Condenser vacuum discussion useful

1. What causes condenser high vacuum in
the steam plant and what effect it does to
the Rankine cycle performance?
The aim of this reaserch is to know the milling plant effect on the condenser vacuum-
effectiveness on the Rankine cycle of the boiler, which currently has condenser high
vacuum.
I got the condenser findings as follow:
 High inlet & outlet temperatures
Heat Exchangers
Engineering Thermophysics
Transport Phenomena
Thermal System Design
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Most recent answer
30th Oct, 2018
Ahmet Çağrı Balcik
Sakarya University
May I ask question about level of gland condenser and air ejector. In our powerplant
arrangement air ejector is at the 10,5 meters and glend condenser 1.5 meters.
What's the reason of that situation ? I mean why air ejector and gland condenser are
not same level? thank you
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All Answers (11)
23rd Jun, 2016
Prem Baboo
Dangote Fertilizer Ltd
Dear Siyamthanda,
The Rankine cycle is the fundamental operating cycle of all power plants where an
operating fluid is continuously evaporated and condensed. The selection of operating
fluid depends mainly on the available temperature range. Attached Figure shows the
idealized Rankine cycle.The Rankine cycle is a model that is used to predict the

2. performance of steam turbine systems. The Rankine cycle is an idealized
thermodynamic cycle of a heat engine that converts heat into mechanical work. The
heat is supplied externally to a closed loop, which usually uses water as the working
fluid.
The pressure-enthalpy (p-h) and temperature-entropy (T-s) diagrams of this cycle
are given in attached Figure
The steam is condensed at low pressure, usually in a surface condenser using
cooling water. In well designed and maintained condensers, the pressure of the
vapor is well below atmospheric pressure, approaching the saturation pressure of
the operating fluid at the cooling water temperature.
The maximum efficiency is obtained at low pressure (vacuum) of the
condenser because the W.D is maximum at low pressure. The maximum ∆P
created by lowering the vacuum.
Regards,
Prem Baboo
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Turbine Condensing
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Rankine
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Vapor Power
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23rd Jun, 2016
D.B. Jani
Gujarat Technological University - GTU
Vacuum pump maintaining vacuum in steam condenser and as vacuum increases
steam pressure at exit of turbine is low so results into fasten the condensation
process.
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3. 23rd Jun, 2016
Siyamthanda Mchophele
Tshwane University of Technology
@D.B Jan I thank you Sir, meaning the condenser will be ineffective to condensate
the exhausted steam from the low pressure turbine, that will results to load loss to
the Rankine cycle.
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23rd Jun, 2016
Siyamthanda Mchophele
Tshwane University of Technology
@Prem Baboo thank you very much sir, I now have extensive knowledge and
assurance from your explanation regard Rankine cycle process.
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24th Jun, 2016
Vijay Raghavan
Indian Institute of Technology Madras
@Siyamthanda, though I am unable to understand your question fully (why mention
is made of a milling plant), I will try to give as complete answer an answer as I can,
to supplement the other answers given. The condensing pressure is entirely a
function of the condensing temperature, which is equal to [mean cooling water
temperature + a driving temperature difference, ΔT].
When a vacuum exists in the condenser, atmospheric air will leak into the condenser
shell through flanges and other leakage points raising the condenser pressure.
Dissolved gas in the water used to raise the steam will also enter the condenser
along with the steam, but will not condense. It will accumulate in the condenser to
contribute to raising the condenser pressure. Therefore a vacuum pump is required
to remove the uncondensed air from the condenser and keep the vacuum high (i.e.,
keep the pressure low).
The lower the condenser pressure, the higher the pressure range of expansion. That
leads to more work output and higher cycle efficiency.
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26th Jun, 2016
Siyamthanda Mchophele

4. Tshwane University of Technology
@Vijay Raghavan thank you Sir for the information you provided, the reason why I
stated mill plant is the fact that Mills are operating at maximum beyond their limit/
load capacity compensating load loss caused by high back pressure inside the
condenser that reduces the efficiency of the LP turbine. I would like to ask which
methods that can used to reduce the condenser high temperature vacuum or back
pressure inside the condenser? And what effects of ineffective ejector vacuum or
pump vacuum in the condenser?
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26th Sep, 2016
Ke Tang
Purdue University
I have one more question.
Is it possible that the steam make the pressure in condenser raise up before it
condensed to water? Or the steam condensed immediately？I have this mind
because the steam exhausted from turbine continually.
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12th Jan, 2017
Erma Dityarangga
Institut Teknologi Sepuluh Nopember
Hi Mr. Siyamthada, vacuum of condenser in rankine cycle influenced by ejector,
temperature, level of cooling water, etc. Last year I make some reserch about
condensers vacuum which calculated based heat transfer and thermodynamic. But
vacuum condition can't be too low and too high. Because It can be influenced in Last
stage in turbine. Futher information, you can read Moran J Saphiro's book, about
Thermodynamics
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12th Jan, 2017
Vijay Raghavan
Indian Institute of Technology Madras
I missed seeing the question of Ke Tang earlier and so, that is the question I am
addressing here.
Heat transfer coefficient of steam condensing in vacuum conditions is very high, in
the order of 30,000 W/m2K. The heat transfer is rapid and one may assume that
condensation occurs as soon as steam comes into contact with the cool surface. As
steam condensation progresses, its velocity decreases (due to a reduction in volume
in changing to the much denser water) and therefore the static pressure of steam

5. rises. (Recall Bernoulli theorem). However, this rise of pressure in power plant
condensers can be ignored in power output calculations.
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2 Recommendations
16th Mar, 2017
Siyamthanda Mchophele
Tshwane University of Technology
@ Vijay Raghavan, Erma Dityarangga and Ke Tang, Thank you for your assistance
including other guys who supported the question.
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In a typical heatexchanger,isthere anyspecificrule thatthe hot fluidshouldflow throughthe inner
tubes??
In anyheat exchanger,forexample;inadouble pipe heatexchanger,how dowe decide whetherthe
hot fluidshouldflowthroughinnertube oroutertube?.Orisit completelyirrelevantwhetherthe
hot fluidisflowingthroughthe innertube oroutertube?
Heat Exchangers
Heat & Mass Transfer
FluidFlow
Mechanical Engineering
Thermal Engineering
Fluid
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Most recentanswer
9th Jul,2019
RaminEhsani
Makhzan FooladRafe (DabooSanat) Co.
And,as I knowthere isno difference inthe case of a double tube heatchanger,someone canfollow
above rule.If the shell-sideheattransfercoefficientissmall comparedtothe tube side,finnedtubes
shouldbe considered.
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PopularAnswers(1)
20th Feb,2016

6. Konijeti RamaKrishna
K L University
The fluidflowingthroughthe tubeswill be decided majorlyonease of operation,frictional effects
and purpose whetheritis tobe cooledorheatedup.Forexample inGas+liquidheatex changer(
steamcondenser) itisdifficulttopushsteamthroughthe tubesandhence liquidismade astube
side fluid.Inliquid+Liquidtype the one whichishavinglow viscosityisgenerallybe the tube
fluid.Andfinallyhotfluidischosenasshell side fluidforeffective heattransferandof course it vary
fromone applicationtoother.
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8 Recommendations
All Answers(20)
19th Feb,2016
KaustubhPhalak
Universityof Miami
It isrelevantanddependsonmultiple factors.
If one of the liquidiscorrosive itwill dependonwhattype of steel/material isusedfortubesorshell
and theirrelative cost.Generallyonshellside youhave low pressure drop.Sodependingonthe loop
withlowpressure dropyoucan selectthe fluid.Highpressure liquidsare generallykepton the tube
side as tubeshave highpressure ratingcomparedtosame thicknessof shell.
From onlyheattransferpointof viewyoushouldlookatwhichfluidhaslowerdeltaTorspecifically
Cp_min*deltaTwiththe ambienttemperature.The fluidwithlow value shouldbe onshell
side/outertube side.
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3 Recommendations
19th Feb,2016
RobertoPili
Technical Universityof Denmark
It isalso importanttohave the hot fluidonthe tube side inorderto minimize the heatlossestothe
environment,whichare of course dependentonthe temperature gradient.Therefore,the lowerthe
temperature close tothe heatexchangerenclosure,the lowerthe losses(orthe lowerthe required
thicknessof the insulatingmaterial).
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7 Recommendations
20th Feb,2016
Konijeti RamaKrishna
K L University

7. The fluidflowingthroughthe tubeswill be decided majorlyonease of operation,frictional effects
and purpose whetheritis tobe cooledorheatedup.Forexample inGas+liquidheatex changer(
steamcondenser) itisdifficulttopushsteamthroughthe tubesandhence liquidismade astube
side fluid.Inliquid+Liquidtype the one whichishavinglow viscosityisgenerallybe the tube
fluid.Andfinallyhotfluidischosenasshell side fluidforeffective heattransferand of course it vary
fromone applicationtoother.
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8 Recommendations
21st Feb,2016
FernandoZorto
National AutonomousUniversityof Honduras
I agree too withKonijeti Ramakrishna.
You needtoknowthe kindof processyouwill doonthe heatexchanger.It´sDifferentadouble pipe
heatexchangerfora Tube and Shell,fora radiantheatexchanger.Youneedtosee where isthe
directionof the heatflux onthe differentcase.
bestregard.
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1 Recommendation
22nd Feb,2016
Mario Álvarez-Fernández
Nuclenor
it's convenienttoflowthe fluidwithhigherpressurethroughthe tubesforsafety/mechanical
reasons.The selectionof whichfluidisgoingtoflow throughthe shell/tubesshould be take into
account mechanical factors,notonlythermal factors.
it isalsoveryimportantthe viscosity(the pressuredropthroughthe heatexchangerisalwayshigher
inthe tubesthaninthe shell).That'swhyinoil coolers,forexample,the oil flows usuallythroughthe
shell.But,again,the pressure of the oil shouldbe lowerthanthe coolingfluid.
Temperature of the fluidisn'tusuallytakenintoaccount:incondensers(powerplants,refrigeration
units,...),the hotfluid(steam, refrigerant,...) flowsthroughthe shell;inevaporators,inchillerunits,
the hot fluid(the water) flowsthroughthe shell,too.
I recommendyouthe designcodespublishedbyTEMA or ASME.
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2 Recommendations
22nd Feb,2016
Omar Labbadlia
Dr. Yahia FaresUniversity of Médéa

8. T.Steven(2008) foundthatthere isa reportof optimumpressure drops:(∆P)_c/(∆P)_h ⋍1.73to
maximize the performance of the heatexchangerbymakingitsdesign,suchaspressure dropcold
side are approximately1.7timeslargerthanthe pressure dropsof the hot side.Inabsolute terms,it
ispossible tolose more coldside pressure,therefore,choose topassthe coldflow inthe tubes.
Tine Stevens.(2008).DesignMethodologiesforEfficientHeatTransferinMicro Systems.
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3 Recommendations
24th Feb,2016
H. Taherian
Universityof AlabamaatBirmingham
A corrosive fluidisbettertoflowinthe innertube.Alsoahighpressure fluidshouldbe onthe inner
tube side.
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2 Recommendations
24th Feb,2016
Kamal NasreldinAbdalla
Universityof Khartoum
Yes I agree withTaherianthatthe corrosive fluidshouldflow inthe innertube justlikewhatwe have
inHVACwater cooledchillerswhere the waterflowsinthe innertubes.Thisdone foreasy
maintenance because afterawhile some scalingmay occurin the inside surface of these tubes
whichneedsscrubbingandcleaningtoremove thesedeposits.
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2 Recommendations
28th Feb,2016
VipinNair
Sardar Vallabhbhai National Instituteof Technology
Thank youeveryone foryourresponse.So,the decisionaboutwhichfluidshouldflow throughinner
or outertubesismainlyonthe basisof Thermal andmechanical design.
Thank youProf.Ramakrishna.Yourreplywasthe mostuseful one.
Thank youOmar for recommendingabook!!
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29th Feb,2016
Jayanti Hadiya
BirlaVishvakarmaMahavidyalayaEngineeringCollege

9. Anotherreason:fluidhavinghighheattransfercoefficient isnormallyflowthroughinnertube and
fluid(normallygas) havinglowheattransfercoefficientflowsthroughshell,because lessarea
available ininnersidecomparedtoouterandhence heattransfercan be balance by higherheat
transferarea at outerside,andtherefore finsare providedongasside (outerside).
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2 Recommendations
7th Mar, 2016
VipinNair
Sardar Vallabhbhai National Instituteof Technology
HelloJayanti
I am sorry ;i dont agree withyourexplanationwhenyousaythat"fluidhavinghigh"heattransfer
coefficient".The heattransfercoefficientisnotapropertyof the fluid.Itdependsonflow
parametersandotherthermophysical properties.Therefore,we dontknow the value of heattransfer
coefficientinadvance.
Or may be you meanthat we should"predict"the heattransfercoefficientsof the twoflow
scenariosbyusingempirical correlationsandthendecideonthe basisof heattransfercoefficient
values.If yes,thenyourapproachiscorrect.
Thank you.
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1 Recommendation
10th Mar, 2016
Kamal NasreldinAbdalla
Universityof Khartoum
You are correct Vipininyourfirstanswerasyoumentionedthatthere isnofluidhavinghighheat
transfercoefficient because forfluidsthe heattransfercoefficientdependsonflow propertieslike
velocity,pressure,temperature....etcandonfluidpropertieslike viscosity,density,volatility.....etcand
so thiswill involve acomplex approachinthe decisionmaking.
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1 Recommendation
14th Mar, 2016
VipinNair
Sardar Vallabhbhai National Instituteof Technology
Thank youProf.Kamal
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31st Mar, 2016

10. AmeyMajgaonkar
SathyabamaInstitute of Science andTechnology
Hi,it is a typical optimizationcase.Designerhastoconsiderspropertiesof fluidsandtheir
application.e.g.Corrosion,viscosity,phase change,heatloss,fouling,pressureandtemp.,
mechanical construction,ease of maintenance, capital andrunningcost,Probabilityof mixing,leak
and hazards.
All these shall governfluidallocationof sidesandthermal &mechanical design.
Sometimesprojectspecificrequirementsalsoneedstobe considered.
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3 Recommendations
1st Apr, 2016
Jayanti Hadiya
BirlaVishvakarmaMahavidyalayaEngineeringCollege
I agree withanswergivenbyAmeyMajgaonkar.
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1 Recommendation
19th Apr,2016
FernandoZorto
National AutonomousUniversityof Honduras
I agree withthe answerof Prof.Konijeti Ramakrishna
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9th Jul,2019
RaminEhsani
Makhzan FooladRafe (DabooSanat) Co.
Obviously,thisisanoptimizationcase andmustbe consideredforeveryheatexchangerbasedon
it's conditions.
But, there issome general rulestoselectthe fluidwhichmustbe flow inthe tubeside.Forexample,
inShell andTube heatexchangers,itisbettertochoose whicheverfluidappearshigherinthe
followinglisttopassinside tubes:
1- Coolingwater,
2- Corrosive fluid,
3- A fluidwhichisfouling,
4- The lessviscousof twofluids,

11. 5- The fluidunderhigherpressure,
6- The hotterfluid,
7- The fluidof lessvolume.