93307801-ĐỒ-an-sẤy-bƠm-nhiỆt-sẤy-ca-rỐt

Khoa Cng Ngh Nhit Lnh n tt nghip

GVHD: ThS. Bi Trung Thnh 1 SVTH: Nguyn Anh Tun

NHN XT CA GIO VIN HNG DN

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NHN XT CA GIO VIN PHN BIN

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Mc Lc

Li cm n ....................................................................................................................... 6

Nhim v n tt nghip .............................................................................................. 7

Li m u ...................................................................................................................... 9

Danh mc cc hnh ........................................................................................................ 11

Danh mc cc bng ....................................................................................................... 12

Chng 1.TNG QUAN V CNG NGH SY LNH .......................................... 13

1.1. Gii thiu phng php sy lnh ....................................................................... 13

1.1.1. Khi nim v bm nhit .............................................................................. 13

1.1.1.1. Lch s hnh thnh v pht trin ca bm nhit .................................... 13

1.1.1.2. Gii thiu cc phng php sy lnh .................................................... 14

1.2. S nguyn l, c im truyn nhit v truyn cht h thng sy lnh ........ 15

1.2.1. Nguyn l lm vic ca h thng sy lnh ................................................. 15

1.2.2. c im qu trnh truyn nhit, truyn cht .............................................. 16

1.3. Phn loi h thng sy lnh ................................................................................ 18

1.3.1. H thng sy lnh nhit nh hn 0oC ................................................. 18

1.3.2. H thng sy lnh nhit ln hn 0oC .................................................. 19

1.4. Cc thit b trong h thng lnh ......................................................................... 20

1.5. Mt s kt qu nghin cu v sy lnh ca cc tc gi trong v ngoi nc .... 22

1.5.1. Cc tc gi trong nc ................................................................................ 22

1.5.2. Cc tc gi nc ngoi ................................................................................ 24

1.6. So snh phng php sy lnh vi phng php sy nng ............................... 27

1.7. nh gi v kt lun ........................................................................................... 31

Chng 2. VT LIU SY LNH XY DNG QUY TRNH CNG NGH VT

LIU SY LNH .............................................................................................. 33

2.1. La chn vt liu sy lnh theo hng nghin cu ca ti ........................... 33

2.1.1. S cng ngh sy rau qu ........................................................................ 34

2.1.2. nh hng ca qu trnh sy n cht lng sn phm .............................. 35



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

lnh ..................................................................................................................... 37

2.3. L thuyt sy rau qu ......................................................................................... 39

2.4. Mt s phng php sy rau qu ....................................................................... 42

2.5. La chn phng php sy lnh theo hng nghin cu ca ti .................. 42

Chng 3. TNH TON THIT K M HNH MY SY LNH S DNG BM

NHIT .......................................................................................................... 44

3.1. Gii thiu bi ton thit k v m hnh thit k ................................................. 44

3.2. Xy dng quy trnh cng ngh sy C rt ......................................................... 46

3.2.1. Gii thiu vt liu sy .................................................................................. 46

3.2.1. Xy dng quy trnh cng ngh sy C rt .................................................... 47

3.3. Xc nh cc thng s u vo ca vt liu ....................................................... 48

3.4. Tnh ton l thuyt ch sy hi lu hon ton .............................................. 48

3.4.1. Xc nh cc thng s im nt trn th sy ........................................... 51

3.4.2. Tnh ton tc sy v thi gian sy ........................................................... 53

3.4.3. Tnh ton nhit qu trnh .............................................................................. 56

3.5. Tnh ton l thuyt ch sy thi b tc nhn ................................................. 58

3.5.1. Xc nh cc thng s im nt trn th sy ........................................... 58

3.5.2. Tnh ton nhit qu trnh .............................................................................. 60

3.6. Xc nh kch thc bung sy .......................................................................... 62

3.7. Cn bng nhit cho qu trnh ............................................................................. 63

3.8. Tnh ton qu trnh sy thc ch hi lu hon ton ...................................... 67

3.9. Tnh ton qu trnh sy thc ch thi b tc nhn ........................................ 70

3.10. Kt lun v ch sy ..................................................................................... 72

3.11. Tnh ton thit k v la chn thit b ph tr ................................................. 73

3.11.1. Cc thng s nhit ca mi cht lnh ......................................................... 73

3.11.2. Tnh ton chu trnh bm nhit .................................................................... 74

3.11.3. Tnh ton thit k cc thit b trao i nhit ............................................... 77

3.11.3.1. Dn ngng ........................................................................................ 77



3.11.3.2. Dn bay hi ...................................................................................... 82

3.11.4. Tnh chn my nn ..................................................................................... 87

3.11.5. Tnh chn ng ng dn mi cht ............................................................ 91

3.11.5.1. ng ng y ................................................................................. 91

3.11.5.2. ng ng ht .................................................................................. 91

3.11.6. Thit b hi nhit ........................................................................................ 92

3.11.7. Tnh ton tr lc v chn qut ................................................................... 97

Chng 4. KHO NGHIM QU TRNH SY THC T TRN M HNH MY

SY LNH ...................................................................................................... 102

4.1. Mc ch ........................................................................................................... 102

4.2. Phng php v phng tin ........................................................................... 103

4.3. Th nghim xc nh cc thng s qu trnh .................................................... 103

4.3.1. Th nghim xc nh vn tc tc nhn sy ................................................. 104

4.3.2. Xc nh m - nhit trung bnh (to, o) ca khng kh ................... 106

4.3.3. Th nghim xc nh m u v m cui ca vt liu sy ................ 106

4.3.4. Xc nh R trung bnh ca vt liu sy v phng php ct lt vt lu ..... 106

4.3.5. Th nghim sy ch hi lu hon ton v ch thi b tc nhn .... 107

4.3.6. Cc kt lun rt ra t thc nghim ............................................................. 113

4.4. ng dng phn mm Labview vo nghin cu thc nghim .......................... 113

4.5. Cc tnh cht nh hng n qu trnh sy ...................................................... 117

Chng 5. TNH TON HIU QU KINH T ........................................................... 119

5.1. Ch ph nguyn liu, nhin liu ....................................................................... 119

5.2. Chi ph lao ng ............................................................................................... 119

5.3. Chi ph khu hao .............................................................................................. 119

Chng 6. KT LUN V NGH .......................................................................... 121

6.1. Kt lun ............................................................................................................ 121

6.2. ngh ............................................................................................................. 121

TI LIU THAM KHO .............................................................................................. 123



Li cm n

Hc 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 quan

tm 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 Cng Nghip TP H Ch Minh.

Tp th ging vin Khoa Cng ngh Nhit Lnh trng i hc Cng Nghip TP

H Ch Minh.

Qu thy c tn tnh ch dy chng ti trong thi gian hc tp ti trng.

c bit, em xin chn thnh cm n Thy trng Khoa Cng Ngh Nhit Lnh

Th.s Bi Trung Thnh 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.

Tp H Ch Minh, thng 6, nm 2010

Sinh vin thc hin ti

Nguyn Anh Tun



TRNG I HC CNG NGHIP TP HCM CNG HA X HI CH NGHA VIT NAM

Khoa Cng Ngh Nhit Lnh c Lp- T Do- Hnh Phc

NHIM V N TT NGHIP

H v tn: MSSV:

Ngnh: Cng Ngh Nhit Lnh Nin Kha: 2006-2010

Tn ti: Nghin cu cng ngh sy lnh, tnh ton, thit k, kho nghim v xc

nh mt s thng s nh hng n cht lng sy cho mt s loi rau qu giu

vitamin trn m hnh my sy lnh bng bm nhit ca khoa CN Nhit Lnh

I/ Thng tin thc hin ti:

13- S liu choo trc: M hnh sy lnh ca khoa Cng Ngh Nhit Lnh

II/ Ni dung ti:

13- Tm hiu cng ngh sy lnh, phng php sy, cc thit b trong h thng sy

lnh.

2- Tm hiu k thut sy lnh trn mt s thc phm v rau qu trong nc v th

gii.

3- Trnh by cc kt qu nghin cu v sy lnh trong nc v th gii t trc

n nay.

4- La chn vt liu sy lnh, xy dng quy trnh cng ngh v x l vt liu trc

sy v sau sy lnh.

5- L thuyt v sy rau qu v thc phm.

6- Tnh ton thit k m hnh my sy lnh s dng bm nhit.

6.1 Gii quyt bi ton sy lnh l thuyt v sy thc theo ch thi b tc

nhn.

6.2 Gii quyt bi ton sy lnh l thuyt v sy thc theo ch hi lu hon

ton kh thi.

7- Tnh ton thit k v la chn cc thit b ph tr cho h thng sy.

8- Kho nghim m hnh my sy lnh xc nh li cc thng s k thut ca m

hnh.



9- B tr th nghim v thc hin sy thc nghim loi rau theo hng nghin cu

ca ti

10- Xc nh mt s yu t chnh nh hng n cht lng sn phm sy lnh

hai ch sy .

11- Kt lun rt ra t thc nghim.

12- Hiu qu kinh t

Xy dng gi thnh 1kg rau sy

13- Cc bn v thit k

III/ Ngy giao nhim v: 01/03/2010

IV/ Ngy hon thnh nhim v: 25/06/2010

TP H Ch Minh, thng 3 nm 2010

Gio vin hng dn

ThS. Bi Trung Thnh



Li m u

Vit 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 lm

cho 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 c xem 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 mt quy

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 ti Nghin cu cng ngh

sy lnh, tnh ton, thit k, kho nghim my sy lnh v xc nh mt s thng s nh

hng n cht lng sy cho mt s loi rau qu giu vitamin trn m hnh my sy



lnh bm nhit ca khoa Cng Ngh Nhit Lnh thc hin da trn c s tm hiu

nhng nguyn l chung nht ca cng ngh sy lnh t 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 h

thng sy lnh.

Tm hiu k thut sy lnh trn mt s loi rau qu giu vitamin, xy dng quy

trnh sy lnh i vi mt s loi rau qu ny.

Tnh ton thit k m hnh my sy lnh s dng bm nhit ch sy hi

lu 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.

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.



Danh sch cc hnh

Hnh 1-1. S nguyn l bm nhit .......................................................................... 11

Hnh 1-2. Hai phng thc trao i nhit qua bung sy .......................................... 12

Hnh 1-3. S qu trnh sy theo hai phng thc trao i nhit ........................... 13

Hnh 1-4. S h thng lnh. .................................................................................... 14

Hnh 1-5. S nguyn l h thng bm nhit kiu mun ....................................... 21

Hnh 1-6. S cng ngh sy rau qu ...................................................................... 32

Hnh 3-1. S nguyn l h thng v th qu trnh sy ....................................... 43

Hnh 3-2. S cng ngh sy C rt ........................................................................ 45

Hnh 3-3. S nguyn l bm nhit s dng trong h thng sy lnh ..................... 47

Hnh 3-4. th I-d ch sy hi lu hon ton ..................................................... 48

Hnh 3-5. th I-d ch sy thi b tc nhn ........................................................ 56

Hnh 3-6. th I-d ch sy thc hi lu hon ton ............................................. 65

Hnh 3-7. th I-d ch sy thc thi b tc nhn ................................................ 68

Hnh 3-8. S tnh ton kh ng trong h thng my sy ....................................... 96

Hnh 3-9. S c tnh k thut ca qut APCR0502AA10/10 ................................ 99

Hnh 3-10. S cu to APCR0502AA10/10 ............................................................ 99

Hnh 4-1. Biu phn b vn tc tc nhn sy qua cc khay ................................ 102

Hnh 4-2. Biu nhit , m ti TP H Ch Minh ngy 15/04/2010 ............... 103

Hnh 4-3. S h thng my sy lnh .................................................................... 105

Hnh 4-4. S cc thng s ch sy hi lu hon ton ..................................... 108

Hnh 4-5. S cc thng s ch sy thi b tc nhn ....................................... 110

Hnh 4-6. Giao din chng trnh ng dng phn mm Labview ............................ 114



Danh mc cc bng

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 ............................... 28

Bng 3-1 Thng s trng thi cc im nt ................................................................. 74

Bng 3-2 Thng s tiu chun ca cc im nt .......Error! Bookmark not defined.88

Bng 3-3. Tn tht kh ng qua bung sy ................................................................. 98

Bng 4-1 Bng kt qu kho st vn tc tc nhn sy ............................................... 102

Bng 4-2 Bng kt qu thc nghim xc nh nhit v m mi trng ........... 103

Bng 4-3 Bng kt qu xc nh xc nh m u vo ca vt liu sy ................ 103

Bng 4-4 Bng kt qu bn knh R ca vt liu .......................................................... 104

Bng 4-5 Bng kt qu th nghim ch sy hi lu hon ton .............................. 106

Bng 4-6 Bng kt qu th nghim ch sy thi b tc nhn.............................. 108



CHNG I

TNG QUAN V CNG NGH SY LNH

1.1. Gii thiu phng php sy lnh

1.1.1. Khi nim v bm nhit

1.1.1.1. 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 rt

quen thuc trong cc lnh vc iu ha khng kh, sy, ht m, un nc

Hnh 1-1. S nguyn l h thng bm nhit



1.1.2. 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 phn p sut 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

qu trnh dch chuyn m trong long vt 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 mi

cht 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

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 1.2).

Hnh 1-2. Hai phng thc trao i nhit thng qua bung sy.



Hnh 1-3. S qu trnh sy theo hai phng thc trao i nhit

Trong trng hp th nht (hnh 1-2.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 1-2.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 1-3 tng ng vi hai trng hp b tr trn hnh 1-2.

1.2. S nguyn l, c im truyn nhit v truyn cht ca h thng sy lnh

1.2.1. Nguyn l lm vic ca h thng sy lnh

Khc vi phng php sy nng, trong phng php sy lnh, ngi ta to ra

chnh phn p sut hi nc gia vt liu sy v tc nhn 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 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 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 t b

mt vo mi trng c th ln hn hoc nh hn nhit mi trng hoc cng c th

nh hn 0oC.

Hnh1-4. S h thng sy lnh

1.2.2. c im qu trnh truyn nhit v truyn cht

Trong k thut sy lnh, th sy ca khng kh tng nh qu trnh tch m dn bc

hi v qu trnh gia nhit bng chnh dn ngng t trong cc my lnh. Yu t c tnh

quyt nh y l qu trnh lm lnh khng kh trong dn lnh, t y s nhn c

khng kh c nhit v cha hi (d) nh m bo cho qu trnh truyn nhit, truyn

cht gia vt sy v tc nhn sy trong bung sy xy ra iu kin gradient nhit

v gradient p sut cng chiu, khng c giai on no xy ra hiu ng Luikov A.V. cn

tr qu trnh sy nh trong phng php sy nng. V vy, ngoi vic tnh ton, thit k

h thng ni chung th iu ti cn thit l ch lm vic ca dn lnh hay ni cch

khc l kh nng ti u nht ca dn lnh c tm quan trng c bit.

Trong k thut sy lnh, tng cng tch m cho h thng, khng kh sy tri qua

giai on tch m dn lnh, v th m trong khng kh c th tn ti ba dng hi,



lng v rn, vi dung m dng hi dh, dng lng dl v dng rn dr, entanpi H ca

khng kh m:

H= tb + (2500+1,93tb)dh + 4,18d1tb + (-335+2,1 tb)dr , kJ/kgkk (1.1)

Trong qu trnh kh m dn lnh, chiu di ng i ca dng khng kh l yu t

c tnh quyt nh, theo m lu lng th tch khng kh cng nh cng sut nhit

2 3/ , /hd P Td m

kg m KdVdt Rdt

- trao i s thay i, khng kh c lm lnh n nhit

im sng ts. Trn mt n v di quan h truyn nhit, truyn cht ny c th biu

din di dng:

2 2'd Q d m dV dT=- c -r . . ,W/m (1.2)

ddx dV.dt dt dX

Trong

* c - nhit dung ring th tch ca khng kh m nhit kh quyn (c =1,23

kJ/m3K).

* r - Nhit ngng t (r=2500 kJ/kg i vi hi nc 00C).

* 2 h 3d P /Td m = ,kg/m K

dVdt R.dt - l nc ngng theo ng 100% (ng vi 1m

3

khng kh m khi nhit gim i 1K) v thay i nhanh qua nhit theo biu

thc:

2

3hd(P /T)d m = ,kg/m KdVdt R.dt

(1.3)

Trong :

- Ph- p sut hi bo ha ca hi nc tng ng vi nhit ca khng kh m.

- Hng s R i vi hi nc trong khng kh m: R=8314/18=861,89 J/kgK

Mt khc c th tnh nhit lng do khng kh truyn cho mi cht lnh tng ng vi

mi n v di ca thit b bay hi bm nhit:

2

0

d Q=k T-T ,W/m (1.4)

d.dx



Vi K1 l h s truyn nhit ca thit b bay hi [W/mK].

T cc c s trn ta c quan h:

's0 0

'1 0

X T -Tc=- ln

X K T -T (1.5) vi ' 3

K.XK = [J/m K]

dV/d

L thng s c trng cho cng sut ca thit b bc hi ca bm nhit (thng khong

1kJ/m3K), X[m] l chiu su ca thit b bc hi, X0 [m] l khong cch t u thit b

vo thit b bc hi n im xut hin qu trnh ngng ng m, Ts l nhit ng

sng, cc ch s 1 v 2 l k hiu u vo v ra ca khng kh qua thit b bc hi.

1.3. Phn loi h thng sy lnh

1.3.1. H thng sy lnh nhit nh hn 00C

a. H thng sy thng hoa

Sy thng hoa l qu trnh tch m khi vt liu sy trc tip t trng thi rn bin

thnh trng thi hi nh qu trnh thng hoa. to ra qu trnh thng hoa, vt liu sy

c lm lnh di im ba th, ngha l nhit ca vt liu t < 00C, p sut tc nhn

sy bao quanh vt P< 620 Pa [19]. T , vt liu sy nhn c nhit lng m t

trng thi rn thng hoa thnh th kh vo mi trng. Nh vy, trong cc h thng sy

thng hoa phi to c chn khng trong vt liu sy v lm lnh vt xung di 0oC.

u im: Phng php gn nh bo ton c cht lng sinh, ha hc ca sn

phm (mu sc, mi v, vitamin, hot tnh,)

Nhc im:

- Chi ph u t cao, phi dng ng thi bm chn khng, my lnh ( kt

ng sn phm v lm ngng kt hi nc)

- H thng cng knh nn vn hnh phc tp, chi ph vn hnh v bo dng

cao.

Sy thng hoa thng c ng dng sy sn phm qu, d bin cht do nhit nh:

mu, vc xin, mt, nhn, vv

b. H thng sy chn khng

Phng php sy chn khng l phng php to ra mi trng gn nh chn khng

trong bung sy, ngha l nhit vt liu t < 0oC, p sut tc nhn sy bao quanh vt P



> 610 Pa. Khi nhn c nhit lng, cc phn t nc trong vt liu sy th rn s

chuyn sang th lng, sau mi chuyn sang th hi v i vo mi trng.

u im: Phng php ny gi c cht lng sn phm, m bo iu kin

v sinh.

Nhc im: H thng c chi ph u t ln, vn hnh phc tp.

- Phng php sy chn khng thng ch sy cc loi vt liu sy l cc sn

phm qu, d bin cht.

- Do tnh phc tp v khng kinh t nn cc h thng sy thng hoa v h thng

sy chn khng ch dng sy nhng vt liu qu him, khng chu c nhit

cao. V vy, cc h thng sy ny l nhng h thng sy chuyn dng, khng

ph bin.

1.3.2. H thng sy lnh nhit ln hn 00C

a) Phng php s dng my ht m chuyn dng kt hp vi my lnh

Phng php ny s dng my ht m kt hp vi my lnh, to ra mi trng

sy c nhit kh thp, c th bng hoc b hn nhit mi trng t 5 n 150C.

u im

- Nng sut ht m ca phng php ny kh ln.

- Kh nng gi cht lng, hm lng dinh dng sn phm cng kh tt (ph

thuc vo nhit sy).

Nhc im

- Chi ph u t ban u kh ln do phi s dng c my ht m chuyn dng v

my lnh

- Cht ht m phi thay th theo nh k

- Vn hnh kh phc tp nn chi ph vn hnh ln

- in nng tiu tn ln do cn chy my lnh v t nng dy in tr hon

nguyn cht hp th.

- Lp t phc tp, kh iu chnh cc thng s ph hp vi cng ngh

- Trong mi trng c bi, cn dng my v sinh cht hp th, tui th thit b

gim.



b. Phng php dng bm nhit nhit thp

Trong phng php ny, ngi ta ch dng mt h thng bm nhit to ra mi

trng sy. Nhit mi trng sy c th iu chnh trong gii hn kh rng t nhit

xp x mi trng n nhit m, ty thuc yu cu ca vt liu sy. Khc vi cc

thit b nhit lnh khc, khi s dng bm nhit sy kh v ht m th c dn nng v

dn lnh u c s dng hu ch nn nng sut tiu th y c th c tn dng

n mc cao nht m nhit khng kh li c th ch cn duy tr mc nhit mi

trng hoc thp hn.

u im:

- Kh nng gi mu sc, mi v v vitamin u tt

- Tit kim nng lng nh s dng c nng lng dn nng v dn lnh, hiu

qu s dng nhit cao

- Bo v mi trng, vn hnh an ton.

- C kh nng iu chnh nhit tc nhn sy ty thuc vo yu cu v kh nng

chu nhit ca tng loi sn phm nh thay i cng sut nhit ca dn ngng

trong

- Cng sut kh ln

- Chi ph u t h thng thp hn so vi cc phng php sy lnh khc

- Vn hnh n gin.

Nhc im

- Thi gian sy thng kh lu do chnh phn p sut hi nc gia vt liu

sy v tc nhn sy khng ln.

- Phi c gii php x bng sau mt thi gian lm vic.

1.4. Cc thit b trong h thng sy lnh

Bm nhit l mt thit b dng bm mt dng nhit t mc nhit thp ln mc

nhit cao hn, ph hp vi nhu cu cp nhit. My lnh cng l mt loi bm nhit

v c chung mt nguyn l hot ng, cc thit b ca chng v c bn l ging nhau.

ch phn bit my lnh vi bm nhit mc ch s dng. My lnh gn vi vic s



dng ngun lnh thit b bay hi cn bm nhit gn vi vic s dng ngun nhit

thit b ngng t. Do s dng ngun nhit nn bm nhit hot ng cp nhit cao hn.

a) Mi cht v cp mi cht:

Mi cht v cp mi cht ca bm nhit c yu cu nh my lnh. Mt vi yu cu

c bit hn xut pht t nhit si v ngng t cao hn, gn ging nh ch nhit

cao ca iu ha khng kh, ngha l cho n nay ngi ta vn s dng cc loi mi

cht nh: R12, R22, R502 v MR cho my tuabin. Gn y ngi ta ch n vic s

dng cc mi cht mi cho bm nhit nhm nng cao nhit dn ngng nh: R22,

R113, R114, R12B1, R142

b) My nn lnh

Cng nh my nn lnh, my nn l b phn quan trng nht ca bm nhit. Tt c

cc dng my nn ca my lnh u c ng dng trong bm nhit. c bit quan

trng l my nn piston trt, my nn trc vt v my nn tuabin. Mt my nn bm

nhit cn phi chc chn, tui th cao, chy m v cn phi c hiu sut cao trong iu

kin thiu hoc ti.

c) Cc thit b trao i nhit

Cc thit b trao i nhit c bn trong bm nhit l thit b bay hi v thit b

ngng t. My lnh hp th c thm thit b sinh hi v hp th. Ging nh my lnh,

thit b ngng t v bay hi ca bm nhit cng bao gm cc dng: ng chm, ng lng

ngc dng, ng ng v ng kiu tm. Cc phng php tnh ton cng ging nh cc

ch iu ho nhit .

d) Thit b ph ca bm nhit

Tt c cc thit b ph ca bm nhit ging nh thit b ph ca my lnh. Xut pht

t yu cu nhit cao hn nn i hi v tin cy, cng ngh gia cng thit b cao

hn. y cng l vn t ra i vi du bi trn v m kn cc loi trong h thng.

Do bm nhit phi hot ng ch p sut v nhit gn st vi gii hn ti a

nn cc thit b t ng rt cn thit v phi hot ng vi tin cy cao phng nga

h hng cc thit b khi ch lm vic vt qu gii hn cho php. i vi van tit

lu, bm nhit c ch lm vic khc my lnh nn cng cn c van tit lu ph hp.



e) Thit b ngoi vi ca bm nhit

Thit b ngoi vi ca bm nhit l nhng thit b h tr cho bm nhit ph hp vi

tng phng n s dng ca n. Thit b ngoi vi ca bm nhit gm mt s loi sau:

Cc phng n ng lc ca my nn nh: ng c in, ng c gas, ng c

diesel hoc ng c givv

Cc phng n s dng nhit thu dn ngng t. Nu l si m th c th s

dng dn ngng trc tip hoc gin tip qua mt vng tun hon cht ti nhit, c

th s dng sy, nu n, ht mMi phng n i hi nhng thit b h tr

khc nhau.

Cc phng n cp nhit cho dn bay hi. Trng hp s dng dn lnh ng

thi vi nng th pha dn bay hi c th l bung lnh hoc cht ti lnh. Ngoi ra

cng c th s dng dn bay hi t ngoi khng kh, dn bay hi s dng nc

ging l mi trng cp nhit. Cng c nhng phng n nh dn bay hi t

di nc, t di t hoc s dng nng lng mt tri.

Cc thit b iu khin, kim tra t ng s hot ng ca bm nhit v cc thit

b h tr. y l nhng thit b t ng iu khin cc thit b ph tr ngoi bm

nhit ph hp vi hot ng ca bm nhit

1.5. 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:

1.5.1. 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 [Ti liu 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 1400

kg/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 1-5.

Hnh 1-5. 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

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 c bit ph

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 sy cng nh

ca vt liu sy.

1.5.2. Cc tc gi nc ngoi

Macio N. Kohayakawa v cc cng s [19] tin hnh nghin cu nh hng ca

cc yu t nh: vn tc gi Var, chiu dy ca vt liu L n h s khuch tn qu trnh

sy Def trong 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 Def nh sau:

Def=4,2625 - 0,61922.Var + 0,380538.Var2 + 1,012517.L 0,90343.Var.L (1.6)

Phng trnh (1.6) cho thy rng nh hng ng thi ca hai thng s cng nh

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

gi Var l ln nht, sau n chiu dy ca vt liu sy. Phng trnh (1.6) 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

e

Mk M M

t

(1.7)

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

k - hng s sy [1/s], c xc nh nh sau: k=0,2865.exp 0,179.Ta (1.8)

Gii phng trnh (1.7) ta xc nh c m ca vt liu khi sy ti thi im t nh

sau:

00 . .

kt kte eM M M M e e

(1.9)

Vi M0 : m ca v liu sy ti thi im t0 = 0

Phng trnh cn bng cht

.p

a

GW M

x G y

(1.10)

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 (1.10), 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

(1.11)

Phng trnh cn bng nng lng

. . / .

. .

cv a pw a ga

a pa pw

h G G W x T TT

x G C C W

(1.12)

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 (1.12), xc nh c nhit khng kh ti u ra:

( / ).

0.d a x

a g gaT T a T T

Trong :

. .a pa pwa G C C W

. .cv a pwW

d h G Cx

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

Phng trnh truyn nhit

. . .

(1.13). .

cv a g a g pw gplg

p pg pl

Wh T T G L C C T

T x

y G C M C

Trong : Lg - nhit n ha hi 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 (1.13) ta s tm c s thay i nhit ca vt liu sy:

0

/

0

1. (1.14)

y y h

g gT f gT e fg

y:

0. . . ; . .cv a g cv pw aa pl

W Wf h T G L g h C C G

x x

. .p pg plh G C M C 1.6. So snh phng php sy lnh vi phng php sy nng

Sy l qu trnh tch nc v hi nc ra khi vt. Tuy nhin, sy l mt qu trnh

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

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 dn n phn p sut 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 (1.15)

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 Phb v phn p sut hi nc

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

sy ra b mt v i vo mi trng.

Do , h thng sy nng thng c phn loi theo phng php cung cp nhit:

H thng sy i lu

Vt liu sy nhn nhit bng i lu t mt dch th nng m thng thng l

khng kh nng hoc khi l. H thng sy i lu gm: h thng sy bung, h

thng sy hm, h thng sy kh ng.

H thng sy tip xc

Vt liu sy nhn nhit t mt b mt nng. Nh vy trong h thng sy tip xc,

ngi ta to ra chnh lch p sut nh tng phn p sut hi nc trn b mt vt

liu sy. H thng sy tip xc gm: h thng sy l, h thng sy tang

H thng sy bc x

Vt liu sy nhn nhit t mt ngun bc x dn m dch chuyn t lng vt

liu sy ra b mt v t b mt vo mi trng. y ngi ta to ra chnh phn

p sut hi nc gia vt liu sy v mi trng bng cch t nng vt.

H thng sy dng dng in cao tn hoc dng nng lng in t trng

Khi vt liu sy t trong mi trng in t th trong vt xut hin cc dng in

v chnh dng in ny s t nng vt.

u im ca phng php sy nng

- Thi gian sy bng cc phng php sy nng ngn hn so vi phng php

sy lnh.

- Nng sut cao v chi ph ban u thp.

- Ngun nng lng s dng cho phng php sy nng c th l khi thi, hi

nc 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.

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 Ph nh

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

Ph = d

dB

621,0

. (1.16)

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 > 0 oC) v cng c th nh hn 0 oC.

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 =2,2-4m/s . Kt qu sn

phm sau th nghim c cc c im v mu sc, mi v, hm lng cht 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 nng Sy thng hoa

v chn khng

Sy lnh s dng

my ht m kt

hp my lnh

1 Cht 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 Thng

thp hn Cao hn nhiu Cao hn

5 Chi ph vn hnh, bo dng Thng 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

7 V sinh an ton thc phm Thng

km hn Tt hn Bng nhau

8 Bo v mi trng Thng

km hn Nh nhau Km hn

9 Phm vi ng dng Rng hn Hp hn Hp hn



1.7. 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

hiu qu 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 p dng 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 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 ngh sy

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.



Chng 2

VT LIU SY LNH XY DNG QUY TRNH CNG

NGH V X L VT LIU SY LNH

2.1. Vt liu sy lnh v la chn vt liu sy lnh theo hng nghin cu

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 sy, bo 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 phi

enzim, phn ng enzim,

Nhng thay i do vi sinh vt

Nhng 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.



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



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

a) nh hng n cu trc

Thay i v cu 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 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 nh

sng v mu sc.

Nhit v s oxi ha trong qu trnh sy gy ra nhng bin i ha hc i vi

carotenoit 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 hp hoc 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 qu trnh

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

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 tc ca 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 nhng qu trnh khng

thun nghch.

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.

2.2 Cc c tnh ha l c bn ca mt s vt liu sy giu vitamin ng dng cng

ngh 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 cht khong, 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) Nc

Tuyt 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. C nhng

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 hc

c 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 ny phi

bng cch em nung ln hoc bng cc tng tc ha hc khc.

Nc lin kt ha l

Kt 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.

Nc lin kt c hc

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 trong sn

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

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 th

- Prolamin 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, protein

trong 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 ti

gluten 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 cc

kho kn hon ton, ng pht hin thy s tng ln ca hm lng Nit phiprotein sau

15 tun l bo qun.

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, cng ngh sy

rau qu c s chung nh sau:

Rau qu ti sau khi ra sch c loi b phn khng tiu chun, c phn c

theo 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 nguyn

liu 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 rau

qu 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) Nhit 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 80-90 oC.

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 liu sy. 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.

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) Lu thng ca khng kh

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 thi gian

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/m2 l ph hp.[20]

2.4. Mt s phng php sy rau qu

a) Phng php sy bng khng kh

Cng vic ny c tin hnh bng cch tri rau qu ln cc loi b mt ngoi tri

nhn nh sang mt tri trc tip. Tuy nhin, sn phm c cht lng km do kh

kim sot c 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 bo v 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 lt

Phng php ny tin hnh sy mt hoc hn hp nhiu loi rau qu ( c x l

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.

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. Sn phm

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 nghin cu 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 III:

Tnh ton thit k m hnh my sy lnh s dng bm nhit s trnh by r ni dung

ny.



Chng 3

TNH TON THIT K M HNH MY SY LNH S DNG

BM NHIT

3.1. Gii thiu v 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 v vt 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.

Nguyn l hot ng ca thit b

My sy lnh hot ng da trn nguyn l ca t 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 lnh rii 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 nn nn 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.

Hnh 3-1. S nguyn l h thng v th qu trnh sy



3.2. Xy dng quy trnh cng ngh sy C rt

3.2.1. Gii thiu v vt liu sy

C rt - Daucus carota L., ssp sativus Hayek.,

thuc h Hoa tn - Apiaceae.

* M t

C rt l loi cy tho sng 2 nm. L ct

thnh bn hp. Hoa tp hp thnh tn kp; trong

mi tn, hoa chnh gia th khng sinh sn v

mu ta, cn cc hoa sinh sn chung quanh th

mu trng hay hng. Ht C rt c v g v lp

lng cng che ph.

* B phn dng

C v qu - Radix et Fructus Carotae.

* Ni sng v thu hi

C rt l mt trong nhng loi rau trng rng ri nht v lu i nht trn th gii.

C rt cng c trng nhiu nc ta. Hin nay, cc vng rau ca ta ang trng ph

bin hai loi C rt: mt loi c c mu ti, mt loi c c mu ng sang mu da

cam.

- Loi v (C rt ) c nhp trng t lu, nay nng dn ta t gi ging; loi

c rt ny c c to nh khng u, li to, nhiu x, hay phn nhnh, km ngt.

- Loi v mu ng sang mu da cam l c rt nhp ca Php (C rt Tim tm)

sinh trng nhanh hn loi trn; t l c trn 80%, da nhn, li nh, t b phn

nhnh nhng c hi ngn, mp hn, n ngon, c th trng a chung.

* Thnh phn ha hc

C rt l mt trong nhng loi rau c nh gi cao v gi tr dinh dng v cha

bnh i vi con ngi. C rt giu lng ng v cc loi vitamin cng nh nng

lng. Cc dng ng tp trung lp v v tht ca c; phn li rt t. V vy c c rt

c lp v dy, li nh mi l c tt.



Trong 100g n c ca C rt, theo t l % c: nc 88,5; protid 1,5; glucid 8,8;

cellulose 1,2; cht tro 0,8. Mui khong c trong C rt nh kalium, calcium, st,

phosphor, ng, bor, brom, mangan, magnesium, molipden...

3.2.2. Xy dng quy trnh cng ngh sy C rt

* C rt phi chn mu , c to v li nh.

* Sau khi ra sch chn trong nc si nhit 87-880C trong thi gian 6-8 pht.

* Ra li loi b v v sunfit ha bng dung dch SO2 c nng 0,2-1%.

* C rt c sunfit ha thi mng thnh lt, tri u trn khay sy m bo sao cho

qu trnh trao i nhit i lu ti u nht.

* C rt l loi rau c nhiu vitamin v cht dinh dng nn khng th tin hnh sy

nhit cao. Thng thng khong nhit thch hp sy C rt trong khong

30 -700C [3]. Ta c s cng ngh sy c rt nh sau:

C rt ti u vo ( m 88,7%)

Ra sch, ct gt

Chn trong nc si nhit (87-880C)

trong thi gian 6-8 pht

Ra li trong dung dch SO2 (0,2-1%)

Loi b v

Thi mng, xp vo khay sy

Sy ( nhit 30-50oC) theo phng php sy lnh

n m yu cu (12-14%)

ng gi bo qun

Hnh 3-2. S cng ngh sy C rt



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

a) Thnh phn dinh dng ca vt liu sy

C rt sy kh rt giu vitamin: C, B1, B2, PP v c bit l tin vitamin A. Thnh

phn ha hc ca C rt sy kh bao gm: 13% nc, 9,2% protit, 1,5% lipit, 48%

ng, 10,4% tinh bt, 9,6% xenluloza, 2% axit, 6,3 % tro. [20]

b) Xc nh kch thc vt liu

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

thc ban u l kch thc ln nht ca cc ming C rt thi trn. Kch thc ngang

(ng knh) o gn gia ming C rt. Tin hnh o th nghim 10 ln v thu c kt

qu trung bnh ca ming C rt.

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 C rt 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 C rt ni ring nhit sy yu cu khng qu

cao. Thng thng i vi cc loi rau qu nhit sy khng qu 600C, 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.

3.4 Tnh ton sy lnh l thuyt theo ch hi lu hon ton kh thi

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

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 tc a 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.

Hnh 3-3. S nguyn l bm nhit s dng trong h thng sy lnh



Hnh 3-4. th I-d ch sy hi lu hon ton

Trng hp tc nhn sy hi lu hon ton Kiu sy hi lu hon ton s dng

Heat 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 l

thuyt c trnh by trn gin I-d nh sau:

1-2: Qu trnh gia nhit tc nhn sy n nhit sy. im (2) l trng thi

khng kh nng trc khi vo bung sy.

2-3: Qu trnh sy ng nhit, tc nhn sy c m thp c thi qua vt liu

sy s 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 trng

thi 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.



3.4.1 Xc nh thng s ca cc im nt trn th qu trnh sy

a) im 0 (Mi trng bn ngoi)

* Nhit t0= 270C c chn theo nhit trung bnh ca khu vc Thnh Ph H Ch

Minh. [Theo kt qu thc nghim chng 4]

* m tng i 0 = 74% [Theo kt qu thc nghim chng 4]

* Phn p sut hi bo ha ca nc

b0

0

4026,42 4026,42P = exp 12- = exp 12- = 0,03548bar

235,5+ t 235,5+ 27

* Dung m ca khng kh

0 b00

a 0 b0

0,74.0,035480,621 0,621 =0,0169 kg/kgkk

0,993-0,74.0,03548

.Pd = =

P - .P

(Ly gi tr Pa = 0,993 bar)

* Entanpy ca khng kh m

I0 = 1,0048.t0 + d0(2500 +1,842.t0)

= 1,0048.27 + 0,0169(2500 + 1,842.27)= 70,22 kJ/kg.kk

* T cc thng s nhit v m khng kh ngoi tri, s dng th I-d ta xc

nh c ts =220 C (T im O (270C, 74%) dng ng d= const ct ng

=100%, ta xc nh c ts)

b) im 1 : Trng thi khng kh sau dn lnh

* Nhit : t1 = 8 0C, theo [5]

* m tng 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

b1

1

4026,42 4026,42P =exp 12- =exp 12- =0,01072 bar

235,5+t 235,5+8

* Dung m ca khng kh

1 b1

11 b1a

.P 1.0,01072d =0,621 =0,621 =0,00678 kg/kgkk

P - .P 0,993-1.0,01072



* Entanpi

Thay cc thng s ca im 1 vo cng thc ta c:

I1 = 1,0048.t1 + d1(2500 +1,842.t1)

= 1,0048.8 + 0,00678.(2500 + 1,842.8) = 25,1 kJ/kgkk

c) im 2 : Tc nhn sy c gia nhit (trng thi khng kh sau dn nng)

* Nhit : t2 = 400C (Nhit ci t trong qu trnh sy)

* Phn p sut bo ho

4026,42 4026,42P =exp 12- =exp 12- =0,0731 barb2 235,5+t 235,5+40

2

* 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 = 0,00678 kg/kgkk

* Entanpy :

I2 = 1,0048.t2 + d2(2500 +1,842.t2)

= 1,0048.40 + 0,00678.(2500 + 1,842.40) = 57,64 kJ/kgkk

* m tng i

2 b22aP .d =

0,621+d2 .P

93307801-ĐỒ-an-sẤy-bƠm-nhiỆt-sẤy-ca-rỐt

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