Question

Liquid helium is stored at its boiling-point temperature of 4.2 K in a spherical container (r = 0.30 m). The container is a perfect blackbody radiator. The container is surrounded by a spherical shield whose temperature is 74 K. A vacuum exists in the space between the container and the shield. The latent heat of vaporization for helium is 2.1 × 104 J/kg. What mass of liquid helium boils away through a venting valve in one hour?

Answer 1

Use the stephan boltzman law to get power (energy/time). https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law
Then mass He/second=Hv*energy/second
mass in an hour: multiply by 3600sec/hr