Accurate air flow measurement requires

Chapter 6, Problem 6.21

(choose chapter or problem)

Accurate air flow measurement requires straight,unobstructed pipe for a minimum of 10 diametersupstream and 5 diameters downstream ofthe measuring device. In one particular application,physical constraints compromised the pipelayout, so the engineer was considering installingthe air flow probes in an elbow (Plan A),knowing that flow measurement would be lessaccurate but good enough for process control.This plan would be acceptable for only 2 years,after which a more accurate flow measurementsystem with the same costs will be available.Plan A has a first cost of $25,000 with annualM&O estimated at $4000. Plan B involves installationof a recently designed submersible airflow probe. The stainless steel probe could beinstalled in a drop pipe with the transmitterlocated in a waterproof enclosure on the handrail.The cost of this system will be $88,000, butbecause it is accurate, it would not have to bereplaced for at least 6 years. Its maintenancecost is estimated to be $1400 per year. Neithersystem will have a salvage value. (a) At i = 12%per year, select A or B on the basis of an AWcomparison. (b) Use future worth analysis to selectbetween A and B.