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Properties
Published in Rudolf Puffr, Vladimír Kubánek, Lactam-Based Polyamides, 2019
Rudolf Puffr, Miroslav Raab, Břetislav Doležel
Convection of the penetrant through channels in porous membranes or interphase cracks leads to permeabilities higher by an order of magnitude. When the radius (r) of the capillaries is small compared to the free path of the gas molecules, the rate of flow can be expressed by the Knudsen equation, v=(r/6ρp) dp/dx
Design and Modeling of Vacuum Pumping for Steady-State Pellet Fueling Systems
Published in Fusion Science and Technology, 2019
T. E. Gebhart, D. Shiraki, J. Baldzuhn, L. R. Baylor, S. J. Meitner
The left side of the Knudsen equation is dominant for the laminar flow regime and the right side of the equation is dominant for the molecular flow regime. To scale the conductance value for helium gas, the molecular flow portion is multiplied by 2.64 and the laminar flow portion of the equation is multiplied by a factor of 0.92 (Ref. 13). Other gasses have different scale factors. The conductance values are calculated at each time step in the code to account for the changes in pressure that occur with time. Pumping speeds for the pump sets (S1, S2, and S3) are also pressure and thus time dependent. Pumping speed curves are provided by pump manufacturers and are fit with a functional approximation and used in the code. This ensures that a realistic pumping speed is used for any given pressure for greater accuracy in the code results. Pumping speeds are provided or corrected for the dominant gas used, helium in this example design. The gas flow from each pellet, Iacc, is input as a sinusoidal function that, when integrated, provides a gas flow of approximately 10% of A at a frequency of 10 Hz (ω = 2π · 10):