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Articles

Boundary Layers of Air Adjacent to Cylinders

Estimation of Effective Thickness and Measurements on Plant Material ¹

^a Department of Environmental Biology, Research School of Biological Sciences, The Australian National University, Canberra, A.C.T., 2601, Australia

Using existing heat transfer data, a relatively simple expression was developed for estimating the effective thickness of the boundary layer of air surrounding cylinders. For wind velocities from 10 to 1000 cm/second, the calculated boundary-layer thickness agreed with that determined for water vapor diffusion from a moistened cylindrical surface 2 cm in diameter. It correctly predicted the resistance for water vapor movement across the boundary layers adjacent to the (cylindrical) inflorescence stems of Xanthorrhoea australis R. Br. and Scirpus validus Vahl and the leaves of Allium cepa L. The boundary-layer thickness decreased as the turbulence intensity increased. For a turbulence intensity representative of field conditions (0.5) and for ^windd between 200 and 30,000 cm²/second (where ^wind is the mean wind velocity and d is the cylinder diameter), the effective boundary-layer thickness in centimeters was equal to [Formula: see text].

¹ This research was made possible by a fellowship from the John Simon Guggenheim Memorial Foundation.