For the given question and solution, for part (b), finding the work input  of the saturated vapour at the inlet state, why couldnt i  use the same formula as part (a) Win = v*(change in pressure) where the v would be the saturated vapour specific volume instead of saturated fluid volume

Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
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For the given question and solution, for part (b), finding the work input  of the saturated vapour at the inlet state,

why couldnt i  use the same formula as part (a) Win = v*(change in pressure) where the v would be the saturated vapour specific volume instead of saturated fluid volume??

(b) Compressor (for gases): Tds = dh – vdP,
ds = 0 (isentropic)
||
From Tds relations
vdP = dh
-[ vdP
-S dh=-(h, – h,)
W,
= -
rev
State 1 (Table A-5):
P =100 kPa, Sat. vapour
s, =7.3589 kJ/kgK
S1
h = 2675.0 kJ/kg
State 2 (Table A-6):
P, =1 MPa, s, = s, = 7.3589 kJ/kgK
h, = 3194.5 kJ/kg
Wroy = -(3194.5- 2675.0)kJ/kg = -519.5 kJ/kg
rev
Less energy to pump liquids than gas between same pressure range
Transcribed Image Text:(b) Compressor (for gases): Tds = dh – vdP, ds = 0 (isentropic) || From Tds relations vdP = dh -[ vdP -S dh=-(h, – h,) W, = - rev State 1 (Table A-5): P =100 kPa, Sat. vapour s, =7.3589 kJ/kgK S1 h = 2675.0 kJ/kg State 2 (Table A-6): P, =1 MPa, s, = s, = 7.3589 kJ/kgK h, = 3194.5 kJ/kg Wroy = -(3194.5- 2675.0)kJ/kg = -519.5 kJ/kg rev Less energy to pump liquids than gas between same pressure range
Determine the pump (compressor) work input required to compress steam
isentropically from 100 kPa to 1 MPa, assuming that the steam exists as (a)
saturated liquid and (b) saturated vapour at the inlet state.
T
P2 = 1 MPa
Process is isentropic:
P, = 1 MPa
1 MPa
(a) Pump (for liquid, v = const.):
PUMP
COMPRESSOR
(b)
V1 = Vf@100kPa
= 0.001043 m'/kg
(a)
100 kPa
P = 100 kPa
P = 100 kPa
W,ey =
-[ vdP = -v, (P, -R)
%3|
(b) Compressing
(a) Compressing
a liquid
rev
a vapor
1 kJ
=-(0.001043 m/kg)[(1000-100) kPa]
=-0.94 kJ/kg
W,
3
1kPa · m
rev
Transcribed Image Text:Determine the pump (compressor) work input required to compress steam isentropically from 100 kPa to 1 MPa, assuming that the steam exists as (a) saturated liquid and (b) saturated vapour at the inlet state. T P2 = 1 MPa Process is isentropic: P, = 1 MPa 1 MPa (a) Pump (for liquid, v = const.): PUMP COMPRESSOR (b) V1 = Vf@100kPa = 0.001043 m'/kg (a) 100 kPa P = 100 kPa P = 100 kPa W,ey = -[ vdP = -v, (P, -R) %3| (b) Compressing (a) Compressing a liquid rev a vapor 1 kJ =-(0.001043 m/kg)[(1000-100) kPa] =-0.94 kJ/kg W, 3 1kPa · m rev
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