Vapor-gas Mixture Research Articles

Feasibility of Obtaining Surface Layer Moisture Flux Using an IR Thermometer

This paper evaluates the feasibility of a method using a single hand-held infrared (IR) thermometer and a mini tower of wet and dry paper towels to psychometrically obtain surface layer temperature and moisture gradients and fluxes. Sling Psychrometers have long been standard measuring devices for quantifying the thermodynamics of near-surface atmospheric gas–vapor mixtures, specifically moisture parameters. However, these devices are generally only used to measure temperature and humidity at one near-surface level. Multiple self-aspirating psychrometers can be used in a vertical configuration to measure temperature and moisture gradients and fluxes in the first 1–2 m of the surface layer. This study explores a way to make multiple vertical psychrometric measurements with a single non-contact IR temperature sensor rather than using two in situ thermometers at each level. The surface layer dry- and wet-bulb temperatures obtained using an IR Thermometer are compared to Kestrel 4000 Weather Meter and Bacharach Sling Psychrometer measurements under various atmospheric conditions and surface types to test the viability of the method. To evaluate the results obtained using this new approach, standard meteorological surface data are collected during each experiment, and moisture parameters are derived via psychrometric equations. The results indicate that, not only is the method possible and practical, but they suggest that the IR Thermometer method may provide more surface layer temperature and moisture gradient and flux sensitivity than other single instrument methods.

Ignition and combustion characteristics of coal-water-oil slurry placed on modified metal surface at mixed heat transfer

We experimentally determined ignition and combustion of a sessile droplet of coal-water-oil slurry on modified steel samples at mixed heat transfer (radiation, conduction, and convection). The surfaces were modified by two different methods: using abradants and nanosecond laser irradiation. It was shown that a texture of steel samples formed by abradants allows changing the spreading diameter of a 50-mg coal-water-oil slurry droplet (0.44 mm in diameter) from 0.628 mm to 0.743 mm, and, thereby, changing the ignition delay time more than 2 times (from 0.108 s to 0.212 s). A multimodal hierarchical texture formed on steel samples after laser texturing allows increasing the effective contact area of a coal-water-oil slurry droplet with a conductive heat source by more than 18% at identical values of the droplet spreading diameter. This intensifies the droplet heating, increases the formation rate of a combustible vapor-gas mixture, and decreases the ignition delay time by 10–20% (to 0.093 s). A texture formed by laser irradiation increases the number of nucleation centers and intensifies puffing. Modification of steel by nanosecond laser irradiation makes it possible to diminish the intensity of ash deposition on the heating surface after the combustion of coal-water-oil slurry.

ТЕРМИЧЕСКИЙ АНАЛИЗ ПРОДУКТОВ ОКИСЛЕНИЯ АКТИВИРОВАННОГО СПЛАВА АЛЮМИНИЯ RAU-85 В РАЗЛИЧНЫХ ОКИСЛИТЕЛЬНЫХ СРЕДАХ

By methods of differential thermal and thermogravimetric analysis, the composition of the thermally active part of the studied multicomponent samples of the products of the interaction of the activated aluminum alloy with various oxidizers was determined, and their thermal behavior was revealed under conditions of dynamic temperature rise. Thermal analysis was carried out in air environment, in the temperature range from 20 to 1000°C. The heating mode of the furnace was linear (dT/dt = 10 grad/min), the reference substance was calcined Al2 O3 . Water, 3% aqueous solution of hydrogen peroxide, 5% aqueous solution of sulfuric acid were used as oxidizing agents. Establishment of the material composition of the active part of powder samples was carried out according to the morphologies of thermal curves and numerical values of the intensities of endo- and exothermic effects using the thermogravimetric readings of TG-lines associated with them. A series of endo- and exothermic effects revealed during the decomposition of the test samples made it possible to follow the order of the stage of their thermal destruction and quantitatively determine the composition of volatile components. A number of features of sample decomposition were established depending on their composition and weight ratios of thermally active sample components. The obtained data on the thermal analysis of the oxidation products of the activated alloy RAU-85 in various oxidizing environments can be successfully applied to develop a technology for cleaning the bottomhole zone of the well from asphalt resin paraffin deposits, based on the thermal gas-chemical interaction of the activated aluminum alloy and formation water, which results in the formation of a large amount of heat and vapor-gas mixture.

Intensification of spray drying granulation process by gas absorption accompanied by chemical dissociation reactions

• Model for slurry droplet drying in gas mixture containing soluble gas is developed. • Filtration of a vapor–gas mixture inside a porous shell is described by Darcy's law. • Presence of active gas enhances evaporation rate during the entire drying process. • Suggested alternative drying method can be used as part of a novel technology. In the present study, we developed a transient model for the drying of a single slurry droplet moving in a multicomponent gaseous mixture containing a soluble gas. The comprehensive model accounts for the effects of the soluble gas absorption/desorption, filtration, and compressibility of the gas–vapor mixture inside the porous crust on the intensity of the drying of the slurry droplet. The model is based on an application of the theory of heat and mass transfer during slurry droplet evaporation, in conjunction with a model for gas absorption/desorption as accompanied by a chemical dissociation reaction. It is shown that the presence of the active gas increases the evaporation rate during the entire drying process. As shown by numerical calculations, in a gas mixture containing air and ammonia with an ammonia mass fraction of 0.2, at a temperature of 293 K and humidity of 50%, the drying time of silica-aqueous slurry droplets with a radius of 250 μ m is approximately 35% shorter than that in a gas mixture not containing an active gas. We also found that at the second stage of a slurry droplet drying, the desorption of the dissolved gas from wet core decreases the temperature of the porous shell and reduces the mechanical stresses inside it that prevent the destruction of porous granules. The computational results obtained using the developed model are validated based on a good agreement with the available experimental data. Accordingly, the suggested model can be considered as a basis for alternative drying technologies.

Synthesis of Nanocomposite TiSiCN Coatings by Titanium Evaporation and Organosilicon Compound Activation in Hollow Cathode Arc Discharge.

TiSiCN coatings have been obtained by anode evaporation of titanium and the decomposition of hexamethyldisilazane in an arc discharge, using a self-heated hollow cathode, at the pressure rate of 1 mTorr of the Ar+N2 gas mixture. The proposed method makes it possible to independently and widely change the amount of metal and precursor vapor flows, the pressure and composition of the vapor-gas mixture and the degree of ionic interaction on the surface of the growing coating within a single discharge system. The paper presents the method and the results of the effect of a current discharge (10–50 A), and the flux of precursor vapours (0–1 g/h), on deposition rates, compositions, and properties of TiSiCN coatings deposited by an advanced combined PVD+PECVD method. Dense homogeneous TiSiCN coatings up to 6 µm thick and up to 27.5 GPa in hardness were obtained at 7.5 µm/h. The composition of the obtained coatings has been studied by X-ray diffraction and X-ray photoelectron spectroscopy, and it has been shown that the presented methods can form nanocomposite coatings with nanocrystallites TiC, TiN, and TiCxN1−x 3–10 nm in the amorphous matrix based on SiCN.

Cooling of a Vapor–Gas Mixture by Evaporating Water Drops

Cooling of a Vapor–Gas Mixture by Evaporating Water Drops

Catalytic activity of semiconductors under the influence of electric fields

For the first time, it was demonstrated that the catalytic properties of semiconductors can be activated using an external electric field only. More particularly, the TiO2 and Fe2O3 were found to produce noticeable amounts of carbon monoxide from carbon dioxide – water vapor gas mixture under the electric field with the strength in the 104 V/cm range. The reported process, i.e. the activation of semiconductors using the electric field is more efficient than the utilization of UV–vis radiation in terms of energy efficiency and amount of products formed.

MATHEMATICAL DESCRIPTION OF THE PROCESS OF FILM CONDENSATION OF VAPORS FROM STEAM-GAS MIXTURES

This article presents an analysis of the mathematical description of the process of film condensation of vapors from vapor-gas mixtures. Taking into account the considerable variety of effects that occur during the flow of films in processes in which phase transformations occur, the complexity of the mathematical description of the flow of condensate films becomes obvious. This complexity of describing the process is aggravated by the combination of heat and mass transfer, non- isothermic, and changes in such properties as surface tension, viscosity, and density. To describe the flow rate and film thickness during film condensation, a fundamental system of equations is used, and the equations of dynamics and continuity in the long-wave approximation are also taken into account. The estimation of the propagation length of nonlinear waves in condensate films with varying flow rates showed that with an increase in the condensation intensity, the role of the proposed corrections increases, but within the limits of the validity of the thin-film approximation does not become decisive and significant. During the description of the process of film condensation of vapors from steam-gas mixtures, it was found that when the basic conditions are met, the influence of undulation manifests itself mainly through an increase in the heat exchange surface, and the contribution of surface forces to the intensification of the process, i.e., an increase in condensate consumption, is no more than 10-12%

Охлаждение парогазовой смеси испаряющимися каплями воды

A model of thermal relaxation in the flow of a hot vapor–gas mixture and cold water droplets is presented. Numerical modeling of vapor and gas cooling during heating and evaporation of droplets has been carried out. Approximation expressions are obtained for the cooling time of vapor and gas in a given temperature range depending on the initial radius of droplets, the mass fraction of droplets, and the initial composition of the vapor-gas mixture.

THERMO CAPILLARY CONVECTION WITH DIFFUSIVE-TYPE EVAPORATION IN A THREE-DIMENSIONAL CHANNEL UNDER THE CONDITIONS OF COMBINED THERMAL LOAD

Three-dimensional generalization of the Ostroumov-Birikh solution of the classical convection equations has been obtained in order to model two-layer flows under the conditions of liquid-vapor phase transition of the diffusive type at the interface. A liquid and gas-vapor mixture fills an endless rectangular duct subjected to the action of a longitudinal temperature gradient and a transversely directed gravity field. The exact solution is interpreted as a solution describing the flows on the working section in a sufficiently long cuvette. The distinguishing characteristics of evaporative convection in the working systems like the ethanol-nitrogen and HFE7100-nitrogen are investigated in the case of different types of the boundary temperature regimes imposed on channel walls. Here, the thermal load is applied on a substrate, according to the linear law with respect to the longitudinal coordinate, whereas the upper and lateral walls are thermally insulated. The longitudinal temperature gradients and transverse temperature drops in the fluid systems, caused both by external thermal load and evaporation processes at the interface, lead to the formation of vortex structures with a complex symmetry and a peculiar vapor concentration field. The flow topology essentially differs with respect to the intensity of the thermal load and type of the liquid coolant. The characteristics of evaporative convection modes, including the evaporative mass flow rate and maximum interfacial temperature and velocity, are analyzed. The study of the characteristic features appearing upon boundary heating allows one to determine flow control mechanisms and to forecast possible forms of instability.

Selection of the Design of a Contact Condenser of a Gas-Steam Plant with Steam Injection into the Combustion Chamber

Due to the importance of the problems of implementing energy-saving technologies in modern conditions, one of the promising areas is the use of gas turbines for combined heat and power generation. One of the areas of effective development and technical re-equipment is the widespread use of highly economical combined steam and gas plants and gas turbines. The operation of the gas turbine unit “Aquarius” SE NPCG “Zorya-Mashproekt” with the injection of steam into the combustion chamber, which operates on the advanced cycle A-STIG and has in its circuit equipment for water regeneration, condensed from a vapor-gas mixture is considered. For condensation of steam from the vapor-gas mixture, a contact condenser-gas cooler is used, which is a mixing heat exchanger of complex design. The efficiency of heat transfer is determined by the design of the nozzle, namely, the developed heat transfer surface, small hydraulic supports, high heat transfer coefficients. An important aspect is the overall dimensions, which must be within certain limits. In the work it is offered to execute a design of the condenser in the form of a packed column. Different types of nozzles are considered to choose the best option. As a result of thermal design calculation of the contact capacitor, it is proposed to use Rashiga rings (15152) as a nozzle, which provide the lowest height of the nozzle at the required diameter of the device.

Characteristics of micro-explosive dispersion of gel fuel particles ignited in a high-temperature air medium

The characteristics of processes developing during the ignition and combustion of single gel fuel particles with a mass of 10 mg in a high-temperature motionless air medium were investigated by means of a hardware and software system. The system featured a high-speed video camera, LED spotlights and a laptop with commercial and custom software. A group of fuel compositions was derived from oil-filled cryogels alone and with the addition of fine solid combustible components. Polyvinyl alcohol with 10 wt% in an aqueous solution was used as an organic polymer thickener. When exposed to rapid heating, fuel compositions (oil + aqueous solution of PVA + emulsifier; oil + coal dust + aqueous solution of PVA + emulsifier) were characterized by the micro-explosive dispersion of particles. The velocities of fine fragments after the micro-explosive dispersion of a fuel melt droplet were established when the air temperature was varied in the range of 700–1000 °C. The gas–vapor mixture temperature in the region of the fuel gas-phase combustion was determined using the original two-color pyrometry technique.

Numerical simulation of the dynamics of a locally heated bilayer system under weak evaporation

The problem of thermocapillary convection under the conditions of weak evaporation in a plane confined volume is studied. The mathematical model to investigate the processes of heat- and mass transfer and phase transition parameters in a bilayer system subjected to local heating is suggested. A two-sided model based on the Boussinesq approximation of the Navier–Stokes equations is formulated in the “stream function–vorticity” terms. It includes governing equations and boundary conditions on the interface which are the consequences of the conservation laws and conditions on the outer boundaries of a cuvette. Special attention is given to the study of the effects of evaporation at the thermocapillary interface. The conditions of the heat and mass balance at the deformable interface with respect to the diffusive-type evaporation are assumed to be fulfilled. The temperature relations on the solid walls of a cell take into account the presence of thermal elements of finite size. The Dufour and Soret effects are considered in the interface conditions and in the governing equations describing the fluid motion in a gas-vapor mixture. A numerical algorithm is developed to calculate the basic characteristics of the liquid–gas system and interface location at any time. The results of the numerical study of the interface evolution and non-stationary flows in a cavity being under normal gravity conditions are presented. The possibility of intensifying the evaporation due to the arrangement of additional thermal elements is discussed. The proposed approach allows one to reliably feature the basic characteristics of convective regimes, to evaluate amplitude of the interface deformations and to forecast parameters of vapor content in a gas phase.

Ignition and combustion enhancement of composite fuel in conditions of droplets dispersion during conductive heating on steel surfaces with different roughness parameters

The ignition and combustion of single organic coal-water fuel (OCWF) droplets made of coal (30%), waste engine oil (35%), and water (35%) during conductive heating on the surfaces of the machine steel modified with abrasive materials and laser radiation were studied experimentally. The experimental conditions (material and temperature of the heating surfaces) corresponded to the operating conditions of modern furnace chambers of boilers at thermal power plants. It is found that the ignition delay and burnout times during conductive heating of OCWF droplets on steel surfaces can be controlled by changing the surface roughness parameters. On the example of 7-mg OCWF droplets with a radius of about 1.2 mm, it is shown that for processing of heating surfaces, it is necessary to use the abrasive materials with an average grit size of 100 μm to decrease the ignition and burnout times. The abrasive materials with an average grit size of more than 100 μm have an insignificant effect on the ignition delay and burnout times of OCWF droplets. However, such processing significantly increases the deposition of solid combustion products (ash deposits) with an increase in the surface roughness. Laser processing of steel surfaces is of particular interest in the implementation of passive ways of controlling the ignition and combustion characteristics of OCWF droplets. This way of changing the surface texture allows controlling the ignition delay and burnout times in a wide range of the heating source temperatures, as well as reducing the intensity of the solid product deposition on the heating surface during the OCWF combustion. The positive effect from laser processing of heating surfaces to intensify the fuel droplet combustion consists in increasing the velocity of vapor flows from combustible fuel components due to the droplet dispersion. This, in turn, intensifies the formation of a combustible vapour-gas mixture and increases the velocities of flame propagation together with the dispersion products of fuel droplets along the textured surface.

Mean-field kinetic theory analysis of vapor flow between evaporating and condensing interfaces in the presence of non-condensable gas molecules

To investigate the vapor kinetic boundary condition (which is the boundary condition for the Boltzmann equation) in the presence of a non-condensable (NC) gas at a non-equilibrium liquid interface, we performed numerical simulations of non-equilibrium vapor (condensable gas) and NC gas mixture flows. The Enskog–Vlasov direct simulation Monte Carlo method (EVDSMC method) was utilized for this two-surface problem to obtain the evaporation and condensation coefficients, which represent the vapor–molecule evaporation and condensation rates, respectively. These coefficients are incorporated in the kinetic boundary condition. The simulation results showed that the evaporation and condensation coefficients decrease with increasing numbers of NC-gas molecules at the liquid interface with the same tendency. To investigate the validity of these coefficients, we also utilized the obtained evaporation and condensation coefficients for Boltzmann equation analysis. Hence, we concluded that these coefficients simply depend on the NC-gas number density at the liquid interface if the liquid temperature is constant. Thus, they are independent of the non-equilibrium or equilibrium state, and therefore, the coefficient values obtained for the equilibrium state can be used in the analysis of a non-equilibrium state. This finding will aid future predictions of non-equilibrium vapor flows with NC gas.

Study of conditions of gas- discharge synthesis of Zinc oxide nanostructures under automatic UV-irradiation of the substrate by plasma

The spectroscopic characteristics of a bipolar, overstressed discharge of nanosecond duration between zinc electrodes in oxygen at a pressure p(O2) = 13.3 kPa are presented. In the process of microexplosions of inhomogeneities on the working surfaces of the electrodes in a strong electric field, zinc vapor is introduced into the discharge gap. This creates the prerequisites for the formation of zinc oxide molecules and clusters in the plasma and the synthesis of thin island zinc oxide films, which can be deposited on a dielectric substrate installed near the center of the discharge gap. The spectral characteristics of the discharge were investigated from the central part of the discharge gap 2 mm in size. The main excited components of the plasma of a vapor-gas mixture based on zinc and oxygen were established at high values ​​of the parameter E / N (where E is the electric field strength; N is the total concentration of particles in the plasma), which, when deposited outside the discharge plasma, can lead to the formation of fine nanostructured films based on zinc oxide.

Decreasing the Weight-Size Parameters of Gas-Steam Turbine Plant by Increasing the Efficiency of Thermodynamic Processes in the Condenser

The aim of this work is decreasing the weight-size parameters of the contact gas-steam turbine plant and contact condenser elements by increasing the efficiency of thermal-gas dynamic processes of condensation through rational irrigation of countercurrent gas-steam flow. To achieve the goal the total efficiency of water-return drops ranging from 0.1 to 1 mm at different initial velocities from 5 to 35 m/s emitted by the multi-nozzle sprinkler was determined by mathematical modeling of the liquid droplet movement processes, heat and mass transfer between the liquid droplet and gas-vapor mixture, and gas-vapor mixture pressure loss. The effect of increasing the gas-steam mixture velocity from 3.3 to 6 m/s on the overall efficiency of water return was determined. The novelty of the obtained results was defined by an increase in the water return into cycle from 12 to 13% with a droplet diameter of 0.3 -- 0.4 mm and the initial velocity from the sprinkler of 5--10 m/s. The velocity of the mixture was to 6 m/s at rational correlations of the initial velocity of the droplets’ escape, which increased the total amount of heat withdrawn to 11%. The positive effect conditions of irrigation processes on thermogasdynamic and weight-size parameters of the condenser elements for the contact gas and steam turbine plant at full pressure recovery coefficients of over 0.967 were substantiated. The most significant result was the reduction of the weight-size parameters of the marine infrastructure object power plant from 8 to 19%.

Characteristics and Parameters of Overstressed Nanosecond Discharge Plasma in Air between an Electrode from Aluminum and Electrode from Chalcopyrite (CuInSe2)

The characteristics and parameters of an overstressed high-current discharge with a duration of 100–150 ns in air, which was ignited between an aluminum electrode and a chalcopyrite electrode (CuInSe2), are presented. The air pressure was 13.3 and 101.3 kPa. In the process of microexplosions of inhomogeneities on the working surfaces of electrodes in a strong electric field, aluminum vapors and chalcopyrite vapors were introduced into the interelectrode gap, which creates the prerequisites for the synthesis of thin films based on quaternary chalcopyrite – CuAlInSe2. The films synthesized from the products of electrode destruction were deposited on a quartz plate at a distance of 2–3 cm from the center of the discharge gap. The current and voltage pulses across the discharge gap of d = 1 mm, as well as the pulse energy input into the discharge, were investigated. The plasma emission spectra were studied, which made it possible to establish the main decay products of the chalcopyrite molecule and the energy states of atoms and singly charged ions of aluminum, copper and indium, which are formed in the discharge. The reference spectral lines of atoms and ions of aluminum, copper, and indium were established, which can be used to control the process of deposition of thin films of quaternary chalcopyrite. Thin films were synthesized from the degradation products of chalcopyrite molecules and aluminum vapors, which may have the composition of the quaternary chalcopyrite CuAlInSe2; the transmission spectra of the synthesized films in the spectral range of 200–800 nm were studied. By the method of numerical simulation of the plasma parameters of an overstressed nanosecond discharge based on aluminum and chalcopyrite vapors in air by solving the Boltzmann kinetic equation for the electron energy distribution function, the temperature and density of electrons, the specific power losses of the discharge for the main electronic processes and their rate constants depending on the value parameter E/N for plasma of vapor-gas mixtures based on air, aluminum vapor and ternary chalcopyrite were modulated.

Экспериментальное обоснование способа повышения огнезащищенности древесных композитов с добавкой вторичного полиэтилентерефталата

The expediency of involvement of the waste in the production of composite materials in the form of secondary polyethylene terephthalate is shown. The results of the experimental researches for justification of technological regimes of production of wood-polymer composite possessing the required thermal and water resistance are presented. The way of its flammability reduction by means of introduction of fire retardant into the binder composition is offered. In the course of experimental studies on increasing fire protection of wood composites with the addition of secondary polyethylene terephthalate, mathematical models reflecting the relationship of controllable factors (specific pressing time, the share of flame retardant addition) and operational indicators of the composite (strength, water and fire resistance) were obtained. Statistical processing of the experimental results confirmed the homogeneity of dispersions of all output values and the adequacy of the obtained mathematical models of the wood composite production process. It was shown that 17 % aluminochromophosphate introduced into the composite at a specific pressing time of 0,53 min/mm ensures a water-resistant composite with the required bending strength and weight loss during the fire action, corresponding to the flammability class G1. It is concluded that a further increase in the specific pressing time is inexpedient because the strength of the wood-polymer composite decreases due to destructive phenomena caused by prolonged heating of the wood component, and the release of a vapor-gas mixture from the aluminochromophosphate. The reduction to a minimum of — 4,8 % of the swelling of the composite in thickness for 2 hours at such a pressing duration was established. The recommendations for technological parameters of the production process, providing obtaining of composite with polyethylene terephthalate additive with the necessary physical and mechanical indicators and reduced loss of mass during combustion were developed.

RESEARCH OF THE COMPOSITION OF PRODUCTS OF MICROWAVE PYROLYSIS OF WOOD

A method of microwave action on wood of various species was developed, as a result of which the pyrolysis process was carried out. Allocated solid, gaseous fractions, as well as as a result of condensation of a vapor-gas mixture, pyrolysate, which is a raw material for the production of low molecular weight organic compounds of various classes. Gas chromatography-mass spectroscopic analysis of the liquid fraction was carried out, the components included in its composition were identified. The proposed method allows liquefaction of wood for 20-30 minutes in the temperature range from 230 to 423 °С.