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Computational Fluid Dynamics: Modelling of Industrial Flashing Processes
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Computational Fluid Dynamics: Modelling of Industrial Flashing Processes

A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Process Control and Monitoring".

Deadline for manuscript submissions: closed (30 June 2023) | Viewed by 5537

Special Issue Editors

Dr. Yixiang Liao

E-Mail Website
Guest Editor
Institute of Fluid Dynamics, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstraße 400, 01328 Dresden, Germany
Interests: computational fluid dynamics; multiphase flow; phase change; heat and mass transfer; nuclear safety
Prof. Dr. Hengjie Guo

E-Mail Website
Guest Editor
School of Power and Energy, Northwestern Polytechnical University, Xi'an 710129, China
Interests: computational fluid dynamics; clean energy and sustainability; multiphase flow; fuel injection and sprays; ML-assisted modeling

Special Issue Information

Dear Colleagues,

Flashing is the phenomenon that a liquid becomes metastable superheated and partially vaporized due to a pressure drop. The industrial application of flashing processes is varied, for example, multi-stage flash-evaporation of seawater for wining desalinated water; flashing sprays in engines for enhancing fuel atomization and improving combustion characteristics; flash drum as an energy-efficient alternative to the conventional distiller to separate two components with different boiling points, and flash steam geothermal power plants. Similar to cavitation, where the phase change is mainly controlled by mechanical non-equilibrium, the vapor generated by flashing at lower pressure regions may condense again as it undergoes pressure recovery. As a result, flow instability that leads to noise and damage may result from flashing, for example, in a natural circulation cooling system. Another extreme example is the boiling liquid expanding vapor explosion (BLEVE), which occurs when a vessel containing a pressurized liquid is ruptured, and the liquid flashes rapidly through the failure. Therefore, the study of the flash phenomenon is important for both economic efficiency and the safe operation of industrial equipment. However, due to complex multiphase and interfacial sub-processes, the understanding and modeling of the flashing phenomenon are still limited. This Special Issue aims to collect work from diverse application backgrounds and provide a platform for interdisciplinary exchange.

Dr. Yixiang Liao
Prof. Dr. Hengjie Guo
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • computational fluid dynamics
  • simulation and modeling
  • flashing
  • evaporation
  • multiphase flow
  • phase change
  • heat and mass transfer
  • industrial application

Published Papers (4 papers)

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Research

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18 pages, 6184 KiB  
Article
Optimization of the Flashing Processes in Mineral Metallurgy Based on CFD Simulations
by Yiting Xiao, Zhengbin Pan, Haotong Xin, Chongmao Xia, Xuefeng Wang, Qifang Li and Bo Kong
Processes 2023, 11(11), 3121; https://doi.org/10.3390/pr11113121 - 31 Oct 2023
Viewed by 955
Abstract
In mineral metallurgy, the flashing unit is key to returning the slurry to atmospheric conditions. Its primary function is to achieve pressure letdown, and during the process, shock waves are generated to maximize energy dissipation. Investigating the location and expansion of shock waves [...] Read more.
In mineral metallurgy, the flashing unit is key to returning the slurry to atmospheric conditions. Its primary function is to achieve pressure letdown, and during the process, shock waves are generated to maximize energy dissipation. Investigating the location and expansion of shock waves is the focal point of this study due to their importance in flashing unit design. A CFD model coupled with a homogeneous relaxation model (HRM) was used to simulate the flashing process of mineral slurry. The flow behavior, including velocity, pressure, and the shape and location of the shock waves, were obtained using simulation under different unit design and operating parameters. These results would provide valuable insights into the design of flashing units and guidance for the safe operation and maintenance of devices. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics: Modelling of Industrial Flashing Processes)
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13 pages, 4399 KiB  
Article
Cavitation Observation and Noise Characteristics in Rectangular Throttling Groove Spool
by Jian Zhang, Jifeng Fu, Xinyang Zhang, Tao Zhang and Yuhang Wang
Processes 2023, 11(10), 2814; https://doi.org/10.3390/pr11102814 - 22 Sep 2023
Cited by 1 | Viewed by 840
Abstract
A hydraulic cavitation platform was developed in order to examine the occurrence of cavitation in the rectangular throttling groove spool and its correlation with noise characteristics. The test valve is constructed using PMMA material, which possesses excellent transparency. This transparency enables direct visual [...] Read more.
A hydraulic cavitation platform was developed in order to examine the occurrence of cavitation in the rectangular throttling groove spool and its correlation with noise characteristics. The test valve is constructed using PMMA material, which possesses excellent transparency. This transparency enables direct visual examination of cavitation occurring at the throttle slot. Additionally, high-speed photography is employed to observe the flow characteristics of the valve port, facilitating the analysis of cavitation morphology changes. Furthermore, a noise meter is utilized to measure and record the noise level and its corresponding spectrum. The flow field and flow phenomena at the rectangular throttling groove spool were studied using high-speed photography, noise spectrum analysis, and other methods. It is discovered that back pressure has the greatest influence on cavitation and flow separation, followed by the influence of intake pressure on cavitation morphology and noise. As the back pressure lowers, the cavitation morphology changes from flaky to cloudy, and the cavitation intensity, distribution area, and noise level increase. Background noise and cavitation noise have distinct frequency differences; cavitation noise in the rectangular throttling groove spool is high-frequency noise, with a frequency of more than 8 kHz, and the higher the frequency, the greater the difference in noise value. The magnitude of the alterations in noise intensity is minimal. The noise values exhibit slight variations of 2.3 dB, 4 dB, and 4.3 dB under varying back pressure circumstances of 3 MPa, 4 MPa, and 5 MPa inlet pressure, respectively. It is recommended to use the frequency of cavitation noise to detect the cavitation state and monitor the cavitation process. In the low-frequency region, the cavitation noise in the rectangular throttle groove valve core is not significantly different. Once the center frequency surpasses 3.15 kHz, a discernible distinction emerges, with the magnitude of the discrepancy in noise value increasing as the frequency rises. In other words, the cavitation cloud does not pulsate at one single frequency, but rather in a range of relatively high frequencies (more than 3.15 kHz). Full article
(This article belongs to the Special Issue Computational Fluid Dynamics: Modelling of Industrial Flashing Processes)
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14 pages, 3241 KiB  
Article
Numerical Simulation of Flashing Flows in a Converging–Diverging Nozzle with Interfacial Area Transport Equation
by Jiadong Li, Yixiang Liao, Ping Zhou, Dirk Lucas and Liang Gong
Processes 2023, 11(8), 2365; https://doi.org/10.3390/pr11082365 - 6 Aug 2023
Cited by 1 | Viewed by 1118
Abstract
Flashing flows of initially sub-cooled water in a converging–diverging nozzle is investigated numerically in the framework of the two-fluid model (TFM). The thermal non-equilibrium effect of phase change is considered by an interfacial heat transfer model, while the pressure jump across the interface [...] Read more.
Flashing flows of initially sub-cooled water in a converging–diverging nozzle is investigated numerically in the framework of the two-fluid model (TFM). The thermal non-equilibrium effect of phase change is considered by an interfacial heat transfer model, while the pressure jump across the interface is ignored. The bubble size distribution induced by nucleation, bubble growth/shrinkage, coalescence, and breakup is described based on the interfacial area transport equation (IATE) and constant bubble number density model (CBND), respectively. The results are compared with the experimental data. Satisfactory prediction of the axial pressure distribution along the nozzle as well as the flashing inception, is achieved by the TFM-IATE coupling method. It was also found that the vapor production in the diverging section was overpredicted, and the radial gas volume fraction distribution deviated from the experiment. The radial diameter profiles exhibit opposite patterns at the nozzle throat and near the outlet, and similar trends can be observed for the superheated degree. A poly-disperse method is suggested to be introduced to describe the evolution of interfacial area concentration. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics: Modelling of Industrial Flashing Processes)
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Review

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20 pages, 3003 KiB  
Review
An Overview of Flashing Phenomena in Pressure Hydrometallurgy
by Junda Liu, Bin Liu, Ping Zhou, Di Wu and Caigui Wu
Processes 2023, 11(8), 2322; https://doi.org/10.3390/pr11082322 - 2 Aug 2023
Cited by 1 | Viewed by 1813
Abstract
Pressure hydrometallurgy has attracted much attention for its characteristics, such as the high adaptability of raw materials and environmental friendliness. Flashing (flash boiling or flash evaporation) refers to the phase change phenomenon from liquid to gas triggered by depressurization, which is an important [...] Read more.
Pressure hydrometallurgy has attracted much attention for its characteristics, such as the high adaptability of raw materials and environmental friendliness. Flashing (flash boiling or flash evaporation) refers to the phase change phenomenon from liquid to gas triggered by depressurization, which is an important connection between high-pressure processes and atmospheric ones in pressure hydrometallurgy. This paper takes the flashing process in zinc leaching and alumina Bayer processes as examples, describes the flashing process in pressure hydrometallurgy in detail for the first time, and shows the importance of the flashing process in energy recovery, solution concentration, and liquid balance, as well as increasing equipment life. According to solid holdup (the volume percentage of solid), this paper proposes to divide the flashing process into solution flashing (low solid holdup) and slurry flashing (high solid holdup). A further focus is put on reviewing the state of the art of related studies. The results reveal that the research on the flashing process in pressure hydrometallurgy is scarce and often oversimplified, e.g., ignoring the BPE (boiling point elevation) and NEA (non-equilibrium allowance) in solution flashing and the effect of solid particles in slurry flashing. Computational fluid dynamic (CFD) simulation is a promising tool for investigating the flashing process. Based on the progress made in other fields, e.g., seawater desalination, nuclear safety analysis, and engine fuel atomization, we suggest that solution flashing can be studied using the CFD–PBM (population balance model) coupled two-fluid model, since a wide size range of bubbles will be generated. For slurry flashing, the effect of solid holdup on the bubble nucleation rate and mechanism as well as other bubble dynamics processes should be accounted for additionally, for which a quantitative description is still lacking. Meanwhile, data for validating the numerical method are scarce because of the harsh experimental conditions, and further research is needed. In summary, this work presents an overview of the flashing processes in pressure hydrometallurgy and some guidelines for future numerical studies. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics: Modelling of Industrial Flashing Processes)
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