Explosion Of Droplets Research Articles

An Experimental study on steam explosion of multiple droplets in different chemical solutions

Motivated by the interest in steam explosion in chemical solutions and seawater, a series of tests were carried out in the MISTEE facility at KTH to investigate steam explosion characteristics as multiple molten droplets of tin were falling through a coolant pool containing deionized water, boric acid solution, neutral solution of boric acid and sodium phosphate, and seawater, separately. The experimental results revealed distinct and complex characteristics of steam explosion of multiple droplets, which were not observed in previous single-droplet steam explosion experiments. The tin melt samples of 5 g and 20 g were employed to formulate different numbers of multiple droplets. In the test with 5 g melt, steam explosion was more energetic at a deeper explosion location − a similar trend found in the single-droplet steam explosion test with 1 g melt. However, the test of 20 g melt did not show a clear trend in a wide range of explosion depth. The peak pressure and impulse increased with increasing mass of melt sample. The steam explosion occurred more closely to the coolant pool surfaces in the seawater and chemical solutions than in deionized water. Steam explosion intensity was significantly reduced in a neutral solution containing 1.2 wt.% boric acid and sodium phosphate. The influence of the chemical solutions on steam explosion was diminishing in the tests with multiple droplets.

An experimental study on the effect of chemical additives in coolant on steam explosion

In assessment of severe accident risk in light water reactors (LWRs), steam explosion is a nonnegligible phenomenon following a relocation of core melt (corium) into coolant, and thus various research efforts have been paid to steam explosion. There had been numerous studies showing that the occurrence of steam explosions is influenced by several factors such as melt and coolant temperatures, melt materials, non-condensable gasses, etc. However, most of the existing experiments used deionized (DI) water or tap water as coolant, with little consideration of the effect of chemicals (e.g. boric acid, sodium hydroxide, sodium phosphate) commonly applied in reactor coolant. To examine the effect of the chemical additives in coolant on steam explosion, the present study performs a series of molten Tin droplet-coolant interaction tests using DI water and different chemical solutions, including H3BO3 solutions, NaOH + H3BO3 neutral solutions, and Na3PO4 + H3BO3 neutral solutions. The experimental results show that adding NaOH and Na3PO4 in boric acid solution significantly affects the occurrence probability of spontaneous steam explosion, because of the presence of PO43− and H+ ions. When different solutions have equivalent concentrations of H3BO3, the peak pressure values of the spontaneous steam explosion of Sn droplets are similar among various solutions. Compared with those in DI water, steam explosion in the chemical solutions occurs predominantly within a narrow range of depth from 28 mm to 40 mm and produces a much higher peak pressure. This implies that more energetic steam explosions may occur in the chemical solutions.

Explosion of metastable droplets in immiscible liquids

Evaporation of metastable droplets in an immiscible liquid can occur in a wide range of practical applications and in particular in cryogenic systems due to the low saturation temperature of the cryogenic liquid. In this article, we show experimentally that the incomplete explosion of a metastable droplet can lead to a ‘film evaporation’ configuration, where a remaining droplet is eventually separated from the host immiscible liquid by an established vapour layer. Based on a transient heat diffusion model, we identified that the necessary but not sufficient condition for the complete explosion of a metastable droplet is that the droplet must absorb, before explosion, an amount of heat larger than the latent heat required for a full evaporation, i.e. the global Jacob number Ja≥1. In addition, the measured superheat limits of pentane and isohexane are 420.65 K and 444.95 K respectively, which are very close to the theoretical Spinodal points (≤ 1.5 K) and other reported values in existing literature. Therefore, the experimental setup reported here can be used as an alternative way to quantify the superheat limit. The Droplet relaxation time was also found scaled to the square root of the diffusion characteristic time.

Breakup and explosion of droplets of two immiscible fluids and emulsions

The explosive breakup of liquid, emulsion, and slurry droplets enables a several-fold increase of their evaporation surface area. This effect reduces the energy and time required for fuel heating, evaporation, and ignition. It also lowers anthropogenic emissions and provides fuller fuel burnout. However, the conditions and possible regimes of explosive breakup of liquid, slurry and emulsion droplets have yet to be found. Knowledge on such processes is necessary for improving the performance of fuel ignition and combustion as well as thermal and flame liquid treatment. Component mixing and storage may differ. The experiments in this research compare the explosive breakup of heated droplets of two immiscible fluids (e.g., water/flammable liquid) and water-in-diesel (W/D) emulsions stabilized by monoethanolamides of fatty acids. The experiments used the most widespread combustible liquids and fuels applied in the industry: kerosene, gasoline, diesel, petroleum oils, as well as petroleum. The most valuable findings are as follows: the experimentally established threshold conditions of droplet breakup, two regimes of droplet fragmentation, four outcomes of the parent droplet heating, as well as the number and size of the resulting fuel aerosol droplets. Another important experimental result consists in determining the maximum droplet heating times to explosive breakup corresponding to the equal proportions of water and flammable liquid (or fuel) in a droplet. If one of the components significantly exceeded the other one in proportion, the shortest heating time to droplet breakup was observed. The focus was on comparing the characteristics and parameters of droplets of W/D emulsions and droplets of two immiscible fluids. W/D emulsion droplets break up to form a fine aerosol, whereas two-component droplets show two breakup regimes: puffing and micro-explosion. The results obtained are important for the development of high-potential gas-vapor-droplet technologies to intensify the evaporation of additives and the ignition of fuel compositions.

Preparation of nanoparticle-embedded thin films by simultaneous feeding of gaseous and solid raw materials in plasma-enhanced chemical vapor deposition process

Titania (TiO2) films in which silica (SiO2) nanoparticles are embedded (SiO2/TiO2 films) are prepared by a combination of a novel aerosolization technique and plasma-enhanced chemical vapor deposition (PECVD). Using titanium tetraisopropoxide (TTIP) in a microwave plasma field, anatase films are prepared on silicon and quartz-glass substrates. By utilizing Coulomb explosion of charged droplets in the plasma field, an aerosol with well-dispersed SiO2 nanoparticles is obtained from the breakup of sprayed droplets of a nanoparticle suspension. Simultaneous feeding of the TTIP vapor as a gaseous raw material and the SiO2 nanoparticle aerosol as a solid raw material enables preparation of the SiO2/TiO2 films with many protrusions. The number and size of the protrusions increase with increasing concentration of the nanoparticle suspension and increasing size of the nanoparticles, respectively. The size of the nanoparticles is related to the surface roughness of the SiO2/TiO2 films. Quantitative evaluation of the protrusions suggests that the mechanism of the protrusion evolution on SiO2 nanoparticles varies with the size of the nanoparticles. Embedding SiO2 nanoparticles into the TiO2 films enhances the photocatalytic activities compared to that of a TiO2-only film probably because the protrusions increase the surface area of the films.

Nanoparticles formation mechanisms through the spark erosion of alloys in cryogenic liquids.

Mechanisms of the formation of nanoparticles of some B2 shape memory intermetallic compounds, glass-forming Zr-based alloy, and pure Ti obtained by spark erosion method in liquid nitrogen and argon are considered. One of peculiarity is a foam-like structure, which covers the surface of micron-sized particles that appear during spark erosion. Such morphology is related to the nanosized particles gathered in agglomerates. Detailed examination of those particles allows proposed several mechanisms of their formation. The mechanisms explains two kinds of nanosized particles: particles of several tens and even hundreds of nanometers are formed due to explosion of molten droplets while the smaller particles having in turn a different structure and morphology are formed as a result of condensation of evaporated constituents under different conditions. The latter have the composition usually different from the target composition while the composition of the former is very close to the target (master alloy) composition.

Biomimetic Acoustically-Responsive Vesicles for Theranostic Applications.

In recent years, biomimetic cell membrane-derived particles have emerged as a new class of drug delivery system with advantages of biocompatibility, ease of isolation and long circulation profile. Here we report the development and potential theranostic applications of a new biomimetic acoustically-responsive droplet system derived from mammalian red blood cell membrane (RBCM). We hypothesized that drug-loaded RBCM droplets (RBCMDs) would undergo a transition from liquid (droplets) to gas (bubbles) upon high intensity focused ultrasound (HIFU) insonation, resulting in on-demand drug release. The generated microbubbles could also serve as a contrast agent to enhance ultrasound imaging. As-synthesized RBCMDs exhibited uniform size, good dispersity and preservation of RBCM-associated proteins that prevented uptake by macrophages. Camptothecin (CPT), an anti-cancer drug, was successfully loaded in the RBCMDs with a loading efficiency of 2-3% and an encapsulation efficiency of 62-97%. A short (3 min) exposure to HIFU irradiation triggered release of CPT from the RBCMDs and the physical explosion of droplets damaged nearby cancer cells resulting in significant cell death. In addition, the acoustically vaporized RBCMDs significantly increased the ultrasound echo signal to 30 dB. Lastly, we demonstrated that RBCMDs could be acoustically vaporized in vivo in target tissues, and enhancing ultrasound imaging. Taken together, we have developed a new class of naturally derived RBCMDs which show great potential for future application in remotely triggered drug delivery and ultrasound imaging enhancement.

Aerosol Generation by a Spray-Drying Technique Under Coulomb Explosion and Rapid Evaporation for the Preparation of Aerosol Particles for Inhalation Tests

In this study, nanosized (<100 nm) aerosol particles with high mass concentrations for inhalation tests were generated by a spray-drying technique with combining Coulomb explosion and rapid evaporation of the droplets. Under typical spray-drying conditions, aerosol particles with average diameter of 50–150 nm were prepared from a suspension of NiO nanoparticles with a primary diameter of 15–30 nm. Under the Coulomb explosion method, the sprayed droplets were charged by being mixed with unipolar ions to break up the droplets, which resulted in the generation of smaller aerosol particles with diameters of 15–30 nm and high number concentrations. Under the rapid evaporation method, the droplets were heated immediately after being sprayed to avoid inertial impaction on the flow path due to shrinkage of the droplet, which increased the mass concentration of the aerosol particles. The combination of the Coulomb explosion and rapid evaporation of droplets resulted in the generation of aerosol particles with size...

Droplet transfer during conventional gas metal arc and plasma-gas metal arc hybrid welding with Al 5183 filler metal

When welding with 5xxx series aluminium filler wires, explosion of droplets occurs during droplet transfer, which results in spatter formation. In plasma-GMA (gas metal arc) hybrid welding, the coaxial plasma arc surrounding the GMA enables more stable droplet transfer and lower GMA current. In this study, bead-on-plate welding tests were conducted using conventional GMA welding and plasma-GMA hybrid welding. Droplet transfer behaviours for both processes were observed using high-speed imaging, and droplet explosion behaviour was analysed under various welding conditions. In plasma-GMA welding, the droplet transfer was stabilized without in-flight explosion, even for high welding current and higher melting rate was achieved by the additional plasma arc.

Archiving and Absolute Quantitation of Solutes Separated by Single Charged Droplet Coulomb Explosion

The electrospray (ES) ion source relies on the transfer of low-volatility solutes to the gas phase as an outcome of coulomb explosion events of charged droplets generated by electrical atomization. Introduced here are two methods for archiving compounds separated by coulomb explosion of single droplets having net charge that had been levitated in an electrodynamic balance. We categorized compounds separated by the explosion as either material ejected, including progeny droplets, or the material retained in the main residue. The potential for this methodology is illustrated by (i) qualitative characterization of solute states, aqueous versus precipitated in the separated material, and (ii) absolute quantitation of solutes separated by such an event. For a droplet containing 5 x 10(7) 20-nm-diameter fluospheres, its first encountered coulomb explosion event resulted in the ejection of 1.70% of them. The capability to acquire such detailed information regarding the individual steps in the process of transferring low-volatility solutes to the gas phase in an ES ion source is essential to develop strategies for absolute quantitation in applications of ES mass spectrometry.

Thermal radiation effect on thermal explosion in gas containing fuel droplets

The effect of thermal radiation on the dynamics of a thermal explosion of a flammable gas mixture with the addition of volatile fuel droplets is studied. This is based on an original physical model of self-ignition. The thermal radiation energy exchange between the evaporating surface of the fuel droplets and burning gas is described using the P-1 model with Marshak boundary conditions. The original system of equations describing the effects of heating, evaporation and the combustion of fuel droplets is simplified to enable their analysis using asymptotic methods. The mathematical formulation is eventually reduced to a singularly perturbed system of ordinary differential equations. This allows us to apply the advanced geometric asymptotic technique (integral manifold method) for the qualitative analysis of the behaviour of the solution. Possible types of dynamic behaviour of the system are classified and parametric regions of their existence are determined analytically. The main attention is concentrated on the situations where delays might occur before the final ignition. Our study is focused on the impact of thermal radiation on the delay time. The dimensionless parameter responsible for the impact of thermal radiation is singled out and analysed. The dependence of the delay characteristics on the physical parameters of the problem under consideration is analysed. An explicit expression for the minimum time delay of the thermal explosion of fuel droplets in the presence of thermal radiation is derived and applied to the thermal explosion of n-decane and tetralin droplets. It is pointed out that the effects of thermal radiation can be significant, especially at high temperatures, and cannot be ignored in the analysis of this phenomenon.

Thermal and optical processes in shattering water aerosol droplets by intense optical radiation

The subject of the present theoretical study is thermal and optical processes occurring in heating and explosion of water aerosol droplets by intense optical radiation propagating in the aerosol. A system of equations is formulated to describe the processes of radiation propagation in the aerosol and its interaction with individual droplets. The space-time distributions of parameters are obtained on the basis of a numerical solution of the formulated system of equations. The effect of the intensity and density of the 10.6 μm radiation energy, number of secondary droplets and vapour fraction formed after radiationinduced thermal explosion of droplets on the parameters of the process is considered. Comparison of some numerical results with experimental data is made.

Propagation of laser breakdown and detonation waves in transparent droplets

A computer model is used to study recent experiments investigating laser-induced plasma formation and explosion of single liquid aerosol droplets. The model accounts for the formation and evolution of the plasma and the resulting fluid flow; it does not account for the initial breakdown. The model shows all the qualitative features of the experiment, including laser-supported detonation waves, which at high laser intensities rapidly convert the whole droplet into a plasma. In addition, quantitative agreement with measured velocities has been obtained to within approximately 50%.

Scattering of optical radiation by fog water droplets

The behavior of local optical characteristics of an aerosol medium in the radiation field of a microsecond-pulse CO2 laser is experimentally investigated. Using measurements of the scattering intensity of a sounding beam, the dynamics behind the formation of a propagation channel over the interaction time is studied for different energy densities, and the characteristic times over which the channel is clouding and clearing, the dimensions of the explosion products, and the degree of their evaporation are established. Scattering of radiation in the visual range by shock waves is observed that is caused by the gas-dynamic explosion of fog droplets.

Laser-induced explosion of H_2O droplets: spatially resolved spectra

Photographs and spatially resolved spectra were obtained with radiation generated by an exploding water droplet. The emission within the droplet consists of stimulated Raman scattering and a continuum associated with the created plasma. The forward plume (outside the shadow face) contains plasma and atomic hydrogen ejected from the droplet. The backward plume (behind the illuminated face) contains plasma, H, and ionized O and N, resulting from ionized air. Mechanisms for laser-induced explosion of large transparent water droplets are briefly discussed.

Explosion of water droplets

We use self-similarity to describe the motion of vapor emanating from a water droplet that has been exploded by a short pulse from a high energy laser. This approach allows us to obtain a qualitative description of the experiment of Kafalas and Herrmann.

Vaporization and explosion of water droplets on exposure to radiation with inhomogeneous internal heat evolution

An analysis is made of the vaporization and explosion of water droplets on exposure to λ = 10.6 μ continuous and pulsed radiation at intensities corresponding to gas-kinetic conditions. Allowance is made for the inhomogeneity of the internal heat evolution. Estimates are made of the influence of the radiation intensity, pulse profile, and droplet parameters on the time taken to achieve explosive vaporization and the required energy is determined.

Combustion of metal droplets ignited by flash heating

The use of single, intense pulses of light from a capacitor discharge lamp to form and ignite submillimeter droplets of metals in a glass oxidation chamber is described. The droplets were photographed in free fall, or were quenched in liquid argon at various stages of combustion and analyzed conventionally. It has been possible to investigate burning droplets of Zr, Ta, Ti, Mo, W, Pu, Sm, Re, and Al by this technique. The combustion of Zr is emphasized here. The violent fragmentation or explosion of zirconium droplets that occurs a short time after ignition has been shown to be related to the presence of nitrogen and possibly other gas-related impurities in the combustion system. Zirconium droplets that do not explode when burning in pure oxygen may be induced to fragmenteither by dissolving a small amount of nitrogen in the metal before ignition or by adding a few per cent of gaseous nitrogen to the oxygen. A similar effect can be produced by coating the metal thinly with a heavy hydrocarbon wax prior to ignition. In the explosion-free combustion of zirconium droplets, it has been possible to observe spearpointing—the abrupt brightening of a droplet near the end of combustion—by photographic techniques. This has been ascribed to the sudden freezing of the droplet and is probably due to nucleation of the droplet after appreciable supercooling. This phenomenon should provide a calibration point for the determination of burning temperatures of certain metal droplets. Direct microweighing of droplets quenched in liquid argon at various stages of combustion has provided preliminary information on the kinetics of oxygen uptake by molten zirconium. In pure oxygen near atmospherie pressure, a 525-μ droplet reacts with less than 3% of the oxygen molecules that strike its surface during combustion, an indication that mass-transfer processes within the droplet limit the rate of oxidation.