energies-logo

Journal Browser

Journal Browser

Heat Transfer and Multiphase Flow

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "J1: Heat and Mass Transfer".

Deadline for manuscript submissions: 31 December 2024 | Viewed by 15749

Special Issue Editors


E-Mail Website
Guest Editor
Department of Mechanical Engineering, Idaho State University, Pocatello, ID 83209, USA
Interests: plasma, multiphysics modeling; combustion; energy
College of Engineering and Computer Science, The University of Texas Rio Grande Valley, Edinburg, TX, USA
Interests: graphene oxide; nanofiltration membranes; graphite

E-Mail Website
Guest Editor
Los Alamos National Laboratory, Los Alamos, NM, USA
Interests: visualization; pattern detection; vector fields; data science; HPC; Lagrangian flow representations; moment invariants; and color theory

Special Issue Information

Dear Colleagues,

Fluid Flow Dynamics and heat transfer of single phase and multiphase flows are always encountered in the energy utilization fields, such as power plants, air conditionings, renewable energy utilization, thermal management, et al. In recent years, many new fundamental studies have been conducted experimentally and numerically in this field. Some new insight of heat transfer mechanism and new methods to enhance heat transfer of single phase and multiphase flows have been discovered. This special issue expects to provide a platform in the area of flow and heat transfer in single phase and multiphase flows. The scope of the special issue includes all aspects of theoretical, numerical, and experimental investigations of fluid flow dynamics and heat transfer.

In this Special Issue on " Heat Transfer and Multiphase Flow”, we welcome review articles and original research papers, fundamental or applied, theoretical, numerical, or experimental investigations on fluid flow dynamics and heat transfer phenomenon.

Dr. Rajib Mahamud
Dr. Ali Ashraf
Dr. Roxana Bujack
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. Energies is an international peer-reviewed open access semimonthly 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 2600 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

  • electrical equipment cooling
  • thermal mangement 
  • heat sinks 
  • heat exchangers 
  • heat pipes 
  • heat transfer enhacement 
  • mini/micro channels 
  • multiphase flows 
  • boiling 
  • condensation 
  • microfluidics 
  • droplets 
  • numerical simulations 
  • md simulation 
  • flow patterns 
  • pressure drops 
  • supercritical fluid 
  • phase change material 
  • heat storage

Benefits of Publishing in a Special Issue

  • Ease of navigation: Grouping papers by topic helps scholars navigate broad scope journals more efficiently.
  • Greater discoverability: Special Issues support the reach and impact of scientific research. Articles in Special Issues are more discoverable and cited more frequently.
  • Expansion of research network: Special Issues facilitate connections among authors, fostering scientific collaborations.
  • External promotion: Articles in Special Issues are often promoted through the journal's social media, increasing their visibility.
  • e-Book format: Special Issues with more than 10 articles can be published as dedicated e-books, ensuring wide and rapid dissemination.

Further information on MDPI's Special Issue polices can be found here.

Published Papers (13 papers)

Order results
Result details
Select all
Export citation of selected articles as:

Research

Jump to: Review

16 pages, 6897 KiB  
Article
An Experimental Study of Boiling Heat Transfer and Quench Front Propagation Velocity During Quenching of a Cylinder Rod in Subcooled Water
by Yuanyang Sun, Huanyan Jian, Ping Xiong and Linglan Zhou
Energies 2024, 17(20), 5236; https://doi.org/10.3390/en17205236 - 21 Oct 2024
Viewed by 501
Abstract
In this study, a quenching experiment was conducted at atmospheric pressure to investigate the flow and heat-transfer characteristics of cylindrical rods made from SS, FeCrAl, and Zr-4 under various subcooling degrees (ΔTsub). The inverse heat-conduction problem (IHCP) method and image-processing [...] Read more.
In this study, a quenching experiment was conducted at atmospheric pressure to investigate the flow and heat-transfer characteristics of cylindrical rods made from SS, FeCrAl, and Zr-4 under various subcooling degrees (ΔTsub). The inverse heat-conduction problem (IHCP) method and image-processing technique were utilized to determine the surface temperature and heat flux, vapor film thickness, and quench front propagation. The results show that smaller solid kρcp and larger ΔTsub result in relatively more efficient quenching boiling heat transfer, thinner vapor film thickness, and greater quench front propagation velocity. The quench front originates at the bottom of the test specimen and becomes progressively larger in velocity with time. It eventually converges with the downward-propagating quench front in the upper middle of the test specimen. Moreover, at the beginning of quench front propagation, the SS and FeCrAl test specimens have a constant velocity region. However, because the Zr-4 test specimen has a small kρcp, the velocities gradually increase from the onset of quench front generation. Furthermore, the measured average quench front velocities are consistent with the experimental datum from the literature. However, the predicted model proposed by Duffey underestimates the propagation velocity due to ignoring the cooling effect of film boiling. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

26 pages, 8524 KiB  
Article
Evaporation Characteristics of Two Interacting Moving Droplets
by Muhammad Ahmed, Muhammad Irfan and Muhammad Mahabat Khan
Energies 2024, 17(20), 5169; https://doi.org/10.3390/en17205169 - 17 Oct 2024
Viewed by 442
Abstract
The droplet evaporation in sprays and clouds is largely influenced by the interacting surrounding droplets. This study presents a numerical investigation on the evaporation dynamics of two inline interacting droplets in a high-temperature vapor domain using ANSYS Fluent. Several methods are available to [...] Read more.
The droplet evaporation in sprays and clouds is largely influenced by the interacting surrounding droplets. This study presents a numerical investigation on the evaporation dynamics of two inline interacting droplets in a high-temperature vapor domain using ANSYS Fluent. Several methods are available to solve the multiphase flow problems with phase change, including level set, phase field, volume of fluid (VOF), and hybrid techniques. In the present study, the multiphase model equations are solved in the framework of the VOF method, which is a well-established and robust solver for multiphase flows with excellent volume conservation properties. The Lee model is used to handle the evaporative phase change at the interface. The droplet spacing, sizes, and arrangement pattern of differently sized droplets are the key parameters varied to explore their effects on the evaporation rate, droplet velocities, and inter-droplet distance. For equal-sized droplets, the evaporation of the trailing droplet slows down due to the low-temperature buffer layer of the droplet vapors generated by the evaporation of the leading droplet; the effects decrease as the initial spacing is increased. For two droplets at center-to-center distances of 2do and 6do, the evaporation of the trailing droplets reduces by 20.8% and 7%, respectively. Decreasing the size of the trailing droplet increases its evaporation rate since the smaller droplet experiences more temperature gradients as it escapes out of the influence of the leading drop buffer layer. For a smaller to larger droplet diameter ratio of 0.9, the evaporation rate of the trailing droplet is reduced by ~26% than expected. However, for the diameter ratio of 0.5, this reduction is only 12.5%. Regarding the arrangement pattern of different-sized droplets, the overall evaporation rate is lower when the bigger droplet follows the smaller one. The fact is attributed to close interaction followed by the coalescence of the bigger droplet with the leading smaller droplet, resulting in a single bigger droplet. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

17 pages, 2627 KiB  
Article
Prediction of Heat Transfer during Condensation of Ammonia Inside Tubes and Annuli
by Mirza M. Shah
Energies 2024, 17(19), 4869; https://doi.org/10.3390/en17194869 - 27 Sep 2024
Viewed by 690
Abstract
Ammonia has been used as a refrigerant since the beginning of the refrigeration industry and it continues to be an important industrial refrigerant. However, there is no well-verified method for predicting heat transfer during condensation in tubes and annuli. Available information is often [...] Read more.
Ammonia has been used as a refrigerant since the beginning of the refrigeration industry and it continues to be an important industrial refrigerant. However, there is no well-verified method for predicting heat transfer during condensation in tubes and annuli. Available information is often contradictory, especially about the effect of oil. In this paper, available test data and predictive methods are reviewed. Reliable test data are identified and compared to well-known general correlations. The effect of oil on heat transfer is investigated. The results of this research are presented, and recommendations are made for design calculations. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

13 pages, 8131 KiB  
Article
Study on Flow Heat Transfer and Particle Deposition Characteristics in a Kettle Reboiler
by Xue Liu, Qi Sun, Hui Tang, Wei Peng, Mingbao Zhang, Gang Zhao and Tairan Fu
Energies 2024, 17(16), 4183; https://doi.org/10.3390/en17164183 - 22 Aug 2024
Viewed by 693
Abstract
A kettle reboiler uses the latent heat from the condensation of high-temperature and high-pressure steam in the tube to produce low-pressure saturated steam in the outer shell. The deposition of particles on the tube may change the boiling heat transfer mode from nucleate [...] Read more.
A kettle reboiler uses the latent heat from the condensation of high-temperature and high-pressure steam in the tube to produce low-pressure saturated steam in the outer shell. The deposition of particles on the tube may change the boiling heat transfer mode from nucleate boiling to natural convection, thereby deteriorating the heat transfer performance of the kettle reboiler. Therefore, it is very important to explore the deposition characteristics of particles in the kettle reboiler. In this study, the RPI boiling model based on the Euler–Euler method is used to analyze the water boiling process on the surface of the tube bundle. The DRW model and critical adhesion velocity model based on the Euler–Lagrangian method are used to calculate the motion of particles during the boiling process and the deposition (rebound) behavior. The results show that the boiling of liquid water enhances the local flow velocity of the fluid, so that the maximum flow velocity appears around the near-wall region. The local high-speed flow disperses the particles in the wake flow of the tube bundle, which inhibits the impact of particles on the wall. As the particle size increases, the wall adhesion and fluid drag on the particles are weakened, and the gravity effect gradually becomes dominant, increasing the residence time of the particles in the tube bundle and the frequency of particle impact on the wall. The particle deposition ratio first decreases and then increases. Ultimately, most particles will be deposited in the low-speed area at the end of the tube bundle. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

26 pages, 4196 KiB  
Article
Numerical Modeling of the Behavior of Bubble Clusters in Cavitation Processes
by Anatoliy Pavlenko
Energies 2024, 17(7), 1741; https://doi.org/10.3390/en17071741 - 4 Apr 2024
Cited by 1 | Viewed by 937
Abstract
To study the behavior of a bubble clusters in cavitation devices, a numerical study of the dynamics of bubbles in a compressible liquid was performed, taking into account interfacial heat and mass transfer. The influence of regime and system parameters on the intensity [...] Read more.
To study the behavior of a bubble clusters in cavitation devices, a numerical study of the dynamics of bubbles in a compressible liquid was performed, taking into account interfacial heat and mass transfer. The influence of regime and system parameters on the intensity of cavitation processes is considered. Physical and chemical transformations during the cavitation treatment of liquids are caused not only by the action of shock waves and emitted pressure pulses but also by extreme thermal effects. At the stage of extreme compression of the bubble, the vapor inside the bubble and the liquid in its vicinity transform into the state of a supercritical fluid. The presented model analyzes the nature of microflows in the interbubble space and carries out a quantitative calculation of the local values of the parameters of the velocity and pressure fields. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

20 pages, 8314 KiB  
Article
Enhancing the Fuel Efficiency of Cogeneration Plants by Fuel Oil Afterburning in Exhaust Gas before Boilers
by Victoria Kornienko, Mykola Radchenko, Andrii Radchenko, Hanna Koshlak and Roman Radchenko
Energies 2023, 16(18), 6743; https://doi.org/10.3390/en16186743 - 21 Sep 2023
Cited by 4 | Viewed by 1222
Abstract
Cogeneration or combined heat and power (CHP) has found wide application in various industries because it very effectively meets the growing demand for electricity, steam, hot water, and also has a number of operational, environmental, economic advantages over traditional electrical and thermal systems. [...] Read more.
Cogeneration or combined heat and power (CHP) has found wide application in various industries because it very effectively meets the growing demand for electricity, steam, hot water, and also has a number of operational, environmental, economic advantages over traditional electrical and thermal systems. Experimental and theoretical investigations of the afterburning of fuel oil in the combustion engine exhaust gas at the boiler inlet were carried out in order to enhance the efficiency of cogeneration power plants; this was achieved by increasing the boiler steam capacity, resulting in reduced production of waste heat and exhaust emissions. The afterburning of fuel oil in the exhaust gas of diesel engines is possible due to a high the excess air ratio (three to four). Based on the experimental data of the low-temperature corrosion of the gas boiler condensing heat exchange surfaces, the admissible values of corrosion rate and the lowest exhaust gas temperature which provide deep exhaust gas heat utilization and high efficiency of the exhaust gas boiler were obtained. The use of WFE and afterburning fuel oil provides an increase in efficiency and power of the CPPs based on diesel engines of up to 5% due to a decrease in the exhaust gas temperature at the outlet of the EGB from 150 °C to 90 °C and waste heat, accordingly. The application of efficient environmentally friendly exhaust gas boilers with low-temperature condensing surfaces can be considered a new and prosperous trend in diesel engine exhaust gas heat utilization through the afterburning of fuel oil and in CPPs as a whole. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

16 pages, 6782 KiB  
Article
Increasing the Efficiency of Turbine Inlet Air Cooling in Climatic Conditions of China through Rational Designing—Part 1: A Case Study for Subtropical Climate: General Approaches and Criteria
by Mykola Radchenko, Zongming Yang, Anatoliy Pavlenko, Andrii Radchenko, Roman Radchenko, Hanna Koshlak and Guozhi Bao
Energies 2023, 16(17), 6105; https://doi.org/10.3390/en16176105 - 22 Aug 2023
Cited by 5 | Viewed by 1019
Abstract
The enhancement of gas turbine (GT) efficiency through inlet air cooling, known as TIAC, in chillers using the heat of exhaust gas is one of the most attractive tendencies in energetics, particularly in thermal engineering. In reality, any combustion engine with cyclic air [...] Read more.
The enhancement of gas turbine (GT) efficiency through inlet air cooling, known as TIAC, in chillers using the heat of exhaust gas is one of the most attractive tendencies in energetics, particularly in thermal engineering. In reality, any combustion engine with cyclic air cooling using waste heat recovery chillers might be considered as a power plant with in-cycle trigeneration focused on enhancing a basic engine efficiency, which results in additional power output or fuel savings, reducing carbon emissions in all cases. The higher the fuel efficiency of the engine, the more efficient its functioning as a source of emissions. The sustainable operation of a GT at stabilized low intake air temperature is impossible without using rational design to determine the cooling capacity of the chiller and TIAC system as a whole to match current duties without overestimation. The most widespread absorption lithium-bromide chillers (ACh) are unable to reduce the GT intake air temperature below 15 °C in a simple cycle because the temperature of their chilled water is approximately 7 °C. Deeper cooling air would be possible by applying a boiling refrigerant as a coolant in ejector chiller (ECh) as the cheapest and simplest in design. However, the coefficients of performance (COP) of EChs are considerably lower than those of AChs: about 0.3 compared to 0.7 of AChs. Therefore, EChs are applied for subsequent cooling of air to less than 15 °C, whereas the efficient ACh is used for ambient air precooling to 15 °C. The application of an absorption–ejector chiller (AECh) enables deeper inlet air cooling and greater effects accordingly. However, the peculiarities of the subtropical climate, characterized by high temperature and humidity and thermal loads, require extended analyses to reveal the character of thermal load and to modify the methodology of designing TIAC systems. The advanced design methodology that can reveal and thereby forecast the peculiarities of the TIAC system’s thermal loading was developed to match those peculiarities and gain maximum effect without oversizing. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

15 pages, 4865 KiB  
Article
Random Forest Model of Flow Pattern Identification in Scavenge Pipe Based on EEMD and Hilbert Transform
by Xiaodi Liang, Suofang Wang and Wenjie Shen
Energies 2023, 16(16), 6084; https://doi.org/10.3390/en16166084 - 21 Aug 2023
Cited by 3 | Viewed by 1006
Abstract
Complex oil and gas two-phase flow exists within an aero-engines bearing cavity scavenge pipe, prone to lubricated self-ignition and coking. Lubricant system designers must be able to accurately identify and understand the flow state of the scavenge pipe. The prediction accuracy of previous [...] Read more.
Complex oil and gas two-phase flow exists within an aero-engines bearing cavity scavenge pipe, prone to lubricated self-ignition and coking. Lubricant system designers must be able to accurately identify and understand the flow state of the scavenge pipe. The prediction accuracy of previous models is insufficient to meet the more demanding needs. This paper establishes a visualized flow pattern identification test system for the scavenge pipe, with a test temperature of up to 370 k, using a high-speed camera to photograph four flow patterns, decomposing the pressure signals obtained from high-frequency dynamic pressure sensors using the ensemble empirical mode decomposition (EEMD) method, and then performing Hilbert transform, using the Hilbert spectrum to quantify the changes of amplitude and frequency with time, and establishing the energy and flow pattern correspondence analysis. Then the energy percentage of IMFs is used as the input of feature values, and the random forest algorithm machine learning is used for predictive classification. The experimental results show that the flow pattern recognition rate established in this paper can reach 98%, which can identify the two-phase flow pattern in the scavenge pipe more objectively and accurately. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

19 pages, 9107 KiB  
Article
Numerical Simulation of Subcooled Flow Boiling in a Threaded Tube and Investigation of Heat Transfer and Bubble Behavior
by Ke Lei, Jinfeng Wang, Jing Xie and Bingjun Wang
Energies 2023, 16(15), 5719; https://doi.org/10.3390/en16155719 - 31 Jul 2023
Cited by 1 | Viewed by 1059
Abstract
Three-dimensional subcooled flow boiling of R134a in a threaded tube was numerically simulated at the conditions of 200~400 kW/m2 heat flux, 3~20 K inlet subcooling, and 0.2~0.6 m/s inlet velocity. The bubble behavior in the horizontal threaded tube with 0.581 mm thread [...] Read more.
Three-dimensional subcooled flow boiling of R134a in a threaded tube was numerically simulated at the conditions of 200~400 kW/m2 heat flux, 3~20 K inlet subcooling, and 0.2~0.6 m/s inlet velocity. The bubble behavior in the horizontal threaded tube with 0.581 mm thread tooth height was observed. The effect of heat flux, inlet subcooling, and inlet velocity on bubble departure diameter and heat transfer coefficient were explored. The results presented the whole growth process of five kinds of bubbles. It was found that the bubbles either collapsed in cold liquid after leaving the heating wall or grew along the axial direction and contacted the heating wall. And there was no bubble sliding during the growth. In addition, the most important and special characteristic of bubble behavior in threaded tubes was the phenomenon of the bubble passing through the cavity. The coalescence and breakup behavior occurred after the bubble passed through the cavity. According to the discussions of the departure diameter and heat transfer coefficient, it was inferred that the bubble departure diameter increased with the increase of heat flux from 200~400 kW/m2 and subcooling from 3~20 K while decreasing with the increase of inlet velocity from 0.2~0.6 m/s. And due to the influence of the threaded tube structure, there are special points in the change of bubble departure diameter. The heat transfer coefficient of the bubbles in the threaded tube was higher than the smooth tube, which was increased by 1.5~12.5%. The heat transfer coefficient increased with the increase of heat flux and subcooling and is closely related to the bubble departure diameter. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

12 pages, 3712 KiB  
Article
Performance Improvement of a Solar-Assisted Absorption Cooling System Integrated with Latent Heat Thermal Energy Storage
by Lana Migla, Raimonds Bogdanovics and Kristina Lebedeva
Energies 2023, 16(14), 5307; https://doi.org/10.3390/en16145307 - 11 Jul 2023
Cited by 1 | Viewed by 1662
Abstract
Phase change materials (PCMs) have emerged as promising solutions for latent heat thermal energy storage (LHTES) systems, offering considerable potential for storing energy derived from renewable sources across various engineering applications. The present study focused on optimization of solar cooling system by integrating [...] Read more.
Phase change materials (PCMs) have emerged as promising solutions for latent heat thermal energy storage (LHTES) systems, offering considerable potential for storing energy derived from renewable sources across various engineering applications. The present study focused on optimization of solar cooling system by integrating LHTES with different PCM tank configurations. TRNSYS simulation software was selected for the study, and the collected experimental data from laboratory system prototype were used for system validation. The results indicate that the use of PCM led to a noteworthy decrease of 6.2% in auxiliary energy consumption. Furthermore, the time during which the heat carrier temperature flow exceeded 90 °C from the storage tank to the auxiliary fluid heater was extended by 27.8% when PCM was utilized compared to that of its absence. The use of PCM in LHTES is more effective under variable weather conditions. On the day when changes in weather conditions were observed, around 98% of the cooling load was provided by produced sun energy. The results of the research can be used to optimize the solar cooling system, which will help reduce the environmental impact of cooling systems running on non-renewable fuels. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

23 pages, 4996 KiB  
Article
Improving Ecological Efficiency of Gas Turbine Power System by Combusting Hydrogen and Hydrogen-Natural Gas Mixtures
by Serhiy Serbin, Mykola Radchenko, Anatoliy Pavlenko, Kateryna Burunsuz, Andrii Radchenko and Daifen Chen
Energies 2023, 16(9), 3618; https://doi.org/10.3390/en16093618 - 22 Apr 2023
Cited by 8 | Viewed by 1906
Abstract
Currently, the issue of creating decarbonized energy systems in various spheres of life is acute. Therefore, for gas turbine power systems including hybrid power plants with fuel cells, it is relevant to transfer the existing engines to pure hydrogen or mixtures of hydrogen [...] Read more.
Currently, the issue of creating decarbonized energy systems in various spheres of life is acute. Therefore, for gas turbine power systems including hybrid power plants with fuel cells, it is relevant to transfer the existing engines to pure hydrogen or mixtures of hydrogen with natural gas. However, significant problems arise associated with the possibility of the appearance of flashback zones and acoustic instability of combustion, an increase in the temperature of the walls of the flame tubes, and an increase in the emission of nitrogen oxides, in some cases. This work is devoted to improving the efficiency of gas turbine power systems by combusting pure hydrogen and mixtures of natural gas with hydrogen. The organization of working processes in the premixed combustion chamber and the combustion chamber with a sequential injection of ecological and energy steam for the “Aquarius” type power plant is considered. The conducted studies of the basic aerodynamic and energy parameters of a gas turbine combustor working on hydrogen-containing gases are based on solving the equations of conservation and transfer in a multicomponent reacting system. A four-stage chemical scheme for the burning of a mixture of natural gas and hydrogen was used, which allows for the rational parameters of environmentally friendly fuel burning devices to be calculated. The premixed combustion chamber can only be recommended for operations on mixtures of natural gas with hydrogen, with a hydrogen content not exceeding 20% (by volume). An increase in the content of hydrogen leads to the appearance of flashback zones and fuel combustion inside the channels of the swirlers. For the combustion chamber of the combined-cycle power plant “Vodoley”, when operating on pure hydrogen, the formation of flame flashback zones does not occur. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

15 pages, 5085 KiB  
Article
Effect of the Density Ratio on Emulsions and Their Segregation: A Direct Numerical Simulation Study
by Oscar Krzeczek, Theresa Trummler, Elias Trautner and Markus Klein
Energies 2023, 16(7), 3160; https://doi.org/10.3390/en16073160 - 31 Mar 2023
Cited by 2 | Viewed by 1918
Abstract
Using direct numerical simulation (DNS) in combination with the volume of fluid method (VoF), we investigate the influence of the density ratio between the carrier and dispersed phase on emulsions, where the baseline simulation approximately corresponds to the ratio of water-in-gasoline emulsions. For [...] Read more.
Using direct numerical simulation (DNS) in combination with the volume of fluid method (VoF), we investigate the influence of the density ratio between the carrier and dispersed phase on emulsions, where the baseline simulation approximately corresponds to the ratio of water-in-gasoline emulsions. For this purpose, homogeneous isotropic turbulence (HIT) is generated using a linear forcing method, enhanced by a proportional–integral–derivative (PID) controller, ensuring a constant turbulent kinetic energy (TKE) for two-phase flows, where the TKE balance equation contains an additional term due to surface tension. Then, the forcing is stopped, and gravitational acceleration is activated. The proposed computational setup represents a unique and well-controlled configuration to study emulsification and segregation. We consider four different density ratios, which are applied in industrial processes, to investigate the influence of the density ratio on the statistically steady state of the emulsions, and their segregation under decaying turbulence and constant gravitational acceleration. At the statistically steady state, we hold the turbulence constant and study the effects of the density ratio ρd/ρc, on the interface area, the Sauter mean diameter (SMD), and the statistical droplet size distribution. We find that all are affected by the density ratio, and we observe a relation between the SMD and ρd/ρc. Furthermore, we assume a dependence of the critical Weber number on the density ratio. In the second part of our work, we study the segregation process. To this end, we consider the change in the center of mass of the disperse phase and the energy release, to analyze the dependence of segregation on the density difference Δρ/ρd. We show that segregation scales with the density difference and the droplet size, and a segregation time scale has been suggested that collapses the height of the center of mass for different density ratios. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

Review

Jump to: Research

33 pages, 10385 KiB  
Review
Assessment of Machine Learning Techniques for Simulating Reacting Flow: From Plasma-Assisted Ignition to Turbulent Flame Propagation
by Mashrur Ertija Shejan, Sharif Md Yousuf Bhuiyan, Marco P. Schoen and Rajib Mahamud
Energies 2024, 17(19), 4887; https://doi.org/10.3390/en17194887 - 29 Sep 2024
Viewed by 639
Abstract
Combustion involves the study of multiphysics phenomena that includes fluid and chemical kinetics, chemical reactions and complex nonlinear processes across various time and space scales. Accurate simulation of combustion is essential for designing energy conversion systems. Nonetheless, due to its multiscale, multiphysics nature, [...] Read more.
Combustion involves the study of multiphysics phenomena that includes fluid and chemical kinetics, chemical reactions and complex nonlinear processes across various time and space scales. Accurate simulation of combustion is essential for designing energy conversion systems. Nonetheless, due to its multiscale, multiphysics nature, simulating these systems at full resolution is typically difficult. The massive and complex data generated from experiments and simulations, particularly in turbulent combustion, presents both a challenge and a research opportunity for advancing combustion studies. Machine learning facilitates data-driven techniques to manage the substantial amount of combustion data that is either obtained through experiments or simulations, and thereby can find the hidden patterns underlying these data. Alternatively, machine learning models can be useful to make predictions with comparable accuracy to existing models, while reducing computational costs significantly. In this era of big data, machine learning is rapidly evolving, offering promising opportunities to explore its integration with combustion research. This work provides an in-depth overview of machine learning applications in turbulent combustion modeling and presents the application of machine learning models: Decision Trees (DT) and Random Forests (RF), for the spatio-temporal prediction of plasma-assisted ignition kernels, based on the initial degree of ionization, with model validations against DNS data. The results demonstrate that properly trained machine learning models can accurately predict the spatio-temporal ignition kernel profile based on the initial energy deposition and distribution. Full article
(This article belongs to the Special Issue Heat Transfer and Multiphase Flow)
Show Figures

Figure 1

Back to TopTop