Heat transfer enhancement for natural convection flow of water-based nanofluids in a square enclosure (original) (raw)
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Numerical Study of Heat Transfer Performance of Homogenous Nanofluids under Natural Convection
The present study aims to identify heat transfer and flow characteristic due to buoyancy forces in a heated enclosure using nanofluid and their behaviors under natural convective heat transfer condition. In the present work nanofluids with water based containing Al 2 O 3 nanoparticle numerically investigated. Numerical works are done on the use of the stable nanofluids under natural convective heat transfer conditions. Process of heating is done in two different ways: in first process the heater mounted to the down wall and in second way it mounted to the left vertical wall with a finite length, also heated and cooled walls keep in a constant temperature. Our numerical simulation has been undertaken incorporating a homogenous solid-liquid mixture. In particular this study deals with Al 2 O 3 nanofluids with Newtonian behavior. Simulation have been carried out in the ranges Ra=10 3-10 6. Our volumetric fraction of nanoparticles was 1.3%. It was shown the Nusselt-Rayleigh number relation and then nanofluid Nu-Ra number diagrams based on found is plotted. Results showed an increasing in Nusselt-Rayleigh number at nanofluids diagrams as compared to Nusselt-Rayleigh relations of pure water. Increase in the average Nusselt number plays a significant role in heat transfer applications. Due to our numerical investigations vertical cavities with nanofluid were better than horizontal cavities. Also the cavities, which we used nanofluid, had better efficiency in natural convection numerical modeling for both horizontal and vertical fluid layer.
Investigation of enhancement of heat transfer in natural convection utilizing of nanofluids
World Academy of Science, Engineering and Technology, International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering, 2015
This paper analyses the heat transfer performance and fluid flow using different nanofluids in a square enclosure. The energy equation and Navier-Stokes equation are solved numerically using finite volume scheme. The effect of volume fraction concentration on the enhancement of heat transfer has been studied icorporating the Brownian motion; the influence of effective thermal conductivity on the enhancement was also investigated for a range of volume fraction concentration. The velocity profile for different Rayleigh number. Water-Cu, water AL2O3 and water-TiO2 were tested.
2021
The effect of nanoparticle shape on the natural convection heat transfer of Cu-Al2O3/water hybrid nanofluid inside a U-shaped enclosure is presented in this paper. The governing equations are transformed into the dimensionless form using dimensionless variables. A three-node triangular finite element method is used with the Newton-Raphson method to solve the problem numerically. The streamlines and isotherms as well as the local and average Nusselt numbers are presented for the fluid flow with Rayleigh number of 10 to 10.It is found that blade nanoparticle shape produces the highest heat transfer rate while sphere is the lowest.
International Journal of Heat and Mass Transfer, 2015
The present work deals with the steady-state natural convection in a cubic enclosure filled with the water-Au nanofluid. The enclosure is heated on the vertical and cooled from the adjacent wall, while the other walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The effects of the volume fraction of nanoparticles in the range 0% 6 u 6 5% on the heat transfer characteristics of Au nanofluids are investigated for the nominal values of base-fluid Rayleigh number 10 1 6 Ra bf 6 10 6. It is shown that adding nanoparticles in a base-fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the mean Nusselt number Nu values for nanofluids u > 0% ð Þare smaller than those obtained in the case of pure fluid with the same nominal value of Rayleigh number Ra bf due to the weakening of convective transport.
A NUMERICAL FORCED CONVECTION HEAT TRANSFER ANALYSIS OF NANOFLUIDS CONSIDERING PERFORMANCE CRITERIA
A nanofluid is a new heat transfer fluid produced by mixing a base fluid and solid nano sized particles. This fluid has great potential in heat transfer applications, because of its increased thermal conductivity and even increased Nusselt number due to higher thermal conductivity, Brownian motion of nanoparticles, and other various effects on heat transfer phenomenon. In this work, the first aim is to predict convective heat transfer of nanofluids. A numerical code is created and run to obtain results in a pipe with two different boundary conditions, constant wall temperature and constant wall heat flux. The v results for laminar flow for thermally developing region in a pipe are obtained for Al2O3/water nanofluid with different volumetric fraction and particle sizes with local temperature dependent conductivity approach. Various effects that influence nanofluid heat transfer enhancement are investigated. As a result, a better heat transfer performance is obtained for all cases, compared to pure water. The important parameters that have impact on nanofluid heat transfer are particle diameter of the nanoparticles, nanoparticle volumetric fraction, Peclet number, and viscous dissipation. Next, a heat transfer performance evaluation methodology is proposed considering increased pumping power of nanofluids. Two different criteria are selected for two boundary conditions at constant pumping power. These are heat transfer rate ratio of the nanofluid and the base fluid for constant wall temperature boundary condition and difference between wall temperature of the pipe at the exit and inlet mean temperature of the fluid ratio for constant wall heat flux case. Three important parameters that influence the heat transfer performance of nanofluids are extracted from a parametric study. Lastly, optimum particle size and volumetric fraction values are obtained depending on Graetz number, Nusselt number, heat transfer fluid temperature, and nanofluid type.
Chemical Engineering Research and Design, 2015
The natural convection heat transfer of two Newtonian nanofluids with different concentrations (0.1, 0.2, 0.5, 1, and 1.5 vol.% of TiO 2 and Al 2 O 3 nanoparticles in water) is examined in an isolated cylindrical enclosure. The upper surface of the enclosure is maintained at a constant temperature. The driving force for heat transfer is provided by exposing the lower surface to a constant heat flux. Experiments are conducted for three different heat fluxes. Results reveal that only adding the Al 2 O 3 nanoparticle to the water leads to an increase in the natural convection heat transfer coefficient of water in the enclosure. There is an optimum concentration of about 0.2% for Al 2 O 3 nanoparticle that heat transfer coefficient has its maximum value at this certain concentration. For all concentrations, the value of the heat transfer coefficient of TiO 2 /water nanofluid is lower than the corresponding value of the base fluid. In this work the effects of inclination angle (Â) and aspect ratio (AR) in three different heat fluxes are also investigated for finding an optimum geometry of the enclosure for natural convection heat transfer. It is revealed that, regardless of the nanofluids concentrations, the natural convection heat transfer of both nanofluids reached its maximum level at the inclination angle of 30 • and aspect ratio of 1.
Natural Convection Heat Transfer in a Nanofluid Filled U-Shaped Enclosures: Numerical Investigations
In the present work, enhancement of convective heat transfer rate in three-dimensional U-shaped enclosures using nanofluids is numerically investigated. Two different types of nanoparticles, namely, Cu, and Al 2 O 3 , with pure water, are the considered single-phase nanofluids. Natural convection and geometric parameter effects on the averaged Nusselt numbers are investigated. Velocity vectors and isotherm fields for the Al 2 O 3 /H 2 O nanofluid are presented at various Rayleigh numbers. The governing dimensionless equations are solved using the commercial finite-volume-based computational fluid dynamics code, FLUENT. Our results are consistent with previously published predictions. In particular, heat transfer enhancement is found to increase with increasing nanoparticles volume fractions, Rayleigh numbers, as well as cooled wall length extensions.
Two numerical modelings of free convection heat transfer using nanofluids inside a square enclosure
Mechanics Research Communications, 2015
This work describes the numerical simulation of natural convection heat transfer of Cu-water nanofluids in a square enclosure for Rayleigh numbers varying from 10 3 up to 10 5. Two different numerical approaches were used: the finite volume method and the finite element method. The nanofluids were assumed to be single-phase fluids with modified thermal properties obtained from experimental results and theoretical models. The results showed that the Nusselt number for nanofluids was basically the same as that obtained for the base fluid. Therefore, the enhancement observed in the heat transfer coefficient was significant due to the augmentation in the thermal conductivity.
International Journal of Thermal Sciences, 2013
Experimental investigation on natural convection heat transfer has been carried out inside vertical circular enclosures filled with Al 2 O 3 nanofluid with different concentrations; 0.0%, 0.85% (0.21%), 1.98 (0.51%) and 2.95% (0.75%) by mass (volume). Two enclosures are used with 0.20 m inside diameter and with two different aspect ratios. The bottom surface of the enclosure is heated using a constant heat flux flexible heater while the upper surface is cooled by an ambient air stream. Various uniform heat fluxes have been used to generate the natural convection heat transfer data. The average Nusselt number is obtained and correlated with the modified Rayleigh number at each concentration ratio of the nanofluid. The average Nusselt number is obtained for each enclosure and correlated with the modified Rayleigh number using the concentration ratio as a parameter. The results show that the heat transfer coefficient increases as the concentration increases up to a specific value of the concentration and then it decreases as the concentration continues to increase compared to the basic fluid of pure water. Furthermore, a general correlation is obtained using the volume fraction and the aspect ratio as parameters.
Advanced Powder Technology, 2017
In the present study, the problem of conjugate natural and mixed convection of nanofluid in a square cav-30 ity containing several pairs of hot and cold cylinders is visualized using non-homogenous two-phase 31 Buongiorno's model. Such configuration is considered as a model of heat exchangers in order to prevent 32 the fluids contained in the pipelines from freezing or condensing. Water-based nanofluids with Cu, Al 2 O 3 , 33 and TiO 2 nanoparticles at different diameters (25 nm 6 d p 6 145 nm) are chosen for investigation. The 34 governing equations together with the specified boundary conditions are solved numerically using the 35 finite volume method based on the SIMPLE algorithm over a wide range of Rayleigh number 36 (10 4 6 Ra 6 10 7), Richardson number (10 À2 6 Ri 6 10 2) and nanoparticle volume fractions 37 (0 6 u 6 5%). Furthermore, the effects of three types of influential factors such as: orientation of conduc-38 tive wall, thermal conductivity ratio (0:2 6 K r 6 25) and conductive obstacles on the fluid flow and heat 39 transfer rate are also investigated. It is found that the heat transfer rate is significantly enhanced by incre-40 menting Rayleigh number and thermal conductivity ratio. It is also observed that at all Rayleigh numbers, 41 the total Nusselt number rises and then reduces with increasing the nanoparticle volume fractions so that 42 there is an optimal volume fraction of the nanoparticles where the heat transfer rate within the enclosure 43 has a maximum value. Finally, the results reveal that by increasing the thermal conductivity of the 44 nanoparticles and Rayleigh number, distribution of solid particles becomes uniform. 45