Research

26 pages, 4196 KiB

Open AccessArticle

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 - 04 Apr 2024

Viewed by 296

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)

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20 pages, 8314 KiB

Open AccessArticle

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 1 | Viewed by 794

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)

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16 pages, 6782 KiB

Open AccessArticle

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 1 | Viewed by 674

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)

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15 pages, 4865 KiB

Open AccessArticle

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

Viewed by 589

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)

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19 pages, 9107 KiB

Open AccessArticle

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

Viewed by 711

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)

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12 pages, 3712 KiB

Open AccessArticle

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 1096

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)

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23 pages, 4996 KiB

Open AccessArticle

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 4 | Viewed by 1259

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)

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15 pages, 5085 KiB

Open AccessArticle

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 1302

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

ρ_{d} / ρ_{c}

, 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

ρ_{d} / ρ_{c}

. 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

Δ ρ / ρ_{d}

. 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)

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