304 CHEMICAL ENGINEERING VOLUME 1 SOLUTIONS
PROBLEM 12.9
Calculate the rise in temperature of water flowing at 4 m/s through a smooth 25 mm
diameter pipe 6 m long. The water enters at 300 K and the temperature of the wall of the
tube can be taken as approximately constant at 330 K. Use:
(a) The simple Reynolds analogy,
(b) The Taylor-Prandtl modification,
(c) The buffer layer equation,
(d)NuD 0. 023 Re^0.^8 Pr^0.^33.Comment on the differences in the results so obtained.Solution
See Volume 1, Example 12.3.
PROBLEM 12.10
Calculate the rise in temperature of a stream of air, entering at 290 K and flowing at 4 m/s
through the tube maintained at 350 K; other conditions remaining the same as detailed in
Problem 12.9.
Solution
See Volume 1, Example 12.4.
PROBLEM 12.11
Air flows through a smooth circular duct of internal diameter 0.25 m at an average velocity
of 15 m/s. Calculate the fluid velocity at points 50 mm and 5 mm from the wall. What
will be the thickness of the laminar sub-layer if this extends touCDyCD5? The density
of air may be taken as 1.12 kg/m^3 and the viscosity of air as 0.02 mN s/m^2.
Solution
See Volume 1, Example 12.1.
PROBLEM 12.12
Obtain the Taylor – Prandtl modification of the Reynolds analogy for momentum and heat
transfer, and give the corresponding relation for mass transfer (no bulk flow).
An air stream at approximately atmospheric temperature and pressure, and containing
a low concentration of carbon disulphide vapour, is flowing at 38 m/s through a series of
50 mm diameter tubes. The inside of the tubes is covered with a thin film of liquid and