1. Please explain the Biot number and its application in solving the transient conduction questions using the Lumped Capacitance Method. 2. A plain carbon steel ball 12 mm in diameter is heated to 1200 K in an oven and then cooled slowly in W 20 K ambient air at 300 K. The convection heat transfer coefficient between air and this steel ball is You can find the density, specific heat and thermal conductivity from the property tables attached in the text book with reasonable assumptions. Please a) derive an equation estimating the changes of the temperature of this ball with time, b) the time needed for this steel ball to be cooled to 400 K with the radiation heat loss ignored, and c) determine if the ignorance of radiation heat loss in this question in reasonable by checking the possible contribution of radiation to heat loss at three temperature points. 771