MASS-TRANSFER WITH FLOW-THROUGH AN ARRAY OF RECTANGULAR CYLINDERS

The mass transfer from an array of naphthalene-coated parallel rectang ular cylinders, through which air passes in a slitlike flow has been m easured. The local Sherwood numbers indicate that the flow,v pattern i s asymmetric in spite of using an array of two-dimensional, equally sp aced identical cylinders. Smoke-wire flow visualization verifies this asymmetry, showing alternate short and long wakes around the cylinders , due probably to the instability of vortex shedding. On the side surf aces of the cylinders with the short wakes, the airflow deflects and r eattaches, resulting in a high mass transfer. Also, a strong impinging effect is observed on the leeward (back) surface of these cylinders a t high Reynolds numbers. Reattachment is not observed on the side surf ace for cylinders with the long wakes. On these, however, the mass tra nsfer on the leeward surface is higher than on the short wake cylinder s. This may be due to the relatively low naphthalene vapor concentrati on in the long wakes. The distribution of the short wakes (and the lon g wakes) is periodic and relatively stable. However, their position ca n be changed from one cylinder to the adjacent one by a disturbance. M easurements were taken over a moderate Reynolds number range of 300 to 3000 (based on the cylinder-to-cylinder pitch and approaching velocit y). The laminar, transition, and turbulent nature in the wake flows ca n be inferred from the results.