Massive Droplets Research Articles

Numerical simulation of condensation flows of humid air in the high-pressure pneumatic pressure-reducing valve

The phenomenon of condensation and ice formation exists in the high-pressure air pressure-reducing valve (HPAPRV), severely impacting the pressure-reducing valve's aerodynamic performance and operational safety. The problem is that the phase change of humid air in a high-pressure supersonic flow is not fully understood. This study aims to elucidate the condensation effect in high-pressure supersonic flows and the influence of the inlet conditions on the behavior of the condensate flow. A computational humid air phase model has been developed to investigate the formation of massive droplets due to phase-change processes. The numerical approach is validated by comparing it with experimental data, demonstrating a strong correlation between the two. The condensation properties of humid air in HPAPRV are described in detail. The effects of the condensation properties of humid air at different inlet conditions are discussed in detail. The results show that an increase in the inlet pressure increases the level of supersaturation, which increases the nucleation rate and the droplet growth rate and promotes droplet production. Increasing the inlet temperature has little effect on the HPAPRV pressure-reducing performance and predicts the temperature range of water vapor condensation before and after the valve port. The liquid mass fraction can be reduced by 50.9% by increasing the inlet temperature by 30 K, from 283 K to 313 K. When the inlet temperature is below 283 K, water vapor condenses in front of the valve port. Decreasing the inlet humidity reduces the degree and extent of supersaturation, which decreases the nucleation rate and the liquid mass fraction. When low inlet humidity (under 10%), the condensation phenomenon did not almost occur inside the pressure-reducing valve.

Three-phase contact line confined dense nanoparticle array for high-capacity DNA synthesis

This paper presents a facile and cost-effective fabrication method of microreactor array chip for high-throughput DNA synthesis with three orders of mangnitude enhancement in synthesis capacity. Inkjet printing was used to dispense a massive droplet array of silica nanoparticle slurry on chemically-modified surface. Dense microreactor array can be simply obtained by following the procedure of three-phase contact line (TCL)-confined nanoparticle aggregating, which is dominated by the receding contact angle (RCA) of the modified substrates. Chip with RCAs greater than 90° transfers the resultant force to a lifting statu as well as enhances the inward force effect, which leading to a dense and compact packing synergistically on limited chip area. Herein, a consequential increasement in effective reaction area contributes to the significant enhancement in synthesis capacity as compared to a planar or porous substtrate. The proposed microarray chip demonstrates great prospects for both high-throughput and high-capacity DNA synthesis.

Breakup regime of flashing jet under thermal nonequilibrium and mechanical forces and its relationship with jet characteristics during depressurized releases of superheated liquid

Accidental superheated liquid emissions into the atmosphere yield two-phase releases. The resulting flashing jet, driven by thermal nonequilibrium and mechanical forces, breaks up into massive droplets, fostering beneficial conditions for fire, explosion, and toxic diffusion. In this work, a 20 L tank was built to examine two-phase flow behaviors during depressurized releases of superheated liquids via a high-speed camera and phase Doppler anemometry. Different breakup regimes of flashing jet and dimensionless groups that effectively represent thermodynamic (RpJa) and mechanical (WevOh) driving effects were determined. Based on the interaction between the two effects, quantitative criteria to distinguish different regimes were developed. The accompanying jet characteristics, including jet angle (θ), area fraction (fA), droplet diameter (dSMD), and droplet velocity (ud), and their relationship with jet breakup were revealed. Results show that non-flashing (NFB), partially flashing (PFB), and fully flashing (FFB) breakups coincide with RpJa(WevOh)1/7 < 41, 41 ≤RpJa(WevOh)1/7 < 223, and 223 ≤RpJa(WevOh)1/7, respectively. For small-sized nozzles (d≤3 mm), θ2 and fA2 increase within 41 ≤RpJa(WevOh)1/7 < 558 and then keep stable. The difference for large-sized nozzles resides in 223 ≤RpJa(WevOh)1/7 < 558 (early FFB regime), where θ2 and fA2 decrease slightly due to the enhanced droplet evaporation. In 41 ≤RpJa(WevOh)1/7, dSMD2 decreases and ud2 increases, but at an extremely low rate within 558 ≤RpJa(WevOh)1/7.

A Novel Dehumidification Strategy to Reduce Liquid Fraction and Condensation Loss in Steam Turbines.

Massive droplets can be generated to form two-phase flow in steam turbines, leading to erosion issues to the blades and reduces the reliability of the components. A condensing two-phase flow model was developed to assess the flow structure and loss considering the nonequilibrium condensation phenomenon due to the high expansion behaviour in the transonic flow in linear blade cascades. A novel dehumidification strategy was proposed by introducing turbulent disturbances on the suction side. The results show that the Wilson point of the nonequilibrium condensation process was delayed by increasing the inlet superheated level at the entrance of the blade cascade. With an increase in the inlet superheated level of 25 K, the liquid fraction and condensation loss significantly reduced by 79% and 73%, respectively. The newly designed turbine blades not only remarkably kept the liquid phase region away from the blade walls but also significantly reduced 28.1% averaged liquid fraction and 47.5% condensation loss compared to the original geometry. The results provide an insight to understand the formation and evaporation of the condensed droplets inside steam turbines.

Modeling the viral load expelled in saliva droplets carrying SARS-CoV-2

One of the most likely routes of transmission of COVID-19 is through the saliva droplets that are produced while speaking, coughing or sneezing by infected people. The expelled droplets, measuring between 0.4 and 450 μm, follow trajectories determined, mainly, by the gravitational, and air frictional forces. We solve numerically the equations of motion in which the linear and quadratic velocity terms in the drag force are considered. In order to model the virus load expelled during respiratory events, we assume log-log Gaussian distributions, with peaks around 10 μm, and analyze four size ranges: the aerosol (0.4–5 μm), the small (5.1–10 μm), the middle (10.1–100 μm), and big (100.1–450 μm) droplet size regimes. In the aerosol regime, the frictional forces quickly stop the droplets in their horizontal movement and they fall extremely slowly pulled down by the gravitational force. The residence time, in a calm environment, goes from 3.83 days to 33.3 min. More massive droplets take shorter times and hit the ground meters away from the source. By assuming a constant density of virions per milliliter, we estimate the expelled amount into the environment. The middle and small size droplets contain the highest amount but since the aerosol droplets remain in the air such a long time, they represent also a high risk for infection. We emphasize the importance of face protection to minimize COVID-19, transmission.

Massive droplet generation for digital PCR via a smart step emulsification chip integrated in a reaction tube.

Step emulsification (SE) devices coupled with parallel generation nozzles are widely used in the production of large-scale monodisperse droplets, especially for droplet-based digital polymerase chain reaction (ddPCR) analysis. Although current ddPCR systems based on the SE method can provide a fully enclosed ddPCR scheme, high demands on chip fabrication and system control will increase testing costs and reduce its flexibility in ddPCR analysis. In this study, a compact SE device, integrating a smart SE chip into a reaction tube, was developed to prepare large-scale water-in-fluorinated-oil droplets for ddPCR analysis. The SE chip contained dozens of droplet-generation nozzles. By adjusting the nozzle height of the SE chip, monodisperse droplets in a picolitre to nanolitre vloume could be prepared at a production rate of tens to hundreds of microlitres per minute. Subsequently, we utilized such an integrated SE device to prepare monodisperse droplets for ddPCR experiments. The volume of PCR reagent and the number of droplets could be flexibly adjusted according to the requirements of the ddPCR analysis. The quantitative results showed that emulsions prepared by the SE device could achieve ddPCR detection with high accuracy, good repeatability, and an adaptive dynamic range, which also demonstrated the robustness and reliability of such devices in the droplet preparation. Thus, this compact SE device provides an inexpensive, flexible, and simplified droplet preparation method for digital PCR quantitative analysis.

The mechanism of surface cooling by a horizontal layer of liquid evaporating at low reduced pressures

We investigated the process of cooling the surface with a thin layer of liquid at low reduced pressures, consisting of two characteristic periods. In the first period, coherent structures in the form of plumes appeared in the layer. In the second period, the layer was destroyed with the formation of structures in the form of moving “craters,” accompanied by a massive droplet ejection, intense mixing, and pressure and temperature growth. At the point of layer destruction, thermodynamic equilibrium was established within the system.

Ultrafast Microdroplet Generation and High-Density Microparticle Arraying Based on Biomimetic Nepenthes Peristome Surfaces.

Manipulation of massive droplets, particles, as well as cells has enabled wide applications. However, most existing technologies require complicated processes, operations, or external setup. This article demonstrates the employment of biomimetic Nepenthes peristome surfaces (NPS) in achieving ultrafast microdroplet generation and high-density microparticle arraying, with the assistance of curvature-induced Laplace pressure in slipping mode and evaporation-driven Marangoni effect in climbing mode, respectively. Different wetting phenomena on the biomimetic NPS were observed under variable contact angles and tilting angles, strongly affecting the microdroplet generation and microparticle array. As the optimal results, 5 μm-size microparticles were arrayed with 85% coverage rate in 65 s and 20 μm-size microdroplets were arrayed with 100% coverage rate in 3 s. In this study, this well-designed bionic surface shows excellent performances as an ultrafast, universal, and straightforward approach to capture and array micro-objects in aqueous solutions for various biological and chemical analyses.

Steam ejector performance considering phase transition for multi-effect distillation with thermal vapour compression (MED-TVC) desalination system

The multi-effect distillation with thermal vapour compression (MED-TVC) desalination system is efficient to produce freshwater. The steam ejector performance is not fully understood as the phase transition has been ignored in many studies. The present work develops a two-phase condensing flow model to assess the steam ejector performance considering nonequilibrium condensation phenomena. The transition of the flow structure from an under-expanded flow to an over-expanded flow in the steam ejector is investigated in detail. We present that the maximum Mach number can reach 4.02 in the under-expanded flow, which is weakened to 2.88 in the over-expanded flow. The steam undergoes several expansion-compression processes in the steam ejector in the under-expanded flow, which induces the formation and evaporation of massive droplets. In the over-expanded flow, the steam is compressed and then expanded after leaving the primary nozzle and the condensation process is not observed in mixing and constant sections. The increasing suction chamber pressure significantly improves the entrainment ratio while leading to an increasing entropy loss coefficient. The entrainment ratio is improved from 0.25 for the under-expanded flow to 1.69 for the over-expanded flow, while the entropy loss increases from 0.081 for the under-expanded flow to 0.29 for the over-expanded flow. This indicates that the transition of the flow structure from an under-expanded flow to an over-expanded flow can entrain more steam from the last effect while causes more entropy losses in a steam ejector for the MED-TVC desalination system.

Droplets behaviors of flashing jet in accidental release of superheated liquid

Structural failure of an industrial superheated liquid tank or pipe usually results in the flashing jet consisting of a mixture of massive droplets and vapor due to the violent phase transition. In this work, experiments on small-scale releases were carried out with a 20 L storage tank to investigate the droplets behaviors of flashing jets after accidental releases of superheated liquid. Distribution of droplets axial, radial and vertical velocities, as well as droplets diameter along the centreline of flashing jet, were acquired employing a Phase Doppler Anemometry (PDA). The influence of storage pressure, superheat, and nozzle diameter was also studied. Results show that the distribution of actual droplets with different velocities and diameters follows the normal distribution. Droplets mean three-dimensional velocities on the central axis of flashing jet decrease exponentially with the increase of axial distance. The droplets mean diameter first decreases exponentially and finally keeps sable at about 10 μm. Among three-dimensional velocities, the axial velocity is the highest and the vertical velocity is the lowest. Droplets mean three-dimensional velocities increase with the increase of storage pressure, superheat, and nozzle diameter. The droplets mean diameter decreases with the increase of superheat and nozzle diameter but increases with the increase of storage pressure.

Analysis of Droplets Spreading on Periodic Plasma Surface

This paper presents the unique spreading process of droplet on dielectric barrier discharge (DBD) actuator periodic plasma surface. High-speed camera is used to capture the droplet spreading process. We use image processing to handle the massive droplets image data. Results show that droplets have more spreading time and much less oscillation cycles on periodic plasma surface, and the spreading diameter is larger while the apex height is lower. Furthermore, the effect of periodic plasma density is studied. And it is revealed that when plasma density increases in certain density range, the maximum and final spreading diameters increase, while the apex height of droplet in stabilization phase decreases.

Wnt directs the endosomal flux of LDL ‐derived cholesterol and lipid droplet homeostasis

The Wnt pathway, which controls crucial steps of the development and differentiation programs, has been proposed to influence lipid storage and homeostasis. In this paper, using an unbiased strategy based on high-content genome-wide RNAi screens that monitored lipid distribution and amounts, we find that Wnt3a regulates cellular cholesterol. We show that Wnt3a stimulates the production of lipid droplets and that this stimulation strictly depends on endocytosed, LDL-derived cholesterol and on functional early and late endosomes. We also show that Wnt signaling itself controls cholesterol endocytosis and flux along the endosomal pathway, which in turn modulates cellular lipid homeostasis. These results underscore the importance of endosome functions for LD formation and reveal a previously unknown regulatory mechanism of the cellular programs controlling lipid storage and endosome transport under the control of Wnt signaling.

Experimental Investigation Into the Efficiency of an Aero-engine Oil Jet Supply System

This paper presents results of investigations on the interaction between a targeted oil jet and a rotating shaft in an aero-engine typical bearing chamber. Measurements were performed at atmospheric temperature and pressure in order to study the influence of the operating conditions, nozzle diameters and impingement angles on the efficiency of such an oil supply system. The flow phenomena of the jet–shaft interaction were visualized. A qualitative analysis of the jet–shaft interaction revealed massive droplet generation due to the jet break-up in the air crossflow and its impact on the shaft. The latter could be reduced with shallower impingement angles. Measurements showed that the oil inflow rate, the shaft speed, and the nozzle diameter have a strong influence on the collected oil quantity, which is expressed as catch efficiency, i.e., the ratio of collected and supplied oil. The impingement angle was also identified to have a strong influence on the catch efficiency. The ratio of the momentum fluxes of supplied oil and chamber air flow is proposed as a parameter to correlate the catch efficiency to the operating conditions.