Numerical investigation on mass transfer enhancement downstream of an orifice

Mass transfer enhancement is an indispensible element in flow accelerated corrosion (FAC). In order to investigate mass transfer enhancement downstream of an orifice, the two-dimensional computational fluid dynamics (CFD) calculation is conducted. First, validation of turbulence model, the ζ-f model, is conducted in the fully developed pipe flow, the flow through an orifice and the flow downstream of a sudden expansion. The validation shows that the model is adequate to predict mass transfer enhancement in all the tested flows. Effects of Reynolds number, orifice thickness and diameter ratio on mass transfer enhancement downstream of an orifice are then investigated based on the numerical calculation. The investigation shows that the mass transfer enhancement ratio decreases with the increasing Reynolds number. However, the locations of reattachment point and the peak transfer rate point are not affected by the Reynolds number. Parametric study on the orifice thickness shows that a thin orifice helps mass transfer enhancement in its downstream. This is attributed to more intense turbulence generation downstream of a thin orifice. Moreover, the peak transfer point appear about 0.4Lr (reattachment length) downstream of the orifice. The results of the parametric study are synthesized as a correlation,StmaxStfd=4.78Re-0.12dD-1.161+0.82(L1/d)31+(L1/d)3which is expected to be valid in the range of 4.2 × 104 ⩽ Re ⩽ 1.3 × 105, 0.4 ⩽ d/D ⩽ 0.75, 0.13 ⩽ L1/d ⩽ 2.61.