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Khoa Cng Ngh Nhit Lnh n tt nghipNHN XT CA GIO VIN HNG DN........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................GVHD: ThS. Bi Trung Thnh1 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipNHN XT CA GIO VIN PHN BIN........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................GVHD: ThS. Bi Trung Thnh2 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipMc LcLi cm n........................................................................................................................6Nhim v n tt nghip................................................................................................7Li m u........................................................................................................................9Danh mc cc hnh..........................................................................................................11Danh mc cc bng.........................................................................................................12Chng 1.TNG QUAN V CNG NGH SY LNH............................................131.1. Gii thiu phng php sy lnh.........................................................................131.1.1. Khi nim v bm nhit................................................................................131.1.1.1. Lch s hnh thnh v pht trin ca bm nhit......................................131.1.1.2. Gii thiu cc phng php sy lnh......................................................141.2. S nguyn l, c im truyn nhit v truyn cht h thng sy lnh..........151.2.1. Nguyn l lm vic ca h thng sy lnh...................................................151.2.2. c im qu trnh truyn nhit, truyn cht...............................................161.3. Phn loi h thng sy lnh.................................................................................18................................................................................................................................1.3.1. H thng sy lnh nhit nh hn 0oC...................................................181.3.2. H thng sy lnh nhit ln hn 0oC....................................................191.4. Cc thit b trong h thng lnh...........................................................................201.5. Mt s kt qu nghin cu v sy lnh ca cc tc gi trong v ngoi nc......221.5.1. Cc tc gi trong nc..................................................................................22GVHD: ThS. Bi Trung Thnh3 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip1.5.2. Cc tc gi nc ngoi..................................................................................241.6. So snh phng php sy lnh vi phng php sy nng.................................271.7. nh gi v kt lun............................................................................................31Chng 2. VT LIU SY LNH XY DNG QUY TRNH CNG NGH VT LIU SY LNH...............................................................................................332.1. La chn vt liu sy lnh theo hng nghin cu ca ti.............................332.1.1. S cng ngh sy rau qu..........................................................................342.1.2. nh hng ca qu trnh sy n cht lng sn phm................................352.2. Cc c tnh ha l ca mt s rau qu giu vitamin ng dng phng php sy lnh.......................................................................................................................372.3. L thuyt sy rau qu...........................................................................................392.4. Mt s phng php sy rau qu.........................................................................422.5. La chn phng php sy lnh theo hng nghin cu ca ti....................42Chng 3. TNH TON THIT K M HNH MY SY LNH S DNG BM NHIT............................................................................................................443.1. Gii thiu bi ton thit k v m hnh thit k...................................................443.2. Xy dng quy trnh cng ngh sy C rt............................................................46 3.2.1. Gii thiu vt liu sy....................................................................................463.2.1. Xy dng quy trnh cng ngh sy C rt......................................................473.3. Xc nh cc thng s u vo ca vt liu.........................................................483.4. Tnh ton l thuyt ch sy hi lu hon ton................................................48GVHD: ThS. Bi Trung Thnh4 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip3.4.1. Xc nh cc thng s im nt trn th sy.............................................513.4.2. Tnh ton tc sy v thi gian sy.............................................................533.4.3. Tnh ton nhit qu trnh................................................................................563.5. Tnh ton l thuyt ch sy thi b tc nhn...................................................583.5.1. Xc nh cc thng s im nt trn th sy.............................................583.5.2. Tnh ton nhit qu trnh................................................................................603.6. Xc nh kch thc bung sy............................................................................623.7. Cn bng nhit cho qu trnh...............................................................................633.8. Tnh ton qu trnh sy thc ch hi lu hon ton........................................673.9. Tnh ton qu trnh sy thc ch thi b tc nhn...........................................703.10. Kt lun v ch sy.......................................................................................723.11. Tnh ton thit k v la chn thit b ph tr...................................................733.11.1. Cc thng s nhit ca mi cht lnh...........................................................733.11.2. Tnh ton chu trnh bm nhit......................................................................743.11.3. Tnh ton thit k cc thit b trao i nhit.................................................773.11.3.1. Dn ngng..........................................................................................773.11.3.2. Dn bay hi........................................................................................823.11.4. Tnh chn my nn.......................................................................................873.11.5. Tnh chn ng ng dn mi cht.............................................................913.11.5.1. ng ng y...................................................................................91GVHD: ThS. Bi Trung Thnh5 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip3.11.5.2. ng ng ht...................................................................................913.11.6. Thit b hi nhit..........................................................................................923.11.7. Tnh ton tr lc v chn qut.....................................................................97Chng 4. KHO NGHIM QU TRNH SY THC T TRN M HNH MY SY LNH.......................................................................................................1024.1. Mc ch............................................................................................................1024.2. Phng php v phng tin.............................................................................1034.3. Th nghim xc nh cc thng s qu trnh......................................................1034.3.1. Th nghim xc nh vn tc tc nhn sy...................................................1044.3.2. Xc nh m - nhit trung bnh (to, o) ca khng kh ......................1064.3.3. Th nghim xc nh m u v m cui ca vt liu sy.................1064.3.4. Xc nh R trung bnh ca vt liu sy v phng php ct lt vt lu.......1064.3.5. Th nghim sy ch hi lu hon ton v ch thi b tc nhn......1074.3.6. Cc kt lun rt ra t thc nghim...............................................................1134.4. ng dng phn mm Labview vo nghin cu thc nghim............................1134.5. Cc tnh cht nh hng n qu trnh sy........................................................117Chng 5. TNH TON HIU QU KINH T.............................................................1195.1. Ch ph nguyn liu, nhin liu .........................................................................1195.2. Chi ph lao ng.................................................................................................1195.3. Chi ph khu hao................................................................................................119Chng 6. KT LUN V NGH............................................................................121GVHD: ThS. Bi Trung Thnh6 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip6.1. Kt lun..............................................................................................................1216.2. ngh...............................................................................................................121TI LIU THAM KHO................................................................................................123Li 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 quan tm ch dn v gip tn tnh ca cc thy c. Qua qu trnh thc hin lun vn ttnghip 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 thigian 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 2010Sinh vin thc hin tiGVHD: ThS. Bi Trung Thnh7 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip Nguyn Anh TunGVHD: ThS. Bi Trung Thnh8 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipTRNG I HC CNG NGHIP TP HCM CNG HA X HI CH NGHA VIT NAMKhoa Cng Ngh Nhit Lnh c Lp- T Do- Hnh PhcNHIM V N TT NGHIPH v tn:MSSV:Ngnh: Cng Ngh Nhit Lnh Nin Kha: 2006-2010Tn 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 LnhI/ Thng tin thc hin ti:13-S liu choo trc: M hnh sy lnh ca khoa Cng Ngh Nhit LnhII/ 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.GVHD: ThS. Bi Trung Thnh9 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip 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 ti10- 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 tXy dng gi thnh 1kg rau sy 13- Cc bn v thit kIII/ Ngy giao nhim v: 01/03/2010IV/ Ngy hon thnh nhim v: 25/06/2010TP H Ch Minh, thng 3 nm 2010Gio vin hng dnThS. Bi Trung ThnhGVHD: ThS. Bi Trung Thnh10 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipLi 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 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 GVHD: ThS. Bi Trung Thnh11 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipch, 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 tiNghin 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 sylnh bmnhit cakhoa CngNgh NhitLnhthchin da trnc 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.GVHD: ThS. Bi Trung Thnh12 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip 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 hnhGVHD: ThS. Bi Trung Thnh13 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipHnh 1-1. S nguyn l bm nhit.............................................................................11Hnh 1-2. Hai phng thc trao i nhit qua bung sy.............................................12Hnh 1-3. S qu trnh sy theo hai phng thc trao i nhit..............................13Hnh 1-4. S h thng lnh.......................................................................................14Hnh 1-5. S nguyn l h thng bm nhit kiu mun..........................................21Hnh 1-6. S cng ngh sy rau qu.........................................................................32Hnh 3-1. S nguyn l h thng v th qu trnh sy..........................................43Hnh 3-2. S cng ngh sy C rt...........................................................................45Hnh 3-3. S nguyn l bm nhit s dng trong h thng sy lnh........................47Hnh 3-4. th I-d ch sy hi lu hon ton........................................................48Hnh 3-5. th I-d ch sy thi b tc nhn..........................................................56Hnh 3-6. th I-d ch sy thc hi lu hon ton................................................65Hnh 3-7. th I-d ch sy thc thi b tc nhn..................................................68Hnh 3-8. S tnh ton kh ng trong h thng my sy.........................................96Hnh 3-9. S c tnh k thut ca qut APCR0502AA10/10..................................99Hnh 3-10. S cu to APCR0502AA10/10..............................................................99Hnh 4-1. Biu phn b vn tc tc nhn sy qua cc khay...................................102Hnh 4-2. Biu nhit , m ti TP H Ch Minh ngy 15/04/2010..................103Hnh 4-3. S h thng my sy lnh ......................................................................105Hnh 4-4. S cc thng s ch sy hi lu hon ton.......................................108GVHD: ThS. Bi Trung Thnh14 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipHnh 4-5. S cc thng s ch sy thi b tc nhn..........................................110Hnh 4-6. Giao din chng trnh ng dng phn mm Labview...............................114Danh mc cc bngBng1-1 nh gi so snh cht lng sn phm sy bng bm nhit sy lnh viphng php sy nng truyn thng v sy hng ngoi .................................. 28Bng 3-1 Thng s trng thi cc im nt ....................................................................74Bng 3-2 Thng s tiu chun ca cc im nt.......Error: Reference source not found 88Bng 3-3. Tn tht kh ng qua bung sy....................................................................98Bng 4-1 Bng kt qu kho st vn tc tc nhn sy..................................................102Bng 4-2 Bng kt qu thc nghim xc nh nhit v m mi trng..............103Bng 4-3 Bng kt qu xc nh xc nh m u vo ca vt liu sy...................103Bng 4-4 Bng kt qu bn knh R ca vt liu.............................................................104Bng 4-5 Bng kt qu th nghim ch sy hi lu hon ton.................................106Bng 4-6 Bng kt qu th nghim ch sy thi b tc nhn.................................108GVHD: ThS. Bi Trung Thnh15 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipCHNG ITNG QUAN V CNG NGH SY LNH1.1. Gii thiu phng php sy lnh1.1.1. Khi nim v bm nhitGVHD: ThS. Bi Trung Thnh16 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip1.1.1.1. Lch s hnh thnh v pht trin ca bm nhitBm 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 trnn rt quen thuc trong cc lnh vc iu ha khng kh, sy, ht m, un ncHnh 1-1. S nguyn l h thng bm nhit GVHD: ThS. Bi Trung Thnh17 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip1.1.2. 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).GVHD: ThS. Bi Trung Thnh18 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipHnh 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 GVHD: ThS. Bi Trung Thnh19 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipthp), 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 lnh1.2.1. 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 lnhGVHD: ThS. Bi Trung Thnh20 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip1.2.2. 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 ( )23/, /hd P Td mkg 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 GVHD: ThS. Bi Trung Thnh21 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip* c-nhitdungringthtchcakhngkhmnhit khquyn(c=1,23 kJ/m3K).* r - Nhit ngng t (r=2500 kJ/kg i vi hi nc 00C).*( )2h 3d P /Td m= , kg/m KdVdt R.dt-lncngngtheong100% (ngvi 1m3 khng kh m khi nhit gim i 1K) v thay i nhanh qua nhit theo biu thc: 23 hd(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/kgKMt 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: ( )20d 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: 's 0 0'1 0X T -T c=- lnX K T -T (1.5)vi' 3K.XK = [J/m K]dV/dL 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, Tsl nhit ng sng, cc ch s 1 v 2 l k hiu u vo v ra ca khng kh qua thit b bc hi.GVHD: ThS. Bi Trung Thnh22 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip1.3. Phn loi h thng sy lnh1.3.1. H thng sy lnh nhit nh hn 00Ca. 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, vvb. 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.GVHD: ThS. Bi Trung Thnh23 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip 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 00Ca) 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 chtlng,hm lngdinhdng sn phm cng khtt(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.GVHD: ThS. Bi Trung Thnh24 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip- 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 imGVHD: ThS. Bi Trung Thnh25 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip- 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 hakhng 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, R142b) My nn lnhCng 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 nhitGVHD: ThS. Bi Trung Thnh26 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip Cc thit b trao i nhit c bn trong bm nhit l thit b bay hi v thit bngng 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 givvCc 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 bayhi. 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 GVHD: ThS. Bi Trung Thnh27 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipmi 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 nhit1.5. Mt s kt qu nghin cu v sy lnh ca cc tc gi trong v ngoi ncVic 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 ncTc 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.GVHD: ThS. Bi Trung Thnh28 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip Hnh 1-5. S nguyn l h thng bm nhit kiu munMt 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 sylnhchophngsylnhs1theonguynlbmnhit kiunguynkhi 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 GVHD: ThS. Bi Trung Thnh29 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghiphp 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 sthng quami linh 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 nhtrong nghin cu camnh.Dovy,cncnhngnghincunh gi vnh hng ca cc yu t ny.GVHD: ThS. Bi Trung Thnh30 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip 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 ( )eMk M Mt (1.7)Trong : M - m cn bng ca vt liu sy ti thi im tMe - m cn bng ca vt liu sy, c xc nh bng thc nghimt - thi gian sy, sk - 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 .paGW Mx 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.sGVHD: ThS. Bi Trung Thnh31 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip Ga - lu lng khng kh chuyn ng qua bng ti, kg/m2.sy - qung ng dch chuyn ca vt liu sy, mGii 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. .PaG MW W xG y (1.11) Phng trnh cn bng nng lng

( ) ( ) ( )( ). . / .. .cv a pw a gaa pa pwh G G W x T TTxG 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/kgKGii phng trnh (1.12), xc nh c nhit khng kh ti u ra:

( )( / ).0.d a xa g g aT T a T T +

Trong : ( ). .a pa pwa G C C W +GVHD: ThS. Bi Trung Thnh32 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip . .cv a pwWd 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 g plgp pg plWh T T G L C C TTxyG C M C _ _ , , + +Trong : Lg - nhit n ha hi ca nc trong vt liu sy, kJ/kgCpg- nhit dung ring ca vt liu sy, kJ/kgKCpl- nhit dung ring ca nc, kJ/kgKGii phng trnh (1.13) ta s tm c s thay i nhit ca vt liu sy: ( )( ) ( ) 0/01. (1.14)y y hg gT f gT e fg _ , + y: ( )0. . . ; . .cv a g cv pw a a plW Wf h T G L g h C C Gx x _ , + ( ). .p pg plh G C M C +1.6. So snh phng php sy lnh vi phng php sy nngGVHD: ThS. Bi Trung Thnh33 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipSy 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: = orpp = exp;'r ohp 2(1.15) Trong Pr -p sut trn b mt ct mao dn, N/m2Po - p sut trn b mt thong, N/m2 - Sc cng b mt thong,N/m2h - mt hi trn ct dch th trong ng mao dn, kg/m30 -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 luGVHD: ThS. Bi Trung Thnh34 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipVt 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 xcVt 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 thngsy tangH thng sy bc xVt 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 trngKhi 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 .GVHD: ThS. Bi Trung Thnh35 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip- 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 = dd B+ 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, vvGVHD: ThS. Bi Trung Thnh36 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipBng1-1 nh gi so snh cht lng sn phm sy bng bm nhit sy lnh viphng php sy nng truyn thng v sy hng ngoi [Vin Cng Ngh Thc Phm, s Cng Nghip H Ni]Th tPhng Php syCh tiu so snhSy nngSy thng hoa v chn khngSy lnh s dng my ht m kt hp my lnh1Cht lng sn phm (mu sc, mi v, vitamin)Km hn rt nhiuTt hn Bng nhau2 Gi thnh sn phm Thp hn t hn nhiu t hn3 Thi gian sy Ngn hn Ngn hnLn hn hoc bng4 Chi ph u t ban uThng thp hnCao hn nhiu Cao hn5 Chi ph vn hnh, bo dngThng r hnt hn nhiu t hn6Kh nng iu chnh nhit tc nhn sy theo yu cu cng nghKh hn Kh hn Kh hn7 V sinh an ton thc phmThng km hnTt hn Bng nhau8 Bo v mi trngThng km hnNh nhau Km hn9 Phm vi ng dng Rng hn Hp hn Hp hn1.7. nh gi v kt luna) So vi sy lnh s dng my ht m chuyn dng kt hp my lnhGVHD: ThS. Bi Trung Thnh37 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip 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 nngNhn 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 lunu 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 GVHD: ThS. Bi Trung Thnh38 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipmy 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.GVHD: ThS. Bi Trung Thnh39 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipChng 2VT LIU SY LNH XY DNG QUY TRNH CNG NGH V X L VT LIU SY LNH2.1. 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 iha sinh: dos oxi ha cacht bo, phn ngsm muphi 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 qutrnh 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.GVHD: ThS. Bi Trung Thnh40 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip2.1.1. S cng ngh sy rau quRau qu (phi thch hp cho qu trnh sy)Lm sch (kh, t)La chn phn loi (theo kch thc)Gt saCt, thi (ty theo yu cu)Chn, hp (ty theo yu cu)X l ha hc (nu cn)Ch Ch pSy Sy C cLm ngui Lm ngui C cSyPhn loi Phn loi Phn loip bnh Nghin nhng gi ng gi ng giSn phm Sn phm dng Sn phm dng nguyn bn mng dng btGVHD: ThS. Bi Trung Thnh41 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipHnh 2-1. S cng ngh sy rau qu2.1.2. nh hng ca qu trnh sy n cht lng sn phma) 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.GVHD: ThS. Bi Trung Thnh42 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipb) nh hng n mi vNhit 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 scC 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, cngnh hotng caenzimpolyphenoloxidaza 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 GVHD: ThS. Bi Trung Thnh43 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipchun 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 GVHD: ThS. Bi Trung Thnh44 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipcu 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 lGVHD: ThS. Bi Trung Thnh45 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip 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 xungb) 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.GVHD: ThS. Bi Trung Thnh46 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip 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 chohmlngaxit amintngln. DolngNitproteingimxungvNit 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 qu2.3.1. Quy trnh x l trc khi sySy 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. GVHD: ThS. Bi Trung Thnh47 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip2.3.2. Cc yu t nh hng n qu trnh sya)Nhit syYu 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 phmsy. 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 khGVHD: ThS. Bi Trung Thnh48 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip 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 qua) 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.GVHD: ThS. Bi Trung Thnh49 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip 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 GVHD: ThS. Bi Trung Thnh50 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipca 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.GVHD: ThS. Bi Trung Thnh51 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipChng 3TNH TON THIT K M HNH MY SY LNH S DNG BM NHIT3.1. 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. GVHD: ThS. Bi Trung Thnh52 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipBi 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.GVHD: ThS. Bi Trung Thnh53 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipHnh 3-1. S nguyn l h thng v th qu trnh sy3.2. Xy dng quy trnh cng ngh sy C rt3.2.1. Gii thiu v vt liu sy C rt - Daucus carota L., ssp sativus Hayek., thuc h Hoa tn - Apiaceae. * M t Crtl loi cy tho sng 2 nm. Lct 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 dngC 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. GVHD: ThS. Bi Trung Thnh54 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip- 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 hcC 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; cellulose1,2; cht tro0,8. Mui khongctrongCrt nhkalium, 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 gtChn trong nc si nhit (87-880C) GVHD: ThS. Bi Trung Thnh55 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghiptrong thi gian 6-8 phtRa li trong dung dch SO2 (0,2-1%)Loi b vThi mng, xp vo khay sy Sy ( nhit 30-50oC) theo phng php sy lnhn m yu cu (12-14%)ng gi bo qunHnh 3-2. S cng ngh sy C rt3.3. 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 phnhahccaCrt sykhbaogm: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 0,054100mm. 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) Xcnh m ca vt liu syGVHD: ThS. Bi Trung Thnh56 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip 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. GVHD: ThS. Bi Trung Thnh57 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipC 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 lnhGVHD: ThS. Bi Trung Thnh58 SVTH: Nguyn Anh TunHnh 3-4. th I-d ch sy hi lu hon tonKhoa Cng Ngh Nhit Lnh n tt nghip Trng hp tc nhn sy hi lu hon tonKiu 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:Qutrnhgianhittcnhnsynnhit sy. im(2)ltrngthi khng kh nng trc khi vo bung sy.GVHD: ThS. Bi Trung Thnh59 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip 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 sya) 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

b004026, 42 4026, 42P = exp 12 - = exp 12 - = 0, 03548bar235, 5 + t 235, 5 + 27 _ _ , ,* Dung m ca khng kh 0 b00a 0 b00,74.0,035480,621 0,621 =0,0169 kg/kgkk0,993-0,74.0,03548.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.kkGVHD: ThS. Bi Trung Thnh60 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip* 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 hob114026,42 4026,42P =exp 12- =exp 12- =0,01072 bar235,5+t 235,5+8 _ _ , ,* Dung m ca khng kh1 b111 b1 a.P1.0,01072d =0,621 =0,621 =0,00678 kg/kgkkP - .P 0,993-1.0,01072* EntanpiThay 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/kgkkc) 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 ho4026,42 4026,42P =exp 12- =exp 12- =0,0731 barb2235,5+t 235,5+402 _ _ , ,GVHD: ThS. Bi Trung Thnh61 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip* Dung m Do qu trnh 1-2 l qu trnh gia nhit tc nhn sy thng qua dn nng ca bmnhit 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) = 57,64kJ/kgkk* m tng i( )2b22 aP .d =0,621+d2 .P =( )0,993.0, 006780, 621 0, 00678 .0, 0731 + = 0,147 = 14,7 %d)im 3Vmtlthuytqutrnhsytrongphngphpsylnhlqutrnhngnhit, t2=t3=400C. Vi m u ra ca tc nhn sy sau khi ra khi bung sy chn =15 %.* Phn p sut hi bo hab334026,42 4026,42P =exp 12- =exp 12- =0,0731 bar235,5+t 235,5+40 _ _ , ,* Dung m: 3 303 b33a .P 0,15.0,0731d =0,621 =0,621 =0,011 kg/kgkkP - .P 0,993-0,15.0,0731*Entanpy I3 = 1,0048.t3 + d3(2500 +1,842.t3) GVHD: ThS. Bi Trung Thnh62 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip= 1,0048.40 + 0,011.(2500 + 1,842.40) = 68,5kJ/kgkk e) im 4* m: 4= 100%.* Dung m: d4 = d3 = 0,011 kg/kgkk* Phn p sut bo ho Pb4 = ( )44 4aP .d0,621+d . = 0,993.0,011(0,621+0,011).1= 0,0173 bar* Nhit t4 = b44026,42-235,512-lnP = 4026,42235,512 ln0,0173 = 15,3 0C* Entanpi I4 = 1,0048.t4 + d4(2500 +1,842.t4) = 1,004.15,3 + 0,011(2500 + 1,842.15,3) = 43,2 kJ/kgkk3.4.2 Tnh ton tc sy v thi gian syTheo yu cu ca ti ta la chn vt liu sy l C rt, Cc thng s vt l ca Crt. m u vo 1 = 88,7% [Xc nh bng thc nghim chng 4] m cui 2 = 12% - 14%. y ta chn m trung bnh ca sn phm 2 = 13%. [Xc nh bng thc nghim chng 4] Khi lng ring 3 =1035kg/m [Ph lc 6 /3/] Tc sy ng tc: S dng dng c o tc gi khi tin hnh thc nghim ta xc nh c vn tc tc nhn sy trong bung sy v = 3,1 m/s. Vn tc tc nhn sy v =3,1m/s < 5 m/s. Theo ti liu [1] ta c h s trao i nhit i lu:GVHD: ThS. Bi Trung Thnh63 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip

21 =6,15+4,17.v=6,15+4,17.3,1=19,1 W/m K Mt dng nhit [1] m 1 1b bJ = (t -t )Vi tm - nhit tc nhn sy, tm = 400C tb - nhit b mt vt liu tb=t = 280C [Xc nh da vo th I-d]

( )21b229,2W/m J =19,1 40-28 = hay 825120 kJ/m2h Cng bay hi m trn b mt vt liu1b2bJJ =rr - nhit n ha hi (theo gi tr p sut) vi tb=280C. Ta c: P=0,04517bar. Ta c:r=2429 (kj/kg)

1b2b8251202 2=340g/m h=0,34kg/m h2429JJ = =r Tc sy ng tc [1]20100bJURVi: o - khi lng ring ca C rt, o =n =1035 (kg/m3) [Ph lc 6 /3/]R- phn na kch thc vt liu sy Theo thc nghim kho st ly R=1,6 mm 02b-3100J 100.0,34U= = =20,53 %/hR1,6.10 .1035 Thi gian t nng vt liu [1]200F R =aGVHD: ThS. Bi Trung Thnh64 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipF0chun s Fure . -Xc nh chun s Bio nh s tng quan gia s trao i nhit trn b mt v tnh dn nhit ca n: Bi = q .R3,92.1,6= =11,4 0,55 Vi: R - bn knh vt liu, m; - h s dn nhit ca vt liu, =0,55 W/mK; [Ph lc 6 /3/]q - h s trao i nhit i lu; Theo ti liu [3]( )( )( )( )0,6 0,6k kq 0,4 0,4U . 2,8.1,128 =3,6 =3,6 =4,52.R 2.1,6, W/m2 Vi: Uk - tc dng kh, m/s; k - khi lng ring khng kh ti nhit sy, kg/m3; 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:

T =1okk-37,5-28= =0,9- 37,5-27tt 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 [Ti liu 3] ta tm c h s 00, 6 F a - h s dn nhit ca vt liu: vaC GVHD: ThS. Bi Trung Thnh65 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipTrong : = 0,55 (w/m2K), = 1035 (kg/m3), Cv= 3,87 (kJ/kgK) [Ph lc 6 /3/] 03 2440, 55 0, 6.(1, 6.10 )1, 373.10 0, 011 h3, 87.1035 1, 373.10a Thi gian sy ng tc [1] Theo cng thc thc nghim Egorov [1] 1/21 2 cb100 =k +0,435.k .ln100- _ ,Vik1, 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= 74% nm trong khong (10%< < 80%) ta c gi tr cc h s k1=2,7 v k2=19,5.Ta c: 1/2cb100 =2,7+0,435.19,5.ln =8,4%100-74 _ ,

cbkcbkcbk 8,4 = = .100=9,1%100- 100-8,4Vy thi gian sy ng tc dk kx1 - =U* d m ban u cu vt liu d = 88,7%ddkd 88,7 = = .100=785%100- 100-88,7* kx m ti hn ca vt liu m

1dkx cb cb785+9,1=445,2%1,8785-445,2=16,5 h20, 531 = + = + = 1,8 Thi gian sy gim tc [1]GVHD: ThS. Bi Trung Thnh66 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipVidk = 785 %

kx cb22k cb2 cb kx cb -2,3 = lnU - 1 1 = + - =

Trong :*d88, 71,8 1,8= = =0,0203%* 2= 13 % 22k2 13 = .100= .100=15%100- 100-13

22k cbk1 12,3 2,3 0,0203 = .ln = ln =11, 7 h0,0203.20,53 - 0,0203.20,53 15-9,1 Tng thi gian sy: = 0 + 1 + 2 = 0,011 + 16,5 +11,7 = 28,2 (h)3.4.3 Tnh ton nhit qu trnha) Xc nh lng m bc hi Lp 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 khay sy ta rt ra t l tng ng ca vt liu sy trn mt m2 khay sy l 4kg/m2. i vi mt m sy khi tin hnh thc nghim ta tin hnh vi khi lng vt liu sy G1 =14,5 kg. GVHD: ThS. Bi Trung Thnh67 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip* Lng m bc hi trong mt m sy11 22 - 88,7-13W=G =14,5. =12, 6100- 100-13

(kg/m) * Khi lng sn phm sau khi syG2 = G1-W = 14,512,6 =1,9 (kg/m)* Thi gian sy = 28,2 (h) theo kt qu tnh ton trn* Lng m bay hi trong 1 gih12,628,2WW = = =0,447 (kg/h)b)Lng khng kh kh cn thit lm bay hi 1 kg m03 21 1l = = =237 kgkk/kgad -d 0,011-0,00678*Lu lng khng kh kh tun hon trong qu trnh sy Llt = W.l0 = 12,6.237 = 2986,2 kgkk/mc)Nhit lng dn nng cung cp cho qu trnh sy lm bay hi 1 kg mqlt = 2 13 2I -Id -d = 57,64-25,10,011-0,00678 = 7711 kJ/kga* Nhit lng dn nng cung cp sy 1 m Qlt = W.qlt = 12,6.7711 = 97157 kJ * Nng lng tiu hao cho qu trnh syQk lt = lt97157= 0, 9628,2.3600Q= kWGVHD: ThS. Bi Trung Thnh68 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip* Lng m ngng tdlt = d3 d2 = 0,011 0,00678 = 0,00422 kgad) Lng nhit thu c t ngng t 1kg mqll lt = l0.(I4 I1) = 237.(43,2 25,1) = 4289,7 J/kga* Lng nhit dn lnh thu cQll lt = W.qll lt = 12,6.4289,7 = 54050kJ * Cng sut dn lnh ca qu trnh syQ0 lt = llltQ532022, 24= =0,53 28,2.3600 kW3.5 Tnh ton qu trnh sy l thuyt thi b tc nhn Vi kiu sy khng hi lu, khng kh mi trng (trng thi 0; (t0, 0)) c qut ht qua dn lnh gim nhit n nhit t1 (trng thi 1), v t2; ti y, lng nc ngng t s c dn ra ngoi. Tc nhn sy sau khi tch m tip tc i qua bung sy, thc hin qu trnh sy v thot ra ngoi (trng thi 4). Qu trnh sy l thuyt c trnh by trn gin I-d nh sau:GVHD: ThS. Bi Trung Thnh69 SVTH: Nguyn Anh TunHnh 3-5. th I-d ch sy thi b tc nhnKhoa Cng Ngh Nhit Lnh n tt nghip 0-1 : Qu trnh lm lnh tc nhn sy n nhit ng sng. im (0) l trng thi khng kh iu kin mi trng, im (1) l trng thi khng kh trong thit b bay hi, lc bt u gim m. Khng kh ngoi mi trng c ht vo dn lnh kh m. 1-2: Qu trnh tch m. im (2) l trng thi khng kh cui giai on gim m trc khi i vo dn nng gia nhit. 2- 3: Qu trnh gia nhit tc nhn sy n nhit sy. im (3) l trng thi khng kh nng trc khi vo bung sy. 3-4: Qu trnh sy 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(qu trnh sy ng nhit). im (4) l trng thi khng kh sau bung sy thi b ra mi trng. 3.5.1. Xc nh cc thng s im nta) im 0 (Trng thi khng kh mi trng): tng t ch hi lu hon ton.b) im 1: Trng thi khng kh trc u dn lnhTa c d1 = d0 =0,0169 kg/kgkk, 1=100%.* Phn p sut hi bo haPb1 = ( )a 11 1P .d0,621+d . = 0,993.0, 0169(0, 621 0, 0169).1 += 0,0263barGVHD: ThS. Bi Trung Thnh70 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip* Nhit t1 = b14026,42-235,512-lnP = 4026,42-235,512-ln0,0263 = 22 0C* EntanpiI1 = 1,0048.t1 + d1(2500 +1,842.t1) = 1,004.22 + 0,0169(2500 + 1,842.22) = 65 kJ/kgkkc) im 2 : Trng thi khng kh sau dn lnh (sau khi kh m)Ta c: 2=100%, t2= 80C* Phn p sut bo ho2b24026,42 4026,42exp 12- =exp 12- =0,01072 bar235,5+t 235,5+8P = _ _ , ,* Dung m ca khng kh2 b222 b2 a .P1.0, 01072d =0,621 0, 621 0, 00678 kg/kgkkP - .P 0,993-1.0, 01072 * Entanpi : Thay cc thng s ca im 2 vo cng thc ta cI2 = 1,0048.t2 + d2(2500 +1,842.t) = 1,0048.8 + 0,00678.(2500 + 1,842.8) = 25,1 kJ/kgkkd) im 3 : Tc nhn sy c gia nhit (trng thi khng kh sau dn nng)* Nhit : t3 = 400C* Phn p sut bo hoGVHD: ThS. Bi Trung Thnh71 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipb334026,42 4026,42P =exp 12- =exp 12- =0,0731 bar235,5+t 235,5+40 _ _ , ,* Dung m: Do qu trnh 2-3 l qu trnh gia nhit tc nhn sy thng qua dn nng ca bm nhit nn : d2 = d3 = 0,00678 kg/kgkk* Entanpy I3 = 1,0048.t3 + d3(2500 +1,842.t3) = 1,0048.40 + 0,00678.(2500 + 1,842.40) = 57,64kJ/kgkk* m tng i( )a 333b3P .d=0,621+d .P =( )0,993.0,006780,621+0,00678 .0,0731 = 0,147 = 14,7 %e) im 4 : Trng thi tc nhn sy thi ra ngoi V mt l thuyt qu trnh sy trong phng php sy lnh l qu trnh ng nhit, t3=t4=40oC. m ca kh tc nhn sy sau khi qua bung sy 4=15%* Phn p sut hi bo ha4b44026,42 4026,42P =exp 12- =exp 12- =0,0731 bar235,5+t 235,5+40 _ _ , ,* Dung m : 2 b222 b2 .P0,15.0,0731d =0,621 =0,621 =0,011 kg/kgkkP - .P 0,993-0,15.0,0731a* Entanpy I4 = 1,0048.t4 + d4(2500 +1,842.t4) GVHD: ThS. Bi Trung Thnh72 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip = 1,0048.40 + 0,011.(2500 + 1,842.40) = 68,5kJ/kgkk3.5.3. Xc nh nhit qu trnh a) Lng m bc hi trn mt m sy* Lng m bc hi trong mt m sy11 22 - 88,7-13W=G =14,5. =12, 6100- 100-13

(kg/m) * Khi lng sn phm sau khi syG2 = G1-W = 14,512,6 =1,9 (kg/m)* Thi gian sy = 28,2 (h) theo kt qu tnh ton trn* Lng m bay hi trong 1 gih12,628,2WW = = =0,447 (kg/h)b) Lng khng kh kh cn thit lm bay hi 1 kg

4 301 1l = = =237 kgkk/kgad -d 0,011-0,00678* Lu lng khng kh kh tun hon trong qu trnh syLlt = W.l0 = 12,6.237 = 2986,2 kgkk/mc) Nhit lng dn nng cung cp cho qu trnh sy lm bay hi 1 kg mqlt = 3 24 3I -Id -d=57,64-25,10,011-0,00678= 7711 kJ/kga* Nhit lng dn nng cung cp sy 1 mGVHD: ThS. Bi Trung Thnh73 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghipQlt = W.qlt = 12,6.7711 = 97157 kJ * Cng sut dn nng qu trnh syQK lt = 971570, 9628, 2.3600ltQ kW/h* Lng m ngng tdlt = d1 d2 = 0,0169 0,00678 = 0,01012 kgad) Lng nhit thu c t ngng t 1kg mqll lt = l0.(I1 I2) = 237.(65 25,1) = 9456,3 J/kga* Lng nhit dn lnh thu c:Qll lt = W.qll lt = 12,6.9456,3 = 119150kJ* Cng sut dn lnh qu trnh syQ0 lt = 1191501,1728, 2.3600ll ltQ kW/h3.6. Xc nh kch thc bung syCc 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 bung chiu di xc nh theo yu cu duy tr ch sy ng u. Chiu di cng ln, ch sy cng km ng u nhng cng tn dng c nhit ca mi cht. V vy cn chn hp l.* Nng sut bung sy:G1 = 14,5 kg/m* Th tch hu dng : Vh = 1.m VGK , m3Trong : m - Khi lng ring ca vt liu sy, m = 1035 kg/m3 [Ph lc 6 /3/]GVHD: ThS. Bi Trung Thnh74 SVTH: Nguyn Anh TunKhoa Cng Ngh Nhit Lnh n tt nghip KV - H s in y. KV = (0,40,5) [3]. Ta chn KV = 0,5Thay vo ta tnh c 314, 50, 0281035.0, 5hV m * Th tch ton b bung sy:V = Vh +V, m3Trong :V -Th tch ca cc khong trng ca knh gi v cc khng gian t qut v cc thit b sy, m3. Theo kinh nghim ta chnV= (30 40%)V [3]. - Ta chnV = 0,3.V = 0,3.0,028 = 0,0084 m3- Vy th tch bung sy l: V = 0,0364 m3Vi V tnh ton c, ta chn cc kch thc ca bung sy: Di Rng Cao l:LBH =0,750,750,7 (m3)3.7. Cn bng nhit cho qu trnh syPhng trnh cn bng nhit cho thit b sy: Q + Qbs + WCntm1 + G2Cmtm1 + LI1 + Gvc.Cvctm1 = G2Cmtm2 + Q5 + LI3 + Gvc.Cvc.tm2 GVHD: ThS. Bi Trung Thnh75 SVTH: Nguyn Anh TunL, I 1, d 1Gcv.Cvc.tm2Q5 G2.C m.t m2(G 2Cn+WC m).tm1THIT B SY Q QbsL, I3', d 3'Gvc.Cvc.tm1Khoa Cng Ngh Nhit Lnh n tt nghip Q + Qbs = L(I3 I1) + G2Cm(tm2 tm1) + Q5 WCn.tm1 + Gvc.Cvc.(tm2 tm1) 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.(tm2 tm1) = Qm -Nhit lng tn tht do vt liu sy mang ra* Q5- Nhit tn tht ra mi trng theo kt cu bao che* Gvc.Cvc.(tm2 tm1) = Qvc- Nhit lng tn tht theo thit b vn chuyn* Q2 = L(I3 I1) - Nhit tn tht do tc nhn syChia 2 v (*) cho W v b qua Qbs Ta c: q = q1 + q2 + qvc + q5 + qmMq = l(I3- I1) hayq = l(I3 I1) = l(I3 I1) + qv +q5 Cntm1 Hayq = l(I3 I1) = Cntm1 - ( qvc + q5 + qm)tCntm1 - (qvc + q5 + qm) = - Tn tht nhit lm bay hi 1 kg m. Suy ra l(I3 I1) = hay I3 = I2 + /l = nhit lng b sung nhit lng tn tht chunga) Tnh nhit tn tht qua kt cu bao che ra mi trngGVHD: ThS. Bi Trung Thnh76 SVTH: Nguyn Anh Tun53' 15 3' 1( )w w w w w( )vc vlvvc v vlQ Q Q Q Lq I I tCq l I I q q q tc + + + + + + Khoa Cng Ngh Nhit Lnh n tt nghip Nhit bn ngoi bung sy:tf2 = t0 = 27oC Nhit 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)Trong * F - Din tch xung quanh ca bung sy, m2 . Bung sy l hnh hp c cc thng s: LBH =0,750,750,7 (m3). Ta tnhtng din tch xung quanh ca bung sy: F = 2(L.B + L.H + B.H) = 2(0,75.0,75 + 0,75.0,7 + 0,75.0,7) = 3,225 (m2) * t - chnh nhit bn trong v bn ngoi bung sy , 0C t = tf1 - tf2 = 40 27= 13oC* K - H s truyn nhit , W/m2K; K = 12 11 1

,_

+ + 1, 2 - h s to nhit t tc nhn sy n vch trong bung sy v h s to nhit t vch 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: q =1(tf1 -tw1) = (tw1-tw2) = 2(tw2 - tf2) Vi tc tc nhn sy trong bung sy = 3,1 m/s (tc khng kh < 5 m/s) nn ta c: H s to nhit 1 c xc nh theo cng thc kinh nghim [1]. 1 = 6,15 + 4,17. = 6,15 + 4,17.3,1 = 19,1 W/m2K Vy mt dng nhit truyn qua GVHD: ThS. Bi Trung Thnh77 SVTH: Nguyn Anh Tuntw2tf2tw1tf112Khoa Cng Ngh Nhit Lnh n tt nghip q = 1(tf1 - tw1) = 19,1 (40 39,1 ) = 17,19 (W/m2)Nhit vch ngoi tng c xc nhtheo cng thc tw2 = tw1 - q. = 39,1 16,05.0, 00346 = 39,09 0CNhit nh tnh:O w2 0mt +t 39,09+27t = = = 33 C2 2Tra bng thng s khng kh vi tm = 33 0C 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 = 32g..t.l

37-6 29,81.0,7.0,75=4.10(16,29.10 ) .(273+0,9)Gr Ta c Gr.Pr = 0,7.4.107= 2,8.107 thuc khong (2.107 1.1013) => Ta c: C = 0,135, n = 0,33- Cng thc tnh Nusselt: Nu = C( )n1Gr.Pr = 0,135.(2,8.107)0,33 = 38,72- H s to nhit:-22 u2N . 38,72.2,697.10 = = =1,39 W/m Kl 0,75 Suy ra q = 2(tw2 - tf2) = 1,39.(39,099 -27) = 16,81 W/m2- So snh q v q:17,19'17,19 16, 810, 022 2, 2% 5%q qqq

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