An experimental and modelling study of a 1 kW organic Rankine cycle unit with mixture working fluid Hyung-Chul Jung * , Leighton Taylor, Susan Krumdieck Department of Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand article info Article history: Received 17 May 2014 Received in revised form 9 October 2014 Accepted 2 January 2015 Available online 24 January 2015 Keywords: Organic Rankine cycle Working fluid Zeotropic mixture Waste heat recovery abstract The ORC (organic Rankine cycle) technology is appropriate for conversion of low-grade industrial waste heat to electrical power due to its utilization of volatile organic fluids as working fluids. It has been proposed that zeotropic fluid mixtures can improve the ORC performance compared to pure fluids. The purpose of this paper was to demonstrate the feasibility of using a zeotropic mixture as working fluid through an experimental study with a lab-scale ORC (organic Rankine cycle) test rig. In this study, a zeotropic mixture of R245fa and R365mfc (48.5%/51.5% on a mole basis) was examined by focusing on its dynamic behavior in the system until reaching steady state and the performance in a scroll expander, a finned-tube heat extractor, an evaporator and a condenser. The test rig used the exhaust gas from a 30 kW Capstone™ Gas Turbine as its heat source. Computer simulation was conducted at system level with steady state conditions and the results were compared to experimental data. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction A huge amount of energy is being released to the surroundings in the form of waste heat from many manufacturing industries. Due to rising fossil fuel prices and environmental impacts, it has become ever more significant to recover waste heat for efficient energy use. Recaptured waste heat can be used for industrial processes to improve energy efficiency or it can be converted to electricity. The ORC (organic Rankine cycle) is a possible option for electrical power generation from low-grade industrial waste heat resources, and in recent years, there has been significant growth in ORC researches. The possibility of waste heat recovery has led more research into ORCs with recent trends exploring supercritical ORCs and ORCs operating with zeotropic fluids as they can achieve higher effi- ciencies compared to the typical ORC [1]. The dynamic process of waste heat has also led to investigating optimal control systems so that the ORC can closely match the waste heat resource [2]. There has been a recent surge in the low temperature waste heat capa- bility of ORCs to further improve the efficiencies of industry by using waste gas streams that have been considered too low for useful energy [3]. The thermo-economic optimization of waste heat recovery ORCs is also an area of research with a large number of papers focusing on modeling both the thermodynamics and eco- nomics of a hypothetical ORC. ORC papers are typically numerical studies of ORC systems because an experimental investigation is costly and time consuming. A number of these papers investigate optimization of ORCs for the best performance for a given heat source with different ORC arrangements. Quoilin [4] investigated the implica- tions working fluid has on this optimization with the results sug- gesting higher evaporating temperatures to increase vapor density, which can lower the cost of the expander and evaporator. Dai et al. [5] used a genetic algorithm to optimize the exergy efficiency of an ORC utilizing waste heat. They showed that the recuperator re- quirements depend on the resource conditions and the greatest impact on the ORCs performance was the turbine inlet conditions. Wei et al. [6] also explored the ORC arrangements with waste heat resources and presented minimizing subcooling in the ORC is beneficial to the ORCs performance. The condensing conditions impact the ORC performance with high ambient temperatures decreasing the system performance by up to 30%. ORC applications extend beyond waste heat uses. Hettiarachchi et al. [7] investigated optimizing ORCs for low temperature geothermal resources. The main aspect of the optimization is an objective function that ratios the total heat exchanger area to the net power output of the ORC. The working fluid selection was also considered at the lower temperatures and it showed that poor working fluid selection can double the cost of an ORC. Wang et al. [8] investigated the working * Corresponding author. Tel.: þ64 3 364 2987x4107; fax: þ64 3 364 2078. E-mail address: hyung-chul.jung@canterbury.ac.nz (H.-C. Jung). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy http://dx.doi.org/10.1016/j.energy.2015.01.003 0360-5442/© 2015 Elsevier Ltd. All rights reserved. Energy 81 (2015) 601e614