This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Water exists as a compressed liquid at the initial state since its pressure is greater than the saturation pressure of 0.3632 psia at 70°F. By approximating the compressed liquid as a saturated liquid at the given temperature,
the properties at the initial state are
State 1: P1
h1 20 psia
70°F sf @ 70°F
hf @ 70°F 0.07463 Btu/lbm · R
38.09 Btu/lbm At the final state, the pressure is still 20 psia, but we need one more property
to fix the state. This property is determined from the energy balance, Ein Eout
3 Net energy transfer
by heat, work, and mass Change in internal, kinetic,
potential, etc., energies Qin Wb
h2 since U Wb H for a constant-pressure quasi-equilibrium process. Then, P2
h2 State 2: U
H m(h2 h1)
(3 lbm)(h2 38.09 Btu/lbm)
1188.1 Btu/lbm 20 psia
1188.1 Btu/lbm s2 1.7759 Btu/lbm · R
(Table A–6E, interpolation) Therefore, the entropy change of water during this process is S m(s2 s1) (3 lbm)(1.7759
5.104 Btu/R 0.07463) Btu/lbm ·...
View Full Document
This document was uploaded on 11/28/2012.
- Spring '09