International Journal of Engineering Research in Africa Vol. 80

Abstract: The energy industry confronts challenges in optimizing its operational processes, which can result in high production costs and unpredictable profitability. Addressing these gaps is crucial due to the scarcity of robust models for energy process optimization. This study introduces a comprehensive model aimed at optimizing energy operations, tackling issues like profitability instability and equipment breakdown-induced production costs. Three models were devised: a profitability simulation model, maintenance cost reduction model, and workforce cost reduction model. These models, along with the Taguchi-fuzzy profitability prediction model, were implemented using meta-heuristic techniques such as Genetic Algorithm (GA), Differential Evolution (DE), and Harmony Search Method (HS). The study demonstrated the success of these models, enhancing compressed natural gas (CNG) production by accurately forecasting profitability and minimizing maintenance costs. Optimizing the system led to peak productivity, with optimal GA chromosomes achieved after 100 iterations and average fitness values of 0.0219, 0.0152, and 0.0149 for GA, DE, and HS respectively.

Abstract: African walnut (Tetracarpidium conophorum) is an underutilized oilseed with potential application as a feedstock for alkyd resin and bio-based coating production. However, efficient extraction of high-quality oil remains a major challenge. This study investigated the optimization of walnut oil extraction using a semi-automated mechanical expeller integrated with microwave pre-treatment. A Box–Behnken design within the framework of Response Surface Methodology (RSM) was employed to evaluate the effects of moisture content (4–12%), microwave exposure time (3–5 min), feed rate (10–20 kg h⁻¹), and screw speed (20–60 rpm) on oil yield and selected quality parameters over 29 experimental runs. The developed quadratic models were statistically significant (p < 0.01), with coefficients of determination (R²) ranging from 0.9714 to 0.9898 and non-significant lack-of-fit values, indicating satisfactory model performance. The optimum extraction conditions were 8.2% moisture content, 4.2 min microwave exposure, 14.2 kg h⁻¹ feed rate, and 23.6 rpm screw speed. Under these conditions, the predicted oil yield was 45.4%, representing an improvement of more than 15% compared with the unoptimized process. The extracted oil exhibited an acid value below 2 mg KOH g⁻¹, an iodine value of approximately 141 g I₂ 100 g⁻¹, and a peroxide value below 2 meq O₂ kg⁻¹, indicating good oxidative quality and suitability for drying-oil applications. These values were within acceptable limits reported for oils used in alkyd resin production. The results demonstrate that microwave-assisted mechanical pressing can improve walnut oil recovery while maintaining desirable physicochemical properties. The developed models provide useful information for process optimization and may support further utilization of African walnut oil in coating and polymer-related applications.

Abstract: Smallholder agro-enterprises in sub-Saharan Africa continue to face major constraints in postharvest cowpea processing due to the absence of reliable electricity, limited mechanization, and the high cost of commercial grading equipment. This study reports the development and performance evaluation of a solar-powered, pneumatic-assisted cowpea grading machine designed to improve seed cleaning, defect removal, and throughput in off-grid rural environments. The system integrates a vibration-based mechanical grader and a pneumatic module configured to deliver an airflow velocity of 6–8 m/s, corresponding to the reported terminal velocity range of cowpea seeds to effectively separate shriveled, lightweight, and low-density grains. Power requirements were matched with a 200 W photovoltaic module and a 12 V, 100 Ah deep-cycle battery, sized through energy-balance calculations covering the 0.5 hp DC motor, blower load, and control circuitry to ensure sustained off-grid operation. A Box–Behnken design under Response Surface Methodology was employed to optimize feed rate (500–1500 g/min), seed moisture content (6–8%), and vibration speed (65–85 rpm) for two cowpea varieties (Efe Brown and Niger White). Under optimal conditions, the machine achieved a throughput of 91.6 kg/h, mechanical grading efficiency of 81.2%, and pneumatic sorting accuracy of 88.6%, outperforming conventional manual and small-scale mechanical methods. The dual-stage solar-powered system significantly reduced labor input, enhanced seed quality, and demonstrated strong potential for scalable deployment in energy-constrained communities. This work provides a low-cost, clean-energy solution that strengthens cowpea value chains and contributes to improved food security across rural sub-Saharan Africa.

Abstract: This study examines the influence of a gyroid-based triply periodic minimal surface TPMS on heat transfer enhancement and flow resistance characteristics in plate heat exchangers PHE, in comparison with conventional chevron-type plates. This concept is biomimetically inspired by complex natural geometries, such as those found in coral and radiolarians' structures. The clear novelty of this work lies in the development and CFD-assessment of a gyroid TPMS-based plate heat exchanger, and in its direct performance comparison with a conventional chevron design under identical operating conditions. A three-dimensional Computational Fluid Dynamics CFD model of a gyroid-structured plate heat exchanger was developed and numerically investigated for Reynolds number Re ranging from 1000 to 2500, under consistent thermal and hydraulic boundary conditions, using ANSYS Fluent R19. The simulations were performed on a representative unit cell to reduce computational cost while preserving geometric periodicity. The proposed geometry was designed as a fully three-dimensional model using SolidWorks. The SST k–ω turbulence model was employed due to its robustness in predicting near-wall and separated flows. A grid independence study was conducted to ensure solution accuracy and numerical stability. Furthermore, the model was validated against previously published data to confirm its reliability. The results indicate that the gyroid TPMS configuration offers an improved thermo-hydraulic performance, achieving a 35.24% enhancement in the Nusselt number Nu compared to a smooth channel, while maintaining a moderate pressure drop ΔP. In addition, an overall performance improvement of 16.85% was observed relative to a conventional chevron-type PHE β = 30°, demonstrating the potential of TPMS-based designs for advanced heat exchanger applications.

Abstract: To address the dynamic response and steady-state accuracy issues in the flow control of centrifugal pumps, this paper proposes a flow throttling control strategy based on robust H-infinity control. A comprehensive simulation model of the system is established, and combined with the design of a robust H-infinity state feedback controller, quadratic stability and disturbance suppression are achieved under uncertain conditions such as speed fluctuations. Simulation results show that the proposed method achieves faster flow tracking. In anti-disturbance tests under multiple operating conditions, the H-infinity controller demonstrates significant performance improvements compared to PI control. Specifically, at 6000 rpm, 7000 rpm, and 8000 rpm, the maximum overshoot is reduced by 82.9%, 71.4%, and nearly 0%, respectively, while the steady-state error is reduced by 20%, 50%, and 50%. In addition, the settling time is shortened by 29.0%, 62.4%, and 30.5% under these conditions. These results indicate that the proposed method not only improves the accuracy and robustness of flow control but also provides an efficient solution for industrial process control, offering significant engineering application value.

Abstract: This study constructs a vector control model for asynchronous motor variable-frequency speed regulation systems in Simulink and establishes a molten level model based on geometric relationships within the molten pool. To address this nonlinear, time-varying system, a fuzzy incremental PID controller is proposed. Compared with fuzzy control and PID control, the fuzzy incremental PID controller adopted in this paper achieves smaller overshoot and shorter settling time for reference tracking and disturbance rejection in the top-side pouring twin-roll casting (TSTRC) process, demonstrating superior control performance. Furthermore, the fuzzy incremental PID controller features a straightforward structure and algorithm that facilitate practical implementation, fully meeting the molten level control requirements of TSTRC equipment.

Abstract: Underwater Visible Light Communication (UVLC) has emerged as a promising alternative to acoustic and radio frequency systems for high-speed, low-latency data transmission in aquatic environments. However, its performance is strongly influenced by water optical properties, particularly absorption and scattering, which vary with environmental conditions. The Atlantic Ocean presents unique challenges for UVLC due to high turbidity, salinity, and suspended particles, all of which contribute to significant attenuation of light signals. Attenuation, caused by absorption, scattering, and reflection, reduces signal strength as light propagates through water, making wavelength selection critical for reliable communication. This study investigates the absorption characteristics of Lagos Atlantic waters of Nigeria to determine the optimum wavelength for UVLC. Seawater samples were collected from 7 beaches, namely Atican, Oniru, Tarkwa-Bay, Landmark, Elegushi, Alpha and HOV along the coast of Atlantic Ocean of Lagos. These samples were analysed by measuring their physicochemical properties using a water quality tester and their absorbance spectra through spectrophotometry across the visible spectrum (400–800 nm) at an interval of 50 nm in reference to ionised water (distilled water). Experimental results revealed that absorbance is highest in the wavelength less than 500 nm and lowest in the wavelength greater than 600 nm, with 700 nm identified as the most suitable wavelength for transmission in these waters. The wavelength of 700 nm was then used for the simulation of UVLC in the ocean at data rates of 100 kb/s, 1 Mb/s, 10 Mb/s and 1 Gb/s for transmitting power of 30 mW at different transmission distances. Simulation results confirm good quality of received signals and reduced bit error rates at this wavelength of 700 nm for the waters of all the seven beaches.

Abstract: The rapid increase in plastic waste generation and the quest for sustainable road construction materials have stimulated interest in utilizing waste plastics as soil stabilizers. This study comparatively investigates the effects of shredded plastic waste (SPW) combined with lime and cement on the geotechnical and strength properties of laterite soil for road pavement applications. Laboratory tests were conducted on the natural and laterite soil samples stabilized with 0–2% shredded plastic waste, combined with 6% lime and 6% cement. Experimental tests performed on the soil specimens include index, compaction, California Bearing Ratio (CBR), and unconfined compressive strength (UCS). Results showed that both lime and cement reduced soil’s plasticity index but enhanced the strength properties of the laterite soil. The PI value decreased by approximately 31% and 38% when adding 6% cement and 6% lime, respectively. Findings further revealed that incorporating shredded plastic waste to soil significantly improved strength when combined with lime or cement. The optimum performance was obtained at 0.5% plastic waste, with increasing soaked CBR value from 20.4% for natural soil to 67.8% and 52.0% under West African Standard (WAS) compaction for 6% lime and 6% cement additions, respectively. Additionally, the corresponding 7 days UCS values were 603.3 kPa and 412.6 kPa, revealing the superior performance of lime-plastic stabilization over the cement. However, 0.5-1.0% plastic waste for both 6% cement and 6% lime produced soaked CBR values that are higher than 30% minimum specified for subbase layer, and this range of plastic addition is therefore recommended for improving the strength of the laterite soil. The research supports the sustainable use of plastic waste and conventional stabilizers in improving pavement layers for low-cost and durable road construction.

Abstract: This research focuses on producing sustainable Compressed Earth Blocks (CEBs) for load-bearing masonry, elaborated by washing sand waste, stabilized with lime and containing Alpha fibers. The base material was essentially sand/silt (Plasticity Index of 18 %). Compaction pressure was found to significantly influence mechanical performance. A crucial objective was mastering shrinkage; a phenomenon directly correlated to applied compression pressure. The optimal compromise dosage, which contained 6% lime and 1% of fibers, presented less deformations and achieved a compressive strength of 7.5 MPa and a flexural strength of 2 MPa, significantly exceeding the required regulatory standard.

Abstract: The need for new infrastructure and expansion of old ones has increased construction activities leading to increasing raw aggregates demand, depletion, carbon-dioxide emission and construction wastes generation. Waste generated can be an alternative source of recycled aggregate (RA) in new concrete. However, this aggregate type is limited by certain constraints. Consequently, this research investigated the effectiveness of enhancing the quality of RA through surface coating with blended slurry mixture of cement-calcined clay. Kenaf fibre (KF) was further added to evaluate its effect in the concrete mixes. The RA was pre-treated before soaking in slurry mixture. Concrete mixes were formed using uncoated and surface coated RA as substitute for gravel at replacement levels of 0, 30, 60, and 90% at 0.25 water-cement ratio, with KF addition at constant amount of 0.75% cement weight. Mixes fluidity was evaluated using slump test, while density, tensile and compressive strength tests were conducted on samples. Morphology of selected samples was examined using scanning electron microscope (SEM), while effect of coating and KF on the concrete was statistically evaluated. Results indicate that workability and density of concrete mixes containing coated RA was marginally improve by about 3% compare to uncoated RA. Meanwhile, compressive and tensile strength of concrete mixes with coated aggregate improve by about 7.8% to 10% respectively at an optimum of 30% replacement level and 0.75% KF addition, as corroborated by the optimization surface model. The SEM images revealed modification at the interfacial zone of the concrete with coated RA. This indicates the effectiveness of surface coating treatment of RA deploy as viable aggregates in making eco-concrete to promote sustainability and minimize impact of construction waste.