Assuming a mixed 3.5m high, 0.95m diameter thermal storage tank (made of thin metal) initially at 90 oC, with no load and no input, how long would it take to cool down to 27oC given it is insulated with 55mm of k=0.023W/m.K insulation, and the ambient temperature is 23oC. How long would it take to cool down if there was no insulation but a convective U value of 12W/m2K on all the tank outer surfaces? State any assumptions