International Journal of Engineering Research in Africa Vol. 14

Abstract: In this paper, unsteady MHD flow of heat and mass transfer of Cu-water and TiO₂-water nanofluids over stretching sheet with a non-uniform heat/source/sink considering viscous dissipation and chemical reaction is investigated. The governing partial differential equations with the corresponding boundary conditions are transformed to a system of non-linear ordinary differential equations and solved using Keller box method. The velocity, temperature and concentration profiles are obtained and the influences of various relevant parameters, namely the magnetic parameter M, Prandtl number Pr, Eckert number Ec, Schmidt number Le , chemical reaction parameter K,unsteadiness parameter S and the Soret number Sr on velocity, temperature and concentration profiles are discussed. The skin-friction coefficient–f''(0), heat transfer coefficient –θ'(0) and mass transfer coefficient –φ'(0) are presented in tables. A comparison with published results is also presented and found in good agreement. Keywords: MHD; Keller box method; unsteady; nanofluid; non-uniform heat/source/sink; chemical reaction; viscous dissipation.

Abstract: Unsteady magneto hydrodynamic (MHD) free convection flow of a viscous, incompressible and electrically conducting, well known non-Newtonian fluid named as Kuvshinski fluid past an infinite vertical porous plate in the presence of homogeneous chemical reaction, radiation absorption and heat source/sink is studied analytically. The plate is assumed to move with a constant velocity in the direction of fluid flow. A magnetic field of uniform strength is applied perpendicular to the plate, which absorbs the fluid with a suction that varies with time. The dimensionless governing equations are solved analytically using two terms harmonic and non-harmonic functions. The expressions for the fields of velocity, temperature and concentration are obtained. With the aid of these the expressions for skin friction, Nusselt number and Sherwood number are derived. The effects of various physical parameters on the flow quantities are studied through graphs and tables. For the validity, we have checked our results with previously published work and found in good agreement. Velocity decreases for an increase in visco elastic parameter α₂, heat absorption coefficient φ, the chemical reaction parameter γ , the magnetic field parameter M, the Prandtl number Pr, the Schmidt number Sc, and increases for increase in Grashof number Gm, the radiation absorption parameter Q ₁

Abstract: Substantiation of a technique earlier employed in determining stress in Copper-Silver thin films at very low temperatures is presented. It is shown that the stress measured at elevated temperatures using Stoney’s equation can be utilized in the determination of stress at very low temperatures. To demonstrate the application of this technique, a case study has been conducted by utilizing stress hysteresis curves obtained from the Cu-6at%Ag thin film heated from room temperature to 400°C and cooled back to room temperature in two cycles. The stresses in the Cu-6at%Ag thin film at various low temperatures up to-197°C have been determined by utilizing data from high temperature stress hysteresis curves.

Abstract: This article reveals a detailed study of temperature cycle formed during Gas Tungsten Arc welding of high carbon steel (AISI 1090) butt joints. Experimental work has been carried out to estimate the temperature distribution along fusion boundary to longitudinal direction of the weldment by mounting thermocouples on the plate along with Data Acquisition System. Heat flux distribution due to moving point heat source has been demonstrated by implementing Gaussian surface heat flux and Angular Torch model. Cooling rate has predicted by application of Adams cooling rate equation. Conduction-convection phenomena plays dominant role for evaluating heat loss from the weld joint and Differential Transform Method (DTM) has been applied to judge non-dimensional temperature distribution. Analytical studies has shown well agreement with experimental temperature distribution.

Abstract: In the present work, an attempt was made to solve the problem of distortions during the trial extrusion of an automobile shock absorption by means of orthogonal test method and HyperXtrude software based on ALE (Arbitrary Lagrangian Eulerian) method. According to orthogonal test arrangement, nine times simulations were carried out to study the effects of four significant parameters on distortions. Analysis shows that the influence of bearing length on the outlet velocity uniformity is the largest among the four selected factors. The material flow will be held up obviously with bearing length increasing because of the friction enlargement. But once the bearing length is beyond a critical value, its influence on flow resistance will decrease suddenly. The analysis also confirms that the baffle-block height and ram speed also have considerable influence on outlet velocity uniformity. And the impact of welding-chamber height on outlet velocity uniformity is slight and could be ignored. Finally, the die structure was optimized on the basis of the optimal combination of parameters obtained though the results and analysis of the simulation test. Extrudate with high quality were obtained.

Abstract: Internal combustion engines normally operate with the nonrenewable sources such as petrol and diesel, which are diminishing at a faster rate. To avoid these problem alternative sources of energy must be opted for the operation of internal combustion engines. In this work biogas is selected as an alternative source of energy for the working of internal combustion engines but possess some limitations due to its high auto ignition temperature and high CO₂ content in it. To overcome the limitations biogas is blended with LPG at different proportions of 5%, 10%, 15% are done. The modification of the internal combustion engine is performed to convert it into a gas engine and the tests are conducted on the modified engine with different proportions of blending at various loads. Based on the results of the test conducted the performance characteristics are analyzed.

Abstract: A simple Fuzzy logic controller (FLC) applied to buck converter is presented in this paper. This approach uses FLC which performs better when compared with the conventional PI controllers. In proposed buck converters, high voltage dc supply is switched at very high frequency and inductively transferred to dc load via a high frequency transformer and rectifier. In this converter four power switches are connected in series to primary of high frequency transformer for large load currents. To achieve large step-down voltage ratios the power switches are turned ON and OFF alternatively with a time gap. The voltage step-down ratios, Total Harmonic Distortion and angular velocity of drive are the parameters to be analyzed. The comparison with the original FLC and comparison of three level DC-DC converter with capacitor and pi filter is carried out by MATLAB-Simulink simulation and Model is designed to verify the proposed method performance.

Abstract: This paper proposes a sensorless procedure to estimate the induction motor speed and the dependable heat contents of the stator and rotor sides. The proposed procedure is based on the electrical models of a three phase Induction Motor (IM). The motor electrical models for normal and abnormal will be discussed and a technique is introduced for accommodating frequency dependent skin effect of the rotor resistance using a simple proposed speed estimation algorithm. The electrical models are customized from the positive and negative sequence networks. The speed detection is based on the rotor parameters slip dependent. The models are then used to analyze different operating conditions of the motor. Two thermal motor protection schemes are suggested. The first scheme is dependent on the stator side while the other scheme is developed for rotor side. The Matlab software is used for this purpose to emulate efficiently the proposed estimation procedures through a complete motor modeling which is fed from the power grid. Finally, the results provide the motor performance characteristics which involve current, torque, speed and stator/rotor temperature versus time for numerous operating conditions. It is concluded that the proposed sensorless procedure is efficient to protect the induction motors against abnormal starting as well as the overheating on either stator or rotor sides. Also, the proposed sensorless estimation for speed and temperature is reliable for submersible motor applications. The proposed schemes can be considered as costless preventive maintenance procedure.Index Terms: induction motor, slip dependent, sensorless, thermal model, abnormal operating conditions.

Abstract: Gas transmission pipelines mainly transport flammable fluids across the length and breadth of the country especially in the Niger Delta region of Nigeria. The associated risk to both the individuals’ encroaching and inhabiting areas along the right-of-way (ROW) and the society at large cannot be underestimated. Thus safety concerns considering the individual and societal risk of pipeline failures has become important. This paper attempts to develop a model for both individual and societal risk assessment for a 12km length natural gas transmission pipeline in Utekon community (commencing from the Benin-Auchi through Uhuwmunode Osina town and terminating in the Benin-Agbor axis) in Edo State using the Chemical Process Quantitative Risk Analysis Method (CPQRA). The CPQRA is used because it examines the hazard zones within a pipeline ROW and the number of persons that would be affected by fire/explosion. Finally, field data was used in this study to validate the model which can be applied to any natural gas pipeline risk assessment scenario.

Abstract: This paper seeks to increase interest level on energy efficiency by bringing to fore payback-period assessment of implementing energy-efficient measures that could help achieve sustainable production processes in a typical medium scale printing manufacturing industry in Lagos, Nigeria. Several energy efficiency measures have been suggested based on identifiable energy management opportunities within this industry. The method used for the economic evaluation and feasibility study is payback period; this approach is aimed at providing guidance for a quick and informed decision on the implementation of the energy efficiency measures identified. The payback for two of these measures namely; turning off equipment when not in use and replacement of drive belts on large motors with energy efficient cog belts, have been found to be immediate. When standard fluorescent lighting and incandescent bulbs are replaced with energy efficient lamps and bank of capacitors are installed to improve the power factor of the motors, the company will recoup its initial investment in less than one year. Also, purchasing and installing an advanced electronic meter with data logging capability to help monitor electrical demand has been shown to give the highest payback of 2.4 years. These payback period results have indicated that investment in the recommended energy efficient technologies are economically viable and worthy of implementation. With this analysis, management of manufacturing industries can now make informed economic decision towards productivity improvement and sustainability.