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수평관과 헬리컬 코일관내 이산화탄소의 냉각 열전달 특성
손창효(Changhyo Son) 한국자동차공학회 2008 한국 자동차공학회논문집 Vol.16 No.1
The cooling heat transfer coefficient of CO₂ (R-744) in a horizontal and helically coiled tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater, evaporator and gas cooler (test section). The test section consists of a horizontal stainless steel tube and hellically coiled copper tube of 4.57 and 7.75 ㎜. The experiments were conducted at saturation temperature of 100 to 20℃, and mass flux of 200 to 500 ㎏/㎡s. The test results showed the variation of the heat transfer coefficient tended to decrease as cooling pressure of CO₂ increased. The heat transfer coefficient with respect to mass flux increased as mass flux increased. The experimental results were also compared with the existing correlations for the supercritical heat transfer coefficient, which generally underpredicted the measured data. However, the experimental data showed a relatively good agreement with the correlations of Pitla et al. except for the pseudo critical temperature.
내경 4.57과 7.75 ㎜인 수평관내 이산화탄소의 증발 압력강하
손창효(Changhyo Son) 한국자동차공학회 2008 한국 자동차공학회논문집 Vol.16 No.3
The evaporation pressure drop of CO₂ (R-744) in horizontal tubes was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of 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 7.75 and 4.57 ㎜ inner diameter. The experiments were conducted at saturation temperature of -5℃ to 5℃, and heat flux of 10 to 40 ㎾/㎡. The test results showed the evaporation pressure drop of CO₂ are highly dependent on the vapor quality, heat flux and saturation temperature. The pressure drop measured during the evaporation process of CO₂ increases with increased mass flux, and decreases as the saturation temperature increased. The evaporation pressure drop of CO₂ is very lower than that of R-22. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the correlation of Choi et al. But existing correlations failed to predict the evaporation pressure drop of CO₂. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation pressure drop of CO₂ in a horizontal tube.
최경민(Kyoung-Min Choi),전민주(Minjoo Jeon),손창효(Changhyo Son),오후규(Hookyu Oh) 대한설비공학회 2010 대한설비공학회 학술발표대회논문집 Vol.2010 No.6
The condensation heat transfer coefficients of CO₂ in smooth and micro-fin tubes were investigated experimentally. The main components of the refrigerant loop are a receiver, a pump, a mass flow meter, a preheater and a condenser(test section). The water loop consists of a pump, an flow meter. The test sections are a micro-fin tube with 4.6 ㎜ inner diameter and smooth tube with 4.95 mm inner diameter. The experiments were conducted at mass flux of 800 to 2000 ㎏/㎡s, saturation temperature of 20 to 30℃. The main results were summarized as follows : the condensation heat transfer coefficients have an effect on the mass flux of R744, saturation temperature and tube shape. Therefore, it is necessary to develop reliable and accurate predictions determining the condensation heat transfer coefficient of CO₂ in the micro-fin tube.
평활관 및 마이크로핀관 내 초임계 이산화탄소의 냉각열전달 특성
이대훈(Daehun Lee),전민주(Minjoo Jeon),손창효(Changhyo Son),오후규(Hookyu Oh) 대한설비공학회 2010 대한설비공학회 학술발표대회논문집 Vol.2010 No.6
The cooling heat transfer characteristics of supercritical CO₂ in smooth and micro-fin tubes were investigated experimentally. The main components of the refrigerant loop are a receiver, a CO₂ compressor, a mass flow meter, an evaporator and a micro-fin tube as a test section. The test was conducted at mass flux from 1200 to 2000 ㎏/㎡s, inlet cooling pressure from 9 to 10 ㎫. The cooling heat transfer coefficients of the micro-fin tube are about 12~39% higher than those of the smooth tube. In comparison with test results and existing correlations, correlations failed to predict the cooling heat transfer coefficient of CO₂ in the micro-fin tube. Therefore, it is necessary to develop reliable and accurate predictions determining the cooling heat transfer coefficient of CO₂ in the micro-fin tube.
정민호(Minho Jung),김동현(Donghyon Kim),안석의(Seokeui An),손창효(Changhyo Son),윤정인(Jungin Yoon),설성훈(Sunghoon Seol),이준혁(Joonhyuk Lee),정한솜(Hansom Jeong),차승윤(Seungyun Cha) 한국해양환경·에너지학회 2021 한국해양환경·에너지학회 학술대회논문집 Vol.2021 No.10
현재 국내에서는 파리기후협약을 위해 2030년까지 전체 발전량의 20%를 재생에너지로 공급하는 목표를 세웠으며, 신재생에너지 중 1.6%를 해양에너지로 공급하고자 하는 계획을 가지고 있다. 조류발전은 풍력발전보다 에너지 밀도가 높고 출력을 정확하게 예측할 수 있는 장점이 있다. 그러나 조류발전의 경우 풍력발전 대비 냉각방식이 제한적이며, 적절한 냉각이 이루어지지 않을 경우 발전기 성능 저하 및 화재의 위험이 존재한다. 따라서 본 연구에서는 열유체 유동해석을 통해 조류발전기의 냉각시스템에 대한 냉각성능을 분석하였다. 시뮬레이션을 위하여 발전기의 발열량은 안전율 등을 고려하여 발전량의 10%인 130kW로 가정하였다. 발전기 고정자의 냉각에는 고정자 내부에 냉각관을 삽입하는 것으로 설계하였으며, 냉각관의 냉각에는 청수를 사용하며, 청수의 냉각에는 해수를 사용하는 것으로 고려하였다. 시뮬레이션 결과 End Winding의 온도가 86.8℃로 분석되어 목표 유지온도보다 낮은 것을 확인하였으나, 유량의 분배가 원활하지 않아 유체의 압력분포가 일정하지 않음을 알 수 있었다. Currently, in Korea, for the Paris climate agreement, the goal of supplying 20% of the total power generation from renewable energy by 2030 is set, and 1.6% of the renewable energy is to be supplied as marine energy. The tidal power generation using marine energy has a higher energy density than wind power generation and the output is easier to predict. However, in the case of tidal power generation, since the cooling method is limited compared to wind power generation, if proper cooling is not performed, there is a risk of deterioration of generator performance and fire. Therefore, in this study, the cooling performance of the cooling system of the tidal generator was analyzed through thermal fluid flow analysis. The assumptions for the simulation analysis are as follows. The heat generation of the generator was assumed to be 130kW, which is 10% of the power generation in consideration of the safety factor. To cool the generator stator, a cooling tube is inserted inside the stator. Freshwater was used to cooling the cooling tube, and seawater was used to cool the freshwater. As a result of the simulation, the temperature of the end winding was observed to be 86.8℃, and it was confirmed that it was lower than the target maintenance temperature.