Asheet of steel 3-mm thick has nitrogen atomospheres on both sides at 900 c and is permitted to achieve a steady-state di usion condition. the di usion coecient for nitrogen in steel at this temperature is 1: 85 m2=s, and the di usion ux is found to be 1: 0 kg=m2s. also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 2 kg=m3. how far into the sheet from this high-pressure side will the concentration be 0.5 kg/m3? assume a linear concentration profile.

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?

Which of the following ziegler nichols tuning methods the response of the controller to a step input should exhibit an s-shaped curve? a)-open loop mode b)-closed loop mode c)-both modes (open & closed) d)-none of the modes (open & closed)

Most leaks in reciprocating air compressors can be detected and minimized by: (clo4) a)-detecting leakage areas using ultrasonic acoustic detector. b)-tightening joints and connections c)-replacing faulty equipment d)-all of the given options