Saturated Film Research Articles

Неисчерпаемые проблемы теплообмена

The article considers the heat transfer problems studied by the researchers of the MPEI Department of Engineering Thermal Physics (DETP) during the last five years. Modes involving low-frequency temperature pulsations have been revealed during heat transfer with liquid metals under the conditions of turbulence being suppressed by magnetic field; these pulsations, which are caused by thermo-gravity convection, present potential danger for the liquid metal cooling systems used in nuclear power engineering and in nuclear fusion installations. The facilities available at the joint laboratory of the Joint Institute for High Temperatures (JIHT) of the Russian Academy of Sciences and the Moscow Power Engineering Institute, which was established on the JIHT territory, have opened the possibilities for studying magnetic hydrodynamics and heat transfer for combinations of parameters close to the conditions under which real liquid metal-cooled systems operate. Numerical investigations of heat transfer, including direct numerical simulation (DNS) of single-phase turbulent flows or processes in heterogeneous systems, are used as an efficient tool for studying the mechanisms governing the relevant phenomena. Along with this, they open the possibility to solve applied problems, also within the framework of commercial agreements. Numerical techniques were used to optimize the metal hydride-based hydrogen cleaning and compressing systems and to study the fluid dynamics and heat transfer in air-cooled condensers. The processes taking place in the experimental section of an air-cooled condenser were for the first time simulated in the conjugated statement with taking into account the performance characteristics of gas removal devices. Solution of the natural convection problem in large-scale closed volumes at high Rayleigh numbers is an example of successful combined application of approximate analytical and numerical analysis methods. Hydrodynamics and heat transfer in two-phase media are widely studied at the Department. A few series of experiments on condensation of ethanol and water vapor mixtures with the mass fraction of alcohol ranging 0.8 to 16% on the surface of horizontal and vertical tubes have been conducted. It has been shown that the heat transfer intensity for such mixtures can increase by more than a factor of 4 as compared with condensation of pure steam. The specific features pertinent to boiling in microchannels on a smooth surface and on a surface microstructured by depositing nanoparticles have been studied. For annular two-phase flows, droplet entrainment and deposition models have been developed, and equations for predicting the distribution of droplets between the liquid film and flow core have been proposed. Comprehensive investigations of film boiling for subcooled liquid have been carried out. A unique array of experimental data on the cooling conditions of high-temperature spheres made of three different metals in four different liquids at pressures ranging from 0.1 to 1.0 MPa in a wide range of subcooling values has been created. A hypothesis about the conditions under which an intensive heat transfer mode may appear during film boiling of subcooled liquid, in which the heat transfer intensity is 20 to 30 times higher than it is during saturated film boiling. Experimental and theoretical investigations of sonoluminescence and hydroluminescence accompanying cavitation in liquids are conducted. Work is underway on developing methods for simulating macroscopically permeable phase interface boundaries in numerically solving heat and mass transfer problems under the conditions of phase transformations.

Wettability and adsorption of PTFE and paraffin surfaces by aqueous solutions of biquaternary ammonium salt Gemini surfactants with hydroxyl

The surface tension of five biquaternary ammonium salt Gemini surfactants with hydroxyl and the corresponding contact angles (θ) on Polytetrafluoroethylene (PTFE) and Paraffin are measured. The interfacial properties of surfactant solution in liquid-air-solid are investigated and changes in spreading coefficient (S), adhesive tension (γLVcosθ) and the work of adhesion (WA) are discussed. The obtained results indicate that the surface tension decreases with the increase of surfactant concentration, and it tends to be stable when the concentration is more than CMC. The contact angle has the similar trend with surface tension. A linear relationship exists between the adhesional and surface tension in a range of certain concentrations, the slope is less than 1. It means that the adsorption amount of the surfactant solution at the liquid-air interface is larger than that at the PTFE-water interfaces. However, there is no linear relationship between the adhesional and surface tension for Paraffin-surfactant solution systems. The adhesional tension increases with the increase of concentration, and it keeps constant when the saturated adsorption film has been formed at both liquid-air and solid-liquid interfaces. The wettability of biquaternary ammonium salt Gemini surfactants with hydroxyl solutions on PTFE is poorer than that of Paraffin. The wettability of C10-OH solution on PTFE surface is best, and C14-OH solution has the best wetting effect on Paraffin.

Film boiling of subcooled liquids. Part II: Steady regimes of subcooled liquids film boiling

As it was shown in the first part of the present study [1], during film boiling of highly subcooled water the particular regime of boiling occurred revealed first in the works [2,3], where the term “micro-bubble boiling” was introduced for this regime. In order to understand general regularities of the cooling process in film boiling it is reasonable to conduct investigations with different subcooled liquids. The present paper presents new systematic data on cooling the metal spheres in subcooled isopropanol and in perfluorohexane (FC-72) at very high subcoolings, up to 160K. About thirty experimental runs with isopropanol and eight runs with perfluorohexane clearly showed that at any subcooling value the micro-bubble boiling regime with high intensity of heat transfer was not observed. Stable film boiling occurred to be the dominant cooling regime; heat transfer intensity in this regime was approximately two-three times greater than in saturated film boiling at the sphere surface. An approximate model of heat transfer in stable film boiling of subcooled liquids has been derived; it accounted for an influence of liquid movement at the vapor/liquid interface due to natural convection effect. The predicting equation obtained, with two empirical numerical factors, manifests good agreement with the experimental data of the present study including the new ones on subcooled ethanol pool boiling and with the available results of other researchers. The experiments showed that film boiling of subcooled liquids is sensible to sphere surface characteristics; some surface defects, even visually undetectable can promote more intensive local heat transfer intensity.

Effect of superheat and electric field on saturated film boiling

The objective of this investigation is to study the influence of superheat temperature and applied uniform electric field across the liquid-vapor interface during film boiling using a coupled level set and volume of fluid algorithm. The hydrodynamics of bubble growth, detachment, and its morphological variation with electrohydrodynamic forces are studied considering the medium to be incompressible, viscous, and perfectly dielectric at near critical pressure. The transition in interfacial instability behavior occurs with increase in superheat, the bubble release being periodic both in space and time. Discrete bubble growth occurs at a smaller superheat whereas vapor columns form at the higher superheat values. Destabilization of interfacial motion due to applied electric field results in decrease in bubble separation distance and increase in bubble release rate culminating in enhanced heat transfer rate. A comparison of maximum bubble height owing to application of different intensities of electric field is performed at a smaller superheat. The change in dynamics of bubble growth due to increasing superheat at a high intensity of electric field is studied. The effect of increasing intensity of electric field on the heat transfer rate at different superheats is determined. The boiling characteristic is found to be influenced significantly only above a minimum critical intensity of the electric field.

Film boiling of subcooled liquids. Part I: Leidenfrost phenomenon and experimental results for subcooled water

Film boiling of subcooled liquids is important, at least, for two applications: for systems of post-accident cooling in nuclear power plants and for quenching technology. An analysis of the previous results shows that at high water subcooling film boiling presents a particular mode of boiling heat transfer, dissimilar greatly to saturated film boiling mainly by high intensity of heat transfer; this statement appears to be true, even though the researchers themselves do not recognize it. As at the temperature much higher than that of homogeneous nucleation, liquid–vapor phase transition occurs practically instantly, an actual temperature at the liquid/solid interface cannot be higher than the attainable limiting temperature of liquid. The possible mechanisms of high intensity heat transfer between the surface and subcooled liquid at the absence of liquid/solid contact and the conditions of this regime incipience require experimental and theoretical investigations. The present paper describes the method and the results of experimental study of heat transfer during cooling the spherical patterns from nickel, stainless steel, and copper with initial temperature above 700°C in water at subcoolings up to 70K. In distinction to all the previous studies temperature was measured in several points of the spheres that gives new information on the cooling process. It is revealed that at high cooling rates the temperature field can lose its spherical symmetry, high temperature gradients are observed not only in the radial direction, but also along the surface. At high subcoolings the heat transfer regime of high intensity arises at the surface temperature 600–700°C that excludes a possibility of liquid/solid direct contact; heat flux density can be as high as 5–7MW/m2.

A scale analysis model for film boiling heat transfer on a vertical flat plate with wide applicability

A model has been developed in present work, for a vertical flat plate under film boiling condition, based on scale analysis. The saturated and subcooled film boiling have been analyzed from heat and mass transfer consideration and appropriate vaporization criteria. The model takes care of natural convection and forced convection mode of heat transfer for subcooled case, while the saturated film boiling is treated with an assisting convection mode. The interfacial wave length is incorporated into the length scale and the effect of radiation heat transfer is accounted in the model. Expressions for Nusselt number have been developed for different situations. The present model recovers the Bromley scale for natural convection under saturated condition. The heat transfer characteristic is shown for relevant non-dimensional numbers pertaining to film boiling for various cases. A wide set of existing experimental data with ranges of wall superheat 260–1200°C, liquid subcooling 0–50°C and flow velocity 0–2.65m/s have been systematically utilized to arrive at the model closure.

Investigation of suppressor polyethylene glycol dodecyl ether on electroplated Cu filling by electrochemical method

In this paper, the use of polyethylene glycol dodecyl ether (POE) with a molecular weight of 1200 (POE-1200) as a suppressor for bottom-up electroplated copper filling of microvias was investigated. Galvanostatic measurement indicated that POE-1200 had much stronger suppression for Cu electrodeposition than PEG-8000 (polyethylene glycol with a molecular weight of 8000) and EPE-8000 (triblock copolymers of ethylene oxide–propylene oxide–ethylene oxide with a molecular weight of 8000). The strong synergistic suppression between POE-1200 and Cl− led to a very thin surface thickness and excellent filling performance of microvias. The cross-sectional observations of the microvias after electroplated confirmed that changing the POE-1200 concentration from 20 to 700 ppm had little effect on the filling performance because of an unchanged positive potential difference. The adsorption strength of POE-1200 on the cathode surface was enhanced greatly only in the presence of Cl− , attributing to a formation of Cl− –Cu+–POE-1200 complex. The critical adsorption concentration of Cl− and POE-1200 to form a saturated barrier film on the electrode surface was studied by Cu stripping peaks of cyclic voltammetry curves. In addition, the relationship between the saturated barrier of Cl− –Cu+–POE-1200 complex and the filling performance has been proposed.

Experimental Investigation of Inverted Annular Film Boiling in a Rod Bundle during Reflood Transient

Heat transfer results for subcooled and saturated inverted annular film boiling (IAFB) obtained from a 7×7 rod bundle during transient reflood are presented in this paper. The test section consists of heater rods of 9.5-mm diameter and 12.6-mm pitch arranged in a square array. Flooding rates considered are 0.076 and 0.152 m/s, pressure varied from 138 to 414 kPa, and inlet subcooling up to 83 K. Evaluation of the data includes estimation of the local void fraction and Nusselt number during IAFB as well as in the inverted slug film boiling (ISFB) regime, which occurs when the inverted annular liquid column disintegrates. Experimental heat transfer results are compared with several film boiling models, and a new correlation for the Nusselt number is proposed for the IAFB and ISFB regimes. Predicted Nusselt numbers using the new correlation deviate from the experimental data by an average error of 15% and root-mean-square error of ∼30%.

Adsorption behaviors of novel betaines on the wettability of the quartz surface.

The contact angle measurements for the aqueous solutions of two pairs of zwitterions on quartz surfaces have been investigated by the sessile drop analysis. The different physicochemical parameters such as the critical micelle concentration (CMC), surface tension, contact angle, surface excess on air-liquid and solid-liquid interfaces and work of adhesion have been estimated. The obtained results show that the contact angle of surfactants such as alkyl carboxylbetaine (ACB) and ditolyl substituted alkyl carboxylbetaine (BCB) remains almost constant in a wide range of surfactant concentration and increases gradually above CMC, which are quite different from traditional surfactants reported in the literature. Surfactants with bigger polar groups have a more steric effect on the quartz surface and the contact angle remains relatively unchanged. Moreover, an increase in quartz-liquid interfacial tension (γSL) has been observed due to the adsorption of four zwitterionic surfactants. Especially for ACB and BCB, at the surfactant concentrations higher than 5 × 10(-5) mol L(-1), a moderate increase in the interfacial tension of the quartz-liquid is observed, which suggests that ACB and BCB can form a saturated adsorption film briefly on the quartz surface and then adsorb again. However, the addition of alkyl sulfobetaine (ASB) and ditolyl substituted alkyl sulfobetaine (BSB) after CMC cannot adsorb on the quartz surface again due to the steric effect of bigger polar groups.

B221 二次元温度場計測を通した高温加熱面の膜沸騰崩壊温度および沸騰熱伝達特性 : 高液サブクール度条件の検討(OS-01:沸騰・凝縮伝熱および混相流の最近の進展(4))

The behavior of rewetting on a high superheated and dry surface, focusing on rewetting temperature just as collapse of saturated and subcooled film boiling was investigated experimentally. Saturated and subcooled impingement jet experiments were conducted by using a silver plate with 40.0× 40.0 mm (length × width) and pure water at atmospheric condition. The liquid subcooling was 0, 10, 20, 30, 40, 50 and 75K, respectivelity. Temperature of the test heater was measured by using a commercial separated-type infrared thermometer from a back side of it. The sputtering temperature, i.e., rewetting initiation temperature, was close to the value given by Nishio's correlation, 200℃, in spite of liquid velocity and liquid subcooling.

Numerical Simulation of Two-dimensional Forced Convective Film Boiling Flow over a Horizontal Flat Surface

In this numerical study, a Coupled Level Set and Volume of Fluid (CLSVOF) interface capturing method with multi-directional advection algorithm is used to investigate the flow and heat transfer characteristics of a two-dimensional, incompressible, laminar, forced convective saturated film boiling over an isothermal horizontal flat plate. In this study, the effects of wall superheats and liquid free stream velocities are considered for water and refrigerant R-134a. In the numerical simulation of forced convection saturated film boiling flows, the wall shear stress and the heat transfer coefficient results are evaluated with Cess and Sparrow1 correlations developed based on the boundary layer approximations. The numerical results show good agreement with the correlations developed based on the boundary layer theory. Both heat transfer coefficient and wall shear stress are strongly dependent on the wall superheats and inflow free stream velocities.

A Coupled Level Set and Volume of Fluid method with multi-directional advection algorithms for two-phase flows with and without phase change

A Coupled Level Set and Volume of Fluid (CLSVOF) interface capturing method using a multi-dimensional advection algorithm for non-uniform grids has been developed for two phase flows with and without phase change for two-dimensional problems. A finite volume method with a collocated grid arrangement is used for solving the governing equations. The SIMPLE algorithm is used for velocity and pressure coupling. The piecewise linear interface calculation (PLIC) based geometrical reconstruction procedure and an Edge Matched Flux Polygon Advection (EMFPA) multi-dimensional algorithm have been implemented for the Volume of Fluid (VOF) method. For the Level Set (LS) advection equation, the convective terms are discretized using the second order accurate essentially non-oscillating (ENO) scheme. The proposed multi-dimensional advection of CLSVOF method requires interface reconstruction for the advection of VOF function and the Level Set function re-initialization only once compared to the requirement of twice interface reconstruction and Level Set re-initialization in the operator-splitting method for 2D problems. The performance of proposed CLSVOF method is evaluated for accurate mass conservation, surface tension force and interface mass transfer through various standard benchmark problems. The numerical study of two-dimensional saturated film boiling flow over a horizontal plane surface was carried out for different constant wall superheats in order to validate the implementation of boiling flow model. The present numerical results of boiling flows show better agreement with the experimental correlations.

Solubility of Nickel Nanoparticles in Simulated Body Fluids

The paper is dedicated to nickel nanoparticles dissolution in simulated body fluids. By the example of industrial electroexplosive nickel nanopowder it has been demonstrated that dissolution degree in simulated lung fluid and simulated saliva can reach 98.0 and 62.8 wt.% for 24 hours, respectively. The mechanism of nickel dissolution has been proposed. It includes the dissolution of energy saturated oxide film, formed in oxygen saturated simulated saliva, the formation of nickel hydroxycitrate in simulated lung fluid as well.

Lipid order, saturation and surface property relationships: A study of human meibum saturation

Tear film stability decreases with age however the cause(s) of the instability are speculative. Perhaps the more saturated meibum from infants may contribute to tear film stability. The meibum lipid phase transition temperature and lipid hydrocarbon chain order at physiological temperature (33 °C) decrease with increasing age. It is reasonable that stronger lipid–lipid interactions could stabilize the tear film since these interactions must be broken for tear break up to occur. In this study, meibum from a pool of adult donors was saturated catalytically. The influence of saturation on meibum hydrocarbon chain order was determined by infrared spectroscopy. Meibum is in an anhydrous state in the meibomian glands and on the surface of the eyelid. The influence of saturation on the surface properties of meibum was determined using Langmuir trough technology. Saturation of native human meibum did not change the minimum or maximum values of hydrocarbon chain order so at temperatures far above or below the phase transition of human meibum, saturation does not play a role in ordering or disordering the lipid hydrocarbon chains. Saturation did increase the phase transition temperature in human meibum by over 20 °C, a relatively high amount. Surface pressure–area studies showing the late take off and higher maximum surface pressure of saturated meibum compared to native meibum suggest that the saturated meibum film is quite molecularly ordered (stiff molecular arrangement) and elastic (molecules are able to rearrange during compression and expansion) compared with native meibum films which are more fluid agreeing with the infrared spectroscopic results of this study. In saturated meibum, the formation of compacted ordered islands of lipids above the surfactant layer would be expected to decrease the rate of evaporation compared to fluid and more loosely packed native meibum. Higher surface pressure observed with films of saturated meibum compared to native meibum suggests greater film stability especially under the high shear stress of a blink.

Magnetic field tunable acoustic resonator with ferromagnetic-ferroelectric layered structure

High overtone acoustic resonator with yttrium iron garnet/zinc oxide layered structure was theoretically considered, fabricated, and experimentally investigated. The theory of the resonator, containing an arbitrary number of magnetic and nonmagnetic dielectric/ferroelectric layers, placed in a transverse magnetic field is presented. The simulation shows the possibility to tune the resonant frequency in the range of ±1 MHz by magnetic field. This tuning is due to the resonance magnetoelastic interaction in the saturated ferrite film and the total phase shift of acoustic wave in the structure. The experiment proves the magnetic field influence on resonance frequencies and attenuation of transverse wave with polarization vector quasicollinear with the field direction. The tuning about 0.25 MHz near the acoustic resonant frequency 2 GHz was obtained in the field 260 Oe. This frequency is close to the ferromagnetic resonance frequency in ferrite film, corresponding to the field applied.

Investigation of vapor film motion regularities at boiling liquids

The experimental investigation of the saturated Freon-113 and distilled water film boiling on spheres with different diameters at atmospheric pressure under conditions of free convection is executed. With high-speed video average thickness and cumulative distribution function of vapor film as a function of the angle was measured. It was found that with increasing the angle the average thickness of vapor film can change by different laws depending on diameter of the sphere and the temperature difference. It was found also that the increase in the average vapor film thickness with increasing angle is more connected with the increase of large components of cumulative distribution function. It also noted the presence of quasi-periodic pulsations of the vapor film thickness in the lower part, which eventually largely determine the behavior of the interface at large angles.

Preparation of novel carbon microfiber/carbon nanofiber-dispersed polyvinyl alcohol-based nanocomposite material for lithium-ion electrolyte battery separator

A novel nanocomposite polyvinyl alcohol precursor-based material dispersed with the web of carbon microfibers and carbon nanofibers is developed as lithium (Li)-ion electrolyte battery separator. The primary synthesis steps of the separator material consist of esterification of polyvinyl acetate to produce polyvinyl alcohol gel, ball-milling of the surfactant dispersed carbon micro-nanofibers, mixing of the milled micron size (~500nm) fibers to the reactant mixture at the incipience of the polyvinyl alcohol gel formation, and the mixing of hydrophobic reagents along with polyethylene glycol as a plasticizer, to produce a thin film of ~25μm. The produced film, uniformly dispersed with carbon micro-nanofibers, has dramatically improved performance as a battery separator, with the ion conductivity of the electrolytes (LiPF6) saturated film measured as 0.119S-cm−1, approximately two orders of magnitude higher than that of polyvinyl alcohol. The other primary characteristics of the produced film, such as tensile strength, contact angle, and thermal stability, are also found to be superior to the materials made of other precursors, including polypropylene and polyethylene, discussed in the literature. The method of producing the films in this study is novel, simple, environmentally benign, and economically viable.

Crystallinity-Controlled Naphthalene-alt-diketopyrrolopyrrole Copolymers for High-Performance Ambipolar Field Effect Transistors

We report high-performance of ambipolar organic field-effect transistors (FETs) based on the low band gap copolymers of pDPPT2NAP-HD and pDPPT2NAP-OD. The polymers are composed of electron-rich 2,6-di(thienyl)naphthalene (T2NAP) and electron-deficient diketopyrrolopyrrole (DPP) units with branched alkyl chains of 2-hexyldecyl (HD) or 2-octyldodecyl (OD). The polymers were polymerized via Suzuki coupling, yielding optical band gaps of ∼1.4 eV. In the transistor performance test, we observed good ambipolar transport behavior in both polymer films, and pDPPT2NAP-OD displayed hole and electron mobilities 1 order of magnitude higher than the corresponding properties of pDPPT2NAP-HD. Thermal annealing of the polymer films increased the carrier mobilities. Annealing at 150 °C provided optimal conditions yielding saturated film crystallinity and maximized carrier mobility. The highest hole and electron mobilities achieved in these polymers were 1.3 and 0.1 cm2/(V s), respectively, obtained from pDPPT2NAP-OD. The polymer structure and thermal annealing affected the carrier mobility, and this effect was investigated by fully characterizing the polymer films by grazing incidence X-ray diffraction (GIXD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) experiments. The GIXD data revealed that both polymers formed highly crystalline films with edge-on orientation. pDPPT2NAP-OD, which included longer alkyl chains, showed a higher tendency to form long-range order among the polymer chains. Thermal annealing up to 150 °C improved the polymer film crystallinity and promoted the formation of longer-range lamellar structures. AFM and TEM images of the films were consistent with the GI-XD data. Theoretical calculations of the polymer structures provided a rationale for the relationship between the torsional angle between aromatic rings and the carrier mobility. From the intensive electrical measurements and full characterizations, we find that the chemical structure of polymer backbone and side alkyl chain has a profound effect on film crystallinity, morphology, and transistor properties.

Adsorption Behaviors of Cationic Surfactants and Wettability in Polytetrafluoroethylene–Solution–Air Systems

Measurements of the advancing contact angle (θ) and adsorption properties were carried out for aqueous solutions of four cationic surfactants, hexadecanol glycidyl ether ammonium chloride (C(16)PC), Guerbet alcohol hexadecyl glycidyl ether ammonium chloride (C(16)GPC), hexadecanol polyoxyethylene(3) glycidyl ether ammonium chloride(C(16)(EO)(3)PC), and Guerbet alcohol hexadecyl polyoxyethylene(3) glycidyl ether ammonium chloride (C(16)G(EO)(3)PC), on the polytetrafluoroethylene (PTFE) surface using the sessile drop analysis. The obtained results indicate that the contact angle decreases to a minimum with the increasing concentration for all cationic surfactants. Surfactants with branched chain show lower θ values. Moreover, an increase of adhensional tension on the PTFE-water interface has been observed for the four cationic surfactants, and the branched ones have larger increases of adhensional tension. It is very interesting that the sharp decrease of θ appears mainly after critical micelle concentration (cmc) for C(16)GPC, C(16)(EO)(3)PC, and C(16)G(EO)(3)PC, which is quite different from traditional cationic surfactants reported in the literature. Especially for C(16)G(EO)(3)PC, there are two saturated adsorption stages on PTFE surface after cmc (which means the saturated adsorption film at air-solution interface has been formed). In the first saturated stage, the C(16)G(EO)(3)PC molecules are oriented parallel to the PTFE surface with saturated monolayer formed through hydrophobic interaction and hydrogen bond. In the second saturated stage, the hemimicelle has been formed on the PTFE surface, which can be supported by the QCM-D and SPR measurements.

Stability in the Special Saturated Liquid Film along an Inclined Heated Plate

Stable analysis of flow and heat transfer in the saturated liquid film of liquid low boiling point gases falling down an inclined heated plate is investigated. Firstly, the boundary value problem of linear stability differential equation (Orr–Sommerfeld equation) on small perturbation is derived representing surface tension by nonlinear relationship on temperature. Then, the expression of the wave velocity is got by solving the boundary value problem of O–S equation using the perturbation method. The effects of the inclined angle and some other factors, such as Reynolds number, wave number, temperature of the plate and the parameter for the physical property, on stability in the saturated liquid film of liquid low boiling point gas N2 are numerically analyzed by MATLAB software. Finally, it is shown and analyzed a new critical Reynolds number which is actually the extension of Yih’s.