EXPERIMENTAL-STUDY ON MASS-TRANSFER FROM A CIRCULAR-CYLINDER IN PULSATING FLOW

Laboratory measurements were made of local mass transfer from a cylinder, which is placed in a pulsating free stream, U = U-0(1 + A(0) cos 2 pi f(p)t). Low turbulence-intensity wind tunnel experiments were conducted for small and moderate Reynolds numbers, 4500 less than or equal to Re-d less than or equal to 12450. Pulsation was generated by means of an acoustic speaker. Mass transfer rates were measured by employing the naphthalene sublimation technique. The present results for non-pulsating flows (A(0) = 0.0) were shown to be consistent with the published data. For pulsating approach flows, plots were constructed to illustrate the distribution of the Sherwood number, Sh, as a function of the azimuthal angle theta measured from the front stagnation point. In the zone of attached boundary layer, the effect of pulsation on Sh is meager. Sh decreases monotonically from the maximum value at the front stagnation point to the minimum value near the separation point theta approximate to 80-90 degrees. In general, Sh increases appreciably with increasing theta, after passing the separation point. The curve of Sh contains a secondary minimum point at around theta approximate to 130-150 degrees. The general magnitude of Sh increases, as A(0) increases. The augmentation of mass transfer is more pronounced for large f(p), such that the flow lock-on phenomenon takes place. At large Re-d, the relative influence of pulsation on Sh weakens.