In a water heating system, cold water at 5°C flowing at a rate of 5 kg/s is mixed adiabatically with hot water at 80°C flowing at a rate of 2 kg/s. The exit temperature of the mixture is
A)26.4°C
B)42.5°C
C)40.0°C
D)64.3°C
E)55.2°C

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_w=4.18 "kJ/kg-C"
Tcold_1=5 "C"
m_dot_cold=5 "kg/min"
Thot_1=80 "C"
m_dot_hot=2 "kg/min"
"The rate form of energy balance for a steady-flow system is E_dot_in = E_dot_out"
m_dot_hot*C_w*Thot_1+m_dot_cold*C_w*Tcold_1=(m_dot_hot+m_dot_cold)*C_w*Tmix 
"Some Wrong Solutions with Common Mistakes:"
W1_Tmix=(Tcold_1+Thot_1)/2 "Taking the average temperature of inlet fluids"

In a Water Heating System, Cold Water at 5°C Flowing