Thiet Bi Truyen Nhiet

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<ul><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 1/31</p><p>.</p><p>1</p><p>baoduongcokhi.com</p><p>THIT B TRUYN NHIT.</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 2/31</p><p>.</p><p>2</p><p>THIT B TRUYN NHIT.1. Gii thiu chung:</p><p>Truyn nhit l qu trnh vn chuyn nhit t mt lu th ny sang lu th khc.Qu trnh truyn nhit l qu trnh mt chiu, dng nhit ch truyn t vng c nhit cao sang vng c nhit thp. V vy, s truyn nhit ch xy ra khi c s chnhlch v nhit trong h hay ni cch khc l h tn ti mt gradient nhit . Nnglng c truyn i di dng dng nhit nn khng tho trc tip gi tr nhitlng m xc nh thng qua i lng vt l c tho c l nhit .</p><p>S phn b nhit v gi tr ca dng nhit(lng nhit truyn qua mt n vdin tch b mt trong mt n v thi gian) l nhng vn quan tm hng u trongnghin cu v thit k cc thit b trao i nhit. Cc phn tch v qu trnh truynnhit l iu ct li quyt nh kch thc v kt cu ca thit b t a ra nhnggii php k thut v kinh t cho mt thit b trao i nhit.</p><p>Ngi ta phn bit qu trnh truyn nhit n nh v qu trnh truyn nhitkhng n nh, trong qu trnh truyn nhit n nh, nhit c th thay i theo</p><p>khng gian nhng khng thay i theo thi gian, cn qu trnh truyn nht khng nnh th nhit thay i theo c khng gian v thi gian. Qu trnh truyn nhit nnh ch xy ra trong cc thit b lm vic lin tc, qu trnh truyn nhit khng nnh xy ra trong cc thit b lm vic gin on hoc trong giai on u v cui caqu trnh lin tc.</p><p>Nhit c truyn t vt ny sang vt khc theo cc phng thc sau y:</p><p> Dn nhit: Dn nhit l qu trnh truyn nhit t phn t ny n phn tkhc trong h khi chng tip xc trc tip vi nhau v c nhit khc nhau. Qutrnh ny thng xy ra trong cc vt th rn. Cc phn t c nhit cao hn th dao</p><p>ng mnh, va chm vi cc phn t ln cn v truyn ng nng cho chng. C nhvy , nhit nng c truyn theo mi hng ca vt th. Dn nhit cng xy ra trongmi trng kh v lng nu cht kh v lng trng thi ng yn hay chuyn ngdng.</p><p>i lu nhit: i lu nhit l hin tng truyn nhit do cc phn t khhoc lng i ch cho nhau. Si ch l do c s chnh lch v khi lng ring dos khc nhau v nhit gia cc phn t hoc do cc tc ng chc nh bm,qut, khuy...</p><p>Bc x nhit: Bc x nhit l qu trnh truyn nht bng sng in t, ngha</p><p>l nhit nng bin thnh cc tia bc x ri truyn i trong mi trng, khi gp vt thcn, mt phn nng lng t cc tia bc xai c vt hp th chuyn thnh nhitnng, mt phn b phn x trli v mt phn i xuyn qua vt th.</p><p>Trong thc t, truyn nhit l nt qu trnh phc tp, khng xy ra vi mtphng thc duy nht no m lun xy ra ng thi 2 hoc 3 phng thc trn. Khixem xt, nghin cu mt qu trnh truyn nhit, tu tng trng hp c th, nu nhhng ca mt phng thc no khng ng k so vi ton b qu trnh th ta cth b qua.</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 3/31</p><p>.</p><p>3</p><p>2. Cc nh lut v truyn nhit.</p><p>2.1 Truyn nhit theo phng thc dn nhit qua b mt vch :</p><p>2.1.1 nh lut Fourier v dn nhit :</p><p>Qu trnh dn nhit tun theo nh lut Fourier: Mt nguyn t nhit lng dQtruyn qua mt nguyn t b mt dA, trong khong thi gian d t l vi gradient</p><p>nhit , vi i lng b mt v thi gian, ngha l:</p><p>.... ddAdn</p><p>dtdQ = [J].</p><p>Vi : dn nhit (W/m.0K).</p><p>Q: lng nhit trao i (J).</p><p>A: din tch b mt vung gc vi dng nhit truyn (m2).</p><p>n: khong cch (m).</p><p>Du () v phi ca phng trnh chng t l dng nhit bin i theo chiugim nhit .Gi s lng nhit truyn khng ph thuc vo thi gian ta c:</p><p> Lng nhit truyn i:</p><p>dAn</p><p>dQ ..</p><p>=</p><p> .</p><p> Dng nhit truyn qua mt n v din tch b mt :</p><p>..ndA</p><p>dQ</p><p>==</p><p>2.1.2 Dn nhit qua vch phng:</p><p> Dn nhit qua vch phng mt lp:</p><p>Xt qu trnh dn nhit qua vch phng, ng nht. Theo nh lut Fourier ta c:</p><p> Lu lng nhit truyn qua vch :</p><p>eAQ 21..</p><p>= </p><p> Dng nhit truyn qua mt n v din tch b mt :</p><p>m</p><p>edAdQ</p><p>== . Vi R = e/m.</p><p>Vi e: chiu dy ca vch (m).</p><p>R: nhit trca vch (m2.0K/W).</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 4/31</p><p>.</p><p>4</p><p> Dn nhit qua vch phng nhiu lp:</p><p>=i</p><p>ieR</p><p>Vi e , : b dy v dn nhit vch th i.</p><p>Nh vy: Lu lng nhit trao i cng ln nu t c mt hoc tt c cc yu tsau y:</p><p>- B mt truyn nhit ln.</p><p>- Chnh lch nhit giu cc lu th ln.</p><p>- Trnhit nh.</p><p>2.1.3 Dn nhit qua vch ng:</p><p>Xt qu trnh dn nhit qua mt ng kim loi c ng knh ngoi de, ngknh trong d, dn nhit .</p><p> Vi mt nguyn t chiu di l ca ng, lu lng nhit trao i c tnh nh sau:</p><p>i</p><p>e</p><p>ei</p><p>d</p><p>dLn</p><p>Q)(..2 </p><p>= .</p><p> Dng nhit truyn qua mt n v din tch b mt :</p><p>i</p><p>ee</p><p>ei</p><p>e</p><p>d</p><p>dLn</p><p>dld</p><p>Q</p><p>..2..</p><p>=</p><p>= </p><p>2</p><p>e</p><p>l 1</p><p>e2</p><p>21 n</p><p>e1 en</p><p>21 3 n n+1l</p><p>de</p><p>i edi</p><p>l</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 5/31</p><p>.</p><p>5</p><p> Nhit tr:</p><p>i</p><p>ee</p><p>d</p><p>dLn</p><p>dR .</p><p>.2 = </p><p>Trng hp nhiu vch tr kp :</p><p>+= m</p><p>e</p><p>ei</p><p>m</p><p>e d</p><p>dLn</p><p>d</p><p>dLndR</p><p>..2</p><p>1</p><p>..2</p><p>1</p><p>. .</p><p>2.2 Truyn nhit theo phng thc i lu nhit :</p><p>Cc nh lut v truyn nhit i lu rt phc tp do chng lin quan n chchuyn ng ca dng chy. Ch thung ng vai tr cho trong ng lcca qu trnh trao i nhit, hn na cn lin quan n cc nh lut v dn nhit. Vthc cht qu trnh trao i nhit i lu n thun khng tn ti m lun i km viqu trnh dn nhit, qu trnh ny cn c gi l to nhit i lu. To nhit i luxy ra khi c s trao i nhit gia b mt vt rn vi cht lng chuyn ng, qutrnh ny rt ph bin trong truyn nhit.</p><p>Trao i nhit i lu ph thuc vo rt nhiu yu t nh : nguyn nhn gy rachuyn ng ca cc lu th, s thay i trng thi ca lu th trong qu trnh truynnhit(truyn nhit c chuyn pha hay khng chuyn pha) ch chuyn ng, tnhcht vt l ca cc lu th v hnh dng, kch thc ca b mt trao i nhit.</p><p>Mt cch tng qut, dng nhit trong trng hp trao i nhit i lu c vitnh sau:</p><p>.. </p><p>=</p><p>= hR</p><p>h=R1 : h s cp nhit hay h s mng.</p><p>2.2.1 H s cp nhit trong trng hp trao i nhit khng c sthay i pha:</p><p>H s cp nhit l c trng ca qu trnh trao i nhit i lu nn cng phthuc vo cc yu t lin quan n qu trnh: thng s hnh hc ca thit b, iu kinlm vic v tnh cht dng chy. Do s ph thuc phc tp , khng th thit lpc mt cng thc tng qut xc nh h s cp nhit h m ty tng trng hpc th ngi ta a ra nhng cng thc thc nghim tnh. Cc cng thc ny cxy dng trn cscc chun s sau:</p><p>Trng hp i lu cng bc, h s cp nhit h c suy ra t cng thc sau:Nu = a.Ren.Prm.</p><p>Hoc: St = a.Ren1.Prm1.</p><p>Cc h s: a, n, m c xc nh theo tng trng hp c th.</p><p>Cc chun s: Nu, Re, St c thit lp tng dng nhit.</p><p>Chun s Nusselt: ..</p><p>lhNu = </p><p>h: H s cp nhit.</p><p>l: Kch thc hnh hc c trng ca thit b(m).</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 6/31</p><p>.</p><p>6</p><p>: h s dn nhit(W/m2.K),</p><p>Chun s Reynolds: ...</p><p>Re</p><p>l= </p><p>l: chiu di hnh hc c trng ca thit b.</p><p>: vn tc trung bnh ca dng chy.</p><p>: khi lng ring ca lu th.: nht ng lc.</p><p>Chun s Re c trng cho ch chuyn ng ca dng chy.</p><p>Re</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 7/31</p><p>.</p><p>7</p><p>lp m lm tng nhit trcp nhit ng thi ngn cn hi tin n b mt truynnhit, lm gim h s cp nhit ca hi.</p><p>H s cp nhit khi qu trnh ngng t ch b khng ch bi trng lc:</p><p>Nu=1.51Re-1/3</p><p>H s cp nhit khi qu trnh ngng t b khng ch bi ma st gia 2 pha lng-hi: Nu=0.22Re0.6Pr0.4</p><p>i vi qu trnh ngng t hon ton: =0.5(1+V</p><p>L</p><p>)</p><p>v, l: Khi lng ring ca hi v lng ngng t.</p><p>H s cp nhit ca hi:</p><p>Nu=0.22Re0.6Pr1/3</p><p>2.3 Truyn nhit theo phng thc bc x nhit:</p><p>Tt c cc vt th c nhit cao hn 0K u c th pht ra nhng tia nng</p><p>lng di dng tia bc x v lan truyn trong khng gian xung quanh vt th. Nichung tia bc x l do kt qu ca s bin i cc dng nng lng khc m thnh,trong ch yu l do s bin i nng lng. Mc bin i ny c xc nhbng trng thi nhit ca vt th, th hin bng nhit ca n.</p><p>Ngi ta chia ra bn loi vt th sau:</p><p>Vt en tuyt i: Tt c cc tia bc xu c vt th hp th hon ton.</p><p>Vt trng tuyt i: Tt c cc tia bc xu c phn x hon ton.</p><p>Vt trong sut: Tt c cc tia bc xu xuyn qua vt.</p><p>Vt th xm: Vt th ch hp th mt phn tia bc x vi mi bc sng.Trong thc t ch c mt vt th duy nht l vt xm, 3 vt th cn li khng tn ti.</p><p>Cc nh lut cbn ca bcx:</p><p>a. nh lut Stphan-Bnzman.</p><p>E0=C0(100</p><p>T)4</p><p>Trong : E0: kh nng bc x ca vt en tuyt i(W/m2).</p><p>C0: H s bc x ca vt en tuyt i, gi tr ca n l 5.7W/m2(0K)4</p><p>Ni mt cch cht ch th nh lut Stphan-Bnzman chng i vi vt entuyt i. Tuy nhin, bng thc nghim, Stphan v cc nh nghin cu khc in kt lun l c thng dung nh lut cho vt xm v phng trnh c dng:</p><p>E=C(100</p><p>T)4</p><p>H s bc x C ph thuc vo loi vt th, trng thi b mt v nhit ca vtth. Gi tr ca n c xc nh bng thc nghim.</p><p>b. nh lut Kichp:</p><p>nh lut kichp thit lp quan h gia kh nng bc x v hng s bc x cavt th.</p><p>A</p><p>E=E0</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 8/31</p><p>.</p><p>8</p><p>Vi A: Kh nng hp th ca vt th.</p><p>Ni dung nh lut: T s gia kh nng bc x v kh nng hp th ca mi vtth l ging nhau v bng kh nng bc x ca vt en tuyt i cuing nhit vch ph thuc vo nhit .</p><p>2.4 H s truyn nhit chung :</p><p>2.4.1 Trng hp truyn nhit qua vch phng:</p><p>Xt qu trnh truyn nhit t lu th nng(lu th 1) c nhit cao, sang luth lnh (lu th 2) c nhit thp.</p><p>Dng nhit:</p><p>=</p><p>=</p><p>++</p><p>= .</p><p>11</p><p>21</p><p>21P</p><p>P</p><p>P</p><p>UR</p><p>h</p><p>e</p><p>h</p><p>.</p><p>Vi R l tng nhit tr.- R1: Nhit trca qu trnh cp nhit t lu th 1 n tng.</p><p>- Rp: Nhit trca tng.</p><p>- R2: Nhit trca qu trnh cp nhit t tng n lu th 2.</p><p>- Up: L h s truyn nhit chung.</p><p>Ta c:21</p><p>111</p><p>h</p><p>e</p><p>hUR</p><p>P</p><p>P</p><p>P</p><p>++==</p><p>.=R1+Rp+R2</p><p>Trong qu trnh truyn nhit, cc cn bn bm trn b ca hai mt vch gy ramt nhit trRS.</p><p>RS = RS1 + RS2.</p><p>Khi h s truyn nhit trong trng hp vch c bm cn c tnh nh sau:</p><p>S</p><p>PS</p><p>RUU</p><p>+=11</p><p>=R1+Rp+R2+Rs</p><p>21 P1P2</p><p>Lu th 1</p><p>eP</p><p>P</p><p>1/h1</p><p>1/h2</p><p>Lu th 2</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 9/31</p><p>.</p><p>9</p><p>2.4.2 Trng hp truyn nhit qua tng ng:</p><p>Dng nhit qua thnh ng, c ng knh ngoi de, ng knh trong d.</p><p>).(1</p><p>..2</p><p>.</p><p>1.. eiPei</p><p>e</p><p>ePe</p><p>i</p><p>e</p><p>P</p><p>e</p><p>PePi</p><p>e</p><p>i</p><p>i</p><p>Pii</p><p>e</p><p>UR</p><p>hd</p><p>dLn</p><p>d</p><p>d</p><p>d</p><p>h</p><p>ld</p><p>Q</p><p>=</p><p>=</p><p>=</p><p>=</p><p>=</p><p>= .</p><p>Vi he : h s mng ngoi ng.</p><p>hi : h s mng trong ng.</p><p>H s truyn nhit chung c tnh nh sau :</p><p>ei</p><p>e</p><p>P</p><p>e</p><p>ieP hd</p><p>dLn</p><p>d</p><p>hU</p><p>1.</p><p>.2</p><p>11++=</p><p>.</p><p>Nhit trca lp cn RS:</p><p>Se</p><p>i</p><p>e</p><p>SiS Rd</p><p>dRR += . .</p><p>RSi, RSe : nhit trdo lp cn ng bn trong v ngoi ng.</p><p>H s truyn nhit khi kn trng hp bm cn US:</p><p>.11</p><p>S</p><p>PS</p><p>RUU</p><p>+= .</p><p>2.5 Cc phng trnh cbn tnh ton lng nhit trao i gia hai lu th quathit b trao i nhit:</p><p> Phng trnh cn bng nhit: lng nhit ca lu th nng truyn i bng lngnhit ca lu th lnh nhn c (b qua tn tht nhit ra mi trng).</p><p>Q = M.CP.(T1 T2) = m.cP.(t2 t1).</p><p>Vi M, m: lu lng khi lng ca lu th nng v lnh.</p><p>CP,cP : nhit dung ring ng p ca lu th nng v lnh.</p><p>T1,T2: nhit vo v ra khi thit b trao i nhit ca lu th nng.</p><p>t1,t2: nhit vo v ra khi thit b trao i nhit ca lu th lnh.Hoc:</p><p>e</p><p>de</p><p>Pi Pedi</p><p>i</p><p>l</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 10/31</p><p>.</p><p>10</p><p>.)(</p><p>)(</p><p>21</p><p>12</p><p>2</p><p>1</p><p>T</p><p>t</p><p>TT</p><p>tt</p><p>C</p><p>C</p><p>=</p><p>= </p><p>Vi: C = M.CP gi l nhit dung lu lng khi lng.</p><p> Phng trnh truyn nhit: nhit lng trao i gia hai lu th thng qua mtnguyn t b mt dA c tnh nh sau:</p><p>dQ = U.(t1 t2).dA.Vi U: h s truyn nhit (W/m2.0K).</p><p>(t1 t2) = t: chnh lch nhit gia hai lu th trn b mt nguyn t dA.</p><p>Ly tch phn theo din tch b mt A phng trnh trn. Ta c:</p><p> =A</p><p>dAtUQ .. .</p><p>S bin thin ca U theo nhit l khng ng k (xem U = Const). Khi :</p><p>AtUQ ..= .</p><p>:t gi l chnh lch nhit trung bnh gia hai lu th (LMTD). Gi trt xc nh tu thuc vo chiu chuyn ng cc lu th v nhit dung lu lng</p><p>khi lng ca cht lng.</p><p> Trng hp hai lu th chuyn ng cng chiu:</p><p>)(</p><p>)()()(</p><p>22</p><p>11</p><p>2211</p><p>tT</p><p>tTLn</p><p>tTtTtcc</p><p>= </p><p> Trng hp hai lu th chuyn ng ngc chiu:</p><p>A</p><p>C &lt; c</p><p>t2</p><p>t1</p><p>T1</p><p>T2</p><p>C &gt; c</p><p>A</p><p>T1</p><p>t2</p><p>t1</p><p>T2</p><p>A</p><p>MC&lt; mcT1</p><p>t2</p><p>t1</p><p>T2</p><p>T1</p><p>t2</p><p>t1</p><p>T2</p><p>MC&gt; mc</p><p>A</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 11/31</p><p>.</p><p>11</p><p>)(</p><p>)()()(</p><p>12</p><p>21</p><p>1221</p><p>tT</p><p>tTLn</p><p>tTtTtnc</p><p>= .</p><p>* Xt quan h nhit ra ca cc lu th v b mt truyn nhit:</p><p>Kho st phng trnh cn bng nhit v phng trnh truyn nhit, ngi ta </p><p>v ra ng c tnh mi quan h gia cc nhit v b mt truyn nhit T-A nhhnh trn. T th trn ta thy rng, trong chuyn ng xui chiu, nhit ra calu th ngui lun b gii hn v lun nh hn nhit u ra ca lu cht nng,trong khi i vi trng hp chuyn ng ngc chiu th c th ln hn.</p><p> Mi quan h gia LMTDCC v LMTDNC:</p><p>LMTDNC = F. LMTDCC.</p><p>i vi cc thit b trao i nhit kiu ng chm, gi tr F xc nh bng cngthc (thit b 1 passe trong ng, 2 passe ngoi ng) hay th thc nghim ph thucvo gi tr R v E nh sau:</p><p>12</p><p>21</p><p>tt</p><p>TTR</p><p>= .</p><p>11</p><p>12</p><p>tT</p><p>ttE</p><p>= .</p><p>Cng vi mt thit b v cc dng lu th nh nhau, nu cc lu th chuyn ngngc chiu c gi tr DTLM ln hn chuyn ng cng chiu.</p><p>1</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 12/31</p><p>.</p><p>12</p><p>- H s cp nhit tng 1.74 ln.</p><p>- Tn tht p sut tng ln 8 ln.</p><p>Nh vy, vic thay i s passe trong ng cho php iu chnh h s cp nhittrong ng, tuy nhin vn cn hn ch khi tn tht p sut ca lu th trong ng khkhng ch.</p><p>Tng t, h s cp nhit bn ngoi ng c iu chnh bng cch thay i tit</p><p>din dng chy ca lu thi trong v bc(shell side) khi thay i ng knh vbc, bc ng v lp t cc tm chn dc theo chm ng. Lu thi ngoi ng khith chuyn ng song song vi cc tm chn, khi th chuyn ng dc theo chm ngqua khong trng gia tm chn v than thit b. Vic thay i lin tc hng cadng chy nh vy cho php tng cng ng k hiu qu truyn nhit v tit dinca dng chy thay i, vn tc lu th tng ln, ch chy ri dt c. Tntht p sut tng khi tng s tm chn trong thit b cng ln v khong trng giathn thit b v tm chn cng nh.</p><p>Vn tc cc lu th trong thit b cng b khng ch do cc qui tc v an ton</p><p>cho thit b nh xi mn chc v cc chn ng trong thit b. Lu lng c khilng ring cng nh, vn tc cho php i trong thit b trao i nhit cng ln</p><p>- Cht lng:</p><p>i trong ng: 1-2.5m/s</p><p>i ngoi ng: 0.3-1m/s</p><p>- Cht kh:</p><p> p sut chn khng: 45-80m/s</p><p> p sut kh quyn 12-30m/s.</p><p> p sut cao 6-12m/s.Khi cc thng s hnh hc ca thit b c cnh, h s cp nhit cn ph</p><p>thuc vo lu lng ca dng. Khi lu thang chy ri, nu tng lu lng ln10%, h s cp nhit trong ng tng khong 8%, trong khi tn tht p sut tngkhong 20%. Nu gim ng k lu lng c th ko theo s thay i ch chuynng ca dng chy v gim mnh h s cp nhit.</p><p>Mt yu t na cng nh hng ln n h s cp nhit l tnh cht vt l calu th: nht, dn nhit v nhit dung ring. Trong , nht c tm quantrng ln nht trong bi ton trao i nhit i lu. i vi nhng cht lng c </p><p>nht ln, ch chy ri kh t c v v vy h s cp nhit trong trng hp nythng thp. Ngc li, h s cp nhit t l thun vi dn nhit ca cht lng.</p><p>Kh nng ng cn ca lu th cng l mt nhn t lm gim h s cp nhit.Tu thuc vo tng lu th v iu kin lm vic( thi gian, vn tc chuyn ng,nhit ...) m lp cn bm ln b mt truyn nhit nhiu hay t. Lp cn ny ngthi lm tng tn tht p sut khi cc lu th chuyn ng trong thit b. Qu trnh tocn khng khng chc, v vy khi thit k lun phi tnh sao cho h s truynnhit cao hn so vi yu cu b vo phn nhit trgy ra cho cc lp cn ny.Ngoi ra, khi la chn cng ngh cng cn phi tnh n kh nng ng cn ca cclu thm bo kh nng tho d, lm sch.</p><p>Cng nh phn tch phn trc, chiu chuyn ng ca lu th cng nhhng rt ln n hiu qu trao i nhit. Vi cng h s truyn nhit v nhit ca</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 13/31</p><p>.</p><p>13</p><p>cc lu th c xc nh, nu cc lu th chuyn ng ngc chiu th gi trLMTD(Log mean temperature difference) tnh c ln hn, v vy b mt truyn</p><p>nhit nh hncc</p><p>nc</p><p>LMTD</p><p>LMTD=</p><p>nc</p><p>cc</p><p>UA</p><p>UA=</p><p>nc</p><p>cc</p><p>A</p><p>A&gt;1. Do vy cch b tr lu th chuyn ng</p><p>ngc chiu c li hn.</p><p>III. PHN LOI THIT B TRAO I NHIT.</p><p>1 Yu cu i vi mt thit b trao i nhit:Mt thit b trao i nhit tt v mt thit k cng nh vn hnh phi cn p</p><p>ng nhng nhu cu sau:</p><p> H s trao i nhit cng ln cng tt. Cng mt lng nhit cn trao i, nuh s truyn nhit cng ln th thit b s gim din tch b mt trao i nhit.</p><p> Tn tht p sut i vi cc dng lu cht cng nh cng tt. Khi s gimcng sut ca bm v qut...</p><p> B mt trao i nhit ca thit b phi thit k sao cho t b bm cn bn, d</p><p>lm sch v sa cha. B mt ngn cch gia cc lu cht nng v lnh phi tt, trnh hin tng hai</p><p>lu th ha trn vo nhau.</p><p> Thit b phi bo m an ton khi vn hnh, tui th cao, kt cu n gin dlp rp, gi thnh thp.</p><p>2 .Phn loi v cu to thit b trao i nhit:</p><p>A. Cu to:</p><p>Mt thit b trao i nhit ( heat exchanger) gm c cc b phn chnh sau:</p><p>- V bc (shell).- u chp v bc ( shell cover).</p><p>- Cc ng (tubes).</p><p>- B phn phn phi dng chy ( channel, channel cover, channel nozzle,channel passrib, channel tubesheet).</p><p>- Chm ng (tube sheet).</p><p>- Cc vch ngn ( baffles).</p><p>- Cc hng vo v ra ( nozzles).</p><p>Mt thit b trao i nhit ( heat exchanger) c chia lm 3 phn chnh sau:Phn u, phn thn v phn ui. Hnh v di y s ch cho ta, hnh dng v cuto ca 3 vng chnh ca 1 heat exchanger.</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 14/31</p><p>.</p><p>14</p><p>B. Phn Loi:</p><p>a. Phn loi theo nguyn l lm vic:</p><p>- Trao i nhit trc tip: Hai lu th tip xc trc tip nhau hoc trn ln vonhau.</p><p>- Trao i nhit gin tip: Truyn nhit gia 2 lu th qua mt b mt phncch.</p><p>- Trao i nhit trn cng mt b mt rn: un nng b mt rn bng mt dng</p><p>ti nhit, sau cho dng ngui i qua b mt vt rn ly nhit. Loi trao inhit ny rt t dng trong cng nghip.</p></li><li><p>7/15/2019 Thiet Bi Truyen Nhiet</p><p> 15/31</p><p>.</p><p>15</p><p>b. Phn loi theo chiu chuyn ng ca lu th:</p><p> Chuyn ng cng chiu: cc lu cht i vo v i ra khi thit bcng mt pha,trong thit b cc lu cht...</p></li></ul>