rising of accentual phrases was greater for Japanese learners of Korean than native speakers of Korean.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.9
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• pp.830-838
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• 2005

The present study investigated the optimization of the absorption performance of the vertical absorber tube with falling film by considering heat and mass transfer simultaneously. Effects of film Reynolds number, geometric parameters by insert device (spring) and flow pattern on heat and mass transfer performances have been also investigated. Especially, effects of coolant flow rate and the flow pattern by geometric parameters has been observed for the total heat and mass transfer rates through both numerical and experimental studies. Based on both predicted values, the optimal coolant flow rate was predicted as 1.98 L/min. The maximum absorption rate of the spring inserted tube was increased by the maximum of $20.0\%$ than those for uniform film of bare tube. Average Sherwood numbers and Nusselt numbers were increased as Reynolds numbers increased under the dynamic and geometric conditions showing the maximum absorption performance.

• Speech Sciences
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• v.12 no.4
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• pp.113-128
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• 2005

The underlying premise of this study was that L1 production is easily transferred into L2 production. In neutral intonation, there is a consonant-tone correlation in Korean: High tone patterns are correlated with voiceless aspirated and tense consonants and Low-High tone patterns are correlated with lax or other voiced consonants. The purpose of this study was to see whether the correlation in Korean (L1) is transferred into English (L2) production and whether the degree of transfer differs depending on the degree of proficiency. Eight Korean speakers and two American speakers participated in the experiment. F0 contours of words and sentences were collected and analyzed. The results of the present study showed that there is a strong correlation between voicing and tone in L2 utterances. When utterance-initial consonant types were voiceless, the word or the sentence began with the H pattern; otherwise it had the LH pattern. The degree of interference differed depending on the degree of proficiency: less proficient speakers showed a stronger correlation in terms of the magnitude (Hz) and size (ms) of the effects on F0. The results indicate that the consonant-tone correlation in L1 is strongly transferred into L2 production and the correlation transfer can be one of the actual aspects that cause L2 speakers to produce deviant L2 accents and intonation.

• Journal of Advanced Marine Engineering and Technology
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• v.15 no.2
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• pp.64-72
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• 1991

The unsteady, two-dimensional laminar flow and heat transfer of an incompressible, constant-property fluid flowing around a circular cylinder are numerically analyzed. The Navier-Strokes equation and the energy equation are solved by the finite difference method. The range of the Reynolds number is 10 to 100 and the Prandtl number considered is 0.7. The contours of the flow pattern, equi-vorticity line and isotherm pattern around a circular cylinder are shown. Also, numerical solutions of the surface vorticity, pressure coefficient, drag coefficient, local Nusselt number and mean Nusselt number are obtained. The numerical results for the final time fo calculation are compared with the other available experimental and theoretical results for the steady state and are found to be in good agreement with them.

• Journal of Embryo Transfer
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• v.11 no.3
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• pp.317-321
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• 1996

본 연구는 수정능획득유기물질로 알려진 카페인 헤파린을 병행처리하여 한우 정자의 첨체 반응율과 생존율을 알아보고 수정능획득과정 중에 단백질의 변화상을 전기영동방법으로 조사하였다. 동결융해후 정자의 생존율은 90%이상이었으나 전배양처리후 0.5시간에 70%로 감소하고 2시간 이후에는 35%로 감소하였다. 정자의 첨체반응율은 동결융해후 정상정자가 85.7%였으나 전배양시간에 따라 53.4%에서 14.3%로 감소하였다. 동결융해후 첨체가 소실된 생존정자는 9.4%였으나 전배양시간에 따라 17.2%에서 46.8%로 증가하였다. 원정액에서는 분자량 20,000정도에서 동결융해후 전자보다 특이적으로 많은 단백질량을 나타내었으나 동결융해 후 정자를 0.5에서 2.0시간으로 전배양하였을 때 전배양시간에 따른 단백질상의 변화는 대조구와 큰 차이가 없었다.