Heated Metal Surface Research Articles

Результаты экспериментальных исследований тепловых процессов в условиях вынужденной конвекции моторного авиационного масла марки МС-20

The paper presents results of experimental study of the thermal processes under conditions of the MS-20 aviation engine oil forced convection in the annular channel with internal heating. Thermal and other problems of the aircraft piston and jet engines oil systems are disclosed, the goal is set, and the tasks of this article are provided. Brief information about the experimental setup and the working sections, the methodology for conducting experimental studies and the operating parameters are given. The paper provides graphs of primary and secondary processing of the obtained experimental materials on heat transfer in regard to the MS-20 oil at various operating parameters for pressure, pumping rate and heat flux density. It analyzes alterations in the wall temperature of the heated working tube, as well as the heat transfer coefficient of the MS-20 aviation engine oil depending on heat flux density, pressure and oil pumping rate in the annular channel. Generalizing dependences of the Nusselt number on the oil pumping rate and on the Reynolds number are shown and analyzed at various heat flux densities and pressures. It was experimentally established that at the temperature of the working section outer wall of 373 K and below, no carbon deposits was forming on it, which confirmed the theory of G.F. Bolshakov on temperature dependence of the sedimentation process in the hydrocarbon liquids. Based on this, authors of the article developed a new method for preventing sludge formation in the aviation motor oils and averting sludge appearance on the heated metal surfaces in the oil volume. Experimental study results became a launching pad for further research in heat transfer intensification to the aircraft engine oils and preventing sludge formation in the aircraft engines using the electrostatic fields. That would be published in the following articles by the authors in this journal.

Considerations for realistic atmospheric environments: An application to corrosion testing

Measured salt compositions in dust collected over roughly the last decade from surfaces of in-service stainless-steel alloys at four locations around the United States are presented, along with the predicted brine compositions that would result from deliquescence of these salts. The salt compositions vary greatly from ASTM seawater and from laboratory salts (i.e., NaCl or MgCl2) commonly used on corrosion testing. The salts contained relatively high amounts of sulfates and nitrates, evolved to basic pH values, and exhibited deliquescence relative humidity values (RH) higher than seawater. Additionally, inert dust in components were quantified and considerations for laboratory testing are presented. The observed dust compositions are discussed in terms of the potential corrosion behavior and are compared to commonly used accelerated testing protocols. Finally, ambient weather conditions and their influence on diurnal fluctuations in temperature (T) and RH on heated metal surfaces are evaluated and a relevant diurnal cycle for laboratory testing a heated surface has been developed. Suggestions for future accelerated tests are proposed that include exploration of the effects of inert dust particles on atmospheric corrosion, chemistry considerations, and realistic diurnal fluctuations in T and RH. Understanding mechanisms in both realistic and accelerated environments will allow development of a corrosion factor (i.e., scaling factor) for the extrapolation of laboratory-scale test results to real world applications.

Computational Simulations of Spray Cooling with Air-Assist Injectors

A new computational procedure for simulating air-assist flat sprays with atomization is described and demonstrated for surface cooling applications. This procedure builds upon and utilizes findings from our previous work; particularly the integral form of the conservation equations which are used to derive explicit quadratic formulas for drop size. These formulations relate the local energetic state to initial drop size produced by primary atomization processes. In this manner, the local liquid and gas phase velocities prior to atomization are used in the quadratic formula to provide the initial drop size and the appropriate local velocities are utilized as the initial droplet momentum state in a discrete particle tracking algorithm. This procedure has been performed and compared to experimental data for drop size and velocity. This furnishes a platform to further study the effects of droplet distributions on heat transfer and momentum transfer between the spray and a heated metal surface. This approach is based on the conservation principles and generalizable, so that it can easily be implemented in any spray geometry for accurate and efficient computations of two-phase flows including spray cooling.

Impact Mechanism of Interfacial Polymer Film Formation in Aqueous Quenchants

The results of studies of the cooling ability, rheological and surface-active properties of aqueous solutions of polyalkyleneglycol, sodium salt of carboxymethyl cellulose and polyacrylamide are presented. The choice of polymers is due to the problem of studying the mechanism of the cooling process in aqueous solutions of polymers. Comparison of the results of complex studies and video surveillance made it possible to propose a substantiated version of the mechanism of heat transfer during cooling of a metal sample in aqueous solutions of polymers. At the moment of shock boiling, a substance is formed in the wall layer, which is a nanosol (for PAG solutions) or a nanogassuspension (for Na-CMC and PAA). Under the action of a shock wave, it is directed from the heated metal surface to the interface between the polymer solution-vapor film, forming an interfacial polymer shock film. One of the stages of the shock mechanism of the formation of a polymer film is the adsorption increase in the polymer concentration on the surface of the bubbles formed during shock boiling; the next stage, the polymer shell of the bubbles, is spent on the formation of an interfacial polymer film. Heat fluxes and heat transfer coefficients are presented as a function of polymer concentration and surface temperature. The research results can be useful for assessing the effect of an interfacial polymer film on the ratio of the initial, first qcr1 and second qcr2 critical heat fluxes density, which determines the passage of heat transfer stages in water-polymer quenching media (WPQM).

Фізичні основи очищення газових сумішей з допомогою фільтрування

Розглянуто форми подрібнених дисперсних матеріалів. Наведено формули визначення еквівалентного діаметра. Подано класифікацію сучасних фільтрів, розкрито їхні особливості. Показано основні чинники, що впливають на роботу фільтрів. Відомо, що сушильні апарати для подрібненої деревини, які часто використовують у виробництві деревостружкових і деревоволокнистих плит, для конвективного підведення тепла до стружки, як об'єкта сушіння, потребують уважного ставлення до енергоощадності. Варто зазначити, що специфічні властивості подрібненої деревини (малі розміри частинок, мала насипна маса, рухомість, парусність) дають змогу використовувати різноманітні способи сушіння: сушіння у щільному, киплячому, розпушеному шарі, а також безпосередній контакт об'єкта сушіння із нагрітою металевою поверхнею. Незважаючи на конструкційне розмаїття сушильних агрегатів для подрібненої деревини, найпоширенішими є конвективні сушарки із пневмомеханічним переміщенням подрібненого матеріалу. Наведені нижче формули дають змогу залежно від форми та розмірів подрібнених частинок і породи деревини зробити правильний вибір типу фільтру. Останнє дає змогу оцінити роботу самих фільтрувальних пристроїв. Адже за мірою накопичення пиловловлюваних подрібнених частинок значно зростає ступінь їх вловлюваності.

Analysis of Passive Temperature Control Systems Using Phase Change Materials for Application to Secondary Batteries Cooling

Abstract Temperature control is one of the most significant factors to improve the performance and extend the cycle life of a battery. It is, therefore, important to design and implement an effective battery thermal management system (TMS). Phase change materials (PCMs) can be used as a cooling means for batteries. In the present paper, a preliminary analysis of the thermal behavior of PCMs used to cool down a heated metal surface was carried out. Tests have shown that pure PCMs are able to limit the temperature increase, but only for relatively low-heat fluxes. At higher values of the heat produced, the thermal conductivity of the PCM was increased by using solid foams characterized by higher thermal conductivity; it was, thus, possible to keep the surface temperature within safe limits for longer times. A computational fluid dynamics (CFD) model of the composite material (PCM + solid foam) was also developed, which allowed to predict the temperature trend within the system under different boundary conditions. However, the average thermal conductivity of the composite system that best fitted the experimental results was found to be much lower than that theoretically predicted by using common semiempirical correlations.

Interaction of Magnesium Cations with Dioctahedral Smectites under HLRW Repository Conditions

AbstractIn some real and up-scale tests using high-level radioactive waste (HLRW), Mg accumulation was observed in smectites at the contact of heated Fe or Cu metal tubes. It is important to understand why Mg accumulated in order to model the long term performance of bentonites in HLRW systems. In some of these tests, an increased number of trioctahedral domains was measured in the smectites using X-ray diffraction (XRD) and infrared spectroscopy (IR). The trioctahedral domains either formed by the dissolution/precipitation of smectites or by the addition of Mg through a solid-state reaction similar to the Hofmann-Klemen effect. The Hofmann-Klemen effect is used in the Greene-Kelly test to distinguish montmorillonites from beidellites. Many studies have been carried out about Li-uptake by smectites, but Mg was rarely taken into account. The present study was, therefore, undertaken to compare the interactions of different bentonites with Li and Mg under various conditions. A significant CEC decrease was found for Li- and Mg-saturated bentonite samples after heating at 250°C under dry conditions. The extent of this CEC reduction depended on the octahedral to tetrahedral charge ratio and was smaller for Mg-saturated samples than Li-saturated samples. This finding proved that it is much more difficult for Mg to enter octahedral vacancies than Li, which probably can be explained by the larger hydration energy and/or slightly larger radius of Mg. The relationship between CEC reduction and the octahedral/tetrahedral charge ratio of both Li- and Mg-saturated samples, however, suggests a similar process. The Mg that can reside at the bottom of the pseudohexagonal holes would not explain this relationship. The important result with respect to understanding HLRW bentonite performance, on the other hand, is that Mg fixation only occurs under dry conditions and that Mg fixation acts as a sink for Mg and, hence, leads Mg to diffuse towards the heated metal surface.

Observation of Thermal Beaming from Tungsten and Molybdenum Bull’s Eyes

Although losses in plasmonic films can be detrimental for optoelectronics, they can be exploited to create novel thermal emitters. Surface plasmon polaritons that are thermally excited on a heated metal surface can be converted to photons with useful properties. We demonstrate highly tailored thermal emission from tungsten and molybdenum films patterned with a series of circular concentric grooves (i.e., a bull’s eye). At 900 °C our structures emit an infrared beam normal to the film that is spectrally narrow (tens of nanometers) and highly directional (∼2° angular divergence). The peak wavelength (3.5 μm) can be tuned with groove periodicity. To enhance the thermal stability of the structures, we add a thin layer of HfO2. Such devices, with their simple design and low thermal mass, provide interesting incandescent light sources for various applications.

Threshold processes of sodium ion emission from NaAu surface alloy

We have studied threshold processes of Na+ ion emission from a semiconductor NaxAuy film formed on the surface of a gold substrate. In contrast to the classical notions of threshold processes involved in the surface ionization of alkali metal ions from heated metal surfaces, the diffusion exchange of atomic species between the surface and volume of the NaxAuy film ensures stable emission of Na+ ions from the substrate in the region of threshold temperatures. A diffusion mechanism of self-regulation of the surface coverage of alkali metal in the NaxAuy film is proposed.

Lotus-like effect for metal filings recovery and particle removal on heated metal surfaces using Leidenfrost water droplets.

A "lotus-like" effect is applied to demonstrate the ability of the Leidenfrost water droplets to recover Cu particles on a heated Al substrate. Cu particles on the heated surface adhere to the rim of the Leidenfrost droplets and eventually coat the droplets' surface to form an aggregation. When Fe filings are added to the Cu particles, the aggregated mixture can then be collected using a strong rare earth magnet (NdFeB) upon evaporation of the water. We also show that the Leidenfrost effect can be effectively utilized to recover both hydrophobic (dust and activated carbon) and hydrophilic (SiO2 and MgO) particles from heated Al surfaces without any topographical modification or surfactant addition. Our results show that hydrophobic and hydrophilic materials can be collected with >92% and >96% effectiveness on grooved and smooth Al surfaces, respectively. Furthermore, we observed no significant differences in the amount of material collected above the Leidenfrost point within the tested temperature range (240 °C vs. 340 °C) as well as when the Al sheet was replaced with a Cu sheet as the substrate. However, we did observe that the Leidenfrost droplets were able to collect a greater amount of material when the working liquid was water than when it was ethanol. Our findings show promise in the development of an effective precious coinage metal filings recovery technology for application in the mint industry, as well as the self-cleaning of metallic and semiconductor surfaces where manual cleaning is not amenable.

Gypsum scale formation on heated metal surfaces: The influence of polymer type and polymer stability on gypsum inhibition

The deposition of gypsum (i.e. calcium sulfate dihydrate) on brass heat exchanger surfaces in the presence of homopolymers and copolymers containing different functional groups from aqueous solution has been studied. The amount of gypsum deposited on the heat exchanger surface (in the absence of bulk or spontaneous precipitation) is strongly dependent on the polymer architecture and the polymer concentration. Scanning electron microscopic investigations on the deposit show morphological changes to the crystals due to interactive effects of some of the polymers. The effectiveness of the polymers as inhibitors was reduced by thermal treatment (150–240°C), likely due to polymer degradation.

Fouling and fouling mitigation on heated metal surfaces

An apparatus was built to study heat transfer fouling on different heat exchanger pipe surfaces by visually observing the progressive fouling deposition under the same solution conditions. Test pipes were centrally located in a cylindrical tank with a concentric vertical agitator to give constant and uniform flow conditions near the pipe surface. Pipes with either smooth or roughened surfaces provided quantitative data on the progressive build-up and the composition of the deposits. The calcium sulphate deposition on four different metal surfaces (copper, aluminium, brass, and stainless steel) was investigated. The results show that fouling increases with time but at a decreasing rate over set intervals. The deposition also increases with the increasing thermal conductivity of the metal, or the total surface energy. Chemical reaction fouling along with particulate and crystallisation fouling occurred on reactive surfaces when corrosive chemicals were used, and this was compared with crystallisation-only fouling on non-reactive surfaces. Bleached Kraft softwood pulp fibres at various concentrations were added to the fouling solution to study their affects on fouling on the hydraulically smooth pipes. Fouling was retarded with only a low fibre concentration and reduced further as fibre concentration was increased.

First field application of a thermal desorption resonance-enhanced multiphoton-ionisation single particle time-of-flight mass spectrometer for the on-line detection of particle-bound polycyclic aromatic hydrocarbons

The on-line analysis of single aerosol particles with mass spectrometrical methods is an important tool for the investigation of aerosols. Often, a single laser pulse is used for one-step laser desorption/ionisation of aerosol particles. Resulting ions are detected with time-of-flight mass spectrometry. With this method, the detection of inorganic compounds is possible. The detection of more fragile organic compounds and carbon clusters can be accomplished by separating the desorption and the ionisation in two steps, e.g. by using two laser pulses. A further method is, using a heated metal surface for thermal desorption of aerosol particles. If an ultraviolet laser is used for ionisation, a selective ionisation of polycyclic aromatic hydrocarbons (PAH) and alkylated PAH is possible via a resonance-enhanced multiphoton-ionisation process. Laser velocimetry allows individual laser triggering for single particles and additionally delivers information on aerodynamic particle diameters. It was shown that particles deriving from different combustion sources can be differentiated according to their PAH patterns. For example, retene, a C(4)-alkylated phenanthrene derivative, is a marker for the combustion of coniferous wood. In this paper, the first field application of a thermal desorption resonance-enhanced multiphoton-ionisation single particle time-of-flight mass spectrometer during a measurement campaign in Augsburg, Germany in winter 2010 is presented. Larger PAH-containing particles (i.e. with aerodynamic diameters larger than 1 μm), which are suspected to be originated by re-suspension processes of agglomerated material, were in the focus of the investigation. Due to the low concentration of these particles, an on-line virtual impactor enrichment system was used. The detection of particle-bound PAH in ambient particles in this larger size region was possible and in addition, retene could be detected on several particles, which allows to identify wood combustion as generic source of these particles. The observed diurnal distribution of these larger particles, however, support the origin by traffic induced re-suspension of sedimented/agglomerated material.

The identification, properties and analysis of N-hydroxyamphetamine—a metabolite of amphetamine

Abstract N-Hydroxyamphetamine (Ib) can be extracted from aqueous solutions at neutral pH, but is readily decomposed into syn- and anti-phenylacetone oximes (II) at alkaline pH values. Gas chromatography of Ib is possible, provided the compound does not come into contact with heated metal surfaces. In aqueous media the hydroxylamine can be determined (1) by extraction from the medium with ether and analysis of the ethereal solution by g.l.c.; (2) by separation of the compound on a thin-layer then oxidation of the hydroxylamine spot with ammoniacal silver nitrate to give phenylacetone oximes which may then be determined by g.l.c.; (3) by reduction with lithium aluminium hydride to amphetamine (Ia) followed by g.l.c.; (4) conversion to phenylacetone oximes by shaking at pH 12 in air, extraction of the oximes, followed by g.l.c.; (5) Alternatively, N-hydroxyamphetamine can be determined directly in aqueous solution by polarography provided the measurement is made immediately after the supporting electrolyte, sulphite/NaOH, has been added.

Tendency of motor oils to form deposits at high temperatures

The tendency of motor oils to form deposits at high temperatures due to destabilization of the colloidal system in thin layers on a heated metal surface is examined. It was assumed that a significant amount of disperse particles (soot) which affect the physicochemical characteristics of diesel oils accumulate in the oils during use. It was shown that the state of internal combustion engine parts and units can be predicted by the change in these characteristics.

Radical Production Processes on Heated Metal Catalyst Surfaces

Free radical species, such as H, O, OH, CH3, and SiH3, can be ejected efficiently to the gas phase by catalytic decomposition of material gases on heated metal surfaces. The detailed reaction mechanisms for the production of these radicals are still hard to be specified, but the mechanisms can be presumed by measuring the radical densities in the gas phase under various conditions. In this review, the results on the detection of these radical species are summarized, and the possible mechanisms taking place on the catalyst surfaces are discussed. The experimental procedures to identify the radical species are also reviewed shortly. In the production of Si atoms from SiH4, the rate determining step changes from Si desorption to SiH4 adsorption with the increase in the catalyst temperature. In the decomposition of H2O, the OH desorption energy depends on the surface coverage. In O2 systems, decomposition takes place not only on the metal surfaces, but also on the second adsorbed layers.

Experimental study of the influence of hydrogenation on synthesis of carbon nanostructures in a reactor with activated hydrogen

The role of backward pyrolysis of carbon during hydrogenation of unstructured carbon black and nanotube growth in a reactor with hydrogen activated by diffusion through a heated metallic wall is studied. If the wall is heated nonuniformly, the amorphous unstructured carbon deposit “climbs” in the course of hydrogenation by active hydrogen and deposits again when falling on the heated metal surface, self-organizing into more ordered nanofibers and nanotubes as a result of forward pyrolysis. It is shown that this effect can be used for raising the concentration of carbon nanotubes growing on catalyst particles in the deposited layer.

Thermal radiation of two-dimensional Bose-Einstein gas of surface plasmons

On a heated metal surface a two-dimensional (2D) Bose-Einstein (BE) gas of surface plasmons (SPs) exists. At the edge of the surface, SP-photon conversion (SPPC) is possible. Here we present the results of a measurement of the electromagnetic radiation caused by the SPPC at the right-angular boundary of the metal surface. The data for the photon angular distribution is in good agreement with the Sommerfeld-Maluzhinets theory. The observed effects may be useful for the measurement of optical characteristics of real metals in the IR region. The proposed method is more accurate than methods based on Fresnel relations.

T0501-2-2 垂直配向単層カーボンナノチューブ膜を接合した加熱面からの沸騰特性(マイクロ・ナノスケールの熱流体現象(2))

T0501-2-2 垂直配向単層カーボンナノチューブ膜を接合した加熱面からの沸騰特性(マイクロ・ナノスケールの熱流体現象(2))

Curvature driven diffusion, Rayleigh-Plateau instability, and Gregory-Laflamme instability

It can be expected that the respective endpoints of the Gregory-Laflamme black brane instability and the Rayleigh-Plateau membrane instability are related because the bifurcation diagrams of the black hole--black string system and the liquid drop--liquid bridge system display many similarities. In this paper, I investigate the nonlinear dynamics of the Rayleigh-Plateau instability in a range of dimensions, including the critical dimension at which the phase structure changes. I show that near the critical dimension and above, depending on a parameter in initial conditions an unstable cylinder will either pinch off or converge to an equilibrium state. The equilibrium state is apparently nonuniform but has a constant mean curvature everywhere. The results suggest that in the gravity side, near the critical dimension and above, the final state of an unstable black string (which is not too long) is a nonuniform black string. The equation of motion adopted to describe the dynamics is the surface diffusion equation, which was originally proposed to describe a grooving process of heated metal surfaces. An interesting correspondence between the diffusion dynamics and black hole (thermo)dynamics is discussed.