Heat transfer and flow velocity study of a row of jets emerging from a perforated pipe at a low Reynolds number

Abstract

Aerodynamic and thermal experimental investigations were carried out on a row of circular low Reynolds jets emerging from a perforated pipe. Particle Image Velocimetry and Infrared Thermography were performed to determine flow velocity fields and local Nusselt number variations along the impinged plate. Jet Reynolds number (1500<Rej<5000), upstream crossflow in the pipe (1.5<VR<9.7), injection-to-plate distance (3<H/d<7) as well as center-to-center jet spacing (2.25<p/d<5.8) were all taken into account. Measurements were compared to those of a fully developed circular jet issuing from a long tube under the same conditions (3000<Rej<5000 and 3<H/d<7). Experimental results showed that jets tend to emerge with an effective cross-sectional area reduced to a crescent shape unlike that of axisymmetric fully developed jets; their specific structure was attributed to flow deflection from the pipe to the holes and resulted in heat transfer specificities differing from those of a fully developed jet. Heat transfer rates were found to be primarily dependent on injection Reynolds number, injection-to-plate distance and center-to-center spacing, and they were found to be relatively low compared to a fully developed jet.