10 pts) A wastewater is to be treated in a typical completely mixed activated-sludge system to a effluent BOD of 5 mg/L. The average flow rate is 18,300 m3/d. The influent BOD is 160 mg/L. The system is to operate at a concentration of 4,000 mg/L MLSS and 15 d mean cell residence time. The secondary clarifier is designed to thicken the sludge to 12,000 mg/L. Assume a yield coefficient of 0.5, an endogenous decay rate (kd) of 0.04 d-1 and the solids concentration in the effluent can be ignored. Design the secondary treatment system by determining: a) The volume of the aeration tank b) The flow rate of the WAS c) The flow rate of the RAS d) The sludge recycle ratio (RAS%) e) The mass of sludge wasted each day (in kg/day) f) Check the F:M

Refrigerant-134a enters the compressor of a refrigerator as superheated vapor at 0.14 mpa and -10°c at a rate of 0.05 ka/s and leaves at 0.8 mpa and 50°c. the refrigerant is cooied in the condenser to 0.72 mpa and 26'c. it is then throttled to 0.15 mpa. sketch the t-s diagram for the system and evaluate: 6) the rate of heat removai from the refrigerated space (kw), it) the power input to the compressor (kw), ii) the isentropic efficiency of the compressor (%), and iv) the cop of the refrigerator.

Water vapor initially at 10 bar and 400 °c is contained within a piston-cylinder assembly. the water lost heat to the surrounding according to isochoric (iso-volumetric) process until its temperature is 150 °c. the water is then condensed isothermally to saturated liquid. for the water as a system, calculate the work in kj/kg

Ashielded metal arc-welding operation is accomplished in a work cell by a fitter and a welder. the fitter takes 5.5 min to load components into the welding fixture at the beginning of the work cycle, and 1.5 min to unload the completed weldment at the end of the cycle. the total ength of the weld seams 1200 mm, and the travel speed used by the welder averages 300 mm/min. every 600 mm of seam length, the welding stick must be changed, which takes 0.8 min. while the fitter is working, the welder is idle (resting): and while the welder is working the fitter is idle. (a) determine the average arc-on time as a fraction of the work cycle time. (b) how much improvement in arc-on time would result if the welder used flux-cored arc welding (manually operated), given that the spool of weld wire must be changed every 10 weldments, and it takes the welder 5.0 min to accomplish the change? (c) what are the production rates for these two cases (weldments completed per hour)? attach your work and solutions.