Unit Operations (III) Part 3
Homework
Spring 2015
Chapter 18
By assuming that the mass-transfer coefficients given in Example 18.3
are applicable to the problem described in Example 18.1, proceed to
calculate the required tower height for removing 99% of ammonia by
absorption in water. Summarize the results for the successful design and
operation of this gas absorption tower. (Hint: Example 18.4 can be
consulted for equilibrium data)
Chapter 19
For a certain process requiring air at controlled temperature and humidity
there is needed 10,000 lb of dry air per hour at 30 percent humidity and
130 oF. This air is to be obtained by conditioning air at 30 percent
humidity and 70 oF by first heating, then humidifying adiabatically to the
desired humidity, and finally reheating the humidified air to 130 oF. The
humidifying step is to be conducted in spray chamber. Assuming the the
air leaving the spray chamber is to be 4 oF warmer than the adiabatic
saturation temperature, to what temperature should the air be preheated,
at what temperature should it leave the spray chamber, how much heat
will be required for pre- and reheating ?
Chapter 24
Planks of wood 25.4 mm thick are dried from both sides by air having a
humidity such that the equilibrium moisture content in the wood is X* =
0.04. If the drying is diffusion controlled and the diffusivity of moisture
through the wood is Dv = 2.97 x 10-6 m2/h, how long will it take to dry the
wood from an initial moisture content of 29% to a final moisture content
of 9%?
Chapter 25
Use the correlation in Fig. 25.4 to predict the amount of n-butanol
adsorbed on carbon for the conditions of Example 25.2, and compare
with the experimental data. (See also Problem 25.6)