Effect of nozzle-exit velocity profile on the performance of a coaxial personalized ventilation nozzle

Personalized ventilation (PV) can improve breathing-zone air quality and accommodate individual thermal preferences; however, its effectiveness depends on air-terminal design and nozzle-exit conditions governing fresh-air delivery. This study proposes a coaxial PV nozzle capable of independently regulating inner and outer flow rates, enabling adjustable nozzle-exit velocity profiles. Computational fluid dynamics simulations were performed in a two-occupant office under mixing ventilation, displacement ventilation, and underfloor air distribution. Nine coaxial flow rate ratios and four single-jet diameters were examined at 4.8 L s −1 . Ventilation performance was evaluated using ventilation coefficient, draught rate, and effective protection radius. PV performance was primarily governed by jet decay characteristics and influenced by ambient airflow disturbances and thermal stratification. A modified top-hat velocity profile at a flow rate ratio of 0.75 provided the best balance between potential core length and jet momentum. This configuration achieved ventilation coefficients of 0.889–0.913, improved inhaled air quality by about 10% over single jets of identical diameter, maintained draught rate below the 20% limit specified for Category II in ISO 7730, and enlarged the effective protection radius by about 60% compared with an existing co-flow PV jet at a similar flow rate.