Droplet Formation Research Articles

Phosphorylation in the Ser/Arg-rich region of the nucleocapsid of SARS-CoV-2 regulates phase separation by inhibiting self-association of a distant helix

The nucleocapsid protein (N) of SARS-CoV-2 is essential for virus replication, genome packaging, evading host immunity, and virus maturation. N is a multidomain protein composed of an independently folded monomeric N-terminal domain that is the primary site for RNA binding, and a dimeric C-terminal domain that is essential for efficient phase separation and condensate formation with RNA. The domains are separated by a disordered Ser/Arg-rich region preceding a self-associating Leu-rich helix. Phosphorylation in the Ser/Arg region in infected cells decreases the viscosity of N:RNA condensates promoting viral replication and host immune evasion. The molecular level effect of phosphorylation, however, is missing from our current understanding. Using NMR spectroscopy and analytical ultracentrifugation we show that phosphorylation destabilizes the self-associating Leu-rich helix 30 amino acids distant from the phosphorylation site. NMR and gel shift assays demonstrate that RNA binding by the linker is dampened by phosphorylation, whereas RNA binding to the full-length protein is not significantly affected presumably due to retained strong interactions with the primary RNA binding domain. Introducing a switchable self-associating domain to replace the Leu-rich helix confirms the importance of linker self-association to droplet formation and suggests that phosphorylation not only increases solubility of the positively charged elongated Ser/Arg region as observed in other RNA binding proteins but can also inhibit self-association of the Leu-rich helix. These data highlight the effect of phosphorylation both at local sites and at a distant self-associating hydrophobic helix in regulating liquid-liquid phase separation of the entire protein.

Glucose Enhances Salinity-Driven Sea Spray Aerosol Production in Eastern Arctic Waters.

Sea spray aerosols (SSA) greatly affect the climate system by scattering solar radiation and acting as seeds for cloud droplet formation. The ecosystems in the Arctic Ocean are rapidly changing due to global warming, and the effects these changes have on the generation of SSA, and thereby clouds and fog formation in this region, are unknown. During the ship-based Arctic Century Expedition, we examined the dependency of forced SSA production on the biogeochemical characteristics of seawater using an on-board temperature-controlled aerosol generation chamber with a plunging jet system. Our results indicate that mainly seawater salinity and organic content influence the production and size distribution of SSA. However, we observed a 2-fold higher SSA production from waters with similar salinity collected north of 81°N compared to samples collected south of this latitude. This variability was not explained by phytoplankton and bacterial abundances or Chlorophyll-a concentration but by the presence of glucose in seawater. The synergic action of sea salt (essential component) and glucose or glucose-rich saccharides (enhancer) accounts for >80% of SSA predictability throughout the cruise. Our results suggest that besides wind speed and salinity, SSA production in Arctic waters is also affected by specific organics released by the microbiota.

Study of droplet formation in parallel flow focusing microchannel under electrostatic field control

To achieve efficient preparation of emulsion droplet, this paper uses a two-dimensional mathematical model coupled with the phase field model and the electrostatic field model to calculate the droplet formation in parallel flow focusing multichannel, and analyzed the effect of electric field strength on the droplet formation process. In addition, the effects of different capillary numbers and dispersed phase viscosity on droplet formation were also analyzed. The results show that the emulsion in the channel always generates droplet by dripping regime, and the droplet have the best monodispersity. Applying appropriate electric field strength can realize droplet formation frequency and size regulation. Increasing the dispersed phase viscosity increases the breakup thread of the dispersed phase fluid, and the droplet size obtained gradually decreases, the difference in droplet size can be slowed down by applying the electric field. Increasing the electrostatic force leads to a higher droplet deformation rate. The droplet shape classification is plotted using the capillary number (Ca) and electrostatic number (CaE). It is found that the droplet flow pattern in the channel remains a circle only when Ca and CaE are sufficiently small.

Differentiation of bone marrow mesenchymal stem cells into Leydig-like cells with testicular extract liquid in vitro.

Differentiation of Leydig cells plays a key role in male reproductive function. Bone marrow mesenchymal stem cells (BMSCs) have emerged as a potential cell source for generating Leydig-like cells due to their multipotent differentiation capacity and accessibility. This study aimed to investigate the morphological and genetic expression changes of BMSCs during differentiation into Leydig-like cells. Testicular extract liquid, which simulates the microenvironment in vivo, induced the third passage BMSCs differentiated into Leydig-like cells. Changes in cell morphology were observed by microscopy, the formation of lipid droplets of androgen precursor was identified by Oil Red Staining, and the expression of testicular specific genes 3β-HSD and SF-1 in testicular stromal cells was detected by RT-qPCR. BMSCs isolated from the bone marrow of Sprague-Dawley (SD) rats were cultured for 3 generations and identified as qualified BMSCs in terms of morphology and cell surface markers. After 14 days of induction with testicular tissue lysate, lipid droplets appeared in the cytoplasm of P3 BMSCs by Oil Red O staining. RT-qPCR detection was performed on BMSCs on the 3rd, 7th, 14th, and 21st day after induction. Relative expression levels of 3β-HSD mRNA significantly increased after 14 days of induction, while the relative expression of SF-1 mRNA increased after 14 days of induction but was not significant. BMSCs can differentiate into testicular interstitial cells with reserve androgen precursor lipid droplets after induction by testicular tissue lysate. The differentiation ability of BMSCs provides the potential to reconstruct the testicular microenvironment and is expected to fundamentally improve testicular function and provide new treatment options for abnormal spermatogenesis diseases.

Understanding droplet formation in T-shaped channels with magnetic field influence: A computational investigation

This study investigates the production of ferrofluid droplets in a T-junction geometry using the level set method and magnetic force manipulation in the three-dimensional. The analysis reveals key insights into droplet formation processes in four stages: entering, blocking, necking, and detachment. The results show that increasing the Capillary number leads to a significant decrease in volume for non-ferrofluid droplets. Application of a magnetic force enhances the balance of forces during droplet formation, directly impacting droplet volume. Moreover, increasing the magnetic Bond number substantially increases droplet volume, with a more pronounced effect at lower Capillary numbers. Modifying magnetic properties influences droplet volume, with doubling the magnetization results in a significant volume increase. Overall, magnetic forces emerge as a crucial control parameter for droplet volume in ferrofluid systems, offering potential applications in droplet-based technologies and microfluidic devices.

Body Fat Distribution Contributes to Defining the Relationship between Insulin Resistance and Obesity in Human Diseases.

The risk for metabolic and cardiovascular complications of obesity is defined by body fat distribution rather than global adiposity. Unlike subcutaneous fat, visceral fat (including hepatic steatosis) reflects insulin resistance and predicts type 2 diabetes and cardiovascular disease. In humans, available evidence indicates that the ability to store triglycerides in the subcutaneous adipose tissue reflects enhanced insulin sensitivity. Prospective studies document an association between larger subcutaneous fat mass at baseline and reduced incidence of impaired glucose tolerance. Case-control studies reveal an association between genetic predisposition to insulin resistance and a lower amount of subcutaneous adipose tissue. Human peroxisome proliferator-activated receptorgamma (PPAR-γ) promotes subcutaneous adipocyte differentiation and subcutaneous fat deposition, improving insulin resistance and reducing visceral fat. Thiazolidinediones reproduce the effects of PPAR-γ activation and therefore increase the amount of subcutaneous fat while enhancing insulin sensitivity and reducing visceral fat. Partial or virtually complete lack of adipose tissue (lipodystrophy) is associated with insulin resistance and its clinical manifestations, including essential hypertension, hypertriglyceridemia, reduced HDL-c, type 2 diabetes, cardiovascular disease, and kidney disease. Patients with Prader Willi syndrome manifest severe subcutaneous obesity without insulin resistance. The impaired ability to accumulate fat in the subcutaneous adipose tissue may be due to deficient triglyceride synthesis, inadequate formation of lipid droplets, or defective adipocyte differentiation. Lean and obese humans develop insulin resistance when the capacity to store fat in the subcutaneous adipose tissue is exhausted and deposition of triglycerides is no longer attainable at that location. Existing adipocytes become large and reflect the presence of insulin resistance.

High Fat Diet Induced Lipid Deposition and Perilipin 2 Expression in Mouse Liver Is Attenuated by Endothelin-1 Receptor A Blockade

Obesity is associated with dyslipidemia and lipid deposition into liver tissue. Circulating endothelin-1 (ET-1) is elevated in patients with obesity, and our lab has demonstrated that ET-1 is increased in liver of mice fed high fat (HFD). Interestingly, treatment with atrasentan attenuates reduces circulating triglycerides and free fatty acids and reduces lipid deposition into liver of mice fed HFD for 10 weeks; however, the mechanisms are not known. Perilipin 2 (Plin2) is a protein expressed in adipocytes and hepatocytes that is integral to lipid droplet formation by forming a coating around the droplet. We hypothesized that ET-1 receptor blockade reduces liver lipid deposition in obese mice by reducing Plin2 expression. To test this hypothesis, mice were fed normal (NMD) or HFD for 10 weeks and treated with the ET-1 receptor A (ETA) antagonist atrasentan for weeks 9-10. ET-1 receptor expression was significantly increased in HFD fed mice compared to NMD. As previously demonstrated, HFD fed mice had significantly higher liver triglyceride content compared to NMD controls, and this was attenuated in mice treated with atrasentan (ATR). As expected, Plin2 expression in liver tissue was significantly elevated in HFD mice compared to NMD (91.7±17.4 vs. 60.8±14.4 copies/pg RNA), an affect that was abolished in mice treated with atrasentan (NMD, 60.8±14.4; HFD, 91.7±17.4; NMD + ATR, 70.2±10.8; HFD + ATR, 26.3±5.8 copies/10pg RNA). These data suggest that ET-1 promotes lipid accumulation in liver of obese mice by reducing Plin2 expression. Funding: R01 DK124437, P30GM149404, and T32HL105324. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Essential oil of oregano (Origanum vulgare L.) reduces infection and proliferation of Toxoplasma gondii in BeWo cells with induction of autophagy and death of tachyzoites through a mechanism similar to necrosis.

Toxoplasmosis poses a global health threat, ranging from asymptomatic cases to severe, potentially fatal manifestations, especially in immunocompromised individuals and congenital transmission. Prior research suggests that oregano essential oil (OEO) exhibits diverse biological effects, including antiparasitic activity against Toxoplasma gondii. Given concerns about current treatments, exploring new compounds is important. This study was to assess the toxicity of OEO on BeWo cells and T. gondii tachyzoites, as well as to evaluate its effectiveness in in vitro infection models and determine its direct action on free tachyzoites. OEO toxicity on BeWo cells and T. gondii tachyzoites was assessed by MTT and trypan blue methods, determining cytotoxic concentration (CC50), inhibitory concentration (IC50), and selectivity index (SI). Infection and proliferation indices were analyzed. Direct assessments of the parasite included reactive oxygen species (ROS) levels, mitochondrial membrane potential, necrosis, and apoptosis, as well as electron microscopy. Oregano oil exhibited low cytotoxicity on BeWo cells (CC50: 114.8µg/mL ± 0.01) and reduced parasite viability (IC50 12.5 ± 0.06µg/mL), demonstrating 9.18 times greater selectivity for parasites than BeWo cells. OEO treatment significantly decreased intracellular proliferation in infected cells by 84% after 24h with 50μg/mL. Mechanistic investigations revealed increased ROS levels, mitochondrial depolarization, and lipid droplet formation, linked to autophagy induction and plasma membrane permeabilization. These alterations, observed through electron microscopy, suggested a necrotic process confirmed by propidium iodide labeling. OEO treatment demonstrated anti-T. gondii action through cellular and metabolic change while maintaining low toxicity to trophoblastic cells.

A patient-based iPSC-derived hepatocyte model of alcohol-associated cirrhosis reveals bioenergetic insights into disease pathogenesis.

Only ~20% of heavy drinkers develop alcohol cirrhosis (AC). While differences in metabolism, inflammation, signaling, microbiome signatures and genetic variations have been tied to the pathogenesis of AC, the key underlying mechanisms for this interindividual variability, remain to be fully elucidated. Induced pluripotent stem cell-derived hepatocytes (iHLCs) from patients with AC and healthy controls differ transcriptomically, bioenergetically and histologically. They include a greater number of lipid droplets (LDs) and LD-associated mitochondria compared to control cells. These pre-pathologic indicators are effectively reversed by Aramchol, an inhibitor of stearoyl-CoA desaturase. Bioenergetically, AC iHLCs have lower spare capacity, slower ATP production and their mitochondrial fuel flexibility towards fatty acids and glutamate is weakened. MARC1 and PNPLA3, genes implicated by GWAS in alcohol cirrhosis, show to correlate with lipid droplet-associated and mitochondria-mediated oxidative damage in AC iHLCs. Knockdown of PNPLA3 expression exacerbates mitochondrial deficits and leads to lipid droplets alterations. These findings suggest that differences in mitochondrial bioenergetics and lipid droplet formation are intrinsic to AC hepatocytes and can play a role in its pathogenesis.

Abstract 2073: StarD4 Is Required For Efficient Clearance Of Extracellular Free Cholesterol Generated From Digestive Exophagy Of Aggregated Low-density Lipoprotein.

In the development of atherosclerotic plaques, macrophages infiltrate the intima of the aortic wall to digest modified lipoproteins. Over time, these macrophages become overloaded with lipids and become plaque-associated foam cells. Most modified lipoproteins are aggregated and cross-linked to the extracellular matrix of the vessel wall, which prevents them from being phagocytosed by macrophages. Our lab has described how macrophages catabolize aggregated LDL extracellularly in a process termed digestive exophagy. Macrophage forms a tightly sealed, acidified extracellular compartment around agLDL that is stabilized by F-actin. Lysosomes are secreted into this extracellular compartment, allowing lysosomal acid lipase to catabolize cholesteryl esters in the core of agLDL to free cholesterol. However, it remains unclear how the extracellular free cholesterol is transported into macrophages for lipid droplet formation. Here, we identify the cholesterol transport protein StarD4 as a major player in the intracellular movement of free cholesterol released by digestive exophagy. We show that StarD4 knockout bone marrow-derived macrophages have delayed onset in foam cell formation when encountering agLDL. However, no difference is observed when StarD4 knockout macrophages are treated with monomeric acetylated LDL, suggesting the effect of StarD4 is specific to cholesterol delivered to the plasma membrane. Moreover, loss of StarD4 does not alter the rate of digestive exophagy, and no difference in lysosome exocytosis is observed between StarD4 knockout and wildtype macrophages. Therefore, our results indicate that StarD4 mediated plasma membrane to ER cholesterol transport is a critical step in digestive exophagy of agLDL. Loss of StarD4 can delay the onset of foam cell formation, which may provide insight into novel therapeutic strategies for atherosclerosis.

Explainable machine learning for the regulatory environment: A case study in micro-droplet printing

Micro-droplet printing remains an invaluable tool for the additive manufacturing industry due to its versatility, efficiency and cost-effectiveness. The design and deployment of a disposable micro-droplet dispenser seeks to facilitate a quick and easy way to alternate between different printing materials (such as ink, metals, bio-materials, pharmaceuticals, etc.) without the need for thorough cleaning or separate delivery systems. While this works well in principle, in practice achieving consistent performance between dispensers can prove challenging. This paper aims to tackle this issue through the use of Machine Learning (ML) in order to (1) build a model that predicts dispenser performance from a set of physical features, (2) explain the model’s predictions by relating features to outcome, and (3) suggest criteria that characterize optimal performance. A micro-droplet dispenser was used in conjunction with a drop-watcher for in-situ monitoring of droplet formation. Using this setup, 300 micro-droplet dispensers were evaluated for printing performance while various physical measurements of the dispensers were taken separately using a high magnification digital microscope. Logistic Regression, Random Forest, Support Vector Machine and Gradient Boosting Machine algorithms were used to train and test classification models based on dispenser performance. AUC scores in the range of 0.75–0.85 were observed for the various algorithms while Partial Dependence Plots were utilized to investigate how the physical attributes of the dispenser impacted performance. Importantly, results were presented and interpreted in the context of providing an insight to transparency for ML in the regulatory environment.

Role of elasticity on polymeric droplet generation and morphology in microfluidic cross-junctions

Recently, our direct numerical simulations [Duan et al., Phys. Fluids 36, 033112 (2024)] showed that fluid elasticity affects the extension length and pinch-off time of the droplet formation process, thus changing the flow pattern. However, the effect of fluid elasticity on the morphology and properties of polymeric droplets is not yet fully understood. In this work, by analyzing the stretched state of the polymer macromolecule and the velocity distribution of the flow process, we find that the increase in fluid elasticity (characterized by the relaxation time) inhibits the contraction of the dispersed phase during droplet pinching and resists the effect of surface tension after droplet generation, which significantly affects the droplet geometry, volume, and generation frequency. The results demonstrate that the length and volume of polymeric droplets increase with the relaxation time of the polymer fluid, while the generation frequency decreases. Meanwhile, the effects of polymer viscosity and the superficial velocity ratio of the continuous to the dispersed phase on the droplets' morphology are investigated. The semi-empirical models for the length, volume, and generation frequency of polymeric droplets are developed for the first time by considering the elastic interaction. The purpose of our work is to provide a better understanding and experimental guidance for controlling the parameters of polymeric droplets with viscoelasticity of different shapes and sizes.

Microdroplet formation of water and alumina nanofluid in a T-junction microchannel

A scarcity of studies about nanofluids’ utilization in droplet formation inside microdevices currently hovers in the literature although potential applications of nanoparticles in a microfluidic environment are foreseen. For this purpose, experimentally assessing both nanofluid and microdroplet characteristics is fundamental. This work reports a series of experimental tests on the microdroplet formation of distilled water (DIW) and DIW-based aluminum oxide (Al2O3) nanofluid in a microfluidic T-junction. While water and nanofluid are used as the dispersed phase, mineral oil is used as the continuous phase. Microdroplet formation in the squeezing, transitional, and dripping regimes is characterized and scaling laws for the non-dimensional droplet volumes are presented. The effects of flow rate, capillary number, microchannel aspect ratio, and nanoparticle concentration are investigated. The addition of Al2O3 nanoparticles to the water is observed to have a major impact in the transitional regime (up to 40% increase), whereas in the dripping regime its influence is lower, with less than 10% difference. This was attributed to the nanofluid's enhanced interfacial tension and viscosity compared to the DIW, as well as possible adsorption at the surface.

Caki-1 Spheroids as a 3D Model for Studying Free Fatty Acid-Induced Proximal Tubule Lipotoxicity

Three-dimensional (3D) multicellular spheroid shows a biological complexity resembling native tissue in comparison to conventional monolayer cultures, making it a better model system to assess drug effcacy and cytotoxicity. The main aim of this study was to examine the usefulness of Caki-1, a human proximal tubule (PT) representative cell line, as a 3D model system for studying free fatty acid-induced PT lipotoxicity. Caki-1 spheroids were generated and maintained on ultra-low attachment plates and characterized regarding time-dependent changes in morphology and functionality. In optimal 3D culture conditions, Caki-1 cells formed well-defined large compact 3D spheroids with uniform morphology, good circularity, and increased diameter from days 2-10. There was no change when the spheroids were incubated with lipid-free bovine serum albumin (BSA, 0.5%) from day 6 to 10. Chronic exposure to palmitate (300 μM) resulted in dispersed and flattened spheroid morphology, with a larger number of dead cells in the peripheral layers and decreased spheroid core. Moreover, palmitate-treated spheroids showed a significant increase in caspase-3 activity at the external layers of the spheroids, suggesting that the detached cells underwent apoptosis. Simultaneous addition of oleate (200 μM) prevents palmitate-induced spheroid disintegration and cell death in Caki-1 3D culture. Mechanistically, palmitate triggered endoplasmic reticulum (ER) stress and autophagy dysfunction, as evidenced by significantly increased protein levels of ER stress markers AFT4 and CHOP, and autophagy substrate p62. Oleate upregulated adipose differentiation-related protein (ADRP, a lipid droplet-associated protein), and promoted lipid droplet formation in palmitate-treated Caki-1 cells. These results indicate that Caki-1 3D spheroids are a simple and reproducible in vitro system for lipotoxicity study. It can potentially be used for evaluating human renal proximal tubular toxicity and drug screening. NIH/NIGMS R16GM149499, NIH TL1DK136047. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Modulation of the Effect of Cisplatin on Nicotine-Stimulated A549 Lung Cancer Cells Using Analog of Marine Sponge Toxin Loaded in Gelatin Nanoparticles.

Nicotine activates nicotinic acetylcholine receptors (nAChRs), which are overexpressed in numerous cancer types, leading to signaling pathways that increase lung cancer invasiveness and resistance to chemotherapeutic agents. In this study, the effects of APS12-2, a synthetic analog of marine sponge toxin that acts as an antagonist of nAChRs, was investigated in vitro on A549 human lung adenocarcinoma cells and non-tumorigenic human lung epithelial BEAS-2B cells. In addition, gelatin nanoparticles (GNPs) loaded with APS12-2 (APS12-2-GNPs) were prepared and their effects were compared with those of free APS12-2. Nicotine reduced cytotoxicity, the formation of reactive oxygen species, and the formation of lipid droplets caused by cisplatin on A549 cells. The effects of nicotine on the decreased efficacy of cisplatin were reduced by APS12-2 and APS12-2-GNPs. APS12-2-GNPs showed a substantial advantage compared with free APS12-2; the cytotoxicity of APS12-2 on BEAS-2B cells was greatly reduced when APS12-2 was loaded in GNPs, whereas the cytotoxicity on A549 cells was only slightly reduced. Our results suggest that both APS12-2 and APS12-2-GNPs hold promise as supportive agents in the cisplatin-based chemotherapy of lung cancer.

Cloud response to co-condensation of water and organic vapors over the boreal forest

Abstract. Accounting for the condensation of organic vapors along with water vapor (co-condensation) has been shown in adiabatic cloud parcel model (CPM) simulations to enhance the number of aerosol particles that activate to form cloud droplets. The boreal forest is an important source of biogenic organic vapors, but the role of these vapors in co-condensation has not been systematically investigated. In this work, the environmental conditions under which strong co-condensation-driven cloud droplet number enhancements would be expected over the boreal biome are identified. Recent measurement technology, specifically the Filter Inlet for Gases and AEROsols (FIGAERO) coupled to an iodide-adduct chemical ionization mass spectrometer (I-CIMS), is utilized to construct volatility distributions of the boreal atmospheric organics. Then, a suite of CPM simulations initialized with a comprehensive set of concurrent aerosol observations collected in the boreal forest of Finland during spring 2014 is performed. The degree to which co-condensation impacts droplet formation in the model is shown to be dependent on the initialization of temperature, relative humidity, updraft velocity, aerosol size distribution, organic vapor concentration, and the volatility distribution. The predicted median enhancements in cloud droplet number concentration (CDNC) due to accounting for the co-condensation of water and organics fall on average between 16 % and 22 %. This corresponds to activating particles 10–16 nm smaller in dry diameter that would otherwise remain as interstitial aerosol. The highest CDNC enhancements (ΔCDNC) are predicted in the presence of a nascent ultrafine aerosol mode with a geometric mean diameter of ∼ 40 nm and no clear Hoppel minimum, indicative of pristine environments with a source of ultrafine particles (e.g., via new particle formation processes). Such aerosol size distributions are observed 30 %–40 % of the time in the studied boreal forest environment in spring and fall when new particle formation frequency is the highest. To evaluate the frequencies with which such distributions are experienced by an Earth system model over the whole boreal biome, 5 years of UK Earth System Model (UKESM1) simulations are further used. The frequencies are substantially lower than those observed at the boreal forest measurement site (< 6 % of the time), and the positive values, peaking in spring, are modeled only over Fennoscandia and the western parts of Siberia. Overall, the similarities in the size distributions between observed and modeled (UKESM1) are limited, which would limit the ability of this model, or any model with a similar aerosol representation, to project the climate relevance of co-condensation over the boreal forest. For the critical aerosol size distribution regime, ΔCDNC is shown to be sensitive to the concentrations of semi-volatile and some intermediate-volatility organic compounds (SVOCs and IVOCs), especially when the overall particle surface area is low. The magnitudes of ΔCDNC remain less affected by the more volatile vapors such as formic acid and extremely low- and low-volatility organic compounds (ELVOCs and LVOCs). The reasons for this are that most volatile organic vapors condense inefficiently due to their high volatility below the cloud base, and the concentrations of LVOCs and ELVOCs are too low to gain significant concentrations of soluble mass to reduce the critical supersaturations enough for droplet activation to occur. A reduction in the critical supersaturation caused by organic condensation emerges as the main driver of the modeled ΔCDNC. The results highlight the potential significance of co-condensation in pristine boreal environments close to sources of fresh ultrafine particles. For accurate predictions of co-condensation effects on CDNC, also in larger-scale models, an accurate representation of the aerosol size distribution is critical. Further studies targeted at finding observational evidence and constraints for co-condensation in the field are encouraged.

Computational insights into gas atomization of FeCoNiCrMoBSi high-entropy alloy: From droplet formation to rapid solidification

The intricate processes governing the gas atomization of molten metal droplets and their subsequent solidification hold paramount significance in materials science. Computational fluid dynamics simulations have emerged as indispensable tools for unraveling the complexities inherent in metal melt atomization. This study employed the volume of fluid method and the shear-stress transport k-ω turbulence model to simulate the primary atomization process of a FeCoNiCrMoBSi high-entropy alloy. Subsequently, the discrete phase model and Taylor analogy breakup model, based on the gas Weber number and incorporating primary atomization outcomes as initial conditions, were utilized to simulate droplet formation during the secondary atomization process. Analysis of the particle size distribution at the outlet of the geometric model demonstrated excellent agreement with experimental data for gas-atomized FeCoNiCrMoBSi high-entropy alloy powder. Furthermore, comprehensive characterization analyses were conducted to probe the phase constitution and structure of FeCoNiCrMoBSi powder produced by gas atomization. The results revealed that, irrespective of particle size, the powder exhibited a face-centered cubic structure and distinctive eutectic microstructural characteristics. The numerical simulation provided insights into the solidification process of secondary droplets by integrating inverse pole figure data for gas-atomized powder across varying particle sizes. The estimated cooling rate of secondary droplets ranged from 1.22 × 104 K/s to 2.64 × 105 K/s. These findings significantly advance the understanding of the gas atomization mechanism of the FeCoNiCrMoBSi high-entropy alloy, paving the way for the development of more efficient manufacturing processes for advanced materials.

ПРИМЕНЯЕМОСТЬ ВОДОГАЗОВЫХ ФОРСУНОК ДЛЯ ПОЖАРОТУШЕНИЯ ТОНКОРАСПЫЛЕННОЙ ВОДОЙ

The low efficiency of traditional water extinguishing systems is due to the formation of large droplets. Large droplets have a small external surface area, which causes poor heat removal from the ignition source. A large external surface area of droplets is provided by fire extinguishing systems with thinly sprayed water. They are effective in extinguishing fires at the initial stage of a fire in confined spaces and ensure the formation of droplets less than 150 microns. The analysis showed that water-gas nozzles with co-directional flows of water and gas are suitable for creating finely dispersed water with a droplet size of less than 100 microns. To ensure significant heat removal from the ignition source, the average diameter of the droplets of finely dispersed water should be less than 80 microns. A technique for determining the size of droplets when sprayed with water-gas nozzles is presented. According to the method, the calculation of the average diameter of droplets was carried out depending on the ratio of volume flow rates of gas and water. It is shown that fire extinguishing with finely sprayed water with the help of water-gas nozzles is effective at a gas pressure in front of the annular gap from 0,4 MPa to 0,6 MPa and the ratio of volumetric air flow to volumetric water flow is more than 2 000.

Effect of fluid properties on intensification of heat transfer process in oil-water droplet flow in a T-shaped microchannel

Droplet-based microfluidics refers to the production and utilization of micrometer-sized droplets. This technology has found widespread applications in drug delivery, biotechnology, disease prevention, chemical analysis, cell research, and functional material synthesis. Cooling of high heat flux electronic systems and hot spots is another application of the droplet flow which is focused by the current work. In this paper, formation and hydrothermal performance of oil droplets in water flow in a T-junction microchannel is studied by a 3D numerical simulation. Effects of different parameters such as surface tension, wettability and heat flux on the droplet size, heat transfer rate and pressure drop are investigated. It is observed that the shear between the discrete and continuous phases results in recirculating zones in both phases which contribute to improved mixing and heat transfer rates. Liquid film thickness adjacent to the heated surface and the droplet velocity are two other factors that positively affect the heat transfer. Decreasing the surface tension is shown to enhance the heat transfer rate. Moreover, an optimum value is found for the contact angle as 135° at which a 23 % heat transfer enhancement is achieved. Results also indicate that droplet size decreases with increase of contact angle while it slightly increases with increase of the surface tension and negligibly varies with the applied heat flux.

Enhancing carbon capture: Exploring droplet wetting and gas condensation of carbon dioxide on nanostructured surfaces

The investigation of carbon dioxide (CO2) condensation on heat exchange surfaces is essential to the advancement of carbon capture, utilization, and storage (CCUS) technology. Molecular dynamics simulations are employed to explore the wetting and condensation behavior of CO2 on nanostructured surfaces. The results indicate that the contact angle of CO2 droplets on nanostructured surfaces is greater than that on smooth surfaces. Increasing the pillar height (h) or solid fraction (f) induces the transition of CO2 droplets from the Wenzel to Cassie state, resulting in an increased contact angle. Nanostructured surfaces significantly enhance the nucleation rate, with molecules initially nucleating at the bottom of the pillars. A higher h or f accelerates the nucleation rate during the condensation. Droplets in the Wenzel state exhibit higher heat transfer efficiency than those in the Cassie state. Additionally, the formation of Cassie-state CO2 droplets undergoes a dewetting transition, altering the heat conduction mode. The dewetting behavior of CO2 droplets favors their detachment from the surface, potentially reducing the initial heat resistance. Therefore, appropriately increasing h and f can promote nucleation and droplet growth, enhancing dewetting transition and mass transfer performance. These simulation results hold great importance for inspiring the design of future CO2-phobic surfaces and guiding CO2 condensation production.