Thermal diffusion phenomena in free jets from concentric annulus

A numerical analysis is performed to investigate thermal diffusion phenomena in vertical free jets using the coaxial flow formed with the annular nozzle, in which the cooled and hot fluids with different injection speeds are injected from the inner and outer pipes, respectively. Emphasis is placed on the effect of injection velocity ratio of hot air to cold air on velocity and thermal fields. It is found that (i) the flow pattern and isotherms in a jet are affected by the injection velocity ratio, and (ii) as velocity ratio is increased, the streamwise velocity gradient along the vertical direction is intensified, resulting in amplification in the thermal diffusion.