329 research outputs found
Numerical Investigation of the Thermo-Hydraulic Performance of Water-Based Nanofluids in a Dimpled Channel Flow using Al₂O₃, CuO, and Hybrid Al₂O₃-CuO as Nanoparticles
In this study, the authors study the impact of spherical dimple surfaces and nanofluid coolants on heat transfer and pressure drop. The main objective of this paper is to evaluate the thermal performance of nanofluids with respect to different Reynolds numbers (Re) and nanoparticle compositions in dimpled channel flow. Water-based nanofluids with Al2O3, CuO, and Al2O3-CuO nanoparticles are considered for this investigation with 1%, 2%, and 4% volume fraction for each nanofluid. The simulations are conducted at low Reynolds numbers varying from 500 to 1250, assuming constant and uniform heat flux. The effective properties of nanofluids are estimated using models proposed in the literature and are combined with the computational fluid dynamics solver ANSYS Fluent for the analysis. The results are discussed in terms of heat transfer coefficient, temperature distributions, pressure drop, Nusselt number, friction factors, and performance criterion for all the cases. For all cases of different nanoparticle compositions, the heat transfer coefficient was seen as 35%-46% higher for the dimpled channel in comparison with the smooth channel. Besides, it was observed that with increasing volume fraction, the values of heat transfer and pressure drop were increased. With a maximum of 25.18% increase in the thermal performance, the 1% Al2O3/water was found to be the best performing nanofluid at Re = 500 in the dimpled channel flow
Second Law Analysis of Al2O3-Water Nanofluid Turbulent Forced Convection in a Circular Cross Section Tube with Constant Wall Temperature:
The present paper proposes an analysis based on the second principle of thermodynamics applied to a water-Al 2 O 3 nanofluid. The nanofluid flows inside a circular section tube subjected to constant wall temperature. The aim of the investigation is to understand, by means of an analytical model, how entropy generation within the tube varies if inlet conditions, particles concentration, and dimensions are changed. To gather these information is of fundamental importance, in order to optimize the nanofluid flow. The results show that according to the inlet condition, there is a substantial variation of the entropy generation, particularly when Reynolds number is kept constant there is an increase of entropy generation, whereas when mass flow rate or velocity are taken constant, entropy generation decreases
Enhancement of heat transfer and entropy generation analysis of nanofluids turbulent convection flow in square section tubes
In this article, developing turbulent forced convection flow of a water-Al2O3 nanofluid in a square tube, subjected to constant and uniform wall heat flux, is numerically investigated. The mixture model is employed to simulate the nanofluid flow and the investigation is accomplished for particles size equal to 38 nm
A Review of Recent Passive Heat Transfer Enhancement Methods
[EN] Improvements in miniaturization and boosting the thermal performance of energy conservation systems call for innovative techniques to enhance heat transfer. Heat transfer enhancement methods have attracted a great deal of attention in the industrial sector due to their ability to provide energy savings, encourage the proper use of energy sources, and increase the economic efficiency of thermal systems. These methods are categorized into active, passive, and compound techniques. This article reviews recent passive heat transfer enhancement techniques, since they are reliable, cost-effective, and they do not require any extra power to promote the energy conversion systems' thermal efficiency when compared to the active methods. In the passive approaches, various components are applied to the heat transfer/working fluid flow path to improve the heat transfer rate. The passive heat transfer enhancement methods studied in this article include inserts (twisted tapes, conical strips, baffles, winglets), extended surfaces (fins), porous materials, coil/helical/spiral tubes, rough surfaces (corrugated/ribbed surfaces), and nanofluids (mono and hybrid nanofluids).Ajarostaghi, SSM.; Zaboli, M.; Javadi, H.; Badenes Badenes, B.; Urchueguía Schölzel, JF. (2022). A Review of Recent Passive Heat Transfer Enhancement Methods. Energies. 15(3):1-55. https://doi.org/10.3390/en1503098615515
A review on graphene based nanofluids: preparation, characterization and applications
A wide range of heat transfer systems require efficient heat transfer management from source to sink and vice versa. Over the last decade, graphene nanoparticles, matrix nanofluids have been one of the most investigated nanoparticles for a wide range of engineering applications. Graphene–based nanoparticles have several advantages over other nanoparticles: high stability, high thermal conductivity, low erosion and corrosion, and higher carrier mobility. Graphene–based nanofluids have found applications such as heat transfer, defect sensor, anti–infection therapy, energy harvesting systems, biomedical and cosmetics. With advancement of technology, more compact and efficient cooling media are needed to ensure efficiency and reliability of engineering systems and devices. This research study reports an overview of experimental and numerical investigations of graphene nanometer–sized particles with different base host fluids for major engineering applications of energy transfer systems and further thermophysical properties of graphene nanofluids
The Influence of Forced Convective Heat Transfer on Hybrid Nanofluid Flow in a Heat Exchanger with Elliptical Corrugated Tubes: Numerical Analyses and Optimization
The capabilities of nanofluids in boosting the heat transfer features of thermal, electrical and power electronic devices have widely been explored. The increasing need of different industries for heat exchangers with high efficiency and small dimensions has been considered by various researchers and is one of the focus topics of the present study. In the present study, forced convective heat transfer of an ethylene glycol/magnesium oxide-multiwalled carbon nanotube (EG/MgO-MWCNT) hybrid nanofluid (HNF) as single-phase flow in a heat exchanger (HE) with elliptical corrugated tubes is investigated. Three-dimensional multiphase governing equations are solved numerically using the control volume approach and a validated numerical model in good agreement with the literature. The range of Reynolds numbers (Re) 50 Re 1000 corresponds to laminar flow. Optimization is carried out by evaluation of various parameters to reach an optimal case with the maximum Nusselt number (Nu) and minimum pressure drop. The use of hybrid nanofluid results in a greater output temperature, a higher Nusselt number, and a bigger pressure drop, according to the findings. A similar pattern is obtained by increasing the volume fraction of nanoparticles. The results indicate that the power of the pump is increased when EG/MgO-MWCNT HNFs are employed. Furthermore, the thermal entropy generation reduces, and the frictional entropy generation increases with the volume fraction of nanoparticles and Re number. The results show that frictional and thermal entropy generations intersect by increasing the Re number, indicating that frictional entropy generation can overcome other effective parameters. This study concludes that the EG/MgO-MWCNT HNF with a volume fraction (VF) of 0.4% is proposed as the best-case scenario among all those considered
Effect of corrugated wall combined with backward-facing step channel on fluid flow and heat transfer
The turbulent fluid flow and heat transfer were numerically studied through backward-facing step combined with various corrugated walls. The governing equation was solved using Finite Volume Method (FVM) and the SIMPLE algorithm was applied to investigate the effect of backward-facing step with corrugated downstream on heat transfer characteristics. A constant heat flux was applied on the downstream wall, while the other walls were considered as adiabatic surfaces. Parameters such as corrugated design, amplitude height (1, 2, 3, 4 and 5 mm) and Reynolds number (Re) in the range of 5000 to 20,000 were used. The performance evaluation criteria (PEC) were estimated to show the heat transfer augmentation. The results indicated that using a corrugated wall with a backward-facing step increased significantly the heat transfer accompanied by a slight increase in the skin friction coefficient simultaneously. The best heat transfer augmentation was observed for the trapezoidal corrugation at 4 mm amplitude height and 20 mm pitch diameter. Combining the corrugated wall with backward-facing step enhanced the Nusselt number (Nu) up to 62% at Re = 5000. The performance evaluation criteria increased with the increase of amplitude height until it reached 4 mm and then decreased steeply
Challenges and progress on the modelling of entropy generation in porous media: a review
Depending upon the ultimate design, the use of porous media in thermal and chemical systems can provide significant operational advantages, including helping to maintain a uniform temperature distribution, increasing the heat transfer rate, controlling reaction rates, and improving heat flux absorption. For this reason, numerous experimental and numerical investigations have been performed on thermal and chemical systems that utilize various types of porous materials. Recently, previous thermal analyses of porous materials embedded in channels or cavities have been re-evaluated using a local thermal non-equilibrium (LTNE) modelling technique. Consequently, the second law analyses of these systems using the LTNE method have been a point of focus in a number of more recent investigations. This has resulted in a series of investigations in various porous systems, and comparisons of the results obtained from traditional local thermal equilibrium (LTE) and the more recent LTNE modelling approach. Moreover, the rapid development and deployment of micro-manufacturing techniques have resulted in an increase in manufacturing flexibility that has made the use of these materials much easier for many micro-thermal and chemical system applications, including emerging energy-related fields such as micro-reactors, micro-combustors, solar thermal collectors and many others. The result is a renewed interest in the thermal performance and the exergetic analysis of these porous thermochemical systems. This current investigation reviews the recent developments of the second law investigations and analyses in thermal and chemical problems in porous media. The effects of various parameters on the entropy generation in these systems are discussed, with particular attention given to the influence of local thermodynamic equilibrium and non-equilibrium upon the second law performance of these systems. This discussion is then followed by a review of the mathematical methods that have been used for simulations. Finally, conclusions and recommendations regarding the unexplored systems and the areas in the greatest need of further investigations are summarized
Modélisation numérique des écoulements convectifs de nanofluides en régimes laminaire et turbulent
Les transferts de chaleur par convection jouent un rôle important dans divers secteurs
industriels tels que la climatisation, le transport, la production chimique, la microélectronique
et la production d’électricité. Les fluides caloporteurs conventionnels tels que l’eau,
l’éthylène glycol et l’huile sont caractérisés par des propriétés thermiques relativement
limitées, ce qui réduit l’efficacité des systémes thermiques mis en jeu. L’avancée récente
dans le domaine des nanotechnologies a donné naissance à un nouveau type de particules
métalliques, et non métalliques, de tailles nanométriques, caractérisées par une conductivité
thermique trés élevée. Ces particules, appelées nanoparticules, sont généralement
dispersées dans un fluide de base et le mélange résultant constitue une nouvelle classe de
fluides caloporteurs nommés nanofluides.
Le domaine des nanofluides est un champ de recherche très vivant et leur application dans
les processus industriels devient de plus en plus répandue pour leurs remarquables propriétés
optiques, magnétiques, diélectriques ou électromagnétiques. Dans le présent projet,
seules les performances thermiques des nanofluides seront abordées.
Les nanofluides ont montré leur capacité à modifier les propriétés de transport et de transfert
de chaleur du fluide de base, ce qui constitue un grand potentiel d’amélioration pour
les processus de transfert de chaleur. Cependant, bien que l’ajout de nanoparticules solides
aux fluides de base augmente leur conductivité thermique, cela s’accompagne d’une
diminution de leur capacité calorifique et d’une augmentation de leur viscosité. Ceci entraine
une augmentation de la puissance de pompage requise. Les coûts de production des
nanoparticules et la difficulté à préparer des nanofluides stables dans le temps rendent,
pour l’instant, l’application des nanofluides dans l’industrie encore limitée.
Dans ce contexte, l’objectif principal de ce projet de recherche est d’évaluer en détail les
caractéristiques d’écoulements de nanofluides et les paramètres clés affectant leur performance
dans le processus de transfert de chaleur. Pour ce faire, des modèles numériques ont
été développés puis validés soigneusement avec des données issues de la littérature pour
des écoulements convectifs en régimes laminaire et turbulent. Bien que les configurations
choisies soient relativement canoniques, elles permettent d’évaluer les possibles avantages
des nanofluides dans des systèmes thermiques industriels et d’étudier l’influence des principaux
paramètres de contrôle, comme le débit d’entrée et la fraction en nanoparticules
entre autres.Abstract: Convective heat transfer plays an important role in various industrial sectors such as airconditioning,
transportation, chemical production, microelectronics or power generation.
Conventional heat transfer fluids such as water, ethylene glycol or oil exhibit relatively limited
heat transfer properties, which hinders the efficiency of thermal systems. The recent
advances in the field of nanotechnology gave rise to a new class of nanometeric metallic
and non-metallic particles characterized by their substantially higher thermal conductivities.
These particles, referred as nanoparticles, are dispersed into a conventional fluid,
creating a new class of heat transfer fluids named nanofluids.
The study of nanofluids is a viable research field and their application in various industrial
processes becomes more widespread due to their thermal, optical, magnetic, and electromagnetic
properties. In the present study, only the thermal efficiency of nanofluids will
be investigated.
Nanofluids have shown their ability to enhance the heat transfer performances of the host
fluid, which constitutes a great potential to increase the energetic efficiency of thermal
systems. However, adding solid nanoparticles to a base fluid would not only increase its
thermal conductivity but, it is also accompanied with a decrease of its heat capacity and
an increase of its dynamic viscosity, which may lead to an increased required pumping
power. The two main drawbacks of nanofluids, which limit their use in industrial systems
remain the prohibitive cost to produce nanoparticles and the difficulty to prepare and
stabilize nanofluids over a wide life cycle.
In this context the main objective of this research project is to study in detail the nanofluid
flow characteristics and the key parameters affecting their performance in heat transfer
process. To this end, Computational Fluid Dynamics techniques are used to propose a
numerical model able to simulate nanofluid flows taking into account several phenomena
due to the presence of the nanoparticles into a base fluid and then evaluate the benefits
from their using in industrial applications
Heat transfer performance investigation of nanofluids flow in pipe
Different types of base fluids, such as water, engine oil, kerosene, ethanol, methanol, ethylene glycol etc. are usually used to increase the heat transfer performance in many engineering applications. But these conventional heat transfer fluids have often several limitations. One of those major limitations is that the thermal conductivity of each of these base fluids is very low and this results a lower heat transfer rate in thermal engineering systems. Such limitation also affects the performance of different equipments used in different heat transfer process industries. To overcome such an important drawback, researchers over the years have considered a new generation heat transfer fluid, simply known as nanofluid with higher thermal conductivity. This new generation heat transfer fluid is a mixture of nanometre-size particles and different base fluids. Different researchers suggest that adding spherical or cylindrical shape of uniform/non-uniform nanoparticles into a base fluid can remarkably increase the thermal conductivity of nanofluid. Such augmentation of thermal conductivity could play a more significant role in enhancing the heat transfer rate than that of the base fluid.
Nanoparticles diameters used in nanofluid are usually considered to be less than or equal to 100 nm and the nanoparticles concentration usually varies from 5% to 10%. Different researchers mentioned that the smaller nanoparticles concentration with size diameter of 100 nm could enhance the heat transfer rate more significantly compared to that of base fluids. But it is not obvious what effect it will have on the heat transfer performance when nanofluids contain small size nanoparticles of less than 100 nm with different concentrations. Besides, the effect of static and moving nanoparticles on the heat transfer of nanofluid is not known too. The idea of moving nanoparticles brings the effect of Brownian motion of nanoparticles on the heat transfer. The aim of this work is, therefore, to investigate the heat transfer performance of nanofluid using a combination of smaller size of nanoparticles with different concentrations considering the Brownian motion of nanoparticles. A horizontal pipe has been considered as a physical system within which the above mentioned nanofluid performances are investigated under transition to turbulent flow conditions.
Three different types of numerical models, such as single phase model, Eulerian-Eulerian multi-phase mixture model and Eulerian-Lagrangian discrete phase model have been used while investigating the performance of nanofluids. The most commonly used model is single phase model which is based on the assumption that nanofluids behave like a conventional fluid. The other two models are used when the interaction between solid and fluid particles is considered. However, two different phases, such as fluid and solid phases is also considered in the Eulerian-Eulerian multi-phase mixture model. Thus, these phases create a fluid-solid mixture. But, two phases in the Eulerian-Lagrangian discrete phase model are independent. One of them is a solid phase and the other one is a fluid phase.
In addition, RANS (Reynolds Average Navier Stokes) based Standard κ-ω and SST κ-ω transitional models have been used for the simulation of transitional flow. While the RANS based Standard κ-ϵ, Realizable κ-ϵ and RNG κ-ϵ turbulent models are used for the simulation of turbulent flow. Hydrodynamic as well as temperature behaviour of transition to turbulent flows of nanofluids through the horizontal pipe is studied under a uniform heat flux boundary condition applied to the wall with temperature dependent thermo-physical properties for both water and nanofluids.
Numerical results characterising the performances of velocity and temperature fields are presented in terms of velocity and temperature contours, turbulent kinetic energy contours, surface temperature, local and average Nusselt numbers, Darcy friction factor, thermal performance factor and total entropy generation. New correlations are also proposed for the calculation of average Nusselt number for both the single and multi-phase models. Result reveals that the combination of small size of nanoparticles and higher nanoparticles concentrations with the Brownian motion of nanoparticles shows higher heat transfer enhancement and thermal performance factor than those of water.
Literature suggests that the use of nanofluids flow in an inclined pipe at transition to turbulent regimes has been ignored despite its significance in real-life applications. Therefore, a particular investigation has been carried out in this thesis with a view to understand the heat transfer behaviour and performance of an inclined pipe under transition flow condition. It is found that the heat transfer rate decreases with the increase of a pipe inclination angle. Also, a higher heat transfer rate is found for a horizontal pipe under forced convection than that of an inclined pipe under mixed convection
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