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Bi tonMt h thng c dc dung dch ng hai ni xui chiu,thit b loi ngtun hon trung tm,nng sut thit b 10 tn/ha theo dung dch u.Nng u ca dung dch l 13% khi lng,nng cui l 56% khi lng.Apssut tuyt i ca hi t ni u l 2.5at v thp ngng t l 0.2at.Cho

bit cc s liu sau:

Dung dch NDR C(kj/kg.)

HSDN (w/m.)

KLR

(kg/m3) nht

(N.s/m2)Ban u 3.82 - - -

Ni 1 3.84 0.482 1070 3.7.10 -4

Ni 2 3.58 0.363 1241 4.10-3

Hy xc nh din tch truyn nhit ca mi ni.Bi lm

I. S ca qu trnh cng ngh c c:

Ghi ch:1:b cha dung dch u2:bn cao v3:thit b gia nhit4:ni c c 15:ni c dc 2

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6:b cha dung dch sau7:thit b ngng t nc ngng baromet8:b cha nc ngng

Nguyn tc hoc ng ca h thng: dung dch t b cha cbm ln bn cao v,t bn cao v chy qua thit b gia nhit n nhit sing vi p sut lm vic ca ni 1.Dung dch dc a vo ni 1.Do schnh lch ap sut gia ni 1vaf ni 2 nn dung dch tip tc chy vo ni 2ri c bm ht ra ri c chuyn vo b cha sn phm.Hi th trongni th nht lm hi t cho ni th 2 tn dng nhit.Hi th ca ni th2 c a vo thit b ngng t baromet va c ht chn khng ra ngoi.

Nguyn l lm vic ca ni c c:phn doi ca thit b la bn tgm cc ng truyn nhit va ng tun hon trung tm.Dung dch s i trongng cn hi t s i trong khong khng gian pha ngoi ng.Nguyn tchot ng ca ng tun hon trung tm l:do ng tun hon c ng knh

ln hn rt nhiu so vi ng truyn nhit nn h s truyn nhit nh,dungdch s si t hn so vi trong ng truyn nhit.Khi si dung dch s c

ddds 5.0= do s to p lc y dung dch t trong ng tun hon sangng truyn nhit.Kt qu la to mt dng chy tun hon trong thit b.Phn

pha trn la bung tch hi ra khi dung dch,trong bung cn c b phntch bt tch nhng git lng ra khi hi th.

II. Tnh cn bng vt liu1 Cn bng vt liu:

Gc=xc

xG dd.=

56

%13.1000.10=2321,4 (kg/h)

Vi xd,xc :nng u ,nng cui ca dung dch ln lt l 13% v 56%(% khi lng).2 Lng hi th bc ln ton b h thng:

Ap dung cong thc : )1(C

DD

x

xGW = kg/h

Trong o:W : Lng hi th cua toan he thong

kg/h

GD : Lng dung dch ban au kg/hxD,xC : Nong o au,cuoi cua dung dch %

khoi lngThay so vao ta co:

6.7678)60

131.()1( 10

4===

C

DD

x

xGW kg/h.

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3. Gia thiet phan phoi hi th trong cac noi :Chon t so gia hi th boc len t noi I va II

la : 1=II

I

W

W

Khi o ta co he phng trnh: 1=

II

I

W

W

WI + WII = WGiai he tren co ket qua :

WI = 3839.3 kg/hWII =3839.3 kg/h

4. Xac nh nong o dung dch tng noi :- Nong o cuoi cua dung dch ra khoi noi I :

xC= %1.213.38391000010000.13.

== ID

DD

WG

xG

%- Nong o cuoi cua dung dch ra khoi noi II :

xC= %563.3839.21000013.10000.

=

= IIID

DD

WWG

xG

III. .CAN BANG NHIET LNG :1. Xac nh ap suat va nhiet o moi noi:Hieu so ap suat cua ca he thong co ac:

Theo au bai ap suat ngng tu la: Png = 0,2 atChon ap suat cua hi ot vao noi I la : P1= 2,5 atKhi o hieu so ap suat cua ca he thong coac la :

Pt =P1 Png = 2,5-0,2 = 2,3 atChon t so phan phoi ap suat gia cac noi la :

5.12

1=

P

P

Ket hp vi phng trnh : P1 + P2 = Pt = 2,3 at

Suy ra : P1 = 1,38 at P2 = 0.92 at

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Da vao cac d kien tren va tra so tay quatrnh thiet b tap I ta co bang sau ay :

Loai

Noi I Noi II Thap ngng tu

Apsuat(at)

Nhieto(0C)

Apsuat(at)

Nhieto(0C)

Apsuat(at)

Nhieto(0C)

Hiot

P1= 2,5T1=126,

25P1=1,12

T2=102,16

Png=0,2tng=59,

7Hith

P1=1.16

t1=103,1

6

P2=0,211

t2 =60,7

2. Xac nh nhiet o ton that :a. Ton that nhiet do nong o tang cao ( ):Ap dung cong thc cua Tiaxenko:

= o . f ay :

o : Ton that nhiet o ap suat thng.f : he so hieu chnh v thiet b co ac lam

viec ap suat khac vi ap suat thng.

f ii

r

t 2)'273(

2.16

+

=

ti : nhiet o hi th cua noi th i

ri : an nhiet hoa hi cua hi nhiet o ti .T cac d kien tren ta lap c bang sau:

ailng

Noi I

xC

(%k.l)

o

(0

C )

t

(

0

C )

r.103

(j/kg )

i

(0

C )Noi I 21,1 0,4

103,16

2252,29

0,407

Noi II 56 2,6 60,72355,

561,99

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T ay ta co tong ton that nhiet do nong otang cao :

= I + II = 0,407+1,99= 2,397 0Cb. Ton that nhiet do ap suat thuy tnh ( ):

Goi chenh lech ap suat t be mat dung dch engia ong la P (N/m2), ta co:

P =2

1 S.g.Hop N/m2

Trong o: s : khoi lng rieng cua dung dch khi soi ,

kg/m3

s =0.5 dd dd : Khoi lng rieng cua dung dch ,kg/m3

Hop: Chieu cao thch hp tnh theo knh quan satmc chat long ,m

Hop = [0.26+0.0014( dd- dm)].HoT P ta se tnh c ap suat trung bnh cua dungdch tng noi thong qua cong thc:

Ptbi= Pi+ Pi( i ): noi th i

Tra so tay ta co c bang sau:

x C ,% t ,0

C dd ,

kg/m3 dm

,kg/m3

Noi I 21,1 103,17 1070 965Noi II 56 60,7 1241 983

Coi dd trong moi noi thay oi khong ang ke trongkhoang nhiet o t be mat en o sau trung bnh cua chat long.

Chon chieu cao ong truyen nhiet la Ho=1.5 m.Noi I:

Hop1 = [0.26+0.0014( dd- dm)].Ho=[0.26+0.0014(1070-965)]*1.5=0,61 ,mAp suat trung bnh:

Ptb1= P1+ P1=1,16+0,5.0,5.1070.10-4.0,61=1,176atTra so tay tai Ptb1=1,176 (at) ta co t1=103,59 0C.

Suy ra : 1=t1 t1= 103,59 103,16=0,428 0C

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Noi II:Hop2 = [0.26+0.0014( dd- dm)].Ho=[0.26+0.0014(1241-

983)]*1.5=0,93 ,mAp suat trung bnh:Ptb2= P2+ P2=0,211+0,5.0,5.1241.10-4.0,93=0,24 at

Tra so tay tai Ptb2 = 0,24 (at) ta co t2= 63,3 0C.Suy ra : 2=t2 t2= 63,3 60,7=2,6 0CVat ton that nhiet cua hai noi la:

= 1+ 2 =0,428+2,6 = 3,028 0Cc. Ton that nhiet do tr lc thuy lc tren ng

ong ( )

Chap nhan ton that nhiet o tren cac oan ongdan hi th t noi nay sang noi no va t noicuoi en thiet b ngng tu la 10C. Do o:

1=1.50C 2 =1.0 0C

d. Ton that chung trong toan he thong co ac: = + + =2,397+3,028+2.5=7,925 0C

3. Hieu so hu ch va nhiet o soi cua tngnoi:

Hieu so nhiet o hu ch moi noi:Noi I: ti1=TI (T2+ 1) =126,25 (102,16+0,407+0,428+1.5)=22,183 0CNoi II: ti2=T2 (tng + 2) =102,16(59,7+1,99+2,6+1)=36,87 0C

Nhiet o soi thc te cua dung dch moi noi:Noi I : ti1=TI tS1 suy ra tS1=T1 - ti1=126,25

22,183 =104,07 0CNoi II : ti2=T2 tS2 suy ra tS2=T2 - ti2=102,16 36,87

= 66,29 0C4. Can bang nhiet lng:

a Lap phng trnh can bang nhiet lng (CBNL):

Noi I:D.i+GD.CD.tD=W1.i1+(GD W1)C1.t1+D.Cng1. 1+Qxq1

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Noi II:W1.i1+(GD W1)C1.t1=W2.i2+(GD

W)C2.t2+W1.Cng2. 2+Qxq2Trong o:

D: lng hi ot dung co he thong ,kg/hi,i1,i2: ham nhiet cua hi ot , hi th noi Iva noi II ,j/kg

tD, t1, t2: nhiet o soi ban au, rakhoi noi Iva noi II cua dung dch , 0C

CD, C1, C2:nhiet dung rieng ban au, ra khoinoi I va noi II cua dung dch , j/kg.o

1, 2:nhiet o nc ngng tu cua noi I vanoi II ,0C

Cng1, Cng2: nhiet dung rieng cua nc ngng noi I va noi II ,j/kg.o.

Qxq1,Qxq2 :nhiet mat mat ra moi trng xungquanh , J

GD : lng dung dch luc ban au ,kg/hChon hi ot , hi th la hi bao hoa, nc

ngng la long soi cung nhiet o, khi o ta co:i- Cng1. 1=r ( 1) va i1- Cng2. 2=r( 2)

au vao au ra noi I au ra noi II

Dung dch NaOH :+ tD=103,6630C+ CD =3820

j/kg.o+ GD=10000 kg/hHi ot:+ 1=126,25 0C+ i= 2720000 j/kg+ Cng1=4256,8

j/kg.o

Dung dch NaOH :+ t1=104,07 0C+ C1=3480

j/kg.oHi th :+ 2 =103,16 0C+ i1 =2684026 j/kg+Cng2 = 4232

j/kg.o

+ W1=3839,3kg/h

Dung dch NaOH:+ t2=66,29 0C+ C2= 2580

j/kg.o+ G2=2321,4 kg/hHi th :+ t2=60,7 0C+ i2=2608444 j/kg+ W2=3839,3 kg/h

Cho : Qxp1=0.05.D.(i Cng1. 1) =0.05.D.r( 1).Qxp1=0.05.W.(i1 Cng2. 2) =0.05.W1.r( 2).

Vi :r )( 1 =2189500 (j/kg )r( 2)=2355560 (j/kg )

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Vay lng hi th boc len noi I la :

=+

+=

1121

112221

.)(.95.0

...).(.

tCir

tCGtCWGiWW DD

= =+

+

07,104*348026084442189500*95.0

07,104*3480*1000029,66*2580*4,23212608444*6,7678

3884,28kg/h

Lng hi th boc len noi II la:W2=W-W1=7678,6 3884,28 =3794,32 kg/h

Lng hi ot tieu ot chung la:

D= =

+

).(95.0

...).(.

111

11111

ng

DDDD

Ci

tCGtCWGiW

=

)25,126*8,42562684026(*95.0

668,103*3820*1000007,104*3840*)28,388410000(2684026*28,3884

+

=4368,91 kg/hc. Kiem tra lai gia thiet phan bo hi th cac

noi:

C%(I) = %5%17,1%1003,3839

3,383928,3884

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tT1 tT2 K=i

tb

t

q

W/m2.o

q1 t2q tm2

Nhiet tai rieng trung bnh:

- Noi I : qtb1=2

21 qq +

Trong o :+ q1 : nhiet tai rieng pha hi ot cap cho thanhthiet b. Ta co cong thc tnh q1:

q1= 1. t1 (1)He so cap nhiet cua hi nc bao hoa ngng tutren be mat ong thang ng c tnh theo cong

thc cua Nusselt: 1=2,04.A.(

1. tH

r

).025 w/m2. (*)

Chn nhit khi qua ng thit b l tT1 =125,9Ta c t1=T1- tT1 =126,25-125,9=0,35 0 CNhit ca lp mng l:

tm1=0,5.( T1 +tT1)=126,075 0 Ctra cc thng s trong bng ta c cc gi tr sauA=189,82 h s ph thuc vo nhit

r( 1)=2189500 (j/kg), H=1,5m =2,04*189,82 *(2189500/(1,5*0,35))0,25=20587,31 w/m2 Thay vo cng thc (1) ta c

q1=20587,31*0,35=7205,56 w/m2

H s cp nhit khi cht lng sin .2 =

Vi :h s hiu chnh vi dung dch va cht lng bt k

n

dd

(= )0.565.[(

n

dd

)2.(

n

dd

C

C).(

n

dd

)]0,435

7,013,0..14,3qpn

=

w/m

2

P :p sut lm vic ,p=1,16 att :hiu s nhit gia thnh v cht lng si, 0 CTra cc thng s trn trong s tay ta c bng gi tr sau: vi tdd=104,070C

(w/m.) (kg/m3) (N.S/m2) C (j/kg.) Nc 0,684 945,18 0,24.10-3 4243,7

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Dung dch 0,482 1070 3,7.10-4 3480Suy ra = 0,726

=n 1605,7 w/m2

Chn tn thc nhit gia b mt truyn nhit vi dung dch

bn trong l t =6 0CVy q2 = tn .. = 0,726*1605,7*6= 6994,5 w/m

2

Kim tra li gi thuyt:

Tha mn iu kin sais

Nhit ti ring trung bnh ca ni 1 l:

qtb1= 53,71002

5,699456,7206

2

21=

+=

+qqw/m2

i vi ni 2:

2

21

2

qqq

tb

+=

Vi q1 nhit ti ring ca hi t cp cho thic b q1= 1. t1

He so cap nhiet cua hi nc bao hoa ngng tu

tren be mat ong thang ng c tnh theo congthc cua Nusselt:

1=2,04.A.(1. tH

r

).025 w/m2.

Chn nhit khi qua ng thit b l tT1 =101,75Ta c t1=T1- tT1 =102,16-101,75=0,4 0 CNhit ca lp mng l:

tm1=0,5.( T1 +tT1)=101,96 0 Ctra cc thng s trong bng ta c cc gi tr sau

A=179,79 h s ph thuc vo nhit r( 2)=2254100 (j/kg), H=1,5m

Suy ra 2 =16147,35 w/m2

Vy nhit ti ring cp ca hi th cp cho thit b lq1=16147,35*0,4=6458,94 w/m2

Nhit ti ring ca thit b cp cho dung dch si ca ni 2 l:

%5%93,2%100*56,7206

5,699456,7206%100.

1

21

1

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q2 = tn ..

Vi cch tnh tng t nh ni mt v cc gi tr c tra trong s taytdd=66,29 0C

(w/m.) (kg/m3) (N.S/m2) C (j/kg.) Nc 0,665 979,87 4,74*10-3 4190,15Dung dch 0,363 1241 4*10-3 2580

p=0,211 at

n

dd

(= )0.565.[(

n

dd

)2.(

n

dd

C

C).(

n

dd

)]0,435=0,686

7,013,0..14,3 qp

n= =1191,79 w/m

2

Chn =t 7,5 0C

q2 = tn .. =0,686*1191,79*7,5=6131,76 w/m2

kim tra li gi thuyt ban u:

Tha mn iu kinsai s

2

21

2qqq

tb

+= =6358,25 w/m2

a. He so truyen nhiet moi noi:- Noi I :

K1=183,22

7100,531 = iI

tb

t

q=320 W/m2.o

- Noi II :

K2= 87,366131,762 =

iII

tb

tq =166,3 W/m2.o

3. Hieu so nhiet o hu ch thc cua moi noi:- Cong thc chung:

=

i

i

i

m

mim

K

Q

t

K

Qt .' 0C

%5%46,3%100*97,6 458

76,6 13194,6 458%100.

1

21

2

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trong o :Qi:nhit do hi th cung cp cho ni th i

Vi Qi= 3600.1 irD

ri l n nhit ngng t ca hi th ni th iTra vo s tay ta c cc gi tr saur1=2189500 j/kgr2 =2255173 j/kg

Suy ra Q1 = =3600

2189500*91,4368265714679,79 w

Q2 = =3600

28,3884*225517324335282,24 w

ti = tiI+ tiII = 22,183+36,87=59,053 0C.

i

i

K

Q= 32.90246.53486.367

71.334

178890

18.512

=+=+

- Tnh cho noi I:

46.1132.902

12.28*86.367.' ==

=

i

i

i

I

IiI

K

Q

t

K

Qt

0C

- Tnh cho noi II:

66.16

32.902

12.28*46.534.' ==

=

i

i

i

II

IIiII

KQ

t

K

Qt

0

C

4. Kiem tra lai hieu so nhiet o hu ch :- Noi I :

%5%8.4%10004.12

46.1104.12%100*

'

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F2 =22

2

'. itK

Q

= 08.32

66.16*71.334

178890= m2

Chon : F1=F2 = 40 m2.