Consider V_1 = 10 L of water T_1 = 20 degree C, P_1 = 20 MPa. Explain how one mi

Question

Consider V_1 = 10 L of water T_1 = 20 degree C, P_1 = 20 MPa. Explain how one might get water to these conditions. If the water is isobarically heated to double the absolute temperature, what is its phase? How do you know? For (b), should the entropy of the water increase or decrease, and why? (Explain on a physical basis for the water molecules) For (b), find the specific entropy difference S_2 - S_1 [J/kg-K] modeling the water as an ideal gas or an incompressible substance as appropriate. (EES) For (b), find the specific entropy difference S_2 - S_1 [J/kg-K]. If the water at conditions (1) is pressurized until P_2 = 2P_1, should the entropy of the water increase or decrease, and why? (Explain on a physical basis for the water molecules) For (f), find the specific entropy difference S_2 - S_1 [J/kg-K].

Explanation / Answer

Given conditions, water is sub cooled. Water at 20 deg.c is taken and when pressurised to 20 Mpa by using a pump, its pressure rised to 20 Mpa.

given T1= 20 deg.c P= 20Mpa , specific entropy = 0.2920 KJ/Kg.K, density =1007 kg/m3 ( from steam table)

mass of water= 10*10-3 m3*1007 Kg/m3=10.07 kg

T1= 20 deg,c= 20+273= 293K, the gas is heated, the entropy is a measure of degree of disorder and degree of disorder increases when temperature is increased. Hence T2= 2*293= 586K

when temperature is 586-273= 313deg.c, specific entropy = 3.33 KJ/Kg.K

entropy change= 3.33-0.2920 = 3.04 Kj/Kg. K= 3.04*1000 J/Kg.k= 3040 J/Kg.K

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