Experimental study on gas–liquid dispersion and mass transfer in shear-thinning system with coaxial mixer

The effects of impeller type, stirring power, gas flow rate, and liquid concentration on the gas–liquid mixing in a shear-thinning system with a coaxial mixer were investigated by experiment, and the overall gas holdup, relative power demand, and volumetric mass transfer coefficient under different conditions were compared. The results show that, the increasing stirring power or gas flow rate is beneficial in promoting the overall gas holdup and volumetric mass transfer coefficient, while the increasing system viscosity weakens the mass transfer in a shearing–thinning system. Among the three turbines, the six curved-blade disc turbine (BDT-6) exhibits the best gas pumping capacity; the six 45° pitched-blade disc turbine (PBDT-6) has the highest volumetric mass transfer coefficient at the same unit volume power.     

Pulsatile flow of discotic mesophases

This paper presents an analysis using computational and scaling methods of pulsatile capillary Poiseuille flow of a model anisotropic viscoelastic discotic liquid crystalline material. The analysis shows that pulsatile pressure drops applied to anisotropic materials can result in flow-rate enhancement or reduction, defined as the relative flow-rate change with respect to the steady-state flow rate, for a given average pressure drop, amplitude, and frequency. It is found that flow-rate modification in pulsatile flow is a direct result of orientation-dependent viscosity. The role of average pressure drop, oscillation amplitude, and frequency on flow enhancement is characterized and explained. The new mechanism of flow-enhancement in liquid crystals subjected to pulsatile pressure is expected to be useful to the fundamental understanding of pulsatile flows of anisotropic suspensions and anisotropic biological fluids.     

基于FLUENT的SK型静态混合器的数值模拟

为提高混合器的优化设计水平和工程应用的速度,应用商业CFD软件—FLUENT,分析了聚酯在SK型静态混合器的混合流动。采用FLUENT中的Carreau模型描述了非牛顿流体聚酯的黏-温特性,得出了混合器的压力降及出口混合温度。     

Fluidization with viscoelastic polymer solutions in the transition flow region

Fluidization of spherical and non-spherical particle beds with shear thinning viscoelastic polymer solutions was investigated experimentally in the transition flow region. It was observed that the influence of elasticity on the anomalous expansion course weakens with the increasing value of Reynolds number. After exceeding a critical value of Reynolds number, which depends on the measure of liquid elasticity, the effect of elasticity vanishes and the expansion curves have the same linear shape as for fluidization with Newtonian (or purely viscous non-Newtonian) fluids. Semi-empirical equations based on the Carreau viscosity model were proposed for predicting the critical value of Reynolds number and the bed expansion in the region of diminishing elasticity effects.     

Onset of pulsing in trickle beds with non-Newtonian liquids at elevated temperature and pressure—Modeling and experimental verification

The onset of pulse flow in trickle-bed reactors involving gas-non-Newtonian liquid systems was predicted from a stability analysis of the solutions around equilibrium steady-state trickle flow of a transient two-fluid model based on the volume-average mass and momentum balance equations. The model was developed for the versatile Herschel-Bulkley constitutive rheological equation from which special solutions for plastic Bingham fluids, power-law shear-thinning and thickening fluids, as well as Newtonian fluids were derived. The impact of yield stress, consistency and power-law indices, and temperature and reactor pressure on the trickle-to-pulse flow transition was analyzed theoretically. Model predictions of the trickle-to-pulse transition for gas-non-Newtonian liquid systems were confronted with elevated temperature and pressure experimental transition data obtained for air-0.25 and 0.5 mass(carboxymethylcellulose) CMC solution systems measured by means of an electrical conductivity technique. In addition the model version offspring corresponding to the Newton case (n=1,k=μ_?,τ₀=0), confronted with measured high temperature/pressure-transition data from this work and high-pressure transition data from Wammes et al. [1990. The transition between trickle flow and pulse flow in a cocurrent gas-liquid trickle-bed reactor at elevated pressure. Chemical Engineering Science 45, 3149; 1991. Hydrodynamics in a cocurrent gas-liquid trickle bed at elevated pressures. A.I.Ch.E. J. 37, 1849] and Burghardt et al. [2002. Hydrodynamics of a tree-phase fixed-bed reactor operating in the pulsing flow regime at an elevated pressure. Chemical Engineering Science 57, 4855] proved equally successful.     

VELOCITY AND CONCENTRATION DISTRIBUTION IN A STEFAN DIFFUSION TUBE

Numerical solutions for the diffusion- and gravity-driven flow in a cylindrical Stefan tube were obtained from the coupled diffusion and Navier-Stokes equations for Peclet numbers, N_Pe = 0.3, 1 and 5. Distributions of binary component concentrations and velocities were calculated. The mass average velocity is parabolic in nature, except at high N_Pe . The solvent is not stagnant but recirculates, even in the absence of gravity. Radial concentration gradients develop which act convectively destabilizing. Consequences for the deduction of diffusion coefficients from Stefan tube experiments are discussed.     

Rheological and volumetric properties of TiO2-ethylene glycol nanofluids

Homogeneous stable suspensions obtained by dispersing dry TiO₂ nanoparticles in pure ethylene glycol were prepared and studied. Two types of nanocrystalline structure were analyzed, namely anatase and rutile phases, which have been characterized by scanning electron microscopy. The rheological behavior was determined for both nanofluids at nanoparticle mass concentrations up to 25%, including flow curves and frequency-dependent storage and loss moduli, using a cone-plate rotational rheometer. The effect of temperature over these flow curve tests at the highest concentration was also analyzed from 283.15 to 323.15 K. Furthermore, the influence of temperature, pressure, nanocrystalline structure, and concentration on the volumetric properties, including densities and isobaric thermal expansivities, were also analyzed.     

Gas-holdup distribution and energy dissipation in an ejector-induced downflow bubble column: the case of non-Newtonian liquid

A precise knowledge of gas-holdup distribution and energy dissipation is essential for designing gas-liquid contactors. A semi-theoretical approach has been presented to obtain the axial distribution of gas holdup through the column for gas-non-Newtonian liquid two-phase flow system. The whole column is distinguished to have three zones based on gas holdup, viz. top, middle and bottom. The middle section where significant accumulation of bubbles takes place, contributes higher gas holdup towards the total compared to the other two sections. Energy dissipation in the column have been calculated from two-phase gas-liquid frictional losses. A comparative study shows that substantial gas holdup are observed in the present system with considerably lower energy losses. The experimental data of gas holdup have been correlated in terms of pressure drop by the modified Lockhart-Martinelli equation.