Sharif Digital Repository

Due to significant reduction in fossil fuel sources, several researches have been conducted recently to explore modern sources of renewable energy. One of the major fields in the category of renewable energy harnessing devices is parabolic trough solar collector (PTC). Several parameters have effect on the overall efficiency of the PTCs. As the effect of these parameters is coupled to each other, a comprehensive investigation is necessary. In the present study, a numerical analysis is performed to examine the efficiency of PTCs via variation of several governing parameters (e.g., wind velocity magnitude, nanoparticles volume fraction, inlet temperature, and reflector's orientation). A... 

In this study, the effect of graphene nanoplatelets (GNP)/distilled water nanofluid on the thermal performance of evacuated tube solar collector (ETSC) water heater was experimentally investigated. The mass percentage of GNP was considered at 0.025, 0.5, 0.075 and 0.1 wt%. The physical and thermal properties of the GNP nanofluids including stability, specific heat capacity, viscosity and thermal conductivity were investigated. The thermal efficiency tests on the solar collector were carried out for varying volumetric flow rate of 0.5, 0.1, and 1.5 L/min while the ASHRAE standard 93–2003 was considered to calculate the efficiency of the collector. The results indicated that the solar... 

This paper investigates numerically the problem of unsteady magnetohydrodynamic nanofluid flow and heat transfer between parallel plates due to the normal motion of the porous upper plate. The governing equations are solved via the fourth-order Runge-Kutta method. Different kind of nanoparticles is examined. The effects of kind of nanoparticle, nanofluid volume fraction, expansion ratio, Hartmann number, Reynolds number on velocity and temperature profiles are considered. Also effect of different types of nanoparticles is examined. Results indicate that velocity decreases with increase of Hartmann number due to effect of Lorentz forces. Rate of heat transfer increase with increase of... 

In this article, a three-dimensional numerical simulation is performed to investigate the effect of magnetic field on the heat transfer of ferrofluid inside a tube which is equipped with twisted tape. This work comprehensively focused on the flow feature and temperature distribution of ferrofluid in presence of non-uniform magnetic field while ferrofluid swirled inside a tube with twisted tape. In this study, it is assumed that the ferrofluid is single phase and laminar and constant heat flux is applied on the outside of the tube. The magnetic field is established by wire in parallel direction with the axis of the tube. The base fluid is water with 0.86 Vol% Nano particles (Fe3O4). The... 

In this paper, an experimental evaluation on the viscosity of water-based manganese ferrite nanofluid with and without magnetic field with 100, 200, 300, and 400 G intensities has been conducted. The Brookfield DV-I PRIME viscometer is implemented to measure the MnFe2O4/water nanofluid viscosity and to evaluate the influence of different volume concentrations (from 0.25% to 3%) and various temperatures (from 20 to 60 °C) on the viscosity. According to the measurements, viscosity incrementally increases with the augmentation of nanoparticles concentration while it remarkably decreases at higher temperatures under absence and attendance of magnetic field. The maximum viscosity ratio of 1.14 is... 

Hydrophobic titania nanoparticles were synthesized by a novel in situ sol-gel method and applied in a single drop liquid-liquid extraction column to enhance the overall dispersed-phase mass transfer coefficient (Kod). The chemical system of toluene, acetic acid and water was used, and the direction of solute (acetic acid) mass transfer was from dispersed phase, including: toluene and acetic acid to the continuous phase of water. For such system, much of the mass transfer resistance exists in the dispersed phase, which is nonpolar organic liquid. Hence, modified titania nanoparticles (MTNP's), prepared by sol-gel route, in five different concentrations of 0.001–0.005 wt.% were added in the... 

Thermal conductivity of nanofluids plays key rol in heat transfer capacity of fluids. adding nanoparticles to a base fluid can lead to enhancement in thermal conductivty ratio. CuO/Ethyle Glycol (EG) is one of the most applicable nanofluids for heat transfer purposes. In the present study, thermal conductivty ratio of CuO/EG nanofluid is modeled by applying Group Method of Data Hnadling and Least Square Support Vector Machine – Gentic Algorithm approaches. Results indicated that the utilized model are very accurate in predicting thermal conductivty ratio of the nanofluid. The R-squared values for the proposed model are equal to 0.994 and 0.991 by applying Group Method of Data Handling and... 

In the present paper, several experimental and theoretical studies conducted on the thermal conductivity of nanofluids are represented and investigated. Based on the reviewed studies, various factors affect thermal conductivity of nanofluids such as temperature, the shape of nanoparticles, concentration and etc. Results indicated the increase in temperature and concentration of nanoparticles usually leads to the higher thermal conductivity of nanofluids. In addition, it is concluded that there are some novel approaches in order to obtain nanofluids with more appropriate thermal properties including using binary fluids as the base fluid or utilizing hybrid nanofluids. © 2018 Elsevier B.V  

We numerically solve the Navier-Stokes equations to study the rarefied gas flow in short micro-and nanoscale channels. The inlet boundary conditions play a critical role in the structure of flow in short channels. Contrary to the classical inlet boundary conditions, which apply uniform velocity and temperature profiles right at the real channel inlet, we apply the same inlet boundary conditions, but at a fictitious position far upstream of the real channel inlet. A constant wall temperature incorporated with suitable temperature jump is applied at the channel walls. Our solutions for both the classical and extended inlet boundary conditions are compared with the results of other available... 

The kinetic-theory-based numerical schemes, such as direct simulation Monte Carlo (DSMC) and information preservation (IP), can be readily used to solve transition flow regimes. However, their high computational cost still promotes the researchers to extend the Navier-Stokes (NS) equations beyond the slip flow and to the transition regime applications. Evidently, a suitable extension would accurately predict both the local velocity profiles and the mass flow rate magnitude as well as the streamwise pressure distribution. The second-order slip velocity model derived from kinetic theory can provide relatively accurate velocity profiles up to a Knudsen (Kn) number of around 0.5; however, its... 

In this study, silicon microchannel heat sink (MCHS) performance using nanofluids as coolants was analyzed. The nanofluid was a mixture of nanoscale Cu particles and pure water with various volume fractions. Based on theoretical models and experimental correlations, the heat transfer and friction coefficients required in the analysis were used. In the theoretical model, nanofluid was treated as a single-phase fluid. In the experimental correlation, thermal dispersion due to particle random motion was included. The microchannel heat sink performances for a specific geometries with Wch = W fin = 100 μm and Lch =300 μm is examined. In this study, flow in laminar and turbulent regimes using the... 

The optimal design of a casting feeding system is considered. The problem is formulated as the volume constrained topology optimization and is solved with the finite element analysis, explicit design sensitivity, and numerical optimization. In contrast to the traditional topology optimization where the objective function is defined on the design space, in the presented method, the design space is a subset of the complement of the objective function space. To accelerate optimization procedure, the nonlinear unsteady heat transfer equation is approximated with a Poisson-like equation. The feasibility of the presented method is supported with illustrative examples. © 2007 Springer-Verlag  

The aim of this research is to conduct atomistic investigations of physical interaction analysis of nanoscale objects manipulation. The system consists of tip, particle and substrate. The manipulation tool moves with a constant speed while pushing the particle in a desired direction. The focus of the research is on ultra-fine metallic nanoparticles. To perform this research, Nose-Hoover dynamics and Sutton-Chen interatomic potential will be used to investigate the behavior of the aforementioned system which is made from different transition metals. The effects of size, material type and temperature on the success of the process have been investigated by planar molecular dynamics. © 2008 IEEE... 

In recent years, the importance of capturing CO2 has increased due to the necessity of minimizing climate change and the detrimental effects of CO2 emissions from industrial processes. CO2 absorption, as one of the most mature carbon capture technologies, has been improved by introducing nanosized particles into liquid absorbents. Nanofluids have been the subject of interest in many studies recently due to their tremendous impact on absorption. This review comprehensively examines the CO2 absorption behavior for nanofluids through the investigation of different absorption systems. Potential mechanisms for improving the absorption/regeneration performance of nanoabsorbents as well as the... 

An enhancement in heat transfer due to nanofluids is essentially required in various thermal systems. Hybrid nanofluids possess high thermal conductivity and, have ability to embellish and enhance the thermal strength of common fluids. Our concern in this paper is to examine the innovative attributes of hybrid nanofluids like Manganese zinc ferrite (MnZnFe2O4) and Nickel zinc ferrite (NiZnFe2O4) in the bio-convective flow of motile gyrotactic microorganisms subject to Darcy Forchheimer medium. The effect of activation energy has also been taken into account. Mathematical treatment is carried out via MATLAB software. The use of MnZnFe2O4 - NiZnFe2O4/H2O exhibits improved thermal... 

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... 

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... 

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... 

Application of nanoparticles for wettability alteration offers a practical approach to resolve some surface-related problems encountered in the nowadays technological process. Examples are underground/subsurface engineering implications, including the enhanced oil recovery from the oil-wet carbonate reservoirs. However, the common wettability evaluating techniques such as contact angle and flotation cannot be representative of the dynamic phenomena occurring at the pore scale and hence are unable to give accurate information about the process. Therefore, in the present work, the electrokinetic evaluations are utilized to explore the wettability alteration of initially oil-wet carbonate rock... 

The creation of surfaces with various super nonwetting properties is an ongoing challenge. We report diverse modifications of novel synthesized zirconia-ceria nanocomposites by different low surface energy agents to fabricate nanofluids capable of regulating surface wettability of mineral substrates to achieve selective superhydrophobic, superoleophobic-superhydrophilic, and superamphiphobic conditions. Surfaces treated with these nanofluids offer self-cleaning properties and effortless rolling-off behavior with sliding angles ≤7° for several liquids with surface tensions between 26 and 72.1 mN/m. The superamphiphobic nanofluid coating imparts nonstick properties to a solid surface whereby...