6. Unsteady-State Diffusion. A small spherical bead is used as a controlled drug-release capsule in the gastrointestinal system. In the particular case, a 0.1-cm-diameter bead has a uniform initial concentration of 0.2 mmol/L of the drug griseofulvin (species A). Determine the time it will take for the concentration of griseofulvin at the center of the bead to reach 10% of its original value. The diffusivity of griseofulvin within the bead material is 1.50 x 10-7 m²/s. Upon release from the bead, the drug is immediately consumed so that the surface concentration is essentially zero. Guide: Use Figure 5.3-9 in Geankoplis (Page 345). Analyze the image of the sphere (top right of the figure). Before you ask for the mass transfer coefficient, see if it is needed.

Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
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6. Unsteady-State Diffusion. A small spherical bead is used as a controlled drug-release capsule in the
gastrointestinal system. In the particular case, a 0.1-cm-diameter bead has a uniform initial concentration of 0.2
mmol/L of the drug griseofulvin (species A). Determine the time it will take for the concentration of griseofulvin
at the center of the bead to reach 10% of its original value. The diffusivity of griseofulvin within the bead material
is 1.50 x 10 m2 /s. Upon release from the bead, the drug is immediately consumed so that the surface
concentration is essentially zero.
Guide:
Use Figure 5.3-9 in Geankoplis (Page 345). Analyze the image of the sphere (top right of the figure).
Before you ask for the mass transfer coefficient, see if it is needed.
Transcribed Image Text:6. Unsteady-State Diffusion. A small spherical bead is used as a controlled drug-release capsule in the gastrointestinal system. In the particular case, a 0.1-cm-diameter bead has a uniform initial concentration of 0.2 mmol/L of the drug griseofulvin (species A). Determine the time it will take for the concentration of griseofulvin at the center of the bead to reach 10% of its original value. The diffusivity of griseofulvin within the bead material is 1.50 x 10 m2 /s. Upon release from the bead, the drug is immediately consumed so that the surface concentration is essentially zero. Guide: Use Figure 5.3-9 in Geankoplis (Page 345). Analyze the image of the sphere (top right of the figure). Before you ask for the mass transfer coefficient, see if it is needed.
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