Editorial

3 pages, 164 KiB

Open AccessEditorial

Gas-Liquid Two-Phase Flow in a Pipe or Channel

by Maksim A. Pakhomov and Pavel D. Lobanov

Water 2021, 13(23), 3382; https://doi.org/10.3390/w13233382 - 01 Dec 2021

Cited by 1 | Viewed by 2265

This Special Issue contributes to highlight and discusses topics related to various aspects of the two-phase gas-liquid flows [...] Full article

(This article belongs to the Special Issue Gas-Liquid Two-Phase Flow in the Pipe or Channel)

Research

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16 pages, 5699 KiB

Open AccessFeature PaperArticle

The Simultaneous Analysis of Droplets’ Impacts and Heat Transfer during Water Spray Cooling Using a Transparent Heater

by Vladimir Serdyukov, Nikolay Miskiv and Anton Surtaev

Water 2021, 13(19), 2730; https://doi.org/10.3390/w13192730 - 02 Oct 2021

Cited by 8 | Viewed by 2569

Abstract

This paper demonstrates the advantages and prospects of transparent design of the heating surface for the simultaneous study of the hydrodynamic and thermal characteristics of spray cooling. It was shown that the high-speed recording from the reverse side of such heater allows to [...] Read more.

This paper demonstrates the advantages and prospects of transparent design of the heating surface for the simultaneous study of the hydrodynamic and thermal characteristics of spray cooling. It was shown that the high-speed recording from the reverse side of such heater allows to identify individual droplets before their impact on the forming liquid film, which makes it possible to measure their sizes with high spatial resolution. In addition, such format enables one to estimate the number of droplets falling onto the impact surface and to study the features of the interface evolution during the droplets’ impacts. In particular, the experiments showed various possible scenarios for this interaction, such as the formation of small-scale capillary waves during impacts of small droplets, as well as the appearance of “craters” and splashing crowns in the case of large ones. Moreover, the unsteady temperature field during spray cooling in regimes without boiling was investigated using high-speed infrared thermography. Based on the obtained data, the intensity of heat transfer during spray cooling for various liquid flow rates and heat fluxes was analyzed. It was shown that, for the studied regimes, the heat transfer coefficient weakly depends on the heat flux density and is primarily determined by the flow rate. In addition, the comparison of the processes of spray cooling and nucleate boiling was made, and an analogy was shown in the mechanisms that determine their intensity of heat transfer. Full article

(This article belongs to the Special Issue Gas-Liquid Two-Phase Flow in the Pipe or Channel)

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16 pages, 3721 KiB

Open AccessArticle

Droplet Evaporation in a Gas-Droplet Mist Dilute Turbulent Flow behind a Backward-Facing Step

by Maksim A. Pakhomov and Viktor I. Terekhov

Water 2021, 13(17), 2333; https://doi.org/10.3390/w13172333 - 26 Aug 2021

Cited by 4 | Viewed by 2024

Abstract

The mean and fluctuation flow patterns and heat transfer in a turbulent droplet-laden dilute flow behind a two-dimensional single-side backward-facing step are numerically studied. Numerical simulations are performed for water droplets, with the inlet droplet diameters d₁ = 1–100 μm; they have [...] Read more.

The mean and fluctuation flow patterns and heat transfer in a turbulent droplet-laden dilute flow behind a two-dimensional single-side backward-facing step are numerically studied. Numerical simulations are performed for water droplets, with the inlet droplet diameters d₁ = 1–100 μm; they have a mass fraction of M_L₁ = 0–0.1. There is almost no influence of a small number of droplets on the mean gas flow and coefficient of wall friction. A substantial heat transfer augmentation in a droplet-laden mist-separated flow is shown. Heat transfer increases both in the recirculating flow and flow relaxation zones for fine, dispersed droplets, and the largest droplets augment heat transfer after the reattachment point. The largest heat transfer enhancement in a droplet-laden flow is obtained for small particles. Full article

(This article belongs to the Special Issue Gas-Liquid Two-Phase Flow in the Pipe or Channel)

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21 pages, 4470 KiB

Open AccessArticle

The Effect of a Backward-Facing Step on Flow and Heat Transfer in a Polydispersed Upward Bubbly Duct Flow

by Tatiana V. Bogatko, Aleksandr V. Chinak, Ilia A. Evdokimenko, Dmitriy V. Kulikov, Pavel D. Lobanov and Maksim A. Pakhomov

Water 2021, 13(17), 2318; https://doi.org/10.3390/w13172318 - 24 Aug 2021

Cited by 4 | Viewed by 2150

Abstract

The experimental and numerical results on the flow structure and heat transfer in a bubbly polydispersed upward duct flow in a backward-facing step are presented. Measurements of the carrier fluid phase velocity and gas bubbles motion are carried out using the PIV/PLIF system. [...] Read more.

The experimental and numerical results on the flow structure and heat transfer in a bubbly polydispersed upward duct flow in a backward-facing step are presented. Measurements of the carrier fluid phase velocity and gas bubbles motion are carried out using the PIV/PLIF system. The set of RANS equations is used for modeling the two-phase bubbly flow. Turbulence of the carrier fluid phase is predicted using the Reynolds stress model. The effect of bubble addition on the mean and turbulent flow structure is taken into account. The motion and heat transfer in a dispersed phase is modeled using the Eulerian approach taking into account bubble break-up and coalescence. The method of delta-functions is employed for simulation of distributions of polydispersed gas bubbles. Small bubbles are presented over the entire duct cross-section and the larger bubbles mainly observed in the shear mixing layer and flow core. The recirculation length in the two-phase bubbly flow is up to two times shorter than in the single-phase flow. The position of the heat transfer maximum is located after the reattachment point. The effect of the gas volumetric flow rate ratios on the flow patterns and maximal value of heat transfer in the two-phase flow is studied numerically. The addition of air bubbles results in a significant increase in heat transfer (up to 75%). Full article

(This article belongs to the Special Issue Gas-Liquid Two-Phase Flow in the Pipe or Channel)

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13 pages, 3442 KiB

Open AccessArticle

Study of Pressure Drops and Heat Transfer of Nonequilibrial Two-Phase Flows

by Aleksandr V. Belyaev, Alexey V. Dedov, Ilya I. Krapivin, Aleksander N. Varava, Peixue Jiang and Ruina Xu

Water 2021, 13(16), 2275; https://doi.org/10.3390/w13162275 - 20 Aug 2021

Cited by 6 | Viewed by 2443

Abstract

Currently, there are no universal methods for calculating the heat transfer and pressure drop for a wide range of two-phase flow parameters in mini-channels due to changes in the void fraction and flow regime. Many experimental studies have been carried out, and narrow-range [...] Read more.

Currently, there are no universal methods for calculating the heat transfer and pressure drop for a wide range of two-phase flow parameters in mini-channels due to changes in the void fraction and flow regime. Many experimental studies have been carried out, and narrow-range calculation methods have been developed. With increasing pressure, it becomes possible to expand the range of parameters for applying reliable calculation methods as a result of changes in the flow regime. This paper provides an overview of methods for calculating the pressure drops and heat transfer of two-phase flows in small-diameter channels and presents a comparison of calculation methods. For conditions of high reduced pressures p_r = p/p_cr ≈ 0.4 ÷ 0.6, the results of own experimental studies of pressure drops and flow boiling heat transfer of freons in the region of low and high mass flow rates (G = 200–2000 kg/m² s) are presented. A description of the experimental stand is given, and a comparison of own experimental data with those obtained using the most reliable calculated relations is carried out. Full article

(This article belongs to the Special Issue Gas-Liquid Two-Phase Flow in the Pipe or Channel)

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20 pages, 6445 KiB

Open AccessArticle

The Flow Pattern Transition and Water Holdup of Gas–Liquid Flow in the Horizontal and Vertical Sections of a Continuous Transportation Pipe

by Guishan Ren, Dangke Ge, Peng Li, Xuemei Chen, Xuhui Zhang, Xiaobing Lu, Kai Sun, Rui Fang, Lifei Mi and Feng Su

Water 2021, 13(15), 2077; https://doi.org/10.3390/w13152077 - 30 Jul 2021

Cited by 4 | Viewed by 2749

Abstract

A series of experiments were conducted to investigate the flow pattern transitions and water holdup during oil–water–gas three-phase flow considering both a horizontal section and a vertical section of a transportation pipe simultaneously. The flowing media were white mineral oil, distilled water, and [...] Read more.

A series of experiments were conducted to investigate the flow pattern transitions and water holdup during oil–water–gas three-phase flow considering both a horizontal section and a vertical section of a transportation pipe simultaneously. The flowing media were white mineral oil, distilled water, and air. Dimensionless numbers controlling the multiphase flow were deduced to understand the scaling law of the flow process. The oil–water–gas three-phase flow was simplified as the two-phase flow of a gas and liquid mixture. Based on the experimental data, flow pattern maps were constructed in terms of the Reynolds number and the ratio of the superficial velocity of the gas to that of the liquid mixture for different Froude numbers. The original contributions of this work are that the relationship between the transient water holdup and the changes of the flow patterns in a transportation pipe with horizontal and vertical sections is established, providing a basis for judging the flow patterns in pipes in engineering practice. A dimensionless power-law correlation for the water holdup in the vertical section is presented based on the experimental data. The correlation can provide theoretical support for the design of oil and gas transport pipelines in industrial applications. Full article

(This article belongs to the Special Issue Gas-Liquid Two-Phase Flow in the Pipe or Channel)

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12 pages, 4589 KiB

Open AccessArticle

Numerical Analysis of Ultrasonic Nebulizer for Onset Amplitude of Vibration with Atomization Experimental Results

by Yu-Lin Song, Chih-Hsiao Cheng and Manoj Kumar Reddy

Water 2021, 13(14), 1972; https://doi.org/10.3390/w13141972 - 19 Jul 2021

Cited by 6 | Viewed by 2559

Abstract

In this study, the onset amplitude of the initial capillary surface wave for ultrasonic atomization of fluids has been implemented. The design and characterization of 485 kHz microfabricated silicon-based ultrasonic nozzles are presented for the concept of economic energy development. Each nozzle is [...] Read more.

In this study, the onset amplitude of the initial capillary surface wave for ultrasonic atomization of fluids has been implemented. The design and characterization of 485 kHz microfabricated silicon-based ultrasonic nozzles are presented for the concept of economic energy development. Each nozzle is composed of a silicon resonator and a piezoelectric drive section consisting of three Fourier horns. The required minimum energy to atomize liquid droplets is verified by COMSOL Multiphysics simulation software to clarify experimental data. The simulation study reports a minimum vibrational amplitude (onset) of 0.365 μm at the device bottom under the designated frequency of 485 kHz. The experimental study agrees well with the suggested frequency and the amplitude concerning the corresponding surface vibrational velocity in simulation. While operating, the deionized water was initially atomized into microdroplets at the given electrode voltage of 5.96 V. Microdroplets are steadily and continuously formed after the liquid feeding rate is optimized. This newly designed ultrasonic atomizer facilitates the development of capillary surface wave resonance at a designated frequency. A required vibrational amplitude and finite electric driving voltage promote not only the modern development in the green energy industry, but also the exploration of noninvasive, microencapsulated drug delivery and local spray needs. Full article

(This article belongs to the Special Issue Gas-Liquid Two-Phase Flow in the Pipe or Channel)

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14 pages, 4814 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Wall Shear Stress on Two Phase Fluctuating Flow of Dusty Fluids by Using Light Hill Technique

by Dolat Khan, Ata ur Rahman, Gohar Ali, Poom Kumam, Attapol Kaewkhao and Ilyas Khan

Water 2021, 13(11), 1587; https://doi.org/10.3390/w13111587 - 04 Jun 2021

Cited by 12 | Viewed by 3323

Abstract

Due to the importance of wall shear stress effect and dust fluid in daily life fluid problems. This paper aims to discover the influence of wall shear stress on dust fluids of fluctuating flow. The flow is considered between two parallel plates that [...] Read more.

Due to the importance of wall shear stress effect and dust fluid in daily life fluid problems. This paper aims to discover the influence of wall shear stress on dust fluids of fluctuating flow. The flow is considered between two parallel plates that are non-conducting. Due to the transformation of heat, the fluid flow is generated. We consider every dust particle having spherical uniformly disperse in the base fluid. The perturb solution is obtained by applying the Poincare-Lighthill perturbation technique (PLPT). The fluid velocity and shear stress are discussed for the different parameters like Grashof number, magnetic parameter, radiation parameter, and dusty fluid parameter. Graphical results for fluid and dust particles are plotted through Mathcad-15. The behavior of base fluid and dusty fluid is matching for different embedded parameters. Full article

(This article belongs to the Special Issue Gas-Liquid Two-Phase Flow in the Pipe or Channel)

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15 pages, 2069 KiB

Open AccessArticle

Physicochemical Effects of Humid Air Treated with Infrared Radiation on Aqueous Solutions

by Olga Yablonskaya, Vladimir Voeikov, Ekaterina Buravleva, Aleksei Trofimov and Kirill Novikov

Water 2021, 13(10), 1370; https://doi.org/10.3390/w13101370 - 14 May 2021

Cited by 4 | Viewed by 3550

Abstract

Water vapor absorbs well in the infrared (IR) region of the spectra. On the other hand, it was recently demonstrated that IR radiation promotes formation of the so-called exclusion zones (EZ) at the interfaces between hydrophilic surfaces and water. EZ-water properties differ significantly [...] Read more.

Water vapor absorbs well in the infrared (IR) region of the spectra. On the other hand, it was recently demonstrated that IR radiation promotes formation of the so-called exclusion zones (EZ) at the interfaces between hydrophilic surfaces and water. EZ-water properties differ significantly from that of bulk water. It was studied for the first time whether treatment of water with humid air irradiated with IR-C band could change its physical-chemical properties, making it EZ-water-like. Humid air irradiated with IR was called coherent humidity (CoHu). Redox potential and surface tension decreased in deionized water and mineral water samples that were treated with CoHu, while dielectric constant increased in such water samples. After such treatment of carbonate or phosphate buffers, their buffer capacity against acidification and leaching significantly increased. No such changes were observed in water samples treated with non-irradiated humid air. Thus, after treatment of tested aqueous systems with humid air exposed to IR radiation, their properties change, making them more like EZ-water. The results suggest that IR irradiation of humid air converts it into a carrier of a certain physical signal that affects water properties. Full article

(This article belongs to the Special Issue Gas-Liquid Two-Phase Flow in the Pipe or Channel)

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10 pages, 2873 KiB

Open AccessArticle

Air Diffusion and Velocity Characteristics of Self-Aerated Developing Region in Flat Chute Flows

by Liaochao Song, Jun Deng and Wangru Wei

Water 2021, 13(6), 840; https://doi.org/10.3390/w13060840 - 19 Mar 2021

Cited by 1 | Viewed by 1936

Abstract

Self-aerated flows in flat chutes are encountered downstream of the bottom outlet, in spillways with a small slope and in storm waterways. In the present study, the development of self-aeration in flat chute flow is described and new experiments are performed in a [...] Read more.

Self-aerated flows in flat chutes are encountered downstream of the bottom outlet, in spillways with a small slope and in storm waterways. In the present study, the development of self-aeration in flat chute flow is described and new experiments are performed in a long flat chute with a pressure outlet for different flow discharge rates. The distribution of air concentration, time mean velocity and velocity fluctuation in flow direction in the self-aerated developing region—where air bubbles do not diffuse next to the channel bottom—were measured and analyzed. The region of self-aeration from free surface was about 27.16% to 51.85% of the water depth in the present study. The analysis results revealed that the maximum distance of air bubble diffusion to the channel bottom increased with the development of self-aeration along the flow direction. This indicates that for flat chute flow, the process of air bubble diffusion from free surface to channel bottom was relatively long. Cross-section velocities increased along the flow direction in the self-aerated developing region, and this trend was much more remarkable in the area near water free surface. The velocity fluctuations in flow direction in cross-sections flattened and increased with the development of self-aerated flow. Higher velocity fluctuations in flow direction corresponded to the presence of much stronger turbulence, which enhanced air bubble diffusion from the water free surface to channel bottom along the flow direction. Full article

(This article belongs to the Special Issue Gas-Liquid Two-Phase Flow in the Pipe or Channel)

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