Details

Autor(en) / Beteiligte

• Kovář, Petr
• Smoleň, Michal
• Pagáč, Jan
• Kincl, Marek
• Slouka, Zdeněk

Titel

Experimental 3D concentration profiles along an electrodialysis channel reveal a strong effect of natural convection

Ist Teil von

• Desalination, 2023-02, Vol.548, p.116302, Article 116302

Ort / Verlag

Elsevier B.V

Erscheinungsjahr

2023

Quelle

Access via ScienceDirect (Elsevier)

Beschreibungen/Notizen

• Electrodialysis and electrodeionization separate ionic components from processed water solutions by applying a DC electric field on a stack of ion-exchange membranes. The ion separation indicates ionic concentration changes along the channels in the membrane modules. Simultaneously, concentration polarization at the ion-exchange membranes causes ionic concentration variations across the channels. We constructed a milifluidic cell with a diluate channel to measure spatial concentration profiles under single-path electrodialysis conditions. Desalination of 0.1 M NaCl solution showed that the concentration decreases linearly along the channel when connecting relatively low average current densities (< 30 A/m2), yielding <70 % desalination. Higher average current densities causing desalination close to 100 % produced nonlinear concentration profiles characterized by a steep linear drop followed by an almost constant and small concentration region. We show that at a current density of 50 A/m2, only one-third of the diluate channel is employed for desalination. Interestingly, uniform concentration profiles developed across the channels even at high polarization current densities. Unlike constant concentrations across the channel, we found substantial concentration variation in the vertical direction of the channel, indicating the effect of density gradients and natural convection. This effect was confirmed by optical microscopy and particle image velocimetry of this convection in stagnant solution layers. Natural convection, thus, can represent a mechanism intensifying the mass transfer from the solution bulk to the membrane surfaces. •Concentration profiles in the diluate channel of a model electrodialysis cell.•Degree of desalination affects the shape of the concentration profiles.•Significant role of natural convection in the diluate channel.•Natural convection is tracked by PIV.