Liquid helium is stored at its boiling-point temperature of4.2
k in a spherical container (r = 0.589 m). thecontainer is
a perfect blackbody radiator. the container issurrounded by a
spherical shield whose temperature is 58.4 k. avacuum exists in the
space between the container and shield. thelatent heat of
vaporization for helium is 2.1 x 104j/kg. what mass of
liquid helium boils away through the ventingvalve in 6.76
hours?