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2 9 . 1 9 Wastewater containing the dissolved contaminant naphthalene is sent to a well - mixed open pond maintained at 2 0 C

29.19 Wastewater containing the dissolved contaminant naphthalene is sent to a well-mixed open pond maintained at 20C, as shown in the figure (next column). The pond allows the naphthalene to transfer from the water to the air. The pond is 10.0m per side and 1.0m deep. Naphthalene is volatile and slightly
soluble in water, and the equilibrium portioning of naphthalene vapor (solute A) and water at 20C follows Henry's Law with H=36.6Pa*m3gmole. The concentration of dissolved naphthalene in the inlet waste water is cAL,o=0.25gmolem3, and the outlet concentration of the exiting waste water is cAL=0.15 gmolem3. Air blows over the entire flat liquid surface of the pond, and it has been determined that the convective mass transfer coefficient for naphthalene across the gas film is kc=0.50cms(3.010-3ms). It has also been determined that the liquid film mass transfer coefficient for naphthalene is kL=4.010-5ms. Assume that naphthalene vapor concentration in the bulk air is zero (e.g.,yA=0,pA=0). The process is at 1.0atm total system pressure and temperature of 20C. At these process conditions, the gas-phase diffusion coefficient of naphthalene in air is 0.065cm2s. The molecular weight of naphthalene (MA) is 128ggmole.
a. Plot out the operating point (pA,cAL) on the pA-cAL diagram. What is the Henry's Law constant, H, as defined by pA,i=HcAL,i? What are pA** and cAL**? Plot out pA**,cAL**,pA,i, and cAL,i.
b. What is the overall mass transfer coefficient based on the liquid phase driving force, KL?
c. What is the velocity of air flowing over the pond (v), in units of ms to achieve kc=0.50cms, and its Reynolds and Schmidt numbers, Re and Sc?
d. What is the inlet volumetric flowrate of wastewater into the pond (vo), in units of m3h?
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