Ashaft is subjected to steady torsional stress τ=25 kpsi and alternating (fully reversed) bending stress σ=30 kpsi. the material is steel with sut=70 kpsi, sy=70 kpsi and se=35 kpsi that includes the modifying factors. a. calculate the static safety factor ηy for yield. b. calculate the fatigue safety factor ηf for infinite life using modified goodman criterion. c. calculate the fatigue safety factor ηf for infinite life using asme elliptic criterion.

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?