수평미세관내 이산화탄소의 비등열전달 특성

최광일(Kwang-Il Choi),A. S. Pamitran(A. S. Pamitran),오종택(Jong-Taek Oh) 대한설비공학회 2003 대한설비공학회 학술발표대회논문집 Vol.2003 No.-

미세관내 NH₃의 압력강하 및 비등열전달

최광일(Kwang-Il Choi),M. Rifaldi,오종택(Jong-Taek Oh),Kiyoshi Saito,정종수(Jong Soo Jeong) 대한설비공학회 2010 대한설비공학회 학술발표대회논문집 Vol.2010 No.11

An experimental study for convective boiling heat transfer was conducted with NH₃ in horizontal smooth minichannels. The test section is made of stainless steel tubes with inner diameters of 1.5 ㎜ and 3.0 ㎜, the length 2000 ㎜ each. The minichannels are uniformly heated by engaging an electric current directly to the test section; all components are well insulated to prevent heat losses. Pressure drop and local heat transfer coefficients were obtained for a heat flux range of 10-80 ㎾/㎡, a mass flux range of 50-800 ㎏/㎡s, saturation temperatures of 0, 5, and 10℃ and quality ranges of up to 1.0. Nucleate boiling heat transfer contribution was predominant, especially at low quality region. The effects of mass flux, heat flux, and inner tube diameter, on pressure drop and heat transfer coefficient are presented. The experimental results are compared against several existing correlations. A new boiling heat transfer coefficient correlation for NH3 was developed with 9.79% MD and -3.57% AD.

수평 마이크로핀튜브 관내 R-410A 응축열전달 특성

최광일(Kwang-Il Choi),Pham Quang Vu,오종택(Jong-Taek Oh),조홍기(Honggi Cho),김태현(Taehun Kim),김중호(Jungho Kim),이창선(Changseon Lee) 대한설비공학회 2013 대한설비공학회 학술발표대회논문집 Vol.2013 No.11

An experimental investigation of condensation heat transfer of R410A was carried out for horizontal micro-fin tubes of 6.61 mm and 7.45 mm inner diameter in this study. The heat transfer coefficient and pressure drop were measured under the following conditions: the saturation temperature was at 48˚C, the mass flux ranged from 200 to 320 kg/m²s, the heat flux ranged from 9 to 12 kg/m²s, the quality of vapor reached to an unit and the length of test section was 1.2m. The effects of mass flux, heat flux and inner diameter on heat transfer coefficient were evaluated. The heat transfer coefficient and pressure drop were also compared using some existing correlations.

어린이집 보육교사의 감정부조화, 직무소진이 정신건강에 미치는 영향

최광일(Kwang Il Choi),이원재(Won Jae Lee) 대한방사선과학회(구 대한방사선기술학회) 2016 방사선기술과학 Vol.39 No.4

이 연구는 어린이집 보육교사의 감정부조화, 직무소진과 정신건강 간의 연관관계를 규명하는 것을 목적으로 467 명의 보육교사를 대상으로 조사하였으며, 5점 척도로 구성한 측정도구를 활용하였다. 수집된 자료는 통계패키지 IBM SPSS 23과 AMOS 21을 사용하여 유의수준 5% 수준에서 검정하였다. 주요 결과는 다음과 같다. 첫째, 어린이 집에 종사하는 보육교사의 감정부조화가 정신건강 하위요인 중 직무스트레스(학부모관계, 업무과부하)에 유의한 영향을 미치는 것으로 나타났다. 둘째, 감정부조화는 직무소진에 모두 유의한 영향이 있는 것으로 나타났다. 셋째, 직무소진은 정신건강 하위요인인 직무스트레스, 심리적 안녕감에 부분적으로 유의한 영향을 미치고 있었다. 넷째, 직무소진은 감정부조화와 정신건강에 대해 부분적 매개효과가 있는 것으로 나타났다. 이러한 연구결과는 어린이집 에서 종사하는 보육교사의 정신건강 증진의 중요성을 제시하고 있으며, 정신건강 증진을 위한 제도적 지원을 모색 할 필요성을 시사한다 This study collected data from 467 nursery teachers and it aimed to investigate the association between mental health and emotional dissonance and job burnout of the day care nursery teachers. Measurement tool was developed, most of the questions having 5-point scale. The data were analyzed structural equation model with the statistical package IBM SPSS 23 and AMOS 21 with 5% percent of significance level. Main results are as follows. First, it was found that emotional dissonance of nursery teachers working in day care centers showed significant effect on the mental health such factors as job-stress (relationships with children and parents and work overload). Second, emotional dissonance were found to have a significant effect on job burnout, too. Third, job burnout had a significant effect on the mental health, job stress and psychological wellbeing. Fourth, job burnout was found to mediate partially on mental health and emotional dissonance. These findings suggest the importance of mental health promotion programs for child care teachers working in the day care centers.

멀티칠러 시스템의 용량제어 특성

최광일(Kwang-Il Choi),Maulana Rifaldi,오종택(Jong-Taek Oh) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5

미나채널 증발기를 이용한 멀티칠러 시스템에서의 용량제어에 관한 실험적 연구를 수행하였다. 시스템 용량은 압축기 및 전자팽창밸브의 회전수와 과열도로 조절하였다. 증발기의 관 내경은 각각 4㎜, 3㎜, 2㎜로써 관외벽 온도는 C-C열전대로 측정하였고 인버터로써 조절된 압축기 회전수는 40-60㎐이며, 냉매 포화온도는 0~10℃의 범위에서 실험하였다. R-22를 이용한 실험결과 주파수가 낮고 열부하 클 때 성적계수가 높게 나타났다. The performance of capacity modulation of multi chiller system was investigated experimentally. The evaporator is a shell and tube heat exchanger type which practically the tube is a minichannel tube. Outside tube wall temperature were measured with thermocouples, the speed variable, inverter, were used to acquire the outlet capacity of the compressor and the superheat control by modulated the electrical expansion valve, EEV. The evaporators have three different minichannel inner diameters, 4㎜, 3㎜, and smallest is 2㎜ inner diameter. The compressor speeds were controlled by an inverter ranged from 40-60㎐. The refrigerant was set to have saturation temperature ranged from 0-10℃. R-22 was circulated in this multi chiller system as the working refrigerant. The modulation capacities of R-22 has yield COP within the system resulting good performances at low frequency and high thermal load

수평미세관내 NH₃ 비등열전달 특성

최광일(Kwang-Il Choi),오종택(Jong-Taek Oh) 대한설비공학회 2013 설비공학 논문집 Vol.25 No.2

This paper is presented an experimental study of flow boiling heat transfer characteristics of ammonia, and is focused on pressure gradient and heat transfer coefficient of the refrigerant flow inside horizontal small tube with inner diameter of 3.0 mm and length of 2000 ㎜. The direct heating method is applied for supplying heat to the refrigerant, where the test tube is uniformly heated by electric current. The local heat transfer coefficients were obtained over a heat flux range of 20 to 80 ㎾/㎡, a mass flux range of 50 to 500 ㎏/㎡s, a saturation temperature range of 0 to 10℃, and quality up to 1.0. The pressure drops increase with increasing mass flux and heat flux, and with decreasing saturation temperature. The heat transfer coefficients increase with increasing mass flux and saturation temperature in middle and high quality region. And the local heat transfer coefficient increase with increasing heat flux in low quality region. The heat transfer coefficient of the experimental result was compared with six existing heat transfer coefficient correlation. A new boiling heat transfer coefficient correlation based on the superposition model for ammonia in small tubes is developed average deviation of -0.17% and mean deviation of 10.85%.

미세관을 이용한 멀티칠러 시스템의 용량제어

최광일(Kwang-Il Choi),오종택(Jong-Taek Oh) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.5

미니채널 증발기를 이용한 멀티칠러 시스템에서의 용량제어에 관한 실험적 연구를 수행하였다. 시스템 용량은 압축기 및 전자팽창밸브의 회전수와 과열도로 조절하였다. 증발기의 관 내경은 각각 4㎜, 3㎜, 2㎜로써 관외벽 온도는 C-C열전대로 측정하였고 인버터로써 조절된 압축기 회전수는 40-60㎐ 이며, 냉매 포화온도는 0~10℃의 범위에서 실험하였다. 작동유체로 R-22를 이용한 실험결과 주파수가 낮고 열부하 클 때 성적계수가 높게 나타났다. In this paper, the performance of capacity control in multi-chiller system was investigated experimentally. The evaporator is a shell and tube heat exchanger type which is made a small tube. Outside tube wall temperature were measured with thermocouples. The capacity of the compressor and the outlet superheat are controlled by the invert and a speed variable with a modulated electrical expansion valve, EEV. The evaporators have three different small tube inner diameters, 4 ㎜, 3 ㎜, and 2 ㎜. The compressor speeds is controlled from 40 to 60 ㎐. The refrigerant is set to have saturation temperature ranged from 0 ~ 10℃. R-22 was circulated in this multi chiller system as the working refrigerant. The modulation capacities of R-22 has yield COP within the system resulting good performances at low frequency and high thermal load.

수평 미세관내 R-1234yf와 R-134a의 비등열전달 특성

최광일(Kwang-Il Choi),Chien Nguyen Ba,김규완(Kyoo-Wan Kim),오종택(Jong-Tack Oh) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.5

수평미세관 직경이 R410A 비등열전달에 미치는 영향

최광일(Kwang-Il Choi),A. S. Pamitran(A. S. Pamitran),오종택(Jong-Taek Oh) 대한설비공학회 2002 대한설비공학회 학술발표대회논문집 Vol.2002 No.-

R-410A 비등열전달에 미치는 미세관경의 영향

최광일(Kwang-Il Choi),A. S. Pamitran,오종택(Jong-Taek Oh),Pega Hrnjak,박창용(Chang Yong Park) 대한설비공학회 2009 설비공학 논문집 Vol.21 No.12

Two-phase flow boiling heat transfer of R-410A in horizontal small tubes was reported in the present experimental study. The local heat transfer coefficients were obtained over a heat flux range of 5 to 40 ㎾/㎡, a mass flux range of 170 to 600 ㎏/㎡s, a saturation temperature range of 3 to 10 ℃, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 0.5 and 3.0 ㎜, and lengths of 330 and 3000 ㎜, respectively. The test section was heated uniformly by applying a direct electric current to the tubes. The effects on heat transfer of mass flux, heat flux, inner tube diameter, and saturation temperature were presented. The experimental heat transfer coefficients are compared with six existing heat transfer coefficient correlations. A new boiling heat transfer coefficients correlation based on the superposition model for R-410A in small tubes was developed with mean deviation of 10.13%.