Influence of dopant fluorination on the heat transfer behaviour of CO2-based mixtures in transcritical power cycles

• Michele Doninelli ^[1] ; Gioele Di Marcoberardino ^[1] ; Costante Mario Invernizzi ^[1] ; Paolo Giulio Iora ^[1]
  1. [1] Università degli Studi di Brescia

     Università degli Studi di Brescia

     Brescia, Italia

     
• Localización: Proceedings of the 7th International Seminar on ORC Power System: (ORC2023) / coord. por David Tomás Sánchez Martínez, María de Lourdes García Rodríguez, 2024, ISBN 978-84-472-2745-7, págs. 333-343
• Idioma: inglés
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  • Texto Completo Libro
• Resumen

  • CO2-based mixtures are recognized to be an effective working fluid to overcome the limitations of pure sCO2 cycles for power production in high-temperature environments. Based on the temperature level of the heat source, several dopants, characterized by high critical temperature, can be adopted for blending CO2. As thermal stability is one of main concern in the working fluids selection, fluorinated compounds have been considered in the recent years as potential solution due to high C-F chemical bond energy. However, the available thermodynamic and transport properties of CO2 mixtures with fluorinated hydrocarbons are relatively scarce, thus further experimental and theoretical investigations are necessary to properly design the power cycle components.

    The CO2-based mixtures are considered in this work for high-temperature heat recovery to assess the influence of fluorine atoms substitution to hydrogen atoms both on cycle efficiency and heat exchangers size. Benzene (C6H6) and two fluorinated derivatives (fluorobenzene C6H5F, hexafluorobenzene C6F6) are considered here to assess the influence of the presence of fluorine atoms in the molecule of the dopant on the transport properties of the CO2-mixtures and their heat transfer behaviour. These three halogenated aromatic dopants possess good thermal stability related with the benzene ring structure and could be potentially exploited for medium-high temperature level applications (350-550°C) such as waste heat recovery and concentrated solar power.

    Specific models for transport properties implemented in Matlab codes are optimized for the considered mixtures with a novel approach, and the design of the PCHE recuperator has been carried out. It turns out that the use of fluorobenzene as CO2 dopant in medium-high temperature heat recovery can be a good solution in terms of heat exchangers sizes, efficiency, cost, and environmental characteristics (GWP and toxicity).