Defect and Diffusion Forum Vol. 444

Abstract: This paper investigates the thermal performance of a longitudinal trapezoidal fin using the Finite Volume Method, considering temperature-dependent thermal conductivity and heat transfer coefficient. The governing energy equation is developed by incorporating nonlinear thermal parameters and transforming these to dimensionless forms. The domain is discretized into control volumes and the energy balance is applied to each node to develop a system of algebraic equations. The effect of parameters like effectiveness factor, fin steepness, thermal conductivity and scale factor on temperature distribution is then studied. The results provide insights into optimizing fin geometry and thermal properties for efficient heat dissipation in engineering applications, while the temperature gradients along the fin length offers useful information for design. The Finite Volume Method ((FVM) proves advantageous in handling irregular geometries and conserving local balances. Overall, this comprehensive numerical approach enables accurate prediction of the intricate thermal response of longitudinal trapezoidal fins.

Abstract: The aim of this work is the numerical study of natural convection in a square enclosure filled with nanofluids, using (Cu-water) and (TiO₂- water) nanofluids. The finite volume method is used to solve the Navier-Stocks and energy equations. The effects of different relevant parameters, such as types of nanoparticles, volume fraction of nanoparticles (0-30%) and whose Rayleigh number varying from 10³ to 10⁶. It appears from this study that heat transfer increases by increasing the Rayleigh number and the volume fraction of the nanoparticles. The use of nanofluid enhances heat transfer, the highest heat transfer enhancement is observed in Cu-nanofluid. Consequently, the type of nanoparticle is a main factor for the enhancement of heat transfer. A comparison of our results with those of Barakos and Mitsoulis revealed a good agreement.

Abstract: Passive Flow Control in Pipelines is gaining increased importance in the field of fluid transport, particularly in oil and gas applications. This approach relies on the installation of passive devices designed to alter fluid flow paths by generating suppression zones. Among these devices, fins are particularly notable. Hence, the objective of this paper is to provide a numerical investigation into the behavior of laminar flow within a bifurcated backward-facing step (BFS), controlled through the installation of a flexible fin at the lower wall of the enlarged duct part, with varying mechanical stiffness and positioning. The study considers a flow through an expanded conduit, where the fluid enters with a predefined velocity profile and subsequently splits into two sub-conduits. The investigation focuses on examining the influence of fin length (0.5 ≤ L_c/H ≤ 1), position (4 ≤ x₀/H ≤ 7), and elasticity on the elasto-hydrodynamic structure of the flow, including vortex formation, flow separation, the maximum displacement of the flexible fin, and the efficiency of the sub-conduits at the outlet. This analysis is governed by the momentum equations, coupled with solid mechanics equations, using the Arbitrary Lagrangian-Eulerian (ALE) framework. The governing equations are solved using the finite element method, implemented through the simulation and the sliding mesh technique in COMSOL Multiphysics 5.7. The numerical results reveal that installing a flexible or rigid fin within the BFS system significantly impacts the non-isothermal flow behavior within the bifurcation ducts. This configuration effectively allows for flowrate regulation at the BFS outlet, also making it possible to equalize flow rates under specific conditions, particularly when using longer fin that extend halfway across the channel. Moreover, the fin placement on the bottom is important for achieving effective flow rate control and heat transfer, aligning with desired requirements for each branch outlet.

Abstract: In the present study, an analytical solution for MHD flow-heat transfer highly non-linear equations of non-Newtonian third-grade nanofluid is established using the AGM method while considering the effect of the magnetic field, the radiation heat transfer, the inclination and the nanoparticles fraction. From dimensionless analysis, the main characteristic parameters are identified, specifically the viscoelastic parameter, the magnetic parameter, the gravitational parameter, the generalized pressure gradient, the thermal radiation parameter, the Brinkman number and the Hamilton number. Two classes of problems, namely, plane Couette flow and plane Poiseuille flow, are considered. Validation was conducted using results from established numerical methods, including Mathematica software, the Adomian Decomposition Method (ADM), and BVP4C solver to benchmark our findings derived via the Akbari Gangi Method. The comparative analysis reveals the reliability and accuracy of the established analytical solutions. The effect of the main parameters of water-SWCNT nanofluid on velocity and temperature profiles are graphically illustrated and discussed. The main results reveal that increasing a magnetic parameter results in a significant drop in the velocity. Furthermore, the rise in Brinkman's number and the radiation parameter affect the temperature differently. Additionally, the viscoelastic and gravitational parameters have opposite velocity and temperature effects. The results demonstrate the complex interaction between several physical characteristic parameters in the fluid dynamics and heat transfer processes. The efficient and highly accurate series-based analytical solutions for flow velocity and temperature obtained through the Akbari-Ganji Method provide valuable insights and are a powerful tool for addressing similar problems in fluid dynamics and heat transfer.

Abstract: Titanium is the material of choice for high performances components, due to the combination of physical and mechanical properties it provides and is widely used in aerospace, automotive, biomedical and marine engineering due to their good hot and cold processing properties, fracture toughness, high specific strength and good deformability. Nevertheless, titanium is also characterized by very high production costs, which are approximately 6 times and 30 times higher, respectively, in comparison to those to obtain the same quantity of aluminum or steel relegating titanium to high demanding sectors. One possible way to reduce the cost of titanium is to use cheaper alloying elements instead of vanadium or niobium to stabilize the body-centered-cubic (B.C.C) β-phase. TIG-welding of high-strength low-cost pseudo-β titanium alloys is complicated, primarily due to the high content of alloying elements, such as iron, molybdenum, as well as the use of oxygen as an alloying elements. By the correct choice of welding modes in most cases, it is possible to obtain welded joints of high-strength pseudo-β titanium alloys with good microstructure and mechanical properties. In this article, we study the weldability and influence of TIG welding on the structure and mechanical properties of low-cost titanium alloy Ti–2.8Al–5.1Mo–4.9Fe.

Abstract: The use of high-strength steels in the vehicle industry is increasing. In many cases, the use of flame straightening is unavoidable to reduce deformation after welding. Due to the not very concentrated but relatively high temperature heat source, the process can cause significant changes in the microstructure and mechanical properties which can endanger the safe use of these steels. This can be particularly true for ultra-high-strength (UHSS) steels, for which we have limited experience and concrete measurement results. Due to the different thermal physical properties of the flammable gases, the resulting heat effect varies depending on the gas and technology. Nowadays, there is a lack of studies that analyse the effect of flame straightening thermal cycles on high-strength steel properties. The changes of the microstructure and mechanical properties were experimentally investigated on S1100M high strength structural steel. A Gleeble 3500 thermomechanical physical simulator was used to perform thermal cycles previously measured by thermocouples during real flame straightening experiments. The effect of two heating flames (acetylene/oxygen, propane/oxygen), three characteristic peak temperatures (1000 °C, 800 °C and 675 °C) and two types of cooling conditions (air cooling and intensive water cooling) were studied. Softening occurred at all 675 °C peak temperatures for both cooling conditions and flammable gases, and softening was also observed at 800 °C peak temperature with air cooling for acetylene and propane heating.

Abstract: The efficiency, precision, and expected lifespan of mechanisms and machine components (such as ball bearings, couplings, and gauges) are significantly influenced by the quality of the materials used. Thus, it is essential to select materials that offer well-defined hardness and stability throughout the product's lifetime. This paper examines the heat treatment applied to 100Cr6 steel to achieve precise hardness in the range of 230–390 HV10, while also meeting requirements for stability and uniformity over the product's lifespan.

Abstract: Extensive research on X80 pipeline steel has been conducted, while there is little research on X60 pipeline steel. In this study, FEM (Finite Element Method) on the double defect pipeline model of the outer and inner walls is conducted using ANSYS Workbench software. The research object is the X60 pipeline with rectangular double corrosion defect. Firstly, the stress distribution is examined; Secondly, by changing the geometric factors of the double defects on the outer and inner walls, the influence law on the failure pressure is examined; Finally, based on the FEM results, the failure pressure calculation formula for X60 pipeline with double corrosion defects on the outer and inner walls was fitted by MATLAB software, and whether the fitting formula was accurate and applicable was examined. The stress cloud map of double defect pipeline has two areas: The area near the defect and that far away from the defect, with the former belonging to the danger zone and the latter belonging to the safe zone, Specific to the double defect pipeline model with inner and outer walls, the failure pressure presents a sharp reduction as the defect depth elevates, and its impact on the failure pressure becomes increasingly significant with the narrowing axial distance between the two defects; the increasing defect length increases is related to decreasing failure pressure. In line with the significantly increased defect length, its impact on pipeline failure pressure gradually weakens; the width variation of double defect impacts pipeline failure pressure very slightly; The MATLAB fitting formula possesses a high fitting degree, and the FEM calculation data is basically distributed on the fitting curve, which can better fit the curve of the limit load variation law; The inner wall double defect model performs better in pressure ratio and error analysis. The conclusions drawn have specific reference significance for the safety assessment of oil and gas pipelines.

Abstract: The purpose of this study is to explore the effect of groove angle on the fatigue life of high-speed train brake discs. A thermal-mechanical coupling model of high-speed train brake discs with different angles (0°, 22.5°, 45°, 67.5°, and 90°) was designed and established. The effects of different groove angles on temperature and stress were studied and analyzed. Experimental specimens were prepared using special processing methods, and friction and wear characteristics experiments were carried out to further verify the simulation results. At the same time, based on the above results, life models of brake discs with different groove angles were established to study the effect of the angle on their fatigue life. Stress has a direct impact on the crack initiation life of groove brake discs, and temperature changes affect the material properties of brake discs, thereby affecting the crack initiation time. The crack growth life of 0° groove brake discs is longer, while the crack growth life of brake discs with other groove angles decreases as the groove angle decreases. Compared with the 0° groove angle, the crack propagation life of the 45° groove angle accounts for approximately 84.7%, while that of the 22.5° groove angle accounts for approximately 80.4%. These research results provide a theoretical basis and numerical research methods for the design of brake disc structures.