||As industry develops, there is an increasing demand on energy. The development of energy-saving devices and renewable energy have been emerging issues around the world. Organic Rankine cycle, ORC, is a technique to generate power from low temperature heat sources. ORC is used in recycling industrial waste heat, solar energy and geothermal power generation. Waste heat below 230°C is called low-grade waste heat. Low-grade waste heat cannot be efficiently reused in process, so it is usually exhausted into the environment. In this research, we perform thermodynamic analysis on low-grade waste heat recycling ORC systems. R134a,R1234yf, R227ea, R245fa, and Propane are used as working fluids and their max system thermal efficiency and net power output is calculated. We discuss the effect of different evaporation pressure and evaporation temperature to the system performance with different conditions of three heat source temperatures, 100°C, 150°C,and 200°C, and four pinch point temperature differences, 5°C,10°C,15°C, and20°C by iteration methods to find the optimum parameters. The result shows that R245fa has the highest net work output of 505.5kW and system thermal efficiency of 15% at heat source temperature of 200°C. In this research, we use brazed plate heat exchangers as example. We use the optimum conditions to calculate the total heat transfer area and evaluate the constructing costs of the heat exchanger. It is found that the higher heat source temperature, the lower cost it needs. When the propane is used as working fluid, the lowest cost can be achieved with heat source temperature at 150°C、200°C.|
|| B. F. Tchanche, G. Lambrinos, A. Frangoudakis, and G. Papadakis, ``Low-grade heat con- version into power using organic rankine cycles--a review of various applications,′′ Renew- able and Sustainable Energy Reviews, vol. 15, no. 8, pp. 3963–3979, 2011.|
 F. Velez, J. J. Segovia, M. C. Mart??n, G. Antol??n, F. Chejne, and A. Quijano, ``A techni-
cal, economical and market review of organic rankine cycles for the conversion of low-grade
heat for power generation,′′ Renewable and Sustainable Energy Reviews, vol. 16, no. 6, pp. 4175– 4189, 2012.
 S. Quoilin and V. Lemort, ``Technological and economical survey of organic rankine cy- cle systems,′′ 2009.
 ``105 年能源統計手冊,′′ 經濟部能源局, 2016.
 C. Vetter, H.-J. Wiemer, and D. Kuhn, ``Comparison of sub-and supercritical organic rank- ine cycles for power generation from low-temperature/low-enthalpy geothermal wells, con- sidering specific net power output and efficiency,′′ Applied Thermal Engineering, vol. 51, no. 1, pp. 871–879, 2013.
 C. He, C. Liu, H. Gao, H. Xie, Y. Li, S. Wu, and J. Xu, ``The optimal evaporation temper- ature and working fluids for subcritical organic rankine cycle,′′ Energy, vol. 38, no. 1, pp. 136– 143, 2012.
 I. H. Aljundi, ``Effect of dry hydrocarbons and critical point temperature on the efficien- cies of organic rankine cycle,′′ Renewable Energy, vol. 36, no. 4, pp. 1196–1202, 2011.
 D. Wang, X. Ling, H. Peng, L. Liu, and L. Tao, ``Efficiency and optimal performance eval- uation of organic rankine cycle for low grade waste heat power generation,′′ Energy, vol. 50, pp. 343–352, 2013.
 ``2015 各國平均電價比較,′′ 台灣電力公司, 2016.
 E. Lemmon, M. Huber, and M. McLinden, Refprop 9.0, nist standard reference database 23, version 9.0 2010.
 J. M. Calm and G. Hourahan, ``Refrigerant data update,′′ HPAC Engineering, vol. 79, no.
1, pp. 50–64, 2007.
 A. Mota-Babiloni, J. Navarro-Esbr??, A. Barragan, F. Moles, and B. Peris, ``Drop-in energy performance evaluation of r1234yf and r1234ze (e) in a vapor compression system as r134a replacements,′′ Applied Thermal Engineering, vol. 71, no. 1, pp. 259–265, 2014.
 H. Xu, N. Gao, and T. Zhu, ``Investigation on the fluid selection and evaporation paramet- ric optimization for sub-and supercritical organic rankine cycle,′′ Energy, vol. 96, pp. 59– 68, 2016.
 R. Turton, R. Bailie, W. Whiting, J. Shaeiwitz, and D. Bhattacharyya, Analysis, synthesis and design of chemical processes. Pearson Education, 2012, ISBN: 9780132618731.
 Chemical engineering, https://www.chemengonline.com/pci.