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Session: Working fluids I
Session starts: Tuesday 08 October, 11:20
Presentation starts: 11:40
Room: Willem Burger Zaal

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Pierre Huck (GE Global Research - Munich, Germany)
Anna Lis Laursen (GE Global Research - Niskayuna, NY, USA)
Jalal Zia (GE Global Research - Niskayuna, NY, USA)
Lance Woolley (GE Power & Water - Cerritos, CA, USA)

Abstract:
Due to the increasing legislative pressure on hydrofluorocarbons with high global warming potential, there is the need to identify replacement options for HFC-245fa, a working fluid currently used in a large number of organic Rankine cycle applications. This study focuses on the assessment of the three hydrofluoroolefins HFO-1234yf, HFO-1234ze(E) and HCFO-1233zd(E) as low global warming replacement candidates for HFC-245fa. The first step of the study was to construct a cycle simulation to assess the impact on key organic Rankine cycle operating parameters for switching from HFC-245fa to one of the three candidate fluids. Keeping the heat source, heat sink parameters as well as size of the heat exchanger equipment unchanged, HFO-1234yf and HFO-1234ze(E) resulted in significant decrease in net power output compared to HFC-245fa and were not further investigated. HCFO-1233zd(E), on the other hand, resulted in a slight net power output increase and there was limited changes in key cycle parameters, including expander specific speed and diameter. These factors qualified HCFO-1233zd(E) as a viable drop-in replacement candidate in units originally designed and optimized for HFC-245fa. This assumption was validated experimentally during the second step of the assessment. The experiment was conducted on a test unit of a productized organic Rankine cycle, which is a recuperated subcritical cycle that uses a radial expander. A test matrix was developed for expander rotating speed, grid power and expander inlet temperature, in order to compare the performance and the dynamic behavior of the test unit running with HCFO-1233zd(E) and HFC-245fa over a large operating range. HCFO-1233zd(E) was observed to result in a stable behavior of the cycle throughout the experimental operation. The duration to reach steady state was similar for both HFC-245fa and HCFO-1233zd(E). There were some working fluid-material compatibility items that were addressed in the process of switching fluids. Additionally, some software modifications to the test unit were required (i.e.: mass flow rate and fluid property differences). HCFO-1233zd(E) data demonstrated an average of 5%pts improvement over HFC-245fa in the expander adiabatic efficiency. Based on a statistical analysis of the experimental results, the overall cycle efficiencies of the test units stayed the same with both fluids and the data showed a slight (1 bar) decrease in inlet pressure. Finally an analysis of HCFO-1233zd(E) after the testing period concluded that the fluid did not decompose during the experiment.