극초음속 비행체용 재생냉각 미세채널 내부 초임계 탄화수소 항공유의 흡열분해 및 대류 열전달 특성 연구

다국어 초록 (Multilingual Abstract)

Hydrocarbon aviation fuels used as coolants in active regenerative cooling systems of hypersonic cruise vehicle undergo endothermic thermal cracking at high temperatures, decomposing into hydrogen and various light-weight hydrocarbons while absorbing heat. Through this process, they can mitigate the severe thermal loads on hypersonic vehicles and scramjet engines and help overcome challenges associated with supersonic combustion. In such systems, the micro-channels that constitute the regenerative cooling system operate under supercritical conditions, and fuel pyrolysis at elevated temperatures induces drastic variations in thermophysical properties. As a result, complex interactions arise among flow, heat transfer, and endothermic decomposition. Therefore, in this study, microchannel flow reactor test rig was developed to investigate the endothermic decomposition and convective heat transfer characteristics of hydrocarbon aviation fuels in micro-channels. Using this facility, the heat sink capacity, one of the key performance indicators of regenerative cooling fuels, was measured over a wide range of operating conditions and the corresponding endothermic performance was analyzed. In addition, computational fluid dynamics (CFD) simulations incorporating an endothermic decomposition model were conducted to quantitatively examine the heat transfer behavior under supercritical conditions with pyrolysis. Finally, heat transfer experiments were performed for supercritical exo-THDCPD using the same flow reactor, and empirical Nusselt number correlations were proposed that can predict the convective heat transfer from the laminar regime up to the pyrolysis dominated region.
First, CFD analyses applying the PPD (Proportional Product Distribution) model for n-dodecane were carried out to evaluate the changes in thermophysical properties with and without pyrolysis and to quantify their influence on flow and heat transfer. Based on these numerical results, a Nusselt number correlation was developed using the Pizzarelli model, which accounts for the strong property variations under supercritical conditions. The proposed correlation for supercritical n-dodecane reproduced the heat-transfer behavior much more accurately than conventional correlations, achieving a coefficient of determination R² of approximately 0.98 and a mean relative error below 5%.
Furthermore, heat transfer experiments of supercritical exo-THDCPD were conducted using the micro-channel flow reactor, and Nusselt number correlations were developed from the experimental data. The correlations were formulated for four flow regimes defined by Reynolds number and fuel temperature: laminar, transition, and two turbulent regions separated by the pseudo-critical temperature (Turbulent lower pseudo-critical temperature and upper pseudo-critical temperature). The proposed correlations were shown to capture the characteristic variation of the Nusselt number, including the laminar-to-turbulent transition and the pronounced change in Nusselt number near the pseudo-critical temperature, with an overall mean relative error of about 6% over all test conditions.

목차 (Table of Contents)

• 1. 서론 1
• 1.1 연구 배경 1
• 1.2 연구 현황 6
• 1.2.1 탄화수소 연료 열분해 모델 및 CFD 기반 해석 6
• 1.2.2 초임계 유체의 대류 열전달 특성 및 상관식 개발 8
• 1.3 연구 제안 10
• 2. 미세채널 유동반응 실험장치 구축 12
• 2.1 미세채널 유동반응 실험장치 구성 12
• 2.2 Fuel supply부 13
• 2.3 Reactor부 15
• 2.4 Cooling and Sampling부 18
• 3. 탄화수소 항공유의 흡열량 측정 및 분석 19
• 3.1 실험 방법 19
• 3.1.1 흡열량 측정 방법 19
• 3.1.2 연료 전환율 측정 방법 22
• 3.2 실험 조건 및 재현성 검증 23
• 3.2.1 실험 조건 23
• 3.2.2 재현성 검증 24
• 3.3 실험 결과 26
• 3.3.1 유량에 따른 흡열 성능 비교 26
• 3.3.2 운용 압력에 따른 흡열 성능 비교 30
• 4. CFD 기반 열전달 correlation 개발 34
• 4.1 수치해석 방법 34
• 4.1.1 수치해석 형상 및 기법 34
• 4.1.2 수치해석 조건 36
• 4.1.3 흡열분해 모델 40
• 4.1.4 격자 의존성 검증 42
• 4.1.5 해석 결과 검증 44
• 4.2 수치해석 결과 49
• 4.2.1 흡열분해에 따른 물성치 변화 49
• 4.2.2 흡열분해에 따른 열전달 특성 53
• 4.3 Nusselt number correlation 개발 57
• 4.3.1 기존 상관식과 비교 및 한계 분석 57
• 4.3.2 Pizzarelli model 기반 correlation 도출 62
• 4.3.3 온도 영역 구분 및 q/G를 고려한 개선 67
• 5. 실험 기반 열전달 correlation 개발 74
• 5.1 실험 방법 74
• 5.1.1 실험부 및 계측 시스템 74
• 5.1.2 실험 조건 76
• 5.2 데이터 분석 방법 79
• 5.2.1 물성치 획득 및 활용 79
• 5.2.2 데이터 처리 및 무차원수 계산 방법 82
• 5.3 Nusselt number correlation 개발 85
• 5.3.1 실험 결과 및 열전달 특성 분석 85
• 5.3.2 층류 영역 89
• 5.3.3 난류 영역 92
• 5.3.4 Nusselt number correlation 검증 97
• 6. 결론 104