Transfer In Air Research Articles

Impedance Spectroscopy Study of Charge Transfer in the Bulk and Across the Interface in Networked SnO2/Ga2O3 Core–Shell Nanobelts in Ambient Air

Metal oxide core–shell fibrous nanostructures are promising gas-sensitive materials for the detection of a wide variety of both reducing and oxidizing gases. In these structures, two dissimilar materials with different work functions are brought into contact to form a coaxial heterojunction. The influence of the shell material on the transportation of the electric charge carriers along these structures is still not very well understood. This is due to homo-, hetero- and metal/semiconductor junctions, which make it difficult to investigate the electric charge transfer using direct current methods. However, in order to improve the gas-sensing properties of these complex structures, it is necessary to first establish a good understanding of the electric charge transfer in ambient air. In this article, we present an impedance spectroscopy study of networked SnO2/Ga2O3 core–shell nanobelts in ambient air. Tin dioxide nanobelts were grown directly on interdigitated gold electrodes, using the thermal sublimation method, via the vapor–liquid–solid (VLS) mechanism. Two forms of a gallium oxide shell of varying thickness were prepared via halide vapor-phase epitaxy (HVPE), and the impedance spectra were measured at 189–768 °C. The bulk resistance of the core–shell nanobelts was found to be reduced due to the formation of an electron accumulation layer in the SnO2 core. At temperatures above 530 °C, the thermal reduction of SnO2 and the associated decrease in its work function caused electrons to flow from the accumulation layer into the Ga2O3 shell, which resulted in an increase in bulk resistance. The junction resistance of said core–shell nanostructures was comparable to that of SnO2 nanobelts, as both structures are likely connected through existing SnO2/SnO2 homojunctions comprising thin amorphous layers.

Mussel-Inspired Polymer-Based Composites for Efficient Thermal Management in Dry and Underwater Environments.

To address the escalating power consumption of processors in data centers and the growing emphasis on environmental sustainability, the prospective shift from traditional air-cooling to immersion liquid cooling necessitates multiple functional integrations in polymer-based thermal conductive materials. Here, drawing inspiration from mussels, we showed a copolymer, poly(dimethylsiloxane-co-dopamine methacrylate) (PDMS-DMA), with a variety of reversible molecular interactions and simply combined with liquid metal (EGaIn) can yield a flexible, waterproof, and electrically insulating thermal conductive composite. The obtained PDMS-DMA/EGaIn composites demonstrate a harmonious blend of attributes, including a low modulus (75.8 kPa), high thermal conductivity of 6.9 W m-1 K-1, and rapid room-temperature self-healing capabilities, capable of complete repair within 20 min, even under water. Based on its electrically insulating and water resistance properties, PDMS-DMA/EGaIn emerges as a promising candidate for efficient and stable heat transfer in both air and underwater thermal management. Consequently, this water-resistant polymer-based composite holds significance for application in thermal protective layers for future immersion liquid cooling systems.

Modelling the Spatial Distribution of Industrial Facilities and Green Areas to Reduce the Ecological Footprint

The work solves conjugated problems of a stationary and non-stationary nature for the processes of transfer and diffusion of harmful substances into the atmosphere emitted by industrial facilities to protect the ecology and environment from man-made factors. When mathematically modelling mass transfer in air, absorption coefficients were considered depending on climatic conditions and external disturbances, as well as adhesion coefficients of aerosol particles with vegetation and other weather and climatic factors. Analytical solutions and dual functionality were obtained, and solutions have been developed to optimize the location of industrial facilities in the region from the perspective of economic development and environmental protection. Numerical calculations have shown that the efficiency of particle capture by vegetation is a key factor depending on the type and size of vegetation and varying throughout the year. Experiments have confirmed that the concentration of harmful substances in the ground layer of the atmosphere decreases with increasing coefficients of absorption and capture of particles by vegetation. Computational experiments carried out on a computer have established that with an increase in the diffusion coefficient, the zone of distribution of pollutants expands.

Experimental Investigation of Enhancement of Natural Convective Heat Transfer in Air Using Ultrasound

One of the methods to improve convective heat exchange is the application of ultrasound assistance. However, little is known about ultrasound application in the air. The main purpose of this study is to investigate the effect of ultrasound on natural convection cooling. The tests are based on the cooling of the metal samples (in four different shapes) preheated to a temperature of 60 °C. Cooling takes place in free convection without and with the use of ultrasound at different powers (50 W, 100 W, 150 W, and 200 W). The study uses a mathematical model based on a small Biot’s number assumption. The values of the convective heat exchange coefficients are determined by using an approximation of the experimental results. The coefficients obtained are an increasing exponential function of the applied ultrasound power. This study indicates the possibility of using ultrasound to improve heat transfer by free convection.

ANALYSIS OF THE ATMOSPHERIC AIR POLLUTION DYNAMICS USING THE METHOD OF NUMERICAL SIMULATION

Problem statement. The task of assessing the level of atmospheric air chemical pollution in the case of an extreme situation resulting in a heptyl spill on the territory of industrial facility is considered. An analysis of the pollution zones formation both at industrial sites and in the residential area located near the industrial facility is conducted. To solve such a problem, it is necessary to develop multifactor mathematical models that allow for the rapid determination of the pollution areas formed in an extreme situation. The purpose of the article. To develop a computer model for operational analysis of pollution areas formed during the emergency emission of chemically hazardous substances into the atmosphere. Methodology. The computer model was developed on the basis of a numerical model, which is a differential analogue of the multifactor kinematic equation for impurities mass transfer in atmospheric air. The mass transfer equation takes into account the three-dimensional field of wind speed, atmospheric diffusion, and the intensity of the chemically dangerous substance release into the air. A four-step finite-difference splitting scheme is used for numerical integration of the three-dimensional mass transfer equation. Determination of the chemically dangerous substance concentration at each cleavage step is implemented according to an explicit formula. An empirical dependence is used to calculate the emission intensity of a chemically hazardous substance from the emergency spill zone. Scientific novelty. A numerical model was developed and its software implementation was conducted for the operational analysis of the formation of accidental pollution areas in the atmosphere. The model takes into account a complex of factors affecting the process of impurity propagation in the atmosphere. Practical value. A program was developed for calculating the dynamics of atmospheric air pollution based on the proposed numerical model. This makes it possible to analyze the consequences of emergency spills on the territory of chemically hazardous objects by the method of a computational experiment. Conclusions. An effective tool for operational analysis of the atmospheric air pollution level due to the emission of chemically hazardous substances is created. The results of the computational experiment are presented.

ANALYTICAL STUDY OF HEAT AND MASS TRANSFER IN AIR WASHER

ANALYTICAL STUDY OF HEAT AND MASS TRANSFER IN AIR WASHER

The modeling of transient phase changes of water droplets in flue gas flow in the range of temperatures characteristic of condensing economizer technologies

Heat transfer and phase change processes of water droplets in humid air flow were investigated by performing experiments and numerical simulations of heat recovery from biofuel exhaust gas at 40–250 °C, which is characteristic for condensing heat exchangers. Compared to the experiments, the numerical investigation was performed within a wider range of boundary conditions considering droplet dispersity and flue gas parameters. The reliability of the simulation was justified through the coincidence between the calculated temperature of the equilibrium evaporation of droplets (convection heat transfer) in humid air and the wet-bulb thermometer temperature. In case of droplet combined heating (radiation and convection), the methodology was justified by coincidence between the calculated equilibrium evaporation velocity and experimental results obtained by other authors. When the temperature of radiation source is lower than 150 °C, the vapor flows calculated at the surface of the droplets in equilibrium evaporation in the cases of combined heating and convective heat transfer differs about 0.1%, therefore, the radiation influence can be neglected. Based on the results obtained in the investigation of the droplet's phase changes, the work includes practical recommendations for technological water injection to ensure optimal heat recovery from wet exhaust gas in condensing economizers.

Chemical and magnetic order in mass-selected large FeRh nanomagnets embedded in a carbon matrix

In this paper, we present some specific chemical and magnetic order results obtained on bimetallic FeRh nanoparticles prepared under non-equilibrium conditions using mass-selected Low Energy Cluster Beam Deposition. Clusters around 7 nm incident diameter are in situ sandwiched between amorphous carbon films before transfer in air, with different surface coverage (from nearly isolated particles to percolating 2D films) in order to artificially increase diameters of the nanoparticles (NPs) by coalescence. On such FeRh@C samples, we observe different NPs morphologies and magnetic responses after UHV thermal treatments. By transmission electron microscopy (TEM), we show that after moderate annealing, nanoalloys evolved from a metastable structure towards the equilibrium CsCl-type (B2) chemically ordered phase with a more spherical shape. While from Superconducting Quantum Interference Device (SQUID) magnetometry measurements on 700 °C-annealed FeRh@C samples, we clearly evidence huge magnetization enhancement for such B2 nanoalloys with robust ferromagnetic (FM) signature even at very low temperature unlike their bulk counterparts.

Development and validation of a comprehensive 1-D model to simulate gas hold-up and gas–liquid transfer in deep air–water bubble columns

This study proposed to develop a model coupling hydrodynamics and mass transfer in order to gain an understanding of measurements taken on air–water bubble columns with low gas hold-up. Three experimental datasets with various operating conditions (water quality, liquid height, air flow range) were chosen. The model analyzes and interprets the significant impact of the local hydrostatic pressure and the effects of contamination on hydrodynamic and mass transfer parameters. The oxygen concentration in gas significantly depletes with the distance from diffusers, which explains the difference between the calculated mean of the local <kLa> and global KLa coefficients. This difference is highly significant for a high bubble column and/or systems with a low mean bubble size. The impact of water quality on mass transfer can be characterized by the contamination angle using comprehensive 1-D modeling and highlights a differentiated impact on the hydrodynamic or mass transfer parameters.

Enhancement of Convection Heat Transfer in Air Using Ultrasound

The use of ultrasound is a new method to enhance convection drying. However, there is little information in the literature on the improvement of convective heat transfer caused by ultrasound. Therefore, the heat transport during ultrasound-assisted convective heating of small samples in a hybrid dryer was experimentally examined. A small Biot number regime of heat transfer was considered. The results confirmed a great enhancement of heat transfer due to the application of ultrasound. Due to the use of ultrasound, the convective heat exchange coefficient increased from 45% to almost 250%. The enhancement is a linear function of applied ultrasound power. It was shown that the energy absorption of ultrasound existed, but the thermal effect of this absorption was very small.

Numerical simulation of air flow and heat transfer in air refrigerated containers using clean energy technologies

Air refrigerated containers are important links and key equipment for air cold chain transportation. The refrigerated container cools the goods through the cold air circulation in the container to achieve the purpose of refrigeration. The key to the design of aviation refrigerators lies in the numerical simulation of the cold air flow and temperature distribution in the containers to determine the best air duct design and optimal air outlet arrangement. This article briefly analyzes the structure of the air refrigerated container, establishes the mathematical and physical models for numerical analysis, and then analyzes the two methods. At the same time, temperatures are tested in physical container with temperature measuring devices and conducts a comparative analysis with numerical simulation. The results show that the existing top on the basis of the air supply, assign a flow channel to each small tuyere and remove the small tuyere beside it. This situation is better for both flow and heat transfer. Temperatures in tests are similar with numerical simulation.

Evaluating the influence of radiative heat flux on convective heat transfer from a vertical plate in air using an improved heating plate

This article examines the influence of radiative heat flux on the accuracy of the results of free convective heat transfer in air. In order to carry out these tests, based on the experience gained during the operation of a plate heated on one side, compensated by a reverse heat loss flux counter-heater, a unique double-sided heating sandwich plate was designed and built, consisting of three thin epoxy resin plates reinforced with glass fibre. The paths of surface resistance thermometers were etched using photolithography on the two outer plates laminated on one side with copper. The traces of two resistance heaters were etched on both sides of the third, bilaterally laminated middle plate.This paper provides a detailed technical description of the new type of plate, the method of its implementation and determination of its operational range, calibration procedures (separately for integrated thermometers and heaters). Also described are the methods for conducting experimental tests in the vertical using the balance method in air and in water, and the gradient method using a thermal imaging camera and a detection mesh in order to validate the results obtained.

Heat transfer and thermoregulation within single cells revealed by transient plasmonic imaging

Summary Cells, as the basic unit of life, undergo continuous heat transfer and dissipation during their metabolism, which is related not only to fundamental cellular functions but also massive applications. Unfortunately, thus far, we still know little about the heat transfer properties at the cellular or subcellular levels. Here, we demonstrated a transient microscopic method to measure the heat transfer in single cells. The thermal conductivity of different regions within a single cell shows a wide heterogeneity, and heat transfer in the region near the cell membrane is more active than the central region. However, the median values of thermal conductivity between different individual cells are quite close. A cellular-level heat regulation that responds to environmental temperature is observed in warm-blooded humans and chickens rather than in cold-blooded bullfrogs. According to the temperature-dependent cell metabolism, we proposed a hypothesis for cellular control of heat dissipation, which might be the cellular-level foundation of body thermoregulation.

Radiolytic ozone yield G(O3) from 210Po alpha-particle radiation in air

Radioactive materials ionize air surrounding them and produce molecules such as ozone and nitrogen oxides. Concentrations of these species above background can serve as a marker for radioactive materials and provide a means for stand-off detection of nuclear materials. Ozone is one of the primary radiolytic products in air and has a lower background level than oxides of nitrogen, so it is a molecule of interest for this study. Actinides of interest include 239Pu and 235U, which are strong alpha emitters which have a high linear energy transfer in air. Ozone yield, saturation, and decay time are dependent on creation and destruction processes which change with charge density, ozone density, radiation dose rate, and type of radiation, motivating measurements of ozone yield and saturation level from alpha radiation with dose rates more typical of actinide sources. As a stand in for Pu and U, studies were performed on ozone yield in air from the alpha particle emitter 210Po. The sample was enclosed in a 0.96 ± 0.01 L Teflon cylinder and both air flow and build-up measurements were performed, with air flow of ~1 L/min and build up times to 3966 min corresponding with 2640 Gy. Build up measurements showed an ozone concentration increase at short times (t ≤ 10 min) with a yield of G(O3) = 7.7 ± 0.3 molecules/100 eV. Air flow measurements showed a radiation chemical yield for ozone of G(O3) = 7.6 ± 0.2 molecules/100 eV. These yields are larger than in previous, very old alpha particle studies but consistent with low rate gamma and electron beam studies. To use ozone as a secondary marker of special nuclear materials the saturation level in still air is important. The extracted ozone saturation level in the cylinder is 1.35 ppm with a half life of 74 ± 3 min.

Enhanced mass transfer in air oscillating in a channel with periodically varying radius

The effect of high frequency oscillations of air column in a channel of variable radius on vapor diffusion is experimentally studied. It is found that significant enhancement of longitudinal mass transfer takes place due to steady vortical flows excited in channel cells. In parallel with experiments in air we conducted PIV experiments with low viscous fluids in order to study the steady flow structure in the same range of dimensionless frequency as in diffusion experiments with air. It is revealed that additional mass transfer Ds associated with the steady flow is a function of steady flow dimensionless velocity V, which depends on frequency ω and pulsating Reynolds number. It is followed from PIV measurements that Ds ∼ V2 and in the studied range of oscillation frequency ω, the additional diffusion rate Ds is an order larger than the molecular diffusion D. Comparison of our experimental data with data of other authors obtained in the experiments with channels of another geometry shows that increase of variation of a channel radius results in significant enhancement of steady flow velocity and, therefore, mass transfer.

Near‐Field Communication Powered Hydrogel‐Based Smart Contact Lens

AbstractNowadays, smart contact lenses (SCLs) display interesting features for healthcare monitoring; however, their comfort and practical usability strongly depend on the outermost material in contact with the eye. In this publication, the embedding of a custom‐made and thermoformed Near‐Field Communication based circuit in a conventional soft CL is presented. The circuit is composed of gold tracks on polyimide between thermoplastic polyurethane layers (insert), while the lens is based on industry standard double‐molding process of poly(2‐hydroxyethyl methacrylate) with proven compatibility with corneal tissue. The lens shows stable geometrical parameters (bevel landing area) thus enabling a practical implementation. Finite element method models are used to optimize the thermoforming process in order to provide a stable and desired curvature of the insert before the embedding process. While the insert is designed to allow oxygen transmission at the center of the lens, a custom‐made ultra‐compact radio‐frequency antenna provides communication and wireless power transfer both in air and inside saline solutions. The successful combination of the intrinsic soft mechanical properties of the wirelessly powered electronic insert with conventional hydrogel materials and manufacturing processes delivers a practical solution for SCLs. This enables non‐invasive applications in fields such as vision correction and/or biomedical sensing.

Assessment of Air Pollution with Polychlorinated Dibenzodioxins (PCDDs) and Polychlorinated Dibenzofuranes (PCDFs) in Lithuania

Polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDD/F) are highly bioavailable in humans, either through direct inhalation or indirectly by trophic transfer from contaminated food or water. The main sources of pollution with PCDD/F include industrial and non-industrial combustion sources, like domestic contaminated wood burning, house fires, burning of leaves from trees, etc. When looking for alternative energy sources and reduced energy costs, solid waste incineration plants are intended to be built in the vicinity of urbanized areas, and thus, the need emerges for examination and prediction of to what extent the solid waste incineration plants might affect the surrounding ecosystem, air pollution, and human health. Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) (or simply PCDD/F congeners) belong to the group of semi-volatile organic compounds with environmental stability and long-range transfer in the ambient air. Dioxin isomers are highly toxic and may have carcinogenic and mutagenic effects in humans. PCDD/F is detected in air, water, sediment, plants and animals. PCDD/F is generally distributed in the particulate phase in ambient air. For solid waste incineration plant emissions, the distribution of PCDD/F particles into particles with a diameter of &lt;10 μm is more than 81% of the total particulate matter, and more than 54% of the PCDD/F is distributed into particles with a diameter of &lt;2.5 μm. The aim of this study is to investigate the sources of PCDD/F, emissions and potential hazards, i.e., a toxic equivalent in Lithuania. The measurements were performed in two largest cities of Lithuania Vilnius and Kaunas, where the level of PCDD/F discovered was from 0.015 to 0.52 pg/m3 and from 0.02 to 0.05 pg/m3, respectively. The sites for the monitoring were selected based on their proximity to the locations of the planned cogeneration power plants in these cities.

Исследование термоконцентрационной конвекции во влажном воздухе методом голографической интерферометрии

The results of a study of convection of moist air in conditions close to atmospheric are presented. Numerical estimates of dimensionless gas-dynamic parameters characteristic of the problem of convection of dry and moist air are presented and analyzed. Distinctive features of convection caused by a change in the concentration of water vapor as a result of its evaporation (condensation) are described. The effect of water vapor concentration on the convective stability of moist air is considered from the point of view of concentration convection, characterized by the concentration Rayleigh number. The technical characteristics of an experimental setup using the principle of holographic interferometry to study the thermoconcentration convection of moist air in the temperature range from 5 to 45 C are shown. The ability to distinguish convective heat and mass transfer in humid air under laboratory conditions is demonstrated.

Experimental Setup for Studying Thermosolutal Convection in Moist Air

The paper is concerned with designing an experimental scheme for studying convection of moist air under conditions closely approximating the atmospheric conditions. Detailed numerical estimates, necessary conditions and dimensionless gas-dynamic parameters characteristic of the problem of dry and moist air convection are presented and analyzed. The distinctive features of convection of dry and wet air at constant pressure caused by changes in the concentration of water vapor as a result of its evaporation (condensation) are discussed. The effect of water vapor concentration on the convective instability of moist air is analyzed in the context of solutal convection, characterized by the Rayleigh concentration number. The obtained numerical estimates are used to demonstrate the possibility of differentiating and comparing between the processes of convective heat and mass transfer in humid and dry air under laboratory conditions. In future, this will allow researchers to obtain experimental data on the influence of the water-vapor phase transition on the intensity of convective motion in moist air. The structure and detailed technical characteristics of the constructed experimental setup designed for studying convection in moist air in the temperature range from 10 to 30 C are described.

ATMOSPHERE PROTECTION FROM POLLUTION IN ACCIDENTAL SITUATIONS AT CHEMICALLY HAZARDOUS OBJECTS

Purpose. The work involves the development of numerical models to assess the effectiveness of the air curtain usage near the building in the event of chemical pollution. Methodology. To describe the process of dispersion of a chemically hazardous substance, emitted in emergency situations, the three-dimensional equation of impurity mass transfer in atmospheric air is used. To calculate the air velocity field near the building in the presence of an air curtain, a potential-flow model is used. The modelling equations take into account the velocity field of the wind flow, atmospheric diffusion, and the intensity of the emission of a chemically hazardous substance into the atmosphere. For the numerical integration of the mass transfer equations, implicit difference schemes are used. The complex of programs was created to solve the problem of calculating pollution zones near buildings in the presence of an air curtain. The application of the developed model allows you to quickly calculate this field of concentration of a chemically hazardous substance near the building in the presence of an air curtain. Findings. Numerical models for calculating the aerodynamics of the air flow and the concentration field near the building when using an air curtain were constructed. They can be used to carry out operational calculations of the size, intensity of pollution zones, which are formed in the atmosphere during the emission of chemicals at industrial sites. The developed numerical models can be implemented on computers of low and medium power, which allows it to be widely used for solving problems in developing an emergency response plan (ERP). For practical application of the developed numerical models, standard input information is required. Authors present the results of a laboratory experiment. Originality. Effective three-dimensional numerical models are proposed for estimating the level of atmospheric air pollution when emission of chemically hazardous substances into the atmosphere and using an air curtain near an industrial building. Models allow you to quickly calculate the effectiveness of the air curtain usage. Practical value. The developed numerical models allow solving applied problems arising in the development of ERP for chemically hazardous objects.