Abstract
To enhance convective heat transfer, injection air was added through a slit into the laminar boundary layer formed on a flat plate. The effect of injection on heat transfer and skin friction characteristics was investigated experimentally.
Friction factor and heat transfer coefficient were measured for air flow with Reynolds number Re=u∞·l/ν between 3.0×104 and 6.4× 105 and with injection rate F=ρ0υ0/ρ∞u∞ between 0.005 and 0.1.
Conclusions were obtained as follows : The heat transfer coefficient and skin friction factor increased over the whole range behind an injection slit and the point of transition moved upstream with increasing injection rate.
The extent of augmentation of the heat transfer coefficient and skin friction factor could be varied by varying the injection rate. This characteristic may have application in automatic control systems. On this point, the injection method has an advantage compared with a fixed separation-inducing obstacle that provides a heat transfer augmentation which is more or less invariable. When a performance evaluation for enhanced heat transfer was made under the condition of constant pumping power, the maximum values of Stanton number St/St0 for F=0.1 and F=0.05 were 1.39 and 1.29 respectively.
