Liquid oxygen, which has a boiling point of 90 K and a heat of vaporization (hfg) 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. 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 to maintain steady-state conditions?