Farrukh, Salman 
ORCID: 0000-0001-6533-3429
(2025).
Low flammability hydrofluorocarbon working fluids for cryogenic-enhanced Organic Rankine Cycles.
University of Birmingham.
Ph.D.
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Farrukh2025PhD.pdf
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Abstract
The global shift away from emission-intensive fossil fuels has spurred the rise of low-carbon cryogenic liquid alternative fuels, such as hydrogen and ammonia. The regasification of cryogenic liquid fuels releases high-quality waste cryogenic exergy, with cryogenic-enhanced Organic Rankine Cycles (ORCs) emerging as the preferred reutilisation technology. This PhD project aims to investigate the feasibility of low flammability hydrofluorocarbons as working fluids for cryogenic-enhanced ORCs, which have traditionally utilised flammable hydrocarbons as working fluids.
An experimental testing rig of the cryogenic-enhanced ORC was constructed, using R410A, hot water, and liquid nitrogen as the working fluid, heat source, and cryogenic heat sink, respectively. The parametric study included varying working fluid flow rates and evaporation temperatures. The operational flexibility, namely preheating of the low-carbon fuel, provided by the cryogenic-enhanced ORC to the downstream applications of cryogenic low-carbon fuels was highlighted. Higher heat exchanger effectiveness was observed at higher temperatures and flow rates. The condenser exhibited the largest exergy destruction, pinpointing optimisation routes. Comparison with hydrocarbon-based cryogenic-enhanced ORCs in literature (Tian et al., 2022) revealed the viability of low flammability hydrofluorocarbon working fluids. The R410A cryogenic-enhanced ORC system achieved a maximum net-work output, thermal efficiency, cryogenic energy efficiency, and cryogenic exergy efficiency of 501.44 W, 7.29 %, 7.67 %, and 8.38 %, respectively.
An advanced dynamic numerical model, based on the physical components employed in the experimental setup, was developed to address the research gap in literature, which only utilise steady-state modelling techniques. Six different low flammability hydrofluorocarbon working fluids were investigated, and system charge was introduced, for the first time, as an objective parameter. The analysis demonstrated that thermophysical properties, particularly density and molar mass, significantly influenced system performance, with lower values providing enhanced system performance. Overcharging led to reduced performance due to condenser flooding and increased pump suction pressure, while undercharging caused pump cavitation and failure. System charge optimisation depended on the working fluid’s density and fixed system volume. Environmental emissions were dependent on leak prevention protocols and marine classification societies-based scenarios were employed. R452B emerged as the optimal working fluid, delivering a maximum net-work output, thermal efficiency, cryogenic energy efficiency, exergy efficiency, and GHG emission reduction of 714.73 W, 10.44%, 11.81%, 7.79%, and 90%, respectively.
| Type of Work: | Thesis (Doctorates > Ph.D.) | ||||||||||||
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| Award Type: | Doctorates > Ph.D. | ||||||||||||
| Supervisor(s): |
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| Licence: | All rights reserved | ||||||||||||
| College/Faculty: | Colleges > College of Engineering & Physical Sciences | ||||||||||||
| School or Department: | School of Engineering, Department of Mechanical Engineering | ||||||||||||
| Funders: | None/not applicable | ||||||||||||
| Subjects: | T Technology > TA Engineering (General). Civil engineering (General) T Technology > TJ Mechanical engineering and machinery |
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| URI: | http://etheses.bham.ac.uk/id/eprint/16263 |
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