Problem 1 In a vacuum chamber, a thick slab is placed - under an array of laser diodes with an output constant pulse. A thermocouple is inserted inside the slab at a depth x=25 mm from the Thermocouple surface and the slab has an initial uniform :l_ temperature 7, =20C. The known properties of the slab are k=639Wm-K and @ =18.8x10 m*/s. If the thermocouple measured a temperature T, =130C after 30 s the slab surface has been exposed to the laser pulse, determine: 1- The validity of the semi-infinite solid assumption in this problem 2- The amount of energy per unit surface area directed on the slab surface 3- the thermocouple reading after 60 s has elapsed Problem 2 The soil temperature in the upper layers of the earth varies with the variations in the atmospheric conditions. Before a cold front moves in, the earth at a location is initially at a uniform temperature of 10C. Then the area is subjected to a temperature of -10C and high winds that resulted in a convection heat transfer coefficient of 40 W/m2K on the earth's surface for a period of 10 h. |13 1- Taking the properties of the soil at that location to be k=09 W/mK a=16x10" m2s, determine the soil temperature at distances 0, 10, 20, and 50 cm from the earth's surface at the end of this 10-h period. [selution: -10C at x=0 cm; -8.5C at x=10 cm; -7.0C at x=20 cm; -2.8C at x=50 cm] 2- Using Matlab or Excel, plot the soil temperature as a function of the distance from the earth's surface as the distance varies from 0 to 1 m, and discuss the results