Polar Fluids Research Articles

Ion Yields in the Coupled Chemical and Physical Dynamics Model of Matrix-Assisted Laser Desorption/Ionization.

The Coupled Chemical and Physical Dynamics (CPCD) model of matrix assisted laser desorption ionization has been restricted to relative rather than absolute yield comparisons because the rate constant for one step in the model was not accurately known. Recent measurements are used to constrain this constant, leading to good agreement with experimental yield versus fluence data for 2,5-dihydroxybenzoic acid. Parameters for alpha-cyano-4-hydroxycinnamic acid are also estimated, including contributions from a possible triplet state. The results are compared with the polar fluid model, the CPCD is found to give better agreement with the data.

An analytical equation of state for water and aliphatic alcohols

An analytical equation of state, developed for water [C. A. Jeffery and P. H. Austin, J. Chem. Phys. 110 (1999) 484–496] is modified and utilized for water and some aliphatic alcohols. The law of corresponding states is used to calculate the temperature-dependant parameter of the equation of state. The critical constants are used as scaling factors in the developed law of corresponding state. Just one adjustable parameter exists in the equation of state. The application of the proposed equation of state to water and thirteen alcohols from methanol to decanol shows that the predicted densities of afore-cited polar fluids, over a range of temperatures and pressures, are well comparable with experimental data.

Predicting solubility parameter of molecular fluids

A molecular thermodynamic-based method has been previously developed by Mansoori-Oghaz et al., (J. Solution Chem., 42 (2013) 544–554) to predict the solubility parameters of normal alkanes from methane to decane. The novelty of the present method is to use the effective soft-sphere (d) diameter rather than the hard-sphere (σ) one to achieve a more realistic model for predicting the solubility parameter of molecular fluids. In the present study, the aim is to assess the performance of Lennard–Jones (12–6) parameters obtained from the second virial coefficients instead of transport properties using inversion method. Our predicted results revealed that, this work outperformed the preceding one. The calculated values of solubility parameter were used to predict several saturation properties including enthalpy of vaporization and saturated vapor-pressures with uncertainty equal to ±5.24%. In this study, a new corresponding states correlation has also been developed for determining the second viral coefficients, B2 of polar molecular fluids such as refrigerants by the help of liquid density and solubility parameter, both at normal boiling point. The uncertainty of the correlated values of B2 was of the order of ±15.64%.

ENTROPY GENERATION IN BOUNDARY LAYER FLOW OF A MICRO POLAR FLUID OVER A STRETCHING SHEET EMBEDDED IN A HIGHLY ABSORBING MEDIUM

An analytical study of entropy generation in steady boundary layer flow, heat and mass transfer characteristic of 2D convective flow of a micro polar fluid over a stretching sheet embedded through a highly absorbing medium is performed. The governing equations are continuity, momentum boundary layer, micro rotation, and energy takes into account of Rosseland approximation for thermal radiation sources are solved analytically. The governing system of partial differential equations is first transformed into a system of non-linear ordinary differential equations using similarity transformation. The transformed equations are non-linear coupled differential equations which are then linearized by quasi-linearization method and solved very efficiently by the Homotopy analysis method. The special case of the first branch (K = 0, classical Newtonian fluid) is compared with the existing numerical results of stretching flow in good agreement. In addition, favorable comparisons with previously published work on various special cases of the problem are obtained. The effects of various physical parameters of entropy generation are presented graphically and in tabular form.

Modeling of Microwave Reflection from the Surface of Water Basins with Spills of Water-Cut Oil

We consider specific features of reflection of microwaves from the surface of a water basin for the two-layer model of oil spills, which are determined by a water-cut-oil film. Within the spill model, the dielectric properties of water were allowed for in accordance with the Debye theory, and the dielectric properties of the water-cut oil, in accordance with the theory developed for binary systems. The data about variations in the values of reflection coefficients depending on the frequency, viewing angle, thickness of the oil film, and moisture content in the film are obtained. The dependences of reflection coefficients on the film thickness are determined for various values of volume content of the water fraction in oil. Complex values of the dielectric permittivity of oil-water emulsions with preset volume moisture content are found. Describing the obtained dependences of the complex dielectric permittivity of the emulsion on the volume moisture content requires application of asymmetrical formulas for the mixture of polar and nonpolar fluids.

Unsteady MHD Mixed Convection, Radiative Boundary Layer Flow of a Micro Polar Fluid Past a Semi-infinite Vertical Porous Plate with Suction

The present study investigates the thermal radiation effect on unsteady magneto hydro dynamic (MHD), mixed convection flow of a micro polar fluid past an infinite, steadily moving plate with variable suction. The dimensionless equations which govern the flow, such as conservation of mass, linear momentum, angular momentum, and energy, are solved by using a regular perturbation method. The expressions for velocity, micro rotation, and temperature are obtained. With the aid of these, the expressions for Skin-friction and Nusselt number are obtained and the behavior of various physical parameters on the above flow quantities is discussed with the help of the graphs. The existence of the magnetic field and as well as radiation decrease the velocity throughout the boundary layer. The effect of increase in the plate moving velocity and the radiation parameter, manifest in a linearly decreasing surface skin-friction on the porous plate, whereas the surface heat transfer from the porous plate tends to increase, with an increase in Prandtl number.

Electrostatics on the sphere with applications to Monte Carlo simulations of two dimensional polar fluids

We present two methods for solving the electrostatics of point charges and multipoles on the surface of a sphere, i.e., in the space S2, with applications to numerical simulations of two-dimensional (2D) polar fluids. In the first approach, point charges are associated with uniform neutralizing backgrounds to form neutral pseudo-charges, while in the second, one instead considers bi-charges, i.e., dumbells of antipodal point charges of opposite signs. We establish the expressions of the electric potentials of pseudo- and bi-charges as isotropic solutions of the Laplace-Beltrami equation in S2. A multipolar expansion of pseudo- and bi-charge potentials leads to the electric potentials of mono- and bi-multipoles, respectively. These potentials constitute non-isotropic solutions of the Laplace-Beltrami equation, the general solution of which in spherical coordinates is recast under a new appealing form. We then focus on the case of mono- and bi-dipoles and build the theory of dielectric media in S2. We notably obtain the expression of the static dielectric constant of a uniform isotropic polar fluid living in S2 in terms of the polarization fluctuations of subdomains of S2. We also derive the long range behavior of the equilibrium pair correlation function under the assumption that it is governed by macroscopic electrostatics. These theoretical developments find their application in Monte Carlo simulations of the 2D fluid of dipolar hard spheres. Some preliminary numerical experiments are discussed with a special emphasis on finite size effects, a careful study of the thermodynamic limit, and a check of the theoretical predictions for the asymptotic behavior of the pair correlation function.

Nonlinear Dynamic Response of an Unbalanced Flexible Rotor Supported by Elastic Bearings Lubricated with Piezo-Viscous Polar Fluids

On the basis of the V. K. Stokes micro-continuum theory, the effects of couple stresses on the nonlinear dynamic response of the unbalanced Jeffcott’s flexible rotor supported by layered hydrodynamic journal bearings is presented in this paper. A nonlinear transient modified Reynolds’ equation is derived and discretized by the finite element method to obtain the fluid-film pressure field as well as the film thickness by means of the implicit Euler method. The nonlinear orbits of the rotor center are determined by solving the nonlinear differential equations of motion with the explicit Euler’s scheme taking into account the flexibility of rotor. According to the obtained results, the combined effects of couple stresses due to the presence of polymer additives in lubricant and the pressure dependent viscosity on the nonlinear dynamic response of the rotor-bearing system are significant and cannot be ignored or overlooked. As expected, these effects are more noticeable for polymers characterized by higher length molecular chains.

Modeling the permittivity of electrolyte solutions

Solution of a strong electrolyte in a high‐density polar fluid gives rise to a dielectric saturation that decreases the orientation polarizability of the solvent molecules in close proximity to the ions wherefore the relative permittivity in this region is determined solely by the atomic and electronic polarization. This causes a substantial decrease in the static permittivity of the solution. By considering the dielectric saturation, a model for the permittivity of an electrolyte solution have been developed and the parameters, the relative permittivities at dielectric saturation in close proximity to the ions, for 17 ions in water at 298.15 K were determined. By scaling these relative permittivities in proportion to the permittivity of the solvent, the model could be extended to calculate the permittivity of solutions of electrolytes in methanol and admixtures of water and ethanol. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2854–2860, 2015

Vapor-liquid equilibrium and polarization behavior of the GCP water model: Gaussian charge-on-spring versus dipole self-consistent field approaches to induced polarization.

We developed the Gaussian charge-on-spring (GCOS) version of the original self-consistent field implementation of the Gaussian Charge Polarizable water model and test its accuracy to represent the polarization behavior of the original model involving smeared charges and induced dipole moments. For that purpose we adapted the recently proposed multiple-particle-move (MPM) within the Gibbs and isochoric-isothermal ensembles Monte Carlo methods for the efficient simulation of polarizable fluids. We assessed the accuracy of the GCOS representation by a direct comparison of the resulting vapor-liquid phase envelope, microstructure, and relevant microscopic descriptors of water polarization along the orthobaric curve against the corresponding quantities from the actual GCP water model.

Permittivity and electrical breakdown response of nylon 6 to chemical exposure

Environmental stress such as unintended exposure of aircraft wire insulation to aviation-related fluids is one cause of wire aging that increases the risk of electrical failure. In this paper, the dielectric properties of nylon 6, a common wire insulation material, were investigated under chemical exposure for up to 8 days in six fluids: distilled water, cleaning fluid, isopropyl alcohol, deicing fluid, jet fuel and hydraulic fluid. Real permittivity e') and dissipation factor (D) of aged samples were measured using an LCR meter over frequency range from 100 Hz to 1 MHz in an ambient environment (23 °C). It was found that e′ and D of aged nylon 6 exhibit distinct shifting behavior according to the polarity of the fluids in which it is immersed. Immersion in polar fluids gives rise to a strong effect of fluid absorption on the increase of polarizability of nylon 6, showing significant increase in e′ and D, along with moving of relaxations to higher frequencies. Electrical breakdown strength of nylon 6 was also observed to reduce dramatically following exposure to polar fluids. A two-parameter Weibull distribution was applied to analyze the distribution of electrical weak sites in chemically-aged nylon 6 and it is concluded that a different electrical breakdown mechanism could be responsible for the narrower distribution observed after polar chemical exposure than for the pristine material. Nylon 6 displayed resistance to aging in non-polar fluids, showing no significant change in complex permittivity and electrical breakdown strength.

Leaning-type polar smectic-C phase in a freely suspended bent-core liquid crystal film.

A rich variety of responsive behavior occurs in complex structured fluids due to their lower symmetries. On the other hand, fluid disorder tends to increase the symmetry of liquid crystal mesophases. Here, we report direct evidence for the existence of a mesophase with CS symmetry. The observations are based on optical studies of director inversion walls in freely suspended films in electric fields under obliquely incident light. This phase is distinguished by the polarization lying in the molecular tilt plane in freely suspended films. Such a low-symmetry polar fluid phase has been long predicted to occur in bent-core liquid crystals. The stability of this phase is attributed to the bent shape of the mesogens and dominating dispersion interactions.

VLE Properties from ISM Equation of State: Application to Pure and Mixture

In this paper, the vapor-liquid equilibrium (VLE) properties of polar and nonpolar fluids are modeled by the use of a statistically-based equation of state (EOS). The equation of state used in this work is that of Ihm-Song-Mason (ISM) EOS. An alternative approach is to revise the isothermal integration on liquid. In this respect, a temperature-dependent revision factor  (T) is introduced to the liquid fugacity coefficient expression which was already derived from traditional isothermal integration. By this modification, the vapor pressure of pure liquids can be successfully reproduced using ISM EOS. This equation of state originally cannot predict the vapor pressure of fluids. The novelty of the present work is to introduce a method such that the ISM EOS is able to predict vapor pressure of pure substances and mixtures. Furthermore, the revisionzaSX method is extended to represent the VLE properties of binary mixtures including noble gases, refrigerants and hydrocarbons. Our computation results on the VLE and PVT behaviors of 24 pure substances and 9 binary mixtures are impressive.

Transport Properties of Refrigerant Mixtures: Thermal Conductivity

In the present work, the integral equations method is used to calculate transport properties of polar fluids. For this goal, we use the Stockmayer potential and examine theoretically the thermal conductivity of several refrigerant mixtures such as R125+R134a, R125+R32, R125+R152a, R134a+R32, R152a+R32, R134a+R143a, and R125+R143a. We solve numerically the Ornstein-Zernike (OZ) equation using the Hypernetted Chain (HNC) approximation for binary fluid mixtures and obtain the pair correlation functions. Finally, the temperature dependence of thermal conductivity is studied using Vesovic-Wakeham method and compared with available results.

Thermodynamics of fluid conduction through hydrophobic channel of carbon nanotubes: the exciting force for filling of nanotubes with polar and nonpolar fluids.

Thermodynamic properties of the fluid in the hydrophobic pores of nanotubes are known to be different not only from the bulk phase but also from other conventional confinements. Here, we use a recently developed theoretical scheme of "two phase thermodynamic (2PT)" model to understand the driving forces inclined to spontaneous filling of carbon nanotubes (CNTs) with polar (water) and nonpolar (methane) fluids. The CNT confinement is found to be energetically favorable for both water and methane, leading to their spontaneous filling inside CNT(6,6). For both the systems, the free energy of transfer from bulk to CNT confinement is favored by the increased entropy (TΔS), i.e., increased translational entropy and increased rotational entropy, which were found to be sufficiently high to conquer the unfavorable increase in enthalpy (ΔE) when they are transferred inside CNT. To the best of our knowledge, this is the first time when it has been established that the increase in translational entropy during confinement in CNT(6,6) is not unique to water-like H bonding fluid but is also observed in case of nonpolar fluids such as methane. The thermodynamic results are explained in terms of density, structural rigidity, and transport of fluid molecules inside CNT. The faster diffusion of methane over water in bulk phase is found to be reversed during the confinement in CNT(6,6). Studies reveal that though hydrogen bonding plays an important role in transport of water through CNT, but it is not the solitary driving factor, as the nonpolar fluids, which do not have any hydrogen bond formation capacity can go inside CNT and also can flow through it. The associated driving force for filling and transport of water and methane is enhanced translational and rotational entropies, which are attributed mainly by the strong correlation between confined fluid molecules and availability of more free space for rotation of molecule, i.e., lower density of fluid inside CNT due to their single file-like arrangement. To the best of our information, this is perhaps the first study of nonpolar fluid within CNT using 2PT method. Furthermore, the fast flow of polar fluid (water) over nonpolar fluid (methane) has been captured for the first time using molecular dynamic simulations.

Self-propulsion of a spherical electric or magnetic microbot in a polar viscous fluid.

The self-propulsion of a sphere immersed in a polar liquid or ferrofluid is studied on the basis of ferrohydrodynamics. In the electrical case an oscillating charge density located inside the sphere generates an electrical field that polarizes the fluid. The lag of polarization with respect to the electrical field due to relaxation generates a time-independent electrical torque density acting on the fluid, causing it to move. The resulting propulsion velocity of the sphere is calculated in perturbation theory to second order in powers of the charge density.

A minimal physical model captures the shapes of crawling cells

Cell motility in higher organisms (eukaryotes) is crucial to biological functions ranging from wound healing to immune response, and also implicated in diseases such as cancer. For cells crawling on hard surfaces, significant insights into motility have been gained from experiments replicating such motion in vitro. Such experiments show that crawling uses a combination of actin treadmilling (polymerization), which pushes the front of a cell forward, and myosin-induced stress (contractility), which retracts the rear. Here we present a simplified physical model of a crawling cell, consisting of a droplet of active polar fluid with contractility throughout, but treadmilling connected to a thin layer near the supporting wall. The model shows a variety of shapes and/or motility regimes, some closely resembling cases seen experimentally. Our work strongly supports the view that cellular motility exploits autonomous physical mechanisms whose operation does not need continuous regulatory effort.

Heat and Mass Transfer on the MHD Flow of Micro Polar Fluid in the Presence of Viscous Dissipation and Chemical Reaction

This paper considers the heat and mass transfer flow of magneto hydrodynamic micro polar fluid in the presence of viscous dissipation and chemical reaction. The governing non-linear partial differential equations are transformed into a system of coupled non-linear ordinary differential equations using similarity transformations and then solved numerically using the finite element method. The numerical results are compared and found to be in good agreement with previous results as special case of (viscous dissipation) the present investigation. The influence of various flow parameters of flow field has been discussed and explained graphically.

Fluid Dynamics of an Electrowetting-on-dielectrics Tube Oscillator

We study the fluid dynamics of polar high-k fluids immersed in non-polar insulating fluids, excited by electrowetting-on-dielectric (EWOD) forces inside a tube with pressure compensation channels. The fluids are set in motion using the electrowetting effect resulting in a pressure difference inside the tube. A model of the pressure field for various viscosities of the surrounding fluid is obtained by finite element analysis of the Navier-Stokes equation. From the time dependent pressure response and the associated viscous damping, a correlation with the fluid's dynamic viscosity is obtained. In the next step, we study the pressure evolution after driving the polar fluid in one direction and stopping it rapidly at the edge of the driving electrode. The decay time of the pressure induced height difference inside the compensation channels can also be related to the surrounding non-polar fluid's viscosity. Subsequently, a cheap alternative fabrication process of an EWOD stack will be shown and used to build a tube oscillator simulated in the steps before.

Evaporation enhancement effect of TiO2 nanoparticles on silicone oil in electrorheological fluid suspension

Electrorheological (ER) fluids are suspensions which consist of dielectric particles and insulation fluid. The ER fluids can change from liquid-like to solid-like state under the applied electric field. For traditional ER fluids, the maximum yield/shear stress is only several kPa and the size of dielectric particles is generally of micron. Since 2003, a series of new type ER fluids have been discovered, of which the yield/shear stress is as high as several hundred kPa. Such a type of ER fluid is called giant ER fluid or polar molecule-dominated ER fluid (PM-ER fluid), in which the size of dispersed particles is of nanoscale. Dimethyl silicone oil is the most commonly used dispersing agent in ER fluids, because of its stable physical and chemical behaviors. There is no obvious evaporation in traditional ER fluids when it is mixed with micron grade particles. However, when it is mixed with nanoparticles to prepare giant ER fluids, the silicone oil volatilizes easily in atmosphere. If time is long enough, the silicone oil in ER suspension can even be evaporated completely. In this paper, the existence of TiO2 nanoparticles in ER suspensions enhances the volatilization phenomenon has been studied through experiment. Analysis shows that the nanoparticles caused convex nanoscale curved surfaces on the gas-solid interface makes the vapor pressure increase greatly at the silicone oil surface, and leads to the enhancement of its volatilization. Influence of particle concentration, environmental temperature and viscosity of silicone oil on the evaporation enhancement effect is also studied and analysed systematically. Results show that the increase of the fraction of nanoparticles, viscosity of silicone oil as well as the temperature would promote the effect of evaporation enhancement of silicone oil in the suspensions.