BME/ChE 259 Problem Set #1 (2010)
1.
The oxygen diffusion coefficient in tissue is about 1.1x10
5
cm
2
/s. The fluid filtration velocity
is typically 1
m/s.
(a)
Assuming that convection and diffusion are equal in this system, how large a distance
between capillaries would be needed for convection to influence oxygen transport to
tissues?
Solution
The relative importance of convection and diffusion is evaluated by the Peclet number.
Solve for L, assuming that convection equals diffusion so that Pe=1,
(b)
Based upon reported values for the distance between capillaries, do you think that
convection is an important mechanism for oxygen transport in tissues?
Solution
The distance between capillaries is 10
4
m = 0.01 cm.
So convection is negligible compared to diffusion in this problem.
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2.
The alveolar epithelium, basement membrane and lung capillary endothelium are typically 1
m thick. Under resting conditions, hemoglobin binding with oxygen reaches a steady state
of about 0.33 seconds. Is oxygen diffusion across the alveolus a significant factor in the time
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 Spring '12
 Leach
 Atherosclerosis, heart rate, Blood vessel

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