Investigation of Heat Transfer of a Square Impinging Air Jet on a Flat Surface using Thermochromic Liquid Crystal Sheet

Convective heat transfer by impinging air jets was investigated experimentally using a thermochromic liquid crystal (TLC) sheet. The effects of jet-to-plate spacings (1.0 <= L/D <= 8.0) and nozzle shapes (circular and rectangular nozzles), were examined at constant Reynolds number Re = 20,000 (based on the jet nozzle diameter). The experimental results showed that average Nusselt number (Nu) increased with decreasing jet-to-plate spacing (L/D), due to a higher impingement velocity. At same jet-to-plate spacing, a square air jet gave higher Nusselt number than a circular one. The superior heat transfer of the square air jet can be attributed to a turbulence/recirculation effect at four corners of the nozzle.