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23 pages, 10205 KiB

Open AccessArticle

Numerical Study of 3D MHD Mixed Convection and Entropy Generation in Trapezoidal Porous Enclosure Filled with a Hybrid Nanofluid: Effect of Zigzag Wall and Spinning Inner Cylinder

by Apichit Maneengam, Tarek Bouzennada, Aissa Abderrahmane, Kaouther Ghachem, Lioua Kolsi, Obai Younis, Kamel Guedri and Wajaree Weera

Nanomaterials 2022, 12(12), 1974; https://doi.org/10.3390/nano12121974 - 08 Jun 2022

Cited by 9 | Viewed by 1438

Abstract

A numerical study was performed to analyze the impact of the combination of several factors on heat transfer rate, flow behavior, and entropy generation in a hybrid nanofluid occupying a porous trapezoid enclosure containing a rotating inner tube. The governing equations were discretized [...] Read more.

A numerical study was performed to analyze the impact of the combination of several factors on heat transfer rate, flow behavior, and entropy generation in a hybrid nanofluid occupying a porous trapezoid enclosure containing a rotating inner tube. The governing equations were discretized and solved using the Finite Element Method using Comsol multiphysics. The effects of the Darcy and Hartman number, nanoparticle volume fraction (from 0 to 6%), the utilization of various zigzag patterns of the hot wall, and the rotation speed of the inner tube (Ω = 100. 250 and 500) are illustrated and discussed in this work. The outputs reveal that flow intensity has an inverse relationship with Hartman number and a direct relationship with the Darcy number and the velocity of the inner tube, especially at high numbers of undulations of the zigzag hot wall (N = 4); also, intensification of heat transfer occurs with increasing nanoparticle volume fraction, Darcy number and velocity of the inner tube. In addition, entropy generation is strongly affected by the mentioned factors, where increasing the nanoparticle concentration augments the thermal entropy generation and reduces the friction entropy generation; furthermore, the same influence can be obtained by increasing the Hartman number or decreasing the Darcy number. However, the lowest entropy generation was found for the case of Ø = 0, Ha = 0 and Da = 0.01. Full article

(This article belongs to the Special Issue New Frontiers in Nanofluids)

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10 pages, 15335 KiB

Open AccessArticle

Experimental Investigation of Thermal Conductivity of Water-Based Fe₃O₄ Nanofluid: An Effect of Ultrasonication Time

by Divya P. Barai, Bharat A. Bhanvase and Gaweł Żyła

Nanomaterials 2022, 12(12), 1961; https://doi.org/10.3390/nano12121961 - 08 Jun 2022

Cited by 11 | Viewed by 1588

Abstract

Nanofluid preparation is a crucial step in view of their thermophysical properties as well as the intended application. This work investigates the influence of ultrasonication duration on the thermal conductivity of Fe

_{3}

O

_{4}

nanofluid. In this work, water-based Fe

_{3}

O [...] Read more.

Nanofluid preparation is a crucial step in view of their thermophysical properties as well as the intended application. This work investigates the influence of ultrasonication duration on the thermal conductivity of Fe

_{3}

O

_{4}

nanofluid. In this work, water-based Fe

_{3}

O

_{4}

nanofluids of various volume concentrations (0.01 and 0.025 vol.%) were prepared and the effect of ultrasonication time (10 to 55 min) on their thermal conductivity was investigated. Ultrasonication, up to a time duration of 40 min, was found to raise the thermal conductivity of Fe

_{3}

O

_{4}

nanofluids, after which it starts to deteriorate. For a nanofluid with a concentration of 0.025 vol.%, the thermal conductivity increased to 0.782 W m

^{- 1}

K

^{- 1}

from 0.717 W m

^{- 1}

K

^{- 1}

as the ultrasonication time increased from 10 min to 40 min; however, it further deteriorated to 0.745 W m

^{- 1}

K

^{- 1}

after a further 15 min increase (up to a total of 55 min) in ultrasonication duration. Thermal conductivity is a strong function of concentration of the nanofluid; however, the optimum ultrasonication time is the same for different nanofluid concentrations. Full article

(This article belongs to the Special Issue New Frontiers in Nanofluids)

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17 pages, 13684 KiB

Open AccessArticle

Irreversibility Interpretation and MHD Mixed Convection of Hybrid Nanofluids in a 3D Heated Lid-Driven Chamber

by Houssem Laidoudi, Aissa Abderrahmane, Abdulkafi Mohammed Saeed, Kamel Guedri, Wajaree Weera, Obai Younis, Abed Mourad and Riadh Marzouki

Nanomaterials 2022, 12(10), 1747; https://doi.org/10.3390/nano12101747 - 20 May 2022

Cited by 15 | Viewed by 1309

Abstract

This paper presents a numerical simulation of a magneto-convection flow in a 3D chamber. The room has a very specific permeability and a zigzag bottom wall. The fluid used in this study is Al₂O₃-Cu/water with 4% nanoparticles. The Galerkin [...] Read more.

This paper presents a numerical simulation of a magneto-convection flow in a 3D chamber. The room has a very specific permeability and a zigzag bottom wall. The fluid used in this study is Al₂O₃-Cu/water with 4% nanoparticles. The Galerkin finite element technique (GFEM) was developed to solve the main partial equations. The hybrid nanofluid inside the container is subjected to the horizontal motion of the upper wall, an external magnetic field, and a thermal buoyancy force. The present numerical methodology is validated by previous data. The goal of this investigation was to understand and determine the percentage of heat energy transferred between the nanofluid and the bottom wall of the container under the influence of a set of criteria, namely: the movement speed of the upper wall of the cavity (Re = 1 to 500), the amount of permeability (Da = 10⁻⁵ to 10⁻²), the intensity of the external magnetic field (Ha = 0 to 100), the number of zigzags of the lower wall (N = 1 to 4), and the value of thermal buoyancy when the force is constant (Gr = 1000). The contours of the total entropy generation, isotherm, and streamline are represented in order to explain the fluid motion and thermal pattern. It was found that the heat transfer is significant when (N = 4), where the natural convection is dominant and (N = 2), and the forced convection is predominant. Full article

(This article belongs to the Special Issue New Frontiers in Nanofluids)

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17 pages, 5415 KiB

Open AccessArticle

Breakdown Performance and Partial Discharge Development in Transformer Oil-Based Metal Carbide Nanofluids

by Konstantinos N. Koutras, Sokratis N. Tegopoulos, Vasilios P. Charalampakos, Apostolos Kyritsis, Ioannis F. Gonos and Eleftheria C. Pyrgioti

Nanomaterials 2022, 12(2), 269; https://doi.org/10.3390/nano12020269 - 14 Jan 2022

Cited by 28 | Viewed by 2645

Abstract

In this work, the influence of semi-conductive SiC nanoparticles on the AC breakdown voltage and partial discharge development in natural ester oil FR3 is examined. Primarily, the dielectric constant and the electrical conductivity of the nanoparticles are measured following the broadband dielectric spectroscopy [...] Read more.

In this work, the influence of semi-conductive SiC nanoparticles on the AC breakdown voltage and partial discharge development in natural ester oil FR3 is examined. Primarily, the dielectric constant and the electrical conductivity of the nanoparticles are measured following the broadband dielectric spectroscopy technique. The nanoparticles are added into the matrix following the ultrasonication process in three weight percentage ratios in order for their effect to be evaluated as a function of their concentration inside the base oil. The processing of the results reveals that the nanofluid containing SiC nanoparticles at 0.004% w/w demonstrates the highest AC dielectric strength improvement and shows the greatest resistance to the appearance of partial discharge activity. The mechanisms behind the aforementioned results are discussed in detail and confirmed by the broadband dielectric spectroscopy technique, which reveals that this particular nanofluid sample is characterized by lower dielectric constant and electrical conductivity than the one with double the weight percentage ratio. Full article

(This article belongs to the Special Issue New Frontiers in Nanofluids)

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19 pages, 1126 KiB

Open AccessEditor’s ChoiceArticle

MHD Williamson Nanofluid Flow over a Slender Elastic Sheet of Irregular Thickness in the Presence of Bioconvection

by Fuzhang Wang, Muhammad Imran Asjad, Saif Ur Rehman, Bagh Ali, Sajjad Hussain, Tuan Nguyen Gia and Taseer Muhammad

Nanomaterials 2021, 11(9), 2297; https://doi.org/10.3390/nano11092297 - 03 Sep 2021

Cited by 51 | Viewed by 2450

Abstract

Bioconvection phenomena for MHD Williamson nanofluid flow over an extending sheet of irregular thickness are investigated theoretically, and non-uniform viscosity and thermal conductivity depending on temperature are taken into account. The magnetic field of uniform strength creates a magnetohydrodynamics effect. The basic formulation [...] Read more.

Bioconvection phenomena for MHD Williamson nanofluid flow over an extending sheet of irregular thickness are investigated theoretically, and non-uniform viscosity and thermal conductivity depending on temperature are taken into account. The magnetic field of uniform strength creates a magnetohydrodynamics effect. The basic formulation of the model developed in partial differential equations which are later transmuted into ordinary differential equations by employing similarity variables. To elucidate the influences of controlling parameters on dependent quantities of physical significance, a computational procedure based on the Runge–Kutta method along shooting technique is coded in MATLAB platform. This is a widely used procedure for the solution of such problems because it is efficient with fifth-order accuracy and cost-effectiveness. The enumeration of the results reveals that Williamson fluid parameter

λ

, variable viscosity parameter

Λ_{μ}

and wall thickness parameter

ς

impart reciprocally decreasing effect on fluid velocity whereas these parameters directly enhance the fluid temperature. The fluid temperature is also improved with Brownian motion parameter

N b

and thermophoresis parameter

N t

. The boosted value of Brownian motion

N b

and Lewis number

L e

reduce the concentration of nanoparticles. The higher inputs of Peclet number

P e

and bioconvection Lewis number

L b

decline the bioconvection distribution. The velocity of non-Newtonian (Williamson nanofluid) is less than the viscous nanofluid but temperature behaves oppositely. Full article

(This article belongs to the Special Issue New Frontiers in Nanofluids)

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Review

Jump to: Research

41 pages, 3918 KiB

Open AccessReview

Mineral and Ester Nanofluids as Dielectric Cooling Liquid for Power Transformers

by Cristian Olmo, Cristina Méndez, Pedro J. Quintanilla, Félix Ortiz, Carlos J. Renedo and Alfredo Ortiz

Nanomaterials 2022, 12(15), 2723; https://doi.org/10.3390/nano12152723 - 08 Aug 2022

Cited by 9 | Viewed by 1694

Abstract

Amidst the new techniques facing the improvement of cooling and insulating efficiency and the design of electric transformers, constrained by the current technologies, one of the more promising is the substitution of traditional dielectric oils for nanofluids. Research on nanofluids for their application [...] Read more.

Amidst the new techniques facing the improvement of cooling and insulating efficiency and the design of electric transformers, constrained by the current technologies, one of the more promising is the substitution of traditional dielectric oils for nanofluids. Research on nanofluids for their application in transformers as a coolant and dielectric medium have been performed during the last two decades and continue today. This review tries to collect and analyze the available information in this field and to offer it already dissected to researchers, focusing on the preparation methods and how nanoparticles affect the main properties of the base fluids. Here we also addressed the influence of different parameters as particle characteristics or environmental conditions in nanofluids performance, the evolution with time of the measured properties, or the neighboring relationship of nanofluids with other transformer components. In this sense, the most reviewed articles reflect enhancements of thermal conductivity or dielectric strength, as well as an improvement of time evolution of these properties, with respect to those that are found in base fluids, and, also, a better interaction between these nanofluids and dielectric cellulosics. Thus, the use of dielectric nanofluids in transformers may allow these machines to work safer or over their design parameters, reducing the risk of failure of the electrical networks and enhancing their life expectancy. Nevertheless, these advantages will not be useful unless a proper stability of nanofluids is ensured, which is achieved in a small part of revised articles. A compendium of the preparation methodology with this aim is proposed, to be checked in future works. Full article

(This article belongs to the Special Issue New Frontiers in Nanofluids)

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30 pages, 9292 KiB

Open AccessReview

Review of Heat Transfer Analysis in Different Cavity Geometries with and without Nanofluids

by Farhan Lafta Rashid, Ahmed Kadhim Hussein, Emad Hasani Malekshah, Aissa Abderrahmane, Kamel Guedri and Obai Younis

Nanomaterials 2022, 12(14), 2481; https://doi.org/10.3390/nano12142481 - 19 Jul 2022

Cited by 33 | Viewed by 1931

Abstract

Many strategies have been attempted for accomplishing the needed changes in the heat-transfer rate in closed cavities in recent years. Some strategies used include the addition of flexible or hard partitions to the cavities (to split them into various pieces), thickening the borders, [...] Read more.

Many strategies have been attempted for accomplishing the needed changes in the heat-transfer rate in closed cavities in recent years. Some strategies used include the addition of flexible or hard partitions to the cavities (to split them into various pieces), thickening the borders, providing fins to the cavities, or altering the forms or cavity angles. Each of these methods may be used to increase or decrease heat transmission. Many computational and experimental investigations of heat transport in various cavity shapes have been conducted. The majority of studies focused on improving the thermal efficiency of heat transmission in various cavity containers. This paper introduced a review of experimental, numerical, and analytical studies related to heat transfer analyses in different geometries, such as circular, cylindrical, hexagonal, and rectangular cavities. Results of the evaluated studies indicate that the fin design increased heat transmission and sped up the melting time of the PCM; the optimal wind incidence angle for the maximum loss of combined convective heat depends on the tilt angle of the cavity and wind speed. The Nusselt number graphs behave differently when decreasing the Richardson number. Comparatively, the natural heat transfer process dominates at Ri = 10, but lid motion is absent at Ri = 1. For a given Ri and Pr, the cavity without a block performed better than the cavity with a square or circular block. The heat transfer coefficient at the heating sources has been established as a performance indicator. Hot source fins improve heat transmission and reduce gallium melting time. Full article

(This article belongs to the Special Issue New Frontiers in Nanofluids)

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28 pages, 1302 KiB

Open AccessReview

Dielectric Fluids for Power Transformers with Special Emphasis on Biodegradable Nanofluids

by Miloš Šárpataky, Juraj Kurimský and Michal Rajňák

Nanomaterials 2021, 11(11), 2885; https://doi.org/10.3390/nano11112885 - 28 Oct 2021

Cited by 32 | Viewed by 2806

Abstract

This review is focused on the research of dielectric fluids, especially commonly used power transformer oils enhanced by nanoparticles, i.e., nanofluids. There are differences between various combinations of base fluids and nanoparticles prepared in different ways. The main goal of this review was [...] Read more.

This review is focused on the research of dielectric fluids, especially commonly used power transformer oils enhanced by nanoparticles, i.e., nanofluids. There are differences between various combinations of base fluids and nanoparticles prepared in different ways. The main goal of this review was to present recent research in this field sorted by the used nanoparticles. Nanofluids based on mineral oils, natural, or synthetic esters were investigated in terms of the nature of nanoparticles, particularly Al₂O₃, TiO₂, Fe₂O₃, Fe₃O₄, graphene, fullerene, and others. The combinations of environmentally friendly oils and nanoparticles were presented. Finally, the article focused on the description of current dielectric fluids usable in power transformers and the possibilities of improving new and existing fluids with nanoparticles, especially their physical, dielectric, and chemical properties, but with regard to environmental aspects. Full article

(This article belongs to the Special Issue New Frontiers in Nanofluids)

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