Temperature Coefficient Of Viscosity Research Articles

Spontaneous imbibition of unsaturated sandstone under different vertical temperature gradients: neutron radiography experiments and dynamic models

To elucidate the imbibition behavior of water in complex temperature and stress environments, spontaneous imbibition experiments were conducted on unsaturated matrix sandstones at different vertical temperature gradients by neutron radiography technology. Additionally, corresponding dynamic models of water imbibition in porous media were established. The research results reveal the phased characteristics of sandstone spontaneous imbibition and the influence of vertical temperature gradient on the evolution of wetting front. Specifically, the initial development speed of the wetting front increases with an increase in the vertical temperature gradient, indicating a direct relationship. However, the growth rate of the wetting front gradually slows down with increasing time, eventually reaching a saturated state. Model validation demonstrates that the traditional Washburn's law is still valid in isothermal conditions without temperature gradient (G=0). Further analysis indicates that the imbibition rate has a direct correlation with linear thermal expansion coefficient (α) and viscosity temperature coefficient (β) across various vertical temperature gradients, and an inverse correlation with surface tension temperature coefficient (γ). Furthermore, when the values of α, β, and γ fall below 0.001, their impact on the imbibition rate becomes negligible. The sensitivity of the imbibition rate to parameters γ, β, and α decreases in that order, with γ being the most sensitive, followed by β, and α being the least sensitive. Moreover, the relative importance of α, β, and γ dictates their specific influence on the imbibition rate, and a synergistic effect exists among these parameters, which collectively influence the water absorption behavior of sandstone.

Some Methods for Determining the Viscosity Index of Hydraulic Oil

Objectives: To determine the viscosity index of hydraulic oil by three methods. These methods are: the viscosity index determined by a mathematical relationship, using a calculation program and the graphic method. The study also intends to determine the viscosity-temperature coefficient for the hydraulic oil. Methods: To determine the kinematic viscosity of the hydraulic oil, we used a calculation formula that transforms the dynamic viscosity into kinetic viscosity knowing the density of the fluid. Thus, we determined the dynamic viscosity of the hydraulic oil with the Schott Ubbelohde viscometer at the temperatures of 40 and 100◦C. To determine the dynamic viscosity of hydraulic oil at 40◦C and 100◦C, we used a water bath. The dynamic viscosity thus obtained was transformed into the kinematic viscosity of the oil by dividing it by density. Findings: The lowest viscosity index of the hydraulic oil determined using the computer program is 101. The viscosity index of the hydraulic oil determined with relation (1) is 58% higher than using the computer program. The viscosity index determined by the graphic method is 50% higher than the one determined by the computer program. The viscositytemperature coefficient has a value of 0.8380. Novelty: Knowing the viscosity index of hydraulic oil is important for starting the engine at high temperatures and at low temperatures. At high temperatures, the oil chemically degrades and the molecules break down. The properties of hydraulic oils depend a lot on the way the hydraulic system works and the limits imposed on them in different conditions. Keywords: Viscosity Index; Viscosity-Temperature Coefficient

DETERMINATION OF THE VISCOSITY TEMPERATURE COEFFICIENT (β) AND PSEUDOPLASTIC INDEX (n) OF POLY(LACTID ACID) (PLA)

Poly(lactic acid) (PLA) is one of the most important ecological thermoplastics due to its good mechanical properties. In light of this, investigations related to the effects of PLA processing parameters are important as they affect the final product performance. This work aimed to determine the viscosity-temperature coefficient (β) and pseudoplastic index (n) of PLA and estimate its degradation rate during processing using an internal mixer. The viscosity coefficient was determined applying different processing temperatures at the same rotors rotation rate, which allowed estimating β = 0.048 ◦C−1. PLA’s pseudoplastic index (n) under the tested conditions suggested a value of approximately 0.71. PLA’s degradation rate was around 4% under rotor rate of 120 rpm and temperature of 190 ◦C.

Viscosity Index for Oil Used as Biodegradable Lubricant

Objectives: To study the viscosity index for oil used as biodegradable lubricant using tree methods. Methods: Viscosity index for oil used as biodegradable lubricant (coconut oil, soybean oil, corn oil, rapeseed oil) was determined using a set of Schott Ubbelohde-type viscometers selected according to the values of their constants, so that the margins of the uncertainty, inherent in the Hagebach–Couette correction, does not exceed the error allowed for the measurements. The measurements were carried out at 40 ± 0.1 and 100 ± 0.1 °C, according to the recommendation of ASTM D2270. Findings: The viscosity index of soybean oil is the highest and the viscosity index of rapeseed oil is the lowest. The viscosity index determined with the calculator for coconut oil is one unit higher than that obtained by the formula (1). The viscosity index of corn oil determined with relation (1) is 151, and the one determined by computer is 25 units higher. The viscosity index of rapeseed determined with relation (1) is 143, and the one determined with the computer program is 23 units higher. The viscosity index determined for soybean oil determined using the program has a negative value. The viscosity oils used as biodegradable lubricant were determined using tree methods: ASTM D 2270 and method graphically using ASTM D 341. Viscosity index calculation was performed with a computer program using kinematic viscosity at 40 °C and 100 °C. The viscosity-temperature coefficient for oils used as biodegradable lubricant can vary by a factor of 10 depending on the temperature. The viscosity of oil oils used as biodegradable lubricant is dependent upon temperature. Viscosity decreases as temperature increases because the molecules vibrate more, and interact less. Application: The three methods for determining the viscosity index can be applied both to vegetable oils used as biodegradable lubricants and to oils of SAE class. The term biodegradable lubricant includes a wide range of lubricants, such as: vegetable oils; hydrogenated vegetable oils; vegetable oils with high oleic acid content; synthetic esters produced from vegetable oils. Keywords: Viscosity Index, Viscosity-Temperature Coefficient.

Obtaining and Properties of L-Aspartic Acid Solutions of Chitosan

Conditions for obtaining L-aspartic acid solutions of chitosan were considered: dissolution of the polymer with the formation of chitosan aspartate occurs in pH range of 3.6–3.8 at a minimum stoichiometric ratio of [acid]/[chitosan (−NH2)] ∼ 0.43. The hydrodynamic, electrochemical, optical and biological properties of aqueous solutions of chitosan aspartic acid salt are investigated. It has been established that macromolecules of polymeric salt exhibit properties of a polyelectrolyte with a partially compensated charge in an aqueous medium. Huggins constants and temperature viscosity coefficients were calculated, which indicate an increased rigidity of the chitosan macrochain in the studied solutions and deterioration in the polymer—solvent interaction with increasing temperature. Chitosan aspartate powders in the form of lamellar microparticles with fractal ordering were isolated. Low biocompatibility and antibacterial activity of the polymeric salt are demonstrated, which allows recommending the production of biomedical products on its basis.

Hydrodynamic behavior of chitosan hydrochloride macromolecules in aqueous solutions of D- and l-ascorbic acid

The hydrodynamic behavior of chitosan hydrochloride macromolecules in aqueous solutions of D- and l-ascorbic acid in a temperature range 25–45°C was studied by capillary viscometry. The intrinsic viscosity, the Huggins constant, and the temperature coefficient of viscosity were estimated. The effect of the ionic strength of the solvent mixture, predetermined by varying the acid concentration or introducing NaCl, on the hydrodynamic volume of macromolecules and their manifestation of polyelectrolyte properties was revealed. It was established that an increased temperature had led to the macromolecular coils getting more compact and the thermodynamic quality of the water-acid medium as a polymer solvent getting poorer. Despite the close values of pH and ionic strength of the aqueous solutions of D- and l-ascorbic acid, chitosan hydrochloride in the d-ascorbic acid solution is characterized by larger macromolecules and the polymer interaction with the solvent mixture components is energetically more favorable. It is suggested that the conformational state of chitosan hydrochloride is affected not so much by the macrochain stiffness as by the isomeric form of ascorbic acid. A comparison was made of the viscometric parameters of the aqueous solution of the aminopolysaccharide in ascorbic acid with its traditional solvent media, namely: water, acetic and hydrochloric acids, and sodium acetate buffer.

Numerical study of viscous dissipation and non-Boussinesq model effects on CMC–TiO2 fluid flow over backward facing step with baffle

The present work examined numerically the mixed convection of a non-Newtonian nanofluid flow through backward facing step with baffle. The Boussinesq and non-Boussinesq models are used to formulate the momentum equation, and the viscous dissipation is taken into account in the energy equation. The governing equations are discretized using the finite volume method. Effects of different key parameters such as Richardson number, temperature–viscosity coefficient, Brinkman number and power law index on both the heat transfer and the fluid flow characteristics are investigated. The results are presented in term of streamlines and isotherms contours as well as the average Nusselt number. The results show that both viscous dissipation and buoyancy forces affect greatly the flow and heat transfer structures. A multicellular zone is observed behind the step when considering the non-Boussinesq approximation for Ri ≥ 5 and taking into account viscous dissipation (Br = 0.5). In addition, the flow behavior for both Boussinesq and non-Boussinesq approximations is identical for Ri = 1 and totally different for Ri ≥ 5. Furthermore, in contrast of the non-Boussinesq approximation, considering the Boussinesq one overestimates the heat transfer rate, especially for low power law index values.

THE RELATIVE VISCOSITY OF AQUEOUS SOLUTIONS OF Na-CARBOXY¬METHYLCELLULOSE AND ITS VARI-ATION DEPENDING ON THE ACIDITY OF THE MEDIUM, TEMPERATURE AND EXPOSURE TO ELECTROMAG-NETIC FIELD

The effect of pH on the relative viscosity of dilute Na-CMC solutions was studied. It shows a monotonic increase with increasing pH. The measurements were carried out in the temperature range 5–30 °C. Based on the dependence of the relative viscosity on temperature, the temperature coefficients of viscosity and the activation energy of the viscous flow of polymer solutions were determined. An increase in the activation energy in alkali solutions of Na-CMC is shown. An increase in the relative viscosity of solutions is established when water, exposed to an electromagnetic field of 170 MHz, is used as a solvent. The effect is observed with all the pH and temperature used in the work. The maximum viscosity increase of 0.1% solutions is observed at a temperature of 15 °C and pH = 12 and is 16.5%. As the polymer concentration increases from 0.1 to 0.5%, higher viscosity values of the solutions prepared in the water irradiated with the electromagnetic field are also observed, as compared to the control samples. An increase in the activation energy of the viscous flow of solutions prepared in irradiated water has also been established. The cause of the observed phenomena can be the weakening of solvation processes in irradiated water and an increase in the rigidity of the chain of macromolecules.

Simulation of phase separation with temperature-dependent viscosity using lattice Boltzmann method.

This paper presents an exploration of the phase separation behavior and pattern formation in a binary fluid with temperature-dependent viscosity via a coupled lattice Boltzmann method (LBM). By introducing a viscosity-temperature relation into the LBM, the coupling effects of the viscosity-temperature coefficient [Formula: see text] , initial viscosity [Formula: see text] and thermal diffusion coefficient [Formula: see text] , on the phase separation were successfully described. The calculated results indicated that an increase in initial viscosity and viscosity-temperature coefficient, or a decrease in the thermal diffusion coefficient, can lead to the orientation of isotropic growth fronts over a wide range of viscosity. The results showed that droplet-type phase structures and lamellar phase structures with domain orientation parallel or perpendicular to the walls can be obtained in equilibrium by controlling the initial viscosity, thermal diffusivity, and the viscosity-temperature coefficient. Furthermore, the dataset was rearranged for growth kinetics of domain growth and thermal diffusion fronts in a plot by the spherically averaged structure factor and the ratio of separated and continuous phases. The analysis revealed two different temporal regimes: spinodal decomposition and domain growth stages, which further quantified the coupled effects of temperature and viscosity on the evolution of temperature-dependent phase separation. These numerical results provide guidance for setting optimum temperature ranges to obtain expected phase separation structures for systems with temperature-dependent viscosity.

Problems of Selection of Lubricants for Ethylene High-Pressure Compressors. 3. Investigation of Viscous-and-Thermal Properties of Lubricants

The viscous-and-thermal properties of naphtene and polyglycol oils and compositions on their basis have been studied. The investigate lubricants for high-pressure ethylene compressors have estimated according to a complex criterion which is included the со-relation of viscosity of oils for two temperatures; relative and interval temperature coefficient of viscosity and three coefficients of an adequate equation of approximation of dependence the logarithm of viscosity on the logarithm of temperature. A comprehensive assessment made it possible to complite the lubrication efficiency rows.

High Pressure Rheological Behavior of 1-Ethyl-3-methylimidazolium n-Hexylsulfate and Trihexyl(tetradecyl)phosphonium Tris(pentafluoroethyl)trifluorophosphate

Ionic liquids have been broadly studied in the past decade for being used as lubricants or lubricant additives. The rheological characterization of these fluids is very important in this context because it determines to a great extent their performance for different lubricants applications, such as hydraulic or gear lubricants. Thus, in this work we have performed the rheometric characterization of two ionic liquids (ILs), 1-ethyl-3-methylimidazolium n-hexylsulfate and trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate, in the temperature range from 298.15 to 353.15 K up to 75 MPa and shear rates up to 1000 s–1. For this aim, the setup of a new device for rheological characterization at high pressure based on Couette flow and concentric cylinders was undertaken in this work. Moreover the pressure–viscosity and temperature–viscosity coefficients of these ILs have been calculated. Both ILs present Newtonian behavior in the studied conditions. The trifluorophosphate IL has strong pressu...

The Relation Between Thermal Wedge and Thermal Boundary Conditions for the Load-Carrying Capacity of a Rectangular Pad and a Slider With Parallel Gaps

In order to understand the load-carrying mechanism of thermal wedge, numerical results for a rectangular pad and a slider with parallel gaps under four types of surface boundary temperature conditions are presented. Two assumptions of rigid-solid and smooth-surface were used to exclude the effects of both thermal deformation and micro-asperity. The relation between thermal wedge and thermal boundary conditions is revealed. The load-carrying mechanism of parallel gaps is explained with the thermal wedge derived not only from the surface temperature difference (STD) as proposed by Cameron but also from the film temperature gradient (FTG) independent of STD. It is also pointed out that in numerical analysis, the very small viscosity–temperature coefficient would result in high oil temperature and therefore, the predicted loading capacity from thermal density wedge would be extremely enlarged.

Analysis on the Side Leakage Amount of the Friction between Piston and Cylinder Block in Axial Piston Pump

The spherical distribution pairs of the plunger and the cylinder friction, has an important influence on the performance of spherical port plate axial piston pump. Based on the analysis of fluid viscosity change with pressure and temperature, considering friction differential pressure flow and shear flow, establishes the mathematics model of the friction pair of leakage. The simulation analysis using MATLAB software, the leakage flow rate is not proportional to pressure, but with the increase of pressure leakage flow was increased, and with the increase of pressure viscosity coefficient and temperature coefficient of viscosity, the leakage flow rate correction coefficient increases obviously, so in the choice of the hydraulic oil cylinder hole, should choose a relatively moving average leakage rate had no effect the piston ring slot.

High pressure viscosity characterization of four vegetable and mineral hydraulic oils

In the long term, environmental friendly oils from renewable sources seem to be the more realistic path to a sustainable future for the industry regarding the lubrication issue. Vegetable bases for lubricants have been studied in the last decade in order to analyze their potential industrial applicability. Their strengths and weaknesses are already known and thus, the next step is to study how the final mixture of vegetable base plus additives might perform in comparison to lubricants used in actual machinery. Here, we present the results obtained for the viscosity behavior of two hydraulic mineral oils and two vegetable oils formulated to substitute the mineral based ones. The measurements were taken at three temperatures: 313.15K, 343.15K and 363.15K and at pressures up to 250MPa using a high-pressure falling-body viscometer. To address the performance of these oils in the elastohydrodynamic lubrication regime, we also calculate the universal pressure–viscosity coefficient, αfilm, and the temperature–viscosity coefficient, β.

Extraction and Analysis of Chemo-physical Properties of Yellow Oleander Oil as Lubricant

Yellow Oleander (Thevetia Peruviana) oil has been extracted and analyzed relevant to lubrication. Oil was extracted from yellow oleander seeds using mechanical expression and solvent extraction methods. Samples generated from these oils were subjected to chemo-physical analysis. Analysis of chemo-physical properties (such as viscosity, specific gravity, viscosity-temperature coefficient and fire point among others) was carried out using simple laboratory equipment. Results obtained showed that yellow oleander oil have properties that fall within the range of standard oil lubricants. High flash and fire points of 350C and 375C respectively were obtained. Free fatty acids content of 5.61% against a standard range of 35%-50% for natural oils. Specific gravity of 0.89-0.92 was obtained against a standard range of 0.76-0.92 for oil lubricants. The oil can be used as lubricant in environmentally sensitive areas such as total loss lubrication and marine ecosystems with associated positive environmental and economic impact.

Modeling and Analysis of the Meshing Losses of Involute Spur Gears in High-Speed and High-Load Conditions

A first-principle based mathematical model is developed in this paper to analyze the meshing losses in involute spur gears operating in high-load and high-speed conditions. The model is fundamentally simple with a few clearly defined physical parameters. It is computationally robust and produces meaningful trends and relative magnitudes of the meshing losses with respect to the variations of key gear and lubricant parameters. The model is evaluated with precision experimental data. It is then used to study the effects of various gear and lubricant parameters on the meshing losses including gear module, pressure angle, tooth addendum height, thermal conductivity, and lubricant pressure-viscosity and temperature-viscosity coefficients. The results and analysis suggest that gear module, pressure angle, and lubricant pressure-viscosity and temperature-viscosity coefficients can significantly affect the meshing losses. They should be the design parameters of interest to further improve the energy efficiency in high-performance, multistage transmission systems. Although the model is developed and results obtained for spur gears, the authors believe that the trends and relative magnitudes of the meshing losses with respect to the variations of the gear and lubricant parameters are still meaningful for helical gears.

Optimum shape design for surface of a thermohydrodynamic lubrication slider bearing

ABSTRACTThis paper utilises a thermohydrodynamic model of bearing to optimise the shape of slider bearing. Friction is minimised subject to load and centre of pressure requirements using a sequential quadratic programming algorithm. A generalised Reynolds equation is solved simultaneously with an energy equation using the finite volume method to obtain bearing characteristics, such as friction, load and centre of pressure. Results show that the coefficient of friction is reduced by the optimisation approach. Results also show that larger temperature–viscosity coefficient and inlet viscosity tend to yield smaller optimal friction, whereas larger thermal conductivity tends to yield larger optimal friction. Copyright © 2012 John Wiley & Sons, Ltd.

Pressure–Viscosity Coefficients for Polyalkylene Glycol Oils and Other Ester or Ionic Lubricants

We present in this article new viscosity and density data for polypropylene glycol monomethyl ether, which completes a series of articles where we have published dynamic viscosity data of poly(propylene glycol) dimethyl ethers, dipentaerythritol esters, and pentaerythritol esters. New dynamic viscosity measurements up to 60 MPa at five temperatures in the range of 303.15–373.15 K, and density values at temperatures ranging from 298.15 to 398.15 K up to 60 MPa are reported in addition to other physical properties that affect the behavior of the fluids in elastohydrodynamic lubrication regime, such as the viscosity index value, VI, the universal pressure–viscosity coefficient, α film, and the temperature–viscosity coefficient, β. The experimental measurements were performed using a rotational automated viscometer Anton Paar Stabinger SVM3000, a rolling-ball viscometer Ruska 1602-830 for high pressures, and an automated Anton Paar DMA HPM vibrating-tube densimeter. Together with these data, we also present a comparison of the film-generating capability for the fluids above mentioned as well as for other five ionic liquids. We analyze the dependence of the molecular structure on the lubrication properties of these oils, which can help the lubricant engineers to develop products with enhanced performance.

Effects of Lubricant Properties on Lubricating Performance of Tripod Sliding Universal Joints under Thermal Condition

The effects of the lubricant properties on the lubricating performance of the tripod sliding universal joint were studied under thermal condition by numerical method. The obtained results show that increasing lubricant viscosity increases the film thickness whereas increasing viscosity-pressure coefficient or viscosity-temperature coefficient is just the reverse. The pressure hardly depends on the viscosity-pressure coefficient or viscosity-temperature coefficient, and a larger lubricant viscosity induces only a remarkable second pressure peak. Increasing lubricant viscosity or viscosity-pressure coefficient increases the temperature whereas the increasing viscosity-temperature coefficient reduces it.

Study of polydiethylsiloxane-based ferrofluid with excellent frost resistance property

The polydiethylsiloxane-based ferrofluid was prepared by dispersing finely divided magnetic Fe 3O 4 particles which are modified with oleoyl sarcosine and lauroyl sarcosine. The optimized experiment parameters including molar ratio of surfactant to Fe 3O 4 (1:5), temperature (80 °C), stirring rate (300 RPM), the surfactant content of lauroyl sarcosine (0 to 33 mol%) and the modification time (25 min) were obtained by the orthogonal test. The magnetic liquid was characterized by a transmission electron microscope (TEM), infrared (IR) spectrometer, X-ray diffractometer (XRD), thermogravimetry (TG), vibrating sample magnetometer (VSM) and differential scanning calorimetry (DSC). It is indicated that the surfactant is mainly bonded to the surface of Fe 3O 4 nanoparticles through covalent bond between carboxylate (COO −) and Fe atom. The modified magnetic particles are equally dispersed into the carrier and remain stable below −12 °C over 4 months. The ferrofluids exhibit excellent frost resistance property and distinctly reduced temperature coefficient of viscosity compared with polydimethylsiloxane-based ferrofluids and hydrocarbon-based ferrofluids, respectively. The saturation magnetization could reach up to 27.7 emu/g.