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Consider a vertical pipe through which humid air flows. The pipe is kept at 5C, which is cooler than the air and, importantly, below the 8C dew point of the air. As a result, water condenses on the inner walls to maintain a thin layer of liquid water. Though the water layer would eventually get thick enough that it would fall due to gravity, you can neglect that here. a. Draw a picture of the physical system, select the coordinate system that best describes the transfer process, and state at least five reasonable assumptions of the mass-transfer aspects of the process. b. What is the simplified form of the general differential equation for mass transfer in terms of the flux of water vapor, NA ? c. What is the simplified differential form of Fick's flux equation for water vapor? d. What is the simplified form of the general differential equation for mass transfer in terms of the molar concentration of water vapor, cA