A certain superinsulation material having a thermal conductivity of 2 x 10^-4 W/m C is used to insulate a tank of liquid nitrogen that is maintained at -196 degrees celsius; 199 kJ is required to vaporize each kilogram mass of nitrogen at this temperature. Assuming that the tank is a sphere having an inner diameter of 0.52 m, estimate the amount of nitrogen vaporized per day for an insulation thickness of 2.5 cm and an ambient temperature of 21 degrees celsius. Assume that the outer temperature of the insulation is 21 degrees celsius.