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![Figure 1. The geometric model in the experiment of Wu et al. [30]. (a)...](profile/Peng-Wang-271/publication/322534874/figure/fig1/AS:664646847574017@1535475565957/The-geometric-model-in-the-experiment-of-Wu-et-al-30-a-The-heat-transfer-section_Q320.jpg)
The current article used four different models (single-phase, Mixture, Eulerian, and discrete phase model) to investigate the flow and heat transfer characteristics of nanofluids under a laminar state. We explored the Al2O3-water nanofluid inside a microscale trapezoidal channel and the CuO-oil inside a circular channel with a regular size. The vel...
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In this work, the turbulent buoyancy driven fluid flow and heat transfer in a differentially heated tall rectangular enclosure filled with nanofluid is quantified numerically. The two dimensional governing differential equations (continuity, momentum, energy and low Reynolds number LRN k-ω turbulence equations) are discretized using the finite volu...
In this study, mixed convection and entropy generation in a vented cavity with inlet and outlet ports are examined under the effects of an inclined magnetic field. Galerkin weighted finite element method was used for the solution of the governing equations. The numerical simulations are performed for various values of Reynolds numbers (between 100...
In this paper, water and CuO-water nanofluids are selected as working fluids. The characteristics of fluid flow and heat transfer in a heat transfer tube are analyzed by means of numerical simulation. The effect of nanofluid concentration on the flow and heat transfer characteristics of the flat tube under the condition with a Reynolds number of 6,...
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With the porous medium-filling inclined channels, we investigate the nanoparticle sphericity of Cu-Al2O3-H2O hybrid nanofluid flows. We consider the constant flow rate through the channels as well as the uniform heat flux on wall channels. We provide analytical solutions for both the velocity and temperature fields. Several parameters are considere...
Citations
... Initially, the concept of stable nanoparticle suspension was employed by Choi and Eastman [6] to generate a modern kind of solidliquid. It is clear that several studies have been done to analyze the impact of using nanoparticle on heat transfer and thermal conductivity in different situations [7][8][9][10][11][12][13][14][15][16]. ...
Copper oxide-thermal oil nanofluid are utilized to be analyzed the effect of nanofluid on forced convection and friction factor in downward flow in slope pipes. Respectively, the shape of flow is fully developed and other boundary condition is isothermal wall of tube. The effectiveness of solid-fluid, and negative slope on forced convection is investigated with Prantle number. The results of forced convection soar slightly when nanoparticle mass concentration augments. A couple of equations advise to be applied for evaluating forced convection and pressure drop in downward flow under contact wall temperature and fully developed flow in this article. The peaked deviation is 18% that can accept for experimental study that can apply in manufacturing usage. The accompanying forced convection rate with pumping power rate is computed. If the rise of pumping power rate is more than forced convection enhancement, it is not to be suitable to utilize copper oxide and thermal oil and negative slope. The FOM rise up to 66% which is computed with 1.5% weight mass fraction and a slope of-30º at Reynolds number of 780. The upshot demonstrate that the most of values are more than unit, so the forced convection improvement is more than the rise of pumping power rate.
... Fig. 1 illustrates the average error in the comparison is within 3%, therefore the mesh quality for the present calculation is acceptable, meanwhile the calculation model and boundary conditions' settings are proved to be ideal. Calculation accuracy of different models are further compared and shown in Fig. 2. Taking the case of 1.5% mass fraction as an example, as shown in Fig. 2, the results from discrete phase model are closer to the experimental data compared to those of the other two ones, which is consistent with the results of Wang et al. [29][30][31]. However, the more accurate models including discrete phase model and Euler model require more calculation resources. ...
A numerical simulation investigation on the flow of nanofluids in a circular tube was carried out. The simulations have two parts. Firstly, pressure drop of pure water (single-phase base fluid) flowing in a circular tube was calculated in order to verify the correctness of the simulation model with experimental results. Secondly, numerical simulations for nanofluids were conducted with consideration of different mass fractions of nanoparticles. The influencing mechanisms of nanoparticles for base fluid were further discussed. On one hand, adding nanoparticles causes changes in the fluid velocity distribution in fluid region which further leads to changed fluid flow properties in the radial direction. On the other hand, nanoparticles increase the heat transfer performance of the whole fluid with changed temperature gradient. The combination of the changed velocity field and temperature gradient field leads to the enhancement of the heat transfer process in nanofluids. The results show that the enhancement of heat transfer by nanofluids is achieved by the augmented synergy of the temperature gradient field and the velocity field. Keywords: Nanofluids, Circular pipe flow, Numerical simulation, Heat transfer enhancement, Field synergy
Electromagnetic and thermal evaluation of transformers are required for better acquaintance with detailed and complex behaviors of the system components as well as accurate description of the corresponding magnetic and thermal performances. Hence, this paper is devoted to a comprehensive study of the impact of CuO nanoparticles on cooling performance enhancement of a three-phase transformer. Besides, as determination of proper values for heat generation rate of the transformer core is indispensable for thermal modeling, the core losses are acquired through electromagnetic modeling as an essential step. The results derived from the transformer with silicon steel core are compared with the case in which a type of nanocrystalline soft magnetic core material, Finemet, is used. In this paper, 3D simulations are performed for electromagnetic and heat transfer analysis of the transformer. The results gained for nanocrystalline core indicate its superior efficiency in lessening the core losses due to the drastic improvement found in its magnetic and thermal characteristics compared to conventional cores used in previous works. It also becomes apparent that the use of CuO nanoparticles in the pure oil as a novel approach leads to lower hotspot temperature accompanied by notable decrease in the average and maximum temperatures of the fluid. Mean heat transfer coefficients of the oil with and without nanoparticles are finally checked against experimental values to show the simulation results preciousness.
In the heat exchangers, twisted tape insert is a technique to enhance heat transfer. In this paper, the experimental and numerical investigations are arranged to analyze thermal performance with entropy generation analysis on single and double strip helical screw tape inserts. The finite volume method is used with shear stress transport K-ω model to analyze fluid flow in tube with inserts. The Nusselt number attained enhancement with double strip as compared to single strip helical screw inserts at decreased values of twist ratio and increased values of Reynolds number. However, the Nusselt number attained maximum enhancement of 112% with double strip helical screw insert than plain tube at 4000 of Reynolds number (Re). The common correlations for Nusselt number and friction factor are generated with respect to Reynolds number, number of the strips and twist ratio. Entropy generation analysis is also performed. The thermal performance factor attained its enhancement with double strip than single strip helical screw inserts at twist ratio of 2.5 and 3; whereas, double strip helical screw insert attained maximum value of 1.5 at twist ratio of 2.5 and Reynolds number of 16000. The double strip helical screw inserts are suitable for miniaturization of heat exchanger.
To capitalize the advantage of oblique fin heat sink (OFHS) with Al2O3–water nanofluids of different volumetric concentration (1, 2, and 4%), a comprehensive computational analysis has been performed for OFHS with nanofluid through the single-phase modeling. The present investigation focuses on the full domain simulation because the conventional periodic computational model approach is unable to investigate the flow migration effect and predicts higher value of Nusselt number. Apart from the disruption of boundary layer, vortices are observed in the secondary oblique channel due to flow separation that promotes an additional heat transfer enhancement. Higher Severity of the flow migration and hence more non-uniformity of nanofluid flow rate through the primary and secondary channels was observed at higher Reynolds numbers. The increment observed in the average Nusselt number (Nuavg) at Re = 750 for OFHS is about 90% and 115% for water and 4% volumetric concentration of nanofluid respectively compared to conventional SCHS. Also, Al2O3–water nanofluid exhibits about 30% higher enhancement at 4% volumetric concentration at Re = 750 in the OFHS with compared to water. The increase in heat transfer exceeded the pressure drop penalty at all the Reynolds numbers.
The field synergy principle has three criteria to qualitatively describe the essence of single-phase convective heat transfer enhancement. However, in practice these criteria are difficult to be applied to convective heat transfer analysis, because there are no corresponding indicators available to quantitatively describe them. Therefore, a unified formula for the field synergy principle was developed based on these three criteria using probabilistic techniques in this study to overcome these defects. The formula is applicable to incompressible flows with constant properties in both laminar and turbulent flow regimes. The formula contains three categories of non-dimensional indicators corresponding to the three criteria of the field synergy principle, respectively, including domain-averaged cosine of synergy angle, the Pearson linear correlation coefficients between the scalar functions contained in the energy governing equation of convective heat transfer, and the variation coefficients of these functions. The physical meanings of these indicators for the field synergy principle and their connections with the known heat transfer enhancing mechanisms were then discussed. Based on this formula, an improved analytical system for the field synergy principle was proposed. It allows an efficient and quantitative analysis of all single-phase constant-property convective heat transfer phenomena. This new system overcomes the limitation of the conventional field synergy analytical system that mainly analyzes convective heat transfer mechanism from the perspective of synergy angle.
