A 15-kg iron ball whose specific heat is 0.45 kJ/kg.°C is at a uniform temperature of -10°C. For an environment temperature of 25°C, the exergy content of this ball is
A)Less than zero
B)0 kJ
C)1.0 kJ
D)15 kJ
E)236 kJ

Question

Quizplus · Accepted Answer

Solved by EES Software. Solutions can be verified by copying-and-pasting the following lines on a blank EES screen. 
m=15 "kg"
Cp=0.45 "kJ/kg.K"
T1=-10+273 "K"
To=25+273 "K"
"Exergy content of a fixed mass is x1=u1-uo-To*(s1-so)+Po*(v1-vo)"
 ex=m*(Cp*(T1-To)-To*Cp*ln(T1/To))
"Some Wrong Solutions with Common Mistakes:"
W1_ex=m*Cp*(To-T1) "Taking the energy content as the exergy content"
W2_ex=m*(Cp*(T1-To)+To*Cp*ln(T1/To)) "Using + for the second term instead of -"
W3_ex=Cp*(T1-To)-To*Cp*ln(T1/To) "Using exergy content per unit mass"
W4_ex=0 "Taking the exergy content to be zero"

A 15-Kg Iron Ball Whose Specific Heat Is 0