Sharif Digital Repository

This work focuses on numerical validation of natural convection heat transfer of TiO2-water nanofluids in a cylindrical container using COMSOL. The main aim of this study is to examine different available approaches to calculate effective thermal conductivity and compare them with experimental data available in the literature. Simulation results show that for considered mixture, average Nusselt number decreases by increasing Rayleigh number and particle volume fraction. It has been found that only one model was able to represent similar trends for given particle volume fractions, compared to experimental results  

In this research, the effect of using nanoparticles on the Nusselt number in the natural convection at high Rayleigh numbers has been investigated. A two-component multiple relaxation times lattice Boltzmann code has been developed to investigate the natural convection of nanofluids in a 2D square enclosure. Three main forces, namely, buoyancy, drag, and Brownian forces are included to consider the interactions of the components. The potential force is also added to the model for the interactions among nanoparticles. The effects of Ra number, volume fraction of nanoparticles (ϕ), and size of nanoparticles (λ) have been investigated for two nanofluids (CuO-water and TiO2-water). Five... 

Nanofluids viscosity is one of the most important thermophysical properties in nanofluids usage especially in chemical and petroleum engineering applications. So it is highly desirable to predict the viscosity of nanofluids accurately. Experimental measurements are impossible in most situations and present models are not comprehensive and efficient especially for high temperature, high volume concentration and high viscosity values. In this study, a new correlation has been developed based on the comprehensive database of water based Al2O3, TiO2, SiO2 and CuO nanofluids viscosity data found in literature. The proposed correlation uses temperature, nanoparticle size, nanoparticle volumetric... 

In this paper, the effect of highly conductive copper oxide nanoparticles on the effective thermal conductivity (ETC) of rock samples was mathematically investigated. To solve the governing conservation equations for the ETC a commercial finite element package (COMSOL Multiphysics) was used. It should be stressed that the single-phase approach was employed to mathematically model the effect of nanofluid on the heat transfer improvement. The computational geometry of the rock samples was obtained by analyzing the microscopic images of the limestone rock samples. The results obtained from the mathematical modeling of the rock samples showed that the conductive heat transfer through porous... 

The aim of this paper is to investigate the thermal conductivity and viscosity of a hybrid nanofluid containing tetramethylammonium hydroxide (TMAH) coated Fe3O4 nanoparticles and gum arabic (GA) coated carbon nanotubes (CNTs), experimentally. The magnetic nanoparticles and CNTs are physically attached as the result of interaction between the TMAH and GA molecules. The morphology and structure of the samples are characterized with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The experiments are carried out in the magnetic nanoparticles volume concentration range of 0.1–0.9 %, CNT volume concentration range of 0.05–1.35 % and the temperature range of 25–55 °C. The... 

Environmentally responsive surface-modified nanoparticles are colloidal nanoparticles coated with, at least, two physicochemically distinct surface groups. Recent advances in the synthesis and production of nanoparticles have enabled the production of environmentally responsive surface-modified nanoparticles with both hydrophilic and hydrophobic surface groups. These nanoparticles act like colloidal surfactants. In this paper, environmentally responsive surface-modified silica nanoparticles are synthesized and used for enhancement of oil recovery. For this purpose, silica nanoparticles are coated with polyethylene glycol chains as hydrophilic agent and propyl chains as hydrophobic agent at... 

In this paper, the effects of both constant and alternating magnetic fields on the laminar forced convective heat transfer of a hybrid nanofluid containing tetramethylammonium hydroxide (TMAH) coated Fe3O4 nanoparticles and gum arabic (GA) coated carbon nanotubes (CNTs) flowing through a heated tube were investigated experimentally. The experiments were carried out over wide range of parameters such as Reynolds number (548-2190), volume concentrations of Fe3O4 (0.5-0.9%) and carbon nanotube (0.25-1.35%) nanoparticles, magnetic field strength (300-700 Gauss) and alternating magnetic field frequency (10-50 Hz). In present study, the experimental observations in the case without magnetic field... 

This paper simulates Al2O3-water nanofluid flow and forced convection around a rotating circular cylinder. The governing parameters are Reynolds number (1 ≤ Re ≤ 100), solid volume fraction of nanoparticles (0 ≤ φ ≤ 0.05) and non-dimensional rotation rate (0 ≤ α ≤ 3). The simulations are performed to study the effects of mentioned parameters on the heat transfer rate and fluid flow characteristics. The governing equations including the continuity, momentum, and energy equations are solved with a finite volume method. It is observed that the reduction of heat transfer with increase in rotation rate is in the vicinity of 6.9% and 32% for Re = 5 and 100, respectively at φ = 0.05. Furthermore,... 

At harsh conditions of high pressure high temperature (HPHT), polymers undergo thermal degradation leading to serious loss in fluid rheological and filtration properties. Nanoparticles are the most promising additives proposed to address this challenge. The stability of nanofluids is perused from various facets including rheological and filtration properties, shale stability, and zeta potential. The presence of nanoparticles could amazingly reduce the filtration at high temperatures even by 95%, and it also had a conspicuous effect on shale stability, thermal conductivity, and zeta potential. Experimental data were fit to rheological models to determine the best models describing the... 

Effects of inclination angle on natural convective heat transfer and fluid flow in an enclosure filled with Al2O3-water nanofluid are studied numerically. The left and right walls of enclosure are kept in hot and cold constant temperature while the other two walls are assumed to be adiabatic. Considering Brownian motion and thermophoresis effect (two important slip velocity mechanisms) the two-phase mixture model has been employed to investigate the flow and thermal behaviors of the nanofluid. The study was performed for various inclination angles of enclosure ranging from γ = 0° to γ = 60°, volume fraction from 0% to 3%, and Rayleigh numbers varying from 105 to 107. The governing equations... 

Oil recovery from carbonate reservoirs can be enhanced by altering the wettability from oil-wet toward water-wet state. Recently, silica nanoparticle (SNP) suspensions are considered as an attractive wettability alteration agent in enhanced oil recovery applications. However, their performance along with the underlying mechanism for wettability alteration in carbonate rocks is not well discussed. In this work, the ability of SNP suspensions, in the presence/absence of salt, to alter the wettability of oil-wet calcite substrates to a water-wet condition was investigated. In the first step, to ensure that the properties of nanofluids have not been changed during the tests, stability analysis... 

In this work, the absorption process of carbon dioxide is performed in a custom designed high pressure experimental setup in which the gas and nanofluid are in direct contact at static state in a closed vessel. The initial condition of the tests are set at 20, 30, and 40 bar and 308 K. Nanoparticles of SiO2, Al2O3, Fe3O4, and carbon nanotubes (CNTs) are dispersed in pure water to form nanofluids at concentrations of 0.02, 0.05, and 0.1 wt %. Also, CNT nanoparticle has been dispersed in methyldiethanolamine and diethanolamine aqueous solutions at the concentration of 0.02 wt %. The absorption performances of different nanofluids are compared with the base solutions and with other nanofluids... 

In this study, the unsteady three dimensional nanofluid flow, heat and mass transfer in a rotating system in the presence of an externally applied uniform vertical magnetic field is investigated. This study has different applications in rotating magneto-hydrodynamic (MHD) energy generators for new space systems and also thermal conversion mechanisms for nuclear propulsion space vehicles. The important effects of Brownian motion and thermophoresis have been included in the model of nanofluid. The governing equations are non-dimensionalized using geometrical and physical flow field-dependent parameters. The velocity profiles in radial, tangential and axial directions, pressure gradient,... 

In this paper, the effect of several different parameters on the thermal resistance of a Closed Loop Pulsating Heat Pipe (CLPHP) has been investigated. These parameters include the working fluid, the inclination angle, the filling ratio and the heat influx. Also, the impact of using nanofluids with different nano-particle concentrations has been analyzed. It was observed that a CLPHP can increase the heat transfer up to 11.5 times compared to an empty pipe. Optimum performance for a system with the water-silver nanofluid was achieved at conditions of 50% filling ratio and 0.9 K/W of thermal resistance, and for the water-titanium oxide system, these optimal conditions were found to be 40%... 

To investigate boiling heat transfer characteristics of nanofluids, transient quenching experiments of a high temperature silver sphere in water-based nanofluids with Ag and TiO2 nanoparticles were performed. A silver sphere with a diameter of 10 mm and an initial temperature of 700 °C was quenched in these nanofluids at a temperature of 90 °C. The results showed a considerable reduction in the quenching ability of nanofluids compared to that of pure water. The presence of nanoparticles in water caused the film boiling mode to vanish at lower temperatures depending on the mixture concentration. Calculated heat transfer rates in nanofluids were lower than those in pure water. In the quenching...