Chapter 7, Problem 7.31P

Interpretation Introduction

Interpretation:

To find the enthalpy (H₂) and entropy (S₂) of steam in its final state

To find the Power (W) required of the compressor

Concept Introduction:

Using Steam Tables, find Enthalpy and Entropy for saturated steam at 125 kPa.

For Isentropic expansion,

$S^{\text{'}}{}_2=S_1$

Where S₁= Entropy of Saturated Steam at 125 kPa

S’₂= Entropy of Saturated Steam after isentropic expansion

$\Delta H=\frac{H{\text{'}}_2-H_1}{\eta }$

Where

$\Delta H$ = Change of Enthalpy

H₁= Enthalpy at initial state at 125 kPa

H’₂= Enthalpy after isentropic expansion, at 700 kPa

$\eta$ = Efficiency of compressor = 78% = 0.78

$\Delta H$ = Change of Enthalpy = H₂- H₁$W=m.\Delta H$

W = Power required for the compressor

M = Mass flow rate = 2.5 kg.s-1

$\Delta H$ = Change of Enthalpy