Journal of Applied Science and Technology

Computer simulation of optimal tilt angles of photovoltaic module for maximum solar irradiation at locations in southern Nigeria

Y.N. Udoakah — 2020-01-29

Numerical algorithm was developed to simulate optimal tilt angles at which maximum solar radiation was incident on south-facing photovoltaic (PV) module. A MATLAB Code was implemented to examine the relationship bet-ween solar irradiation and module tilt angles for four locations in Southern Nigeria, and the results were validated with data from Meteorological Agency of Nigeria. The Code facilitated faster computation of the optimal tilt angles, rather than manual and time consuming calculations; and ensured accurate installation of PV systems for imp-roved efficiency and performance; thereby enhancing the prospects of solar energy utilization. The simulation algorithm was based on mathematical formulation of global solar intensity as a function of solar declination angle, hour angle, irradiation on horizontal and tilted surfaces, clearness index and diffused radiation at the location. The optimum tilt angles were determined for each month by selecting the corresponding values of angles for which the highest radiation intensities were received. The computer simulation confirmed that Calabar, Uyo, Warri and Owerri on nearly same latitudes had identical optimum monthly tilt angles; and for best performance, fixed solar PV module must be oriented to face south at optimal tilt angle equivalent to the latitude (°) of the location.

Keywords: Optimum Tilt Angle, Photovoltaic Module, Solar Angles, Albedo, Hour Angle, Global Irradiation

Predicting molar composition of biogas by reaction kinetics and temperature dependence on anaerobic digestion

A.L. Fagbemi — 2020-01-29

Mathematical model was developed and simulated to predict the molar composition of biogas produced by anaero-bic digestion. Several models have been developed for anaerobic processes with reduced number of parameters, but requiring data resolution, thus posing problem of data precision. The prediction model was based on reaction kinetics of anaerobic digestion, while Ratkowsky's formulation was used to examine the dependence of temperatu-re on methanogenic process. The reaction kinetics model was simulated using SciLab coding of fourth order Ru-nge Kutta numerical algorithm. Comparison of numerical experimentation results with published experimental data gave satisfactory agreement. The cumulative volume of methane was predicted in the temperature range of 20 - 40 °C, and the maximum volume of methane generated was 26.39 L at 35 °C for mesophilic bacteria.

Keywords: Anaerobic Digestion, Hydrolysis, Acidogenesis, Acetogenesis, Methanogenesis, Mesophilic Bacteria

Profiles of amino acids and volatile organic compounds from dawadawa produced by defatting and fermentation of locust bean (P. biglobosa), soy bean (G. max) and roselle (H. sabdariffa) seeds

A.A. Shahidah — 2020-01-29

Free amino acids and volatile organic compounds generated in dawadawa produced by defatting and fermentation of locust bean (P. biglobosa), soy bean (G. max) and roselle (H. sabdariffa) seeds were profiled. The amino acids were determined using amino acid analyser, while the volatile organic compounds were analysed using Gas Chro-matography-Mass Spectrometry. The ground, defatted and fermented P. biglobosa and G. max seeds only showed slight increase in contents of essential amino acids and non-essential amino acids (arginine and glutamic acids). Serine and glutamic acids were the major amino acids in the ground, defatted and fermented seeds of P. biglobosa and G. max. The ground, defatted and fermented H. sabdariffa seeds showed minor differences in threonine, valiine, isoleucine, leucine and glutamic acids, compared with the full fat, ground and fermented seeds. Diverse volat-ile organic flavour compounds identified in dawadawa produced from P. biglobosa, G. max and H. sabdariffa seeds were acid-class flavour volatiles, alcohols, aldehydes, ketones, amides, carbonyl, esters, hydrocarbons and phenol. The ground, defatted seeds of G. max showed presence of various volatile organic compounds with n-He-xadecanoic acid, 9, 12- Octadecadienoic acid (Z, Z)- and 9-Octadec-enamide (Z)- of varying degree of abundance. For ground full fat and defatted seeds of H. sabdariffa, seven volatile organic compounds were detected, where six were unique to the H. sabdariffa seeds; and were detected irrespective of the seeds being defatted, or not, or fermented. Of the volatiles, hexadecanoic acid, ethyl ester and eicosane increased in quantity for defatted and fermented dawadawa produced from H. sabdariffa seeds. Defatting of all three seeds generated amino acids and volatile organic compounds in dawdawa produced.

Keywords: Amino acids, Volatile Organic Compounds, Dawadawa, Condiment, Fermentation, Defatting

Numerical computation of efficiency of beta polynomial kernel using product approach

I.U. Siloko — 2020-01-29

The efficiency values of beta polynomial kernel functions were computed using bivariate product approach, which involved multiplication of two univariate beta kernel functions. The statistical properties of bivariate beta kernel functions, in terms of roughness and variance, were evaluated to compute the efficiency values. The efficiency values of univariate form of beta polynomial kernels were also determined, and compared with values of bivariate beta kernel functions, since most applications of kernel estimators are in the bivariate form. The kernel estimator is a non-parametric density estimator with direct applications in data analysis and visualization. The computations showed that efficiency values tended to be smaller for bivariate beta polynomial kernel functions than for univari-ate kernel functions, due to effects of dimensionality associated with non-parametric statistics.

Keywords: Bivariate Kernel, Kernel Estimator, Product Approach, Efficiency of Beta Polynomial

Characterization of crystallinity and molecular functional groups of silver nanoparticle-Piptadeniastrum africanum (Dahoma) sawdust composites synthesized in-situ

D Gyasi-Antwi — 2020-01-29

Silver nanoparticles prepared by Turkevich method of reacting trisodium citrate as reducing agent with silver nitr-ate were incorporated in-situ with P. africanum (Dahoma) sawdust to produce nano-composite. Conventional X-ray powder diffraction of the nano-composite showed complex diffraction pattern, with line peak broadening in the crystalline phase and particle size widening in the amorphous region. The Miller indices of the four main peaks identified were (111), (200), (220) and (311); which confirmed the permitted reflections attributed to the presce-nce of crystalline silver. The mean lattice parameter calculated by Bragg’s law was 4.0903 Å, corresponding to face centred cubic Bravais lattice of silver. Using Scherrer formula, the crystallite sizes ranging from 4.95 – 15.25 nm were calculated for the broadened line peaks. The particle sizes in the amorphous phase were determined from the distorted peak or widening of the non-reflecting diffraction angles, and ranged from 1.35 - 4.10 nm. Fourier transform infrared (FTIR) spectroscopy of the nano-composite showed spectra lines of absorption peaks attributed to molecular functional group C-H-O at 1422.24 cm^-1 (major component of sodium citrate), while a band centred at 3450 cm^-1 was assigned to O-H bending or stretching of the interlayer water molecules (of H-bound and OH group vibrations), and the spectra line at 515.14 cm^-1 indicated the presence of Ag-O stretching modes. The crystalline characteristics of the nano-composites could be indicative of potential applications in industry.

Keywords: Nano-composite, X-ray Powder Diffraction, Crystallites, Lattice Parameter, Infrared Spectroscopy, Molecular Functional Groups

Impact resistance and electrical conductivity of copper nanoparticle-Milicia excels sawdust composites

D Gyasi-Antwi — 2020-01-29

Copper nanoparticles (Cu(NPs)) prepared by chemical reduction of cupper (II) sulphate pentahydrate using ascorbic acid were blended with Milicia excels (Odum) sawdust and Polyvinyl Formal/Calcium Carbonate wood adhesive as matrix to produce rectangular slabs of nano-composites with potential applications for industrial pack-aging or building panelling. The nano-composites were characterized by Fourier Transform Infrared (FTIR) Spec-troscopy, and hydroxyl (OH) groups -CH₂- (Alkane groups), C=C (Alkene or Aromatic groups), C-O (Carbonyl) groups of lignin, cellulose or hemicelluloses or C-O-C Ester groups of cellulose and hemicelluloses were identifi-ed. The mechanical toughness of the nano-composites were tested to determine the impact resistance, using Tinius Olsen IT 406 High Energy Pendulum Impact Machine. The impact energy of 26.89 ± 0.02 J exceeded values for individual constituents of the composites, was comparable to natural fibre reinforced composites, and the nano-composites could serve as panelling or packaging materials. The electrical characteristics of the nano-composites were examined by determining the electrical conductivity, resistivity and electric field strength, using simple dire-ct current Ohms bridge, and the values were respectively, (1.73 ± 0.05) x 10^-2 ohm^-1 m^-1, 57.8 ± 0.5 Ω m, and 186.3 ± 0.5 V m^-1. The low value of electrical conductivity was suggestive that the Cu(NP)-sawdust composite could be likened to intrinsic semiconductor, but the process for transition into extrinsic semiconductor was not in-vestigated. The imposed voltage increased with percentage moisture content, presumably due to hydrolyzed bon-ds on the surfaces of the nano-composite. The nano-composites could be used as insulating and packaging materi-als for sensitive electronic equipment.

Keywords: Cu(NPs), Ascorbic Acid, FTIR Spectroscopy, Polyvinyl Formal, Impact Test, Electrical Resistivity

Occupational dose assessment for radiation staff at nuclear reactor research centre, 2011 – 2015 (prior to core conversion)

M.A. Addo — 2020-01-29

Radiation absorbed dose data of staff at the Nuclear Reactor Research Centre (NRCC) of Ghana Atomic Energy Commission, from 2011 to 2015, was analyzed to evaluate the performance of personnel monitoring program prior to the reactor core conversion, and to set baseline criteria for compliance after the core conversion. Personnel radiological deep dose data Hp (10) and surface dose data Hp (0.07) of three radiation workgroups, each of 4 wor-kers were extracted from Thermolumiscent Dosimeters (TLDs). The reactor dose rate data from coolant water was used as control factor influencing radiation absorbed by the staff. The mean dose rate values were respectively, 0.56 mSv and 0.48 mSv for H_p(10) and H_p (0.07), which were very low compared to the annual occupational limit of 20 mSv/year averaged over any 5-year period set by the International Commission on Radiological Protection. Statistical analyses were performed using Repeated Measure Analysis of Variance, Multivariate Analysis and Mauchly test. Significant differences were found in both Hp (10) (F_{(11, 36)} = 7.45, p < 0.05) and Hp (0.07) (F_{(11, 36)} = 4.51, p < 0.05) per year, however, no significant differences were found among the three workgroups. The dose data showed reduction in personnel radiological dosage over the five-year period, indicating either effec-tiveness of radiological protection program, reduction in reactor power due to burn out of nuclear fuel after 20 years of operation or reduced staff workload.

Keywords: Occupational Dose, Thermolumiscent Dosimeter, Effective Dose, Personnel Monitoring, Analysis of Variance

Regulatory framework for nuclear power plant fire safety and risk assessments from global perspective

M Asamoah — 2020-01-29

The evolution of regulatory framework for fire safety and risk assessments at Nuclear Power Plants (NPPs) is on-going globally. The first generation commercial NPPs were designed and operated with minimal radiological risk posed by fire, as evidenced by the Brown Ferry (Alabama) NPP station cable tray accident in 1975. The present-ation provides global perspective of insights and integration of fire safety in the planning, design, construction, and operation of NPPs, with the aim for setting up safety regulations, particularly for countries embarking to oper-ate NPPs. Prescriptive fire safety regulations were instituted for commercial NPPs already in operation before 1979, leading to significant modification. The implementation challenges and cost of modifications provided sch-emes for voluntary risk-informed regulations. Since then, the regulatory framework has evolved from prescriptive to risk-informed performance-based assessments, with integrated system of combining deterministic and probabil-istic approaches, and other requirements in risk-informed decision making at the nuclear facility. From global per-spectives and experiences, such system-wide regulatory framework would identify generic issues of fire safety which could be resolved through design, construction and operation of NPPs by applications of risk-informed methodologies.

Keywords: Prescriptive Regulation, Risk-informed Decision, Performance-based Assessment, Deterministic Approach, Defense-in-Depth, Probabilistic Safety and Risk Assessments, Suppressants

Nucleation and growth of spherical water bubbles in hydrothermal grown quartz (A Review)

A Ayensu Gyeabour I. — 2020-01-29

Formation of water bubbles by precipitation of supersaturated water vapour and interactions of the bubbl-es with dislocations are fundamental for understanding the phenomenon of hydrolytic weakening of quartz during high temperature deformation. Annealing deformed synthetic quartz crystals at temperature in excess of 500 °C leads to phase-separation of grown-in water into hydroxyl (OH) species and molecular water (H₂Om). By homoge-neous inter-conversion hydroxyl reaction of H₂Om and O (anhydrous oxygen), the excess OH groups agglomerate into clusters to form embryos. Embryonic-nuclei of radii less than Gibbs critical size dissolve, while embryos of larger sizes grow to form stable nuclei in equilibrium with the supersaturated vapour. Ostwald ripening dissoluti-on-diffusion growth of nuclei at near critical state is limited by OH diffusion and surface vacancy kinetics. Chemi-cal potential difference of OH at the nucleus-bulk interface leads to changes in interfacial energy and higher OH concentration for growth of larger nucleus, as described by Gibbs-Thompson equation. For size evolution of nuclei, concentration gradients provide additional driving force for growth of larger nuclei at expense of smaller nuclei. La Mer model accounts for separation of nucleation and growth. Irreversible aggregation of stable nuclei form macrobubbles at the supercritical stage, which coalesce into spherical water bubbles of equilibrium sizes.

Hydroxyl groups of low solubility in quartz are considered as interstitial defects, which are primarily tra-pped by vacancies. The spherical bubbles consisting of OH-vacancy complexes grow by absorbing OH monomers and coalescing with other bubbles under annealing conditions. The rate-controlling steps for bubble growth are migration by volume, surface diffusion, and interaction with lattice defects. By coalescence events of random co-llisions and OH capture, the bubbles gain energy for growth due to reduction of surface energy, limited by vacancy relaxation of strain fields produced by excess pressure in the bubble.

The review examines mechanisms of nucleation and growth of water bubbles in quartz and presents com-prehensive models describing the processes occurring during bubble formation from evolution of clusters, embryonic-nuclei dissolution and growth, stable nuclei aggregation into nanobubbles, and coalescence to form macro-bubbles, which grow into equilibrium bubbles. The mathematical formulations governing clustering, dissolution-diffusion growth, coalescence events, interfacial hydroxyl mass diffusion, and surface adsorption kinetics for the physical processes of nucleation and growth of water-filled bubbles in quartz crystals are also presented.

Keywords: Embryonic-Nucleus, La Mer Model, Ostwald Ripening, Interfacial Energy, Chemical Potential, Coale-scence Event, Rate Theory