Cacuci, D. G.

Onea, A.

Wörner, Martin

English

KITopen

Forschungszentrum Karlsruhe In der Helmholtz-Gemeinschaft Institut für Reaktorsicherheit, Postfach 3640, D-76021 Karlsruhe Contact: Dr. Martin Wörner, E-mail: woerner@irs.fzk.de September 2006 Numerical Simulation of Interfacial Mass Transfer Accompanied by a First-Order Chemical Reaction in Segmented Gas-Liquid Flow within a Mini-Channel A. Onea1, M. Wörner1, D.G. Cacuci2 1 Forschungszentrum Karlsruhe, Institut für Reaktorsicherheit, Karlsruhe, Germany 2 Universität Karlsruhe, Institut für Kerntechnik und Reaktorsicherheit, Karlsruhe, Germany   Introduction Advantages and applications of segmented gas-liquid flow in square narrow channels: • Monolithic catalyst reactor: gas bubbles segment the liquid and enhance its mixing • Micro bubble column: efficient mass transfer due to high interfacial area per unit volume • Goal: Get insight in local instantaneous mass transfer phenomena by means of direct numerical simulations  Numerical method • In-house code TURBIT-VOF solves incompressible Navier-Stokes equation with surface tension by a Volume-of-Fluid method with local planar interface reconstruction • Implementation of species transport equation under assumption of no feed-back on hydrodynamics • The physical concentration field c is transformed into c%  which is continuous at the interface  Fig. 1: Transformation of concentration field c  into c%  using Henry number H.  Bubble train flow Hydrodynamics • Developed bubble train flow (BTF) is fully described by a unit cell (UC) with one bubble and one liquid slug • BTF is numerically represented by one unit cell and periodic boundary conditions in vertical axial direction (see Fig. 2)          Fig. 2: Sketch of computational domain. • Simulations of air / silicon oil BTF in a square channel with Lx = Lz = 2 mm for three different unit cell length Luc = 2, 2.75 and 3.5 mm and a void fraction ε = 33% • Computed bubble diameter and velocity are in good agreement with experimental data [1]  Mass transfer • Mass transfer of an artificial species from gas phase (initial concentration cG0) into the liquid phase (initial concentration 0) • Simulations for mass transfer with and without 1st order homo-genous (liquid bulk) and hetero-geneous (channel walls) chemical reaction • Henry number H ≡ (cL  / cG)eq. = 0.03 and 3, DL/DG = 0.31; liquid phase Schmidt number = 0.8; bubble Reynolds number = 10             Fig. 3: Concentration field c%  for H = 0.03 (left) and c for H = 3 (right) in vertical mid-plane for t ≈ 0.01s.         Fig. 4: Mean concentration cG(t) for H = 0.03 and different values of Luc. For small Luc the equilibrium concentration cGeq = cG0/(1+H(1/ε-1)) is reached faster.              Fig. 5: Concentration field c%  for H = 0.03 (left) and H = 3 (right) in a vertical mid-plane for mass transfer with heterogeneous chemical reaction. Conclusions • Mass transfer occurs mainly across the bubble tip and bottom (in agreement with [3]), while the liquid film is saturated (Fig. 3) • Short unit cells are more efficient for mass transfer with / without homog. chemical reaction (Fig. 4) • Long unit cells are slightly more efficient for mass transfer with heterogeneous chemical reaction in case of small Henry number and fast film saturation Literature: [1]  Thulasidas, Abraham, Cerro: Chem. Eng. Sci. 50 (1995) 183-199 [2]  Ghidersa, Wörner, Cacuci: Chem. Eng. J. 101 (2004) 285-294 [3] Berčić & Pintar: Chem. Eng. Sci. 52 (1997) 3709-3719 

Numerical simulation of interfacial mass transfer accompanied by a first-order chemical reaction in segmented gas-liquid flow within a mini-channel

Repository KITopen

https://publikationen.bibliothek.kit.edu/230065666/150946094

Numerical simulation of interfacial mass transfer accompanied by a first-order chemical reaction in segmented gas-liquid flow within a mini-channel

Abstract

Similar works

Full text

Available Versions

KITopen

Repository KITopen