AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Vapor Pressure Measurements Using Aerosols of Low-Volatile Materials
MATTHEW B. HART, Vasanthi Sivaprakasam, Jay D. Eversole, Naval Research Laboratory
Abstract Number: 459 Working Group: Aerosol Physics
Abstract We have previously described an experimental arrangement for studying aerosols that permits measurements of individual droplet evaporation rates with high precision and relative ease. This capability provides a means for obtaining fundamental molecular properties of different compounds of interest under varying environmental conditions.
The fundamental description of droplet evaporation includes the product of the vapor pressure and the diffusion coefficient of the vaporized material into the surrounding atmosphere [1, 2]. In this presentation, we describe implementation of our experimental technique, which follows a previously demonstrated approach [3], to determine both the vapor pressure and the vapor-gas diffusion coefficient of the droplet material. This is achieved by comparing evaporation rates of liquid aerosols that are electrodynamically levitated in different surrounding gas species and temperatures. In many cases, these specific thermodynamic properties have proven difficult to accurately measure using more conventional methods with bulk materials. Consequently, there is a need for data for many compounds of interest, and while estimates can be made using statistical mechanical relationships, there is a large gap of experimental validation and verification for a range of realistic environmental conditions. Our measurement method provides a high level of precision, and can yield reliable and accurate values from low volatility compounds with vapor pressures less than 10 8 Torr (10-6 Pa). We will discuss results of applying this technique on single, low-volatile droplets levitated in different pure atmospheres of: helium, nitrogen and argon.
1. Fuchs, N., Phys. Z. Sowjet., 6, 225 (1934). 2. Bradley, R. S., et al, “The Rate of Evaporation of Droplets. Evaporation and Diffusion Coefficients, and Vapour Pressures of Dibutyl Phthalate and Butyl Stearate,” Proc. R. Soc. Lond., A186 (1946). 3. Davis, E. J. & Ray, A. K., “Determination of diffusion coefficients by submicron droplet evaporation,” The journal of chemical physics, 67, pp. 414–419 (1977).