Chapter.3RefrigerantsSecondaryRefrigerantandMoistureair

一?Choice

Undesirablerefrigerantcharacteristicsare:

nonflammableandnontoxic

highlatentheatandlowboilingpoint

highcriticaltemperatureandlowfreezingpoint

lowcriticaltemperatureandhighfreezingpoint

(RefrigerationLicenseExaminations,USA)

Adesiredchemicalrefrigerantcharacteristicis:

itmixesreadilywithoil

stability

itcaneasilychangefromaliquidtovaporandback

alloftheabove

Whatrefrigerantbreaksdownandformsphosgeneinthepresenceofacarbonflame?

R-718 c.R-764

R-717 d.R-ll

Anhydrousammoniais:

amixtureofammoniaandwater

29%aquaammonia

ammoniawithoutanywater

noneoftheabove

Refrigerantissubcooledto:

increasetherefrigerationeffect

increasedensity

increasemiscibilityinoil

noneoftheabove

AnywaterintherefrigerantofaFreonsystemwouldcause:

acloggedoiltrap

acloggedscaletrap

afrozendischargevalve

afrozenexpansionvalve

Ofthefollowingrefrigerants,whichistheleastflammableandtheleasttoxic?

methylchloride. c.propane

ammonia d.RI34a

Calciumchloridefreezesat:

-41°F c.35°F

-32°F d.20°F

Thetermtoxicitymeans:

acidityorcorrosiveness c.diffusiveness

poisonousness d.internalfriction.

Ofthefollowingtemperatures,whichisthelowestrecommendedforusewithcalciumchloridebrine?

0℃ c.-41.8℃

-35.7℃ d.-61.2℃

WhichchemicalderivedfromCFCdepletestheozonelayerintheatmosphere?

carbondioxide c.carbonmonoxide

chlorinemonoxide d.calciumchloride

Ofthefollowingthermalpropertiesofarefrigerant,theundesirableonesare:

highviscosityandlowpourpoint

highlatentheatofevaporation

lowcriticalandhighfreezingtemperature

highviscosityandhighfilmheatconductivity

R-718is:

methylchloride c.carbondioxide

dichlorodifluoromethane d.water

Containersshouldnotbecompletelyfilledwithliquidrefrigerantbecause:

theywouldbetooheavytocarry

ifthetemperaturegoesup,hydrostaticpressurescouldrupturethecontainer

therewouldn'tbeanyvaporpresent

moistureintheliquidcancausephosgene

Ifthespecificgravityofcalciumbrineincreasedfrom1.29to1.30,thefreezingpointwould:

notbeaffected c.drop

fluctuateupanddown d.rise

Sodiumchloridecannotbeusedforabrinesolutionbelow:

a.-15°F c.30°F

b.15°F d.noneoftheabove

Abrinesolutiontobeusedat-25°Fmaynotcontain:

calciumchloride c.ethyleneglycol

sodiumchloride d.alcohol

Theamountofchromaterequiredtomake1,000cubicfeetofcalciumbrineis:

50lbs. c.125lbs

75lbs. d.200lbs

Thefreezingpointofbrineshouldbe:

32°F

0°F

10to15°Fbelowthelowestrefrigerantsaturationtemperature

-59°F

Theevaporatorabsorbsheatfromairorbrinebecauseliquidrefrigerantenteringit:

hasalowertemperaturethantheairorbrine

hasahighertemperaturethantheairorbrine

boilstoalow-pressuregas

boilstoahigh-pressuregas

WhichchemicalderivedfromCFCdepletestheozonelayerintheatmosphere?

carbondioxide c.R12

R407C d.RI34a

Thetemperatureatwhichmoistureintheairstartstocondenseinthesurfaceoftubeinaircoolerisknownas:

relativehumidity c.eutecticpoint.

dewpoint d.wet-bulbtemperature

二、Questionandanswer

WhatareCFC,HCFC,HFC,ODPandGWP,whyareCFCsphase-out?WhatisPhaseOutDateaboutCFCsandHCFCs,respectively?

Whatisheatpump?whatisthedifferencebetweenrefrigerationmachineandheatpump?

三?Calculation

Calculatethesensibleheat(enthalpyofdryair)of5kgofairhavingaDryBulbtemperatureof15℃andaDewPointtemperatureof3℃.

Determinethelatentheat(enthalpyofthewatervapor)of10kgofairhavingaDryBulbtemperatureof18℃andaDewPointtemperatureof8℃.

ReadingsfromaslingpsychrometerindicatethattheairinaroomhasaDryBulbtemperatureof39℃andaWetBulbtemperatureof26℃.Fromthepsychrometricchart,determinethehumidityratio,DewPointtemperature,approximatespecificvolume,specificenthalpyatsaturation,enthalpydeviation,actualspecificenthalpy,andapproximaterelativehumidity.

OnethousandkilogramsOfairperhourhaveDryBulbandDewPointtemperaturesof28℃and16crespectively,andarepassedacrossacoolingcoilandcooledtoafinalDryBulbtemperatureof8℃.Assumingthattheairleavingthecoilissaturated.Determine:(a)themassofthewatervaporcondensedfromtheairinkilogramsperhourand(b)therateoflatentheatremovalinkilowatts.(c)Calculatethetotalheatinkilowattsremovedfromtheair.

TwokilogramsofairpersecondhavinginitialDryBulbtemperatureandWetBulbtemperatureof21℃and16℃arepassedacrossheatingcoil,andtheDryBulbtemperaturetemperatureisraisedto33℃.Plottheprocessonapsychrometricchartanddetermine:(a)thefinalWetBulbtemperatureoftheair,(b)thesensibleheattransferredinkJ/s.(c)thetotalheattransferredinkJ/s.

Twentykilogramsofa