جستجوی مقالات مرتبط با کلیدواژه "viscosity" در نشریات گروه "مکانیک"

 The present study investigates the ability to improve the stability and heat transfer performance of water coolant fluid by dispersing aluminum oxide nanoparticles in water. Surfactant-free nanofluid with 4 different volume fractions of 0.05%, 0.5%, 1% and 2% were prepared by two-step method. The stability of the nanofluid was monitored by continuous imaging (visualization) and dynamic light scattering (DLS) techniques. Thermal conductivity, viscosity and density of aluminum oxide-water nanofluid were measured in 4 concentrations and at temperatures of 25, 35 and 45 °C. The results showed that the thermal conductivity and viscosity of aluminum oxide-water nanofluid increases with rising concentration. The viscosity of nanofluids in all concentrations were higher than the base fluid. This is while the increase in viscosity was almost independent of the increase in temperature. The highest percentage increase in the thermal conductivity of nanofluid is equal 49%, which was obtained at a concentration of 2% and a temperature of 45 °C. New correlations with high precision were presented based on the experimental data of thermal conductivity and viscosity of nanofluids. The heat transfer performance and pumping power of nanofluid were analyzed based on several performance criteria. The advantageous results of increasing the heat transfer capability made aluminum oxide-water nanofluid a potential candidate for cooling fluid in practical applications.

The cooling system is one of the most important components that affects the performance of an engine. This system increases the heat transfer and fuel economy, leading to improved the engine performance. Most internal combustion engines have a coolant fluid that can be air or a liquid coolant that flows through a heat exchanger (radiator) and is cooled by air. The rheological and thermophysical properties of the nanofluid are of great importance for calculating the performance of pumping in this system. The heat transfer inside the radiator can be increased by increasing the heat transfer surface area and increasing the heat transfer coefficient. The heat transfer coefficient can be increased by appropriate heat transfer methods or by improving the thermophysical properties of the heat transfer medium such as coolant fluids. In this study, two samples of the thermophysical properties of the base fluid, which is a solution of distilled water and ethylene glycol with equal presence percentages, were investigated after adding titanium dioxide and silicon dioxide nanoparticles, at the temperatures of 30°C and 60°C. The viscosity, shear stress, and thermal conductivity coefficient of the prepared nanofluid were measured at two volume concentrations of 1% and 2% and then, validated using various theoretical models. The results indicated an improvement in heat transfer by 8% and 17% for the temperatures of 30°C and 60°C, respectively. The rheological behavior of the prepared nanofluid at two volume concentrations of 1% and 2% was also examined and validated using different theoretical models. Additionally, the results showed a decrease in the shear stress with increasing the temperature and an increase in the shear stress with increasing the volume concentration of nanoparticles.

The investigation of the properties of two hybrid nano-lubricants MWCNT (30%)/ZnO(70%)-SAE40 and MWCNT(50%)/ZnO(50%)-SAE40 in different conditions by experimental and modeling methods and introducing a better nano-lubricant are done in this study. Experiments are performed in the temperature range of 25-50°C, volume fraction of 0.0625-1% and shear rate of 666.5-9331s-1 and the viscometer of Brookfield CAP 2000+ is used the results showed that both nano-lubricants have non-Newtonian and pseudo-plastic behavior. The highest increase of viscosity is occurred for nano lubricant of MWCNT-ZnO (50%-50%)/SAE40 by 28%, and the highest drop is occurred for nanolubricant MWCNT-ZnO (30%-70%)/SAE40 by 3% and therefore MWCNTZnO (30%-70%)/SAE40 nanolubricant has better performance. The results of the correlation provided by rsm method are in good agreement with the experimental data and R2 = 0. 9998 is obtained. The value of -0.95% <MOD < 1.10% is obtained and indicates a low modeling error. The sensitivity of nano-oil also increased with increasing the volume fraction. 

In this study, the effect of the ratio of different nanoparticle compositions on the viscosity performance of the base oil is investigated. The aim of this study is to achieve the characteristics of optimal nanolubricants. The experiments are performed at temperatures of 5-55°C, volume fractions of 0.05-1% and shear rates of 665.5-10664s-1. Experimental results showed that nanofluids have a non-Newtonian and quasi-plastic behavior. The maximum viscosity reductions are obtained for MWCNT / Al2O3 (10%: 90%) - 10W40 and MWCNT / Al2O3 (40%: 960%) - 10W40 at -8.13% and -10.85%, respectively. The results show that MWCNT / Al2O3 (10%: 90%)/10W40 nanofluids have better lubrication performance at engine start (lower oil viscosity) and engine movement (more controlled behavior) than competing nanofliud. Using the response level method, to predict the target response data, a normalized three-variable-three-degree model with the characteristics of the power transfer function, λ = -0.15 and a constant value equal to zero is presented. Margin of deviation is in the range of -"2.72" %<MOD<"2/66" %. More viscosity sensitivity also occurred at higher volume fractions.

Nanofluids are a new generation of fluids with very high potential in industrial applications. In this study, the effect of temperature and concentration of nanoparticles consisting of Al2O3 nanoparticles and graphene nanoplates on the rheological behavior of the base fluid consisting of water and ethylene glycol was studied. Also, 0.2%vol. of oleic acid and 0.2%wt. of sodium dodecyl sulfonate were added to the base fluid as a surfactant to disperse the nanoparticles. The volume fraction of nanoparticles in this study was considered 0.05, 0.1, 0.5, 1, 1.5, 2, and 2.5% by volume, and also to investigate the effect of temperature, the tested temperatures were selected in the temperature range of 263-293K. The morphology and microstructure of the nanoparticles were investigated by scanning and transmission electron microscopy. Detection of phases in nanoparticles was performed by X-Ray Diffraction analysis. Also, the specific area and porosity of nanoparticles were determined. The dynamic viscosity of hybrid nanofluids was measured and compared with the base fluid. The results showed that the rheological properties of nanofluid were dependent on temperature and nanoparticle concentration, especially at sub-zero temperatures. Hybrid nanofluid samples with solid volume fraction less than 0.5% showed Newtonian behavior, while samples with higher solid volume fractions showed non-Newtonian shear thinning behavior.

The first purpose of this paper was to obtain non-linear equations for describing pressure waves in a liquid with gas bubbles. For this purpose, non-linear equations of fourth order and some of their special cases for describing pressure waves in a mixture of fluid and gas were considered. Then, considering the influence of heat transfer and viscosity in fluid, a differential relation between pressure and perturbation radius of gas bubbles is obtained. It is shown that the Burgers, the KdV and KdV- Burger’ equations are special cases for describing pressure waves. Also, we introduced a -expansion method, which can obtain exact solutions of non-linear differential equations without requiring the boundary and initial conditions. In this method, by choosing special constants in the obtained solutions, more solutions of these equations can be obtained. These features exhibit the superiority of the introduced approach. compared to the other methods. Furthermore, exact solutions of these equations are obtained using -expansion method, which has many applications in science and engineering.

In recent years,the addition of the nanoparticles in base oils has been considered in order to improve the energy absorption and viscosity of oils by researchers. In this regard, in this paper, the effects of the addition of metal oxide nanoparticles, including CdO, NiO, Fe3O4, and ZnO with different weight percentages, on the damping ratio and the viscosity of the glycerin as base fluid has been investigated. The choice of this base fluid is due to its application in some lubricants, which can enhance the energy absorption and also improve the friction coefficient in the contact area of the two surfaces. The metal oxide nanoparticles are synthesized by chemically deposited and they are suspended in glycerin by ultrasonic stimulation. After that, viscosity experiments and OMA method are carried on for measuring viscosity and damping ratio, respectively. To reduce the probability of precipitating nanoparticles, mass fraction of nanoparticles include 0.2, 0.4 and 0.6 grams were chosen. Although, the results show that, the viscosity decreasein different nanoparticles with 0.2 gr mass, it enhance with 0.6 gr mass of the ZnO, CdO and Fe3O4 nanoparticles. On the other hand, despite the fact that all of the nanoparticles have enhanced the damping ratio, the results indicate that trend of variations of the NiO and ZnO nanoparticles are positive and CdO and Fe3O4 nanoparticles are negative.

One of the most important challenging subjects for scientists is the numerical simulation of the transport phenomena in heterogeneous media. The discontinuity in the properties causes computational errors leading to incorrect estimation of the exact values. Various methods were rendered to reduce the error. Most of these methods are based on the remeshing of the elements to align with discontinuities increasing the calculation cost significantly. One of the powerful methods introduced recently is extended finite element method (XFEM). XFEM is based on the modification of the interpolation functions to capture discontinuities throughout the domain. Using this method in fluid mechanic was merely addressed but recently the approach has been changed. So, in the present study, attempts were made to study the affecting factors on the deformation of Newtonian/Newtonian and non-Newtonian/Newtonian systems. The obtained results showed a good agreement with the experimental results by other scientists. Because of pressure field modification, studying droplet deformation becomes possible, even when rheological properties of component like viscosity ratio and interfacial tension are very different. The obtained results indicated that by fixing all rheological parameters, there will be an inverse relationship between the final droplet size and viscosity ratio of components.

In the current paper, the optimum conditions for bioethanol production from sugars were surveyed. Then the operational condition effect on some physical characteristics of bioethanol fuel was investigated. 27 types of bioethanol samples from sugarcane molasses, sugar beet molasses and sugar cane juice were produced at anaerobic fermentation condition in three different temperature levels of 25 ˚C, 30˚c and 35 ˚C and in three different time levels of 24h, 48 h and 72 h. Then the values of density, kinematic viscosity and flash point were calculated in triplets. The results showed that with increasing the temperature and time processing, the viscosity, density and flashpoint would be decreased. The sugar type had a significant effect on these parameters. The closest value of viscosity to its standard amount was related to sugarcane molasses, producing at 25 ˚C and after 72 h fermentation, which was 1.5174 cSt. The nearest amount of density to its standard value was reported 0.9560 which was attributed to sugarcane juice producing at 35˚C and after 72 hours and for flashpoint it was 24.5 ˚C which belonged to sugarcane juice at 30 ˚C and 72 hours. The most bioethanol concentration was 74 gr.L-1 which was produced from sugarcane juice at 35 c◦ and after 72h.

Using an appropriate lubricant is a vital issue for systems like internal combustion engines that they are constantly exposed to friction and wear due to the relative movement of their own components. Since improving properties of engine oil affects the better performance of engine, the addition of nanoparticles is proposed as a solution. Nanoparticles used in this study are Al2O3 which are polar in spite of their excellent characteristics like high thermal conductivity and high wear resistance. In this study, oleic acid is employed as a surface modification agent to prolong the dispersion stability of nanofluid. To examine the effect of nanoparticles size and viscosity of base fluid on dispersion stability of nanofluid, alumina nanoparticles were purchased and surface modified in two particle size of 40-60 nm and 20 nm and they were dispersed in engine oil as base fluid with viscosity of 20w50 and 10w40, both at the same concentration of 0.1wt% as the time passed the samples were photographed and results revealed that nanofluid sample made of 20w50 base fluid and nanoparticles of 40-60 nm exhibited the longest stability of 36 days. The discussed additive powder becomes super fine after surface modification which increases their tendency to agglomerate and precipitate and also the lower viscosity of base fluid which indicates its lower inner friction that will not prevent the precipitation of nanoparticles, are the reasons of lower dispersion stability of other nanfluid samples.

In the present paper, using the non-equilibrium molecular dynamic (NEMD) method, thermal conductivity coefficient of water based nanofluids was calculated and the influence of the metal nanoparticles type with four particle types including copper, silver, platinum, and gold inside a cooper nanochannel was investigated. Also, Pcff force field was used for modeling of the bonded and unbonded interactions among the molecules of water, nanoparticles, and the walls. The results, show that the silver nanoparticle has the maximum effect on the increasing of the nanofluid thermal conductivity coefficient. The interaction and tendency between water and nanoparticles were investigated by using of the radial distribution function (RDF) analysis and the diffusion coefficient of the nanofluid inside the nanochannel was then evaluated. Moreover, the thermodynamic properties of nanofluids including Cv and Cp were studied by using equilibrium molecular dynamic (EMD) method. The studies indicate that by adding nanoparticles to water, the specific heat value is reduced in constant pressure and volume, of which the minimum and maximum specific heat reduction is related to copper and platinum nanoparticles. By investigating the diagram of atoms’ density distribution, it was found that the highest density is related to the silver nanoparticle and the maximum thickness of water layer is formed alongside with the gold nanoparticle. The viscosity of the nanofluids was also calculated by two methods of equilibrium and non-equilibrium dynamics and it was specified that the viscosities obtained for the nanofluids were increased by adding the nanoparticles to water fluid.

Polychloroprene liquid adhesives are widely used in packaging industries. These types of liquid adhesives are widely used to connect carton and cartonplast boxes, wooden and metal boxes, while the price of this liquid adhesive is relatively low. The viscosity of the liquid adhesive is influenced by adhesion properties. As the temperature changes, the viscosity of the adhesive changes and as a result the adhesion and bonding properties will change. In this study, using Brookfield type viscometer at a temperature range of 15-30 °C, the viscosity of this type of liquid adhesive is measured experimentally, and in order to reduce the test time and avoid the cost of the test, the experimental data of viscosity isregressed to the Vogel theory model and also is fitted to determine the reasonable viscosity. In this case, viscosity can be readily achieved by calculating the viscosity with the Vogel theory model at the desired temperature fast. The results of this study showed that the percentage error of experimental viscosity and the calculated viscosity of polychloroprene liquid adhesive is in the range of 0.03-2.63%, which is very acceptable percentage of error compared to other theories. Therefore instead of performing the long stages of the experimental to determine the polychloroprene liquid adhesive viscosity, using the Vogel theory model to obtain and predict the best conditions for bonding the surfaces with this liquid glue easily.

Heavy fuel oil (Mazut) has high viscosity that doesn't flow at the ambient temperature and should be warmed up to flow. One of the fuel warming up solutions is the steam tracing system. In this method, a steam pipe with 3/4 or 1 inch diameter is installed in parallel with Mazut pipe connected with specific bounds. The condensate is collected using steam traps installed in a proper distances and returns to the condensate tank. In this paper, the heat transfer process is simulated numerically in the steam tracing system installed on the Masut pile lines using Ansys-Fluent commercial software. Mazut pipes are simulated in different conditions including the pipes without insulation, with insulation and with steam tracing & insulation, and then numerical results are compared to each other. In addition, the effects of different steam temperature on the Mazut viscosity are investigated. It is concluded that steam tracing system is not needed essentially for the short length pipes. Besides, using the steam tracing with the insulation will cause constant fuel oil temperature and this will be critical in cold ambient temperature. Moreover, increasing the steam temperature has little effect on the steam tracing system efficiency so that the higher steam temperature just leads to higher heat loss and reduces the overall efficiency of the system.

One of the most important issues affecting engine efficiency is the internal friction of the engine. One of the important factors in the friction of the engine is the type of oil and its viscosity. In this paper, we tried to measure the amount of friction of the ring and pistons by the motoring method with two kinds of 10W40 and 20W50 oils with different viscosities and at temperatures of 35, 60 and 90 °C. In the next step, the semi-empirical equations for friction were compared with the results of the experimental validation tests for 90 °C. In the final step, the coefficients of the semi-empirical correlations were confirmed for other temperatures. The experimental results showed the significant effect of the viscosity at 35°C and 60 °C on the friction while its effect was negligible at 90°C. Also, the results of semi-empirical equations revealed that the friction contribution of the piston skirt was greater than the friction of the rings, and also the friction of the piston skirt increases with increasing speed.

This paper presents molecular dynamics modeling for calculating viscosity of nanofluids containing copper nanoparticles. In the first case, the copper nanoparticles were located as a spherical region in water-based fluid module SPC. System under specified boundary conditions, and writing code by LAMMPS software, and nanofluid ratios of 3.2,4.4,6.9 and 9.1 percented by Brownian motion of atoms, was carried out. three popular potential function, LennardJones, Coulomb, and embedded atom method were used. Between equilibrium molecule dynamic, and non- equilibrium molecule dynamic, (EMD) and Green-kubo formula were used to calculate viscosity. The results show that by increasing the amount of voloume fraction, viscosity increases. nanofluids in addition to other factors, such as volume fraction of particles in Brownian motion and clustering phenomenon, each in turn causes changes in viscosity. The simulation results were compared with other's works and found that the obtained results are remarkably accurate.