Research Paper Economic research of the transcritical Rankine cycle systems to recover waste heat from the marine medium-speed diesel engine Min-Hsiung Yang a,⇑ , Rong-Hua Yeh b a Department of Naval Architecture and Ocean Engineering, National Kaohsiung Marine University, Taiwan, Republic of China b Department of Marine Engineering, National Kaohsiung Marine University, Taiwan, Republic of China graphical abstract 0.116 0.118 0.12 0.122 3.2 3.6 4 0.9 0.95 1 R1234yf P L (MPa) P H (MPa) NPI (W/$) article info Article history: Received 21 January 2016 Accepted 28 August 2016 Available online xxxx Keywords: Transcritical Rankine cycle (TRC) Economic performance Working fluids Optimization Waste heat recovery Diesel engine abstract The aim of this study is to investigate the economic performance of a transcritical Rankine cycle (TRC) system for recovering waste heat from the exhaust gas of a marine medium-speed diesel engine. The variation of net power output, total cost of equipments and exergy destruction are investigated for the TRC system. Furthermore, to evaluate the economic performance of energy utilization, a parameter, net power output index, which is the ratio of net power output to the total cost, is introduced of the TRC system using R125, R143a, R218 and R1234yf as working fluids. The results show that R1234yf performs the highest economic performance, followed by R143a, R125 and R218 of the TRC system. It reveals that R1234yf not only has the smallest high and low pressures of the TRC system for reducing the purchased cost of equipments, but also promotes a larger pressure ratio of the expander for generat- ing power output among these working fluids. The comparisons of optimal pressure ratios obtained from thermodynamic and economic optimizations for these working fluids in the TRC system are also reported. In addition, an evaluation method using thermal efficiency and operating pressure ratio as parameters is proposed to assess the suitability of the working fluids of TRC system in economic analysis for waste heat recovery from the exhaust gas of a diesel engine. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Recently, waste heat recovery has become an important topic for energy utilization due to the energy shortage and growing carbon dioxide emissions in the world. The organic Rankine cycle system has advantages to recover waste heat source to produce useful power [1–3]. However, a pinch point exists between work- ing fluid and the heat source in the evaporator on account of the http://dx.doi.org/10.1016/j.applthermaleng.2016.08.195 1359-4311/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: No. 142, Haizhuan Rd., Nanzi Dist., Kaohsiung City 81157, Taiwan, Republic of China. E-mail address: mhyang@webmail.nkmu.edu.tw (M.-H. Yang). Applied Thermal Engineering xxx (2016) xxx–xxx Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng Please cite this article in press as: M.-H. Yang, R.-H. Yeh, Economic research of the transcritical Rankine cycle systems to recover waste heat from the mar- ine medium-speed diesel engine, Appl. Therm. Eng. (2016), http://dx.doi.org/10.1016/j.applthermaleng.2016.08.195