The role of geometry in rough wall turbulent mass transfer

Kaveh Sookhak Lari, Maarten van Reeuwijk, Čedo Maksimović

Heat and Mass Transfer · 2013

DOI: 10.1007/s00231-013-1165-4
Mass TransferRANSBoundary LayersDrag

Corrigendum: 2013 (DOI)

Abstract

We report on RANS simulations of high Schmidt number turbulent mass transfer due to a first-order reaction on the surface of a d-type rough wall. We find that for low reaction coefficients, the additional surface area of the rough wall causes an increased mass transfer in com- parison with a smooth wall. However, when the reaction coefficient is high, the mass transfer becomes lower than for a smooth wall. A detailed analysis shows that the mass transport in the cavity is dominated by diffusion which becomes the limiting factor at high reaction coefficients. A conceptual model, which is in good agreement with the simulations, highlights that the influence of geometry roughness is not confined to the roughness Reynolds number for molecular-diffusion-dominated cavities. Nomenclature Symbols a1-3 Empirical coefficient ( -) b Empirical constant ( -) Cf Normalized local viscous drag ( -) Cp Normalized local pressure drag ( -) C Concentration (ML-3) D Diffusion coefficient ( L2T-1) d Cavity depth ( L) J Mass flux ( ML-2T-1) k Decay coefficient ( L-1) k Turbulent kinetic energy ( L2T-2) kf Mass transfer coefficient ( LT-1) kw Wall demand coefficient ( LT-1) n Surface normal coordinate ( L) n~ Surface normal vector ( L) p Kinematic pressure ( L2T-2) rh Hydraulic radius ( L) s Surface tangential coordinate ( L) s~ Surface tangential vector ( L) t Time (T) U Crosswise mean u (LT-1) u Velocity (LT-1) us Friction velocity ( LT-1) v Wall normal velocity ( LT-1) w Cavity width ( L) x Streamwise coordinate ( L) x~ Unit vector for x coordinate (L) y Wall normal coordinate ( L) a Variable (-) d Channel halfwidth ( L) ee Energy dissipation rate ( L2T-3) k Periodic length ( L) m Kinematic viscosity ( L2T-1) W Stream function ( L2T-1) Dimensionless numbers Re Reynolds number ( -) Red Roughness Reynolds number ( -) Res Shear Reynolds number ( -) Sc Schmidt number ( -) Sh Sherwood number ( -) Super- and subscripts X0 Fluctuation K. Sookhak Lari ( &) /C1M. van Reeuwijk /C1Cˇ . Maksimovic´ Department o