Problem 2: Engineers sometimes use pipes as reactors in treatment plants. Suppose that the plant flow is 3.3 ft3 /s (about 2.1 million gallons per day, mgd) and a cylindrical pipe is to be used for disinfection. A. Draw a sketch of the system. Indicate the control volume by a dashed line. What kind of hydrodynamic model should you use for a pipe? What mixing conditions should you assume? B. Write the integrated mass balance equation for the pollutant in symbols at steady state. (“Integrated” means that your mass balance looks like: C = …) Define your symbols. C. For a pipe 3.5 feet in diameter and 50 feet long, what is the hydraulic residence time in minutes? D. For the pipe in Part C, what value of the first-order rate constant (in min–1 ) is needed to achieve a 99% removal of bacteria
Problem 2: Engineers sometimes use pipes as reactors in treatment plants. Suppose that the plant flow is 3.3
ft3
/s (about 2.1 million gallons per day, mgd) and a cylindrical pipe is to be used for disinfection.
A. Draw a sketch of the system. Indicate the control volume by a dashed line. What kind of hydrodynamic
model should you use for a pipe? What mixing conditions should you assume?
B. Write the integrated mass balance equation for the pollutant in symbols at steady state. (“Integrated” means
that your mass balance looks like: C = …) Define your symbols.
C. For a pipe 3.5 feet in diameter and 50 feet long, what is the hydraulic residence time in minutes?
D. For the pipe in Part C, what value of the first-order rate constant (in min–1
) is needed to achieve a 99% removal of bacteria?
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