Defect and Diffusion Forum Vol. 447

Abstract: This study investigates the production of biogas through the co-anaerobic digestion of cow dung and sawdust, utilizing thermochemical pretreatment to enhance lignin breakdown. A 50:50 and a 75:25 mixture of the substrates (Cowdung:sawdust) were subjected to sodium hydroxide pretreatment and thermal conditioning at 80°C. Lignin content reduced from 31.94% to 22.73%. The results demonstrated approximately a 43% increase in biogas yield for both the 50:50 and 75:25 substrate ratios. A four-day earlier gas production onset was recorded for pretreated substrates compared to untreated samples. The methane content of the biogas reached 56% (50:50 ratio) and 60% (75:25 ratio), with hydrogen sulfide at about 1% in both ratios. Process parameters such as pH, and temperature were measured. This study provides a scalable approach for waste-to-energy applications and demonstrates the role of pretreatment in improving substrate digestibility and biogas yield.

Abstract: A numerical study investigates the flow behavior inside a three-sided lid-driven cavity. The physical problem is represented by a square cavity with two opposite horizontal walls moving translationally and independently to the right. The left vertical sidewall moves upward while the right vertical sidewall remains stationary. This study applies different Reynolds numbers to the moving walls to define three different configurations. In each configuration, two moving walls operate at the same Reynolds number (Re=100), while the Reynolds number of the remaining wall varies (Re=200, 400, 800, 1600, 3200, and 6400). We explore the flow patterns for each case, including the generated primary and secondary vortices, vorticity, velocity profiles, and fluid properties. Special attention is given to the formation and evolution of primary and secondary vortices to provide insights into the complex flow mechanisms governing this type of flow. The study reveals that varying the Reynolds number of one of the moving walls significantly impacts the flow structure within the three-sided lid-driven cavity. The asymmetry in wall motion is a powerful trigger for vortex genesis and evolution. The findings also lead to a better understanding of the flow mechanisms of driven cavity flows bounded by three walls with asymmetric boundary conditions.

Abstract: The present study explores combined free-forced convective flow and entropy generation in a constant-volume double lid-driven trapezoidal cavity. All configurations of the isosceles trapezoidal cavity were meticulously designed to possess identical leg lengths and constant volume, ensuring that the same amount of heat is transferred from the cavity’s legs. The cavity has left and right lid-driven walls capable of oscillating upward and downward, while all other domain boundaries remain stationary. The left wall is sustained at a consistently high temperature, whereas the right wall is kept at a stable low temperature, and the upper and lower horizontal walls are thermally insulated. The modelling of this problem was carried out based on the finite volume technique. The obtained results were carefully validated against existing literature related to similar problems. The influence of relevant parameters such as Richardson number (0.01 ≤ Ri ≤ 100), aspect ratio (0.4 ≤ AR ≤ 1) and three distinct moving arrangements (Case-A, Case-B and Case-C) were examined. The findings revealed that heat transport was restricted at high Ri for all the presented aspect ratios, especially for Case-C. For all the presented aspect ratios and cases, entropy generation decreases as Ri increases, with the lowest values ​​observed for Case-A. Trapezoidal cavities with AR = 0.4, 0.6, and 0.8 generate lower entropy than the square cavity at high Ri, but higher entropy at low Ri.

Abstract: This study investigates the steady magnetohydrodynamic flow of the Walter-B ternary nanofluid (composed of water-ethylene glycol (WEG) base fluid with graphene, alumina, and titanium dioxide nanoparticles) over a nonlinear stretching sheet, incorporating the effects of cross-diffusion, couple stress, and viscous dissipation. Using similarity transformations, the governing equations are converted to ordinary differential equations and solved numerically with MATLAB's bvp4c solver. A Bayesian-regularized artificial neural network (BRANN) is developed to predict skin friction, Nusselt, and Sherwood numbers with R² > 0.99 accuracy. Results reveal that fluid velocity decreases with increasing couple stress but enhances with the Deborah number and Darcy parameter, while temperature rises with the Eckert and Dufour numbers. Concentration profiles decline with chemical reaction but grow with the Soret number. Entropy generation intensifies with Brinkman and Biot numbers, whereas the Bejan number shows opposite behavior. Empirical correlations for skin friction, Nusselt, and Sherwood numbers are developed, showing a 6.3% rise in skin friction with the Forchheimer number and a 13.14% improvement in heat transfer with thermal radiation. This work provides critical insights for thermal management systems, leveraging machine learning to optimize ternary nanofluid flows in porous media under cross-diffusion effects.

Abstract: Fossil fuels continue to dominate energy use, despite growing environmental concerns, underscoring the need for renewable energy solutions. Photovoltaic cells convert sunlight but lose efficiency from heat, requiring cooling methods such as photovoltaic thermal systems. Tthis study evaluated a PVT system with three serpentine tubes under varied conditions using computational fluid dynamics simulations. Testing involved water coolant flow rates of 0.001, 0.005, and 0.009 kg/s, radiation intensities of 200, 400, and 600 W/m², and tube diameters of 15 mm and 17 mm. Increasing the mass flow rate significantly reduced temperature and improved thermal efficiency, while electrical efficiency remained stable as the PV panel temperature mainly influenced it. The optimal cooling performance was achieved with a 0.009 kg/s mass flow rate and a 15 mm tube diameter at 600 W/m² radiation intensity. These findings suggest water-based cooling may increase PV system performance and reliability, especially in high solar locations.

Abstract: Ice slurry offers a promising solution for enhancing energy efficiency and environmental sustainability in industrial refrigeration and thermal energy storage applications. This review critically examines the effects of additives and production methods on the thermo-physical properties of ice slurry, focusing on viscosity and heat transfer performance. Additives such as ethylene glycol (6.5–10.3%), sodium chloride (up to 9%), and propylene glycol (5–24%) significantly enhance heat transfer coefficients by up to 33%, while alumina-based nanofluids (0.2 wt%) increase thermal conductivity by as much as 67%. Optimal ice packing factors (10–25%) and advanced production techniques, including direct contact and fluidized bed methods, improve energy efficiency, scalability, and operational reliability while mitigating issues such as particle agglomeration and viscosity rise. The study emphasizes rigorous methodological transparency with explicit equation definitions, controlled variables, and standardized measurement units (e.g., W/m²K for heat transfer, kg/m·s for viscosity). These findings provide valuable insights to guide the development of robust, high-performance ice slurry systems for large-scale cooling and energy storage applications.