저온 작업환경이 인간의 생리적 반응 및 작업 수행도에 미치는 영향

구학근,곽효연,Ku, Hak-Keun,Kwak, Hyo-Yean 한국마린엔지니어링학회 2007 한국마린엔지니어링학회지 Vol.31 No.5

Some worker is occupationally exposed to cold and freezing environment. The cold stimuli in the working environment impose physiological and psychological loads on workers to decrease the task performance. The purpose of this study is to investigate the cold stimuli of cold and freezing stores widely used in Busan can make an effect on human's physiological responses and task performance, experimentally and analytically. In the experiment, 5 workers are selected as subjects, and then their skin temperatures of hand and ear, heart rates, blood pressure, and ring test performances in cold($3^{\circ}C$) and freezing($-22^{\circ}C$) stores were measured for 21 minutes and analyzed by using statistical method. It is observed that a physiological variation and the task performance are significantly influenced by an exposure time as well as a strength of cold stimuli. Also, it is suggested the exposure limiting times for the useful manual work and the performance predict model of the ring tasks. The result of this study will be useful for a fundamental data of which design the standard task time of manual tasks and solve the job placement problem of worker selection and placement in cold environment.

4.57 mm 세관 열교환기 내 이산화탄소의 증발열전달 특성

구학근,Ku, Hak-Keun 한국마린엔지니어링학회 2007 한국마린엔지니어링학회지 Vol.31 No.2

The evaporation heat transfer coefficient of $CO_2$(R-744) in a horizontal tube was investigated experimentally. The main components or the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator(test section). The test section consists of a smooth, horizontal stainless steel tube of inner diameter of 4.57 mm. The experiments were conducted at mass flux of 200 to $500\;kg/m^2s$, saturation temperature of -5 to $5^{\circ}C$, and heat flux of 10 to $40\;kW/m^2$. The test results showed the heat transfer of $CO_2$ has a greater effect on nucleate boiling more than convective boiling. Mass flux of $CO_2$ does not effect nucleate boiling too much. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the correlation of Jung et al. But existing correlations failed to predict the evaporation heat transfer coefficient of $CO_2$, therefore, it is necessary to develope reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

액-가스 열교환기를 이용한 R170(에탄)용 냉동시스템의 성능 특성

구학근(Hak-Keun Ku) 한국동력기계공학회 2016 동력시스템공학회지 Vol.20 No.5

This paper considers the influence of internal heat exchangers to the efficiency of a refrigerating system using R170. These liquid-gas heat exchangers(internal or suction-line heat exchangers) can, in some cases, yield improved system performance while in other cases they degrade system performance. A steady state mathematical model is used to analysis the performance characteristics of refrigeration system with internal heat exchanger. The influence of operating conditions, such as the mass flowrate of R170, inner diameter tube and length of internal heat exchanger, to optimal dimensions of the heat exchanger is also analyzed in the paper. The main results were summarized as follows : the mass flowrate of R170, inner diameter tube and length of internal heat exchanger, and effectiveness have an effect on the cooling capacity, compressor work and RCI(Relative Capacity Index) of this system. Exception for the effect of inner diameter, the RCI of R170 with respect to refrigerant mass flowrate, the length and effectiveness of internal heat exchanger is about 2.1~3.3% higher than that of R13 at the same experimental conditions. With a thorough grasp of these effect, it is necessary to design the R170 compression refrigeration cycle using internal heat exchanger.

흡입관 열교환기를 이용한 탄화수소계 냉매용 냉동사이클의 성능 탄화수소계 냉매용 냉동사이클의 성능

구학근(Ku, Hak-Keun) 한국산학기술학회 2009 한국산학기술학회논문지 Vol.10 No.9

본 논문은 R290, R600a, R1270과 같은 탄화수소계 냉매를 사용하는 냉동사이클의 효율에 대한 흡입관 열교 환기의 영향을 고려하였다. 이러한 흡입관 열교환기는 냉동시스템의 성능을 향상시킬 수도 있지만, 성능을 저하시킬 수도 있다. 본 논문에서는 흡입관 열교환기를 가진 냉동사이클의 성능 특성을 파악하기 위해서 정상상태의 수학적 모 델을 사용하였다. 그리고 탄화수소계 냉매유량, 흡입관 열교환기의 내관 직경, 길이, 유용도 등과 같은 운전조건의 영 향을 분석하였다. 연구결과는 흡입관 열교환기의 내관 직경, 길이, 유용도, 탄화수소계 냉매의 질량유량은 냉동사이클 의 상대냉동능력지수, 냉동능력, 압축일량에 영향을 미치는 것을 알 수 있었다. 따라서 이러한 영향을 상세히 파악하 여, 흡입관 열교환기를 설치한 탄화수소계 냉매용 증기압축식 냉동사이클을 설계할 필요가 있다. This paper considers the influence of suction-line heat exchangers on the efficiency of a refrigeration cycle using hydrocarbon refrigerants such as R290, R600a and R1270. These suction-line heat exchangers can, in some cases, yield improved system performance while in other cases they degrade system performance. A steady state mathematical model is used to analyze the performance characteristics of refrigeration cycle with suction-line heat exchanger. The influence of operating conditions, such as the mass flowrate of hydrocarbon refrigerants, inner diameter tube and length of suction-line heat exchanger, to the performance of the cycle is also analyzed in the paper. Results showed that the mass flowrate of hydrocarbon refrigerants, inner diameter tube and length of suction-line heat exchanger, and effectiveness have an effect on the cooling capacity, compressor work and RCI(Relative Capacity Index) of this system. With a thorough grasp of these effect, it is necessary to design the compression refrigeration cycle of hydrocarbon refrigerants using suction-line heat exchanger.

단열 모세관내 R600a의 유동 특성

구학근(Ku, Hak-Keun) 한국산학기술학회 2010 한국산학기술학회논문지 Vol.11 No.2

본 논문은 균질유동모델을 적용하여 단열 모세관내 R600a의 유동 특성을 이론적으로 조사하였다. 이 모델은 시뮬레이션 해석에 필요한 기본적인 질량, 에너지, 운동량 방정식에 근거하고 있다. 또한 2개의 마찰인자와 점성계수 모델을 이용하여 유동특성을 조사하였다. R600a의 열역학 및 전달 물성치는 EES 물성치 코드를 이용하여 계산하였 다. 작동변수들에 대한 기초 설계자료를 제공하고자 단열 모세관내 R600a의 유동 특성을 분석하였다. 본 연구의 작동 변수에는 응축온도, 증발온도, 과냉각도, 모세관의 직경이 있다. 주요 결과를 요약하면 다음과 같다. R600a용 단열 모 세관내 응축온도, 증발온도, 과냉각도, 관직경은 모세관 전체길이에 영향을 준다. 즉 R600a용 모세관 전체길이는 식 (15)와 같은 상관식으로 나타낸다. In this paper, flow characteristics of R600a in an adiabatic capillary tube were investigated employing the homogeneous flow model. The model is based on fundamental equations of mass, energy and momentum which are solved simultaneously. Two friction factors(Churchill) and viscosity(McAdams) are comparatively used to investigate the flow characteristics. Thermodynamic and transport properties of R600a are calculated employing EES property code. Flow characteristics analysis of R600a in an adiabatic capillary tube is presented to offer the basic design data for the operating parameters. The operating parameters considered in this study include condensation temperature, evaporation temperature, subcooling degree and inner diameter tube of the adiabatic capillary tube. The main results were summarized as follows: condensation and evaporation temperature, inlet subcooling degree and inner diameter tube of an adiabatic capillary tube using R600a have an effect on length of an adiabatic capillary tube. The length of an adiabatic capillary tube using R600a is expressed to the correlation shown in Eq. (15).

마이크로핀관내 냉동기유가 초임계 이산화탄소의 열전달과 압력강하에 미치는 영향

구학근(Ku, Hak-Keun) 한국산학기술학회 2012 한국산학기술학회논문지 Vol.13 No.4

본 논문은 수평 마이크로핀관내 초임계 CO2와 PAG 혼합물의 열전달과 압력강하 특성에 대해서 실험적으로 연구 한 것이다. CO2와 PAG 혼합물의 열전달계수는 압력이 10 MPa이고, 질량유속은 520 kg/m2s이며, PAG 오일 농도는 0.06∼ 2.26%에서 측정하였다. PAG 오일농도가 0.3%인 경우, CO2와 PAG 혼합물의 열전달계수와 압력강하는 순수 CO2 냉매의 열전달계수와 동일한 경향을 나타내었다. 그리고 PAG 질량농도가 2.26%인 경우, 초임계 온도근처에서 측정한 열전달계 수는 순수 CO2의 열전달계수 보다 약 50%정도 낮게 나타났다. 마찰압력강하는 60℃의 CO2 평균온도에서 순수 CO2의 압력강하보다 약 1.6배 더 높게 나타났다. This paper presents an experimental study of heat transfer and pressure drop characteristics of supercritical carbon dioxide with PAG inside a horizontal microfin tube. Heat transfer coefficient and pressure drop gradients were measured at 10 MPa in pressure and 520 kg/m2s in mass flux with variation of PAG mass concentration from 0.06% to 2.26%. The tendencies of both heat transfer and frictional pressure drop characteristics show the same as those of pure CO2 up to 0.3% in PAG mass concentration. In case of 2.26% in PAG mass concentration, measured heat transfer coefficients showed 50% lower than those of pure CO2 near the pseudocritical temperature and measured frictional pressure drop gradients show 1.6 times higher in comparison with those of pure CO2 at 60℃ in CO2 bulk temperature.

R744-R410A용 이원 냉동시스템 성능 특성

구학근(Ku, Hak-Keun) 한국산학기술학회 2013 한국산학기술학회논문지 Vol.14 No.4

본 논문은 R744-R410A용 이원 냉동시스템의 작동변수에 대한 기초 설계자료를 제공하고자 이원 냉동시스템 의 성능 특성을 분석한 것이다. 이원 냉동시스템의 성능은 EES 프로그램을 이용하여 분석하였다. 작동변수로는 R410A용 고온사이클과 R744용 저온사이클의 압축기효율, 응축과 증발온도이다. 이원 냉동사이클의 응축온도가 감소 할수록 이원 냉동사이클의 COP는 증가하며, 증발온도가 증가할수록 COP가 증가함을 알 수 있다. 또한, 이원 냉동사 이클의 압축효율이 증가할수록 COP가 증가한다. 그러므로 압축효율, 증발온도, 응축온도 등의 인자들이 R410A와 R744용 이원 냉동사이클의 COP에 영향을 주는 것을 알 수 있다. 그리고 이 이원 냉동사이클은 각각의 변수들에서 최고 효율을 가지는 캐스케이드 증발온도가 존재함을 알 수 있다. 따라서 이러한 인자들을 고려하여 R410A와 R744 용 이원 냉동사이클을 설계하는 것은 중요하다. This paper presents the analysis on performance characteristics of R744-R410A cascade refrigeration system to offer the basic design data for the operating parameters of this system. The performance of cascade refrigeration system is analyzed by using EES program. The operating parameters include compressor efficiency, and condensing and evaporating temperature in R410A high- and R744 low-temperature cycle, respectively. The COP of this system increases with the decrease of condensing temperature, and increases with the increasing evaporating temperature. And the COP of this system increases with the compression efficiency. Therefore, it can be seen that the compression efficiency, and evaporating and condensing temperature of R744-R410A cascade refrigeration system have an effect on the COP of this system. Also, it can be known that the cascade evaporation temperature with the highest efficiency in each parameter is present. Thus, it is an important to design R744-R410A cascade refrigeration system by considering these parameters.

내부 열교환기를 이용한 R-1270용 냉동시스템의 성능 분석

구학근(Hak-Keun Ku) 한국동력기계공학회 2014 동력시스템공학회지 Vol.18 No.4

This paper considers the influence of internal heat exchangers on the efficiency of a refrigerating system using R-1270. These internal heat exchangers(liquid-gas or suction-line heat exchangers) can, in some cases, yield improved system performance while in other cases they degrade system performance. A steady state mathematical model is used to analysis the performance characteristics of refrigeration system with internal heat exchanger. The influence of operating conditions, such as the mass flowrate of R-1270, inner diameter tube and length of internal heat exchanger, to optimal dimensions of the heat exchanger is also analyzed. The main results were summarized as follows : the mass flowrate of R-1270, inner diameter tube and length of internal heat exchanger, and effectiveness have the influences on the cooling capacity, compressor work and RCI(Relative Capacity Index) of this system. With a thorough grasp of it is possible to design the R-1270 compression refrigeration cycle using internal heat exchanger.

다층형 열교환기를 이용한 제습기의 전면 풍속 변화에 따른 성능 특성에 관한 연구

구학근(Ku, Hak-Keun) 한국산학기술학회 2010 한국산학기술학회논문지 Vol.11 No.7

저온환경에서의 자동화 설비, 반도체, 제조공정 및 수분 접촉이 되는 화학생산 라인 공정 등의 수분 제거를 위하여 다층형 열교환기를 이용한 제습장치를 구성하였다. 이 장치의 주요구성은 핀 피치가 다른 증발기 4대, 2대의 압축기, 2대의 응축기 그리고 팽창밸브로 각각 제작되었다. 본 연구에서는 제 1 열교환기(증발기)의 전면 풍속을 변화 시켜 제습기의 성능 특성을 분석하였다. 즉, 제1 열교환기의 정면 풍속을 1.0m/s에서 4.0m/s까지 0.5 m/s의 간격으로 증가시켜 각 측정지점에서 온도와 상대습도를 측정하여 엔탈피를 구하여 각 열교환기의 냉각능력을 구했다. 그 결과 제1 열교환기의 정면 풍속이 2.0 m/s에서 각 열교환기의 냉각능력이 가장 좋은 것을 알 수 있었다. The experimental apparatus consists of dehumidifier with multi-layer type heat exchangers to remove the moisture from automatic equipments, semiconductors, and manufacturing processes under the low temperature environment, and chemical production lines which are likely to take moisture. The major components of this system are four evaporators with different fin pitch, two compressors, two condensers and an expansion valve. In this study, the performance characteristics of dehumidifier is analyzed by the variations of frontal air velocity in the first heat exchanger(evaporator). The cooling capacity of each heat exchanger is acquired by the enthalpy calculating from measuring point of temperature and relative humidity of the first heat exchanger from 1.0m/s to 4.0m/s with increasing interval 0.5m/s, and the front air velocity. As a result, it is found that cooling capacity of the first heat exchanger showed the best cooling capacity when its frontal air velocity is 2.0 m/s.

액-가스 열교환기를 적용한 R290(프로판)용 냉동시스템의 성능 분석

하수정(Soo-Jeong Ha),구학근(Hak-Keun Ku) 한국동력기계공학회 2019 동력시스템공학회지 Vol.23 No.4

This paper considers the influence of liquid-gas heat exchangers to the efficiency of a refrigerating system using R290. These liquid-gas heat exchangers can, in some cases, yield improved system performance while they degrade system performance in other cases. A steady state mathematical model is used to analyze the performance characteristics of refrigeration system with liquid-gas heat exchanger. The influence of operating conditions, such as the mass flowrate of R290, inner diameter tube and length of liquid-gas heat exchanger, to optimal dimensions of the heat exchanger is also analyzed in the paper. The main results were summarized as follows: the mass flowrate of R290, inner diameter tube and length of liquid-gas heat exchanger, and effectiveness have an effect on the cooling capacity, compressor work and RCI (Relative Capacity Index) of this system. With a thorough grasp of these effect, it is necessary to design the R290 compression refrigeration cycle using liquid-gas heat exchanger.