Measuring deformations of the heated liquid film by the fluorescence method

The fluorescence method was used to measure the instantaneous thickness field of the falling nonisothermal water film. The process of rivulet formation in a heated film was registered. Measurement averaging allowed determination of the degree of transverse deformation of a film. In the lower half of the heater within the interrivulet zone of the non-isothermal film, the wave amplitude decreases with a rise of the heat flux and reduction of the average thickness. Two zones of the heat flux effect on liquid film deformation were distinguished. At low heat fluxes, the film flow is weakly deformed. At high heat fluxes the thermal-capillary forces provide formation of rivulets and a thin film between them. The work was financially supported by the President of RF (NSh-6749.2006.8), Russian Foundation for Basic Research (Grants Nos. 05-08-33325-a, 06-01-00360-a), National Center on Science and Innovations (State contract No. 02.438.11.7002), and SB RAS (Interdisciplinary Integration Project No. 111).     

Measurement of the wave characteristics of a film under the effect of external perturbations

The effect of artificial perturbations on structure formation in the water film flow over a vertical plate with a heater was studied experimentally. To measure the film thickness an eight-channel capacitance probe was used. It is shown that artificial perturbations on the liquid film surface can change the distance between rivulets from the values corresponding to the thermocapillary-wave regime of rivulet formation to the values related to the thermocapillary regime. The distance between the rivulets can be changed at Reynolds numbers higher than those corresponding to the thermocapillary regime. Artificial perturbations do not change significantly the relative amplitude of large waves, but they affect the character of amplitude dependence on the heat flux density. The work was financially supported by the Russian Foundation for Basic Research (Grants Nos. 05-08-33325-a, 06-01-00360-a) and SB RAS (Interdisciplinary Integration Project No. 111).     

Influence of the plate inclination angle on rivulet formation and breakdown of non-isothermal liquid film

The influence of the plate inclination angle relative to the horizon on a distance between formed rivulets and breakdown of a falling water film was studied experimentally on a heater of 150×150 mm. Dependences of the distance between rivulets on the heat flux density and plate inclination angle were examined. In experiments two zones of influence of the heat flux on a distance between rivulets were revealed: at θ ≥ 20° distances between the rivulets do not depend on the heat flux, and at θ ≤ 15° they decrease with a rise of the heat flux. Data on film breakdown were generalized with consideration of evaporation effect. It is shown that there is almost no effect of inclination angle on film breakdown in the whole range of studied Reynolds numbers. The work was financially supported by the President of RF (No. NSh-6749.2006.8), Russian Foundation for Basic Research (Grants Nos. 05-08-33325-a, 06-01-00360-a) and SB RAS (Interdisciplinary integration project No. 111).     

Heat transfer and crisis phenomena with intense boiling in the falling wave liquid films

Experimental data on heat transfer with intense evaporation in the falling films of liquid nitrogen were analysed. According to data generalization, heat transfer at evaporation becomes more intense under the precrisis modes at high heat fluxes for two studied boundary conditions on the heat-releasing surface: T _w ≈ const and q _w ≈ const. The relative contributions of conductive and convective components of heat transfer for different heat fluxes were estimated due to statistical treatment of the wave characteristics carried out by the capacitance probes for measurement of the local liquid film thickness. It was found out that heat transfer intensification is mainly caused by a drastic decrease in thermal resistance of the local zones with intensely evaporating residual layer between large waves. At that, the convective component of heat transfer related to wave perturbations on a free surface of a liquid film decreases significantly with a rise of heat fluxes. New data on pulsations of the local temperature of the heat-releasing surface were obtained at different points along the flow with the modes of “dry spot” formation. The work was financially supported by the Russian Foundation for Basic Research (grant No. 03-02-04027-NNIO-a) and DFG (Deutsche Forschungsgemeinschaft, project Nos. Re-463-37-1 and SFB-540).     

Thermocapillary waves in a liquid film

This paper investigates two-dimensional waves in a heated liquid film in the presence of the thermocapillary effect. The waves in the film are described using the integral model. The first part of the paper considers film instability for cases of fixed temperature of the plate and fixed heat flux in the plate. The liquid temperature disturbance is calculated from the energy equation for arbitrary values of Peclet number. In the second part, the evolution of waves in a heated film is modeled based on the system of equations for film thickness, flow rate, and the energy equation. In numerical modeling of the wave evolution, the boundary of the region of growing disturbances agrees well with results of stability analysis. The calculations show that for a vertical film the thermocapillary effect leads to broadening of the instability region only at low Peclet numbers.     

Interconnection between dynamics of liquid boiling-up and heat transfer crisis for nonstationary heat release

This paper deals with investigation results on crisis phenomena for nonstationary heat release under the conditions of free convection and in falling liquid films. It is shown that the character of the crisis development and the critical heat flux for nonstationary heat release significantly depend on the characteristics determining the temperature head of liquid boiling-up. According to experimental data with an arbitrary temporal function of heating, the character of the dependence between the critical heat flux and the heat release increasing rate is significantly effected by ready nucleation sites. It is found that a change in the nonstationary critical heat flux in the range of high times between impulses for periodic heat release is connected with deactivation of ready nucleation sites on the heat-releasing surface. According to new experimental results, in the studied range of irrigation degree alteration (Re_in = 30–1660), parameters characterizing decay of the falling liquid film with stepped heat release (the distribution of the time of boiling-up expectation along the liquid film, the velocities of movable boundaries in the boiling-up and drying fronts, the intensity of liquid ejection from the heat-releasing surface) complexly depend on the Reynolds number, wave characteristics, and heat flux density. The text was submitted by the authors in English.     

Features of dry spot evolution at the film flow of cryogenic liquids at non-stationary heat release

Transitional processes with dry spot formation and drying crisis development were studied experimentally for the gradual and quasi-stationary laws of heat release on a thin-wall heater cooled by a falling film of cryogenic liquid. It is shown that for low densities of the heat flux, the laminar-wave liquid film decays with formation of a self-organizing system of metastable regular structures with boiling liquid jets and large dry zones between them. The numerical experiment modelling the process of repeated wetting of a superheated surface dried by impulse heat release was carried out. It was found for the first time that the local motion velocities of different zones of the 2D wetting front differ significantly. Reliability of results obtained by numerical methods was proved by direct comparison with experimental data. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 5-08-18022-a) and Siberian Branch of RAS (Integration project of SB RAS together with ITP of UB RAS No. 2.5).     

Perturbation theory for equilibrium properties of molecular fluids

Perturbation theory for the angular pair correlation function g(r₁₂ ω ₁ ω ₂), using a fluid with isotropic intermolecular forces as the reference system, is applied to the calculation of a variety of macroscopic properties. Comparisons with experiment are made for methane, oxygen and nitrogen (and carbon monoxide for infra-red and Raman band moments) in the dense fluid and liquid states. Theoretical expressions are given and calculations made for thermodynamic properties (isothermal compressibility, pressure, configurational energy, entropy and specific heat) both along and away from the vapour-liquid co-existence curve, for infra-red and Raman band moments, and for neutron scattering cross sections. Excellent agreement with experiment is obtained for all properties, except for the infra-red and Raman band moments; this latter comparison is inconclusive because of large experimental uncertainties. The anisotropic intermolecular forces are found to have very little effect on the liquid isothermal compressibility, in agreement with the first-order theory. Molecular anisotropy has a relatively small effect on the configurational energy and on the Helmholtz free energy, but the effect is large for pressure and specific heat. The pressure is more sensitive to short-range anisotropic forces than the other properties, whereas the specific heat is particularly sensitive to the long-range anisotropic forces. Mean squared torques (derived from infra-red and Raman band moments) are very sensitive to the strengths of the anisotropic forces, and are more sensitive to higher terms in the multipole series than are the other properties. The structure factors for oxygen and nitrogen are found to be little affected by the anisotropic forces.     

Experimental studies of the thermal properties of thin films by a probe technique with periodic heating

The thermal properties of SrTiO₃ thin films are investigated experimentally by recording the amplitude and phase of the temperature oscillations of a flat probe with the heat flux perpendicular to the plane of the film. Results are given from measurements of the specific heat and thermal conductivity of a leucosapphire substrate and the thermal conductivity of a SrTiO₃ film of thickness 2 μm. Fiz. Tverd. Tela (St. Petersburg) 39, 1299–1302 (July 1997)     

Heat transfer and crisis phenomena at boiling in Freon mixture films falling down the structured tube

Investigation results on hydrodynamics, heat transfer, and crisis phenomena in laminar-wave liquid films falling down the surfaces of different geometry are presented in this study. Freon mixture R21/R114 with initial concentration of low-boiling component of 4?C16.6 % was used as the working liquid. The film Reynolds number at the inlet to the experimental section varied from 60 to 700. The heat flux density was changed within 0?C5 W/cm². The images of wave surface of the falling liquid film and formation of dry spots were visualized and recorded by the high-speed video camera. Results of investigation of the wave structure of the film surface, measurements of heat transfer coefficients under the conditions of boiling, and critical heat fluxes in the film flow over the smooth and structured surfaces are presented.     

Study of dynamics of thin liquid layer breakdown under conditions of spot heating and formation of a droplet cluster

Breakdown dynamics was studied experimentally for the horizontal layers of various liquids (ethanol, water) with the thickness of 300 μm under the conditions of spot heating from the substrate. The main stages of the process of liquid layer breakdown were determined, and time of dry spot formation was measured. Time of dry spot formation for ethanol at the heat flux of 12.6 W/cm² was 7.85 s, and for water at the heat flux of 117 W/cm², it was 0.13 s. It was found that for both working liquids, a residual layer appears in the region of spot heating before liquid layer breakdown. It is shown that together with the thermocapillary effect, evaporation is one of the main factors affecting dynamics of liquid layer breakdown and dry spot formation.     

Heat transfer at evaporation of falling films of Freon mixture on the smooth and structured surfaces

The paper presents the results of experimental investigation of heat transfer and hydrodynamics of falling films of binary mixtures of R21 and R114 freons on the surfaces with complex configuration. The vertical tubes of 50-mm diameter with the smooth and structured surfaces, made of D16T alloy, were used as the working sections. The range of film Reynolds number at the inlet to the working section was Re =10÷155. The image of wave surface of the falling liquid film was visualized and recorded by a high-speed digital video camera. At evaporation the heat transfer coefficients on the smooth and structured surfaces are determined by the liquid flow rate and weakly depend on the heat flux. At low liquid flows, the heat transfer coefficients on the structured surface decrease in comparison with the smooth surface because of liquid accumulation and enlargement of efficient thickness in microtexture channels. At high liquid flows, a change in the structure of the wave film surface leads to an increase in heat transfer coefficients in comparison with the smooth surface.     

高Tc超导薄膜约瑟夫逊结光探测研究

我们研制了具有约瑟夫逊效应的高Tc GdBa₂Cu₃O₇-薄膜双晶晶界结,对其交直流约瑟夫逊效应进行了观测,并用其进行光探测,用波长为0.6328μm的He-Ne激光器辐照双晶结结区,系统观测了双晶晶界结的光响应特性,得到的最好结果如下噪音等效功率NEP=1.9×10^-13W,归一化探测率D=53×109cmHz^1/2W^-1,响应率Rv=4.2×10⁷V/W,响应时间τ=4.35×10^-7s.     

Doppler-shifted cyclotron resonance in tungsten plates with atomic pure surface

The surface resistance of thin monocrystalline W plates as a function of the constant magnetic field H directed along the normal to the sample surface is studied in the r.f. spectrum region. The sample surface was cleaned in high vaccum (10^-11 torr) or coated with the monomolecular impurity film. The oscillating with the magnetic field part R_osc due to the Doppler-shifted cyclotron resonance is studied. The doppleron oscillation amplitude is found to depend on the surface state and increases with the crystal cleaning. The observed changes are caused by the increase of the specular reflection coefficient for resonance electrons. With the deviation of the magnetic field from the normal to the plate surface, the doppleron wave undergoes a collisionless magnetic Landau damping and the signal amplitude decreases down to values comparable with that of Gantmakher-Kaner oscillations. Cleaning of the surface (and related increase of specularity) gives rise to a further decrease of the doppleron amplitude and appearance of additional interference maxima induced by the Gantmakher-Kaner effect.     

Localized endomorphisms of the chiral Ising model

Based on the treatment of the chiral Ising model by Mack and Schomerus, we present examples of localized endomorphisms ? ₁ ^loc and ? _1/2 ^loc . It is shown that they lead to the same superselection sectors as the global ones in the sense that unitary equivalence π₀ ο ? ₁ ^loc ? π₁ and π₀ ο ? _1/2 ^loc ? π_1/2 holds. Araki's formalism of the selfdual CAR algebra is used for the proof. We prove local normality and extend representations and localized endomorphisms to a global algebra of observables which is generated by local von Neumann algebras on the punctured circle. In this framework, we manifestly prove fusion rules and derive statistics operators.     

Particles of different density in thermocapillary liquid bridges under the action of travelling and standing hydrothermal waves

We observed particles of different density ratio α = ρ _p /ρ _f in thermocapillary liquid bridges with steady and with time-dependent flow under normal- and under microgravity. Particle accumulation structures (PAS) visualize some features of the hydrothermal wave in the liquid bridge. Relatively fast formation of PAS from particles which are considerably less dense than the fluid (α = 0.42) in oscillatory thermocapillary flow of top-heated liquid bridges was observed and explained by an additional buoyancy-assisted mechanism which brings the particles into the surface flow. This PAS from particles with α = 0.42 will persist under normal gravity for infinite time. In contrast to these less dense particles the heavier particles with α > 1 settle down under normal gravity on the lower end face of the liquid bridge after some time and are no longer in suspension and PAS will fade out. On the other hand, particles with α = 0.42 will be less suited for experiments under microgravity than particles with α > 1 because most of them will be trapped in the vortex centre of the thermocapillary flow. The sedimented particles with α > 1 are a means to visualize some features of standing hydrothermal waves which are visualzed and discussed for the first time.     

Experimental investigation of 3-dimensional wavy liquid films under the coupled influence of thermo-capillary and electrostatic forces

Three-dimensional interfacial waves developing on the free surface of falling liquid films are known to intensify heat and mass transfer. In this context, the present paper studies the effect of electrostatic as well as of thermo-capillary forces on a falling film of a dielectric liquid. Therefore, measurements of the local film thickness using a confocal chromatic imaging method were performed under isothermal and heated conditions. The experimental results show that both forces destabilize the flow. It is found, that the application of an additional electric field under heating conditions enhances the generation of rivulets, thereby reducing the overall heat transfer coefficient.     

Effect of viscosity on thermocapillary breakdown of a falling liquid film

Thermocapillary breakdown of a liquid film flowing due to gravity over a vertical plate with a heater of 150×150 mm is studied in a wide range of liquid properties (in particular, dynamic viscosity at the initial temperature varies from 0.91·10^-3 to 16.9·10^-3 Pa·s) and film Reynolds number (Re = 0.15-53.5). It is found that liquid viscosity has a significant effect on the threshold heat flux corresponding to film breakdown. To take into account the effect of liquid properties, the breakdown criterion traditionally used in literature was modified. This allowed successful generalization of all data obtained.     

Nanoscale laser-induced spallation in SiO2 films containing gold nanoparticles

A phenomenological theory of ultraviolet pulsed-laser-induced spallation is proposed to interpret crater formation in SiO₂ thin films containing absorbing 18.5-nm gold particles. The theory considers a spherical thermoacoustic stress wave propagating from a thermal source produced by laser-energy absorption inside the particle and surrounding ionized volume. Calculations show that the tensile stress associated with such an acoustic wave may exceed the local strength of the material and cause fracture and spallation of the top film portion. The theory provides an explanation of the experimentally observed complex (two-cone) shape of craters formed in the film with particle-lodging depth exceeding 110 nm. Theoretical estimates for the threshold stress amplitude and peak temperature in the thermal source are in qualitative agreement with the experimental observations. PACS 61.80.Ba; 42.70.-a; 52.38.Mf     

Capillary oscillations of a thin film of viscous liquid on a solid substrate and its instability against surface charge

In a numerical analysis of the dispersion relation describing capillary motions in a thin film of a viscous, surface-charged liquid with fluctuation forces taken into account, it is found that the critical conditions of instability of the free surface of the liquid for a fixed thickness d of the liquid film in the region where the influence of the fluctuation forces is large (d<100 nm) depend strongly on the wave number and do not depend on the viscosity of the liquid, that the fluctuation forces strongly affect the wave number of the most unstable wavelength and decrease the instability growth rate, and that the capillary motions of the liquid admit an analogy with gravity-capillary motion and can be interpreted as fluctuation-capillary motions. Zh. Tekh. Fiz. 68, 27–31 (October 1998)