Influence of operating and geometric parameters on internal thermo-fluid structures and CO2 enrichment in a Ranque-Hilsch vortex tube

초록

This study investigates the coupled mechanisms governing thermal and CO2 enrichment behavior in a Ranque–Hilsch vortex tube using an N2/CO2 (80/20) mixture as a simplified carbon capture pretreatment stream. Although vortex tubes have attracted attention because of their simple structure and compact configuration, the relationship between internal flow structures and outlet CO2 enrichment behavior remains insufficiently understood. To address this issue, a validation-based computational framework was developed by combining experiments with three-dimensional unsteady computational fluid dynamics simulations. The numerical model was validated against experimental measurements with total deviations below 5% and was subsequently applied to investigate the effects of inlet temperature, inlet pressure, cold outlet mass fraction, and diameter ratio. The results showed that the cold outlet mass fraction strongly influenced outlet performance, increasing the CO2 recovery fraction from 11.4 to 90.9% while reducing the cold outlet CO2 concentration from 22.7 to 20.2%. Inlet pressure exhibited a non-monotonic effect, with an optimum near 4 bar producing a temperature difference exceeding 30 K together with the highest CO2 enrichment. Increasing the diameter ratio enhanced thermal stratification and outlet temperature separation but reduced CO2 enrichment because the stagnation point moved toward the hot outlet control valve, extending the reverse flow region and increasing the interaction length between the inner reverse flow and outer swirling flow. In contrast, inlet temperature had only a minor influence on both cold outlet CO2 concentration and CO2 enrichment performance, with only a slight displacement of the stagnation point toward the cold outlet. The results demonstrate that the trade-off between thermal separation and CO2 enrichment is governed by the coupled interaction among swirl induced pressure gradients, reverse flow development, stagnation point behavior, and species transport across the shear layer. The present study provides a physically consistent framework linking internal vortex tube flow structures to outlet CO2 enrichment performance and offers design guidance for the optimization of vortex tube based CO2 pretreatment applications. Copyright © 2024. Published by Elsevier Ltd.

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