증기압축식 냉동시스템의 열유체 동적모사에 관한 문헌연구

정의국(Eui Guk Jung),손지은(Ji Un Sohn),김낙훈(Nak Hoon Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.5

다 증발기 및 응축기를 가지는 상업용 에어컨의 열유체 제어기법을 개발하기 위해 증기압축 냉동시스템에 관한 동적 모델링 방법이 문헌을 통하여 조사되었다. 시스템의 동적 거동을 제어하기 위한 여러 가지 천이 수학적 모델링 기법이 소개되었다. 특히, 질량, 운동량 및 에너지보존의 지배방정식을 통하여 주요 상태변수들이 유도되었다. 냉매의 물성과 시스템을 구성하는 요소의 기학적 크기가 주요 천이변수들로 나타나며, 이들을 포함하는 1차원 수학적 모델링이 제시되었다. 냉동사이클을 구성하는 모든 구성요소를 포함한다는 점에서 동적 제어이론이 실질적이다. 본 연구결과는 향후에 건물공기조화장치와 같은 상업용 에어컨의 작동성능예측의 도구로 활용될 것이다. Previous studies of dynamic control modeling of the vapor compression refrigeration system were reviewed in order to develop thermo- hydraulic control method of commercial air conditioner with multi-evaporator and condenser by the literatures. Transient mathematical modeling was introduced to predict dynamic behavior of system. Particularly, main transient variables were derived by the mass, momentum and energy conservative equations. They were expressed as refrigerant physical properties and geometrical size of the components included for the system, and 1D mathematical modeling including these was introduced by the literatures. Feasible dynamic control theory is practicable for including all components of refrigeration cycle like evaporator, condenser, compressor, expansion valve, sub-cooler and accumulator. In the future, these results were applied to the performance prediction tool on commercial air conditioner for the building management.

고온 태양열 흡수기의 후벽 각도 변화에 따른 열전달 특성에 관한 수치적 모사

정의국(Eui Guk Jung),부준홍(Joon Hong Boo),강용혁(Yong Hyeog Kang) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

A numerical analysis was conducted to predict the heat transfer characteristics of a high-temperature, high heat flux solar receiver as the end-wall angle varied. The concentration ratio of the solar receiver ranges from 200 to 1000 and the concentrated heat is required to be transported to a certain distance for specific applications. This study deals with a solar receiver incorporating high-temperature sodium heat pipe as well as a typical one that employs a molten-salt circulation loop with the same outer dimensions. The isothermal characteristics in the receiver section is of major concern. The diameter of the solar thermal receiver was 120 ㎜ and the length was 400 ㎜. FLUENT, a commercial software, was employed to deal with the radiative heat transfer inside the receiver cavity and the convection heat transfer along the channels and heat pipes. The numerical results were compared and analyzed from the view point of heat transfer characteristics the solar receiver system.

시스템의 신뢰도를 높이기 위한 교환제어모듈 설계

정의국(Euikuk Jeong),장경배(Kyung-Bae Chang),심일주(Il-Joo Shim),박귀태(Gwi-Tae Park) 대한전기학회 2004 대한전기학회 학술대회 논문집 Vol.2004 No.7

박막이론을 적용한 평판형 증발부를 갖는 루프히트파이프에 대해 박막이론을 적용한 해석적 모델링

정의국(Eui Guk Jung),부준홍(Joon Hong Boo) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5

평판형 증발부를 가지는 루프히트파이프(LHP)에 대한 정상상태 해석모델을 제시하였다. 관련문헌의 이론적 고찰에 기초하여 LHP의 중요한 지점인 증발부, 액체저장조(보상챔버), 증기이송관, 액체이송관 및 응축부에서 온도와 압력을 예측할 수 있도록 계산과정을 제시하였다. LHP에서 유일하게 모세관 구조물을 가지는 증발부의 해석에 관심을 두었다. 증발부에서 액체 - 기체 경계면 근처에서 압력과 온도의 영향을 고려하기 위해 박막이론을 사용하였다. 수정된 기체분자운동이론에서 응축경계면온도를 산정하는데 있어서 독특한 방법을 도입하였다. 응축부에서는 상변화 경계면을 단순화하여 처리함으로써 응축부 형상 변화에 상대적인 융통성을 구비하도록 하였. LHP 의 정상상태 해석 모델은 잘 알려진 문헌의 실험결과에 의해 타당성이 증명되었다. 실험결과와 해석결과의 비교과정을 통해서 절대온도를 기준으로 한 3% 이내로서 합리적으로 잘 일치하고 있음을 확인하였다. A steady state analytical model was presented for a loop heat pipe (LHP) of which the evaporator was of a flat geometry. Based on a series of theoretical reviews of the relevant literature, a sequence of calculations was proposed to predict the temperatures and pressures at each important part of the loop heat pipe: evaporator, liquid reservoir (compensation chamber), liquid line, vapor line, and the condenser. An emphasis was laid on the analysis of the evaporator, which is the only part having the capillary structure in a LHP. The thin-film theory is employed to account for the pressure and the temperature in the adjacent region of the liquid-vapor interface in the evaporator. A unique method was introduced to calculate the liquid temperature in the modified kinetic theory. Relative freedom was assumed in the configuration of condenser with a simplified liquid-vapor interface. A steady state model for a LHP was validated by the experimental results, which were available the literature. Relative error of comparisons was within 3% in the absolute temperature scale and reasonable agreement was obtained.

평판형 증발부와 폴리프로필렌 윅을 가지는 루프히트파이프의 과열제거에 대한 실험적 연구

정의국(Eui Guk Jung),임원호(Won Ho Lim),이찬희(Chan Hee Lee),권정훈(Cheong Hoon Kwon) 항공우주시스템공학회 2023 항공우주시스템공학회 학술대회 발표집 Vol.2023 No.05

루프히트파이프는 특별하게 시동하는 동안 증발부 벽 온도에 대한 과열 문제를 종종 겪는다. 평판형 증발부와 폴리프로필렌윅을 가지는 루프히트파이프의 과열문제를 해결하기 위해 증발부와 액체저장조 사이에 바이패스라인이 설치되었다. 증발부와 응축부는 40 mm (W) × 50 mm (L)의 크기를 가진다. 벽과 튜브 재료는 스테인리스 스틸이며 작동유체는 메탄올이다. 평판형 증발부에 역사다리꼴 형상의 그루브를 통하여 증가가 공급되었다. 액체 및 증기 이송관의 내부직경은 각각 2 mm와 4 mm이며, 두 라인의 길이는 각 0.5 m이다. 열부하 범위는 응축부 냉각원 온도, 10˚C를 가지는 수평기울기에 대하여 최대 90 W까지이다. 실험결과를 통하여 바이패스라인은 증발부 벽 온도에 대한 과열문제를 제거하는 효과를 얻을 수 있었다.

히트파이프 배열을 갖는 태양열 축열시스템의 열전달 해석

정의국(Jung Eui-Guk),김종규(Kim Jong-Kyu),강용혁(Kang Yong-Heack),부준홍(Boo Joon-Hong) 한국태양에너지학회 2010 한국태양에너지학회 학술대회논문집 Vol.2010 No.4

Heat transfer analysis results were shown for the solar thermal storage system which used heat pipe array. The thermal storage system was composed of thermal storage tank and charging/discharging heat exchanger by connection with the heat pipes. Heat pipe heat exchanger was attached to system, and could carry out charging and discharging to thermal storage tank at the same time. Height of the thermal storage tank was 600 ㎜, and that of the charging/discharging heat exchanger was 400 ㎜. Length of the heat pipe was the same as the total height of thermal storage system, and outer and inner diameter were 25.4 ㎜(O.D.) and 21.4 ㎜(I.D.) respectively. Diameter of the circular was 43 ㎜(O.D.), and fin geometries were considered as the design parameters. High temperature phase change material(PCM), KNO₃ was charged to storage tank to adjust melting temperature. Energy relations between heat exchanger and thermal storage tank were defined by the thermal resistance and node temperature. Physical transient equations of the heat pipe heat exchanger/thermal storage and PCM was modeled with energy conservation. Furthermore, melting/solidification phase change interface radius were calculated based on latent and sensible heat. Thermal storage system sizes satisfying inlet and outlet conditions of the charging/discharging heat exchanger were predicted according to heat pipe fin pitch variation of the thermal storage. Maximum and minimum heat pipe row was predicted to 899 and 808 respectively.

타워형 태양열 발전용 공기흡수기의 열전달 성능해석

정의국(Eui Guk Jung) 대한기계학회 2012 大韓機械學會論文集B Vol.36 No.3

타워형 태양열 발전용 체적식 공기흡수기의 열전달 성능 해석을 수행하였다. 타당한 관련문헌에 기초하여 채널 한 개의 벽과 공기 온도분포를 지정된 기하학적 크기와 입력조건에서 예측 할 수 있는 계산과정들이 제시되었다. 더 나아가서 흡수기 유용도의 수학적 모델이 온도프로파일 해석을 통해 유일하게 제시되었다. 흡수기 재질은 실리콘 카바이드이다. 공기 흐름을 유도하는 정사각형 직선채널 크기는 2 ㎜(W) × 2 ㎜(H) × 0.2 ㎜(t) × 320 ㎜(L)이며, 모듈 한 개에는 225 개의 채널이 성형되었다. 일정한 일사량 및 공기유량 가정하에서 채널과 모듈 수의 변화에 따른 열전달량, 온도분포 및 유용도 추이가 제시되었다. 태양열 발전에 응용하기 위해서는 흡수기 출구 공기온도가 700℃ 이상에 도달하여야 한다. 본 수치모델은 200 ㎾ 급 타워형 태양열 공기흡수기의 설계에 사용되었으며, 지정된 기하학적 조건과 입력조건에서 요구되는 열전달 성능을을 만족하는 모듈 수를 얻을 수 있었다. In this study, a heat-transfer performance analysis is carried out for a multi-channel volumetric air receiver for a solar power tower. On the basis of a series of reviews regarding the relevant literature, a calculation process is proposed for the prediction of the wall- and air- temperature distributions of a single channel at given geometric and input conditions. Furthermore, a unique mathematical model of the receiver effectiveness is presented through analysis of the temperature profile. The receiver is made of silicon carbide. A total of 225 square straight channels per module are molded to induce the air flow, and each channel has the dimensions of 2 ㎜ (W) × 2 ㎜ (H) × 0.2 ㎜ (t) × 320 ㎜ (L). The heat-transfer rate, temperature distribution and effectiveness are presented according to the variation of the channel and module number under uniform irradiation and mass flow rate. The available air outlet temperature applied to the solar power tower should be over 700℃. This numerical model was actually used in the design of a 200 kW-level commercial solar air receiver, and the required number of modules satisfying the thermal performance could be obtained for the specified geometric and input conditions.

평판형 증발부를 갖는 루프히트파이프에 대해 박막이론을 적용한 해석적 모델링

정의국(Eui Guk Jung),부준홍(Joon Hong Boo) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.12

평판형 증발부를 갖는 루프히트파이프(LHP)에 대한 정상상태 해석모델을 제시하였다. 관련문헌의 고찰에 기초하여 LHP 의 주요 부분인 증발부, 액체저장조(보상챔버), 증기이송관, 액체이송관 및 응축부에서 온도와 압력을 예측할 수 있도록 계산과정을 제시하였으며, LHP 에서 유일하게 모세관 구조물을 가지는 증발부의 해석에 중점을 두었다. 증발부에서 액체 ?기체 경계면 부근에서 압력과 온도의 영향을 고려하기 위해 박막이론을 사용하였으며, 수정된 기체분자운동이론에서 응축경계면 온도를 산정하는데 있어서 독특한 방법을 도입하였다. 응축부에서는 상변화 경계면을 단순화하여 처리함으로써 응축부 형상 변화에 상대적인 융통성을 구비하도록 하였다. 본 연구의 LHP 정상상태 해석 모델은 문헌 상의 실험결과에 의해 타당성이 증명되었다. 해석모델에 의한 예측치는 실험치와 비교할 때 절대온도를 기준으로 최대 상대오차 3% 이내로서 합리적으로 잘 일치하였다. A steady-state analytical model was presented for a loop heat pipe (LHP) with an evaporator that has a flat geometry. On the basis of a series of reviews of the relevant literature, a sequence of calculations was proposed to predict the temperatures and pressures at each important part of the LHP: the evaporator, liquid reservoir (compensation chamber), liquid line, vapor line, and condenser. The analysis of the evaporator, which is the only part in the LHP that has a capillary structure, was emphasized. Thin-film theory is applied to account for the pressure and temperature in the region adjacent to the liquid-vapor interface in the evaporator. The present study introduced a unique method to estimate the liquid temperature at the interface. Relative freedom was assumed in the configuration of a condenser with a simplified liquid-vapor interface. Our steady-state model was validated by experimental results available in the literature. The relative error was within 3% on the absolute temperature scale, and reasonable agreement was obtained.

루프히트파이프의 정상상태 열성능 해석 모델로 예측한 설계변수의 영향

정의국(Eui Guk Jung),부준홍(Joon Hong Boo) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

This study deals with a mathematical modeling for the steady-state temperature characteristics of an entire loop heat pipe. The lumped layer model was applied to each node for temperature analysis. The flat type evaporator and condenser in the model had planar dimensions of 40 ㎜ (W) × 50 ㎜ (L). The wick material was a sintered metal and the working fluid was methanol. The molecular kinetic theory was employed to model the phase change phenomena in the evaporator and the condenser. Liquid-vapor interface configuration was expressed by the thin film theories available in the literature. Effects of design factors of loop heat pipe on the thermal performance were investigated by the modeling proposed in this study.

히트파이프와 루프히트파이프의 성능향상에 관한 최신기술

정의국(Eui Guk Jung),권정훈(Cheong Hoon Kwon),부준홍(Joon Hong Boo) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11

This paper has dealt with the three latest technologies for performance improvement of heat pipe and loop heat pipe. First, a part of the liquid in the condenser is bypassed to the evaporator in order to reduce the interface flow resistance caused by the counter flow of liquid and vapor inside the heat pipe. By applying this technology, the maximum amount of heat transfer caused by dry-out of the heat pipe was increased, and the experimental results were introduced, which improved the heat transfer performance by reducing the thermal resistance. Second, a technique of bypassing a portion of the vapor generated from the evaporator to the liquid reservoir was introduced in order to overcome the operational limit of the loop heat pipe. Through the application of the vapor bypass technology, the temperature overshoot on the evaporator wall of the loop heat pipe could be eliminated, and the heat transfer performance could be improved at high heat load range. Third, a performance prediction model of the micro heat pipe was developed. In this study, a performance prediction model for micro heat pipe to which the augmented Young-Laplace equation is applied is presented. This mathematical model has the advantage of being able to predict the shape of the phase change interface created inside the micro heat pipe more precisely than the previous model. The three latest technologies mentioned above can be studied more popularly in the future and can contribute to the technological expansion of heat pipe and loop heat pipe.