An 8-m-long, uninsulated square duct of cross section 0.2 m x 0.2 m and relative roughness 10-3 passes through the attic space of a house. hot air enters the duct at 1 atm and 80c at a volume flow rate of 0.15 m^3 /s. the duct surface is nearly isothermal at 60c. determine the rate of heat loss from the duct to the attic space and the pressure difference between the inlet and outlet sections of the duct. evaluate air properties at a bulk mean temperature of 80c. is this a good assumption?

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?

Ajournal bearing has a journal diameter of 3.250 in with a unilateral tolerance of 20.003 in. the bushing bore has a diameter of 3.256 in and a unilateral tolerance of 0.004 in. the bushing is 2.8 in long and supports a 700-lbf load. the journal speed is 900 rev/min. find the minimum oil film thickness and the maximum film pressure for both sae 20 and sae 20w-30 lubricants, for the tightest assembly if the operating film temperature is 160°f. a computer code is appropriate for solving this problem.

Draw the engineering stress-strain curve for (a) bcc; (b) fcc metals and mark important points.