因為超臨界二氧化碳布雷頓循環在復熱器（recuperator）裡冷側流體的比熱大於熱側流體，使得熱回收的效益不彰，因此利用再壓縮循環改善此問題。本研究欲探討在渦輪機入口溫度為580 K與壓縮比1.86的條件下，使用再壓縮循環對於整體發電效率的增益。首先對復熱器的pinch temperature設定做分析，發現主要影響循環熱效率的復熱器效能參數為低溫復熱器的pinch temperature，雖然如此，高溫復熱器的pinch temperature也會影響低溫復熱器的熱側進口溫度，而影響LTR與HTR的UA值。從模擬結果也發現，當主壓縮機的流量愈低，循環熱效率愈高，雖然兩個壓縮機總耗功增加，造成淨輸出功降低，但也減少了需要從熱源取得的熱。
本研究亦針對壓縮比為1.86的主壓縮機（main compressor）葉輪幾何與尺寸作設計，使用Ansys的BladeGen建立轉子模型，Turbogrid建立網格後，最後以CFX軟體進行流場模擬，確定設計的葉輪符合需求。經過理論分析與設計流程後得到一流量2 kg/s，轉速60,000 rpm，壓縮比1.93與等熵效率50%的壓縮機轉子設計，符合當初之設計點。在未來將會針對轉子葉片角度改良並設計擴散器（diffuser），以更進一步完成整個壓縮段的設計。

Supercritical carbon dioxide Brayton cycles are a novel technology to generate electricity from a wide range of heat sources. One of this cycle characteristics is that the specific heat capacity of the cold side flow is much higher than that of the hot side flow. In recuperators this effect decreases the efficiency of heat recovery. Recompression cycle designs are a possible solution for this problem.
This study is divided into two parts. The first part aims at determining the effect of the recompression cycle for a turbine inlet temperature of 580 K and a compression ratio of 1.86 through simulations by utilizing Aspen Plus. The second part targets to design an impeller based on the results of the first part. As expected, Aspen Plus simulation results show that as the main compressor flow rate decreases, the heat input from the surroundings also declines. However, the net work output decreases while the overall thermal cycle efficiency increases. Through the thermodynamic analysis, this study obtained both temperature and pressure at every station. Next, a main impeller geometry could be designed and sized based upon the design point. To ensure the design meets the requirements, this study utilizes Ansys Bladegen, Turbogrid and CFX software to create the model, meshes, and flow field simulation, respectively.
After the theory analysis and design procedure, a main compressor model with a mass flow rate of 2 kg/s, a rotational speed of 60,000 rpm, a compression ratio of 1.93 and an isentropic efficiency of 50% has been attained. Hence, this impeller meets the design point. The compression stage of the supercritical carbon dioxide Brayton cycle will be completed after the improvement of the impeller blade angle distribution and the diffuser design in the future.

[1] International Nuclear Event Scale. (2016, November 14). In Wikipedia, the free encyclopedia. Retrieved November 25, 2016, from https://en.wikipedia.org/wiki/International_Nuclear_Event_Scale
[2] 穹頂之下 (紀錄片) (2016年10月19日)。2016年11月25日，取自：維基百科，自由的百科全書：https://zh.wikipedia.org/wiki/%E7%A9%B9%E9%A1%B6%E4%B9%8B%E4%B8%8B_(%E7%BA%AA%E5%BD%95%E7%89%87)
[3] 經濟部能源局 (2016年11月9日)。2015年能源統計年報。2016年11月25日，取自：http://web3.moeaboe.gov.tw/ecw/populace/content/ContentLink.aspx?menu_id=378
[4] Galanis, N., Cayer, E., Roy, P., Denis, E. S., & Desilets, M. (2009). Electricity generation from low temperature sources. Journal of Applied Fluid Mechanics, 2(2), 55-67.
[5] Sims, R. E., Rogner, H. H., & Gregory, K. (2003). Carbon emission and mitigation cost comparisons between fossil fuel, nuclear and renewable energy resources for electricity generation. Energy policy, 31(13), 1315-1326.
[6] Evans, A., Strezov, V., & Evans, T. J. (2009). Assessment of sustainability indicators for renewable energy technologies. Renewable and sustainable energy reviews, 13(5), 1082-1088.
[7] Kaltschmitt, M., Streicher, W., & Wiese, A. (Eds.). (2007). Renewable energy: technology, economics and environment. Springer Science & Business Media.
[8] Bajpai, P., & Dash, V. (2012). Hybrid renewable energy systems for power generation in stand-alone applications: a review. Renewable and Sustainable Energy Reviews, 16(5), 2926-2939.
[9] Johnson, I., Choate, W. T., & Davidson, A. (2008). Waste Heat Recovery. Technology and Opportunities in US Industry. BCS, Inc., Laurel, MD (United States).
[10] 陳昱霖. (2013). 工廠廢熱回收設備配置最佳化規劃. 國立雲林科技大學工業工程與管理研究所學位論文, 1-58.
[11] Supercritical fluid. (2016, November 24). In Wikipedia, the free encyclopedia. Retrieved November 25, 2016, from https://en.wikipedia.org/wiki/Supercritical_fluid
[12] Dostal, V., Driscoll, M. J., & Hejzlar, P. (2004). A supercritical carbon dioxide cycle for next generation nuclear reactors. Massachusetts Institute of Technology. Dept. of Nuclear Engineering, Cambridge, MA, Paper No. MIT-ANP-TR-100.
[13] United Nations Environment Programme. Ozone Secretariat. (1998). UNEP 1998 Report of the Solvents, Coatings and Adhesives Technical Options Committee (STOC): 1998 Assessment. UNEP/Earthprint.
[14] Air Conditioning and Refrigeration Industry Board網站： http://www.acrib.org.uk/
[15] Shao, W., Wang, X., Yang, J., Liu, H., & Huang, Z. (2016, June). Design Parameters Exploration for Supercritical CO2 Centrifugal Compressors Under Multiple Constraints. In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition (pp. V009T36A008-V009T36A008). American Society of Mechanical Engineers.
[16] Ahn, Y., Bae, S. J., Kim, M., Cho, S. K., Baik, S., Lee, J. I., & Cha, J. E. (2015). Review of supercritical CO 2 power cycle technology and current status of research and development. Nuclear Engineering and Technology, 47(6), 647-661.
[17] Cayer, E., Galanis, N., Desilets, M., Nesreddine, H., & Roy, P. (2009). Analysis of a carbon dioxide transcritical power cycle using a low temperature source. Applied Energy, 86(7), 1055-1063.
[18] Persichilli, M., Kacludis, A., Zdankiewicz, E., & Held, T. (2012). Supercritical CO2 Power Cycle Developments and Commercialization: Why sCO2 can Displace Steam Ste. Power-Gen India & Central Asia.
[19] Vélez, F., Chejne, F., Antolin, G., & Quijano, A. (2012). Theoretical analysis of a transcritical power cycle for power generation from waste energy at low temperature heat source. Energy Conversion and Management, 60, 188-195.
[20] Vélez, F., Segovia, J., Chejne, F., Antolín, G., Quijano, A., & Martín, M. C. (2011). Low temperature heat source for power generation: exhaustive analysis of a carbon dioxide transcritical power cycle. Energy, 36(9), 5497-5507.
[21] Feher, E. G. (1968). The supercritical thermodynamic power cycle. Energy conversion, 8(2), 85-90..
[22] Angelino, G. (1968). Carbon dioxide condensation cycles for power production. Journal of Engineering for Power, 90(3), 287-295.
[23] Wright, S. A., Radel, R. F., Vernon, M. E., Rochau, G. E., & Pickard, P. S. (2010). Operation and analysis of a supercritical CO2 brayton cycle. Sandia Report, No. SAND2010-0171.
[24] Bahamonde Noriega, J. S. (2012). Design method for s-CO2 gas turbine power plants: Integration of thermodynamic analysis and components design for advanced applications (Doctoral dissertation, TU Delft, Delft University of Technology).
[25] Garg, P., Kumar, P., & Srinivasan, K. (2013). Supercritical carbon dioxide Brayton cycle for concentrated solar power. The Journal of Supercritical Fluids, 76, 54-60.
[26] S. Schuster, F.-K. Benra, & D. Brillert. (2016, March). Small scale sCO2 compressor impeller design considering real fluid conditions. In Proceedings of the 5th International Symposium on Supercritical CO2 Power Cycles.
[27] Milani, D., Luu, M. T., McNaughton, R., & Abbas, A. (2016). A comparative study of solar heliostat assisted supercritical CO 2 recompression Brayton cycles: Dynamic modelling and control strategies. The Journal of Supercritical Fluids, 120, 113-124.
[28] Lemmon, E., Huber, M., & McLinden, M. (2013). REFPROP 9.1. NIST Standard Reference Database, 23.
[29] 林柏宏. (2016). 超臨界二氧化碳布雷頓循環之渦輪機葉片分析與研究. 清華大學動力機械工程學系學位論文, 1-66.
[30] 林俋伸. (2014). 超臨界二氧化碳布雷頓循環發電模組配置與性能分析. 清華大學動力機械工程學系學位論文, 1-73.
[31] Bryant, J. C., Saari, H., & Zanganeh, K. (2011, May). An analysis and comparison of the simple and recompression supercritical CO2 cycles. In Supercritical CO2 Power Cycle Symposium, Boulder, CO.
[32] Dyreby, J., Klein, S., Nellis, G., & Reindl, D. (2014). Design Considerations for Supercritical Carbon Dioxide Brayton Cycles With Recompression. Journal of Engineering for Gas Turbines and Power, 136(10), 101701.
[33] 王啟川. (2007). 熱交換設計. 五南.
[34] Jansohn, P. (Ed.). (2013). Modern gas turbine systems: High efficiency, low emission, fuel flexible power generation. Elsevier.
[35] Dixon, S. L., & Hall, C. (2013). Fluid mechanics and thermodynamics of turbomachinery. Butterworth-Heinemann.
[36] Schwind, R., & Abdallah, S. (2015). A Look at Compressor Impeller Technologies for Turbochargers Focusing on Surge Mitigation. Global Journal of Technology and Optimization, 2015.
[37] Nassar A, Hagpurwala QH, Reddy KB (2006) Design and CFD investigation of centrifugal compressor for turbocharger and parametric study on splitter blades.Sas Tech 2: 35-41.
[38] Wu, C. H. (1952). A general theory of three-dimensional flow in subsonic and supersonic turbomachines of axial-, radial, and mixed-flow types (No. NACA-TN-2604). NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON DC.
[39] Kenneth, E., & Nichols, P. E. (2012). How to select turbomachinery for your application. Barber-Nichols Inc, 5-6.
[40] Ventura, C. A., Jacobs, P. A., Rowlands, A. S., Petrie-Repar, P., & Sauret, E. (2012). Preliminary design and performance estimation of radial inflow turbines: An automated approach. Journal of Fluids Engineering, 134(3), 031102.
[41] Vasmate, S. (2014). Computational fluid dynamics (CFD) analysis of intermediate pressure steam turbine. International Journal of Mechanical Engineering and Robotics Research, 3(4), 459.
[42] Robinson, C., Casey, M., Hutchinson, B., & Steed, R. (2012, June). Impeller-diffuser interaction in centrifugal compressors. In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition (pp. 767-777). American Society of Mechanical Engineers.
[43] Schiff, J. (2013). A Preliminary Design Tool for Radial Compressors. ISRN LUTMDN/TMHP--13/5287--SE.
[44] Wang, J., Huang, Y., Zang, J., & Liu, G. (2016, June). Preliminary Design and Considerations of a MWe Scale Supercritical CO2 Integral Test Loop. In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition (pp. V009T36A002-V009T36A002). American Society of Mechanical Engineers.
[45] Pasch, J. J., Conboy, T. M., Fleming, D. D., & Rochau, G. E. (2012). Supercritical CO2 recompression Brayton cycle: completed assembly description (No. SAND2012-9546). Sandia National Laboratories.
[46] Utamura, M., Hasuike, H., Ogawa, K., Yamamoto, T., Fukushima, T., Watanabe, T., & Himeno, T. (2012, June). Demonstration of supercritical CO2 closed regenerative Brayton cycle in a bench scale experiment. In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition (pp. 155-164). American Society of Mechanical Engineers.
[47] Kim, S. G., Lee, J., Ahn, Y., Lee, J. I., Addad, Y., & Ko, B. (2014). CFD investigation of a centrifugal compressor derived from pump technology for supercritical carbon dioxide as a working fluid. The Journal of Supercritical Fluids, 86, 160-171.
[48] Wang, Y., Shi, D., Zhang, D., & Xie, Y. (2017). Investigation on Unsteady Flow Characteristics of a SCO2 Centrifugal Compressor. Applied Sciences, 7(4), 310.
[49] Kim, C., Lee, H., Yang, J., Son, C., & Hwang, Y. (2016). Study on the performance of a centrifugal compressor considering running tip clearance. International Journal of Refrigeration, 65, 92-102.
[50] Ganesh, C. S., Nagpurwala, Q. H., & Dixit, C. B. (2010). Effect of leading edge sweep on the performance of a centrifugal compressor impeller. SASTech J, 9(2), 55-62.
[51] 谢龙汉, 赵新宇, & 张炯明. (2012). ANSYS CFX 流体分析及仿真. 电子工业出版社, 北京.
[52] Balje, O. E. (1981). Turbomachines-A guide to design, selection, and theory. John Wiley & Sons.
[53] Whitfield, A. (1992, June). Conceptual Design of a Centrifugal Compressor Including Consideration of the Effect of Inlet Prewhirl. In ASME 1992 International Gas Turbine and Aeroengine Congress and Exposition (pp. V001T01A004-V001T01A004). American Society of Mechanical Engineers.
[54] Came, P. M., & Robinson, C. J. (1998). Centrifugal compressor design. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 213(2), 139-155.
[55] Brasz, J. J. (1992). U.S. Patent No. 5,145,317. Washington, DC: U.S. Patent and Trademark Office.
[56] Ganesh, C. S., Nagpurwala, Q. H., & Dixit, C. B. (2010). Effect of leading edge sweep on the performance of a centrifugal compressor impeller. SASTECH Journal, 9(2), 55-62.
[57] Xu, C. (2009). U.S. Patent No. 7,563,074. Washington, DC: U.S. Patent and Trademark Office.
[58] Pecnik, R., Rinaldi, E., & Colonna, P. (2012). Computational fluid dynamics of a radial compressor operating with supercritical CO2. Journal of Engineering for Gas Turbines and Power, 134(12), 122301.
[59] Monge, B. (2014). Design of supercritical carbon dioxide centrifugal compressors. University of Seville.