Test 4.pdf

# Test 4.pdf - UNIVERSITY OF ARIZONA DEPARTMENT OF CHEMICAL...

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UNIVERSITY OF ARIZONA DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL ENGINEERING CHEE 305 TRANSPORT PHENOMENA SPRING 2017 Test 4 Wednesday, May 10 Problem 1 (40 %) To oxygenate water, small water droplets (R = 1 mm) are contacted with a large volume of pure oxygen (A) gas at 1 atm and 20 ºC. The water to be used already has some oxygen because it was at equilibrium with atmospheric air, which has a partial pressure of oxygen P A = 0.21 atm. The diffusivity of oxygen in liquid water (B) at 20 ºC is 3.24 × 10 -9 m 2 /s. The equilibrium partitioning of oxygen between a gas and liquid water is governed by Henry’s law, Aw A Hc P , H = 0.77 m 3 atm/mol at 20 ºC Neglect water evaporation. 1. Calculate the maximum number of moles of oxygen that the droplet can have at the end of this oxygenation process. 2. Calculate the contact time necessary to load the droplets with 99% of the maximum total moles. 3. If the water droplets were contacted with a gas at a total pressure of 1.5 atm that is a mixture of oxygen (partial pressure 1 atm) and nitrogen (partial pressure 0.5 atm) instead of pure oxygen at 1 atm, would the answer to part 2 change? If so, would the needed contact time be longer or shorter? Explain in detail.

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Problem 2 (60 %) During a certain stage of ripening and in the presence of excess oxygen, a banana produces 5 × 10 -7 L of ethylene gas (measured at 25 ºC and 1 atm) per hour and per kg of flesh. We will model the banana
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