Heat is lost through a plane wall steadily at a rate of 750 W. If the inner and outer surface temperatures of the wall are 50°C and 15°C, respectively, the rate of entropy generation within the wall is
A)0.0289 W/K
B)2.10 W/K
C)2.08 W/K
D)0.111 W/K
E)48.0 W/K

Question

Quizplus · Accepted Answer

Solved by EES Software. Solutions can be verified by copying-and-pasting the following lines on a blank EES screen. 
Q=600 "W"
T1=20+273 "K"
T2=5+273 "K"
"Entropy balance S_in - S_out + S_gen= DS_system for the wall for steady operation gives" 
Q/T1-Q/T2+S_gen=0 "W/K" 
"Some Wrong Solutions with Common Mistakes:"
Q/(T1+273)-Q/(T2+273)+W1_Sgen=0 "Using C instead of K"
W2_Sgen=Q/((T1+T2)/2) "Using avegage temperature in K" 
W3_Sgen=Q/((T1+T2)/2-273) "Using avegage temperature in C" 
W4_Sgen=Q/(T1-T2+273) "Using temperature difference in K"

Heat Is Lost Through a Plane Wall Steadily at a Rate