Energy conversion mechanisms in turbomachines for high-temperature endothermic reactions: Redefining energy quality

Abstract

A new class of turbomachines, called turbo-reactors, have emerged to decarbonize high-temperature chemical processes. These applications unlock a new aerothermochemical design space for turbomachines. This paper explains how the turbo-reactor has the potential to be a “chemically tuned” device. In contradiction with conventional design wisdom, this can be achieved by balancing entropy generation within the flow against heat absorption by the reaction. This enables the “design” of a reaction-efficient temperature profile. To do this, it is necessary to understand and quantify the distribution of the entropic and isentropic mechanisms responsible for energy conversion. This paper uses high- and low-fidelity computations to decompose the energy conversion process into mechanisms based on a spatial decomposition. A range of Mach and Reynolds number regimes are studied, as well as a multistage configuration without vaneless space. The energy conversion breakdown analysis indicates that the entropic energy conversion dominates over the isentropic component with a contribution of 65%. The dominant source of entropy production is viscous dissipation generated by the thick diffuser trailing edge, accounting for 25% of the total. The shock system provides 20% of the energy conversion, almost entirely due to reversible pressure rise rather than entropy production. The energy conversion coefficient is independent of Reynolds number over engine-relevant conditions, whereas Mach effects are more significant. Across the Mach numbers range 1.1 to 1.5, the energy conversion coefficient increases by 20%. This is lower than expected as a result of the opposing effects of reversible and irreversible energy conversion contributions.