Defect and Diffusion Forum Vol. 449

Abstract: This work presents a numerical study of natural convection heat transfer in a cavity filled with an ionanofluid. The governing equations are solved using the finite volume method and the SIMPLEC algorithm. This study aims to analyze the effects of key parameters influencing the flow structure and heat transfer, including the Rayleigh number (Ra), the volume fraction (𝜑), the inclination angle, and the type of base fluid.The results indicate that increasing the volume fraction (𝜑) enhances heat transfer and underscores the superiority of ionic fluids over water as a base fluid. Additionally, heat transfer reaches its maximum at a specific inclination angle.

Abstract: Throughout this study, the Lewis number influence on double-diffusive natural convection inside a rectangular cavity horizontally disposed, filled with Copper nanoparticles dispersed in water, heated and salted by constant thermal and solutal fluxes on the side walls while the horizontal ones are assumed thermally adiabatic and solutally impermeable, is studied analytically (parallel flow approximation) and numerically (finite difference method) for a large range of the aspect ratio, 1 ≤ A ≤ 16, the Lewis number, 10-3 ≤ Le ≤ 103, and the nanoparticles volume fractions, φ = 0 and 0.05. The results revealed that the numerical and analytical outcomes showed a good agreement. Both the aspect ratio and the Lewis number have a range responsible for variations in heat and mass transfer rates, A ≤ 12 and 10-2 ≤ Le ≤ 10 for Nusselt number and Le ≥ 10-2 for Sherwood number. The results obtained by examining the interest of using nanofluids in the considered configuration were against all expectations, that they led to a degradation of the rates of heat and mass transfers with the increase in the nanoparticle volume fraction.

Abstract: The mixed convection of fluid flow and heat transfer in a discretely heated square lid-driven cavity has been numerically investigated using the lattice Boltzmann method. The fluid inside the inclined cavity is a water-based nanofluid, enhanced with Al₂O₃ nanoparticles. The cavity is discretely heated from the left and bottom walls and cooled from the right wall, while the top wall is adiabatic and moves at a constant velocity. Simulations have been performed to analyze the effects of key controlling parameters, including the Richardson number (Ri), inclination angle (θ), and the solid volume fraction of nanoparticles (ϕ). The results indicate that increasing the inclination angle enhances heat transfer on the left wall but reduces it on the bottom wall. Furthermore, to achieve the lowest mean fluid temperature, an inclination angle of 90° is recommended, regardless of the Richardson number and nanoparticle volume fraction. Additionally, the introduction of nanoparticles into the base fluid improves the heat transfer rate and increases the average temperature within the cavity. Nomenclature

Abstract: In this work, we present a numerical study of mixed convection flows around large-scale heat sinks. It is based on the Cascade Lattice Boltzmann Method (LBM) for values of the Rayleigh number, in transitional regime, in the range 5×10⁷≤Ra≤5×10⁸ and for a Reynolds value fixed at Re=1000. The study is carried out in a rectangular cavity of dimension H subjected to periodic thermal and dynamic boundary conditions on its vertical walls. Two heat sources of (L', l', H/2) with a hot temperature T_h, are placed on the bottom wall of the cavity to simulate heat sinks. Fresh air (for cooling these heat sinks) is injected at a temperature T_c< T_h from the bottom of the cavity through two openings of length L''. The hot air is extracted through an opening (2L'' long) managed on the upper horizontal wall. The preliminary results, presented in this paper, are in the form of streamlines, isotherms and thermal profiles in the range of the Rayleigh number considered. Heat transfer is studied in terms of the average Nusselt number calculated over the entire surface of the two heat sources.

Abstract: The numerical study of natural convection of confined air flow within a closed square cavity was conducted using the lattice Boltzmann Method (LBM) employing the BGK model. In this setup, the right side of the enclosure is maintained at a cooling temperature, while the left side exhibits a linear decreasing temperature profile from the heated bottom wall to the adiabatic top one. The effect of buoyancy, induced by gravitational acceleration and influencing the convection force, was assessed through the Rayleigh number, varied between (laminar regime). The analysis of heat transfer was conducted using the Nusselt number for different Rayleigh values. The results are represented by streamlines, isotherms, as well as velocity and temperature profiles. By analyzing these results, it can be concluded that an increase in the Rayleigh number leads to an increase in natural convection heat exchange inside the cavity.

Abstract: This study presents an analytical and numerical approach to thermosolutal mixed convection in a vertical rectangular cavity containing a Newtonian fluid of Prandtl number, Pr = 7. The vertical walls are mobile and subject to constant heat and mass fluxes, while the horizontal walls are considered impermeable and adiabatic. The mathematical model is based on the Navier-Stokes equations, as well as the conservation of energy and concentration equations. An analytical solution, based on the parallel flow approximation, has been developed for elongated cavities (A >> 1). At the same time, the governing equations were solved numerically using the finite-difference method. The results show that the analytical solution is in good agreement with the numerical one for all the considered parameters. Rayleigh number and Peclet number growth play roles in enhancing mixed convection, thus influencing the overall flow and heat transfer characteristics.

Abstract: Abstract. The topic of free convection thermal transmission through different geometrical shapes of enclosures is an engaging subject. It has caught the attention of the researchers during the last decades according to its significance in lots of engineering applications. Nuclear reactors, solar collectors, cooling electronic equipment, Oil wells, cooling electric components (as in the copper electric wires that are surrounded by the housing), and many industrial systems. Many parameters are discussed and analyzed to see their effect on the process of transferring heat such as: the effect of the geometrical shape, Nusslet number, and Rayliegh number. The studies were divided into seven categories based on the geometrical shape of the enclosure ( square , triangular, circular, trapezoidal, polygonal, elliptical, and wavy). The governing equations of the free convective thermal transmission were stated. The objective of this study is to collect the data from a large number of previous studies and compare them to reach a conclusion about the best results.

Abstract: Aerodynamics contributed directly on the energy efficiency and fuel consumption reduction of heavy vehicles in addition to its stability. The present study examines numerically the aerodynamics of heavy vehicles considering different drag-reduction devices using SolidWorks programme. Four different drag-reduction devices such as Base flaps, filled boat tail, Deflector and Rear offset plate in order to compare them with the baseline model. the results showed that the reflector contribute in more drag formation while Rear offset plate leads to lower drag.

Abstract: Biodiesel represents a renewable alternative fuel that reduces dependence on petroleum and lowers greenhouse gas emissions. In this study, biodiesel was produced from castor oil via alkaline transesterification to investigate the influence of temperature on mass transfer between the immiscible oil and alcohol phases. A series of transesterification experiments were carried out using methanol and a homogeneous alkaline catalyst (1.12 wt% KOH). The temperature was varied at 35 °C, 50°C, and 65°C to evaluate its influence on the mass transfer rate between the oil and alcohol phases. The molar ratio of methanol to oil was maintained at 14.12:1, and each experiment was conducted for a reaction time of 60 minutes. Increasing temperature significantly enhanced interfacial diffusion, reduced viscosity, and increased miscibility between the two phases. The intersection of TG and FAME curves occurred earlier at higher temperatures, at 65 °C, triglyceride (TG) conversion reached 92% within 10 min and approximately 99% after 60 min, while slower conversions were observed at 35 °C and 50 °C. Product composition and FAME yield were evaluated by GC-MS examination at the Ministry of Industry and Minerals' Industrial Research and Development Authority. Overall, the study highlights that optimized temperature conditions minimize mass transfer limitations, improves phase interaction and conversion efficiency also shortens the total reaction time supporting the creation of an effective and sustainable method of producing biodiesel process from renewable castor oil feedstock.