An industrial wastewater treatment plant consists of a primary clarifier followed by a biological tower (trickling filter). the soluble bod concentration leaving the primary clarifier is 250 mg/l, and the corresponding flow rate is 1.0 million gals per day (mgd). the biological tower consists of a high-density, crossflow packing media with dimensions of 480 ft2 by 20 ft high. it has a specific area of 42.0 ft2 /ft3 , n = 0.5, and k20 = 0.0035 (gpm/ft2 ) 0.5. the recirculation ratio, r = 1.0; the water temperature is 15°c. calculate the soluble bod concentration in the biological tower effluent.

Air is to be cooled in the evaporator section of a refrigerator by passing it over a bank of 0.8-cm-outer-diameter and 0.4-m-long tubes inside which the refrigerant is evaporating at -20°c. air approaches the tube bank in the normal direction at 0°c and 1 atm with a mean velocity of 4 m/s. the tubes are arranged in-line with longitudinal and transverse pitches of sl- st 1.5 cm. there are 30 rows in the flow direction with 15 tubes in each row. determine (a) the refrigeration capacity of this system and (b) pressure drop across the tube bank. evaluate the air properties at an assumed mean temperature of -5°c and 1 atm. is this a good assumption?

During a steady flow process, the change of energy with respect to time is zero. a)- true b)- false

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