In the experimental determination of the hat transfer coefficient between a heated steel ball and crushed mineral solids, a series of 1.5% carbon steel balls were heated to a temperature of 700?C and the center temperature-time history of each was measured with a thermocouple while it was cooling in a bed of crushed iron ore, which was placed in a steel drum rotating horizontally at about 30 rpm. For a 5-cm-diameter ball, the time required for the temperature difference between the ball center and the surrounding ore to decrease from 500?C initially to 250?C was found to be 64, 67, and 72 s, respectively, in three different test runs. Determine the average heat transfer coefficient between the ball and the ore. Compare the results obtained by assuming the thermal conductivity to be infinite with those obtained by taking the internal thermal resistance of the ball into account.GIVENHeat steel balls are put in crushed iron oreBalls are 1.5% carbon steel ballsInitial temperature of balls (To) = 700?CBall diameter = 5 cm = 0.05 mTemperature difference between the ball center and the oreCenter temperature of the balls decreases from 500?C to 250?CTime taken was found to be 64, 67, and 72 s, respectively, in three different test runsASSUMPTIONSTemperature of the iron ore is uniform andconstant

Thermocouple Steel Ball Drum D= 5 cm 0 = 30 RPM Crushed Iron Ore