The ultimate BOD of the Susquehanna River just below a sewage outfall from Harrisburg is 50.0 mg/L, and the DO is at the saturation value of 10.0 mg/L. The deoxygenated rate coefficient (kd) is 0.30 day-1, and the reaeration rate constant (kr) is 0.90 day-1. The river is flowing at a speed of 48 miles/day. The only source of BOD is the sewage outfall. Required:
a. Find the critical distance downstream at which DO is a minimum.
b. Find the minimum DO.
c. If a wastewater treatment plant were to be built, what fraction of BOD would need to be removed from the sewage to ensure that downstream DO concentrations stay above 5.0 mg/L

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?

Afour cylinder four-stroke in-line engine has a stroke of 160mm, connecting rod length of 150mm, a reciprocating mass of 3kg and its firing order is 1-3-4-2. the spacing between cylinders is 100mm. i. show that the engine is in balance with regard to the primary inertia forces and primary 3. a and secondary inertia couples. li determine the out of balance secondary inertia force ii. propose ways of balancing this out of balance force and discuss the challenges that will arise

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