Nanofluid Mediated Gas- Liquid Mass Transfer Enhancement In Pulsed Plate Column

Abstract

Oxygen transfer limitations result in poor performance in bioreactors and reduced efficiency in catalytic and photocatalytic reaction systems where oxygen transfer is involved. Adequate oxygen transfer can be achieved by increasing the volumetric oxygen transfer coefficient (kLa). Several investigations have shown that the enhancement of kLa can be achieved in the presence of nanofluid which is a colloidal suspension of nanoparticles in any base fluid. Nanoparticles may be intentionally added to the reactor fluid or may be inherently present in the reactor to form a nanofluid. Pulsed plate column (PPC) is widely used as an aerobic bioreactor and gas-liquid contactor for various applications. In the present study, the influence of TiO2, SiO2, and α-Fe2O3 nanofluids with water as the base fluid on kLa was studied in PPC. The effect of nanofluid parameters such as nanofluid type in terms of nanoparticles used, their size and loading along with the column parameters such as frequency (f) and amplitude (A) of pulsation, pulsing velocity (A×f) and gas velocity (Ug) was studied. The use of nanofluids led to kLa enhancement. It was found that kLa increased as the nanoparticle loading increased, attained a maximum at the critical loading, and then reduced as the loading was further increased. The critical loading depended on the nanofluid. kLa was found to increase with the increase in A, f, and Ug. The nanoparticle loading and A×f showed an interacting effect on kLa resulting in one or more hydrodynamic regimes depending upon the type of nanofluids, size, and loading of the nanoparticles. Nanofluids with lower-size nanoparticles showed higher kLa compared to those with larger sizes. TiO2 nanofluid provided a better kLa enhancement than SiO2 and α-Fe2O3 nanofluid. The maximum enhancement factors were obtained with TiO2, SiO2, and α-Fe2O3 nanofluids at the critical loading conditions. The order of magnitude analysis implied that the convective currents caused by the Brownian movement of the nanoparticles in the fluid can be the possible reason for mass transfer enhancement in PPC. Pseudo-homogeneous model was tested and it was found to accurately predict the enhancement only till the critical loading conditions. The developed dimensionless correlations and artificial neural network models could accurately predict kLa and thus may find potential applications in the design of pulsed plate column when used as gas-liquid mass transfer contactors, bioreactors, or photocatalytic reactors. The results of this study indicate that the pulsing conditions required to achieve the desired mass transfer characteristics can be reduced by using a nanofluid instead of the base fluid, thus potentially leading to tremendous saving of energy.