• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.2
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• pp.254-266
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• 1996

Boiling heat transfer coefficients of pure refrigerants(R22, R32, R125, R134a, R290, and R600a) and refrigerant mixtures(R32/R134a and R290/R600a) are measured experimentally and compared with several correlations. Convective boiling term of Chen's correlation predicts experimental data for pure refrigerants fairly well(root-mean-square error of 12.1% for the quality range over 0.2). An analysis of convective boiling heat transfer of refrigerant mixtures is performed for an annular flow to study degradation of heat transfer. Annular flow is the subject of this analysis because a great portion of the evaporator in refrigeration or air conditioning system is known to be in the annular flow regime. Mass transfer effect due to composition difference between liquid and vapor phases, which is considered as a driving force for mass transfer at interface, is included in this analysis. Correction factor $C_F$ is introduced to the correlation for the pure substances through annular flow analysis to apply the correlation to the mixtures. The flow boiling heat transfer coefficients are calculated using the correlation considering nucleate boilling effect in the low quality region and mass transfer effect for nonzazeotropic refrigerant mixtures.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.907-910
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• 2008

The wheel radiation noise characteristic of Korean tilting train(Hanvit 200) on curved rail under the field test conditions is analyzed in this paper. The test railroad track was selected from Seodaejon to Songjeongri in Honam line. $5^{th}$ and $6^{th}$ car are decided to measure radiation noise level among a train of six cars. The test subject curve radius executed from R400, R500, R600, R700 and R800 segments. The speed of test trains when from R600 and R800 curves existing operation speed and speed up 20% of existing speed. On curved rail at the time of operation speed of Hanvit 200 trains from below 95km/h wheel radiation noise level at $94dBA{\sim}99dBA$, the operation speed from between $100km/h{\sim}144km/h$ wheel radiation noise level at $100dBA{\sim}106dBA$.

• The Korean Journal of Zoology
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• v.6 no.2
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• pp.11-15
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• 1963

A total of 220 adult male mice (18-20g) of the S.M. strain were divided into ten experimental and control groups. The total-body X-ray irradiation doses used were 50 r, 100r, 200r, 400r, 600r, 800r, 1,000r, 1,200r, 1,400r, and1,600r. The respiratory arrest (mortality) caused by each irradiation doses were observed for 30 days. Relationships between irradiation doses and survival time and percentage of response were examined. From this experiment, a formula was obtained to express the relationship among three factors, which may be presented as follows : {{{{{{{{P= { 10} over { SQRT { 2 pi } } INT _{ - INF }^{ p'} e-{(p'-50)^2 } over {200 }dp···(a) p'=100 LEFT { t^0.3- LEFT ( { { 16.9965} over {D-60 } } RIGHT ) ^{ { 1} over {2.5 } } } / LEFT { LEFT ( { 26372.43} over {D-81.86 } RIGHT ) ^{ { 1} over {2.5 } } -( { { 16.9965} over {D-60 } } RIGHT ) ^{ { 1} over {2.5 } } ···(b) p= { (D-60) t^0.75-16.9965} over {0.2186 t^0.75 +263.55434 }····(c) }} {{{{P= { 10} over { SQRT { 2 pi } } INT _{ - INF }^{ p'} e-{(p'-50)^2 } over {200 }dp···(a) p'=100 LEFT { t^0.3- LEFT ( { { 16.9965} over {D-60 } } RIGHT ) ^{ { 1} over {2.5 } } } / LEFT { LEFT ( { 26372.43} over {D-81.86 } RIGHT ) ^{ { 1} over {2.5 } } -( { { 16.9965} over {D-60 } } RIGHT ) ^{ { 1} over {2.5 } } ···(b) p= { (D-60) t^0.75-16.9965} over {0.2186 t^0.75 +263.55434 }····(c)

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.110-110
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• 2018

여러 니켈합금 중 인코넬 600은 원전 가압경수로(PWR)의 튜브 재료로 널리 사용되는 재료이다. 스테인리스강과 비교하여 우수한 내식성과 기계적 특성으로 인해 화학설비, 발전설비, 그리고 해양설비 등과 같은 여러 산업분야에서도 널리 사용되고 있다. 그러나 가압경수로용 증기 발생기의 튜브 재료와 같은 특수 환경에서 예민화에 따른 입계부식 및 입계응력부식 등의 문제가 흔히 보고되고 있다. 이러한 내구성 문제는 설비 및 장비의 수명, 내구성 그리고 안정성 등의 치명적인 영향을 미친다. 따라서 용접, 열처리, 그리고 가공과정에서 발생하는 Inconel 600의 예민화 및 입계부식에 관한 연구가 활발히 진행되고 있다. 그러나 100시간 이상 장시간 열화된 시편에 대한 예민화 연구는 전무한 실정이다. 본 연구에서는 장시간 열화된 Inconel 600의 예민화를 평가하기 위해 최대 1,000시간까지 열화를 실시하였으며, 이에 대한 평가방법으로 Double-Loop Electrochemical Potentiokinetic Reactivation(DL-EPR) 시험법을 적용하였다. 본 실험에서 사용된 인코넬 600의 화학성분(wt, %)은 0.01 C, 0.05 Si, 0.14 Mn, 15.3 Cr, 0.5 Cu, 0.015 S, 그리고 나머지는 Ni 이다. 예민화 평가를 위한 등온 열화는 전기열처리로를 이용하여, $550^{\circ}C$와 $650^{\circ}C$에서 최대 1000시간까지 실시하였다. 열화에 따른 미세조직 변화는 scanning electron microscope와 energy dispersive x-ray spectroscopy를 이용하여 실시하였다. DL-EPR 실험은 $25^{\circ}C$의 0.1M $H_2SO_4$ + 0.001M KSCN(potasium thiocyanate) 수용액 하에서 실시하였으며, 분극은 OCP로부터 600 mV(SSE vs.)까지 1.67mV/s 주사속도로 forward scan을 실시 후, 동일한 속도로 OCP까지 reverse scan을 실시하였다. Degree Of Sensitization(DOS)값은 anodic scan peak($I_a$) 값과 reverse scan peak($I_r$) 값의 비로 산출하였다. $$i.e.\;DOS=I_r/I_a{\times}100$$. 그 결과, 온도 변수에 따른 Inconel 600강의 예민화 거동은 서로 상이한 경향을 나타내었다. $550^{\circ}C$의 경우, 열화가 진행됨에 따라 DOS값은 급격하게 증가하는 경향을 나타냈다. 반면, $650^{\circ}C$에서는 일정시간 이후부터 Cr 확산 현상에 의한 탈 예민화 현상이 관찰되었다.

• Journal of Power System Engineering
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• v.12 no.3
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• pp.19-25
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• 2008

This paper deals with the heat transfer and pressure drop characteristics of R-290 (Propane), R-600a (Iso-butane) and R-1270 (Propylene) as an environment friendly refrigerant and R-22 as a HCFC's refrigerant for condensing. The test section is a horizontal double pipe heat exchanger. Condensing heat transfer and pressure drop measurements were Peformed for 12.70 mm micro-fin tube and compared with the results in smooth tube. The local condensing heat transfer coefficients of hydrocarbon refrigerants were superior to those of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-600a. The average condensing heat transfer coefficients in hydrocarbon refrigerants showed 20 to 28% higher values than those of R-22. Hydrocarbon refrigerants have a higher pressure drop than that of R-22 with respect to refrigerant qualify and mass flux. Also, the condensing heat transfer coefficient and pressure drop of working fluids in smooth and micro-fin tube were compared. The heat transfer enhancement factor (EF) between smooth and micro-fin tube varied from 2.2 to 2.6 in all experimental conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.2 s.233
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• pp.271-278
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• 2005

In this paper, the performance of Kim-chi refrigerator with three evaporator and one compressor was investigated in employing $55\%$ propane and $45\%$ isobutane (R290/R600a) refrigerant mixture as an alternative refrigerant of R134a. The drop-in test was performed by varying both refrigerant charge and capillary tube length in order to find both the performance and reliability of a small multi-refrigeration system. Results show that the power consumption is decreased by about $15\%$ and COP is increased by about $10\%$, respectively as compared to the baseline system using R-134a. In addition, the propane/isobutane refrigerant mixture system took advantage of the minimization of modification and redesigning of system components because thermodynamic properties such as saturation pressure, temperature, normal boiling point(NBP) characteristics are similar to those of R134a. The reduction of sales cost is caused by the decrease of refrigerant cost per unit mass and refrigerant charge amount necessary for the refrigeration system.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10b
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• pp.185-190
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• 1993

The POSTECH Hand adopting coupled tendon driven technique with planar two fingers is developed. The hand is designed to emulate principal motions of the human hand which has two and three joints respectively. Its kinematic parameters are determined through a parameter optimizing technique to aim at improving the isotropy of fingertip motions with new criterion functions of design. For the control of the hand, tension and torque control algorithms are developed. Based on the virtual stiffness concept, we develop the stiffness control method of a grasped object with redundant finger mechnism and investigate experimentally.

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.743-751
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• 2012

This paper investigates an experimental behavior of circular columns and beam-columns made of HSB600 high strength steel as a fundamental study to enhance the applicability of HSB steel. The applicability of the current Standard such as KBC and Eurocode 3 is also evaluated. A total of six specimens are fabricated and tested. The main parameters are slenderness ratio(KLe/r = 12, 14, 40, 65), diameter-to-thickness ratio(D/t = 25, 40), and eccentricity ratio(e/D = 0, 0.5). It is drawn from the experiment that both the KBC and Eurocode 3 can be used to predict the strength of circular columns and beam-columns made of HSB600 high strength steel.

• Journal of the Korea Institute of Building Construction
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• v.17 no.3
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• pp.269-277
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• 2017

In this work, as a preliminary experimental works, which focuses on utilizing separated pastes from activated (or radioactive) concrete as solidifying agents for radioactive waste immobilization, were performed. It was found that density of hydrated cement paste, which was lower than that of ordinary portland cement, increased as temperature for heat treatment increased. Highest compressive strength was observed with the specimens that was heat treated at $600^{\circ}C$. However, heat treatment over $700^{\circ}C$ showed higher CaO content that caused higher heat of hydration after in contact with water, lows of workability, and lower strength. Based on experimental results, it is suggested that $600^{\circ}C$ heat treatment is more appropriate for waste cement paste to be used as a solidifying agent.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.6
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• pp.1017-1022
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• 2020

LTE-R(Long Term Evolution-Railway) for high speed railway system operation as an essential technology is based on LTE. Recently, moving speed of high speed train is on going to 600[km/h] level over commercial speed 400[㎞/h]. LTE-R as communication technology for a high speed railway system can be able to provide seamless communication to support moving speed for high speed railway system. In this study, a handover method based on prediction is suggested and performance of the suggested method is evaluated. Computer simulation based on NS(Network Simulator)-3 is used for this study.