5.1 Shell-and-Tube Heat Exchangers

Transcription

1 4 5. Shll-and-Tub Ha Exchangrs Th ms cn yp f ha xchangr n ndusral applcans s shll-and-ub ha xchangrs. Th xchangrs xhb mr han 65% f h mark shar wh a vary f dsgn xprncs f abu 00 yars. Shll-and ub ha xchangrs prvd ypcally h surfac ara dnsy rangng frm m /m 3 and ar asly cland. Th dsgn cds and sandards ar avalabl n h TEMA (999)-Tubular Exchangr Manufacurrs Asscan. A smpl xchangr, whch nvlvs n shll and n pass, s shwn n Fgur 5.8. Shll nl Tub Shll Tub ul Tub nl Shll sh Baffls Shll ul End channl Fgur 5.8 Schmac f n-shll n-pass (-) shll-and-ub ha xchangr. Baffls In Fgur 5.8, baffls ar placd whn h shll f h ha xchangr frsly suppr h ubs, prvnng ub vbran and saggng, and scndly drc h flw hav a hghr ha ransfr cffcn. Th dsanc bwn w baffls s baffl spacng. Mulpl Passs Shll-and-ub ha xchangrs can hav mulpl passs, such as -, -, -4, -6, and -8 xchangrs, whr h frs numbr dns h numbr f h shlls and h scnd numbr dns h numbr f passs. An dd numbr f ub passs s sldm usd xcp h - xchangr. A - shll-and-ub ha xchangr s llusrad n Fgur 5.9.

2 4 Tub ul Pass parn Shll nl Tub Shll End channl Baffls Tub nl Shll ul Fgur 5.9 Schmac f n-shll w-pass (-) shll-and-ub ha xchangr. L B s Fgur 5.0 mnsns f - shll-and-ub ha xchangr mnsns f Shll-and-Tub Ha Exchangr Sm f h fllwng dmnsns ar pcurd n Fgur 5.0. L ub lngh N numbr f ub N numbr f pass p s Shll nsd damr N b numbr f baffl B baffl spacng Th baffl spacng s band L B (5.8) N + b

3 43 Shll-Sd Tub Layu Fgur 5. shws a crss scn f bh a squar and rangular pch layus. Th ub pch P and h claranc C bwn adjacn ubs ar bh dfnd. Equan (5.30) f h quvaln damr s rwrn hr fr cnvnnc 4A c (5.9) P had Frm Fgur 5., h quvaln damr fr h squar pch layu s 4 ( P πd 4) (5.30a) πd Frm Fgur 5., h quvaln damr fr h rangular pch layu s 3P πd (5.30b) πd Th crss flw ara f h shll C B A c s dfnd as s A c (5.3) PT d d Flw d C P d C P (a) (b) Fgur 5. (a) Squar-pch layu, (b) rangular-pch layu. Th damr ra d r s dfnd by d d r (5.3) d Sm damr ras fr nmnal pp szs ar llusrad n Tabl C.6 n Appndx C. Th ub pch ra P r s dfnd by

4 44 P P r (5.33) d Th ub claranc C s band frm Fgur 5.. C P d (5.34) Th numbr f ub N can b prdcd n far apprxman wh h shll nsd damr s. N π 4 (5.35) s ( CTP) ShadAra whr CTP s h ub cun cnsan ha accuns fr h ncmpl cvrag f h shll damr by h ubs, du ncssary claranc bwn h shll and h ur ub crcl and ub mssns du ub pass lans fr mulpl pass dsgn []. CTP 0.93 fr n-pass xchangr CTP 0.9 fr w-pass xchangr (5.36) CTP 0.85 fr hr-pass xchangr ShadAra CL (5.37) P whr CL s h ub layu cnsan. CL fr squar-pch layu (5.38) CL sn(60 ) fr rangular-pch layu Pluggng Equan (5.37) n (5.35) gvs N π CTP π CTP s s 4 CL P 4 CL Pr d (5.39) Tabl 5. Suary f shll-and-ub ha xchangrs scrpn Equan q m& c p( T T ) (5.40) Basc Equans m& c T T (5.4) ( ) q p Ha ransfr aras f h nnr and ur surfacs f an nnr pp A A π d N L π d N L (5.4a) (5.4b)

5 45 Ovrall Ha Transfr Cffcn U h A A d ln d + + πkl h A (5.43) Tub sd ρu md md & Rynlds numbr R µ A µ Lamnar flw (R < 300) A c Nu πd 4 hd k N N f p c 3 d R Pr µ.86 L µ s 0.4 (5.44) (5.44a) (5.45) 0.48 < Pr < 6,700 µ < 9.75 µ s < ( ) Us Nu f Nu < Turbuln flw (R > 300) Nu hd k f ( f / )( R 000) +.7 Pr 3 ( f / ) ( Pr ) (5.46) Pr < R < 5 0 [4] Frcn facr f (.58 ln( R ) 3.8) (5.47) Shll sd Squar pch layu (Fgur 5.) 4 ( P πd 4) (5.48a) πd Trangular pch layu 3P πd (Fgur 5.) (5.48b) πd Crss flw ara sc B (5.49) A c P ρu m m & Rynlds numbr R µ A µ (5.50) c

6 46 Nussl numbr ε-ntu Mhd h Nu 0.36 R k f 000 <R < x Pr 3 µ µ s 0.4 (5.5) Ha ransfr un NTU (NTU) ( mc & p ) mn Capacy ra Effcvnss On shll (, 4,.. passs) C r U A ( mc & p ) mn ( mc & p ) max (5.5) (5.53) ε + C r + [ ] r ( ) ( ) + xp NTU + Cr + Cr xp NTU ( + C ) (5.54) NTU NTU N p E E + ε ( + Cr ) whr E + C Ha ransfr un (NTU) NTU ( + Cr ) ln Effcvnss ( ) r ( m& c )( T T ) ( mc & ) ( T T ) Ha ransfr ra ( mc & ) ( T T ) p ( m& c )( T T ) ( mc & ) ( T T ) p (5.55) q p p ε q (5.56) max mn q p mn ε (5.57) mn Tub Sd Prssur rp Prssur drp f L + ρ P 4 N p v (5.58) d Lamnar flw Turbuln flw ( ( ) ) Shll Sd Prssur rp f 6 R (5.59) f.58 ln R 3.8 (5.60)

7 47 P f s ( N +) ρ v b ( ln( )) f xp R s (5.6) (5.6)

8 48 Exampl 5. Mnaur Shll-and-Tub Ha Exchangr A mnaur shll-and-ub ha xchangr s dsgnd cl ngn l n an ngn wh h ngn clan (50% hyln glycl). Th ngn l a a flw ra f 0.3 kg/s nrs h xchangr a 0 C and lavs a 5 C. Th 50% hyln glycl a a ra f 0.47 kg/s nrs a 90 C. Th ub maral s Cr ally (k w 4.7 W/mK). Fulng facrs f 0.76x0-3 m K/W fr ngn l and 0.353x0-3 m K/W fr 50% hyln glycl ar spcfd. Ru h ngn l hrugh h ubs. Th prmssbl maxmum prssur drp n ach sd s 0 kpa. Th vlum f h xchangr s rqurd b mnmzd. Snc h xchangr s cusm dsgnd, h ub sz can b smallr han NPS /8 (N 6 ) ha s h smalls sz n Tabl C.6 n Appndx C, whrn h ub pch ra f.5 and h damr ra f.3 can b appld. sgn h shll-and-ub ha xchangr. Fgur E5.. Shll and ub ha xchangr MahCA frma slun: sgn cncp s dvlp a MahCA mdlng fr a mnaur shll-and-ub ha xchangr and hn sk h slun by rang h calculans by varyng h paramrs sasfy h dsgn rqurmns. I s rmndd ha h dsgn rqurmns ar h ngn l ul mpraur lss han 5 C and h prssur drp lss han 0 kpa n ach sd f h fluds. Th prprs f ngn l and hyln glycl ar band usng h avrag mpraurs frm Tabl C.5 n Appndx C. T ( 0 C + 5 C ) ( 90 C + 00 C) l : 7.5 C T cl : 95 C (E5..)

9 49 Engn l (subscrp )-ub sd 50% Ehyln glycl (subscrp )-shll sd ρ : 88 kg ρ : 00 kg m 3 m 3 c p : 307 J c kg K p : 3650 J kg K (E5..) k : 0.35 W k m K : 0.44 W m K µ.07 0 N s : µ N s : m m Pr : 75 Pr : 6.6 Th hrmal cnducvy fr h ub maral (Chrmum ally) s gvn k w : 4.7 W m K (E5..3) Gvn nfrman: Th nl mpraurs ar gvn as T : 0 C T : 90 C Th mass flw ras ar gvn as md : 0.3 kg md s : 0.47 kg s Th fulng facrs fr ngn l and 50% hyln glycl ar gvn as R f m K : R W f : m K W (E5..4) (E.5..5) (E5..6) sgn rqurmn: Th ngn l ul mpraur mus b lss han 5 C. T 5 C (E5..7) Th prssur drp n ach sd mus b P 0kPa (E5..8)

10 50 sgn paramrs b sugh by rans Inally, sma h fllwng bxd paramrs and hn ra h calculans wh dffrn valus ward h dsgn rqurmns. s :.0n Shll nsd damr s 50.8 L : 5n Tub lngh L 38 d : 8 n Tub usd damr d 3.75 (E5..9) (E5..0) (E5..) Th damr ra (d r d /d ) s gvn as suggsd n h prblm dscrpn. d r :.3 d : d d d.44 r (E5..) Th ub pch ra (P r P /d ) s gvn as suggsd n h prblm dscrpn. P r :.5 (E5..3) Th ub pch s hn band frm Equan (5.33). P : P r d (E5..4) Th baffl spacng s assumd and may b rad, and h baffl numbr frm Equan (5.8) s dfnd. 8 B : 8 n B 5.4 (E5..5) L N b : B N b 4 Th numbr f passs s dfnd by (E5..6) N p : (E5..7) Th ub claranc C s band frm Fgur 5. as C : P d C (E5..8)

11 5 Frm Equan (5.36), h ub cun calculan cnsans (CTP) up hr-passs ar gvn CTP : 0.93 f N p 0.9 f N p 0.85 hrws (E5..9) Frm Equan (5.38), h ub layu cnsan (CL) fr a rangular-pch layu s gvn by CL: (E5..0) Th numbr f ubs N s smad usng Equan (5.39) and rundd ff n pracc. N ha h numbr f ubs n h shll nsd damr dfnd arlr ndcas h cmpacnss f a mnaur xchangr. A 53-ub xchangr n a.5-nch shll usd damr s crcally avalabl fr a -nch shll damr. ( ) N ub s, d, P r π CTP s : N 4 CL ub s, d, P r P r d ( ( )) N : rund N ub s, d, P r N 38 ( ) (E5..) (E5..) Tub sd (Engn l) Th crssflw ara, vlcy and Rynlds numbr ar dfnd as π d N A c : 4 N p A c m md v : ρ A c v 0.43 m s ρ v d R : µ R (E5..3) (E5..4) (E5..5) Th Rynlds numbr ndcas vry lamnar flw. Th vlcy n h ubs appars accpabl whn cnsdrng a rasnabl rang f m/s n Tabl 5.4 fr h ngn l.

12 5 Th frcn facr s drmnd aumacally whhr s hr lamnar r urbuln usng h fllwng prgram as ( ) : (.58 ln( R ) 3.8 ) f R 6 hrws R f R > 300 (E5..6) Th Nussl numbr fr urbuln r lamnar flw s dfnd usng Equans (5.45) and (5.46) wh assumng ha µ changs mdraly wh mpraur. Th cnvcn ha ransfr cffcn s hn band. ( ) Nu h, L, R, Pr : f( R ).86 ( R 000) Pr f R 0.5 > 300 f( R ) Pr h R Pr L 3 hrws (E5..7) ( ) Nu : Nu d, L, R, Pr Nu (E5..8) Nu k h : h d W m K (E5..9) Shll sd (50% hyln glycl) Th fr-flw ara s band usng Equan (5.3) and h vlcy n h shll s als calculad s C B A c : A P c m (E5..30) md v : v ρ A.786 m c s (E5..3)

13 53 Th vlcy f.786 m/s n h shll s accpabl bcaus h rasnabl rang f..4 m/s fr h smlar flud shws n Tabl 5.4. Th quvaln damr fr a rangular pch s gvn n Equan (5.48b) as P 3 π d 4 8 : 4 π d.95 (E5..3) ρ v R : R µ (E5..33) Th Nussl numbr s gvn n Equan (5.5) and h ha ransfr cffcn s band Nu : 0.36 R Pr (E5..34) Nu k h : h W m K (E5..35) Th al ha ransfr aras fr bh fluds ar band as A : π d L N A 0.403m A : π d L N A 0.54 m (E5..36) (E5..37) Th vrall ha ransfr cffcn s calculad usng Equan (5.43) wh h fulng facrs as A U : U d W ln m K R f d R f h A A π k w L A h A (E5..38)

14 54 ε -NTU mhd Th ha capacs fr bh fluds ar dfnd and hn h mnmum and maxmum ha capacs ar band usng h MahCA bul-n funcns as C : md c p C W K (E5..39) C : md c p C W K ( ) ( ) C mn : mn C, C C max : max C, C (E5..40) (E5..4) Th ha capacy ra s dfnd as C mn C r : C C r max (E5..4) Th numbr f ransfr un s dfnd as U A NTU : NTU 0.07 C mn (E5..43) Th ffcvnss fr shll-and-ub ha xchangr s gv usng Equan (5.54) as NTU NTU : N p (E5..44a) xp NTU ε hx + C r + C + C r : + r ε 0.5 hx 0.8 xp NTU + C r (E5..44b) Usng Equan (5.56), h ffcvnss s xprssd as ε hx ( ) ( ) q C T T q max C mn T T ( ) ( ) C T T C mn T T (E5..45) Th ul mpraurs ar rwrn fr cmparsn wh h ul mpraurs.

15 55 T 0 C T 90 C ( ) C mn T : T ε hx T C T T C (E5..46) ( ) C mn T : T + ε hx T C T T C (E5..47) Th ngn l ul mpraur f C s cls nugh h rqurmn f 05 C. Th ha ransfr ra s band ( ) q : ε hx C mn T T q W (E5..48) Th prssur drps fr bh fluds ar band usng Equans (5.58) and (5.6) as ( ) L f R P : 4 + N d p ρ v P 9.35 kpa (E5..49) ( ) s ( ) P f R N b + ρ : v P 5.4 kpa (E5..50) Bh h prssur drps calculad ar lss han h rqurmn f 0 kpa. Th ran bwn Equans (E5..9) and (E5..46) s rmnad. Th surfac dnsy β fr h ngn l sd s band usng h rlanshp f h ha ransfr ara vr h vlum f h xchangr. A β : β m π s m 3 4 L (E5..5) Suary f h dsgn f h mnaur shll-and-ub ha xchangr Gvn nfrman T 0 C ngn l nl mpraur T 90 C 50% hyln glycl nl mpraur

16 56 md md 0.3 kg mass flw ra f ngn l s 0.47 kg mass flw ra f 50% hyln glycl s R f m K fulng facr f ngn l W R f m K fulng facr f 50% hyln glycl W Rqurmns fr h xchangr T 5 C P 0kPa Engn ul mpraur Prssur drp n bh sds sgn band N p numbr f passs s d 50.8 shll nsd damr s n 3.75 ub ur damr d.44 ub nnr damr L 38 ub lngh L 5n N 38 numbr f ub C B ub claranc 5.4 baffl spacng B n N b 4 numbr f baffl T T q C ngn l ul mpraur C 50% hyln glycl ul mpraur.895 kw ha ransfr ra β 679 m surfac dnsy m 3 P 9.35 kpa prssur drp fr ngn l

17 57 P 5.4 kpa prssur drp fr 50% hyln glycl Th dsgn sasfs h rqurmns. Prblms (crrcd) Shll-and-Tub Ha Exchangr 5.3 A mnaur shll-and-ub ha xchangr s dsgnd cl glycrn wh cld war. Th glycrn a a flw ra f 0.5 kg/s nrs h xchangr a 60 C and lavs a 50 C. Th war a a ra f 0.54 kg/s nrs a 8 C, whch s shwn n Fgur P5.3. Th ub maral s Cr ally (k w 60.5 W/mK). Fulng facrs f 0.53x0-3 m K/W fr war and 0.335x0-3 m K/W fr glycrn ar spcfd. Ru h glycrn hrugh h ubs. Th prmssbl maxmum prssur drp n ach sd s 30 kpa. Th vlum f h xchangr s rqurd b mnmzd. Snc h xchangr s cusm dsgnd, h ub sz may b smallr han NPS /8 (N 6 ) ha s h smalls sz n Tabl C.6 n Appndx C, whrn h ub pch ra f.5 and h damr ra f.3 can b appld. sgn h shll-and-ub ha xchangr. Fgur P5.3 Shll-and ub ha xchangr