ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
A frequency response device has been designed and built based on previous efforts by Y. Yasuda, L. C. V. Rees, F. Meunier, and Ph. Grenier. This design uses the best attributes of the three previous devices and is improved in five specific ways. First, the device makes use of the fast response capacitance manometer. Second, the device uses a servomotor to push and pull a metal bellows pump, which drives the sinusoidal input function, removing the chance of "floating" the bellows. Third, both sinusoidal and step-change volume perturbations can be studied. Fourth, the overall cost of the device was kept below $30 000. Finally, the pressure transducer is mounted only 8 cm from the sample, instead of ∼30 cm, thus removing any averaging of the pressure signal at higher frequencies. The device is currently capable of measuring frequencies between 0.005 and 5 Hz, a range of three full orders of magnitude. The system can operate at temperatures between room temperature and 473 K and pressures between 0.3 and 300 Torr. Two systems were used to test the device, n-hexane/silicalite and methanol/silicalite. The model developed by Yasuda is used to analyze the frequency response of these systems. This model can describe a system as having more than one diffusivity and accounts for the presence of a surface resistance to diffusion. The results for n-hexane/silicalite and methanol/silicalite are compared to those of van den Begin and Nayak, respectively, and are in good agreement. Also, the diffusivities measured using this device are comparable to those estimated in 1997 by Rees using the frequency response method. In addition to measuring the diffusion rate processes, the kinetic parameters associated with a surface resistance to diffusion were also estimated. © 2001 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1408931
