Acoustic measurements of condensation/evaporation and crystal growth

Abstract

Using a volume-modulation technique developed to study thermoacoustics, the complex compressibility of a liquid in coexistence with its vapor is measured. Such a system exhibits a distinctive behavior. At low frequencies, the inverse complex compressibility vanishes because the pressure remains at the equilibrium vapor pressure as the total volume is changed slowly. The volume change is accompanied by an exchange of molecules between the two phases. At higher frequencies, however, this exchange is too slow, and the pressure response approaches that which would be expected in the absence of the liquid phase. The presence of the liquid acts effectively as a high-pass filter whose time constant depends on the rate of condensation/evaporation. The application of this technique to the measurement of condensation coefficients of liquids will be discussed. The same technique can also be applied to solid/vapor systems where the results provide a measure of the crystal growth rate. A unique feature of this technique is that the crystal growth rate can be monitored continuously as a function of temperature. [Work supported by Ohio University Research and Sponsored Programs.]