Applied Sciences

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16 pages, 3654 KiB

Open AccessArticle

Study of Deformation and Breakup of Submillimeter Droplets’ Spray in a Supersonic Nozzle Flow

by Oleg A. Gobyzov, Mikhail N. Ryabov and Artur V. Bilsky

Appl. Sci. 2020, 10(18), 6149; https://doi.org/10.3390/app10186149 - 4 Sep 2020

Cited by 7 | Viewed by 2024

The problem of secondary atomization of droplets is crucial for many applications. In high-speed flows, fine atomization usually takes place, and the breakup of small droplets determines the final products of atomization. An experimental study of deformation and breakup of 15–60 µm size [...] Read more.

The problem of secondary atomization of droplets is crucial for many applications. In high-speed flows, fine atomization usually takes place, and the breakup of small droplets determines the final products of atomization. An experimental study of deformation and breakup of 15–60 µm size droplets in an accelerated flow inside a converging–diverging nozzle is considered in the paper. Particle image velocimetry and shadow photography were employed in the experiments. Results of gas and liquid phase flow measurements and visualization are presented and analyzed, including gas and droplets’ velocity, shape and size distributions of droplets. Weber numbers for droplets’ breakup are reported. For those small droplets at low Weber numbers, the presence of well-known droplets’ breakup morphology is confirmed, and rare “pulling” breakup mode is detected and qualitatively described. For the “pulling” breakup mode, a consideration, explaining its development in smaller droplets through shear stress effect, is provided. Full article

(This article belongs to the Special Issue Heat and Mass Transfer in Intense Liquid Evaporation)

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25 pages, 6211 KiB

Open AccessArticle

The Influence of Surfactants, Dynamic and Thermal Factors on Liquid Convection after a Droplet Fall on Another Drop

by Sergey Y. Misyura, Vladimir S. Morozov and Oleg A. Gobyzov

Appl. Sci. 2020, 10(12), 4414; https://doi.org/10.3390/app10124414 - 26 Jun 2020

Cited by 5 | Viewed by 2537

Abstract

The regularities of the processes and characteristics of convection in a sessile drop on a hot wall after the second drop fall are investigated experimentally. The movement of a particle on a drop surface under the action of capillary force and liquid convection [...] Read more.

The regularities of the processes and characteristics of convection in a sessile drop on a hot wall after the second drop fall are investigated experimentally. The movement of a particle on a drop surface under the action of capillary force and liquid convection is considered. The particle motion is realized by a complex curvilinear trajectory. The fall of droplet with and without surfactant additives is considered. Estimates of the influence of the thermal factor (thermocapillary forces) and the dynamic factor (inertia forces) on convection are given. The scientific novelty of the work is the investigation of the simultaneous influence of several factors that is carried out for the first time. It is shown that in the presence of a temperature jump for the time of about 0.01–0.1 s thermocapillary convection leads to a 7–8 times increase in the mass transfer rate in drop. The relative influence of inertial forces is found to be no more than 5%. The fall of drops with surfactant additives (water + surfactant) reduces the velocity jump inside the sessile drop 2–4 times, compared with the water drop without surfactant. Thermocapillary convection leads to the formation of a stable vortex in the drop. The dynamic factor and surfactant additive lead to the vortex breakdown into many small vortices, which results in the suppression of convection. The obtained results are of great scientific and practical importance for heat transfer enhancement and for the control of heating and evaporation rates. Full article

(This article belongs to the Special Issue Heat and Mass Transfer in Intense Liquid Evaporation)

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14 pages, 4675 KiB

Open AccessFeature PaperArticle

Effect of Liquid Viscosity and Flow Orientation on Initial Waves in Annular Gas–Liquid Flow

by Sergey V. Isaenkov, Ivan S. Vozhakov, Mikhail V. Cherdantsev, Dmitry G. Arkhipov and Andrey V. Cherdantsev

Appl. Sci. 2020, 10(12), 4366; https://doi.org/10.3390/app10124366 - 25 Jun 2020

Cited by 6 | Viewed by 2292

Abstract

The complex wave structure of annular gas–liquid flow with disturbance waves and liquid entrainment is a result of the evolution of high-frequency initial waves, appearing at the very inlet of the flow, prior to the hydrodynamic stabilization of liquid film. This stage of [...] Read more.

The complex wave structure of annular gas–liquid flow with disturbance waves and liquid entrainment is a result of the evolution of high-frequency initial waves, appearing at the very inlet of the flow, prior to the hydrodynamic stabilization of liquid film. This stage of flow evolution is studied experimentally, using a shadow technique, and theoretically, using a linear stability analysis of the Orr–Sommerfeld equation in both phases. The present work is focused on the comparison of earlier results obtained in air–water downward flow with the new results obtained in upward flow and with more viscous liquids. The flow orientation affects the shape of the liquid film prior to stabilization; the initial film area is thicker but shorter in upward flow. Upward flow orientation also leads to a lower frequency and the increment of growth of initial waves. The viscosity effect is found to be weak if flow rates of both phases are the same. The model is mostly able to reproduce the qualitative trends, but the quantitative agreement is not reached. Experimental observations indicate that the liquid flow within the initial area is significantly different from the stabilized flow of gas-sheared liquid film, which is used in the model. This difference could explain the discrepancy; further development of the model should be aimed at taking into account the evolution of the velocity profile inside the liquid film during the stage of hydrodynamic stabilization. Full article

(This article belongs to the Special Issue Heat and Mass Transfer in Intense Liquid Evaporation)

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14 pages, 1863 KiB

Open AccessArticle

Boiling Flow Pattern Identification Using a Self-Organizing Map

by Iwona Zaborowska, Hubert Grzybowski and Romuald Mosdorf

Appl. Sci. 2020, 10(8), 2792; https://doi.org/10.3390/app10082792 - 17 Apr 2020

Cited by 2 | Viewed by 2086

Abstract

In the paper, a self-organizing map combined with the recurrence quantification analysis was used to identify flow boiling patterns in a circular horizontal minichannel with an inner diameter of 1 mm. The dynamics of the pressure drop during density-wave oscillations in a single [...] Read more.

In the paper, a self-organizing map combined with the recurrence quantification analysis was used to identify flow boiling patterns in a circular horizontal minichannel with an inner diameter of 1 mm. The dynamics of the pressure drop during density-wave oscillations in a single pressure drop oscillations cycle were considered. It has been shown that the proposed algorithm allows us to distinguish five types of non-stationary two-phase flow patterns, such as bubble flow, confined bubble flow, wavy annular flow, liquid flow, and slug flow. The flow pattern identification was confirmed by images obtained using a high-speed camera. Taking into consideration the oscillations between identified two-phase flow patterns, the four boiling regimes during a single cycle of the long-period pressure drop oscillations are classified. The obtained results show that the proposed combination of recurrence quantification analysis (RQA) and a self-organizing map (SOM) in the paper can be used to analyze changes in flow patterns in non-stationary boiling. It seems that the use of more complex algorithms of neural networks and their learning process can lead to the automation of the process of identifying boiling regimes in minichannel heat exchangers. Full article

(This article belongs to the Special Issue Heat and Mass Transfer in Intense Liquid Evaporation)

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22 pages, 6978 KiB

Open AccessFeature PaperArticle

Temperature Fields of the Droplets and Gases Mixture

by Roman S. Volkov, Ivan S. Voytkov and Pavel A. Strizhak

Appl. Sci. 2020, 10(7), 2212; https://doi.org/10.3390/app10072212 - 25 Mar 2020

Cited by 3 | Viewed by 2088

Abstract

In this research, we obtain gas–vapor mixture temperature fields generated by blending droplets and high-temperature combustion products. Similar experiments are conducted for droplet injection into heated air flow. This kind of measurement is essential for high-temperature and high-speed processes in contact heat exchangers [...] Read more.

In this research, we obtain gas–vapor mixture temperature fields generated by blending droplets and high-temperature combustion products. Similar experiments are conducted for droplet injection into heated air flow. This kind of measurement is essential for high-temperature and high-speed processes in contact heat exchangers or in liquid treatment chambers, as well as in firefighting systems. Experiments are conducted using an optical system based on Laser-Induced Phosphorescence as well as two types of thermocouples with a similar measurement range but different response times (0.1–3 s) and accuracy (1–5 °C). In our experiments, we inject droplets into the heated air flow (first scheme) and into the flow of high-temperature combustion products (second scheme). We concentrate on the unsteady inhomogeneous temperature fields of the gas–vapor mixture produced by blending the above-mentioned flows and monitoring the lifetime of the relatively low gas temperature after droplets passes through the observation area. The scientific novelty of this research comes from the first ever comparison of the temperature measurements of a gas–vapor–droplet mixture obtained by contact and non-contact systems. The advantages and limitations of the contact and non-contact techniques are defined for the measurement of gas–vapor mixture temperature. Full article

(This article belongs to the Special Issue Heat and Mass Transfer in Intense Liquid Evaporation)

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19 pages, 6353 KiB

Open AccessFeature PaperArticle

The Impact of Single- and Multicomponent Liquid Drops on a Heated Wall: Child Droplets

by Anastasia V. Demidovich, Svetlana S. Kropotova, Maxim V. Piskunov, Nikita E. Shlegel and Olga V. Vysokomornaya

Appl. Sci. 2020, 10(3), 942; https://doi.org/10.3390/app10030942 - 1 Feb 2020

Cited by 10 | Viewed by 2906

Abstract

This paper presents the experimental research into the impingement of single- and multicomponent liquid drops on a solid wall. We focus on studying the conditions and characteristics of two impact scenarios: rebound and breakup. We performed a comprehensive analysis of the effect of [...] Read more.

This paper presents the experimental research into the impingement of single- and multicomponent liquid drops on a solid wall. We focus on studying the conditions and characteristics of two impact scenarios: rebound and breakup. We performed a comprehensive analysis of the effect of a group of factors on the drop transformation and fragmentation characteristics. These factors include the drop velocity and size, Weber number, impinging angle, wall temperature, thermophysical properties of the wall material, surface roughness, hydrophilic and hydrophobic behavior of the surface, homogeneity and inhomogeneity of the drop composition, as well as viscosity and surface tension of the liquid. We compared the outcomes of one, two, and three drops with the same total volume on a wall. Histograms were plotted of the number and size distribution of the emerging secondary droplets. The results include the critical conditions for the intense breakup of drops. Such factors as wall heating, its roughness, impinging angle, drop size and velocity affected the breakup conditions most notably. The variation of a group of these factors could provide a 2–25-fold increase in the liquid surface area as a result of the impact. Full article

(This article belongs to the Special Issue Heat and Mass Transfer in Intense Liquid Evaporation)

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21 pages, 4767 KiB

Open AccessFeature PaperArticle

Secondary Atomization of a Biodiesel Micro-Emulsion Fuel Droplet Colliding with a Heated Wall

by Alexander E. Ashikhmin, Nikita A. Khomutov, Maxim V. Piskunov and Vyacheslav A. Yanovsky

Appl. Sci. 2020, 10(2), 685; https://doi.org/10.3390/app10020685 - 18 Jan 2020

Cited by 20 | Viewed by 3756

Abstract

Using high-speed video recording, we establish the following regimes of hydrodynamic interaction of a biodiesel micro-emulsion fuel droplet with a heated wall: deposition (including drop spreading and receding), drop hydrodynamic breakup, and rebound. Collision regime maps are plotted using a set of dimensionless [...] Read more.

Using high-speed video recording, we establish the following regimes of hydrodynamic interaction of a biodiesel micro-emulsion fuel droplet with a heated wall: deposition (including drop spreading and receding), drop hydrodynamic breakup, and rebound. Collision regime maps are plotted using a set of dimensionless criteria: Weber number We = 470–1260, Ohnesorge number Oh = 0.146–0.192, and Reynolds number Re = 25–198. The scenarios of droplet hydrodynamic disintegration are studied for transient and film boiling. We also estimate the disintegration characteristics of a biodiesel micro-emulsion droplet (mean diameter of child droplets, their number, and evaporation surface area increase due to breakup). The study establishes the effect of water proportion on the micro-emulsion composition (8–16 vol.%), heating temperature (300–500 °C), droplet size (1.8–2.8 mm), droplet velocity (3–4 m/s), rheological properties of the examined compositions, and emulsifier concentration (10.45 vol.% and 20 vol.%) on the recorded characteristics. The results show that the initial liquid surface area can be increased 2–19 times. The paper analyzes ways to control the process. The hydrodynamic disintegration characteristics of a biodiesel micro-emulsion fuel droplet are compared using 2D and 3D recording. Full article

(This article belongs to the Special Issue Heat and Mass Transfer in Intense Liquid Evaporation)

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21 pages, 4902 KiB

Open AccessFeature PaperArticle

Rates of High-Temperature Evaporation of Promising Fire-Extinguishing Liquid Droplets

by Geniy V. Kuznetsov, Svetlana S. Kralinova, Ivan S. Voytkov and Anastasia G. Islamova

Appl. Sci. 2019, 9(23), 5190; https://doi.org/10.3390/app9235190 - 29 Nov 2019

Cited by 7 | Viewed by 4449

Abstract

Differences in the rates of heating and evaporation of droplets with the component composition are important parameters of heat transfer processes and phase transformations. This paper presents the values of high-temperature (up to 600 °C) evaporation rates of droplets of promising fire-extinguishing compositions [...] Read more.

Differences in the rates of heating and evaporation of droplets with the component composition are important parameters of heat transfer processes and phase transformations. This paper presents the values of high-temperature (up to 600 °C) evaporation rates of droplets of promising fire-extinguishing compositions (water, bentonite suspension, bischofite solution, EA-5 solution, and foaming agent emulsion) at convective (in the air stream), conductive (on a heated surface), and radiation (in a muffle furnace) heating. A high-speed video recording system and tracking software algorithms are used. At identical initial sizes of droplets of fire-extinguishing suspensions, known as emulsions and solutions, the times of their complete evaporation are shown to differ 3.7 times when heating on the substrate, 1.25 times in the air flow, and 1.9 times in the muffle furnace. A general approximation expression is formulated, and the empirical constants are calculated to predict the evaporation rate of the droplets of extinguishing agents in a wide range of temperatures (up to 600 °C) and heat fluxes (up to 100 kW/m²), which are characteristic of forest fires. With the use of the experimental data obtained, it is possible to predict the completeness of evaporation of promising extinguishing liquids at different schemes of heat supply. Full article

(This article belongs to the Special Issue Heat and Mass Transfer in Intense Liquid Evaporation)

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