A4-pole, 60hz, y-connected, 3-phase generator has a regulated line voltage
of vab = 450∠30° vrms, a synchronous reactance of 0.05-ω, a stator resistance of 0.003ω,
and lsf = 0.018 h. the balanced 3-phase load draws 3 mw at a lagging 0.75 power
factor.
a. compute the 3-phase complex power of the load (magnitude and angle).
s3p =
b. compute the generator phase current (magnitude and angle; hint: the angle of the
current should be negative for the load to have a lagging power factor).
ias =
c. find the required excitation voltage.
ea =
d. calculate the required field current.
if =
e. state the required speed of the prime mover (rpm) nm =

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?

An air compression refrigeration system is to have an air pressure of 100 psia in the brine tank and an allowable air temperature increase of 60°f for standard vapor compression cycle temperatures of 77 f entering the expansion cylinder and 14 f entering the compression cylinder, calculate the coefficient of performance a. 2.5 b 3.3 c. 4.0 d. 5.0

Awall of 0.5m thickness is to be constructed from a material which has average thermal conductivity of 1.4 w/mk. the wall is to be insulated with a material having an average thermal conductivity of 0.35 w/mk so that heat loss per square meter shall not exceed 1450 w. assume inner wall surface temperature of 1200°c and outer surface temperature of the insulation to be 15°c. calculate the thickness of insulation required.