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3. A spherical tank containing liquid oxygen at its boiling point, To= -183 C, is buried underground and surrounded by a large volume of soil (see figure). Far from the tank surface, the temperature of the soil is Too = 15 C. Conduction heat transfer from the soil to the tank will evaporate the liquid oxygen in the tank. During the process, the temperature of the oxygen inside the tank can be assumed to be uniform and constant. The thermal conductivity of the tank wall material is kw=0.5 W/m K and the thermal conductivity of the soil is ks = 2 W/m K. The tank wall dimensions are: internal radius: R1 = 2.0 m, external radius: R2= 2.1 m. Assume that the heat conduction process in the soil and the tank wall is at steady state. = =