Liquid oxygen, which has a boiling point of 90 K and a latent heat of vaporization of 214 kJ/kg, is stored in a spherical container whose outer surface is of 500-mm diameter and at a temperature of -10°C. The container is housed in a laboratory whose air and walls are at 25°C.
(a) If the surface emissivity is 0.20 and the heat transfer coefficient associated with free convection at the outer surface of the container is 10 W/m2 · K, what is the rate, in kg/s, at which oxygen vapor must be vented from the system?
(b) Moisture in the ambient air will result in frost forma- tion on the container, causing the surface emissivity to increase. Assuming the surface temperature and convection coefficient to remain at -10°C and 10 W/m2 · K, respectively, compute the oxygen evap- oration rate (kg/s) as a function of surface emissivity over the range 0.2 s 0.94.