Entropy Generation and Natural Convection of CuO-Water Nanofluid in C-Shaped Cavity under Magnetic Field
TL;DR: It is found that the applied magnetic field can suppress both the natural convection and the entropy generation rate, and the nanoparticles addition can be useful if a compromised magnetic field value represented by a Hartman number of 30 is applied.
Abstract: This paper investigates the entropy generation and natural convection inside a C-shaped cavity filled with CuO-water nanofluid and subjected to a uniform magnetic field. The Brownian motion effect is considered in predicting the nanofluid properties. The governing equations are solved using the finite volume method with the SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm. The studied parameters are the Rayleigh number (1000 ≤ Ra ≤ 15,000), Hartman number (0 ≤ Ha ≤ 45), nanofluid volume fraction (0 ≤ φ ≤ 0.06), and the cavity aspect ratio (0.1 ≤ AR ≤ 0.7). The results have shown that the nanoparticles volume fraction enhances the natural convection but undesirably increases the entropy generation rate. It is also found that the applied magnetic field can suppress both the natural convection and the entropy generation rate, where for Ra = 1000 and φ = 0.04, the percentage reductions in total entropy generation decreases from 96.27% to 48.17% for Ha = 45 compared to zero magnetic field when the aspect ratio is increased from 0.1 to 0.7. The results of performance criterion have shown that the nanoparticles addition can be useful if a compromised magnetic field value represented by a Hartman number of 30 is applied.
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TL;DR: In this paper, the effects of a heat sink and the source size and location on the entropy generation, MHD natural convection flow and heat transfer in an inclined porous enclosure filled with a Cu-water nanofluid are investigated numerically.
Abstract: The effects of a heat sink and the source size and location on the entropy generation, MHD natural convection flow and heat transfer in an inclined porous enclosure filled with a Cu-water nanofluid are investigated numerically. A uniform heat source is located in a part of the bottom wall, and a part of the upper wall of the enclosure is maintained at a cooled temperature, while the remaining parts of these two walls are thermally insulated. Both the left and right walls of the enclosure are considered to be adiabatic. The thermal conductivity and the dynamic viscosity of the nanofluid are represented by different verified experimental correlations that are suitable for each type of nanoparticle. The finite difference methodology is used to solve the dimensionless partial differential equations governing the problem. A comparison with previously published works is performed, and the results show a very good agreement. The results indicate that the Nusselt number decreases via increasing the nanofluid volume fraction as well as the Hartmann number. The best location and size of the heat sink and the heat source considering the thermal performance criteria and magnetic effects are found to be D = 0.7 and B = 0.2. The entropy generation, thermal performance criteria and the natural heat transfer of the nanofluid for different sizes and locations of the heat sink and source and for various volume fractions of nanoparticles are also investigated and discussed.
175 citations
TL;DR: In this article, the authors present a review of the contributions on entropy generation of nanofluids and hybrid nanoparticles in different types of thermal systems for different boundary conditions and physical situations.
Abstract: This paper presents a review of the contributions on entropy generation of nanofluids and hybrid nanofluids in the different types of thermal systems for different boundary conditions and physical situations. The relevant papers are classified into three categories: entropy generation in minichannel, entropy generation macrochannel and entropy generation in cavities. The viscous dissipative, streamwise, electromagnetic effects, as well as nanoparticles concentration, the temperature and the flow regime on entropy generation, were analyzed. The reviewed literature indicates that the implementation of nanofluids/hybrid nanofluids in microchannels, minichannels, and cavities may be an important alternative to the traditional thermal systems and an interesting topic of study.
169 citations
TL;DR: Hybrid-nanofluids as mentioned in this paper is a new fluid produced by dispersing two dissimilar types of nano-particles into the base fluid, which can be used to improve heat transfer performance.
Abstract: Hybrid-nanofluids are potential fluids that present superior thermophysical properties and thermal performance than common heat transfer fluids mono-nanofluids. Hybrid nanofluid is a new fluid produced by dispersing two dissimilar types of nano-particles into the base fluid. Some researchers have reported that conventional coolants could be replaced by hybrid-nanofluids, particularly fluids that work at very high temperatures. Accordingly, these types of nanofluids could lead to saving energy as well as less harmful environmental impacts. Many researches have been performed on nanofluids in the past decade. Despite the uncertainties in the nanofluids thermal-conductivity, they are still considered as heat transfer fluids with a new technology. In recent years, researchers have been trying to utilize hybrid-nanofluids designed by mixing different nanofluids in mixtures or composite forms. The idea of hybrid-nanofluids to improve heat transfer performance and their advantages has led to relatively good expectations for their applications. This article evaluates recent researches on hybrid-nanofluids, including methods of fabrication, thermophysical properties, nano-particle types and their shapes, pressure drop and heat transfer characteristics, and their applications. Finally, the challenges, environmental and destructive effects of nano-particles on the human body and future approaches in the application of hybrid-nanofluids in heat transfer devices are discussed.
158 citations
TL;DR: In this article, the effects of hybrid nanoparticles on the melting process of a nano-enhanced phase-change material (NEPCM) inside an enclosure were investigated and it was found that increasing the values of the nanoparticles volume fraction, viscosity and conductivity parameters leads to significant variations in the solid-liquid interface for large values of Fourier number.
Abstract: The present study deals with the effects of hybrid nanoparticles on the melting process of a nano-enhanced phase-change material (NEPCM) inside an enclosure. The bottom side of the cavity is isothermal at a hot temperature while the top wall is isothermal at a cold temperature and the left and right walls are insulated. The governing partial differential equations are first non-dimensional form and then solved using the Galerkin finite element method. Some of the dimensionless parameters are kept constant such as the Prandtl number, the Rayleigh number, the Stefan number and the ratio between the thermal diffusivity of the solid and liquid phases while the volume fraction of nanoparticles, the conductivity and viscosity parameters, and the Fourier number are altered. It is found out that increasing the values of the nanoparticles volume fraction, viscosity and conductivity parameters leads to significant variations in the solid-liquid interface for large values of Fourier number. Moreover, increasing the conductivity parameter and decreasing the viscosity parameter at the same time can cause an augmentation in the liquid fraction.
142 citations
135 citations
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TL;DR: In this article, the authors focus on heat and mass transfer, fluid flow, chemical reaction, and other related processes that occur in engineering equipment, the natural environment, and living organisms.
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9,565 citations
"Entropy Generation and Natural Conv..." refers methods in this paper
...The effective electrical conductivity of nanofluid was presented by Maxwell [47] as follows:...
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...The effective electrical conductivity of nanofluid was presented by Maxwell [47] as follows: σn f σf “ 1` 3 pγ´ 1q φpγ` 2q ´ pγ´ 1q φ , γ “ σs σf (15) The local Nusselt number over the heat transfer walls is calculated by: Nu “ ´ kn f k f ˆ Bθ Bn ˙ n with n “ pX, Yq (16) The mean Nusselt number over the heat transfer walls is evaluated as: Num “ 1 3 « ż B A Nu dX` ż C B Nu dY` ż D C Nu dX ff (17)...
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TL;DR: In this paper, numerical heat transfer and fluid flow are used to transfer heat from a nuclear power plant to a nuclear fluid flow system, and the resulting fluid flow is used for nuclear power plants.
Abstract: (1981). Numerical Heat Transfer and Fluid Flow. Nuclear Science and Engineering: Vol. 78, No. 2, pp. 196-197.
3,386 citations
"Entropy Generation and Natural Conv..." refers methods in this paper
...The SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm [48] was followed for pressure velocity linkage....
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1,198 citations
"Entropy Generation and Natural Conv..." refers background in this paper
...The local entropy generation equation given in [1] can be adopted for nanofluid as:...
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TL;DR: In this paper, an experimental correlation for the thermal conductivity of Al2O3 nanofluids as a function of nanoparticle size over a wide range of temperature (from 21 to 71°C).
Abstract: In this letter, we report an experimental correlation [Eqs. (1a) and (1b) or (1c)] for the thermal conductivity of Al2O3 nanofluids as a function of nanoparticle size (ranging from 11nmto150nm nominal diameters) over a wide range of temperature (from 21to71°C). Following the previously proposed conjecture from the theoretical point-of-view (Jang and Choi, 2004), it is experimentally validated that the Brownian motion of nanoparticles constitutes a key mechanism of the thermal conductivity enhancement with increasing temperature and decreasing nanoparticle sizes.
1,188 citations
"Entropy Generation and Natural Conv..." refers background in this paper
...[44] proposed the following empirical relation for the thermal conductivity of Al2O3-water nanofluid with spherical particles: knf kf “ 1` 64....
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