A piece of Al weighing 6 kg and initially at a temperature of 300^{O}C is suddenly immersed in a fluid at a temperature of 20^{O}C. The convectice heat transfer coefficient is 58 W/m2. ^{0}C. Taking the Aluminum as a sphere having the same weight as that given, estimate the time require to cool the aluminum to 90 0C using the lumped-capacity method of analysis.