This study examines the thermo-hydraulic performance of a heat exchanger tube equipped with special fixed ring inserts and twisted tape elements, using a hybrid nanofluid composed of Al₂O₃-CuO/water. Simulations are carried out under turbulent flow conditions, covering Reynolds numbers from 6000 to 14,000. The impact of varying twisted tape torsion ratios (TR = 5, 10, and 15) and hybrid nanofluid volume concentrations (ϕ = 0.3%, 0.6%, and 0.9%) is systematically evaluated. A validated CFD model in ANSYS Fluent demonstrates strong agreement with benchmark data. The results show that, at Re = 14,000, inserting a twisted tape (TR = 5) into a plain tube boosts the Nusselt number (Nu) by 36.28% and the convective heat-transfer coefficient (h) by 36.3% compared to pure water. The tape promotes turbulence and disrupts the thermal boundary layer, enhancing convective heat transfer. However, these gains incur an 8.0% pressure-drop penalty (ΔP). Furthermore, the study highlights the critical role of nanofluid concentration in optimizing heat-exchanger performance. At a 0.9% volume fraction of Al₂O₃–CuO/water nanofluid added to the twisted-tape (TR = 5) configuration, the Nusselt number climbs an additional 3.2%, while the convective heat‐transfer coefficient rises by 18.2%. This nanofluid boost comes with a modest 6.1% pressure-drop penalty (ΔP increases from 284.8 to 302.2 Pa) yet drives the thermal performance factor (TPF) from 1.38 to 3.29. These findings provide a comprehensive understanding of how synergistic passive heat transfer methods and nanofluids can be strategically utilized to enhance the efficiency of industrial heat exchangers.

The reduction in greenhouse gas emissions from conventional vehicles powered by internal combustion engines remains a critical challenge for sustainable transportation. Improving fuel efficiency through optimized transmission gear ratio design directly influences engine operation under diverse driving conditions. In this study, a machine learning-based Bayesian Optimization (BO) framework, integrated within vehicle modeling, was employed to optimize gear ratio configurations for a six-speed transmission representative of midsize passenger cars. The Worldwide Harmonized Light Vehicle Test Cycle (WLTC) was used to assess fuel economy under transient operating conditions. The BO algorithm was structured to minimize fuel consumption while ensuring acceptable performance and compliance with WLTP regulations. The results showed that the optimized gear ratios reduced overall fuel consumption by 6.2% compared to the baseline, without requiring any modifications to the engine or other hardware components. Although the largest percentage reductions occurred in cruising (−22.9%) and deceleration (−14.4%), deceleration contributed the largest absolute share of the total saving, whereas acceleration contributed a significant share owing to its dominant baseline consumption (68.9%) despite a smaller relative reduction (−4.2%). Sensitivity analysis indicated that upper gears, particularly sixth gear, had the greatest influence on optimization outcomes. The findings demonstrate that Bayesian Optimization provides an effective and computationally efficient methodology for transmission gear ratios optimization, offering a machine-learning enabled pathway to enhance fuel economy in passenger vehicles.

A total of 0.3%C-Cr-Mo-V steel, a high-strength alloy steel widely used in rocket motor housings, suspension systems in high-performance vehicles, etc., is noted due to its high strength-to-weight ratio. However, its high carbon equivalent (CE > 1%) makes it challenging to weld, as it is prone to brittle martensitic formation, which increases the risk of cracking and embrittlement. The present paper focuses on enhancing the microstructure and mechanical properties of 0.3% C-Cr-Mo-V steel by gas tungsten arc welded (GTAW) joints, utilizing post-weld heat treatment and cooling strategies (PWHTCS). A systematic experimental approach was employed to ensure a defect-free weld through dye penetrant testing (DPT) and X-ray radiography techniques. Subsequently, test specimens were extracted from the welded sections and subjected to PWHT protocols, including hardening, tempering, and rapid quenching using air and oil cooling (AC and OC, respectively) mediums. Results show that OC has enhanced tensile strength and hardness while simultaneously maintaining and improving ductility, ensuring a well-balanced combination of strength and toughness. Fractography analysis revealed ductile fracture in AC samples, whereas OC weldments exhibited a mixed ductile–brittle fracture mode. Thus, the findings demonstrate the critical role of PWHTCS, with OC, as an effective method for achieving enhanced mechanical performance and microstructural stability in high-integrity applications.