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Alternative layouts for coupling a parallel expander to a Brayton cycle configuration developed from commercial turbochargers
Thesis (PhD (Mechanical Engineering))--University of Pretoria, 2025.
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University of Pretoria
2025
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| _version_ | 1867613677738262528 |
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| access_status_str | Open Access |
| author2 | Le Roux, Willem G. |
| author_browse | Le Roux, Willem G. |
| author_facet | Le Roux, Willem G. |
| collection | Thesis |
| dc_rights_str_mv | © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Thesis (PhD (Mechanical Engineering))--University of Pretoria, 2025. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/107249 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:39:57.392Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/107249 Alternative layouts for coupling a parallel expander to a Brayton cycle configuration developed from commercial turbochargers Le Roux, Willem G. u19008253@tuks.co.za Cockcroft, Caitlin Claudia UCTD Sustainable Development Goals (SDGs) Solar Thermal Energy Brayton Cycle Gas Turbine Turbocharger Thesis (PhD (Mechanical Engineering))--University of Pretoria, 2025. Microturbines developed from commercial turbochargers may present feasibility for providing electricity to regions with poor power infrastructure. However, turbochargers operate at low pressure ratios where performance is sensitive to the addition of pressure-drop components, which may be required for solar thermal hybridisation and cogeneration. Parallel-flow Brayton cycles have therefore been proposed to reduce the effect of pressure losses on performance when introducing recuperation. This study investigates the feasibility of parallel-flow Brayton cycles using automotive turbochargers, focussing on obtaining maximum thermal efficiency at steady state, while considering various power turbine split-off points. The cycles are investigated by considering turbine inlet air cooling (which can be used for cogeneration via water heating), recuperation, solar hybridisation, and multi-dish setups, with comparisons to single-shaft layouts. Various turbocharger combinations and counter-flow recuperator dimensions are considered, while maintaining turbine inlet temperatures and solar receiver temperatures below the recommended limits. Solar heat inputs are introduced using constant geometry in the form of a 4.8-m-diameter solar dish and an open-cavity tubular receiver, while considering different receiver placements (before the combustor or before the power turbine). Various multi-dish setups are also modelled using two solar receivers. Results show that turbine inlet air cooling extends the pressure ratio range of an unrecuperated parallel-flow cycle and improves performance, particularly in cycles where gasifier turbine inlet temperatures approach manufacturer limits. Of all the recuperated parallel-flow cycles investigated, a recuperated low-temperature turbine (LTT) layout produces the lowest power output but also offers the highest thermal efficiency of 19.2%. For unrecuperated solar cycles, the high-temperature turbine (HTT) cycle with the solar receiver before the combustor provides the best thermal efficiency of 7%. For recuperated solar cycles, the LTT cycle with the solar receiver before the power turbine achieves the highest thermal efficiency of 22%, showing that the LTT cycle offers viability in cycles with many components. In recuperated parallel-flow cycles and recuperated solar parallel-flow cycles, thermal efficiency performance improves under increased combustion pressure losses, from 6% up to 11%, in contrast to the declining performance of single-shaft cycles. At a pressure ratio of 1.8, results show that the recuperated solar parallel-flow LTT configuration can outperform its single-shaft counterpart for combustion pressure losses exceeding 8.7%, with thermal efficiencies increasing from 13.5% to 19.9% with an increase in pressure loss from 6% to 11%. A cycle with a larger solar dish to form a multi-dish setup further enhances thermal efficiency. In the best-performing multi-dish cycle, consisting of the recuperated LTT cycle, the thermal efficiency improves by 69% over the single-dish cycle. Multi-dish parallel-flow configurations have greater solar heat capture through better heat distribution allowing for lower solar receiver surface temperatures. These results demonstrate that parallel-flow Brayton cycles, consisting of automotive turbochargers, can achieve meaningful thermal efficiency improvements over conventional single-shaft configurations, particularly when using optimised split-off points for cogeneration and solar hybridisation. The LTT configuration consistently offers strong performance at low pressure ratios and elevated combustion pressure losses, making it a promising option for small-scale, solar hybridised power generation. DSTI (Department of Science, Technology, and Innovation) as part of the UP Solar Thermal Spoke Mechanical and Aeronautical Engineering PhD (Mechanical Engineering) Unrestricted Faculty of Engineering, Built Environment and Information Technology SDG-07: Affordable and clean energy 2025-12-15T11:40:53Z 2025-12-15T11:40:53Z 2026-04 2025-09 Thesis * A2026 http://hdl.handle.net/2263/107249 https://doi.org/10.25403/UPresearchdata.30821309 en © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | UCTD Sustainable Development Goals (SDGs) Solar Thermal Energy Brayton Cycle Gas Turbine Turbocharger Alternative layouts for coupling a parallel expander to a Brayton cycle configuration developed from commercial turbochargers |
| title | Alternative layouts for coupling a parallel expander to a Brayton cycle configuration developed from commercial turbochargers |
| title_full | Alternative layouts for coupling a parallel expander to a Brayton cycle configuration developed from commercial turbochargers |
| title_fullStr | Alternative layouts for coupling a parallel expander to a Brayton cycle configuration developed from commercial turbochargers |
| title_full_unstemmed | Alternative layouts for coupling a parallel expander to a Brayton cycle configuration developed from commercial turbochargers |
| title_short | Alternative layouts for coupling a parallel expander to a Brayton cycle configuration developed from commercial turbochargers |
| title_sort | alternative layouts for coupling a parallel expander to a brayton cycle configuration developed from commercial turbochargers |
| topic | UCTD Sustainable Development Goals (SDGs) Solar Thermal Energy Brayton Cycle Gas Turbine Turbocharger |
| url | http://hdl.handle.net/2263/107249 https://doi.org/10.25403/UPresearchdata.30821309 |