Composite Fouling on Heat Exchange Surface in Australian Sugar Mill Evaporator

Composite scale of amorphous silica and calcium oxalate is very intractable; it imposes a significant fraction of scale management cost in sugar mill evaporators. This work evaluates silica and calcium oxalate composite fouling using dynamic fouling-loop experiments under different operating conditions with and without sugar. A novel closed-loop setup simulating in a single run the effect of feed concentration in successive stages of evaporation cycle was used. Experiments under constant composition and varying thermal hydraulic effect were conducted. Results indicated synergistic effects for initial silica and calcium oxalate supersaturation values of 2.6 and 1.7. Sugar effects became significant for concentrations in the third effect and above. The fouling mechanism was particulate deposition of silica and calcium oxalate colloidal species strengthened by consolidation; fouling rate increased with decreasing interfacial energy barrier between the surface and foulant, assessed by zeta-potential analysis. Deposit characteristics and deposition rates were concentration and thermal hydraulics dependent. Results confirmed the need that the 5 × 5 (types × stages of fouling) matrix of Epstein needs to be expanded to a 6 × 6 matrix to include composite fouling as a type of fouling. In this study the composite fouling was a surface-controlled process for which the activation energy was similar to typical chemical bond strengths, explaining the role of consolidation in composite fouling. The results contribute to advancement of fundamental understanding of heat exchanger fouling and to development of scale control strategies for composite fouling minimization in sugar mill evaporators.     

Transient heat transfer in a fixed bed of slab-shaped and spherical particles with intraparticle conduction

The mathematical equations for heat transfer between a flowing fluid and both slab-shaped and spherical particles with intraparticle conduction in a fixed bed, are numerically solved using the method of lines. The solution for spherical particles was used to confirm previous results for zero and non-zero Biot numbers. Conditions are identified under which heat transfer to beds of slabs should not be approximated by available solutions for spheres.     

In vitro deposition of lysozyme on etafilcon A and balafilcon A hydrogel contact lenses: effects on adhesion and survival of Pseudomonas aeruginosa and Staphylococcus aureus.

PURPOSE: To compare lysozyme adsorption and absorption and bacterial adhesion interactions on conventional (etafilcon A) and silicone (balafilcon A) hydrogel contact lenses. METHOD: Lysozyme concentrations and activities associated with the lenses were determined after solvent extraction (trifluoroacetic acid/acetonitrile) and directly on the lenses without extraction with micrococcal- and micro-bicinchoninic acid (BCA) assays. Cells of bacteria with radiolabeled leucine and a cell recovery procedure were used in determinations of bacterial adhesion to lenses. RESULTS: Lysozyme was adsorbed and absorbed to the conventional etafilcon A lens at about a 10-fold greater concentration than to the balafilcon A silicone hydrogel lens. Enzyme activities on the surfaces of both lenses were similar but replenished after saline extraction only with the etafilcon A lens. Lysozyme on the lens surface showed significant lysis of Micrococcus luteus but had a negligible effect on the adhesion and survival of Staphylococcus aureus. Lysozyme did not appear to affect the survival of Pseudomonas aeruginosa on lenses. CONCLUSION: In vitro experiments show that concentrations of active lysozyme on the surface of the etafilcon A lens, unlike the balafilcon A lens which showed negligible absorption, may be sustained from the lens matrix. Lysozyme deposited on hydrogel lenses had marked activity against M. luteus but relatively minor effects on the primary adhesion of P. aeruginosa and S. aureus.     

Dependence of Semiconductor to Metal Transition of VO2(011)/NiO{100}/MgO{100}/TiN{100}/Si{100} Heterostructures on Thin Film Epitaxy and Nature of Strain

We have studied semiconductor to metal transition (SMT) characteristics of VO₂(011) thin films integrated epitaxially with Si(100) through NiO{001}/MgO{001}/TiN{001} buffer layers and correlated with the details of epitaxy and nature of residual stresses and strains across the VO₂/NiO interface. Thin film epitaxy at both room and elevated temperatures is studied in detail by electron microscopy and in situ high‐temperature X‐ray diffraction techniques. The epitaxial relationship across the interface between monoclinic VO₂ and NiO is determined to be (011)_VO2||{100}_NiO and [01]_VO2||[001]_NiO at room temperature. The epitaxial alignment at the temperature of growth where tetragonal VO₂ is stable is determined as: (110)_VO2||{100}_NiO and [001]_VO2||[100]_NiO. A cube‐on‐cube crystallographic alignment is established across the NiO{100}/MgO{100}/TiN{100}/Si{100} interfaces. The misfit strains across the VO₂/NiO interface at the growth temperature are calculated and the mechanism of strain relaxation is discussed. The out‐of‐plane orientation is found to be relaxed in both monoclinic and tetragonal states of VO₂. It is shown that a compressive strain of 31.65% along the [001] direction of tetragonal VO₂ is fully relaxed via matching of multiple domains. However, a small tensile misfit strain of about 5% along [10] direction cannot relax and remains in the lattice. This tensile residual strain leads to a compressive strain along [001] axis which, in turn, results in an SMT temperature slightly lower than that of freestanding strain‐free VO₂. SMT characteristics of VO₂(011) epilayers are assessed where an amplitude of near five orders of magnitude, and a hysteresis of less than 3.6 ^°C are obtained. This study introduces VO₂/NiO thin film heterostructure integrated with silicon as a promising candidate for multifunctional devices with novel characteristics where a combination of sensing, manipulation, and response functions is needed.     

Micro arc oxidation of nano-crystalline Ag-doped TiO2 semiconductors

Simple synthesis of silver doped TiO₂ nanostructured layers by micro arc oxidation process is reported for the first time. The layers consisted of anatase and rutile phases whose characteristic XRD-peaks shifted toward lower diffraction angles when compared to the pure micro arc oxidized TiO₂ layers. Silver-doping was confirmed by XPS technique. The anatase phase crystalline size was determined as 27.6 and 21.8 nm for the layers grown under the voltages of 350 and 500 V. Employing a UV-Vis spectrophotometer, a red shift in the absorption edge of the layers was observed when silver was incorporated into the titania lattice.     

Hydrothermal synthesis and characterization of TiO2 nanostructures using LiOH as a solvent

In the present study, we performed hydrothermal method as a simple and efficient route for the synthesis of rutile TiO₂ nanostructures in various concentrations of lithium hydroxide solutions. TiO₂ nanopowders with average sizes of 15 and 23 nm were prepared using 4 M and 7 M LiOH solutions. X-ray diffraction analysis (XRD), transmission electron microscope (FEG-STEM), scanning electron microscopy (SEM), and Brunauer–Emmet–Teller (BET) analyses were used in order to characterize the obtained products and comparison of the morphology of the powders obtained in different concentrations of LiOH solvent. It was shown that alkali solution concentration has affected the crystallinity, agglomeration ratio, particle size and specific surface area of the obtained rutile phases.     

A new cerium (III) ion selective electrode based on 2,9-dihydroxy-1,10-diphenoxy-4,7-dithia decane, a novel synthetic ligand

In the present study, a novel electrode based on 2,9-dihydroxy-1,10-diphenoxy-4,7-dithiadecane (DHDPDTD) that is selective to cerium (III) cations was evaluated electrochemically, and a Nerenstian slope (19.3 ± 1 mV decade⁻¹) over a concentration range of 1.0 × 10⁻⁸–1.0 × 10⁻¹ M and a detection limit of 2.1 × 10⁻⁹ M were observed. The proposed electrochemical sensor displayed a rapid response time of 10 s, improved selectivity towards Ce (III) cations in the presence of alkali, alkaline earth, transition and heavy metal cations, and could be used in a pH range of 5.0–8.0. Additionally, the proposed sensor was used as an indicator in the potentiometric titration of fluoride and the determination of F⁻ ions in real samples.     

Influence of multi-walled carbon nanotubes on creep behavior of adhesively bonded joints subjected to elevated temperatures

Polymeric materials are prone to creep loading. This paper is aimed to study the effect of multi-walled carbon nanotubes (MWCNTs) on creep behavior of adhesively bonded joints. Neat and MWCNTs-reinforced adhesively bonded joints were manufactured and tested under creep loading at elevated temperatures. Two MWCNT weight percentages of 0.1 and 0.3 were used for reinforcing the single lap joints (SLJs) and the joints were tested at different temperature and load levels. The results showed that 0.1 wt% of MWCNTs resulted maximum improvements in creep behavior of adhesive joints. Adding 0.1 wt% of MWCNTs into the adhesive layer caused maximum reductions of 57%, 60% and 47% in the steady-state creep rates of the joints tested at 30, 40 and 50°C, respectively. Furthermore, 0.1 wt% of MWCNTs resulted maximum reductions of 29%, 33% and 37% in the creep strains corresponding to a specific creep loading time and maximum reductions of 23%, 45% and 49% in the elastic strains corresponding to the time at which creep loading started.     

Selective uranyl cation detection by polymeric ion selective electrode based on benzo-15-crown-5

A uranyl cation selective electrode based on benzo-15-crown-5(B15C5) incorporated into a polyvinylchloride (PVC) membrane has been developed. The electrode was prepared by coating the surface of a graphite rod by a membrane containing dioctylphtalate (DOP) as plasticizer, B15C5 as an ionophore, carbon powder and polyvinylchloride (PVC) in tetrahydrofuran (THF). The best composition of the coated membrane (w/w%) was found to be: 4% ionophore, 20% plasticizer, 56% PVC and 20% carbon powder. The electrode exhibits a Nernstian slope (29.5 ± 2 mv) over the concentration range from 1.0 × 10^? 4 to 1.0 × 10^? 1 M. The detection limit of the electrode is 1.0 × 10^? 4 M. The effects of the pH and the possible interfering cations and anions were investigated and the optimized conditions for electrode were evaluated. The response time of the electrode is about 15 s and it can be used for more than 6 weeks without observing any divergence in potentiometric response. The electrode was applied as indicator electrode in potentiometric titrations.