A theoretical and experimental study of HFE-7000 in a small scale solar organic Rankine cycle as a thermofluid

Authors: Huseyin Utku, H. and Khan, Z.

http://eprints.bournemouth.ac.uk/29849/

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2653651&resultClick=1

Start date: 26 June 2017

Publisher: ASME

Place of Publication: USA

ISBN: 978-0-7918-5761-8

DOI: 10.1115/POWER-ICOPE2017-3194

The use of thermofluids with boiling temperatures lower than the water, allows the operation of low and medium temperature solar thermal systems on an Organic Rankine Cycle (ORC) to generate both mechanical and heat energy. At the same time, the selection of appropriate thermofluid is an important process and has a significant effect both on the system performance and the environment. Conventional thermofluids such as Chlorofluorocarbons (CFCs) and Hydrochlorofluorocarbons (HCFCs) have high ozone depletion (ODP) and high global warming (GWP) potential. It is therefore important to investigate novel and environmentally friendly thermofluids to address environmental impacts as global warming and ozone layer depletion. Hydrofluoroethers (HFEs) have zero ODP and relatively low GWP and therefore can be used as a replacement for CFCs and HCFCs. In this study, a small scale solar ORC is designed and commissioned to use HFE 7000 as a thermofluids. The system has a flat plate collector and a vane expander as the heat source and prime mover of the cycle respectively. The system performance is determined through energy analysis. Then, a mathematical model of the cycle is developed and the effect of various operating conditions on the components, as well as the whole cycle is examined through performing simulation analyses. Both the experimental and theoretical research indicates that HFE 7000 offers a viable alternative to be used efficiently in small scale solar ORCs to generate mechanical and heat energy.

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Authors: Helvaci, H.U. and Khan, Z.A.

http://eprints.bournemouth.ac.uk/29849/

Journal: American Society of Mechanical Engineers, Power Division (Publication) POWER

Volume: 2

ISBN: 9780791857618

DOI: 10.1115/POWER-ICOPE2017-3194

Copyright © 2017 ASME. Renewable energy technologies and sources have been playing a key role in reducing CO2 emissions and its footprint. Solar energy which is one of the major renewable energy sources can be utilized by means of solar Photovoltaic (PV) or solar collectors. Concentrating solar collectors supply thermal energy from medium to high grade where as non-concentrating collectors (flat plate) delivers low-grade thermal energy. The use of thermofluids with boiling temperatures lower than water, allows the operation of low grade solar thermal systems on an Organic Rankine Cycle (ORC) to generate both mechanical and heat energy. At the same time, the selection of an appropriate thermofluid is an important process and has a significant effect both on the system performance and the environment. Hydrofluoroethers (HFEs) are non-ozone depleting substances and they have relatively low global warming potential (GWP). In this study, a solar ORC is designed and commissioned to use HFE 7000 as a thermofluid. The proposed system consists of a flat-plate solar collector, a vane expander, a condenser and a pump where the collector and the expander are used as the heat source and prime mover of the cycle respectively. The performance of the system is determined through energy analysis. Then, a mathematical model of the cycle is developed to perform the simulations using HFE-7000 at various expander pressure values. Experimental data indicates that the efficiency and the net mechanical work output of the cycle were found to be 3.81% and 135.96 W respectively. The simulation results show that increasing the pressure ratio of the cycle decreased the amount of the heat that is transferred to HFE 7000 in the collector due to the increased heat loss from the collector to the environment. Furthermore, the net output of the system followed a linear augmentation as the pressure ratio of the system increased. In conclusion, both the experimental and theoretical research indicates that HFE 7000 offers a viable alternative to be used efficiently in small scale solar ORCs to generate mechanical and heat energy.

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