Question
Water flowing at the rate of 1 kg/s through a system is heated using an electric heater such that the specific enthalpy of the water increases by 2.50 kJ/kg and the specific entropy increases by 0.007 kJ/kg.K. The power input to the electric heater is 2.50 kW. There is no other work or heat interaction between the system and the surroundings. Assuming an ambient temperature of 300 K, the irreversibility rate of the system is _________kW (round off to two decimal places).
Answer :
2.1
ṁ = 1kg/s 
ẇ = 2.50 kW
h2 – h1 = 2.50 KJ/kg
s2 – s1 = 0.007 KJ/kgK
İ = T0Ṡgen = 300 x Ṡgen
Ṡgen = Ṡexit - Ṡinlet = (ṁs2) - (ṁs1+0) (Entropy associated with work is zero)
= ṁ(s2-s1) = 1 x 0.007 = 0.007
İ = 300 x 0.007 = 2.10kW
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