diagram psychrometric

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  • a

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

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

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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,o1.0133 x Id -/s,o

    kg HrO/kg an0.622pn-n

    ib H.O/tb air

    aH (0.00283 + 0.0O456 )/'Xrc + 273) f3 mixrure/kg air (0.0252 + 0.0405 Xlro + 460) ft3 mixture/lb aircs l0O5 + 1884 ),'J for mixrure/(kg art . .C 0.24 + 0.45Y'Btu for mirture/Qb an) . "Fto 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

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    100 030166 790275 580461 500

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    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

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    Ffture 7.6 Solutions to Illustrations 1.6 and 1.7.

    (a) By vertical interpolation berween the adjacent curves of coDstant percnt humidity,tile sample has a percentage humidity :26.17o' Alternatively, tle saturadon humidity at 55'Crs 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 saturatedair 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

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