We consider a simple model of maghemite nanoparticles and study their magnetic properties using Monte Carlo methods. The particles have a spherical geometry with diameters ranging from 3 nm to 8 nm. The interior of the particles consists of core spins with exchange interactions and anisotropy given by the values in the bulk material. The outer layer of the particles consists of surface spins with weaker exchange interactions but an enhanced anisotropy. The thermal behaviour of the total, core and surface magnetizations are calculated as well as the hysteresis loops due to the application of an applied field. The effect of the surface anisotropy on the blocking temperature, the coercive and exchange bias fields is studied.
The impacts of MHD and heat generation/absorption on lid‐driven convective fluid flow occasioned by a lid‐driven square enclosure housing an elliptic cylinder have been investigated numerically. The elliptic cylinder and the horizontal enclosure boundaries were insulated and the left vertical lid‐driven wall was experienced at a fixed hot temperature, and the right wall was exposed to a fixed cold temperature. COMSOL Multiphysics 5.6 software was used to resolve the nondimensional equations governing flow physics. A set of parameters, such as Hartmann number (0 ≤ italicHa ≤ 50 $0\le {Ha}\le 50$), Reynolds number (1 0 2 ≤ italicRe ≤ 1 0 3 $1{0}^{2}\le {Re}\le 1{0}^{3}$), Grashof number (1 0 2 ≤ italicGr ≤ 1 0 5 $1{0}^{2}\le {Gr}\le 1{0}^{5}$), heat generation‐absorption parameter (− 3 ≤ J ≤ 3 $-3\le J\le 3$), and elliptical cylinder aspect ratio (AR) (1.0 ≤ italicAR ≤ 3.0 $1.0\le {AR}\le 3.0$) have been investigated. The current study discovered that for low Reynolds number, the adiabatic cylinder AR of 2.0 provided the optimum heat transfer enhancement for the model investigated, also the impact of cylinder size diminishes beyond Gr = 104. But for high Reynolds (Re = 1000), the size of the cylinder with AR = 3.0 offered the highest heat transfer augmentation. The clockwise flow circulation reduces because of an increase in AR, which hinders the flow circulation. In addition, heat absorption supports heat transfer augmentation while heat generation can suppress heat transfer improvement.
Water contamination is an issue requiring continuous remedy on daily basis because of the high demand for clean quality water. Scientists have proffered numerous ways of making this possible but the techniques involved is often difficult to replicate at small scale. For this reason, easier and cheaper techniques for contaminated water treatment are often sought after. One way of actualizing this is via nanotechnology, which involves the use of smaller particles (< 100 nm in size) to coagulate suspended substances and inhibit microbial growth in the targeted water. The mechanisms involved have been presented for zinc and magnetite nanoparticles in this write-up. This technology provides way of getting clean quality water for domestic, agricultural and industrial applications.
Environmental issues resulting from production and application of wood charcoal can be addressed by using biomass briquettes as alternative. This research was undertaken to develop and evaluate briquette from jatropha, groundnut and melon seed residues. Samples of the briquette were formed from mixtures of 0.32-0.39 kg carbonised residues, 0.30-0.40 kg starch and 0.02- 0.04 kg water. Physical and mechanical properties of the briquette samples including calorific value, bulk density and breaking force were determined using standard methods. Box-Bekhen Design Methodology was used to determine the optimum briquette blend. The results showed that the optimal briquette blend gave values of 4711.87 kcal.kg–1 calorific value, 282.59 kg m–3 bulk density and 1.36 kN breaking force, with a desirability index of 61.5%. A comparative analysis of the properties of the optimal briquette with that of a wood charcoal indicates no significant difference (P<0.05). This implies that the briquette can serve as an alternative energy source for cooking in rural communities.
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