A cold cellar built of concrete (k=0.69 W/mC) with 10 cm thick walls requires maintaining an interior temperature of -5C, when the outside ambient temperature is 21C. Under these conditions, there are combined coefficients of convection and radiation: internal of 3.8 W/m2 C and external of 7.6 W/m2 C. Asbestos insulation (k = 0.149 W/mC) is to be added to the outer wall of the cellar to halve the heat flux entering. Consider an area of 1 m2. Determine: a) the thickness of insulation required for the desired reduction in heat flux. (15 points) b) Explain the mechanisms of heat transfer that occur in the system, and if they occur simultaneously or subsequently. You should explain each mechanism you identify. (15 points)