•A thermodynamic approach to describe experimental data on the efficiency of film cooling with gas-droplet jets has been developed under the assumption that the temperature and vapor concentration ...are constant in the vicinity of the adiabatic wall.•Using the values of the total enthalpy of the vapor‒gas‒droplet mixture, experimental data on thermal efficiency were generalized in a wide range of initial conditions.•The efficiency of surface cooling by two-phase jets is significantly (3‒5 times) higher than by the single-phase ones even at relatively low contents of liquid droplets (∼2% by weight) at the inlet.
Experimental data on the efficiency of a gas-drop cooling on an adiabatic wall at various temperatures of the external flow and concentrations of the liquid phase were analyzed. Air was used as a gas phase; water was used as a liquid phase. A model for generalization of the measurement results, based on the constancy of temperatures and concentrations of components near the adiabatic wall, as well as the state of vapor phase saturation, is proposed. The distribution of the vapor concentration near the wall is studied, and a generalization of the experimental data on a change in the components of the vapor‒gas‒droplet mixture with variations in temperature and concentration conditions at the inlet is obtained using the asymptotic approach. The parameter of thermal efficiency of cooling, recorded by means of the total enthalpies of the vapor-gas and liquid phases on the wall, in the gap and in the flow core, taking into account the heat of phase transition, allowed generalization of the experimental data in the framework of the asymptotic approach of the Kutateladze – Leontiev theory of film cooling. The obtained relationships on component concentration and efficiency of a two-phase wall jet allow us to evaluate the thermal state of surfaces when they are protected by gas-droplet curtains. It was found that the thermal efficiency parameter of the two-phase curtain can be 3–5 times higher than in the single-phase cooling regime with a relatively low mass content of the droplet phase in the wall film, not exceeding 2% by mass.
The obtained relations for the concentration of components and effectiveness of a two-phase wall jet make it possible to estimate the thermal state of surfaces protected by the gas-droplet cooling.
Experimental data have been presented on the evaporation rate of suspended droplets of both pure water and water containing ≈1.5 wt % surfactant, sodium dodecyl sulfate. Evaporation occurs in a ...convective flow of dry air, with its velocity and temperature being varied within ranges of
U
0
= 1–5 m/s and
T
0
= 20–80°C, respectively. The density of the mass flux from the surface of the surfactant-containing droplets is 2–3 times lower than that in the case of pure water. For droplets in a dry air flow, the change in their diameter can be described by a set of similarity criteria, and a generalized linear empirical dependence of the evaporation rate on thermodynamic parameters may be constructed for these droplets.
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The dominant rocks in the area between the village of Kovda and township of Zelenoborskii in northern Karelia, Russia, are amphibole–biotite and biotite plagiomigmatites, which develop after ...amphibolites. These plagiomigmatites contain epidote that replaces the amphibole and biotite and is found in reaction relations with these minerals. The epidote occurs as thin rims around mineral grains it replaced and in large euhedral crystals. The rocks contain 5–15% epidote. The epidote contains relatively little FeO (no more than 10.57 wt %) but elevated concentrations of CaО (up to 27.53 wt %) and Al
2
O
3
(up to 31.28 wt %), i.e., the mole fraction of the pistacite end member is 0.14–0.22. The mineral crystallized at 400–600°C and 5 kbar. It was formed by metasomatic processes, when components of the replaced minerals interacted with components of the fluid. The amphibole–biotite and biotite rocks in which the epidote crystallized resemble amphibole–biotite and biotite gneisses. Geological, petrographic, and geochemical characteristics of the rocks indicate that they are plagiomigmatites that developed after amphibolites. The paper reports features that enable distinguishing between the plagiomigmatites and similar gneisses. The transformations of the amphibolite at its migmatization starts with the replacement of the hornblende by biotite, up to the complete replacement of the former at a certain progress of this process. Chemically, the original rocks in their migmatization sequence are gradually depleted in Fe, Ti, Mg, and Ca and enriched in Si, Na, and K. The normalized REE patterns of the plagiomigmatites are strongly fractionated: (La/Yb)
n
= 18.3 for the biotite plagiomigmatite and 30.9 for the biotite–hornblende plagiomigmatite. The rocks of the area occur in a tectonized zone, which is the boundary between two domains in the Belomorian Belt exhumed at 1.8 Ga according to the mechanism of metamorphic cores. This was favorable for the intense inflow of fluids, created a certain pressure (both total and that of H
2
O + CO
2
), temperature, and elevated oxidation potential, i.e., conditions required for epidote crystallization.
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Secondary quartzites on Tyuters Island in the Gulf of Finland host long linear zones, up to 3 m thick, that are easily discernible in detailed satellite imagery. The zones consist of ...sillimanite–magnetite–kaolinite metasomatites, rocks that were first found in these zones. The metasomatites were produced at shattering of the quartzites and subsequent fluid introduction of material enriched in various components. The metasomatites are enriched in Al
2
O
3
(16–23 wt %, as compared to 2–5 wt % in the quartzites). In contrast to the quartzites, iron in the metasomatic is contained mostly in the form of ferric oxide (whereas it occurs dominantly as ferrous oxide in the quartzites). The metasomatites contain practically no alkalis and alkali-earth elements and are enriched in Zn (146–199 ppm) and some other trace elements, including REE, first of all Ce (34 ppm) and La (17 ppm). Both the metasomatites and the quartzites show similar and insignificant REE fractionation: (La/Yb)
n
= 6.55 and 6.17. The metasomatites consist of the same minerals as the quartzites, but the proportions of these minerals and their composition in these rock types are different. It is worth mentioning magnetite of the metasomatites: it hosts abundant quartz inclusions with kaolinite rims. The quartz inclusions host, in turn, inclusions of magnetite crystallites. The metasomatites were produced in a number of stages of a metasomatic process, with changes in the fluid composition and its pH. The development of the metasomatites in the linear zones, the disintegration of their protolithic quartzites, and the high kaolinite contents in the rocks make these metasomatites similar, in a sense, to weathering crusts. However, the facts that the metasomatites and their protolithic quartzites consist of the same minerals, that the metasomatites contain absolutely no sulfides and sulfur but contain magnetite with complicated mineral inclusions make these rocks different from classic weathering crusts.
Based on analytical data on the geochemistry of tectonic pseudotachylytes and their host rocks, the specific trends of redistribution of major, trace, and rare earth elements in the course of ...seismogenic frictional melting of the arkosic metaterrigenous rocks from three zones of regional metamorphism with different temperatures (greenschist, amphibolite, and granulite) in the Northern Ladoga region are discussed. Oppositely directed trends of changes in the contents of the oxides of major elements in the protolith–blastocataclasite–pseudotachylyte triad were revealed, and a unidirectional increase in the basicity of the frictional melt as compared with the protolith was established at the same time. Geochemical evidence for partial selective melting of the protoliths is discussed. The specific features of the fractionation of trace and rare-earth elements during the transition of the protolith into the melt, as well as during its subsequent partial recrystallization, are shown. The emergence of a peak of elevated europium contents relative to the protolith in the melt matrix of all three sampling points is noted. Based on changes in the concentrations of these elements in the zones of pseudotachylyte substrate generation and in the areas of its moving and injection, the estimates of their differential mobility during frictional melting in a dynamic slip zone are given.
Detailed studies of the deeply metamorphosed Early Precambrian rocks of the Northern Ladoga region allowed us to distinguish three deformation stages of the Svecofennian tectogenesis during which ...there occurred significant structural and compositional transformations of the "cover (Paleoproterozoic) – basement (Archean)" system. In addition to the structural-paragenetic analysis, which allowed to allocate transversal structural paragenesis in both floors, there are some other opportunities in the recognition of their-hosted granitoid veined bodies with a positive Eu anomaly. The rock varieties with this anomaly are always high in barium and do not show a direct correlation between the Eu anomaly and (La/Yb)
n
, Ca and Sr. This is contrary to the ideas about the occurrence of a positive Eu anomaly due to the substitution of divalent strontium by Eu
++
and suggests that the formation of such rocks took place under the influence of deep reduced fluids. It was found that granitoids with a positive Eu anomaly were formed during the first and last stages of the structure evolution, with a predominance of brittle deformations and a deep-reduced fluid breakthrough. At the second stage, with the dominant manifestation of plastic deformations, when such fluids could be "blocked" within the system, there was a formation of granitoids with low barium concentrations and a negative Eu anomaly.
The first results of the geochronological dating of the specific sill-like gabbrodiorite–granodiorite intrusive bodies within the areal extent of the Paleoproterozoic Ladoga complex, singled out at ...an early stage of the tectono–metamorphic evolution of the Svecofennides in the southeastern part of the Fennoscandian Shield are presented. Their affinity to the fold-and-thrust paragenetic assemblage of the Meyeri zone, which separates the northern and southern domains of the Ladoga region, in the shape of plated or tabular-like magmatic bodies that fill the feather joints of low-angle thrust faults, is shown. The results of zircon dating by two technologies of the U–Pb method, indicating the time span of the early kinematic stage of the Svecofennian tectogenesis and the according plutonic igneous and metamorphic events at ca. 1.87 Ga, as well as the time limit of the imprinted folding event of the second deformation stage at about 1.83 Ga, are compared.
The results of experimental and numerical investigations of the nonstationary process of evaporation of droplets of pure liquids into a dry air at variable initial temperature of a droplet, ...temperature of the gas medium, and relative velocity of flow around a droplet are presented. The regions of application of the well-known laws of change in the size of an evaporating droplet in time depending on the thermal gas-dynamic conditions and thermophysical properties of the liquid and gas phases have been analyzed.
New data on the U–Pb age (SHRIMP-II) and trace element composition (SIMS) of zircons from granites of Bolshoi Tyuters Island (Outer Islands of the Gulf of Finland) are presented. The upper ...intersection of the discordia (1825 ± 11 Ma) is taken as the age of crystallization of granites cutting through secondary quartzites and thereby determines their youngest age. Subconcordant zircons located in the upper part of the discordia have growth oscillatory zoning and geochemical characteristics of zircons of magmatic origin. The age of the lower intersection of discordia and concordia is about 570 Ma. It is supported by the independent zircon generation represented by black CL domains and rims in magmatic zircons characterized by increased contents of non-formula elements (light REEs, Ca, P, Ti, Nb, etc.), up to anomalous values. The age of the lower intersection of discordia and concordia can be considered as related to the Timan (Ediacaran) or Finnmark (Early Caledonian) thermal activation of the Fennoscandian Shield discovered earlier based on zircons from Kola Group gneisses.
