Microstructure and surface mechanical properties of pulse electrodeposited nickel

The surface of carbon steel was modified by electrochemical deposition of Ni in a standard Watt's bath using dc and pulse plating electrodeposition. The aim was to compare the microstructure and surface mechanical properties of the deposit obtained by both techniques. Materials characterization was conducted using field emission scanning electron microscope fitted with scanning transmission electron detector, atomic force microscope and X-ray diffractometer. Nanoindentation hardness, elastic modulus, adhesion, coefficients of friction and wear rates were determined for both dc and pulse electrodeposits. Experimental results indicate that pulse electrodeposition produced finer Ni grains compared to dc plating. Size of Ni grains increased with deposition. Both dc and pulse deposition resulted in grain growth in preferred (2 0 0) orientation. However, presence of Ni (1 1 1) grains increased in deposits produced by pulse deposition. Pulse plated Ni exhibited higher hardness, creep and coefficient of friction and lower modulus of elasticity compared to dc plated Ni.     

Fluid Flows Through Two-Dimensional Channels of Composite Materials

The present analysis relates to the study of the full two-dimensional Brinkman equation representing the fluid flow through porous medium. The steady, incompressible fluid flow, with a negligible gravitational force, is constrained to flow in an infinitely long channel in which the height assumes a series of piecewise constant values. The control volume method is used to solve the Brinkman equation which involves the parameter, =/Da, where Da is the Darcy number and is the ratio of the fluid viscosity _f to the effective viscosity . An analytical study in the fully developed section of the composite channel is presented when the channel is of constant height and composed of several layers of porous media, each of uniform porosity. In the fully developed flow regime the analytical and numerical solutions are graphically indistinguishable. A geometrical configuration involving several discontinuities of channel height, and where the entry and exit sections are layered, is considered and the effect of different permeabilities is demonstrated. Further, numerical investigations are performed to evaluate the behaviour of fluid flow through regions which mathematically model some geological structures of various sizes, positions and permeability, for example a fault or a fracture, where the outlet channel is offset at different levels. The effect on the overall pressure gradient is also considered.     

Assessing concrete density using infrared thermographic (IRT) images

This paper presents the results of a study conducted to evaluate the possibility of utilizing infrared thermography to assess the quality of concrete. Concrete specimens were prepared with varying water to cement (w/c) ratio, cement content and consolidation effort. The concrete specimens were heated and the IRT images were recorded as they cooled down. The IR thermographs indicated a good variation in the surface temperature with varying concrete composition and consolidation effort. Concrete with similar composition exhibited a greater variation in surface temperature as the consolidation effort was decreased; indicating the presence of less dense structure in the specimens prepared with low consolidation effort. An increase in the water–cement ratio also increases the temperature variation indicating a decrease in the concrete denseness. The variation in cement content also influenced the denseness of concrete as indicated by the enhanced variation in the surface temperature. Concrete specimens with cement content of 300 kg/m³ (less dense) exhibited a greater temperature variation compared to those prepared with cement content of 400 kg/m³ (more dense).     

Combined Free and Forced Convection in Vertical Channels of Porous Media

In this paper we investigate the combined free and forced convection of a fully developed Newtonian fluid within a vertical channel composed of porous media when viscous dissipation effects are taken into consideration. The flow is analysed in the region of a first critical Rayleigh number in order to interpret the multiple-valued solutions and discuss their validity. The governing fourth-order, ordinary differential equation, which contains the Darcy and the viscous dissipation terms, is solved analytically using perturbation techniques and numerically using D02HBF NAG Library. A detailed investigation of the governing O.D.E. is performed on both clear fluid and porous medium for various values of the viscous dissipation parameter, , when the wall temperature decreases linearly with height, and the pressure gradient is both above and below its hydrostatic value. Although mathematically the results in all cases show that there are two solution branches, producing four possible solutions, the study of the velocity and buoyancy profiles together with the Darcy effect indicate that only one of the two solutions at any value of the Rayleigh number appears to be physically acceptable. It is shown that the effect of the Darcy number decreases as the critical Rayleigh numbers increase.     

A New Model for Viscous Dissipation in Porous Media Across a Range of Permeability Values

In this paper a unified mathematical theory for the viscous dissipation term in the governing Brinkman equation is derived. This term has, unlike other models, the correct asymptotic behaviour in both the fully Darcy and Newtonian fluid flow limits.