Papers by Keyword: Natural Convection

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 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: In this study, natural convection of a hybrid nanofluid inside a cubic cavity under the influence of a constant external magnetic field is numerically investigated by using control volume method. The cavity is partially heated from the left wall with uniform temperature and cooled from the opposite wall while the other sides are kept adiabatic. Analysis is focused on the impact of some parameters, including Hartmann number (0≤Ha≤100), Rayleigh number (10³≤Ra≤10⁶), nanoparticle volume fraction (0≤Φ_s≤0.06) and heater band width (1/3≤ ɛ ≤1). The Analysis of the results related to the dynamic and thermal structures, as well as the average Nusselt number, revealed that the effect of the external magnetic field exerts a negative influence on heat transfer within the cavity. However, more favorable findings were observed when the volume fraction of nanoparticles was increased, as well as when the width of the heater band was increased.

Abstract: Lattice boltzmann method (LBM) has emerged as a powerful numerical technique for simulating fluid flows due to its inherent simplicity and efficiency. In this paper we studied a convective heat transfer occurring naturally within a cubic enclosure differentially heated filled with air (Pr=0.71) to compare the obtained results with those obtained from the literature. For this a fortran code program utilized for simulating natural convective phenomena in two and three dimensions (2d and 3d LBM) considerate a single relaxation time LBM (SRT-LBM). The results are presented in terms of isotherms, velocity and average nusselt number. The verification of the lattice boltzmann method code shows a good agreement with the literature.

Abstract: This article presents a comprehensive numerical study of natural convection in a water-filled triangular cavity using the multi-relaxation time lattice Boltzmann method (MRT-LBM). The main objective of this study is to thoroughly analyze the influence of the heated chip's position along the left wall and the Rayleigh number on crucial aspects such as isotherms, streamlines, velocity, and temperature profiles, as well as the Nusselt number. In this setup, the hypotenuse wall is kept completely cold, while the other parts of the left wall and the bottom wall are adiabatic. Simulations are conducted for three different positions of the heated chip, with Rayleigh numbers, Ra, set at 10³ and 10⁵. The results of these investigations reveal that the heating position plays a crucial role in optimizing control, providing significant implications for various applications. Validation results demonstrate satisfactory agreement with existing literature, reinforcing the robustness and reliability of our numerical approach based on MRT.

Abstract: Effective thermal management is essential for maintaining the performance and reliability of high-power semiconductor devices. This study presents a combined numerical and experimental evaluation of heat sink geometries under natural convection cooling to reduce junction temperatures in compact electronic packages. A three-dimensional finite volume model was developed in ANSYS Fluent to simulate the thermal behavior of a semiconductor package consisting of a chip, controller, thermal pad, and heat sink. The model was validated experimentally using thermocouples and a data acquisition system, with simulation results closely matching measured data, showing errors below 0.5%. Parametric investigations were conducted to assess the effects of heat sink fin number, fin height, and fin shape on junction temperature. Results showed that increasing the number of fins initially enhances heat dissipation, with an optimal range observed between 6 and 8 fins. Fin height had a strong influence, with taller fins significantly reducing junction temperature, up to 29.66 °C compared to the baseline model. Among the evaluated shapes, parallel and pin-fin heat sinks achieved the best performance, with over 23 °C reduction in junction temperature, while the wavy-fin design was less effective due to induced airflow disturbance. These findings provide practical insights into heat sink geometry optimization for passive cooling systems and offer guidance for thermal design in high-performance semiconductor applications.

Abstract: Natural convective in enclosures are very important topics in thermal engineering because they find versatile industrial applications. An internal circular cylinder's vertical position and heat source on fluid flow and heat transfer in a triangular cavity are investigated. Numerical simulations were carried out to analyze variations in the average Nusselt number, streamline topology, temperature distribution, and velocity fields by using ANSYS Fluent. The results show that the Nusselt number rises from approximately 0.91–0.94 at lower positions (Y = 0.1–0.3) to a maximum of about 0.97 near Y = 0.4 driven by intensified thermal gradients and buoyancy-induced circulation. Within the upper-to-mid region (Y = 0.2–0.4) the formation of large adjacent vortices enhances macro-scale mixing, resulting in nearly a 4% improvement in heat transfer relative to the reference case. At mid-level positions (Y = 0.4–0.6) quasi-steady symmetric circulations are sustained, maintaining effective convection with Nu values of 0.95–0.97. In contrast, at higher locations (Y = 0.7–0.9), the weakening of vortex strength leads to flow stagnation and localized deterioration in heat transfer, reducing Nu to about 0.90–0.92. Overall, the findings underscore the critical importance of internal component placement in improving natural cooling performance, and further suggest that the most efficient thermal behavior is achieved when the cylinder and heat source are positioned within 0.2 < Y < 0.4, offering practical guidance for optimizing the thermal design of triangular enclosures.

Abstract: This work offerings a numerical study of natural convection heat transfer within a triangular enclosure having a centrally positioned cylindrical heating source. The effect of the heat source size is investigated by varying its non-dimensional diameter from 0.1 to 0.5. The eating source cylinder and enclosure are maintained at constant temperatures. The buoyancy-driven flow field is analyzed using streamline distributions, non-dimensional velocity magnitudes, and isotherm contours. Results reveal that the size of the internal heating source significantly affects the thermal performance of the combined structure. For small values of , the flow remains weak and localized, with limited convective motion. As increases to moderate values ≈0.3, recirculation regions intensify, velocity fields expand, and thermal plumes rise symmetrically, which indicates enhanced convective transport. However, additional increasing of values leads to flow constriction, reduced circulation strength, and causes less effective heat transfer. It is found that the average Nusselt number decreases with increasing due to diminished temperature gradients and restricted fluid motion despite the larger surface area provided by bigger cylinders. The results are applicable for the design of passive electronic cooling systems, solar thermal collectors, and other natural heat convection-based enclosures.

Abstract: Drying is the fundamental process for preserving agricultural products and food items, requiring a significant amount of energy. There are quality issues associated with the conventional drying processes and methods. The conventional drying methods are prone to the inclusion of impurities and surface damage, and their drying rates are very slow. In this research, a Concentrated Direct Forced Convection Solar Dryer (CDFCSD) dryer, having two DC brushless fans to regulate the air, was used to dry the test specimens, and the results were compared with the performance of a Direct Natural Convection Solar Dryer (DNCSD). The apple samples were selected as the test product. The drying process involves slicing the apples and placing them into the dryer. The apples were weighed before and after each drying mode, and moisture removal was evaluated and compared. The results show that moisture content removal was 58.15% in the Concentrated Direct Forced Convection Solar Dryer (CDFCSD) and 51.85% by the Direct Natural Convection Solar Dryer (DNCSD). 6.3% more moisture was removed using CDFCSD as compared to DNCSD, which shows a better effective moisture extraction rate using CDFCSD.