Trace Of Droplets Research Articles

Characterization of nanofluids using multifractal analysis of a liquid droplet trace

The article presents an innovative approach to the analysis of nanofluids using a nonlinear multifractal algorithm. The conducted research concerned nanofluids prepared from SiO2 nanoparticles (~ 0.01 g) suspended in 100 ml of demineralized water and in 100 ml of 99.5% isopropanol. Subsequently, the nanofluids were subjected to conventional characterization methods such as: determination of the contact angle, determination of zeta potential, pH, and particle size analysis. The obtained results show that the prepared nanofluid is stable in terms of agglomeration over time (nanofluid suspension) and properly prepared in terms of dissolving and dispersing powder particles. The authors, analyzing the results of the presented methods for characterizing nanofluids, proposed a multifractal analysis, which allows detailed local descriptions of complex scaling behaviour, using a spectrum of singularity exponents. Nonlinear analyzes show that the use of multifractal algorithm for nanofluids can improve the process of fluid quality analysis and its preparation based on the multifractal spectrum.

Monitoring COVID-19 Transmission Risks by Quantitative Real-Time PCR Tracing of Droplets in Hospital and Living Environments.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) environmental contamination occurs through droplets and biological fluids released in the surroundings from patients or asymptomatic carriers. Surfaces and objects contaminated by saliva or nose secretions represent a risk for indirect transmission of coronavirus disease 2019 (COVID-19). We assayed surfaces from hospital and living spaces to identify the presence of viral RNA and the spread of fomites in the environment. Anthropic contamination by droplets and biological fluids was monitored by detecting the microbiota signature using multiplex quantitative real-time PCR (qPCR) on selected species and massive sequencing on 16S amplicons. A total of 92 samples (flocked swabs) were collected from critical areas during the pandemic, including indoor (three hospitals and three public buildings) and outdoor surfaces exposed to anthropic contamination (handles and handrails, playgrounds). Traces of biological fluids were frequently detected in spaces open to the public and on objects that are touched with the hands (>80%). However, viral RNA was not detected in hospital wards or other indoor and outdoor surfaces either in the air system of a COVID hospital but only in the surroundings of an infected patient, in consistent association with droplet traces and fomites. Handled objects accumulated the highest level of multiple contaminations by saliva, nose secretions, and fecal traces, further supporting the priority role of handwashing in prevention. In conclusion, anthropic contamination by droplets and biological fluids is widespread in spaces open to the public and can be traced by qPCR. Monitoring fomites can support evaluation of indirect transmission risks for coronavirus or other flu-like viruses in the environment.IMPORTANCE Several studies have evaluated the presence of SARS-CoV-2 in the environment. Saliva and nasopharyngeal droplets can land on objects and surfaces, creating fomites. A suitable indicator would allow the detection of droplets or biofluids carrying the virus. Therefore, we searched for viral RNA and droplets and fomites on at risk surfaces. We monitored by qPCR or next generation sequencing (NGS) droplets through their microbiota. Although the study was performed during the pandemic, SARS-CoV-2 was not significantly found on surfaces, with the only exception of environmental areas near infectious patients. Conversely, anthropic contamination was frequent, suggesting a role for biofluids as putative markers of indirect transmission and risk assessment. Moreover, all SARS-CoV-2-contaminated surfaces showed droplets' microbiota. Fomite monitoring by qPCR may have an impact on public health strategies, supporting prevention of indirect transmission similarly to what is done for other communicable diseases (e.g., influenza and influenza-like infections).

Influence of negative ambient temperature on the morphology of blood droplet traces

The aim of this study was to identify the peculiarities of blood droplets on the street in frosty weather on the surfaces of objects with a negative temperature. The effect of negative ambient temperature (-19 °C) on the morphology of blood droplet traces was experimentally established. On cold trace surfaces, the droplet footprint was smaller, relatively flat and with wave-shaped edges; there was no splashing. Such a morphological presentation in frosty weather arises from the rapid cooling of the falling drop of blood which crystallizes in contact with the cold surface. There was no complete spreading of liquid droplets. The data obtained should be taken into account when assessing the traces of blood droplets detected at the scene of the incident on the street in winter, in order to avoid expert errors in determining their mechanism and the height of the blood source.

The water droplets dynamics and phase transformations in biofuel flue gases flow

This work presents the phase transformations and movement dynamics in a case of complex transfer processes self-interaction on sprayed water droplets in biofuel furnace flue gases flow. The droplet phase transformation cycle is defined according to a numerical iterative scheme which is created by heat flow balance condition onto the droplet surface, where combined solutions for the tasks of external heat transfer and phase change as well as internal heat transfer in a droplet, are designed. The flue gases velocity, temperature and droplet dispersity are named as defining factors of droplets trace to full evaporation in flue gases at biofuel furnace. Relevant secondary factors are recognized as sprayed water temperature, initial velocity provided for droplets, humidity of flue gases and specifics of droplets heat transfer. It is based on, that boundary conditions, which ensures the fastest and the slowest water droplets evaporation, do not define the marginal trace of droplets till evaporation. In biofuel flue gases flow at droplet phase transformation regimes cycle two, practically equivalent periods are distinguished. In the first period significant is droplet growth due to influence of condensation, warming water expansion and droplets slipping decrease in flue gases. In the second period the trace of droplets is already defined by flue gases flow velocity. The combined droplet heating process is more significant for larger droplets, while for smaller than 70 µm diameter droplets impact of thermal radiation is neglect.

Temperature and velocity fields of the gas-vapor flow near evaporating water droplets

Experimental studies of unsteady temperature and velocity fields of the gas-vapor flow in the immediate vicinity of evaporating water droplets were performed in the interests of developing high-temperature (over 300°С) gas-vapor-droplet applications. The formation time of virtually homogeneous (temperature variations of under 2–3°С) temperature fields of evaporating water droplets was established using Particle Image Velocimetry, Laser Induced Phosphorescence, Planar Laser Induced Fluorescence. We observed highly inhomogeneous and unsteady temperature and velocity fields of the gas-vapor mixture and determined the lateral and transversal dimensions of the aerodynamic and thermal traces of evaporating water droplets. The degree of impact of several parameters on the latter was evaluated: initial temperature (20–500 °C) and velocity of the incoming flow (0.5–5 m/s), as well as the initial droplet size (1–2 mm). The role of evaporation and convective heat exchange between a droplet and gases in forming of thermal and aerodynamic trace was analyzed. The heat flow density was found to vary nonlinearly with time (in the immediate vicinity of an evaporating droplet), and the impact of droplet trace temperature and velocity on the heat flow density was evaluated. Both advantages and limitations of the used techniques are established in terms of reliable plotting of unsteady temperature and velocity fields of gas-vapor mixture in the trace of evaporating water droplets, considering the heating lag of the latter.

Temperature traces of water aerosols, water-based emulsions, solutions and slurries moving in a reversed flow of high-temperature gases

Over the recent years, a number of studies have been dedicated to heat and mass transfer during the interflow of gases and aerosols. The most important task here is to control the temperature of the forming gas-vapor mixture. The temperature of the latter is difficult to maintain for a long time on a level, required for the application in thermal and flame liquid-cleaning systems, fire extinguishing, or production of power-efficient heat carriers based on flue gases, water vapor, and droplets. Temperature prediction is difficult due to nonlinear dependence of phase transformation rate, which is dominant in extensively heated gas-steam-droplet systems, versus temperature. This work provides experimental study of temperature variation range in typical sections of combustion product flow during aerosol injection. To extend the practical value of the studies for the aforementioned applications – fire extinguishing in the first place – the experiments were conducted with water aerosols as well as water-based solutions, suspensions, and slurries. Initial temperature of combustion product flow was varied in the range of 400–1000 K. Aerosol properties: droplet size 0.01–0.35 mm, droplet volume density (3.8–10.3) · 10−5 m3 of droplets/m3 of gas, initial injection velocity 1–3 m/s, concentration of additives (foam agent, slurry particles, etc.) 0.5–5%. We have established the lifetimes of the aerosol temperature trace. They may differ severalfold depending on the liquid composition used, for instance, water, solutions, slurries, and emulsions. In particular, dependences are presented showing a significant temperature variation in the trace of a droplet aerosol when a small amount (under 1%) of solid or liquid dopants is added. We have derived the approximating equations for all the dependences determined. We have also analyzed several causes of decreases in the temperature of gas-vapor mixture due to heat and mass transfer as well as the predominating phase transformations. Furthermore, we have established the effect of different commonly used additives on forming the sustained temperature trace of water aerosol flow. The experimental distributions of temperatures in the droplet trace and their recovery time serve as a basis for models of heat and mass transfer and phase transformations induced by droplet flows passing through high-temperature gases.

Temperature of gases in a trace of water droplets during their motion in a flame

The paper experimentally investigates the integral characteristics of the processes involved in the reduction of gas temperature by injecting the aerosol flow of water droplets into a counter flow of combustion products (period of steady low gas temperature Tg’ compared to the initial Tg, range of temperature decrease (ΔTg=Tg-Tg’), rate of temperature recovery, the geometric dimensions of the temperature traces and their lifetime). We use the following recording devices: fast-response thermocouples (heat inertia less than 0.1 s), a multichannel recorder, a high-speed video camera (up to 105 frames per second), as well as a cross-correlation hardware and software package (with optical methods for recording the front and trace of the aerosol). The temperature trace of an aerosol is defined as the area with the temperature Tg’ lower than the initial Tg by at least 10 K. We determine how the following group of factors affects the characteristics of temperature traces of water droplets: size (0.04-0.4 mm) and concentrations (3·10-5- 11·10-5 m3 of droplet/m3 of gas) of droplets in a pulse, the initial temperature of water (280-340 K), the duration of a pulse (1-5 s), the temperature (350- 950 K) and velocities (0.5-5 m/s) of combustion products. The temperature in a trace of water droplets during their motion in a flame can be reduced due to rapid vaporization or heat exchange between the gases and water. The conditions are identified, under which the low temperature of gases in a trace of droplet aerosol can be preserved for a long time (20–30 s). Finally, we forecast the parameters of temperature traces under the conditions of actual fires with combustion product temperatures over 1000 K.

Reducing the flue gases temperature by individual droplets, aerosol, and large water batches

This study examines the traces of water droplets moving through high-temperature combustion products (initial temperatures are 430–950K). The temperature of a gas-vapor mixture in the area of droplet traces is measured using low-inertia thermocouples (thermal lag is less than 0.1s). The paper considers aerosol flows with droplet size of 0.04–0.4mm and concentration of 3.8·10−5–10.3·10−5m3 of droplets/m3 of gas, as well as individual droplets (sized 1.5–2.5mm), and relatively large water massifs (sized 22–30mm). The typical gas temperature reduction in the trace of a moving liquid ranges from 15K to 140K. The times of keeping the low temperature of the gas-vapor mixture in the droplet trace are from 3s to 30s relative to the initial gas temperature. The study indicates how such factors as initial droplet size, velocities of the high-temperature gas flows, volume concentration of droplets, combustion products temperature and initial water temperature influence the integral characteristics of temperature traces of droplets. For the experiments with single drops, large masses and aerosol drops, the comparative analysis takes place for conditions, at which the convective heat transfer between liquid and combustion products dominates over an evaporation. The experimental data substantiate the hypothesis which suggests that the temperature traces of water droplets are kept during quite a long time even for small droplets. The experimental data are a key basis for the development of the drip systems of controlled gas temperature reduction via the intensification of phase transitions.

Presepsin for Early Infection Diagnosis during Acute Necrotizing Pancreatitis

This study examines the traces of water droplets moving through high-temperature combustion products (initial temperatures are 430–950 K). The temperature of a gas-vapor mixture in the area of droplet traces is measured using low-inertia thermocouples (thermal lag is less than 0.1 s). The paper considers aerosol flows with droplet size of 0.04–0.4 mm and concentration of 3.8·10−5–10.3·10−5 m3 of droplets/m3 of gas, as well as individual droplets (sized 1.5–2.5 mm), and relatively large water massifs (sized 22–30 mm). The typical gas temperature reduction in the trace of a moving liquid ranges from 15 K to 140 K. The times of keeping the low temperature of the gas-vapor mixture in the droplet trace are from 3 s to 30 s relative to the initial gas temperature. The study indicates how such factors as initial droplet size, velocities of the high-temperature gas flows, volume concentration of droplets, combustion products temperature and initial water temperature influence the integral characteristics of temperature traces of droplets. For the experiments with single drops, large masses and aerosol drops, the comparative analysis takes place for conditions, at which the convective heat transfer between liquid and combustion products dominates over an evaporation. The experimental data substantiate the hypothesis which suggests that the temperature traces of water droplets are kept during quite a long time even for small droplets. The experimental data are a key basis for the development of the drip systems of controlled gas temperature reduction via the intensification of phase transitions.

Fabrication of Mesoscale Channel by Scanning Micro Electrochemical Flow Cell (SMEFC)

A unique micro electrochemical machining (ECM) method based on a scanning micro electrochemical flow cell (SMEFC), in which the electrolyte is confined beneath the tool electrode instead of spreading on the workpiece surface, has been developed and its feasibility for fabricating mesoscale channels has been investigated. The effects of the surface conditions, the applied current, the feed rate, the concentration of the electrolyte and several geometrical parameters on the machining performance have been investigated through a series of experiments. The cross-sectional profile of the channels, the roughness of the channel bottom, the width and depth of the channel, the microstructures on the machined surface and the morphologies of the moving droplet have been analyzed and compared under different machining conditions. Furthermore, experiments with different overlaps of the electrolyte droplet traces have also been conducted, in which the SMEFC acts as a “milling tool”. The influences of the electrode offset distance (EOD), the current and the feed rate on the machining performance have also been examined through the comparison of the corresponding cross-sectional profiles and microstructures. The results indicate that, in addition to machining individual channels, the SMEFC system is also capable of generating shallow cavities with a suitable superimposed motion of the tool electrode.

가열된 금속표면에 놓인 증발하는 액적의 내부유동 가시화

This study aims to visualize the Marangoni flow inside a droplet placed on heated hydrophobic surface and to measure its internal velocity field. The experimental result shows that the internal velocity increases with the increase of the plate temperature. In addition, the temperature difference induces the initial flow and drives the Marangoni circulation inside the droplet as soon as the evaporation starts (i.e. the thermal Marangoni flow). The fluorescence particles in the droplet trace two large-scale counter-rotating vortex pairs yielding the downwards flow along the vertical central axis. These vortex pairs gradually become small and move towards the contact line as time goes by, and this Marangoni flow sustains only for a half of the total evaporation time.

Gas temperature in the trace of water droplets streamlined by hot air flow

In order to obtain the knowledge necessary for developing new effective fire extinguishing technologies, we determined experimentally the gas temperature in the trace of water droplets streamlined by hot air flow. It was important to establish how much the temperature in the droplet trace decreases and how fast it recovery to the initial temperature field after the droplet evaporation. The following parameters were varied: droplet size from 1.3mm to 1.7mm, velocity from 1m/s to 5m/s, initial airflow temperature from 473K to 773K, number of droplets (one or two), and the arrangement of droplets relative to the hot inflow (serial or parallel). The study proves the theoretical hypothesis about a significant influence of evaporation on the temperature in the water droplet trace. When a temperature trace of water droplets is formed, irrespective of their arrangement, the role of the evaporation process strengthens with the gas flow temperature rising. Furthermore, the study specifies typical longitudinal dimensions of the aerodynamic and temperature traces of water droplets. It has been established that when droplets are located in series and in parallel, their combined impact on the temperature and velocity of the gas flow in the medium differs rather considerably.

Use of the PLIF and LIP methods for definition of non-stationary temperature fields of water droplets

This study illustrates the results of experiments to determine the unsteady and non-uniform temperature fields of evaporating water droplets. It is shown that during the warming up of the droplet inside it an inhomogeneous temperature field is formed. In the droplet trace, formation of a region with lower (relative to the gas flow) temperatures of the vapor-gas mixture is observed. The experiments were carried out for droplets with initial radii of 1-2 mm. The speed of the air flow was 0.5-5 m/s. The temperatures of the gaseous medium varied in the range of 20-600 °C. During the research, modern panoramic methods of non-contact flow diagnostics such as “Planar Laser Induced Fluorescence” and “Laser Induced Phosphorescence” (LIP) were used.

Development of the heat and mass transfer model for the study of the temperature traces water droplets in a flame

The heat and mass transfer model is developed with using Ansys Fluent. The typical temperature of gases in the trace of water droplets is determined (initial temperature of gases 1170 К). Several types for the location of water droplets are studied: two successive water droplets; two parallel water droplets; five water droplets in checkerboard order. The hypothesis about gas temperature reduction in the trace of a moving liquid is confirmed.

Экспериментальное исследование температурных следов капель воды, водных массивов и аэрозольных потоков, движущихся через высокотемпературные продукты сгорания

The experimental investigations of temperature, varying in a trace of water droplets, water flow masses and aerosol flows, moving through high-temperature combustion products, were conducted. The temperature values of vapor-gas mixture in an area, corresponding to the trace of water droplets, moving through high-temperature combustion products (initial temperature values were 450-950 K) were measured by quick-response thermocouples (time of thermal delay was less than 1 sec). The objects of investigations were aerosol flows with droplet sizes, equal to R d » 0.04÷0.40 mm, and droplet concentration, equal to g d » 3·10 -5 ÷12·10 -5 m 3 of droplets/m 3 of gas; single droplets with R d » 1.5÷2.5 mm, and significant water flow masses with characteristic size of 22-30 mm. Application of the quick-response thermocouples allowed defining the ranges of maximal reduction of gaseous medium temperature T g in a trace of extinguishing liquid according to a group of factors, such as a method of supplying of water into the combustion zone, characteristic size of the elements of liquid flow R d , droplet concentration in a water flow g d , temperature of the combustion products T g . The variation of combustion product temperature in a trace of motion of atomized flow, droplets and liquid flow masses was determined in the analysis of temperature trends, ranged from 15 K to 140 K. The values of preservation time t of low temperature of vapor-gas mixture in a trace of droplet flow, single droplets and significant liquid flow masses were determined relative to initial gas temperature: t » 4÷28 sec. It was experimentally defined that maximum values of time t correspond to supplying the atomized water, with characteristic sizes of elements, equal to R d » 0.15÷0.30 mm, and concentration, equal to g d » 3·10 -5 ÷12·10 -5 m 3 of droplets/m 3 of gas, into the standardized fire. The conditions when the characteristics of temperature and concentration traces have significant influence on processes of evaporation and heat exchange between gases and moving liquid (with accumulation of liquid energy) were determined. The ascertained experimental data prove the earlier made theoretical hypothesis about sufficiently long periods of preservation the temperature traces of water droplets, even if they are small. The obtained experimental information become the basis for developing the method of the effective reduction of fire temperature (flame and combustion products) in the technologies of polydisperse aerosol fire extinguishing.

Experimental determination of the retention time of reduced temperature of gas–vapor mixture in trace of water droplets moving in counterflow of combustion products

We have experimentally studied temporal variation of the temperature of gas–vapor mixture in the trace of water droplets moving in the counterflow of high-temperature combustion products. The initial gas temperature was within 500–950 K. The water droplet radius in the aerosol flow varied from 40 to 400 μm. The motion of water droplets in the counterflow of combustion products in a 1-m-high hollow quartz cylinder with an internal diameter of 20 cm was visualized by optical flow imaging techniques (interferometric particle imaging, shadow photography, particle tracking velocimetry, and particle image velocimetry) with the aid of a cross-correlation complex setup. The scale of temperature decrease in the mixture of combustion products and water droplets was determined for a pulsed (within 1 s) and continuous supply of aerosol with various droplet sizes. Retention times of reduced temperature (relative to the initial level) in trace of water droplets (aerosol temperature trace) are determined. A hypothesis concerning factors responsible for the variation of temperature in the trace of droplets moving in the counterflow of combustion products is experimentally verified.

Registration of Times of Preserving the Lowered Temperatures of Combustion Products in The Trace of the Aerosol Flow

This study examines the traces of water droplets moving through high-temperature combustion products (initial temperatures are 430–950 K). The temperature of a gas-vapor mixture in the area of droplets’ traces is measured using low-inertia thermocouples (thermal lag is less than 0.1 s). The experiments revealed that the temperature in the trace of water droplets is significantly reduced (from 15 K to 140 K) even when using an aerosol flow with small droplets. The experiments showed that the times of keeping low temperatures in the trace of water droplets may reach 30 s.

Numerical Investigation of Water Droplets Shape Influence on Mathematical Modeling Results of Its Evaporation in Motion through a High-Temperature Gas

The numerical investigation of influence of a single water droplet shape on the mathematical modeling results of its evaporation in motion through high-temperature gases (combustion products of a typical condensed substance) has been executed. Values of evaporation time, motion velocity, and distance passed by various droplet shapes (cylinder, sphere, hemisphere, cone, and ellipsoid) in a high-temperature gases medium were analyzed. Conditions have been defined when a droplet surface configuration affects the integrated characteristics of its evaporation, besides temperature and combustion products concentration in a droplet trace, insignificantly. Experimental investigations for the verification of theoretical results have been carried out with using of optical diagnostic methods for two-phase gas-vapor-liquid flows.

Investigation of Regularities of Heat and Mass Transfer and Phase Transitions during Water Droplets Motion through High-Temperature Gases

The macroscopic regularities of heat and mass transfer and phase transitions during water droplets motion through high-temperature (more than 1000 K) gases have been investigated numerically and experimentally. Water droplet evaporation rates have been established. Gas and water vapors concentrations and also temperature values of gas-vapor mixture in small neighborhood and water droplet trace have been singled out. Possible mechanisms of droplet coagulation in high-temperature gas area have been determined. Experiments have been carried out with the optical methods of two-phase gas-vapor-droplet mixtures diagnostics (“Particle Image Velocimetry” and “Interferometric Particle Imaging”) usage to assess the adequateness of developed heat and mass transfer models and the results of numerical investigations. The good agreement of numerical and experimental investigation results due to integral characteristics of water droplet evaporation has been received.

EHD atomization characteristics of a point-plate system with a porous point electrode

An electrohydrodynamic (EHD) atomization from a point-to-plate system, with a wet porous point as a corona electrode, has been studied. And the atomized water droplets from the wet porous point, as well as the water droplet traces, the water droplet charge-to-mass ratios, and the water droplet number concentrations, were investigated. It was observed that the wet porous point can atomize abundant amounts of water droplet, 2.8, 2.6 and 2.2 mg/min for negative, AC and positive corona, respectively. The migrated water droplet traces were observed. The positive wet porous point atomized very fine water droplets than those obtained with the negative wet porous point. Moreover, the water droplets atomized from the AC corona showed granular-like larger traces. A weak corona discharge can atomize water droplets very effectively. On the other hand, an intensive corona discharge can eject more water droplets. As a result with the wet porous point, the maximum corona-current-based and corona-power-based water droplet atomization yield s of Y C = 3.34, 3.32 and 3.25 μg/μAs and Y P = 0.35, 0.40 and 0.27 mg/Ws have been obtained for the negative, AC and positive corona discharges.