A 2m3 insulated tank containing ammonia at 20C 80 quality is

A 2-m^3 insulated tank containing ammonia at -20°C, 80% quality is connected by a valve to a line flowing ammonia at 2 MPa, 60°C. The valve is opened, allowing ammonia to flow into the tank. At what pressure should the valve be closed if the manufacturer wishes to have 15kg of ammonia inside at the final state?

Solution

CV: Tank USUF process QCV + mihi = m2u2 - m1u1 + WCV ; QCV = WCV = 0 m1 = V / v1 = 2 / 0.49927 = 4.006 kg, mi = m2 - m1 = 15 - 4.006 = 10.994 kg u1 = 1057.5, hi = 1509.9 u2 = mihi + m1u1 m2 = 10.994x1509.9 + 4.006x1057.5 15 = 1389.1 kJ/kg v2 = V/m2 = 2/15 = 0.1333 m3/kg Therefore, v2, u2 fix state 2. By trial and error, P2 = 1081 kPa & T2 = 50.4° C