Condensation Mode Research Articles

Self-Stacked 1T-1H Layers in 6R-NbSeTe and the Emergence of Charge and Magnetic Correlations Due to Ligand Disorder.

The emergence of correlated phenomena arising from the combination of 1T and 1H van der Waals layers is the focus of intense research. Here, we synthesize a self-stacked 6R phase in NbSeTe, showing perfect alternating 1T and 1H layers that grow coherently along the c-direction, as revealed by scanning transmission electron microscopy. Angle-resolved photoemission spectroscopy shows a mixed contribution of the trigonal and octahedral Nb bands to the Fermi level. Diffuse scattering reveals temperature-independent short-range charge fluctuations with propagation vector qCO = (0.25 0), derived from the condensation of a longitudinal mode in the 1T layer, while the long-range charge density wave is quenched by ligand disorder. Magnetization measurements suggest the presence of an inhomogeneous, short-range magnetic order, further supported by the absence of a clear phase transition in the specific heat. These experimental analyses in combination with ab initio calculations indicate that the ground state of 6R-NbSeTe is described by a statistical distribution of short-range charge-modulated and spin-correlated regions driven by ligand disorder. Our results demonstrate how natural 1T-1H self-stacked bulk heterostructures can be used to engineer emergent phases of matter.

MATHEMATICAL MODELING OF THE AUTONOMOUS HEAT SUPPLY SYSTEM WITH TUBULAR GAS HEATERS IN BUILDING STRUCTURES WHEN OPERATING IN THE CONDENSATION MODE

Problem statement. The application of modern autonomous heat supply systems is one of the directions of reducing the consumption of natural energy resources. There are many different autonomous systems of heat supply of objects. One of the variants of such systems is the system with tubе gas heaters. A tube gas heater consists of a gas burner, a radiating tube and a fan. One of the technical solutions for such heat supply systems is a tubular heater located inside the building structure. Increase of the efficiency of gas equipment can be achieved by operating this equipment in the condensation mode. Therefore, the operation of tubular gas heaters in building structures in the condensation mode is quite interesting in terms of increasing the efficiency of utilisation of the thermal potential of gaseous fuel and ensuring its saving. For research and practical design of autonomous heat supply systems with gas tube heaters in building structures with regard to the condensation mode of operation it is essential to develop a mathematical model for calculating the thermal and hydraulic modes of the system. The purpose of the article is to develop a mathematical model of an autonomous heat supply system with tubular gas heaters in building structures when operating in the condensation mode. Conclusion. The mathematical model of hydraulic and thermal modes of autonomous heat supply system with tubular gas heaters in building structures when operating in the condensation mode was developed. It is presented in the form of differential equations. The model is based on the equations of conservation of mass, motion and energy for the gas-air mixture inside the canal in two-phase flow, the equation of heat transfer inside the building structure, the equation of heat transfer from the external surface of the heater to the environment. The mathematical model of hydraulic and thermal modes of autonomous heat supply system with tubular gas heaters in building structures when operating in the condensation mode will be used to calculate and design such systems.

First‐Principles Investigations of the Structural Phases of Low‐Spin State of BiCoO3

Herein, from first‐principles calculations, the phase diagram of the low‐spin (LS) state of BiCoO3 is scrutinized. The phonon‐dispersion curves of the cubic phase are analyzed to identify all the possible unstable modes and assessed the energy gain of the resulted distorted phases. In the findings, the presence of similar phases is revealed in both LS and high‐spin (HS) states, including ferroelectric and octahedra rotations distortions. However, the relative energy ordering of these phases differs significantly between the two states. Notably, the energy gain from mode condensation is considerably less pronounced in the LS case compared to HS state. Furthermore, it is identified that the common Pnma phase is the ground state of the LS state of BiCoC3, closely followed by the Imma octahedra rotation phase and the R3c ferroelectric phase, hence, different from the P4mm ferroelectric ground state of the HS state.

Neural network for predicting operating modes and calculating energy characteristics of steam turbine plants

The article describes the results of work on the creation of neural networks calculating the technical and economic parameters of all possible modes of operation of a thermal turbine unit with a steam turbine of type PT-60-130/13. In accordance with the objectives set, recommendations for the preparation of training data samples are formulated. The input and output parameters of the condensing and heating modes of operation of the steam turbine are determined. The results of research on determining the most optimal architecture of neural networks for calculating the energy characteristics of steam turbine plants of the heating type are presented. The results of calculations of the mean squared errors of neural network predictions from the results of calculations performed using a verified object-oriented model of a PT-60-130/13 turbine unit are tabulated.Graphs of the dependence of the specific heat consumption for the generation of electrical energy on the power of a PT-60-130/13 turbine unit for condensation and heating modes of operation using neural networks are plotted. The conclusion is formulated about the possibility of using neural networks for the development of energy characteristics and regulatory documentation on fuel use of equipment of thermal power plants.

Numerical challenges of CFD simulations of two-phase injectors working in the direct contact condensation mode

Numerical challenges of CFD simulations of two-phase injectors working in the direct contact condensation mode

Self-supervised learning of shedding droplet dynamics during steam condensation

Knowledge of condensate shedding droplet dynamics provides important information for the characterization of two-phase heat and mass transfer phenomena. Detecting and segmenting the droplets during shedding requires considerable time and effort if performed manually. Here, we developed a self-supervised deep learning model for segmenting shedding droplets from a variety of dropwise and filmwise condensing surfaces. The model eliminates the need for image annotation by humans in the training step and, therefore, reduces labor significantly. The trained model achieved an average accuracy greater than 0.9 on a new unseen test dataset. After extracting the shedding droplet size and speed, we developed a data-driven model for shedding droplet dynamics based on condensation heat flux and surface properties such as wettability and tube diameter. Our results demonstrate that condensate droplet departure size is both heat flux and tube size dependent and follows different trends based on the condensation mode. The results of this work provide an annotation-free methodology for falling droplet segmentation as well as a statistical understanding of droplet dynamics during condensation.

Self-similar evolution of wave turbulence in Gross-Pitaevskii system.

We study the universal nonstationary evolution of wave turbulence (WT) in Bose-Einstein condensates (BECs). Their temporal evolution can exhibit different kinds of self-similar behavior corresponding to a large-time asymptotic of the system or to a finite-time blowup. We identify self-similar regimes in BECs by numerically simulating the forced and unforced Gross-Pitaevskii equation(GPE) and the associated wave kinetic equation(WKE) for the direct and inverse cascades, respectively. In both the GPE and the WKE simulations for the direct cascade, we observe the first-kind self-similarity that is fully determined by energy conservation. For the inverse cascade evolution, we verify the existence of a self-similar evolution of the second kind describing self-accelerating dynamics of the spectrum leading to blowup at the zero mode (condensate) at a finite time. We believe that the universal self-similar spectra found in the present paper are as important and relevant for understanding the BEC turbulence in past and future experiments as the commonly studied stationary Kolmogorov-Zakharov (KZ) spectra.

Preliminary Design of a Cryogenic System with GM Cryocooler for Testing the Hydrogen Condensers of the Distillation Columns

The Experimental Pilot Plant for Tritium and Duterium Separation has been designed and built at the Rm. Valcea National Research and Development Institute for Cryogenics and Isotopic Technologies to separate deuterium and tritium from deuterated and tritiated water based on two combined processes: catalytic isotope exchange and cryogenic distillation. For this, additional experimental stands were developed for testing different components of the columns, such as the cold box, heat exchangers, condensers, and boilers. This paper presents the design of a new generation of fin condensers that avoids film condensation and allows the dropwise condensation mode. A small-scale cryogenic system equipped with a hydrogen liquefaction unit is presented as an alternative for condenser conductivity testing. The condenser is fixed on a hydrogen tank that is protected by a radiation shield and mounted inside a vacuum chamber. The proposed method is to continuously liquefy hydrogen using a two-stage Gifford McMahon 4K cycle cryocooler. A method for estimating the liquefaction rate was proposed and confirmed by the test results.

Size Distribution and Secondary Formation of Particulate Organic Nitrates in Winter in a Coastal Area

Understanding the size distribution, variation patterns, and potential formation mechanisms of particulate organic nitrates (PONs) is crucial for assessing their influences on atmospheric chemistry, air quality, and the regional climate. This study investigates PONs in the coastal atmosphere of Qingdao, China by collecting size-resolved particulate matter samples and analyzing six types of organic nitrates, namely pinene keto nitrate (PKN229), monoterpene hydroxyl nitrate (MHN215), monoterpene dicarbonyl nitrate (MDCN247), oleic acid hydroxyl nitrate (OAHN361), oleic acid keto nitrate (OAKN359), and pinene sulfate organic nitrate (PSON295), using ultrahigh-performance liquid chromatography(mass spectrometry). The mean total concentration of organic nitrates in fine particles reaches 677 ng m−3. The predominant compound is MHN215, followed by PKN229 and MDCN247. All six organic nitrates exhibited distinct concentration peaks in the droplet mode, with MDCN247 and OAHN361 showing a minor peak in the condensation mode. In addition, an apparent concentration peak is observed in the coarse mode for OAKN359. Comparative analyses under various conditions highlight the significant influences of primary emissions and secondary formation processes on the abundance and size distribution of organic nitrates. For instance, both firework displays during festivals and high NOx emissions from fuel combustion significantly increase the concentrations of condensation-mode organic nitrates, whereas dust particles enhanced the heterogeneous formation of coarse-mode particles. Furthermore, the high humidity of the coastal area promotes aqueous formation in droplet-mode particles.

Dynamic melting and condensation of topological dislocation modes

Dynamic melting and condensation of topological dislocation modes

Size‐Dependent Nighttime Formation of Particulate Secondary Organic Nitrates in Urban Air

AbstractParticulate secondary organic nitrates play a key role in understanding secondary organic aerosol production, ozone formation, and the atmospheric nitrogen cycle. However, the formation of particulate secondary organic nitrates in ambient air remains poorly understood. In this study, the nighttime formation processes of particulate secondary organic nitrates were investigated based on size‐resolved aerosols measured in urban air of China with a soot particle long‐time‐of‐flight aerosol mass spectrometer. The results show a bimodal size distribution of particulate secondary organic nitrates, peaking at ∼350 nm in condensation mode (100–400 nm) and ∼750 nm in droplet mode (400–2,500 nm), respectively. The nighttime formation processes of particulate secondary organic nitrates in the two size modes were respectively governed by temperature‐dependent condensation and aqueous‐phase processing. In particular, the mass concentration of particulate secondary organic nitrates in condensation mode was positively correlated with nitrate radical production and negatively correlated with temperature, suggesting that the formation processes were associated with the gas‐particle conversion of nitrate radical oxidation products. In contrast, the enhanced particulate secondary organic nitrates in droplet mode were predominantly contributed by aqueous‐phase processing, as indicated by the strong positive correlation with aerosol liquid water content and typical fragment ions from aqueous processing products (r = 0.52–0.59, P < 0.01). Our results highlight the potential of a size‐dependent mechanism to elucidate the formation processes of particulate secondary organic nitrates.

Condensation mode transition and droplet jumping on microstructured surface

Condensation enhancement on the micropillar structured surfaces is studied using a three-dimensional lattice Boltzmann model, and the optimal micropillar configuration is assessed. The impacts brought by varying micropillar geometric parameters on heat transfer and droplet dynamics during dropwise-to-filmwise transition are explored. Increasing micropillar width and spacing or decreasing height accelerates nucleation and improves nucleation density in the dropwise condensation stage, while radial contraction of the liquid film is hindered and the heat transfer area is increased in the filmwise condensation stage. Compared with its plain competitor, the maximum number of the isolated droplets is increased by 525%, the nucleation time is advanced by 57.1% and the heat flux is increased by 187.4% on the optimal micropillar surface. The entire condensation process spanning over nucleation, coalescence and jumping of multiple condensate droplets on the micropillar surface is realized using the present three-dimensional lattice Boltzmann model for the first time. The effects of height and spacing of micropillar arrays on jumping height and velocity are analyzed. The results show that the micropillar height poses little effect on the jumping height and velocity when the micropillar spacing is 0.1. When the micropillar spacing is 0.15, the jumping height and velocity first increase but then decrease with the increase of the micropillar height. Finally, the condensation heat transfer mechanism under different subcooling on the hierarchical surface is analyzed in detail.

Chemicals-CO2 mechanisms of inhibiting steam heat transfer and enhancing oil film strip: Steam flow through the wall-adhering oil film surface in porous medium

The CO2 and Sodium Dodecyl Sulfate (SDS) assisted steam flooding technology was an effective approach addressed the persistent issues that have hindered the stable development of high-viscosity cold oil through steam injection. However, in the process of steam flow through porous media, the synergistic influence of the oil film adsorbed in near wellbore porous media, and the CO2-SDS on steam heat transfer has not been investigated. Steam heat transfer is the key factors affecting heavy oil recovery. The primary objective of this study was to research the effect of CO2-SDS on steam heat transfer and oil film stripping by designing experiments. The study results demonstrated that in the initial stage of displacement, the heat transfer resistance between the steam and the porous medium was increased by the oil film adsorbed in near wellbore area. In additional, the condensation mode of the steam was altered from bead condensing to film condensing by the composite thermal fluid flooding, preventing the steam heat dissipation near wellbore area and transferring more thermal to the long-distance area. At the later stage of displacement, the interfacial tension between oil-water and oil-gas was reduced by CO2-SDS, improving the fluidity of oil and providing the seepage channel for steam, and increasing the steam thermal sweep range. Compared to the sandpack experiment of steam flooding, the temperature at the output end of the sandpack model increased from 69.8 °C to 88.7 °C, indicating an expansion of the steam heat sweep range and successful long-distance heat transfer during composite thermal fluid flooding. In the process of composite thermal fluid flooding, the maximum displacement pressure difference increased from 2.28 MPa to 3.07 MPa, and the maximum oil recovery rate increased from 2.48 g/mL to 2.81 g/mL. The peak of the high production period was raised, resulting in a 40.97% to 51.86% increase in recovery rates.

Modeling analysis of non-azeotropic and immiscible binary mixed vapors condensation under natural convection

A calculation model describing the condensation heat and mass transfer process of non-azeotropic immiscible binary mixed vapors on the vertical wall under natural convection conditions was developed in this study. The model includes the two possible condensation modes of mixed vapors on the vertical wall as well as the conversion conditions between them. Cyclohexane and water were used as non-azeotropic immiscible mixtures. The reliability of the model was verified first, then the influence of vapor mass concentration and wall subcooling on the condensation mode and heat and mass transfer of the mixed vapors were analyzed. The results showed that the maximum deviation between the model results and the experimental results was less than 21%, confirming that the model was reliable. When the mixed vapors mass concentration was nearly eutectic or the wall subcooling was large, the condensation Mode B (Co-condensation) was more likely to occur than Mode A (Single condensation) due to the decrease in vapor-liquid interface temperature. The condensation mode may change from B to A as the wall length increased along the gravity direction of the condensation wall, and the condensation heat transfer coefficient and mass flux decreased. The thermal resistance of the vapor and liquid phases during condensation was also calculated. In Mode A, regulation of the thermal resistance of the vapor-liquid two phases can be achieved by adjusting the vertical length of the condensation wall and the vapor mass concentration. Condensation Mode B can only be realized by adjusting the wall subcooling. The results of this work may provide a workable reference for condensation heat transfer and enhancement of non-azeotropic immiscible mixed vapors in industrial environments.

Enhancement of Dropwise Condensation Heat Transfer through a Sprayable Superhydrophobic Coating.

Improving the shedding rate of condensed droplets has many applications in industries and daily problems, including increasing heat transfer and self-cleaning properties. One way to achieve this goal is by enhancement of the wetting properties of surfaces. In this research, the hierarchical superhydrophobic coating over aluminum has been applied using a relatively cost-effective method, spraying, which is also applicable to any metal surface used as a condenser. According to the results obtained from the experimental tests, the fabricated surface is highly superhydrophobic, with a contact angle of 158° and contact angle hysteresis of less than 5°. The results show that the presented surface increases the heat transfer coefficient by 20.6% at the subcooling temperature of 25.5 °C when the surface temperature and relative humidity are 70 °C and 98%, respectively. In addition, this coated surface showed great potential at lower surface temperatures by increasing the water condensation rate as much as 50.5% at the subcooling temperature of 12 °C, when the surface temperature and relative humidity are 11.25 °C and 70%, respectively. Therefore, it is found that for the fabricated superhydrophobic paint in the present study, the effectiveness of the dropwise condensation mode profoundly depends on surface temperatures besides subcooling temperatures. In other words, a surface with lower temperatures shows better performance for the same subcooling temperatures. In addition, various types of durability tests are carried out. The results reveal that this coating has good durability against high surface temperatures, submerged conditions for 30 days, imposing hot steam for 150 h, corrosion, and organic solvents. Hence, it is suitable for industrial applications.

Lubricant-infused iron palmitate surfaces with high durability and stable condensation heat transfer

Slippery liquid-infused porous surfaces are vulnerable to lubricant depletion caused by three major factors encompassing, the evaporation, cloaking, and shearing. Herein, lubricant-infused iron palmitate surfaces (LI-IPSs) are presented addressing the challenges of (1) evaporation-driven lubricant depletion enabled by the immensely clustered micro-/nano-structures of iron palmitate surface (IPS), (2) completely suppressing the wetting ridge even with miscible water-oil combinations enabled by only the handful uptake of oil by IPS. The apparent contact angle θa and sliding angle α of water on LI-IPSs are 98° ± 2° and 3° ± 1°, respectively. Under evaporation-driven lubricant depletion analysis, the shelf-durability of LI-IPSs has been found to last for 10 days in partially open environment at the ambient temperature (25 °C). The heat fluxes and condensate fluxes have been determined. The highest condensate flux on LI-IPSs (14 kgh−1 m−2) is ascribed to the dropwise condensation mode with efficient droplet dynamics. However, the service durability of LI-IPSs has lasted only for 50 ± 5 min under rigorous condensation, which is further addressed by developing a LI-IPS prototype. Based on the excellent wicking capability of IPS, LI-IPS prototype is capable of maintaining the dropwise condensation unless the oil is available in the oil tub. The LI-IPS prototype has been subjected to open environment at ambient temperature for 168 h, and even after that, the stable dropwise condensation has been achieved with the same range of droplet speed as had been observed in the first hour. Meantime, the high condensation heat fluxes at various subcooling temperatures are obtained, justifying the promising ability of LI-IPS.

Temperature- and pressure-induced structural transformations in NbN: A first-principles study

Structural transformations at high temperatures and pressures, elastic moduli, hardness, fracture toughness, Debye temperature, stress-shear strain relations, electronic structure, and lattice dynamics in the experimentaly observed NaCl–NbN (δ, Fm-3m), anti-TiP-NbN (ε, P63/mmc), anti-NiAs-NbN (δ′, P63/mmc), WC-NbN (η, P-6m2), and TiP–NbN (ε′, P63/mmc) phases and hypothetical new tP4-129 (P4/nmm), hP6-189 (P-62m), oP8-25 (Pmm2) and cP2-221 (Pm-3m) structures are studied by using first-principles calculations and molecular dynamics simulations. The possible mechanisms of the phase transitions between these structures based on the condensation of a certain phonon mode with subsequent spontaneous strains are suggested. The ε, η and δ′, and cP2-221 structures are brittle materials and exhibit highest shear moduli (200.5–216.8 GPa), Young moduli (492.4–528.8 GPa), Vickers hardness (23.9–27.1 GPa), fracture toughness (4.54–4.72 MPa m1/2), and Debye temperatures (730.5–767.0 K). It is found that the main slip systems should be (0001)<10-10> for ε and η, and both (0001)<10-10> and (0001)<-12-10> for δ’.

Ways to increase the maneuverability characteristics of the CCGT when operating in load control modes (for example, CCGT-450)

THE PURPOSE The article is devoted to the analysis of the problems that arise during the operation of heating CCGTs of the type CCGT-450 at reduced loads with their participation in the regulation of electrical and thermal loads. The description of the main limitations of the adjustment range of gas turbines, and the maneuverability characteristics of the CCGT, an analysis of some existing technical proposals for expanding the adjustment range is given. It is shown that the application of these proposals, expanding the boundaries of the adjustment range in small quantities, does not solve the problem as a whole. The description and research results of the proposed new technical solutions to expand the adjustment range and maneuverability characteristics of the CCGT - 450 are given.METHODS. When solving the tasks, the analysis, comparison and generalization of energy characteristics, modeling of modes were carried out.RESULTS. It is shown that: the use of methods for converting part of the central heating system and the central heating system as a whole of the T-125/150 steam turbine into a low-steam mode together with bypass steam distribution will expand the adjustment range to a level comparable to the adjustment range of condensing power units on gas-fuel oil;. when shutting down the CCGT-450 operating in condensation mode and when operating it in the GTU-CHP mode during periods of night failure of the electrical load, the conversion of the steam turbine to motor mode significantly improves the maneuverability and reliability characteristics of the steam turbine and the CCGT as a whole. conclusion. The use of methods for transferring part of the central heating system and central heating system as a whole and bypass steam distribution expand the adjustment range of the CCGT-450, respectively, by 7.8, 10.1 and 16.0% of the rated power; When the CCGT-450 is operating in condensation mode when the CCGT is stopped and when it is operating in the GTU-CHP mode during periods of night failure of the electric load, the steam turbine is transferred the MR significantly improves the maneuverability and reliability characteristics of the steam turbine by reducing the duration of start-up and loading of the steam turbine by 40 and 14.5 minutes, respectively, reducing starting fuel losses, eliminating temperature fluctuations of steam and metal of the steam intake organs of the central pump and the control stage during start-up;

Review on the Theories and Applications of Dynamic Condensation and Component Mode Synthesis Methods in Solving FEM-based Structural Dynamics

Review on the Theories and Applications of Dynamic Condensation and Component Mode Synthesis Methods in Solving FEM-based Structural Dynamics

Experimental study for enhancing condensation on large-scale surface using hybrid hydrophilic-hydrophobic patterns

Improving condensation on large-scale surfaces promotes a wide range of manufacturing fields. To take advantage of both dropwise and filmwise condensation properties, both hydrophobic and hydrophilic surfaces can be developed on one hybrid surface. In this paper, experimental studies were performed on vapor condensation over a flat vertical plate. Three different surfaces were utilized: hydrophilic (aluminum), hydrophobic (coated), and hybrid surfaces with distinctive hydrophilic and hydrophobic patterns. The effect of the volume flow rate of the cooling water was investigated from 5 L/min to 15 L/min. For the hybrid surfaces, three types of patterns were studied: separated holes of hydrophilic patterns (the island) with two different diameters, arrow pattern, and tree pattern. According to the results, the heat transfer rate varied as the surface conditions changed. For the aluminum surface that resulted in filmwise condensation mode, the observed heat transfer rate was less than that of the coated surface, which showed a combination of filmwise and dropwise condensation modes. For the hybrid surfaces, the observed heat transfer rate was higher than that of the coated surface. From all the surfaces in this study, the highest heat transfer rate was for the 2.0 mm diameter island pattern.