GATE 2018 ME (ME1) – Question 54
A 0.05 m³ tank contains saturated water and steam at 200°C, with 8 kg liquid. Saturation pressure is 1.5538 MPa; vf = 0.001157 m³/kg, vg = 0.12736 m³/kg, sf = 2.3309 kJ/kg K and sfg = 4.1014 kJ/kg K. Mixture specific entropy, to two decimals, is ______ kJ/kg K.
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Correct answer: 2.45 to 2.55
Explanation
Liquid volume is $8(0.001157)=0.009256$ m³. Vapour mass is $(0.05-0.009256)/0.12736=0.319912$ kg, giving quality $x=0.319912/(8+0.319912)=0.038451$. Entropy is $s_f+xs_{fg}=2.3309+0.038451(4.1014)=2.49$ kJ/kg K.