Bao Cao Th Truyen Nhiet_decrypted

B CNG THNG

TRNG H CNG NGHIP TP H CH MINH

TRUNG TM MY V THIT B

BO CO THC HNH

CC QU TRNH V THIT B TRUYN NHIT

GVHD: L Nht Thng

SVTH: FCC

MSSV: 1234567

T: 2

Lp HP: Sng ch nht

Thnh ph H Ch Minh, thng 11 nm 2010

LI NHN XT

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

LI M U

Truyn nhit l lnh vc ng vai tr quan trng, khng th thiu trong hu ht

cc qu trnh ha hc, thc phm, sinh hc, mi trng...

Chng ta hiu c qu trnh truyn nhit din ra nh th no th cha ,

chng ta cn phi bit cch tnh ton x l s liu o c v cao hn na l thit

k ch to mt h thng thit b truyn nhit ph bin trong cng nghip na. Khi

chng ta s s c tit kim c nng lng v thi gian rt nhiu trong vic

gim lng nhit hao ht, cch b tr dng chy sao cho t hiu sut cao nht,

thit b gn nh, d lp t v bo tr.

Vic hc mn Thc hnh Cc qu trnh v thit b truyn nhit rt b ch i

vi chng em hn l nhng tit hc l thuyt. Qua s ch bo tn tnh ca thy

Thng, bn em bit cch vn hnh mt thit b truyn nhit, hiu c nguyn

l hot ng v qua mi ngi t x l s liu. Mc d trong quyn bo co

thc hnh ny cc kt lun ca em c th sai (v rt t qu trnh thc nghim) do

s liu sai, nhng em tin vo cch tnh ton ca mnh bi v em nghin cu kh

k lng.

Mc d rt cn thn nhng cng khng trnh khi nhng sai lm, thiu st nn

em mong thy ng gp kin nhn xt bi bo co thc hnh c hon thin

hn.

MC LC Ta Trang Bi 1: Thit b truyn nhit loi ng lng ng ng .............................................. 1 1.1. Mc ch th nghim...................................................................................... 1 1.2. S liu thc hnh ........................................................................................... 1 1.3. X l s liu .................................................................................................. 2 1.4. Kt qu tnh ton ........................................................................................... 7 1.5. th ........................................................................................................... 10 1.6. Bn lun ....................................................................................................... 14 Bi 2: Thit b truyn nhit loi ng xon ............................................................ 17 2.1. Mc ch th nghim..................................................................................... 17 2.2. S liu thc hnh .......................................................................................... 17 2.3. X l s liu ................................................................................................. 18 2.4. Kt qu tnh ton .......................................................................................... 23 2.5. th ........................................................................................................... 26 2.6. Bn lun ....................................................................................................... 30 Bi 3: C c gin on dung dch CuSO4 ............................................................ 34 3.1. Mc ch th nghim..................................................................................... 34 3.2. S liu thc hnh .......................................................................................... 34 3.3. X l s liu ................................................................................................. 35 3.4. Kt qu tnh ton .......................................................................................... 36 3.5. Bn lun ....................................................................................................... 37 Bi 4: Thit b truyn nhit loi ng chm ............................................................ 39 4.1. Mc ch th nghim..................................................................................... 39 4.2. S liu thc hnh .......................................................................................... 39 4.3. X l s liu ................................................................................................. 40 4.4. Kt qu tnh ton .......................................................................................... 45 4.5. th ........................................................................................................... 48 5.6. Bn lun ....................................................................................................... 52 Nhn xt v nh gi v 3 bi truyn nhit ........................................................... 55 Danh mc sch tham kho v tra cu ................................................................... 57

Bo co thc hnh Truyn Nhit GVHD: L Nht Thng

1

Bi 1: Thc hnh truyn nhit ng lng ng ng Ngy thc hnh: 17-10-2010

Sinh Vin: FCC

M s: 1234567

Lp thc hnh: Sng Ch nht

T thc hnh: 2

im: Li ph ca thy:

1. Mc ch th nghim:

Kho st qu trnh truyn nhit khi un nng hoc lm ngui gin tip gia hai dng lu

cht qua mt b mt ngn cch (bi thc hnh ny ch yu kho st qu trnh lm ngui).

Tnh ton hiu sut ton phn da trn cn bng nhit lng nhng lu lng dng khc

nhau.

Kho st nh hng ca chiu chuyn ng ln qu trnh truyn nhit trong hai trng hp:

ngc chiu v xui chiu.

Xc nh h s truyn nhit thc nghim KTN ca thit b, t so snh vi kt qu tnh ton

l thuyt KLT.

2. S liu thc hnh:

2.1. Trng hp xui chiu:

Th

nghim VN (l/ph) VL (l/ph)

T1 (oC)

Ni un T2 (

oC) Nng ra

T3 (oC)

Nng vo T4 (

oC) Lnh ra

T5 (oC)

Lnh vo 1 2 71 65 70 35 30

2 4 71 64 70 33 30

3 6 71 64 71 32 30

4

2

8 71 63 71 32 30

5 4 2 72 68 71 36 30


2

6 4 72 68 71 33 30

7 6 72 67 71 33 30

8 8 71 67 71 33 30

9 2 71 69 71 37 30

10 4 71 68 71 35 30

11 6 71 68 71 34 30

12

6

8 71 67 71 33 30

13 2 71 69 71 38 30

14 4 71 69 71 35 30

15 6 71 68 71 34 30

16

8

8 71 68 71 33 30

2.2. Trng hp ngc chiu:

Th nghim

VN (l/ph) VL (l/ph) T1 (

oC) Ni un

T2 (oC)

Nng ra T3 (

oC) Nng vo

T4 (oC)

Lnh vo T5 (

oC) Lnh ra

1 2 71 66 70 30 35

2 4 71 65 70 30 34

3 6 71 65 71 30 33

4

2

8 71 65 71 30 32

5 2 72 69 71 30 36

6 4 72 68 71 30 35

7 6 71 67 71 30 33

8

4

8 71 67 71 30 33

9 2 72 69 71 30 37

10 4 71 69 71 30 33

11 6 71 68 71 30 34

12

6

8 71 68 71 30 33

13 2 71 69 71 30 38

14 4 71 69 71 30 36

15 6 71 69 71 30 34

16

8

8 71 68 71 30 34

3. X l s liu:

3.1. Tnh ton hiu sut nhit :

-Hiu s nhit ca cc dng v hiu sut nhit trong cc qu trnh truyn nhit:

.100%N N

V RN N L

V V

T T

T T

.100%L L

R VN N L

V V

T T

T T


3

2

N Lhi

Ta c: _ _N nong vao nong raT T T

_ _L lanh ra lanh vaoT T T

3.2. Xc nh hiu sut ca qu trnh truyn nhit:

-i lu lng th tch sang lu lng khi lng:

310

. .60

N N nuocG V

310

. .60

L L nuocG V

Vi nuoc ph thuc vo nhit theo cng thc thc nghim:

3 20,000015324364. 0,00584994855. 0,016286058705. 1000,04105055224nuoc T T T

(Tnh NG th 2 3

2

T TT

; tnh LG th

4 5

2

T TT

)

-Tnh nhit lng dng nng, dng lnh, nhit tn tht:

3. . 4,19.10 . .N N N N N NQ C G T G T (Cp= 4,19.103 J/kg 710C)

3. . 4,18.10 . .L L L L L LQ C G T G T (Cp= 4,18.103 J/kg 710C)

f N LQ Q Q

-Tnh hiu sut ca qu trnh truyn nhit:

.100%L

N

Q

Q

3.3. Tnh ton h s truyn nhit:

3.3.1. H s truyn nhit thc nghim:

-Trng hp xui chiu:

ax _ _m nong vao lanh vaot t t

min _ _nong ra lanh rat t t


4

-Trng hp ngc chiu:

Ta xt: 1 _ _nong vao lanh rat t t

2 _ _nong ra lanh vaot t t

Ci no ln hn th l axmt . Ci no b hn th l mint .

-Tnh ax min

logax

min

ln( )

m

m

t tt

t

t

-Tnh din tch truyn nhit:

. .tdF d L .

Vi 2

i otd

d dd

, L=0.5 (m)

-Theo cng thc: log. .Q K F t

log.

NTN

QK

F t

3.3.2. H s truyn nhit l thuyt:

c tnh theo cng thc:

1 2

1

1 1LTK

(Chuyn tng ng qua tng phng do 2

1

2r

r )

C 02

id d

(m), _ 93dong thau (W/m.K). Ch vic tnh 1 v 2 .

* Tnh h s cp nhit 1 (dng nng):

-Chun s Reynolds: w.

Re id

Trong : w l vn tc ca dng nng: 2

w

.4

N

i

G

d


5

v l nht ca dng nng, c th tra bng hoc tnh theo cng thc thc

nghim sau:

( 6) 5 4 3

2

(10 )*(( 0.00000000064*( )) (0.000000182875*( )) (0.000021590001*( ))

(0.001417871822*( )) (0.060504453881*( )) 1.790265284068)

v T T T

T T

(m2/s)

-Chun s Prandtl: _

. .Pr N nuoc

dong nong

C

_dong nong c th c tnh bng cch tra bng hay tnh theo pp ni suy (trong chc nng thng

k ca my tnh Casio)

T ly theo nhit trung bnh u ra v u vo.

-Chun s Grashoff (da vo gi tr ca Re ri sau mi i tnh):

3

2

.. .

g lGr t

v

Vi g=9.81 (m/s2), l l ng knh tng ng y l=di , l h s gin n th tch c

tra trong bng tra cu, t l chnh lch nhit _tuong nong vaot t t .

-H s hiu chnh k : ph thuc vo gi tr Reynolds v i

L

d (tra trong bng 1.1 trang 33-

sch QT & TB truyn nhit ca TT my v thit b-nm 2009).

-Tnh chun s Nusselt:

Nu dng nng chy xoy: 0,8 0,430,021. .Re .PrkNu ( n gin ta cho Pr

1PrT

)

Nu dng nng chy qu : 0,8 0,430,008. .Re .PrkNu

Nu dng nng chy dng: 0,33 0,43 0,10,158. .Re .Pr .kNu Gr


6

* Tnh h s cp nhit 2 (dng lnh): nh dng nng ch thay i cc tham s c trng

ca dng lnh.


ReLtdd

Trong : w l vn tc ca dng lnh: 2

w

.( )4

N

Ltd

G

d

Vi

2 20

0

.( )44. 4.

.( )

iL uottd

uot i

D DFd

C D D

-Chun s Prandtl: _

. .Pr L nuoc

dong lanh

C

_dong lanh c th c tnh bng cch tra bng hay tnh theo pp ni suy (trong chc nng thng

k ca my tnh Casio)



3

2

.. .

g lGr t

v

Vi g=9.81 (m/s2), l l ng knh tng ng y Ltdl d , l h s gin n th tch c

tra trong bng tra cu, t l chnh lch nhit _tuong lanh vaot t t .

-H s hiu chnh k : ph thuc vo gi tr Reynolds v Ltd

L





7

Nu dng lnh chy xoy: 0,8 0,430,021. .Re .PrkNu ( n gin ta cho Pr

1PrT

)

Nu dng lnh chy qu : 0,8 0,430,008. .Re .PrkNu

Nu dng lnh chy dng: 0,33 0,43 0,10,158. .Re .Pr .kNu Gr

4. Kt qu tnh ton:


Bng kt qu tnh ton hiu sut nhit

Th nghim

NT

(0C) NT

(0C) N

(%) L

(%) hi

(%) 1 5 5 12.5 12.5 12.5 2 6 3 15.0 7.5 11.3 3 7 2 17.1 4.9 11.0 4 8 2 19.5 4.9 12.2 5 3 6 7.3 14.6 11.0 6 3 3 7.3 7.3 7.3 7 4 3 9.8 7.3 8.5 8 4 3 9.8 7.3 8.5 9 2 7 4.9 17.1 11.0 10 3 5 7.3 12.2 9.8 11 3 4 7.3 9.8 8.5 12 4 3 9.8 7.3 8.5 13 2 8 4.9 19.5 12.2 14 2 5 4.9 12.2 8.5 15 3 4 7.3 9.8 8.5 16 3 3 7.3 7.3 7.3

Bng kt qu tnh ton hiu sut truyn nhit Th

nghim GN

(kg/s) GL

(kg/s) QN (W)

QL (W)

Qf (W)

(%) 1 0.03264 0.033164 683.8 693.1 -9.3 101.4 2 0.032649 0.066349 820.8 832.0 -11.2 101.4 3 0.03264 0.099538 957.3 832.1 125.2 86.9 4 0.032649 0.132717 1094.4 1109.5 -15.1 101.4 5 0.065204 0.033159 819.6 831.6 -12.0 101.5 6 0.065204 0.066349 819.6 832.0 -12.4 101.5 7 0.065223 0.099523 1093.1 1248.0 -154.9 114.2 8 0.065223 0.132697 1093.1 1664.0 -570.9 152.2 9 0.097777 0.033153 819.4 970.1 -150.7 118.4 10 0.097806 0.066328 1229.4 1386.3 -156.8 112.8 11 0.097806 0.099507 1229.4 1663.8 -434.3 135.3 12 0.097835 0.132697 1639.7 1664.0 -24.3 101.5 13 0.13037 0.033148 1092.5 1108.5 -16.0 101.5 14 0.13037 0.066328 1092.5 1386.3 -293.8 126.9 15 0.130408 0.099507 1639.2 1663.8 -24.5 101.5 16 0.130408 0.132697 1639.2 1664.0 -24.8 101.5


8

Bng kt qu tnh ton h s truyn nhit: Th

nghim QN (W)

tmax (0C)

tmin (oC)

tlog (oC)

KLT (W/m

2.K)

KTN (W/m

2.K)

1 683.8 40 30 34.8 359.7 659.1 2 820.8 40 31 35.3 469.1 778.9 3 957.3 41 32 36.3 481.4 883.3 4 1094.4 41 31 35.8 486.9 1025.2 5 819.6 41 32 36.3 770.8 756.2 6 819.6 41 35 37.9 1544.3 724.2 7 1093.1 41 34 37.4 1674.0 979.6 8 1093.1 41 34 37.4 1754.4 979.6 9 819.4 41 32 36.3 849.1 756.0 10 1229.4 41 33 36.9 1886.9 1117.7 11 1229.4 41 34 37.4 2084.8 1101.7 12 1639.7 41 34 37.4 2206.0 1469.4 13 1092.5 41 31 35.8 896.7 1023.4 14 1092.5 41 34 37.4 2130.8 979.0 15 1639.2 41 34 37.4 2383.8 1468.9 16 1639.2 41 35 37.9 2547.5 1448.4



Th nghim

NT

(0C) NT

(0C) N

(%) L

(%) hi

(%) 1 4 5 10.0 12.5 11.3 2 5 4 12.5 10.0 11.3 3 6 3 14.6 7.3 11.0 4 6 2 14.6 4.9 9.8 5 2 6 4.9 14.6 9.8 6 3 5 7.3 12.2 9.8 7 4 3 9.8 7.3 8.5 8 4 3 9.8 7.3 8.5 9 2 7 4.9 17.1 11.0 10 2 3 4.9 7.3 6.1 11 3 4 7.3 9.8 8.5 12 3 3 7.3 7.3 7.3 13 2 8 4.9 19.5 12.2 14 2 6 4.9 14.6 9.8 15 2 4 4.9 9.8 7.3 16 3 4 7.3 9.8 8.5


9


nghim GN

(kg/s) GL

(kg/s) QN (W)

QL (W)

Qf (W)

(%) 1 0.032631 0.033164 546.9 693.1 -146.2 126.7 2 0.032640 0.066338 683.8 1109.2 -425.4 162.2 3 0.032631 0.099523 820.3 1248.0 -427.7 152.1 4 0.032631 0.132717 820.3 1109.5 -289.2 135.3 5 0.065185 0.033159 546.2 831.6 -285.4 152.2 6 0.065204 0.066328 819.6 1386.3 -566.6 169.1 7 0.065223 0.099523 1093.1 1248.0 -154.9 114.2 8 0.065223 0.132697 1093.1 1664.0 -570.9 152.2 9 0.097777 0.033153 819.4 970.1 -150.7 118.4 10 0.097777 0.066349 819.4 832.0 -12.6 101.5 11 0.097806 0.099507 1229.4 1663.8 -434.3 135.3 12 0.097806 0.132697 1229.4 1664.0 -434.6 135.3 13 0.130370 0.033148 1092.5 1108.5 -16.0 101.5 14 0.130370 0.066317 1092.5 1663.2 -570.7 152.2 15 0.130370 0.099507 1092.5 1663.8 -571.3 152.3 16 0.130408 0.132677 1639.2 2218.4 -579.1 135.3


nghim QN (W)

tmax (0C)

tmin (oC)

tlog (oC)

KLT (W/m

2.K)

KTN (W/m

2.K)

1 546.9 36 35 35.5 363.0 516.2 2 683.8 35 36 35.5 474.9 645.4 3 820.3 35 38 36.5 487.4 753.5 4 820.3 35 39 37.0 494.0 743.6 5 546.2 39 35 37.0 784.3 495.2 6 819.6 38 36 37.0 1600.2 742.4 7 1093.1 37 38 37.5 1736.5 976.8 8 1093.1 37 38 37.5 1823.2 976.8 9 819.4 39 34 36.4 864.9 753.3 10 819.4 39 38 38.5 1964.8 713.1 11 1229.4 38 37 37.5 2182.7 1098.6 12 1229.4 38 38 38.0 2319.1 1084.0 13 1092.5 39 33 35.9 914.3 1019.2 14 1092.5 39 35 37.0 2235.9 990.3 15 1092.5 39 37 38.0 2515.7 963.5 16 1639.2 38 37 37.5 2697.5 1464.7


10

5. th: 5.1. Trng hp xui chiu:

H s truyn nhit thc nghim

Quan h gia Lu lng-h s truyn nhit

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1400.0

1600.0

VN=2 l/ph VN=4 l/ph VN=6 l/ph VN=8 l/ph

Lu lng dng nng

KT

N

(W/m

2.K

)

VL=2 (l/ph)

VL=4 (l/ph)

VL=6 (l/ph)

VL=8 (l/ph)

H s truyn nhit l thuyt

Quan h gia Lu lng-h s truyn nhit

0.0

500.0

1000.0

1500.0

2000.0

2500.0

3000.0


Lu lng dng nng

KL

T

(W/m

2.K

)

VL=2 (l/ph)

VL=4 (l/ph)

VL=6 (l/ph)

VL=8 (l/ph)


11

th biu din KTN v KLT

Trng hp xui chiu

0.0

500.0

1000.0

1500.0

2000.0

2500.0

3000.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

K

(W/m

2.K

)

KTN

KLT



Quan h gia Lu lng-h s truyn nhit (ngc chiu)

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1400.0

1600.0


Lu lng dng nng

KT

N

(W/m

2.K

)

VL=2 (l/ph)

VL=4 (l/ph)

VL=6 (l/ph)

VL=8 (l/ph)


12


Quan h gia Lu lng-h s truyn nhit (ngc chiu)

0.0

500.0

1000.0

1500.0

2000.0

2500.0

3000.0


Lu lng dng nng

KL

T

(W/m

2.K

)

VL=2 (l/ph)

VL=4 (l/ph)

VL=6 (l/ph)

VL=8 (l/ph)


Trng hp ngc chiu

0.0

500.0

1000.0

1500.0

2000.0

2500.0

3000.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

K

(W/m

2.K

)

KTN

KLT


13

5.3. Quan h gia chiu chuyn ng v h s truyn nhit:


Quan h chiu chuyn ng-h s truyn nhit

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1400.0

1600.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

KT

N (

W/m

2.K

)

Xui chiu

Ngc chiu


Quan h chiu chuyn ng-h s truyn nhit

0.0

500.0

1000.0

1500.0

2000.0

2500.0

3000.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

KL

T (

W/m

2.K

)

Xui chiu

Ngc chiu


14

6. Bn lun:

V u d bo sai nn ta s khng ni n cc yu t ph thuc nhit c sai s ln nh

N , L v hi m i xt n cc yu t quan trng, nhng tnh ton cui cng trong bi ny.

Ta s i nh gi s nh hng cc yu t qua h s truyn nhit. H s truyn nhit c

trng cho lng nhit truyn t lu th nng ti lu th ngui qua 1m2 b mt tng phng

trong mt n v thi gian khi hiu s chnh lch nhit gia hai lu th l mt . H s

truyn nhit cng ln th lng nhit m lu th lnh nhn c t lu th nng cng tng.

Ngha l qu trnh truyn nhit cng t hiu qu (hiu sut cao v L

N

Q

Q )

6.1. nh hng ca lu lng dng n qu trnh truyn nhit:

-Trong cng mt lu lng nng bng nhau (VN=const), khi tng lu lng dng lnh

(VL=2, 4, 6, 8 l/ph) th h s truyn nhit s tng dn.

-Nhn thy nu lu lng dng lnh bng nhau (VL=const) v qua cc mc tng lu lng

dng nng (VN=2, 4, 6, 8 l/ph) th h s truyn nhit cng s tng ln.

6.2. nh gi s nh hng ca chiu chuyn ng cc dng n qu trnh truyn nhit:

-i vi h s truyn nhit tnh t thc nghim ta nhn thy KTN khi xui chiu th ln hn

cht xu so vi trng hp ngc chiu.

-i vi h s truyn nhit tnh theo l thuyt th ta thy KLT khi ngc chiu nhnh hn so

vi khi xui chiu nhng khng ng (hai ng trn th gn nh trng nhau)

Qua ta c th kt lun, trong trng hp truyn nhit ng lng ng ng loi thng th

chiu chuyn ng khng c lin quan nhiu n h s truyn nhit (rt t thc nghim).

6.3. So snh h s truyn nhit thc nghim vi h s truyn nhit l thuyt:

Trong c hai trng hp ngc chiu v xui chiu, ta u thy mc lu lng VN= 2 l/ph

KTN ln hn KLT cn mc VN=4, 6, 8 l/ph tr i th KLT ln hn nhiu so vi KTN.

-S d c s khc nhau nh vy l v trong qu trnh tnh ton KTN ch c tnh n QN v

logt m 2 yu t ny li ph thuc vo nhit do cc u d bo v.


15

log.

NTN

QK

F t

Vic u d bo sai chng ta c th hiu chnh c. Nhng Qf m m th theo em ngh l

do qu trnh truyn nhit t dng nng sang dng lnh, nhit lng b mt mt hao tn ra

bn ngoi. Lng nhit tn tht ny khng th o chnh xc. Chnh n lm cho vic tnh

ton khng n nh. Bi v khi tng lu lng dng lnh hay lu lng dng nng cng ln,

nhit truyn t dng nng sang dng ngui cng cao, th lng nhit tn tht ny cng tng ln

nhanh chng. C th thy r trn th ti cc mc lu lng VL=4, 6, 8 l/ph h s truyn nhit

khng c chnh lch nhiu so vi VL=2 l/ph; trong khi ng h s truyn nhit l thuyt c

s tng vt ca VL=4, 6, 8 l/ph so vi VL=2 l/ph.

-Trong qu trnh tnh ton KLT th ta s i tnh cc chun s ng dng nh Nusselt,

Reynolds, Prandlt, Grashoff tnh h s cp nhit ca dng nng 1 v ca dng lnh 2 . Ta

nhn thy 1 ca dng nng c gi tr xp x bng nhau cng mt mc lu lng VN v tng

ln khi VN tng. i vi 2 ca dng lnh th tng dn khi VL tng hoc VN tng, iu ny

c gii thch l do VL tng dn n vn tc dng lnh tng dn n Re tng dn n Nusselt

tng t l thun vi 2 . Hn na mc VL= 2 l/ph, dng lnh ch yu l chy qu

Re 2300 10000 , nn c 2 thp nht khi p dng cng tnh chun s Nusselt.

Ta thy rng h s cp nhit 2 ca dng lnh ln hn hn 1 dng nng. C ngha l dng

lnh nhn c lng nhit t ngun nng trong mt n v thi gian l rt ln v kh nng

cp nhit ca dng nng l cha tng xng vi dng lnh.

Bng kt qu tnh h s cp nhit

Th nghim 1 dng nng

(W/m2.K)

2 dng lnh

(W/m2.K)

1 525.7 1198.3 2 524.5 5436.6 3 525.7 7492.0 4 524.5 9430.8 5 2379.6 1202.6 6 2379.6 5436.6 7 2374.2 7519.8 8 2374.2 9465.8

Trng hp

cng chiu

9 3298.9 1206.9


16

10 3291.4 5476.5 11 3291.4 7547.4 12 3283.9 9465.8 13 4113.0 1211.3 14 4113.0 5476.5 15 4103.7 7547.4 16 4103.7 9465.8 1 526.9 1198.3 2 525.7 5456.6 3 526.9 7519.8 4 526.9 9430.8 5 2385.0 1202.6 6 2379.6 5476.5 7 2374.2 7519.8 8 2374.2 9465.8 9 3298.9 1206.9 10 3298.9 5436.6 11 3291.4 7547.4 12 3291.4 9465.8 13 4113.0 1211.3 14 4113.0 5496.4 15 4113.0 7547.4

Trng hp

ngc chiu

16 4103.7 9500.5

6.4. Mt vi nhn xt v thit b:

-Thit b truyn nhit loi ng ng s dng trong bi th nghim ny c th s dng c

cho 4 bi: ng lng ng ng, ng lng ng Inox, ng xon, ng chm. Kho st qu trnh

truyn nhit trong hai trng hp chy xui chiu v chy ngc chiu.

-Thit b d tho lp d dng khi thay b phn, nhng mt vi ch cn khim khuyt nh

khng c b phn cch nhit gia ni un vi mi trng bn ngoi, khng c b phn cch

nhit vi gia ng ng vi mi trng bn ngoi gim ti thiu nhit tn tht , b iu

khin s dng l loi ON-OFF nn tr thi gian ln, u d nhit hay o sai, v tr t

u d khng chnh xc (s dng u d xn cha m ci chnh l ta phi t ng v tr

trong dng chy). ci thin nhng iu ny th kh thc hin, cn phi c thm thi gian v

cng sc.


17

Bi 2: Thc hnh truyn nhit ng xon Ngy thc hnh: 24-10-2010

Sinh Vin: FCC

M s: 1234567


T thc hnh: 2

im: Li ph ca thy:

1. Mc ch th nghim:




nhau.




l thuyt KLT.

2. S liu thc hnh:


Th


T1 (oC)

Ni un T2 (

oC) Nng ra

T3 (oC)

Nng vo T4 (

oC) Lnh ra

T5 (oC)

Lnh vo 1 2 70 55 70 48 31

2 3 69 54 69 47 31

3 4 69 51 69 41 31

4

2

5 69 50 68 39 31

5 3 2 68 57 68 47 30


18

6 3 67 55 67 42 30

7 4 66 55 66 42 29

8 5 66 53 66 40 29

9 2 66 57 65 47 29

10 3 65 56 65 46 29

11 4 65 54 65 42 29

12

4

5 65 53 65 39 29

13 2 64 57 64 46 29

14 3 64 56 64 46 29

15 4 64 55 64 42 29

16

5

5 63 54 63 40 29


Th nghim


oC) Ni un

T2 (oC)

Nng ra T3 (

oC) Nng vo

T4 (oC)

Lnh vo T5 (

oC) Lnh ra

1 2 64 50 63 28 41

2 3 64 49 64 28 41

3 4 64 48 64 28 40

4

2

5 64 47 64 28 38

5 2 64 54 64 28 42

6 3 65 54 64 28 43

7 4 64 53 64 28 42

8

3

5 64 51 64 28 41

9 2 64 56 64 28 44

10 3 64 55 64 28 44

11 4 64 54 64 28 43

12

4

5 63 53 64 28 42

13 2 63 57 63 28 44

14 3 63 56 63 28 44

15 4 63 55 63 28 43

16

5

5 62 53 63 28 42

3. X l s liu:



.100%N N

V RN N L

V V

T T

T T


19

.100%L L

R VN N L

V V

T T

T T

2

N Lhi





310

. .60

N N nuocG V

310

. .60

L L nuocG V


3 20,000015324364. 0,00584994855. 0,016286058705. 1000,04105055224nuoc T T T

(Tnh NG th 2 3

2

T TT

); tnh LG th

4 5

2

T TT

)




f N LQ Q Q


.100%L

N

Q

Q



-Trng hp xui chiu:



20


-Trng hp ngc chiu:




-Tnh ax min

logax

min

ln( )

m

m

t tt

t

t


. .tdF d L .

Vi 2

i otd

d dd

, _. . vong xoanL n D


log.

NTN

QK

F t


c tnh theo cng thc:

1 2

1

1 1LTK


1

2r

r )

C 02

id d

(m), _ _ 17,5thep khong ri (W/m.K). Ch vic tnh 1 v 2 .



Re id


21


w

.4

N

i

G

d


nghim sau:

( 6) 5 4 3

2

(10 )*(( 0.00000000064*( )) (0.000000182875*( )) (0.000021590001*( ))

(0.001417871822*( )) (0.060504453881*( )) 1.790265284068)

v T T T

T T

(m2/s)

-Chun s Prandtl: _

. .Pr N nuoc

dong nong

C

_dong nong c th c tnh bng cch tra bng hay tnh theo pp ni suy (trong chc nng

thng k ca my tnh Casio)



3

2

.. .

g lGr t

v

Vi g=9.81 (m/s2), l l ng knh tng ng y l=di , l h s gin n th tch

c tra trong bng tra cu, t l chnh lch nhit _tuong nong vaot t t .


L




Nu dng nng chy xoy: 0,8 0,430,021. .Re .PrkNu ( n gin ta cho

Pr1

PrT )


22




ca dng lnh.


ReLtdd


w

.( )4

N

Ltd

G

d

Vi

2 2 2_ _ _

_ _ _

.( ( ) )44. 4.

.( ( ))

vo binh vong xoan vong xoan oL uottd

uot vo binh vong xoan vong xoan o

D D D dFd

C D D D d

Vi _ 150vo binhD mm, _ 100ong xoanD mm, d 0= 13 mm

-Chun s Prandtl: _

. .Pr L nuoc

dong lanh

C

_dong lanh c th c tnh bng cch tra bng hay tnh theo pp ni suy (trong chc nng




3

2

.. .

g lGr t

v


23

Vi g=9.81 (m/s2), l l ng knh tng ng y Ltdl d , l h s gin n th tch

c tra trong bng tra cu, t l chnh lch nhit _tuong lanh vaot t t .


L

d . i vi ng xon c tnh

theo cng thc: _

1 3,54. ikvong xoan

d

D


Nu dng lnh chy xoy: 0,8 0,430,021. .Re .PrkNu ( n gin ta cho

Pr1

PrT )



4. Kt qu tnh ton:



Th nghim

NT

(0C) NT

(0C) N

(%) L

(%) hi

(%) 1 15 17 38.5 43.6 41.0 2 15 16 39.5 42.1 40.8 3 18 10 47.4 26.3 36.8 4 18 8 48.6 21.6 35.1 5 11 17 28.9 44.7 36.8 6 12 12 32.4 32.4 32.4 7 11 13 29.7 35.1 32.4 8 13 11 35.1 29.7 32.4 9 8 18 22.2 50.0 36.1 10 9 17 25.0 47.2 36.1 11 11 13 30.6 36.1 33.3 12 12 10 33.3 27.8 30.6 13 7 17 20.0 48.6 34.3 14 8 17 22.9 48.6 35.7 15 9 13 25.7 37.1 31.4 16 9 11 26.5 32.4 29.4


24


nghim GN

(kg/s) GL

(kg/s) QN (W)

QL (W)

Qf (W)

(%) 1 0.032732 0.033083 2057.2 2350.9 -293.7 114.3 2 0.032749 0.049634 2058.3 3319.5 -1261.2 161.3 3 0.032776 0.066251 2471.9 2769.3 -297.3 112.0 4 0.032793 0.082842 2473.2 2770.2 -297.0 112.0 5 0.049097 0.033096 2262.9 2351.8 -88.9 103.9 6 0.049137 0.049688 2470.6 2492.4 -21.7 100.9 7 0.049150 0.066262 2265.3 3600.7 -1335.3 158.9 8 0.049176 0.082856 2678.6 3809.7 -1131.1 142.2 9 0.065516 0.033102 2196.1 2490.6 -294.5 113.4 10 0.065534 0.049662 2471.3 3529.0 -1057.7 142.8 11 0.065569 0.066262 3022.1 3600.7 -578.6 119.1 12 0.065586 0.082870 3297.6 3463.9 -166.3 105.0 13 0.081917 0.033108 2402.6 2352.6 50.0 97.9 14 0.081939 0.049662 2746.6 3529.0 -782.4 128.5 15 0.081961 0.066262 3090.7 3600.7 -509.9 116.5 16 0.082003 0.082856 3092.4 3809.7 -717.4 123.2


nghim QN (W)

tmax (0C)

tmin (oC)

tlog (oC)

KLT (W/m2.K)

KTN (W/m2.K)

1 2057.2 39 7 18.6 177.5 648.6 2 2058.3 38 7 18.3 200.1 659.7 3 2471.9 38 10 21.0 216.4 692.3 4 2473.2 37 11 21.4 230.0 677.8 5 2262.9 38 10 21.0 178.6 633.7 6 2470.6 37 13 22.9 200.4 632.4 7 2265.3 37 13 22.9 218.5 579.9 8 2678.6 37 13 22.9 233.1 685.7 9 2196.1 36 10 20.3 178.4 635.5 10 2471.3 36 10 20.3 202.1 715.1 11 3022.1 36 12 21.8 219.5 812.5 12 3297.6 36 14 23.3 234.0 831.5 13 2402.6 35 11 20.7 178.3 680.6 14 2746.6 35 10 20.0 202.4 808.4 15 3090.7 35 13 22.2 220.0 817.3 16 3092.4 34 14 22.5 234.3 805.8



Th nghim

NT

(0C) NT

(0C) N

(%) L

(%) hi

(%) 1 13 13 37.1 37.1 37.1 2 15 13 41.7 36.1 38.9 3 16 12 44.4 33.3 38.9 4 17 10 47.2 27.8 37.5


25

5 10 14 27.8 38.9 33.3 6 10 15 27.8 41.7 34.7 7 11 14 30.6 38.9 34.7 8 13 13 36.1 36.1 36.1 9 8 16 22.2 44.4 33.3 10 9 16 25.0 44.4 34.7 11 10 15 27.8 41.7 34.7 12 11 14 30.6 38.9 34.7 13 6 16 17.1 45.7 31.4 14 7 16 20.0 45.7 32.9 15 8 15 22.9 42.9 32.9 16 10 14 28.6 40.0 34.3


nghim GN

(kg/s) GL

(kg/s) QN (W)

QL (W)

Qf (W)

(%) 1 0.032835 0.033142 1788.5 1801.0 -12.4 100.7 2 0.032835 0.049713 2063.7 2701.4 -637.7 130.9 3 0.032843 0.066296 2201.8 3325.4 -1123.6 151.0 4 0.032852 0.082897 2340.0 3465.1 -1125.1 148.1 5 0.049189 0.033137 2061.0 1939.2 121.9 94.1 6 0.049189 0.049697 2061.0 3116.0 -1054.9 151.2 7 0.049202 0.066273 2267.7 3878.3 -1610.6 171.0 8 0.049227 0.082856 2681.4 4502.4 -1821.0 167.9 9 0.065551 0.033125 2197.3 2215.4 -18.1 100.8 10 0.065569 0.049688 2472.6 3323.1 -850.5 134.4 11 0.065586 0.066262 2748.0 4154.6 -1406.6 151.2 12 0.065603 0.082842 3023.6 4847.9 -1824.3 160.3 13 0.081939 0.033125 2059.9 2215.4 -155.5 107.5 14 0.081961 0.049688 2403.9 3323.1 -919.2 138.2 15 0.081982 0.066262 2748.0 4154.6 -1406.6 151.2 16 0.082025 0.082842 3436.8 4847.9 -1411.1 141.1

Bng kt qu tnh ton h s truyn nhit:

Th nghim

QN (W)

tmax (0C)

tmin (oC)

tlog (oC)

KLT (W/m2.K)

KTN (W/m2.K)

1 1788.5 22 22 22.0 165.7 477.5 2 2063.7 21 23 22.0 188.4 551.4 3 2201.8 20 24 21.9 206.1 589.5 4 2340.0 19 26 22.3 221.3 615.9 5 2061.0 26 22 23.9 168.5 505.6 6 2061.0 26 21 23.4 190.7 517.1 7 2267.7 25 22 23.5 209.0 567.6 8 2681.4 23 23 23.0 224.3 684.8 9 2197.3 28 20 23.8 168.8 542.8 10 2472.6 27 20 23.3 191.8 622.6 11 2748.0 26 21 23.4 210.4 689.5 12 3023.6 25 22 23.5 226.2 756.8 13 2059.9 29 19 23.6 168.8 511.6 14 2403.9 28 19 23.2 191.9 608.4 15 2748.0 27 20 23.3 210.7 692.0 16 3436.8 25 21 22.9 226.6 879.9


26

5. th: 5.1. Trng hp xui chiu:


Quan h gia Lu lng-H s truyn nhit (Xui chiu)

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0


Lu lng dng nng

KT

N

(W/m

2.K

)

VL=2 (l/ph)

VL=3 (l/ph)

VL=4 (l/ph)

VL=5 (l/ph)



0.0

50.0

100.0

150.0

200.0

250.0


Lu lng dng nng

KL

T

(W/m

2.K

)

VL=2 (l/ph)

VL=3 (l/ph)

VL=4 (l/ph)

VL=5 (l/ph)


27


Trng hp xui chiu

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

K

(W/m

2.K

)

KTN

KLT

5.2. Trng hp ngc chiu


Quan h gia Lu lng-H s truyn nhit (Ngc chiu)

0.0100.0

200.0300.0400.0500.0

600.0700.0800.0

900.01000.0


Lu lng dng nng

KT

N

(W/m

2.K

)

VL=2 (l/ph)

VL=3 (l/ph)

VL=4 (l/ph)

VL=5 (l/ph)


28



0.0

50.0

100.0

150.0

200.0

250.0


Lu lng dng nng

KL

T

(W/m

2.K

)

VL=2 (l/ph)

VL=3 (l/ph)

VL=4 (l/ph)

VL=5 (l/ph)


Trng hp ngc chiu

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0

1000.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

K (W

/m2.K

)

KTN

KLT


29



Quan h chiu chuyn ng-H s truyn nhit

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0

1000.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

KT

N (

W/m

2.K

)

Xui chiu

Ngc chiu


Quan h chiu chuyn ng-H s truyn nhit

0.0

50.0

100.0

150.0

200.0

250.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

KL

T (W

/m2.K

)

Xui chiu

Ngc chiu


30

6. Bn lun:



Ta s i nh gi s nh hng cc yu t qua h s truyn nhit K. H s truyn nhit K

c trng cho lng nhit truyn t lu th nng ti lu th ngui qua 1m2 b mt tng phng




N

Q

Q )


- trng hp xui chiu: Trong cng mt lu lng nng bng nhau (VN=const), khi tng

lu lng dng lnh (VL=2, 3, 4, 5 l/ph) th h s truyn nhit K s tng dn nhng khng ng

k.-Nhn thy nu lu lng dng lnh bng nhau (VL=const) v qua cc mc tng lu lng

dng nng (VN=2, 3, 4, 5 l/ph) th h s truyn nhit K cng s tng ln nhng khng ng k.

Nh vy trong trng hp xui chiu khi tng lu lng dng lnh hoc dng nng th h s

truyn nhit tng chm, ngha l hiu sut ca qu trnh truyn nhit t chu nh hng ca lu

lng dng.

- trng hp ngc chiu: ch khc xui chiu l khi tng lu lng dng lnh th h s

truyn nhit K tng ln nhanh chng. Nh vy trong trng hp ngc chiu chu nh hng

ca lu lng nhiu hn trng hp xui chiu.


-i vi h s truyn nhit tnh t thc nghim ta nhn thy KTN khi xui chiu th ln hn

so vi trng hp ngc chiu.

-i vi h s truyn nhit K tnh theo l thuyt th ta thy KLT khi xui chiu nhnh hn so

vi khi ngc chiu nhng khng ng (hai ng trn th gn nh trng nhau)

Qua ta c th kt lun, trong trng hp truyn nhit ng xon th chiu chuyn ng

theo trng hp xui chiu s c li hn v h s truyn nhit.


31


Trong c hai trng hp ngc chiu v xui chiu, ta u thy KTN ln hn KLT rt nhiu.



log.

NTN

QK

F t






nhanh chng.




ln khi VN tng. i vi 2 ca dng lnh th ch tng khi VL tng , iu ny c gii thch l

do VL tng dn n vn tc dng lnh tng dn n Re tng dn n Nusselt tng t l thun

vi 2 .

-Ta thy rng h s cp nhit 1 ca dng nng ln hn rt nhiu 2 dng lnh. C ngha l

dng lnh nhn c lng nhit t ngun nng trong mt n v thi gian l rt ln v kh

nng nhn nhit ca dng lnh l cha tng xng vi dng nng. iu ny c gii thch l

do dng nng chy trong ng chm c ng knh nh, ch chy xoy (Re>10000) c s

i lu gia cc lp nc lm cho qu trnh cp nhit nhanh hn. Cn dng lnh chy trong

ng c ng knh ln hn rt nhiu, ch chy qu (2300


32

Bng kt qu tnh h s cp nhit

Th nghim 1 dng nng

(W/m2.K)

2 dng lnh

(W/m2.K)

1 4446.3 191.0 2 4426.7 217.4 3 4396.8 236.8 4 4376.7 253.4 5 6150.0 189.9 6 6109.1 214.8 7 6095.3 235.8 8 6067.6 252.9 9 7690.0 188.6 10 7672.7 215.2 11 7637.8 235.1 12 7620.2 251.8 13 9172.2 187.7 14 9151.4 214.6 15 9130.5 234.5

Trng hp

cng chiu

16 9088.5 250.8 1 3194.7 177.5 2 3194.7 203.8 3 3187.1 224.6 4 3179.5 242.8 5 4470.9 177.8 6 4470.9 202.6 7 4460.6 223.4 8 4439.8 241.2 9 5653.8 176.7 10 5640.9 202.0 11 5627.9 222.8 12 5614.9 240.5 13 6758.8 175.8 14 6743.4 200.9 15 6727.9 221.7

Trng hp

ngc chiu

16 6696.7 239.4

Ta nhn thy rng truyn nhit trong ng xon th n nh hn so vi truyn nhit ng lng ng

ng v ng chm (nhn th).

6.4. Mt vi nhn xt v thit b:







33





cng sc.


34

Bi 3: C c gin on dung dch CuSO4 Ngy thc hnh: 31-10-2010

Sinh Vin: FCC

M s: 1234567


T thc hnh: 2

im: Li ph ca thy:

1. Mc ch th nghim:

Qu trnh c c l mt qu trnh c ng dng rng ri trong cng nghip. N lin quan

n nhiu sn phm quan trng: dc phm, thc phm, nng sn, ha cht...Qu trnh ny i

hi kht khe trong vic vn hnh. Do , mc ch ca bi th nghim:

-Gip sinh vin hiu r hn v qu trnh v thit b c c.

-Tnh ton cn bng vt cht, cn bng nng lng xc nh cc thng s cn thit.

-Gip sinh vin vn hnh chnh xc thit b, o c cc thng s ca qu trnh v thit b.

-Xc nh nng sut v hiu sut ca qu trnh.

-nh gi qu trnh hot ng gin on v lin tc.

2. S liu thc hnh:

Nhp liu: Vdd = 6 (lt)

(pht)

W1 (W)

T1 (oC)

T2 (oC)

T5 (oC)

Vdm (lt)

Nng c im

21.95 2000 100.1 28.5 35.8 0 0.0752 Gia nhit 31.95 1500 100.1 28.5 36.4 0 0.0752 Hon lu 96.95 1600 100.1 28.5 38 2 0.1150 Kt thc


35

3. X l s liu:

3.1. Cn bng vt cht:

-Khi lng dung dch CuSO4 7,52% l: dd_dau 30. o Cm V d =6,480 (kg).

_ tan dd _ dd _. 6, 48.7,52% 0,487chat dau daum m x (kg)

-Khi lng dung dch CuSO4 11,50% tnh theo cn bng khi lng cht tan:

_ tan_ _ tan_chat dau chat cuoim m

dd _ dd _ dd _ dd _. .dau dau cuoi cuoim x m x

dd _

dd _ dd _

dd _

7.52%. 6, 48. 4, 237

11,50%

dau

cuoi dau

cuoi

xm m

x (kg)

-Khi lng dung mi bc hi (hi th):

dd _ dd _ 6, 480 4, 237 2, 243dm dau cuoim m m (kg)

3.2. Cn bng nng lng:

-Nhit lng m ni un cung cp trong sut qu trnh th nghim:

1 1 1 11 1 1 2 2 3 3W . W . W . W . 2000.(21,95.60) 1500.(10.60) 1600.(65.60) 9 774 000i iQ t t t t (J)

-Nhit lng un nng dd CuSO4 ln 100,1oC (Qu trnh gia nhit):

42 dd _ uS dd_dau. .(100,1 27, 2) 4186.(1 0.0752).6, 48.(100,1 27, 2) 1 828 730.0C OQ C m (J).

V dd CuSO4 c nng


36

1 2 3 4 fQ Q Q Q Q (J)

-Nu b qua nng lng tn tht 0fQ , th ta s tnh c phn nhit lng cn li Q 4 gia

nhit cho dung dch dung mi bc hi trong hai qu trnh hon lu v qu trnh kt thc.

4 1 2 3Q Q Q Q (J)

-Tnh nng lng _ _boc hoi riengQ ni un cn cung cp bc hi 1 kg dung mi (hi th):

Trong bi th nghim nng lng '

1Q cung cp thu c 2,243 kg dung mi bng (b qua

giai on hon lu).

' 1 11 1 1 2 2W . W . 2000.(21,95.60) 1600.(65.60) 8 874 000,0Q t t (J).

'1

_ _

8 874 000,03 956 937,5

2,243 2, 243boc hoi rieng

QQ (J)

-Cng sut gia nhit cn thit lm bay hi 2,243 kg dung mi (hi th).

'1

1

8 874 000,01 701,0

(21,95 65).60

QN

t

(W)

4. Kt qu tnh ton:

Cn bng vt cht

dd _ daum (kg)

dd _ cuoim (kg)

dd _ daux (%)

dd _ cuoix (%)

_ tanchatm

(kg) dmm

(kg)

6,480 4,237 7,52 11,50 0,487 2,243

Cn bng nng lng

Q1 (J) Ni un

Q2 (J) un nng ln 100,1 oC

Q3 (J) Gii nhit

Q4 (J) Gia nhit hon lu-kt thc

_ _boc hoi riengQ

(J)

N1 (W)

9 774 000,0

1 828 730,0 4 828 021,9

3 117 248,1

3 956 937.5 1701,0


37

5. Bn lun:

5.1. Nhn xt v nng o c:

- y thit b l mt ni c c lm vic gin on nhng cng th chuyn sang lm vic lin

tc.

- ch c c gin on dung dch cho vo mt ln ri cho bc hi, mc dung dch trong

thit b s gim dn cho n khi t n nng yu cu, lc ta s tho dung dch ra lm sn

phm v thc hin mt m mi.

-Trong bi th nghim v dd CuSO4 n nh nhit nn ta khng cn dng hi th m truyn

nhit trc tip qua b phn in tr. un nng dd cho n khi hi th (hi nc) bc hi th

ta cho hon lu hon ton cho qu trnh ngng t hi th din ra n nh mt thi gian.

Trong thit b ngng t, nc lnh chy trong ng xon tip xc gin tip vi hi th v hi

th s c ngng t li thnh lng chy qua ng ng ring tr li ni un. Ta cho hon

lu 10 pht, sau ta chuyn qua ly hi th cho 2 lt.

-Hi th y l nc, v nc l lng d bay hi, CuSO4 l rn cn dd ng Sunfat nng hn

rt nhiu khng th bay hi. Tuy vy trong hi th ly ra c th ln lng rt nh CuSO4 do b

nc bay hi li cun.

-Nng ban u l 7,5 %, nng cui l 11,5%. M theo tnh ton l thuyt th lng hi

th i ra phi l 2,243 kg hay 2,258 lt m trong khi lng hi th thu c ch l 2 lt

thi ! iu ny cng d gii thch do cu to ca thit b c c, hi th ngng t c cho

bnh o theo ng t di ln nn c kh nng lng cn st li 0,258 lt cn ng li trong

ng ng.

-Khi tnh ton nhit lng trong c c gin on, ta nhn thy qu trnh lm lnh thu nhiu

nhit nht Q3 = 4 828 021,9 (J) v nhit lng do hi nc ta ra l rt ln, tip n l qu trnh

un nng dd ln 100,1 oC cng thu nhiu nng lng Q2 = 1 828 730,0 (J). Cui cng l l hai

qu trnh gia nhit hon lu-kt thc thu mt lng nhit Q4 = 3 117 248,1 (J). Tng cng

li ( b qua tn tht nhit) th bng 9 774 000,0 (J) l lng nhit m ni un ta ra cung cp

cho ton b th nghim.

Nu b qua giai on hon lu th tng nng lng m ni un cung cp ch bng 8 874 000.0

(J).


38

Qua ta tnh c nhit lng bc hi ring cho kg dung mi bay hi bng 3 956 937.5 (J).

V cng sut gia nhit trung bnh ca ni un lm bc hi 2.243 kg dung mi bng

1 701,0 (J).

5.2. Cc nguyn nhn gy sai s v cch khc phc:

C nhiu cch nhp liu nhng chnh xc nht l ta ong vo ng ong cho 6 lt ri

vo ni un.

Thit b lm ch yu quan st, khng c b phn cch nhit nn lng nhit tht thot ra

ngoi l rt ln v rt kh tnh ton chnh xc cn bng nng lng.

Ngoi ra vic s dng u d o nng gy sai s rt ln, v vy chc n l ta ly mt

lng dd i sy kh hoc tt ht l nung 300 oC trong 30 pht chuyn v dng tinh th

CuSO4 trng v em cn, bm my tnh l ra nng . Trong th nghim ca bn em s dng

pp sy th vn cn tinh th CuSO4.5H2O v phi ch trong thi gian lu.

o nng mt ln cha , ta c th o tng cng 3 ln kt qu chnh xc hn.


39

Bi 4: Thc hnh truyn nhit ng chm

Ngy thc hnh: 7-11-2010

Sinh Vin: FCC

M s: 1234567


T thc hnh: 2

im: Li ph ca thy:

1. Mc ch th nghim:




nhau.




l thuyt KLT.

2. S liu thc hnh:


Th


T1 (oC)

Ni un T2 (

oC) Nng ra

T3 (oC)

Nng vo T4 (

oC) Lnh ra

T5 (oC)

Lnh vo 1 4 72 60 73 43 31

2 6 71 57 72 41 31

3 8 71 56 72 38 31

4

2

10 70 54 71 36 31

5 3 4 69 59 71 41 31


40

6 6 68 59 70 39 31

7 8 67 58 68 36 30

8 10 67 57 68 35 30

9 4 66 57 67 40 29

10 6 66 56 67 37 29

11 8 65 55 66 34 29

12

4

10 65 54 66 33 29

13 4 64 56 65 39 29

14 6 64 56 65 37 29

15 8 64 55 64 35 29

16

5

10 63 55 64 33 29


Th nghim


oC) Ni un

T2 (oC)

Nng ra T3 (

oC) Nng vo

T4 (oC)

Lnh vo T5 (

oC) Lnh ra

1 4 69 50 67 28 33

2 6 69 52 68 28 33

3 8 69 52 68 28 33

4

2

10 69 52 68 28 33

5 4 68 55 68 28 33

6 6 68 55 68 28 36

7 8 68 56 68 28 35

8

3

10 68 55 68 28 34

9 4 68 57 67 28 38

10 6 68 56 68 28 36

11 8 68 55 68 28 35

12

4

10 68 55 68 28 34

13 4 67 58 67 28 38

14 6 67 58 67 28 38

15 8 67 57 67 29 36

16

5

10 66 57 66 29 35

3. X l s liu:



.100%N N

V RN N L

V V

T T

T T

.100%L L

R VN N L

V V

T T

T T


41

2

N Lhi





310

. .60

N N nuocG V

310

. .60

L L nuocG V


3 20,000015324364. 0,00584994855. 0,016286058705. 1000,04105055224nuoc T T T

(Tnh NG th 2 3

2

T TT

; tnh LG th

4 5

2

T TT

)




f N LQ Q Q


.100%L

N

Q

Q



-Trng hp xui chiu:




42

-Trng hp ngc chiu:




-Tnh ax min

logax

min

ln( )

m

m

t tt

t

t


19. . .tdF d L .

Vi 2

i otd

d dd

, L=0.5 (m)


log.

NTN

QK

F t


c tnh theo cng thc:

1 2

1

1 1LTK


1

2r

r )

C 02

id d

(m), _ _ 17,5thep khong ri (W/m.K). Ch vic tnh 1 v 2 .



Re id


w

.4

N

i

G

d


nghim sau:


43

( 6) 5 4 3

2

(10 )*(( 0.00000000064*( )) (0.000000182875*( )) (0.000021590001*( ))

(0.001417871822*( )) (0.060504453881*( )) 1.790265284068)

v T T T

T T

(m2/s)

-Chun s Prandtl: _

. .Pr N nuoc

dong nong

C

_dong nong c th c tnh bng cch tra bng hay tnh theo pp ni suy (trong chc nng




3

2

.. .

g lGr t

v

Vi g=9.81 (m/s2), l l ng knh tng ng y l=di , l h s gin n th tch

c tra trong bng tra cu, t l chnh lch nhit _tuong nong vaot t t .


L




Nu dng nng chy xoy: 0,8 0,430,021. .Re .PrkNu ( n gin ta cho

Pr1

PrT )




ca dng lnh.


ReLtdd


w

.( )4

N

Ltd

G

d


44

Vi

2 20

0

.( 19. )44. 4.

.( 19. )

iL uottd

uot i

D dFd

C D d

-Chun s Prandtl: _

. .Pr L nuoc

dong lanh

C

_dong lanh c th c tnh bng cch tra bng hay tnh theo pp ni suy (trong chc nng




3

2

.. .

g lGr t

v

Vi g=9.81 (m/s2), l l ng knh tng ng y Ltdl d , l h s gin n th tch

c tra trong bng tra cu, t l chnh lch nhit _tuong lanh vaot t t .


L




Nu dng lnh chy xoy: 0,8 0,430,021. .Re .PrkNu ( n gin ta cho

Pr1

PrT )




45

4. Kt qu tnh ton:



Th nghim

NT

(0C) NT

(0C) N

(%) L

(%) hi

(%) 1 13 12 31.0 28.6 29.8 2 15 10 36.6 24.4 30.5 3 16 7 39.0 17.1 28.0 4 17 5 42.5 12.5 27.5 5 12 10 30.0 25.0 27.5 6 11 8 28.2 20.5 24.4 7 10 6 26.3 15.8 21.1 8 11 5 28.9 13.2 21.1 9 10 11 26.3 28.9 27.6 10 11 8 28.9 21.1 25.0 11 11 5 29.7 13.5 21.6 12 12 4 32.4 10.8 21.6 13 9 10 25.0 27.8 26.4 14 9 8 25.0 22.2 23.6 15 9 6 25.7 17.1 21.4 16 9 4 25.7 11.4 18.6


nghim GN

(kg/s) GL

(kg/s) QN (W)

QL (W)

Qf (W)

(%) 1 0.032659 0.066227 1778.9 3322.0 -1543.0 186.7 2 0.032696 0.099376 2054.9 4153.9 -2099.0 202.1 3 0.032705 0.132569 2192.5 3879.0 -1686.5 176.9 4 0.032732 0.165766 2331.5 3464.5 -1133.0 148.6 5 0.049030 0.066251 2465.2 2769.3 -304.1 112.3 6 0.049043 0.099410 2260.4 3324.3 -1063.9 147.1 7 0.049084 0.132634 2056.6 3326.5 -1269.9 161.7 8 0.049097 0.165820 2262.9 3465.6 -1202.7 153.1 9 0.065481 0.066285 2743.7 3047.8 -304.1 111.1 10 0.065499 0.099476 3018.8 3326.5 -307.6 110.2 11 0.065534 0.132697 3020.5 2773.4 247.1 91.8 12 0.065551 0.165897 3295.9 2773.8 522.1 84.2 13 0.081917 0.066296 3089.1 2771.2 317.9 89.7 14 0.081917 0.099476 3089.1 3326.5 -237.4 107.7 15 0.081961 0.132677 3090.7 3327.5 -236.8 107.7 16 0.081961 0.165897 3090.7 2773.8 316.9 89.7


46


nghim QN (W)

tmax (0C)

tmin (oC)

tlog (oC)

KLT (W/m2.K)

KTN (W/m2.K)

1 1778.9 42 17 27.6 120.1 179.7 2 2054.9 41 16 26.6 158.1 216.0 3 2192.5 41 18 27.9 189.9 219.1 4 2331.5 40 18 27.6 217.8 236.3 5 2465.2 40 18 27.6 129.5 249.8 6 2260.4 39 20 28.5 175.5 221.8 7 2056.6 38 22 29.3 215.3 196.2 8 2262.9 38 22 29.3 253.3 215.8 9 2743.7 38 17 26.1 129.3 293.4 10 3018.8 38 19 27.4 175.0 307.5 11 3020.5 37 21 28.2 215.8 298.6 12 3295.9 37 21 28.2 254.4 325.8 13 3089.1 36 17 25.3 129.4 340.6 14 3089.1 36 19 26.6 176.0 324.3 15 3090.7 35 20 26.8 218.0 322.0 16 3090.7 35 22 28.0 256.6 308.2



Th nghim

NT

(0C) NT

(0C) N

(%) L

(%) hi

(%) 1 17 5 43.6 12.8 28.2 2 16 5 40.0 12.5 26.3 3 16 5 40.0 12.5 26.3 4 16 5 40.0 12.5 26.3 5 13 5 32.5 12.5 22.5 6 13 8 32.5 20.0 26.3 7 12 7 30.0 17.5 23.8 8 13 6 32.5 15.0 23.8 9 10 10 25.6 25.6 25.6 10 12 8 30.0 20.0 25.0 11 13 7 32.5 17.5 25.0 12 13 6 32.5 15.0 23.8 13 9 10 23.1 25.6 24.4 14 9 10 23.1 25.6 24.4 15 10 7 26.3 18.4 22.4 16 9 6 24.3 16.2 20.3


47


nghim GN

(kg/s) GL

(kg/s) QN (W)

QL (W)

Qf (W)

(%) 1 0.032801 0.066369 2336.4 1387.1 949.3 59.4 2 0.032776 0.099553 2197.3 2080.7 116.6 94.7 3 0.032776 0.132737 2197.3 2774.2 -576.9 126.3 4 0.032776 0.165922 2197.3 3467.8 -1270.5 157.8 5 0.049124 0.066369 2675.8 1387.1 1288.7 51.8 6 0.049124 0.099507 2675.8 3327.5 -651.7 124.4 7 0.049111 0.132697 2469.3 3882.7 -1413.4 157.2 8 0.049124 0.165897 2675.8 4160.7 -1484.9 155.5 9 0.065481 0.066317 2743.7 2772.1 -28.4 101.0 10 0.065481 0.099507 3292.4 3327.5 -35.1 101.1 11 0.065499 0.132697 3567.7 3882.7 -315.0 108.8 12 0.065499 0.165897 3567.7 4160.7 -593.0 116.6 13 0.081829 0.066317 3085.8 2772.1 313.7 89.8 14 0.081829 0.099476 3085.8 4158.1 -1072.3 134.8 15 0.081851 0.132656 3429.6 3881.5 -451.9 113.2 16 0.081873 0.165846 3087.4 4159.4 -1072.0 134.7


nghim QN (W)

tmax (0C)

tmin (oC)

tlog (oC)

KLT (W/m

2.K)

KTN (W/m

2.K)

1 2336.4 22 34 27.6 115.6 236.7 2 2197.3 24 35 29.2 153.3 210.4 3 2197.3 24 35 29.2 185.6 210.4 4 2197.3 24 35 29.2 214.2 210.4 5 2675.8 27 35 30.8 125.4 242.4 6 2675.8 27 32 29.4 172.4 253.9 7 2469.3 28 33 30.4 213.4 226.6 8 2675.8 27 34 30.4 251.1 246.0 9 2743.7 29 29 29.0 128.2 264.2 10 3292.4 28 32 30.0 174.0 306.9 11 3567.7 27 33 29.9 215.9 333.2 12 3567.7 27 34 30.4 254.5 328.1 13 3085.8 30 29 29.5 128.7 292.1 14 3085.8 30 29 29.5 176.1 292.1 15 3429.6 28 31 29.5 218.7 324.9 16 3087.4 28 31 29.5 258.2 292.5


48

5. th:




0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

VN= 2 (l/ph) VN= 3 (l/ph) VN= 4 (l/ph) VN= 5 (l/ph)

Lu lng dng nng

KT

N

(W/m

2.K

)

VL=4 (l/ph)

VL=6 (l/ph)

VL=8 (l/ph)

VL=10 (l/ph)



0.0

50.0

100.0

150.0

200.0

250.0

300.0


Lu lng dng nng

KL

T

(W/m

2.K

)

VL=4 (l/ph)

VL=6 (l/ph)

VL=8 (l/ph)

VL=10 (l/ph)


49


Trng hp xui chiu

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

K

(W/m

2.K

)

KTN

KLT




0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0


Lu lng dng nng

KT

N

(W/m

2.K

)

VL=4 (l/ph)

VL=6 (l/ph)

VL=8 (l/ph)

VL=10 (l/ph)


50



0.0

50.0

100.0

150.0

200.0

250.0

300.0


Lu lng dng nng

KL

T

(W/m

2.K

)

VL=4 (l/ph)

VL=6 (l/ph)

VL=8 (l/ph)

VL=10 (l/ph)


Trng hp xui chiu

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

K (W

/m2.K

)

KTN

KLT


51



Quan h gia chiu chuyn ng-H s truyn nhit

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

KTN (W

/m2.K

)

Xui chiu

Ngc chiu


Quan h gia chiu chuyn ng-H s truyn nhit

0.0

50.0

100.0

150.0

200.0

250.0

300.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Th nghim th i

KLT (

W/m

2.K

)

Xui chiu

Ngc chiu


52

6. Bn lun:



Ta s i nh gi s nh hng cc yu t qua h s truyn nhit K. H s truyn nhit K

c trng cho lng nhit truyn t lu th nng ti lu th ngui qua 1m2 b mt tng phng




N

Q

Q )


Ta thy h s truyn nhit K rt khng n nh theo lu lng dng, hiu sut ca qu trnh

truyn nhit t cao nht mc VN=5 l/ph v VL=2 l/ph trng hp cng chiu; VN=4 l/ph v

VL=8 l/ph trng hp ngc chiu (nh gi theo h s truyn nhit K).


-i vi h s truyn nhit tnh t thc nghim ta nhn thy KTN khi xui chiu th gn nh

tng ng so vi trng hp ngc chiu (nhn trn th thy hai ng ny xon li vi

nhau).

-i vi h s truyn nhit K tnh theo l thuyt th ta thy KLT khi xui chiu nhnh hn so

vi khi ngc chiu nhng khng ng bao nhiu (hai ng trn th gn nh trng nhau).

Qua ta c th kt lun, trong trng hp truyn nhit ng chm th chiu chuyn ng

theo trng hp xui chiu hay ngc chiu cng c (rt t thc nghim).


Thy rng h s truyn nhit K trong bi ny th nh hn rt nhiu so vi 2 bi truyn nhit

ng lng ng ng v ng xon.

Trong c hai trng hp ngc chiu v xui chiu, ta u thy KTN ln hn KLT .




53

log.

NTN

QK

F t






nhanh chng.




ln khi VN tng. i vi 2 ca dng lnh th ch tng khi VL tng , iu ny c gii thch l

do VL tng dn n vn tc dng lnh tng dn n Re tng dn n Nusselt tng t l thun

vi 2 .

-Ta thy rng h s cp nhit 1 ca dng nng ln hn rt nhiu 2 dng lnh. C ngha l

dng lnh nhn c lng nhit t ngun nng trong mt n v thi gian l rt ln v kh

nng nhn nhit ca dng lnh l cha tng xng vi dng nng. iu ny c gii thch l

do dng nng chy trong ng xon c ng knh nh, ch chy xoy (Re>10000) c s i

lu gia cc lp nc lm cho qu trnh cp nhit nhanh hn. Cn dng lnh chy trong ng c

ng knh ln hn rt nhiu, ch chy dng (Re


54

13 5820.4 133.4 14 5820.4 183.4 15 5793.9 229.5 16 5793.9 272.6 1 1065.9 130.6 2 1073.3 180.6 3 1073.3 227.4 4 1073.3 271.8 5 3885.3 130.6 6 3885.3 182.3 7 3894.0 228.8 8 3885.3 272.6 9 4901.6 132.6 10 4901.6 182.3 11 4890.7 228.8 12 4890.7 272.6 13 5872.6 132.6 14 5872.6 183.4 15 5859.6 230.2

Trng hp

ngc chiu

16 5846.6 274.3

Ta nhn thy rng truyn nhit trong ng chm th khng n nh so vi truyn nhit ng

lng ng ng v ng xon (nhn th).

4. Mt vi nhn xt v thit b:










cng sc.


55

NHN XT V NH GI V 3 BI TRUYN NHIT

Rt t thc nghim:

Yu t

Bi 1: TN ng lng ng ng Bi 2: TN ng xon Bi 3: TN ng chm

H s truyn

nhit K

Ln nht Trung bnh Nh nht

Tng lu lng dng nng v

dng lnh K tng nhanh K tng chm

Khng n nh (tng gim quanh 1 v tr)

H s cp nhit

ca dng nng < ca dng

lnh

ca dng nng >> ca dng lnh

Nh nht

Ln nht Trung bnh

H s cp nhit dng nng

Tng khi tng VN v hu nh khng i khi tng VL

Ln nht Nh nht Nh nht H s cp nhit

dng lnh

Tng khi tng VL v hu nh khng i khi tng VN

dng nng

Chy xoy Chy xoy Chy xoy Ch

chy dng ngui

Chy xoy Chy dng Chy qu

K thc nghim

K xui chiu > K ngc chiu

Tng ng

Chiu chuyn ng K l

thuyt K ngc chiu > K xui chiu

K xui chiu > K ngc

chiu

Bng nhau

Tnh n nh khi

truyn nhit

Trung bnh n nh nht Km n nh


56

u im

-Ch to n gin

-Ch to n gin c th lm bng vt liu chng n mn, d kim tra v sa cha

-Cu to gn, chc chn, tn t kim loi (tnh theo mt n v truyn nhit), d lm sch pha trong ng

Ngoi quan

Nhc im

-Cng knh, gi thnh cao, tn nhiu vt liu ch to (tnh theo mt n v truyn nhit), kh lm sch khong trng gia hai ng

-Cng knh, h s truyn nhit nh do h s cp nhit ngoi b, kh lm sch pha trong ng, tr lc thy lc ln hn ng thng.

-Kh ch to bng vt liu khng nong v hn c nh gang, thp silic...

Qua nhng so snh trn ty theo mc ch s dng v tnh kinh t m chng ta chn thit b sao

cho t hiu qu lm vic cao nht.


57

DANH MC SCH THAM KHO & TRA CU

[1]. Qu trnh v thit b truyn nhit (2009); TT My v Thit B; Trng H Cng Nghip tp

HCM; tr26-35, tr 116-130. [2]. Gio trnh thc hnh Cc qu trnh v thit b truyn nhit (2010); nhm 3 lp DHVC3;

Trng H Cng Nghip tp HCM; (c 3 bi truyn nhit) [3]. Gio trnh thc hnh Cc qu trnh v thit b truyn nhit (2009); TT My v Thit B;

Trng H Cng Nghip tp HCM; tr 299-332 (bi c c). [4]. Bng tra cu qu trnh c hc, truyn nhit-truyn khi (2010); B mn my v thit b

trng H Bch Khoa tp HCM; tr 28, tr 35. [5]. S tay Qu trnh v thit b cng ngh ha cht-Tp 1 (2006); TS. Trn Xoa, TS. Nguyn

Trng Khung, KS. H L Vin; tr 152, tr 357-358. [6]. S tay Qu trnh v thit b cng ngh ha cht-Tp 2 (2006); TS. Trn Xoa, TS. Nguyn

Trng Khung, TS. Phm Xun Ton; tr 11-20, tr 55-74.

Documents

Bao Cao Th Truyen Nhiet_decrypted