Experiments were performed to study the heat transfer from longitudinal fin arrays in turbulent air flow in the combined hydrodynamic and thermal entry region of a rectangular channel. The thermal resistance of the fin arrays was measured for fin heights of 1 and 1.9 cm and for tip-clearances varying from 0 to 2 cm (i.e. clearance to height ratio varies from 0 to 2). Results indicate that, for a given mass flow rate, the thermal resistances for the two fin heights are close when the tip-clearance is zero. With a clearance of 2 cm, the thermal resistance increases by 85 percent in the short fins, and by 210 percent in the tall fins. Extending the concept of wetted perimeter, a heating diameter is proposed to define the Reynolds and Nusselt numbers. With these modified definitions, experimental data can be fit into a single correlation which is 42 percent higher than that proposed by Petukhov and Popov (1963) for smooth round pipes. A design equation is then derived to predict the effect of the tip-clearance on the heat transfer coefficient for fin arrays with different heights, spacings and thicknesses. Agreement has been found between the present prediction and past experimental results by Sparrow and Kadle (1986) with clearance to height ratio varying from 0 to 0.33.

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