Mass Transfer With Flow Through an Array of Rectangular Cylinders

The mass transfer from an array of naphthalene-coated parallel rectangular cylinders, through which air passes in a slitlike flow, has been measured. The local Sherwood numbers indicate that the flow pattern is asymmetric in spite of using an array of two-dimensional, equally spaced 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 surfaces of the cylinders with the short wakes, the airflow deflects and reattaches, resulting in a high mass transfer. Also, a strong impinging effect is observed on the leeward (back) surface of these cylinders at high Reynolds numbers. Reattachment is not observed on the side surface for cylinders with the long wakes. On these, however, the mass transfer on the leeward surface is higher than on the short wake cylinders. This may be due to the relatively low naphthalene vapor concentration in the long wakes. The distribution of the short wakes (and the long wakes) is periodic and relatively stable. However, their position can be changed from one cylinder to the adjacent one by a disturbance. Measurements were taken over a moderate Reynolds number range of 300 to 3000 (based on the cylinder-to-cylinder pitch and approaching velocity). The laminar, transition, and turbulent nature in the wake flows can be inferred from the results.