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14:20   Session 2C: Working Fluid Selection Chair: Davide Bonalumi 14:20 20 mins Integrating working fluid design into the thermo-economic design of ORC processes using PC-SAFT Johannes Schilling, Dominik Tillmanns, Matthias Lampe, Madlen Hopp, Joachim Gross, André Bardow Abstract: To exploit the full thermo-economic potential of an Organic Rankine Cycle (ORC) application, the process, equipment and working fluid have to be optimized simultaneously. Today, working fluid selection and thermo-economic process optimization are commonly separated: In a first step, working fluid candidates are preselected based on heuristic knowledge. The process and equipment are thermo-economically optimized for each preselected working fluid, in a second step. However, if the preselection fails, the thermo-economically optimal working fluid is excluded and the approach leads to suboptimal solutions. In this work, we present an approach for the integrated thermo-economic design of ORC process, equipment and working fluid using consistent thermodynamic modelling. The approach is based on the Continuous-Molecular Targeting–Computer-aided Molecular Design (CoMT-CAMD) [1] framework. In CoMT-CAMD, the properties of the working fluid are modelled by the physically-based Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation of state [2]. A CAMD formulation allows the design of novel fluids during the process optimisation. So far, CoMT-CAMD was limited to equilibrium thermodynamics and thus thermodynamic cycle optimization. Recently, we developed models for the transport properties viscosity [3] and thermal conductivity [4] based on entropy scaling of PC-SAFT which allow designing the equipment within the CoMT-CAMD framework. In particular, the heat exchanger of the ORC can be designed using detailed correlations for single phase, evaporation and condensation heat transfer. Based on the equipment sizing, a thermo-economic objective function can be considered in the resulting mixed-integer nonlinear optimisation problem. Thereby, the thermo-economically optimal working fluid is identified in one single optimization problem jointly with the corresponding optimal process and equipment. The resulting approach is demonstrated for the design of a subcritical ORC for waste heat recovery. We show that the predicted specific purchased-equipment costs are in good accordance with real ORC applications. References [1] Schilling, J., Lampe, M., Gross, J., and Bardow, A., 1-stage CoMT-CAMD: An approach for integrated design of ORC process and working fluid using PC-SAFT, Chem. Eng. Sci., 2016, http://dx.doi.org/10.1016/j.ces.2016.04.048. [2] Gross, J. and Sadowski, G., Perturbed-chain SAFT: An equation of state based on a perturbation theory for chain molecules. Ind. Eng. Chem. Res., 2001, 40(4):1244–60. [3] Lötgering-Lin, O., and Gross, J., Group Contribution Method for Viscosities Based on Entropy Scaling Using the Perturbed-Chain Polar Statistical Associating Fluid Theory, Ind. Eng. Chem. Res., 2015, 54(32):7942–52. [4] Hopp, M., and Gross, J., Group-contribution method for thermal conductivity using PC-SAFT and entropy scaling, in: Proceedings of PPEPPD 2016, Porto, Portugal, 2016. 14:40 20 mins Material compatibility of ORC working fluids with polymeres Sebastian Eyerer, Peter Eyerer, Markus Eicheldinger, Sebastian Sax, Christoph Wieland, Hartmut Spliethoff Abstract: In this study, the material compatibility of refrigerants focusing on hydrofluoroolefines (HFO) with typical polymers in ORC plants and refrigeration units is analyzed with consistent testing conditions and a complete uncertainty analysis of the results. Therefore, one state-of-the-art refrigerant, namely R245fa, as well as the low-GWP fluids R1233zd-E and R1234yf are taken into account. The investigated polymers are ethylene-propylene-diene rubber (EPDM), fluoric rubber (FKM) and polytetrafluoroethylene (PTFE). In the case of EPDM, two different compositions are analyzed. To complement the study also the material compatibility with a polyolester (POE) lubricant is investigated. The material compatibility is evaluated by changes in volume, weight, Shore A as well as in small load hardness. With the small load hardness measurements, the hardness directly at the samples surface can be evaluated and thus important information on chemical interaction are provided. This study points out the importance of material compatibility testing especially investigating the difference between hydrofluorocarbons (HFC) and HFO, because the unsaturated characteristic of the HFO may lead to considerable changes in material compatibility compared to HFC refrigerants. 15:00 20 mins Integrated computer-aided working-fluid design and thermoeconomic ORC system optimisation Martin White, Oyeniyi Oyewunmi, Maria Anna Chatzopoulou, Antonio Pantaleo, Andrew Haslam, Christos Markides Abstract: The successful commercialisation of organic Rankine cycle (ORC) systems across a range of power outputs and heat-source temperatures demands step-changes in both improved thermodynamic performance and reduced investment costs. The former can be achieved through high-performance components and optimised system architectures operating with novel working-fluids, whilst the latter requires careful component-technology selection, economies of scale, learning curves and a proper selection of materials and cycle configurations. In this context, thermoeconomic optimisation of the whole power-system should be completed aimed at maximising profitability. This paper couples the computer-aided molecular design (CAMD) of the working-fluid with ORC thermodynamic models, including recuperated and other alternative (e.g., partial evaporation or trilateral) cycles, and a thermoeconomic system assessment. The developed CAMD-ORC framework integrates an advanced molecular-based group- contribution equation of state, SAFT-γ Mie, with a thermodynamic description of the system, and is capable of simultaneously optimising the working-fluid structure, and the thermodynamic system. The advantage of the proposed CAMD-ORC methodology is that it removes subjective and pre-emptive screening criteria that would otherwise exist in conventional working-fluid selection studies. The framework is used to optimise hydrocarbon working-fluids for three different heat sources (150, 250 and 350 ◦C). In each case, the optimal combination of working fluid and ORC system architecture is identified, and system investment costs are evaluated through component sizing models. It is observed that optimal working fluids that minimise the specific investment cost (SIC) are not the same as those that maximise power output. For the three heat sources the optimal working-fluids that minimise the SIC are isobutane, 2-pentene and 2-heptene, with SICs of 4.03, 2.22 and 1.84 £/W respectively. 15:20 20 mins Prospects of the use of nanofluids as working fluids for Organic Rankine Cycle power systems Maria Mondejar, Jesper Andreasen, Maria Regidor, Stefano Riva, Georgios Kontogeorgis, Giacomo Persico, Fredrik Haglind Abstract: The search of novel working fluids for organic Rankine cycle power systems is driven by the recent regulations imposing additional phase-out schedules for substances with adverse environmental characteristics. Recently, nanofluids (i.e. colloidal suspensions of nanoparticles in fluids) have been suggested as potential working fluids for organic Rankine cycle power systems due to their enhanced thermal properties, potentially giving advantages with respect to the design of the components and the cycle performance. Nevertheless, a number of challenges concerning the use of nanofluids must be investigated prior to their practical use. Among other things, the trade-off between enhanced heat transfer and increased pressure drop in heat exchangers, and the impact of the nanoparticles on the working fluid thermophysical properties, must be carefully analyzed. This paper is aimed at evaluating the prospects of using nanofluids as working fluids for organic Rankine cycle power systems. As a preliminary study, nanofluids consisting of a homogenous and stable mixture of different nanoparticles types and a selected organic fluid are simulated on a case study organic Rankine cycle unit for waste heat recovery. The impact of the nanoparticle type and concentration on the heat exchangers size, with respect to the reference case, is analyzed. The results indicate that the heat exchanger area requirements in the boiler decrease around 4 % for a nanoparticle volume concentration of 1 %, without significant differences among nanoparticle types. The pressure drop in the boiler increases up to 18 % for the same nanoparticle concentration, but this is not found to impact negatively the pump power consumption. 15:40 20 mins Thermodynamic optimization of heat recovery ORCs for heavy duty internal combustion engine: Pure fluids vs. zeotropic mixtures Roberto Scaccabarozzi, Michele Tavano, Costante Mario Invernizzi, Emanuele Martelli Abstract: This article focuses on the optimization of ORCs for heat recovery from heavy duty Internal Combustion Engines (ICEs), with particular attention to the optimal fluid selection. We considered two different ICEs featuring same power (10 MW) but different architectures: a two-stroke engine with exhaust temperature 250°C and a four-stroke engine with 350°C exhaust temperature. The analysis tackles the optimization of the heat integration between heat sources and ORC, the optimization of the cycle variables as well as the selection of the working fluid. In addition to conventional pure substances, such as hydrocarbons, refrigerants, and siloxanes, and recently synthesized refrigerants, (i.e., HFOs, HCFOs, and HFEs), also binary zeotropic mixtures have been considered. The optimization algorithm combines the evolutionary optimization algorithm PGS-COM with a systematic heat integration methodology which maximizes the heat recovered from the available heat sources. The methodology allows optimizing also the mixture composition. In total 36 pure fluids and 36 mixtures have been evaluated. HCFO-1233zde turns out to be the best or second best fluid for most cases. Cyclopentane is the best fluid for the engine with high exhaust temperature. Another promising fluid is NovecTM 649. The optimal cycles are supercritical with T-s diagrams resembling the ideal triangular cycle. The use of the mixtures leads to an increase of the exergy efficiency of around 2.5 percentage points (about 3.5 percentage point increase in net power output). Since the optimal cycle is supercritical, the temperature glide can be exploited only in condensation and, as a result, the advantage of mixtures compared to pure fluids is lower than the values reported in the literature.