Uma carga elétrica trifásica equilibrada cuja impedância ZAB=10+j15 Ω está ligada em triângulo e é alimentada por um gerador trifásico equilibrado por meio de condutores cuja impedância é desprezível. A sequência de fase do gerador é ABC e a tensão de linha VAB é igual 380 V fase zero. A corrente de linha IA e de fase IAB valem: A) 48,76<-16,90 A; 16,25<-46,90 A B) 36,51<-86,31 A; 12,17<-56,31 A C) 36,51<-86,31 A; 21,08<-56,31 A D) 63,24<-86,31 A; 21,08<-56,31 A E) 36,51<-56,31 A; 12,17<-86,31 A

Fluids at rest possess no flow energy. a)- true b)- false

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?

Aquick transition of the operating speed of a shaft from its critical speed will whirl amplitude. (a) increase (b) limit (c) not affect (d) zero