3. the design criteria for oxidation ponds (also called facultative ponds, aerated facultative ponds) specified that (1) bod loading into the primary cell (or pond) shall not exceed 25 lbs bod/acre/day, (2) the minimum total water retention time, based on influent flow and all cells at water depth of 5 ft should not be less than 120 days., (3) the volume of winter storage between the water depths of 1.5 and 5 ft shall be sufficient so that no discharge is necessary for a four-month period, and (4) pond system should have at least two primary cells and one or more secondary cells. size the ponds for a community that generates 160,000 gpd wastewater with a bod of 220 mg/l. based on the climate of the area, the net water loss (evaporation plus seepage minus precipitation) during the storage months is 1.0 inch/month.

Thermal stresses are developed in a metal when its a) initial temperature is changed b) final temperature is changed c) density is changed d) thermal deformation is prevented e) expansion is prevented f) contraction is prevented

Awall of 0.5m thickness is to be constructed from a material which has average thermal conductivity of 1.4 w/mk. the wall is to be insulated with a material having an average thermal conductivity of 0.35 w/mk so that heat loss per square meter shall not exceed 1450 w. assume inner wall surface temperature of 1200°c and outer surface temperature of the insulation to be 15°c. calculate the thickness of insulation required.

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?