臺灣博碩士論文加值系統

sCO2 Brayton Cycle近年來十分熱門的研究主題，相較於傳統上使用空氣作為工作流體的Brayton Cycle, 或是應用於燃煤電廠的Steam Rankine Cycle，SCO2 Brayton Cycle不但能提供更高的效率，在相同發電量下，根據GE研究，sCO2 Brayton Cycle渦輪機的體積甚至能縮小至燃煤電廠使用之Steam Rankine Cycle的1/10，可望能降低其製造和維護的成本。此外，sCO2 Brayton Cycle的熱源非常廣泛，從集中式的太陽能發電、地熱到化石燃料等，皆可做為其熱源。
由於近年來全球暖化問題日益嚴重，和人類大量使用化石燃料絕對脫不了關係，尤其是在發電上，由於發電成本考量，以及無知政客推波助瀾下之不理性之反核聲浪，較高汙染的燃煤發電比例上始終居高不下。其中工業用電佔整體超過50%以上，然而工業的能源有將近一半的能源以廢熱或者其餘無法加以利用之型態的型態排放至空氣中，這是一種非常浪費能源的行為。因此，能夠如何有效利用這些廢熱，成為非常熱門的主題。其中，最著名的大概是本研究室研發多年的Organic Rankine Cycle(ORC)，最後也成功商轉。不過，ORC主要適用於低溫廢熱源，其效率在較高溫的廢熱相對低落。因此，能夠用於較高溫廢熱源的sCO2 Brayton Cycle成為極具吸引力的研究主題。
不過，由於在超臨界態的CO2介於液態和氣態的特殊性質，使得渦輪機¬-壓縮機-發電機系統(TAC system,Turbine-Alternator-Compressor system )開發不易，尤其在壓縮機的進口，其溫度和壓力十分接近臨界點，需十分留意防止二氧化碳進入次臨界態，以防止流體性質劇烈變動造成壓縮機效能不彰。
本研究是國家第二期能源計畫(NEPII)--sCO2 Brayton Cycle發電系統開發的子計畫之一，壓縮機和渦輪機的系統開發中，有關渦輪機設計的部分。本計畫將使用大約450 °C作為廢熱源溫度參考。另外，因為超臨界二氧化碳的性質，本研究將採用Radial-Inflow Turbine作為渦輪機的類型。
Radial Inflow Turbine雖在設計上文獻中有許多經驗公式可供參考，但僅能得到建構模型所需之大部分參數，此模型仍須帶入CFD模擬，若未達到預期效率能須修改設計，如此反覆後，若模擬結果達到要求，即可進行加工和實驗測試。

The research of Supercritical CO2 (sCO2) Brayton Cycle has been popular over the past decade, due to its higher efficiency and smaller component size compared with those of steam Rankine cycle and air Brayton Cycle. Studies showed that SCO2 Brayton Cycle can accommodate a wide range of temperature as the heat source, starting from 260°C to 1200 °C. Thus, various research had been investigated to apply sCO2 Brayton Cycle into fields such as concentrated solar power, nuclear power, geothermal power, and waste heat recovery, making it a viable option for renewable energy.
This study is a subproject of SCO2 Brayton Cycle power generation system, a project under the National Energy Program-Phase II in Taiwan, with the objective of designing a power generation system using waste heat as heat source. The temperature of the waste heat is set to be 450°C, conforming to mid-range waste heat. The aim of this subproject is to design a turbine with the inlet total pressure of 14.1 MPa and total temperature of 573K, respectively, and outlet pressure of 8.5 MPa, corresponding to an expansion ratio of 1.658. Due to its small size and low mass flow rate, radial inflow turbine is selected instead of the axial flow turbine.
Some efforts were made by previous member of this lab to modify the existing turbine model to avoid the complexity of designing a turbine model from scratch. The efficiency, however, turned out to be lower the expectation. Therefore, in this study, the previously modified turbine model would be discarded and the new turbine would be built from square one.
This study tried to use Meanline Analysis from the literature as a preliminary design tool. Although most studies devoting to the design of radial inflow turbine were developed for turbine using air as working fluid, recent studies about the design of SCO2 turbine indicated that Meanline Analysis is qualified to be a preliminary design tool.
The simulation result of the Meanline Analysis was shown to be deviate from the design point, as expected. Fortunately, with the aid of CFD, the problem predicted by the simulation could be corrected and the model could be adjusted accordingly. At the end, with some bold assumption, the turbine model close to the expected pressure ratio and power output was devised.

List of Figures ______________________________________________________________ 4
List of tables _______________________________________________________________ 6
Chapter 1 Introduction_______________________________________________________ 7
1.1 Motivation ___________________________________________________________ 7
1.2 Literature Review ______________________________________________________ 9
1.2.1 Supercritical CO2 (sCO2) _____________________________________________ 9
1.2.2 sCO2 Brayton Cycle ________________________________________________ 11
1.2.3 Introduction to Radial Inflow (RIF) Turbine______________________________ 16
1.3 Purpose of the research ________________________________________________ 24
Chapter 2 Theory and governing equations______________________________________ 27
2.1 Velocity Triangle ______________________________________________________ 27
2.2 The governing equations _______________________________________________ 28
2.2.1 Continuity Equation________________________________________________ 29
2.2.2 Euler Turbine Equation _____________________________________________ 29
2.2.3 Energy Equation __________________________________________________ 29
2.3 Dimensionless Parameters ______________________________________________ 31
2.3.1 Specific Speed
_______________________________________________ 31
2.3.2 Specific Diameter______________________________________________ 31
2.4 Turbine Efficiency _____________________________________________________ 33
Isentropic Process________________________________________________________ 34
Chapter 3. Methodology ____________________________________________________ 35
3.1 sCO2 Brayton Cycle State Analysis ________________________________________ 35
3.2 Preliminary Design for RIF Turbine________________________________________ 37
3.2.1 Spouting Velocity ______________________________________________ 39
3.2.2 Velocity ratio and Rotor Tip Velocity ___________________________ 40
3.2.3 Specific Speed _________________________________________________ 412
3.2.4 Total-to-static efficiency− ______________________________________ 41
3.2.5 Rotor inlet absolute angle_______________________________________ 41
3.2.6 Tangential component of rotor inlet absolute velocity ________________ 42
3.2.7 rotor inlet absolute velocity______________________________________ 42
3.2.8 Meridional component of rotor inlet velocity ______________________ 43
3.2.9 Rotor inlet radius ______________________________________________ 43
3.2.10 Rotor inlet relative flow angle ___________________________________ 43
3.2.11 Rotor Leading edge Blade Thickness ______________________________ 44
3.2.12 Rotor Trailing edge Blade Thickness______________________________ 44
3.2.13 Rotor inlet height_____________________________________________ 44
3.2.14 Meridional component of rotor exit absolute velocity ______________ 45
3.2.15 Rotor outlet hub height ______________________________________ 45
3.2.16 Rotor outlet shroud height _____________________________________ 45
3.2.17 Mean Radius at rotor outlet _____________________________________ 46
3.2.18 The Axial Length of the rotor ___________________________________ 46
3.2.19 Mean blade speed at rotor outlet ________________________________ 47
3.2.20 Mean relative velocity at rotor exit ______________________________ 47
3.2.21 Mean relative flow angle at rotor exit _____________________________ 48
3.2.22 Hub and shroud relative flow angle at rotor exit ______________ 48
3.2.23 Number of rotor blades ________________________________________ 49
3.2.24 Stator Outlet Diameter _______________________________________ 50
3.2.25 Stator Inlet Diameter __________________________________________ 51
3.2.26 Number of stator blades ________________________________________ 51
3.3 Flow Simulation ______________________________________________________ 51
3.3.1 ANSYS Bladegen___________________________________________________ 52
3.3.2 ANSYS TurboGrid __________________________________________________ 53
3.3.3 ANSYS CFX _______________________________________________________ 54
Chapter 4 Preliminary Design and its Simulation Results ___________________________ 573
4.1 Result of the preliminary design _________________________________________ 58
4.2 Result of the simulation ________________________________________________ 61
4.2.1 The Turbine model ________________________________________________ 61
4.2.2 Mesh of the rotor and the stator _____________________________________ 62
4.2.3 Settings of boundary conditions ______________________________________ 65
4.2.4 Result of the simulation ____________________________________________ 66
4.2.5 Summary ________________________________________________________ 68
Chapter 5 Modified Design and Simulation ______________________________________ 69
5.1 Modification one _____________________________________________________ 70
5.2 Modification Two _____________________________________________________ 73
5.2.1 Method of modification ____________________________________________ 73
5.2.2 Simulation Results _________________________________________________ 76
5.3 Modification three ____________________________________________________ 78
5.3.1 Method of modification ____________________________________________ 78
5.3.2 Result of the simulation ____________________________________________ 82
Chapter 6 Conclusion and Future Work _________________________________________ 89
References _______________________________________________________________ 90

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