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13 pages, 1650 KiB

Open AccessArticle

Study on Artificial Neural Network for Predicting Gas-Liquid Two-Phase Pressure Drop in Pipeline-Riser System

by Xinping Li, Nailiang Li, Xiang Lei, Ruotong Liu, Qiwei Fang and Bin Chen

Energies 2023, 16(4), 1686; https://doi.org/10.3390/en16041686 - 8 Feb 2023

Cited by 1 | Viewed by 1987

Abstract

The pressure drop for air-water two-phase flow in pipeline systems with S-shaped and vertical risers at various inclinations (−1°, −2°, −4°, −5° and −7° from horizontal) was predicted using an artificial neural network (ANN). In the designing of the ANN model, the superficial [...] Read more.

The pressure drop for air-water two-phase flow in pipeline systems with S-shaped and vertical risers at various inclinations (−1°, −2°, −4°, −5° and −7° from horizontal) was predicted using an artificial neural network (ANN). In the designing of the ANN model, the superficial velocity of gas and liquid as well as the inclination of the downcomer were used as input variables, while pressure drop values of two-phase flows were determined as the output. An ANN network with a hidden layer containing 14 neurons was developed based on a trial-and-error method. A sigmoid function was chosen as the transfer function for the hidden layer, while a linear function was used in the output layer. The Levenberg-Marquardt algorithm was used for the training of the model. A total of 415 experimental data points reported in the literature were collected and used for the creation of the networks. The statistical results showed that the proposed network is capable of calculating the experimental pressure drop dataset with low average absolute percent error (AAPE) of 3.35% and high determination coefficient (R²) of 0.995. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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23 pages, 5288 KiB

Open AccessArticle

Research on the Mixing Mechanism and Parameter Optimization of Liquid Nitrogen Foam Generator

by Yulin Liu, Dongming Wang, Min Xie, Huanhuan Xu and Xiaohan Ren

Energies 2022, 15(22), 8714; https://doi.org/10.3390/en15228714 - 20 Nov 2022

Viewed by 1595

Abstract

Nitrogen foam is expected to be an effective method to extinguish large-scale fires and suppress explosions. The key to its foaming process is that gas nitrogen (N₂) and a foam solution are mixed uniformly in a foam generator. Moreover, liquid nitrogen [...] Read more.

Nitrogen foam is expected to be an effective method to extinguish large-scale fires and suppress explosions. The key to its foaming process is that gas nitrogen (N₂) and a foam solution are mixed uniformly in a foam generator. Moreover, liquid nitrogen (LN₂) has been proposed as a source of gas nitrogen to generate nitrogen foam in previous experimental works. In this paper, the flow and heat transfer characteristics between liquid nitrogen and the foam solution are explored by numerical methods, which are then utilized to optimize the parameters of the foam generator. It is found that the flow pattern of the foam generator with a cone spoiler is a stratified flow by establishing the mixture and Lee’s evaporation-condensation model in ANSYS Fluent. Moreover, the spoiler in the foam generator plays a crucial role in breaking LN₂ into droplets and increasing the contact area between phases, and a distance of 10 mm from the inlets to the spoiler is recommended. From previous results, an unreasonable flow rate ratio of LN₂ to a foam solution may lead to icing or a low volume fraction of nitrogen, thus a flow rate ratio of 1:50 is determined in the foam generator. As for the shape of the spoiler, the spiral spoiler shows the best foaming performance compared to cone and semisphere spoilers, due to its fluid rotation instead of translation, which effectively increases the N₂ volume fraction of foam from 0.616 to 0.717. Therefore, the mixing characteristics of the foam generator in this work lays a foundation for devising a practical nitrogen foam generator. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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17 pages, 6037 KiB

Open AccessArticle

Experimental and Numerical Study on the Elimination of Severe Slugging by Riser Outlet Choking

by Nailiang Li, Bin Chen, Xueping Du and Dongtai Han

Energies 2022, 15(19), 7284; https://doi.org/10.3390/en15197284 - 4 Oct 2022

Cited by 1 | Viewed by 1765

Abstract

Severe slugging is an unstable multiphase flow pattern occurs in a pipeline riser with low gas and liquid flowrates. It is highly undesired in practical operation because of the pressure and mass flow oscillations induced. Riser outlet choking has shown effectiveness in eliminating [...] Read more.

Severe slugging is an unstable multiphase flow pattern occurs in a pipeline riser with low gas and liquid flowrates. It is highly undesired in practical operation because of the pressure and mass flow oscillations induced. Riser outlet choking has shown effectiveness in eliminating or reducing the severity of the slugging. This work presents an experimental and numerical study on the elimination of severe riser-induced slug by means of riser outlet choking. The test loop consists of a horizontal pipeline with 50 mm i.d. and 15 m in length, followed by a downward inclined section and a vertical riser of 2 m. It was found that by choking the flow at riser outlet, flow pattern in the riser changes from severe slugging first into slug flow and then into bubbly flow. The recognition of the flow regimes was basically according to the trends of the riser base pressure. The flow patterns were characterized in terms of pressure at riser base, as well as liquid holdup at riser top. A numerical model was developed accordingly using OLGA to investigate the dynamic behavior in the process of riser outlet choking. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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22 pages, 5613 KiB

Open AccessArticle

CFD-DEM Simulation of Particle Fluidization Behavior and Glycerol Gasification in a Supercritical Water Fluidized Bed

by Jia Luo, Jingwei Chen and Lei Yi

Energies 2022, 15(19), 7128; https://doi.org/10.3390/en15197128 - 28 Sep 2022

Cited by 3 | Viewed by 1827

Abstract

In this study, a mathematical model of hydrogen production from glycerol gasification in supercritical water was established based on the CFD-DEM method. The fluidization process of a supercritical water fluidized bed and the effects of bed height and feed structure on particle distribution [...] Read more.

In this study, a mathematical model of hydrogen production from glycerol gasification in supercritical water was established based on the CFD-DEM method. The fluidization process of a supercritical water fluidized bed and the effects of bed height and feed structure on particle distribution and residence time of feedstock were analyzed. Additionally, the temperature field in the fluidized bed, the reaction rate distribution of each reaction and the influence of wall temperature on gas yields were also studied. The simulation results show that the bubble channel is easy to form along the wall at one side of the feed inlet. When the initial bed height is high, and the double symmetric feed inlet structure is used, the residence time of the feedstock is prolonged. The pyrolysis of glycerol mainly occurs in the middle and lower part of the fluidized bed reactor, and the reaction rate of the water gas shift reaction and methanation reaction are highest near the outlet, and a high wall temperature is conducive to the glycerol gasification. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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11 pages, 1997 KiB

Open AccessArticle

Study on Hydrogen Production by Supercritical Water Gasification of Unsymmetrical Dimethylhydrazine under Multi-Parameters

by Lei Yi, Jingwei Chen, Zhigang Liu, Huiming Chen, Daoxiu Liu, Zheng Liu and Bin Chen

Energies 2022, 15(19), 7081; https://doi.org/10.3390/en15197081 - 27 Sep 2022

Cited by 1 | Viewed by 1630

Abstract

Unsymmetrical dimethylhydrazine (UDMH) is very toxic and hard to decompose in traditional ways. In this paper, the gasification of unsymmetrical dimethylhydrazine (UDMH) in supercritical water was studied in a batch reactor under different conditions. The hydrogen production process of supercritical water gasification of [...] Read more.

Unsymmetrical dimethylhydrazine (UDMH) is very toxic and hard to decompose in traditional ways. In this paper, the gasification of unsymmetrical dimethylhydrazine (UDMH) in supercritical water was studied in a batch reactor under different conditions. The hydrogen production process of supercritical water gasification of UDMH in metal containers is a multiphase reaction process. The effects of reaction temperature, alkaline catalysts, residence time, and oxidation on gasification were systematically studied. COD and ammonia nitrogen of the residual liquid were tested. Results showed that the maximum molar fraction and yield of hydrogen were 87.0% and 97.9 mol/kg, respectively, with KOH at 600 °C, 23 MPa. The COD removal efficiency in relation to alkaline catalysts was in the following order: NaOH > Na₂CO₃ > KOH > K₂CO₃. The highest COD removal efficiency (up to 95%) can be obtained at the temperature of 600 °C, 23 MPa with NaOH as the catalyst, and a residence time of 20 min. Ammonia nitrogen can be decreased by adding an oxidant. The COD and ammonia nitrogen of the residual liquid can meet the requirement of the Chinese emission standard of water pollution for space propellants. In addition, the organic compounds formed under different conditions were also identified. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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12 pages, 4177 KiB

Open AccessArticle

Study on Two-Phase Permeation of Oxygen and Electrolyte in Lithium Air Battery Electrode Based on Digital Twin

by Qiang Li, Tanghu Zhang, Tianyu Zhang, Zhichao Xue and Hong Sun

Energies 2022, 15(19), 6986; https://doi.org/10.3390/en15196986 - 23 Sep 2022

Cited by 5 | Viewed by 1408

Abstract

In this paper, the saturation of electrolytes on the mass transfer property of porous electrodes in non-aqueous lithium air batteries has been studied based on digital twin. Herein, we reconstruct the porous cathode based on X-ray micro-computed tomography (μct) and quantitatively analyze the [...] Read more.

In this paper, the saturation of electrolytes on the mass transfer property of porous electrodes in non-aqueous lithium air batteries has been studied based on digital twin. Herein, we reconstruct the porous cathode based on X-ray micro-computed tomography (μct) and quantitatively analyze the pore size distribution, specific surface area, triple-phase interface area, conductivity and diffusion coefficient of reactants at varying filling degrees of the electrolyte. The results derived from digital twin provide insight into the gas–liquid two-phase mass transfer performance in the porous cathode with various degrees of electrolyte saturation and demonstrate that the optimum electrolyte saturation is 60%. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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16 pages, 3840 KiB

Open AccessFeature PaperArticle

Comparative Analysis of Dynamic Behavior of Liquid Droplet Impacting Flat and Circular Wires

by Yu Meng, Shenglin Quan, Yali Guo and Shengqiang Shen

Energies 2022, 15(18), 6623; https://doi.org/10.3390/en15186623 - 10 Sep 2022

Cited by 1 | Viewed by 1747

Abstract

The performance of droplets captured by the wire mesh demister in a seawater desalination system seriously affects the quality of water desalination. Therefore, it is of great significance to study the droplet impact in the wire mesh demister to improve the demister’s efficiency. [...] Read more.

The performance of droplets captured by the wire mesh demister in a seawater desalination system seriously affects the quality of water desalination. Therefore, it is of great significance to study the droplet impact in the wire mesh demister to improve the demister’s efficiency. In this paper, a two-dimensional model of the droplet impacting the wire is established. The processes of the droplet impacting a flat wire and a circular wire are simulated by using the VOF model in Fluent, and a comparative analysis is conducted. The results demonstrate that both wires experience spreading and splashing stages, but when the wire is circular, the length of the lifted lamella is longer, the peak force on the wall is larger, the splash’s start time is earlier, and the number of secondary droplets is greater; the variation rule of the force on the wall caused by the change of initial velocity is similar, and the increase in initial velocity will promote the occurrence of splash phenomenon, but the role of the initial velocity on the splash effect is more obvious for the circular wire; and when the droplet impacts the flat wire, the influence of incident angle on the critical splash velocity is non-monotonic, but the critical splash velocity increases with an increase in incident angle when the wire is circular. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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12 pages, 5028 KiB

Open AccessArticle

Theoretical Prediction on Hydraulic Lift of a Coandă Effect-Based Mining Collector for Manganese Nodule

by Hao Jia, Jian Yang, Xianghui Su, Qiu Xia and Kexin Wu

Energies 2022, 15(17), 6345; https://doi.org/10.3390/en15176345 - 30 Aug 2022

Cited by 19 | Viewed by 2195

Abstract

The undersea collecting vehicle is one of the three main parts in the deep-sea exploitation system. The Coandă effect-based collector picks up manganese nodules by providing an adverse pressure difference over the nodule, through the jet flowing around a curved wall. In order [...] Read more.

The undersea collecting vehicle is one of the three main parts in the deep-sea exploitation system. The Coandă effect-based collector picks up manganese nodules by providing an adverse pressure difference over the nodule, through the jet flowing around a curved wall. In order to overcome the drawbacks of repeated prototyping and experimenting in the traditional design procedure of the Coandă effect-based collector, the theoretical guide should be well placed to ensure correct design of the strongly related parameters of the collector. In this paper, a simplified model of curved wall jets was developed and the solution of approximate closed form was obtained to predict the lift force of the nodules. The variational tendencies of velocity, pressure and single-particle lift index perpendicular to the curved wall were investigated and the Coandă effects were found to be stronger with higher initial velocity, higher non-dimensional jet slot height and lower non-dimensional wall height. A CFD-DEM simulation of a number of particles was additionally performed to give more insight into the predictive accuracy of the simplified theory. Target lift force was found to be related to high efficiency in collection of particles, resulting in certain predictability of the theoretical model to the nodule lifting in a pre-prototype hydraulic device based on the Coandă effect. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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15 pages, 7156 KiB

Open AccessArticle

Flow and Heat Transfer Characteristics of S-CO₂ in a Vertically Rising Y-Tube

by Xiaohong Hao, Su Du, Qiguo Yang, Sen Zhang and Qi Zhang

Energies 2022, 15(9), 3312; https://doi.org/10.3390/en15093312 - 2 May 2022

Cited by 1 | Viewed by 1812

Abstract

The supercritical carbon dioxide Brayton cycle has gradually become a research focus, but we also see a deficiency in research related to the flow and heat transfer characteristics of S-CO₂ boiler staves with high parameters. In this paper, the flow and heat [...] Read more.

The supercritical carbon dioxide Brayton cycle has gradually become a research focus, but we also see a deficiency in research related to the flow and heat transfer characteristics of S-CO₂ boiler staves with high parameters. In this paper, the flow and heat transfer of supercritical carbon dioxide is investigated in a 1000 MW supercritical boiler cooled wall tube in the parameters of a pressure of 30.42 MPa, a mass flux of 1592~2207 kg/(m²·s), and a heat flux of 39.8~71.2 kw/m²; a three-dimensional model of supercritical CO₂ fluid in the cooling wall tube is established with the RNG k-epsilon turbulence model. Numerical simulations are carried out according to the following boundary conditions: an adiabatic half side, a heated half side, and a Y-type three-way two-to-one. The effects of the mass flux, inlet temperature, and heat flux on the flow and heat transfer characteristics in the Y-tube are analyzed, which exerts great influence on the research of S-CO₂ boiler stave thermodynamics. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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15 pages, 4708 KiB

Open AccessArticle

The Effect of Different Pressure Conditions on Shock Waves in a Supersonic Steam Ejector

by Yiqiao Li, Shengqiang Shen, Chao Niu, Yali Guo and Liuyang Zhang

Energies 2022, 15(8), 2903; https://doi.org/10.3390/en15082903 - 15 Apr 2022

Cited by 4 | Viewed by 2489

Abstract

The complex flow phenomena in a three-dimensional supersonic steam ejector were simulated with a non-equilibrium condensation model including real physical properties in different pressure conditions. The different working conditions include discharge pressure, motive pressure, and suction pressure. The influence of different pressures on [...] Read more.

The complex flow phenomena in a three-dimensional supersonic steam ejector were simulated with a non-equilibrium condensation model including real physical properties in different pressure conditions. The different working conditions include discharge pressure, motive pressure, and suction pressure. The influence of different pressures on shock waves in the steam ejector was investigated comprehensively. The intrinsic causes of shock wave variation with pressure conditions were explained in detail. The results show that the width of the primary shock train region expand with an increase in the motive pressure or a decrease in suction pressure. The diamond shock waves move downstream with an increase in motive pressure or a decrease in suction pressure. The shocking position in the diffuser moves upstream until it reaches the diffuser entrance with an increase in discharge pressure or a decrease in motive pressure or suction pressure. The intensity and number of oblique shock waves in the diffuser increase with an increase in motive pressure and suction pressure or a decrease in discharge pressure. The existence of only one shock wave in the diffuser is a necessary and insufficient condition for the ejector to enter a double choking mode. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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9 pages, 10432 KiB

Open AccessArticle

Bubble Dynamics during Laser Irradiated Thermo-Mechanical Response of Pigmented Skin Phantom

by Jiafeng Wang and Bin Chen

Energies 2022, 15(6), 2019; https://doi.org/10.3390/en15062019 - 10 Mar 2022

Cited by 2 | Viewed by 2350

Abstract

During the laser treatment of pigmented dermatosis such as Nevus of Ota, vapor bubbles will be generated by the laser with short pulse width and high energy density. Laser irradiation is efficacious for the clinical treatment of Ota’s Nevus caused by hyperplasia of [...] Read more.

During the laser treatment of pigmented dermatosis such as Nevus of Ota, vapor bubbles will be generated by the laser with short pulse width and high energy density. Laser irradiation is efficacious for the clinical treatment of Ota’s Nevus caused by hyperplasia of melanosomes in dermis. Since the mechanism of the laser–melanosome interaction is not yet clear, the clearance rate is generally low and bleeding of irradiated skin frequently occurs. This work conducted a flow visualization experiment to investigate the laser–melanosome interaction mechanism by using high-speed imaging. Pigmented phantom was prepared to simulate the diseased dermis tissue, where agar acted as substrate and synthetic melanin particles was infused as hyperplastic melanosomes. Putting the phantom into water, its thermo-mechanical responses to single-pulse 1064-nm Nd:YAG laser irradiation with energy density of 4–7 J/cm² and pulse duration of 6 ns were recorded. The results indicated that laser-induced bubble formation caused by the gasification of tissue moisture is the key mechanism of laser–melanosome interaction, and an optimal energy density of 6 J/cm² is recommended. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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Review

Jump to: Research

29 pages, 7845 KiB

Open AccessReview

Spray Cooling as a High-Efficient Thermal Management Solution: A Review

by Jing Yin, Shangming Wang, Xuehao Sang, Zhifu Zhou, Bin Chen, Panidis Thrassos, Alexandros Romeos and Athanasios Giannadakis

Energies 2022, 15(22), 8547; https://doi.org/10.3390/en15228547 - 15 Nov 2022

Cited by 24 | Viewed by 7499

Abstract

As one of the most promising thermal management solutions, spray cooling has the advantages of high heat-transfer coefficient and maintaining a low temperature of the cooling surface. By summarizing the influential factors and practical applications of spray cooling, the current challenges and bottlenecks [...] Read more.

As one of the most promising thermal management solutions, spray cooling has the advantages of high heat-transfer coefficient and maintaining a low temperature of the cooling surface. By summarizing the influential factors and practical applications of spray cooling, the current challenges and bottlenecks were indicated so as to prompt its potential applications in the future. Firstly, this paper reviewed the heat-transfer mechanism of spray cooling and found that spray cooling is more advantageous for heat dissipation in high-power electronic devices by comparing it with other cooling techniques. Secondly, the latest experimental studies on spray cooling were reviewed in detail, especially the effects of spray parameters, types of working fluid, surface modification, and environmental parameters on the performance of cooling system. Afterwards, the configuration and design of the spray cooling system, as well as its applications in the actual industry (data centers, hybrid electric vehicles, and so on) were enumerated and summarized. Finally, the scientific challenges and technical bottlenecks encountered in the theoretical research and industrial application of spray cooling technology were discussed, and the direction of future efforts were reasonably speculated. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Multiphase Flow)

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