Experimental studies of the local mass transfer characteristics of annularly finned tubes in crossflow are presented. Variations due to boundary layer development, forward-edge separation, the tube wake, horseshoe vortices, and tip vortices are discussed. In addition, regularly located local maxima in mass transfer rates associated with the horseshoe vortex system are found, and conjecture as to their mechanism is offered. Inferring heat transfer behavior from the mass transfer results, we find that the true fin efficiency is always less than that obtained with an assumed constant convective heat transfer coefficient. The difference is 3–7 percent for high-conductivity materials such as aluminum alloys, and 9–17 percent for low-conductivity materials such as mild steels.

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