scholarly journals Vaporizable endoskeletal droplets via tunable interfacial melting transitions

2020 ◽  
Vol 6 (14) ◽  
pp. eaaz7188 ◽  
Author(s):  
Gazendra Shakya ◽  
Samuel E. Hoff ◽  
Shiyi Wang ◽  
Hendrik Heinz ◽  
Xiaoyun Ding ◽  
...  
Keyword(s):  
Gas Phase ◽  
Liquid Core ◽  
Secondary Phase ◽  
Intermolecular Forces ◽  
Droplet Evaporation ◽  
Melting Transition ◽  
Emulsion Droplet ◽  
Droplet Vaporization ◽  
Liquid Emulsion ◽  
Droplet Phase

Liquid emulsion droplet evaporation is of importance for various sensing and imaging applications. The liquid-to-gas phase transformation is typically triggered thermally or acoustically by low–boiling point liquids, or by inclusion of solid structures that pin the vapor/liquid contact line to facilitate heterogeneous nucleation. However, these approaches lack precise tunability in vaporization behavior. Here, we describe a previously unused approach to control vaporization behavior through an endoskeleton that can melt and blend into the liquid core to either enhance or disrupt cohesive intermolecular forces. This effect is demonstrated using perfluoropentane (C5F12) droplets encapsulating a fluorocarbon (FC) or hydrocarbon (HC) endoskeleton. FC skeletons inhibit vaporization, whereas HC skeletons trigger vaporization near the rotator melting transition. Our findings highlight the importance of skeletal interfacial mixing for initiating droplet vaporization. Tuning molecular interactions between the endoskeleton and droplet phase is generalizable for achieving emulsion or other secondary phase transitions, in emulsions.

Numerical Study of Bicomponent Droplet Vaporization in a High Pressure Environment

1996 ◽  
Author(s):  
J. Stengele ◽  
H.-J. Bauer ◽  
S. Wittig
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Gas Phase ◽  
Numerical Study ◽  
Droplet Evaporation ◽  
Single Component ◽  
Vapor Concentration ◽  
Diffusion Limit ◽  
Evaporation Process ◽  
Droplet Vaporization

The understanding of multicomponent droplet evaporation in a high pressure and high temperature gas is of great importance for the design of modern gas turbine combustors, since the different volatilities of the droplet components affect strongly the vapor concentration and, therefore, the ignition and combustion process in the gas phase. Plenty of experimental and numerical research is already done to understand the droplet evaporation process. Until now, most numerical studies were carried out for single component droplets, but there is still lack of knowledge concerning evaporation of multicomponent droplets under supercritical pressures. In the study presented, the Diffusion Limit Model is applied to predict bicomponent droplet vaporization. The calculations are carried out for a stagnant droplet consisting of heptane and dodecane evaporating in a stagnant high pressure and high temperature nitrogen environment. Different temperature and pressure levels are analyzed in order to characterize their influence on the vaporization behavior. The model employed is fully transient in the liquid and the gas phase. It accounts for real gas effects, ambient gas solubility in the liquid phase, high pressure phase equilibrium and variable properties in the droplet and surrounding gas. It is found that for high gas temperatures (T = 2000 K) the evaporation time of the bicomponent droplet decreases with higher pressures, whereas for moderate gas temperatures (T = 800 K) the lifetime of the droplet first increases and then decreases when elevating the pressure. This is comparable to numerical results conducted with single component droplets. Generally, the droplet temperature increases with higher pressures reaching finally the critical mixture temperature of the fuel components. The numerical study shows also that the same tendencies of vapor concentration at the droplet surface and vapor mass flow are observed for different pressures. Additionally, there is almost no influence of the ambient pressure on fuel composition inside the droplet during the evaporation process.

Determining Parametric Effects for Droplet Evaporation on Nanoporous Superhydrophillic Surfaces Using Machine Learning Techniques

2021 ◽  
Author(s):  
Emma R. McClure ◽  
Van P. Carey
Keyword(s):  
Machine Learning ◽  
Cooling System ◽  
Spray Cooling ◽  
Droplet Evaporation ◽  
Contact Angles ◽  
Machine Learning Techniques ◽  
Metallic Surfaces ◽  
Droplet Spreading ◽  
Droplet Vaporization ◽  
Speed Accuracy

Abstract Experimental results demonstrate that droplet vaporization on metal surfaces can be significantly enhanced with the application of a nanoporous, superhydrophilic surface coating. A thin layer of ZnO nanopillars can be easily seeded and grown on most metallic surfaces to achieve nanoscale pores between pillars, and ultra-low apparent contact angles. These surface coatings have the potential to improve spray cooling processes, and can be easily scaled up to larger and more complex heat exchangers. In order to characterize the potential improvement to a spray cooling system it is important to understand the dependence on system parameters, and to have a clear model of droplet vaporization on such surfaces. There are a number of surface and impact parameters that will affect the droplet spreading and subsequent vaporization on the surface. The surface contact angle, wicking speed and impact velocity all interact to affect the maximum spread of the droplet and the speed at which the droplet reaches this state. Along with variations in droplet volume and wall superheat, the model for droplet vaporization becomes more complex and nonlinear. Instead of exploring a single parameter at a time, machine learning tools can be utilized to determine the dependence of droplet evaporation time on these parameters simultaneously. In this study a genetic algorithm and a neural network were used to develop a droplet evaporation model for these superhydrophilic surfaces. Each algorithm demonstrated clear advantages depending on whether speed, accuracy, or an explicit mathematical model was prioritized.

Comparison of Droplet Evaporation and Nucleate Boiling Mechanisms on Nanoporous Superhydrophilic Surfaces

2019 ◽  
Author(s):  
Samuel Cabrera ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Droplet Evaporation ◽  
Transfer Performance ◽  
Nanostructured Surface ◽  
Nanostructured Surfaces ◽  
Droplet Vaporization

Abstract Recent studies have indicated that at slightly superheated surface temperatures, droplet evaporation on a nanoporous superhydrophilic surface exhibits onset of nucleation and nucleate boiling effects similar to pool boiling processes. This paper discusses water droplet evaporation experiments and pool boiling experiments conducted on nanostructured surfaces of a 45° downward facing pyramid copper and aluminum substrate. The nanostructured surfaces were used to conduct both droplet evaporation experiments and pool boiling experiments and thus allow direct comparison of the underlying heat transfer performance and mechanisms for these two different processes. The four surfaces tested were the following: bare copper surface, nanostructured surface on copper, bare aluminum surface, and nanostructured surface on aluminum. Mean heat flux values at varying superheats were obtained through temperature and time measurements. To better understand the heat performance of each surface, the wetting and wicking characteristics of each surface were also tested. Experimental results indicate that many of the mechanisms associated with pool boiling may also play a role in droplet vaporization, and their presence can produce levels of heat transfer performance comparable to, or even higher than, that observed in pool boiling at a comparable wall superheat. The results demonstrate that the nanostructured surface affects onset of nucleate boiling and maximum heat flux in both droplet vaporization and nucleate boiling on these surfaces. The implications of these results for strategies to enhance spray cooling and pool boiling are also discussed.

A Semi-Analytical Model for Evaporating Fuel Droplets

2005 ◽  
Vol 127 (2) ◽  
pp. 199-203 ◽  
Author(s):  
Achintya Mukhopadhyay ◽  
Dipankar Sanyal
Keyword(s):  
Gas Phase ◽  
Computational Cost ◽  
Lewis Number ◽  
Droplet Evaporation ◽  
Solution Procedure ◽  
Droplet Surface ◽  
Spray Combustion ◽  
Fuel Droplet ◽  
Cfd Model ◽  
Fuel Droplets

An algorithm for solution of a model for heating and evaporation of a fuel droplet has been developed. The objective of the work is to develop a computationally economic solution module for simulating droplet evaporation that can be incorporated in spray combustion CFD model that handles a large number of droplets. The liquid-phase transient diffusive equation has been solved semi-analytically, which involves a spatially closed-form and temporally discretized solution procedure. The model takes into account droplet surface regression, nonunity gas-phase Lewis number and variation of latent heat with temperature. The accuracy of the model is identical to a Finite Volume solution obtained on a very fine nonuniform grid, but the computational cost is significantly less, making this approach suitable for use in a spray combustion code. The evaporation of isolated heptane droplet in a quiescent ambient has been investigated for ambient pressures of 1 to 5 bar.

Axisymmetric Unsteady Droplet Vaporization and Gas Temperature Distribution

1989 ◽  
Vol 111 (2) ◽  
pp. 487-494 ◽  
Author(s):  
S. K. Lee ◽  
T. J. Chung
Keyword(s):  
Gas Phase ◽  
Gas Temperature ◽  
The Finite Element Method ◽  
Grid Spacing ◽  
Droplet Model ◽  
Time Step ◽  
Two Phase ◽  
Droplet Vaporization ◽  
Droplet Liquid ◽  
Injection Pulse

Droplet vaporization and temperature distributions of axisymmetric unsteady sprays are investigated. The so-called discrete droplet model of two-phase flows, often known as the Eulerian–Lagrangian method, is used. Calculations are carried out with Eulerian coordinates using finite elements for the gas phase and the method of characteristics using the second-order Runge–Kutta scheme for the droplet liquid phase. The sensitivity of the numerical results to changes in time step, injection pulse time, grid spacing, and number of droplet characteristics is examined. Through a simple example, it is shown that applications of the finite element method to more complicated problems appear to be promising.

scholarly journals Contrast-enhanced sonography with biomimetic lung surfactant nanodrops

2020 ◽  
Author(s):  
Alec N. Thomas ◽  
Kang-Ho Song ◽  
Awaneesh Upadhyay ◽  
Virginie Papadopoulou ◽  
David Ramirez ◽  
...  
Keyword(s):  
Ultrasound Imaging ◽  
Lung Surfactant ◽  
Liquid Core ◽  
Acoustic Droplet Vaporization ◽  
Droplet Vaporization ◽  
Contrast Enhanced ◽  
Biomimetic Approach ◽  
The Stability

AbstractNanodrops comprising a perfluorocarbon liquid core can be acoustically vaporized into echogenic microbubbles for ultrasound imaging. Packaging the microbubble in its condensed liquid state provides distinct advantages, including in situ activation of the acoustic signal, longer circulation persistence, and the advent of expanded diagnostic and therapeutic applications in pathologies which exhibit compromised vasculature. One obstacle to clinical translation is the inability of the limited surfactant present on the nanodrop to encapsulate the greatly expanded microbubble interface, resulting in ephemeral microbubbles with limited utility. In this study, we examine a biomimetic approach to stabilizing an expanding gas surface by employing the lung surfactant replacement, Beractant. Lung surfactant contains a suite of lipids and surfactant proteins that provides efficient shuttling of material from bilayer folds to the monolayer surface. We therefore hypothesized that Beractant would improve stability of acoustically vaporized microbubbles. To test this hypothesis, we characterized Beractant surface dilation mechanics and revealed a novel biophysical phenomenon of rapid interfacial melting, spreading and re-solidification. We then harnessed this unique spreading capability to increase the stability and echogenicity of microbubbles produced after acoustic droplet vaporization for in vivo ultrasound imaging. Such biomimetic lung surfactant-stabilized nanodrops may be useful for applications in ultrasound imaging and therapy.Graphical Abstract

scholarly journals Two-Dimensional Clusters of Colloidal Particles Induced by Emulsion Droplet Evaporation

Nanomaterials ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 156 ◽  
Author(s):  
Hai Pham-Van ◽  
Linh Tran-Phan-Thuy ◽  
Cuong Tran-Manh ◽  
Bich Do-Danh ◽  
Hoang Luc-Huy
Keyword(s):  
Colloidal Particles ◽  
Three Dimensional ◽  
Droplet Evaporation ◽  
Dimensional System ◽  
Geometrical Approach ◽  
Two Dimensional ◽  
Emulsion Droplet ◽  
Second Moment ◽  
Minimization Principle ◽  
Metropolis Monte Carlo

The minimization principle of the second moment of the mass distribution ( M 2 ) is responsible for the unique structure of three-dimensional clusters by using emulsion droplet evaporation. Herein we study the structure of two-dimensional clusters of colloidal particles bound at the interface of liquid droplets in the plane. We found that, differently from the three-dimensional system, the two-dimensional clusters have multiple degenerate configurations (isomers). An interesting feature of such two-dimensional clusters is that they have the same packings as those belonging to a class of geometric figures known as polyiamonds. In particular, except for the six-particle cluster, many higher order clusters of polyiamond have not been reported previously. Using a simple geometrical approach, based on the number of ways to generate a packing, we calculated the occupation probabilities of distinct isomeric clusters. The level of agreement with the results of metropolis Monte Carlo simulations was good for clusters containing up to nine particles, suggesting that our two-dimensional cluster structures are not a result of the minimization of the second moment. In addition, the structure of these clusters is somewhat insensitive to the range and depth of the interparticle potential, in good agreement with the results in the literature.

Synthesis and Laser Spectroscopy of Monoclinic Eu3+: Y2O3 Nanocrystals

1996 ◽  
Vol 457 ◽  
Author(s):  
Bipin Bihari ◽  
Brian M. Tissue
Keyword(s):  
Gas Phase ◽  
Monoclinic Phase ◽  
Nanocrystalline Material ◽  
Secondary Phase ◽  
Nitrogen Atmosphere ◽  
Starting Material ◽  
Line Broadening ◽  
Transmission Electron ◽  
Laser Heated ◽  
Cation Sites

ABSTRACTGas-phase condensation of CO2 laser-heated EU3+:Y2O3 ceramics produces monoclinic-phase nanocrystalline material. Transmission electron microscopy shows particle diameters in the range 7–30 nm for particles quenched at 60 °C under 400 Torr of nitrogen atmosphere. The optical spectra of nanocrystals produced from 0.1% Eu3+:Y2O3 starting material have narrow lines, and the 5D0 lifetimes are 1.8, 1.2 and, 1.3 ms for the three Eu3+ cation sites. Nanocrystals obtained from 0.7 –5 % Eu3+:Y2O3 starting material show line broadening and the presence of Eu2O3 secondary phase.

Deflagration Analysis of Aluminum Droplet Combustion

2012 ◽  
Author(s):  
Birce Dikici ◽  
M. L. Pantoya ◽  
B. D. Shaw
Keyword(s):  
Gas Phase ◽  
Flame Propagation ◽  
Diffusion Flame ◽  
Dominant Role ◽  
Experimental Studies ◽  
Droplet Evaporation ◽  
Combustion Model ◽  
Single Droplet ◽  
Aluminum Particles ◽  
Combustion Dynamics

The evaporation and combustion of nanometric aluminum particles with an oxidizer MoO3 is analyzed. The analysis was performed to correlate individual Al particle gasification rates to macroscopic flame propagation rates observed in flame tube experiments. Examination of various characteristic times relevant to propagation of a deflagration reveals that particles below about 1.7 nm in diameter evaporate before appreciable chemical reactions occur. Experimental studies use Al particles greater than 1.7 nm in diameter such that a diffusion flame model was developed to better understand the combustion dynamics of multiphase Al particles. The results showed that it is unlikely that droplets will fully evaporate before reacting in the gas phase. A droplet evaporation and combustion model was further applied to quantify single droplet reaction velocities in comparison to the bulk flame propagation measurements observed in the literature. The diffusion flame model predicted orders of magnitude slower propagation rates than experimentally observed. These results imply that another reaction mechanism is responsible for promoting reaction propagation or modes other than diffusion play a more dominant role in flame propagation.

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