Forced convection from a surface covered with flexible fibers

The heat transfer, friction and mechanical (elastic) interaction between an external laminar flow and a solid surface covered by a layer of fibers is investigated numerically. The flow is initially perpendicular to the surface, and the fibers can bend. The study has two parts. In the first part it is assumed that the fibers are inflexible. It is shown that the effect of the fiber layer on the overall heat transfer can be correlated in terms of the fraction of the external flow that penetrates into the fiber layer. The second part focuses on the effect of fiber bending, which is described by a new dimensionless group: the stiffness number S = EI/(pU 2 ∞ L 4). It is shown that the wall heat transfer, friction and fiber layer flow fraction exhibit a sudden decrease when S drops below a critical value, S c . The critical stiffness number can be correlated as S c = C(H/L)5(D/H)2/(1 -ø), where C is a constant of order 0.4, H and D are the fiber length and diameter, L is the half-length of the solid wall, and ø is the porosity of the fiber layer.