Stainless steel (AISI 304) ball bearings, which have uni- formly been heated to 850C, are hardened by quench- ing them in an oil bath that is maintained at 40C. The ball diameter is 20 mm, and the convection coefficient associated with the oil bath is 1000 W/m2 K. (a) If quenching is to occur until the surface tempera- ture of the balls reaches 100C, how long must the balls be kept in the oil? What is the center tempera- ture at the conclusion of the cooling period? (b) If 10,000 balls are to be quenched per hour, what is the rate at which energy must be removed by the oil bath cooling system in order to maintain its temper- ature at 40C?

Liquid flows at steady state at a rate of 2 lb/'s through a pump, which operates to raise the elevation of the liquid 100 ft from control volume inlet to exit. the liquid specific enthalpy at the inlet is 40.09 btu/lb and at the exit is 40.94 btub. the pump requires 3 btu/s of power to operate. if kinetic energy effects are negligible and gravitational acceleration is 32.174 tt/s, the heat transfer rate associated with this steady state process is most closely 1)-2,02 btu/s from the liquid to the surroundings 2)-3.98 btu/s from the surroundings to the liquid. 3)-4.96 btu/s from the surroundings to the liquid. 4)-1.04 btu/s from the liquid to the surroundings.