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超 低溫 液化가스 氣化器의 熱傳達 特性에 관한 硏究

A Study on the Heat Transfer Characteristics of Liquefied Gas Vaporizer with Super Low Temperature,

이상철 (Lee, Sang Chul, 경상대학교 대학원)

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초록/요약moremore
The vaporizer means machine to vaporize the liquefied gas as liquid nitrogen(LN2), liquefied natural gas(LNG), liquid oxygen(LO2) etc. Recently, many researchers have been concentrating on the super low temperature fields due to the increasing demand of the LNG which has numerous applications such a...
The vaporizer means machine to vaporize the liquefied gas as liquid nitrogen(LN2), liquefied natural gas(LNG), liquid oxygen(LO2) etc. Recently, many researchers have been concentrating on the super low temperature fields due to the increasing demand of the LNG which has numerous applications such as rapid freezing, cryogenic energy power generation, low temperature refrigeration etc. LNG consists of methane(CH4) as the main compound, which is produced by cooling and pressurization process of natural gas. LNG is transported and stored as liquid phase below 111 K from the source country. LNG must be vaporized as used as fuel in the industries, home application and so on. In this vaporization process, cold energy in the form of latent heat(502.4 kJ/kg) and sensible heat(334.9 kJ/kg) are generated. This cold energy can be utilized; however, additional cost of facilities which is needed for vaporization process of LNG reduces its benefit. Therefore, to utilize cold energy and to develop better vaporizer are very important task. Generally, the vaporization method of LNG is divided into two types. The first method uses ambient air and the other method uses seawater. The seawater type is used in the coastal LNG station where much heat is required for vaporization process. However, frost deposition from seawater on the surface of vaporizer can cause some problems. Generally, the local LNG station uses air type vaporizer. In the air type vaporizer, the frozen dew is also created by temperature drop (below 273 K) on vaporizer surface. This problem increases as the time progresses and humidity increases. In addition, the frozen dew gradually becomes frost deposit consequently, heat transfer through vaporizer decreases because frost deposit form adiabatic sheet. Because of this reason, recent vaporizer system is installed as parallel type, this vaporizer system needs more expensive installation costs and more space. LNG vaporizer system must yet be small, efficient, and easy to operate and maintain. Nowadays, The domestic researches are still at the early phase for super low temperature vaporizer and LNG cold energy utilization technology. Therefore, there are still insufficient practical and theoretical data for super low temperature fields. Also, piping line for NG transportation was almost worked in Korea. The vaporizer using air heat source is required, because piping work in a part local town is difficult or impossible. Accordingly, this paper was investigated on the heat transfer characteristics of liquefied gas vaporizer with super low temperature which is air fin one, and this paper was carried out the numerical and experimental study about air fin vaporizer with super low temperature. Firstly the numerical analysis on the heat conduction was studied on the effect of geometric parameters of the vaporizer, which are number, thickness and length of vaporizer fins. Secondly the experimental study was investigated the heat transfer characteristics and performance on the tube length 4000 mm, 6000 mm and 8000 mm of three vaporizer models as FINLESS, 4FIN75LE, 8FIN50LE, and was analyzed for evaluating the optimum efficiency on the vaporizer. The third, the experimental study on the open and close system of air forced draft vaporizer with aero-fin coil tube was also carried out, which have parameters on air velocity and flow rate of working fluid. here, not only vaporization characteristic of liquefied gas vaporizer but also utilization of cold energy was investigated by experiment. Liquefied nitrogen as working fluid was used at all experimental study. The result from numerical and experimental study is as follows. The increasement of vaporizer fin number has not an effect on temperature variation of vaporizer fin at same boundary condition. But the heat transfer was increased with increasement of vaporizer fin number due to increasing of heat transfer area. The increasement of fin thickness and length have also an effect on rising the heat transfer. But, temperature variations of vaporizer fin by increasement of fin thickness and length had different tendency. The fin temperature of vaporizer decreased with increase of fin thickness but it decreased with increase of fin length. Therefore, fin length must be increased with fin thickness to be zero of temperature difference between fin tip and ambient air. And, the vaporizer with fin thickness 2 mm must be expanded to 80 mm fin length for maximum heat transfer at working fluid temperature of 77 K, ambient air temperature of 293 K and heat transfer coefficient of 103 W/m2K. In increasing of the vaporizer volume length, the vaporization gas temperature of the vaporizer outlet was increased by increase of the heat transfer area, but fin effective of vaporizer was decreased. And, phase change behavior of vaporizer working fluid inner could be predicted by measuring the working fluid temperature and pressure at inlet and outlet of vaporizer The heat exchange efficiency of 4FIN75LE with vaporizer length of 8000 mm is 96.81 %, and 4FIN75LE vaporizer model was more heat transfer performance than FINLESS and 8FIN50LE at vaporizer length of 6000 mm and 8000 mm. The surface temperature of vaporizer was rapidly reached in steady state according to increasing of working fluid flow rate. Layer of the freezing moisture was created thicker than those of the close system, and heat transfer on vaporizer was promoted because the increase of air velocity has increasing the temperature of vaporizer surface and exhausted nitrogen gas. The open type system is very useful to vaporize the liquefied nitrogen quickly. On the other side, the advantage of close type system is that this system can be obtained lower temperature than open system, and air temperature in front of the chamber can be decreased down to 183 K according to increasing velocity because of recycling the cooling air. In the vaporization process, working fluid of inner vaporizer and surface temperature of vaporizer along the length direction have unique phenomenon of temperature variation, this was considered due to the effects by the pressure pulsation, shock wave and vaporization of compressible fluid.
목차moremore
Ⅰ. 서론 1
1. 연구 배경 1
2. 선행연구 탐색 5
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Ⅰ. 서론 1
1. 연구 배경 1
2. 선행연구 탐색 5
3. 연구내용 및 목적 17
Ⅱ. 초 저온 액화가스 기화기의 열전달 수치해석 19
1. 연구내용 및 범위 19
2. 수치해석 모델 20
3. 수치해석 접근방법 24
4. 지배방정식 및 경계조건 41
5. 결과 및 고찰 44
6. 요약 53
Ⅲ. 초 저온 액화가스 기화기의 길이변화 특성 실험 54
1. 연구내용 및 범위 54
2. 이 론 56
3. 실험장치 60
4. 실험방법 및 조건 71
5. 결과 및 고찰 78
6. 요약 125
Ⅳ. 강제통풍식 초 저온 액화가스 기화기의 공급유량 및 풍속변화 특성 실험 126
1. 연구내용 및 범위 126
2. 실험장치 구성 및 설계 128
3. 실험방법 및 조건 134
4. 결과 및 고찰 144
5. 요약 170
Ⅵ. 결론 171
참고문헌 176
Appendix 183
연구실적 193