Laminar boundary layer development around a circular cylinder: Fluid flow and heat-mass transfer characteristics

Abstract

This paper presents a comprehensive computational work on the hydrodynamic, thermal, and mass transfer characteristics of a circular cylinder, subjected to confined flow at the cylinder Reynolds number of Re(d) = 40. As the two-dimensional, steady and incompressible momentum and energy equations are solved using ANSYS-CFX (version II.0), the moisture distributions are computed by a new alternating direction implicit method based software. The significant results, highlighting the influence of blockage (beta = 0.200-0.800) on the flow and heat transfer mechanism and clarifying the combined roles of beta and moisture diffusivity (D = 1 X 10(-8)-1 X 10(-5) m(2)/s) on the mass transfer behavior, are obtained for practical applications. It is shown that the blockage augments the friction coefficients (C(f)) and Nusselt numbers (Nu) on the complete cylinder surface, where the average Nu are evaluated as Nu(ave) = 3.66, 4.05, 4.97, and 6.51 for beta = 0.200, 0.333, 0.571, and 0.800. Moreover, the blockage shifts separation (theta(s)) and maximum C(f) locations (theta(Cf-max)) downstream to the positions of theta(s) = 54.10, 50.20, 41.98, and 37.30 deg and theta(Cf-max) = 51.5, 53.4, 74.9, and 85.4 deg. The highest blockage of beta = 0.800 encourages the downstream backward velocity values, which as a consequence disturbs the boundary layer and weakens the fluid-solid contact. The center and average moisture contents differ significantly at the beginning Of drying process, but in the last 5% of the drying period they vary only by 1.6%. Additionally, higher blockage augments mass transfer coefficients (h(m)) on the overall cylinder surface; however, the growing rate of back face mass transfer coefficients (h(m-bf)) is dominant to that of the front face values (h(m-ff)), with the interpreting ratios of (h) over bar (m-bf)/(h) over bar (m)= 0.50 and 0.57 and h (h) over bar (m-ff)/(h) over bar (m) = 1.50 and 1.43 for beta = 0.200 and 0.800.