HEAT-TRANSFER IN COAXIAL JET MIXING WITH SWIRLED INNER JET

Convective heat transfer data are presented for coaxial jet mixing in a constant-diameter tube. The inner jet diameter was approximately twi ce the annular gap dimension. Water, with a nominal inlet Prandtl numb er of 6, was used as the working fluid. For the inner jet Reynolds num bers of 30,000 and 100,000 were examined and the swirl number was vari ed 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 n umbers show minima and maxima corresponding to the separation and reat tachment associated with wall-bounded recirculation. As inner jet swir l strength increased from zero to its maximum value, the location of p eak Nusselt number shifted upstream. Local Nusselt numbers achieved ma gnitudes as high as 9.7 times fully developed values for cases with hi gh swirl and low annular flow rate. As the annular jet's flow rate was increased, the heat transfer enhancement decreased while the near-wal l 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.