Simulation of CuO-water nanofluid natural convection in a U-shaped enclosure with a T-shaped baffle (original) (raw)
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Journal of the Taiwan Institute of Chemical Engineers, 2018
Research on nanofluid for heat transfer enhancement of thermal systems has received great attention owing to the lack of energy sources. In this study, fluid flow and natural convection heat transfer of Al 2 O 3-Water or TiO 2-water nanofluid inside a U-shaped cavity consist of a hot obstacle has been investigated numerically by lattice Boltzmann method (LBM). In this paper, different parameters are investigated such as Rayleigh number, the solid volume fraction of the nanoparticles, the U-shaped cavity's aspect ratio and heating obstacle's height on the flow field and heat transfer in the enclosure. The results showed that the Rayleigh number (Ra), cavity aspect ratio (AR) and obstacle's height can be affected on isotherms, streamlines and local and average Nusselt number. The average Nusselt number of the obstacle sides increased by increasing the Ra number and solid volume fraction of nanoparticles (φ) regardless the AR. In addition, by increasing the AR , the average Nusselt number increased. At low Ra , the effect of nanoparticles on increment of heat transfer for narrow cavities was more than wide ones.
Enhancement of Heat Transfer in a Cavity Filled with Cu-water Nanofluid
This paper summarizes a numerical study of natural convection in a square cavity with a corner heater filled with water based nanofluid (water with Cunanoparticles). Finite volume method is used for solving momentum and energy equations in the form of stream function-vorticity. One wall of the enclosure is isothermal but its temperature is colder than that of heaters while the remaining walls are adiabatic. Calculations were performed for Rayleigh number (10 3 ≤ Ra≤ 10 6); dimensionless lengths of heater in x and y directions (0.25 H≤ H x ≤ 0. 5 H, 0.25 H ≤ H y ≤ 0.5 H) and volume fraction of nanoparticles (0 ≤ φ ≤ 0.1). The results indicate that dimensionless lengths of heater are an important parameter affecting the flow pattern and temperature field. Nusselt number increases with increasing both the Rayleigh number. It is also observed that at a given Rayleigh number and definite dimensionless lengths of heaters, the average Nusselt number increases linearly with the increase in the solid volume fraction of nanofluid.
Scientia Iranica, 2012
This article presents a numerical study of natural convection and entropy generation of Cu-water nanofluid within an enclosure with a conductive baffle embedded on bottom hot wall. The governing equations are solved numerically with Finite Volume Method using the SIMPLER algorithm. Effects of Rayleigh number, position of conductive baffle and volume fraction of nanoparticles on the streamlines, isotherms, mean Nusselt number, entropy generation, Bejan number and irreversibility factor have been studied. At Ra = 10 4 the convection heat transfer is very weak and the dominant conduction weakens by displacing the baffle toward the center of the cavity, thus the mean Nusselt number decreases. At higher Rayleigh numbers due to enhanced convection, the improved mean Nusselt number increases by increasing the volume fraction and displacing the baffle toward the center of the cavity. The effect of volume fraction and position of the baffle on entropy generation and Bejan number at Ra = 10 4 is different from Ra = 10 5 and 10 6 . This is due to the effects of addition of nanoparticles on the effective viscosity and conductivity of nanofluid and conduction dominance. It has been shown that assuming a constant irreversibility factor, χ, with change of Ra and ϕ is not correct.
Analysis of Convection Phenomenon in Enclosure Utilizing Nanofluids with Baffle Effects
Energies
The behavior of convective heat transfer in an enclosure filled with Cu–water nanofluid with a baffle has been numerically studied using the finite element method. The enclosure’s top and bottom walls were adiabatic, while the other two were maintained at various temperatures. The left hot wall had an effective thickness and a baffle was added to the bottom wall. The influence of different parameters like the nanoparticle’s concentration (ϕ), Rayleigh number (Ra), the thermal conductivity ratio of the thick wall (Kr), baffle angle (Ø), and the hot wall thickness (D) on the isotherm and fluid flow patterns were examined. The result showed that the average Nusselt number was enhanced, owing to the strength of the buoyancy force becoming more effective. Furthermore, as the baffle inclination angle increased, the maximum stream function at the core corresponded to the angle when it reached Ø=60°, then it gradually decreased to the minimum value as the baffle angle reached close to Ø=120°.
Journal of Thermal Analysis and Calorimetry, 2020
Natural convection characteristics in an enclosure having U-shape that contains nanofluid are studied by extensively examining the effect of aspect ratio. The three outer walls of cavity are at isothermal high temperature, and facing inner walls are at a uniform low temperature. Computations are performed to explore the effect of the aspect ratios of cold wall to hot walls of the U-shaped cavity in the horizontal and vertical directions on the velocity and temperature characteristics in the cavity. The impact of various Rayleigh numbers and nanoparticle volume fractions of CuO is also studied. The computational results showed that all the considered parameters have a considerable influence on the heat transfer performance. Furthermore, the augmentation in heat transfer rate introduced by nanoparticles is more profound for larger vertical aspect ratios and low Rayleigh numbers. In addition, a noticeable relationship between the contribution of nanoparticles and the two different aspect ratios studied in this work is observed. Furthermore, the influence of vertical aspect ratio on the heat transfer is more pronounced compared to the horizontal aspect ratio, i.e., increasing the height of the cold wall is more effective than increasing the width of the cold wall for most of the cases. As a result of the comprehensive analysis, a correlation for mean Nusselt number including the influence of aspect ratio of cold rib, Rayleigh number and nanoparticle concentration is proposed.
International Journal of Thermal Sciences, 2010
This work focuses on the study of natural convection heat transfer characteristics in a differentiallyheated enclosure filled with a CuOeEGeWater nanofluid for different published variable thermal conductivity and variable viscosity models. The problem is given in terms of the vorticityestream function formulation and the resulting governing equations are solved numerically using an efficient finite-volume method. Comparisons with previously published work are performed and the results are found to be in good agreement. Various results for the streamline and isotherm contours as well as the local and average Nusselt numbers are presented for a wide range of Rayleigh numbers (Ra ¼ 10 3 e10 5 ), volume fractions of nanoparticles (0 4 6%), and enclosure aspect ratios (½ A 2). Different behaviors (enhancement or deterioration) are predicted in the average Nusselt number as the volume fraction of nanoparticles increases depending on the combination of CuOeEGeWater variable thermal conductivity and viscosity models employed. In general, the effects the viscosity models are predicted to be more predominant on the behavior of the average Nusselt number than the influence of the thermal conductivity models. The enclosure aspect ratio is predicted to have significant effects on the behavior of the average Nusselt number which decreases as the enclosure aspect ratio increases.
Molecules
The proper process of applying heat to many technological devices is a significant challenge. There are many nanofluids of different sizes used inside the system. The current study combines this potential to improve convection effects, considering numerical simulations of natural convection using Cu/water nanofluids in a square enclosure with bottom blocks embedded in baffles. The enclosure consists of two vertical walls with isothermal boundary conditions; the left wall is the sinusoidal heat source, whereas the right wall is cooled. The investigations dealt with the influences of nanoparticle concentration, Rayleigh number, baffle length, and thermal conductivity ratioon isotherms, stream functions, and average Nusselt number. The results present that, when the Rayleigh number rises, the fluid flow velocity increases, and the heat transfer improves. Furthermore, the baffle length case (Lb = 0.3) provides higher heat transfer characteristics than other baffle height cases.
Rayleigh-benard convection of cu-water and cuo-water nanofluids in rectangular enclosure
2016
The heat transfer by natural convection of nanofluid inside a horizontal cavity heated from below (Rayleigh–Bénard problem) was numerically investigated. Two different nanofluids are considered: Cu-Water and CuO-Water nanofluids, for which viscosity and thermal conductivity were determined using Brownian motion models. We supposed that nanofluid is mono-constituent fluid. In this work, simulations have been carried out for different cavity aspect ratios (width/height) and Rayleigh number and nanoparticle volume fraction are taken up to 0.04 to ensure a Newtonian behavior of the mixture. It is found that the presence of nanoparticles affects the flow and thermal boundary layer and that is due to the high viscosity and thermal conductivity in the nanofluids. The nanofluid Nusselt number exhibits a slight increase as function of aspect ratio comparing to that in pure fluid. That enhancement is strongly influenced by Rayleigh number and the cavity aspect ratio. INTRODUCTION Nanofluids a...
Mixed convection in a square cavity filled with CuO-water nanofluid heated by corner heater
a r t i c l e i n f o Keyword: Cavity Lid driven Corner heater Nanofluid Finite differences a b s t r a c t This paper investigates the heat transfer and fluid flow in a lid-driven cavity filled with CuO-water nanofluid and heated by a corner heater. The left vertical wall is cooled isothermally and moves upward. The corner heater is configured to be acting in the horizontal and vertical right walls. The remainder walls are adiabatic. Temperature dependent models for thermal conductivity and dynamic viscosity have been invoked. The governing equations have been solved using finite difference method. The governing parameters are nanofluid volume fraction í µí¼ = 0.0-0.07, Richardson number Ri = 0.01-100, Reynolds number (Re = 100-300) and five configurations of corner heater governed by the distance of its lower edge Δ = 0-1. The results show that for low and intermediate values of Richardson number (i.e., Ri = 0.01 and Ri = 1) the effects of the nanoparticles on heat transfer enhancement is not greatly pronounced. However, for high values of Richardson number (i.e., Ri = 10 and Ri = 100) the Nusselt number enhances due to the addition of nanoparticles. A single case of heat transfer deterioration, due to the presence of nanoparticles, is observed for the case of Ri = 0.01 and Δ = 0. For all studied Richardson numbers, the case of Δ = 0 gives the best scenario for heat transfer when compared to other heater's location.
Heat and Mass Transfer, 2013
This paper discusses the results of a study related to natural convection cooling of a heat source located on the bottom wall of an inclined isosceles triangular enclosure filled with a Cu water-nanofluid. The right and left walls of the enclosure are both maintained cold at constant equal temperatures, while the remaining parts of the bottom wall are insulated. The study has been carried out for a Rayleigh number in the range 10 4 B Ra B 10 6 , for a heat source length in the range 0.2 B e B0.8, for a solid volume fraction in the range 0 B /B0.06 and for an inclination angle in the range 0°B dB45°. Results are presented in the form of streamline contours, isotherms, maximum temperature at the heat source surface and average Nusselt number. It is noticed that the addition of Cu nanoparticles enhances the heat transfer rate and therefore cooling effectiveness for all values of Rayleigh number, especially at low values of Ra. The effect of the inclination angle becomes more noticeable as one increases the value of Ra. For high Rayleigh numbers, a critical value for the inclination angle of d = 15°is found for which the heat source maximum temperature is highest.