Youguang Ma

The viscosity distribution around a rising bubble in shear-thinning non-newtonian fluids

The viscosity distribution of the liquid around a rising bubble in carboxymethyl cellulose (CMC) aqueous solutions was measured experimentally by particle image velocimetry (PIV). The effect of the concentration of CMC solutions on the viscosity distribution around a bubble and the coupling relations between the viscosity field, flow field and shear stress field were also studied. Results indicated that the specific viscosity (non-dimensionalized by η0) decreases with the increase in CMC solution concentration due to a shear thinning effect. Within the experimental range, similar viscosity distributions of liquids around a rising bubble were found: a hollow cylindrical low viscosity region around the bubble wake and a high viscosity region in the central bubble wake.

Experimental investigation of the liquid volumetric mass transfer coefficient for upward gas-liquid two-phase flow in rectangular microchannels

The gas-liquid two-phase mass transfer process in microchannels is complicated due to the special dynamical characteristics. In this work, a novel method was explored to measure the liquid side volumetric mass transfer coefficient kLa. Pressure transducers were utilized to measure the pressure variation of upward gas-liquid two-phase flow in three vertical rectangular microchannels and the liquid side volumetric mass transfer coefficient kLa was calculated through the Pressure-Volume-Temperature correlation of the gas phase. Carbon dioxide-water, carbon dioxide-ethanol and carbon dioxide-n-propanol were used as working fluids, respectively. The dimensions of the microchannels were 40 µm×240 µm (depth×width), 100 µm×800 µm and 100 µm×2000 µm, respectively. Results showed that the channel diameter and the capillary number influence kLa remarkably and that the maximum value of kLa occurs in the annular flow regime. A new correlation of kLa was proposed based on the Sherwood number, Schmidt number and the capillary number. The predicted values of kLa agreed well with the experimental data.

Mass transfer of SO2 absorption with an instantaneous chemical reaction in a bubble column

Gas absorption accompanied by an instantaneous irreversible chemical reaction in bubble columns has been analyzed theoretically. A mass transfer model based on the Dankwerts surface-renewal model as well as the penetration theory for surface stretch proposed by Angelo et al. was developed, in which the effects of bulk motion and turbulence on mass transfer were taken into account. The analytical expressions for the time-average mass transfer coefficient and the enhancement factor have been obtained. The fast reactive absorption of SO2 from gas mixtures into aqueous NH4HCO3 solution was investigated experimentally in a bubble column reactor to validate the mass transfer model, and the results calculated by the present model agree well with the experimental results.