Stainless steel ball bearings (r = 8085 kg/m3, k =15.1 W/m·°C, cp = 0.480 kJ/kg·°C, and a = 3.91 * 10-6 m2/s) having a diameter of 1.2 cm are to be quenched in water. The balls leave the oven at a uniform temperature of 900°C and are exposed to air at 30°C for a while before they are dropped into the water. If the temperature of the balls is not to fall below 850°C prior to quenching and the heat transfer coefficient in the air is 125 W/m2·°C, determine how long they can stand in the air before being dropped into the water.

Students are casting an aluminum cylinder of diameter D = 2.5 cm and length of L = 10 cm from molten aluminum. The heated aluminum comes out of the mold at Ti = 530°C where it is quenched to T = 30°C by a cold-water faucet at T∞= 20°C and ℎ=1000 W/m2⋅K. Assume the thermophysical properties of aluminum are k = 230 W/m⋅K, ρ= 2710 kg/m3, and cp = 0.9 kJ/kg⋅K. First, determine whether the Lumped Capacitance Method is valid. Then, use the appropriate equation to determine how much time the aluminum cylinder must remain under the faucet to reach the desired temperature.

Calculate the amount of heat required (in kJ) to raise the temperature of 23.4 g of ice at -11°C to steam at 135°C.   ΔHvap = 40.67 kJ/mol, ΔHfus = 6.008 kJ/mol, Cice = 2.092 J/g°C, Cwater = 4.184 J/g°C, Csteam = 1.841 J/g°C, Melting point = 0.00°C, Boiling Point = 100.0°C

Air at a dry bulb temperature of 40℃ and a wet bulb temperature of 20℃ is first heated in a heater to a dry bulb temperature of 90℃. Then it is passed through a bed of apricot slices to dry them. The air exiting from the top of the apricot bed is at a dry bulb temperature of 60℃. Clearly show the various paths of the process on a psychrometric chart! Determine the amount of moisture removed, in grams of water/second from the apricot bed!