Temperature Variation Of Viscosity Research Articles

Magneto-radiative gas near an unsmooth boundary with variable temperature

PurposeThis paper aims to study the magneto-radiative gas (water vapor) on an unsmooth boundary.Design/methodology/approachThis paper provided a numerical treatment via the implicit Chebyshev pseudo-spectral method to investigate unsteady compressible magneto-radiative gas (water vapor Pr = 1) flow near a heated vertical wavy wall through porous medium in the presence of inclined magnetic field. The impacts of viscous dissipation, temperature-dependent fluid properties, thermal conductivity and viscosity in the presence of nonlinear thermal radiation are studied. The sinusoidal surface is transformed into a flat one using a suitable transformation. The comparison figures of published data with the present outcomes illustrate a good match. The present steady-state outcomes are presented for the temperature, velocity, Nusselt number and the shearing stress through figures for several interested physical parameters, namely, compressibility, magnetic, radiation, viscosity–temperature variation, thermal conductivity–temperature variation, surface sinusoidal waveform and porous parameters.FindingsThe present numerical outcomes confirm the importance of applying nonlinear thermal radiation cases in all studies that investigate heat transfer under the influence of thermal radiation.Originality/valueA mathematical model is established for a wavy boundary, and Chebyshev pseudo-spectral method is adopted for the numerical study.

Rheological and mechanical properties of dynamic covalent polymers based on imine bond

AbstractDynamic covalent polymers based on imine bond (FPIs), which are capable of reorganizing their constitution on the molecular level, are prepared from bio‐based dimer fatty acids. The irregular structure of carbon chains in dimer fatty acids leads to the amorphous nature of FPIs. The effect of imine bond on the glass transition temperature of FPIs is studied by differential scanning calorimetry. The linear viscoelasticity of FPIs is investigated by small amplitude oscillatory shear tests and analyzed by using the Likhtman‐McLeish theory. It is found that the rheological behavior of FPIs is similar with that of static, linear entangled polymers predicted by Likhtman‐McLeish theory, when the dynamic chain arrangements caused by imine‐bond exchange is not active enough. For FPIs, the temperature variation of viscosity is still following the Arrhenius law with an activation energy of ~50 kJ mol−1. Owing to the thermal adaptability, FPIs demonstrate great malleability, self‐healing capability and processing stability at elevated temperatures.

Towards edible ionic liquids - cholinium taurate

In this work, the possibilities and benefits of using an ionic liquid as a potential dietary supplement are presented and discussed for the first time. Ionic liquids prevent the development of microorganisms due to high ion concentration and thus, prevent perishability of the food products. Thermal stability, structure, as well as the experimental density and viscosity in the temperature range from 20 to 50?C and at the atmospheric pressure 1x105 Pa of newly synthesized cholinium taurate ionic liquid, [Chol][Tau], are determined. According to the performed physicochemical characterization, it can be concluded that the synthesized ionic liquid is suitable for application in the food industry. The temperature variation of viscosity and density is discussed in terms of processes, packaging, and storage of [Chol][Tau]. Also, the antiproliferative activity of [Chol][Tau] is determined and compared with those obtained for ascorbic acid and Aspirin? as the standards.

New friction factor and Nusselt number equations for laminar forced convection of liquid with variable properties

Friction factor and heat transfer coefficient of liquid flow with variable properties can significantly differ from that with constant properties. Existing equations obtained by regression analysis of experimental data use correction factors to account for variable property effect. They are limited to specific kind of fluid and low or medium temperature differences. The correction factors of the equations for heating and cooling conditions are different. New explicit friction factor and Nusselt number equations for laminar forced convection of liquid with variable properties are derived with a first order approximation of dynamic viscosity-temperature variation. The new equations are applicable to all kinds of liquids and can be used for large temperature differences. Governing equations of laminar forced convection of water and ethanol are numerically solved using computational fluid dynamics (CFD) method and the results are used to verify the derived equations. The derived equations show good predictions of friction factors and Nusselt numbers for both heating and cooling conditions and show more accurate predictions than the existing equations. A dimensionless number is also introduced based on theoretical analysis to evaluate property variation effects on friction factors and heat transfer coefficients.

Clearance and lubricant selection for avoiding seizure in a circumferential groove journal bearing based on a lumped model analysis

This study presents a new simple lumped model for analyzing the thermally induced seizure of fully lubricated eccentric circumferential groove journal bearings (CGJB). The model represents a significant upgrade of a previous seizure lumped model developed by Pascovici & Kucinschi, in 2002. Main upgrades consist of: eccentric operation, introduction of hydrodynamic lubricant flow rate component, and evaluation of friction power losses based on the short bearing theory with Barwell’s hypothesis on the divergent zone. The viscosity–temperature variation is replaced with Tipei’s viscosity-clearance relationship, as in the previous model. The decrease of viscosity, as a consequence of temperature increase, does not always limit clearance loss, and the seizure process ends with a concentric journal-bushing merged system. Although CGJB’s are less sensitive to this seizure mechanism, the threat still exists and must be avoided. As a result, bearing designers and users should check whether if several safe-operation criteria are met. A recent Institute Pprime experiment on CGJB’s provided a base set of operating parameters, from which numerical simulations have been performed to determine in what conditions the CGJB fails, under thermally induced seizure.

Effects of non-Newtonian rheology on the film-height history between non-parallel sliding-squeezing surfaces

The effects of flow rheology of non-Newtonian fluids on the time-dependent film-thickness history between non-parallel sliding-squeezing surfaces are studied. On the basis of the power-law fluid model, the hydrodynamic film pressure is obtained from the non-Newtonian dynamic Reynolds-type equation by considering the transient squeezing-action effect. The hydrodynamic film force is then applied to derive the non-linear motion equation of the squeezing part. Using the non-linear transient method, the film-height trajectory of the squeezing part is presented. The results of the present study provide a reference for engineer applications in machine tools, the matched gears, the rolling elements, and the piston-cylinder systems when viscosity-pressure dependence, viscosity-temperature variation, and elastic deformations of the contacting surfaces are neglected.

Viscosity and surface tension of liquid Fe–metalloid glass-forming alloys

Amorphous and nanocrystalline Fe-based alloys have a wide range of applications as soft magnetic materials. This paper summarises our recent advances in investigation of those thermophysical properties of liquid Fe–metalloid alloys with relevance for both structural evolution of the melt and technological application. Viscosity measurements at high temperatures were performed by oscillating-cup method. Surface tension was determined by the sessile drop method. Composition dependence of the viscosity and surface tension for Fe–B alloys [Phys. Stat. Sol. (a) 31 (1975) K41] in the glass-forming range is discussed. A short review of the results on the temperature variation of viscosity and surface tension for FeBSi alloys is presented. High viscosity values near the liquidus temperature and a specific behaviour of this structure-sensitive property during heating and cooling the molten alloys were found [Jpn. J. Appl. Phys. 17 (1978) 1911]. These results are related to clustering effects in these melts with preferential interaction between unlike atoms.

Viscosity of the Grain-Boundary Phase and Sintering of TiB2-Modified Alumina

A model is proposed for the sintering of powders via the sliding of particles facilitated by a grain-boundary phase. Data on the initial-stage sintering kinetics of TiB2-modified alumina are used to assess the temperature-dependent viscosity of the grain-boundary phase, formed by Al2O3 , oxidation products of TiB2 , and impurities present on the surface of alumina particles. In the range 1570–1620 K, the temperature variation of viscosity is fitted well by the expression 25.9exp (143 308/ RT).

CFD Based Design Techniques for Thermal Prediction in a Generic Two-Axial Groove Hydrodynamic Journal Bearing

There are many physical parameters that influence the thermal condition of a hydrodynamic journal bearing. This remains the case even when appropriate nondimensionalization procedures have been applied. However, two dimensionless parameters are particularly useful, since they embody lubricant shearing, convection, conduction and viscosity temperature variation. In this paper, these parameters are varied to obtain design charts for the maximum bearing shell and journal temperatures. Computational fluid dynamics (CFD) techniques are used in this process. They are applied to a generic two-axial groove circular bearing having a section of journal that extends beyond the width of the shell. The results demonstrate the usefulness of the charts through example design studies.

FREE CONVECTION IN A VERTICAL DUCT OF SQUARE CROSS SECTION WITH VARIABLE VISCOSITY

Nusselt numbers and dimensionless flow rates have been calculated as functions of Prandtl number, Grashof number, and a viscosity parameter that takes into account variation of viscosity with temperature. The dependence of heat transfer coefficient and flow rate on the viscosity parameter is shown to be strong enough to require consideration of temperature variation of viscosity for accurate calculations. The results are useful in the design of heat sink assemblies having square vertical slots.

A mixing rule approach for predicting the viscosity of CO 2-saturated cold lake bitumen and bitumen fractions

Mixing rules are described and evaluated for predicting the viscosity of Cold Lake bitumen and its five fractions saturated with CO 2. The viscosity-temperature variation for all bitumen fractions and light gases is expressed as: [log ( μ + 0.8) = ± 10 b1 T b2 ], where μ is viscosity in mPa s at temperature T in K. A linear cross-correlation between parameters b 1 and b 2 in the above relationship is identified and used subsequently to derived the one-parameter viscosity equation: [ log ( μ + 0.8) = Θ( ΦT) b ], where Θ = 160, Φ = 0.008 for bitumen fractions and Θ = −0.1, Φ = 0.015 for gases. The two mixing rules for viscosity are: [ log ( μ + 0.8) ] and [ log ( μ + 0.8) = Σv ilog(μ i + 0.8) + ΣΣv i v jB ij ], where v represents the geometric mean of mass and mole fractions. Experimental viscosity-temperature-composition data are used to evaluate the binary interaction term B ij in the second viscosity mixing formula. Predictions for the viscosity of CO 2-saturated Cold Lake bitumen, which is modeled as a six-component mixture, are validated with experimental data at temperatures from 20 to 150°C and pressures up to 10 MPa.

Stability of free-convection flows of variable-viscosity fluids in vertical and inclined slots

The stability of the buoyancy-driven parallel shear flow of a variable-viscosity Newtonian fluid between vertical or inclined plates maintained at different temperatures is studied theoretically. The analysis is capable of dealing with arbitrary viscosity-temperature relations. Depending on the Prandtl number, angle of inclination, and form of the viscosity-temperature variation, the flow may become unstable with respect to two-dimensional longitudinal or transverse disturbances. Outstanding questions arising in previous investigations of the stability of parallel free-convection flows of constant-viscosity fluids in inclined slots and of variable-viscosity fluids in vertical slots are discussed. We find that, in a variable-viscosity fluid, non-monotonic dependence of the critical Rayleigh number on the inclination angle can occur at significantly higher Prandtl numbers than is possible in the constant-viscosity case. Results are also presented for the stability of the free-convection flow of several glycerol-water solutions in an inclined slot.

Effect of disorder on diffusion and viscosity in condensed systems

A simple theoretical model describing the influence of disorder on transport properties (viscosity, diffusion coefficients, etc.) in undercooled melts and crystals is suggested. The basic assumption is that structural disarray results in a random probability distribution of energy barriers for diffusion characterized by dispersion σ around some mean value 〈 E〉. It is shown that the effect of σ on the mean jump frequency 〈 v(E)〉 may lead to corrections of many order of magnitude as compared to the hopping frequency calculated traditionally in terms of the average activation energy 〈 E〉 only. The temperature course of 〈 v(E)〉 is then examined making use of the relation between σ and the entropy of the system S. Thus an analytical formula is obtained which properly describes molecular transport in both the crystalline and the amorphous state. Even in a simplified form, η= η 0 exp( β/ T α ), it reproduces well the existing data on temperature variation of viscosity η (or self-diffusion) in glassforming melts. In another aspect - in terms of the percolation theory - the model describes the diffusion of a foreign particle in a rigid host structure and yields also a qualitative estimate of the variation of the percolation threshold E p with the degree of amorphisation σ.

Analysis of the Lubricant Film Formation Process in Plane Strain Forging

A thermal Reynolds’ equation is developed for a lubricant with an exponential viscosity-temperature variation. The equation is used to analyze the film formation process in liquid lubricated plane strain forging. The effects of temperature and pressure induced viscosity changes on the film formation process are described.

Temperature variation of viscosity and the structure of liquids

The ratio a of the energy of activation of viscous flow to the energy of vaporization at the same temperature is determined for a large number of liquids of diverse types. For all but a relatively small number of molecules approching most closely to spherical shape, the ratio is found to be sensibly constant for non-associated liquids, and is independent of size, shape, and polarity. The significance of this constancy is discussed in terms of a simple flow model. High values of a appertain for liquids known to be associated through the formation of intermolecular hydrogen-bonds, and it is argued that the viscous flow process does not in itself lead to rupture of such bonds.

Discontinuities in Supercooled Ionic Melts

DURING the course of a systematic investigation on the electrochemistry of boron trifluoride co-ordination compounds1, discontinuities were observed in the temperature variation of viscosity on passing from the normal liquid to the supercooled state. In both temperature regions the viscosity could be expressed by an exponential relation of the form η = η0exp(B/RT), but the activation energy B was approximately 10 per cent greater for the supercooled state. The temperature coefficient of the specific volume (v) shows no such discontinuity at the melting point, and this fact may be used for emphasizing the discontinuous behaviour of the viscosity by the application of Batchinski's equation2 ρ = C/(v—b), where C and B are constants. For example, if the fluidity ϕ = 1/η is plotted as a function of specific volume for acetoxytrifluoroboric acid, H[CH3.CO.OBF3], there ia a well-defined discontinuity at a point corresponding to the melting point, 37.5° C. The change in slope is 34 per cent, compared with an increase of 10 per cent for the activation energy B for this compound.

Viscosity–Volume Relation for Liquids

DR. JOBLING, in his letter published in Nature of October 16, states that the dependence of the viscosity of a liquid on temperature is "certainly for ether above 0° C. and probably for many other liquids" due entirely to the change of volume. That this is not so in general has often been pointed out by one of the present writers1. For example, for mercury (a monatomic liquid and so more suitable than ether to be cited in support of a theory of liquid viscosity) the temperature variation of viscosity at constant pressure in the range 30–75° C. is reduced only by some thirty per cent when the volume, instead of the pressure, is kept constant2 ; for isoamyl alcohol, working at constant volume reduces the temperature variation by some twenty-two per cent only : nowhere in the whole range of recorded experiments on carbon dioxide is the viscosity a function of the specific volume alone. Dr. Jobling also states that on Born and Green‘s theory the part of the viscosity that depends upon molecular attraction is a "volume effect" : this, however, is not proved, or even asserted, by the authority quoted by him, and is certainly not asserted or implied by Born and Green3. The only experimental results that Dr. Jobling brings forward to support his contention refer to ether above 0° C. However, even for ether in the temperature-range considered, from 0° to 32°, the evidence fails.

XXXVII. The temperature variation of viscosity in non-polar and dipolar inorganic liquids

Click to increase image sizeClick to decrease image size Additional informationNotes on contributorsA.E. MorganCommunicated by the Authors.

On the determination of molecular fields. —II. From the equation of state of a gas

The investigation of a preceding paper has shown that the temperature variation of viscosity, as determined experimentally, can be satisfactorily explained in many gases on the assumption that the repulsive and attractive parts of the molecular field are each according to an inverse power of the distance. In some cases, in argon, for example, it was further shown that the experimental facts can be explained by more than one molecular model, from which we inferred that viscosity results alone are insufficient to determine precisely the nature of molecular fields. The object of the present paper is to ascertain whether a molecular model of the same type will also explain available experimental data concerning the equation of state of a gas, and if so, whether the results so obtained, when taken in conjunction with those obtained from viscosity, will definitely fix the molecular field. Such an investigation is made possible by the elaborate analysis by Kamerlingh Onnes of the observational material. He has expressed the results in the form of an empirical equation of state of the type pv = A + B/ v + C/ v 2 + D/ v 4 + E/ v 6 + F/ v 8 , where the coefficients A ... F, called by him virial coefficients , are determined as functions of the temperature to fit the observations. Now it is possible by various methods to obtain a theoretical expression for B as a function of the temperature and a strict comparison can then be made between theory and experiment. Unfortunately the solution for B, although applicable to any molecular model of spherical symmetry, is purely formal and contains an integral which can be evaluated only in special cases. This has been done up to now for only two simple models, viz., a van der Waals molecule, and a molecule repelling according to an inverse power law (without attraction), but it is shown in this paper that it can also be evaluated in the case of the model, which was successful in explaining viscosity results. As the two other models just mentioned are particular cases of this, the appropriate formulæ for B are easily deduced from the general one given here.