Mixing time in an agitated multi‐lamp cylindrical photoreactor using electrical resistance tomography

BACKGROUND: There is scarce information on the application of electrical resistance tomography (ERT) in UV photoreactors, in which mixing and mass transfer are important. Therefore, the feasibility of an ERT system in an agitated multi‐lamp UV photoreactor was investigated to monitor the mixing process. RESULTS: The locations of the UV tubes had a significant impact on the mixing time, particularly at the lower impeller speeds (45 and 150 rpm). Also, at the higher impeller speeds (250, 350, and 500 rpm) and the same radial position (r), changing the angle θ from 15 to 45°, resulted in only a slight variation of the mixing time. Finally, the maximum mixing time occurred when UV tubes were positioned at r = 13 cm (r/R = 0.68) and θ = 0°, while minimum mixing time occurred at location r = 16 cm (r/R = 0.83) and θ = 45°. CONCLUSION: The experimental results demonstrated the feasibility of the ERT system to monitor the mixing process in the UV photoreactor. The ERT results also indicated that the locations of the UV tubes had a significant effect on the mixing performance of the photoreactor. Furthermore, the mixing time varied inversely with the rotational speed, and this effect was more pronounced at lower speeds. Copyright © 2008 Society of Chemical Industry     

Water resistance and thermal stability of hybrid lignocellulosic filler–PVC composites

In this study, composites based on polyvinyl chloride (PVC), pulp fiber (PF), and wood flour (WF) were made by injection molding. The effects of two variable factors, namely the filler form and filler loading level, on the composite physical properties were examined. The result clearly showed that the major part of water absorption was due to water absorption of PF. It was found that the water absorption in the lignocellulosic material base composites is significantly higher than the neat PVC. Besides, the water absorption increased sharply with increasing cellulosic filler loadings in the composites. In case of hybrid composites, the rate of water uptake correlated with percentage weight of WF, lower WF (higher PF) loadings in composites exhibit higher rate of absorption. The higher onset of degradation temperature indicates the improved thermal stability of the samples. In other words, the result clearly illustrates that the thermal property of the composites increases after using PF and further increases after addition of WF.     

Compatibilised LDPE/LLDPE/nanoclay nanocomposites: I. Structural,mechanical, and thermal properties

Nanocomposites of LDPE/LLDPE/nanoclay have been prepared using a lab‐scale co‐rotating twin screw extruder. Using XRD, tensile testing, AFM, TGA, effects of some material properties and one processing parameter on mechanical and thermal properties of the prepared nanocomposites were evaluated. Tensile properties indicated that all the prepared nanocomposites exhibited a significant improvement in elastic modulus and toughness compared to pristine LDPE/LLDPE blends of the same composition. Thermal stability of nanocomposites in the air and nitrogen atmosphere was improved. XRD patterns and AFM micrographs showed semi‐exfoliated and intercalated microstructures for the prepared nanocomposites with different orders of mixing.     

Effects of organoclay on the compatibility and interfacial phenomena of PE/EVA blends with UCST phase behavior

The compatibilization effects of organically modified nanoclay on the miscibility window, phase separation kinetics, biphasic morphology, interfacial tension, and final properties of polyethylene/ethylene vinyl acetate copolymer blends exhibiting UCST behavior have been investigated. Regardless of blend composition, intercalated nanoclay decreases the phase transition temperatures to lower values and changes the symmetry of phase diagram. The miscibility of PE and EVA phases in the amorphous regions of nanocomposites noticeably enhances and finer biphasic morphology is obtained by the incorporation of organoclay. The pinning influence of the nanofiller on polymer chain diffusion causes much slower phase separation kinetics for the nanocomposites. Similar to conventional compatibilizers such as block copolymers, the interfacial activity of nanoclay leads to a sharp decline in the interfacial tension of PE/EVA up to 2‐orders of magnitude. Moreover, the results show that imposing restrictions on the phase separation phenomenon increases the impact strength of the virgin blend and related nanocomposite. However, this improvement has been much more noticeable in the presence of nanoparticles, which is due to the simultaneous roles of organoclay as an effective compatibilizer and reinforcement. POLYM. COMPOS., 35:2329–2342, 2014. © 2014 Society of Plastics Engineers     

Effect of impeller type on continuous‐flow mixing of non‐Newtonian fluids in stirred vessels through dynamic tests

Mixing of non‐Newtonian fluids with axial and radial flow impellers is prone to a significant extent of nonideal flows (e.g., dead zones and channelling) within the stirred reactors. To enhance the performance of the continuous‐flow mixing of pseudoplastic fluids with yield stress, close‐clearance impellers were utilised in this study. We explored the effects of various parameters such as the type of close‐clearance impeller (i.e., the double helical ribbon (DHR) and anchor impellers), impeller speed (25–500 rpm), impeller pumping direction, fluid rheology (0.5–1.5% xanthan gum solution), fluid flow rate (3.20–14.17 L min^?1) and the locations of outlet (configurations: top inlet–top outlet, top inlet–bottom outlet) on the dynamic performance of the mixing vessel. The performance of the DHR impeller was then compared to the performance of various types of impellers such as axial‐flow (Lightnin A320) and radial‐flow (Scaba 6SRGT) impellers. The dynamic tests showed that the DHR impeller was the most efficient impeller for reducing the extent of nonideal flows in the continuous‐flow mixer among the impellers employed in this study. In addition, the mixing quality was further improved by optimising the power input, increasing the mean residence time, decreasing the fluid yield stress, using the up‐pumping impeller mode and using the top inlet–bottom outlet configuration. © 2011 Canadian Society for Chemical Engineering     

CFD analysis of two‐phase turbulent flow in internal airlift reactors

The hydrodynamic performance of three internal airlift reactor configurations was studied by the Eulerian–Eulerian k–ε model for a two‐phase turbulent flow. Comparative evaluation of different drag and lift force coefficient models in terms of liquid velocity in the riser and downcomer and gas holdup in the riser was highlighted. Drag correlations as a function of Eötvös number performed better results in comparison to the drag expressions related to Reynolds number. However, the drag correlation as a function of both Reynolds and Eötvös numbers fitted well with experimental results for the riser gas holdup and downcomer liquid velocity in configurations I and II. Positive lift coefficients increase the liquid velocity and decrease the riser gas holdup, while opposite results were obtained for negative values. By studying the effects of bubble size and their shape, the smaller bubbles provide a lower liquid velocity and a gas holdup. The effects of bubble‐induced turbulence and other non‐drag closure models such as turbulent dispersion and added mass forces were analysed. The gas velocity and gas holdup distributions, liquid velocity in the riser and downcomer, vectors of velocity magnitude and streamlines for liquid phase, the dynamics of gas holdup distribution and turbulent viscosity at different superficial gas velocities for different reactor configurations were computed. The effects of various geometrical parameters such as the draft tube clearance and the ratio of the riser to the downcomer cross‐sectional area on liquid velocities in the riser and the downcomer, the gas velocity and the gas holdup were explored. © 2011 Canadian Society for Chemical Engineering     

Occurrence of aflatoxin M1 in white cheese samples from Tehran, Iran

This study was undertaken to determine the occurrence of aflatoxin M₁ (AFM₁) in 50 white cheese samples from 2 dairy factories in summer 2008 and winter 2009. Enzyme-linked immunosorbent assay (ELISA) method was used for analysis of the samples. Aflatoxin M₁ was found in 60% of the cheese samples, ranging from 40.9 to 374 ng/kg. Toxin levels in 6% of the samples exceeded the Iranian national standard limit i.e. 200 ng/kg. Considering seasonal variability, mean concentration of AFM₁ in the samples collected in winter was significantly (P < 0.03) higher than those collected in summer. Therefore, high occurrence of AFM₁ in cheese samples could be a potential hazard for public health.