Host Liquid Research Articles

Experimental and numerical study on heat transfer intensification in turbulent flow of CuO–water nanofluids in horizontal coil

This work presents experimental and CFD simulation results of heat transfer for water and CuO-water nanofluid flow systems stabilized by capping agents. The experiments were carried out in a helically coiled tube in the range of turbulent flow regime with Reynolds numbers from 6000 to 21,968, for practical applications importance. Nusselt number enhancement with regard to host liquid was observed, up to 18–35 % for nanofluids under investigation. Numerical calculations were performed using the ANSYS® Fluent® package employing homogenous single-phase model with the assumption of constant wall temperature condition. The k-ε Realizable Turbulence and Enhancement Wall Treatment models were applied in all analyzed cases. New type stabilizer CTAC was employed which lead to enhanced heat transfer in coil in obtained nanofluids.

Theoretical investigation of enhanced sensing property in 1D TiO2/SiO2 periodic layers containing a defect layer of the nanocomposite with different radii of silver nanoparticles in the host liquid crystal

In this paper, we have theoretically investigated the effective dielectric permittivity of the nanocomposite (NC) layer of liquid crystal (LC) with silver nanoparticles at different radii using the Maxwell-Garnett model. The optical properties of a one-dimensional periodic structure (1DPS) of TiO2/SiO2 dielectric materials containing defect NC layer, (TiO2|SiO2)3|NC|(TiO2|SiO2)3, with different radii of silver nanoparticles studied theoretically using the well-known transfer matrix method (TMM). The effective permittivity of NC for = 0° and 90° orientation angles of LC is calculated with varying sizes of the nanoparticles because the size of the silver nanoparticles affects the surface plasmon resonance (SPR). The transmission of defect mode wavelength peaks for 0° and 90° orientation angle of the LC is studied for different radii of nanoparticles. Besides this, we have also studied the absorption characteristics of the considered NC defect structure for different orientation of the LC with varying radii of the nanoparticles.

Investigation of the spectroscopic features along with the media polarity effect in some symmetrical disc-shaped liquid crystals

Disc–shaped liquid crystals with interesting structural features are an important research field in the science and technology. Function of these strongly depends on their molecular structure and the media that surrounds them. This paper highlights spectral features of three symmetrical disc–shaped liquid crystals with similar structures and dissimilar substituent groups in various surrounding media to recognize their interactional and structural similarities and differences. Determining the type of molecular interactions in these liquid crystals and their effect is of great importance in accurate determination of host–guest interactions for diverse applications in polymer–dispersed liquid crystal displays, elastomers and optical industries, and so on. For this purpose, spectral variations were analyzed through KAT (Kamlet–Abboud–Taft) model and the dipole moments were measured through UV–visible spectroscopic technique, too. The dipole moment results reveal that the electron cloud resides in the central part of these liquid crystals. The experimental data were validated via DFT (Density Functional Theory) calculations. Both experimental and theoretical data assist to better identify the spectroscopic features of these liquid crystals and give useful information about their performance in various media that can be valuable for designing applicable guest–host or mixture liquid crystal systems.

Convection-dominated dissolution for single and multiple immersed sessile droplets

We numerically investigate both single and multiple droplet dissolution with droplets consisting of less dense liquid dissolving in a denser host liquid. In this situation, buoyancy can lead to convection and thus plays an important role in the dissolution process. The significance of buoyancy is quantified by the Rayleigh number , which is the buoyancy force over the viscous damping force. In this study, spans almost four decades from 0.1 to 400. We focus on how the mass flux, characterized by the Sherwood number , and the flow morphologies depend on . For single droplet dissolution, we first show the transition of the scaling from a constant value to , which confirms the experimental results by Dietrich et al. (J. Fluid Mech., vol. 794, 2016, pp. 45–67). The two distinct regimes, namely the diffusively and the convectively dominated regimes, exhibit different flow morphologies: when , a buoyant plume is clearly visible, which contrasts sharply with the pure diffusion case at low . For multiple droplet dissolution, the well-known shielding effect comes into play at low , so that the dissolution rate is slower as compared to the single droplet case. However, at high , convection becomes more and more dominant so that a collective plume enhances the mass flux, and remarkably the multiple droplets dissolve faster than a single droplet. This has also been found in the experiments by Laghezza et al. (Soft Matt., vol. 12 (26), 2016, pp. 5787–5796). We explain this enhancement by the formation of a single, larger plume rather than several individual plumes. Moreover, there is an optimal at which the enhancement is maximized, because the single plume is narrower at larger , which thus hinders the enhancement. Our findings demonstrate a new mechanism in collective droplet dissolution, which is the merging of the plumes, which leads to non-trivial phenomena, contrasting the shielding effect.

Study on the morphologies and electro-optical properties of cyano-phenyl-ester liquid crystals/polymer composite films prepared by a stepwise polymerisation

ABSTRACT In this work, a series of liquid crystal molecules containing cyano-phenyl-ester was designed and synthesised. Subsequently, a novel cyano-phenyl-ester liquid crystals (CPE-LCs) with a wide temperature range from −30°C to 96.4°C were developed by mixturing these liquid crystal compositions. Then as the host materials, the CPE-LCs were used for preparing polymer-dispersed and polymer-stabilised cholesteric liquid crystals (PD&SCLC) composite films by a stepwise polymerisation. The morphologies and electro-optical properties of the as-made composite films were systematically investigated through varying the acrylate liquid crystalline polymerisable monomers content, chiral doping R1011 content, applied electric field intensity and polymerisation time. Indeed, the formation of homeotropically aligned anisotropic polymer networks (HAAPNs) enabled to reduce the driving voltage of PD&SCLC from 86.6 V to 22.2 V with a reasonable contrast ratio. This work provides a new method to optimise PD&SCLC composite films in terms of the host liquid crystals.

Shape oscillations of a viscoelastic droplet suspended in a viscoelastic host liquid

The small-amplitude oscillation of a liquid droplet suspended in an immiscible host liquid is studied, where both liquids are assumed viscoelastic. An analytical characteristic equation is derived, and the damping rate and angular frequency that describe the droplet oscillation are numerically solved. The effect of the properties of the host liquid, including its density, viscosity and elasticity, on the viscoelastic droplet oscillation is examined for the quadrupole mode. The host liquid is found to make the droplet oscillation more complex and the mechanisms behind that are discussed.

Binary Supramolecular Chirality "1/0" Switched by Hierarchical Photoisomerization of a Flower-Like Compound with a Binaphthol Core and Alkyl-Functionalized Azobenzene Side Chains.

Chiral supramolecular assemblies are abundant in nature, but controlling the chirality of artificial systems still remains a challenge. In this work, we developed a system where supramolecular chirality can be controlled between chiral and achiral states, namely a chiral "1/0" switch using a flower-like azobenzene compound with a binaphthol core. Upon photoisomerization by ultraviolet irradiation, the terminal alkyl tails envelop the chiral "centre" with a reduction in the dihedral angle of the binaphthol moiety from 76.1° to 61.4°, like "closing petals". In the doped liquid crystal E7 matrix, this hierarchical conformational transition prevents the transfer of chirality to the host liquid crystal, resulting in a degradation from cholesteric phase (HTP value: 13.84 μm-1 ) to an achiral nematic phase.

Nonlinear propagation and anomalous absorption of ultrasound in liquid

Recent work has rendered possible the formulation for the nonlinear propagation of pressure waves in liquids by using the generalized Navier - Stokes equations and the modified equations of state, with the heat transfer and fluid viscidity taken into consideration. And the nonlinear approximation solution of the second order term is obtained. The conclusion concerns the acoustic pressure, phase speed, attenuation, and velocity distribution function. When the amplitude of driving acoustic pressure is higher than the cavitation threshold of the host liquid, the cavitation occurs. The cavitation bubbles will prevent the sound field from spreading in the liquid, and the acoustic energy accumulates near the cavitation zone. So when studying the transmission characteristics of acoustic wave in the liquid, the cavitation attenuation must be considered. Note that the particularity of cavitation bubble movement, cavitation bubble vibration and viscous force are simulated under the initial driving sound. Through the analysis, it is found that the transmission of sound is influenced by the viscosity of the fluid, heat transfer, driving sound pressure (amplitude, frequency, duration) and cavitation bubble in liquid. The physical mechanism is that the higher driving pressure causes the cavitation to turn stronger, the acoustic loss to be faster, the sound propagation distance to be smalletr and the vibration of bubbles to transfer energy from the fundamental wave to harmonics. As a result, the stronger absorption from the liquid causes abnormal phenomena, and the output sound is lower finally. It shows that the nonlinear radial motion of cavitation bubble is mainly responsible for the sound intensity attenuation.

Framing the hydrothermal features of magnetized TiO2–CoFe2O4 water-based steady hybrid nanofluid flow over a radiative revolving disk

PurposeHybrid nanofluids are of significant engrossment for their considerable heat transport rate. The steady flow of an incompressible viscous electrically conducted hybrid nanofluid is considered over a rotating disk under a magnetic field. Titanium oxide (TiO2) and ferrous (CoFe2O4) nanoparticles are used with their physical properties and water is considered as host liquid. The purpose of this paper is to analyze how hydrothermal integrity varies for hybrid nanosuspension over a spinning disk in the presence of magnetic orientation.Design/methodology/approachGoverning equations with boundary conditions are transformed by similarity transformations and then solved numerically with RK-4 method. A comparison of linear and nonlinear thermal radiation for the above-mentioned parameters is taken and the efficiency of nonlinear radiation is established, the same over nanofluid and hybrid nanofluid is also discussed. Heat lines are observed and discussed for various parameters like magnetic field, concentration, suction and injection parameter, radiation effect and Prandtl number.FindingsSuction and increasing nanoparticle concentration foster the radial and cross-radial velocities, whereas magnetization and injection confirm the reverse trend. The rate of increment of radial friction is quite higher for the usual nanosuspension. The calculated data demonstrate that the rate for hybrid nanofluid is 8.97 percent, whereas for nanofluid it is 15.06 percent. Double-particle suspension amplifies the thermal efficiency than that of a single particle. Magnetic and radiation parameters aid the heat transfer, but nanoparticle concentration and suction explore the opposite syndrome. The magnetic parameter increases the heat transport at 36.58 and 42.71 percent for nonlinear radiation and hybrid nanosuspension, respectively.Originality/valueNonlinear radiation gives a higher heat transport rate and for the radiation parameter it is almost double. This result is very significant for comparison between linear and nonlinear radiation. Heat lines may be observed by taking different nanoparticle materials to get some diverse result. Hydrothermal study of such hybrid liquid is noteworthy because outcomes of this study will aid nanoscience and nanotechnology in an efficient way.

Analysis on flow features of unsteady Williamson fluid inaugurated by melted wedge in the presence of heat generation–absorption: an extensive computational study

After various thought-provoking experimental and theoretical investigations on heat transfer characteristics of usual liquids, researchers recommended the idea of inclusion of nano-sized structures into host liquid. This idea yielded a tremendous revolution in the world of fluid mechanics and brought researchers’ and scientists’ attention in this direction. The present paper is addresses enhancing the unique flow features of Williamson fluid by the inclusion of nano-sized particles. The Williamson fluid model along with prominent factors like magnetic field, heat generation–absorption, stagnation point, and active heat–mass flux are considered over a wedge. The mathematical formulation for the concerned problem is addressed in the form of a system of ordinary differential equations under acceptable governing laws. The attained system of coupled equations is hard to solve analytically. Therefore, a self-coded algorithm known as the shooting method is executed to report a numerical solution. A graphical representation of pertinent profiles and the parameters that affect them are included. Tabular and graphical trends present the influence of involved variables on Williamson momentum conservation and thermal and mass fields. In addition, the physical quantities at the surface of the wedge are also examined. In addition, reliability of the current work is established by constructing a comparison for skin friction values with the published literature. Our result indicates that increment in unsteadiness parameter causes temperature and concentration drop of flowing fluid over the wedge, whereas a positive effect on momentum profile is manifested. Furthermore, viscosity ratio parameter tends to follow the temperature and increase the velocity field. Magnetic field controls the turbulence by decreasing the velocity and increases the temperature. Accelerating behavior in velocity field and diminishing pattern in velocity is portrayed.

Encapsulation with an interfacial liquid layer: Robust and efficient liquid-liquid wrapping

HypothesisWe developed an impact driven liquid-based encapsulation method by utilizing the fundamental thermodynamic tendency of a suitable three-liquid combination towards formation of a core-shell structure. ExperimentsStable wrapping is achieved by impinging a core drop from a vertical separation on an interfacial liquid film floating on a host liquid bath. The resulting interfacial dynamics is captured using a high-speed camera. Several combinations of impact height and interfacial film thickness are investigated for a quantitative description of the phenomena. FindingsThe stability and integrity of the liquid encapsulating layer are confirmed both experimentally (by analyzing the under-liquid wetting signature) and theoretically (by equilibrium thermodynamic analysis). Effect of viscous dissipation on the dynamics is explained and a consequent theoretical threshold for minimum allowable drop size is provided. A non-dimensional experimental regime is also constructed for successful encapsulation in terms of impact kinetic energy and interfacial layer thickness. Additionally, the encapsulating layer is shown to protect the core drop even when the core and host liquids are miscible. The demonstrated method is simple to implement yet robust, offers flexibility regarding varying both the size and the material properties of the core and shell liquids and consistently produces stable monodispersed encapsulated drops in an ultrafast manner.

Isochronal superpositioning in the equilibrium regime of superpressed propylene carbonate to ∼ 1.8 GPa: A study by diffusivity measurement of the fluorescent probe Coumarin 1

We address the problem of glass-forming of liquids by superpressing. We study the pressure-induced dynamic change of the fragile van der Waals liquid propylene carbonate towards the glassy state in the equilibrium regime by measuring the diffusivity of the fluorescent probe Coumarin 1 embedded in the host liquid. The probe diffusivity is measured by the fluorescence recovery after photobleaching (FRAP) technique across a bleached volume generated by the near-field diffracted pattern of a laser beam. The recovered fluorescence intensity fits to a stretched exponential with the diffusive time [Formula: see text] and the stretched exponent [Formula: see text] as free parameters. In the pressure range [0.3-1.0]GPa the diffusivity decouples from the Stokes-Einstein relation. The decoupling correlates well to a decrease of [Formula: see text]. The variation of [Formula: see text] is non-monotonous with [Formula: see text] showing a minimum at [Formula: see text] s. We evidence an isochronal superpositioning over about 3 decades of [Formula: see text] between ∼ 10 s and [Formula: see text] s and a density scaling in the whole investigated pressure range. The pressure at which [Formula: see text] is minimum coincides to the dynamical crossover pressure measured by other authors. This crossover pressure is compatible with the critical point of MCT theory. As our studied pressure range encompasses the critical pressure, the non-monotonous variation of [Formula: see text] opens new insight in the approach to the critical point.

Microdroplet nucleation by dissolution of a multicomponent drop in a host liquid

Multicomponent liquid drops in a host liquid are very relevant in various technological applications. Their dissolution or growth dynamics is complex. Differences in solubility between the drop components combined with the solutal Marangoni effect and natural convection contribute to this complexity, which can be even further increased in combination with the ouzo effect, i.e. the spontaneous nucleation of microdroplets due to composition-dependent miscibilities in a ternary system. The quantitative understanding of this combined process is important for applications in industry, particularly for modern liquid–liquid microextraction processes. In this work, as a model system, we experimentally and theoretically explore water–ethanol drops dissolving in anethole oil. During the dissolution, we observed two types of microdroplet nucleation, namely water microdroplet nucleation in the surrounding oil at drop mid-height, and oil microdroplet nucleation in the aqueous drop, again at mid-height. The nucleated oil microdroplets are driven by Marangoni flows inside the aqueous drop and evolve into microdroplet rings. A one-dimensional multiphase and multicomponent diffusion model in combination with thermodynamic equilibrium theory is proposed to predict the behaviour of spontaneous emulsification, i.e. microdroplet nucleation, that is triggered by diffusion. A scale analysis together with experimental investigations of the fluid dynamics of the system reveals that both the solutal Marangoni flow inside the drop and the buoyancy-driven flow in the host liquid influence the diffusion-triggered emulsification process. Our work provides a physical understanding of the microdroplet nucleation by dissolution of a multicomponent drop in a host liquid.

Helical twisting power and compatibility in twisted nematic phase of new chiral liquid crystalline dopants with various liquid crystalline matrices

ABSTRACTFour chiral dopants exhibiting smectic LC phases themselves were prepared and their helical twisting power (HTP) and thermal phase behaviour in mixtures with four various LC hosts were studied. The influence of host liquid crystal on HTP was evaluated and generally higher values were found for hosts with high birefringence. Unexpectedly, high enhancement was found for an LC-chiral dopant pair, both having a similar aromatic core – biphenyl ring substituted with polar group. All studied chiral dopants exhibited limited compatibility with the LC hosts in twisted nematic phase at room temperature. For one of the studied mixtures, it was able to obtain single twisted nematic phase with selective light reflection band with maximum at wavelength about 1.0 µm. Carboxylic acid-type dopants exhibited total compatibility with the studied host in single twisted nematic phase at elevated temperatures, allowing preparation of mixtures with reflection band in the visible range. In case of the carboxylic acid dopants, blue phases for optimised compositions were observed. Intermolecular hydrogen bonding between carboxylic acid proton and pyridine nitrogen of chiral dopants was found. Doping the LC host with these dopants led to slight enhancement of HTP value and higher solubility in the LC host.

A vesicle-to-sponge transition via the proliferation of membrane-linking pores in ω-3 polyunsaturated fatty acid-containing lipid assemblies

We investigate the nanostructure evolution and the membrane reorganization of diluted lipid dispersions of self-assembled monoolein (MO)/eicosapentaenoic acid (EPA, 20:5) mixtures by synchrotron small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) microscopy. The nonlamellar lipid phase containing a ω-3 polyunsaturated fatty acid was fragmented into stable nanoscale objects with the help of PEGylated lipids. The Cryo-TEM imaging revealed the transformation pathway of the vesicular bilayer membranes into sponge nanoparticles (spongosomes) in excess aqueous medium. At ambient temperature, the topological transition occurred through the proliferation of membrane-linking pores (MLP) within the individual lipid nanoparticles. The density of the MLP pores varied starting from the nanoparticle center toward the periphery. The generation of MLP is governed by the amphiphilic composition and leads to formation of 3D networks of aqueous channels inside the nanoparticles, i.e. spongosomes. A higher density of MLP pores was established at increasing fraction of EPA in the mixed lipid membranes. This corresponded to sponge particles of less hydrated internal structure, i.e. with smaller-size aqueous compartments. Synchrotron SAXS patterns characterized the overall structural transition from vesicles to sponge membranes in the studied lipid systems. It can be concluded that the incorporation of a ω-3 polyunsaturated fatty acid at increasing concentration causes swelling inhibition (dehydration) of the host liquid crystalline architectures.

A microscopic approach to heating rate of ferrofluid droplets by a magnetic field

In this work, we study the heating process of colloidal ferrofluids by a magnetic field. The heating of the fluid occurs by the magnetic relaxation of the nanoparticles which provide thermal energy for the host liquid. In the limit of small volumes, the relaxation process occurs through the Néel mechanism since the magnetic nanoparticles present superparamagnetic behavior. Within this limit, we have used a microscopic model for the coupling to phonons and external magnetic field in order to model the relaxation mechanism and to obtain an expression for the heating rate of the fluid as a function of microscopic parameters. The analysis allows determining appropriate conditions for an optimal heating rate for ferrofluids based on superparamagnetic nanoparticles.

Impacts of Heat-Conducting Solid Wall and Heat-Generating Element on Free Convection of Al2O3/H2O Nanofluid in a Cavity with Open Border

Development of modern electronic devices demands a creation of effective cooling systems in the form of active or passive nature. More optimal technique for an origination of such cooling arrangement is a mathematical simulation taking into account the major physical processes which define the considered phenomena. Thermogravitational convection in a partially open alumina-water nanoliquid region under the impacts of constant heat generation element and heat-conducting solid wall is analyzed numerically. A solid heat-conducting wall is a left vertical wall cooled from outside, while a local solid element is placed on the base and kept at constant volumetric heat generation. The right border is supposed to be partially open in order to cool the local heater. The considered domain of interest is an electronic cabinet, while the heat-generating element is an electronic chip. Partial differential equations of mathematical physics formulated in non-primitive variables are worked out by the second order finite difference method. Influences of the Rayleigh number, heat-transfer capacity ratio, location of the local heater and nanoparticles volume fraction on liquid circulation and thermal transmission are investigated. It was ascertained that an inclusion of nanosized alumina particles to the base liquid can lead to the average heater temperature decreasing, that depends on the heater location and internal volumetric heat generation. Therefore, an inclusion of nanoparticles inside the host liquid can essentially intensify the heat removal from the heater that is the major challenge in different engineering applications. Moreover, an effect of nanosized alumina particles is more essential in the case of low intensive convective flow and when the heater is placed near the cooling wall.

On the Sputtering of Titanium and Silver onto Liquids, Discussing the Formation of Nanoparticles

Titanium and silver atoms were magnetron-sputtered either onto pentaerythritol ethoxylate (PEEL) or 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIMTFSI) ionic liquid (IL), and the formation of nanoparticles (NPs) is discussed based on the chemical interaction between the metal atoms and the host liquid. In the case of PEEL, our data reveal that titanium atoms sputtered in low-pressure argon plasma first form a film over the liquid surface. However, the latter dissolves as the film gets oxidized when vented to the air; asymmetric and faceted titanium dioxide NPs are finally obtained as if they were originating from a dismantled polycrystalline thin film. In the case of silver sputtered on PEEL, a film forms and solvation never occurs even after exposing the sample to air because the oxidation of silver is thermodynamically much less favorable than titanium. Quantum-chemical calculations confirm that the chemical interaction of TiO2 with PEEL molecules is favored as compared to metallic...

Liquid Crystals: Control of Transmittance by Thermally Induced Phase Transition in Guest–Host Liquid Crystals (Adv. Sustainable Syst. 10/2018)

Liquid Crystals: Control of Transmittance by Thermally Induced Phase Transition in Guest–Host Liquid Crystals (Adv. Sustainable Syst. 10/2018)

Confinement of an antiferroelectric liquid crystal in a polymer nanonetwork: thermal and dielectric behaviour

We report the thermal and dielectric investigations on a liquid crystal exhibiting an antiferroelectric phase and confined in a polymer network of sub-micron dimensions. Two different photo-polymerizable monomers have been employed for the purpose: one of them (HDDA) is bereft of any aromatic parts, while the other (RM82) contains aromatic as well as aliphatic units and, in fact, forms a liquid crystalline phase in its monomeric state. The polymerization, which is carried out in the presence of the liquid crystalline host, is expected to yield a nanosegregated structure for HDDA and blended structure for the RM82 case, the difference reflecting the morphologies of the networks, as evidenced by SEM images. Surprisingly, even a small concentration of the latter polymer added to the former variety has substantial influence on the morphology. The main work focusses on calorimetry and dielectric relaxation spectroscopy of the host liquid crystal confined in these nanonetworks created by the polymers, which can be considered to form virtual surfaces with a finite anchoring energy. We have investigated the in-phase and antiphase modes in the antiferroelectric phase, and the soft mode in the paraelectric phase preceding the antiferroelectric phase. The relaxation frequencies of all these modes are substantially influenced by the network, with the results showing certain surprises in cases containing both HDDA and RM82.