a

-

;t

tl

,8000-l

6000

-5 00r1

40{)0

1000

2 000

I 000s800

(r00

:00.1( )( ,

I

I tr'-r

0.{).1

0.lr i

c.0 :

LJ.0l

280

260

220

200

180

i60

140

100

80

,'iO

40

20

0

1.4

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!_sL'

:>:o>';

EU,]t

ll \

i).9

0. l5

0 tt

0. l.l

'J. l:

11. I

0. l0

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008

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80 tl 90 100

\.'zi-l {-1

*t

(il)

Flgure .5 (a) Psychrometric chart for air-water vapor, I std atrn abs, in Sl units

'a

t:d

)a;E

6IE

!il

!-

r30

[0

IIO

I00

9')

lr0

70

60

50

40

30

:0

1.. 30 40 50 60 ?0 80 90 100 I t0 Il0 130 140 r50 l('0 170 180 I90 200 210 120 130 140 250 160

Tcmperature oF

. (b)

Flgure ?5 (6) Psychromctric chart for air-water vapor, I std atm abs, in English engineering units.

c

€;c

tcil

fa.

0.I4

0Ll

0l:

0il

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009

o ori

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00:

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23 uass-rn,tNsFER opERATToNS

Table 7.1 Psvchrometric relations for t}e syslem air (B)-water (A)at I std atm pressure

SI rrnit5 6[9, m, N, "C) English cnpnering mia(Btu, fr3, lh. "F. tVinr)

M^ 18.02 kg/kmol, H2O 18.02 lbllb mol. HrO

MB 28-97 kg/kmo| air 28.97 lb/lb mol, air

Y'O.622pH.o

l.0t33xtd-Fu,o kg HrO/kg air0.622FH{

ta"ra -; lb H:o/lb air

v' O.522ps,o

1.0133 x Id -/s,okg HrO/kg an

0.622pn-nib H.O/tb air

aH (0.00283 + 0.0O456 )/'Xrc + 273) f3 mixrure/kg air (0.0252 + 0.0405 Xlro + 460) ft3 mixture/lb air

cs l0O5 + 1884 ),'J for mixrure/(kg art . .C 0.24 + 0.45Y'Btu for mirture/Qb an) . "F

to 0'c 32"F

Io 2 502 3U J /kg 1075.8 Btullb

H (1005 + 1884y')tc + Z 502 3C,y'J for nlxture,/l6g air,referred to gaseous air andsatuated liquid H.O, 0"C

(0.24 + O.45y'Xr6 - j:) + 1075.8 r,Btu for mixrurc/lb ai,referred to ga.eous r,ir and l-quid H2O,32"F

H r,'c Hi, I/kg t, "F H:.0

l020

4050

60

9 4'79

29 3@57 570

100 030166 790

275 580461 500

32

406080

100

t20l.lrC

4.0747._s45

It 7RN

36.0206{.090

1 12.00

i 98.40

hc/ k'y 95O J /kg . K 0.227 Btu/lb . "F

necessar]'. The series of curves marked '.adiabatic-saturation cufv.es,, on thechart s'ere plotted accorcing.lo gq. (1 .2t),-n be considered 1:r:r. For nostpurposes these can be considerea- ui curves of constanr .rrJuipy for thevapor-gas mi_xture per unit mass of gas.

Ilhxrredoa 7'6 A:r air @)-water-vapor (A) sample haq a cin.-r,.lb teapcr=:ure 55.c aad aaabsorure humri\iity 0030 kg water/kga.yu; "-'ria atm pressure. Tabu.rar i,s characteristics.

SoLt-no:{ T-r. point of coordilates /c:55.C, y,:0.030 is locared on ihe psychrometricchan fig' ?'f a\. 2 56[s641ic version oiwhich rt rn"*r in Fig. ?.6. This is pc"int D ir Fig. 7.6.t _-a

:'.i.'

",..n,

t{U}{lDIFlC.\llON OI'ITRAIIONS Ltf,

tali?

Fi:i:i.1oI

I

I

II

I

io. _ ,1,,9E

" a.::'

{,)

)P 92

f ntbolp

6l

55Igmpgr6llrg

Ffture 7.6 Solutions to Illustrations 1.6 and 1.7.

(a) By vertical interpolation berween the adjacent curves of coDstant perc€nt humidity,

tile sample has a percentage humidity :26.17o' Alternatively, tle saturadon humidity at 55'C

rs y; : 0.1 15, and the percenl.age humidity at , is therefore (0.03010'l i5)1ffi : 26'lV"'

(D) The rnolal absolute humidity : Y : Y'(MB/ M ^)

= 0.030(28.97 /18.C2) :0.tx82 k-mol water/kmol dry ar.

(c) The partial pressure of water vapor in the sample, by E4. fi'E)' is

F^: #i: qo4q'?l.l#I8+'O = 4660 Nr/m:

(d) The vapor Pressure of water at 55'C: l18 mmHg or ll8(li3 l) - 15 730 N/m2 *.c^. The relative humidity : F^(|ffi)/p^: 466q100)/15 730:79'6%-

(e) Dew poi_nt. From poiot D proceed at constant humidity to the saturation c'rve at

point E, at which the dew point temperature is 31.5"C.

O I{umid voluae.,\t 55"C, the specific vclume of dry air is a'% n3/kg' The h:'nidvolume of saturated air - l.l0 m3,/kc dry air. Interpolatingfct 76'I% humidity,

or : 0.93 + (1.10 - 0.93X0.261) : 0'974 rarilkg dj) air

(g) Hunid heaq Eq. (7.10):

Cs - Cs + Y'C^- 1005 + 0.030(1884): 106l.5J(forwet"n)/(rgdrvan)'K

(l) Enrhalpy. Ar 55"C, the en'.halpy of dry air is 56000 l/kSu:- air; that for saturated

air is 352 000 N'm/kg dry at. Interpolating for 26.19':humidity gives

H' : 56 000 + (352 0@ - 56 0mX0.261) : ll3 300 J.i"kg drv air

.{lternatively, Eq. (7.13) or Table 7.1:

H' = CsUo - ,J + r'\: (1005 + tg8/Y')tc + 2 502 3{0r'

: [1005 + 18&4(0'030)]5 5 + 7 5OZ lux0'030) = 133'a U/kg drv ar