Addition of boron nanoparticles to liquid oxygenated fuel lead to the formation of nano‑boron slurries with high energy density. This study focuses on ignition and combustion characteristics of single droplets of nano‑boron slurries during ultrasonic levitation and effects of different oxygenated fuels on ignition and combustion characteristics of single droplets. In this study, nano‑boron slurries of boron/ethanol, boron/1-hexanol, boron/dimethyl carbonate, boron/triacetate, boron/propylene glycol monomethyl ether and boron/tripropylene glycol monomethyl ether with 10 wt% solid loading were prepared. Moreover, an ultrasonic levitation system was designed and established, which was used for igniting single droplets in ultrasonic levitation state. The results indicate that ignition and combustion process of levitated single droplets of nano‑boron slurries can be divided into three stages: a stable endothermic stage, an oscillation and micro-explosion stage and an aerosol combustion stage . Smoke was observed before aerosol combustion stage of boron/triacetate and boron/tripropylene glycol monomethyl ether, whereas flame jets were observed during combustion of other fuels. Furthermore, emission spectra of BO 2 with high intensity could be observed during aerosol combustion stage. A shorter main chain length of oxygenated fuel facilitates ignition of nano-B slurries. Boron/propylene glycol monomethyl ether exhibited shortest ignition delay , which was approximately 13.8% shorter than that of boron/tripropylene glycol monomethyl ether with the longest ignition delay. Furthermore, a longer main chain length of oxygenated fuel facilitates combustion of nano-B slurries. Nano‑boron slurries with longer main chains (boron/1-hexanol, boron/triacetate and boron/tripropylene glycol monomethyl ether) exhibited brighter and larger flames, regardless of whether they were alcohols, esters or ethers, and quenched zones with bright and clearly delineated edges were observed. Intensity integral and maximum intensity of emission of these three fuels were also higher than those of other fuels. Boron/triacetate demonstrated the best combustion performance, with maximum intensity and intensity integral at 547.8 nm being 3.88 times and 1.9 times those of boron/ethanol, respectively, which has the worst combustion performance. This study provides a theoretical basis and experimental reference for the application of oxygenated-fuel-based nano‑boron slurries and their base liquid fuel selection.
Evaporation of cyclohexane and ethanol binary drops under acoustic levitation was investigated. The aim was to understand the effect of acoustic levitation on the evaporation dynamics and involved physical processes of the binary drops. We report the occurrence of liquid-phase separation of the binary drop during evaporation under acoustic levitation. Through systematic experiments, it was found that the enhanced evaporation rate of the drop under acoustic levitation led to a significant temperature decrease. In addition, driven by external acoustic streaming, water vapor tended to be enriched and condensed on the drop surface. Because ethanol is extremely soluble in water, tiny cyclohexane droplets were extracted from ethanol owing to water condensation. In addition, driven by the internal flow of the acoustically levitated drop, the extracted cyclohexane droplets coalesced, eventually resulting in macro-segregation in the drop. These findings provide new insights into the evaporation dynamics of acoustically levitated drops, thus, shedding light on industrial purification and separation of volatile liquids with opposite water solubilities, such as cyclohexane and ethanol.
Concentrating a trace amount of molecules from liquids, solid objects, or the gas phase and delivering them to a localized area are crucial for almost any trace analyte detection device. Analytes within a liquid droplet resting on micro/nanostructured surfaces with liquid-repellent coatings can be concentrated during solvent evaporation. However, these coatings suffer from complex manufacturing procedures, poor versatility, and limited analyte enrichment efficiency. Here, we report on the use of an acoustic levitation platform to losslessly concentrate the analyte molecules dissolved in any volatile liquid, attached to solid objects, or spread in air. Gold nanoparticles can be simultaneously concentrated with the analytes in different phases, realizing sensitive, surface-enhanced Raman scattering detection even at attomolar (10 −18 mol/L) concentration levels. The acoustic levitation platform-enabled, lossless analyte enrichment can significantly increase the analytical performance of many conventional microsensing techniques.
危险品化学品经营许可证（带存储）