CHAP. 10: TRANSPORT PROCESSES [CONTENTS] 339
Example
A total of 90.2 cm^3 of air flew through a tube with a length of one metre and a radius of 1 mm
in 100 seconds. The pressure at the beginning of the tube was 102 kPa and at its end 101 kPa.
The volume was measured at a pressure of 101 kPa. Calculate the viscosity of air at a given
temperature.
Solution
Under the given conditions, equation (10.13) can be used for air:
η=
π r^4 (p^21 −p^22 )
16 V L p 0
τ=
3. 14 ×(10−^3 )^4 (102 000^2 −101 000^2 )
16 × 90. 2 × 10 −^6 × 1 ×101 000
100 = 1. 8 × 10 −^5 kg m−^1 s−^1.
