Laminar Boundary Layer Development Around a Circular Cylinder: Fluid Flow and Heat-Mass Transfer Characteristics

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 $Red=40$⁠. As the two-dimensional, steady and incompressible momentum and energy equations are solved using ANSYS-CFX (version 11.0), the moisture distributions are computed by a new alternating direction implicit method based software. The significant results, highlighting the influence of blockage $(β=0.200–0.800)$ on the flow and heat transfer mechanism and clarifying the combined roles of $β$ and moisture diffusivity $(D=1×10−8–1×10−5m2/s)$ on the mass transfer behavior, are obtained for practical applications. It is shown that the blockage augments the friction coefficients $(Cf)$ and Nusselt numbers (Nu) on the complete cylinder surface, where the average Nu are evaluated as $Nuave=3.66$⁠, 4.05, 4.97, and 6.51 for $β=0.200$⁠, 0.333, 0.571, and 0.800. Moreover, the blockage shifts separation $(θs)$ and maximum $Cf$ locations $(θCf−max)$ downstream to the positions of $θs=54.10$⁠, 50.20, 41.98, and 37.30 deg and $θCf−max=51.5$⁠, 53.4, 74.9, and 85.4 deg. The highest blockage of $β=0.800$ 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 $(hm)$ on the overall cylinder surface; however, the growing rate of back face mass transfer coefficients $(hm−bf)$ is dominant to that of the front face values $(hm−ff)$⁠, with the interpreting ratios of $h¯m−bf/h¯m=0.50$ and 0.57 and $h¯m−ff/h¯m=1.50$ and 1.43 for $β=0.200$ and 0.800.