Natural Convection Research Articles

Study on three-dimensional natural convection heat transfer in a house with two heating surfaces

Study on three-dimensional natural convection heat transfer in a house with two heating surfaces

Optimization of Ionomer for High‐Performance Self‐Humidifying Air‐Breathing Proton‐Exchange Membrane Fuel Cells in Portable Device Power Systems

This study investigates the impact of ionomer types and content in the catalyst layer on the performance of proton exchange membrane fuel cells (PEMFCs) under room temperature and atmospheric pressure. Four commercially available ionomers with varying equivalent weights (EWs) and side‐chain lengths are evaluated as catalyst layer binders in membrane‐electrode assemblies (MEAs). The assessments are conducted at room temperature and ambient pressure without additional humidification, focusing on understanding the distinctive characteristics of each ionomer. In addition, this study investigates the prospective application of an air‐breathing passive‐type cell, dependent exclusively on natural convection for air supply. The notable performance of the passive‐type cell shown in this study indicates its suitability as a compact mobile power source, especially for drone applications. Furthermore, the stability of various ionomer binders is also compared to establish a correlation between EW and side‐chain length of ionomer binder stability. Overall, the findings will serve as a valuable reference for optimizing ionomer selection and composition in specialized applications for powering portable devices.

Hybrid Nanoparticle-Enhanced Fluid Flow and Heat Transfer Behaviors in a Parabolic Cavity with a Heat Source

AbstractNatural convection of nanofluids holds considerable importance in both scientific research and engineering applications due to their exceptional heat transfer capabilities, which occur spontaneously without the need for additional energy input. In this paper, the natural convection of nanofluid inside a parabolic cavity containing a hot obstacle is studied numerically. The shape of the hot obstacle is selected as either circular or elliptical. Additionally, the effects of the Rayleigh number, nanoparticle volume fraction, and the position of the heat source are investigated. The computational fluid dynamics model was computed using COMSOL Multiphysics. It is observed that the average Nusselt number tends to increase with both the Rayleigh number and the volume fraction of nanoparticles in the fluid. When the heat source moves from the bottom region to the top area, the heat transfer performance of the heat source increases. When Ra ≤ 105, the cases with circular heat sources exhibit better heat transfer performance than those with elliptical heat sources. However, at Ra = 106, the average Nusselt number of the elliptical heat source is higher than that of the circular one.

Reevaluation of Plate-Fin Heatsink Natural Convection Correlations for Sideways and Three-Dimensional Inclinations

The common orientations of the plate-fin heat sink for natural convection cooling of electronics are vertical and upward-facing horizontal. However, depending on various use scenarios, the heat sink may be inclined, intentionally or otherwise. In our previous papers concerning this subject, the author proposed a set of correlations for plate-fin heat sinks covering all inclination angles backward and forward (pitch rotation) from the vertical position of the heat sink. The set was based on a series of computational simulations with a validated model. At the time, tilting the heat sink sideways (roll rotation) was not considered. In the present study, though, the sideways inclination of the plate-fin heat sinks is simulated using our previous model only by adjusting the direction of the gravitational acceleration vector, thus requiring no additional validation. It is determined that the previously proposed correlation is valid up to 80° sideways inclinations of the heat sink. Interesting flow structures are observed when the heat sink is tilted 90° sideways. Furthermore, it is demonstrated that the correlation surprisingly remains valid if the heat sink is simultaneously rotated in both axes (pitch and roll).

Thermal management for the prismatic lithium-ion battery pack by immersion cooling with Fluorinated liquid

This study constructs a novel FS49-based battery thermal management system (BTMS), proposing an optimization method for the system energy density and an indirect control method for the system cooling capacity. The boiling of dielectric refrigerant occurred at the battery surface, which provided strong and uniform cooling for each battery cell. The results show that the peak temperature difference of liquid immersion cooling (LIC) module during 1C rate discharging and charging was reduced by 91.3% and 94.44%, respectively, compared to the natural convection (NC) module. The reduction of temperature nonuniformity greatly reduced the state of charge (SOC) inhomogeneity of different cells within the module. Moreover, the energy density of LIC module can be optimized by reducing the cell spacing and liquid filling ratio. Comparing with 100% filling rate, the module maximum temperature corresponding to 25% filling rate (with wick) during 2C rate discharging is only increased by 1.6℃, however, the module peak temperature difference is reduced by 53.3%, and the energy density is increased by 13.14%. In addition, Equivalent circuit model (ECM) and volume of fluid (VOF) model were used to simulate the LIC module, and the numerical results are in good agreement with the experimental data. This study provides a systematic design plan and numerical method for the engineering application of LIC in the field of BTMS.

Cascaded lattice Boltzmann simulation of Newtonian and non-Newtonian mixture nanofluids with variable thermophysical properties in a cavity with vertical heat radiator

The central moments-based cascaded lattice Boltzmann method (CLBM) for then Newtonian and non-Newtonian Buongiorno’s model mixture nanofluids (CuO, ZnO, Al2O3-water) has been implemented and applied in a square chamber with a vertical heat radiator using accelerated graphics processing unit (GPU) computing through compute unified device architecture (CUDA) C/C++ platform. Due to the higher numerical stability, the CLBM is a superior numerical tool to the raw moments-based MRT-LBM (multiple-relaxation-time lattice Boltzmann method). Three different models for the viscosity and thermal conductivity of the nanofluids: (i) the Binkmann model for the constant viscosity and the Maxwell model for the constant thermal conductivity (ii) Binkmann and Maxwell model with temperature dependent Brownian motion and (iii) Corcione model with non-Newtonian fluid where the temperature and strain rate determine the nanofluid effective thermal conductivity and viscosity, have been used. The enclosure’s upper and bottom walls are thermally adiabatic, but the left and right walls are uniformly cold. A vertical heater is immersed in the middle position of the cavity. The benchmark results for non-Newtonian, Newtonian, and nanofluids for the various computational domains are used to validate the current code adequately. The Bingham number (Bn), the Rayleigh number (Ra), and The volume fraction of the nanoparticles (ϕ) are the three key parameters that are varied in this investigation to demonstrate the effects of natural convection on the isotherms, streamlines, isolines of nanoparticle volume fractionation, yielded and unyeilded zone, and average Nusselt number (Nu¯). The Brownian motion effects of the nanoparticles augmented the average rate of heat transfer and the use of the Bingham nanofluids reduced the heat transfer enhancement. For the CuO-water nanofluid, the augmentation of the rate of heat transfer is 15.42% from ϕ=0 to 4% while Ra=106 and the corresponding heat transfer enhancement for the ZnO-water nanofluid is 11.11%. For the Bingham fluid, the rate of heat transfer increases 7% from Ra=105 to Ra=106 while ϕ=2% and Bn=0.3. The findings can be applied to optimize automotive radiator systems, which are crucial for maintaining engine temperature.

Thermal performance of nanofluid natural convection magneto-hydrodynamics within a chamber equipped with a hot block

In this study, flow and free convection thermal performance within a chamber in the presence of a permanent magnetic field are simulated. Boussinesq approximation and the Lorentz force equation are used for the density variation in free convection, and the magnetic field, respectively. The steady-state, two-dimensional, and incompressible governing equations are simulated using the Semi-Implicit Method for Pressure Linked Equations (SIMPLE). The present study is simulated for different Rayleigh numbers (Ra) corresponding to the situation where the conduction mechanism was predominant (Ra = 100) and the convection heat transfer was predominant (Ra = 105). Also, different intensities of the magnetic field (0 ≤ Ha ≤ 40) and different directions of the magnetic field along with the effects of three different nanoparticles Ag, Cu, and Al2O3 are given. The present study showed that in the case of the dominant convection mechanism, the presence of the magnetohydrodynamics (MHD) condition decreases the Nusselt number (Nu). However, if the conduction is predominant, the applied magnetic field improves the average Nu number. The optimum state for the magnetic field strength was found in the low Rayleigh number. The presence of nanoparticles also intensifies the magnetic field effects. In the high Rayleigh number, the heat transfer rate reduces by 13.5% with the increase of the Hartmann number.

Exploring Natural Convection and Entropy Generation in a Closed Water Tank Utilizing Nanofluid: a Computational Study

Theoretical framework: This study presents a comprehensive investigation into three-dimensional natural convection within a confined cavity filled with an alumina-water nanofluid. Objective: Utilizing numerical simulations, we explore the influence of nanoparticles' volume fraction and Rayleigh number () on entropy generation, heat transfer efficiency, and fluid behavior within the water tank. Method: The study delves into the conservation equations governing mass, momentum, and energy within the context of three-dimensional laminar natural convection. It focuses on steady, incompressible flow, employing the Boussinesq approximation to account for variations in fluid density due to temperature gradients. Results and conclusion: Our findings indicate that increasing Rayleigh numbers lead to heightened entropy generation, with values ranging from to, primarily driven by intensified buoyant flow. However, the presence of nanoparticles significantly mitigates entropy generation, enhancing the overall thermal performance of the system. Moreover, nanofluids demonstrate superior heat transfer capabilities compared to pure fluids, with higher nanoparticle concentrations resulting in increased heat transfer rates, ranging from to alumina. Research implications: As a result of such thorough research, qualitative examinations of velocity fields and entropy generation patterns further highlight the role of nanofluids in improving heat transfer efficiency while reducing irreversible processes within the cavity.

Numerical Analysis of Natural Convection in an Annular Cavity Filled with Hybrid Nanofluids under Magnetic Field

This paper presents a numerical study of natural convection in an annular cavity filled with a hybrid nanofluid under the influence of a magnetic field. This study is significant for applications requiring enhanced thermal management, such as in heat exchangers, electronics cooling, and energy systems. The inner cylinder, equipped with fins and subjected to uniform volumetric heat generation, contrasts with the adiabatic outer cylinder. This study aims to investigate how different nanoparticle combinations (Fe3O4 with Cu, Ag, and Al2O3) and varying Hartmann and Rayleigh numbers impact heat transfer efficiency. The finite volume method is employed to solve the governing equations, with simulations conducted using Fluent 6.3.26. Parameters such as volume fraction (ϕ2 = 0.001, 0.004, 0.006), Hartmann number (0 ≤ Ha ≤ 100), Rayleigh number (3 × 103 ≤ Ra ≤ 2.4 × 104), and fin number (N = 0, 2, 4, 6, 8) are analyzed. Streamlines, isotherms, and induced magnetic field contours are utilized to assess flow structure and heat transfer. The results reveal that increasing the Rayleigh number and magnetic field enhances heat transfer, while the presence of fins, especially at N = 2, may inhibit convection currents and reduce heat transfer efficiency. These findings provide valuable insights into optimizing nanofluid-based cooling systems and highlight the trade-offs in incorporating fins in thermal management designs.

Analysis of heat transfer modes in the cooling of blocks generating different heat quantities

Achieving improved cooling efficiency and control in electronic components with varying heat outputs can be realized through a thorough analysis of different heat transfer modes, focusing on their contributions and interactions within the system. The analysis is conducted within a cavity containing three circular blocks generating varying amounts of heat. The blocks are affixed to an insulated plate, dividing the cavity into two identical sections with different fluids and different cooling mechanisms. In the open portion of the divided cavity, block cooling is achieved through forced convection using a nanofluid, while the closed section dissipates heat through natural convection and surface radiation. The numerical solution of the governing equations is performed using Galerkin's Finite Element Method, with detailed examination of the cooling process considering various parameters, such as block displacement (1.5cm≤y1≤3.25cm) and dimensions (0.25cm≤R≤1.5cm), Reynolds number (10≤Re≤1000), nanoparticles nature and volumetric fraction(0 %–10 %), emissivity (0≤ε≤1), thermal heat ratio(0.125 to 8), and cavity inclination angle(0°–180°). The results show that the combination of natural convection and surface radiation can be highly effective, rivaling forced convection in cooling the blocks. The study shows that an increase in the Reynolds number results in a temperature reduction of up to 6 °C, while increasing the emissivity leads to a more significant drop of around 10 °C. Additionally, miniaturizing the blocks by reducing their radius by a factor of six causes the maximum temperature to rise by over 20 °C.

A hybrid numerical approach for characterising airflow and temperature distribution in a ventilated pallet of heat-generating products: Application to cheese

Temperature control throughout the cold chain is of crucial importance in the preservation of the quality of cheese. As a result of cheese heat generation, both natural and forced convection need to be considered. This numerical study aimed to characterise the airflow and temperature fields within a ventilated pallet of heat-generating cheeses. An original computational fluid dynamics (CFD) hybrid approach was developed. This approach is based on a combination of a porous media approach for the contents of the boxes and a direct CFD approach for the outer cardboard walls, including vent size and position. The computational domain is limited to one pallet level. The simulations were conducted on a steady state for two upwind air velocities 0.31 m/s and 0.73 m/s and three generated heat fluxes 0.05 W, 0.15 W, and 0.3 W per product item (250 g). The model was validated by comparison with experimental results related to velocity and product temperature profiles obtained on a full-scale experimental set-up. The hybrid approach shows good accuracy while reducing the mesh size and the computational time in comparison with the direct CFD approach.

Natural Convection in an Open and Wavy Porous Cavity Submitted to a Partial Heat Source

Natural Convection in an Open and Wavy Porous Cavity Submitted to a Partial Heat Source

Effect of heat production on MHD natural convection transport of nanofluid flow via a vertical uniform perforated plate: An unsteady analysis

This article statistically investigates the impact of heat production on the unstable MHD natural convection transport of nanofluid flow via a perforated sheet. The ordinary differential equations (ODEs) are derived from the partial differential equations (PDEs) by using of the similarity transformation. The dimensionless ordinary differential equations (ODEs) may be numerically resolved with the help of the MATLAB ODE45 tool and the finite difference method (FDM) along with the shooting strategy. Four innovative water-based nanofluids such as TiO2, Cu, Al2O3, and Ag are considered nanoparticles. The numerical results have been explained for the role of numerous non-dimensional numbers or parameters such as heat generation or absorption (Q), nanoparticle volume fraction (φ), Dufour number (Df), Prandtl number (Pr), magnetic force parameter (M), Soret number (Sr), and Schmidt number (Sc) on the fluid flow, and heat and mass transfer rates. The fluid temperature drops but velocity is enhanced for higher amounts of Q. Copper nanoparticle volume fraction up to 4 % shows a rise in temperature, concentration, and velocity curves. Heat transfer rate ( − θ′(0)) diminishes by about 124 %, while the values of f′(0) promote by approximately 26 % owing to an increase in the values of Q (heat generation) from 1.0 to 2.0. The value of ( − θ′(0)) increases by 49 %, but f′0 decreases by 15 % due to a rise in Q (heat absorption) from -3.0 to -10.0. The local skin friction coefficient (f′(0)) diminishes by about 65.21 % due to an increase in the values of the magnetic force parameter (M) from 0.5 to 3.5 whereas the rate of heat and mass transfer remain unchanged. As φ increased from 0.01 to 0.04, the local skin friction coefficient (f′(0)) exhibited a 36 % increase, while the heat transport rate (θ′(0)) decreased around by 10 %. In conclusion, a comparison was made between our findings and those of the published research. The comparison indicates a high degree of consistency.

Exploring the Influence of Vibration on Natural Convection in Hybrid Nanofluids via the IB-STLBM

Exploring the Influence of Vibration on Natural Convection in Hybrid Nanofluids via the IB-STLBM

Numerical Study on the Impact of the Richardson Number on Convection in an Enclosure, with Moving Sidewalls for Three Aspect Ratios: A = 1, 2 and 0.5

Using mathematical models, this research investigation seeks to explore how varying aspect ratios and the Richardson number impact the mixing effectiveness, fluid flow velocity, and heat transfer characteristics in a rectangle-shaped space where cooling occurs along the sides and warm with a steady temperature exists throughout the 80% of the bottom section's center. Discretizing the governing equations through the finite volume approach, we solved them iteratively using the Tri-diagonal Matrix Algorithm, where pressure-velocity coupling was successfully implemented via the SIMPLER procedure. Innovative approaches for convection and diffusion terms involved employing a power-law difference scheme alongside a central differential scheme. In various simulations with specified parameters (Re = 100, Pr = 0.71), we visualized results in forms like streamlines, isothermal lines, and temperature/velocity profiles, along with local and average Nusselt numbers. We observe five unique structure formations during flow behavior by analyzing how Richardson numbers impact heat transmission within a specific geometric configuration (enclosure size A = 1). A change in aspect ratio leads to improved control over fluid movement while minimizing structural distortion. A subtle rise in heat transmission emerged as the average Nusselt number and Richardson number intersection strengthened force convection's domination while experiencing significant escalation under conditions conductive to natural convection. Decreasing the aspect ratio increased heat transfer efficiency when the Richardson number rose.

Numerical study of the porous cavity with different square size vanes with a high focus on Nusselt number

This study extensively analyzes various regular and irregular vanes in pipe porous cavities on natural convection, thermal entropy generation, stream function, and temperature distribution in fluid and solid phases. The finite element method (FEM) is employed to study stream function, temperature distribution in the fluid phase and solid phase, and various γ for Nuf, ave and Nus, ave in SR, TR, SIR, and TIR. In the present study, a significant contribution of this research is the investigation into the effects of regular versus irregular vanes in the context of enclosures formed by pipe porous cavities that the SIR specimen has the most influence on stream function and thermal effect in the fluid phase and solid phase that aims to enhance system performance and optimize energy efficiency. In addition, the significant influence of geometrical parameters constitutes many heated obstacles in the middle of SIR, various heated vanes in the left of SIR, and employed Ra and ε in the analysis of Nuf, ave and Nus, ave in SIR are carried out to investigate the percentage discrepancies obtained, notably 89.35 % and 89.72 %, respectively. In validation, the calculation in results was adapted accurately to the finite element method's stream function, the temperature distribution in the fluid phase and solid phase, and various γ for Nuf, ave and Nus, ave which means that the percentage differences in obtaining results reached under 1 %. Numerical results revealed that the Hartman number has a significant influence in Shtf, ave, Shts, ave, Tyave, Nuf, ave and Nus, ave in TR, SR, TIR, and SIR.

Natural convection of Al2O3–Cu/water hybrid nanofluid within a tilted cavity: Investigation of effect of thermal boundary conditions and angle of magnetic field

The project focuses on simulating natural convection in a tilted quarter-elliptical chamber filled with [Formula: see text]–Cu/Water hybrid Nanofluid, influenced by a magnetic field (MF) at various angles. The chamber’s elliptical shape is modelled with a constant height-to-length ratio of 2. The chamber’s curved wall is cold, while one smooth wall is adiabatic, and the larger wall undergoes three types of heating. The Hartmann number (Ha), MF angle ([Formula: see text]), chamber wall heating type, inclination angle ([Formula: see text], and Rayleigh number (Ra) are studied. Results indicate that increasing Ra leads to enhanced convection and a higher average Nusselt number. At [Formula: see text], heat transmission is primarily through conduction, resulting in the lowest flow power. The presence of a MF slows down heat transportation, especially at [Formula: see text]. The MF’s impact is most significant when applied at a [Formula: see text] angle. Constant temperature chamber wall heating yields 75% and 85% higher average Nusselt values compared to sinusoidal and linear heating, respectively. The worst scenario occurs at [Formula: see text], where the computed Nusselt values and current power are lowest, highlighting the MF’s influence. According to the study, when thermal boundary circumstances and MF angles are just right, the [Formula: see text]–Cu/water hybrid nanofluid greatly improves the transfer of natural convection heat in a tilted cavity. This suggests that thermal management in cooling structures, electronics, and energy-efficient buildings may be improved.

Thermal Stress Analysis of Compact Heat Exchanger Produced by Additive Manufacturing

Abstract Compact heat exchangers are renowned for their high heat transfer rates and efficiency, achieved by incorporating mini and micro-channels in their core design. However, operating under conditions of high-pressure fluctuations and significant temperature differences between hot and cold streams can potentially induce fatigue failure. To the best of our knowledge, this study represents the first investigation into the thermal stresses experienced by heat exchanger samples manufactured by selective laser melting technology, focusing on circular channels. Experiments were conducted using hot water in the inner channel, while the remaining channels and the sample surface were subjected to natural convection in ambient air. Strain gauges, thermocouples, and RTDs were employed to measure strain and temperature variations over time. These data were utilized as inputs for a numerical model based on finite element method. The strain measurements were compared with those obtained from the numerical model, revealing an average difference of approximately 20%. Lastly, a thermal fatigue analysis based on the maximum equivalent stresses predicted by the numerical model is presented. The evaluation considered both S-N curves: outlined in the ASME standard and the one obtained with specimens produced through selective laser melting. In the case of circular channels manufactured through additive manufacturing evaluated in this work, thermal stresses alone are insufficient to cause component failure due to fatigue. However, significant pressure cycles superimposed on the model can reverse this situation, making the combined effect of thermal and mechanical stresses influential in determining the component's fatigue behavior.

Experimental study on a direct-expansion micro-channel PV/T evaporator using water-ZnO nanofluid as the spectral beam splitter

Introducing nanofluid (NF) as the spectral beam splitter (SBS) in photovoltaic/thermal (PV/T) evaporators can significantly enhance their performance and energy flexibility. In this study, a novel direct-expansion micro-channel evaporator using water-ZnO nanofluid as SBS (i.e., NF-MC-PV/T evaporator) was manufactured. Particularly, the stability of low-viscosity water-ZnO nanofluid was first optimized and natural convection within the NF-MC-PV/T evaporator was directly formed. Further, a direct-expansion heat pump system based on the NF-MC-PV/T evaporator was developed and tested. According to the findings, adding sodium hexametaphosphate as a dispersant with the dispersion ratio of 1:5 and ultrasonic treatment for 1.5 h can achieve the optimal stability of water-ZnO nanofluid. The nanofluid's natural convection can reduce the evaporator's operating temperature and improve the PV module's temperature distribution uniformity. Specifically, the NF-MC-PV/T evaporator's operating temperature was lower than the environment temperature and a pure PV module. Besides, the PV module's temperature distribution was uniform in the direction perpendicular to the refrigerant flow with a max temperature gradient of only 4.59 °C. The typical photothermal efficiency of the NF-MC-PV/T evaporator reached 102.55 % while the heat loss coefficient was only 4.37. Moreover, the average photothermal efficiency, photovoltaic efficiency, and COP of the system were 103.58 %, 12.03 %, and 5.09, respectively.

Enhanced Peltier refrigerator using an innovative hot-side heat-rejection mechanism; Experimental study under both transient and steady-state conditions

Peltier refrigerators are an environmentally friendly cooling method, as they require no refrigerants and have no moving parts. However, effective cooling requires optimal-strong heat rejection from the hot side of the Peltier module. This research proposes and tests a self-capillary ultra-thin (0.1 mm) water-attracting coated PVC membrane (SCCP) as an innovative effective heat rejection mechanism. The SCCP cools the hot side of the Peltier module to temperatures even lower than ambient air, without external power. The cooling effect is achieved through the evaporation of a thin water film on the hot surface, driven by capillary action, which releases latent heat. This process can occur under natural or forced convection, both of which are investigated under various voltage and temperature conditions. The SCCP method was compared to traditional heatsinks and showed superior performance, with the hot side temperature being not only cooler than that in heatsink mode but also cooler than the ambient temperature in most cases. Additionally, the SCCP method demonstrated reduced sensitivity to ambient temperature changes, with only a 2–3° increase in the hot side temperature when the ambient temperature was raised by 10°. The findings suggest that SCCP is a promising technique, with further results discussed.