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Energies 2017, 10(10), 1649; https://doi.org/10.3390/en10101649

Prospects of Mixtures as Working Fluids in Real-Gas Brayton Cycles

Department of Mechanical and Industrial Engineering, University of Brescia, Via Branze 38, 25123 Brescia, Italy
Received: 9 September 2017 / Revised: 7 October 2017 / Accepted: 16 October 2017 / Published: 19 October 2017
(This article belongs to the Section Energy Fundamentals and Conversion)
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Abstract

This paper discusses the thermodynamic characteristics of the closed Brayton cycles in which the compression is placed near the critical point of the working fluid. Under these conditions, the specific volumes of the fluid during the compression are a fraction of the corresponding values under ideal gas conditions, and the cycle performances improve significantly, mainly at moderate top temperatures. As the heat is discharged at about the critical temperature, the choice of the correct working fluid is strictly correlated with the environmental temperature or with the temperature of potential heat users. To resort to mixtures greatly extend the choice of the right working fluid, allowing a continuous variation of the critical temperature. These cycles have a high power density, and the use of ordinary turbomachinery is accompanied by high capacities (tens of megawatts). In the low power range, microturbines or reciprocating engines are required. One important constraint on the choice of the right working fluid is its thermochemical stability that restricts the operative temperatures. Among the organic compounds, the maximum safe temperatures are limited to about 400 °C and, forecasting high temperature applications, it could be interesting to explore the potentiality of the inorganic compounds as secondary fluids in binary mixtures. View Full-Text
Keywords: closed Brayton cycles; supercritical gas; real-gas effects; organic working fluids; distributed energy production closed Brayton cycles; supercritical gas; real-gas effects; organic working fluids; distributed energy production
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Invernizzi, C.M. Prospects of Mixtures as Working Fluids in Real-Gas Brayton Cycles. Energies 2017, 10, 1649.

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