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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)