Chapter 8, Problem 8.6P

8.6. Table B.7 of Appendix B gives the following values for steam at 400°C and 150 bar:

   $\hat{H}$= 2975 kJ/kg, $\hat{U}$= 2744 kJ/kg, $\hat{V}$= 0.0157 m³/kg

1. The value 2975 is not the true specific enthalpy of steam at the given condition. Why not? State the
process [H ₂O(

) ? H₂O(

)] for which the specific enthalpy change is 2975 kJ/kg. (Enter the

phase, temperature, and pressure of water at the initial and final conditions within the parentheses.)

Estimate the specific enthalpy of steam at 100°C and 1 atm relative to steam at 400°C and 150 bar using the steam tables. Repeat the calculation assuming ideal-gas behavior and Table B.2 or APEx.

What is the physical significance of the difference between the two values calculated in Part (b)?

Given the first and third of the tabulated values at 400°C and 150 bar (i.e., 2975 and 0.0157), calculate the second value. (Hint: Begin with the definition of $\hat{H}$.) Don’t worry if your calculated value differs slightly from 2744—the difference is just round-off error. If the difference is on the order of 1% or more, however, you’ve done something wrong.