Vibrating mesh atomizers (VMA) are increasing in demand for various aerosol applications due to their ability to generate uniformly sized droplets. Currently there are two types of VMA (commercial metallic membranes and silicon based). High Uniformity and control of small droplet size are the basic requirements for many aerosol applications, for which ultrasonic or VMA are employed. However, there is limited research on understanding the droplet size distribution of different types of atomizers. In this study three aerosol generators were investigated: Ultrasonic, metallic VMA, and MEMS-based silicon VMA. The primary objective was to compare these devices on droplet size distribution and mechanism of action. A systematic study to compare the performance of the two VMA was investigated based on droplet distribution, volumetric median diameter (VMD) using liquids with different physiochemical properties. Size distribution of the droplet produced by the metallic VMA was twice the span compared to silicon VMA for fluids with viscosity <2cP. The metallic VMA also resulted in an increase in VMD as the viscosity increased, whereas the Si VMA did not see a significant increase in VMD. The silicon-based VMA demonstrated a 4-15x increase in fine particle fraction control compared to metallic VMA. The results demonstrate that silicon based VMA has narrower droplet distribution with more uniform droplet size and lower span compared to metallic VMA.
A coaxial turbulent spray burner was used to determine the suppression characteristics of twelve different fire fighting agents in elevated temperature hydraulic fluid and jet he1 (JP-8) spray flames. The effectiveness of the gaseous agents, being considered as alternatives to halon 1301, was compared based upon the mass required for suppression and the equivalent storage volume, normalized by the amount of halon 1301 required to suppress the flame. The elevated temperature results were compared to measurements previously obtained with the incoming air and JP-8 at ambient temperature. No statistically significant difference in relative agent performance was found between the heated hydraulic flame and the previous JP-8 experiments. There was a trend toward higher agent concentrations when the fuel was JP-8 and the temperature of the incoming reactants was 150 "C. In all three experiments, the halon 1301 required the least mass to extinguish the flame, followed by nitrogen. The rest of the alternative fluorinated agents considered required between 1.2 and 2.4 times more mass to suppress the various flames.
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