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Dew Point in Compressed Air Helping you make a better measurement.
DewPointinCompressedAir
Helping you make a better measurement.
BruceMcDuffee MichaelBoetzkes
WebinarPresenters&HumidityExperts
Agenda&TakeawaysAgenda• DefinitionofDewPoint• PressureEffect• ISOAirClasses&Dryers• DesiccantDryersandEfficiency• WaterinAir– practicalexample• Summary
Takeaways• Understandingtheparameterhelpstomakeabettermeasurementandpreventwater.
• Learnthecauseofliquidwaterinthesystem.
• Understandhowpressureaffectsthemeasurement.
• Understanddryerperformanceanddewpoint.
DefinitionofDewPoint
DefinitionofDewPointTemperature
• Dewpointtemperatureisthetemperatureatwhichwatervaporwillbegintocondense.
• Thetemperatureatwhichamoistgasissaturatedoveraplanesurfaceofpureliquidwater.
Note– Dewpointtemperaturedoesnotchangeastemperaturechanges.
WhataboutFrostPoint?
• Thetemperatureatwhichamoistgasissaturatedoveraplanesurfaceofpureice.
• Whichoneareyoumeasuring?• Whichonemattersincompressedair?
Note– Dewpointislowerthanfrostpoint(byabout4Cat-40).
WhyIsDewPointTemperaturesoImportant?
• Waterincompressedaircausesproblems.
• IfDp reachesambienttemperature,condensationoccurs.
• Dewpointtemperaturechangeswithpressureandwithdryerperformance.
PressureEffects
PressureEffectsonDewPoint
Ruleofthumb:• Aspressureincreases,dewpointtemperaturerisesandapproachessaturation.
• Aspressuredecreases,dewpointtemperaturegoeslowerandtheairbecomesdryer(relativelyspeaking)
PressureDewPointvs AtmosphericDewPoint
• PressureDewPointisthedewpointattheactualpressure.
• AtmosphericDewPointiswhatthatdewpointwouldbeiftheairwereexpandedtoatm pressureor0psig.
• Knowwhatyourhygrometerisreporting– pressureDp orAtm Dp.
HowdoYouKnowATMorPressure?
• Istheprobeonthepressureline?• Isthereasamplelinefromthemainline?• Istherearegulator?
Whatifyouhavetoconvert?
Whatifyouhavetoconvert?
Comments&Questions
Ifwedon’tgettoyourquestiontoday,we’llrespondviaemailafterthewebinar.
Application
WhereShouldyouMeasureDewPoint?
AirClassification- ISO8573.1(pressuredewpointonly)Class Particles
max inmicronsDewPoint C DewPointF Oil
mg/m3
1 0.1 -70 -94 0.012 1 -40 -40 0.13 5 -20 -4 14 15 3 38 55 40 7 45 >56 - 10 50 -
HeatlessDesiccantDryersDewPoint
DewpointDemandSwitching• Heatlessregenerativedryers• Highcostinpurgeairisreduced• SomeHDDconsumeupto15%oftheirratedcapacityinpurgeairwithoutDDS.
For example:• If a dryer is rated for -40 Dp at 1000 cfm, it requires
150cfm just for purge air.• This is equal to a 35HP compressor running 24/7 just to
purge the dryer.
PracticalExamples
PracticalExample– willitfreeze?
Case:AtmosphericDewpoint=38°FInsidetemperatureis77°FAirlinegoesoutsidein30°FCompressedairlinesat100psig
• Dewpointinstrumentreads-20°FDPfromsampleofgastakenfromsystem
• Willthelinesfreeze?
PracticalExample– willitfreeze?
CriticalInformationAtm DP:-20°FPressure:100psigLowestTemperature:30°F
PressureDP:???
PracticalExample– willitfreeze?
CalculateMixingRatio:0.00034782kg/kgPressureDP:24.1°F
PressureDP(24.1°F)<OutsideTemperature(30°F)NoIce!
PracticalExample:Whatisyourrealdewpointtemperature?
Case:• Pressureis70psig• Dewpointis+2F
2.0
PracticalExample:Whatisyourrealdewpointtemperature?
Case:• Pressureis70psig• Dewpointis+2F
• Pressuredewpointis+39Fat70psig• At90psig– dewpointis+45F
2.0
Comments&Questions
Ifwedon’tgettoyourquestiontoday,we’llrespondviaemailafterthewebinar.
NextWebinarsHumidityTheory,Terms&TipsThursday,November16, 1:00PMEST
HumidityMeasurementTechnologyPros&ConsThursday,December21, 1:00PMEST
HowtoChooseaBest-fitHumidityInstrumentThursday,January18, 1:00PMEST
