Experimental and numerical investigation of coupled temperature and CO2 separation in a counter-flow vortex tube

Vortex tubes convert a pressure drop into a temperature split without moving parts, and are applied to pressurized gas streams that often contain CO 2 . Whether the species redistribute between the outlets, and how this couples to the internal flow structure, remains unclear. Coupled temperature and CO 2 separation in a counter-flow vortex tube was therefore investigated experimentally and by validated numerical simulation. A binary N 2 –CO 2 mixture with 20.0 vol% CO 2 was supplied at 2–4 bar and 20 °C, while the cold outlet mass fraction was varied from 0.1 to 0.9. Simulations resolved the temperature and CO 2 concentration fields, turbulent kinetic energy, shear layer development, and radial mixing. Temperature separation decreased as the cold outlet mass fraction increased, whereas it increased with inlet pressure. The cold outlet CO 2 concentration exceeded the feed value at every condition; at 4 bar it fell from 22.7 vol% at 0.1 to 20.2 vol% at 0.9, the best balance between enrichment and recovery occurring near 0.4. A species balance across the two outlets gave a separation factor of approximately 1.2, confirming genuine CO 2 partitioning while showing that the single-stage effect is modest. Six nozzles gave the strongest coupled separation, yielding a temperature separation of 37.4 °C with a CO 2 enrichment rate of 9.5%, whereas a higher inlet temperature weakened separation because enhanced turbulent radial mixing eroded thermal and compositional stratification. These results clarify the coupling mechanism and quantify its modest magnitude, providing a physical basis for assessing where vortex tubes may be useful on CO 2 -containing streams.