| AVS 65th International Symposium & Exhibition | |
| Vacuum Technology Division | Monday Sessions |
| Session VT-MoM |
| Session: | Vacuum Measurement |
| Presenter: | Martin-Victor Johansson, Aix Marseille University, France |
| Authors: | M.V. Johansson, Aix Marseille University, France M. Wuest, INFICON, Liechtenstein P. Perrier, Aix Marseille University, France I.A. Graur Martin, Aix Marseille University, France |
| Correspondent: | Click to Email |
The gas flow through the low permeable porous media have a great interest, especially in vacuum technology for filtering, separation process, protection and flow control. It can combine high mass flow rate and a high level of rarefaction. This property makes it particularly suitable as a leak element, by taking advantage of the constancy of conductance in free molecular regime, for example for calibration of ionization gauges or mass spectrometer [1]. The transient experimental technique, developed previously for the mass flow rate measurements through the microchannels [2], is generalized to obtain the permeability directly from the pressure variation measurements. The present experimental methodology, allowing for step by step data verification, leads to higher accuracy than the similar and commonly used method such as "pulse-decay" techniques [3]. The measured data are fitted according to the exponential function with the pressure relaxation time as a single fitting parameter. The new expression for the permeability is proposed involving besides of the geometrical parameters, the ratio between the gas relaxation time (inverse of the gas collision frequency) and the pressure relaxation time. The permeability of the microporous media with the characteristic pore size of 0.2 and 0.5 microns is measured for different gases. It was found that the permeability at low pressure (3 Torrs) increases 50 times compared to atmospheric pressure permeability . This permeability increasing depends essentially on the gas nature.
References:
[1] Hajime Yoshida, Kenta Arai, Hitoshi Akimichi, and Tokihiko Kobata. Newly developed standard conductance element for in situ calibration of high vacuum gauges. Measurement, 45(10):2452 – 2455, 2012. Special Volume.
[2] M Rojas Cardenas, I Graur, P Perrier, and J G Meolans. Thermal transpiration flow: a circular cross-section microtube submitted to a temperature gradient. Phys. Fluids, 23:031702, 2011.
[3] W. F. Brace, J. B. Walsh, and W. T. Frangos. Permeability of granite under high pressure. Journal of Geophysical Research, 73(6):2225–2236, 1968.