Mass Fraction Of Nanoparticles Research Articles

Effects of half spherical bulges on heat transfer characteristics of CPU cooled by TiO2-water nanofluids

TiO2-water nanofluids are prepared by a two-step method, and the stabilities of nanofluids are studied by sedimentation observation method and transmittance method respectively. Related experimental system for studying the heat transfer characteristics of CPU cooled by nanofluids is established, and the reliability of the experimental system is researched. The heat transfer and flow characteristics of CPU cooled by TiO2-water nanofluids are experimentally investigated. The effects of half spherical bulges arrangement modes (aligned and staggered arrangement) on the heat transfer enhancement of CPU are discussed. It is found that the surface temperatures of CPU cooled by nanofluids with aligned arrangement and staggered arrangement can be reduced by 10.5% and 12.5% at best compared with base fluid respectively. Also, the effects of nanoparticle mass fractions (ω = 0.1%, 0.2%, 0.3%, 0.4% and 0.5%) and Reynolds numbers (Re = 98, 185, 274, 323, 365, 400, 478, and 548) on the thermo-hydraulic performances are analyzed. It is found that nanofluids with ω = 0.4% show the best heat transfer performance, and the arrangement model and nanoparticle mass fraction have little effect on the resistance coefficient at high Reynolds number (Re > 365). Lastly, the comprehensive performances of nanofluids in the CPU are investigated.

Experimental and Numerical Investigation of Inlet Temperature Effect on Convective Heat Transfer of γ-Al2O3/Water Nanofluid Flows in Microtubes

ABSTRACTNanofluids are the combination of a base fluid with nanoparticles with sizes of 1–100 nm. In order to increase the heat transfer performance, nanoparticles with higher thermal conductivity compared to that of base fluid are introduced into the base fluid. Main parameters affecting single-phase and two-phase heat transfer of nanofluids are shape, material type and average diameter of nanoparticles, mass fraction and stability of nanoparticles, surface roughness, and fluid inlet temperature. In this study, the effect of inlet temperature of deionized water/alumina (Al2O3) nanoparticle nanofluids was both experimentally and numerically investigated. Nanofluids with a mass fraction of 0.1% were tested inside a microtube having inner and outer diameters of 889 and 1,067 µm, respectively, for hydrodynamically developed and thermally developing laminar flows at Reynolds numbers of 650, 1,000, and 1,300. According to the obtained numerical and experimental results, the inlet temperature effect was more pronounced for the thermally developing region. The performance enhancement with nanoparticles was obtained at rather higher Reynolds numbers and near the inlet of the microtube. There was a good agreement between the experimental and numerical results so that the numerical approach could be further implemented in future studies on nanofluid flows.

A new correlation for estimating the thermal conductivity and dynamic viscosity of CuO/liquid paraffin nanofluid using neural network method

In this study the effects of CuO nanoparticles mass fraction and temperature was studied on the dynamic viscosity and thermal conductivity of CuO/viscous paraffin nanofluid. TEM and DLS analysis as well as zeta potential test were performed for obtaining the morphology and nanoparticles stability within the basefluid. The results of TEM and DLS images exhibited that the average CuO nanoparticles diameter was ranged from 15 to 30 nm. Moreover, Zeta potential analysis showed high stability of nanoparticles in the basefluid. In addition, the results showed that with the increment of nanoparticles mass fraction and temperature the ratio of the thermal conductivity of nanofluid to basefluid increased and this parameter increases significantly with the temperature at the temperature below 40 and 70 °C where the mass fraction was chosen below and higher than 2.5 wt%, respectively. Also the results showed that with the increase of temperature the ratio of dynamic viscosity of nanofluid to basefluid decreases insignificantly and with the increment of nanoparticle load this parameter enhances tangibly. Moreover, two separated correlation including temperature and mass fraction of CuO nanoparticle was estimated by using hybrid GMDH-type neural network method for estimating relative dynamic viscosity and thermal conductivity of nanofluid. The results declared that the deviation of the data obtained by correlation from the experimental values was mostly <5% for both the thermal conductivity and dynamic viscosity. Finally, the value of relative Pr number was calculated at various temperature and mass fraction of CuO nanoparticles based on obtained correlations. The results of sensitivity analysis for relative Pr number exhibited that this parameter is more sensitive to mass fraction of nanoparticles in comparison with the temperature.

Experimental study on enhancement of falling film absorption process by adding various nanoparticles

Absorption air conditioning system containing no chlorofluorocarbons is considered environmentally friendly and a competitive alternative to conventional vapor compression air conditioning system. One of the most commonly used refrigeration working pair is LiBr/H2O. This paper experimentally studies the falling film absorption of LiBr/H2O with various kinds of nanoparticles dispersed, such as Cu, Al2O3 and CNT. The results show that the variety, mass fraction and size of nanoparticles, as well as solution flow rate are considered as the key parameters. The smaller the nanoparticles size, the better the effective absorption ratio. The larger the nanoparticles mass fraction, the better the effective absorption ratio. The best enhancement is achieved by adding Cu nanoparticles for all the studied nanoparticles species. The effective absorption ratios for all the studied cases are higher than 1.0, which proves that the dispersed nanoparticles have positive effects on the absorption process.

The numerical modeling of water/FMWCNT nanofluid flow and heat transfer in a backward-facing contracting channel

In recent years, the study of rheological behavior and heat transfer of nanofluids in the industrial equipment has become widespread among the researchers and their results have led to great advancements in this field. In present study, the laminar flow and heat transfer of water/functional multi-walled carbon nanotube nanofluid have been numerically investigated in weight percentages of 0.00, 0.12 and 0.25 and Reynolds numbers of 1–150 by using finite volume method (FVM). The analyzed geometry is a two-dimensional backward-facing contracting channel and the effects of various weight percentages and Reynolds numbers have been studied in the supposed geometry. The results have been interpreted as the figures of Nusselt number, friction coefficient, pressure drop, velocity contours and static temperature. The results of this research indicate that, the enhancement of Reynolds number or weight percentage of nanoparticles causes the reduction of surface temperature and the enhancement of heat transfer coefficient. By increasing Reynolds number, the axial velocity enhances, causing the enhancement of momentum. By increasing fluid momentum at the beginning of channel, especially in areas close to the upper wall, the axial velocity reduces and the possibility of vortex generation increases. The mentioned behavior causes a great enhancement in velocity gradients and pressure drop at the inlet of channel. Also, in these areas, Nusselt number and local friction coefficient figures have a relative decline, which is due to the sudden reduction of velocity. In general, by increasing the mass fraction of solid nanoparticles, the average Nusselt number increases and in Reynolds number of 150, the enhancement of pumping power and pressure drop does not cause any significant changes. This behavior is an important advantage of choosing nanofluid which causes the enhancement of thermal efficiency.

Effect of different surface modified nanoparticles on viscosity of nanofluids

Resistance to fluid flow creates various problems, and fluid viscosity reduction can effectively control these problems. Hydrophilic TiO2-water and hydrophilic-lipophilic TiO2-water nanofluids were prepared by stirring and ultrasonic mixing; the rotational viscometer was used to measure the viscosity of nanofluids that formed by different surface modifications of nano-titanium dioxide and deionized water. The results show that the viscosity of TiO2-water nanofluid increases with the decrease in the temperature and increase in the mass fraction of nanoparticles, the hydrophilic TiO2-water nanofluids has a slightly larger viscosity than the hydrophilic-lipophilic TiO2-water nanofluids, and the higher the mass fraction of the nanoparticles is, the greater the difference is.

Experimental Investigation of the Effect of Nano Heavy Metal Oxide Particles in Piperazine Solution on CO2 Absorption Using a Stirrer Bubble Column

In this work, absorption of CO2 into a nanofluid of TiO2, ZnO, and ZrO2 in piperazine solution was investigated experimentally in a continuous stirrer bubble column. The dosage range of nanofluids was 0.01 to 0.1 wt% in the experiments. The process parameters, such as nanoparticles type, solid loading, and stirrer speed, were varied to the hydrodynamics and absorption performance, including gas holdup, Sauter mean diameter, CO2 loading, CO2 removal efficiency, absorption rate, mass transfer flux, and overall mass transfer coefficients. The results showed that the nanoparticle mass fraction and range of stirrer speed have an optimum value for the above-mentioned performance. The optimum value of TiO2, ZnO, and ZrO2 nanoparticles were 0.05, 0.1, and 0.05 wt%, respectively. The maximum absorption rate of TiO2, ZnO, and ZrO2 compared with that of pure Pz solution was 14.7% (0.05 wt%), 16.6% (0.1 wt%), and 3.7% (0.05 wt%), respectively. Also, with an increase of the stirring speed, the absorption performance i...

Optimization and parametric analysis of a nanofluid based photovoltaic thermal system: 3D numerical model with experimental validation

In this study, the effects of ZnO/water nanofluid and pure water as working fluids on the electrical and thermal energy efficiencies of a photovoltaic thermal system (PVT) are numerically investigated. The governing equations are discretized and solved using the pressure-based finite volume method by the ANSYS Fluent 16.2 software. The 3D numerical model is validated by comparing the simulation results with those of the measurements. The experiments are performed on selected days in August and September at the Ferdowsi University of Mashhad, Mashhad, Iran. To investigate the reliability of the measurements, an uncertainty analysis is performed for the experiments. The effects of the important operating parameters on the electrical and thermal energy efficiencies of the PVT system with ZnO/water nanofluid are studied. Moreover, the Taguchi method is applied to determine the optimum performance of the nanofluid based PVT system. The considered parameters include: absorbed solar irradiation, wind speed, ambient temperature, coolant inlet temperature, coolant mass flow rate, and nanoparticles mass fraction in the ZnO/water nanofluid. Based on the results of this study, reducing the coolant inlet temperature from 40 °C to 20 °C enhances the thermal energy efficiency of the nanofluid based PVT system by 16.21%. Moreover, it is found that the considered parameters in this study have slight effects on the electrical energy efficiency of the PVT system. The Taguchi analysis shows that the coolant inlet temperature is the most effective parameter on the efficiency of the nanofluid based PVT system.

Improved Thermal Energy Storage Behavior of CuO/Palmitic acid Composite as Phase Change Material

The present work aims to study the preparation and thermal energy storage behavior of CuO based composite PCM for thermal energy storage. Composite PCM comprises palmitic acid as base material and CuO nanoparticles (NPs) as supporting materials. Different mass fractions of NPs have been dispersed in the base material so as to determine the maximum thermal conductivity enhancement. SDBS has been selected as the surfactant for ensuring the uniform dispersion of NPs in base material. With the help of DSC measurements, the newly prepared composite PCMs have been tested to determine their phase change temperatures as well as latent heats during melting and solidification. Thermal conductivities of the composite PCMs with all mass fractions of NPs have been measured. Based on the test results, the newly prepared composite PCM could be considered to be a potential candidate for thermal energy storage.

The Influence of Al2O3- ZnO-H2O Nanofluid on the Thermodynamic Performance of Photovoltaic- Thermal Hybrid Solar Collector System

A thermodynamic analysis was conducted after testing two working fluids to particularly assess the effect of Nanofluid as heat transfer agent on improving thermal, electrical, and exergetic efficiencies of thermally biased solar photovoltaic/thermal (PV/T) hybrid collector system under State of Qatar climate, using experimentally and computationally obtained data. The investigated two fluids were water, and Al2O3-ZnO-H2O Nanofluid mixed with Ethylene Glycol as surfactant. Mass fractions of Nanoparticles were 0.05 wt.% Al2O3 with particle size of 5 nm and 0.05 wt.% ZnO with particles size of 10-30 nm. The results showed that in comparison between water as absorption medium and the mentioned Nanofluid, an increase in thermal and hence total efficiency of the system was recorded for the latter absorption medium scenario, despite considering concentrations of the Nanoparticles relatively low. A very general trend of dramatic decrease in the positive effect of Nanofluid in consistency with the ambient temperature increase was also observed after fitting the data to segments of straight lines. For 0.05 wt.% mass fraction of Nanoparticles the averaged increment in total efficiency was 4.1%, and in total useable energy (exergy) efficiency was 4.6%.

Modeling spectral properties of transparent matrix composites containing core-shell nanoparticles

Optical properties of transparent matrix composites containing metal nanoparticles coated with an oxide shell were numerically simulated based on the Aden-Kerker theory applicable for concentric spheres. Using pentaerythritol tetranitrate composites (containing Al/Al2O3 nanoparticles) as an example, the linear scattering and absorption coefficients as well as the total reflectance and transmittance and collimated beam transmittance were shown to be determined by the sample thickness, the nanoparticle radius, the mass fraction of nanoparticles, and mass fraction of the oxide in the nanoparticles. An approach to determining the said parameters based on the comparison of the calculated spectral dependencies of the reflectance and transmittance with the experimental ones was suggested. The nanoparticle radius was determined with the minimum error (of about 2-3%), while the nanoparticle mass fraction and oxide mass fraction were weak parameters determined with a 25% error.

Latent heat of fusion prediction for nanofluid based phase change material

This paper presents a study on the effect of mass fraction of nanoparticles, cooling rates and prediction of latent heat of fusion for Barium Chloride Dehydrate solutions (BaCl2·2H2O) by separately adding a mass fraction of 0.2 wt%–1 wt% magnesium oxide (MgO) and multi-walled carbon nanotubes (MWCNTs) and various cooling rates applied. The data was then compared with existing prediction model and a new correlation developed. The results show that the latent heat of fusion reduced by 7% and 5.2% for MWCNT and MgO nanofluids respectively at a mass fraction of 1 wt% and at a cooling rate of 5 °C/min. Mass loss equation maximum deviation was 5.55% and 4.16% for MWCNT and MgO nanofluid respectively at a mass fraction of 1 wt% and at a cooling rate of 5 °C/min. The new correlation maximum absolute deviation was 1.2% at a mass fraction of 0.4 wt% and at a cooling rate of 5 °C/min for MWCNT nanofluid while for MgO nanofluid, the deviation was 1.7% at a mass fraction of 1 wt% and at a cooling rate of 10 °C/min confirming the accuracy of the new correlation and therefore can be applied to predict the latent heat of fusion of any nanofluid.

Experimental study on thermo-hydraulic performances of TiO2-H2O nanofluids in a horizontal elliptical tube

Stable TiO2-water nanofluids are prepared by a two-step method, and the morphologies of nanoparticles and the stability of nanofluids are investigated. The heat transfer and flow characteristics of nanofluids flowing through a horizontal circular tube and a horizontal elliptical tube are experimentally investigated. The effects of nanoparticle mass fractions (φ = 0.1 wt%, φ = 0.3 wt%, φ = 0.5 wt%) and Reynolds numbers (Re=5000-15,275) on the Nusselt number and flow frictional resistance coefficient are discussed. In addition, computational formulas for heat transfer and flow performances are put forward based on the experimental data using the polynomial fit technique. Also, thermo-hydraulic comprehensive performances of nanofluids in the horizontal circular tube and the horizontal elliptical tube are studied.

Investigation of permeability effect on slip velocity and temperature jump boundary conditions for FMWNT/Water nanofluid flow and heat transfer inside a microchannel filled by a porous media

The fluid flow and heat transfer of a nanofluid is numerically examined in a two dimensional microchannel filled by a porous media. Present nanofluid consists of the functionalized multi-walled carbon nanotubes suspended in water which are enough stable through the base fluid. The homogenous mixture is in the thermal equilibrium which means provide a single phase substance. The porous media is considered as a Darcy- Forchheimer model. Moreover the slip velocity and temperature jump boundary conditions are assumed on the microchannel horizontal sides which mean the influences of permeability and porosity values on theses boundary conditions are presented for the first time at present work. To do this, the wide range of thermo physical parameters are examined as like Da = 0.1 to 0.001, Re = 10,100, dimensionless slip coefficient from 0.001 to 0.1 at different mass fraction of nanoparticles. It is observed that less Darcy number leads to more local Nusselt number and also applying the porous medium corresponds to higher slip velocity.

Processing and Mechanical Properties of Ultra-high Molecular Weight Polyethylene Reinforced by Silver Nanoparticles

The present study was designed to investigate the mechanical performance of ultra high molecular weight polyethylene (UHMWPE) reinforced by silver nanoparticles. The Ag/UHMWPE nanocomposites were prepared by a plate vulcanizing machine and tested with a contact angle micrometer, UMT friction tester, electronic universal testing machine and MicroXAM three-dimensional profilometer to characterise the wettability, ball indentation hardness, creep resistance, compression properties, and friction and wear performance. A scanning electron microscope (SEM) was employed to describe the morphology of the Ag/UHMWPE nanocomposites surfaces following the friction and wear tests. These results demonstrate that the compressive yield strength, ball indentation hardness and creep resistance increased with an increase in the content of silver nanoparticles. The contact angle of the Ag/UHMWPE nanocomposites with bovine calf serum decreases with an increase in the content of silver nanoparticles and this change increases the wettability of the Ag/UHMWPE nanocomposites. Therefore, the friction coefficient decreases, but the wear mechanism changes from scratch and furrow to fatigue flakes when the mass fraction of silver nanoparticles exceeds 0.3%. The composite with a silver nanoparticles mass fraction of 0.3% exhibits a low friction coefficient and good wear resistance.

Study on stabilities, thermophysical properties and natural convective heat transfer characteristics of TiO2-water nanofluids

TiO2-water nanofluids with different mass fractions (ω = 0.1 wt%, ω = 0.3 wt% and ω = 0.5 wt%) are prepared respectively, and the stabilities are studied by scanning electron microscope, transmission electron microscope, dynamic analysis method and settlement observation method. Additionally, thermophysical properties of nanofluids are discussed, and models of thermophysical properties are deduced. Then, an experimental installation and a two-phase lattice Boltzmann model for natural convection heat transfer are established in this paper and the effects of cavity ratio, heating power and nanoparticle mass fraction on heat transfer are discussed respectively. It can be obtained that the thermal conductivities of TiO2-water nanofluids can be improved by 5.23% to the utmost extent. However, the heat transfer can be enhanced by 34.2% in the maximum with the increase of nanoparticle mass fraction at the lowest heating power and the largest cavity ratio.

Experimental study on thermo-hydraulic performances of CPU cooled by nanofluids

Stable Al2O3-water and TiO2-water nanofluids are prepared, and the morphology of nanoparticles and the stability of nanofluids are analyzed. An experimental set for heat transfer characteristics of CPU cooled by nanofluids is established in this paper. The heat transfer and flow characteristics of nanofluids in the CPU heat sink are experimentally studied. The effects of nanoparticle mass fractions (Al2O3-water: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 1.5% and 2%; TiO2-water: 0.1%, 0.2%, 0.3%, 0.4%, 0.5% and 1%) and Reynolds numbers (Re: 146, 275, 406, 479, 541, 593, 707 and 812) on the heat transfer and flow characteristics are discussed. In addition, the comprehensive evaluation for thermo-hydraulic performance of nanofluids is investigated. It is found that the nanofluids with the highest nanoparticle mass fraction have not the best heat transfer performance, and Nusselt number firstly increases and then decreases with nanoparticle mass fraction, and the critical nanoparticle mass fractions for the best heat transfer performance of Al2O3-water and TiO2-water nanofluids are ω=1.0% and ω=0.4% respectively. It is also found that Al2O3-water and TiO2-water nanofluids can reduce the temperature of CPU by 23.2% and 14.9% at best compared with water respectively.

Investigation of the use of nano-refrigerants to enhance the performance of an ejector refrigeration system

In this work, the performance of an ejector refrigeration system using nano-refrigerants is investigated. A new hypothesis is proposed for flow boiling modeling, where nanoparticles are assumed to not migrate to the vapor phase as phase changes occur continuously; this causes a significant increase in nanoparticle mass fraction for high vapor quality values. This assumption shows a reasonable correlation with previously published data for R113/CuO mixtures, where an average deviation of 9.24% was obtained. A parametric analysis is performed to investigate the variation in heat transfer coefficient (HTC) with temperature, nanoparticle type, size, and mass fraction. Finally, the effect of nanoparticles on the coefficient of performance (COP) of the ejector refrigeration cycle as a response to the augmented flow boiling HTC is investigated by simulating a 5-kW cooling refrigeration cycle. Considering the advantage of using nano-refrigerants, a higher quality vapor was attained at the evaporator exit, resulting in an increase in the enthalpy difference in the evaporator in the ejector cooling cycle. As a result, a lower mass flux inside the evaporator is required to attain the same cooling capacity. Improved refrigerant-side HTCs improve the overall HTCs of the evaporator, allowing the evaporator to operate at lower temperature differences and higher pressures, which consequently increases the cycle COPs. Furthermore, the refrigerant vapor quality increases at the evaporator exit, leading to an enhanced COP of the cycle. The augmentation in COP reached 24.7% and 12.61% for R134a with 2wt.% CuO and Al2O3, respectively, whereas the vapor quality for the refrigerant leaving the evaporator increased from 0.7616 for the case of the pure refrigerant to 0.8212 for R134a/CuO 2wt.% nano-refrigerant.

Synthesis and characterization of fluorinated polyimide/TiO2 nanocomposites: enhancement of separation of four gases, thermal, optical and mechanical properties

Nanocomposite gas transport and thermally stable membrane-based fluorinated polyimide/TiO2 nanoparticles were prepared via in situ sol–gel fabrication. PI/TiO2 nanocomposites containing 4, 8, and 12% TiO2 were successfully fabricated by in situ sol–gel fabrication. The obtained PI/TiO2 nanocomposites were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry analysis, X-ray powder diffraction, field emission-scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). Thermogravimetric analysis data indicated an increased thermal stability of the PI/TiO2 nanocomposites compared to the pure polymer. The results of gas permeation showed the permeability of ethylene and propylene increased in PI/TiO2 nanocomposites compared to the pure PI. The diffusion coefficients of prepared hybrid membranes were determined by the time lag method. The results showed an increase in the solubility coefficient and a decrease in the diffusion coefficient of gases while increasing the TiO2 nanoparticle mass fraction.

Experimental investigation of the effects of temperature and mass fraction on the dynamic viscosity of CuO-paraffin nanofluid

In this study the effects of mass fraction of CuO nanoparticles and temperature was investigated on the dynamic viscosity of liquid paraffin based nanofluid. For this purpose, CuO nanoparticles were prepared by using precipitation method in which Cu(NO3)2·3H2O was used as a precursor. Moreover, in order to assess the morphology and stability of nanoparticles, TEM and DLS analysis as well as zeta potential test were performed on CuO nanoparticles. The results of TEM analysis indicated that the average nanoparticles diameter was ranged from 15 to 30nm. In addition, the results of experiments indicated that with the enhancement of nanoparticles load the ratio of the dynamic viscosity of nanofluid to basefluid increases and with the increase of temperature the viscosity of nanofluid declines significantly. Moreover it was concluded that dynamic viscosity of nanofluid increases at the condition where CuO mass fraction was chosen to be above 1.5wt% while at the condition below 1.5wt% the change in viscosity is not highly tangible. Finally, a unique empirical correlation including temperature and mass fraction of CuO nanoparticles was obtained based on regression analysis and used for calculating the relative viscosity of nanofluid. The results of regression analysis exhibited that the deviation of the data obtained by correlation from the experimental values was mostly less than 5% and the results of sensitivity analysis showed that the nanofluid viscosity is more sensitive to nanoparticles mass fraction in comparison with the temperature.