HEAT-TRANSFER FROM A CYLINDER AND FINNED TUBE IN A PULSATING CROSS-FLOW

Experiments have shown that the convective heat transfer from heated cylinders and finned tubes is very sensitive to the frequency of pulsation of the approaching crossflow. A specially developed wind tunnel, which had facility for generating a time-dependent flow, was used for the experimental testing. The circular cylinder and finned tube test specimens had isothermal surfaces, and tests were performed over a Reynolds number range of 2000-14,000 to determine average heat transfer coefficients. The effect of a pulsating flow on the forced convective heat transfer from the cylinder was to decrease the heat transfer relative to the steady-flow case with the same mean flow conditions for low dimensionless frequencies and to increase the heat transfer for high dimensionless frequencies. In the case of the finned tube, a significant increase in the heat transfer was noted for high values of the dimensionless frequencies. At low dimensionless frequencies, the heat transfer did not vary appreciably. In general, the data obtained indicated that heat transfer is enhanced at higher dimensionless frequencies and diminished at lower ones. This study has stimulated interest in a numerical study that will consider the effects of the so-called ac boundary layers and, for the case of the finned tube, the effects of vorticity amplification on the convective heat transfer. The vorticity is generated by the boundary layer flow over the fins, and the amplification would be due to the flow accelerating over the cylindrical core.