Heterogeneous Nucleation Model Research Articles

Kinetic study and advanced decomposition models of superthermite-based nitrocellulose nanocomposite

ABSTRACT Superthermites are well-known for their exceptional combustion characteristics. α ferric oxide nanoparticles (NPs) were synthesized using hydrothermal synthesis. Co-precipitation technique was employed to integrated superhermite (Al/Fe2O3) colloidal particles into nitrocellulose (NC) energetic matrix. Morphology NC nanocomposite was investigated using scanning electron microscope. The integration of superthermite particles into NC matrix experienced enhanced decomposition enthalpy by 40% using Differential Scanning Calorimetry (DSC) as the decomposition enthalpy has incresed to reach above 1640J/kg. In the mean time, superthermite particles offered decrease in NC activation energy by 17.3% and 16.0% using Kissinger-Akahira-Sunose (KAS) approach and Kissinger models, respectively. The hydrous surface of ferric NPs could secure novel catalytic action. At low temperatures, the reactive hydroxyl groups could be released; active ȮH radicals would attack the NC heterocyclic ring and abstract hydrogen atom. Addition of NPs enhanced the rapid release of different decomposition products of NC such as NO2 ,CO, NO, HCHO, and HCOOH at low temperature. Kinetic models indicated that the heterogeneous solid-state reaction and A2 nucleation model were confirmed via KAS and Kissinger models.

Effects of heterogeneous nucleation model on computational fluid dynamics simulation of flow boiling heat transfer in the mini-channel

Bubble nucleation is the initial stage of flow boiling and plays an important role in boiling heat transfer. However, bubble nucleation occurs at a microscopic scale, rendering it challenging for the macroscopic computational fluid dynamics method to realistically simulate this intricate process. In this paper, based on the coupled volume-of-fluid and level set method, a heterogeneous nucleation model is improved and conducted to simulate the subcooled flow boiling in a rectangular mini-channel, considering these conditions both in the presence and absence of a microlayer. The coefficient of the original heterogeneous nucleation model is adjusted across a range from 0.1 to 10.0 times its previous value to establish multiple new nucleation models for illustrating their effects on flow patterns and heat transfer characteristics. For flow boiling without a microlayer, when the coefficient of the original heterogeneous nucleation model is halved, the nucleate boiling intensity upstream of the channel diminishes, resulting in a reduction in the heat transfer coefficient. Nevertheless, this alteration mitigates the formation of slug flow and the appearance of dry patches near the channel outlet, consequently averting a sharp increase in outlet wall superheat. Quantitatively, relative differences of 23.83% and 90.48% in average and local maximum wall superheat are observed, respectively. In contrast, the presence of a very thin microlayer beneath the growing and slipping bubble in flow boiling with a microlayer is notable. This microlayer quickly evaporates, dissipating more than 77% of the input heat flux and substantially expanding the bubble volume. Consequently, under identical wall superheat conditions, the influence of variations in the number of activated bubbles induced by different heterogeneous nucleation models on heat transfer and flow patterns in flow boiling is significantly attenuated. Specifically, when the difference in nucleus site density remains within a tenfold range, the differences in the average and maximum wall superheat are limited to just 16.78% and 33.86%, respectively. Concerning flow boiling in a mini-channel featuring a microlayer, the simulation results verify that large deviations in the activated bubble number have few effects on the flow pattern and wall superheat, greatly reducing heterogeneous nucleation model requirement and promoting the numerical study of flow boiling.

Refining mechanism for TiN and solidification structure through a nucleating chain in magnesium-yttrium-treated ultrapure ferritic stainless steel

To investigate the refining phenomena of TiN inclusion and macro-/microstructure through heterogeneous nucleation of δ-Fe at TiN encapsulating oxide during solidification in ultrapure ferritic stainless steel, five samples were prepared, denoted as the initial, low-yttrium-treated, moderate-yttrium-treated, high-yttrium-treated, and magnesium-yttrium-treated samples. Based on the results of TiN inclusions, the minimum value of the average size (2.61 μm) and the maximum value of the number density (346.70 mm−2) were observed after magnesium-yttrium (Mg–Y) treatment. Combined with the mechanism analysis, these results reveal that the TiN can be refined because of the following three reasons: (ⅰ) the pure oxides, possessing low planar and/or linear disregistry with TiN; (ⅱ) the complex oxides, including the phase, which possesses extremely low disregistry with TiN; and/or (ⅲ) the increasing number of the oxides. By comparison, finer macrostructures were yielded with the addition of Y-/Mg–Y-based modifiers because of the decreasing nucleation barrier, and the finest macrostructure with equiaxed grain ratio of 100% and average grain size of 1.099 mm was observed in the Mg–Y-treated sample. Coupled with the results of TiN inclusions, therefore, the refining efficiency of macrostructure increases with the number of TiN. Referring to the results of differential scanning colorimetry, a general rule of solidification for metallic materials has been revealed. In addition, the in-situ nucleation-growth of δ-Fe was observed using high temperature laser confocal microscopy, and the microstructures were refined after Y/Mg–Y treatment. Eventually, the interfacial wetting-lattice mismatch heterogeneous nucleation model is successfully applied to evaluate the refining phenomenon of macro-/microstructures.

Identification of a common ice nucleus on hydrophilic and hydrophobic close-packed metal surfaces

Establishing a general model of heterogeneous ice nucleation has long been challenging because of the surface water structures found on different substrates. Identifying common water clusters, regardless of the underlying substrate, is one of the key steps toward solving this problem. Here, we demonstrate the presence of a common water cluster found on both hydrophilic Pt(111) and hydrophobic Cu(111) surfaces using scanning tunneling microscopy and non-contact atomic force microscopy. Water molecules self-assemble into a structure with a central flat-lying hexagon and three fused pentagonal rings, forming a cluster consisting of 15 individual water molecules. This cluster serves as a critical nucleus during ice nucleation on both surfaces: ice growth beyond this cluster bifurcates to form two-dimensional (three-dimensional) layers on hydrophilic (hydrophobic) surfaces. Our results reveal the inherent similarity and distinction at the initial stage of ice growth on hydrophilic and hydrophobic close-packed metal surfaces; thus, these observations provide initial evidence toward a general model for water-substrate interaction.

Lithium metal deposition under the geometrical confinement effect: Dendritic copper foam current collector

Dendrite-free lithium is the ultimate goal in achieving the commercial application of lithium metal anode. In this paper, Dendritic Copper Foam Current Collector (DCFC) is prepared by an electrometallurgy method to realize the homogeneous deposition of lithium metal. The deposition behavior of Cu and Li on different interfaces was studied. Firstly, the Cu dendrites constructed on the surface of Cu foam are induced and formed by the potential oscillation generated by the hydrogen evolution reaction. Secondly, the heterogeneous nucleation model reveals that the reason for the dendrite-free lithium deposition on the dendritic copper foam is the geometrical confinement effect. Compared with commercial copper foam, DCFC with hierarchical structure significantly reduces the nucleation energy and deposition overpotential of lithium metal. The in situ optical microscope observation and finite element simulation results confirm our ideas. Electrochemically, DCFC works stably after 1200 h at a lower potential of 36 mV in a DCFC@Li symmetric battery, which is much superior to 75 mV for just 340 h in Cu foam. The ideal collector with a dendritic structure has broad prospects for the practical application of lithium metal anode.

Mechanism for TiN refinement and resultant heterogeneous nucleation of δ-Fe in magnesium-rare earth-treated ultrapure ferritic stainless steel

The effect of magnesium rare-earth (Mg-RE) treatments on TiN epitaxial nucleation to refine the as-cast structure of ultrapure ferritic stainless steel was investigated. Four samples with different melt treatments were prepared, namely an initial sample, a low-RE-treated sample, a high-RE-treated sample, and a Mg-RE-treated sample. The results reveal that TiN can be refined after the RE/Mg-RE treatment because of the co-crystallization of TiN and RE-Mg-Al-O. Moreover, the size of the inclusions increased with the RE content owing to the decreasing number of oxides. Compared to the low-RE treated sample, the average inclusion size of the Mg-RE-treated sample was further reduced because of the presence of more oxides. These results suggest that the number of oxides is a key factor in TiN refinement. However, few changes were observed in the 3D morphology of the composite TiN under such circumstances. In addition, compared with the Initial sample, the RE/Mg-RE treatment yielded finer solidification structures, indicating that the addition of RE/Mg-RE modifiers decreased the nucleation barrier. The solidification structure coarsened with increasing RE content because of the decrease in the inclusion number density, particularly for TiN. The Mg-RE treatment yielded the finest solidification structure with completely equiaxed grains. In addition, high temperature laser confocal microscopy was successfully applied to observe the in-situ nucleation-growth of δ-Fe, showing that the average grain size after Mg-RE treatment decreased by 38.09%. To reveal these phenomena, a new interfacial wetting-lattice mismatch heterogeneous nucleation model is established, accounting for the high-temperature wetting angle (θ1). Using differential scanning calorimetry, the upper limit of the heterogeneous nucleation rate (Iheter.) of δ-Fe was determined from the number density of all the TiN inclusions. Crystallization of primary δ-Fe and Iheter. depend on the critical degree of undercooling (∆Tc∗).

Energetic contributions to deformation twinning in magnesium

Modeling deformation twin nucleation in magnesium has proven to be a challenging task. In particular, the absence of a heterogeneous twin nucleation model which provides accurate energetic descriptions for twin-related structures indicates a need to more deeply understand twin energetics. To address this problem, molecular dynamics simulations are performed to follow the energetic evolution of tension twin embryos nucleating from an asymmetrically-tilted grain boundary. The line, surface and volumetric terms associated with twin nucleation are identified. A micromechanical model is proposed where the stress field around the twin nucleus is estimated using the Eshelby formalism, and the contributions of the various twin-related structures to the total energy of the twin are evaluated. The reduction in the grain boundary energy arising from the change in character of the prior grain boundary is found to be able to offset the energy costs of creating the other interfaces. The defect structures bounding the stacking faults that form inside the twin are also found to possibly have significant energetic contributions. These results suggest that both of these effects could be critical considerations when predicting twin nucleation sites in magnesium.

An extreme value statistics model of heterogeneous ice nucleation for quantifying the stability of supercooled aqueous systems.

The propensity of water to remain in a metastable liquid state at temperatures below its equilibrium melting point holds significant potential for cryopreserving biological material such as tissues and organs. The benefits conferred are a direct result of progressively reducing metabolic expenditure due to colder temperatures while simultaneously avoiding the irreversible damage caused by the crystallization of ice. Unfortunately, the freezing of water in bulk systems of clinical relevance is dominated by random heterogeneous nucleation initiated by uncharacterized trace impurities, and the marked unpredictability of this behavior has prevented the implementation of supercooling outside of controlled laboratory settings and in volumes larger than a few milliliters. Here, we develop a statistical model that jointly captures both the inherent stochastic nature of nucleation using conventional Poisson statistics as well as the random variability of heterogeneous nucleation catalysis through bivariate extreme value statistics. Individually, these two classes of models cannot account for both the time-dependent nature of nucleation and the sample-to-sample variability associated with heterogeneous catalysis, and traditional extreme value models have only considered variations of the characteristic nucleation temperature. We conduct a series of constant cooling rate and isothermal nucleation experiments with physiological saline solutions and leverage the statistical model to evaluate the natural variability of kinetic and thermodynamic nucleation parameters. By quantifying freezing probability as a function of temperature, supercooled duration, and system volume while accounting for nucleation site variability, this study also provides a basis for the rational design of stable supercooled biopreservation protocols.

Investigation on the Atomic Mechanism for Grain Refinement of Magnesium Alloys by Mg-Zr Master Alloy.

The valence electron structure, bond energy, and cohesive energy of Mg, Zr, and α-Mg containing Zr, and α-Zr containing Mg crystals were calculated using the empirical electron theory of solids and molecules (EET). The calculation results show that the bond and cohesive energies of Zr were much greater than those of Mg, so Zr particles could precipitate ahead of α-Mg in general magnesium alloy melts or insoluble Zr particles exist when the magnesium melt temperature is relatively low. The bond energy of α-Zr decreases with the increase in Mg content; therefore, at the end of the growth of Zr particles, the remaining Zr atoms in the melt exist in the form of Mg-Zr clusters. In order to reduce the surface energy of Zr particles, the outer surface of Zr particles tends to terminate with a Zr-Mg atomic layer, that is, a stable two-dimensional Zr-Mg atomic layer is formed first on the (0001) crystal surface of the outermost surface of Zr particles. Furthermore, on the basis of the calculated results, a complementary criterion to the edge-to-edge model of heterogeneous nucleation is also proposed. {ure and single Zr particles cannot become the heterogeneous nucleus of α-Mg, but when there is an atomic layer of two-dimensional Zr-Mg on its surface, the nucleation of particles can be activated. Mg atoms in the liquid phase preferentially attach to the Zr-Mg/Mg-Zr atomic layer on the surface of Zr particles to grow and form a stable ordered structure, which lastly transforms Zr particles into efficient heterogeneous cores.

Three-dimensional microstructure evolution of Ti–6Al–4V during multi-layer printing: a phase-field simulation

Remelting and grain growth in deposited layers and the columnar-to-equiaxed transition (CET) have a significant impact on microstructural evolution during the multilayer printing process. A three-dimensional phase-field model incorporating a heterogeneous nucleation model was developed to study the microstructural evolution under different scanning strategies and scanning velocities during directed energy deposition (DED) additive manufacturing. An experiment was performed to validate the predicted grain morphologies using the proposed model. The results indicate that undercooling determines the extent of heterogeneous nucleation and controls the CET. In comparison with constitutional undercooling and curvature undercooling, thermal undercooling contributes more to the DED of Ti–6Al–4V. The maximum undercooling occurs on the top layer leading to a higher ratio of equiaxed grain formation. The undercooling increases with the build height, which is beneficial for the CET. The growth direction of the columnar grains is controlled by the size and shape of the melt pool. The bidirectional scanning strategy leads to bent columnar grains as a result of the changing growth direction between adjacent deposited layers. The decrease in the scanning velocity leads to coarsening of the grains.

Effect of nanodisperse powders on the spreading and crystallization of a metal drop on a porous substrate

The influence of modifying nanopowders on the spreading and crystallization of a nickel droplet on a porous steel substrate is analyzed. For this purpose, a model has been developed for the spreading of a drop of liquid metal after its high-speed collision with a heated porous substrate. Due to the high impact velocity, the process of metal crystallization is considered after the complete spreading of the drop using the model of heterogeneous nucleation and macroscopic growth of the solid phase, taking into account the size and capillary effects. The influence of the impact velocity and substrate porosity on the thickness and diameter of the formed splat, the penetration depth, and the volume of liquid that penetrated the substrate has been studied. The numerical study of heterogeneous crystallization of a metal drop has made it possible to evaluate the influence of the modifying nanoparticle parameters, the impact velocity, and substrate porosity on the heterogeneous nucleation and on the resulting splat macrostructure.

Promoting effect of AlN foreign particles on crystallization of sodium sulfate decahydrate

Crystallization is a major separation technology in chemical process engineering and wastewater treatment. The promotion of nucleation is a primary concern because it affects both product purity and separation efficiency. In this study, the effect of aluminum nitride foreign particles on the crystallization of sodium sulfate decahydrate was investigated. Also the influence of aluminum nitride foreign particles on kinetics and thermodynamics of sodium sulfate decahydrate nucleation was determined. Induction time, metastable zone width and solubility of sodium sulfate decahydrate in the aluminum nitride foreign particles were determined by the application of a turbidity monitoring technique in stable and uniform temperature conditions by drip titration method unlike the traditional polythermal and isothermal methods commonly applied in the unstable temperature conditions. In the presence of aluminum nitride foreign particles, induction time and metastable zone width decreased 30% and 13% respectively and solubility did not show significant changes. The experimental results were analyzed by empirical secondary nucleation model, classical nucleation theory and empirical Kashchiev heterogeneous nucleation model. It was found that the secondary nucleation model can better illustrate the influence of aluminum nitride foreign particles on nucleation. In the presence of aluminum nitride foreign particles, the surface tension decreased which results in lower induction time.

Simulation of the evaporation/boiling transition for the vaporization of a bi-component droplet under wide-temperature environments

A boiling model was proposed and coupled with a quasi-dimensional evaporation model to simulate the vaporization of a bi-component droplet under wide-temperature environments. Different from previous droplet evaporation models, the transition between droplet evaporation and boiling was especially focused on in this study. In the boiling model, the bubble point temperature of the bi-component mixture was employed to determine the critical condition for the occurrence of the boiling phenomenon. The mass rate of the boiling vaporization of the droplet was calculated by combining the heterogeneous nucleation model, bubble growth model, and bubble fragmentation model. Based on the measurements of the vaporization of an n-heptane/n-hexadecane droplet, the results indicate that the present vaporization model can satisfactorily reproduce the droplet lifetime and diameter evolution under wide ambient temperatures. The simulation results of the vaporization process are greatly affected by the boiling mass rate as the droplet enters the boiling stage. The heterogeneous nucleation rate is the main factor affecting the boiling mass rate, and the decrease of effective thermal conductivity slows down the overall droplet vaporization rate.

Effect of Transient Thermal Conditions on Columnar-to-Equiaxed Transition during Laser Welding: A Phase-Field Study

The columnar-to-equiaxed transition (CET) is commonly observed in laser welds. It is able to prevent the growth of large columnar grains and consequently improve the mechanical properties of welded joints. In this paper, the CET behaviors at different locations in the laser weld of an Al–Mg alloy are observed experimentally and studied systematically. In order to describe the dynamic CET behaviors, an integrated phase-field (PF) model coupled with transient thermal conditions and a Gaussian heterogeneous nucleation model is developed. Investigations on columnar growth under steady conditions are performed first. In particular, the effects of thermal conditions, i.e., solidification rate and temperature gradient, on the constitutionally undercooled degree and region ahead of the solidification front are quantitatively studied. In a laser weld, it is found that the CET behaviors vary significantly along the thickness direction. Our PF simulation results indicate that the CET depends strongly on the locally transient thermal conditions in the fusion zone. The transient thermal conditions affect CET behaviors by dynamically adjusting the constitutionally undercooled degree and region during the solidification process. The predicted CET behaviors under transient conditions exhibit reasonably good agreements with corresponding experimental results.

Ice nucleation imaged with X-ray spectro-microscopy.

Ice nucleation is one of the most uncertain microphysical processes, as it occurs in various ways and on many types of particles. To overcome this challenge, we present a heterogeneous ice nucleation study on deposition ice nucleation and immersion freezing in a novel cryogenic X-ray experiment with the capability to spectroscopically probe individual ice nucleating and non-ice nucleating particles. Mineral dust type particles composed of either ferrihydrite or feldspar were used and mixed with organic matter of either citric acid or xanthan gum. We observed in situ ice nucleation using scanning transmission X-ray microscopy (STXM) and identified unique organic carbon functionalities and iron oxidation state using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in the new in situ environmental ice cell, termed the ice nucleation X-ray cell (INXCell). Deposition ice nucleation of ferrihydrite occurred at a relative humidity with respect to ice, RHi, between ∼120–138% and temperatures, T ∼ 232 K. However, we also observed water uptake on ferrihydrite at the same T when deposition ice nucleation did not occur. Although, immersion freezing of ferrihydrite both in pure water droplets and in aqueous citric acid occurred at or slightly below conditions for homogeneous freezing, i.e. the effect of ferrihydrite particles acting as a heterogeneous ice nucleus for immersion freezing was small. Microcline K-rich feldspar mixed with xanthan gum was also used in INXCell experiments. Deposition ice nucleation occurred at conditions when xanthan gum was expected to be highly viscous (glassy). At less viscous conditions, immersion freezing was observed. We extended a model for heterogeneous and homogeneous ice nucleation, named the stochastic freezing model (SFM). It was used to quantify heterogeneous ice nucleation rate coefficients, mimic the competition between homogeneous ice nucleation; water uptake; deposition ice nucleation and immersion freezing, and predict the T and RHi at which ice was observed. The importance of ferrihydrite to act as a heterogeneous ice nucleating particle in the atmosphere using the SFM is discussed.

THE MIXTURE HETEROGENEOUS BUBBLE NUCLEATION MODEL BASED ON THERMODYNAMIC PROPERTIES OF NONIDEAL FLUIDS

THE MIXTURE HETEROGENEOUS BUBBLE NUCLEATION MODEL BASED ON THERMODYNAMIC PROPERTIES OF NONIDEAL FLUIDS

Mechanism of Heterogeneous Bubble Nucleation in Polymer Blend Foaming.

A three-dimensional heterogeneous bubble nucleation model is constructed to provide a reasonable explanation at the molecular level for the foaming mechanism of polypropylene (PP) and polystyrene (PS) blends. CO2 solubilities and supersaturation rations are quantitatively calculated to help interpret the contribution of each phase of the blend in the CO2 dissolution stage. The spatial density profiles of polymer/CO2 binary melt around different polymer chains are presented to give an intuitive perspective to the thermodynamic driving force. The predicted interfacial tension and contact angles of critical bubbles provide valid evidence to distinguish the wettability of CO2 in different regions. The values of predicted free-energy barriers, critical radii, and nucleation number densities imply that bubbles that nucleate in the PP and PS blend interfacial region attached to the PS-rich phase achieve the smallest size and largest number density. The reliability of the theoretical model has been tested by partial available experimental data.

Моделирование кристаллизации модифицированного наноразмерными частицами расплава при лазерной обработке поверхности металла

A 2D mathematical model is proposed for the modification of an iron-based alloy with refractory nanosized particles. Numerical simulation of the processes during the modification of the surface layer of the substrate metal using the energy of a laser pulse has been carried out. Within the framework of the proposed model, the processes of heating and melting of metal on a substrate covered with a layer of nanosized refractory particles penetrating into the molten metal, convective heat transfer in the melt, and solidification after the end of the pulse are considered. Metal melting is considered in the Stefan approximation, and when the melt is cooled, the model of heterogeneous nucleation and subsequent crystallization is used. The fluid flow is described by the Navier-Stokes equations in the Boussinesq approximation. The distribution of nanoparticles in the melt is modeled by moving markers. Based on the results of calculations, the mode of pulsed laser action is determined, in which a flow is formed for a homogeneous distribution of particles of the modifying substance in the presence of a surfactant in the metal. The volume of the solid phase formed around the nucleus determines the size of the grain structure in the solidified alloy. The liquidus temperature changes depending on the concentration of dissolved carbon in the melt. In the numerical simulation of the solidification of the surface layer of the metal, it was found that the conditions of nucleation and crystallization differ significantly in the volume of the melt. It is determined that the duration of nucleation in a supercooled melt is several tens of microseconds. The maximum number of crystallization centers occurs in areas where heat removal occurs most rapidly. With the growth of the solid phase in the melt and the release of the latent heat of crystallization, the value of supercooling decreases, the nucleation stops and the number of formed crystallization centers does not change further. The distribution of the dispersion of the crystal structure over the volume of the melted metal is estimated. It was found that as the melt cools, sequential-volume crystallization occurs.

Development and validation of a semi-analytical framework for droplet freezing with heterogeneous nucleation and non-linear interface kinetics

We present a novel, semi-analytical framework which accurately predicts every stage of droplet freezing. Supercooling degree of the freezing droplet is computed by coupling the 1-D transient heat conduction equation in spherical coordinates with a modified heterogeneous nucleation model. The coupling connects atomic-scale thermodynamic properties with bulk thermophysical properties and yields interesting insights into the freezing process. The study also develops a novel dendritic growth model for crystal propagation that takes into account the effects of non-linear interface kinetics and surface curvature. This non-equilibrium phase-change formulation during the recalescence stage is coupled with quasi-steady phase change approximation using perturbation series for equilibrium freezing stage to yield an accurate closed form solution of freezing dynamics. The temperature curves, nucleation rates, dendritic growth velocities and mass fraction evolution from the model are validated or verified with the available experimental or numerical data in the literature. The analytical framework developed is a reduced-order freezing model that is fast to compute and yields accurate results. The framework presented can be useful as a subgrid model for high-fidelity crystal growth and spray freezing simulations.

Analytical and experimental study on boiling vaporization and multi-mode breakup of binary fuel droplet

In this paper, the boiling vaporization and breakup of single droplets of n-butanol, n-hexadecane and their binary mixtures with 10-50 w.t.% n-butanol have been studied. The experiments of droplet evaporation with an elevated ambient temperature range of 537-609 K were conducted through the pendant drop method and high-speed camera technology. The mathematical method was also proposed to predict the heterogeneous superheat limit and nucleation rate within the droplet. The experimental results indicate that mono-component droplets only go through the transient heating and stable evaporation phases. While for bi-component droplets, the characteristics show strong two-phase flow instability. With increasing n-butanol concentration or ambient temperature, the heterogeneous nucleation will occur inside the blended droplet, which experiences fluctuation evaporation between the transient heating and stable evaporation phases. The droplet vaporization characteristics gradually change from normal evaporation to partial rupture or passive breakup and then to micro explosion which reduces the droplet lifetime considerably. The novelty of this work is that various ambient temperature conditions and compositions are adopted to study the droplet evaporation to identify the conditions that favor flash boiling, and a new analytical model of heterogeneous nucleation is proposed, which can be used to estimate the temperature at the instant of bubble nucleation.