11:20
Working fluids I
Chair: Dr. Ryan Nannan
11:20
20 mins
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ULTRA-LOW GWP WORKING FLUID FOR ORGANIC RANKINE CYCLES
Konstantinos (Kostas) Kontomaris, Barbara Minor, Claus-Peter Keller
Abstract: A new refrigerant, DR-2 has been developed which is a nonflammable with very low global warming potential (GWP) and is suitable for use in organic rankine cycles (ORCs). DR-2 is a hydrofluoro-olefin-based (HFO) fluid with an ozone depletion potential of zero and a GWP of less than 10. It is non-flammable and has a favorable toxicity profile based on testing to date. DR-2 is chemically stable in the presence of lubricant and metals up to the maximum temperature tested of 250 oC. DR-2 has a boiling point of 33ºC and relatively high critical temperature, which generates relatively low vapor pressures and enables high cycle energy efficiencies. DR-2 thermodynamic performance under cycle conditions representative of ORC applications was evaluated through computational modeling. It can enable more environmentally sustainable ORC cycle platforms for the utilization of low temperature heat to generate electrical power at higher temperatures and with higher energy efficiencies than incumbent working fluids.
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11:40
20 mins
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IDENTIFICATION AND TEST OF LOW GLOBAL WARMING POTENTIAL ALTERNATIVES TO HFC-245FA IN ORGANIC RANKINE CYCLES
Pierre Huck, Anna Lis Laursen, Jalal Zia, Lance Woolley
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.
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12:00
20 mins
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AN ASSESSMENT OF WORKING-FLUID MIXTURES IN ORGANIC RANKINE CYCLES FOR WASTE-HEAT RECOVERY USING SAFT-VR
Oyeniyi Oyewunmi, Aly Taleb, Andrew Haslam, Christos Markides
Abstract: Minimizing exergetic loss associated with irreversibility in the working fluid evaporator is significant in the effort to improve the efficiency of organic Rankine cycles. Mixtures of working fluids are known to undergo non-isothermal phase change, providing a better thermal match with the heat source. This work presents results of computer simulations of an organic Rankine cycle using a decane-butane binary fluid mixture as the working fluid. Thermodynamic properties for the fluid mixture are generated using the SAFT-VR Mie equation of state approach. Significant performance improvements and cost reductions are reported compared to a single-component reference working fluid.
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12:20
20 mins
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APPLICATION OF CO2 /HCs MIXTURES IN THE ORGANIC RANKINE CYCLE
Baolin An, Yuanyuan Duan, Zhen Yang
Abstract: The utilization of low-to-medium temperature heat sources is great importance for efficient energy utilization. Low-to-medium temperature heat sources can not be used with water based cycles due to their low efficiencies. The organic Rankine cycle (ORC) using organic fluid as the working fluid can make better use of these heat sources.
HCs have low GWP and good thermal performance but high flammability. ORCs using HCs are mostly subcritical cycles that always have large heat transfer temperature differences. The natural working fluid CO2 is non-flammable, but has poor efficiencies and high operating pressures. The mixtures of CO2/HCs may have good thermal performance and low flammability.
This study analyzed the thermal efficiencies, exergy efficiencies and system power outputs of ORC with CO2/ethane, CO2/propylene, CO2/propane, CO2/isobutane and CO2/cyclopentane mixtures. The CO2 molar fractions in these mixtures were varied from 0 to 100. The systems were assumed to be connected to geothermal, engine exhaust or cement kiln exhaust heat source, with a geothermal source temperature of 393.15 K, an engine exhaust temperature of 523.15 K and a cement kiln exhaust temperature of 603.15 K. The 50% CO2 and 50% HCs molar fraction mixtures were selected to analyze the correlations between the thermal efficiencies, exergy efficiencies and system power outputs with the peak cycle pressures. The concept of pure fuel minimum ignition energy was extended to the mixtures to analyze the flammability, and the CO2/propane minimum ignition energy was calculated.
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