International Journal of Engineering Research in Africa Vol. 5

Abstract: This paper describes an innovative use of plastic bottle waste as cement-substitution within composite materials for preventing chemical attacks or repairing various reinforced concrete structures. Various weight fractions of cement varying from 2.5% to 7.5% were substituted by the same weight of polyethylene terephthalate (PET). The specimens were tested in flexure and compressive strength and for chemical resistance to acid, basic solutions at 5% and for chloride ion permeability. From this study, it was found that the PET-modified mortars exposed to aggressive environments showed better resistance to chemical attack and higher resistance to chloride ion penetration than unmodified one without substantially affecting the mechanical strength in tap water. The addition of PET to the modified mortars, means reducing the penetration of aggressive agents. So, the mass loss of composites exposed to hydrochloric and acetic acid solutions is lower than those of unmodified mortar. The basic solutions are harmless for composite materials. The formations which appear such as different calcium salts were determined by X-ray diffraction and FT-IR.

Abstract: This paper focuses on the optimization of ball milling as a dry mixing method and comparison with the wet method for manufacturing phenolic/multi-wall carbon nanotube (MWCNT) composites. In the ball milling, the effect of milling-time on the properties of composites containing functionalized and pristine MWCNT in two MWCNT concentrations has been investigated. At first in the wet method, polymer was dissolved in acetone and then mixed with MWCNT by sonication method. Also, the effect of functionalization by use of acid nitric refluxing was considered. The material properties were characterized by the DSC, FTIR, Raman, electrical conductivity, SEM, TEM and bending strength analyses. The results of electrical conductivity and bending tests showed that the best time for ball milling is about 2 hrs. In addition, functionalization had a positive effect on bending strength and a negative effect on electrical conductivity. The results of DSC indicated that the composite manufactured by ball milling method resulted in more thermal stability than that manufactured by the wet method. It was also shown that the functionalization increases the thermal stability; however, the increasing MWCNT concentration leads to agglomeration, thereby decreasing the thermal stability.

Abstract: This paper considers the bicriteria scheduling problem of minimizing the total earliness and the total tardiness on a single machine with release dates. In view of the fact that the problem has been characterized as NP-Hard, we propose two approximation algorithms (labeled as ETA1 and ETA2) for solving the problem. The proposed algorithms were compared with the MA heuristic selected from the literature. The two criteria (the total earliness and the total tardiness) were aggregated together into a linear composite objective function (LCOF). The performances of the algorithms were evaluated based on both effectiveness and efficiency. The algorithms were tested on a set of 1200 randomly generated single machine scheduling problems. Experimental results show that both the ETA1 and ETA2 algorithms outperformed (in terms of effectiveness and efficiency) the MA heuristic under all the considered problem sizes. Also, the ETA1 algorithm outperformed the ETA2 algorithm when the number of jobs (n) ranges between 20 and 500.

Abstract: In this paper the effect of semi die angle on drawing load in cold tube drawing has been investigated numerically using the finite element method. The equation governing the stress distribution was derived and solved using Galerkin finite element method. An isoparametric formulation for the governing equation was utilized along with C0 cubic isoparametric element. Numerical experimentation showed that the results obtained using the present method is very close to the analytical solution and more accurate than finite difference solution. Having established the accuracy of the present solution method, parametric studies were carried out to show the effect of semi die angle on the drawing load for different tube drawing processes. The analysis was carried out using a Visual Basic.Net program developed by the authors. The results are presented in both graphical and tabular forms.

Abstract: The recent interest in boiling heat transfer in small diameter tubes has led to the study of boiling heat transfer outside a compact tube bundle of diameter 3mm. The bank comprised 3 columns each of 10 stainless steel electrically heated tubes of 3mm outside diameter, with pitch to diameter ratio of 1.5 in an in-line arrangement. These tests were carried out using distilled water and R113 at nominal atmospheric pressure over a range of heat fluxes between 4-21 kW/m2 for mass fluxes from G=5.6 - 32.8 kg/m2s. The recent three-zone evaporation model developed by Thome, Dupont and Jacobi for boiling inside micro channels was used to compare with experimental results as photographic study showed that bubbles confined within the bundle were responsible for the heat transfer enhancement observed. It was observed that the three state model was promising in its application to the bundle arrangement as the confinement number Co for bundle has been shown to be in the order of 0.63

Abstract: Crude oil samples from four oil wells in Nigeria were analyzed for the following seven trace elements: V, Cr, Mn, Fe, Co, Ni and Pb using Atomic Absorption Spectrometric (AAS) analytical technique. The mean concentrations of these elements on a weight to weight basis were found to range from 0.017 ± 0.005 to 1.977 ± 0.397ppm. The results also show that V was the most abundant metal with Ovia 1 Long String (OLS) Oil well containing the highest concentration of V. The V/Ni ratio from the method used shows that Ovia 1 Long String (OLS) and Ovia 1 Short String (OSS) were the most and the least matured oil wells respectively. All the samples had comparably the same V/Ni ratio (1.16—1.77) implying identical source for all the oils. Furthermore, the calculated values of American Petroleum Institute (°API) gravity determined using the measurement of specific gravity (S.G.) of the crude oil samples range from 47.80 to 55.50. This suggests that the samples fall into one category of crude oil classification which in this case is light crude.

Abstract: The use of non-essential materials in Ghana like granites, cocoa pod ash and shells as fluxes has been studied in the composition of a local brown glaze in the Na2O-K2O-CaO-Al2O3-SiO2 systems to support electrical porcelain glaze development which hitherto relied totally on imported glazes. Chemical analyses have been performed on the various materials and revealed the presence of the right quantities of aluminous-silicate minerals necessary for combinations in glaze development using the Segar classification. It was found that the range of 0.2 - 0.4 molecular weight of the granites, 0.1 - 0.3 for the cocoa pod ash and 0.4 - 0.8 for the shells forming the R2O/RO2 group and the ratio of 1:12 for the clay and the sand was sufficient to cause excellent melt at 1200OC when 5% - 8% of local manganese and 5% local iron oxide were added to the recipe. The molecular weights of the various oxides in the R2O group were calculated from the chemical analyses of the various materials to reflect the right quantities of the oxides. The results also indicate that holding the RO/R2O group within the above limits and varying the clay to sand ratio from1:8 - 1:12, other glaze melting surfaces from matt to gloss are achievable. Physical examination of the melted glaze on the electrical porcelain bodies showed consistent rich brown colour, well vitrified with no crazing, peeling or pin holes, at pottery temperatures of 1140 - 12000C.