An application of paired quasilinearization on double‐diffusive convection flow over a cone embedded in a porous medium in the presence of nanoparticles

Mixed convection flow of a nanofluid near a vertical cone embedded in a a porous medium with Soret and Dufour effects is exercised. The bearing of a porous medium is recounted by the Darcy model. The partial differential equations, modeling the concerned problem, is nondimensionalised by implementing compatible transformations, which results in a similar form. A new paired spectral quasilinearization method is adopted to get the accurate numerical solution. Convergence and accuracy of the solution is elaborated by analyzing the norm of residual and solution errors. Alteration of velocity, temperature, nanoparticle and solute concentration profiles due to flow controlling parameters, namely, Brownian motion, thermophoresis, Soret, Dufour, Lewis number, and buoyancy ratio is outlined by reproducing the obtained numerical solution in graphs and tables. Analysis reveals that the flow profiles are greatly influenced by the physical parameters under investigation.     

Residents’ relationship with green infrastructure in Cosmo City,Johannesburg

Scholars have expressed concerns about environmental sustainability in low-income housing development in South Africa in terms of the poor households’ relationship with, access to and benefit from natural ecosystems and green spaces. Using a qualitative research approach – discourse-based methods (semi-structured interviews, focus group discussion and transect walks), this paper shows how low-income households in Cosmo City, Johannesburg (South Africa) benefit from green infrastructure at the domestic, neighbourhood and riparian scales. The central lesson from this case is that landscape/urban design, planning and management must recognise and respond to socio-economic and socio-ecological realities and dynamics inherent in the ways low-income households relate with green infrastructure.     

When green is grievous: downsides in human-nature interactions in informal urban settlements

Considering how poor households relate with natural ecosystems is crucial to achieving environmentally sustainable low-income communities in South Africa and beyond. This paper presents negative experiences associated with residents’ interactions with, perceptions of, and appropriations of natural ecosystems and green spaces in informal settlements in Johannesburg. In-depth interviews with residents in two communities, key informants, and transect walks were used to identify problems associated with domestic gardens and vegetation in riparian and non-riparian open spaces. Inadequate services and infrastructure exacerbates these problems. This work contributes to knowledge regarding undesirable aspects of green infrastructure in the context of urban poverty. Understanding the downsides in human-nature interactions can usefully inform ecologically sound intervention in low-income informal urban areas.     

Numerical Analysis of the Effects of Selected Geometrical Parameters and Fluid Properties on MHD Natural Convection Flow in an Inclined Elliptic Porous Enclosure with Localized Heating

Magnetohydrodynamic (MHD) natural convection flow and associated heat convection in an oriented elliptic enclosure has been investigated with numerical simulations. A magnetic field was applied to the cylindrical wall of the configuration, the top and bottom walls of the enclosure were circumferentially cooled and heated, respectively, while the extreme ends along the cross‐section of the elliptic duct were considered adiabatic. The full governing equations in terms of continuity, momentum, and energy transport were transformed into nondimensional form and solved numerically using finite difference method adopting Gauss–Seidel iteration technique. The selected geometrical parameters and flow properties considered for the study were eccentricity (0, 0.2, 0.4, 0.6, and 0.8), angle of inclination (0°, 30°, 60°, and 90°), Hartmann number (0, 25, and 50), Grashof number (10⁴, 10⁵, and 10⁶), and Darcy number (10^?3, 10^?4, and 10^?5). The Prandtl number was held constant at 0.7. Numerical results were presented by velocity distributions as well as heat transfer characteristics in terms of local and average Nusselt numbers (i.e., rate of heat transfer). The optimum heat transfer rate was attained at e value of 0.8. Also, the heat transfer rate increased significantly between the angles of inclination 58° and 90°. In addition, Hartmann number increased with decreased heat transfer rate and flow circulation. A strong flow circulation (in terms of velocity distribution) was observed with increased Grashof and Darcy numbers. The combination of the geometric and fluid properties therefore can be used to regulate the circulation and heat transfer characteristics of the flow in the enclosure.     

MHD natural convection inside an inclined trapezoidal porous enclosure with internal heat generation or absorption subjected to isoflux heating

A steady laminar two‐dimensional magneto‐hydrodynamic natural convection flow in an inclined trapezoidal enclosure filled with a fluid‐saturated porous medium is investigated numerically using a finite difference method. The left and right vertical sidewalls of the trapezoidal enclosure are maintained at a cold temperature. The horizontal top wall is considered adiabatic while the bottom wall is subjected to isoflux heating. A volumetric internal heat generation or absorption is embedded inside the trapezoidal enclosure while an external magnetic field is applied on the left sidewall of the enclosure. In the current work, the following parametric ranges of the non‐dimensional groups are used: Hartmann number is varied as , Darcy number is taken as , 10^?4, and 8 × 10^?5, Rayleigh number is varied as , Prandtl number is considered constant at Pr = 0.7, the dimensionless internal heat generation or absorption parameter is varied as Δ = ?0.2, 0, 1, and 2.0, while the trapezoidal enclosure inclination angle is varied as . The results indicated a strong flow circulation occurs when the Darcy and the Rayleigh numbers are high. In addition, it is found that the Hartmann number, internal heat generation or absorption parameter and inclination angle have an important role on the flow and thermal characteristics. It is also found that when the enclosure inclination angle and Hartmann number increase the average Nusselt number along the hot bottom wall decreases. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21013     

Chemical composition and toxic trace element composition of some Nigerian edible wild mushrooms

Two essential amino acids (methionine and tryptophan); anti‐nutritional factors (tannin and trypsin inhibitor) and toxic elements (Pb, Cd, Ni, As, Hg and Cr) were determined spectrophotometrically from five edible wild mushrooms. The tryptophan content was between 1.00 and 1.82 g (100 g)^?1 but methionine was low at 0.26–1.38 g (100 g)^?1. Tannin content was high (30.3–40.0 mg g^?1) but trypsin inhibitor was low (22.0–39.5 TIU g^?1). Trace elements analysis reviled Pb (0.34–5.06 mg kg^?1) to be the highest of all the trace elements. Cd was (0.06–1.70 mg kg^?1), Ni (0.26–2.08 mg kg^?1), As (0.17–0.92 mg kg^?1), Hg (0.01–0.05 mg kg^?1) and Cr (0.04–0.22 mg kg^?1). These mushrooms are nutritious but must be well processed to eliminate or at least reduce the levels of tannin and Pb to improve their nutritional values.     

CFD modelling of liquid fluidized beds in slugging mode

Computational Fluid Dynamics (CFD) modelling has been used to simulate a liquid fluidized bed of lead shot in slugging mode. Simulations have been performed using a commercial code, CFX4.4. The kinetic model for granular flow, which is already available in CFX, has been used during this study. 2D time-dependent simulations have been carried out at different water velocities. Simulated aspects of fluidization such as voidage profiles, slug formation, pressure drop and pressure fluctuations have been analysed. The fluid-bed pressure drop was found to be greater than the theoretical one at all velocities, in agreement with experimental observations reported for fully slugging fluidized beds. Power spectral density analysis of the pressure signal was used to investigate the development of the flow pattern and the structure of the fluid-bed with increasing fluidizing velocity. A comparison between experimental and simulated results is also reported.     

Stability analysis and CFD validation of a new fluid-particle interaction force for mono-component gas-solid fluidized beds

A new closure relationship for the fluid-particle interaction force has been developed for the CFD modelling of gas fluidized beds. As a first step in verifying the applicability of the new closure, the mono-dimensional version of the equations of change for the fluid and solid phases has been examined analytically. Here, linear stability analysis theory has been applied to the continuity and momentum equations in the face of small fluctuations in the voidage or particle velocity. The effort leads to the development of a new stability criterion for homogenous gas fluidized beds with better predictive capability than the Foscolo and Gibilaro [P. Foscolo, L. Gibilaro, A fully predictive criterion for the transition between particulate and aggregate fluidisation, Chem. Eng. Sci. 39 (1984) 1667-1675.] criterion. This was attributed to the better predictive ability of the dynamic wave velocity developed in this work and which is expressed as a function of the local concentration of the particles. CFD validation of the drag force closure equation is also carried out. Here predictions of bed height and bed voidage obtained from the CFD simulation of a Geldart [D. Geldart, Types of gas fluidization, Powder Technol. 7 (1973) 285.] Group A material FCC catalyst (70 μm) were used to validate the model. Results from simulations showed a very good agreement with predictions from the Richardson-Zaki [J. Richardson, W. Zaki, Sedimentation and fluidization, Trans. Inst. Chem. Eng. 32 (1954) 35.] equation. In the final part of the paper, CFD simulations of three Group B industrial powders are presented comparing the model predictions obtained for the case where the solid stress tensor is at first neglected and subsequently included in the model via the standard granular kinetic theory, results revealed that the collisional stresses do not dominate the macroscopic fluid bed predictions for bubbling dense gas-solid systems.     

Acid-acid function of Eichhornia crassipes roots as inhibitor for mild steel in 0.5 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript> solution

The inhibitory potential of an acid extract of Eichhornia crassipes constituents on corrosion of mild steel in 0.5 M H₂SO₄ solution was the basis of this study. Acid extract of the root was employed to create the same type of environment for acidic cleaning and pickling. The roots of Eichhornia crassipes (water hyacinth) were sun-dried and pulverized into powdered form. Acid extraction was carried out by weighing 10 g of the pulverized roots into a beaker containing 1000 mL of 0.5 M H₂SO₄, placed in water bath at 90°C for 6 h and filtered the second day. The mild steel with a known weight was immersed inside the respective concentration of the blank and inhibitors (2–10% vol/vol) solutions at room temperature, after which it was retrieved and weighed at 1-day interval progressively for 12 days. A collection of compositional data was from AAS, FTIR. Polarization resistant, current density (I _corr), and corrosion potentials (E _corr) obtained from Methro Ohms Potentiostat. Phytochemical screening of the corrosion product was carried out using Spectrophotometer. Polarization calculation shows that the root acid extracts on mild steel have corrosion resistance potentials even after preserving it for 60 days.