Browsing by Subject "size distribution"
Now showing 1 - 3 of 3
- Results Per Page
- Sort Options
Item Capillary pressure in a porous medium with distinct pore surface and pore volume fractal dimensions(2008-02) Deinert, M. R.; Dathe, A.; Parlange, J. Y.; Cady, K. B.; Deinert, M. R.; Deinert, M. R.The relationship between capillary pressure and saturation in a porous medium often exhibits a power-law dependence. The physical basis for this relation has been substantiated by assuming that capillary pressure is directly related to the pore radius. When the pore space of a medium exhibits fractal structure this approach results in a power-law relation with an exponent of 3-D-v, where D-v is the pore volume fractal dimension. However, larger values of the exponent than are realistically allowed by this result have long been known to occur. Using a thermodynamic formulation for equilibrium capillary pressure we show that the standard result is a special case of the more general exponent (3-D-v)/(3-D-s) where D-s is the surface fractal dimension of the pores. The analysis reduces to the standard result when D-s=2, indicating a Euclidean relationship between a pore's surface area and the volume it encloses, and allows for a larger value for the exponent than the standard result when D-s>2.Item Effect of pore structure on capillary condensation in a porous medium(2009-02) Deinert, M. R.; Parlange, J. Y.; Deinert, M. R.; Deinert, M. R.The Kelvin equation relates the equilibrium vapor pressure of a fluid to the curvature of the fluid-vapor interface and predicts that vapor condensation will occur in pores or irregularities that are sufficiently small. Past analyses of capillary condensation in porous systems with fractal structure have related the phenomenon to the fractal dimension of the pore volume distribution. Recent work, however, suggests that porous systems can exhibit distinct fractal dimensions that are characteristic of both their pore volume and the surfaces of the pores themselves. We show that both fractal dimensions have an effect on the thermodynamics that governs capillary condensation and that previous analyses can be obtained as limiting cases of a more general formulation.Item The Relationship Between The Optical Depth Of The 9.7 ?m Silicate Absorption Feature And Infrared Differential Extinction In Dense Clouds(2007-09) Chiar, J. E.; Ennico, K.; Pendleton, Y. J.; Boogert, Adwin C. A.; Greene, T.; Knez, Claudia; Lada, C.; Roellig, T.; Tielens, Aggm; Werner, M.; Whittet, D. C. B.; Knez, ClaudiaWe have examined the relationship between the optical depth of the 9.7 mm silicate absorption feature (tau(9.7)) and the near-infrared color excess E(J - K-s), in the Serpens, Taurus, IC 5146, Chameleon I, Barnard 59, and Barnard 68 dense clouds/cores. Our data set, based largely on Spitzer IRS spectra, spans E(J - K-s) p = 0.3-10 mag (corresponding to visual extinction between about 2 and 60 mag). All lines of sight show the 9.7 mu m silicate feature. Unlike in the diffuse ISM where a tight linear correlation between the 9.7 mu m silicate feature optical depth and the extinction (A(V)) is observed, we find that the silicate feature in dense clouds does not show a monotonic increase with extinction. Thus, in dense clouds, tau(9.7) is not a good measure of total dust column density. With few exceptions, the measured values fall well below the diffuse ISM correlation line for E(J - K-s) > 2 mag (AV > 12 mag). Grain growth via coagulation is a likely cause of this effect.