Heat Transfer in Coaxial Jet Mixing With Swirled Inner Jet

Abstract

Convective heat transfer data are presented for coaxial jet mixing in a constant-diameter tube. The inner jet diameter was approximately twice the annular gap dimension. Water, with a nominal inlet Prandtl number of 6, was used as the working fluid. For the inner jet, Reynolds numbers of 30,000 and 100,000 were examined and the swirl number was varied from zero to one. Annular flow rates were characterized by a ratio of annular-to-inner jet axial momentum, which was varied from 0 to 8.3. In all cases the annular jet was unswirled. Plots of local Nusselt numbers show minima and maxima corresponding to the separation and reattachment associated with wall-bounded recirculation. As inner jet swirl strength increased from zero to its maximum value, the location of peak Nusselt number shifted upstream. Local Nusselt numbers achieved magnitudes as high as 9.7 times fully developed values for cases with high swirl and low annular flow rate. As the annular jet’s flow rate was increased, the heat transfer enhancement decreased while the near-wall recirculation zones were stretched and shifted downstream, until at sufficiently high values of the momentum flux ratio, the zones were no longer in evidence from the heat transfer data.