M.J.H. Simmons

Drop size distributions in dispersed liquid–liquid pipe flow

Abstract This paper examines drop size distributions in a 0.063 m pipe for a two-phase mixture of kerosene and aqueous potassium carbonate solution. Measurements have been made for both vertical upflow and horizontal geometries, for mixture velocities ranging from 0.8 to 3.1 m/s. Two optical measurement techniques, a backscatter technique using a Par-Tec 300C and a diffraction technique using a Malvern 2600, have been used to obtain the drop size distributions of the dispersions created. Both measurement techniques have been found to be limited to different concentration ranges. Stratification of drop size was observed for low mixture velocities in a horizontal geometry. This did not occur for the vertical geometry. The drop distributions obtained were found to fit an upper limit log-normal distribution (ULLN). The theory of Hinze has been found to agree well with experimentally determined values of maximum drop diameter at low dispersed phase concentrations. At high concentrations, neither Hinze theory, nor a modified version proposed previously, adequately describe the data obtained.

Particle and droplet size analysis from chord distributions

Two methods of estimating particle or droplet size distributions from chord measurements are presented and evaluated. The first is a probability apportioning method (PAM). This assumes that particles are cut randomly and calculates a diameter probability distribution from each chord size detected. The distribution is then accumulated over all chord measurements. PAM has proved to be a fairly robust method when the particle diameters are known. The second is a finite element method (FEM) that has been found to be more generally applicable where there is a wide range of unknown particle diameters. Both methods have been rigorously tested on sets of chord data developed from either the ideal probability functions, a distinct element simulation or true data from a chord measuring instrument (Par-Tec).

Droplet size measurements in horizontal annular gas-liquid flow

Abstract Measurements of drop size distributions in air–water annular flow have been made in a horizontal 0.0953 m pipe, at atmospheric pressure. A laser diffraction technique has been employed, using a Malvern Spraytec R5008 instrument. Stratification of the droplets has been observed by obtaining measurements at the pipe centre line, and 0.019 m above and below it. The stratification, which is caused by the effects of gravitational settling and the asymmetry of the liquid film, decreases with increasing gas velocity. Measured Sauter mean diameters at the pipe centre are similar to what has been observed in vertical pipes. However, they show a stronger effect of liquid flow rate than predicted by the correlation of Azzopardi, that was developed from measurements made with an earlier diffraction technique that did not account for multiple scattering. A log-normal or an upper limit log-normal distribution underpredicts the measured contributions of small diameter drops.

Engineering biofilms for biocatalysis.

Biofilm, friend not foe: Single species biofilms can be engineered to form robust biocatalysts with greater catalytic activity and significantly improved catalytic longevity than purified and immobilised enzymes. We report the engineering, structural analysis and biocatalytic capability of a biofilm that can mediate the conversion of serine and haloindoles to halotryptophans.

Comparison of laser-based drop-size measurement techniques and their application to dispersed liquid-liquid pipe flow

Two laser-based, optical techniques for drop-size measurement, which have been employed to obtain drop sizes in liquid-liquid pipe flow, are described. The measurement systems used are a laser diffraction technique (Malvern 2600 instrument) and a laser backscatter technique (Par-Tec 300C). The instruments are checked through measurement of a batch of glass beads suspended in water in a stirred cell. An image analysis technique and a phase doppler anemometer provide independent measurements of the size of the beads. The pipe, which is 0.063 m in diameter is installed on a liquid-liquid flow rig. The liquids used are kerosene (continuous phase) and aqueous potassium carbonate solution (dispersed phase). Special test sections are used to deploy the instruments. There are significant differences between the results from the two instruments.

The Instability of Shear Thinning and Shear Thickening Spiralling Liquid Jets: Linear Theory

The linear instability of a power law liquid emerging as a jet from an orifice on the surface of a rotating container is investigated, with applications to industrial prilling. Asymptotic methods are used to examine the growth rate and wavenumber of the most unstable traveling wave mode for different flow index numbers. Comparison with Newtonian liquids show that for small rotation rates shear thinning liquids are most stable to disturbances. In contrast for higher rotation rates we find shear thickening liquids are more stable than shear thinning liquids. The influence of viscosity, surface tension, and rotation rate on the growth rates and most unstable wavenumbers associated with both types of liquids are also examined.

Characterisation of spin coated engineered Escherichia coli biofilms using atomic force microscopy

The ability of biofilms to withstand chemical and physical extremes gives them the potential to be developed as robust biocatalysts. Critical to this issue is their capacity to withstand the physical environment within a bioreactor; in order to assess this capability knowledge of their surface properties and adhesive strength is required. Novel atomic force microscopy experiments conducted under growth conditions (30°C) were used to characterise Escherichia coli biofilms, which were generated by a recently developed spin-coating method onto a poly-l-lysine coated glass substrate. High-resolution topographical images were obtained throughout the course of biofilm development, quantifying the tip-cell interaction force during the 10 day maturation process. Strikingly, the adhesion force between the Si AFM tip and the biofilm surface increased from 0.8 nN to 40 nN within 3 days. This was most likely due to the production of extracellular polymer substance (EPS), over the maturation period, which was also observed by electron microscopy. At later stages of maturation, multiple retraction events were also identified corresponding to biofilm surface features thought to be EPS components. The spin coated biofilms were shown to have stronger surface adhesion than an equivalent conventionally grown biofilm on the same glass substrate.

Influence of the flow field in curtain coating onto a prewet substrate

The onset of air entrainment for curtain coating onto a surface prewetted with the coating fluid was studied. The substrate used was a polished, scraped steel wheel and coating was performed over ranges of dimensionless parameters observed in commercial coating processes (Reynolds number, 0.14<Re=ρQ∕μ<33.02; Capillary number, 0.19<Ca=μU∕σ<25.07). The substrate velocity for the onset of air entrainment was obtained as a function of the curtain flow rate per unit width of curtain (1<Q<9cm2s−1), fluid dynamic viscosity (0.0326<μ<0.878Pas), curtain height (0.035<h<0.095m), and thickness of the prewet film (1×10−7<c<3×10−5m). A remarkable and strong dependence of the onset of air entrainment on curtain flow rate was observed (hydrodynamic assist) and the general features of the hydrodynamics were very similar to those observed for previous works onto dry substrates. However, the presence of the prewet film led to higher maximum substrate velocities at the onset of air entrainment than observed for dry substrat...

Bubble Behaviour in Three Phase Capillary Microreactors

Two-phase flow characteristics in vertical capillary downflow were investigated in order to obtain understanding of the behaviour of three-phase monolith reactors. Experiments were conducted using air and dyed water in round and square capillary tubes of 2 mm and 3 mm diameter. The flow regimes and transitions observed were recorded using high speed videography and this data was used to produce flow maps for each tube. The gas and liquid superficial velocities used ranged from 0.001 to 10 m/s and 0.0001 to 1 m/s respectively. The flow regimes and their transitions were found to be a strong function of tube geometry and surface tension effects, and some differences were observed between capillaries of round and square section. This has significant implications for the design of microchannel reactors. Annular, slug-annular, slug, bubbly and churn flow regimes were observed in the round tubes; channelling/irregular flow was observed in the square tubes in place of annular and slug-annular flow.

Understanding the impact of media viscosity on dissolution of a highly water soluble drug within a USP 2 mini vessel dissolution apparatus using an optical planar induced fluorescence (PLIF) method.

In this study, planar induced fluorescence (PLIF) was used for the first time to evaluate variability in drug dissolution data using Rhodamine-6G doped tablets within small volume USP 2 apparatus. The results were compared with tablets contained theophylline (THE) drug for conventional dissolution analysis. The impact of hydrodynamics, sampling point, dissolution media viscosity and pH were investigated to note effects on release of these two actives from the hydrophilic matrix tablets. As expected mixing performance was poor with complex and reduced velocities at the bottom of the vessel close to the tablet surface; this mixing became even worse as the viscosity of the fluid increased. The sampling point for dissolution can affect the results due to in-homogenous mixing within the vessel; this effect is exacerbated with higher viscosity dissolution fluids. The dissolution profiles of RH-6G measured via PLIF and THE measured using UV analysis were not statistically different demonstrating that RH-6G is an appropriate probe to mimic the release profile of a highly soluble drug. A linear correlation was accomplished between the release data of the drug and the dye (R(2)>0.9). The dissolution profile of the dye, obtained with the analysis of the PLIF images, can be used in order to evaluate how the viscosity and the mixing performance of USP 2 mini vessel affect the interpretation of the dissolution data of the targeted drug.