Organic Rankine cycle systems for engine waste-heat recovery: Heat exchanger design in space-constrained applications

Li, X., Song, J., Yu, G. , Liang, Y., Tian, H., Shu, G. and Markides, C. N. (2019) Organic Rankine cycle systems for engine waste-heat recovery: Heat exchanger design in space-constrained applications. Energy Conversion and Management, 199, 111968. (doi: 10.1016/j.enconman.2019.111968)

Abstract

Organic Rankine cycle (ORC) systems are a promising solution for improving internal combustion engine efficiencies, however, conflicts between the pressure drops in the heat exchangers, overall thermodynamic performance and economic viability are acute in this space-constrained application. This paper focuses on the interaction of the heat exchanger pressure drop (HEPD) and the thermo-economic performance of ORC systems in engine waste-heat recovery applications. An iterative procedure is included in the thermo-economic analysis of such systems that quantifies the HEPD in each case, and uses this information to revise the cycle and to resize the components until convergence. The newly proposed approach is compared with conventional methods in which the heat exchangers are sized after thermodynamic cycle modelling and the pressure drops through them are ignored, in order to understand and quantify the effects of the HEPD on ORC system design and working fluid selection. Results demonstrate that neglecting the HEPD leads to significant overestimations of both the thermodynamic and the economic performance of ORC systems, which for some indicators can be as high as >80% in some cases, and that this can be effectively avoided with the improved approach that accounts for the HEPD. In such space-limited applications, the heat exchangers can be designed with a smaller cross-section in order to achieve a better compromise between packaging volume, heat transfer and ORC net power output. Furthermore, we identify differences in working fluid selection that arise from the fact that different working fluids give rise to different levels of HEPD. The optimized thermo-economic approach proposed here improves the accuracy and reliability of conventional early-stage engineering design and assessments, which can be extended to other similar thermal systems (i.e., CO2 cycle, Brayton cycle, etc.) that involve heat exchangers integration in similar applications.

• Item Type: Articles
• Additional Information: This work was supported by National Key R&D Program of China (2018YFB01059000). The authors would also like to thank the UK Engineering and Physical Sciences Research Council [grant number EP/ P004709/1] and the China Scholarship Council for a joint-PhD scholarship that supported Xiaoya Li for this research.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Liang, Dr Youcai and Yu, Dr Guopeng
• Authors: Li, X., Song, J., Yu, G., Liang, Y., Tian, H., Shu, G., and Markides, C. N.
• College/School: College of Science and Engineering > School of Engineering > Systems Power and Energy
• Journal Name: Energy Conversion and Management
• Publisher: Elsevier
• ISSN: 0196-8904
• ISSN (Online): 0196-8904
• Published Online: 28 August 2019
• Copyright Holders: Copyright © 2019 Elsevier
• First Published: First published in Energy Conversion and Management 199:111968
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher