Exposure to high concentration of gaseous ammonia can cause lung damage. To prevent gaseous ammonia from leaking out, ammonia is transported in its liquid state through a pipe (k = 25 W/m · K, D_i, _pipe = 2.5 cm, D_o, _pipe = 4 cm, and L = 10 m). Since liquid ammonia has a normal boiling point of -33.3°C, the pipe needs to be properly insulated to prevent the surrounding heat from causing the ammonia to boil. The pipe is situated in a laboratory, where air at 20°C is blowing across it with a velocity of 7 m/s. The convection heat transfer coefficient of the liquid ammonia is 100 W/m² · K. Calculate the minimum insulation thickness for the pipe using a material with k = 0.75 W/m · K to keep the liquid ammonia flowing at an average temperature of -35°C, while maintaining the insulated pipe outer surface temperature at 10°C.