Liquid oxygen at -180oC is stored in a horizontal cylindrical tank of 1.0 m diameter and 5 m total length has hemispherical ends. It is required to insulate the tank so as to reduce the boil-off rate of oxygen in steady state to 10 kg/h. Determine the thermal conductivity of the insulating material if its maximum thickness is limited to 70 mm. Additional data, ambient air is at 25oC and the inner surface of the tank is at -180oC, Latent heat of vaporization 210 kJ/kg respectively