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- Study on the instability of FC-72 vapor–liquid interface in a
rectangular channel under different gravity conditions-
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Abstract: Abstract This paper investigates the instability of FC-72 vapor–liquid interface in a rectangular channel under different gravity conditions employing short-term microgravity experimental systems designed based on the drop tower platform. Visual observations and numerical simulations were conducted to monitor the behavior of vapor–liquid interface. The study reveals significant fluctuations, with liquid climbing along both sides of the channel after drop cabin releases. Higher initial liquid levels result in increased maximum liquid phase heights and decreased minimum values, with noticeable fluctuations. In microgravity, the maximum height gradually rises with significant fluctuations, while minimum height remains relatively stable. Increasing contact angle leads to reduced variation in maximum and minimum heights, with a distinctive upward slope of vapor–liquid interface observed at a 90° contact angle. The temporal evolution of vapor–liquid interface observed in simulations closely aligns with experimental findings. This study highlights the importance of considering various factors in designing experiments involving fluid systems with low surface tension, particularly in aerospace applications, and calls for further research to develop more sophisticated models and techniques for understanding and controlling vapor–liquid interface instability. PubDate: 2024-08-22
- Analytical Analysis of the Effects of the Porosity Distribution on
Liquid–Water Management in the Cathode of a Polymer Electrolyte Membrane Fuel Cell-
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Abstract: Abstract Proton Exchange Membrane Fuel Cell (PEMFC) technology has been receiving more attention recently and can play a more expanded role in space missions with low gravity or microgravity. The liquid water generation in the Gas Diffusion Layer (GDL) of a Proton Exchange Membrane Fuel Cell (PEMFC) increases the resistance to oxygen flow toward the catalyst layer. Water flooding inside the GDL can affect the PEMFC performance especially at higher current densities. Therefore, a good understanding of the effect of liquid water amount in the GDL is crucial to water management and, subsequently, to the performance of the fuel cell. The purpose of the present study is to investigate the effect of the microstructure characteristics of the GDL on the water flooding and liquid water distribution inside the GDL. A one-dimensional theoretical model has been developed. Results indicate that the porosity gradient has a significant effect on the liquid water saturation and the performance of the PEM fuel cell. PubDate: 2024-08-19
- Exploring Enhanced Heat Transfer in a Ventilated Cavity through Thermal
Vibration-Induced Convection: Under Microgravity and Terrestrial Conditions-
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Abstract: Abstract An integration of both passive and active techniques to enhance the heat exchange has emerged as a promising research area over the past few decades. Our present investigation focuses on the heat exchange due to thermal convection in a square cavity driven by a channel, utilizing ternary hybrid nanofluid. The governing equations were derived from the averaged formulations describing thermal vibrational convection, illustrated using the vorticity of the mean velocity and stream functions relevant to both the mean and fluctuating flows. The influence of vibration on the system is quantified using a dimensionless vibration factor, denoted as Gershuni number (Gs), which is proportional to the ratio of the mean vibrational buoyancy force to the product of momentum and thermal diffusivities. All computations were conducted with fixed values of the Prandtl number (Pr = 6.1) and Reynolds number (Re = 100). The influence of physical parameters, including the Grashof number ( \(10^3 \le Gr \le 10^6\) ), Gershuni number ( \(10^3 \le Gs \le 10^6\) ), and volume fraction of nanomaterials ( \(0\% \le \Phi \le 4\%\) ), particularly under two scenarios: microgravity ( \(Gr= 0\) ) and terrestrial conditions, on the streamlines for both the mean and fluctuating flows, isotherms, and mean Nusselt number are discussed graphically. Numerical results indicate that an increase of Grashof number boosts heat exchange by 250% under buoyancy effects. Elevating nanomaterial volume fractions enhances thermal conductivity, increasing heat exchange by 30%. However, heightened thermal vibration reduces heat exchange. PubDate: 2024-08-16
- Effect of Simulated Microgravity on Artificial Single Cell Membrane
Mechanics-
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Abstract: Abstract The study of cell membrane structures under microgravity is crucial for understanding the inherent physiological and adaptive mechanisms relevant to overcoming challenges in human space travel and gaining deeper insight into the membrane-protein interactions at reduced gravity. However, the membrane dynamics under microgravity conditions is not unraveled yet. Moreover, the complexity of cells poses significant challenges when investigating the effects of microgravity on individual components, including cell membranes. Giant Unilamellar Vesicles (GUVs) serve as valuable cell-mimicking models and act as artificial cells, providing insights into the biophysics of membrane architecture. Herein, we have elucidated the membrane dynamics of artificial cells under simulated microgravity conditions. GUVs were synthesized in the size range of 20 ± 2.1 μm and their morphological changes were examined under simulated microgravity conditions using a random positioning machine. We observed that the well-defined spherical GUVs were transfigured and deformed into elongated structures under microgravity conditions. The membrane fluidity of GUVs increased sevenfold under microgravity conditions compared to GUVs under normal gravity conditions at 48 h. It is also noted that there is a reduction in the membrane microviscosity. The study sheds light on the membrane mechanics under microgravity conditions and contributes valuable insights to the broader understanding of membrane responses to microgravity and its implications for space exploration and biomedical applications. PubDate: 2024-08-13
- Influence of Microgravity on Cerebrovascular Complications: Exploring
Molecular Manifestation and Promising Countermeasures-
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Abstract: With NASA and other space agencies planning for longer-duration spaceflights, such as missions to Mars, and the rise in space tourism, it is crucial to comprehend the impact of the space environment on human health. However, there is a lack of information on how spaceflight impacts cerebrovascular health. The absence of gravitational force negatively affected various physiological functions in astronauts, especially posing risks to the cerebrovascular system. Exposure to microgravity leads to fluid changes that impact cardiac function, arterial pressure, and cerebrovascular structural changes that may be the cause of cognitive impairment. Numerous experiments have simulated microgravity to study the damage caused by prolonged spaceflight and reported similar findings. Understanding the effect of simulated microgravity on cerebrovascular structure and function has important implications for cerebrovascular health on Earth and in space. Simulated microgravity has been shown to induce endothelial dysfunction, altering nitric oxide (NO) synthesis pathways and increasing oxidative stress. Dysregulation of the Renin-Angiotensin system, NADPH oxidases, K+ Channels, and L-type Ca2+ Channels contributes to vascular dysfunction, while mitochondrial complexes expression and Ca2+ concentration exacerbate oxidative stress. This knowledge is essential for creating effective countermeasures to protect astronaut health during extended space missions. Therapeutic interventions targeting mitochondrial ROS and NADPH oxidases showed promise in mitigating these effects. This review article delves into the significant challenges posed by extended spaceflight, focusing on the cerebrovascular systems. It also provides a comprehensive understanding of molecular mechanisms associated with microgravity-induced cerebrovascular dysfunction and potential therapeutic interventions, paving the way for safer and more effective space travel. Graphical  PubDate: 2024-08-07
- Critical Heat Flux and Bubble Dynamics on Mixed Wetting Surfaces
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Abstract: Abstract To study the effect of micro-structured surface with wedge-shaped channel on pool boiling heat transfer performance of FC-72, four kinds of mixed wettability surfaces with area ratio of the micro-pillar region to the smooth channel region of approximately 1:1 were fabricated in this study (the surfaces were denoted as the Multi tip surface, Multi star surface, Less tip surface and Less star surface). The experimental results indicated that the CHF increases with the increase of liquid subcooling. The structural surface parameters will affect the bubble dynamics behavior and thus affect CHF. The effect of capillary wick suction on the mixed wetting surface first increases and then decreases. The capillary wick suction plays a significant role in the increase of CHF, and the capillary wick force on the Less tip surface with the best heat transfer performance is the largest. The Zuber model is modified by combining three factors to propose a critical heat flux model suitable for mixed wetting surfaces. With the increase of heat flux, the bubble detachment frequency decreases, the bubble detachment diameter increases and the nucleation site density basically shows exponential growth. Bubbles in the micro-pillar array region will be driven to slip onto the smooth channel due to energy difference and the bubbles in smooth channels will also migrate in the direction of wider smooth channels under the action of Laplace force. PubDate: 2024-07-17
- Effect of Forced Convection on the Combustion Chemistry of PMMA Spheres in
Microgravity-
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Abstract: Abstract The influence of the forced convection rate on the chemical structure of a polymethyl methacrylate (PMMA) flame in an oxidizer flow under microgravity conditions was studied using numerical modeling. Gas flow around a solid sphere was simulated using the full Navier–Stokes equations for a multicomponent mixture. A multistep chemical kinetic mechanism was considered in the gas phase. The heat transfer and radiation in both the condensed and gas phases were considered in the modeling. On the PMMA surface, the pyrolysis reaction leading to the transformation of fuel from the condensed phase to the gas phase is specified. The forced convection speed varied in the range from 3 to 20 cm/s. Analysis of CO2 concentration fields near the burning surface under microgravity conditions showed that the maximum CO2 concentration is observed in the downstream zone. The width of the flame zone and its chemical structure depend on the intensity of forced convection. The width of the flame against the flow decreases, and the maximum CO concentration increases as the forced convection rate increases. Analysis of the rates of fuel consumption reactions showed that at a low convection speed (vst=3 cm/s), the reaction with the H radical, which has the highest diffusion coefficient, plays a crucial role in MMA oxidation. PubDate: 2024-07-13
- Effect of Interfacial Heat Transfer on Hydrothermal Wave Propagation of
Nanofluid Thermocapillary Convection in Rectangular Cavity-
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Abstract: Abstract For surface tension driven flow, interfacial heat transfer can alter the flow regime and its transition condition. This paper investigates the influence of interfacial heat transfer on critical transition and hydrothermal wave propagation of nanofluid thermocapillary convection for the first time, and three environment temperature conditions is considered, e.g. the cold-end temperature, the average temperature of the hot and cold-end, and a linear temperature distribution. The results indicate that, as nanoparticles volume fraction increases the critical Marangoni number decreases under various ambient temperature conditions, meanwhile, the fundamental frequency of the velocity oscillations exhibits a linear decrease, and the propagation angle and temperature fluctuation range of hydrothermal waves are decreased. Furthermore, for the three ambient temperature scenarios, the linear temperature distribution condition can amplify the propagation angle and temperature fluctuation range of hydrothermal waves. Consequently, the manipulation of both the nanoparticle volume fraction and ambient temperature condition provides a means to control the instability of nanofluid thermocapillary convection. PubDate: 2024-07-06
- Experimental Investigation of Composite Formation Flying Using
Disturbance-Free Payloads-
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Abstract: Abstract Precise formation control is increasingly demanded in high-resolution remote sensing formations, gravitational detection interferometers and distributed space telescopes. One composite formation flying method using disturbance-free payloads was previously proposed to enhance formation accuracy and payload stability. This method divided satellite formation into coarse formation using conventional satellite buses and fine formation using precise payloads. To verify the effectiveness of the proposed formation method and the payload stability performance, this paper develops an experimental system using two air-floating satellite prototypes. First, the experimental design is proposed and the experimental system model is established. Second, the experimental prototype development and system architecture are described in detail. Finally, the composite formation flying effectiveness is further demonstrated by coarse and fine formation control experiments. The experiment results indicate that the composite formation flying method effectively improves the formation accuracy for distributed payloads and isolates microvibrations from satellite buses to enhance payload stability. PubDate: 2024-07-02
- The Electro-Elastic Instability of Viscoelastic Fluid in a Microchannel
with Obstacles Under Heterogeneous Surface Potential-
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Abstract: Abstract In this paper, the Electro-elastic instability(EEI) of an Oldroyd-B fluids flow the microchannel with the obstacles and heterogenous surface charged is studied. The changes in fluid flow are presented by considering three different ranges of Weissenberg numbers(Wi), the expansion lengths \(\textrm{EL}\) , and the asymmetric potential distributions. Under the combined effects of heterogeneous surface potential and elastic stresses, not only the vortices but also lip vortices are generated near the obstacles. At lower Weissenberg numbers, the stable and symmetric flow field is observed. As Wi increases, it is worth noting that the flow field becomes unstable and chaotic due to the enhanced electro-elastic instability. But the asymmetry of the velocity diminishes as \(Wi>10\) . In addition, the presence of different vortex dynamics is observed as the Wi varies, such as the lip vortices, angular vortices, and oscillating lip vortices. Further, the flow of fluid at different expansion ratios is investigated. With the decrease of expansion lengths \(\textrm{EL}\) , the backflow and asymmetry are reduced, the lip vortex disappears and then the angular vortex appears. Finally, by increasing the upper zeta potential \((\zeta _{\textrm{w}})\) of the obstacles, the mixing efficiency is improved. The research results may be helpful to the electrodynamic transport of viscoelastic fluids in porous media and the analysis of micromixers for industrial applications. PubDate: 2024-07-02
- Numerical and Experimental Investigation of Heat Transfer in the Porous
Media of an Additively Manufactured Evaporator of a Two-Phase Mechanically Pumped Loop for Space Applications-
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Abstract: Abstract Two-phase pumped cooling systems are applied when it is required to maintain a very stable temperature for heat dissipation in a system. A novel additively manufactured evaporator for two-phase thermal control was developed at NASA Jet Propulsion Laboratory (JPL). The Two-Phase Mechanically Pumped Loop (2PMPL) allows to manage the heat transfer with much wider breadth of control authority compared to capillary-based systems, while alleviating the system's sensitivity to pressure drops. The focus of this work is the understanding and capturing the micro-scale evaporation occurring in the porous structure of the evaporator. The Boiling and Phase Change Heat Transfer Laboratory at the University of California, Los Angeles (UCLA) developed an all-encompassing numerical simulation tool to predict the operational thermal behavior of the evaporator considering the effect of the liquid-vapor interface at the wick-to-vapor boundary. The numerical model incorporated the behaviour of the liquid-vapor meniscus at particle level located along the evaporative boundary between the wick structure and the vapor chamber. The numerical model allowed to study the effect of different parameters, such as boundary conditions, geometry, wick and fluid properties. An experimental setup was built at UCLA in order to characterize the heat transfer within an additively manufactured porous sample fabricated at JPL and in particular its evaporative heat load under certain heat inputs. The experimental efforts served as validation for the numerical results and aided in the characterization of the transient phenomena, such as dry-out. PubDate: 2024-06-29
- Development of the Microbial Online Monitoring Module (MOMM) for the
Chinese Space Station-
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Abstract: Abstract The enclosed space environment demands sustainable environmental control systems. Space stations and interstellar missions, both need reliable environmental control and life support systems for crewed flights and long-term habitation. These long-duration space missions require monitoring for potential pathogens and microbial contamination, which is crucial for astronaut health and the reliable operation of space equipment. To meet this critical need, the China Space Station (CSS) is equipped with the Microbial Online Monitoring Module (MOMM), which integrates two methods for microbial detection, the first method involves cultivating microorganisms in culture dishes for observation, while the second method uses isothermal nucleic acid amplification and detection technology based on Loop-mediated Isothermal Amplification(LAMP). This equipment is applied in the microgravity environment of the space station to achieve rapid detection of microbial species and abundance in orbit. Hardware function validation tests and validation experiments of the sensitivity and shelf life of the reagents were conducted on the ground, and several full-process microbial detection experiments were carried out to ensure the function and feasibility of the MOMM. Subsequently, an experimental process of microbial cultivation and observation was successfully carried out on the CSS using air samples from the space station. The MOMM allows for early detection of microbes in orbit, contributing to implementing targeted biosecurity and maintenance measures. PubDate: 2024-06-27
- Mitigation of Force and Vibration Transmission by the Hifim Jump Sled
during Repeated Jumping in Microgravity-
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Abstract: Abstract High Frequency Impulse for Microgravity (HIFIm) is an exercise countermeasure that is designed to minimize force and vibration transmission to the spacecraft during exercise without the need for an additional VIS. The purpose of this study was to evaluate the effectiveness of HIFIm in mitigating force transmission in microgravity during parabolic flight. Force between HIFIm and the aircraft was measured using a custom-made arrangement of load cells during repeated jumping by two participants. Mean peak force transmission to the aircraft was 4.79 ± 0.68 N.kg− 1. In addition, the frequency spectra for the upper and lower fixations to the aircraft were within the envelope of what is permissible for an exercise countermeasure on Gateway. These data support the design concept of HIFIm and suggest that HIFIm could be installed in a space habitat with no, or minimal, additional VIS. Measuring the force and vibration transmission of exercise countermeasures in microgravity during parabolic flight is highly challenging due to the safety constraints of the experimental platform and the extreme changes in acceleration (from 0 to 1.8 g). The fact that this performance can be directly measured for HIFIm is a key advantage. The results presented here add to the mounting evidence that HIFIm is the future of exercise countermeasures. PubDate: 2024-06-24
- Research Trends on Astronaut Physical Training as Countermeasures: A
Bibliometric Analysis from Past 30 Years-
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Abstract: Abstract Astronauts are exposed to microgravity-induced health problems in spaceflight missions. Countermeasures and physical exercises have received increasing attention and its current research trends and landscapes warranted investigation. We conducted a comprehensive bibliometric analysis on astronaut training/countermeasures using the available data from the Web of Science Core Collection database from 1992 to 2022 to summarize the research trends and identify future directions. A total of 1,520 relevant articles were identified. Annual publications of the field have been increased over the years with the emergence of new and effective countermeasures. ‘Microgravity’ was the centered hotspot surrounded by the topics included ‘spaceflight’, ‘hind leg hanging’, ‘simulated microgravity’, and ‘simulated weightlessness’. The top countries that produced the most publications included United States (726 articles), Germany (129 articles), and France (84 articles). The United States played a dominant role in the collaboration network with other countries. Meanwhile, NASA from the United States led the global collaborations and dominated the literature. Future research trend might lie on the design of physical training exercises to tackle the potential health problems on osteoporosis, muscle atrophy, and abnormality on the nervous and cardiovascular system; and artificial/simulated gravity with interdisciplinary sports countermeasure research on physiology, brain science, biomechanics, and aerospace medicine. PubDate: 2024-06-21
- Study on Liquid Climbing Behavior During Filling Process in Tank Models
Aboard the Chinese Space Station-
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Abstract: Abstract Propellant tanks provide non-entrained propellant for thrusters of satellites, which plays an important role in space mission. And the fluid transfer efficiency of tanks is the key to supply non-entrained propellant. An experiment cabin containing two different scaled tank models are designed and experiments of liquid reorientation under microgravity are carried out in the Chinese Space Station. Experiment results present the high liquid transportation efficiency of the two kinds of propellant management devices. Finite element models of the two tank models are established and verified by simulation matching with experiments. Furthermore, methylhydrazine is adopted to carry out more simulation analysis by considering different liquid contact angles and surface tension, and numerical results show smaller liquid contact angle and bigger surface tension can increase liquid flow speed. This research can provide theory and data support for the design of plate type tanks. PubDate: 2024-06-19
- A Perspective Review of Droplets and Bubbles Formation in Microfluidics
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Abstract: Abstract Gas-liquid and liquid-liquid two-phase flow are widely used in chemical engineering, biomedical engineering and other fields such as separation, reaction, and mass transfer in microfluidic systems. Studying the formation methods of droplets and bubbles in microfluidics is of great significance to the application of microchemical technology. In this review, according to the methods of droplets and bubbles formation, the research progress and development trend of droplets and bubbles formation in microfluidics in recent years are reviewed. Formation methods are divided into passive methods and active methods according to whether external energy is required. Passive methods include T-junction, flow-focusing, co-flowing and step emulsification. Active methods include surface acoustic waves, DC/AC electric fields, magnetic fields, and thermal fields. Finally, this review points out the future direction of research on liquid droplets and bubbles. This review sheds new light on monodisperses, highly controllable droplets and bubbles formation and its applications. PubDate: 2024-06-13 DOI: 10.1007/s12217-024-10120-0
- Experimental Study of the Dynamics of Coating Flow on Fiber Array
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Abstract: Abstract The present paper investigated the dynamics of coating flow on array of cylindrical fibres. In the experiments, it is observed that there exist three distinct flow regimes when the fiber array is fully coated by liquid film, namely, regime ‘a’, ‘b’ and ‘c’. The flow regime ‘a’ is characterized by the formation of a streamwise uniform film; The flow regime ‘b’ and ‘c’ are in the form of traveling waves consisting of asymmetrical wavy structures and symmetrical beads, respectively. We conducted a comprehensive parametric study on the dynamics of the coating flow on fiber array, including the flow rate, fiber spacing and droplet amplitude, all of which serve as reliable indicators of different flow regimes. PubDate: 2024-06-07 DOI: 10.1007/s12217-024-10121-z
- Application of Multiple Scales Method to the Problem About Characteristics
of the Ionic Layer Near The Surface of Lithium Niobate Crystal in a Benzoic Acid Melt-
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Abstract: Abstract The authors present an analytical solution of equations describing the diffusion transfer and recombination of positive lithium ions and negative benzoate ions in benzoic acid after their injection from the surface of a protonated lithium niobate substrate. In the course of the solving one-dimensional stationary problem, the profiles of ions concentrations and electric potential distribution have obtained, corresponding to different values of governing parameters. The benzoate ions form thin boundary layer, while the ions of lithium completely fill considered region and have relatively uniform distribution. The comparison of analytical solution with numerical results permits to estimate the degree of the influence of electric field on the final distributions, which is formed due to the difference of ions concentrations. The expression, which determines the thickness of boundary layer, is obtained by the multiple scales method. PubDate: 2024-05-24 DOI: 10.1007/s12217-024-10113-z
- Auditory Go/NoGo Task in the Dry Immersion Model of Microgravity
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Abstract: Abstract The effects of a ground-based model of microgravity on executive functions (namely, inhibition) were investigated in this study. Volunteers participated in so-called dry immersion (DI), during which they spent 21 days in a water-filled tub in the supine position. During this period, they performed an auditory Go/NoGo task while multichannel EEG activity was recorded. The Go/NoGo task was performed one time outside of the DI and two times during the stay in the DI. ERPs were computed on correct NoGo and Go trials. While no behavioral deterioration of the Go/NoGo task was found during their stay in the DI, a significant difference was found in amplitudes between NoGo N2 ERP peaks before DI and during DI. The N2 peak was smaller on the 17th day of DI, indicating a potentially lower level of inhibitory control during simulated microgravity conditions. The amplitudes of the N1 and P3 peaks did not change significantly. The dry immersion procedure reproduces some of the important physiological factors of real space flights (support withdrawal, bodily liquid redistribution), thus our results hint at possible brain and behavioral alterations in real space flight that have so far been unnoticed. PubDate: 2024-05-18 DOI: 10.1007/s12217-024-10118-8
- Low Temperature n-Dodecane Droplet Combustion Experiments Aboard the
International Space Station-
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Abstract: Abstract This paper presents data from large, isolated n-dodecane droplets burning in microgravity on the International Space Station, along with preliminary comparisons with numerical and analytic predictions indicating general agreement in trends. The tests involved were primarily in air (a few in reduced oxygen) at ambient pressures ranging from 0.50 to 5.0 atm. After ignition, the droplets burn with a hot flame that extinguishes when the radiant energy loss causes the flame temperature to drop below the hot-flame-required value. The total flame radiative loss at extinction is nearly independent of pressure, while the peak flame diameter prior to hot-flame extinction decreases with increasing pressure. The maximum hot-flame temperature, inferred from fiber-support radiative emisssions, decreases with increasing pressure, and the hot flames become dimmer with increasing pressure. At 1.0 atm and below there is a prolonged period of coolflame burning that ends with cool-flame extinction at a finite droplet size; the cool-flame-extinction droplet diameter increases and the cool-flame burning rate decreases with decreasing ambient pressure. Above 1.25 atm warm-flame burning and hot-flame re-ignitions become prevalent. At 5.0 atm, there is no abrupt hot-flame extinction with transition to a cool flame; the flame gradually gets dimmer, and the flame temperature decreases over a much longer time, the transition between hot-flame and warm-flame burning becoming almost undiscernible. PubDate: 2024-05-13 DOI: 10.1007/s12217-024-10115-x
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