A certain superinsulation material having a thermal conductivity of 2*10[-][/4] w/m.c is used to insulate a tank of liquid nitrogen that is maintained at -196 c, 199 Kj, is required to vaporize each kilogram mass of nitrogen at this temp. assuming that the tank is sphere having an inner dia. (0.52) m, estimate the amount of nitrogen vaporized per day for an insulation thickness of 2.5 cm and an ambient temp. of 21 c, assume that the outer temp. of the insulation is 21 c.