Steel balls at 150°C with a specific heat of 0.50 kJ/kg.°C are quenched in an oil bath to an average temperature of 70°C at a rate of 15 balls per minute. If the average mass of steel balls is 1.2 kg, the rate of heat transfer from the balls to oil is
A)22.5 kJ/s
B)12 kJ/s
C)48 kJ/s
D)10.5 kJ/s
E)2880 kJ/s

Question

Quizplus · Accepted Answer

Solved by EES Software. Solutions can be verified by copying-and-pasting the following lines on a blank EES screen. 
C=0.50 "kJ/kg.K"
m1=1.2 "kg"
T1=150 "C"
T2=70 "C"
n=15 "balls/min"
m=n*m1/60 "kg/s"
"Applying energy balance E_in-E_out=dE_system gives"
"-E_out = dU_system"
Qout=m*C*(T1-T2) "kJ/s"
"Some Wrong Solutions with Common Mistakes:"
W1_Qout = m*C*T1 "Using T1 only" 
W2_Qout = m1*C*(T1-T2) "Using one ball only" 
W3_Qout = m*C*T2 "Using T2 only" 
W4_Qout=m1*C*(T1-T2)*60 "Finding kJ/min"

Steel Balls at 150°C with a Specific Heat of 0