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Li cm nHc tp l mt qu trnh lu di, mi giai on ng mt vai tr quan trng trong

vic hnh thnh nhn cch, o c ca mi con ngi. T nhng ngy bc chn vo

ging ng i hc cho n lc hon thnh lun vn ny, em nhn c s quantm ch dn v gip tn tnh ca cc thy c. Qua qu trnh thc hin lun vn tt

nghip em xin by t long bit n chn thnh n:

Ban gim hiu trng i hc Nha Trang. Tp th ging vin Khoa Cng ngh Nhit Lnh trng i hc Nha Trang. Qu thy c tn tnh ch dy chng ti trong thi gian hc tp ti trng. c bit, em xin chn thnh cm nTh.s L Nh Chnh trc tip theo di,

tn tnh hng dn em trong thi gian thc hin ti.Tuy nhin, do hn ch v thi gian thc hin, ti khng trnh khi nhng thiu

st. Mong nhn c s ch bo ca qu thy c v gp ca cc bn.

Nha Trang, thng 3, nm 2012

Sinh vin thc hin ti

Bi Vn Vnh

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Li m uVit Nam l mt nc nhit i c nhiu iu kin pht trin ngnh trng trt

v ch bin rau qu. Tuy nhin, t l tn tht sau thu hoch l rt ln 25-30% [20].

Nguyn nhn chnh l do cng ngh ch bin v bo qun ca chng ta cn lc hu nn

lmcho rau qu ca Vit Nam c gi tr thp trong th trng trong nc cng nh

xut khu, iu ny nh hng trc tip n i sng ca ngi nng dn, v vy vic

nghin cu a ra cc quy trnh cng ngh cng nh ng dng trin khai chuyn giao

cc kt qu nghin cu, cc quy trnh cng ngh bo qun, ch bin rau qu, ng vai

tr ht sc quan trng trong chin lc pht trin ngnh rau qu.

Rau qu hin nay ch yu c s dng dng ti, nh bit rau qu l loi

sn phm c tnh thi v, thi gian thu hoch ngn, kh nng vn chuyn v bo qun

hn ch, trong khi k thut bo qun rau qu ti vn ch da vo cc kinh nghin c

truyn, mang tnh th cng chp v. Cng ngh sy ng dng trong ch bin rau qu

kh c tin hnh t kh lu nhng cho n nay vn bc l nhiu hn ch v cng

ngh cha khc phc c cht lng u ra ca sn phm, cha p ng c cc yu

cu v c tnh ha l, mi, mu, thnh phn dinh dng nn kh p ng cho nhu cu

tiu th v xut khu trong v ngoi nc. Vic u t nghin cu mt quy trnh cng

ngh mi gii quyt nhng vn ny l thc s cn thit. Cng ngh sy lnh cxem l mt cng ngh mi, ra i t yu cu cp thit .

u im ca cng ngh sy lnh l c th xy dng c tng quy trnh cng

ngh sy hp l i vi tng loi rau, c, qu. Sn phm sy gi c nguyn mu sc,

mi v, hn ch ti a tht thot dinh dng (khong 5%) [20], t tiu chun v sinh an

ton thc phm ca Vit Nam v cc ch tiu k thut, cht lng sn phm tng

ng mt s nc khc trn th gii.

Vic pht trin cng ngh sy lnh c nhiu thnh tu. Tuy nhin, c mtquy trnh cng ngh hon chnh, ti u vi cc thng s ph hp nht i hi chng ta

phi tin hnh nghin cu su rng hn. c s phn cng tiKho st v tnh

thit k my sy bm nhit tng si sy hnh l xut khu nng sut 100kgmthc

hin da trn c s tm hiu nhng nguyn l chung nht ca cng ngh sy lnh t

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c th xy dng nn quy trnh sy i vi tng loi rau qu khc nhau. gii quyt

nhng vn , ti nghin cu nhng ni dung chnh sau:

Tm hiu v cng ngh sy lnh, phng php sy v cc thit b trong hthng sy lnh. Tm hiu k thut sy lnh trn mt s loi rau qu giu vitamin, xy dng quytrnh sy lnh i vi Hnh l ct nh.

Tnh ton thit k m hnh my sy lnh s dng bm nhit ch sy hilu hon ton v ch thi b tc nhn.

Tnh ton thit k my sy lnh v la chn cc thit b ph tr. Thc nghim nghin cu trn m hnh thc t. So snh hiu qu ca h thng sy lnh vi sy nng nh my.

Vi nhng c tnh u vit, cng ngh sy lnh ha hn s l mt cng ngh tin

tin, cho lnh vc sy thc phm giu vitamin, c th p dng rng ri vi quy m ln

p ng c v vn li ch kinh t v bo v mi trng.

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CHNG I

TNG QUAN V K THUT SY

1.1. Khi nim qu trnh sy

1.1.1. Khi nim

Sy l qu trnh tch m (hi nc v nc) ra khi VLS, trong VLS nhn

nng lng m t trong lng VLS dch chuyn ra b mt v i vo mi trng tc

nhn sy (TNS). Qu trnh sy l qu trnh truyn nhit, truyn cht sy ra ng thi.

Trong lng VLS l qu trnh dn nhit v khuch tn m hn hp. Trao i nhit - m

gia b mt VLS vi TNS l qu trnh trao i nhit v trao i m i lu lin hp.

Qu trnh bn trong VLS ch yu chu nh hng ca dng lin kt m vi ct kh cavt liu, qu trnh b mt VLS ch yu chu nh hng ca c cu trao i nhit m

v cc thng s ca TNS cng nh VLS.

1.1.2. Phn loi phng php sy

- Sy t nhin: Sy bng khng kh khng dc t nng, phng php ny thigian sy di, kh iu chnh qu trnh v m cui ca vt liu cn kh ln

nht l nhng quc gia ckh hu nhit i nh nc ta.- Sy nhn to: L qu trnh sy c s cp nhit t bn ngoi, ngha l phi dng

n tc nhn sy c gia nhit nh khi nng, khng kh nng hoc hi

1.1.3. Mc ch ca qu trnh sy

Sy khng ch l qu trnh cng ngh, trong cc tnh cht cng ngh lun lun

thay i. Tnh cht cng ngh ca vt liu gm: tnh cht ho l, tnh cht c kt cu,

tnh cht sinh ho.

Qu trnh sy nhm tng cng mt s c tnh cng ngh phc v nhiu mc

ch khc nhau. Khi sy sn phm gm th nhm mc ch lm bn ca n tng ln

tip tc gia cng; sy ht ging th phi lm t l v kh nng ny mm cao ln; sy

nng sn thc phm th gi c hng v, mu sc, nguyn t vi lng m tng c

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thi gian bo qun, gim c gi thnh vn chuyn, gim c th tch kho bo

qun.

1.1.4. Nhng bin i c bn ca qu trnh sy

nghin cu v cng ngh sy, trc ht cn nghin cu v cc dng lin kt

m, cc dng dch chuyn m v th dch chuyn m trong VLS nhm hiu r c ch

dch chuyn m v nh hng phng php tc ng tng cng hoc hn ch dng

dch chuyn m phc v cc yu cu cng ngh. Theo dng lin ktm vi ct kh ca

vt, VLS chia thnh 3 nhm: Vt keo, vtxp mao dn v vt keo xp mao dn.

1.1.4.1. Cc dng dch chuyn v th dch chuyn trong vt keo

Lin kt m trong vt keo l lc hp th v lc khuch tn thm thu.Do , mt

dng m lng j2k t l thun vi gradient p sut thm thu ttp . Vi cha m

thng thng ca vt trng n gii hn, p sut thm thu (trng n) l hm ca

cha m M. Do ta c:

MaMM/pDpDj0k2tt2ptt2pk2 (1.1)

Vtkeo l vt c cu trc mao mch phn t qu trnh khng ng nhit dch

chuyn m lng dng mng c dng: Gradient

tkMkj 0t

m2om2m2 (1.2)

Dng m lng dch chuyn s bng:

tkMkajjj 0t

m2om2k2m2k22 (1.3)

Dch chuyn m dng hi c xc nh gn ng bi qu trnh khuch tn phnt. Mt dng phn t j1t l nghch vi gradient ca T/p1 . Vi p1l p sut cahi m. Trong qu trnh on nhit p1l hm ca cha m v nhit nn dng j1s

bng:

` taMaj 0t

ct10ct11 (1.4)

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Dng dch chuyn m tng (lng v hi) xc nh theo M v t trong vt keo

s bng:

taMajjj0

t

mk0mk21 (1.5)

Trong :

m2k2ct1mk kaaa (1.6)

tm2

tct1

tmk kaa (1.7)

1.1.4.2. Cc dng dch chuyn v th dchchuyn m trong vt xp mao dn

Dch chuyn lng mao dn (Khuch tn mao dn) trong vt xp mao dn, c ccmchln (r > 10-5), gn lin vi lin kt c l. Trong vt xp cu trc a mao mch,

dng m lng t l thun vi gradient th mao dn

: kj md2 (1.8)

Th mao dn trong trng hp ngnhit t l thun vi cha m M.

Trong iu kin khng ng nhit, dng m lng khch tn mao dn j2mdc xc nh:

taMakj0

t

md20md2md2 (1.9)

a2md v t md2a l h s khch tn lng mao dn v h s khch tn nhit ca lng mao

dn. Ga tr ca chng ph thuc vo sc cng b mt,gc dnh t, nht ca lng,

bn knh mao dn.

Khi m ca vt vt gi tr ht m cc ith trong cc mao mch ln ca vt

xp cha y nc, dch chuyn lng lc ny l do chnh lch th mao dn. Khc vi

trng hp thm lng mao dn xy ra do vt tip xc trc tip vi cht lng (do p sut

thy tnh), th mao dn l khng ng nht, lng lng c ht vo c gii hn v

lng khng th in y ton b vt do b hn ch bi phn ct kh ca vt. Th mao

dn vi phn t mao mch bng:

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212

r

1

r

12(1.10)

Nh vy iu kin c th dch chuyn lng mao dn, gn vi s bay hi v ngng t

lng, l s khc bit bn knh ca mao mch, r1 r2.

Vi s tn ti ca qu trnh bay hi, dch chuyn hi m trong cc mao mch ln

(r > 10-5), c xc nh theo quy lut khch tn phn t. Cn vi cc mao mch nh

qu trnh ny xy ra theo quy lut chy trn. Ngoi ra, vi qu trnh bay hi lng trong

vt xp, cn tn ti dch chuyn m i lu v m c gi l khch tn trt (hay l

khch tn thy ng). Khi dng hi tng ng vi p sut tng p = const s gm dng

khch tn phn t j1pt, dng khch tn i lu j1dl = k1 v. v dng chy trn j1ct. p sutbay hi p1l hm ca cha m v nhit , p1=f(M,t). Vy nn, dng dch chuyn

m c th th hin bng quan h:

taMajjjj0

t

md10md1ct1dl1pt11 (1.11)

Vy dng m tng dch chuyn trong xp mao dn l:

taMajjj 0t

Mmd0Mmd21 (1.12)

Trong :Mm d

a v tMmd

a l h s khch tn m v h s khch tn nhit ca m mao dn,

vi:

md2md1Mmd aaa (1.13)

t

m d2

t

m d1

t

Mm d aaa (1.14)

Ngoi ra, cn c dch chuyn m lng v hi do lc thm mao dn (c nghin cutrong l thuyt thm). Githit dng thm lng v hi c lp nhau, c th vit:

i

i

iiii p

)(kvj

i=1,2 (1.15)

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1.1.4.3. Cc dng dch chuyn m trong vt keo xp mao dn

Qa trnh dch chuyn m trong vt keo xp mao dn c xc nh bng cc

hin tng dch chuyn khc nhau v c phn tch trong vt keo v vt mao dn

trn.

Nu b qua nh hng ca lc trng trng th s chuyn m trong VLS do cc

lc nhit ng khc nhau v cc lc nhit ng ny u l hm ca cha m M v

nhit t, do chng c th biu din qua t,M .

Dch chuyn m qua vt keo xp mao dn c xc nh bng cng thc:

(1.16)

Trong :M

a v tMa l h s khch tn v h s khch tn nhit ca m, l h s

khch tn nhit tng i, tMM a/a .

mkMmd

mkkMmdmd

t

mk

t

Mmd

t

M

mkMmdM

aa

aa

aaa

aaa

(1.17)

Cc h s khch tn m aM v l hm ca cha m v nhit . c

trng cho s thay i ca h s aMvi cha m khc nhau c xc nh theo dng

lin kt m v dng dch chuyn m (lng v hi). Vi vt xp mao dn in hnh , h

s aMtng khi cha m tng, v vi cha m ln thi h s aMkhng i. Nu qu

trnh l dch chuyn m lng th hs aMs tng hoc khng i ph thuc vo ng

cong phn b hang xp theo ng knh. H s aMca cc vt liu c xc nh bng

thc nghim di dng bng s hoc cng thc.

1.1.4.4. Dch chuyn m i lu trong vt liu sy

Trong qu trnh sy cng cao, nu nhit ca vt liu sy ln hn 100OC

th phn p sut hi nc bo ha p1s ln hn p sut ring phn ca hi nc trong

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TNS. Khi , dng dch chuyn m do khch tn trong vt xp c thay th bi dng

dch chuyn m i lu.

Gradient p sut tng )p( xut hin khi nhit ca vt liu sy ln hn

100OC, tuy nhin nu qu trnh c thc hin bng vic t nng bn trong (v d sycao tn) th )p( xut hin ngay c khi nhit b hn 100OC

S tn ti ca )p( gy nn dng dch chuyn m i lu ca hn hp

khhi trong mi trng xp, nn khi tnh dng nhit dch chuyn m ( lng, hi )

tng qut cn b sung dng dch chuyn ny. Mt dng hi dch chuyn bi dng

ny l:

pkpkvj p1011 (1.18)

Vi /110

l nng tng i ca hi nc, kpl h s dng nng phn t:

)d1/(kdkk10p

(1.19)

Vi d l dung m ca khng kh.

Dng m tnti gradient p sut tng bng:

pktaMajp0

t

M0M (1.20)

Biu thc (1.20) cha k n dch chuyn lng di tc dng ca lc trong trng v

gradient p sut thy tnh (dng lng qua mi trng xp). Cng ca dng dch

chuyn mthm i lu ln hn nhiu ln dng dch chuyn m di tc ng ca lc

mao dn v khch tn. Qa trnh ny thng c nghin cu c lp vi qu trnh dchchuyn m trong VLS.

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1.2. C cht thot m ra khi vt liu sy

Mun lm kh phi t nguynliu trong mi trng khng kh m, nc

dch chuyn vo mi trng khng kh, c s chnh lch vt cht (th vt cht) . Hot

ca nc trong nguyn liu phi m bo di hot ng ca vi sinh vt hot ng.

Khi lm kh xy ra qu trnh nc tch ra khi vt liu: nc t b mt nguyn

liu dch chuyn vo mi trng kh. y l iu kinkin quyt qu trnh lm kh

xy ra. Ngoi ra lm kh phi c qu trnh dch chuyn m t cc lp pha trong i ra

cc lp b mt. S dch chuyn m t trong ra ngoi hnh thnh khi m v nc t trung

tm nguyn liu dch chuyn ra b mt v lp xung quanh m bo m lp trung

tm bng cc lp xung quanh.1

Qu trnh thot m ra khi vt liu trong qu trnh sy c chia lm 2 giai on:

1.2.1. Qua trnh khuch tn ngoi

L qu trnh dch chuyn m t lp b mt ca vt liu sy vo mi trng khng

kh xung quanh. ng lc ca qu trnh ny l do chnh lch p sut hi trn b mt ca

vt m v p sut ring phn hi nc trong mi trng khng kh.

Lng nc bay hi:

Hoc (1.21)

Trong : Ps : p sut ring phn hi nc trn b mt

Ph: p sut ring phn khng kh

K: H s bay hi

F: Din tch b mt bay hi

: Gradient m

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Lng bay hi trn mt n v din tch t l thun vi gradient chnh lch m

gia nguyn liu v mi trng xung quanh.

S chnh lch xy ra: nc t b mt dch chuyn vo mi trng xung quanh

lm m lp khng kh tng ln, ng thi lm lng m trn b mt VLS gim i.

Gradient m gim, qu trnh bay hi chm li. Nu m b mt cn bng

vi mi trng khng kh th qu trnh ngng bay hi, nhng m ca hai lp khng

kh k tip chnh lch nn m ca khng kh th nht khch tn sang lp th hai v

m t trong VLS khch tn sang lp khng kh th nht.

Gradient m ph thuc vo tnh cht ca mi trng lm kh: nhit , p

sut, s lun chuyn ca khng kh, v ph thuc vo b mt nguyn liu: nhn, hnhdng, kch thc b mt.

1.2.2. Qu trnh khuch tn ni

L qu trnh dch chuyn mt lp bn trong ra lp b mt ca vt m. ng lc

ca qu trnh ny l do chnh lch nng m gia cc lp bn trong v cc lp b mt,

ngoi ra qu trnh khch tn ni cn xy ra do chnh lch nhit gia cc lp bn

trong v cc lp b mt.

(1.22)Trong : D: H s khch tn ni

F: Din tch khch tn

: Gradient m

H s khch tn ni (D) ph thuc ch yu v thnh phn, tnh cht nguyn liu,

gin tip ph thuc vo yu t mi trng.

Qua nghin cu ta thy rng m dch chuyn t ni c nhit cao n ni c

nhit thp.V vy, ty theo phng php sy v thit b sy m dng m dch chuyn

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di tc dng ca nng m v dng m dch chuyn di tc dng ca nhit c

th cng chiu hoc ngc chiu vi nhau.

Nu hai dng m dch chuyn cng chiu vi nhau s lm thc y qu trnh

thot mrt ngn thi gian sy. Nu 2 dng m dch chuyn ngc chiu nhau s kmhm s thot mko di thi gian sy.

1.2.3. Mi quan hgia qu trnh khuch tn ngoi v qu trnh khuch tn ni

Khch tn ni v khch tn ngoi c mi quan h cht ch vi nhau, qu trnh

khch tn ngoi l qu trnh khi u v quyt nh n giai on u ca qu trnh sy

v qu trnh khch tn ni lng lc ca qu trnh khch tn ngoi. Tc l qu trnh

khch tn ngoi c tin hnh th qu trnh khch tn ni mi c tip tc v nh th m ca nguyn liu mi c gim dn. Tuy nhin trong qu trnh sy ta phi lm

cho 2 qu trnh ny cn bng vi nhau, trnh trng hp khch tn ngoi ln hn qu

trnh khch tn ni. V khi s lm cho s bay hi trn b mt xy ra mnh lit lm

cho kh b mt, hn ch s thot m, khi xy ra hin tng phi khc phcbng

cch m (sy gin on) mcch l thc y qu trnh khch tn ni.

1.3. Cc giai on trong qu trnh sy

c im ca qu trnh sy i vi vt th c m tng i cao, nhit sy

v tc chuyn ng ca khng kh khng qu ln xy ra theo ba giai on l giai

on lm nng vt, giai on sy tc khng i, giai on tc sy gim dn. i

vi cc trng hp sy vi iu kin khc th qu trnh sy cng xy ra ba giai on

nhng cc giai on c th an xen kh phn bit hn.

1.3.1. Giai on nung nng vt liu

Giai on ny bt u t khi a vt vo bung sy tip xc vi khng kh nng

cho ti khi nhit vtt c bng nhit k t. Trong qu trnh sy ny ton b

vt c gia nhit. m lng trong vt c gia nhit cho n khi t c nhit si

ng vi phn p sut hi nc trong mi trng khng kh trong bung sy. Do c

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lm nng nn m ca vt c gim cht t do bay hi m cn nhit ca vt th tng

dn cho n khi bng nhit k c. Tuy vy, s tng nhit trong qu trnh xy ra

khng u phn ngoi v phn trong vt. Vng trong vt t n nhit k c

chm hn. i vi vt d sy th giai on lm nng vt xy ra nhanh.

1.3.2. Giai on sy ng tc

Kt thc giai on gia nhit, nhit vt bng nhit k c. Tip tc cung cp

nhit, m trong vt s ha hi cn nhit ca vt gi khng i nn nhit cung cp ch

lm ha hi nc. m s ha hi lp vt liu st b mt vt, m lng bn trong

vt s truyn ra ngoi b mt vt ha hi. Do nhit khng kh nng khng i,

nhit vt cng khng i nn chnh lch nhit gia vt v mi trng cng khng

i. iu ny lm cho tc gim ca cha m vt theo thi gian cng khng i,

c ngha l tc sy khng i.

Trong giai on ny bin thin ca cha m theo thi gian l tuyn tnh. m

c thot ra trong giai on ny l m t do. Khi m ca vt t n tr s ti hn

Uk = Ucbmaxth giai on sy tc khng i chm dt. ng thi cng l chm dt

giai on thot m t do chuyn sang giai on sy tc gim.

1.3.3. Giai on sy gim tc

Kt thc giai on sy tc khng i m t do bay hi ht, cn li trong vt

l m lin ktca lin kt ha l v lin kt ha hc. Nng lng bay hi m lin kt

ln hn m t do v cng tng ln khi m ca vt cng nh. Do vy , tc bay hi

m trong giai on ny nh hn giai on sy tc khng i c ngha l tc sy

trong giai on ny nh hn v cng gim i theo thi gian sy. Qu trnh sy cng tip

din, m ca vt cng gim, tc sy cng gim cho n khi m ca vt gimn bng m cn bng vi iu kin mi trng khng kh m trong bung sy th

qu trnh thot m ca vt ngng li, c ngha tc sy bng khng.

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1.4. Cc phng php v thit b sy

Sy c th c chia ra hai loi: sy t nhin v sy nhn to.

- Sy t nhin: qu trnh phi vt liu ngoi tri, khng c s dng thit b.

- Sy nhn to: cc phng php sy nhn to thc hin trong cc thit b sy.C nhiu phng php sy nhn to khc nhau. Cn c vo phng php cung cp

nhit c th chia ra cc loi: sy i lu, sy bc x, sy tip xc, sy thng hoa, sy

bng in trng dng cao tn, sy in tr

1.4.1. Cc phng php sy

1.4.1.1. Phi v sy bng nng lng mt tri

Sy bng cch phi nng (khng c s dng thit b sy) c s dng rng ri

nht trong ch bin nng sn

Trong cc phng php phc tp hn (sy bng nng lng mt tri), nng lng

mt tri c thu nhn gia nhit tc nhn sy hoc s dng nng lng mt tri sy

trc tip.

1.4.1.2. Sy i lu

Nguyn l hot ng:

Khng kh nng hoc khi l c dng lm tc nhn sy c nhit , m, tc

ph hp, chuyn ng chy trm ln vt sy lm cho m trong vt sy bay hi ri i

theo tc nhn sy.

Khng kh c th chuyn ng cng chiu, ngc chiu hoc ct ngang dng

chuyn ng ca sn phm. Sy i lu c th thc hin theo m (gin on) hay lin

tc. Trn hnh v di l s nguyn l sy i lu bng khng kh nng.

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1.4.2. Thit b sy

1.4.2.1. My sy thng quay

- Cu to: Gm thng hnh tr 1 t dc khong 6 8 so vi mt phng nm

ngang. C 2 vnh ai trt trn cc con ln ta 4 khi thng quay. Khong cch gia cc

con ln c th iu chnh c, thay i gc nghing ca thng. Thng quay c

nh lp cht trn thn thng, bnh rng 2 n khp vi bnh rng 3 ni vi mt thng

qua hp gim tc. Thng quay vi vn tc khong t 1 8 vng/pht. Bnh rng t ti

trng tm ca thng.

My sy thng quay lm vic p sut kh quyn. Tc nhn sy c th l khng

kh hay khi l. Thng th vt liu sy hay tc nhn sy chuyn ng cng chiu

trnh sy qu kh v tc nhn sy khi mang theo vt liu sy nhiu nh sy ngc

chiu. Vn tc ca khng kh hay khi l i trong thngkhong 2 3 m/s.

Vt liu ut qua phu 10 ri vo thng u cao v c chuyn ng trong

thng nh nhng m chn 11. m chn va phn b u vt liu theo tit din thng,

va xo trn vt liu, va lm cho vt liu tip xc vi tc nhn sy tt hn.Vt liu

sy sau khi sy kh c a ra ca 6 nh vt ti 7 a ra ngoi. Cn khi l hay khng

kh thi ra c cho qua xyclon 8 gi li nhng ht vt liu b ko theo ri thi rangoi tri qua ng khi. trnh cc kh thi chui qua cc khe h camy sy, lm nh

hng n sc kho cng nhn, ngi ta t qut ht 5 b sung cho sc ht ca ng

khi v to p sut m trong my sy.

My sy thng quay c s dng rng ri trong cng nghip ho cht, thc

phm sy mt s ho cht, qung Pi-rt,phn m, ng cc ng

- u im:

+ Qa trnh sy u n v mnh lit, tip xc gia vt liu sy v tc nhn sytt.

+ Cng lm vic tnh theo lng m kh cao, c th ti 100 (kg/m 3h)

+ Thit b cu to gn, chim mt bng nh.

-Nhc im: Vtliu d b v vn.

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- Ch :

+ Nu sy bng khi l th dn khi l vo my bng ca 9.

+ ng knh thng quay thng c qui chun ( D = 1,2; 1,4; 1,6m t l gia

chiu di v ng knh thng khong: 3,5 7)

Hnh 1.2 :My sy thng quay

1.4.2.2. Thit b sy kiu phun bi (sy phun)

a. Loi thp:

-Cu to: Gm c thp cao 5, nh thp c vi phun 3 c nh hoc quay. Dung

dch cha b 1 c nhit thch hp nh bm 2 bm ln nh thp v phun qua vi

thnh sng m.

-Sn phm ly ra y thp gin on hay lin tc.-Thp c th cao n 60m.

Hnh 1.3:Thit b sy phun kiu thp.

em chan

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b. Loi thng:

-Cu to:Gm mt thng hnh tr 1 c y nn. Np trn c t mt 2 ni vi

u vi phun 3 c tc quay rt ln 2000 6000 vng/pht. Caloriphe si 4 t

nng khng kh. Sn phm thu hi xyclon 5, cn khng kh thi ra ngoi nh qut 6.

Hnh 1.4: Thit b sy phun kiu thng.

c. C ch ca qu trnh, cc phng php phun bi v ng dng:

-C ch: Vic phun cht lng thnh bi m trong phng sy v qu trnh tin hnh

rt nhanh n mc cha kp t nng vt liu ln qu thi hn cho php th vt liu kh. Sn phm thu c dng bt mn nn sau khng cn nghin tn na.

Cng sy tng t l thun vi s tng ca b mt tip xc gia VLS v TNS;

tc l ph thuc vo phn tn ca cht lng thnh bi.

Cc phng php phun bi:

+ Ly tm:Cho cht lng i vo mt da quay nhanh khong 2000 6000 v/pht, c

th phun huyn ph v cht lng nht thnh bi.

+ Ckh:Nh vi phun, trong cht lng c y bng bm vi p lc 200 at.- phun u v to tia nh, cc vi phun c c nhiu l nh vi ng knh 0,5

mm.

- Loi ny khng thun tin i vi dung dch huyn ph v cc dung dch nht.

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+ Dng khnn: Nh cc vi phun trong cht lng c y bng khng kh

nn vi p sut 2,5 6 at.

- Ch : Trong 3 loi trn, thng dng loi ly tm v n c hiu qu cao nht

nhng c nhc im l tiu hao nng lng nhiu nht.

-ng dng: My sy phun c dng sy cc dung dch nh : bt c ph, ca

cao, sa b,

1.4.2.3. Thit b sy tng si

- Cu to:

Hnh 1.5:Thit b sy tng si.

-Nguyn tc lm vic:

Qut 1 a khng kh vo trn vi khi l (hay khng kh + khi l) phng 2 rivo bn di phng sy 3, qua li phn phi 4 ri tin hnh sy vt liu.

Vt liu cho vo phu v nh vt ti 5 a vo pha trn bung sy. y chng

gp hn hp kh nng i t di ln v to thnh tng si. Vt liu kh c thi q ua

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tm chn 6 sang thng cha 7 ri ra ngoi. Cn nhng ht nh b dng kh cun theo s

c thu hi bi xyclon 8.

Tc nhn sy c th l khng kh, khi l hoc khng kh + khi l.

- u nhc im:

+ u im: Cng sy mnh lit, cho php sy nhit cao hn nhit cho

php v thi gian tip xc ngn. Hiu qu s dng nhit cao, c kh nng iu khin t

ng. Loi ny ang c s dng rng ri.

+ Nhc im: Khng sy c vt liu c m qu ln, cc to, d v.

+ Tr lc thu lc ln, thit b mau hao mn.

1.4.2.4. Mt s thit b sy khc

a.Thit b sy bng bng ti:Gm mt phng hnh ch nht, trong c mt vi bng ti chuyn ng chm

nh cc tay quay. Cc bng ny ta trn cc con ln khi b vng xung, bng ny

lm bng si bng tm cao su, bng kim loi hay li kim loi v chuyn ng vi tc

khong 0,3 0.6 m/pht. Loi thit b ny c th dng sy rau qu, ng cc, than

- Cu to:

Hnh 1.6:Thit b sy bng bng ti.

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b.Thit b sy bng kh thi.

Hnh 1.7:Thit b sy bng kh thi.

- Dng sy vt liu dng ht nh hay tinh th.- Vt liu vo my v c dng kh c tc 10 20 (m/s) cun theo ln ng

thng ng di t 10 20 (m/s). sau vo phng gim tc ri vo xyclon

thu hi sn phm.

- Thi gian sy rt ngn t 5 7 (s).- u im: B mt tip xc kh ln, nn qu trnh sy rt mnh lit, thi gian sy

nhanh nn cho php sy nhit cao. Thit b cu to gn, n gin.

- Nhc im: Kh iu chnh qu trnh, tn nhiu nng lng.

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c.Sy bng tia bc x.

Hnh 1.8:Thit b sy bng tia bc x.

-Nng lng bc x tia hng ngoi pht ra c th truyn cho vt liu mt lngnhit ln v t c tc bay hi m cao hn so vi sy i lu v tip xc.

-Sy bc x thng dng sy b mt sn trong cng nghip ch to my, syhng dt, giy cht do, cc sn phm g, thc phm

d.Sy trc.-C th gm mt hay hai trc. My sy c cng sy cao (c th 60 70

kg/m2h).

-Sy c cc vt liu nho, km bn vng nhit cao. Tit kim c nhinliu v t mt nhit. Nhc im l m cui ca sn phm kh cao.

e. My sy chn khng.My sy lm vic chn khng c u im so vi my sy lm vic p sut kh

quyn l: sy c vt liu khng chu c nhit cao hay d b oxy ho, vt liu d

b bi hay vt liu thot ra dung mi qu cn thu hi v vt liu d n.

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f. My sy thng hoa:Ngi ta sy vt liu trng thi ng bng trong mi trng chn khng cao

0,1 1 (mmHg). Mc ch l to s chnh lch nhit gia vt liu sy v

ngun nhit bn ngoi.Ngi ta dng bm chn khng ht hi m v to chn khng. u im ca

loi my sy ny l sn phm thu c c cht lng cao. Vt liu sy khng b bin

cht, bo v vitamin nh lc ti.

g.Thit b sy kiu thng ng:

Hnh 1.9:Thit b sy kiu thng ng.

-Gm mt thng hnh tr t c nh, bn trong c mt trc gn nhiu da quay vkhong cch gia cc da bng nhau. S lng da v tc quay ca da ph thuc vo

vo tnh cht ca vt liu v yu cu k thut. Trn thnh thng c gn nhng phu

hng vt liu. Qu trnh sy ngc chiu.

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-Khng kh c qutchnh a qua caloriphe si ri vo thng sy t di ln.Vt liu sy vo ca trn, ri xung da. Do a quay, vt liu vng ra thnh thng ri

li xung da di nh phu hng liu. C nh th, vt liu sy v tc nhn sy s tip

xc vi nhau khi ra khi my sy, vt liu kh t yu cu. Tc nhn sy c qut

ht ph a sang xyclon thu hi sn phm dng bi nh. thu hi trit sn

phm, ngi ta cho dng kh nng i vo thit b thu hi t trc khi ra ngoi.

-Vic b tr hai qut l cn thit m bo cho tc nhn sy thng c tr lcv lu thng trong ton h thng.

-Thit b sy kiu thng ng tn t nng lng hn my sy thng quay v tchim mt bng hn.

-Nhc im l vt liu d b v vn nhiu.1.5. Tng quan v sy nhit thp

1.5.1. Gii thiu cc phng php sy lanh

1.5.1.1. Lch s hnh thnh v pht trin ca bm nhit

Bm nhit c qu trnh pht trin lu di, bt u t khi Nicholas Carnot xut

nhng khi nim u tin. Mt dng nhit thng thng di chuyn t mt vng nng

n mt vng lnh, Carnot a ra lp lun rng mt thit b c th c s dng o

ngc qu trnh l bm nhit. u nhng nm 1850, Lord Kelvin pht trin cc l

thuyt v bm nhit bng lp lun, cc thit b lm lnh c th c s dng gia

nhit. Sn phm bm nhit u tin c bn vo nm 1952. T khi xy ra cuc khng

hong nng lng vo u thp k 70, bm nhit li bc vo mt bc tin nhy vt

mi. Hng lot bm nhit mi kch c cho cc ng dng khc nhau c nghin cu

ch to, hon thin v bn rng ri trn th trng. Ngy nay, bm nhit tr nn rtquen thuc trong cc lnh vc iu ha khng kh, sy, ht m, un nc

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Hnh 1.10 S nguyn l h thng bm nhit

1.5.1.2. Gii thiu cc phng php sy lnh

Trong phng php sy lnh, ngi ta ra chnh phn p sut hi nc gia

vt liu sy v tc nhn sy bng cch gim p sut ring phn ca hi nc trong tc

nhn sy nh gim lng cha m. phng php sy lnh, nhit b mt ngoi nh

hn nhit bn trong vt, ng thi do tip xc vi khng kh c m v phn p

sut hi nc nh nn lp b mt cng c phn p sut hi nc nh hn pha bn trong

vt. Ni khc i, y gradient nhit v gradient p sut c cng du nn gradient

nhit khng km hm qu trnh dch chuyn m nh khi sy nng m ngc li, n

c tc dng tng cng qutrnh dch chuyn m trong lngvt ra ngoi bay hi lm

kh vt. Khi , m trong vt liu dch chuyn ra b mt v t b mt vo mi trng c

th ln hn hay nh hn nhit mi trng hoc cng c th nh hn 0o.

Qu trnh truyn nhit thc hin c thng qua s thay i pha lm vic ca micht lnh. Mi cht lnh trong gin bay hi hp th nhit v bay hi nhit thp v

p sut thp. Khi hi mi cht lnh ngng t nhit cao, p sut cao ti dn ngng

t, n thi nhit p sut cao hn. Khi s dng trong qu trnh sy, h thng sy s

dng bm nhit lm lnh khng kh ca qu trnh n im bo ha, v sau ngng t

nc (kh m), do lm tng kh nng sy ca khng kh. Trong qu trnh ny ch

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tun hon mc nhit thp (nhit hin v nhit n) t khng kh. Cu trc ca dn bay

hi v dn ngng t c b tr nh hnh v (hnh 1.11)

Hnh 1.11 Hai phng thc trao i nhit thng qua bung sy.

Hnh 1.12 S qu trnh sy theo hai phng thc trao i nhit

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Trong trng hp th nht (hnh 1.11 a), my sy lnh hot ng va nh mt

my kh m va nh mt b gia nhit khng kh. Trong cch b tr th hai (hnh 1.11

b), dn bay hi c xen vo dng khng kh m trong khi khng kh sch li c a

ton b vo dn ngng t. Vic sp xp theo kiu ny, nhit n (cng vi mt lng ln

nhit hin) c hi lu bng cch kh m kh thi v truyn cho tc nhn sy qu trnh

thng qua dn ngng t. M hnh ny thch hp khi khng kh mi trng kh ( m

tng i thp), nhng n li khng kinh t, bi v dng kh thi tng t nh khng

kh bn trong. Trong c hai m hnh trn, kh thi t bung sy c th c hi lu li

i n dn bay hi ngha l khng kh c th tun hon ton b hay tng phn. Ta c

th qu trnh sy nh hnh 1.12 tng ng vi hai trng hp b tr trn hnh 1.11

1.5.2. Nguyn l lm vic ca h thng sy lnh

Khc vi phng php sy nngtrong phng php sy lnhngi ta to ra

chnh phn p sut ring phn ca hi nc gia tc nhn sy v vt liu sy bng cch

gim phn p sut trong tc nhn sy nh gim lng cha m. phng php sy

lnh, nhit b mt ngoi ca vt nh hn nhit bn trong vt, ng thi do tip

xc vi khng kh c m v phn p sut hi nc nh nn b mt cng c phn p

sut hi nc nh hn pha bn trong vt. Ni khc i, y gradient nhit v

gradient p sutc cng du nn gradient nhit khng km hm qu trnh dch

chuyn m nh khi sy nng m ngc li, n c tc dng tng cng qu trnh dch

chuyn m trong lng vt ra ngoi bay hi lm kh vt. Khi m trong vt liu dch

chuyn ra b mt v tb mt vo mi trng c th ln hn hoc nh hn nhit

mi trng hoc cng c th nh hn 0oC.

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Hnh 1.13 S h thng sy lnh

Nguyn l hot ng ca thit bMy sy lnh hot ng da trn nguyn l ca qu trnh sy nhng tc nhn sy

c x l tch m trc khi vo bung sy. Nguyn tc tch m tc nhn sy bng

cch s dng dn lnh ca my lnh lm gim nhit ca tc nhn sy di nhit

im sng hi nc trong khng kh m ngng t thnh nc v c ly ra

ngoi. Phn tc nhn sy sau khi tch m c gia nhit li bi dn nng ca my lnhrii tip tc a vo bung sy thc hin qu trnh sy.

Khng kh ngoi tri trng thi O (t0, 0) c a qua dn lnh. Khi my hot

ng mi cht lnh c my nnnn ln dn ngng t sau i qua van tit lu ri v

dn lnh trao i nhit vi khng kh ngoi tri c ht vo, qu trnh lm lnh lm

cho khng kh lnh tr nn bo ha nc ngng t thot ra ngoi, lc ny khng kh

ngoi tri c nhit l t2 trng thi 2, sau tc nhn sy tip tc i qua dn nng,

nng nhit tc nhn ln n nhit t3 trng thi 3. Tc nhn sy ny sau c

dn qua cc khay vt liu sy thc hin qu trnh sy tch m ng nhit. Qu trnh

sy sau tip tc vi lng tc nhn hi lu cha m vt liu sy.

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1.6. Mt s kt qu nghin cu v sy lnh ca cc tc gi trong v ngoi nc

Vic s dng bm nhit trong cng nghip cng nh dn dng sy, si, ht

m, iu ha khng kh, c nghin cu v ng dng rt nhiu trn th gii. Sau

y l tng quan mt s cng trnh nghin cu :

1.6.1. Cc tc gi trong nc

Tc gi Phm Vn Ty v cc cng s tin hnh nghin cu v ng dng

thnh cng h thng bm nhit sy lnh ko Jelly, ko Chew, Caramel, ko Cng

ti cng ty bnh ko Hi H [19].

Nm 1997, 1998 cc tc gi thit k ln lt hai h thng lnh theo nguyn l bm

nhit nhit thp kiu mun. sy ko Jelly vi nng sut 1100 kg/ngy v 1400kg/ngy hin nay vn cn c s dng cho phng sy lnh s 2 v s 3 Nh my thc

phm Vit Tr - Cng ty c phn bnh ko Hi H. Thng s nhit khng kh bung

sy 22-280C, m 30-40%. S nguyn l h thng nh hnh 1.14

Hnh 1.14 S nguyn l h thng bm nhit kiu mun

Mt h thng my ht m h tr cho dy chuyn sn xut ko Caramem ca

Cng Ha Lin Bang c ci to t my iu ha khng kh c cho phn xng ko

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caramem v h thng bm nhit ht m cng sut lnh 120.000 Btu/h s dng 4 my

lnh Trane TTK 530 cng sut mi my l 30.000 Btu/h hin nay ang s dng cho

phng bao gi ko cng thuc X nghip Cng ty CP Bnh ko Hi H c lp t

t nm 1999. Qua thc t s dng, thy rng ngoi u im r tin (gim khong 50%

vn u t) v tit kim nng lng (in nng tiu th gim gn 50%) so vi phng

n dng my ht m, cc h thng ht m v sy lnh ny hot ng n nh, lin tc v

gim chi ph bo dng. Tuy nhin, n cn c nhc im l cng knh, s dng nhiu

qut v ng c xen k, trong h thng nhiu bi bt nn phi bo dng ng c li

phi thc hin trong khng gian hp, kh thao tc.

khc phc nhng nhc im trn nm 2005 nhm tc gi thit k ch to

my sy lnh cho phng sy lnh s 1 theo nguyn l bm nhit kiu nguyn khi BK-

BSH18A.So vi cng ngh dng cc bm nhit kiu m un th BK-BSH18A c thit

b x l khng kh c ch to dng t hp gn c th t ngoi nh, trong nh hay

trong bung sy v tc khng kh c th thay i ph hp vi yu cu ca vt liu

sy khc nhau.

Vic s dng bm nhit nhit thp ht m v sy lnh c nhiu u im v

rt c kh nng ng dng rng ri trong iu kin kh hu nng m ph hp vi thc t

ti Vit Nam, mang li hiu qu kinh t - k thut ng k. Bm nhit sy lnh cbitph hp vi nhng sn phm cn gi trng thi, mu, mi, cht dinh dng v khng

cho php sy nhit cao, tc gi ln. Cc h thng ht m v c bit l cc h

thng sy lnh c cu trc lun thay i ph thuc vo c tnh ca vt liu sy, cu

trc ca dn lnh s dng, nn khng c mt cu trc chung cho tt c cc i tng

sy, tuy nhin vn c chung nguyn tc v phng php tnh ton thit k. Do , cn

phi tip tc nhng nghin cu c bn, y v cc qu trnh, cc gii hn k thut v

cc vn t ng iu chnh khng ch lin hon nhit v m ca tc nhn sycng nh ca vt liu sy.

1.6.2 Cc tc gi nc ngoi

Macio N. Kohayakawa v cc cng s [19] tin hnh nghin cu nh hng cacc yu t nh: vn tc gi Var, chiu dy ca vt liu L n h s khuch tn qu trnh

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sy Deftrong h thng sy xoi bng bm nhit. Mi cht lnh s dng trong h thng

l R22. H thng sy xoi s dng hai dn ngng trong gia nhit cho khng kh.

Nhit khng kh trong qu trnh th nghim thay i t 40oC n 56oC. Vn tc gi

thay i t 1,6 m/s n 4,4 m/s, chiu dy vt liu sy thay i t 5,8 mm n 14,2 mm.

Khi lng vt liu sy mi m l 300g, thi gian sy l 8h/m. Da vo cc quan h

l thuyt tnh ton h s khuch tn, s dng phng php quy hoch trc giao v kt

hp vi s liu thc nghim, cc tc gi xy dng c phng trnh hi qui xc

nh h s khuch tn Defnh sau:

Def = 4,2625 - 0,61922.Var + 0,380538.Var2 + 1,012517.L0,90343.Var.L (1.23)

Phng trnh (1.23) cho thy rng nh hng ng thi ca hai thng s cng nh

mc nh hng ca chng n h s khuch tn D ef. y, nh hng ca tc

gi Varl ln nht, sau n chiu dy ca vt liu sy. Phng trnh (1.23) cng cho

bit nh hng ln nhau gia hai thng s thng qua mi lin h cho nhau gia chng.

Tuy nhin, phng trnh ny khng cp n nh hng ca nhit , m sy mc

d nh hng ca chng l ln n h s khuch tn. iu ny cng c chnh tc gi

khng nh trong nghin cu ca mnh. Do vy, cn c nhng nghin cu nh gi v

nh hng ca cc yu t ny.

Phani K.Adapa, Greg J.Schoenau v Shahab Sokhansanj [19] tin hnh nghin

cu l thuyt v thc nghim qu trnh sy bng bm nhit i vi cc vt liu c bit.

Cc tc gi tin hnh thit lp cc quan h tnh ton l thuyt qu trnh sy lp mng.

Cc tc gi thit lp phng trnh cn bng nng lng, cn bng cht, truyn nhit

v truyn m gia vt liu v khng kh cho mt phn t th tch vt liu sy nh sau:

Phng trnh truyn m

eM

k M Mt

(1.24)Trong :

M: m cn bng ca vt liu sy ti thi im t

Me: m cn bng ca vt liu sy, c xc nh bng thc nghim

t: Thi gian sy, s

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k: Hng s sy [1/s], c xc nh nh sau: k=0,2865.exp 0,179.Ta (1.25)

Gii phng trnh (1.24) ta xc nh c m ca vt liu khi sy ti thi im t nh

sau:

0

0 . .kt kt

e eM M M M e e

(1.26)Vi M0: m ca vliu sy ti thi im t0 = 0

Phng trnh cn bng cht.

p

a

GW M

x G y

(1.27)

Vi: W: cha hi ca khng kh

x: Chiu dy ca vt liu sy

Gp: Lu lng vt liu sy chuyn ng qua bng ti, kg/m.s

Ga: Lu lng khng kh chuyn ng qua bng ti, kg/m2.s

y: Qung ng dch chuyn ca vt liu sy, m

Gii phng trnh (1.27), thu c cng thc xc nh s thay i ca cha hi W

theo chiu dy vt liu sy (gi thit tnh cht ca vt liu sy l ng u theo phng

dch chuyn y):

0 . .P

a

G MW W x

G y

(1.28)

Phng trnh cn bng nng lng

. . / .

. .

cv a pw a ga

a pa pw

h G G W x T T T

x G C C W

(1.29)

Trong : Ta: Nhit ca khng kh sy, 0C

Tg: Nhit ca vt liu sy,0C

hcv: H s truyn nhit th tch, kJ/m3.ph.K

Cpa: Nhit dung ring ca khng kh kh, kJ/kgK

Cpw: Nhit dung ring ca hi nc, kJ/kgK

Gii phng trnh (1.29), xc nh c nhit khng kh ti u ra:

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( / ) . 0.d a xa g gaT T a T T Trong :

. .a pa pwa G C C W

. .cv a pw Wd h G C x

Ta0 -Nhit khng kh ti v tr ban u x0 = 0,0C

() ( ( ) ) ( )

(1.30)

Trong : Lg - nhit n hahi ca nc trong vt liu sy, kJ/kg

Cpg- nhit dung ring ca vt liu sy, kJ/kgK

Cpl- nhit dung ring ca nc, kJ/kgK

Gii phng trnh (1.30) ta s tm c s thay i nhit ca vt liu sy :

(

)

(1.31)

y:

0. . . ; . .cv a g cv pw aa plW W

f h T G L g h C C Gx x

. .p pg plh G C M C 1.7. So snh phng php sy lnh vi phng php sy nng nh my

Sy l qu trnh tch nc v hi nc ra khi vt. Tuy nhin, sy l mt qutrnh cng ngh i hi sau khi sy, vt liu phi m bo cht lng cao, tiu tn nng

lng t v chi ph vn hnh thp. C hai phng php sy:

a) Phng php sy nng ti nh my

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Trong phng php sy nng, tc nhn sy v vt liu sy c t nng. Do tc nhn

sy c t nng nn m tng i gim p sut ring phn ca hi nc Pam

trong tc nhn sy gim. Mt khc do nhit ca vt liu sy tng ln nn mt hi

trong cc mao qun tng v phn p sut hi nc trn b mt vt cng tng theo cng

thc:

=o

r

p

p= exp

ro

h

p

2

Trong Pr: p sut trn b mt ct mao dn, N/m2

Po: p sut trn b mt thong, N/m2

:Sc cng b mt thong,N/m2

h: Mt hi trn ct dch th trong ng mao dn, kg/m3

0: Mt dch th, kg/m3

Nh vy trong h thng sy nng c hai cch to ra chnh phn p sut hi

nc gia vt liu sy v mi trng:

Gim phn p sut ca hi nc trong tc nhn sy bng cch t nng. Tng phn p sut hi nc trong vt liu sy.Tm li, nh t nng c tc nhn sy v vt liu sy hoc ch t nng vt liu

sy m hiu s gia phn p sut hi nc trn b mt vt P hbv phn p sut hi nc

trong tc nhn sy Phtng ln dn n qu trnh dch chuyn m t trong lng vt liu

sy ra b mt v i vo mi trng.

H thng sy ti nh my l h thng sy i lu tc nhn sy nhn nhit t c c

thanh in tr v c qut thi qua vt liu sy.

u im ca phng php sy nng ti nh my- Thi gian sy bng cc phng php sy nng ngn hn so vi phng php

sy lnh do c th iu chnh c nhit t 30OC120OC

- Nng sut cao v chi ph ban u thp.

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- Ngun nng lng s dng cho phng php sy nng c th l khi thi, hinc nng, hay cc ngun nhit t du m, than , rc thi,...cho n in

nng.

- Thi gian lm vic ca h thng cng rt cao.Nhc im

- Ch sy c cc vt sy khng cn c cc yu cu c bit v nhit .- Sn phm sy thng hay b bin mu v cht lng khng cao.- V nh my dng in tr sy nn lng nhit ta ra l rt ln, qun tnh nhit

cao kh iu chnh nhit

- Chi ph in nng cao- Sn phm sau khi sy cht lng khng ng u, xy ra tnh trng nguyn

liu b chy do qun tnh nhit ln cao.

b) Phng php sy lnh

Trong phng php sy lnh, ngi ta to ra chnh p sut hi nc gia vt

liu sy v tc nhn sy bng cch gim phn p sut hi nc trong tc nhn sy P h

nh gim cha m d. Mi quan h c th hin theo cng thc:

Ph =d

dB621,0

.

Trong B - p sut mi trng (p sut kh tri).

Khi , m trong vt liu dch chuyn ra b mt v t b mt vo mi trng c

th trn di nhit mi trng (t > 0oC) v cng c th nh hn 0oC.

c) So snh phng php sy lnh v phng php sy nng

tin hnh so snh thc nghim phng php sy lnh vi phng php sy

nng, cc loi rau c thc phm v dc liu nh c rt, c ci, hnh l, da, mt, nhn,

mng ct, hnh ty, hn hp dch p gng v bt avicel, c sy th nghim vi

khong thng s nhit sy t = 250C n 400C, tc gi tng si =2,2 4 m/s .

Kt qu sn phm sau th nghim c cc c im v mu sc, mi v, hm lng cht

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dinh dng v trng thi vt sy c bo ton hn hn cc cng ngh sy nng truyn

thng, ngay c khi so snh vi k thut sy hin i bng tia hng ngoi. iu chng

t nhng c im u vit ca cng ngh sy lnh trong vic ng dng sy nhng loi

rau qu giu vitamin, c gi tr dinh dng cao trong thc t [19].

Di y l bng so snh cc phng php sy khc nhau vi phng php sy

lnh s dng bm nhit nhit ca Vin Cng Ngh Thc Phm, s Cng Nghip H

Ni da trn cc tiu ch v cht lng sn phm, gi thnh sn phm, thi gian

sy, chi ph u t, chi ph vn hnh v bo v mi trng, phm vi ng dng, vv

Bng1.1: nh gi so snh cht lng sn phm sy bng bm nhit sy lnh

vi phng php sy nng truyn thng v sy hng ngoi

[Vin Cng Ngh Thc Phm, s Cng Nghip H Ni]

Th

t

Phng Php sy

Ch tiu so snh

Sy nngSy thng hoa

v chn khng

Sy lnh s dng

my ht m kt hp

my lnh

1Cht lng sn phm (mu

sc, mi v, vitamin)

Km hn rt

nhiu Tt hn Bng nhau

2 Gi thnh sn phm Thp hn t hn nhiu t hn

3 Thi gian sy Ngn hn Ngn hn Ln hn hoc bng

4 Chi ph u t ban u thp hn Cao hn Cao hn

5 Chi ph vn hnh, bo dng r hn t hn nhiu t hn

6

Kh nng iu chnh nhit

tc nhn sy theo yu cu

cng ngh

Kh hn Kh hn Kh hn

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7 V sinh an ton thc phm km hn Tt hn Bng nhau

8 Bo v mi trng km hn Nh nhau Km hn

9 Phm vi ng dng Rng hn Hp hn Hp hn

1.8. nh gi v kt lun

a) So vi sy lnh s dng my ht m chuyn dng kt hp my lnh

Sy lnh s dng bm nhit nhit thp t ra u th vt tri v chi ph u t

ban u, gim tiu hao in nng. Vi iu kin ca Vit Nam th nn dng phng

php sy lnh s dng bm nhit nhit thp. Trong thc t, mt s nh my nhp

dy chuyn cng ngh sy s dng my ht m chuyn dng kt hp vi my sy

khng t hiuqu v chuyn sang dng bm nhit nhit thp.

b) So vi sy thng hoa v sy chn khng

Cht lng sn phm ca hai phng php ny thng tt hn sy lnh s dng

bm nhit nhit thp nhng cc ch tiu quan trong 2 v 5 li km hn nn ch pdng hai phng php ny khi yu cu v cht lng sn phm cao (ch tiu 1, 7), cn

li nn s dng phng php sy lnh bng bm nhit nhit thp.

c) So snh vi sy nng

Nhn chung, c mt s vt liu sy lnh khng c hiu qu nh sy g, cc loi

hoa qu c v dy th buc phi s dng sy nng. i vi cc vt liu cn li, nu vt

liu sy nhy cm vi nhit, d mt mu, d mt mi, cht dinh dng, gi thnh sn

phm c th trng chp nhn v thi gian sy khng i hi phi nhanh th nn sy

bng phng php sy lnh s dng bm nhit nhit thp.

Nh vy, phng php sy lnh bng bm nhit nhit thp t ra c hiu qu,

nht l i vi mt s sn phm c th (nhy cm vi nhit ) Do , ty vo tng

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trng hp c th, xem xt cc ch tiu trong bng trn, ch tiu no l quan trng th

quyt nh phng php sy ph hp.

d) Kt lun

u im ca cng ngh sy lnh c th xy dng c tng quy trnh cng nghsy hp l i vi tng loi rau, c, qu. Sau khi sy, nng sn, thc phm gi c

nguyn mu sc, mi v, thnh phn dinh dng tht thot khng ng k, t tiu

chun v sinh an ton thc phm ca Vit Nam v cc ch tiu k thut, cht lng sn

phm tng ng mt s nc khc trn th gii. Vit Nam l mt nc c kh hu

nng m, v th my sy lnh l cng ngh c bit ph hp vi cc loi nng sn, thc

phm, m bo c cht lng cng nh hm lng dinh dng, mu sc, mi v cho

sn phm. i vi cc sn phm nh c c rt, th l, hnh hay cc loi ko chocolate,

ko Caramen, Jelly... Mi trng ch bin nhng sn phm ny yu cu v nhit

khng c qu cao v m phi nh hn 45-50%. Tnh mi ca cng ngh ny l

qu trnh sy c thc hin nhit thp, to mi trng nhit cng chiu vi

mi trng m tng cng sy. Ngoi ra, cng ngh ny c nhiu u im k

thut khc nh: ht m nhng khng lm tng nhit mi trng nh my ht m

thng thng, sy kh c cc sn phm khng cho php lm kh trong mi trng

nhit cao.

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CHNG II

TM HIU V CNG NGH SY HNH L

2.1. Vt liu sy

Tt c cc sn phm u chu bin i trong qu trnh sy v bo qun sau .

Yu cu t ra i vi qu trnh sy l bo v ti mc tt nht cht lng, hn ch

nhng h hi trong qu trnh sybo qun ng thi nng cao hiu qu kinh t mt cch

ti u nht. Xt v c bn nhng thay i trong qu trnh sy c th chia ra:

Nhng thay i l hc: st m, gy, v, Nhng thay i ha l: trng thi tnh cht ca nhng keo cao phn t b thay

i.

Nhng thay i ha sinh: do s oxi ha ca cht bo, phn ng sm mu phienzim, phn ng enzim,

Nhng thay i do vi sinh vtNhng thay i lm thay i cu trc mu sc mi v, gi tr dinh dng v c

nh hng n tnh hi nguyn ca sn phm sau khi sy. Cc phng php sy khc

nhau c nhng u im v nhc im trong qu trnh sy cc sn phm rau qu. Trong

, phng php sy nng p ng c cc yu cu v nng sut, thi gian sy nhng

li khng p ng tt cc i hi v cht lng sn phm. Ngc li, i vi cc sn

phm sy yu cu nhit thp i hi phi c quy trnh sy ph hp hn. Cng ngh

sy lnh l mt cng ngh mi c dng gii quyt cc vn khng th gii quyt

i vi cng ngh sy nng. T nghin cu thc nghim chng minh nhng u im

vt tri ca cng ngh sy lnh trong qu trnh xy dng quy trnh sy i vi cc loi

rau c qu c gi tr kinh t.

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2.1.1. S cng ngh sy rau qu

Rau qu (phi thch hp cho qu trnh sy)

Lm sch (kh, t)

La chn phn loi (theo kch thc)

Gt sa

Ct, thi (ty theo yu cu)

Chn, hp (ty theo yu cu)

X l ha hc (nu cn)

Ch Ch p

Sy Sy C c

Lm ngui Lm ngui C c

Sy

Phn loi Phn loi Phn loi

p bnh Nghin nh

ng gi ng gi ng gi

Sn phm Sn phm dng Sn phm

dng nguyn bn mng dng bt

Hnh 2.1 S cng ngh sy rau qu

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2.1.2. nh hng ca qu trnh sy n cht lng sn phm

a) nh hng n cu trc

Thay i vcu trc ca cc vt liu l mt trong nhng nguyn nhn quan trng

lm gim cht lng sn phm. Bn cht v mc ca cc bin php x l rau qu

trc khi sy u c nh hng n cu trc ca cc sn phm sau khi hi nguyn.

Nguyn nhn l do s h ha ca tinh bt, s kt tinh ca xenluloza v s hnh thnh

cc sc cng bn trong do khc bit v m cc v tr khc nhau. Kt qu la s to

thnh cc vt nt gy, cc t bo b nn p vn vo vnh vin, lm cho sn phm c b

ngoi b co ngt, nhn nheo. Trong qu trnh lm t tr li sn phm ht nc chm,

khng th ly li hnh dng nh ban u.

Cc sn phm khc nhau c s dao ng v mc co ngt v kh nng hp th

nc tr li. Sy nhanh nhit cao lm cho cu trc b thay i nhiu hn so vi sy

vi tc va phi nhit thp. Trong qu trnh sy, cc cht ha tan di chuyn theo

nc t bn trong ra b mt ngoi ca sn phm. Qu trnh bay hi lm c c cc cht

tan b mt, kt hp vi nhit khng kh (c bit khi sy tri cy, c, tht,) gy ra

cc phn ng l ha phc tp ca cc cht tan b mt ngoi nn lp v cng khng

thm c. Hin tng ny gi l hin tng cng v (case hardening), lm gim tc sy v lm cho sn phm c b mt kh, nhng bn trong th m. V vy cn kim sot

nhit sy trnh chnh lch m qu cao gia bn trong v b mt sn phm. i

vi k thut sy lnh hon ton c th gii quyt c vn ny. H thng sy lnh c

nhit tng i thp cho nn qu trnh kh ca b mt vt liu s chm hn trong khi

m c ly ra nhiu bng s chnh lch phn p sut hi ngoi b mt v bn trong vt

liu sy.

b) nh hng n mi v

Nhit lm tht thot cc thnh phn d bay hi ra khi sn phm v vy phn

ln cc sn phm sy b gim mi v. Mc tht thot ph thuc vo nhit v

m ca vt liu sy, p sut hi nc v ha tan ca cc cht bay hi trong nc.

Nhng sn phm c gi tr kinh t cao nh vo c tnh mi v (nh gia v) cn c

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sy nhit thp. Mt s sn phm c kt cu xp to iu kin cho oxi khng kh d

dng tip xc vi sn phm, gy ra cc phn ng oxi ha cht tan v cht bo trong qu

trnh bo qun lm thay i mi v ca sn phm.

Tc ca qu trnh gy h hng ph thuc vo nhit bo qun v hot

ca nc. Phn ln rau qu ch cha mt lng nh lipit. Tuy nhin, s oxi ha cc cht

bo khng no to ra cc hydroperoxit tham gia vo cc phn ng polime ha, phn ng

tch nc hoc oxi ha to thnh aldehit, Kenton v cc axit gy mi i thui kh

chu.

c) nh hng n mu sc

C nhiu nguyn nhn gy ra s mt mu hay thay i mu trong sn phm sy,

nh l:

S thay i cc c trng b mt ca sn phm gy ra s thay i phn x nhsng v mu sc.

Nhit v s oxi ha trong qu trnh sy gy ra nhng bin i ha hc i vicarotenoit v clorophyl, cng nh hot ng ca enzim polyphenoloxidaza gy

nn s sm mu trong qu trnh bo qun cc sn phm rau qu.

C th ngn nga c nhng thay i ny bng cc phng php chn hphoc

x l tri cy bng axit ascorbic hoc SO2.

d) nh hng n gi tr dinh dng

Cc s liu v s tht thot cc cht dinh dng ca cc tc gi thng khng

thng nht, c th do s khc bit ng k trong cc qu trnh chun b sy, nhit v

thi gian sy, cng nh iu kin bo qun. rau qu, tht thot dinh dng trong qu

trnh chun b thng vt xa qu trnh sy. V d, tht thot vitamin C trong qu trnh

chun b to sy (dng khi) l 8% do qu trnh ct gt, 62% do chn hp, 10% do qutrnh nghin pu r v 5% do qu trnh sy.

Vitamin c ha tan trong nc khc nhau v khi qu trnh sy din ra, mt vi

loi (v d: vitamin B2 riboflavin) t trng thi bo ha v kt ta khi dung dch, nh

vy chng t b tn thng. Mt s khc, v d: axit ascorbic, ha tan ngay c khi m

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ca sn phm h xung n mc rt thp, chng phn ng vi cc cht tan vi tc

cng lc cng cao hn trong qu trnh sy. Vitamin C cng rt nhy cm vi nhit v

oxy ha. V th trnh nhng tht thot ln cn sy trong thi gian ngn, nhit

thp, bo qun m thp v nng kh oxi thp. Thiamin (Vit B1) cng nhy cm

vi nhit, tuy nhin cc vitamin khc ha tan trong nc bn vi nhit v oxy ha hn

v tn tht qu trnh sy him khi vt qu 5-10%, ngoi tr tht thot do qu trnh

chn hp.

S tn tht cc vitamin c th hn ch ng k hoc ngn nga hon ton khi s

dng cc phng php sy nhanh v n ha (nh sy phun), c bit bng phng php

sy thng hoa i vi cc nguyn liu nghin nt, nguyn cht dng ct nh.

Cc cht dinh dng nh cht bo (v d: cc axit bo khng thay th c v

cc vitamin A, D, E, K) phn ln cha trong phn cht rn ca sn phm v chng

khng b c c trong khi sy. Tuy nhin nc l dung mi ca cc kim loi nng, l

nhng cht xc tcca qu trnh oxy ha cc cht dinh dng khng no. Khi nc b

mt, cht xc tc tr nn hot ng hn v lm tng tc oxy ha. Cc vitamin tan

trong cht bo b bin i mt i khi tip xc vi peroxit c sinh ra do s oxy ha

cht bo. gim tht thot trong qu trnh bo qun ngi ta h thp nng oxy,

nhit bo qun v loi tr nh sang tip xc vi sn phm.e) nh hng n s hi nguyn sn phm (rehydration)

Sn phm sau khi sy khng th tr li tnh trng ban u khi lm t tr li. Sau

khi sy, t bo b mt p sut thm thu, tnh thm thu ca t bo b thay i, cc cht

tan di chuyn, polysacarit kt tinh v protein t bo b ng t, tt c gp phn vo s

thay i cu trc, lm tht thot cc cht d bay hi v y u l

Nhit trong qu trnh sy lm gim kh nng hydrat ha tinh bt v tnh n hi ca

thnh t bo, lm bin tnh protein, gim kh nng gi nc ca chng. Tc v mc

thm nc tr li c th c dng nh ch s nh gi cht lng sn phm sy.

Nhng sn phm sy trong nhng iu kin ti u, t h hi hn s thm t tr li

nhanh hn, hon ton hn.

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2.2. Cc c tnh ha l ca mt s rau qu giu vitamin ng dng phng php

sy lnh

Bt k mt loi nng sn phm no, trong thnh phn ca n u c cha cc

nhm hp cht hu c nh protein, gluxit, lipid, vitamin, axit hu c v cc chtkhong, cc sc t v.v vi t l khc nhau. Do mun bo qun tt tng loi sn

phm cn nghin cu k thnh phn ha hc v nhng bin i ca n di tc ng

ca cc nhn t bn ngoi. Thng thng trong thnh phn ca chng c cha nhng

hp cht sau:

a) NcTuyt i a s nng sn phm u c cha mt lng nc nht nh, n thay

i ty theo hnh thi gii phu v trng thi keo a nc trong t bo sn phm. Cnhng loi cha nhiu nc nh rau qu ti cha 65-95% nc, ht lng thc cha

tng i t hn t 11-20%. Nhng nhn chung trong t bo cc loi nng sn phm u

c cha cc dng nc sau y: (theo phn loi ca vin s P.A Rebinde)

Nc lin kt ha hcc c trng bng quan h nh lng rt chnh xc gia sn phm v nc.

y l loi lin kt rt bn vng. V d: Na3CO3.3H2O. Nu mun tch lng nc nyphi bng cch em nung ln hoc bng cc tng tc ha hc khc.

Nc lin kt ha lKt hp vi vt liu khng theo mt t l nht nh. N bao gm c nc hp

th, nc thm thu, nc cu trc. Mun tch lng nc ny ra cn tiu hao mt nng

lng bin n thnh th hi. Dng nc ny km bn hn.

Loi ny kt hp vi sn phm khng theo mt lng nht nh, chnh l lng

nc t do trong sn phm y l dng km bn vng nht. N c chuyn dch trongsn phm dng th lng. Mun tch ra phi bng cch sy kh nhit 105oC.

Hm lng nc trong sn phm cao hay thp c nh hng ln n cht lng

v kh nng bo qun ca chng. i vi nhng sn phm c hm lng nc cao, vic

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bo qun kh khn hn v nc chnh l mt mi trng thun li vi sinh vt hot

ng, lm cho cht lng sn phm b gim xung.

b) Nhng hp cht c Nit v s bin i trong qu trnh bo qun

Protein l hp cht cha Nit ch yu trong nng sn phm v n l thnh phn

dinh dng ch yu ca nhng sn phm c ht. N c gi tr dinh dng cao. Cc loi

sn phm khc nhau, hm lng protein cha trong chng khc nhau. La cha 7-10%,

ng 10-12%, cao lng 10-13%, u H Lan 22-26%, u tng 36-42%, crt 2% cc

loi qu ch di 1% (Tt c tnh theo % trng lng cht kh).

Trong thnh phn protein c mt y cc nhm: albumin, prolamin, glutein,

globulin.

Trong albumin c cha cc axt amin khng thay thProlamin c nhiu trong cc cy ha tho, c bit thnh phn protein cha trong

ht ng th nhm ny ch yu chim ti 50% l zein ca ng.

Globulin c cha nhiu trong ht c du, ht cy h u nh u tng, proteintrong u tng. Protein trong u tng c 8 axit amin khng thay th.

Glutelin cng l protein c trng ca ht cy ha tho, c bt ngi ta ch tigluten ca la m. rau qu hm lng protein rt t, ch chim khong 1-2%, thng ch yu

cc loi rau cao cp nh supl, crt, khoai ty tuy vy n c gi tr dinh dng rt

cao. Trong qu trnh bo qun, ni chung Nit tng s hu nh khng thay i hoc

thay i rt t, nhng Nit protein ha tan thay i kh nhiu, chng phn gii thnh cc

axit amin lm cho hm lng axit amin tng ln. Do lng Nit protein gim xung

v Nit phiprotein trong qu trnh ny cng tng ln mt cch r rt. Trong nhng cng

trnh nghin cu ca Gasiorowski v ht la m bo qun trng thi ti m trong cckho kn hon ton, ng pht hin thy s tng ln ca hm lng Nit phiprotein sau

15 tun l bo qun.

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2.3. L thuyt sy rau qu

2.3.1. Quy trnh x l trc khi sy

Sy rau qu thng thng c thc hin 3 dng ch yu: dng nguyn (hoc

ming); dng bn mng v dng bt hoc nh tng. Tu theo dng sn phm, cngngh sy rau qu c s chung nh sau:

Rau qu ti sau khi ra sch c loi b phn khng tiu chun, c phn ctheo kch thc, lm sch, ct ming. Sau rau qu c chn (hp), x l ho cht.

Tip theo, cc hnh thc sn phm khc nhau c ch bin theo cc s khc nhau.

Trong khi chn (hp), do tc dng ca nhit v m nn tnh cht ho l ca nguynliu b bin i c li cho s thot nc khi sy. ng thi vi sinh vt b tiu dit v

h thng enzim trong nguyn liu b mt hot tnh, hn ch ti a kh nng bin mu

trong khi sy rau qu v rt ngn thi gian sy. Ngoi ra qu trnh chn lm gim

ht m ca rau qu kh.

Trong cng nghip sy rau qu, ngn nga qu trnh oxy ho lm bin mu rauqu khi sy, ngi ta s dng cc cht chng oxy ho nh axit sunfur, axit ascobic,

axit xitric v cc mui natri ca axit Sunfur (nh sunfit, bisunfit, metabisunfit, ...)

x l ho cht cho rau qu trc khi sy.2.3.2 . Cc yu t nh hng n qu trnh sy

a) nh hng ca nhit tc nhn sy

Yu t nh hng nhiu n cht lng sn phm rau qu kh l nhit sy

Nu nhit sn phm trong qu trnh sy cao hn 60 oC th prtin b bin tnh. Nu

loi rau qu t thnh phn protin th nhit t nng sn phm c th ln n 80-90oC. Nu tip xc nhit trong thi gian ngn nh sy phun th nhit sy c th ln n

150 oC. i vi sn phm khng chn nh chui, u th c th sy nhit cao, giai

on u 90-100oC, sau gim dn xung.

Qu trnh sy cn ph thuc vo tc tng nhit ca vt liusy. Nu tc

tng nhit qu nhanh th b mt mt qu b rn li v ngn qu trnh thot m. Ngc

li, nu tc tng chm th cng thot m yu.

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b) m khng kh

Mun nng cao kh nng ht m ca khng kh th phi gim m tng i

ca n xung. C 2 cch lm gim m tng i ca khng kh [19]* Tng nhit khng kh bng cch dng calorife.* Gim nhit khng kh bng cch dng my ht m.Thng thng khi vo l sy, khng kh c m 10 - 13%. Nu m ca

khng kh qu thp s lm rau qu nt hoc to ra lp v kh trn b mt, lm nh

hng xu n qu trnh thot hi m tip theo. Nhng nu m qu cao s lm tc

sy gim. Khi ra khi l sy,khng kh mang theo hi m ca rau qu ti nn m

tng ln (thng thng khong 40 - 60%). Nu khng kh i ra c m qu thp th s

tn nng lng; ngc li, nu qu cao s d b ng sng, lm h hng sn phm

sy. Ngi ta iu chnh m ca khng kh ra bng cch iu chnh tc lu thng

ca n v lng rau qu ti cha trong l sy.

c) nh hng vn tc gi ca tc nhn sy

Trong qu trnh sy, khng kh c th lu thng t nhin hoc cng bc. Trong

cc l sy, khng kh lu thng t nhin vi tc nh (nh hn 0,4m/s), do vy thigian sy thng ko di, lm cht lng sn phm sy khng cao. khc phc nhc

im ny, ngi ta phi dng qut thng gi cng bc vi tc trong khong 0,4 -

4,0 m/s trong cc thit b sy. Nu tc gi qu ln (trn 4,0 m/s) s gy tn tht nhit

lng [20].

d) dy ca lp sy

dy ca lp rau qu sy cng nh hng n qu trnh sy. Lp nguyn liu

cng mng th qu trnh sy cng nhanh v ng u, nhng nu qu mng s lm gim

nng sut ca l sy. Ngc li, nu qu dy th s lm gim s lu thng ca khng

kh, dn n sn phm b " m hi" do hi m ng li. Thng thng nn xp lp

hoa qu trn cc khay sy vi khi lng 5 8 kg/m2l ph hp.[20]

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2.4. Mt s phng php sy rau qu

a) Phng php sy bng nng lng mt tri

Cng vic ny c tin hnh bng cch tri rau qu ln cc loi b mt ngoitri nhn nh sang mt tri trc tip. Tuy nhin, sn phm c cht lng km do

kh kim sotc vn v sinh, iu chnh m, nhit v tc sy.

Ngi ta ch to my sy dung nng lng mt tri nhm khc phc nhng

nhc im trn. Thit b ny s dng mt c cu rt n gin c tc dng tng cng

nhit t mt tri v bo v sn phm.

Cn ch phn bit gia sy trc tip v sy gin tip bng nng lng mt tri.

i vi sy trc tip, sn phm c t di nh nng mt tri v kt qu l s thay

i v mu sc, thnh phm vitamin. i vi sy gin tip, nguyn liu ny c bov

khi nh sng trc tip t mt tri. phng php ny, ngi ta s dng mt phng

ring thu nhn nhit lng t mt tri v ti , khng kh c cp nhit ri thi

qua phng cha sn phm.

My sy c hc dng nhin liu t nng khng k mt cch trc tip, thc

phm c sy bng kh t, hoc mt cch gin tip thc phm c sy bng khng

kh nng do kh t. Hai hnh thc ny u c kh nng kim sot tt hn so vi sy

bng mt tri v c th tin hnh c ngy ln m, khng ph thuc vo thi tit. Tuy

nhin, chi ph u t v vn hnh cho thit b ny kh cao. i vi cc sn phm

c la chn phn loi tt t nguyn liu ban u, cng on ra v x l cng quan

trng nh cng on sy.

b) Phng php sy rau qu dng lt

Phng php ny tin hnh sy mt hoc hn hp nhiu loi rau qu ( c xl bng dioxyt sunfua nhm hn ch mt mu v vi sinh vt pht trin) dng lt mng.

Loi ny thng c dng nh thc phm n nh, c th tng ngt bng cch b

sung ng vo nguyn liu ban u hoc thay i thnh phn nh thm hnh nhn,

da no hay bt gia v.

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c) Phng php sy b sung

V d nh chui c sy trc nhm loi b lp ng dnh tip tc c

sy b sung. Vic ng gi v bo qun sn phm sy kh i hi nhiu yu cu. Snphm sau khi sy cn c bo qun trnh nh sng mt tri, m v nhit nhm

ngn nga s gim hng v v h hng. Ngi ta thng dng dng c cha bng

gm, thy tinh, kim loi hay nha cho ti khi chng c ng hp. Gii php r nht

l s dng ti mng mng PE vi iu kin phi c ghp mng bng. Ni bo qun

cn thong mt, trnh xa nh sng mt tri, cn trng v loi gm nhm. a s, sn

phm sy u n nh cht lng trong nhiu tun.

2.5. La chn phng php sy lnh theo hng nghin cu ca ti

T nhng c tnh u vit ca cng ngh sy lnh ta nhn thy rng cng ngh

ny c nhiu u im v hiu qu kinh t cao trong vic ng dng vo sy cc sn phm

rau qu c gi tr kinh t. Tuy nhin, t l thuyt n thc tin l mt qu trnh lm vic

lu di i hi qu trnh u t nghin cu t m. Cng ngh sy lnh c th gii quyt

hn ch ca cng ngh sy nng trong cc quy trnh sy rau qu. Tuy nhin, vic ng

dng cng ngh sy lnh i vi cc loi sn phm rau c khc nhau cn phi nghincu c lp, t xy dng nhng quy trnh cng ngh chun cho cc loi hoc cc

dng rau qu. T yu cu thc t , cn thit phi tnh ton thit k mt m hnh thc

t v kim tra thc nghim i vi cc quy trnh cng ngh. Ni dung thc hin

Chng IV: Tnh ton thit k m hnh my sy lnh s dng bm nhit s trnh by

r ni dung ny.

2.6. Xy dng quy trnh cng ngh sy hnh

2.6.1. Gii thiu vt liu sy

Vng nguyn liuHnh l l loi gia v, khng th thiu trong cc ba n hng ngy, mc d vn

u t v cng lao ng cao hn cc loi rau gia v khc, nhng vn t hiu qu kinh t

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cao.

Hnh thn tho, cy sng lu nm, c mi c bit. C 5-6 l, l hnh tr rng,

di 30-50 cm, pha gc l phnh to, trn u thun nhn. Hoa t mc trn ng hnh tr,

rng. Hoa t dng hnh xim, c ngn thnh hnh tn gi trng ta hnh cu. Qu nang,

trn. Hnh c trng khp ni, ch yu l lm gia v. ng thi hnh cng l mt v

thuc nam c dng cha nhiu loi bnh: thuc ho, tr m, li tiu, st trng...

Hnh l l loi rau mu c bit l hnh kh, gia v ny v ang c b con

cc tnh nh Hi Dng vng ng Bng Sng Hng v b con BSCL c bit l

tnh VnhLong trng vi din tch kh ln. Nu nh trc yloicy trng ny ch

sn xut ri rc mt vi ni, th nay c trng nhiu a phng. Thm ch cn

hnh thnh nhng vng chuyn canh ln.

Vi gi tr kinh t cao hin nay hnh ang c thu mua vi s lng ln dng

ph v nhu cu trong nc v xut khu ra cc th trng ln nh Trung Quc, i

Loan c bit l Nht vi s lng ln.

c im v thnh phn ha hc ca hnh

Hnh ta tn khoa hc l Allium fistilosum Linn, thuc h Liliaceae.Hnh ta l mt loi c sng nhiu nm, cao khong 50cm, c mi c bit. Tp

hnh mu trng hoc hi nu nu, khng phnh ln. L gm 5 - 6 l, 3 cnh phi di,

hnh tr, phn trn, rng, di 30 - 50cm ng knh 4 8mm, pha gia phnh ln, u

thun nhn. Trc pht hoa cao bng l. Tn hnh cu, 1 2 l hoa, trng, mng. Phin

hoa trng, 5mm, c sc xanh, qu nang, hnh trn, ng knh chng 6mm. Ht hnh 3

cnh mu en.

Tinh du c mi c bit. Khng nh hnh ty v ti, thnh phn ha hc cahnh ta t c nghin cu su rng. Trong hnh ta c l c Alliin (allylcystein

sulfoxide) ging nh trong ti, nhng t hn. Alliin khi b thy gii bng iu t

alliinnase clora Allicin, acid pyruvic v amonia (xem thnh phn ha hc ca ti).

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Allicin l mt cht khng an nh nn d b thy gii v phng thch allyl bisulfide, c

mi c bit.

2.6.2. Xy dng quy trnh cng ngh sy Hnh

Chn nhng bi hnh tng i ng u, ng tui, sinh trng tt, khng b nhimsu bnh.

Ra sch v ro nc trc khi syHnh sau khi ra c thi mng ty thuc vo yu cu ca khch hang sau tri

u trn khay sy m bo sao cho qu trnh trao i nhit i lu ti u nht.

Hnh cha nhiu vitamin v cht dinh dng nn khng th tin hnh sy nhit cao. Thng thng khong nhit thch hp sy Hnh trong khong 40 - 600C

[3].Ta c s cng ngh sy c rt nh sau:

Hnh ti u vo ( m 92%)

Ra sch v ro nc

Phn loi hnh

Thi mng theo yu cu

Xp hnh vo thnh tng khay

Sy ( nhit 40-60oC) theo phng php sy lnh

n m yu cu (3 - 8%)ng gi bo qun

Hnh 2.2. S cng ngh sy C rt

2.7. Xc nh cc thng s u vo ca vt liu

a) Thnh phn dinh dng ca vt liu sy

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Gi tr dinh dng v thnhphn ha hc trong 100g hnh l : Nng lng

32,1Kcal 1%, Carbohydrates 7,34g 6% , Protein 1,83g 3% , Tng s cht bo 0,3g 3% ,

Cht x 2,6g 7% . Vitamin : Folates 64 g 16% , Niacin 0.525 mg 3% , Pantothenic

acid 0.075 mg 1.5% , Pyridoxine 0.61 mg 5% , Riboflavin 0.080 mg 6% , Thiamin

0.055 mg 5% , Vitamin A 997 IU 33% , Vitamin C 18.8 mg 31%

Vitamin E 0.55 mg 4% , Vitamin K 207 g 172% . Electrolytes : Sodium 16 mg 1% ,

Potassium 276 mg 6% . Minerals : Calcium 72 mg 7 % , Copper 0.083 mg 9% , Iron

1.48 mg 18.5% , Magnesium 20 mg 5% , Manganese 0.160 mg 7% , Phosphorus 37 mg

5% , Selenium 0.6 g 1% , Zinc 0.39 mg 3.5% . Phyto-nutrients: Carotene- 598 g ,

Crypto-xanthin- 0 g, Lutein-zeaxanthin 1137 g.

b) Xc nh kch thc vt liu

S dng thckp c chnh xc l 0,05mm c thang o t 0,05100mm. Kch

thc ban u l kch thc ln nht ca cc lt hnh thi mng c kch thc 3 5 mm

c) Xc nh m ca vt liu sy

m l mt thng s k thut quan trng v lm c s cho qu trnh sy. Cn

c vo m u v cui m chng ti c th tnh c thi gian sy l thuyt cng

nh thi gian bo qun.m u ca hnh c xc nh bng phng php t sy

d) Phng php xc nh mu, mi

Bng cch nh gi cm quan ca nhiu ngi v mu sc ca nguyn liu u

vo v sn phm.

e) La chn ch sy

i vi rau qu ni chung cng nh Hnh ni ring nhit sy yu cu khng

qu cao. Thng thng i vi cc loi rau qu nhit sy khng qu 60 OC, v nu

cao hn c th lm tn thng cc thnh phn vitamin, cht dinh dng v mu sc

trong sn phm dn n lm gim gi thnh sn phm. y ta tnh ton theo hai ch

sy khc nhau, mt l ch sy hi lu hon ton tc nhn sy v ch thi b tc

nhn sy.

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CHNG III

KHO STTHC TRNG V LA CHN PHNG PHP SY

3.1. Kho st my sy ti nh my

L mt doanh nghip chuyn ch bin tm xut khu sang th trng cc nc

trong khu vc, nm 2007, trc tnh hnh nguyn liu tm ngy cng c nhiu bin

ng v mt gi c, Chi nhnh Cng ty c phn thy sn Bc Liu ti Khnh Ha

chuyn hng sang ch bin nng sn xut khu. Bc i ny khng ch mang v li

nhun hng nm ln n 9 triu USD cho cng ty, gip th trng tiu th hng ha n

nh m cn gip Cng ty d dng hn trong vic ch ng ngun nguyn liu phc v

sn xut v xut khu.

Trong xu th cnh tranh ca nn kinh t th trng, cng vi l vn b ng

v ngun nguyn liu thy sn, thng xuyn nh hng n hot ng sn xut ca

doanh nghip, nm2007, Chi nhnh Cng ty c phn thy sn Bc Liu ti Khnh Ha

mnh dn th nghim xut khu nhng l hng nng sn u tin. Thi gian u,

doanh nghip sn xut song song va ch bin tm va ch bin c tm v u bp, sau nhn thy li nhun tnhng mt hng nng sn, chi nhnh chuyn hn sang ch

bin rau qu xut khu. Hin nay, ngoi c tm v u bp, n v tng cng thm 3

mt hng rau qu khc l b ngi, t v hnh l. Cng vi mt hng nng sn l cc mt

hng kh, hin nay hnhl kh ang c xut khu vi s lng ln qua th trng

nht.

H thng sy ca nh my c u t ban u vi 12 bung sy mi bung c

cng sut 100kg/m, mi bung c din tch 4m2bn di c thit k cc mt sng

c cc l nh, vi 18thanh in tr mi thanh c cng sut 3kW vi3 qut mi qut c

cng sut 0,75kw v vy mlng in ta ra do mi bung lm vic l rt ln. Hin

nay my sy ti nh my ch phc v cho vic sy hnh v mt s mt hng nng sn c

nhu cu ca khch hng v lng in ta ra l rt ln.

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Lng in tiu hao ca nh my trong qu trnh sy:

/hNng sut mi m sy l 6h: Ta c tng in nng tiu th l

W = E.h = 56,27.6 = 337,5 kw

3.2. Nhim v thit k

Bn cnh vic nghin cu iu tra ngun nguyn liu ca nh my cung cp

cho h thng sy, vic phn b nguyn liu trong nm , phng thc vn chuyn

nguyn liu v ngun tiu th. Ngoi ra vic xc nh vic ngun nng lng cung cp

cho h thng, cui cng ta xc nh sn lng cn sy trong nm. Trn c s ta xcnh cng xut thit b sy theo sn phm G2, kg/h. Bc tip theo ta tin hnh nghin

cu cc thng s ch yu ca vt liu sy, yu cu v cht lng sn phm.

Da trn kt qu ta xc nh cng xut thit b sy G2, kg/h . m u ca

vt liu v m sau cng khi sy. Cui cng l cht lng ca sn phm v so snh

vih thng sy ca nh my khi sy bng in tr.

3.3. Chn phng n thit k

Qua qu trnh kho st ta la chn phng n thit k l sy vt liu bng bm

nhit vi thit k l h thng sy tng si: rt ph hp vi sy hnh, di tc dng ca

TNS vi thng s thch hp VLS lun trng thi bay l lng. Qa trnh sy lien tc s

cho hnh c kh v nh phn trn ca lp si d dng ly ra khi thit b sy

Trong h thng ny s truyn nhit v m gia tc nhn sy v vt liu sy l rt

tt nn trong cc h thng sy ln th sy tng si c cng xut ln , thi gian sy nhanhv vt liu sy c cht lng rt u.

3.4. Chon tc nhn sy v nng sut sy

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Tc nhn ca h thng sy phi m bo y cc yu cu v nhit , m,

iu kin v sinh Khng kh m y l tc nhn sy ph bin nht hin nay dng cho

hu ht cc loi sn phm v m bo v sinh cho sn phm.

3.5. S h thng sy

Hnh 3.1: S h thng sy lnh

Nguyn l lm vic ca h thng: Mi cht lnh sau khi trao i nhit vi khng

kh nng ( tc nhn sy ) c a tr li my nn, ti y my nn xy ra qu trnh p

nn on nhit tng nhit tngp sut v c a qua dn nng v trao i nhit

vi khng kh lnh gim nhit gim p sut sau khi trao i nhit mi cht tip tc

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c a vo bnh cha cao p qua thit b hi nhitv c tit lu gim nhit

gim p sut v quaytr v dn lnh.

th I d qu trnh sy:

Nguyn l: Qu trnh gia nhit tc nhn sy n nhit syt im E ti B.

im Bl trng thi khng kh nng trc khi vo bung sy.Sau khi nhn nhit t sn

phm sy tch m khi vt liu v mang ra khi bung sy giai on tip theo l qu

trnh lm lnh tc nhn sy n nhit ng sng. im C l trng thi khng kh

sau bung sy c hi lu hon ton, im D l trng thi khng kh trong thit b bay

hi lc bt u tch m, giai on D E l trng thi khng kh cui giai on tch m.

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CHNG IV

TNH TON THIT K M HNH MY SY LNH

S DNG BM NHIT

4.1. Gii thiu bi ton thit k v m hnh thit k

Cc loi rau qu rt nhy cm vi nhit cao, c bit l cc loi vitamin v

khong cht, nhit trn 600C cc cht ny bt u phn hy, dn n lm gim gi

tr dinh dng cng nh gi thnh ca sn phm [20]. i vi cc phng php sy

nng, vic ly m t vt liu ch thc hin c bng vic t nng vt liu hoc tc

nhn sy ln n nhit cao, s khng p ng c cc yu cu v cht lng.

gii quyt vn ny, my sy lnh s dng bm nhit ra i, l phng php sy m

vic ly m t vt liu sy c thc hin bng cch to ra s chnh p gia tc nhn

sy vvt liu sy cho nn khng i hi phi gia nhit tc nhn sy ln nhit qu

cao. Cng cng nguyn l dch chuyn m t bn trong nhn ra ngoi b mt vt liu

sy nhng c th d dng nhn thy rng, i vi phng php sy nng tc nhn sy

nhit cao s lm kh b mt vt liu nhanh hn do s cn tr qu trnh dch

chuyn m. Hn na, cc vt liu sy khc nhau c cu trc t bo v thnh phn ha l

khc nhau, vic s dng phng php sy lnh chng ta c th xy dng quy trnh cng

ngh i vi cc loi rau qu khc nhau. Bi ton thit k m hnh my sy lnh s dng

bm nhit sy C rt c thc hin xc nh cc thng s qu trnh t thc nghim.

4.2. Tnh ton qu trnh sy l thuyt

Mc ch tnh ton nhit ca qu trnh l xc nh tiu hao khng kh dng cho

qu trnh sy L, kg/h v tiu hao nhit Q, kJ/h. Trn c s tnh ton nhit xc nh cc

kch thc c bn ca thit b. ng thi qua vic thit lp cn bng nhit, cn bng

nng lng ca h thng s xc nh c hiu sut s dng nhit v hiu sut s dng

nng lng ca h thng cng nh tiu hao nhit ring ca bung sy v h thng.

My sy lnh da trn nguyn l ca t sy, nhng tc nhn sy c x l tch

m trc khi i vo bung sy. Nguyn tc tch m tc nhn sy dng dn lnh ca my

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lnh lm gim nhit ca tc nhn sy di nhit im sng bc hi nc

trong khng kh m ngng t thnh nc v ly ra ngoi. Phn tc nhn sy sau khi tch

m c gia nhit li bi dn nng ca my lnh ri tip tca vo bung sy thc

hin qu trnh sy.

C s ca phng php ny c thc hin bng cch gim m tng i

trong khng kh to ra s chnh lch p sut gia hi nc trong khng kh v hi

nc trong nng sn, thc phm. Bng cch ny m s tch ra khi nng sn, thc

phm, v i vo khng kh. Khi lm lnh khng kh trong thit b trao i nhit xung

thp hn nhit ng sng, hi bo ho m s ngng t v tch ra khi khng kh.

Khng kh sau i qua dn nng s sy kh vt liu.

Trng hp tc nhn sy hi lu hon ton Kiu sy hi lu hon ton s dngHeat pump dryer, tc nhn sy sau kh i qua bung sy (trng thi 3 c qut

ht tr v theo ng ng hi lu, sau qua dn lnh gim nhit n nhit

t4(trng thi 4) v n nhit t1(trng thi 1), ti y lng nc ngng t

s c dn ra ngoi. Tc nhn sy sau khi tch m tip tc i qua dn nng,

nng nhit ln t2(trng thi 2), ri i qua bung sy, thc hin qu trnh sy.

Qu trnh sy lthuyt c trnh by trn gin I-d nh sau:

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Hnh 4.1: th I-d ch s hi lu hon

1-2: Qu trnh gia nhit tc nhn sy n nhit sy. im (2) l trng thikhng kh nng trc khi vo bung sy.

2-3: Qu trnh sy ng I, tc nhn sy c m thp c thi qua vt liu sys nhn m thot ra t vt liu v mang ra khi bung sy.

3-4: Qu trnh lm lnh tc nhn sy n nhit ng sng. im (3) l trngthi khng kh sau khi i qua bung sy c hi lu hon ton, im (4) trng thi

khng kh trong thit b bay hi, lc bt u gim m.

4-1: Qu trnh tch m. im (1) l trng thi khng kh cui giai on tch m.4.2.1. Xc inh cc im nt trn th Id qu trnh sy

a) im 0 (Mi trng bn ngoi)*Nhit t0 = 260C c chn theo nhit trung bnh ca khu vc Thnh Ph Nha

Trang.

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* m tng i 0 = 81%* Phn p sut hi bo ha ca nc

* *

* Dung m ca khng kh

(Ly gi tr Pa = 0,993 bar)

* Entanpy ca khng kh mI0 = 1,0048.t0 + d0(2500 +1,842.t0)

= 1,0048.26 + 0,017(2500 + 1,842.26)= 69,94 kJ/kg.kk

* T cc thng s nhit v m khng kh ngoi tri, s dng th I-d ta xcnh c ts = 24

0 C (T im O (260C, 81%) dng ng d= const ct ng

=100%, ta xc nh c ts)

b)im 1: Trng thi khng khsau dn lnh*Nhit : t1 = 0 0C, theo [5]* mtng i v tc nhn sy n dn lnh ngng t m nn tc nhn sy trng

thi bo ha nn chn 1 = 100%.

* Phn p sut bo ho *

* Dung mca khng kh

* Entanpi

Thay cc thng s ca im 1 vo cng thc ta c:

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I1 = 1,0048.t1 + d1(2500 +1,842.t1)

= 1,0048.0 + 0,0062.(2500 + 1,842.0) = 15,5 kJ/kgkk

c) im 2: Trng thi khng kh sau dn nng*Nhit : t2 = 40

0

C (Nhit ci t trong qu trnh sy)* Phn p sut bo ho

* * * Dung m

Do qu trnh 1-2 l qu trnh gia nhit tc nhn sy thng qua dn nng ca bm

nhit nn : d1

= d2

= 0,0062 kg/kgkk

* Entanpy :I2 = 1,0048.t2 + d2(2500 +1,842.t2)

= 1,0048.40 + 0,0062.(2500 + 1,842.40) = 56,14 kJ/kgkk

* m tng i

d)im 3 : Trng thi khng kh trao i nhit vi tc nhn sy V mt l thuyt qu trnh sy trong phng php sy lnh l qu trnh ng Entaphi

t3 = 350C, I2 = I3 = 56,14 kJ/kgkk Vi m u ra ca tc nhn sy sau khi ra khi

bung sy chn = 15 %.

* Phn p sut hi bo ha

*

*

* Dung m:

I3 = 1,0048.t3 + d3(2500 +1,842.t3) -> d3 = 0,0082 kg/kgkk

e) im 4: Trng thi khng kh trc dn lnh* m: 4= 100%.* Dung m: d4 = d3 = 0,0082 kg/kgkk* Phn p sut bo ho

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Pb4 =

4

4 4

aP .d

0,621+d .=

*Nhit

t4 =b4

4026,42-235,512-lnP = * Entanpi

I4 = 1,0048.t4 + d4(2500 +1,842.t4)

= 1,004.10,8 + 0,0082(2500 + 1,842.10,8) = 30,5 kJ/kgkk

4.2.2. Tnh ton tc sy v thi gian sy

Theo yu cu ca ti ta la chn vt liu sy l Hnh, Cc thng s vt l caHnh.

m u vo 1 = 92% m cui 2 = 3% - 5%. y ta chn m trung bnh ca sn phm 2 = 4%. Khi lng ring [20]Tc sy:

Tiu chun Fe [2] :

iu kin nhit : t = 0,5.( t1 + t2 ) = 0,5.( 40 + 35 ) = 37,5

OC

t1: Nhit tc nhn sy vo bung sy

t2: Nhit khng kh ra khi bung sy

Vi t = 37,5OC ta c vk = 16,7.10-6 m2/s, , chiucao lp hnh

c dt = 1mm v .

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Ta ly ch sy ti u theo tiu chun:

Re1 = 0,5(0,190,259).Fe1,56 = 0,224.3385,11,56 =71842,2

Do :

Ta ta c h s trao i nhit i lu:

Mt dng nhit [1]

Vi tm : Nhit tc nhn sy, tm = 350C

tb : Nhit b mt vt liu tb = t = 270C [Xc nh da vo th I-d]

Hay 2629692 kj/m2h

Cng bay hi m trn b mt vt liu1b

2b

JJ =

r

r: Nhit n ha hi (theo gi tr p sut) vi tb = 270C. Ta c: P = 0,04517 bar.

Ta c: r = 2429 (kj/kg)

Tc sy ng tc [1]2

0

100bJU

R

Vi: o - khilng ring ca Hnh, o = n = 944 (kg/m3)

R -phn na kch thc vt liu sy

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Theo thc nghim kho st ly R= 2 mm

Thi gian t nng vt liu [1]

2

0

0

F R =

a

F0 chuns Fure- Xc nh chun s Bio nh s tng quan gia s trao i nhit trn b mt v tnh

dn nhit ca n:

Vi: R: Bn knh vt liu, m;

: H s dn nhit ca vt liu, = 0,35 W/mK; [20]

q : H s trao i nhit i lu;

Theo ti liu [3]

Vi: Uk : Tc dng kh, m/s;k: Khi lng ring khng kh ti nhit sy, kg/m

3;

R: Bn knh vt liu xc nh t thc nghim, mm;

- Chun s nhit T xc nh i lng t nng vt liu ti 1 im bt k:

Vi:

tk : Nhit trung bnh ca tc nhn sy trong khng gian sy, tk = tm = 37,50C;

o : nhit vt liu a vo thit b sy, o = to;

1: nhit b mt bay hi ca vt liu, 1= t ;

Tra theo th hnh 5.11 [3] ta tm c h s 0 0,6F

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a - h s dn nhit ca vt liu:v

aC

Trong : = 0,35 (w/m2K), = 944 (kg/m3), Cv = 3,47 (kJ/kgK) [20]

Thi gian sy ng tc [1]Theo cng thc thc nghim Egorov [1]

*Vi k1, k2: Hng s thc nghim v c on nh trong nhng khong m cn

bng ht cb v m tng i khng kh . Vi m khng kh 0 = 81% nm

trong khong (80%< < 100%) ta c gi tr cc h s k1 = 4,5 v k2 = 30,5.

Ta c:

Vy thi giansy ng tc

dk kx

1

- =

U

* d m ban u cu vt liu d = 92%

* kx m ti hn ca vt liu m

Thi gian sy gim tc [1]Vi dk = 1150 %

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Trong :

Tng thi gian sy: = 0+ 1+ 2 = 0,022 + 9,1 +0,046 = 9,58 (h)

4.2.3. Tnh ton nhit qu trnh

a)Xc nh lng m bc hiLp vt liu sy liu c b tr nm trn cc khay sy bng kim loi sao cho dng

tc nhn sy c th d dng di qua b mt ca vt liu nhng ng thi phi m bo

cho qu trnh truyn nhit v truyn m ca tc nhn sy din ra thun li nht. Qua

thc t kho nghim khi tin hnh cc th nghim b tr vt liu trn 1 khay sy ta c

khi lng vt liu sy G1 = 100 kg/m

* Lng m bc hi trong mt m sy

* Khi lng sn phm sau khi syG2 = G1-W = 10091,66 = 8,34 (kg/m)

* Thi gian sy = 9,58(h) theo kt qu tnh ton trn* Lng m bay hi trong 1 gi

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b)Lng khng kh kh cn thit lm bay hi 1 kg m

* Lu lng khng kh kh tun hon trong qu trnh syLlt = W.l0 = 91,66.500 = 45830 kgkk/m

c) Nhit lng dn nng cung cp cho qu trnh sy lm bay hi 1 kg m

*Nhit lng dn nng cung cp sy 1 mQlt = W.qlt = 91,66.20320 = 1862531,2 kJ

*Nng lng tiu hao cho qu trnh sy

* Lng m ngng tdlt = d3d2 = 0,00820,0062 = 0,002 kga

d)Lng nhit thu c t ngng t 1kg mqll lt = l0.(I4I1) = 500.(30,515,5) = 7500 J/kga

* Lng nhit dn lnh thu cQll lt = W.qll lt = 91,66.7500 = 687450 kJ

* Cng sut dn lnh ca qu trnh sy

4.2.4. Xc nh kch thc bung sy

Cc kch thc c bn gm Chiu di L, chiu rng B, chiu cao H. Trong ,

chiu di L xc nh theo thi gian sy v nng sut sy. i vi thit b sy tng si

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chiu cao xc nh theo yu cu duy tr ch sy ng u v tn dng c ti a

nhit ca mi cht.

Qua qu trnh kho st nh my ta c tng din tch bung sy S = 22,7 m2

4.3. Cn bng nhit cho qu trnh

Phng trnh cn bng nhit cho thit b sy:

Q + Qbs + WCntm1 + G2Cmtm1 + LI1 + Gvc.Cvctm1 = G2Cmtm2 + Q5 + LI3 + Gvc.Cvc.tm2

Q + Qbs = L(I3I1) + G2Cm(tm2tm1) + Q5WCn.tm1 + Gvc.Cvc.(tm2tm1)

Q + Qbs = Q2 + Qm + Q5 + Q1 + Qvc (*)

Trong :

* Q -Nhit lng cung cp gia nhit tc nhn sy* Qbs - Nhit lng b sung. Do khng dng thit b gia nhit cho khng kh sau

dn nng nn Qbs

= 0

* Q1 = - WCmtm1 -Nhit hu ch do m mang vo* G2Cm.(tm2tm1) = Qm - Nhit lng tn tht do vt liu sy mang ra* Q5 -Nhit tn thtra mi trng theo kt cu bao che* Gvc.Cvc.(tm2tm1) = Qvc - Nhitlng tn tht theo thit b vn chuyn* Q2 = L(I3I1) -Nhit tn tht do tc nhn sy

L, I 1, d 1

G cv.C vc.tm2

Q 5 G2.C m.t m2

(G 2C n+WC m).

tm1

THIT B SY

Q Q bs

L, I3'

, d 3'

G vc.C vc.tm1

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Chia 2 v (*) cho W v b qua Qbs

Ta c: q = q1 + q2 + qvc + q5 + qm

M q = l(I3- I1) hay q = l(I3I1) = l(I3I1) + qv +q5Cntm1c

Hay q = l(I3I1) = Cntm1 - ( qvc + q5 + qm)

t Cntm1 - (qvc + q5 + qm) = - Tn tht nhit lm bay hi 1 kg m.

Suy ra l(I3I1) = hay

= nhit lng b sung nhit lng tn tht chungTrong qu trnh sy thc tlng nhit dn ngng cung cp cho qu trnh:

Qtt = q.w

a) Tnh nhit tn tht qua kt cu bao che ra mi trng

Nhit bn ngoi bung sy: tf2 = t0 = 26oCNhit bn trong bung sy: tf1 = 40oC Bung sy c tng lm bng thp c chiu dy 3 mm. Tra bng ph lc 2 [5],ta

c h s dn nhit = 46 W/mK

Nhit tn tht ra mi trng c tnh theo cng thc Q5 = K.F.t , (W)

53' 1

53' 1

( )w w w w w

( )

vc vlv

vc vvl

QQ QQ Lq I I tC

q l I I q q q tc

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Trong

* F - Din tch xung quanh ca bung sy, m2tng din tch xung quanh ca bungsy: F = 22,75 m2

* t - chnh nhit bn trong v bn ngoi bung sy , 0Ct = tf1 - tf2 = 4026 = 14

oC

* K - H s truyn nhit , W/m2K;K =

1

21

11

Chiu dy lp tn, lp cch nhit

1, 2 - h s to nhit t tc nhn sy n vch trong bung sy v h s to nhit tvch ngoi ti khng kh bn ngoi , W/m2K. xc nh 1, 2 ta dng phng

php lp

Gi thit tw1 = 39,1oC (nhit vch trong ca tng ), phng trnh cn bng nhit:

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q = 1(tf1 -tw1) =

(tw1-tw2) = 2(tw2 - tf2)

Vi tc tcnhn sy trong bung sy = 12m/s nn ta c: H s to nhit 1cxc nh theo cng thc kinh nghim [1].

1 = 6,15 + 4,17. = 6,15 + 4,17.12 = 56,19 W/m2K

Vy mt dng nhit truyn quaq = 1(tf1 - tw1) = 56,19 (4039,1 ) = 50,57 (W/m

2)

Nhit vch ngoi tng c xc nh theo cng thctw2 = tw1 - q.

= 39,150,57.

0,003

46= 39,09 0C

Nhit nh tnh:

Tra bng thng s khng kh vi tm = 330C ta c cc thng s sau:

= 2,697.10-2 W/m2K; = 16,29.10-6 m2/s; Pr = 0,7

- Tiu chun Grashoft :

Gr=3

2

g..t.l

Ta c Gr.Pr = 0,7.7,5.108 = 5,3.108thuc khong (2.1071.1013)

=> Ta c: C = 0,135 ; n = 0,33

- Cng thc tnh Nusselt:

Nu = C

n1Gr.Pr = 0,135.( 5,3.108)0,33 = 102

- H s to nhit:

Suy ra q = 2(tw2 - tf2) = 1,37.(39,09 -26) = 18 W/m

2

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- So snh q v q:

| | || Sai s ny rt nh nn cc kt qu tnh trn c th chp nhn c

Vy, h s truyn nhit: K =

1 2

1

1 1

Hay

- Nhit tn thtra mi trng trong 1 giy l

Q5 = 1,27.22,75.14 = 406,7 J/s

- Nhit tn tht ra mi trng trong qu trnh sy:

Q5 = 406,7.9,58.3600 =14025910,2J =14025,9102kJ

Vy

b) Tn tht nhit do vt liu sy mang i qm (kj/kga)

Qm= G2.Cm(21), kJ

Trong : Cm = 3,87 kJ/kgK -Nhit dung ring ca Hnh [Ph luc 6 /3/]

Nhit vt liu sy vo: 1 = t0 = 27oC

Nhit vt liu sy ra: 2 = tf1 =40oC

Vy nhit tn tht do vt liu sy mang i:

Qm= 8,34.3,87.(4026) = 452 kJ

Suy ra:

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c) Tn tht nhit lm nng lisy qvc (kj/kga)

Lisyc b dy 1 mm c gia c bng cc thanh thp. Ta c thng s ca li

l: CAl = 0,22 kJ/kg; Al= 270 kg/m3 [5]. Vi din tch tnh ton, ta chn lisy c F

= L B = 2 2 = 4 m2. S lisy l n = 1 khay.

* Vy tng din tch khay syFk = F.n = 4.1 = 4 m

2

* Khi lng nhm lm khay syGAl= V.Al = Fk..Al = 4.0,001.270 = 1,08 kg

* Nhit tn thtQvc = GAl.CAl(21) = 1,08.0,22.(4026) = 3,33 kJ

Vy

d) Nhit hu ch do m mang vo q1

q1 = - Cn.tm1

Trong : Cn -Nhit dung ring ca nc, Cn = 4,18 kJ/kgaK

Vy: q1 = - 4,18.26 = -108,68 kJ/kga

Ta c: =108,68(153,02 + 4,93 + 0,036) = -49,306 kJ/kga ; < 0

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Hnh 4-3. th I-d ch sy thc hi lu hon ton

4.4. Tnh ton qu trnh sy thc t

a) Qa trnh sy thc t trn th I - d

im 0 - Trng thi khng kh ngoi tri. im 1 - Trng thi khng kh sau dn lnh. im 2 - Trng thi khng kh sau dn nng. im 3- Trng thi khng kh sau khi trao i nhit vi SP sy trong trng hp

sy thc t.

im 4- Trng thi khng kh trong dn lnh trong trng hp sy thc t. 1-2: Qu trnh gia nhit trong dn nng.

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2-3: Qu trnh sy thc t trong thit b sy (qu trnh sy ng nhit) 3-4-1: Qu trnh lm lnh khng kh v ngng t m trong dn lnh trong

trng hp sy thc t.

b) Tnh ton qu trnh sy thc t

Thng s ti cc im nt ca th

im 0, 1, 2:Thng s ti cc im 0, 1, 2 khng thay i so vi qu trnh sy l thuyt.

im3:*Nhit : t

3= 350C. cha m d

3ca qu trnh sy thc

Da vo th qu trnh sy thc ta suy ra c

I3I2 =l

= (d3d2)

I2 = Ckt2 + (2500 + 1,842t2)d2

I3 = Ckt3 + (2500 + 1,842t3)d3

I2I3 = Ck (t2t3) + (2500 + 1,842t2)d2(2500 + 1,842t3)d3

Ta t - A = Ck (t2t3) + (2500 + 1,842t2)d2- B = (2500 +1,842)t3

I2I3 = A -Bd3 = (d3d2)

* Entanpi * m:

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im 4

* m: 4 = 100%.* Dung m: d4 = d3 = 0,0105 kg/kgkk* Phn p sut bo ho:

4'

4' 4'

aP .d

0,621+d .

Nhit

* Entanpi: Thay cc gi tr t4, d4vo cng thc ta c

Bng 4.1: Thng s cc im nt trn th i d

Thng s

imT (

OC) (%) d (kg/kgkk) I (kJ/kgkk)

0 26 81 0,017 69,94

1 0 100 0,0062 15,5

2 40 13,4 0,0062 56,14

3 35 13,3 0,0105 46,02

4 12,3 100 0,0105 38,9

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c) Tnh ton nhit qu trnh sy thc t

Lng khng kh kh cn thit lm bay hi1 kg m

Lng khng kh kh thc t: Lu lng khng kh tun hon trong qu trnh sy: Lu lng khng kh tun hon trong 1s:

Khi I3tm c:

Nhit dn ngng cn cung cp:

Vy :

* Nhit ta ra thit b lm lnh:

Cng sut nhit dn nng:

calorifer = 0,7Hiu sut nhit ca dn nng

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Cng sut bm nhit:

b: Hiu sut nhit ca bm nhit t 3 5 ta chn b = 4

Ta c:

Nhit ta ca dn ngng l:

4.5. Tnh ton thit k v la chn thit b ph tr

4.5.1. Cc thng s nhit ca mi cht lnh

a) Nhit ngng t

Dn ngng ca bm nhit c nhim v gia nhit cho khng kh nn mi trng lm mt

dn ngng chnh l tc nhn sy.

Vi: tw2 - l nhit khng kh ra khi dn ngng. tw2 = 400C

kt - l hiu nhit ngng t yu cu

i vi dn ngng gii nhit bng gi, kt = (10150C).

Ta chn kt = 100C. Khi , nhit ngng t ca mi cht l:

kt b) Nhit bay hi

Theo kt qu nghin cu a ra nhit bay hi tt nht t l ttnht, v trnh x tuyt trong quy trnh ta chn l tt nht

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b) Nhit hi ht m bo my nn khng ht phi lng ngi ta phi m bo hi ht vo

my nn nht thit phi l hi qu nhit.

ht Vi mi cht R22, ta chn ht = 25

0C. Vy nhit hi ht

th = 0 + 25 = 250C

4.5.2. Tnh ton chu trnh bm nhit

a) Chn chu trnh

Vi nhit bay hi t0v nhit ngng t tk chn, tra bng tnh cht nhit ng

ca R22 trng thi bo ha ta c p sut bay hi v ngng t tng ng l:

t0 = 00C p0 = 4,9797 bar

tk = 500C pk = 19,395 bar

Nh vy, ta c t s nn:

= 3,894 < 12 nn ta chn my nn 1 cp.Mt khc, mi cht lnh s dng y l

R22 nn ta chn s my nn lnh 1 cp dng thit b hi nhit.

b) S , nguyn l lm vic

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Nguyn l lm vicHi mi cht sau khi ra khi thit b bay hi c a vo thit b hi nhit, nhn

nhit ng p ca lng cao p tr thnh hi qu nhit 1. Hi qu nhit ny c ht

v my nn v c nn on nhit trong my nn t p sut bay hi p0ln p sut

ngng t pk. Hi cao p 2 i vo thit b ngng t, nh nhit ng p cho tc nhn

sy, ngng t thnh lng si 3. Sau , lng cao p 3 i vo thit b hi nhit, nh

nhit ng p cho hi h p tr thnh lng cha si 3. Lng 3 i vo van tit lu

gim p sut xung p sut bay hi p0(im 4) ri i vo thit b bay hi nhn nhit

ca tc nhn sy va ra khi bung sy, ha hi ng p ng nhit thnh hi bo

ha m v chu trnh li tip tc.

c) Xy dng th v lp bng xc nh cc gi tr ti cc im nt

th:

MN: My nn

TL: Tit Lu

BH: Bay hi

HN: Hi nhit

NT: Ngng t

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Cc qu trnh:

o 1-1 - Qu nhit hi mi cht trong thit b hi nhito 1-2 -Nn on nhit hi mi cht t p0n pko 2-3 - Lm mt v ngng t ng p ng nhit trong thit bi ngng to 3-3 - Qu lnh lng cao p trong thit b hi nhito 3-4 - Qu trnh tit lu ng Entanpio 4-1 - Qu trnh bay hi ng p ng nhit trong thit b bay hi

d) Bng cc thng s ti cc im nt ca th

Tra bng cc tnh cht nhit ng ca R22 trng thi bo ha v bng cc tnh cht

nhitng ca hi qu nhit R22 Ta c bng cc thng s nhit ng ca mi cht trn

th nh sau:

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Bng 3-1 Thng s trng thi cc im nt

im Trng thiP

bar

T0C

v.103

m3/kg

i

kJ/kg

S

kJ/kgK