Authors:C Akowanou, G Degan, V Prodjinonto Abstract: Forced convective flow through anisotropic porous saturated circular tube was analysed to determine the entrance length to the hydrodynamic flow. The porous medium saturated with an incompressible viscous fluid was characterized by anisotropy permeability ratio, inclination angle of the principal axes and Prandtl number. The flow field was a succession of two distinct flow regions, the entrance region followed by fully developed flow regime. The boundary-layer regime prevailing at the thermal entrance region was analysed by integral relations approach, and analytical expressions of the entrance length, wall friction and heat transfer rate were obtained. Limiting cases for flow applicable to low and high porosity media were also observed. The anisotropic properties of the porous medium were significant where permeability ratio was either greater or less than 1.Keywords: Forced convection, Porous medium, Hydrodynamic flow field, Anisotropy Permeability ratio, Wall friction PubDate: 2017-01-23 Issue No:Vol. 21, No. 1-2 (2017)
Authors:R Bhattacharyya Abstract: Hydriding reactions of spherical and flat plate geometries of zirconium cobalt (ZrCo) and lanthanum penta-nickel (LaNi5) intermetallic alloys were studied using kinetic data, and modified shrinking core model to account for concentration and temperature gradients in the gas film and ash layer under pseudo steady state non-isothermal conditions of 300, 310 and 320 K. The volumetric expansion of the alloy particle due to changing density was assumed during the hydriding reactions. The total hydriding time of 109 s was determined by numerical computati-on for different bulk temperatures, hydrogen concentrations and particle sizes; and the rate controlling process was identified to be diffusional. The values of the reaction times were very high, but could serve as data for predicting the length of hydriding cycle during hydrogen storage and recovery.Keywords: Hydriding reactions, Intermetallic alloys, Hydrogen storage, Shrinking core, Non-linear kinetics PubDate: 2017-01-23 Issue No:Vol. 21, No. 1-2 (2017)
Authors:R.G. Agbokpanzo, T.K. Houngan, F.X. Fifatin, M Saleh, C Espanet Abstract: Thermal factors contributing to the ageing of Insulated Gate Bipolar Transistor (IGBT) inverters were investigat-ed, with special reference to temperature variation as the main source of degradation of the electrical insulations and material layers. The inverter configuration was analysed in order to predict the lifetime based on thermal age-ing. Therefore, a lifetime prediction model based on NSGA-II algorithm was implemented to identify optimal design condition as a compromise between the average temperature and total mass of the inverter. The option of either choosing design configuration according to using the device during the entire lifetime or half of the lifetime of the solar panel was the major decision. The research findings would contribute to better adaptation of IGBT inverter-solar panel for grid electricity connectivity in relation to the replacement of the invertor once over the lifetime of the panel.Keywords: IGBT inverter, solar PV-Grid electricity, NSGA-II algorithm, Thermal ageing, Lifetime prediction PubDate: 2017-01-23 Issue No:Vol. 21, No. 1-2 (2017)
Authors:E.O. Falayi, J.O. Adepitan, K Giwa, J.D. Ayanda, F.O. Ogunsanwo Abstract: The annual mean solar indices of MgII core to core wing ratio, solar flux 10.7 cm and sunspot number over an eleven (11) year period, 2000 – 2010, were correlated with the annual mean rainfall, maximum temperature, relati-ve humidity, cloud cover and wind speed of 8 meteorological stations in Nigeria. Correlation analyses were perfo-rmed to determine relationships between the solar indices and the meteorological parameters at the same temporal scale. In general, weak correlation and significant levels were exhibited between solar indices and meteorological parameters, except Sokoto, Ilorin and Yola, where there were strong negative and positive correlations with high level of significance between solar indices and meteorological parameters. The observations indicated that increa-sed solar activities might have contributed to decrease in rainfall, cloud cover, and relative humidity; but elevated maximum temperature; implying that variability of solar indices affected galactic cosmic radiation reaching the earth’s atmosphere.Keywords: MgII core to core wing ratio, Solar flux, Sunspot number, Solar activities, Meteorological parameters, Correlation coefficient PubDate: 2017-01-23 Issue No:Vol. 21, No. 1-2 (2017)
Authors:S Bawa, R Lumor Abstract: A new apron pavement for parking aircrafts was constructed in 2014, but major depressions occurred when used by aircrafts soon after the construction. Failure analysis revealed structural design inconsistent with the United States Federal Aviation Administration Design Code AC 150-5320-6E. The methodologies for the technical investigations of the failures encompassed field investigation (including visual condition survey), sampling core materials for verification tests, non-destructive and destructive tests to evaluate the integrity and characteristics of the pavement layers. The sample of cores tested in an accredited laboratory were inconsistent with the site tests. Air voids and Marshall Stability for wearing course were low. Binder specification should have been PG82, instead of PG76, which was not appropriate for aprons subjected to large static loads. The low air voids in the wearing course were linked with the compaction regime adopted. Fuel resistant polymer modified bitumen was adopted for the construction, without correct application techniques, thereby affecting the pavement performance. The key factors underlying the pavement failures were binder specifications, tenderness of the mix, compaction regime and structural design, which contributed to the immediate distress and possible long term performance of the pavement.Keywords: Apron Pavement, Wearing course, Cores, Air voids, Marshall stability, Compacting regime, Polymer modified bitumen PubDate: 2017-01-23 Issue No:Vol. 21, No. 1-2 (2017)
Authors:L.A. Fagbemi, D.G.F. Adamon, E.A. Sanya Abstract: To optimize the efficiency of the wood gasification, tar which limits the use of syngas in thermal engines must be reduced. The quantity, quality and composition of syngas produced after thermal cracking of tar were analysed, and mathematical equations formulated based on Newton’s bivariate polynomial interpolation were used to estimate the molar fraction of the gases. The conceptual analysis of the problem was based on experimental data of temperature and residence time, and the semi-empirical model was simulated using Matlab to predict the composition of the syngas and the tar content in the gas mixture. The thermal cracking of tar increased the amount of syngas produced; in particular, the molar fraction of carbon monoxide and hydrogen. The gasification energy efficiency also improved with temperature and residence time, as the quantity of tar was reduced during cracking. The model was validated by comparing the experimental and numerical data.Keywords: Syngas, Gasification, Pyrolysis, Residence time, Thermal cracking of tar, Semi-empirical model PubDate: 2017-01-23 Issue No:Vol. 21, No. 1-2 (2017)
Authors:S Bawa, A.O. Agyemang Abstract: Small-scale mining involves exploitation of mineral deposits using rudimentary implements and at low levels of production with minimal capital investment. South-Western Ghana has the largest concentration of mining operat-ions of both large companies and small scale miners. Illegal mining activities have impacted negatively on road constructions in the Region. A typical case is the construction of the Tarkwa-Bogoso-Ayanfuri highway, which provides very important link between Western and Central Region of Ghana. Prior to the rehabilitation, illegal small-scale miners operated in close proximity to the old road, often impacting on the structural integrity in many sections, but with the construction of the new road, the activities of the small-scale miners assumed prominence. The impact assessment presented in this paper reveals the negative effects of illegal mining on the road constructi-on project; particularly, project delivery schedule, time delays for completion, additional cost to the project and security on the project, which were critical issues of concerns. Future formulation of road projects for South-Western Ghana must take cognizance of the issues, which must be factored in the project management.Keywords: Impact assessment, Small-Scale Mining, Project Delivery, Project Cost, Project management, Alternative livelihood PubDate: 2017-01-23 Issue No:Vol. 21, No. 1-2 (2017)
Authors:K.O. Akyea-Larbi, C Schandorf, F Hasford, S Inkoom, T.A. Sackey, G.F. Acquah Abstract: Advances in diagnostic medical imaging in the past few decades using procedures such as computed tomography (CT), have significantly enhanced health care delivery. The effective doses and associated cancer incidence and mortality risks were estimated for adult patients undergoing the five most common types of CT examinations, namely, head, neck, chest, abdomen and pelvis, at Sweden Ghana Medical Centre (SGMC) in Accra, Ghana. The two methods employed in the study were patients’ data collection and phantom measurements to verify the patien-ts’ data. The effective doses were estimated using the dose length product (DLP) from the control console of the CT machine and the anatomic region specific conversion factors. The lifetime attributable risks of cancer inciden-ce and cancer mortality for each patient for a particular examination were both determined from the effective dose, age and sex of each patient using the standard Biological Effects of Ionizing Radiation (BEIR) VII criteria. The effective doses were all within the range of 1 - 10 mSv recommended for CT examinations. The average risk for all the examinations was observed to be very low, i.e. 1 in 10001 to 1 in 10 000. The average lifetime attributable risk (LAR) of cancer incidence was 0.049 % (1 in 2041), while for risk of cancer mortality, the average was 0.030 % (1 in 3333).Keywords: Computed tomography, Effective dose, Dose length product, Life attributable risk, Cancer incidence, Cancer mortality PubDate: 2017-01-23 Issue No:Vol. 21, No. 1-2 (2017)
Authors:H.E.A. Allognon, E Agoua, A Vianou Abstract: Knowledge of thermo-physical properties of local building materials are necessary for thermal comfort design and construction of residential accommodation. Thermal diffusivity of cement-stabilized laterites were measured under conditions of transient thermal field and induced surface stress, assuming constant temperature within the samples. The laterites were stabilized by 4 %, 8 % and 12 % cement content, and tested at water saturated and un-saturated states. The values of thermal diffusivity of dry and saturated samples were respectively ~ 5.01 x 10-7 m2/s and ~ 5.35 x 10-7 m2/s, and the two values indicated the suitability of stabilized laterite for providing thermal comfort in buildings.Keywords: Laterite, Cement-stabilization, Thermal diffusivity, Thermal comfort, Constant temperature bath PubDate: 2017-01-23 Issue No:Vol. 21, No. 1-2 (2017)
Authors:A Ayensu Gyeabour I., A Owusu Abstract: Speciation, supersaturation and phase separation of water in hydrothermal grown (synthetic) quartz cryst-als have been examined as fundamental issues determining clustering, nucleation and bubble formation, which have profound influence on hydrolytic weakening, dislocation-bubble interactions and high temperature deformat-ion of quartz. Details of water speciation are necessary for explaining cluster dynamics and dislocation motion in quartz, and are also relevant in understanding magma evolution and eruption dynamics, since quartz and other sil-icates are important minerals of the earth crust. Infrared absorption studies strongly suggest that water bubbles in quartz contain hydrous species of hydroxyl ion (OH-) and molecular water (H2Om), originating from phase separat-ion of supersaturated water vapour after prolonged heat treatment of quartz at temperatures in excess of 500 °C. leading to decomposition of the hydrolyzed bonds. The hydrous species interconnect through a homogeneous spe-ciation reaction, condense, cluster and nucleate to form water bubbles, either homogeneously by thermal fluctuati-ons or heterogeneously on defects and other grown-in occlusions. The nucleation is a first order phase transition of creating liquid nucleus within the vapour phase, and chemical potential difference (related to the level of super-saturation) is the thermodynamic driving force.The unique properties of water that affect the mechanical deformation of quartz is due not only to the di-pole character, but even more to the geometrical structure of the molecules which form extended four coordinated networks. Incorporation of water tetrahedra in silicate framework [SiO4] produce electron-unsaturated chemical bonds. By sp3-hybridization of electron bonds, the water molecule exhibits a tetrahedral charged structure, leading to various water point defects in the form of substitution of SiO2 by two H2O substitutional defects (4H)Si, interstit-ial water molecules in channels parallel to the c-axis, hydrolyzed Si-O-Si bonds, and H-like alkali ions associated with substitutional impurities (such as Al3+ or Fe3+) to maintain charge balance. Water-related defects in quartz have complex structures and compositions, and the aqua-complexes are either bonded with different cations or are structurally bonded in the quartz matrix. The formation of combined defect [SiO4]-H2O-M+ [M3+O4] upon water speciation (M+ is metallic ion), is an indication of the presence of hydrous species.Keywords: Speciation, Supersaturation, Phase separation, Phase transition, Infrared absorption, Nucleation PubDate: 2017-01-22 Issue No:Vol. 21, No. 1-2 (2017)
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