Numerical investigation of effective parameters of falling film evaporation in a vertical-tube evaporator

Wastewater treatment is one of the most effective solutions to manage the problem of water scarcity. Falling film evaporators are excellent technology in wastewater treatment plants. These wastewater evaporators provide high heat transfer, short residence time in the heating zone, and high-purity distilled water. In the present study, the mechanism of turbulent falling film evaporation in a vertical tube has been investigated. A model has been developed for symmetrical two-dimensional pure and saline water flow in a vertical tube under constant wall heat flux. The numerical simulation has been carried out by a commercial computational fluid dynamics code. The evaporation of saturated liquid film is simulated utilizing a two-phase volume of fluid method and Tanasawa phase-change model. The main objective of this study is to evaluate the effects of water salinity, liquid Reynolds number, wall heat flux, and liquid film thickness on the two-phase heat transfer coefficient and vapor volume fraction. The numerical heat transfer coefficients are compared with the obtained results by Chen's empirical correlation. With a MAPE ≤ 11%, this study proves that the numerical method is highly effective at predicting the heat transfer coefficient. Moreover, the empirical coefficient of the Tanasawa model and the minimum thickness of the falling film are determined.     

Nanosized polypyrrole affected by surfactant agitation for emulsion polymerization

Nanosized conductive polypyrrole (PPy) powders were prepared using emulsion polymerization with aid of high speed agitation. Different agitation speeds from 650 to 24,000 rpm were used with different anionic, cationic, and non-ionic surfactants. Then, the effects of the agitation speed and surfactant species were examined in terms of their physical and electrical properties of conductivity and powder size. Prepared PPy nanopowders exhibited high conductivity values of 10 S/cm regions, when sodium dodecylbenzenesulfonate (SDBS) and sodium dodecylsulfate (SDS) were used. The powder dispersion of the resultant PPy was also observed to be dependent on the agitation speed and surfactant type. The morphology shown by SEM and TEM revealed that the anionic SDBS surfactant could effectively disperse into nanosized aggregates of the PPy. The results showed that the combination of the anionic surfactants and high agitation in the emulsion polymerization could produce nanosized PPy powders with higher conductivity.     

Effect of indium concentration on morphology and optical properties of In-doped ZnO nanostructures

In-doped ZnO nanostructures with different indium concentrations were grown using a thermal evaporation method. The In-doped ZnO nanostructures with a low concentration of indium exhibited a javelin shape, while the In-doped ZnO nanostructures with a high concentration of indium showed a flake shape. In addition, undoped ZnO nanojavelins were grown under the same conditions, but the sizes of these undoped ZnO nanojavelins were larger than the In-doped ZnO nanojavelins. It was shown that the In³⁺ cations played a crucial role in controlling the size. X-ray diffraction and Raman spectroscopy clearly showed hexagonal structures for all of the products. However, the Raman results demonstrated that the In-doped ZnO nanoflakes had a lower crystalline quality than the In-doped ZnO nanojavelins. Furthermore, photoluminescence (PL) measurements confirmed the Raman results. Moreover, the PL results demonstrated a larger band-gap for the In-doped ZnO nanostructures in comparison to the undoped ZnO.     

Analysis of antibiotic resistance patterns and detection of mecA gene in Staphylococcus aureus isolated from packaged hamburger

Presence of Staphylococcus aureus, antibiotic resistance pattern and PCR detection of mecA gene in isolated strains were investigated in total of 256 packaged hamburgers in Iran-Tehran. For this purpose we used standard disk-diffusion method and sensitive and specific PCR technique, respectively. Results showed that 25% of samples were positive for S. aureus. Resistance to meticillin, erythromycin, penicillin G, cefazolin, ciprofloxasin, vacomycin and amoxiclave was determined 89%, 20.3%, 18.7%, 15.6%, 14%, 26.6% and 12.5%, respectively. According to the obtained results from PCR analysis of methicillin-resistant S. aureus (MRSA), mecA gene was present in 100% of the resistant isolates, 0% of intermediate-resistance isolates and 25% of susceptible isolates. The results obtained from PCR detection of mecA gene showed high correlation with standard disk diffusion test.     

Two strategies for multi-objective optimisation of solid oxide fuel cell stacks

This paper focuses on multi-objective optimisation (MOO) to optimise the planar solid oxide fuel cell (SOFC) stacks performance using a genetic algorithm. MOO problem does not have a single solution, but a complete Pareto curve, which involves the optional representation of possible compromise solutions. Here, two pairs of different objectives are considered as distinguished strategies. Optimisation of the first strategy predicts a maximum power output of 108.33 kW at a breakeven per-unit energy cost of 0.51 $/kWh and minimum breakeven per-unit energy cost of 0.30 $/kWh at a power of 42.18 kW. In the second strategy, maximum efficiency of 63.93%at a breakeven per-unit energy cost of 0.42 $/kWh is predicted, while minimum breakeven per-unit energy cost of 0.25 $/kWh at efficiency of 48.3% is obtained. The present study creates the basis for selecting optimal operating conditions of SOFC under the face of multiple conflicting objectives.     

Role of Double Oxide Film Defects in the Formation of Gas Porosity in Commercial Purity and Sr-containing Al Alloys

The role of double oxide film(bifilm) defects in the formation of gas porosity in commercial purity and Srcontaining Al alloys was investigated by means of a reduced pressure test(RPT) technique.The liquid metal was poured from a height into a crucible to introduce oxide defects into the melt.The melt was then subjected to different hydrogen addition and holding in liquid state regimes before RPT samples were taken.The RPT samples were then characterized by determining their porosity parameters and examining the internal surfaces of the pores formed in them by scanning electron microscopy.The results indicated oxide defects as the initiation sites for the growth of gas porosity,both in commercial purity and Sr-containing Al alloys.The results also rejected reduction of the surface tension of the melt,increase in the volumetric shrinkage and reduction in interdendritic feeding as the possible causes of an increase in the porosity content of the Al castings modified with strontium.The change in the composition of the oxide layers of double oxide film defects was suggested to be responsible for this behaviour.