3. A certain super-insulation material having a thermal conductivity of 2.0 x 10-4 W/mC is used to insulate a tank of liquid nitrogen that is maintained at -320F. 85.8 Btu is required to vaporize each pound mass of nitrogen at this temperature. Assuming that the tank is a sphere having an ID of 2.0 ft, estimate the amount of nitrogen vaporized per day for an insulation thickness of 1.0 inch and an ambient temperature of 70.0F. 4. Assuming that the heat transfer to the sphere in the previous problem occurs by free convection with a heat transfer coefficient of 2.7 W/mC, calculate the temperature difference between the outer surface of the sphere and the environment.