Dependence Of Viscosity Research Articles

Thermal inspection of hybrid nanofluid flows over a stretched cylinder at an oblique stagnation point with variable characteristics

AbstractThe enhanced thermal characteristics of hybrid nanofluids make them more versatile compared to conventional fluids. These improved thermal properties render hybrid nanomaterials highly practical for a wide range of applications, including solar systems, energy production, and cooling processes. In line with this perspective, the current study concentrates on evaluating the thermal performance of two unique hybrid nanofluid flows that impinge obliquely on a stretched cylinder. Two base fluids, FC‐77 and a binary mixture of water and ethylene glycol (50:50)%, have been considered, with the addition of nanoparticles such as single‐walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs). The said model's novelty is enhanced by the temperature dependent viscosity and thermal conductivity. Appropriate transformations are applied to derive a system of ordinary differential equations (ODEs), which are then solved numerically using the bvp4c method. A thorough examination is conducted on the physical phenomenon of pertinent parameters, accompanied by graphical representations. The results revealed that, for the FC‐77 coolant‐based hybrid nanofluid, mounting the particle volume fraction leads to a significant reduction in temperature distribution. Additionally, it is perceived that the presence of a variable viscosity parameter causes a reduction in the surface drag coefficient as well as the axial and tangential velocities. The validity of the proposed flow model is demonstrated by comparing the results with those from an earlier study.

Control of temperature dependent viscosity for manufacturing of Bi-doped active fiber

Bi-activated photonic materials are promising for various applications in high-capacity telecommunication, tunable laser, and advanced bioimaging and sensing. Although various Bi-doped material candidates have been explored, manufacturing of Bi heavily doped fiber with excellent optical activity remains a long-standing challenge. Herein, a novel viscosity evolutional behavior mediated strategy for manufacturing of Bi-doped active fiber with high dopant solubility is proposed. The intrinsic relation among the evolution of Bi, reaction temperature and viscosity of the glass system is established. Importantly, the effective avenue to prevent the undesired deactivation of Bi during fiber drawing by tuning the temperature dependent viscosity evolution is built. By applying the strategy, for the first time we demonstrate the success in fabrication of heavily doped Bi active fiber. Furthermore, the principal fiber amplifier device is constructed and broadband optical signal amplification is realized. Our findings indicate the effectiveness of the proposed temperature dependent viscosity mediated strategy for developing novel photonic active fiber, and they also demonstrate the great potential for application in the next-generation high-capacity telecommunication system.

The new analytical and numerical analysis of 2D stretching plates in the presence of a magnetic field and dependent viscosity

This study explores heat transfer in a system involving Jeffery fluid of MHD flow and a porous stretching sheet. The mathematical representation of this system is initially described using a partial differential equation (PDE), which is then converted into an ordinary differential equation (ODE) through numerical techniques such as Lie similarity and transformation methods, along with the shooting approach. The results indicate that altering the variables of Jeffery fluid, heat source, porosity on a stretching sheet, and the physical characteristics of the magnetic field within the system leads to an upward trend. Implementing this enhanced heat transfer system can yield benefits across various domains, including industrial machinery, mass data storage units, electronic device cooling, etc., thereby enhancing heating and cooling processes. Furthermore, the study also utilized Akbari-Ganji’s Method, a new semi-analytical method designed to solve nonlinear differential equations of heat and mass transfer. The results obtained from this method were compared with those from the finite element method for accuracy, efficiency, and simplicity. This research provides valuable insights into heat transfer dynamics in complex systems and offers potential applications in various industrial settings. It also contributes to developing more efficient and effective heat transfer techniques.

Experimental setup for researching the stability of fluid flow

The problem of studying the stability of the flow of a thermoviscous liquid is relevant in connection with the need to develop methods for controlling flow regimes in industrial condensers and heat exchange devices. These devices play an important role in a variety of technological processes, from food production to materials processing, and their effectiveness is directly dependent on the flow regime they establish. Awareness of the importance of both laminar and turbulent flow regimes leads to the need to balance between energy efficiency, which is often preferable to laminar flow, and heat and mass transfer efficiency, which is characteristic of turbulent flow. This makes it important to study and control the stability of the flow. As the speed of fluid flow increases, laminar flow loses stability and disturbances arise, which can lead to the formation of a secondary nonlinear regime that preserves the main characteristics of laminar flow, or to flow turbulization, which in turn can have a significant impact on the efficiency of technical devices. Although a lot of work has been done to study the stability of the flow of homogeneous liquids in channels and their spectral characteristics, the importance of taking temperature differences into account is often overlooked. However, it is the dependence of liquid viscosity on temperature that plays a significant role in determining flow patterns and requires additional study. Despite the ongoing numerical studies of the stability of fluid flow, there remains a need to compare experimental data with the results of numerical modeling to obtain a more complete understanding of the processes occurring in the system. In this regard, within the framework of this work, an experimental setup of an annular channel was developed and assembled in order to conduct a detailed experimental study of the stability of fluid flow and subsequently compare the results obtained with numerical simulations, which will provide more accurate data for further improving the design and operation of industrial devices.

Influence of shear deformation on the formation of dynamic structure in protic ionic liquids. Representation of the temperature dependence of viscosity within the framework of Angell’s fragility concept

The rheological properties of a liquid containing two types of basic centers and hydroxyl groups (BGE-Im), as well as protic ionic liquids (ILs) derived from it, were studied in a wide range of shear rates (γ̇) (10−6–103 s−1) at various temperatures from 10 to 50 °C. Viscosity (η) of the BGE-Im does not depend on the scanning direction of shear stress (σ), i.e. this compound behaves like a Newtonian fluid over the entire range of σ. The dependence log η (1/T) of BGE-Im in Arrhenius coordinates is linear. Protonation of basic centers of BGE-Im leads to a strong increase in the viscosity of ILs obtained on its basis, and the temperature dependence of the viscosity of these ILs is described by the Vogel–Fulcher–Tammann (VFT) equation. It has been established that in the region of low shear rates, the viscosity of the ILs increases with decreasing shear rate, which leads to the appearance of a yield stress (σY). This indicates the formation of a fluctuation rheopectic structure in the ILs. In this sense, ILs are heterogeneous systems and their behavior is similar to that of highly concentrated suspensions and emulsions. For the first time, a quantitative comparison between the parameters of the VFT equation, the fragility (according to Angell’s model) of ILs, the relative coordination number of ILs molecules and the rheological yield stress characterizing the shear-induced fluctuation rheopectic structure of ILs has been made and the relationship between these characteristics has been shown.

On the Flow of a Cement Suspension: The Effects of Nano-Silica and Fly Ash Particles.

Additives such as nano-silica and fly ash are widely used in cement and concrete materials to improve the rheology of fresh cement and concrete and the performance of hardened materials and increase the sustainability of the cement and concrete industry by reducing the usage of Portland cement. Therefore, it is important to study the effect of these additives on the rheological behavior of fresh cement. In this paper, we study the pulsating Poiseuille flow of fresh cement in a horizontal pipe by considering two different additives and when they are combined (nano-silica, fly ash, combined nano-silica, and fly ash). To model the fresh cement suspension, we used a modified form of the power-law model to demonstrate the dependency of the cement viscosity on the shear rate and volume fraction of cement and the additive particles. The convection-diffusion equation was used to solve for the volume fraction. After solving the equations in the dimensionless forms, we conducted a parametric study to analyze the effects of nano-silica, fly ash, and combined nano-silica and fly ash additives on the velocity and volume fraction profiles of the cement suspension. According to the parametric study presented here, larger nano-silica content results in lower centerline velocity of the cement suspension and larger non-uniformity of the volume fraction. Compared to nano-silica, fly ash exhibits an opposite effect on the velocity. Larger fly ash content results in higher centerline velocity, while the effect of the fly ash on the volume fraction is not obvious. For cement suspension containing combined nano-silica and fly ash additives, nano-silica plays a dominant role in the flow behavior of the suspension. The findings of the study can help the design and operation of the pulsating flow of fresh cement mortars and concrete in the 3D printing industry.

Saturated Porous Ferroconvection in a Ferrofluid Layer with Viscosity as a Function of Magnetic Field: Focus on Convective Boundary Condition

The present work aims to examine the influence of magnetic field dependent (MFD) viscosity on the onset of ferroconvection (FC) in a horizontal porous layer saturated with a quiescent ferrofluid (FF) and subjected to a uniform vertical magnetic field. It is assumed that the porous boundaries at the bottom and top are rigid-paramagnetic. The thermal conditions consist of a constant heat flux at the lower surface and a convective boundary condition at the upper surface, encompassing fixed temperature and uniform heat flux cases. The application of the Galerkin technique to the resulting eigenvalue problem reveals that the stability region expands as the porous parameter, Biot number, MFD viscosity parameter and magnetic susceptibility increase in magnitude. Conversely, the stability region contracts as the magnetic number and non-linearity of magnetization increase. Furthermore, it is noted that under uniform heat flux boundary conditions, the criterion for the initiation of ferroconvection remains unaffected by the non-linearity of fluid magnetization.

Temperature dependence of polymer melt viscosity obtained based on DSC data and the consistency between thermodynamic and kinetic fragility

AbstractThe viscosity of the polymer melt has an impact on both the processing and properties of the product. However, conventional viscosity measurement methods have limitations such as strict testing conditions, large sample sizes, and long response times. This paper proposes a simplified method that utilizes differential scanning calorimetry to determine the viscosity–temperature relationship of the polymer melt. The research subjects consist of four noncrystalline polymers and five crystalline polymers. A new thermodynamic fragility formula of crystalline polymer is obtained. Additionally, high‐temperature limiting viscosity shows a good linear relationship with fragility. Compared with the traditional viscosity measurement, this method is a simpler and more effective way to model the viscosity of polymer melt and has broad prospects in application.

Physicochemical properties of ammonium acetate / propionic acid as a novel deep eutectic solvent and its binary mixtures with water in (298.15–353.15) K range

Emergence of deep eutectic solvents as potential replacements for volatile organic solvents has attracted interest of the scientific community in diverse fields of applications. Compared to ionic liquids, which exhibit similarity in many respects with this new class of green solvents, deep eutectic solvents (DESs) show low toxicity, and are easy to prepare from cheap and abundantly available starting materials. Knowledge of physicochemical properties of DESs is a prerequisite for their safe applications in technological fields and to understand the nature of interactions present in these systems. Although physicochemical properties of choline chloride based DESs are widely investigated, similar information on ammonium acetate based DESs is scant.In this work, a novel ammonium acetate/propionic acid deep eutectic solvent (AA/PA DES) is reported which is prepared by mixing ammonium acetate (AA) and propionic acid (PA) in the 1:3 mol ratio and characterized by FTIR, 1H and 13C NMR, TGA and DSC techniques. The density (ρ), sound velocity (u), viscosity (η) and conductivity (κ) of the pure DES and its binary mixtures with water are investigated over the entire composition range and temperatures (298.15–353.15) K. The excess properties, VmE, KSE, Δη, and ΔG*E are calculated and corelated using Redlich-Kister equation (RKE). Temperature dependence of conductivity and viscosity is satisfactorily described by the Vogel – Fulcher – Tamman (VFT) equation rather than Arrhenius equation. The pure DES shows a wide electrochemical potential window ranging from – 1000 mV to + 1000 mV, which coupled with its better solubilizing characteristics, could be exploited for electrochemical work.

ЗАДАЧА О НЕЛИНЕЙНОМ ФИЛЬТРАЦИОННОМ ПОЛЕ ДАВЛЕНИЯ В СРЕДЕ СО СЛАБОСЖИМАЕМЫМ СКЕЛЕТОМ

The solution of the problem of the pressure field during filtration of a compressible fluid in a porous medium with an incompressible skeleton in the presence of high-amplitude disturbances is presented. The equation describing pressure changes during field development takes into account the compressibility of the fluid and is presented in a nonlinear form. The known dependences of the density of the filtered medium on the pressure are approximated by a linear function. The movement is assumed to be one-dimensional and horizontal. The porosity, density and permeability of the porous medium skeleton, as well as the viscosity of the filtered medium are considered constant. The solution of the problem is found using an asymptotic expansion by a formal parameter added in the problem as a factor to the compressibility of the fluid. An approximate analytical solution of the nonlinear problem of the filtration pressure field in the zero and first approximations is found. The zero and first coefficients are represented by solutions of quasi-stationary equations, in which time is included as a parameter through the dimensions of the perturbation zone determined by the law of conservation of mass. It is established that taking into account the nonlinearity leads to a decrease in the size of the zone of disturbances of the pressure field. An approach to determining the upper boundary of the perturbation zone in nonlinear problems of this kind, which is based on the use of conservation laws, is proposed. It is shown that the special case of the zero approximation coincides with the solution of the linear problem obtained by the method of changing successive stationary states. The expressions found expand the possibilities of studying high-amplitude filtration processes, and the proposed approach removes the limitations of classical approaches associated with neglecting the dependence of fluid density on pressure in the divergent term of the continuity equation. The method used makes it possible to construct analytical expressions for decomposition coefficients orders of magnitude higher than the first, in addition, it creates the possibility of studying the contribution of nonlinearity caused by the dependence of permeability and viscosity on pressure.

Synthetic oils based on pentaerythritol esters. Kinematic viscosity

One of the main characteristics of lubricants is the viscosity index, which shows the dependence of oil viscosity on temperature. The higher the viscosity index, the better the lubricating properties of the oil. Esters of various polyols, in particular pentaerythritol, are very effective in this direction. This work examines a wide range of high-purity pentaerythritol esters of 14 compounds of varying degrees of branching and studies the temperature dependences of kinematic viscosity in the temperature range from melting temperatures to 150 °C. Based on the obtained data, the values of viscosity indexes were calculated, and the contribution of the carboxylic acid structure to the viscosity properties was also considered.

Relative entropy inequality for capillary fluids with density dependent viscosity and applications

We derive a relative entropy inequality for capillary compressible fluids with density dependent viscosity. Applications in the context of weak–strong uniqueness analysis, pressureless fluids and high-Mach number flows are presented.

Spherical geometry convection in a fluid with an Arrhenius thermal viscosity dependence: The impact of core size and surface temperature on the scaling of stagnant-lid thickness and internal temperature

The rock and rock-ice mixtures of the core-enveloping spherical shells comprising terrestrial body interiors have thermally determined viscosities well described by an Arrhenius dependence. Accordingly, the implied viscosity contrasts determined from the activation energies (E) characterizing such bodies can reach values exceeding 1040, for a temperature range that spans the conditions found from the lower mantle to the surface. In this study, we first explore the impact of implementing a cut-off to limit viscosity magnitude in cold regions. Using a spherical annulus geometry, we investigate the influence of core radius, surface temperature, and convective vigour on stagnant lid formation resulting from the extreme thermally induced viscosity contrasts. We demonstrate that the cut-off viscosity must be increased with decreasing curvature factor, f (=rin/rout, where rin and rout are the inner and outer radii of the annulus, respectively), if the solutions are to be not only computationally manageable but physically valid. We find that for statistically-steady systems, the mean temperature decreases with core size, and that a viscosity contrast of at least 107 is required for stagnant lid formation as f decreases below 0.5. Inverting the results from over 80 calculations featuring stagnant lids (from a total of approximately 180 calculations), we apply an energy balance model for heat flow across the thermal boundary layers and find that the non-dimensionalized temperature in the Approximately Isothermal Layer (AIL) in the convecting region under a stagnant lid is well predicted by TAIL′=12−2Tout′+γ+γ2+4γ1+Tout′ where γ is a function of E and f, and Tout′ is the non-dimensionalized surface temperature. Moreover, the normalized (i.e., non-dimensional) thickness of the stagnant lid, L′, can be obtained from a measurement of the non-dimensional surface heat flux once TAIL′ is determined. Stagnant-lid thicknesses increase from 10 to 30% of the shell thickness as f is decreased, and thick lids can overlie vigorously convecting underlying layers in small core bodies, potentially delaying secular cooling and suggesting that small objects with small cores may have developed thick elastic outer shells early in the solar system's history while maintaining vigorously convecting interiors. However, we also find that for the small number of 3-D calculations that we examined, parametrizations based on 2-D calculations overestimate the temperature of the convecting layer and the thickness of the conductive lid when f is small (less than 0.4).

New empirical correlations for the viscosity of selected organic phase change materials

Although there are many methods and instruments for measuring viscosity, it is still difficult to determine a reliable value of the dynamic viscosity of complex chemicals such as paraffins and fatty acids. This is due to the complex and heterogeneous structure of these compounds in the case of commercial products. On the other hand, the measuring instrument should be selected very carefully, including its measuring principle and measuring range. This paper presents results of viscosity measurements of three organic PCMs (phase change materials) obtained in four different research institutions. Commercial products: paraffin, myristic acid (97%) and mixture of palmitic acid (55%) and stearic acid (45%) were selected as PCMs. Four different viscometers, namely Fungilab V-Pad, Rheotest LK 2.2, Rheometer Anton Paar MCR 102, and Brookfield DV-II + Pro have been used to determine temperature dependent dynamic viscosity of the tested PCMs. Using a large database of present measurement results, correlations were developed to calculate the dynamic viscosity of fatty acids and paraffins, which predict the experimental data within a band of ±20%.

A Novel Model for Evaluating the Natural Antioxidant Carnosic Acid to Improve the Stability of Rapeseed Oil in the Thermal Degradation.

The quality and stability of oil during thermal processing reflect the reactions in vegetable oil. The deterioration of the oil is close to the viscosity, fatty acid composition (FA), total polar compounds (TPC), etc. Carnosic acid (CA) is the main antioxidant component of rosemary extract; it is a natural and clean-label antioxidant that is allowed to be added to prolong oil processing and storage. To achieve a clear correlation of this situation, a novel stability evaluation model was used to predict the thermal degradation of rapeseed oil (RSO) with CA. The RSO with CA (200 mg/kg, 400 mg/kg, and 700 mg/kg), the tert-Butylhydroquinone (TBHQ, 200 mg/kg), and the fresh RSO (without additives) during thermal processing (180 ± 5 °C) were studied. The temperature dependency of viscosity fits well with the Lioumbas model (R2 ≥ 0.999). The parameter b value in the Lioumbas model showed a decrease linearly with the processing time (tP, R2 ≥ 0.965). The multiple linear regression analysis showed that the accuracy of the model in predicting viscosity was less than ±2 mPa·s-1, and the deviation% was less than ±10% in all the samples. After 32 h of thermal degradation, the addition of 700 mg/kg CA showed the lowest degradation rate (13.84%) of polyunsaturated fatty acids (PUFAs), and the TPC content was 26.00 ± 0.50%. The TPC showed a positive relationship with viscosity (r = 0.99, p < 0.01), tP (r = 0.97, p < 0.01), and effective carbon numbers (ECN, r = 0.84, p < 0.05). In conclusion, this study can make a potential prediction for the stability of RSO.

Silicon gels with sustainable self-replenishment: Fluid drag reduction through viscosity dependency

Slippery liquid infused surfaces (SLISs) provide excellent dynamic lubrication properties by storing the lubricant internally to form a homogeneous liquid layer to insulate external ambient fluids. However, the kinetic instability caused by lubricant depletion gradually degrades the surface slippery performance. Herein, inspired by skin gland secretion system, silicon gels with sustainable self-replenishment were prepared using polydimethylsiloxane (PDMS) and commercially available dimethyl silicone oils. By carefully tuning the kinematic viscosity and content of infused oil, the surfaces of corresponding silicon gels demonstrated significant syneresis behavior, and the lubricating oils released from the surface were still detected after continuous wiping for more than 120 days. More importantly, when the ratio of working fluid to infused oil was 6.8, the maximum drag reduction of silicon gel in Couette flow could reach up to about 16%, while the surfaces remained long-lasting water repellency under the continuous shear action of encapsulated water. Self-replenishable silicon gels exhibiting strong kinetic stability were expected to provide valuable design insights for robust slippery interfaces.

Inviscid limit for the compressible Navier-Stokes equations with density dependent viscosity

We consider the compressible Navier-Stokes system describing the motion of a barotropic fluid with density dependent viscosity confined in a three-dimensional bounded domain Ω. We show the convergence of the weak solution to the compressible Navier-Stokes system to the strong solution to the compressible Euler system when the viscosity and the damping coefficients tend to zero.

Numerical computation of joule heating and chemical reaction for the radiated Casson fluid on the slender parabolic surface

AbstractThis work dealing to solve the numerical results of magnetohydrodynamic flow material (Casson fluid) moving over the slender parabolic surface with temperature dependent viscosity. To make the enhancement in the thermal and solutal fields, we have determined the impact of thermal radiation, viscous dissipation, joule heating, and chemical reaction on the considered flow material. Due to huge applications in coating processes and aerodynamic industries, the suction/Injection is assumed at the surface. With the help of assumed assumptions, the governing equations are obtained in partial differential equation forms, and these equations are translated into ordinary differential equations form by using the Levy‐Lee similarity transformations. The translated forms of ODE's are then numerically solved by using the Adams‐Milne (Predictor–Corrector) technique. The graphical and numerical findings are determined by producing the emerging parameters. The decrement in velocity is noted due to fluid parameter and suction coefficient whereas the enhancement happens due to natural convection. The numerical determination of physical quantities including, Nusselt number, Skin friction and Sherwood number are also examined here and compared the findings with two numerical techniques (Adam‐Milnes and Bvp4c method).

Physical Limit of Nonlinear Brownian Oscillators in Quantum Trap.

Quantum trap, a quantum and thermal fluctuations-induced nonmonotonous potential, offers a chance to build up microscopic mechanical systems completely dominated by fluctuations. Here, we explore the physical limit of the effective damping ratio of the nonlinear Brownian oscillator in a quantum trap, set by the finite separation for avoiding molecular-scale effects on the trap potential and the surface confinement effect-induced diverging damping and random forces. The quasiharmonic approximations and Langevin dynamics simulations show that the lowest effective damping ratios of the suspended Au plate and Au sphere upon a Teflon coating of 10 nm can be ∼210 and ∼145, respectively, at room temperature. Perforation is proposed as an effective route to reduce the damping ratio (down to 6.4) by attenuating the surface confinement effect. An unexpected result due to the temperature dependences of dielectric function and viscosity of ethanol is a further reduced damping ratio at 400 K (1.3). The nonlinear Brownian oscillator in the quantum trap shows promise of probing near-boundary hydrodynamics at nanoscale.

Analytical Studies of Fluid Conveying Pipes on Viscoelastic Foundation Using Differential Transforms Method

This study presents an analytical investigation of the vibration of fluid-conveying pipes on viscoelastic foundations using the differential transform method. The effects of a new time dependent viscosity parameter in the modified Winkler viscoelastic foundation is studied and analyzed. The governing equation is a fourth-order partial differential equation with pinned-pinned boundary conditions, which required a special analytical method for solution. The differential transform method was applied to obtain the solution of the governing partial differential equation for the fluid-conveying pipes on viscoelastic foundations. The time-dependent viscosity parameter in the modified Winkler viscoelastic model was implemented and simulated to determine the behavior of the viscoelastic foundation. The obtained analytical solution was validated with Runge-Kutta order four numerical method. The effects of foundation stiffness , coefficient of foundation damping and the frequency mass ratio on the governing model equation were investigated. In addition, the bending and deflection of the pipe on a viscoelastic foundation are compared with those on an elastic foundation. The analytical and the numerical solutions are in good agreement. From the study, it is observed that an increase in the foundation stiffness results in increase in the pipe inherent frequencies. Furthermore, the vibration of the pipe on a viscoelastic foundation shows better control and reduction compared with its vibration on an elastic foundation.