Free-Radical Graft Copolymerization of Polar Monomers on Low-Density Polyethylene Under Melt-Processing Conditions

Free-radical graft co polymerization of acrylic acid and ethyl methacrylate on low-density polyethylene (LDPE) was studied under simulated melt-processing conditions. Initiators benzoyl peroxide and dicumyl peroxide were evaluated for their grafting efficiency. Benzoyl peroxide was found to be an excellent catalyst for the grafting of both monomers, whereas dicumyl peroxide was quite ineffective. Effect of reaction time, initiator concentration, and reaction temperature was studied for benzoyl peroxide initiated graft co polymerization of the two monomers. The changes in the torque and temperature of the reaction melt in the course of the reaction were recorded. More or less quantitative grafting of both monomers could be achieved, using low initiator concentrations, in very short reaction times. The possibility of modifying LDPE during melt extrusion in the extruder itself has been clearly demonstrated. This would be a highly cost-effective way of diversifying the properties and applications of LDPE. Cross linking was found to be relatively higher in the graft co polymerization of acrylic acid but within acceptable limits. Possible mechanisms of this are discussed.     

A study of the effects of ullage during the burning of horizontal PMMA and MMA surfaces

Experimental and numerical investigations of burning of horizontal surfaces of poly methyl methacrylate and methyl methacrylate are presented. A burner used in this study allows for the fuel surface to be oriented horizontally at a given distance from the burner rim. One of the aims of this study is to understand the effects of ullage (distance between burner rim and fuel surface) on the burning rate of the fuel and the flame structure. In the case of poly methyl methacrylate, the surface at an initial ullage regresses during its burning, and in the case of methyl methacrylate, the pool level is maintained at the given ullage by supplying the fuel at the rate of its burning. Careful repeatable measurements of temperature and species fields are carried out. These reveal the structure of a small‐scale pool flame established over a polymeric fluid such as methyl methacrylate, and such data are scarce in literature. In order to complement the experimental results, fire dynamics simulator is employed to simulate the experimental cases. Flame structure and flow field in the gas phase have been presented and discussed. As the ullage increases, the burning rate decreases. This trend is explained using surface convective heat flux results.     

Stabilization of hexagonal phase in spray-deposited CdTe films by the presence of electric field

The metastable hexagonal phase of cadmium telluride is stabilized in polycrystalline thin films by spray deposition in presence of a high DC voltage. The X-ray diffraction pattern shows peaks closely corresponding to the hexagonal phase. The CdTe films are grown in the stable cubic phase if the electric field is removed. A higher value of the band gap (1.47 eV) of the films deposited in presence of electric field compared to that (1.43 eV) for the films deposited in the absence of the electric field supports the formation of hexagonal regions. The AFM image reveals the formation of rod-shaped particles for the films deposited in the presence of electric field that contribute to the stabilization of hexagonal phase and randomly distributed spherical particles in the absence of electric field.     

Suspended Wash Load Transport of Nonuniform Sediments

The results of an experimental study on transport of suspended wash load through a coarse-bed stream are presented. The experiments were conducted under different concentrations of fine suspended sediment (wash load of uniform size, 0.064 mm diameter) and with three different coarse-bed sediments: two having uniform sizes and one with nonuniform size distribution. For any equilibrium concentration of wash load in suspension, a definite proportion of the wash material was observed to be present within the bed material. No difference is found in this regard between wash load and suspended load transport. Therefore, the relationship, as stated by Samaga et al., for the parameter representing sheltering—exposure and interference effects in the suspended load transport of nonuniform sediments was applied in a modified form by using the present data and the data collected from the literature.     

Sediment Removal Efficiency of Settling Basins

Experimental investigations have been carried out on the sediment removal efficiency of settling basins. Laboratory data on removal efficiency from the present and earlier studies were first used for checking the accuracy of the existing empirical and analytical methods for determination of the sediment removal efficiency of settling basins. The existing relationships were not found to yield satisfactory results over the whole range of data. Therefore, reanalysis of these data was done and a new relationship developed. The effect of continuous flushing of a sediment-water mixture from the settling basin on its removal efficiency was also studied through analysis of experimental data.     

Numerical simulation of hydrogen impinging jet flame using flamelet generated manifold reduction

A transitional hydrogen–air non-premixed impinging jet flame is studied using three-dimensional direct numerical simulation (DNS) and flamelet generated manifolds (FGM) based on detailed chemical kinetics. The simulations are used to investigate the buoyancy instability and the spatial and temporal patterns of the impinging jet flame. The computational domain employed has a size of 4 jet diameters in the streamwise direction and 12 jet diameters in the cross-streamwise direction. The results presented in this study were performed using a uniform Cartesian grid with 200 × 600 × 600 points. Reynolds number used was Re = 2000, based on the inlet reference quantities. The spatial discretisation was carried out using a sixth-order accurate compact finite difference scheme and the discretised equations were advanced in time using a third-order accurate fully explicit compact-storage Runge–Kutta scheme. Results show that the buoyancy and jet shear instability lead to form both inner and outer vortical structures in the primary and wall jet regions, thus complex spatial and temporal variations occur in the mixture fraction, progress variable and temperature fields. Moreover, DNS results suggest that the near-wall vortical structures play an important role in the near-wall heat transfer. These findings may provide useful guidelines for the near-wall combustion modelling using Reynolds-averaged Navier–Stokes modelling or large eddy simulation techniques.     

Molecular dynamics (MD) simulations of the dependence of C–C bond lengths and bond angles on the tensile strain in single-wall carbon nanotubes (SWCNT)

Molecular dynamics (MD) simulations of tensile pulling of carbon nanotubes (SWCNTs) (both armchair and zigzag configurations) were conducted using the Brenner potential to investigate the variation of the six carbon–carbon bond lengths and bond angles of the hexagons in single-walled carbon nanotubes (SWCNT) as a function of tensile strain. The correlations between stress–strain, bond lengths and bond angles with strain, and the variation of a parameter in the interaction potential, namely, D_min have been studied. Simulations at higher values of strain were also performed to obtain the values of breaking strain. A sharp change in the stress–strain behavior, C–C bond lengths, and bond angles with strain was observed for strains equals to 0.30 for the armchair and 0.18 for the zigzag SWCNTs. The dependence of bond stretching and breaking strain on the chirality of the nanotubes and the functional form of the empirical potential has been investigated. The results of our investigations suggest that the presence of attenuation functions in empirical potentials may cause problems, if bond distances or strains become larger than the onset point of these functions. The effect of the duration of relaxing/thermostating of the nanotube after every stretch on the value of the breaking strain has also been discussed.     

Effect of extrusion pressure and number of finishing cycles on surface roughness in magnetorheological abrasive flow finishing (MRAFF) process

Magnetorheological abrasive flow finishing (MRAFF) was developed as a new precision finishing process for complicated geometries using smart magnetorheological polishing fluid. This process introduces determinism and in-process controllability of rheological behaviour of abrasive laden medium used for finishing intricate shapes. Magnetorheological polishing (MRP) fluid is comprised of carbonyl iron powder and silicon carbide abrasives dispersed in a viscoplastic base of grease and mineral oil and exhibits change in rheological behaviour in presence of external magnetic field. This smart behaviour of MRP fluid is utilized to precisely control finishing forces. The process performance in terms of surface roughness reduction depends on process variables like hydraulic extrusion pressure, magnetic flux density in the finishing zone, number of finishing cycles, and composition of MRP fluid. In the present work, experiments were conducted on a hydraulically powered MRAFF experimental setup to study the effect of extrusion pressure and number of finishing cycles on the change in surface roughness of stainless steel grounded workpieces. A new observation of “illusive polishing” action with the initial increase in number of finishing cycles is reported. The actual finishing action is possible only after removal of initial loosely held material remaining after grinding.     

Investigation of the influence of swirl on a confined coannular swirl jet

Large Eddy Simulations are used to model a turbulent confined coannular combustor and examine the effects of swirl on the flow field and mixing. Three separate simulations with relatively high mesh resolutions and different swirl numbers have been carried out using a finite volume method on a Cartesian non-uniform structured grid. A localised dynamic Smagorinsky model is used to parameterize the sub-grid scale turbulence. The snapshots of the axial and swirl velocities and velocity vector fields show the complex flow patterns developing with increased swirl number and the rapid decay of axial momentum. Precessing vortex cores (PVC) were identified for all three cases and the mean axial velocity plots indicate that the upstream extremity of the vortex breakdown bubble shifts towards the inlet as the swirl number increases. The calculated power spectra indicate the distinct precession frequency for high swirl number. Probability density functions of axial velocity showed the changes of their distributions from approximately Gaussian to non-Gaussian with increased swirl number. The swirl has a large effect on the rate of decay of the axial velocity throughout the domain, whereas only has a significant effect on the decay of swirl velocity in the near field close to the jet inlet. The relation between swirl number and the axial extent of the recirculation zone is approximately linear. Radial plots of mean passive scalar and its variance also demonstrate an increase in the rate of mixing with increasing swirl number.