Feed Heaters Performance

(1)

Feed Heaters & Condenser

Performance

By: By: M.V. Pande M.V. Pande Director Director NPTI, Badarpur NPTI, Badarpur

(2)

St

(3)

Effect of no. of feed-water heaters on thermal

efficiency of the cycle

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Vital Measures of an Operating Heater

•

• Terminal temperature difference (TTD) =Terminal temperature difference (TTD) =

inlet steam saturation temperature -Feedwater inlet steam saturation temperature -Feedwater outlet temperature

outlet temperature

•

• Drains cooler approach (DCA) = shell drainsDrains cooler approach (DCA) = shell drains outle

outlet tet tempermperaturature -e - ffeedweedwataterer inleinlet tempt tempereraturaturee

•

• FeedwaterFeedwater tempertemperature ature rise (TR) = frise (TR) = feedwaeedwaterter outle

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Zones of Feed Water Heaters

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Zones of Feed Water Heaters

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Horizontal Feed Water Heater

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Vertical Feed Water Heater

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HP Heater

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HP Heater

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HP Heater Installation

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Key Performance Indicator

•

• TTD - TTTD - Terminal Terminal Temperaemperature Diffture Differenceerence •

• TTD = TS -TTD = TS - FW OFW OUTUTLELET TET TEMPMP

TS saturation temperature corresponding to TS saturation temperature corresponding to shell pressure shell pressure • • DCADCA • • TRTR •

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Thermal profile in different zones of

H P HEATER

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High TTD Causes

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TTD and Feed Water Temp.

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Hig

h Dr

ain C

ool

ing A

ppr

oac

h -

DCA

(Level control valve (Level control valve))

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T

emperature Profile

of

a cl

osed

Feed

Water Heater

(18)

Effect of HP Heaters TTD on NTHR

(Net Turbine Heat Rate)

(19)

Effect of LP Heaters TTD on NTHR

(Net Turbine Heat Rate)

(20)

Effect of DCA on NTHR

(Net Turbine Heat Rate)

(21)

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Low Temperature Rise

TR = FW ou

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Feed Heaters Survey

•

• Feed heaters survey evaluate the performanceFeed heaters survey evaluate the performance

of heaters & predicts the

of heaters & predicts the deteriordeterioration causesation causes

•

• Following parameters are noted downFollowing parameters are noted down

-- StSteam pream pressessurure at hee at heataterer

-- SteaSteam tem tempermperaturature ae at heat heaterter

-- FeeFeed watd water inleer inlet & outlet tt & outlet temperemperaturaturee -- HeatHeater der drairain tn temperemperaturaturee

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Feed Heaters Survey

 Evaluate the steam flow to each heater by heatEvaluate the steam flow to each heater by heat balance

balance

 Compare the flow values with optimumCompare the flow values with optimum

 CalcCalculate ulate TT..TT.D. for .D. for each each heaterheater

 The results indicate following problemsThe results indicate following problems

-- The The elevaelevated ted TTDs TTDs on on the the heateheater r train train suggests suggests watwaterer side contamination (oil)

side contamination (oil)

-- The high stThe high steam flow team flow to particular heato particular heater maer may be duey be due to lower feed water inlet temperature,suggesting the to lower feed water inlet temperature,suggesting the problem in previous heater

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Sampl

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Calculations

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Deterioration

•

• Air accumulation

Air accumulation

•

• Steam side fouling

Steam side fouling

• Water side fouling

• Drainage defects

• Parting plane leakage

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Air accumulation

• Increased

• Increased TTDTTD

• Possible elevation of steam

• Possible elevation of steam-to-heater-to-heater temperature

temperature

• Reduced temperature rise of feed water or • Reduced temperature rise of feed water or

condensate. condensate.

• 0.5 %

• 0.5 % steam is venting inevitable for goodsteam is venting inevitable for good

venting venting

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Steam side fouling

• Progressive

• Progressive increase of TTDincrease of TTD

• Drain temperature unaffected • Drain temperature unaffected

• Reduced feed water temperature rise • Reduced feed water temperature rise • Eventual tube failure due to mechanical • Eventual tube failure due to mechanical

weakening weakening

• Accumulation of debris in the heater shell. • Accumulation of debris in the heater shell.

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W

ater side

fouling

•

• Gradual increase of TTD.Gradual increase of TTD. •

• OilOil

–

– LPT bearing oil through sealsLPT bearing oil through seals

–

– Deposition occurs in HP Deposition occurs in HP heaterheaters, worst hit ats, worst hit at highest pressure heater

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Drainage d

ef

ects

•

• DamageDamaged flsahbd flsahbooxx intinternernalsals •

• Reduced orifice openingReduced orifice opening •

• Enlarged orifice openingEnlarged orifice opening •

• Heater drain CV/ bypass valveHeater drain CV/ bypass valve

malfunction. malfunction.

(32)

Parting plane leakage

• Short circuiting of FW • Short circuiting of FW • TTD high • TTD high • DCA high • DCA high • TR less • TR less

(33)

HP He

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Partition Plane Damage

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Heat Exchanger

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SURFACE CONDENSER

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EFFECT OF VARYING THE BACK PRESSURE

•

• A large amount of the extra work is done by theA large amount of the extra work is done by the steam, when the back pressure is reduced.

steam, when the back pressure is reduced.

•

• However, the trouble is that as the back pressureHowever, the trouble is that as the back pressure improves, certain losses also

improves, certain losses also increase-1) CW Pumping Power.

1) CW Pumping Power. 2) Leaving losses.

2) Leaving losses. 3)

3) Reduced Reduced condensate condensate TTemperature.emperature. 4) Wetness of the steam.

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Increased CW Pumping Power

•

• Assuming that the CW inlet temperature is lowAssuming that the CW inlet temperature is low enough, the back pressure can be reduced by enough, the back pressure can be reduced by putting more and more CW through condenser putting more and more CW through condenser tubes.

tubes. •

• However, this will require more CW pumpingHowever, this will require more CW pumping

power and the gain from improved back pressure power and the gain from improved back pressure must be offset against extra power absorbed by must be offset against extra power absorbed by the pumps. So, the CW pumps should be run only the pumps. So, the CW pumps should be run only when the cost of running the pump is equal to, or when the cost of running the pump is equal to, or less than the gain in

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Increasing leaving loss

•

• The steam leaves the last The steam leaves the last row at a velocityrow at a velocity

which depends upon the conditions prevailing which depends upon the conditions prevailing at the point. As this velocity is not utilized

at the point. As this velocity is not utilized usefully

usefully, it , it represents a loss of represents a loss of possible workpossible work known as the leaving loss. So velocity steam known as the leaving loss. So velocity steam through

through fixed fixed annulus annulus must must also also double. double. ButBut leaving losses varies a

leaving losses varies as square of s square of the velocitythe velocity.. So it will increase four times.

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Reduced condensate temperature /

increased bled steam

•

• The condensate in the condenser is atThe condensate in the condenser is at

saturation tempera

saturation temperature corresponding to ture corresponding to thethe back pressure. It back

back pressure. It back pressure is reduced,pressure is reduced, saturation temper

saturation temperature will drop. When ature will drop. When itit enter

enters first LP heaters it will s first LP heaters it will be cooler thanbe cooler than befo

before consequently more steam re consequently more steam willwill

automatically be bled to the heater. The extra automatically be bled to the heater. The extra steam is no longer available to do work in

steam is no longer available to do work in thethe turbine will be deprived of some work.

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Increase wetness of the steam

•

• The lower the back pressure, the greater the wetness ofThe lower the back pressure, the greater the wetness of

steam. The extra moisture could result in damage to the steam. The extra moisture could result in damage to the moving blade. Also with increased wetness, volume of moving blade. Also with increased wetness, volume of

steam is reduced water droplets being heavier than steam steam is reduced water droplets being heavier than steam moves slowly. So the front edge of moving blades have to moves slowly. So the front edge of moving blades have to push the droplets out of the way. This can cause damage to push the droplets out of the way. This can cause damage to blades. Theref

blades. Therefore, it is ore, it is usual to fit usual to fit satellite erosion shieldssatellite erosion shields to the leading edge to reduce this damage. As a rough

to the leading edge to reduce this damage. As a rough guide, it can be

guide, it can be assumed that every 1% wetness will assumed that every 1% wetness will reducereduce efficiency of associated stage by 1%.

efficiency of associated stage by 1%.

•

• The reduction in back pressure will result in netThe reduction in back pressure will result in net

improvement in heat consumption until a point is reached improvement in heat consumption until a point is reached beyond which benefit due to improve back pressure is

beyond which benefit due to improve back pressure is outweighed by the losses

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Blades erosion damage due to wet steam

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Condenser Low Condenser Low Vacuum Causes Vacuum Causes

(44)

V

acuum

E

fficiency

& Cond

enser

E

fficiency

•

• Vacuum EfficiencyVacuum Efficiency



 It is the ratio of the actualIt is the ratio of the actual vacuumvacuum at the steam inlet toat the steam inlet to the maximum obtainable

the maximum obtainable vacuumvacuum in a perfectin a perfect

condensing

condensing plant, i.e., it is plant, i.e., it is the ratio ofthe ratio of actual

actual vacuumvacuum to idealto ideal vacuumvacuum..

•

• Condenser Condenser EfEfficiencyficiency



 In thermal power plants, the purpose of aIn thermal power plants, the purpose of a surface

surface condensercondenser is to condense the exhaust steamis to condense the exhaust steam from a steam turbine to obtain maximum

from a steam turbine to obtain maximum efficiencyefficiency,, and also

and also to convert the turbine exhaust steam intoto convert the turbine exhaust steam into

pure water (referred to as steam condensate) so that it pure water (referred to as steam condensate) so that it may be reused in the

may be reused in the steam genersteam generator or boiler asator or boiler as boiler feed water.

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Condenser Condition

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Deviation due to CW inlet

temperature

•

• Plot a line vertically from the actual CW inletPlot a line vertically from the actual CW inlet temperature to intersection with the optimum temperature to intersection with the optimum CW rise. Then

CW rise. Then plot horizontally to the plot horizontally to the interintersectionsection with optimum terminal differ

with optimum terminal difference (TTD) line, ence (TTD) line, andand then vertically downwards to cut the saturated then vertically downwards to cut the saturated steam temperature line to obtain the

steam temperature line to obtain the

corresponding back pressure. (Refer fig in corresponding back pressure. (Refer fig in previous slide)

previous slide) •

• Hence the loss due to the high CW inletHence the loss due to the high CW inlet

temperature can be calculated by subtracting the temperature can be calculated by subtracting the optimum value from the actual

(48)

Deviation due to C.W. flow

•

• Plot a line from the actual CW inletPlot a line from the actual CW inlet

tempera

temperature vertically to the ture vertically to the interintersection section withwith actual CW rise Then plot horizontally to the

actual CW rise Then plot horizontally to the optimum T

optimum TTDTD, then vertically downward to, then vertically downward to the saturation steam temperature to obtain the saturation steam temperature to obtain the actual

the actual back pressure. the differback pressure. the differenceence between the actual back pressure and the between the actual back pressure and the optimum back gives the loss due to the

optimum back gives the loss due to the incorrect CW flow.

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Deviation due to air/dirty tubes

•

• ThThee eeffffeecctt ooff tthhee aaiirr aanndd ddiirrttyy ttuubbeess oonn tthhee

h

heeaatt ttrraannssffeerr iiss ttoo iinnccrreeaassee tthhee TTTTDD aabboovvee o

oppttiimmuumm.. AAss tthheeyy bbootthh ggiivvee tthhee ssaammee eeffffeecctt ,, tthheeyy aarree cclluubbbbeedd ttooggeetthheerr iinn tthhiiss eexxeerrcciissee.. PPlloott lliinnee ffrroomm tthhee aaccttuuaall CCWW iinnlleett tteemmppeerraattuurree ttoo tthhee aaccttuuaall CCWW rriissee aanndd tthheenn aaccrroossss tthhee aaccttuuaall T

TTTDD lliinnee pplloottttiinngg vveerrttiiccaallllyy ddoowwnnwwaarrddss ttoo a

adjdjaacceenntt sstteeaamm tteempmpeerraatuturree babacckk pprreessssuurree.. SoSo tthhee ddeevviiaattiioonn dduuee ttoo aaiirr//ddiirrttyy ttuubbeess ccaann bbee ffoouunndd oouutt..

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CASE STUDY

Khaparkhe

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Design Data.

Condenser tubes

Condenser tubes specificatispecificationon

1. Tube diameter (outside diameter) 1. Tube diameter (outside diameter)

25.4mm 25.4mm

2. Tube thickness 1.0mm 2. Tube thickness 1.0mm

3. Tube diameter ( inside diameter) 3. Tube diameter ( inside diameter)

23.4mm 23.4mm 4. Tube length 7.5m 4. Tube length 7.5m 5. Number of tubes 19208 5. Number of tubes 19208 6. Cross sectional area per t

6. Cross sectional area per tubeube 430.05m3

430.05m3

7. Surface area per tube 0.60m2 7. Surface area per tube 0.60m2 8. Total surface area of tube 11495 8. Total surface area of tube 11495

m2 m2

9. Specific heat of CW 1.00kcal/kg/0C 9. Specific heat of CW 1.00kcal/kg/0C

10. Density of CW 1000kg/ m3 10. Density of CW 1000kg/ m3 11. Condenser vacuum 650.06mm of 11. Condenser vacuum 650.06mm of Hg Hg

12. Condenser back pressure 12. Condenser back pressure 0.09kg/cm2

0.09kg/cm2

13. Sat. temperature at condenser back 13. Sat. temperature at condenser back pressure 43.6

pressure 43.6oo_C_C

14. Average temperature of CW inlet 14. Average temperature of CW inlet 30.500C 30.50 30.500C 30.50 oo_C_C 15. Average temperature of CW at 15. Average temperature of CW at outlet 39.20 outlet 39.20oo_C_C

16. CW temperature rise across 16. CW temperature rise across condenser 8.79

condenser 8.79oo_C_C

17. Terminal temperature difference 17. Terminal temperature difference

4.40 4.40 oo_C_C

(52)

Calculation for the TEST-1

1) If all values of C.W. Inlet (C.W.), C.W. Rise (C.W.R) ,T.T.D. are as per design then 1) If all values of C.W. Inlet (C.W.), C.W. Rise (C.W.R) ,T.T.D. are as per design then

C.W.I+C.W.R.+T.T.D. = 30.5 + 8.79 +4.4 = 43.7 = 89.11 mbar C.W.I+C.W.R.+T.T.D. = 30.5 + 8.79 +4.4 = 43.7 = 89.11 mbar 2) If only inlet

2) If only inlet water temwater temperaturperature is ace is actual thentual then

(C.W.I)a.+C.W.R.+T.T.D.=29 +8.79 +4.4 = 42.2= 82.46 mbar (C.W.I)a.+C.W.R.+T.T.D.=29 +8.79 +4.4 = 42.2= 82.46 mbar 3) If both the

3) If both the inlet temperainlet temperature and temperaturture and temperature rise is e rise is actual thenactual then (C.W.I)a.+C.W.R)a.+T.T.D.=29 +10.2 +4.4 = 43.6 = 89.11 mbar

(C.W.I)a.+C.W.R)a.+T.T.D.=29 +10.2 +4.4 = 43.6 = 89.11 mbar 4) If all

4) If all parametparameters are actual theners are actual then

(C.W..I)a.+(C.W.R)a.+(T.T.D)a=29+10.2 +7.1 =46.3 = 102.4 mbar (C.W..I)a.+(C.W.R)a.+(T.T.D)a=29+10.2 +7.1 =46.3 = 102.4 mbar

Now effect of various parameters is as a follows Now effect of various parameters is as a follows #1) Cooler Circulating Water improves vacuum by #1) Cooler Circulating Water improves vacuum by (82.4

(82.46 -89.6 -89.11) = -6.11) = -6.65 mbar = -65 mbar = - 5 mm of Hg.5 mm of Hg. #2) Dirtiness of

#2) Dirtiness of tubes deterioratubes deteriorates vacuum bytes vacuum by (89.1

(89.11 -1 - 82.4682.46) = 6.65 m) = 6.65 mbar = 5 mm of Hg.bar = 5 mm of Hg. #3) Air ingress

(53)

Conclusion:

#1) Inlet temperature is slightly lower than #1) Inlet temperature is slightly lower than

design value and hence little improvement in design value and hence little improvement in vacuum by 5 mm of Hg.

vacuum by 5 mm of Hg.

#2) Tubes are dirty which deteriorates vacuum #2) Tubes are dirty which deteriorates vacuum

by 5mm of Hg. by 5mm of Hg.

#3) There is a little air ingress which

#3) There is a little air ingress which causescauses vacuum deteriora

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Calc

ula

tion f

or the T

est -

2

1) If all values of C.W. Inlet C.W. Inlet (C.W.), C.W. Rise (C.W.R) , T.T.D. 1) If all values of C.W. Inlet C.W. Inlet (C.W.), C.W. Rise (C.W.R) , T.T.D. are as per design

are as per design

then-C.W.I.+C.W.R.+T.T.D. =30.5 +8.79+4.4 =43.7 = 89.11 mbar C.W.I.+C.W.R.+T.T.D. =30.5 +8.79+4.4 =43.7 = 89.11 mbar 2) If only inlet

2) If only inlet water temwater temperaturperature is ae is actual thenctual then

(C.W.I)a. +C.W.R.+ T.T.D.= 22 + 8.79 + 4.4 =35.19 = 56.6 mbar (C.W.I)a. +C.W.R.+ T.T.D.= 22 + 8.79 + 4.4 =35.19 = 56.6 mbar 3) If both the

3) If both the inlet temperainlet temperature and temperaturture and temperature rise is e rise is actual thenactual then (C.W.I)a.+(C.W.R)a.+ T.T.D.=22 + 10 +4.4 =36.4 =61.18 mbar

(C.W.I)a.+(C.W.R)a.+ T.T.D.=22 + 10 +4.4 =36.4 =61.18 mbar 4) If all

4) If all parametparameters are actual theners are actual then

(C.W.I)a.+(C.W.R)a.+(T.T.D)a= 22+10+7.9=39.9=73.15 mbar (C.W.I)a.+(C.W.R)a.+(T.T.D)a= 22+10+7.9=39.9=73.15 mbar Now effect of various parameters is as a follows

Now effect of various parameters is as a follows #1) Cooler Circulating Water improves vacuum by #1) Cooler Circulating Water improves vacuum by (56.6

-(56.6 - 89.1189.11) =-32.) =-32.5 mbar =-25 mbar =-24.4 mm of Hg.4.4 mm of Hg. #2) Dirtiness of

#2) Dirtiness of tubes deterioratubes deteriorates vacuum bytes vacuum by (61.1

(61.18 -8 - 56.6) = 4.56.6) = 4.58 mbar =3 m58 mbar =3 mm of Hg.m of Hg. #3) Air ingress

#3) Air ingress deteriordeteriorates vacuum byates vacuum by (73.1

(55)

Conclusion

design value and hence little improvement in design value and hence little improvement in vacuum by 24.4 mm of Hg.

vacuum by 24.4 mm of Hg.

by 3mm of Hg. by 3mm of Hg.

#3) There is a little air ingress which causescauses vacuum deteriora

(56)

Cal

cul

a

tio

n fo

r the T

ES

T -

3

1) If all values of C.W. Inlet (C.W.), C.W. Rise (C.W.R) , T.T.D. are as per 1) If all values of C.W. Inlet (C.W.), C.W. Rise (C.W.R) , T.T.D. are as per design then

design then

C.W.I.+C.W.R.+T.T.D.=30.5 + 8.79 +4.4 = 43.7 89.11 mbar C.W.I.+C.W.R.+T.T.D.=30.5 + 8.79 +4.4 = 43.7 89.11 mbar 2) If only inlet water temperature is actual then

2) If only inlet water temperature is actual then

(C.W.I)a.+C.W.R.+T.T.D. =27.82 + 8.79 +4.4 =41 = 73.5 mbar (C.W.I)a.+C.W.R.+T.T.D. =27.82 + 8.79 +4.4 =41 = 73.5 mbar

3) If both the inlet temperature and temperature rise is actual then 3) If both the inlet temperature and temperature rise is actual then (C.W.I)a.+(C.W.R)a.+T.T.D.=27.82 + 11 +4.4 = 43.2 = 87.11 mbar

(C.W.I)a.+(C.W.R)a.+T.T.D.=27.82 + 11 +4.4 = 43.2 = 87.11 mbar 4) If all parameters are actual then

4) If all parameters are actual then

(C.W.I)a.+(C.W.R)a.+(T.T.D)a=27.82+11+15.4 = 54.22 = 151.62 mbar (C.W.I)a.+(C.W.R)a.+(T.T.D)a=27.82+11+15.4 = 54.22 = 151.62 mbar

Now effect of various parameters is as follows Now effect of various parameters is as follows #1) Cooler Circulating Water improves vacuum by #1) Cooler Circulating Water improves vacuum by (73.5

-(73.5 - 89.1189.11) = -15.6) = -15.61 mbar = -11 mbar = -11.74 mm o1.74 mm of Hg.f Hg. #2) Dirtiness of tubes deteriorates vacuum by #2) Dirtiness of tubes deteriorates vacuum by (87.1

(87.11 -1 - 73.5) = 13.73.5) = 13.61 mbar =61 mbar =10.23 mm of Hg.10.23 mm of Hg. #3) Air ingress deteriorates vacuum by

#3) Air ingress deteriorates vacuum by (151.

(57)

Conclusion

design value and hence little improvement in design value and hence little improvement in vacuum by about 13 mm of Hg.

vacuum by about 13 mm of Hg.

by 10.23 mm of Hg. by 10.23 mm of Hg.

#3) There is a little air ingress which causescauses vacuum deterioration by around 50 mm of