Finite element analysis of an implant-assisted removable partial denture with different positions of the rest arm

When implants are incorporated into an existing removable partial denture, fracture of the acrylic base often occurs. The aim of this study is to analyse the effects of the rest arm position on an implant-assisted removable partial denture using finite element analysis (FEA). A Faro Arm scan was used to extract the geometrical data of a human partially edentulous mandible. A standard plus regular neck (4.8 x 12 mm) Straumann implant and titanium matrix, tooth roots and periodontal ligaments were modelled using a combination of reverse engineering in Rapidform XOR2 and solid modelling using the Solid Works CAD program. The model incorporated a removable partial denture (RPD) and was loaded with realistic bilateral forces. The commercial FEA program ANSYS Workbench 14.0 was used to analyse the stress and strain distributions in the implant assisted RPD and in the metal framework. It is found that moving the position of the rest arm from the mesial to distal side of abutment teeth improves the stress distribution in the metal framework and acrylic denture base structures. The metal frame work and acrylic structures were subjected to lower stresses in an implant-assisted removable partial denture (IARPD) with a distal arm design compared to an IARPD with a mesial arm design

Early detection of agglomeration in a polyethylene fluidized bed at high temperature and pressure by vibration signature analysis

Analysis of vibration signatures was used as a reliable non-intrusive technique for detecting the hydrodynamic state of a polyethylene fluidized bed for early detection of agglomeration. Experiments were carried out in a pilot scale gas-solid fluidized bed at 15-25 bar and 100 degrees C. The bed was operating in the bubbling regime of fluidization. Accelerometers were used to record wall vibration generated by flow of particles and bubbles through the bed at various operating pressures and initial particle sizes. Time and frequency domains and state space methods were applied to analyze the experimental data. These methods were able to detect the agglomeration only when the bed has become defluidized. Analyzing the experimental data by the S-test showed that changes in the particle size due to agglomeration can be detected at least 4 degrees C before defluidization of the bed. This study confirmed that using vibration signatures and applying S-test to the vibration data is a satisfactory approach for early detection of agglomeration in fluidized beds. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved

2D CFD-PBM simulation of hydrodynamic and particle growth in an industrial gas phase fluidized bed polymerization reactor

In an industrial fluidized bed polymerization reactor, particle size distribution (PSD) plays a significant role in the reactor efficiency evaluation. The computational fluid dynamic (CFD) models coupled with population balance model (CFD-PBM) have been extensively employed to highlight its potential to analyze the industrial-scale gas phase polymerization reactor (FBRs) utilizing ANSYS Fluent software. The predicted results reveal an acceptable agreement with the observed industrial data in terms of pressure drop and bed height. Courant number independent study has been carried out to record the mesh and time step independent results for large scale FBRs. Furthermore, the minimum fluidization velocity (U-mf) and size-dependent particle growth rate have been assessed to emphasize the impact of PSD along the reactor. The results show transient regime in the case of minimum fluidization velocity. The simulation results signify that in order to improve the polymerization yield, the amount of gas velocity can be increased without change in the fluidization regime, i.e. segregation. Hence, the 2D CFD-PBWDQMOM coupled model can be used as a reliable tool for analyzing and improving the design and operation of the gas phase polymerization FBRs. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved

Biotreatment of formaldehyde-contaminated air in a trickle bed bioreactor

A biofilm developed on polyurethane packing in a trickle bed bioreactor was used to effectively remove formaldehyde from contaminated air. Formaldehyde removal depended on the retention time of the gas in the bed as well as on the gas-liquid mass transfer coefficient. Both retention time and the mass transfer coefficient depended on the gas flow rate. At 25±1°C and pH 7, a 99% removal of formaldehyde from air with an initial contamination level of 450 mg L -1 was achieved at a hydraulic retention time of 132 s. The degradation rate was likely limited by oxygen mass transfer. The bioreactor could be operated stably over the pH range of 5 to 7 at 25±1°C. Formaldehyde removal in the bioreactor was mathematically modeled to facilitate design and scale up. The model was shown to agree well with the experimental data. Trickle bed bioreactors offer a potentially viable option for cleaning air streams contaminated with formaldehyde

Density and viscosity of aqueous mixtures of N-Methyldiethanolamines (MDEA) and ionic liquids

The density and viscosity of aqueous mixtures of N-methyldiethanolamine (MDEA) and the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), 1-butyl-3-methylimidazolium dicyanamide (bmimDCA), and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (emimOTf) were determined. The measurements were carried out at 1 atm pressure and temperatures ranging from (303.15 to 363.15) K. The concentration of MDEA was fixed at (2.0 and 4.0) M, whereas the IL concentration was varied from (0.5 to 2.0) M. Both densities and viscosities were increased with increasing IL concentration. Correlation equations of density and viscosity for pure substances and for MDEA and ILs aqueous mixtures as a function of temperature and concentration of MDEA and ILs were also determined. The linear correlation for density had an excellent accuracy with less than 0.98 % deviation for all aqueous mixtures of MDEA and ILs. Meanwhile, the extended Arrhenius equation for viscosity achieved acceptable precision with less than 30 % of deviation from experimental data except for 2.0 M MDEA and 1.5 M bmimDCA mixtures

Contamination of TiO2 thin films spin coated on borosilicate and rutile substrates

The present work reports data for TiO2 thin films on borosilicate glass and (001) single-crystal TiO2, annealed at 200–550 °C for 8 h. Characterization included GAXRD, laser Raman microspectroscopy, AFM, UV–Vis, XPS, SIMS, TEM, ellipsometry, and methylene blue (MB) dye degradation. The substrate determined the TiO2 polymorph that formed, while the annealing temperature and boron contamination from the substrate determined most of the associated properties. The films on glass substrates were amorphous following annealing at 200 °C but were anatase at higher temperatures. The films on rutile exhibited epitaxial growth at all annealing temperatures. Annealing caused diffusion of glass component elements into the films and counterdiffusion of Ti into the glass substrates. Since aqueous MB testing caused decreased glass ion concentrations, the diffusion mechanism is via the grain boundaries. Volatilization of boron occurred during annealing at 550 °C. The morphological features dominated the optical properties; the anatase films exhibited high transmissions and low reflectances, while the rutile films exhibited the converse. The band gap decreased slightly with increasing annealing temperatures, reflecting increasing crystallinity. The refractive indices showed an anomalous trend of decrease with increasing annealing temperature and associated crystallinity; this is attributed to the effects of boron volatilization and associated air-filled pore formation. Although the anatase films outperformed the rutile films, the effect of annealing temperature is likely to have been dominant in that it determined the relative extents of crystallinity, grain size, RMS roughness, optical indirect band gap, and oxygen vacancy concentration