Chapter 2.6, Problem 17P

(A)

Interpretation Introduction

Interpretation:

The change in specific enthalpy using steam tables.

Concept Introduction:

The expression to obtain the change in specific enthalpy $\left(\Delta \widehat{H}\right)$.

$\Delta \widehat{H}={\widehat{H}}_{\text{final}}-{\widehat{H}}_{\text{initial}}$

Here, final specific enthalpy or enthalpy at exit is ${\widehat{H}}_{\text{final}}$, and initial specific enthalpy or inlet enthalpy is ${\widehat{H}}_{\text{initial}}$.

(B)

Interpretation Introduction

Interpretation:

The change in specific enthalpy using approximation that ${\widehat{C}}_P=\text{4}\text{.19}\text{J}/\text{g}\cdot \text{K}$ for liquid water.

Concept Introduction:

The expression to obtain the change in enthalpy of liquid water $\left(\Delta \widehat{H}\right)$.

$\begin{array}{c}\Delta \widehat{H}={\widehat{C}}_P{\displaystyle \underset{T_{\text{initial}}}{\overset{T_{\text{final}}}{\int }}dT}\\ ={\widehat{C}}_P{\displaystyle \int \left(T_{\text{final}}-T_{\text{initial}}\right)}\\ ={\widehat{C}}_P\left(T_{\text{final}}-T_{\text{initial}}\right)\end{array}$

Here, constant pressure is ${\widehat{C}}_P$, boiling temperature is $T_{\text{final}}$, initial temperature is $T_{\text{initial}}$, and temperature difference is $dT$.

(C)

Interpretation Introduction

Interpretation:

The reason for the difference between the answers to part A and part B.