The determination of heat-transfer coefficients from finned cylinders in an air stream at varying fin-plane/air-stream angles, fin spacing, and air velocities

Since the turn of the twentieth century, many investigations have been made in the field of heat-transfer from finned cylinders in an air-stream with the fin-plane parallel to the air-stream. Most of these investigations have been made by the National Advisory Committee on Aeronautics (NACA) at Langely Memorial Aeronautical Laboratory, Langely Field, Virginia.

The problem of determining the rate of heat-transfer from finned cylinders is extremely complex due to many variables such as fin space; fin width; fin thickness; cylinder diameter; and cooling air conductivity, viscosity, turbulence, and velocity. In the literature reviewed, there have been no successful theoretical equations for the determination of the rate of heat—transfer. Therefore, all information on the rate of heat-transfer must be based on experimental results or on empirical relationships which closely approximate the experimental values.

The rate of heat-transfer from finned cylinders is a very important factor in the design of air-cooled internal combustion engines and high rate heat-exchangers. It is known that the rate of heat-transfer for the range of fin-plane/air-stream angles between 30 and 60 degrees is nearly twice that of a zero fin-plane/air-stream angle, Since the subject of heat-transfer from finned cylinders in an air-stream with the fin-plane parallel to the air-stream has been thoroughly investigated by the NACA, the author decided to conduct this investigation on finned cylinders in an air—stream with varying fin-plane/air-stream angles. Due to the limiting size of equipment available, this investigation was conducted on finned cylinders with a cylinder diameter of about one inch, while the test carried on by the NACA covered a range of cylinder diameters from 3.66 to 6.34 inches.⁵ The difference in the cylinder diameters may provide a valuable correlation for the variation of the rate of heat-transfer due to cylinder diameter.