Nhn xt ca Gio Vin ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................ ........................................................................................

Mc lc Li ni u...............................................................................3 1.1 Khi nim...........................................................................4 1.2 Nguyn tc lm vic v cu to....................................... 4 1.3 L thuyt tnh ton....................................................... 11 1.3.1 Trao i nhit khi khi sy tip xc vi b mt nng11 1.3.2 H thng sy tip xc trong cht lng nng...............15 2 Tnh ton v la chn my sy.........................................17 2.1 Tnh ton thit b sy......................................................17 2.1.1 Yu cu tnh ton.........................................................17 2.1.2 Phn tnh ton..............................................................18 2.2 Chn la my sy............................................................21 2.2.1 C s cho vic chn la...............................................21 2.2.2 Phng php chn.......................................................25 3 Khi nim............................................................................27 4 V Tr ca sng in dng cao tn....................................27 5 Nguyn l lm vic.............................................................27 6 Qu trnh lm nng bng in trng cao tn................29 7 u, nhc im..................................................................30 7.1 u im............................................................................30 7.2 Nhc im......................................................................31 8 ng dng.............................................................................31

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Li ni uNc ta l mt nc c nn nng nghip rt pht trin vi sn lng xut khu nng sn rt ln, trong nm 2011 ring mt hng go th tng lng go xut khu c th t 8 triu tn vi kim ngch t gn 4 t USD. V mt cng on rt quan trng trong sn xut nng nghip l khu bo qun sau thu hoch, trong my sy l mt thit b khng th thiu trong cng vic bo qun nng sn. V vi bi bo co v thit b sy tip xc chng ti hi vng s mang n cho cc bn mt ci nhn khi qut v thit b sy ny. Trong qu trnh thu thp ti liu, nghin cu cng nh bin son khng th thiu nhng sai st, do mong cc bn thng cm v rt hn hnh nhn c nhng ng gp t cc bn.

PHN I3

THIT B SY TIP XC1.1 KHI NIMH thng sy tip xc l mt h thng chuyn dng. Vt liu nhn trc tip bng dn nhit hoc t mt b mt nng hoc t mi trng cht nng. Ngi ta chia h thng sy tip xc thnh hai loi: loi tip xc trong cht lng v loi tip xc b mt.

1.2 NGUYN TC LM VIC V CU TONguyn tc c bn ca thit b sy tip xc l qu trnh gia nhit vt liu sy bang cch cho tip xc trc tip gia vt liu sy vi b mt gia nhit. loi thit b ny b mt gia nhit l cht rn (vch phng, vch tr). Cht ti nhit (hi nng hoc khi l) chuyn ng pha bn kia ca vch. Pha kia ca vch tip xc trc tip vi vt liu sy. Sy tip xc c th p sut mi trng, m bc ra ha vo khng kh mi trng lt vo. Am c ht ra v thi vo mi trng. Sy tip xc vi b mt nng c th tin hnh di p sut kh quyn hay trong chn khng. Khi sy tip xc di p sut kh quyn th lng m thot ra s ha vo khng kh trong mi trng xung quanh, nh vy cn b tr h thng thng gi m bo m v nhit thch hp trong khng gian t thit b sy, p ng tt cho qu trnh sy cng nh iu kin lm vic ca ngi vn hnh. Trng hp sy tip xc trong chn khng lng m thot ra c qut ht ra ngoi. Nh vy cn xy dng bung kn bao bc khng gian cha b mt nng v vt sy ngn khng kh bn ngoi lt vo. Trng hp sy trong cht lng nng (du, cht lng v c, hu c) cht lng cp nhit m thot ra t vt sy xuyn qua cht lng ra ngoi. Cht lng cn c nhit si ln hn nc p sut kh quyn.Trong phng php ny, vt liu sy c nhng ngp vo cht lng nng nh du, cc loi cht lng v c hoc hu c khc. Cht lng ng vai tr cp nhit, m thot ra t vt lieu sy xuyn qua cht lng thot ra ngoi, ha vo khng kh ca khng gian t thit b sy. Trong cng nghip giy v dt may s dng ph bin phng php ny. Trong cng nghip thc phm: cng nghip hp, sy rau qu, dc phm.

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Hnh 1.1. H thng sy kiu trng (trc cn) 1- Thng sy V thit b 4- B phn khuy 5- B phn gt 6- Vt ti 2- C cu cp liu 3-

My sy kiu trc cnTrong kiu ny b mt gia nhit l mt trc rng, mi cht gia nhit l hi nc ngng t bn trong. Vt liu sy l cc loi bt nho nh sa, thc n gia sc. Vt liu sy c vo b mt trc. Trc quay lm vt liu c cn thnh lp mng v c sy kh. Chiu dy lp vt liu khong 1 2 mm. Cng bay hi m trn b mt A = 30 70 kg/m2h ty thuc vo loi vt liu v p sut hi nc bn trong. V d, khi sy sa : 1 = 88 92% ; 2 = 5 10% th A = 50 70 kg/m2h.

Sy tang trng (sy trc ln) (roller dryer)

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Hnh 1.2 . S thit b sy tang trng trc n

Hnh 1 .3. S thit b sy tang trng trc kp

Cc trc rng bng thp quay chm c un nng bn trong bng hi nc p sut cao n 120-170oC. Mt lp mng nguyn liu c tri u ln b mt bn ngoi bng phng php nhng, phun, tri hoc bng cc trc ln np liu ph. Trc khi trc ln hon thnh 1 vng quay (khong 20 giy n 3 pht) sn phm sy c co ra bng li dao tip xc u vi mt trc theo chiu di ca n. Thit b sy c th c 1 trc, 2 trc hoc trc kp. Thit b n trc c s dng rng ri, v chng linh ng, t l din tch b mt trc s dng sy ln, d dng tip cn bo dng v khng c nguy c b h hi do kim loi ri vo gia hai trc. Thit b sy trc c tc sy cao, hiu qu nng lng cao, chng thch hp vi nguyn liu dng st c kch thc cc cu t ln qu mc c th sy phun c. Sy trc ln dng trong sn xut khoai ty dng mnh (flake), ng cc nu sn, mt ng, xp bt, pu r tri cy v sa tch kem (whey). Tuy nhin, do gi thnh trc ln cao v thnh phn nguyn liu nhy cm nhit d b h hi, nn trong sn xut ln chng b thay th bng phng php sy phun.

My sy kiu l quay

Hnh 1.4. Nguyn l lm vic ca l sy giy 1- Chn m 2- Chn kh 3- Bng giy 4- Khng kh nng

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5- Mi trng gia nhit chn

B mt gia nhit l nhng l hnh tr rng. Cht ti nhit l hi nc a vo u trc ny ca l v nc ngng bay ra u trc kia hoc a hi vo v ly nc ngng ra cng mt u trc. Vt liu sy c dng tm mng nh giy, vi; vt lieu p st vo cc l v chuyn ng cng vi l quay nh kiu bng ti. Bng vt lieu (vi, giy) chuyn ng p st vo b mt cc l sy, n c gia nhit v sy kh. Sn phm c cun li thnh cun. Cc l sy quay vi s vng quay 40 50 v/ph. Khi sy giy, m bo giy khng b t ngi ta phi dng bng bang chn len cng chuyn ng p st vi bng giy.

Sy bng qu cu nngBung sy c gn vi vt ti quay chm c cha cc qu cu bng s, c lm nng bng khng kh nng, thi vo bung sy. Nguyn liu dng vin, cc c sy ch yu do s dn nhit do s tip xc vi nhng qu cu nng v c dch chuyn qua bung sy bng vt ti, thot ra y. Thi gian sy c kim sot bng tc vt ti v nhit ca nhng qu cu nng.My sy bng chuyn chn khng v k sy chn khng (vacuum band dryer, vacuum shelf dryer)

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Hnh 1.5 : S thit b sy bng chuyn chn khng

Nguyn liu di dng st c tri hoc phun ln 1 bng chuyn thp chy qua 2 trc ln rng trong 1 bung chn khng c p sut 1-70 mmHg. Lc u nguyn liu c sy bng trc ln c lm nng bng hi nc v sau bng ng xon trao i nhit c hi nc lm nng hoc cc thit b cp nhit bc x t pha trn cc bng chuyn. Sn phm sy c lm ngui bng trc ln th 2 c nc lnh trong v c tch ra bng li dao. K sy chn khng gm cc k t trong 1 bung chn khng vi p st 1-70 mmHg. Nguyn liu c t thnh 1 lp mng trn cc khay thp phng c lm cn thn m bo s tip xc tt vi cc k. Hi nc hoc nc nng chy qua cc k cp nhit cho qu trnh sy. Qu trnh sy nhanh v s h hi do nhit n sn phm c hn ch gip cho 2 phng php ny thch hp vi cc nguyn liu nhy cm vi nhit. Tuy nhin, cn cn thn trnh sn phm khi b chy trn cc khay trong cc k sy chn khng v s co ngt lm gim s tip xc gia nguyn liu vi b mt nng c 2 thit b. Chng c gi thnh cao, chi ph vn hnh cao v nng sut thp, c dng ch yu sn xut cc sn phm sy phng (puff dried).

Mt s hnh nh v thit b sy tip xc

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Hnh 1.6. H thng sy kiu l quay 1- L sy 2- Bnh xe nh hng 3- ng dn hi nc 4- Van thi nc ngng 5- Bnh rng tr 6- Bnh rng cn 7- Bng ti vo my sy

H thng sy kiu trng dng sy cc loi bt nho. Vt liu bm vo b mt tr c hm nng. Vt liu nhn nhit bng dn nhit qua lp vt liu dy 1,2 mm v thi m trc tip vo khng gian my. Vt liu kh c tho ra bng h thng dao gt khi b mt trng. Cng bay hi m A = (30-70) kg/m2h. Loi rul sy ti, giy vv, vt liu bm vo cc l sy v cng chuyn ng vi n. Vt liu nhn nhit t l sy c t nng v thi m vo mi trng. Sn phm c cun vo tng cun. Cc l sy quay 40-50 vng/pht. Khi sy giy, giy khng b t, rch ta dng bng kiu chn len p st vo bng giy v cng chuyn ng. Nhn xt: -Sy tip xc: nhit c cung cp bng dn nhit - u im chnh so vi sy i lu : + khng cn thit phi un nng lng ln khng kh trc khi sy do hiu qu nhit cao hn. 10

+ qu trnh sy c th thc hin khng cn s c mt ca oxy nn cc thnh phn d b oxy ho ca nguyn liu c bo v. - Nhu cu nhit ring thng thng l 2000-3000 kJ/kg nc bay hi so vi 4000-10.000 kJ/kg nc bay hi ca my sy i lu. Tuy nhin, thc phm c dn nhit thp, tr thnh kh hn nn kh dn nhit hn trong qu trnh sy, v vy cn phi sy lp mng nhit dn nhanh, trnh gy h hi cho sn phm.

1.3 L THUYT TNH TON1.3.1. Trao i nhit khi khi sy tip xc ( dn nhit) vi b mt nng.

Hnh 1.4 trnh by ng cong nhit v ng cong sy xenlul trn b mt nng vi nhit t = 1300C. Hnh 1.5 cho ta ng cong nhit v ng cong tc sy t = 1170

Hnh 1.7. ng cong nhit v ng cong sy trn mt nng

Hnh 1.8. ng cong tc sy v ng cong nhit

I Nhit 0,8 mm so vi mt nng: II khong cch 0,2 mm III khong cch 0,35 mm; IV khong cch 0,43 mm

Trn th cho thy sau pha hm nng (khong 0,07 0,1 so vi thi gian c qu trnh). Nhit vt liu tng nhanh, sau khong thi gian no tr nn khng i, v sau bt u gim v thi k th hai li nng ln mt ln na. Vic gim nhit l do sc 11

cn nhit tng do s tip xc ca lp di vt liu v b mt nng b ph hoi, v nguyn nhn chnh l chi ph nhit tip xc tin vi qu trnh to nn hi m. Tip xc vi mt truyn nhit gim, lm gim nhit vt liu. Khi lng m ban u ca vt liu cao v nhit b mt tip xc cao(>1000C). Trong giai on th nht, c th trong thi gian ngn, nhit vt liu trc tip tip xc vi mt nng c th t nhit 1000C v xy ra s bc hi ca lng. ng cong nhit xc nhn vic gy ra graien nhit bn trong vt liu hng v b mt nng.

Hnh 1.6 cho trng nhit v m trong vt liu t = 1160C. th cho thy s phn b nhit lp c nhit cao hn tip xc vi mt nng. Nhit thp hn ca vt liu mt thong. c tnh ca trng nhit v m cho thy s ngng t nc bn trong vt liu khng xy ra. Gradien m v nhit l nguyn nhn chnh to thnh hi trong lp tip xc v trn mt thong.Cng to hi ph thuc vo nhit b mt tHnh 1.9. Trng nhit (ng chm) v hm lng m(ng lin) khi sy tip xc vt liu xp mao qun

nng t v chiu dy lp vt liu.

Theo B.B Kratnhicp, su vng bc hi giai on sy th hai tun theo lut tuyn tnh Tuy nhin tc su trong vng II, 7 10 ln(i vi xenlul) vt qu tc su c trng u giai on th hai (b2 = 7 10 ln b1). H s b1,b2 c trng cho tc su vng bc hi

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Hnh 1.10. ng cong gii tch, c trng su vng bc hi khi tip xc vi xenlul Nhit su vng bc hi tbh thay i theo thi gian Trong ca vt liu) S chuyn hi qua khi sy tip xc, gn ng th nht c th vit y qm mt dng phn t ca hi (kg/m2s) - Gradien p sut hi nc bn trong vt liu (Pa/m hoc mmHg/m) Kp H s dch chuyn phn t hi (s dn hi) trong vt xp ng mao (kg/msPa) hoc (kg/ms.mmHg) H s Kp khng ph thuc thng s ch l sc cn thy lc ca vt liu. Gim chiu dy vt liu,Kp tng t ngt ( hnh 1.7). p sut hi bo ha Ph cht lng trong ng mao l hm ca nhit v bn knh ng mao r ttx nhit vt liu trong mt tip xc vi mt t nng K thng s thc nghim ph thuc vo loi vt liu, t , g(khi lng ring

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Gradien hm lng m c dng :

Trong : fs(r) Hm phn b ng mao theo tit din vt liu - mt cht lng v cht kh Thay vo cng thc(1.1) gi tr ca ta c:

Khi t > 1000, thnh phn th nht ca phng trnh ng vai tr chnh do c th b qua s ph thuc vo ph vo r v u. Khi i vi thi k sy th nht vt liu mng, mt ca dng phn t s l

Khi t < 65 850C mt dng khuch tn m biu din qua phng trnh dn m khng ng nhit. Nh khuch tn nn xy ra s di chuyn m khi vng bc hi. Ngoi tr lp tip xc hng gradien nhit trng vi hng gradien m bn trong vt liu, do cng dn nhit m s tng mnh trong sut qu trnh. c trng c cu to thnh v di chuyn hi bn trong vt liu trong qu trnh sy tip xc, B.B Krasnhicop dng m hnh ha chun bin i pha.

Trong :

-qm: dng hi chung that khi vt liu qm dng hi to thnh trong lp tip xc hoc bn trong vt liu(thi k th sau bt u thi k th hai, gim t ngt ti gi tr

hai) Trong thi k th nht Thi k chun

khng i trong vng I ca thi k th hai. Sau

bt u tng mt cht.

c tnh nh i vi dng nhit tng ng.

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y:

qh dng nhit di chuyn bc hi q dng nhit chung, nhn c t b mt nng qd dng nhit dn nhit qua vt liu ch nhit dung ring ca hi c trng % dng dn nhit

Ch rng trong qu trnh sy dn nhit (tip xc), vai tr l di chuyn ca m lng ra khi lp, gn mt tip xc vi mt nng ra mt thong ca vt liu(7,5% dng nhit chung). H s dn nhit tng ng c tnh ti di chuyn nhit ca lng, s tng nhit khi nhit trong bnh ca vt liu tng.(xenlul khi u = 0,6 1,8 kg/), = 1,16(0,095 0,288.10-2t) W/m0k Bng 1.1 Ch tiu sy tip xc sn phm ra trn my sy chn khng 1 trc

1.3.2. H thng sy tip xc trong cht lng nng Trong thit b ny, ngi ta dng cht lng lm mi cht gia nhit cho vt lieu. Sn phm sy c nhng ngp vo trong cht lng u im ca phng php ny l cng bay hi m cao, c th gim ng k thi gian sy, vt lieu c gia nhit u n hn so vi cc phng php sy khc.

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V d: Sy g trong cht lng hu c vi nhit 120 150 0C, g c chiu dy 25 mm, m ban u 60%, m cui 12%, thi gian sy l 6 10h. Trong khi nu sy trong bung sy i lu thi gian sy l 60 70 h. Nhc im: hi m cng cc cht kh c hi lm nhim mi trng lm vic ca khu vc t thit b sy, trnh nhim mi trng dng bung sy kn. Cc cht kh v hi nc thot ra c ht v x ra ngoi s c x l hay thot vo ng x c chiu cao ph hp vi quy nh v iu kin v sinh mi trng. B phn chnh l b cha cht lng v b phn t nng n. Vt liu sy nhng ngp trong cht lng, nn tnh ton nhit l tnh tiu hao cho mt chu k sy. Nhit lng tiu hao Q gm: t nng Q1, sy Q2, giai on ly vt liu ra Q = Q1 + Q 2 + Q 3 Nhit giai on t nng: Q1 = Qvl + Qvc + Qmt + Qbx Nhin liu nng vt liu Qvl = Gvl.Cvl(tvl2 tvl1) Nhit hm nng c cu vn chuyn: Qvc = Gvc.Cvc(tvc2 tvc1) Nhit thi ra mi trng: trong giai on t nng: Nhit thi ra mi trng trong giai on t nng l tn tht qua thnh y v mt thong ca b cha. V mt thong c nhit cao, nn cn tnh ti trao i nhit bc x. Fi(I = 1N) l din tch mt trao i nhit th i , h s truyn nhit Ki v chnh lch +Nhit giai on sy Q2 = Qbh + Qqn + Qn +Nhit bc hi Qbh = W.r r nhit n ha hi tvl2 +Nhit lng qu nhit 16 , W = G 1 G2 W lng m cn bc hi trong giai on sy (Kg)

Qqn = Ch(tn2 tbh) Nhit tc nhn sy ln hn nhit bo ha t bh, hi nc bay hi khi vt liu cn cn t nng t tbh ti nhit cht lng nng tn2. Ch nhit dung ring hi qu nhit. +Nhit t nng m Nhit lng Qn dng t nng m W = G1. ( - m tng i thi im t1) Qn = W. Cn (tbh tvl1) Cn nhit dung ring ca nc trong vt liu Tng nhit lng chi ph trong giai on sy Q2 = W[ r + Ch(tn2 tbh)] + W . Cn(tbh tvl1) +Nhit giai on ly vt liu ra Q3- Thi gian ly vt liu ra v a cc vt liu sy gia m vo. Nhit lng tnh l tn tht ra mi trng trong thi gian Q3 = Qmt .

2. TNH TON V LA CHN MY SY: 2.1. TNH TON THIT B SY 2.1.1. YU CU TNH TONCc yu cu c bn ca mt thit b sy l c kh nng bc m cao nht, sn phm sy kh u, m bo cht lng sn phm, c nhng iu kin theo di v iu chnh cc thng s ca qu trnh sy mt cc d dng, c kh nng thch ng vi cc dng sn phm khc nhau...nhng ng thi phi kinh t nht. Cc yu cu ny ph thuc vo mc ch ca sn phm sy, ch sy, cu to ca thit b sy v mt s thng s la chn trong khi tnh ton. V vy khi tnh ton thit b sy phi ch n loi thit b sy, chn ch sy v phng thc sy thch hp nht. Khi tnh ton thit b sy ta cn bit hoc chn cc s liu sau : - V thit b : Nng sut loi tc nhn sy (khng kh nng, nc nng, khi l...)

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phng thc cung cp nhit (i lu, tip xc...) cch un nng tc nhn sy (loi calorife) phng thc tun hon ca tc nhn sy (cng bc, t nhin...) - V sn phm sy : m ban u v ban cui, nhit cho php cc i, thnh phn nhy cm nht i vi nhit, khi lng ring, nhit dung ring, kch thc ln nht, b nht ca sn phm sy. - V ch sy : cc thng s ca khng kh bn ngoi v ca tc nhn sy, nhit un nng cho php cc i m, vn tc ca tc nhn, thi gian sy, nhit vo v ra ca tc nhn sy... Ngoi nhng s liu cho trc theo yu cu ca thit k, nhng cng c s liu ngi thit k phi t chn ph hp vi iu kin c th. Ni dung tnh ton gm cc phn c bn sau : - Phn chung : la chn my sy v phng thc sy.

2.1.2. PHN TNH TON: NI DUNG TNH TON1) Tnh cc kch thc c bn ca my sy. 2) Tnh hm lng m bay hi t sn phm sy. 3) Tnh lng khng kh tiu tn cho qu trnh sy. 4) Tnh lng nhit cho qu trnh sy : - Nhit tiu tn cho qu trnh bc m. - Nhit tiu tn un nng sn phm t nhit to n t1. - Nhit tn tht ra mi trng xung quanh. 5) Tnh ton h thng un nng tc nhn sy : - Tc nhn sy l khng kh nng, dng calorife hi nc : + Tnh b mt truyn nhit. + Chn lai calorife v s lng. 18

+ Tnh lng hi nc tiu tn cho qu trnh sy. - Tc nhn sy l khng kh nng, dng calorife l t : + Tnh b mt truyn nhit. + Tnh kch thc calorife l t. + Tnh kch thc l t. + Tnh lng nhin liu tiu tn. - Tc nhn sy l khng kh nng, dng calorife in tr : + Chn v tnh kch thc ca dy in tr. + Tnh kch thc ca calorife in tr. + Tnh cng sut in tiu th. - Tc nhn sy l khi l : + Tnh kch thc l t. + Tnh kch thc ca phng lng bi v trn kh. + Tnh nhin liu tiu tn. - Tc nhn sy l nc nng : + Tnh b mt truyn nhit. + Tnh hoc chn vn tc nc nng i trong b phn truyn nhit. + Tnh khi lng nc nng v h thng i lu. + Tnh lng nhin liu tiu tn un nc nng. 6) Tnh h thng thng thong cho qu trnh sy. - Thng thong cng bc (dng qut). + V s h thng qut. + Tnh hoc chn nng sut ca qut 19

(bng lng khng kh dng cho qu trnh sy). + Tnh p sut ca qut : p sut ng hc v tnh hc. + Chn lai qut (da nng sut v p sut). + Tnh cng sut qut. - Cng bc bng h chn khng : + Tnh tr lc v chn bm chn khng, chn khng. - Thng thong t nhin : + Tnh chiu cao ng thot m (vn tc thng thong t nhin 0,4-0,6 m/s) 7) Tnh ton thit b ph : - Tnh cc dng c cha nguyn vt liu sy. - Cc c cu a nguyn liu vo v ra. - Phng tin vn chuyn trong qu trnh sy. - iu khin v t ng ho... Trn y l ni dung c th cn tnh ton, nhng v trnh t tnh ton th tu trng hp c th ta b tr thch hp cho tng loi thit b v phng thc sy.

2.2. CHN LA MY SY 2.2.1. C S CHO VIC CHN LAMun chn my sy thch hp nht cho mt nguyn liu nht nh t nhiu loi my sy, cn phi xem xt tt c cc thng s quan trng i vi qu trnh lm vic ca my sy. - Tnh cht vt liu sy :

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Rt t my sy thch hp cho nhiu loi sn phm sy c hnh dng khc nhau. Vic chn la my sy ph thuc vo : hnh dng, kch thc v thnh phn ho hc ca vt liu sy, dng vt liu (dng lt, dng cc, dng bt, dng c, dng lng...). Ngoi ra cn bits thay i hnh dng v trng thi ca vt liu trong qu trnh sy nh s co dm, s rn nt, s phn lp...tnh cht no b thay i mnh nht. Hnh dng, kch thc + i vi nguyn liu giu tinh bt, lp sy dy (thng sy chm) : s dng phng sy, hm sy, thp sy... + i vi vt liu ri, nh v lp sy mng : s dng my sy nhanh, nh my sy phun, my sy kh ng, hoc my sy trc ln. sy nhanh ngi ta c th lm nh, lm mng vt liu trc khi sy. i vi lp sy mng : c th s dng my sy bc x. C th s dng nhng my sy c kt cu c hc c bit phn b u vt liu sy, v d : my sy cnh o, my sy thng quay, my sy a quay...C th kt hp my sy vi my nghin trc vt. Tnh cht m : + bc m t do : dng nhng my sy tun hon tit kim nng lng (c th tch m t do v m dnh t nhanh nht bng ly tm v p). i vi vt liu keo : c th s dng nhng my sy nhanh, sau khi nguyn liu c x l thnh dng bt hoc lp sy mng. + tch nc lin kt ngi ta thng s dng my sy, m sn phm sy chu c nhit cao hn. + Ngi ta cng cn ch n m ban u v ban cui ca sn phm. Nu m cui ca sn phm sy c php cn li tng i cao : c th s dng my sy nhanh. Nu m cui ca sn phm b : thi gian sy lu nn my sy cn cho php ko di

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thi gian sy ca n. C th phi hp 2 my sy, v d : i vi sn phm dng ri c th kt hp my sy kh ng tc dng nhanh vi my sy thng quay tc dng chm. i vi sn phm dng pasta c th kt hp my sy trc ln vi my sy bng ti. S nhy cm vi nhit ca sn phm sy Nhng vt liu cho php s dng nhit cao : c th dng loi my sy c tc nhn sy l khi l. Tit gia sc, cc cht chit t ng thc vt cn phi sy trng thi n ho, gi li nhng tnh cht c gi tr ca n. Trong my sy phun v sy kh ng, sn phm ch lu li thi gian rt ngn nn c php s dng nhit cao hn so vi sy hm. Trong tt c nhng my sy ph bin th nhng my sy i lu kim sot nhit ca sn phm sy tt nht, v c th d dng iu chnh trng thi khng kh thch hp. Trong my sy tip xc, sn phm sy nhn nhit ca b mt b un nng nhng ch tip xc, bi vy ch s dng i vi nhng sn phm nhy cm vi nhit , qu trnhsy xy ra rt nhanh Khng s dng my sy bc x i vi nhng sn phm nhy cm vi nhit , v sn phm d b un nng cc b gy nguy him cho sn phm. i vi mt s sn phm cn ch n s nhy cm v sc cng, d b co ngt, nt n trong qu trnh sy di tc dng sc cng c hc mnh : c th s dng my sy i lu cho php iu chnh c cc thng s sy thch hp vi tng loi sn phm sy. Trong mt s trng hp c th s dng nhng phng php sy c bit : sy bng dng in cao tn, sy chn khng v sy thng hoa. i vi mt s sn phm khng c php s dng tc nhn sy l khi l, nhng sn phm d b oxy ho, b chy : s dng my sy chn khng hoc my sy dng kh tr tun hon.

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i vi nhng sn phm c tc dng n mn my sy : cn sy trong nhng my sy c cu to chng n mn. - Nng sut sn phm : i vi nng sut nh v loi sn phm thay i hnh dng : thng s dng loi my sy lm vic gin on. i vi nng sut ln, nguyn vt liu ng nht thng dng my sy lm vic lin tc. - Tnh cht sn phm sau khi sy : Thng gi tr thng mi ca sn phm ph thuc vo cm quan v ng u. Sn phm khng c khc bit nhiu v cht lng v m, nu m cha t yu cu cn phi c sy li. Sn phm cn c ng gi v trang tr bao b theo khi lng nht nh tin li cho ngi s dng. Cu to ca my sy c th nh hng n tnh cht ni trn. - Khc phc bi v ngng t hi nc : + i vi nhng my sy, c bit l my sy i lu thng dng khng kh lm tc nhn sy, dng khng kh mang theo nhng phn t nh tp cht v sn phm sy v bi ny c thi ra mi trng xung quanh. Vi nhng sn phm sy s dng khi lng khng kh t hoc vn tc khng kh nh th t sinh ra bi, v d : cc loi my sy tip xc, th c th khng x dng b phn tch bi. Ngc li, ngi ta cn phi lm sch bi ca khng kh khi i ra khi my sy i vi nhng my sy gy ra bi nhiu. + i vi vt liu sy cha hm m cao, hi nc sinh ra trong qu trnh sy c th ngng t, lm t cc b sn phm sy, gy h hi hoc gim cht lng sn phm trong qu trnh bo qun. khc phc hin tng ny ngi ta c th dng qut ht cui my sy hoc bo n xung quanh my sy, c bit khi my sy lm vic lc tri ma v thi tit ma ng. - Lm v sinh my sy :

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+ Trong qu trnh lm vic ca my sy, nhng phn t rt nh ca tp cht v sn phm sy, ngay c mt phn sn phm sy bm cht mt s v tr bn trong my sy, ngn cnqu trnh sy v nu lu s sinh ra nhng khi vi sinh vt cc b. V vy cu to ca my sy phi m bo vic v sinh my sy c d dng v nhanh chng. - Din tch hot ng ca my sy + Din tch hot ng ph thuc vo loi my sy : nhng my sy dng calorife bng in cn din tch hot ng nh hn my sy dng calorife hi nc hoc l t. Ngy nay ngi ta thng s dng cc my sy hot ng theo chiu cao, u im ca loi ny chim din tch hot ng nh, c th khc phc bi d dng. - Nhu cu v nng lng : + Bao gm nhu cu v nhit bc m ca vt liu sy v nhu cu v in dng cho ng lc (qut, vn chuyn...). Ni chung nhng my sy tip xc c nhu cu nng lng thp cn my sy i lu v nhng my sy un nng sn phm bng nhiu con ng (hn hp) c nhu cu nng lng cao, v vy nn s dng ch nhit khng kh sy thp i vi nhng my sy ny. - Gi thnh sy : + Ga thnh sy quyt nh cui cng chn my sy. i vi nhng sn phm c gi tr cao ngi ta c th s dng nhng my sy hin i dng nng lng in, hi nc, kh t hoc nhin liu lng. + i vi nhng sn phm r tin, gi tr thp c th s dng cc my sy n gin vi ngun nhin liu r tin. Nhng my sy lm vic gin on yu cu vn c nh tng i thp, nhng i hi nhiu ngi phc v, tiu tn nng lng ln. Nhng my sy lm vic lin tc th ngc li. My sy chn khng i hi vn c nh v vn lu ng cao hn my sy lm vic p sut thng, nhng n to ra nhng sn phm c cht lng tt hn.

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+ Phng php sy t nht l sy thng hoa v sy bng in trng cao tn. Cc phng php ny thng ch s dng i vi sn phm cao cp, yu cu cht lng c bit.

2.2.2. PHNG PHP CHN:- Bc tip theo l tin hnh th nghim cc thng s cn bit. + Nhng hng ch to ln c uy tn, thng c phng th nghim thc hin nhng th nghim cho khch hng. Trong qu trnh th nghim c i din ca khch hng tham gia. Khch hng phi bit nhng yu cu v cht lng sn phm, nhng chi tit v k hoch sn xut v c th nh gi c cht lng ca sn phm sy sau ny c th ng nh kt qu th nghim hay khng. Sau khi nh gi kt qu th nghim, nhng thng s v k thut, kch thc v cu to c bit ca my sy c xc nh, ngi ch to ch dn v gi c, nhu cu nhit v nng sut ca my sy. + la chn mt cch d dng : so snh vi chi ph ca mt loi my sy c s dng tt. + y ngi ta cn phi tnh thm vo chi ph v ng kin, vn chuyn, thu, lp t v nh bao che.T c th tnh chi ph sn xut nh : khu hao, iu khin, an ton, chi ph nng lng, ng lc, nc lm ngui ng lc, vn hnh, bo qun, qun l v cui cng l gi thnh sy v li. + Mt s my sy c gi thnh sy thp do nhng trang b c bit nh : tit kim nng lng, tn dng ph liu, my phn loi v ng gi vi chi ph thp nht. so snh mt cch trn vn ngi ta cn phi nh gi : cht lng ca sn phm sau khi sy, tn tht cht kh, tn tht cht ho tan v cc tn tht khc; chi ph v cc trang b ph : h thng cp liu v ht bi v.v... + S khc nhau ln trong nhng vn ni trn c th lm tng gi thnh sy.

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PHN II THIT B SY DNG IN TRNG DNG CAO TN3) KHI NIM :-Qu trnh sy l qu trnh tch m , ch yu l nc hi nc khi vt liusy thi vo mi trng m c trong vls nhn c nng lng theo mt phng thc no tch khi VLS dch chuyn t trong long vt ra b mt t b mt vt vo mi trng bao quanh (qu trnh lm kh VLS ) -Sy l khu quan trng trong dy truyn cng ngh c s dng nhiu ngnh cng nghip ch bin cc loi nng lm hi sn ., sy l khu quan trng Trong dy truyn cng ngh nhiu ngnh cng nghip ch bin cc loi nng lm hi sn ., qu trnh sy khng phi ch l qu trnh tch nc v hi nc ra khi vt liu mt cch thun ty m l mt qu trnh cng ngh phc tp . -Sn phm sau khi sy i hi phi m bo cht lng theo mt ch tiu no vi mt chi ph nng lng ti thiu .

4)VI TR CA SNG IN DNG CAO TN :- Vi sng (microwave) chng c tn s t 1-100mhz hoc t 300MHz n 300GHz i vi vi sng . - Theo tha thun quc t , tn s un nng c s dng l 915MHz (hoc 896MHz chu u )v 2450MHz

5)NGUYN L LM VIC :- Vt liu sy t gia 2 bn t c in p tn s cao .di tc dng ca in trng tn s cao vt liu c gia nhit v m trong vt liu x ha hi v thot ra ngoi - Sy bng in trng tn s cao c u im hn cc kiu sy khc l s gia nhit vt lu c thc hin trong ton b th tch vt nn nhit d ng u hn .khi gia 26

nhit bng in trng cao tn . tm vt x c nhit cao hn gradien nhit v gradient m cng chiu , do to thun li cho qu trnh sy . ng thi cch ra nhit bng in trng cao tn cho php iu chnh nhit bn trong vt v duy tr nhit thch hp khng ph thc nhit b mt vt liu . do c im ca qu trnh gia nhit nh vy , phng php ny thch hp vi cc vt liu dy v c hnh dng phc tp m gia nhit bng i lu , bc x hay tip xc u kh thc hin . - Do nhng c im nu trn , phng php sy ny ch sy cc sn phm v chi tit c bit khng th sy bng cc phng php khc . v d , sy cc khung l chu la c hnh dng phc tp v chiu dy ln , nu sy bng phng php khc rt kh khn v vt liu ny d nt khi sy . nhng vt liu nh cng c th s dng phng php ny v sy bng in rt tin li , qu trnh gia nhit vt th thc hin tt hn , do cht lng sn phm cao , thit b d thc hin t ng ha . S cu to thit b sy dng in trng tn s cao :

Hnh :1:v thit b ;2:bn cc ;3:vt liu sy ; 4:xe gong - to nn in trng cao tn , ngi ta dng my pht cao tn . my pht cao tn bin dng in mt chiu hay xoay chiu tn s cng nghip thnh dng in xoay chiu tn s cao . c hai loi my pht cao tn l my pht kiu in t v my pht kiu c kh .

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- Dng in cao tn c a t my pht n hai bn cc ca t in . dng in cao tn x to ra in trng bn trong vt liu t gia 2 bn cc t in , t lm nng vt liu v sy kh vt liu .trn hnh l s cu to thit b sy dng in trng cao tn v bn cc kiu ng , thit b ny dng sy g

6) QU TRNH LM NNG BNG IN TRNG CAO TN :- Phn ln thc phm c cha mt lng nc ng k . cu trc phn t nc gm c oxy mang in tch m v 2 nguyn t hydro mang in tch dng hnh thnh nn lng cc . khi thc phm c t vo trong mt in trng dng cao tn , lng cc ca phn t nc v mt vi thnh phn ion nh mui n c nh hng chng trng trng (tng t nh nam chm trong t trng ). Do trng in tch dao ng rt nhanh thay i t dng sang m v ngc li hng triu ln trong mt giy , cc lng cc ny c thay i theo v qu trnh ny to ra nhit ma st . s tng nhit ca phn t nc lm nng cc cu t xung quanh nh qu trnh dn nhit hoc c th i lu . - Nhit lng sinh ra ph thuc ch yu vo hm lng nc v mui trong nguyn liu - Nng lng hp th p(w/cm3)c xc nh bng cng thc P=55,61. .E.f Trong f:tn s bc x (Hz) E :lc in trng (v/cm ) :loss factor (LF) LF ph thuc vo m , nhit , trng thi ng bng hay khng v cng ph thuc vo tn s bc x

Chiu su bc x xm nhp c xc nh bng cng thc

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d=

2 ( 1 / 2 )

Ttrong : bc sng - Tn s LF cng thp , chiu su thm nhp cng ln . - Nc c LF cao , nn hp th bc x tt - Nc ng bng c LF thp , thy tinh , giy v cc loi polymer c LF thp , v vy khng b un nng bng vi sng - Kim loai phn x sng in trng dng cao tn , v vy lm tng hiu qu nng lng ca thit b .

7. U ,NHC IM :7.1 u im : - Khc phc nhng nhc im ca i lu . -Tc truyn nhit chm do dn nhit ca nguyn liu kh km . -H hi cc gi tr cm quan v dinh dng cho thi gian sy lu v qu nhit b mt .-Oxy ha cc sc t v vitamin . -Gy hin tng cng v . -Sy in trng dng cao tn ngn nga s h hi b mt , ci tin s truyn m p giai on sau ca qu trnh sy v loi b hin tng cng v . bc x ch lm nng nhng vng m , khng nh hng ti vng khc . khng can phi un nng lng ln khng kh v oxy ha c hn ch ti thiu .

7.2 NHC IM :

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- Chi ph u t ln , quy m nh nn ch gii hn ng dng n sy kt thc sn phm . - Tiu hao nng lng ln (2,5n 5kwh/kg m ), hn na thit b ny rt phc tp , vic vn hnh bo dng i hi ngi c trnh chuyn moan su trong lnh vc ny .V d : trong sy bt nho:sy s b n 18%bng i lu , sau kt hp sy i lu vi sy vi sng gim m n 13%nh thi gian sy rt ngn t 8h xung cn 90 pht . -Trong sy thng hoa , tc truyn nhit n b mt thng hoa km c khc phc bng vic sy vi sng . tuy nhin cn kim sot iu kin sy trnh tan bng cc b gay ra vic tan chy day truyn lm kt thc qu trnh thng hoa .

8)NG DNG :-My sy sy g ti s dng cng ngh sng cao tn (sng viba) nhn hiu GOSABA VIBA 20 va c ng LNG NGC D & ng V HIP , cng ty TNHH Thng Tin Minh D , cho ra i . -Nguyn l hot ng ca my dng cc neon cao tn ph v cc phn t nc ra khi g . chic my sy ny c th cho sy kh trong 4 gi mt lng g m m sy bng nhit phi mt 15 pht mi thc hin c . -My cho php sy kh nhng thanh g c kch thc ti a 20 .20.110cm . vi cng sut 4m3/ngy . my ny cn c th sy kh cc loi hng nng sn ,thc phm hoc vi , cc tng m khng h lm thay i tnh cht ban u.

Ti liu tham kho30

Gio trnh K Thut Sy Ts.inh Thnh Ngn http://nhietlanh.sky.vn http://www.nhietlanhvietnam.net

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