In this work, the natural convective transport was numerically investigated for nanofluids in a metal-foam cavity. A lattice Boltzmann (LB) model for the nanofluid natural convection in a porous ...medium was established by using the volume-averaging method. The velocity and temperature fields were obtained, and flow and thermal characteristics of the nanofluid convection in a porous medium were presented. The effects of the Rayleigh Number, the Darcy Number, the porosity, the solid thermal conductivity of porous medium, the nanoparticle thermal conductivity and the nanoparticle concentration on natural convection were examined. The average velocity was put forward to evaluate the convection effect and the natural convection onset was also discussed. It is shown that the Nusselt number of the natural convection increases with an increase in the Darcy number, the Rayleigh number, the porosity and the effective thermal conductivity. The change from the heat conduction regime to the convection regime is clearly shown from the numerical result, which verifies the onset point of the nanofluid natural convection in a porous medium. The highly conductive porous foam and the nanofluid can promote the thermal performance of the natural convection, which own great potential in practical thermal applications.
Phase change materials (PCMs) are capable of storing energy as latent energy by changing the phase and provide the stored energy when they are returned to their initial phase at a desired time. Due ...to the varying melting temperature of these materials, their application in air conditions of buildings, as well as the provision of hygienic hot water has received much attention, recently. This paper first provides a detailed illustration of phase change materials and their working principle, different types, and properties. Then a characteristic example of PCMs in solar energy storage and the design of PCMs are reviewed and analyzed. Next, this paper focuses on the heat transfer, melting and freezing processes of PCM/nano-PCMS including different models and experimental research on the natural convection and thermal energy storage. Finally, some challenges and suggestions are presented following the conclusion of this article. It is found that these materials generally improve system efficiency. Without using mechanical equipment, these materials are naturally adapted to the temperature fluctuations of the environment, leading to a reduction in energy consumption and subsequently energy management.
Modern commercial aircraft can experience significant solar loading during turnaround when the aircraft is stationary on the tarmac. With the increased usage of composite materials, a change in the ...aircraft thermal environment results due to the substantial difference in metal and composite thermal properties. In this paper, an experimental study is undertaken to compare the thermal environment established in a CFRP and aluminium wingbox compartment due to solar loading for levels of 81 W/m2, 396 W/m2, 700 W/m2 and two further cases with a constant wing skin temperature of 100 °C. It was found that conduction through the vertical front and rear spars established a complex but stable flow environment comprising of four counter-rotating circulations which interact strongly with the spar walls, a criterion using scale analysis was also established to determine whether the induced flow would persist. Nusselt number measurements were carried out for each circulation and compared to existing correlations from the literature for differentially heated and top wall heated cavities. The measurements provide aircraft thermal designers with representative values for the heat transfer coefficient which can be used in the thermal modeling of aircraft wing structures.
•Seminal visualization of established flow structures for an enclosure heated on the top wall only.•Nusselt numbers compared to that of a differentially heated cavity successfully.•Experimental results support CFD design engineers in calculation of thermal performance.
•Heating experiments were conducted using a small pool test apparatus to investigate thermal stratification in a water pool with a vertical heat source.•Spatial distributions of temperature and ...velocity in thermal stratification in the small pool were measured using thermography and PIV and analyzed to characterize their spatial distributions.•The mesh size of CFD simulations must be sufficiently small to resolve the flow structure of internal convection, including the thermal stratification boundary.
Thermal stratification is a common phenomenon observed in various systems, including bathtubs, lakes, and pools in nuclear facilities. It is considered system-dependent; thus, its occurrence in different systems must be investigated. In this study, heating experiments were performed in a two-dimensional water pool to investigate the thermal stratification mechanism where a source is immersed in a pool, as in spent fuel pools in nuclear power plants. In addition to temperature measurements using thermocouples, the spatial structure of thermal stratification was obtained by visualizing the temperature and velocity fields using thermography and particle image velocimetry (PIV). Computational fluid dynamics (CFD) simulations were also performed as a benchmark analysis using the experimental data, and the simulated and experimental results are in good agreement.
•Simulation of heat transfer of a nanofluid in an inclined closed enclosure with radiation effect.•Placing a hot fin in the form of a part of an oval in the lower part of the bottom left ...wall.•Evaluating heat transfer rate and the entropy generation under different conditions.•Considering radiation mechanism leads to an increase in the heat transfer and entropy generation.•The heat transfer rate and entropy generation increase with the aspect ratio.
In this work, the free convection of Al2O3/water nano-fluid in a tilted enclosure is investigated. The enclosure is under a magnetic field. A curved shape fin is placed in the lower part of the enclosure. The fin is at a higher temperature of Th, and the right wall is cooled with the temperature of Tc. The top, bottom, and left walls are insulated. The SIMPLE algorithm is used to solve the equations governing the nano-fluid flow. Finally, the effects of magnetic field strength, the variations of Rayleigh number (Ra), radiation parameter, nanoparticles concentration, inclination angle (IA), and aspect ratio (AR) are studied on the heat transfer rate (HTR) and irreversibilities. The findings show that the HTR and the maximum entropy generation augment 2.69 and 3.77 times, respectively, by augmenting the Ra from 103 to 105. Also, increasing Ha number from 0 to 40 causes 38% and 66% reductions for the HTR and entropy generation, respectively. Considering the radiation mode of heat transfer causes an increase of HTR and entropy generation and a decline of thermal irreversibilities. The average Nusselt number and the entropy generation increase by 10% and 12%, respectively for the concentration of 6% while disregarding the radiation phenomena. The HTR and entropy generation rise with the AR.
•The oil/water separator geometry applicable in power plant is considered.•The effects of various parameters on the heat transfer are investigated.•The entropy generation number is calculated in this ...work.•A new correlation for average Nusselt number is developed.
The oily water from various sources in combined cycle power plants is collected in oil/water separator in which the oil separates from water due to the density difference. The idea of the presented geometry is taken from conventional oil/water separators. This paper studies the natural convection of the CuO-water nanoliquid in a rectangular cavity with fins attached to the insulated wall and porous media. Discretion of Navier-Stokes equations is done by Finite Element Method and assumptions are laminar, steady and incompressible flow. Heat transfer performance and entropy generation are investigated for distinct Rayleigh numbers (103–105), Darcy numbers (10−2–10−4), and Hartmann numbers (0, 10, 20). Different sizes of the fins are also studied to show consequences of fin size on heat transfer in cavity. This is the first time that these parameters and their impacts on Nusselt number and entropy generation are studied for a conventional oil/water separator cavity. Corollaries demonstrate that increasing Rayleigh number and Darcy number improves heat transfer performance and average Nusselt number. Nevertheless, Hartmann number has a reverse effect with average Nusselt number. Finally, a new equation for average Nusselt number is developed with regard to Rayleigh number, Hartmann number, and Darcy number.
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A numerical study of MHD natural convection in an upright porous cylindrical annulus filled with magnetized nanomaterial is made by using the specificity of nanoliquids to improve the phenomenon of ...heat transport. The upper and lower walls are thermally insulated, whereas the outer wall is kept at a lesser temperature. The finite volume method is used to treat the governing equations via computer code with Fortran programming. The results obtained are given for the values of the Rayleigh number between 103 and 106, aspect ratio Ar = 2, radii ratio λ = 2, Hartmann number (0 ≤ Ha ≤ 80), Darcy number (10−5 ≤ Da ≤ 10−2), porosity ratio (0.1 ≤ ε ≤0.9), and the nanoparticles volume fraction (0 ≤ φ ≤ 0.1). The transferred thermal flux, in laminar natural convection, increases with the growth of the nanoparticle concentration, the Darcy number, the porosity, the Rayleigh number and, the length of the source.
•The magnetohydrodynamics nanofluid hydrothermal treatment in a cubic cavity heated from below is investigated.•A new model is proposed for thermal conductivity of nanofluid.•The Lattice Boltzmann ...method with Koo–Kleinstreuer–Li correlation is used.•Simultaneous effects of Hartmann number, nanoparticle volume fraction and Rayleigh number are also taken into account.•The physical interpretations of pertinent obtained results are illustrated by graphs and tables.
In this paper magnetohydrodynamics nanofluid hydrothermal treatment in a cubic cavity heated from below is presented. The mathematical model consists of continuity and the momentum equations, while a new model is proposed to see the effects Brownian motion on the effective viscosity and thermal conductivity of nanofluid. The Lattice Boltzmann method is utilized to simulate three dimensional problems. The Koo–Kleinstreuer–Li correlation is also taken into account. Numerical calculation is made for different values of Hartmann number, nanoparticle volume fraction and Rayleigh number. The results are presented graphically in terms of streamlines, isotherms and isokinetic energy as well as Nusselt number. It is observed that the applying magnetic field results in a force opposite to the flow direction that leads to drag the flow and then reduces the convection currents by reducing the velocities. Also it can be concluded that Nusselt number is an increasing function of Rayleigh number and nanofluid volume fraction while it is a decreasing function of Hartmann number.
•A 3-D numerical model of the square LHS unit melting process is established.•The melting properties of four different structures are quantitatively compared.•The melting time, temperature uniformity ...and total heat storage are discussed.•The effect of strengthening method is studied in depth by dynamic temperature study.
The low thermal conductivity of phase change materials limits the large-scale application of latent heat storage technology. It is meaningful to improve the thermal conductivity of phase change materials by corresponding means. In order to improve the performance of latent heat storage device, this paper takes square latent heat storage device as the research object, and uses fin and foam metal to enhance its melting performance. A 3-D numerical model is established and verified by visualization experiment. The quantitative comparison of melting properties of four different structures (pure paraffin, fin, metal foam, fin-metal foam) is presented. The results show that compared with pure paraffin structure, the complete melting time of phase change materials corresponding to fin, metal foam, and fin-metal foam structure is reduced by 47.48%, 79.53%, and 83.68%, respectively. The temperature uniformity increased by 28.97%, 79.37%, and 91.12%, and the total heat storage decreased by 6.0%, 4.6%, and 11.64%, respectively. It shows that the addition of fin and foam metal is beneficial to improve the melting performance and the overall temperature uniformity of the device, but it has a negative effect on total heat storage. Dynamic temperature studies were conducted to further explore the effect of fins and metal foam on the internal melting process compared with pure paraffin structure.
A numerical model is employed for the nanofluid flow and heat transfer from an infinite vertical plate in the existence of a magnetic field, thermal radiation and viscous dissipation. The solution of ...the basic governing equations was obtained by the finite element procedure. A collection of nanofluids with a fraction of nanoparticle volume comprising nanoparticles of aluminium oxide, copper, and titanium oxide is included less than or equal to 0.04. With the aid of non-dimensional flow parameters, the mathematical results of velocity and temperature distributions are analysed and shown diagrammatically. It is found that velocity and Temperature profiles enhance by enhancing the value of radiation parameter. The current simulations outlined are relevant for the processing of magnetic nanomaterials in the chemical industry and the metallurgy sector.
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