truyền nhiệt ống lồng ống

1. TRCH YEU

1.1 Muc ch th nghiem

Lam quen vi thiet b truyen nhiet ong long ong, cac dung cu o nhiet o va lu lng lu chat. Xac nh he so truyen nhiet trong qua trnh truyen nhiet gia 2 dong lanh, nong, qua vach kim loai, cac che o chay khac nhau. Thiet lap can bang nhiet lng.

1.2 Phng phap th nghiem

Tien hanh th nghiem vi cac loai ong khac nhau (ong B va ong C) nhng che o chay khac nhau t o tnh toan xac nh he so truyen nhiet gia hai dong lanh va nong. Cu the: Vi moi loai ong, ta lam th nghiem vi nhieu gia tr lu lng dong nong, vi moi gia tr dong nong ta o cac gia tr dong lanh khac nhau. oc nhiet o au vao va au ra tng ng vi moi loai ong va lu lng dong nong, dong lanh.

1.3 Ket qua th nghiem

Bang 1: So lieu th nghiem nhiet o au vao va ra tng ng vi lu lng dong nong, lanh cho ong B va ong C

NGLu lng dong nong (ft3/ph)0,20,30,40,44

Lu lng dong lnh (ft3/ph)t1Vt1Rt2Vt2Rt1Vt1Rt2Vt2Rt1Vt1Rt2Vt2Rt1Vt1Rt2Vt2R

B0,1685713036897833399484374494853845

0,2486712934907832389483364295843743

0,3287712933917731369582344096843641

0,488712832927730359682343896833640

C0,1670613440787038448780414887814148

0,2470603439807137428880404788804047

0,3270593438827136418879394589804045

0,472603437867337418978384489793944

1.4 Nhn xet kt qu

Nhiet o au vao va au ra khong on nh, thay oi lien tuc cai dong lanh va nong.Chenh lech gia nhiet o au vao va ra cua dong nong ong B ln hn so vi ong C, con chenh lech dong vao va ra cua dong lanh cua ong C xap x ong C.

2. LY THUYET TH NGHIEM

Qua trnh truyen nhiet trong thiet b dang ong long ong la mot v du cua s truyen nhiet phc tap. ay dien ra s trao oi nhiet gia hai lu chat c ngan cach bi vach ngan kim loai, bao gom truyen nhiet oi lu t dong nong en vach, dan nhiet qua thanh ong kim loai va oi lu nhiet gia dong lanh vi thanh ong.

2.1 Phng trnh can bang nhet lng cho hai dong lu chatQ = G1C1(tV1 tR1) = G2C2(tR2 tV2) , WTrong o :G1, G2 : lu lng dong nong va lanh, kg/s.C1, C2 : nhiet dung rieng trung bnh cua dong nong, dong lanh (J/kg.K)tV1, tR1 : nhiet o vao va ra cua dong nong, 0CtV2, tR2 : nhiet o vao va ra cua dong lanh , 0C

2.2 Phng trnh bieu dien qua trnh truyen nhietQ = Kl.tlog.LTrong o:L : Chieu dai ong, mKl : He so truyen nhiet dai, W/mKtlog : Chenh lech nhiet o trung bnh logarit, K

2.3 o chenh lech nhet o trung bnh logarit

2.4 He so truyen nhiet l thuyet, K*1

Trong o:dng, dtr : ng knh ngoai va trong cua ong truyen nhiet, m. : He so dan nhiet cua ong, W/mK.rb : Nhiet tr cua lp cau.db : ng knh lp cau, m.

2.5 He so cap nhiet 1,2 gia vach ngan va dong lu chata. Xac nh che o chay cua lu chat bang chuan so Re

Trong o:w : Van toc dong, m/s

: o nht ong hoc cua lu chat, m2/s l : Kch thc hnh hoc ac trng, m. Trng hp lu chat chuyen ong qua tiet dien khong tron, l c tnh bang ng knh tng ng dtd

Trong o:F : Dien tch mat cat (tiet dien ngang ma dong lu chat chuyen ong qua), m2 : Chu vi tiet dien t (chu vi ma chat long tiep xuc vi be mat trao oi nhiet), mThong so c xac nh nhiet o trung bnh cua lu chat.

b. Xac nh chuan so Nu Phng thc chay ngang (ong kieu B)

5 < Re < 103

103 < Re 104

Gia tr cua 1 phu thuoc t le l/d khi Re 104, 1 phu thuoc vao ReRel/d

1020304050

1.1042.1045.1041.1051.1061.231.181.131.101.051.131.101.081.061.031.071.051.041.031.021.031.021.021.021.0111111

Chuan so Pr:

Trong o:: o nht ong hoc cua lu chat, m2/s.a: He so dan nhiet cua lu chat, m2/s. Chuan so Gr:

Trong o:t: hieu nhiet o gia thanh ong va lu chat.: he so gian n the tch, 1/KPr: chuan so Prandtl cua lu chat c xac nh nhiet o trung bnh cua lu chat.Prv: chuan so Prandtl cua lu chat c xac nh nhiet o bang nhiet o trung bnh cua thanh ong.Neu nhiet o cua thanh ong (vach) khong biet, viec tnh toan co the thc hien theo trnh t sau:t2tV2tV1t1tlogtVt1t2

Hnh 1: S o phan bo nhiet o khi truyen nhiet gia cac lu chat qua vach ngan.t1 = t1 tv1t2 = tv2 t2Ta thc hien phep tnh lap.Khi iem ta chon gan ung hieu so gia nhiet o lu chat va vach ngan nh sau:

Hieu so nhiet o log bieu dien nh sau:

T o tnh c:

T ay ta tnh c nhiet o trung bnh cua lu chat va vach ngan, do o tnh va Nu.

, W/m2KTrong o:: he so dan nhiet cua lu chat, W/mK.l: kch thc hnh hoc ac trng, m.Sau khi co ket qua tnh 1, 2 ta kiem tra t1, t2 bang phng trnh sau:

Suy ra: Sai so cho phep la 5% neu cha at, qua trnh tnh c lap lai vi gia tr t1, t2 mi nay.

3 DNG C, THIT B & PHNG PHAP TH NGHIM

3.1 Dung cu va thiet b th nghiemHe thong thiet b th nghiem co 3 kieu ket cau be mat truyen nhiet nh sau: Kieu A : Loai ong nhun (ong an hoi c). Kieu B : Loai ong long ong ma lu chat chay ngang mat ngoai cua ong trong. Hai dong chay co phng vuong goc vi nhau. Kieu C : Loai ong long ong n gian, lu chat chay doc be mat ngoai cua ong trong. Hai dong chay co phng song song vi nhau. Kch thc ong.Kieu ongng knh (mm)Chieu dai (mm)

Ong trongOng ngoai

BC14/1614/1626/2826/289251000

3.2 Phng phap th nghiem

a. Chuan b:

1) Lam quen vi he thong thiet b, tmhieu cac van va tac dung cua no.2) Lam quen vi thiet b o nhiet o, cac v tr o va cach ieu chnh cong tac e o nhiet o.3) Lam quen vi thiet b o lu lng va cach ieu chnh lu lng.4) Xac nh cac ai lng can o.5) o lu lng dong nong, dong lanh, nhiet o cac v tr can thiet. 6) Lap bang ghi ket qua o.

b. Trnh t th nghiem:

1) Cap nc ay vao noi un (khi nc bat au chay qua ong chay tran).2) ong cau dao R1, R2, R3 va R4 e un nc.3) Trong luc ch nc at nhiet o can thiet, tm hieu ng i cua cac dong tren he thong th nghiem va cac van 2 chieu I va II. (mac nh bai nay van I co nh)4) Khi nc soi, bat au tien hanh th nghiem.5) M cac van V1, V2, V3, V6 va V7. Van V5 luon ong. 6) ong cau dao P1 e khi ong bm, bm dong nong vao he thong thiet b th nghiem. 7) Muon khao sat ong nao ta m van chan tng ng au vao dong nong (VN1, VN2, VN3, VN4, VN5) va au ra dong lanh (VL1, VL2, VL3, VL4, VL5) cua ong o. Khoa tat ca cac van khac lai.8) ong t t van V3 e ieu chnh lu lng cua dong nong (hoan lu mot phan dong nong ve lai noi un).9) Chu y rang dong nong c o lien tuc va c hoan lu e giam ton that nhiet. Do ch co mot lu lng ke nen ta dung van II e co nh lu lng dong nong, sau o oi chieu van II e o lu lng dong lanh (ng vi moi lu lng dong nong o 4 gia tr lu lng dong lanh).10) Ghi cac ai lng can o khi qua trnh on nh hoan toan.11) ieu chnh lu lng cac dong e thay oi che o chay va lap lai th nghiem vi thong so on nh mi.Trong bai nay, ta ch o gia tr ong B va ong C.

4 KET QUA TH NGHIEM 4.1 ng B

4.1.1 Ket qua tnh toan30

G1.104 (m3/s)G2.104 (m3/s)t1V (oC)t1R (oC)t1TB (oC)1 (kg/m3)C1 (J/kg.)1 (W/m.)1.104 (N.s/m2)Pr1

0,9430,75857178,0973,241900,67363,6522,278

1,13867178,5972,941900,67403,6272,261

1,51877179,0972,641900,67433,6012,244

1,89887179,5972,341900,67473,5762,227

1,42

0,75897883,5969,641900,67683,4102,119

1,13907884,0969,241900,67703,3902,106

1,51917784,0969,241900,67703,3902,106

1,89927784,5968,941900,67733,3702,093

1,89

0,75948489,0965,741900,67953,1901,976

1,13948388,5966,141900,67933,2101,989

1,51958288,5966,141900,67933,2101,989

1,89968289,0965,741900,67953,1901,976

2,080,75948589,5965,441900,67983,1701,963

1,13958489,5965,441900,67983,1701,963

1,51968490,0965,041900,68003,1501,950

1,89968389,5965,441900,67983,1701,963

Bang 2: Thong so dong nong

Bang 3: Thong so dong lanh


0,9430,75303633,0994,841800,62287,5995,087

1,13293431,5995,441800,62047,8205,254

1,51293331,0995,641800,61967,8935,309

1,89283230,0996,041800,61808,0405,420

1,42

0,75333936,0993,641800,62767,1584,754

1,13323835,0994,041800,62607,3054,865

1,51313633,5994,641800,62367,5265,032

1,89303532,5995,041800,62207,6735,143

1,89

0,75374440,5991,841800,63476,5164,272

1,13364239,0992,441800,63246,7174,421

1,51344037,0993,241800,62927,0114,643

1,89343836,0993,641800,62767,1584,754

2,080,75384541,5991,441800,63616,4084,195

1,13374340,0992,041800,63406,5704,310

1,51364138,5992,641800,63166,7914,477

1,89364038,0992,841800,63086,8644,532

Bang 4: Nhiet lng Q va ton that Q

G1.104 (m3/s)G1 (kg/s)G2 (kg/s)C1 (J/kg.)C2 (J/kg.)t1V-t1Rt2R-t2V Q1 (W)Q2 (W)Q (W)

0,9430,09180,0751419041801465385,291882,863502,43

0,09180,1127419041801555768,182355,003413,18

0,09170,1503419041801646150,832512,503638,32

0,09170,1879419041801746533,243141,893391,35

1,42 0,13720,0750419041801166323,151880,594442,56

0,13710,1125419041801266895,492822,024073,47

0,13710,1501419041801458044,743137,474907,27

0,13710,1877419041801558616,253923,424692,83

1,890,18220,0748419041801077633,992190,055443,94

0,18230,1123419041801168400,432817,485582,95

0,18230,1499419041801369927,783759,676168,11

0,18220,18754190418014410687,583134,327553,26

2,080,20030,074841904180977554,912189,165365,74

0,20030,1123419041801169233,782816,346417,43

0,20030,14984190418012510069,563131,166938,40

0,20030,18734190418013410912,653131,797780,85

Bang 5:He so Re vi dong nong va lanhG1.104 (m3/s)lnong (m)w1 (m/s)1.107 (m2/s)Re1llnh (m)G2.104 (m3/s)w2 (m/s)2.107 (m2/s)Re2

0,9430,0140,61313,753228740,0260,7550,008167,639278

0,0140,61313,728230280,0261,130,012247,856405

0,0140,61313,702231830,0261,510,016327,928535

0,0140,61313,677233420,0261,890,020408,072657

1,420,0140,91973,517366080,0260,7550,008167,204294

0,0140,91973,498368110,0261,130,012247,349433

0,0140,91973,498368110,0261,510,016327,566561

0,0140,91973,478370160,0261,890,020407,711688

1,890,0141,22623,303519700,0260,7550,008166,570323

0,0141,22623,323516640,0261,130,012246,768470

0,0141,22623,323516640,0261,510,016327,059601

0,0141,22623,303519700,0261,890,020407,204736

2,080,0141,34883,284575060,0260,7550,008166,464328

0,0141,34883,284575060,0261,130,012246,623480

0,0141,34883,264578500,0261,510,016326,841620

0,0141,34883,284575060,0261,890,020406,914767

Bang 6:Tnh tlog,Kl1,Kl2tL= t1V-t2RtN= t1R-t2V

tlogL (m)Q1 (W)Kl1 (W/m.K)Q2 (W)Kl2 (W/m.K)

49410,178244,880,9255385,29129,721882,8645,35

52420,213646,820,9255768,18133,182355,0054,37

54420,251347,750,9256150,83139,262512,5056,89

56430,264249,210,9256533,24143,513141,8969,02

50450,105447,460,9256323,15144,051880,5942,84

52460,122648,940,9256895,49152,322822,0262,34

55460,178750,370,9258044,74172,683137,4767,34

57470,192951,840,9258616,25179,693923,4281,82

50470,061948,480,9257633,99170,222190,0548,83

52470,101149,460,9258400,43183,622817,4861,59

55480,136151,420,9259927,78208,723759,6779,04

58480,189252,840,92510687,58218,653134,3264,12

49470,041747,990,9257554,91170,182189,1649,31

52470,101149,460,9259233,78201,842816,3461,56

55480,136151,420,92510069,56211,713131,1665,83

56470,175251,370,92510912,65229,663131,7965,91

Bang 7:He so cap nhiet 1,2 (lap lan 1)t1t2tvach1tvach2Prv1Prv2Nu1Nu21 (W/m2.K)2 (W/m2.K)

0,5242,8677,4875,862,2962,351140,7918,756774,0449,2

0,7844,5477,7276,042,2882,345140,8223,126778,8551,8

1,0445,2177,9676,212,2792,339140,8426,776783,6638,0

1,3146,4178,1976,412,2712,332140,8730,086788,3714,9

0,3745,5983,1381,592,1292,169181,7718,888786,7455,7

0,5546,8983,4581,892,1202,161181,8423,258793,5559,8

0,7348,1383,2781,632,1252,168181,7427,008788,6647,7

0,9249,4283,5881,922,1172,160181,8230,358795,3726,0

0,2946,6988,7187,191,9842,023218,4618,8010603,2459,0

0,4347,5388,0786,532,0002,040218,1323,1410583,4562,8

0,5749,3587,9386,352,0042,045218,0326,9710578,6652,6

0,7250,6388,2886,631,9952,038218,1630,3210588,4731,8

0,2646,2389,2487,731,9702,009231,5818,7711244,0459,3

0,4047,5689,1087,561,9732,013231,4823,1011239,1563,2

0,5349,3989,4787,891,9642,005231,6226,9011250,0653,5

0,6649,2188,8487,211,9802,022231,2830,0911229,5729,9

Bang8:Kiem tra lan 11 (W/m2.K)2 (W/m2.K)Cu (W/m.K)dtrong(m)dngoai(m)Kl*t1*Sai s t1 (%)t2*Sai s t2 (%)

6774,0449,23840,0140,01620,960,13973,312,09595,11

6778,8551,83840,0140,01625,340,17577,662,15095,17

6783,6638,03840,0140,01628,910,20480,502,16495,21

6788,3714,93840,0140,01632,020,23282,232,20495,25

8786,7455,73840,0140,01621,600,11768,192,24995,07

8793,5559,83840,0140,01626,190,14673,572,29095,12

8788,6647,73840,0140,01629,980,17276,572,33195,16

8795,3726,03840,0140,01633,280,19678,632,37795,19

10603,2459,03840,0140,01621,960,10065,392,31995,03

10583,4562,83840,0140,01626,630,12471,222,34095,08

10578,6652,63840,0140,01630,590,14974,102,41095,12

10588,4731,83840,0140,01634,030,17076,322,45795,15

11244,0459,33840,0140,01622,030,09464,362,30295,02

11239,1563,23840,0140,01626,730,11870,392,34895,06

11250,0653,53840,0140,01630,750,14173,452,42095,10

11229,5729,93840,0140,01634,090,15676,242,39995,13

Bang 9: He so cap nhiet 1,2 (lap lan 2)t1*t2*tvch1tvch2Prv1Prv2Nu1Nu21 (W/m2.K)2 (W/m2.K)

0,1392,09577,8677,962,2832,280140,9918,906783,6452,6

0,1752,15078,3278,192,2672,272141,1423,316794,2556,2

0,2042,16478,8078,372,2512,265141,2926,996805,0643,1

0,2322,20479,2778,612,2352,257141,4430,326815,8720,7

0,1172,24983,3883,842,1222,110181,9119,018793,5458,8

0,1462,29083,8584,182,1102,101182,0723,418804,5563,7

0,1722,33183,8383,962,1102,107182,0627,208803,8652,3

0,1962,37784,3084,302,0982,098182,2230,578815,0731,3

0,1002,31988,9089,511,9791,963218,6018,9510609,8462,5

0,1242,34088,3888,871,9921,979218,3523,3110594,0567,1

0,1492,41088,3588,761,9931,982218,3427,1810593,2657,7

0,1702,45788,8389,081,9801,974218,5530,5610607,4737,7

0,0942,30289,4190,031,9651,949231,7118,9211250,3462,8

0,1182,34889,3889,911,9661,952231,6923,2711249,4567,5

0,1412,42089,8690,311,9541,944231,9227,1111264,6658,6

0,1562,39989,3489,611,9671,960231,6630,3211248,0735,7

Bang10:Kiem tra lan 21 (W/m2.K)2 (W/m2.K)Cu (W/m.K)dtrong(m)dngoai(m)Kl**t1**Sai s t1 (%)t2**Sai s t2 (%)

6783,64452,633840,0140,01621,110,1400,582,0940,05

6794,18556,183840,0140,01625,530,1760,522,1490,05

6804,98643,143840,0140,01629,130,2040,442,1630,05

6815,83720,743840,0140,01632,260,2330,372,2030,05

8793,45458,833840,0140,01621,740,1170,572,2480,04

8804,47563,673840,0140,01626,360,1470,532,2890,04

8803,76652,273840,0140,01630,180,1730,492,3300,04

8814,96731,253840,0140,01633,510,1970,462,3760,05

10609,78462,533840,0140,01622,120,1010,662,3190,03

10594,04567,053840,0140,01626,820,1250,622,3390,04

10593,20657,683840,0140,01630,820,1500,602,4090,04

10607,37737,693840,0140,01634,280,1710,572,4560,05

11250,33462,813840,0140,01622,190,0950,672,3010,03

11249,45567,523840,0140,01626,930,1180,642,3470,04

11264,58658,593840,0140,01630,980,1410,602,4190,04

11248,03735,683840,0140,01634,340,1570,582,3980,04

Ta thay sai so a nam di mc 5%,a at yeu cau ve tnh toan 1, 2, Kl* ay e n gian ta coi la K** la K*Bang 11: So lieu Kl1,Kl2 va Kl* theo Re1,Re2G1 (ft3/ph)G2 (ft3/ph)DONG NONGDONG LNH

Re1Kl1Kl*Re2Kl2Kl*

0,20,1622874129,7221,1127845,3521,11

0,2423028133,1825,5340554,3725,53

0,3223183139,2629,1353556,8929,13

0,423342143,5132,2665769,0232,26

0,30,1636608144,0521,7429442,8421,74

0,2436811152,3226,3643362,3426,36

0,3236811172,6830,1856167,3430,18

0,437016179,6933,5168881,8233,51

0,40,1651970170,2222,1232348,8322,12

0,2451664183,6226,8247061,5926,82

0,3251664208,7230,8260179,0430,82

0,451970218,6534,2873664,1234,28

0,440,1657506170,1822,1932849,3122,19

0,2457506201,8426,9348061,5626,93

0,3257850211,7130,9862065,8330,98

0,457506229,6634,3476765,9134,34

4.1.2 o tha. Anh hng cua dong lanh

Hnh 2: o th K1* va K12 theo Re2 khi lu lng dong nong la 0,2 ft3/phut




b. Anh hng cua dong nongHnh 6: o th K1* va K11 theo Re1 khi lu lng dong lanh la 0,16 ft3/phut

Hnh 7: o th K1* va K11 theo Re1 khi lu lng dong lanh la 0,24 ft3/phut


Hnh 9: o th K1* va K11 theo Re1 khi lu lng dong lanh la 0,4 ft3/phut4.2 Ong C4.2.1 Ket qua tnh toanBang 11: Thong so dong nong G1.104 (m3/s)G2.104 (m3/s)t1V (oC)t1R (oC)t1TB (oC)1 (kg/m3)C1 (J/kg.)1 (W/m.)1.104 (N.s/m2)Pr1

0,9430,755706165,5980,341860,66404,3482,744

1,13706065,0980,541850,66354,3802,765

1,51705964,5980,841850,66314,4122,787

1,89726066,0980,041860,66444,3162,722

1,420,755787074,0975,641900,67083,8562,414

1,13807175,5974,741900,67193,7802,363

1,51827176,5974,141900,67263,7292,329

1,89867379,5972,341900,67473,5762,227

1,890,755878083,5969,641900,67683,4102,119

1,13888084,0969,241900,67703,3902,106

1,51887983,5969,641900,67683,4102,119

1,89897883,5969,641900,67683,4102,119

2,080,755878184,0969,241900,67703,3902,106

1,13888084,0969,241900,67703,3902,106

1,51898084,5968,941900,67733,3702,093

1,89897984,0969,241900,67703,3902,106

Bang 12: Thong so dong lanh


0,9430,755344037,0993,241800,62927,0114,643

1,13343936,5993,441800,62847,0854,699

1,51343836,0993,641800,62767,1584,754

1,89343735,5993,841800,62687,2324,810

1,420,755384441,0991,641800,63546,4624,233

1,13374239,5992,241800,63326,6444,366

1,51364138,5992,641800,63166,7914,477

1,89374139,0992,441800,63246,7174,421

1,890,755414844,5990,241800,64036,0843,964

1,13404743,5990,641800,63896,1924,041

1,51394542,0991,241800,63686,3544,156

1,89384441,0991,641800,63546,4624,233

2,080,755414844,5990,241800,64036,0843,964

1,13404743,5990,641800,63896,1924,041

1,51404542,5991,041800,63756,3004,118

1,89394441,5991,441800,63616,4084,195

Bang 13: Nhiet lng Q va ton that Q

G1.104 (m3/s)G1 (kg/s)G2 (kg/s)C1 (J/kg.)t1V - t1R C2 (J/kg.)t2R - t2V Q1 (W)Q2 (W)Q (W)

0,9430,09250,075041869418063483,311879,831603,47

0,09250,1125418510418053870,872350,271520,60

0,09250,1500418511418044258,532507,451751,08

0,09240,1875418612418034643,782351,212292,57

1,420,13800,074841908418064627,351876,812750,54

0,13790,112341909418055200,972347,432853,54

0,13780,1498419011418056352,823131,163221,66

0,13760,1872419013418047494,013130,534363,47

1,890,18290,074741907418075365,102186,513178,58

0,18290,112141908418076129,323281,102848,23

0,18290,149641909418066897,983752,103145,88

0,18290,1871419011418068430,864692,013738,85

2,080,20110,074741906418075056,692186,512870,18

0,20110,112141908418076742,263281,103461,16

0,20110,149641909418057582,303126,124456,18

0,20110,1870419010418058427,823909,224518,60

Bang 14:He so Re vi dong nong va lanhG1.104 (m3/s)lnong (m)w1 (m/s)1.107 (m2/s)Re1llnh (m)G2 (m3/s)w2 (m/s)2 (kg/m3)2.107 (m2/s)Re2

0,9430,0140,61314,436193520,010,7550,2288993,27,0593241

0,0140,61314,467192150,011,130,3432993,47,1324812

0,0140,61314,499190810,011,510,4576993,67,2046351

0,0140,61314,404194900,011,890,5719993,87,2777860

1,420,0140,91973,952325760,010,7550,2288991,66,5173511

0,0140,91973,878332040,011,130,3432992,26,6965125

0,0140,91973,828336380,011,510,4576992,66,8416688

0,0140,91973,677350120,011,890,5719992,46,7688450

1,890,0141,22623,517488110,010,7550,2288990,26,1443723

0,0141,22623,498490810,011,130,3432990,66,2515490

0,0141,22623,517488110,011,510,4576991,26,4107138

0,0141,22623,517488110,011,890,5719991,66,5178777

2,080,0141,34883,498539890,010,7550,2288990,26,1443723

0,0141,34883,498539890,011,130,3432990,66,2515490

0,0141,34883,478542900,011,510,4576991,06,3577197

0,0141,34883,498539890,011,890,5719991,46,4648849

Bang 15:Tnh tlog,Kl1,Kl2tL = t1V - t2RtN = t1R - t2V

tlogL (m)Q1 (W)Kl1 (W/m.K)Q2 (W)Kl2 (W/m.K)

30271,1110,105428,4713483,31122,331879,8366,02

31261,1920,175928,4313870,87136,172350,2782,68

32251,2800,246928,3614258,53150,182507,4588,43

35261,3460,297330,2814643,78153,372351,2177,66

34321,0630,060632,9914627,35140,271876,8156,89

38341,1180,111235,9615200,97144,622347,4365,27

41351,1710,158237,9216352,82167,533131,1682,57

45361,2500,223140,3317494,01185,803130,5377,62

39391,000-39,0015365,10137,572186,5156,06

41401,0250,024740,5016129,32151,353281,1081,02

43401,0750,072341,4816897,98166,293752,1090,45

45401,1250,117842,4518430,86198,604692,01110,53

39400,975-39,5015056,69128,022186,5155,35

41401,0250,024740,5016742,26166,483281,1081,02

44401,1000,095341,9717582,30180,673126,1274,49

45401,1250,117842,4518427,82198,533909,2292,09

Bang 16:He so cap nhiet 1,2 (lap lan 1)t1t2tvach1tvach2Prv1Prv2Nu1Nu21 (W/m2.K)2 (W/m2.K)

3,8723,1061,6360,102,8892,97485,9914,724078,2926,1

5,3921,5359,6158,033,0023,09085,1431,354035,01970,0

6,7120,1557,7956,153,1043,19684,4045,653997,52864,8

8,2720,5157,7356,013,1073,20484,4759,644008,73738,2

3,0628,4370,9469,432,5102,575123,8517,275934,11097,2

4,6129,8570,8969,352,5122,578123,9234,255946,82168,6

6,0430,3870,4668,882,5302,598123,7649,285945,23112,4

7,5531,2871,9570,282,4662,538124,7564,826011,64099,5

2,6634,8480,8479,342,1812,232162,2219,377841,81240,1

3,9235,0780,0878,572,2072,258161,7836,967823,32361,1

5,1034,8878,4076,882,2642,316160,7252,247768,93326,8

6,2434,7177,2675,712,3032,356160,0466,877736,04249,0

2,4535,5581,5580,052,1702,208175,3519,428479,51243,4

3,6035,4080,4078,902,1962,247174,8237,008453,72364,0

4,7435,7379,7678,232,2182,270174,4352,708438,13359,7

5,7735,1878,2376,682,2702,323173,3867,298384,34280,6

Bang 17:Kiem tra lan 11 (W/m2.K)2 (W/m2.K)Cu (W/m.K)dtrongdngoaiKl*t1*Sai s t1 (%)t2*Sai s t2 (%)

4078,2926,13840,0140,01636,890,25893,341,13495,09

4035,01970,03840,0140,01663,340,44691,730,91495,76

3997,52864,83840,0140,01678,820,55991,660,78096,13

4008,73738,23840,0140,01690,510,68491,730,73396,43

5934,11097,23840,0140,01645,420,25291,761,36695,20

5946,82168,63840,0140,01676,610,46389,951,27195,74

5945,23112,43840,0140,01697,360,62189,721,18696,10

6011,64099,53840,0140,016115,070,77289,771,13296,38

7841,81240,13840,0140,01652,640,26290,151,65595,25

7823,32361,13840,0140,01687,820,45588,411,50695,71

7768,93326,83840,0140,016111,580,59688,321,39196,01

7736,04249,03840,0140,016130,270,71588,551,30196,25

8479,51243,43840,0140,01653,370,24989,861,69595,23

8453,72364,03840,0140,01689,600,42988,081,53595,66

8438,13359,73840,0140,016115,320,57487,891,44195,97

8384,34280,63840,0140,016134,870,68388,161,33896,20

Bang 18: He so cap nhiet 1,2 (lap lan 2)t1*t2*tvach1tvach2Prv1Prv2Nu1Nu21 (W/m2.K)2 (W/m2.K)

0,2581,13465,2438,132,7554,51787,0213,264127,0834,3

0,4460,91464,5537,412,7844,59786,7628,394111,71783,8

0,5590,78063,9436,782,8114,66786,5241,524097,82606,0

0,6840,73365,3236,232,7514,72887,0854,114132,43391,6

0,2521,36673,7542,372,4234,128124,9515,355986,7975,1

0,4631,27175,0440,772,3794,251125,6230,226028,21913,7

0,6211,18675,8839,692,3504,345126,0643,336055,92737,0

0,7721,13278,7340,132,2534,300127,6056,826148,93593,2

0,2621,65583,2446,162,1263,836163,2716,927892,61083,1

0,4551,50683,5545,012,1183,925163,4732,197904,82056,5

0,5961,39182,9043,392,1344,049163,1145,437884,52893,2

0,7151,30182,7942,302,1384,133163,0558,117881,73692,0

0,2491,69583,7546,202,1123,833176,5316,928536,51083,3

0,4291,53583,5745,032,1173,922176,4332,198531,72056,7

0,5741,44183,9343,942,1084,007176,6745,728546,22914,9

0,6831,33883,3242,842,1244,092176,2958,418525,13715,6

Bang19:Kiem tra lan 21 (W/m2.K)2 (W/m2.K)Cu (W/m.K)dtrongdngoaiKl**t1**Sai s t1 (%)t2**Sai s t2 (%)

4127,0834,33840,0140,01634,000,2358,911,1602,33

4111,71783,83840,0140,01659,740,4137,430,9524,18

4097,82606,03840,0140,01675,540,5236,510,8225,36

4132,43391,63840,0140,01687,540,6416,170,7826,61

5986,7975,13840,0140,01641,230,22710,021,3952,15

6028,21913,73840,0140,01670,310,4199,471,3214,00

6055,92737,03840,0140,01690,260,5658,981,2515,44

6148,93593,23840,0140,016107,650,7068,541,2086,73

7892,61083,13840,0140,01646,940,23211,401,6902,10

7904,82056,53840,0140,01679,330,40610,591,5623,72

7884,52893,23840,0140,016101,880,53610,031,4614,99

7881,73692,03840,0140,016120,070,6479,531,3816,08

8536,51083,33840,0140,01647,430,21911,721,7292,00

8531,72056,73840,0140,01680,690,38310,771,5893,51

8546,22914,93840,0140,016104,810,51510,261,5094,76

8525,13715,63840,0140,016123,810,6179,711,4155,76

Bang 20: He so cap nhiet 1,2 (lap lan 3)t1**t2**tvch1tvch2Prv1Prv2Nu1Nu21 (W/m2.K)2 (W/m2.K)

0,2351,16065,2738,162,7544,51487,0313,264127,3834,4

0,4130,95264,5937,452,7834,59386,7728,394112,21784,2

0,5230,82263,9836,822,8094,66386,5441,534098,42606,6

0,6410,78265,3636,282,7504,72387,0954,134133,13392,6

0,2271,39573,7742,392,4224,126124,9615,355987,3975,2

0,4191,32175,0840,822,3774,247125,6430,236029,11914,1

0,5651,25175,9339,752,3484,338126,0943,356057,22738,1

0,7061,20878,7940,212,2514,294127,6356,846150,43594,5

0,2321,69083,2746,192,1253,833163,2916,927893,31083,3

0,4061,56283,5945,062,1173,920163,4932,207905,92057,0

0,5361,46182,9643,462,1334,044163,1445,457886,02894,1

0,6471,38182,8542,382,1364,127163,0858,137883,33693,4

0,2191,72983,7846,232,1123,830176,5516,928537,21083,5

0,3831,58983,6245,092,1163,918176,4632,208532,92057,3

0,5151,50983,9944,012,1064,001176,7045,748547,82915,9

0,6171,41583,3842,912,1224,086176,3358,438526,83717,0

Bang19:Kiem tra lan 31 (W/m2.K)2 (W/m2.K)Cu (W/m.K)dtrongdngoaiKl***t1***Sai s t1 (%)t2***Sai s t2 (%)

4127,3834,43840,0140,01634,010,2350,011,1600,00

4112,21784,23840,0140,01659,760,4130,010,9520,00

4098,42606,63840,0140,01675,560,5230,010,8220,00

4133,13392,63840,0140,01687,560,6410,010,7810,01

5987,3975,23840,0140,01641,230,2270,001,3950,00

6029,11914,13840,0140,01670,320,4190,011,3210,00

6057,22738,13840,0140,01690,300,5650,011,2510,01

6150,43594,53840,0140,016107,680,7060,011,2080,00

7893,31083,33840,0140,01646,950,2320,011,6900,00

7905,92057,03840,0140,01679,350,4060,011,5620,00

7886,02894,13840,0140,016101,910,5360,011,4610,00

7883,33693,43840,0140,016120,110,6470,011,3800,01

8537,21083,53840,0140,01647,440,2190,011,7290,00

8532,92057,33840,0140,01680,710,3830,011,5890,00

8547,82915,93840,0140,016104,840,5150,011,5090,00

8526,83717,03840,0140,016123,850,6170,011,4140,01

Ta thay sai so a nam di mc 5%,a at yeu cau ve tnh toan 1, 2, Kl* ay ta xem K*** la K* cho n gianBang 11: So lieu Kl1,Kl2 va Kl* theo Re1,Re2G1 (ft3/ph)G2 (ft3/ph)DONG NONGDONG LNH

Re1Kl1Kl*Re2Kl2Kl*

0,20,1619352122,3334,01523866,0234,01

0,2419215136,1759,76777782,6859,76

0,3219081150,1875,561026588,4375,56

0,419490153,3787,561270377,6687,56

0,30,1632576140,2741,23567456,8941,23

0,2433204144,6270,32828365,2770,32

0,3233638167,5390,301081082,5790,30

0,435012185,80107,681365777,62107,68

0,40,1648811137,5746,95601856,0646,95

0,2449081151,3579,35887381,0279,35

0,3248811166,29101,911153690,45101,91

0,448811198,60120,1114185110,53120,11

0,440,1653989128,0247,44601855,3547,44

0,2453989166,4880,71887381,0280,71

0,3254290180,67104,841163374,49104,84

0,453989198,53123,851430192,09123,85

4.2.2 o tha. Anh hng cua dong lanh




Hnh 13: o th K1* va K12 theo Re2 khi lu lng dong nong la 0,44 ft3/phutc. Anh hng cua dong nong





5 BAN LUAN5.1 Ton that nhiet co ang ke khong. Tai sao?T ket qua tnh toan, ta thay ton that nhiet la ang ke, nhiet lng mat i cua dong nong ln hn nhieu lng nhiet dong lanh nhan vao, trong o ton that nhiet ong B cao hn ton that nhiet ong C.Mot so nguyen nhan gay ra: Do s mat nhiet cua dong lu chat ra moi trng ngoai do be mat cach nhiet cua thiet b khong c tot. Lu lng lu chat khong on nh gay mat on nh trong qua trnh truyen nhiet. Mot phan nhiet b gi lai ben trong thanh ong. Be mat ong tao khong ong eu, ro r chat long trong ong. Dong chat long chay trong ong B theo phng ngang lam giam thi gian tiep xuc so vi ong C dan en ton that nhiet ln hn.5.2 Mc o sai so, nguyen nhan gay ra sai so trong luc th nghiem? Bien phap khac phuc? Mc o sai so: Mc o sai so trong bai nay la kha ln. Nguyen nhan gay ra: Lu lng dong nong va dong lanh i vao hai ong khong on nh trong suot qua trnh th nghiem. Dong nong c hoan lu lien tuc lam nhiet o dong vao khong on nh. Ton that nhiet do phai lam nong toan he thong va s trao oi nhiet gia ong vi moi trng ben ngoai. S ro r lu chat qua he thong ong. Gia tr nhiet o tren bang oc khong on nh ma luon bien thien trong mot khoang nhat nh do o sai so do chu quan cua ngi oc la khong the tranh khoi. Sai so do thiet b o lu lng va thiet b o nhiet o Th nghiem ch tien hanh mot lan nen khong the kiem chng mc o lap lai cua ket qua. Cac sai so do viec tra so lieu, quy tron so lieu cung mot phan anh hng en ket qua tnh toan.Ngoai ra, cac thong so nhiet o dung e tnh toan ta dung nhiet o trung bnh nen ket qua khong chnh xac. Bien phap khac phuc: Th nghiem nhiet o lu chat khong qua cao. Cach nhiet that tot cac ong truyen nhiet e am bao ch co s trao oi nhiet gia hai dong nong va lanh qua vach kim loai cua ong truyen nhiet. Tien hanh th nghiem, oc ket qua nhiet o that nhanh e tranh sai so. Tien hanh th nghiem lap nhieu lan trong cung mot che o van hanh e tm ra gia tr chnh xac nhat vi sai so nho nhat.

5.3 So sanh he so truyen nhiet dai thc nghiem K1 vi he so truyen nhiet dai ly thuyet K1*.Da vao o th ta thay Kl ln hn Kl* . Nguyen nhan do lng nhiet ton that van cha bu c sai so trong qua trnh lam th nghiem. Ly do la: Nhiet o trung bnh be mat tnh co sai so so vi thc te, nen Prv ma ta tnh khong thc s chnh xac. ay la qua trnh truyen nhiet phc tap nen khi ta tnh toan ch ke en nhng anh hng chnh: Kieu ong B ( truyen nhiet ngang ) ta a bo qua anh hng chu yeu gay ra sai so o la oi lu t nhien trong dong chay mang, chnh anh hng nay lam thay oi c che cua s truyen nhiet va co khi dan en sai so rat cao, no lam tang cng s truyen nhiet khi dong chay xuat hien xoay roi.Khi lu lng cua lu chat tang th ca Kl va Kl* ca 2 dong nong va lanh eu tang.o th kieu ong B co Re-Kl va Re-Kl* cho dong nong co Kl ln hn Kl* do ton that nhiet trong trng hp vi ong B rat ln.o th kieu ong C co Re-Kl va Re-Kl* cat nhau va dang o th co phan khac nhau la do nhng sai so tren gay ra.S sai khac gia Kl va Kl* v s truyen nhiet con b anh hng cua nhieu yeu to nh lp can ban, nhiet t ben ngoai truyen vao.Quan trong nhat la khi tnh toan Kl* a bo qua be day lp cau ban tren thanh ong truyen nhiet v khong the xac nh c, cho nen co s sai khac ln gia Kl va Kl*

6. PHU LUC6.1 Cac thong so vat ly va oi n v (kg/m3), C(J/kg.o), (W/m.K), (N.s/m2),Pr c tra t bang tra cu Qua trnh c hoc truyen nhiet-truyen khoi,TP.HCM-2012.G(kg/s)= (kg/m3).G(m3/s)

(m2/s)=6.2 Knh thc hnh hoc ac trng cua cac loai ongLu chat chuyen ong qua tiet dien tron: dt = dtr=lOng B:Dong lanh:F = 0,925.(0,026 0,016) = 9,25.10-3 (m2)dt = llanh=dng = 0,016 (m)Dong nong:dt = lnong=dtr = 0,014(m).

Ong C:Dong lanh:

dt =llanh= d2tr - d1ng = 0,026 0,016 = 0,010 (m).Dong nong:

dt = llanh=dtr = 0,014(m)6.3 Tnh nhiet lng QNhiet lng Q1 cua dong nong truyen cho dong lanh va nhiet lng Q2 dong lanh nhan c c tnh theo cong thc:Q = G.C.(tv tr)G: Lu lng cua lu chat, kg/sC: Nhiet dung rieng trung bnh cua lu chat, J/kg.otv, tr: nhiet o vao va ra cua lu chat, 0CThc te dong lanh khong nhan toan bo nhiet lng do dong nong truyen qua ma se co mot phan nhiet b mat mat, ta co can bang nhiet lng:G1.C1.(tv1- tr1) = G2.C2.(tr2 tv2) + QG1, G2: lu lng dong nong va lanh, kg/s.C1, C2: nhiet dung rieng trung bnh cua hai dong nong va dong lanh, J/kg.K.tv1, tR1: nhiet o vao va ra cua dong nong, 0C.tv2, tR2: nhiet o vao va ra cua dong lanh, 0C. Q: Lng nhiet ton that. Tm c nhiet ton that Q6.4 Tnh nhiet o logarit trung bnhTruyen nhiet ngc chieu:

6.5 Tnh he so truyen nhiet dai thc nghiem Kl va he so truyen nhiet dai ly thuyet K1*He so truyen nhiet dai thc nghiem Kl c tnh theo cong thc:Q = Kl.tlog.LL: chieu dai ong, m.Kl: he so truyen nhiet dai, W/m.Ktlog: chenh lech nhiet o trung bnh logarit, KHe so truyen nhiet dai ly thuyet Kl* oi vi tng loai ong c tnh theo cong thc sau:

dng, dtr: ng knh ngoai va trong cua ong truyen nhiet, m.: he so dan nhiet cua ong, W/mK.rb: nhiet tr cua lp cau.db: ng knh lp cau, m. bai nay ta bo qua anh hng cua lp cau.T cac gia tr cua tng che o chay cua tng loai ong tren, lay = 384W/m.K cho ong truyen nhiet lam bang ong o, ta tnh c cac gia tr K* tng ng.6.6 Tnh chuan so Re

Trong o: w : Van toc dong, m/s : o nht ong hoc cua lu chat, m2/s l : Kch thc hnh hoc ac trng va c tnh vi ng knh tng ng dt,m.6.7 Tnh he so cap nhiet 1, 2He so cap nhiet c tnh thong qua cong thc:

: he so dan nhiet cua lu chat, W/m.Kl: kch thc hnh hoc ac trng, m Nu: chuan so Nusselt, c tnh theo cong thc tuy thuoc vao Re:Vi kieu B:5 < Re < 103 Nu = 0,5.Re0,5.Pr0,38(Pr/Prv)0,25103 < Re

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