International Journal of Engineering Research in Africa Vol. 4

Abstract: In this work, the effect of peel and reject losses on the value added to the dried pineapple fruits was analyzed. The major factors include final moisture content, Xwf; peel loss rate, Rp; reject loss rate, Rrj; and the reject-to-peel ratio, Rrj/Rp. The value added was expressed as the percent increase in value (PVA) which is an indication of price of dried fruits. Material losses were expressed as percent raw material lost (PRML), and total raw material lost per kg of raw material. The PVA decreases with increasing Xwf for all levels of initial moisture content. The PVA increases faster for Rp > 0.1 kg/kg from 67% to 90%. The PVA decreased with increasing Rrj/Rp. The PRML, on the other hand, increased faster with Rp for Rp > 0.1 kg/kg. However, PRML decreased faster as Rrj/Rp was increased. The total losses decreased with increasing Rrj/Rp and also with increasing Rrj.

Abstract: This paper presents the results of drainage capillary pressure and relative permeability measurements made on cores having different bulk volumes ranging from 0.5 to 12 cm3. The aim of the experiments was to provide reliable experimental data which can be used to validate the predictive value of micro-CT based network models for capillary pressure and relative permeability. The micro-CT based network models use realistic networks constructed from the X-ray images of the rock samples having a typical bulk volume of 0.3 cm3. Experimental data for drainage capillary pressure were obtained using the centrifuge technique. The results of the largest cores were verified by the data obtained on the same sample using the porous plate technique. Relative permeability data were obtained by history matching the unsteady state displacement data. Homogeneous model sandstones (Berea and Bentheim) and carbonate (Mt. Gambier) were used in the experiments. Air-brine and oil-brine fluid-systems were used for drainage capillary pressure and relative permeability measurements, respectively. The relative permeability data were compared with those predicted from empirical and geometry based models using capillary pressure data. Good agreement was obtained for the drainage capillary pressure measured on all samples used. The residual saturations obtained from the cores used in the displacement experiments were also in good agreement. The models were found to predict relative permeability of oil and water with varying degrees of success. For water relative permeability, the Pirson model predicts the experimental data successfully while the Corey, Corey-Brooks/Burdine and van Genuchten/Burdine models predict the data of oil relative permeability better than the others. The results demonstrate for the first time that reliable drainage capillary pressure and relative permeability measurements can be made on small model sandstone and carbonate cores of representative scales used in micro-CT-imaging.

Abstract: Natural gas hydrates are ice-like materials which exist in permafrost regions and in the continental margins of oceans. They constitute a huge unconventional reservoir of natural gas around the globe including offshore Nigeria. The paper is a review of this important global resource with particular focus on the Nigerian deposits. The reasons for the interest on hydrates are discussed including the potential for the recovery of large quantities of methane, the climate change and ocean floor instability that may result from their dissociation. They may also be exploited for large-scale CO2 sequestration. The geographical distribution of hydrates deposits on earth, the thermodynamics of why they occur in those particular places and source of the methane gas that is eventually enchlathrated into hydrates are discussed. The natural gas in the Nigerian hydrate is essentially biogenic in origin and is almost pure methane (more than 99% methane). The hydrates exist in finely disseminated or massive aggregate forms within clay-rich sediment.

Abstract: Quantitative microscopy techniques for manually measuring parameters on light, scanning, and transmission electron microscope images are presented in this review. The numerical techniques contained in this paper are also employed in the algorithms of automated image analysers. Only the most important parameters are covered in detail and these are grain and particle sizes in addition to the volume fractions and mean free path of the microconstituents. Apart from metallic materials, some of the techniques which are described in this review can also be used for polymeric, ceramic and biological materials.

Abstract: AlSiMg (A357) composites containing 10 vol. % zirconia (ZrO2) particulates have been synthesized by the stir process followed by squeeze casting. Pressures of 25 and 50 MPa were maintained during solidification in specially designed die and ram and maintained at 250°C. Results show that with increasing squeeze pressure, the density increases while porosity decreases. The hardness of squeeze cast composite is higher than that of stir casting by about 10%. The compression properties have been evaluated and compared. The results show that compressive strength increases with squeeze pressure.

Abstract: Project portfolio selection involves decision making and it plays a crucial role in any organization. Therefore selecting not just the right projects but also the right mix of projects for the portfolio is considered as one of the most important tasks for organisations to ensure the achievement of the corporate strategy within limited resources and capabilities of the organization. Prioritizing and selecting optimal project portfolio can be very challenging especially with a large number of projects with multiple constraints and interdependences. In an ideal world with unlimited budget the project selection process would be very straightforward. However, this is not the case in life situations. In this work, an attempt is made to address this challenge. An integer linear programming model for project selection was developed and applied in a selected organization in Nigeria. The model seeks to optimize the mix of the projects to be undertaken while keeping the total cost and project interdependency as constraints. The analysis of the results showed that a total of 11 projects out of 16 were eligible for selection in the period under review. The total cost of the selected project was 92,840,000 Naira, which was about 90% of the total budget. Ordinarily, apart from not prioritizing and obtaining an optimal project mix, the community would have spread its entire resources on the 16 projects with some of them being abandoned later. The model can also be used to plan an optimal mix of project portfolio for a future date within the limitations of a given set of constraints and interdependence.

Abstract: This paper presents a Neuro-Fuzzy based modeling of electrostatic fields for harmattan season in Zaria, Nigeria based on online based data capturing mechanism, which involved the use of a data acquisition system interfaced with a digital electrostatic field strength meter (model 257D) and a computer system. The acquired electric field data were captured by the computer using the Microsoft Office Excel Program for twenty-four months (February 2007 – February 2009). The focus of the analysis is determining the effect of environmental factors such as temperature, pressure and relative humidity on the static electric field during the harmattan season. The plots of the electrostatic field against the variation of the environmental factors were used as the qualitative analytical tools and yielded a non-linear relationship. The data was analyzed using Neuro-Fuzzy technique, which is a hybrid intelligent system combining the benefits of computational techniques of Fuzzy Logic and Artificial Neural Networks. The result of the analyses yielded good neural statistical values of Root Mean Square (RMS) of 0.32, Average Absolute Error of 0.18, and Pearson R value of 0.96 for the harmattan scenario, which are reflections of a good model. The result was further buttressed by the 3D plot of the Neuro-Fuzzy based modeling of the experimental parameters. With the insignificant values of the RMS and Average Absolute value, the empirical model gave a fairly good prediction which could be relied upon to predict the electrostatic fields during harmattan in Zaria, Nigeria.