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8/9/2019 Rel Humidity
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Temperature
- t -
(oC)
Density
- -
(kg/m3)
Specific Weight
- -
(N/m3)
-40 1.514 14.85
-20 1.395 13.68
0 1.293 12.6
5 1.269 12.45
10 1.24 12.23
15 1.225 12.01
20 1.204 11.81
25 1.184 11.61
30 1.165 11.43
40 1.12 11.05
50 1.109 10.88
60 1.060 10.400 1.029 10.09
80 0.9996 9.803
90 0.921 9.533
100 0.9461 9.28
200 0.461 .31
300 0.6159 6.040
400 0.5243 5.142
500 0.4565 4.4
Relative humidity
http://www.engineeringtoolbox.com/temperature-d_291.htmlhttp://www.engineeringtoolbox.com/density-specific-weight-gravity-d_290.htmlhttp://www.engineeringtoolbox.com/density-specific-weight-gravity-d_290.htmlhttp://www.engineeringtoolbox.com/temperature-d_291.htmlhttp://www.engineeringtoolbox.com/density-specific-weight-gravity-d_290.htmlhttp://www.engineeringtoolbox.com/density-specific-weight-gravity-d_290.html8/9/2019 Rel Humidity
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!r"m Wi#ipe$ia% the free encyc&"pe$ia
'ump t"( na)igati"n%search
This artic&e is written like apersonal reflection or essayrather than an
encyclopedic description of the subject. *&ease he&p impr")e it+y re,riting it
in an encyc&"pe$ic sty&e. (September 2012)
http://en.wikipedia.org/wiki/Relative_humidity#mw-headhttp://en.wikipedia.org/wiki/Relative_humidity#mw-headhttp://en.wikipedia.org/wiki/Relative_humidity#p-searchhttp://en.wikipedia.org/wiki/Wikipedia:What_Wikipedia_is_not#PUBLISHERhttp://en.wikipedia.org/wiki/Wikipedia:What_Wikipedia_is_not#PUBLISHERhttp://en.wikipedia.org/w/index.php?title=Relative_humidity&action=edithttp://en.wikipedia.org/wiki/Wikipedia:Encyclopedic_stylehttp://en.wikipedia.org/wiki/File:Relative_Humidity.pnghttp://en.wikipedia.org/wiki/Relative_humidity#mw-headhttp://en.wikipedia.org/wiki/Relative_humidity#p-searchhttp://en.wikipedia.org/wiki/Wikipedia:What_Wikipedia_is_not#PUBLISHERhttp://en.wikipedia.org/w/index.php?title=Relative_humidity&action=edithttp://en.wikipedia.org/wiki/Wikipedia:Encyclopedic_style8/9/2019 Rel Humidity
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The re&ati)e humi$ity "f an air-,ater miture is $efine$ as the rati" "f thepartia&
pressure"f ,ater )ap"r 72 in the miture t" the saturate$ )ap"r pressure"f
,ater at a prescri+e$ temperature.
e&ati)e humi$ity is n"rma&&y epresse$ as a percentage an$ is ca&cu&ate$ +y using thef"&&",ing euati"n(:1;
Measurement
The humi$ity "f an air-,ater )ap"r miture is $etermine$ thr"ugh the use "f
psychr"metric charts if +"th the$ry +u&+ temperatureT an$ the ,et +u&+
temperatureTw "f the miture are #n",n. These uantities are rea$i&y estimate$ +yusing a s&ingpsychr"meter.
There are se)era& empirica& c"rre&ati"ns that can +e use$ t" estimate the saturate$
)ap"r pressure "f ,ater )ap"r as a functi"n "f temperature. The nt"ine euati"nis
am"ng the &east c"mp&e "f these f"rmu&as% ha)ing "n&y three parameters % % an$
. ther c"rre&ati"ns% such as the th"se presente$ +y
8/9/2019 Rel Humidity
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Significance
Climate control
&imate c"ntr"& refers t" the c"ntr"& "f temperature an$ re&ati)e humi$ity f"r humanc"mf"rt% hea&th an$ safety% an$ f"r the technica& reuirements "f machines an$
pr"cesses% in +ui&$ings% )ehic&es an$ "ther enc&"se$ spaces.
Comfort
7umans are sensiti)e t" humi$ air +ecause the human +"$y uses e)ap"rati)e c""&ing
as the primary mechanism t" regu&ate temperature. Bn$er humi$ c"n$iti"ns% the rate
at ,hich perspirati"n e)ap"rates "n the s#in is &",er than it ,"u&$ +e un$er ari$
c"n$iti"ns. ecause humans percei)e the rate o& %eat tran'&erfr"m the +"$y rather
than temperature itse&f%:5;,e fee& ,armer at a gi)en temperature ,hen the re&ati)e
humi$ity is high than ,hen it is &",.
!"r eamp&e% if the air temperature is 24 > 5 >! an$ the re&ati)e humi$ity is @er"
percent% then the air temperature fee&s &i#e 21 > 69 >!.:6;Af the re&ati)e humi$ity is
100 percent at the same air temperature% then it fee&s &i#e 2 > 80 >!. :6;An "ther
,"r$s% if the air is 24 > 5 >! an$ c"ntains saturate$ ,ater )ap"r% then the human
+"$y c""&s itse&f at the same rate as it ,"u&$ if it ,ere 2 > 80 >! an$ $ry.:6;The
heat in$ean$ the humi$eare in$ees that ref&ect the c"m+ine$ effect "f
temperature an$ humi$ity "n the c""&ing effect "f the atm"sphere "n the human +"$y.
uildings
!"r c&imate c"ntr"& in +ui&$ings using 7systems% the #ey is t" maintain the
re&ati)e humi$ity at a c"mf"rta+&e range C &", en"ugh t" +e c"mf"rta+&e +ut high
en"ugh t" a)"i$ pr"+&ems ass"ciate$ ,ith )ery $ry air.
When the temperature is high an$ the re&ati)e humi$ity is &",% e)ap"rati"n "f ,ater is
rapi$ s"i& $ries% ,et c&"thes hung "n a &ine "r rac# $ry uic#&y% an$ perspirati"n
rea$i&y e)ap"rates fr"m the s#in. W""$en furniture can shrin#% causing the paint that
c")ers these surfaces t" fracture.
When the temperature is high an$ the re&ati)e humi$ity is high% e)ap"rati"n "f ,ateris s&",. When re&ati)e humi$ity appr"aches 100 percent% c"n$ensati"n can "ccur "n
surfaces% &ea$ing t" pr"+&ems ,ith m"&$% c"rr"si"n% $ecay% an$ "ther m"isture-re&ate$
$eteri"rati"n.
ertain pr"$ucti"n an$ technica& pr"cesses an$ treatments in fact"ries% &a+"rat"ries%
h"spita&s% an$ "ther faci&ities reuire specific re&ati)e humi$ity &e)e&s t" +e maintaine$
using humi$ifiers% $ehumi$ifiersan$ ass"ciate$ c"ntr"& systems.
!ehicles
e&ati)e humi$ity% a&s" ca&&e$ %#midit$ ratiois c&assifie$ in three ,ays(
http://en.wikipedia.org/wiki/Relative_humidity#cite_note-4http://en.wikipedia.org/wiki/Relative_humidity#cite_note-hswref-5http://en.wikipedia.org/wiki/Relative_humidity#cite_note-hswref-5http://en.wikipedia.org/wiki/Relative_humidity#cite_note-hswref-5http://en.wikipedia.org/wiki/Relative_humidity#cite_note-hswref-5http://en.wikipedia.org/wiki/Heat_indexhttp://en.wikipedia.org/wiki/Humidexhttp://en.wikipedia.org/wiki/HVAChttp://en.wikipedia.org/wiki/Dehumidifierhttp://en.wikipedia.org/wiki/Relative_humidity#cite_note-4http://en.wikipedia.org/wiki/Relative_humidity#cite_note-hswref-5http://en.wikipedia.org/wiki/Relative_humidity#cite_note-hswref-5http://en.wikipedia.org/wiki/Relative_humidity#cite_note-hswref-5http://en.wikipedia.org/wiki/Heat_indexhttp://en.wikipedia.org/wiki/Humidexhttp://en.wikipedia.org/wiki/HVAChttp://en.wikipedia.org/wiki/Dehumidifier8/9/2019 Rel Humidity
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1. "n the +asis "f pressure partia& pressure "f )ap"r in air E pressure "f saturate$
air
2. "n the +asis "f mass mass "f )ap"ur present in air E mass "f $ry air
3. "n the +asis "f $ensity $ensity "f the )ap"ur present in air E $ensity "f $ry air
&& three in a specific )"&ume "f the m"ist air at a sing&e gi)en temperature. The same+asic princip&es as in +ui&$ings% a+")e% app&y. An a$$iti"n there may +e safety
c"nsi$erati"ns. !"r instance% high humi$ity insi$e a )ehic&ecan &ea$ t" pr"+&ems "f
c"n$ensati"n% such as misting "f ,in$shie&$san$ sh"rting"f e&ectrica& c"mp"nents.
An sea&e$ )ehic&es an$pressure )esse&ssuch as pressuri@e$ air&iners%su+mersi+&esan$
spacecraft% these c"nsi$erati"ns may +e critica& t" safety% an$ c"mp&e en)ir"nmenta&
c"ntr"& systemsinc&u$ing euipment t" maintainpressureare nee$e$. ir&iners
"perate ,ith &", interna& re&ati)e humi$ity% "ften un$er 10=% especia&&y "n &"ng
f&ights. The &", humi$ity is a c"nseuence "f $ra,ing in the )ery c"&$ air ,ith a &",
a+s"&ute humi$ity%,hich is f"un$ at air&iner cruising a&titu$es. Su+seuent ,arming
"f this air &",ers its re&ati)e humi$ity. This causes $isc"mf"rt such as s"re eyes% $rys#in% an$ $rying "ut "f muc"sa% +ut humi$ifiers are n"t emp&"ye$ t" raise it t"
c"mf"rta+&e mi$-range &e)e&s +ecause the )"&ume "f ,ater reuire$ t" +e carrie$ "n
+"ar$ can +e a significant ,eight pena&ty. s air&iners $escen$ fr"m c"&$er a&titu$es
int" ,armer air perhaps e)en f&ying thr"ugh c&"u$s a fe, th"usan$ feet a+")e the
gr"un$% the am+ient re&ati)e humi$ity can increase $ramatica&&y. S"me "f this m"ist
air is usua&&y $ra,n int" the pressuri@e$ aircraft ca+in an$ int" "ther n"n-pressuri@e$
areas "f the aircraft an$ c"n$enses "n the c"&$ aircraft s#in. Fiui$ ,ater can usua&&y
+e seen running a&"ng the aircraft s#in% +"th "n the insi$e an$ "utsi$e "f the ca+in.
ecause "f the $rastic changes in re&ati)e humi$ity insi$e the )ehic&e% c"mp"nents
must +e ua&ifie$ t" "perate in th"se en)ir"nments. The rec"mmen$e$ en)ir"nmenta&
ua&ificati"ns f"r m"st c"mmercia& aircraft c"mp"nents is &iste$ in T D-160.
"viation
"&$ humi$ air can pr")"#e the f"rmati"n "f ice% ,hich is a $anger t" aircraft as it
affects the ,ing pr"fi&e an$ increases ,eight. ar+urete$ engines ha)e a further
$anger "f ice f"rming insi$e thecar+uret"r. )iati"n ,eather rep"rts /TGs
theref"re inc&u$e an in$icati"n "f re&ati)e humi$ity% usua&&y in the f"rm "f the $e,
p"int.
An a$$iti"n% air ,ith higher humi$ity is &ess $ense% pr")i$ing &",er &ift an$ &",erpr"pe&&er "r tur+ine efficiency this is s"me,hat "ffset +y $ecrease$ $rag. *i&"ts must
ta#e humi$ity int" acc"unt ,hen ca&cu&ating ta#e"ff $istances +ecause high humi$ity
,i&& reuire &"nger run,ays an$ ,i&& $ecrease the c&im+ gra$ient.
Pressure dependence
The re&ati)e humi$ity "f an air-,ater system is $epen$ent n"t "n&y "n the temperature
+ut a&s" "n the a+s"&ute pressure "f the system "f interest. This $epen$ence is
$em"nstrate$ +y c"nsi$ering the air-,ater system sh",n +e&",. The system is c&"se$
i.e.% n" matter enters "r &ea)es the system.
http://en.wikipedia.org/wiki/Vehiclehttp://en.wikipedia.org/wiki/Windshieldhttp://en.wikipedia.org/wiki/Short_circuithttp://en.wikipedia.org/wiki/Pressure_vesselhttp://en.wikipedia.org/wiki/Pressure_vesselhttp://en.wikipedia.org/wiki/Airlinerhttp://en.wikipedia.org/wiki/Submersiblehttp://en.wikipedia.org/wiki/Submersiblehttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Environmental_control_systemhttp://en.wikipedia.org/wiki/Environmental_control_systemhttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Humidity#Absolute_humidityhttp://en.wikipedia.org/wiki/Humidity#Absolute_humidityhttp://en.wikipedia.org/wiki/Mucosahttp://en.wikipedia.org/wiki/Carburetorhttp://en.wikipedia.org/wiki/Carburetorhttp://en.wikipedia.org/wiki/METARhttp://en.wikipedia.org/wiki/METARhttp://en.wikipedia.org/wiki/Dew_pointhttp://en.wikipedia.org/wiki/Dew_pointhttp://en.wikipedia.org/wiki/Vehiclehttp://en.wikipedia.org/wiki/Windshieldhttp://en.wikipedia.org/wiki/Short_circuithttp://en.wikipedia.org/wiki/Pressure_vesselhttp://en.wikipedia.org/wiki/Airlinerhttp://en.wikipedia.org/wiki/Submersiblehttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Environmental_control_systemhttp://en.wikipedia.org/wiki/Environmental_control_systemhttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Humidity#Absolute_humidityhttp://en.wikipedia.org/wiki/Mucosahttp://en.wikipedia.org/wiki/Carburetorhttp://en.wikipedia.org/wiki/METARhttp://en.wikipedia.org/wiki/Dew_pointhttp://en.wikipedia.org/wiki/Dew_point8/9/2019 Rel Humidity
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Af the system at State is is"+arica&&y heate$ heating ,ith n" change in system
pressure then the re&ati)e humi$ity "f the system $ecreases +ecause the saturate$
)ap"r pressure "f ,ater increases ,ith increasing temperature. This is sh",n in State.
Af the system at State is is"therma&&y c"mpresse$ c"mpresse$ ,ith n" change in
system temperature then the re&ati)e humi$ity "f the system increases +ecause the
partia& pressure "f ,ater in the system increases ,ith increasing system pressure. This
is sh",n in State .
Theref"re a change in re&ati)e humi$ity can +e ep&aine$ +y a change in system
temperature% a change in the a+s"&ute pressure "f the system% "r change in +"th "f
these system pr"perties.
http://en.wikipedia.org/wiki/File:Changes_in_Relative_Humidity.png8/9/2019 Rel Humidity
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#nhancement factor
The enhancement fact"r is $efine$ as the rati" "f the saturate$ )ap"r pressure "f
,ater in m"ist air t" the saturate$ )ap"r pressure "f pure ,ater.
The enhancement fact"r is eua& t" unity f"r i$ea& gas systems. 7",e)er% in rea&
systems the interacti"n effects +et,een gas m"&ecu&es resu&t in a sma&& increase "f the
saturati"n )ap"r pressure "f ,ater in air re&ati)e t" saturate$ )ap"r pressure "f pure
,ater )ap"r. Theref"re% the enhancement fact"r is n"rma&&y s&ight&y greater than unity
f"r rea& systems.
The enhancement fact"r is c"mm"n&y use$ t" c"rrect the saturate$ )ap"r pressure "f,ater )ap"r ,hen empirica& re&ati"nships% such as th"se $e)e&"pe$ +y We&er%
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gas in this c"ntet is referre$ t" as saturate$ ,hen the )ap"r pressure "f ,ater in the
air is at the eui&i+rium )ap"r pressure f"r ,ater )ap"r at the temperature "f the gas
an$ ,ater )ap"r miture &iui$ ,ater an$ ice% at the appr"priate temperature ,i&&
fai& t" &"se mass thr"ugh e)ap"rati"n ,hen ep"se$ t" saturate$ air. At may a&s"
c"rresp"n$ t" the p"ssi+i&ity "f $e,"r f"gf"rming% ,ithin a space that &ac#s
temperature $ifferences am"ng its p"rti"ns% f"r instance in resp"nse t" $ecreasing
temperature. !"g c"nsists "f )ery minute $r"p&ets "f &iui$% primari&y he&$ a&"ft +y
is"static m"ti"n in "ther ,"r$s% the $r"p&ets fa&& thr"ugh the air at termina& )e&"city%
+ut as they are )ery sma&&% this termina& )e&"city is )ery sma&& t""% s" it $"esnGt &""# t"
us &i#e they are fa&&ing% an$ they seem t" +e he&$ a&"ft.
The statement that re&ati)e humi$ity 7= can ne)er +e a+")e 100=% ,hi&e a fair&y
g""$ gui$e% is n"t a+s"&ute&y accurate% ,ith"ut a m"re s"phisticate$ $efiniti"n "f
humi$ity than the "ne gi)en here. n argua+&e ecepti"n is the Wi&s"n c&"u$ cham+er%
,hich uses% in nuc&ear physics eperiments% an etreme&y +rief state "f
Hsupersaturati"nH t" acc"mp&ish its functi"n.
!"r a gi)en $e,p"intan$ its c"rresp"n$inga+s"&ute humi$ity% the re&ati)e humi$ity
,i&& change in)erse&y% a&+eit n"n&inear&y% ,ith the temperature. This is +ecause the
partia& pressure "f ,ater increases ,ith temperature I the "perati)e princip&e +ehin$
e)erything fr"m hair $ryerst" $ehumi$ifiers.
http://en.wikipedia.org/wiki/Dewhttp://en.wikipedia.org/wiki/Dewhttp://en.wikipedia.org/wiki/Foghttp://en.wikipedia.org/wiki/Foghttp://en.wikipedia.org/wiki/Wilson_cloud_chamberhttp://en.wikipedia.org/wiki/Supersaturationhttp://en.wikipedia.org/wiki/Dewpointhttp://en.wikipedia.org/wiki/Dewpointhttp://en.wikipedia.org/wiki/Absolute_humidityhttp://en.wikipedia.org/wiki/Absolute_humidityhttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Hair_dryerhttp://en.wikipedia.org/wiki/Hair_dryerhttp://en.wikipedia.org/wiki/Dehumidifierhttp://en.wikipedia.org/wiki/Dehumidifierhttp://en.wikipedia.org/wiki/File:Relative_Humidity.pnghttp://en.wikipedia.org/wiki/Dewhttp://en.wikipedia.org/wiki/Foghttp://en.wikipedia.org/wiki/Wilson_cloud_chamberhttp://en.wikipedia.org/wiki/Supersaturationhttp://en.wikipedia.org/wiki/Dewpointhttp://en.wikipedia.org/wiki/Absolute_humidityhttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Hair_dryerhttp://en.wikipedia.org/wiki/Dehumidifier8/9/2019 Rel Humidity
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*hysica& uantities
http://en.wikipedia.org/wiki/Category:Physical_quantitieshttp://en.wikipedia.org/wiki/Category:Physical_quantities