Question

Cryogenic liquids (liquid N2, He, etc) are typically stored in Dewar flasks (fancy thermos bottles) that consist of mirrored glass walls (to reduce radiative heating) separated by vacuum (a cylinder within a cylinder). How long would a liter sample of liquid argon last in a flat bottomed cylindrical Dewar with an inner radius of 5cm and height of 20cm and an outer radius of 10cm and height of 25 cm assuming that the only energy transfer that occurs is radiative between the walls of the Dewar (the top surface does not receive any radiation). The emissivity of silvered glass is 0.02 over all wavelengths, the outer surface of the Dewar is at 300K, the temperature of liquid Argon is 87 K, the density of liquid argon is 1.40 g cm3 , and the latent heat of vaporization is 1200 J/g. , The latent heat of vaporization is a measure of how much “extra” energy is required to vaporize a substance at its boiling point (the boiling point of argon is 87K). (Assume that all of the energy impinging on the inner cylinder is used to vaporize the Argon).

Answer 1