Leakage current analysis, FFT calculation and electric field distribution under water droplet on polluted silicon rubber insulator

In this paper, an experimental test results on silicon rubber insulator with voltage of 20 kV have been shown. Artificial aging on insulator has been done using solid layer methods according to IEC60507 standard. Leakage current waveforms during the experimental studies were measured. Normally Fast Fourier transform method used to find the harmonic spectrum in the leakage currents. Three states of analysis are considered. In the first state, it is done with nominal voltage and without arc. In the second state, it is done in the presence of dry band arcing and corona discharge and in the last case, continuous arc is investigated and in each state harmonic analysis is performed. It is observed that in second state the third harmonic components increase rather than in the first state. Artificial aging on insulator has been done using solid layer methods according to IEC60507 standard. Leakage current waveforms during the experimental studies were measured. Eventually, to distinguishing pollution intensity, equivalent salt deposit density calculations are implemented. At the end, finite element method has been investigated for the results of water droplets existing on the surface of silicone rubber materials and electric field distribution along the surface of insulator.     

Effects of different silicon-based surface active additives on degradability of clearcoats exposed to bird droppings

A series of clearcoats separately loaded with different concentrations of functional silicon–polyacrylate and polydimethyl siloxane additives were prepared. Optical performances of the cured films were studied by gonio-spectrophotometry. Dynamic mechanical thermal analysis was used in order to investigate viscoelastic properties of the additive-containing films. Contact angle measurements, (FTIR) spectroscopy, scanning electron microscopy equipped with energy-dispersive analysis of X-ray, and atomic force microscopy techniques were utilized to evaluate surface properties of the clearcoats. It was shown that clearcoat surface free energy decreased and its crosslinking density increased in the presence of the additives. Results revealed that addition of both additives to the clearcoat enhanced its resistance against pancreatin (simulated bird droppings). A decrease in surface degradation was observed in the presence of the additives. Results also showed that functional polydimethyl siloxane influenced coating viscoelastic, surface chemistry, and biological resistance more effectively compared to that of the functional silicon–polyacrylate one.     

CFD modeling of mass transfer in annular reactors

A computational fluid dynamics (CFD) investigation of single-phase flow mass transfer prediction in annular reactors was conducted. Different hydrodynamic models including laminar, standard k–ε, realizable k–ε, Reynolds stress (RSM), and the Abe-Kondoh-Nagano (AKN) (a low Reynolds number turbulence model) were evaluated against experimental data in terms of their mass transfer predication capabilities. The laminar model predicted successfully the average mass transfer in the flows under laminar regime (Re < 1500). Among the four evaluated turbulence models, the AKN model provided a better prediction of the average mass transfer rates in the systems when operated both under transitional and turbulent conditions (3000 < Re < 11000). The RSM performed very similarly to the AKN model, except for the entrance region of the reactors where it predicted lower mass transfer rates. These results make the AKN and RSM models very attractive to be integrated in CFD-based simulations of turbulent annular reactors.