6.20 A machine component is loaded so that stresses at the critical location are σ 1 = 20 ksi , σ 2 = − 15 ksi , and σ 3 = 0 . The material is ductile, with yield strengths in tension and compression of 60 ksi. What is the safety factor according to (a) the maximum-normal-stress theory, (b) the maximum-shear-stress theory, and (c) the maximum-distortion-energy theory? Which theory would be expected to agree most closely with an actual test? [Partial ans.: (a) 3.0,(b) 1.71,(c) 1.97]

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?

Water at 70°f and streams enter the mixing chamber at the same mass flow rate, determine the temperature and the quality of the exiting stream. 0 psia is heated in a chamber by mixing it with saturated water vapor at 20 psia. if both streams enters the mixing chamber at the same mass flow rate, determine the temperature and the quality of the existing system.

The drive force for diffusion is 7 fick's first law can be used to solve the non-steady state diffusion. a)-true b)-false