Chuong 2- Tinh Chat Vat Ly

Bi ging

CNG NGH KH

Chng 2:

TNH CHT VT L V NGUYN LNG LC HC CA KH THIN NHIN

GVGD: ThS. Hong Trng QuangGVTG: ThS. H Quc Vit

NI DUNG

Tnh cht vt l ca kh thin nhinGII THIUKH L TNG V KH THCT TRNG V KHI LNG RINGTNH CHT GI TI HNH S LCH KHH S TH TCH THNH HH S NN NG NHIT NHTNHIT T CHY CA KHENTROPYENTANPI

Nguyn l ng lc hc ca kh thin nhin

2Trng i hc Bch khoa Tp. HCM

GII THIU

Tnh cht ca kh thin nhin bao gm: t trng,khi lng ring, p sut v nhit gi ti hn, nht, h s lch kh, h s nn ng nhit.S am hiu nhng thng s ny l cc k quantrng thit k v phn tch h thng khai thcv x l.Khi thnh phn ca kh c bit th nhng tnhcht ca kh c th c xc nh thng qua cctng quan. y trnh by cc tng quan c pht trint nhng th nghim khc nhau.


KH L TNG KH THC

nh lut kh l tng: P.V = n.R.T

nh lut kh thc: p.Va = z.n.R.T

Vi: P - p sut tuyt i (psia).V - th tch (ft3).

n - s mole (lb-mole).

R - hng s = 10,73 psia.ft3/lb.mole.R.T - nhit tuyt i (R).z - H s lch kh.


KH L TNG KH THC

Mole: Lng vt cht (s nguyn t hoc phn t) c khilng bng trng lng nguyn t hoc phn t ca vtcht .

Khng kh: M = 28,97 lbm/lb-mol = 28,97 kg/kmol Ethane: M = 30,07 lbm/lb-mol = 30,07 kg/kmol Oxygen: M = 32 lbm/lb-mol = 32 kg/kmol


KH L TNG KH THC

Th tch kh tiu chun: Th tch m 1 lb-mol chon ch nhng iu kin chun v p sut (14,7 psia = 1 atm = 760mmHg) v nhit (60F = 15,5 C = 520 R)

(SCF- Standard Cubic Feet, ft3)

Mt lng kh rng c th c biu din theo:

ft3 ( mt nhit v p sut nht nh)S mole,S pound hay s phn t.

SCF437971452073101

PTRnVtc ,

,

.,.'..


KH L TNG KH THC

V d 1.1: Tnh lng kh ethane trong bn cha theo s mole, pound,s phn t v SCF. Cho bit V = 1000 ft3 p sut p = 100 psia v nhit T = 100 F.Gii:

Gi s nh lut kh l tng c tha mn: PV = nRT S mole: Khi lng: S pound: S phn t

Ch : H thng BES, trng lng (lb) = khi lng (lbm = lb.s2/32,2 ft) g(= 32,2 ft/s2).

Th tch kh ethane iu kin chun:

moles-lb641656073101000100

TRPVn ,

.,

.

'

lbm450007306416Mnm ,,,. lb450007306416MnG ,,,.

2626 10545107332n .,).,.(

SCF6316SCF,.nVtc

6379


KHI LNG RING & T TRNG

1. Khi lng ring

2. T trng:

( cng p sut v nhit )

(khng ph thuc vo p sut vnhit )

V d 1.2: T trng ca mt cht kh l g = 0,75 th khi lng mole can l: M = 28,97g=28,970.75=21,7 lbm/lb-mole.

T'RpM

V

MT'R

PV

VM.n

tchThelngKhoi

ph thuc vo p sut v nhit

airg

g

9728M

TR9728pTR

pMg

,

'

,.

'


KHI LNG RING CA KH TRONG VA

S mole kh cha trong V = 1 ft3 ca va:

Khi lng mol ca 1 mol kh: M = 28,97g

Khi lng ring ca kh trong va:

V d 1.7: Hy tnh khi lng ca kh trong va bit g =0,665, z = 0,91 p = 3250 psia v T = 213 F.

Gii:

TzRp

TzRpVn

''

TzRp9728nM gg

'

..,

cuft/lbm.)(..,.,.,

g 5394602137310910325066509728


TNH CHT GI TI HN

Nhit ti hn Tc l nhit m trn n, trng thi kh khngth chuyn thnh trng thi lng d c tng p sut.V d: nc 374 C, CO2 31,1 C

p sut ti hn pc l p sut cn phi t c cht khngng t thnh lng nhit ti hn.Tng t nh khi lng mole biu kin, nhng tnh cht tihn ca kh c th c xc nh da trn tnh cht ti hn catng thnh phn trong kh. Nhng tnh cht nh th gi l tnhcht gi ti hn.

p sut gi ti hn (ppc):

Nhit gi ti hn (ppc)pci v Tci l p sut v nhit ti hn ca thnh phn


TNH CHT GI TI HN

V d: Xc nh khi lng mol biu kin; p sut v nhit gi ti hn; t trng ca hn hp kh thin nhin sau:


Gii: lp bng tnh

TNH CHT GI TI HN


Nu ch bit t trng ca kh m khng bit ccthnh phn th p sut v nhit gi ti hn cth xc nh t th hoc cc tng quan datrn th.Mt tng quan n gin:

c s dng vi iu kin: H2S < 3%, N2 < 5% v tngthnh phn ngoi lai nh hn 7%

TNH CHT GI TI HN


i vi kh chua th thng kt hp phngphp th v tng quan.Phng php Wichert-Aziz (1972)

p sut hiu chnh

Nhit hiu chnh

Phng php Ahmed (1989)

TNH CHT GI TI HN


ng dng p sut v nhit gi ti hn tnhp sut gi gim (pseudoreduced pressure): pprNhit gi gim (pseudoreduced temperature): Tpr

Da trn hai thng s:

Tra th Standing & Katz nhng i lng cn tm

TNH CHT GI TI HN


H S LCH KH

H s lch kh:

z = 0,7 1,2 (Z = 1 i vi kh l tng)C 04 phng php tnh h s lch kh z

Phng php oc tnh t t trngPhn tch cc thnh phn ca khTnh t cc tng quan

gasideal

actual

VV

z

The university of technology in HCM city 16

PHNG PHP 1: O TH TCH MU KH

o th tch mu kh nhit v p sut cn tnh h slch kh ri o th tch mu kh nhit v p sutsao cho c h s lch kh 1.

V d 1.3: Mt mu kh c Va1 = 364,6 ft3 213 F v 3250psia, Va2 = 70860 ft3 82 F v 14,8 psia (z2 1). Tnh hs lch kh?Gii:

2a22

11a1

21

22a2111a11

VpT

TVp

zz

.n.R.Tz.Vp.n.R.Tz.Vp

910z9107086081482460

21346063643250

1z

11 ,,.,

,.

The university of technology in HCM city 17

PHNG PHP 2: C TNH Z T T TRNG g CA CHT KH

Phng php ca Sutton:

1. Tnh p sut v nhit gi ti hn theo (1) v (2)

2. Tnh p sut v nhit gi gim theo (3) v (4)

3. Tra z nh th ca Standing & Beggs (H.1.2).

p sut gi ti hn:

ppc = 756,8 - 131,0g - 3,6g2 (0,57 < g < 1,68) (1)Nhit gi ti hn:

Tpc = 169,2 + 349,5g - 74g2 (0,57 < g < 1,68) (2)p sut gi gim: ppr = p/ppc (3)

Nhit gi gim: Tpr = T/Tpc (4)

Dng th ca Standing & Katz (ppr, Tpr, z) z.18Trng i hc Bch khoa Tp. HCM

Ch :ng cong h s lch kh l

ng quan h (p, z)

Nhit ti hn l nhit mtrn n, trng thi kh khng th

chuyn thnh trng thi lng d c

tng p sut. V d : nc 374

C, CO2 31,1 C

p sut ti hn l p sut cn phit c cht kh ngng t

thnh lng nhit ti hn.

PHNG PHP 2: C TNH Z T T TRNG g CA CHT KH


V d 1.4: Cht kh trong va c g = 0,665, p = 3250 psia, T = 213 F.Tnh z?

Gii:

1. Da theo cng thc (1.14) v (1.15)

ppc = 668 psia, Tpc = 369 R

2. Cng thc (1.16) v (1.17)

ppr = 4,87 v Tpr = 1,82, tra th H.1.2 z = 0,918.

821369213160p874668

3250p prpr ,;,

PHNG PHP 2: C TNH Z T T TRNGg CA CHT KH


PHNG PHP 3: PHN TCH THNH PHN CA KH

z c tnh theo gi thit rng cc p sut v nhit gi ti hn i vi mi thnh phn kh th t lthun vi th tch ca thnh phn kh v vi psut v nhit ti hn ca n.

Dng th ca Standing & Katz (ppr, Tpr, z) z.


V d 1.5: Tnh z ca mt cht kh t cc thnh phn ca n 3250 psia v 213 F.Thnh phn

kh(1)

T lmole

(2)

Mo

(3)

p sutti hn pc

(4)

Nhit ti hn Tc

(5)

Mg(2) x (3)

(6)

ppc(2) x (4)

(7)

Tpc(2) x (5)

(8)

Methane CH4 0,8612 16,04 673 343 13,81 579,59 295,39Ethane C2H6 0,0591 30,07 708 550 1,78 41,84 32,51Propane C3H8 0,0358 44,09 617 666 1,58 22,09 23,84Butane iC4H10 0,0172 58,12 550 766 1,00 9,46 13,18Pentane nC5H12 0,0050 72,15 490 846 0,36 2,45 4,23CO2 0,0010 44,01 1070 548 0,44 1,07 1,07N2 0,0207 28,02 492 227 0,58 10,18 4,70Tng 1,0000 19,55 666,68 374,92

675097285519

g ,,

, ; 8754686663250ppr ,

,

; 80192374213460Tpr ,

,

T th Standing & Katz (ppr, Tpr, z) z = 0,91.

PHNG PHP 3: PHN TCH THNH PHN CA KH


PHNG PHP 4: XC NH T MI TNG QUAN

Vander Wals:Z3 (1 + B)Z2 + AZ AB = 0A = a*p/(R2*T2) , B = b*p/R/Ta = 27*R2*Tc2/64/Pc, b = R*Tc/8/Pc

Peng Robi:Z3 (1 - B)*Z2 + (A - 2B - 3B2)*Z (AB B2 - B3) = 0A = a*p/(R2*T2) , B = b*p/R/Ta = 0,45724*R2*T2c/(pc*d), b = 0,00778R*Tc/pcd0,5 = 1+m(1-Tr0,5), m = 0,37464 + 1,54226W2, Tt = T/Tc

The university of technology in HCM city 23Trng i hc Bch khoa Tp. HCM

Brill and Beggs (1974):



V d: Xcnh nhth s lch khca hn hpkh c t trng0.65, 10% N2,8%CO2 psut 10.000psia v nhit 180oF.Kt qu:



Hall v Yarborough (1973):

Y thng c gii bng phngphp lp.



V d: Xcnh h slch kh cakh thinnhin c ttrng 0.71 5000 psi v180 oF.



H S HNH THNH TH TCH KH

scscscsca,scsc

a

pTnRz

pTznR

VvaTP(matbetrenkhtchTheVT) vap( vatrongkhtchThe

'

'

)

pT

zz

Tp

VV

scscsc

scaa ,

pzT

TpBscscg

SCF/ftPzT

,Bg3028290

vi Va,sc = 1 SCF v zsc = 1

Khi psc = 14,7 psia v Tsc = 60 F

(1.18)

(1.19)

(1.20)


V d. Cht kh trong va p = 3250 psia v T = 213 F, cz = 0,91. Tnh h s th tch thnh h kh Bg?Gii:

Suy ra 1 SCF th tch kh iu kin chun trn b mt schim th tch Va = 0,00533 ft3 trong va 3250 psia v213 F.

1000 ft3 th tch kh trong va 3250psia v 213F stng ng vi th tch:

=188000SCF= 188MSCF iu kin chun.

SCFcuft0053303250460213910028290B g /,)(,,

0053301000,

H S HNH THNH TH TCH KH


pzTnRp

TznRV ''

p1

dpdz

z1

dpdV

Vi

p1

pTznR

dpdz

z1

pTznR

pTznR

dpdz

pTnR

dpdV

2

''''

dpdz

z1

p1C g

p1C0dp

dzltg ,

(T khng i)

i vi kh l tng th z = 1 nn

H S NN NG NHIT


g : pcprpcpr pppp

pp .

prtpcprpcprt

g ppddz

zi

pp1

dpdz

z1

p1C

)(.

prTpcpr

pcgpr dpdz

z1

p1pCC

prpr

Tdpdz

(1.23)

Cpr- ).

1-6g psi1050020001

p1C . (ppr, Tpr

Standing & Katz.

H S NN NG NHIT


H S NN NG NHIT


V d 1.9: Kh c g = 0,72, tnh Cg 2000 psia v 140 F trong trng hp: Kh ltng v kh thc

Gii:1- Kh l tng: psia66608713948756720637201318756p 2pc ,,,,),(,),(, 2- Kh thc: R4382438625121697207472053492169T 2pc ,,,,),(),(,,

5714382600T0336660

2000p prpr ,,

,,

,

; 0250dpdz

571Tpr pr,

,

T th Standing & Katz (H.1.2) z = 0,82 T th ny, tm c: 3610030503300250820

10331Cpr ,,,),(

,,

1610546 psi.pC

Cpc

prg ; ;,T

TTpc

pr 581424460212 214

6362680

,

ppppc

pr

H S NN NG NHIT


H S NHT

H s nht ng lc g: ph thuc vo nhit , p sutv cu to ca kh.n v: centipoise (cp) = 0.001 Pa.s = 0.01 g/ cm.s = 0.01poise = 6.72 10-4 lbm/ft-secH s nht ng hc g : nht ng hc t s dng trong cng ngh khNu nht ca cc thnh phn kh c bit th nhtca hn hp kh thin nhin c th xc nh:


XC NH H S NHT NG LC

1. Phng php th th ca Carr, Kobayashi v Burrows c

tnh g t p sut gi gim ppr v nhit gi gimTpr (H.1.4c).

H s nht ng lc 1 p sut 1 atm v nhit va ph thuc nhit va T v t trng kh g(H.1.4a).

Cc gin H.1.4b gip hiu chnh h s nht1 p sut 1 atm khi cht kh c cha N2, CO2v/hay H2S.


XC NH H S NHT NG LC


Hnh 1.4. Cc th Carr, Kobayashi & Burrows dng tnh h s nht nglc ca cht kh

XC NH H S NHT NG LC


V d: Dng cc th trn H.1.4 c tnh g. Bit p sut va =2680 psia, nhit va = 212 F, g = 0,9, Tpc = 424 R, ppc = 636psia, hm lng CO2 = 5%mol.

Gii: T H.1.4a, vi g = 0,9 v T = 212 F 1 = 0,0117 cp Hiu chnh i vi CO2: t H.1.4b i vi CO2 c hm lng 5% 1 = 0,0003 cp

1 = 1 + 1 = 0,012 cp; 611g

,

T H.1.4c, vi Tpr = 1,58 v ppr = 4,21

iSCF/STB/ps177012002500337567

dpdR so

,

g = 1,6 1 = 0,0192 cp T = 212 F v p = 2680 psia

XC NH H S NHT NG LC


2. Phng php tng quan (Carr, Kobayashi v Burrows) Tnh nht iu kin kh quyn 1:

trong :

XC NH H S NHT NG LC


Dempsey (1965) thit lp quan h sau:

XC NH H S NHT NG LC


trong :

XC NH H S NHT NG LC


Gi tr nht ng lc hc cui cng c xcnh:

V d: Xc nh nht ng lc hc cahn hp kh c t trng 0.65, 10% N2,8%CO2 p sut 10.000 psia v nhit 180oF.

XC NH H S NHT NG LC


Kt qu:

XC NH H S NHT NG LC


3/21/2014 44

NHIT T CHY CA KH

Nhit t chy ca kh l lng nhit c to ra khikh c t chy mt cch hon ton to thnh khCO2 v hi nc.Nhit t chy ca kh thng s dng h n v Anhtrn cu ft kh iu kin chun BUT/scf.Cng ngh du kh thng s dng bn c tnh thhin cc gi tr nhit t chy ca kh:

Nng sut ta nhit kh ton phnNng sut ta nhit thcNhit t chy kh tNhit t chy kh kh


45

NHIT T CHY CA KH

Khi s dng cc gi tr nhit t chy, cc t t v khmun m ch n iu kin ca trc khi t chy. Kh tc cha mt lng hi nc, khong 1,75%, kh kh khngcha hm lng hi nc.Nng sut nhit ton phn l lng nhit c to ra khi schy xy ra hon ton di gi tr p sut khng i theo ccsn phm chy c lm lnh ti cc iu kin chun vnc trong cc sn phm chy c ngng t to thnhtrng thi lng.Gi tr ny cng cn c gi l gi tr nhit t chy tngcng.Nng sut nhit thc c xc nh tng t nh nng sutton phn ngoi tr lng nc vn tn ti dng hi tiiu kin chun.


46

NHIT T CHY CA KH

S khc bit gia hiu sut nhit ton phn v nng sut nhitthc l nhit lng ha hi ca nc chy. Trong cc gi tr trnth gi tr c s dng nhiu trong cng ngh kh l gi tr nngsut nhit ton phn.Cc gi tr th hin trong ph lc l gi tr nhit t chy kh. Gi trnhit ca mt kh l tng c xc nh:

Trong mt trng hp khc, iu ny c tnh bng cch chia gitr thc cho h s lch kh ca kh cc iu kin chun:

j

cjidealc LyL

z

LL idealcrealc


47

NHIT T CHY CA KH

H s lch tm iu kin chun c tnh bng cch sdng h s lch kh z cho trong bng ph lc:

S thay i t kh l tng sang kh thc cc gi tr nngsut to nhit thng nh hn 0,5 % nn thng c bqua. Nng sut to nhit thc ca kh kh c chuyn sangnng sut ta nhit ca kh t cho bi phng trnh:

2

11

j

j zyz

dryccwet LL )0175,01( 47Trng i hc Bch khoa Tp. HCM

48

NHIT T CHY CA KH

Trong h s 0,0175 l phn mol ca hi nc trong khc tch ra iu kin chun. Nng sut ta nhit tonphn ca kh kh c th c chuyn qua nng sut tanhit ton phn ca kh t theo phng trnh sau:Trong 0,9 l gi tr nhit c gii phng trong sut qutrnh ngng t ca hi nc trong kh trc b xy ra qutrnh t chy.

- Ngoi ra cng c th s dng phng trnh sau tnhton gi tr nng sut ta nhit ca kh nhin liu t khi bithm lng nc. khi xt iu kin chun (600F, 14,7 psi):

9,0)0175,01( drycwetc LL


49

NHIT T CHY CA KH

Trong :L: nng sut ta nhit tng cng (Btu/scf kh l tng).Pstd : p sut nn tnh bng (scf).Pwvap: p sut hi nc ti nhit T.50,4 = (Hwvap)(Pstd)(MWw)/(R)(T).Ti 60F, Pwvap =0,25636 psia.MWw: khi lng phn t nc.

std

wvap

wvap

wvapstddrycwetc P

PP

PPLL 5,50

)(


ENTROPY

Entropy nhit ng lc (hay gi n gin l entropy)dS l mt n v o lng khi lng nng lng dQpht tn/hp th khi mt h vt l chuyn trng thi timt nhit tuyt i xc nh T (dS = dQ / T).nh lut th hai: c nhiu cch pht biu nh lutth hai ca nhit ng hc nh:

Nhit ch c th t truyn t vt nng hn sang vtlnh hn hocTrong bt k mt qu trnh t din bin no, ntropitng ca h v mi trng xung quanh phi tng


ENTROPY

xc nh entropy, cn s dng phng trnh trng thica Redlich-Kwong-Barxuk.


ENTROPY - BNG TRA H S

52

ENTROPY

Qu trnh tit lu qua van: H1 = H2Hn hp theo dng: m*H = mi * hiQu trnh gia nhit: H tngQua my nn, bm, Expander: S1 = S2Qua bnh tch: H = 0


ENTHALPY

Enthalpy: hm trng thi nhit ng ca h, thng c khiu l H, c nh ngha nh sau

i vi mt h nhit ng c th trao i nhit v cngvi mi trng xung quanh H = U + pV; trong U lni nng, p - p sut v V - th tch. H c th nguynca nng lng. Nhit lng m h trao i trong qutrnh ng p bng bin thin ca H.Tng nng lng ca mt h tr ng nng v thnng.Enthalpy i khi cn c gi l hm nhit lng.

Ngi ta lp sn cc th tra enthapy ca hn hphydrocarbon da vo khi lng phn t, p sut v nhit


ENTHALPY

55

TH ENTHALPY CA HC THEO MW, T, P = 1400 ~ 2100 KPa

56


57


58

Gin n qua van hoc van iu tit.

Bm, my nn, qut.

Truyn nhit.

NG DNG CA NHIT NG HC


BI TP

Bi 1: Tnh t trng ca hn hp kh t nhin sau (cc khthnh phn xc nh theo t l phn trm s mol).

Bi 2: Xc nh khi lng ring ca hn hp kh trn 1,525 psia v 750F.

p s: 0.705

p s: 7.62 lbm/cuft (0.122/cm3)


HoangTranNotetinh theo bang tra %*khoi luong/28,97

BI TP

Bi 3: Xc nh h s lch kh z cho lu cht va nhit 307oF v p sut 6,098 psia. Cho t l C7+ c:

v gi tr thc nghim z = 0.998 p s: 0.962119gM)API(. o408250


KHI LNG RING,TH TCH RING CA KH HYDROCACBON

T phng trnh PV = ZnRT Xt n kmoles kh c th tch Vs nng nMW kgKhi lng ring (kg/m3) = n

Do =

Th tch ring v(m3/kg) = 1/ =

Lu V(m3) l th tch mole P,T khc vi th tch ringv(m3/kg)

VMW

ZRTMWP

MWPZRT.


NHT CA HN HP KH

Trong :m : nht ca hn hp kh.i : nht ca tng thnh phn.yi : Phn moles thnh phn i.MWi : Khi lng phn t thnh phn i.

5.05.0

ii

iiim MWy

MWy


NHT CA HYDROCACBON LNG

m : nht ca hn hp lng centipoice (cp).i : nht ca tng thnh phn i tra th hnh 2.26:xi : Phn moles thnh phn i.

31 iIm x


P SUT HI BO HA

i lng ny ph thuc vo nhit tnh ton theo phng trnh Antoine nhsau

Vi:

Trong :P: p sut hi bo ho ca hn hp lng (psia) nhit T (R)Tc: Nhit ti hn (R)Tb: Nhit si trung bnh (R)


H S KHNG NG B

W

Trong :Pvp l p sut hi bo ho TR = 0,7i vi hn hp W=yiwi

V d tnh wi ca cc cu t:

Bng cch tra Pvp TR=

Sau tnh W

1log

c

vp

PP

7,0cT

T

1log

c

vp

PP

66

ENTHANPY

Trong khi thc hin cc bi ton v nhit ng hc tathng gp biu thc u+pv v sau biu thc ny c tn lentanpy H. Trong nhiu trng hp lng bin i Hmang ngha nng lng.Trong cc phng php gii tch xc nh enthanpy ngita s dng phng php da trn c s phng trnhtrng thi ca Redlich-Kwong-Barxuk p dng cho hhydrocacbon C1 n C10 c th c cha N2, CO2, H2S.enthanpy c tnh theo biu thc


ENTHALPY

kgkJ

MWZmT

TTCByRZRTHy

Hc

oiiioii

/,1ln.121

6

6

5

5

4

4

3

3

2

21

100100100100100100187,4 TATATATATATAHoi


ENTROPY

Entropy l loi thng s trng thi m lng bin i can trong mt qu trnh thun nghch no c gi tr bngdS= Q/T. Trong cc phng php gii tch xc nhentropy ngi ta s dng phng php da trn c sphng trnh trng thi ca Redlich-Kwong-Barxuk pdng cho h hydrocacbo C1 n C10 c th c cha N2,CO2, H2S. entropy c tnh theo cc phng trnh

23,2ln1ln..

MWP

mZRZm

rRSS

ohh

hh

Sohh = yiSoi - R(yi * lnyi)


NHIT DUNG RING

Nhit dung ring ca mt cht l lng nhit cn thit nng mt n v khi lng tng thm 1oC.Nhit dung ring ca hn hp hydrocacbon kh c xcnh t phng trnh:

Cp: Nhit dung mole ca hn hp kh hydrocacbon P,TCopi: Nhit dung mole ca cu t i trng thi l tng T tmbng cch tra th hnh 2.46.

Cp: i lng hiu chnh cho p sut P tm bng cch tra th hnh 2.47.

Trng i hc Bch khoa Tp. HCM 70

Cp = Copi.yi + Cp

NHIT LNG

Tnh nhit lng theo s thay i entropi:Entropy l loi thng s trng thi m lng bin i ca

bin i ca n trong mt qu trnh thun nghch no c gi trbng: dS = Q/Ti vi 1kg mi cht cng thc vit li nh sau: ds = q/TTa cng c quan h: dS = G*ds

Trong : ds lng bin i entropy trong qu trnh thun nghch vcng b vi khi lng 1kg.


%63,4%1001,2

5,29,2

5,55

92 YYYY

NHIT LNG

Tnh nhit lng theo s thay i nhit :Khi c s trao i nhit lng gia hn hp kh v mi trngnhit ca hn hp kh thng thay i. Nhit lng trao i nyc th tnh qua cng thc:

Q = Ci*mi*ti


73

Phng trnh nhit ng hc kh thin nhinH s lch tm

Nm 1936, Pitzer a ra h s lch tm w gii thch cc lchda vo s khc nhau theo cc iu kin c th.Pitzer nhn thy rng i vi argon khi gp dng cht lng ngin c xc nh bi l Ps/Pc = 0,1 khi TR = 0,7.H s lch tm c xc nh bi phng trnh:

V th h s lch tm o c c s khac nhau gia cht lng trngthi hp cht phc tp v cht lng n gin.Vic nghin cu cc phng trnh trng thi c k thm thng s w,thng s ny ph thuc vo thnh phn c lin quan, lm tng ngk chnh xc ca cc phng trnh.

1log7,0

RTc

s

PP

Phng trnh nhit ng hc kh thin nhin


74

Phng trnh nhit ng hc kh thin nhinPhng trnh Soave v Peng-Robinson

Trong : a(T) v b trong phng trnh ny c xc nh theo

phng trnh:

a(T): c xc nh nh trong phng trnh Soave. Nthay i theo nhit c gim xung da theo phngtrnh Soave nhng hm lim quan n thng s m vi hs lch tm th khc:

)(45724,022

Rc

c TPTR

a

c

c

PRTb

m

0778,0

26992,054226,137464,0 2



75

Phng trnh nhit ng hc kh thin nhinPhng trnh trng thi phi khi

Cc phng trnh dng ny phc tp hn cc phng trnhc a ra trc y. N bao gm mt lng ln hn ccthng s, c thit lp hiu chnh mc chnh xc cacng vic tnh ton. Thng thng c nhiu hn ba thng sv i hi qu trnh tnh ton thc tp hn, lu hn.Phng trnh BWR (Benedict v cc tc gi khc) c xutpht t phng trnh virial, thng c s dng th hincc c tnh ca pha kh iu kin p sut trung bnh.Phng trnh virial c thit lp theo s pht trin ca h slch kh bng dy s Taylor trong 1/V:

....1 2 VC

VB

RTPVZ



76

Phng trnh nhit ng hc kh thin nhinPhng trnh trng thi phi khi

N thng c b qua s hng ng pha trc s hng1/V2. H s B v C c gi tng ng l h s virial th haiv th ba.Phng trnh BWR c hai s hng hiu chnh c a ra tthc nghim. Phng trnh ny c vit bng cch biu thgi tr nghch otheo th tch khi:

Trong c 8 h s ca phng trnh trn ph thuc vo loithnh phn cn quan tm.

)exp()1()()( 2223

6322 MM

MMMM

o

ooM Tc

abRTTC

ARTBTRP



77

Phng php Lee KeslerNguyn tc chung ca phng php Lee Kesler bao gm cctnh ton gi tr Fp ca c tnh nhit ng, t gi tr F(o) v F(r) cac tnh ny i vi cht lu n cht c v i vi cc cht lumu nh cho bi phng trnh:

Phng trnh trng thi cho mt thn phn vi h s lch tmc tnh ton t phng trnh trn, tip s tnh ton h s lchkh:

Cc s hng Z(o), Z(r) c xc nh nh l mt hm s theo VR vTR bng cch chn phng trnh trng thi.

)( orr

o

p FFFF

orr

o ZZZZ



78


p dng cho hn hpCc phng trnh c cp trn c th c m rngp dng cho cc hn hp, a ra cc h s ca cc phngtrnh ny p dng cho hn hp c th lin quan ti cc cht khsch .i vi cc phng trnh pht trin trn c s bin i tphng trnh Van Der Waals nh cc phng trnh Redlich Kwrong, Soave v phng trnh Peng Robinson, cc nguyntc kt hp thng c p dng khi thnh phn c xcnh di dng phn mole


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