Natural Convection Heat Transfer Research Articles (Page 1)

This study presents a comprehensive numerical investigation of natural convective heat transfer in a wavy-walled enclosure filled with a hybrid nanofluid consisting of copper ( Cu ) and aluminum oxide ( Al2O3 ) nanoparticles dispersed in a water-ethylene glycol (EG) base fluid. Natural convection in such enclosures is widely encountered in electronics cooling, energy devices, and magnetic field-controlled thermal systems, which motivates the present study. A range of water-EG mixture ratios ( 95%−5%, 90%−10%, 80%−20%, 60%−40%, 50%−50%), including the limiting cases of pure water and pure EG, is considered to evaluate the influence of base fluid composition on thermal performance. The aim of this work is to clarify how variations in base fluid ratio,nanoparticle loading, and magnetic field strength affect convective transport. The governing equations are solved numerically using the finite element method to capture coupled buoyancy and magnetohydrodynamic effects. The nanoparticle volume fractions are systematically varied from 0.1% to 0.5% to capture the impact of particle loading, while the Rayleigh number ranges from 103 to 106, and the Hartmann number from 0 to 40 , to assess the effects of buoyancy and magnetic fields. The results show that increasing the Rayleigh number significantly enhances convective heat transfer, while variations in base fluid composition lead to only marginal differences in the average Nusselt number. For example, the average Nusselt number increases by nearly one order of magnitude as Ra rises from 103 to 106, while nanoparticle addition yields up to ∼ 18% enhancement, with copper providing the highest gains. In contrast, increasing Ha from 0 to 40 reduces the heat flux by as much as ∼ 22%. The inclusion of Cu and Al2O3 nanoparticles improves thermal performance, with copper demonstrating a greater enhancement due to its superior thermal conductivity. Furthermore, increasing the Hartmann number suppresses convective currents and reduces the total heat flux, especially near regions of high thermal activity. The wavy geometry intensifies convective mixing and promotes localized heat transfer, with observable peaks in the heat flux distribution aligned with the undulations of the hot wall. These findings highlight the synergistic effects of nanoparticle composition, base fluid selection, magnetic field control, and enclosure geometry on thermal transport, providing valuable insights for designing advanced cooling systems in electronics, energy, and thermalmanagement applications. These insights highlight the relevance of the results for designing advanced cooling systems in electronics, renewable energy devices, and thermal management technologies.

ABSTRACT Natural convection heat transfer from a closed vertical cylindrical vessel with a shroud has been investigated experimentally. The experimental study has been performed for the large‐diameter cylindrical vessel having a diameter of 0.8 m. The steam at atmospheric pressure has been injected into the vertical cylindrical vessel. The shroud around the vessel has been used to enhance the heat transfer performance. Experiments were conducted at different steam injection rates at atmospheric pressure and saturated steam conditions. The vessel outer wall temperatures and the air temperatures in the gap between the vessel and shroud at different vertical locations were measured during experiments using thermocouples. The heat transfer coefficients, Nusselt numbers, and Rayleigh numbers at different vertical locations have been calculated. The Rayleigh number varies from 4.48 × 10 7 to 6.03 × 10 9 based on the locations from the bottom to the top section of the closed vertical cylindrical vessel with ellipsoidal head. In the steady state, similar natural convection behavior of air between the vessel and shroud has been observed for different steam injection rates, as the outer wall temperature of the vessel at various vertical locations reaches a temperature close to that of saturated steam temperature, irrespective of the steam injection rate. The heat transfer coefficient was observed to decrease slightly from the bottom to the top vertical location on the vessel. The average heat transfer coefficient was found to be ≈ 7.98 ± 1.09 W/m 2 K. The variation in air temperature, vessel temperature, Nusselt number, and Rayleigh number along the vertical locations of the vessel has been discussed. The Rayleigh number was found to increase significantly along the height of the vessel. A correlation for the Nusselt number as a function of the Rayleigh number has been developed for the closed vertical cylindrical vessel with ellipsoidal head using experimental values. The comparison between developed correlation and well‐known published correlations has been performed. The values predicted by the published correlations were found to underpredict the results, possibly due to differences in shape and geometry.

Analysis for enhanced heat transfer in natural convection modified nanofluid with shaped optimized nanoparticles

Effect of buoyancy-induced natural convection heat transfer on thermal qualification of lead-shielded radioactive material transport packages

This research supports that renewable energy sources were used to power the drying process for design in a solar dryer, leading to the preservation of agricultural products and suitable preservation systems. The drying system involves complex physical atmospheric mechanisms, with relations between the dry air and the moisture content of each product, which affect the performance of solar drying systems. Steady laminar natural convection heat transfer formulas that are accurate based on a boundary-layer have been used to evaluate the flow caused by nonuniform density in an air flow based on dimensionless equations, and natural flow (buoyancy) inside the indirect solar dryer. Results show the heat transfer coefficient for natural convection 5 – 6 W/m2°C, heat energy 25 - 65 J/s, collector efficiencies 29 - 40.6 % and drying rate 0.18 - 0.98 kg/hr. The heat and mass increased according to dry-air flow through the dryer under trends of solar radiation 312 - 513 W/m2 and temperatures inside the indirect solar dryer 39.7 - 53.7°C, respectively, as ambient temperature 30.5 - 42.5°C, relative humidity 36 - 52% schedule 08:00 a.m. - 04:00 p.m. (daylight clear sky recorded). Experimentation, a test with a similar climate condition, with an initial moisture content of 85% to the final moisture content of 15% on a wet basis, showed a drying rate of 0.08 - 0.19 kg/hr.

Purpose This research explores natural convection heat transfer within a square cavity, simulating an electronic cabinet with finite-thickness solid walls and heated fins. The aim is to understand how different fin configurations and thermal properties impact heat dissipation and cooling efficiency. Design/methodology/approach This study uses dimensionless, two-dimensional partial differential equations with appropriate initial and boundary conditions. Computational simulations analyze key dimensionless parameters. These parameters include volume fraction (2% ≤ ϕ ≤ 6%), Hartmann number (10 ≤ Ha ≤ 100), Rayleigh numbers (104 ≤ Ra ≤ 106) and aspect ratio (0.1 ≤ AR ≤ 0.3). The average Nusselt number (Nuavg) is also examined. The analysis is conducted under constant temperature and insulated vertical wall conditions. This approach allows for a focused investigation of heat transfer characteristics. Findings Fins notably influence heat transfer efficiency within an enclosure. Thermal conductivity ratios play a significant role, with values above or below one either enhancing or reducing heat transfer compared to systems without fins. Increasing the number and size of fins boosts the heat enhancement factor. Different fin arrangements provide crucial information for improving thermal performance. Optimizing fin geometry is essential for maximizing heat transfer. These findings offer valuable insights for designing more effective thermal management systems. Originality/value This study uniquely examines natural convection in electronic cabinets, considering solid walls and heated fins. It analyzes fin geometry and thermal properties to improve cooling. This research offers practical insights for better thermal management in electronics. It provides key guidance for boosting cooling efficiency. By using realistic conditions, this work aids the design of more effective electronic cooling systems. It helps optimize thermal strategies.

Purpose This paper aims to study the natural convection from a heated T-open pipe of nanoencapsulated phase change material in a cavity. The impact of the presence of nanoencapsulated phase change materials (NEPCM) in water was studied on the thermal behavior of these novel nanoliquids in the presence of natural convection flows. The entropy generation for these nanoliquids was also investigated. Design/methodology/approach The NEPCM is modeled as a lumped phase change nanoparticle with a phase change material core and a polymer shell. The governing equations for a uniform mixture of NEPCM-water are written based on the conservation of mass, energy and also fluid motion. The natural convection effects were also taken into account. The finite element method was used to solve the governing equations. The entropy generation was also computed and studied. Findings Increasing the aspect ratio (AR) from 0.05 to 0.2 enhanced the average Nusselt number by 9%, while total entropy generation rose by 13%, indicating improved convective heat transfer near the bottom wall due to increased surface area. Enhancing the NEPCM nano particles volume fraction from 0 to 0.05 led to a 15% increase in heat transfer efficiency and a 9% rise in entropy, with negligible change in flow patterns. Growing the NEPCM fusion temperature from 0.1 to 0.5 slightly improved the Nusselt number by 5% and increased entropy by 3%, showing minor thermal gains with limited hydrodynamic impact. Practical implications NEPCMs have demonstrated significant potential in heat and mass transfer for cooling systems and thermal energy storage. Encapsulation technology has been widely used to improve the stability, specificity and bioavailability of essential food ingredients, as well as the performance of NEPCM suspensions in cooling applications. Additionally, the NEPCM suspensions use the latent heat of nanoparticles and can effectively control surface temperatures. Originality/value The natural convection heat transfer and the entropy generation of NEPCM suspension are addressed in an enclosure with T-open heated walls for the first time.

Innovative air duct-enhanced thermal management and natural convection heat transfer intensification in the busbar compartment of an air-insulated medium-voltage switchgear

Abstract This study investigated the role of fin flexibility to control the fluid flow on natural convection heat transfer within a square cavity containing a heated triangular block. Two flexible fins, attached to the cavity’s cold vertical walls, interact with an incompressible fluid under varying Rayleigh numbers (Ra) and elasticity modulus (Et), highlighting how these parameters affect thermal and fluid dynamics and the interaction between the top and the bottom regions of the cavity. The novelty of this study is to create passive control over the flexible fins to control the fluid flow and creating a separation between the top region or the bottom region using these mentioned parameters. Using the Arbitrary Lagrangian-Eulerian (ALE) technique, the fluid-structure interaction (FSI) model captured the bending response of the fins and the resulting convective heat transfer. Results indicated that lower fin rigidity (low Et) significantly enhanced thermal mixing and heat transfer due to increased fluid flow, driven by the bending of the fins at higher Ra. Hence, the top and the bottom regions of the cavity interacted with each other. Conversely, higher Et values restricted fluid circulation, maintaining thermal stratification and reducing heat transfer efficiency and separated these regions. This study provides insights into controlling and optimizing heat transfer in systems with flexible structures, with potential applications in thermal management and energy-efficient design.

Comment on “Nanoparticles impacts on natural convection nanofluid flow and heat transfer inside a square cavity with fixed a circular obstacle” [Case Studies in Thermal Engineering, 44 (2023) 102829

Simulation of natural convection heat transfer in dielectric liquids for single-phase immersion cooling rack server

Abstract Solar collectors play a crucial role in harnessing solar radiation and converting it into thermal energy, functioning as efficient heat exchangers. Among them, solar dish concentrators are particularly notable for their ability to operate at high temperatures, making them an effective solution for both heat and electricity generation. Owing to their high efficiency in capturing and utilizing solar energy, dish collectors have attracted significant interest in solar thermal applications. These concentrators come in various cavity receiver designs—such as open, spiral, hollow, and volume configurations—allowing for versatile energy conversion. Building on this concept, the present study investigates natural convection heat transfer within a two-dimensional ‘C’-shaped cavity filled with a porous medium and hybrid nanofluids, specifically Ag-MgO (silver-magnesium oxide) and Ag-TiO $$_2$$ 2 (silver-titanium dioxide oxide). The cavity features adiabatic upper and lower surfaces, with a heated slit on the left and a cooled wall on the right. As solar devices become more compact and efficient, the shape of the cavity plays a critical role in ensuring proper thermal management to prevent overheating and sustain optimal performance. To enhance heat transfer in solar collectors, the study applies a machine learning technique, evaluating the influence of two distinct hybrid nanoparticles. Furthermore, machine learning is used to analyze how different parameters vary with the type of nanoparticle, aiming to determine the most effective combination for optimizing heat transfer. The governing equations are solved using the finite difference method coupled with the Marker and Cell (MAC) technique. The findings indicate that an increase in the Rayleigh number improves heat transfer owing to intensified buoyancy-driven convection, with Ag-MgO exhibiting greater efficacy compared to Ag-TiO $$_2$$ 2 . Raising the nanoparticle volume fraction significantly boosts heat transfer at $$\textrm{Ra}=10^6$$ Ra = 10 6 , with Ag-MgO and Ag-TiO $$_2$$ 2 nanofluids showing improvements of 12.32% and 11.93%, respectively. ANN analysis identifies Darcy number, Rayleigh number, and nanoparticle volume fraction as primary influencers of Nusselt number. For Ag-MgO, their impacts are 37.15%, 22.15%, and 13.79%, while Ag-TiO $$_2$$ 2 shows similar contributions: 37.07%, 23.51%, and 13.79%. At 5% volume fraction, Ag-MgO outperforms Ag-TiO $$_2$$ 2 by 11.35% at $$\textrm{Ra}=10^5$$ Ra = 10 5 and maintains a 0.451% lead at $$\textrm{Ra}=10^6$$ Ra = 10 6 , indicating consistently superior thermal performance.

ABSTRACT This paper presents an experimental investigation of a finned heat sink to examine the combined effects of natural convection and radiation heat transfer with the property of introducing notches, perforations, and inclination. The results, when compared with the solid fin configuration, show a 26% increase in the average heat transfer coefficient (hav) and the average Nusselt number (Nus) for the case in a horizontal position as the removal area increased to 19.08%. Moreover, when the removal area reached 20.89%, the average heat transfer rate was enhanced by 32%.

Numerical modeling of natural convection heat transfer from a horizontally positioned tube layer immersed in a tank

This study investigated how microparticle size affects natural convective heat transfer in high-viscosity suspensions. Suspensions were formulated using 0.5% xanthan gum and 3% stearic acid, with particle sizes ranging from 120 to 750 nm. Key thermal properties, including thermal conductivity (0.598-0.679 W/m·K), specific heat, and the volumetric thermal expansion coefficient (0.990-1.000/°C), were measured. Rheological analysis based on the Herschel-Bulkley model revealed that reducing the particle size increased the consistency index from 0.56 to 0.75 Pa·s, while reducing the flow index from 0.63 to 0.50. This indicates enhanced shear-thinning behavior. A Rayleigh-Bénard convection system revealed that suspensions containing smaller particles exhibited higher Rayleigh and Nusselt numbers under large temperature gradients. Nusselt numbers reached values of up to 100 at a temperature difference of 9 °C. Conversely, suspensions containing larger particles exhibited relatively higher Rayleigh and Nusselt numbers under smaller temperature differences. These results demonstrate that optimizing microparticle size can enhance the efficiency of heat transfer in high-viscosity suspensions depending on the applied thermal gradient. This has practical implications for improving heat transfer in food and other viscous systems where convection is limited.

ABSTRACT The induced convective flow of three‐dimensional Casson nanofluid governed by a bi‐directional stretching surface has potential practical implications in numerous engineering fields, such as heat exchangers, cooling systems for heat‐generating devices, and more. This investigation aims to analytically examine the natural convection mechanism and heat transfer analysis of a Casson nanofluid inside a porous surface exposed to a uniform magnetic field. Moreover, this research explores the physical insights of thermal characteristics by incorporating the effects of chemical reactions, velocity slip, Brownian diffusion, and heat sources/sinks on the transient magnetohydrodynamic flow of the nanofluid. The proposed flow framework is described by a system of partial differential equations, which are transformed into dimensionless ordinary differential equations using appropriate variables. The closed‐form solutions of a set of leading characteristic dimensionless equations are obtained analytically through the efficient homotopic analysis method. Furthermore, stability and convergence analyses of the series solutions are performed to validate the computational results explicitly. The computational findings reveal a significant decrease in flow velocity, temperature, and particle concentration profiles as the Casson fluid parameter increases. Additionally, the effects on skin friction, Nusselt number, and Sherwood number are discussed in detail. This study aims to enhance the understanding of flow dynamics and heat and mass transfer mechanisms across various applications, offering valuable insights for engineering and scientific advancements. The authors accept that all the computational outcomes in this research, both analytical and numerical, are authentic and not published elsewhere.

Combined thermal radiation and buoyancy-driven conjugate natural convection in an inclined porous enclosure filled with Carreau fluid

A FORTRAN in-house code is elaborated to investigate the two-dimensional and laminar natural convection flow for a Newtonian fluid in an open square enclosure saturated with a nanofluid and subjected to an external magnetic field. Except for the bottom wall, which is heated with linear varying temperature, all cavity walls are held at a constant cold temperature. Applying magnetic fields in certain directions can serve to regulate and control fluid flow patterns and heat transmission for cooling electronic components. By embracing the stream function vorticity formulation, the physical phenomenon is modeled mathematically by a set of transport equations. The dimensionless governing equations are discretized utilizing the finite volume method and solved numerically using a relaxation iterative method. The examination of specific parameters encompassing the Hartmann number, nanoparticle volume fraction, magnetic field inclination angle, and Rayleigh number over a wide range was accomplished to understand their effects on heat transfer and flow patterns. The outcomes denote that, in convection heat transfer, regardless of the magnetic field’s inclination angle, increasing its intensity diminishes the volume of fluid drawn into the cavity and also causes poorer heat transfer and diminished fluid motion. Conversely, the incorporation of nanoparticles enhances heat transfer and influences fluid motion in distinct ways: It promotes fluid movement in the absence of a magnetic field, whereas in the presence of a magnetic field, it hinders fluid motion.

Purpose This study aims to examine how natural convection heat transfer and fluid movement function within star-shaped porous cavities containing Fe3O4-Al2O3/water hybrid nanofluid while being subjected to magnetic fields and thermal radiation. The study examines how magnetic field inclination and hybrid nanofluids interact with star-shaped geometries containing three, four, five and six points to enhance heat transfer mechanisms within intricate structures. This research investigates how geometry and multiple physical effects impact system performance to enhance thermal efficiency in irregular enclosure settings. In addition, the study explores entropy generation and the Bejan number to evaluate thermodynamic irreversibilities across geometries. Design/methodology/approach The development of a two-dimensional numerical model enabled the resolution of steady-state equations governing mass, momentum and energy conservation. The research varied key dimensionless parameters such as the Rayleigh number (Ra), Hartmann number (Ha), thermal radiation (Rd) and nanoparticle volume fraction (ϕ) to determine their influence on the stream function (Ψ), temperature field (θ), entropy generation (Sgen), Bejan number (Be) and Nusselt number (Nu). The finite element method enabled numerical simulations, which led to the creation of an empirical correlation for average Nusselt number and entropy generation using Ra, Ha and ϕ parameters. Findings The six-point star geometry achieves the most homogeneous heat distribution, whereas the three-point star geometry achieves maximum localized heat transfer enhancement when magnetic field inclination reaches p/2. Localized Nusselt number enhancement reaches up to 37% from the three-point star configuration when influenced by magnetic field inclination. The six-point star geometry achieves up to 42.6% higher average Nusselt number when the nanoparticle volume fraction rises from 0% to 30%. The research illustrates how buoyancy-driven flow, magnetic damping and improved thermal conductivity from nanoparticles combine to affect thermal performance, while entropy maps and Bejan number fields offer insights into irreversibility patterns. The empirical correlations created during this study serve as tools to predict and optimize both heat transfer and entropy generation performance. Originality/value The investigation provides novel understanding of how hybrid nanofluids interact with magnetic field orientation and atypical porous cavity forms. The study’s systematic analysis of star-shaped cavities reveals a new method to boost thermal performance in complex shapes. Current literature lacks studies that combine magnetic field inclination, radiation effects and hybrid nanofluids in star-shaped cavities. The new empirical correlation alongside performance maps offers valuable tools for designing thermal systems that include solar collectors and electronic cooling systems as well as porous enclosures with complicated geometries, where managing both heat transfer and thermodynamic irreversibility is critical.

Abstract This study employs the Taguchi method to determine the optimal design parameters for fin arrays attached to a cylinder under natural convection. The research investigates the effects of fin material, heat input, cylinder tilt angle, and the number of fins on the net heat transfer rate. Using the Nusselt number as the performance parameter, an $$L_{16} \ (4^3 \cdot 2^1)$$ L 16 ( 4 3 · 2 1 ) experimental plan was selected to identify the optimum design for maximizing natural convection heat transfer. A notable aspect of this study is the use of functionally graded annular fins composed of aluminum and copper, in addition to homogeneous aluminum fins. The results from the Taguchi method indicate that optimal heat transfer is achieved with a heat input of $$Q_0 = 150 \ \text {W}$$ Q 0 = 150 W , the number of fins $$N = 7$$ N = 7 , tilt angle $$\theta = 0^\circ$$ θ = 0 ∘ , and functionally graded material for the fins. These findings demonstrate that functionally graded materials enhance heat transfer by 18% compared to homogeneous aluminum fins.