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Spheronization of cylindrical extrudates on a rotating friction plate involves breakage and rounding. Little attention has been given to the breakage stage and quantitative modeling of this process is scarce. Two simple models are compared with experimental data obtained for the early stages of spheronization of microcrystalline cellulose/water extrudates. Tests were conducted for different times (t), rotational speeds (ω), initial loadings, and on pyramidal friction plates with different dimensions. The first model, describing the number of pellets, validated ω3t as a characteristic time scale for the breakage stage. The kinetic parameters obtained by fitting showed a systematic dependence on plate dimensions expressed as a scaled gap width. The second model, a simple population balance, described the evolution of the number and length of pellets. The pseudo rate constants provided insights into the kinetics: extrudates tended to break near the middle, while breakage of smaller pellets was slowed down by more pellet–pellet collisions. [ABSTRACT FROM AUTHOR]

Purpose: Emulsification of silicone oil (SiOil) in a vitrectomized eye was investigated using a 3D model of the vitreous cavity to test the hypothesis that oil droplet formation arises from the breakdown of the bulk SiOil‐aqueous interface during eye saccadic movement. Methods: Round bottom flasks filled with SiOil and a saline phase modelled the vitrectomized SiOil‐filled eye. A stepper motor imposed saccadic movements and the oil/aqueous interface was monitored with digital cameras. A range of SiOil viscosities, flask diameters, motion scenarios and levels of fill were studied. Estimates of velocity profiles in the fluid on the equatorial plane of a sphere subject to saccadic motion were obtained from an analytical solution to the Navier‐Stokes equations. Results: Interfacial waves were observed at saccadic motions with higher acceleration, amplitude and frequency. Low interfacial tension between the two fluids, lower oil viscosity and smaller level of SiOil fill all promoted large deformations of the interface. No droplets were formed at the bulk SiOil‐aqueous interface. However, formation and detachment of oil droplets were observed at the three‐phase contact line under certain conditions. Conclusions: The stresses generated at the liquid‐liquid interface are not large enough to form droplets in the bulk region for conditions representative of these in the eye. Bulk emulsification of the SiOil, reported as the main formation mechanism by some workers, is not responsible for droplet formation in a vitrectomized SiOil‐filled eye set‐up. This result confirms recent finding on droplet formation driven by a surface emulsification mechanism. [ABSTRACT FROM AUTHOR]

The effect of fouling in heat-transfer devices (HTDs) is complicated by aging of the fouling deposits. Aging is, like deposition, often sensitive to temperature, so that heat transfer, deposition, and aging are coupled phenomena. Ishiyama et al. ( AIChE J. 2010;56:531-545) presented a distributed model of the aging of deposits formed by chemical reaction fouling and illustrated its effect on thermal and hydraulic performance of a HTD operating in the turbulent flow regime. Two-layer models, simpler than the distributed model, are explored. The deposit is considered to consist of two layers, fresh and aged; this simple picture is shown to be sufficient to interpret thermal and hydraulic aspects of deposit aging when HTDs are operated at constant heat flux (as reflecting laboratory experiments) but not in cases where the constant wall temperature approximation is more realistic. © 2011 American Institute of Chemical Engineers AIChE J, 2011 [ABSTRACT FROM AUTHOR]

The gelation kinetics of β-lactoglobulin (βLg) solutions has been determined in the alkaline regime over a wide range of protein concentrations, gelling temperatures and gelation pH (pHgel), set using NaOH. The behaviour is compared with caustic-induced gelation of whey protein concentrate and the alkaline dissolution of heat-induced whey gels. The gelation time decreases significantly between neutral conditions and pHgel 9, because of the activation of the free cysteine groups and displacement to the monomeric form, and between pHgel 10 and 11, due to the base denaturation of βLg. Both transitions are associated with a significant decrease in the activation energy of gelation. At pHgel >11.5 the gelation time is observed to increase with pHgel, owing to destruction of interprotein crosslinks. These results are consistent with the recently reported observation that a minimum pH for the dissolution of βLg gels and aggregates exists around 11.6 [ Biomacromolecules 8 (2007) 1162]. This phenomenon has been assigned to the destruction of non-covalent interactions that would inhibit the final percolation of the gel. [ABSTRACT FROM AUTHOR]