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A mixture of n-hexane vapor and air leaves a solvent
Chapter 8, Problem 8.50(choose chapter or problem)
A mixture of n-hexane vapor and air leaves a solvent recovery unit and flows through a 70-cm diameter duct at a velocity of 3.00 mls. At a sampling point in the duct the temperature is 40C, the pressure is 850 mm Hg, and the dew point of the sampled gas is 25C. The gas is fed to a condenser in which it is cooled at constant pressure, condensing 60% of the hexane in the feed. (a) Perform a degree-of-freedom analysis to show that enough information is available to calculate the required condenser outlet temperature CC) and cooling rate (kW). (b) Perform the calculations. (c) If the feed duct diameter were 35 cm for the same molar flow rate of the feed gas, what would the gas velocity be?
Questions & Answers
QUESTION:
A mixture of n-hexane vapor and air leaves a solvent recovery unit and flows through a 70-cm diameter duct at a velocity of 3.00 mls. At a sampling point in the duct the temperature is 40C, the pressure is 850 mm Hg, and the dew point of the sampled gas is 25C. The gas is fed to a condenser in which it is cooled at constant pressure, condensing 60% of the hexane in the feed. (a) Perform a degree-of-freedom analysis to show that enough information is available to calculate the required condenser outlet temperature CC) and cooling rate (kW). (b) Perform the calculations. (c) If the feed duct diameter were 35 cm for the same molar flow rate of the feed gas, what would the gas velocity be?
ANSWER:A. (a) The degree of freedom analysis shows that two equations and two unknowns are provided in this problem. The two equations are the first law of thermodynamics and the energy rate balance, which both depend on the temperature, molar fraction, pressure, and velocity information given in the problem statement. This means that the two unknowns, the condenser out