Constrictivity

from Wikipedia, the free encyclopedia

Constrictivity ( English : constrictivity , from Latin : constringere "to tie up, tie up, paralyze") is a dimensionless geometric quantity that describes the resistance of narrow pores to transport processes such as diffusion . It depends on the ratio of the diameter of the dissolved particle to the pore diameter:

The narrower a pore for a dissolved particle, the greater the value of the constrictivity, but always smaller than 1.

The resistance to transport is caused by an increase in the viscosity of the solvent near the pore walls. This effect is particularly effective with very narrow pores or pore constrictions, the diameter of which is of the same order of magnitude as the diameter of the dissolved particles. Constrictivity needs to be clearly distinguished from Knudsen diffusion , which occurs when diffusing particles collide with pore walls more often than with other particles.

There are a number of empirical formulas for estimating the constraint . For simple pore geometries, it can be derived from the geometry. In practice, the constrictivity together with the tortuosity is often used in models as a purely empirical parameter to determine the effective diffusion coefficient of an entire pore space .

Individual evidence

  1. ↑ Renkin, EM (1954): Filtration, diffusion and molecular sieving through porous cellulose membranes. J. Gen. Physiolog., 38: 225-243
  2. ↑ Beck, RE, Schultz, JS (1970): Hindered diffusion in microporous membranes with known pore geometry. Science, 170: 1302-1305
  3. ↑ Satterfield, CN, Colton, CK (1973): Restricted diffusion in liquids within fine pores. AIChE J., 19: 628
  4. ↑ Chantong, A., Massoth, FE (1983): Restrictive diffusion in aluminas. AIChE J., 29 (5): 725-731
  5. ↑ Petersen, EE (1958): Diffusion in a pore of varying cross section. AIChE J., 4 (3): 343-345
  6. ↑ Curie, JA (1960): Gaseous diffusion in porous media, Parts 1 and 2. Br. J. Appl. Phys., 11: 314-324
  7. ↑ Michaels, AS (1959): Diffusion in a pore of irregular cross section. AIChE J., 5: 270-271

literature

  • P. Grathwohl: Diffusion in natural porous media: Contaminant transport, sorption / desorption and dissolution kinetics . Kluwer Academic Publishers, 1998, ISBN 0-7923-8102-5
  • van Brakel, J., Heertjes, PM (1974): Analysis of diffusion in macroporous media in terms of a porosity, a tortuosity and a constrictivity factor. Int. J. Heat Mass Transfer, 17: 1093-1103