The initial ultimate bod after mixing of the bergelmir river is 12.0 mg · l−1. the do in the bergelmir river after the wastewater and river have mixed is at saturation. the river temperature is 10◦ c. at 10◦ c, the deoxygenation rate constant (kd) is 0.30 day−1 , and the reaeration rate constant (kr) is 0.40 day−1 . determine the critical point (tc) and the critical do. tc = 2.88 days. critical do = 7.53 mg · l−1

For the closed feedwater heater below, feedwater enters state 3 at a pressure of 2000 psia and temperature of 420 °f at a rate of ix10 ibhr. the feedwat extracted steam enters state 1 at a pressure of 1000 psia and enthalpy of 1500 btu/lbm. the extracted er leaves at an enthalpy of 528.7 btu/lbm steam leaves as a saturated liquid. (16) a) determine the mass flow rate of the extraction steam used to heat the feedwater (10) b) determine the terminal temperature difference of the closed feedwater heater