Heat transfer of impinging jet at low reynolds number

Thermal characteristics at impact axisymmetric air jet impingement on a flat obstacle have been studied experimentally and numerically. The influence of Reynolds number (100<Re<12000) on heat transfer at jet outflow from a long pipe (with diameter d=3.2 mm and relative length h/d =200) was studied at a distance to the obstacle h/d=20 and at constant wall temperature. In the area of Re<4000, in contrast to the known monotonous growth of heat transfer, the maximum heat transfer has been discovered. For the outflow from the tube there is a significant increase in Nusselt number up to 200-600% in comparison with the case when the jet outflows from the nozzle. At Re>4000 the difference in thermal transfer for the two versions of jet formation (from the tube and from the nozzle) asymptotically decreases. The numerical results qualitatively agree with experimental data in laminar and turbulent flow regimes.