International Journal of Engineering Research in Africa Vol. 1

Abstract: This paper presents comparisons between drainage capillary pressure curves computed directly from 3D micro-tomographic images (micro-CT) and laboratory measurements conducted on the same core samples. It is now possible to calculate a wide range of petrophysical and transport properties directly from micro-CT images or from equivalent network models extracted from these images. Capillary pressure is sensitive to rock microstructure and the comparisons presented are the first direct validation of image based computations. The measured data include centrifuge and mercury injection drainage capillary pressure for fired Berea, Bentheimer and Obernkirchner sandstones and unfired Mount Gambier carbonate. The measurements cover a wide range of porosities and permeabilities. The measurements were made on core samples with different diameters (2.5 cm, 1.5 cm, 1 cm and 0.5 cm) to assess the effect of up-scaling on capillary pressure measurements. The smallest diameter samples were also used to obtain the 3D micro-CT images. Good agreement was obtained between the experimental measurements and direct computations on 3D micro-CT images.

Abstract: In this paper, simulation study was conducted to investigate the effect of spatial heterogeneity of multiple porosity fields on oil recovery, residual oil and microemulsion saturation. The generated porosity fields were fed into UTCHEM for simulating surfactant flooding in heterogeneous two-layered porous media. From the analysis, surfactant flooding was more sensitive than water flooding to the spatial distribution of multiple porosity fields. Residual oil saturation in upper and lower layers after water flooding was about the same with the reservoir heterogeneity. On the other hand, both residual oil and microemulsion saturation in the two layers after surfactant flooding became more equal as porosity distribution standard increased. Spatial heterogeneity of multiple porosity fields had only a small effect on residual oil saturation and recovery factor. The variation of recovery factor due to the reservoir heterogeneity was under 4.2%.

Abstract: All organizations, regardless of their size or complexity are faced with the challenge of implementing an Occupational Health and Safety (OH&S) management system that will prevent injuries and ill health to persons that are working under the control of the organization. The purpose of this paper is to show how organizations can improve their health and safety performance through the effective implementation of existing statutory requirements and regulations. Using a case study from a Printing Industry organization, the key requirements needed to implement a H&S programme and focus on the concept of hazard identification, risk assessment and risk control were investigated. The organization is a large company, which has implemented a system to the requirements of the Occupational Health and Safety Act: 2005. Findings reveal that there is a lack of control procedures to ensure compliance to legal requirements. The Health and Safety Policy needs to be reviewed. Significant hazards need to be prioritized. The company does not regularly conduct risk assessments. Employees need more training on H&S issues. Use of hazardous substances must be properly controlled. Appropriate H&S objectives and targets have to be set and regularly monitored. Internal auditing, which has up to now been limited to their ISO 9000:2008 certification, should be extended to the OH&S Management systems. To enable a better control of the situation, it is recommended that OHSAS 18001:2007 should be implemented, including the concept of continual improvement, to assist in more effective control of the Occupational Health and Safety regulations.

Abstract: Concerned that management of job-oriented accidents has remained a daunting challenge for all stakeholders in Nigeria oil-industry, a longitudinal study was made to appraise the patterning of episodic incidence of industrial accidents in a typical oil and gas company operating in the Nigeria flank of the oil-rich Niger Delta Basin. A 10-year historical accident data were characterized and found to have absorbing chain properties. Four open-and-shot transition states namely : fatality, accident, near-miss and unsafe act, that are subject to ergodicity, were identified and used to craft a value digraph which define the stable transition probability matrix. The results, which suggest that on the average, 59% of staff are wasted through fatality or severe accidents, also points to escalating rates of fatalities and disabilities stemming from accidents thus calling for the need to review the existing hazard operations studies (HAZOPS) and hazard identification schemes (HAZIDS) so as to assist in whittling down, as low as reasonably practicable, the perceived unpleasant trend. The author is of the opinion that industrial accident victims, unlike in road traffic accident (RTA), habituate several times before entering the absorbing state.

Abstract: The thermochemical properties of varieties of species involved in the formation and consumption or destruction of tropospheric ozone during chemical reactions have been established. Ozone in the troposphere is produced during the day-time; hence it is a photochemically induced transformation process. This compound acts as precursor specie in many atmospheric transformations and constitutes a baseline component worth investigating. This study utilized electronic structure methods of computational model chemistries to evaluate for Gibbs free energies and enthalpies of formation and reactions of the various species. Ten prominent gas-phase and aqueous-phase reactions were analysed using five computational approaches consisting of four ab initio methods and one density functional theory (DFT) method. The computed energy values in comparison to those obtained through experimental approaches yielded an error of mean absolute deviation of 0.81%. The most relevant species that tend to enhance the production of ozone in the troposphere were O* and H2O2 for the gas-phase and aqueous-phase reactions respectively. Chemical equilibrium analysis indicated that the ozone formation and consumption reactions are more favourable in colder regions and at winter.

Abstract: Novel biobased additives prepared from rubber seed oil were evaluated as thermal stabilizer for PVC. Divalent metal (barium and cadmium) soaps of rubber seed oil were prepared by metathesis in aqueous alcohol and characterized by thermal methods (differential scanning calorimetry and thermogravimetry). The stabilizing effect of the soaps and their admixtures on the thermal degradation of PVC powder and plasticized PVC was examined by dynamic thermogravimetry and dehydrochlorination studies at 160oC using the Thermomat equipment. The metal soaps showed multiple decomposition endotherms but were generally stable (with weight loss less than 5%) within the temperature range (180 – 220oC) frequently used in the processing of PVC. Using the Broido model, values of apparent activation energy of decomposition of between 50 and 200 kJmol-1 were obtained for the soaps. The biobased additives were found to be relatively effective in stabilizing PVC in powder and plasticized forms against thermal degradation. Using inhibition/retardation time, temperature of incipient decomposition, and temperature at which various extents of decomposition was attained as indices of thermal stabilization, the results from this study indicate a potential for the application of the biobased additives as thermal stabilizer for PVC in rigid and flexible formulations.

Abstract: A mathematical model for the hydrodynamic lubrication of finite slider bearings with velocity slip and couple stress lubricants is presented. A numerical solution for the mathematical model using finite element scheme is obtained using four node linearly interpolated quadrilateral elements. Stiffness integrals obtained from the weak form of the governing equations were solved using Gauss Quadrature to obtain a finite number of stiffness matrices. The global system of equations was obtained for the bearing and solved using Gauss Seidel iterative scheme. The converged pressure solution was used to obtain the load capacity of the bearing. Numerical experiments reveal the existence of an optimum velocity slip for which maximum benefit is obtained for the slider bearing in terms of bearing load. Increase in the slip parameter beyond this optimum value was shown not to augment the bearing load. Computations put forth also affirm that the bearing load is augmented with increase in couple stress parameter. An optimal film thickness ratio was also obtained for which load capacity is maximized with or without the application of slip to the bearing surfaces.

Abstract: This paper presents an overview of the concept of second law applications to all processes of thermofluid systems. The presentation is motivated by the need for engineers to be familiar with the new concept of exergy and entropy generation minimization, EGM which are used to design industrial production plants or individual components to maximize their energetic efficiency, and to minimize their environmental impact. It is essential for understanding to what extent resource and energy scarcities, nature’s capacity to assimilate loss as well as the irreversibility of transformation processes, constrain economic action. With these techniques and computational fluid dynamics, CFD, which is used for the conversion of the differential equations of flow to algebraic equations, designers can use the second law to focus on particular regions where design modifications can be made to improve and optimize thermofluid systems performance. Two case studies of exergy/EGM computations are presented for the design of open cycle simple gas turbine and vapour compression refrigeration.