LOW TEMPERATURE FLOW CHARACTERISTICS OF SOME WAXY CRUDE OILS IN RELATION TO THEIR COMPOSITION : PART II EFFECT OF WAX COMPOSITION AND CONCENTRATION ON THE DEW AXED CRUDE OILS WITH / WITHOUT ADDITIVES

In this part of the work the effect of wax concentrations on the rheologica! properties of the dewaxed Duliajan (Assam) and Lingaia crude oils have been studied. The dewaxing of the crude oil was done by removing n-paraffins from the crude oil by urea adduction. The urea adducted n-paraffins concentrate-the wax- was characterized by its carbon number distribution. The urea non adducted oil portion - the denormalized crude oil (DNO)- was characterized for its pour point. The wax in different concentration was then added in the DNO and the change in the rheological properties like pour point, yield stress and plastic viscosity were studied using a Haake Rota Viscometer. The effect of carbon number distribution, i.e. the composition of the wax, on these rheological properties was also investigated. Four different commercial pour point depressanl additives have been used to study their effects on the pour point, yield stress and plastic viscosity of the reconstituted (wax mixed DNO) crude oils.

From this study it has been found that wax concentration and its composition are primarily responsible for the variation in the pour point of the DNO, and the DNO composition has a small effect. However, as seen in the Part I of this paper, the response of the pour point depressant additive in effecting the change in the pour point is primarily governed by the composition of the DNO. The additives have shown better response in the DNO having more aromatic concentrate, as has been found in the case of Duliajan (Assam) DNO.     

Failure mechanisms in SiC-fiber reinforced 6061 aluminum alloy composites under monotonic and cyclic loading

Micromechanisms influencing crack propagation in a unidirectional SiC-fiber (SCS-8) continuously reinforced Al-Mg-Si 6061 alloy metal-matrix composite (SiC_f/Al-6061) during monotonie and cyclic loading are examined at room temperature, both for the longitudinal (0 deg or L-T) and transverse (90 deg or T-L) orientations. It is found that the composite is insensitive to the presence of notches in the L-T orientation under pure tension loading due to the weak fiber/matrix interface; notched failure strengths are ∼1500 MPa compared to 124 MPa for unreinforced 6061. However, behavior is strongly dependent on loading configuration, specimen geometry, and orientation. Specifically, properties in SiC_f/Al in the T-L orientation are inferior to unreinforced 6061, although the composite does exhibit increasing crack-growth resistance with crack extension (resistance-curve behavior) under monotonie loading; peak toughnesses of ∼16 MPa√m are achieved due to crack bridging by the continuous metal phase between fibers and residual plastic deformation in the crack wake. In contrast, such bridging is minimal under cyclic loading, as the ductile phase fails subcritically by fatigue such that the transverse fatigue crack-growth resistance is superior in the unreinforced alloy, particularly at high stress-intensity levels. Conversely, fatigue cracks are bridged by unbroken SiC fibers in the L-T orientation and exhibit marked crack deflection and branching; the fatigue crack-growth resistance in this orientation is clearly superior in the composite.     

Optimization of Tool Geometry and Cutting Parameters for Hard Turning

In the hard-turning process, tool geometry and cutting conditions determine the time and cost of production which ultimately affect the quality of the final product. So reliable models and methods are required for the prediction of the output performance of the process. In the present work, experimental investigation has been conducted to see the effect of the tool geometry (effective rake angle and nose radius) and cutting conditions (cutting speed and feed) on the surface finish during the hard turning of the bearing steel. First- and second-order mathematical models were developed in terms of machining parameters by using the response surface methodology on the basis of the experimental results. The surface roughness prediction model has been optimized to obtain the surface roughness values by using genetic algorithms. The genetic algorithm program gives minimum values of surface roughness and their respective optimal conditions.     

Liquid-vapour equilibria of binary systems of acetonitrile with chlorobenzene and n-butyl acetate

Vapour-liquid equilibrium data of the systems acetonitrile-chlorobenzene and acetonitrile-n-butyl acetate are measured at 760 mmHg pressure. Both systems are non-ideal in behaviour and show positive deviations from Raoulc's law. The two systems form symmetrical solutions and are well represented by single constant Margules equations.     

Non-linear bending of antisymmetric cross-ply plates

The bending of antisymmetric cross-ply plates, based on Von-Karman plate theory, is investigated in this paper with one term approximations for the in-plane and transverse displacements. Rayleigh-Ritz solutions are presented for the non-linear response of cross-ply laminates with various modular and aspect ratios and subjected to sinusoidal transverse loading.     

Stability of stiffened plates using high precision finite elements

High precision finite elements for both thin plate and stiffener are developed in this paper to analyse the stability of thin plates subjected to arbitrary membrane loading with arbitrarily oriented stiffeners. Application of these elements to some complex stability problems show high accuracy even with a relatively coarse finite element mesh. For all the problems considered the predicted critical loads are accurate upper bounds.     

Vibrations of thick plates using a high precision triangular element

In this paper vibrations of thick plates using a high precision triangular element are studied. The effect of transverse shear is included in the derivation of the stiffness matrix and the effect of rotatory inertia is included in the derivation of the mass matrix of the element. Explicit expressions for stiffness and mass matrices of the element are presented. The numerical examples considered show that the natural frequencies obtained are accurate even with a coarse finite element subdivision.     

Vibrations of thin rectangular plates with arbitrarily oriented stiffeners

Free vibration of plates with arbitrarily oriented stiffeners are studied using high precision plate bending and stiffener elements. Good convergence of frequency values for coarse mesh is demonstrated. Natural frequencies of square plates with various arrangement of stiffeners are determined for both simply supported and clamped boundary conditions.     

Effect of pH,Aging, and Drying on the Size of CdS Nanocrystallites,Monolithicity, and Transparency of Nanocrystalline CdS-Doped Silica Xerogels

CdS semiconductor nanocrystals are prepared in SiO₂ matrix xerogels by a sol–gel method using ethanolic tetraethylorthosilicate [TEOS, Si(OC₂H₅)₄], catalyst (HCl or NH₄OH), cadmium acetate [Cd (CH₃COO)₂ 2 H₂O], and thiourea [SC (NH₂)₂] and drying the alcogels at room temperature and heating up to 250°C. The effect of alcosol pH on the CdS crystallite size in silica matrix, color, monolithicity, and transparency of the xerogels is studied by varying the pH from 1 to 10, and maintaining the CdS/SiO₂ molar ratio constant at 0.0025. It was found that the color of samples varied from light yellow to orange and transparency decreased from 85 to 15% with the variation of alcosol pH from 1 to 10, respectively. The cracked sample were found for pH < 3, opaque, powdery samples for the pH > 8, and transparent monolithic yellow-colored samples in the pH range 3–7. The quantum size effect was observed in the optical absorption spectra of the samples. The threshold peak decreased from 520 to 250 nm, energy increased from 2.4 to 4.9 eV, and the CdS crystallite size decreased from 6 to 1 nm with the variation of pH of the alcosol from 10 to 1, respectively. In the case of the effect of aging, a minimum of 5 days aging is required for monolithic samples and the CdS crystallite to increase in size with and remain constant, even when the aging period is increased for 10 days. Monolithic samples were obtained with drying and heating rates of <0.4 wt.% loss/h and 30–50°C/h range and cracked samples with >0.4 wt.% loss/h and >50°C/h drying and heating rates, respectively. The density of the CdS crystallites doped-silica xerogels decreased from 1.57 to 1.30 gm/cm³ with an increase in pH from 1 to 10, respectively. From XRD spectra, the CdS crystallite structure was found to be a hexagonal wurtzite structure. The intensity of the peaks increased and the breadth decreased with the variation of pH of the alcosol from 1 to 10 because of an increase in CdS crystallite size.