Influence of the boundary conditions on heat and mass transfer in spacer-filled channels

Mass transfer in ducts with transpiring walls

“…( 3) remains close to the theoretical no-transpiration value Sh0 (e.g. 8.24 for plane channels with uniform imposed wall mass flux [13]). Figure 13 shows Shdiff as a function of the transpiration number, computed by 2-D CFD under the same conditions as Figure 12 (Re=8, Sc=500, Fl/Tr=2).…”

Membrane Deformation and Its Effects on Flow and Mass Transfer in the Electromembrane Processes

“…When γ = 0°, Figure 8(a), for any applied TMP the Sherwood number on the upper wall changes little with Re up to ~10, while for γ = 90°, Figure 8(c), the departure from this flat behaviour occurs earlier (Re ≈ 2). For γ = 0° or 90°, the Sherwood number at low Reynolds numbers ranges between ~3 and ~7 and thus is less than the theoretical value for a void plane channel of indefinite width (~8.24 under uniform mass flux conditions [52]). This indicates that in this Reynolds number range, the “shadow” effects of the profiles hinder mass transfer.…”

“…Under this hypothesis, from the Nernst-Planck equations and the mass balances of the two ions of a binary electrolyte, a convective-diffusive transport equation can be derived [51,59,60,61]. This simplifies the calculations, requiring only the need for a choice concerning the boundary condition at the membrane-solution interface (uniform concentration, uniform flux, or mixed condition); however, the influence of the boundary conditions on the mass transfer coefficient is small [8,52]. Please note that the potential is eliminated from the transport equation, and therefore the electric field and associated phenomena (e.g., Ohmic resistance) are not calculated by this simulation approach.…”

CFD prediction of flow, heat and mass transfer in woven spacer-filled channels for membrane processes

“…On the other hand, commercial applications of MD usually adopt two-side heat transfer since each feed channel is sandwiched between two condensate channels [30]. As discussed in [31], the single active wall of the one-side heat transfer arrangement may exhibit a different mean heat transfer coefficient than either wall of the two-side arrangement, so that the total heat transfer is not one half. It can be observed that the difference between one-and two-side heat transfer is large in the low Reynolds number range, while it decreases with Re and becomes negligible for Re>400, in correspondence with the transition from laminar to turbulent flow (as defined in Section 2.3 above).…”