재생 에너지는 안정적인 에너지 수급을 가능하게 하고, 화석 연료 의존성을 줄이는데 기여한다. 수력발전은 발전단가가 낮고, 신뢰할 수 있는 재생 에너지원 중 하나이다. 마이크로 수력 터빈은 상수도 파이프 라인, 하수 처리 및 운송 플랜트, 화학 및 정유공장 등과 같은 시스템에서 버려지는 에너지를 회수하여 지속 가능한 발전을 위한 연구 주제로 각광을 받고 있다. 현수준의 연구는 온수 수송용 파이프의 미사용 에너지를 차압 제어 밸브를 통해 회수하는 방법을 다루고 있다. 하지만 차압 밸브는 내부에서 캐비테이션이 발생하여 에너지 손실을 야기하고, 파손되는 문제가 있다. 본 연구에서는 이러한 문제를 해결하기 위해 차압 밸브를 대체할 수 있는 용적형 수력 터빈을 개발하였다. 용적형 수력 터빈은 유량이 매우 작고, 고양정이 요구되는 장소에 적합하다. 전산유체역학을 통하여 용적형 수력 터빈의 설계와 성능 예측을 수행하였고, 경제성 분석을 통해 차압 밸브를 용적형 수력 터빈으로 교체할 경우 에너지 절약과 CO2 배출 감소에 도움이 된다는 결론을 얻었다. 용적형 유체기기에서는 간극에서 발생하는 누설 유량이 수력학적 성능에 매우 중요한 역할을 한다. 본 연구에서는 용적형 수력 터빈의 수력학적 성능에 대한 축 및 반경 방향 간극 효과를 분석하였고, 서로 다른 축 및 반경 방향 간극의 용적형 수력 터빈을 제작하여 성능 실험을 수행하였다. 또한 전산유체역학을 통해 간극의 크기 (0.025-0.6mm)에 대한 매개변수 연구를 수행하였고, 반경 방향 간극은 0.025-0.6mm 의 범위에서 수력학적 성능에 민감한 영향을 미치는 것으로 확인되었다. 간극이 0.6mm 이상일 때 간극의 부피는 용적형 수력 터빈 부피의 4% 밖에 되지 않지만, 간극에서 발생하는 누설 유량은 터빈 전체 유량의 1/3에 달했다. 아울러, 로터 비틀림 효과의 영향을 분석하기 위해 전산유체역학을 사용하여 유동 맥동, 누설 손실 및 수력학적 성능에 대한 매개변수 연구를 수행하였고, 누설 손실을 정성적 및 정량적으로 분석하기 위한 메커니즘을 개발하였다. 로터 형상이 비틀리게 되면 유동 맥동과 캐비테이션이 크게 감소하는 것을 발견하였다. 그러나, 로터 사이의 간극에서 누설 유동이 증가하여 수력학적 성능이 약간 감소하였다. 유동 맥동, 캐비테이션 및 수력학적 성능을 고려하였을 때 최적 비틀림 각도는 45°로 밝혀졌다. 본 연구에서 개발된 용적형 수력 터빈의 입·출구 관 단면적 형상이 유동 맥동과 수력학적 성능에 미치는 영향을 분석하였다. 기존의 단면적 형상은 원형으로 제작되었다. 사각형 및 평행사변형 단면 형상의 입·출구 관을 사용하여 영향성을 분석하였고, 매개변수 연구를 수행하였다. 매개변수 연구 결과, 평행사변형 단면의 관을 사용할 때 유동 맥동이 현저히 감소하는 것이 발견되었고, 기존의 원형 단면적 관과 비교하여 수력 효율이 0.824% 향상되었다. 비틀어진 로터형상과 원형 입·출구 관을 가진 용적형 수력 터빈이 최종형상으로 선정되었고, 정격 조건에서 66.2%의 수력 효율과 7.15kW 출력 성능이 실험을 통해 검증되었다.
Renewable energy will play an important role in achieving the energy stability and reducing the dependence on fossil fuels. Hydropower is one of the cheapest and reliable sources of renewable energy. Micro hydro turbines are getting renewed research interest in recovering unused energy from systems like water supply pipelines, sewage treatment and transportation plants, chemical and oil refineries, etc. and making them energy efficient for sustainable development. The present work dealt with this aspect wherein the unused energy of the hot water transportation pipelines, which was earlier throttled by pressure differential control valve (PDCV), was harvested and used elsewhere. A special class of multipurpose micro hydro turbine known as the positive displacement turbine was developed, which involved very low flow rates with moderate to high heads and very low specific speeds, to replace the PDCV which was frequently failing due to cavitation causing loss of energy. A framework was developed for designing such turbines and predicting their performance using Computational Fluid Dynamics (CFD). The socio-economic analysis was also carried out which concluded that the PDT will aid in energy conservation and reduction in CO2 emissions. Flow leakage through the clearance gaps play a vital role in influencing the performance of positive displacement type of machines. The present work illustrated the effect of axial and radial clearance on the overall performance of the PDT. Experimental studies were conducted with PDT having different combination of axial and radial clearances. A parametric study was undertaken using CFD to find the sensitivity of these clearances in the range of 0.025-0.6 mm. From the analysis, it was inferred that radial clearance was sensitive for clearance range of 0.025-0.6 mm. The leakage flowrate was very high and was close to one-third of the total flowrate through the turbine at higher clearance of 0.6 mm, although the clearance volume was close to 4% of the total turbine volume. Parametric study was done to find the effect of twist in rotor geometry on the flow pulsations, leakage losses and the overall performance using CFD. A mechanism was developed to qualitatively and quantitatively analyze and calculate the leakage losses. It was inferred that twisting the rotors significantly reduced the flow pulsations and occurrence of cavitation; however this increased leakage flow from the rotor-rotor clearance, causing a slight reduction in the performance. The optimum twist angle was found to be 45°. The effect of inlet and outlet pipe’s cross-sectional shape on the fluid flow pulsations and overall performance of the developed PDT was analyzed using CFD. Initially, the cross-sectional shape of the pipe used for transporting the working fluid to and from the turbine rotors was circular. Subsequently, the influence of square and rectangular cross-sectional shaped pipe designs was analyzed. Also, parametric studies were performed to find the dimensions of rectangular and variable cross-sectional shaped pipes. It was observed that the initial flow pulsations greatly reduced for specified variable cross-sectional pipe compared to the other shapes. Also, an increment of 0.824% in hydraulic efficiency was observed compared to the initial circular pipe. At the rated conditions, the PDT with twisted rotors having fully circular shaped pipe developed 7.15 kW of output power with a hydraulic efficiency of 66.2% from the experimental study.
List of Figures ·························································· ⅰList of Tables ···························································· vAbbreviation ···························································· vi1. Introduction ··························································· 11.1 Background and application of the present work ············· 11.2 Scope and objective of present work ··························· 31.3 Literature review ················································· 71.4 Outline of the thesis ··············································· 102. Conceptual Design of PDT & Numerical Modeling Strategy.. 123. Experimental study ···················································· 214. Results and Discussion ················································ 254.1 Grid Independency test and validation ························· 254.2 Parametric study on the effect of twist in the rotors··········· 314.3 Leakage loss estimation for different clearances ·············· 454.4 Cavitation and its elimination ···································· 514.5 Sensitivity and influence of axial and radial clearance ······· 574.5.1 Experimental investigation of the influence of clearance gap on the performance of PDT ·············574.5.2 Parametric study on the sensitivity of the axial and radial clearance ·············································· 614.5.3 Effect of reduction in clearance ··························· 654.6 Effect of Inlet and Outlet pipe’s shapes ························· 764.6.1 Effect of inlet and outlet pipe’s cross-sectional shape 784.6.2 Parametric study on Rectangular pipe geometry ······ 924.6.3 Parametric study on variable cross-sectional inlet and outlet pipe shape ········································ 944.7 Socio-Economic analysis ········································· 1035 Summary and conclusions ··········································· 1056 Scope for future work ················································ 111Bibliography ································································ 113Published paper list ······················································· 122Acknowledgement ························································· 127