KHOA HOC - CONG NGHE
NGHIEN ClhJ, TiNH TOAN NHIET CHO HE THONG SAY MIEN DONG QUY MO LANG NGHE OHA NQI
Ngd Xudn Bgi', Tg Hong Bite'
TOM TAT
Miin dong Id mdt logi thuc phdm dgng sgi dugc sdn xudt tie bgi cu cdy dong riing. Vdn di cdn nghien ciru hien nay Id ndng cao chdt lirong sdn phdm ddm bdo ve sinh an todn thirc phdm, tiet kiem ndng lugng vd bdo ve mdi truong trong qud trinh sdn xudt mien dong. Viec tinh lodn thiit ki he thong sdy miin dong phu hgp quy mo ldng nghe la mgt viec ldm cdn thiet gop phdn xdy dimg nong thon mai a Viet Nam. Bdi bdo trinh bdy kit qud nghien ciru vi tinh todn nhiel cho qud trmh sdy lu do mgt hi thong sdy mien dong dugc thiit ki cd the chi tgo vd dua vdo dp dung a ldng nghe.
RESEARCH, MONITOR HEAT FOR ARROWROOT VERMICELLI DRYER SYSTEM AT VILLAGE SCALE HA NOI
Ngo Xuan Dai', Ta Hong Duc^
SUMMARY
Arrowroot vermicelli is a fibrous food that is produced from arrowroot flour, Matters on the current research is to improve the quality of products, ensure the safety of food, save expenditure energy and environmental protection in the production process of vermicelli. The design of vermicelli drying system matching village scale in Hanoi is a necessary work to contribute to building new rural areas in Vietnam..
The paper presents results of research and computational heat for drying from a drying system which is considered vermicelli to designed and applied for manufacture.
Keywords: Arrowroot vermicelli, arrowroot, dryer system.
I. BAT VANDE
Vide lam khd mien dong bang phuang phap phoi ndng theo truydn thdng cd rdt nhidu nhupc didm nhu: Khdng chu dpng dupc kd hoach san xudt vi phu thpc vao thdi tidt. San phdm mien dong phoi ndng ngoai trdi chu yeu tgi cac dia didm gdn dudng giao thdng va khdng che day nen de bi nhidm bin, do vay khdng dam bao vd sinh an toan thuc phdm ddc bidt ddi vdi dgng banh trudc khi thai. Vide phai nang tdn nhieu nhdn cdng va vide tim chd phai rat khd khan do qua trinh dd thi hda nhanh dien tlch san phoi bi thu hep.
Vi vgy, vide lam khd mien dong bdng may sdy la rdt cdn thidt. Ngudn nang lupng cung cap cho may sdy rat da dang nhu: ndng lugng didn, ' Vien Ca dien nong nghiap va Cong nghe STH.
2 TS. Vi^n Ky thuat h6a hoc, Dai hoc Bach khoa HN.
TAP CHI CONG NGHIEP NONG THON - SO 19 - 2015
nang Iugng tir chat ldng, tif khi, tu ngudn ndng lupng sinh khdi (ctii trau, ciii gd, ciii gd, cui cdng nghidp, phe phu phdm nong nghidp...), nang lupng mat trdi...
Ci nudc ta hien nay chua sir dung phd bidn thiet bi say mien dong nao. Do vay tinh todn nhiet chinh xdc dd dam bao tiet kidm nhien lieu va dap img ydu cdu nhidt lugng cho qua trinh say la viec Idm quan trpng ciia vide thidt ke hd thdng say mien dong d lang nghe.
II. PHlTOfNG PHAP NGHIEN CtTU
Phuang phap kd thira: Kd thii'a cac thanh tuu nghien cuu ve thidt kd may say, cac ddc tinh cua qua trinh say... ciia cac tdc gia trong va ngoai nudc.
Phuong phap tinh toan thiet ke: Tinh toan qua trinh say dua tren do thi I-d, mgt sd thdng
25
"57
KHOA HQC - CONG NGH$
sd tdn thdt nhidt dua trdn cac tdi lidu tham khdo. Mgt sd kdt cdu d\ra vao thirc td va cdc tu van cua chuydn gia.
m . KET QUA VA THAO LUAN
3.1. So- dh qua trinh thay dhi trying thdi cua tac nhSn say
Khdng khi ngoai trdi tai didra A (hinh 1) cd trgng thdi xdc djnh bdi (To; (po) dugc qugt II hut qua bd trao ddi nhidt I. Trong bg trao ddi nhiet, khdng khi dugc gia nhidt ddn trang thdi d diem B xac dinh bdi cap thdng sd (Tj; cpi) va dugc qugt ddy vdo budng sdy III. Trong budng sdy, tac nhan sdy thuc hidn qua trinh say ly thuyet. Q day, Tl la nhidt do vao budng say dugc quyet dinh bdi tinh chdt vat ly ciia vat lidu sdy va che do cdng nghd say. Tdc nhdn say khi ra khdi budng say d diem C cd trang thai dupc xac dinh bdi (T2; 92), trong dd T2 dugc chpn trudc theo cdng nghe.
P-A I—
Hinh 1. Sa dd qud Irinh thay ddi trang Ihdi tdc nhdn sdy Qua trinh say ly thuyet la qua trinh siy dugc thuc hien tren mpt thiSt hi siy ly tuong. Vi vay, ngucri ta xem qua trinh sfy ly tuong la qua trinh dang entanpy (doan B-C), day chinh la dac tnmg CO ban ciia qua trinh sdy ly thuydt (hinh 2).
41-.8iifcl:j
Hinh 2. Trang thdi cm tdc nhdn sdy Iren do th] I-d trong qud trinh sdy ly thuyit
26 TAP 3.2. Tfnh toan can bang vat chat Tir thuc xi phan tich do am ciia nguyen lieu miSn dong dku vao la 65%, va dp Sm san phSm miin dong Uio la 14%, chpn nang su4t diu ra la 100 leg san phim kho/m^, nhiet do siy cho miSn dong la 45°C, thoi gian siy la 2,5 gio/me.
Trong sufit qu^ trinh say, xem nhu khong c6 hi?n tupng mit m^t vSt chit, do do lupng chat kho tuyft d6i coi nhu khong thay doi.
3.2.1. Phuang Irinh cdn bdng vdt chdt G, = G2 + (D.t (kg) Trong do:
Gl: khoi lupng mign dong dira vao may siy, kg G2: kh6i luong miin dong kho ra khoi may say, kg
(o: Luong im b6c hoi trong 1 gio, kg/h t: Thai gian siy, h
Lupng chit kho tuygt dai dua vao thifa bi say la:
„ „ lOO-^j ,„„ 100-14 „^ , G^=G,x i = 100x = 86 kg
' 100 100 ^ 3.2.2. Khoi luang mi&n dong (nguyen lieu) dua vdo thiel bi sdy
Voi nang suit siy: 100 kg miin dong kho/me, lupng nguyen lieu miin dong nguyen lieu cho mpt me siy xac djnh duoc la [1]:
G , = G , l ^ = 1 0 0 l H £ ^ = 243kg ' ^\-W^ 100-65 Trong do Wa la dp im miin dong kh6 = 14%.
Dp im cua mien dcng uot Wi = 65%
3.2.3. Luang dm bay hai trong 1 gia G,-G, 243-100 „ . , , 1 ^ ffl = —' - = = 57,2 kgam/h
I 2,5 3.3. Tfnh toan qua frinh say ly thuyet 3.3.1. Xdc dinh cdc thdng sd khdng khi moi Irudng (diem A)
Moi truimg co ap suit B = 760 mmHg. Tren d6 thj I-d, trang thai khong khi moi truomg tai diim A dupc xac djnh bod cap thong s6 (To; (po)
= (20°C; 85%). Cac thong si Iupng chiia im (do) CHf CONG NGHIEP NONG THON - SO 19 - 2015
KHOA HOC - CONG NGHE
va entanpy (Io) co thi tmh theo cac cdng thiirc dung ngon ngtt lap trinh sau nay fhi phuong giai tich hoac xac dinh true tiep tren do thi I-d. phap giai tich dupc sir dung. Vol cong thiic thuc Trong tinh toan du6i ddy, de thuan lpi cho viec nghiem ctia Antoine[2]:
- Ap suat bao hoa cua khdng khi ling vol To = 20''C:
4026,42 1 _ ^^_ f 4026,4 235,5+ r„ J ™''l 235,5 4
- Luong chua am do cua khong khi moi trucmg ben ngoai dupc xac dinh theo cong thiic [I]:
= e x p ^ ! 2 - ; ^ ^ ^ f ^ ^ = e x p ^ I 2 - ^ = ^ | ^ } = 0,0233 bar
rf„ = 0 , 6 2 1 x - g i i ^ = 0,621x "•85x0,0233 ^ kgim/kgkk B - ^ . x n „ M _ 0,85x0,0233
750 - Entanpy cua khong khi 6 To = 20°C [1]:
^ = C ^ x r o + r f . x ( r + C ^ x r J (kJ/kgkk) Trong do:
Cpk - nhiet dtmg rieng cia khong khi kho, kJ/kgkk.K.
Cpa - nhiet dung rieng ciia hoi nuac, kJ/kg im.K r - nhiet an hoa hoi, kJ/kg im.K
Liy Cpk = 1,004 (kJ/kgkk.K)vaCp.= 1,842 (kJ/kg im.K) var = 2500 (kJ/kgim.K) [3],tac6:
/„ =I,004x20 + 0,0124x(2500 + l,842x20) = 51,5 kJ/kgkk
3.3.2. Xdc dmh trgng Ihdi khdng khi sau khi xac dinh boi cap thong s6 (Ti; di) = (Ti; do) qua Irao ddi nhiel vao budng sdy (diem B). = (45°c* 0 0124 kg/kgkk)
Do qua trinh nhan nhiet ciia khong khi trong v .*• i. .* .»•« - I L - I I -
^, • • ^ , •* Xac dinh duac do am khong khi ipi va bo trao doi nhiet la qua trinh co lupng chiia am ^^^^^ ,_ ^ ^ y^.^^ ^ . ^^^ y ^ ^,^ ^^.^^
khong doi uen d,= do siy nhu sau:
Nhu vdy trang thai khdng khi d diem B dugc
Ap suat bao hoa tuong tiing vdi nhiet dp Tl = 45 C la:
f,^ 4026,62 1 f,^ 4026,62 1 ^ „.,, ,
?., =exp-^12 • ^ = exp-^12 ^ = 0,073 bar
" ^ [ 235,5 + 7; J *^1 235,5 + 45]
Dp am tuong ddi cua tac nhdn say sau khi ra khdi trao ddi nhiet:
^ x 0,0124
•S"''. _ 750. _n-,-,o/.
' Pj, X (0,621+ rf,) 0,073 X (0,621+ 0,0124) ' Entanpy cua tac nhan say khi ra khoi bp trao doi nhigt:
I,=C^>'T,+d,x{r + C^xT,} (kJ/kgkk) /, =I,004x45 + 0,0124x(2500 + l,842x45) = 72,l kJ/kgkk
3.3.3. Xdc dtnh thdng so aia khong kht sau I-d boi cap thong sfl (T2; I2). Do qua trinh siy ly khi ra khoi budng sdy (diem C) thuyit la qua trinh dang entanpy nen I2 = li =
Trang thai ciia tac nhan siy a diim C sau 72,1 (kJ/kgkk). Nhiet dp ctia tac nhan siy T2 sau qua trinh siy ly thuyet dupc xac dinh tren d6 thi qua trinh siy dupc chpn truoc sao cho t6n thit
TAP CHi CONG NGHIEP NONG THON - SO 19 - 2015 27
KHOA HOC - CONG NGHE
nhiet do tac nhan siy mang di la be nhat phu Nhu v&y s8 phai xac dinh cac thong so con hop voi quy trinh cong nghg va d6ng thoi phai lai cua tac nhan say la: lupng chiia am d2 va dp dam bao khong xay ra hign tupng dpng suong. am tuong d6i 92. Sau khi tinh dupc 92, tiin hanh Noi each khac nhigt dp T2 duoc chon sao cho kiim tra lai digu kign lp2= (55 ± 10)%, niu chua tren d6 thi I-d dp im tuong d6i ciia tac nhan say thoa man, phai chpn lai nhigt dp tac nhan say ra sau khi ra khoi buing siy (|)2 nim duai duong cp khoi bu6ng say T2 va tinh lai.
= 100%. Dg dam bao kha nang siy, co thg chpn Vai T2 = 33°C, va I2 = Ii = 72,1 kJ/kgkk thi:
T2 theo diiu kien dg 92 = (55 ± 10)%, chon so bp T2 = 33°C.
Lupng chiia im d2 sau qua trinh siy ly thuyit:
rf, = 72,1-1,004x33 : 0,0152 kgam/kgkk C^xfj 2500 + 1,842x33
Ap suit bao hoa tuong ilng 6 nhiet dp T2 = 33°C la:
L 4026,42 1 f 4026,42] „ „ , , P., =expi\2 ^ = exp'^12 ^ ^ = 0,05 bar
" ^\ 235,5 + r J 1 235,5 + 33j Dp im tuong dii cua tac nhan say sau khi ra khoi buong say:
Bxd, 760 750 -X 0,0152
= 0,484
*'' P„x{0,62\ + d,) 0,05 X (0,621+ 0,0152)'
Nhu vay (p2 = 48,4% da dam bao thoa man digu kien <P2 = (55 ± 10)%:
3.3.4. Luang khdng khi khd ly thuyet cdn thiit de bde hai 1 kg dm
Theo nguyen ly bao toan vat chat, phucmg trinh can bing am nhu sau[l]:
,G,xW, , , G, L,-xd„+- = Xn X rf, + -
100x( ' lOOxr Trong do:
Lfl - lupng khong khi kho ly thuyet di vao, kg/h Gl - Khgi lupng vat lieu mien dong nguyen ligu vao say, kg
Dodo:
_(G|X^)-(G;X>r,)_ (243x65)-(100x14) (rfj-rf„)xlOOxr
G2 - Khoi lupng san pham mign dong kho sau khi say, kg
Wi - Dp im ban diu ciia mign dpng uot, % W2 - Dp im cua mien dong san pham, % do - Lupng am chiia trong 1 kg khong khi mgi truang, kg im/kgkk
d2 - Lupng am chiia trong 1 kg tac nhan khi ra khoi buong say, kg dmykgkk
t - Thai gian say, h
h
•• 20.564,3 kgkk/h(0,0152-0,0124)xI00x2,5
Til do, lupng khong khi khg can thiit di bic hoi 1 kg im dupc xac dinh nhu sau[I]:
L„ 20.564,3
57,2 = 359,5 kgkk/kgam
Trong do: to - Lupng am boc hoi trong 1 gio da tinh 6 tren (~ 57,2 kg im/h)
28 TAP CHl CONG NGHIEP NONG THON - SO 19 - 2015
KHOA HOC - C 6 N G NGHE
3.3.5. Luu lugmg the tich trung binh Tdc nhdn sdy trudc khi dua vao budng say d didm B cd Tl = 45*'C, cpi = 27%, va ra khdi budng sdy sau qua trinh sdy ly thuydt d diem C cdT2 = 33°C,(p2 = 4 8 , 4 % .
Luu lupng the tich trung binh cua tac nhdn say dupc tinh theo:
Va = r (m /h)
Trong dd:
VB = LQ.VB la luu lugng the tich cua tdc nhdn say d diem B, (m'^/h).
Vc = Lo-vc la luu luong thd tich ciia tac nhdn sdy d diem C, (m'^/h).
VB Id the tich khdng khi "am cd chiira 1 kg khdng khi khd tai diem B, (m^/kgkk)
vc la thd tich khdng khi dm cd chua 1 kg khdng khi khd tai didm C, (m /kgkk)
Tlie tich cua khdng khi am cd chua 1 kg khdng khi khd tmdc khi vdo vd sau khi ra khdi budng say tuong ling bdng VB = 0,923 m /kgkk iing vdi nhiet
dp Tl = 45*'C, (p, = 27% va vc = 0,91 m^/kgkk ling vdi nhi?t dp T2 = 33''C, <p2 = 48,4% [3].
D o d o :
V B = 20.564,3 x 0,923 = 18.980,8 m^/h Vc = 20.564,3x0,91 =18.713,5 m^/h Vdy:
V,= 18.980,8 + 18.713,5
18.847,2 m^/h
= (5,2 mVs) 3.3.6. Nhiet luang tieu hao Qo
Nhidt Iupng tidu hao qo dd bay hoi 1 kg dm dupc tinh theo cdng thiirc[I]:
<la=h^(h-h) kJ/kgdm q^ = 3 5 9 , 5 x ( 7 2 , l - 5 1 , 5 ) = 7 4 0 V kJ/kgdm Tdng nhidt lugng tidu hao Qo dd bay hoi dm trong 1 gid dupc tinh theo cdng thuc[l]:
Qo = qo X CO = 7405,5 x 57,2 - 423.594,6 kJ/h (= 117,7 kW).
3.4. Tinh toan qua trinh say thirc 3.4.1 Sa do nguyen ly thiet ke tong the thiet bi sdy:
4>
Hinh 3. Sa do nguyin ly thiet ke tdng the thiet bi say mien dong
a) Nguyen ly thiet kd tdng thd thiet bi: mat trdi va Id ddt cui trdu. Mdi thidt bi gia nhiet Thidt bi sdy hoat ddng theo nguydn ly sdy nay dugc tinh toan thidt kd dd cung cap du nhidt ddi Iuu cuang biic. Nhidt lugng cua tac nhan sdy Iirgng cho budng say khi can hoat ddng rieng biet.
dupc gia nhidt bdi hai thidt bi thu ndng luang Cau tao budng say gdm khung sat hinh chiu lire,
TAP CHf CONG NGHIEP NONG THON - SO 19 - 2015 29
KHOA HOC - CONG NGHE
dupc bao quanh bdi cdc tdm vdch cd hai mait vdi dp day 5ph = 0,0005 m. Vdy moi phdn cd bpc tdn 1 - 2mm, giiia la Idp xdp each nhidt ddy kh6i luong mi^n dong la:
40mm. Ben trong cd bd tri kdnh dan nhidt, kenh hut dm va quat dao gid. Trong budng say cd 4 xe godng dd chua 300 phdn mien dong.
Trdn co sd cdc thdng sd ca bdn ciia midn dong dugc khdo sdt bdng thuc td: 300 phdn banh cho 243kg nguydn lieu. Kich thudc phdn bdnh (mm):dxrxc = 2200x 1000x5mm
Cae phdn mi^n dong dugc xdp trong long ciia budng say phdi dam bao khodng cdch giua cac phdn midn dong lam sao cho tdc nhdn sdy tidp xuc deu vdi hai mgt cua midn dong, thudn tidn cho vide sap xdp, vdn chuyen dua vao va ldy phdn banh ra khdi budng sdy thi xe godng la lua chpn tdi uu nhdt. Cac phdn banh midn dong ddt trdn 04 xe godng. Mdi xe godng chiia 75 phdn, dung nghidng so vdi phuong thang dumg 1 gdc 2-^4° trong ldng xe.
b) Sc b$ xac dinh cdc thong so kich thu-oc buong say:
Kich thudc phdn midn dong hien dang sir dung d lang nghd la: (dph x rph) = (2,2 x 1) m,
2,lx0,8x0,0005x982,5=2,0097=0,82kg/phdn.
Do vay, de duac 243 kg midn dong nguydn lieu phdi cdn cd 300 phen.Cdc phdn chua midn dong dupc dat tren xe day. Vdi kich thudc phdn da cd, dua vdo each xdp phdn, xe ddy dugc thidt ke chiia 75 phdn thi kich thudc xe ddy la:
(dxd X Txd X Cxd) = (1,25 x 3,1 X 2,0) m, va cdn 4 xe de chira hdt 300 phSn. Do dd, kfch thudc trong long budng sdy dugc thidt kd la:
D X Rx C = 5,5 x 3,2 X 3,0 m.
3.4.2. Tinh todn cdc ton thdt nhiet a) Thn thk ra he thong bao che, Qec Tdn thdt ra he thdng bao che dugc xac dinh:
QBC = QXQ + QTR + QN Trong dd:
QXQ: la tdn thdt nhidt ra xung quanh budng sdy;
QTR: la tdn that nhiet qua trdn budng sdy;
QN: la tdn thdt nhidt qua nen budng say.
Tir kdt cdu cua budng say va kich thudc cua phen sdy, cd the tinh dupc tiet didn tu do cua budng say:
^S^xn,)+(r^,xS,xn,)+ (r^, xS^xn,)}
F,,=(DxR) Trong dd:
D; R - Chidu dai va chieu rdng long budng sdy, m dxd; fxd - Chidu rdng va bd ddy xe ddy, m Tph; 5ph - Chieu rdng va bd day phdn, m
Si; §2 - Bd rpng thanh khung xe ddy, va bd rdng thanh dd phdn, m n; Uph - Sd xe ddy va sd phdn chua trdn 1 xe.
ni; nj; nj - Sd thanh ddi, sd thanh ngang trdn tidt dien xe va sd thanh dd phdn
= (>:
»+l)- = (-!-x75 + I ) - 2 =3,1 24
Do d6 tinh dupc:
i=;^=(5,5x3,2)-4x{(lx0,005x75) + (l,25x0,04x2) + (3,lx0,02x24)} = 9,748m^
Nhu v&y toe dp ly thuyet ciia tac nhan siy trong bu5ng siy la:
V 5 2
i'o=-^ = —^— = 0,531 m/s F,„ 9,784
30 TAP CHi CONG NGHIEP NONG THON - SO 19 - 2015
KHOA HOC - CONG NGHE
Vl luu lupng tdc nhan sdy trong qua trinh sdy thuc phai ldn hon trong qud trinh sdy ly thuyet ndn tdc dd tac nhdn sdy gia thidt dd tinh todn cdc tdn thdt ciing phai ldn hon VQ. Gid sii lay V = 0,54 m/s de tinh todn, sau khi tinh todn se kidm tra Isii gia thidt nay.
Nhidt dd cua khdng khi ndng:
T _ 7 ; + r ; _ 4 5 + 33
= 3 9 T Nhiet dp ciia khdng khi mdi trudng:
Tf2 = To = 20*'C
Tinh dugc tdn thdt nhiet cua budng sdy ra mdi trudng xung quanh qua ket cau bao che nhu sau:
- Tdn thdt nhidt qua kdt cau bao che xung quanh:
Q X Q = 18.760,59 kJ/h - Tdn that qua trdn budng sdy:
QTR = 335,06 kJ/h.
- Tdn that qua san (ndn budng sdy):
QN = 265,72 kJ/h
Nhu vdy, tdn that ra mdi trudng qua ket cdu bao che:
QBC = QXQ + QTR + Q N
= 18.760,59 + 355,06 + 265,72
= 19.381,37 kJ/h
Vd tdn thdt ra mdi trudng qua ket cdu bao che tinh cho 1 kg dm bdng:
<1BC-
19.381,37
57,2 = 338,84 kJ/kgdm.
b) Tdn that do vSt li^u say mang di, Qv Tdn thdt do vdt lieu sdy mang di trong 1 gid dugc xdc dinh theo cdng thuc:
Qy=^^Cyx(Ty,-Ty,) (kJ/h)
Trong do:
QV - nhiet do vat lieu say mang di;
G2 khdi lugng sdn pham khd ra khdi budng sdy (nang sudt trong 1 me);
Cv - nhidt dung ridng cua vdt lieu sdy;
Tvi, Tv2 - tuong ling la nhiet do vao vd nhidt dp ra cua vdt lieu sdy.
Cv la nhidt dung ridng ciia mien dong khd d dp dm 14% da dugc tinh: Cpb2= 1,841 kJ/kg
Nhidt do ciia mien dong nguydn Hdu khi vdo budng say bdng nhiet dp mdi trudng Tvi = To = 20 C. Nhidt do mien dong khd khi ra khdi budng say theo kinh nghidm ldy nhd han nhiet do tdc nhan say trung binh tir 5 -^ 10°C, cu thd IdyTv2 = 3 6 , 5 - 5 , 5 = 31°C.
Vdy tdn thdt do vat lieu say mang di bdng:
e ( , = — x l , 8 4 1 x ( 3 1 - 2 0 ) = 810,04 kJ/h Va tdn thdt do vat lieu sdy mang di tinh cho 1 kg dm, qv:
Qy 810,04 , , , , , , „ . qy = -=^ = = 14,16 kJ/kg am
6) 5 7 , 2
c) Ton that do thiet bi chuydn tai, Q C T Thidt hi chuydn tdi ciia may say gdm cd: cac xe ddy va cac phen tre. Do dd, ton thdt do thiet bi chuydn tai mang di trong 1 gid tinh bang:
QcT=Q..+Qr>. (kJ/h) Trgng lupng xe day: 60 kg/xe, do dd tdng trpng lugng xe day: m^d = 60 x 4 = 240 kg.
Trpng lupng phdn (phdn dugc lam bdng tre, dan nan thua mdng 0,005 m vdi thanh khung xung quanh day 0,001 m) dupc xdc dinh bdng thuc td: 1 kg. Tdng trpng lupng cua 300 phdn la:
mph = 600 x 1 = 300 kg.
Nhiet dung ridng ciia vat lieu lam xe ddy (sdt): Cs = 0,46 kJ/kgJK, va nhidt dung ridng ciia phen tre: Cph = 1,65 kJ/kg.K (l4y 0,^ = 30% cua Cgs)
Thdi gian sdy t = 2,5 gid.
Vdi nhidt dp mdi trudng 20''C, gid sii nhiet dp vdo trung binh ciia xe day va phdn Id: Tcri - 23"C. Nhiet dp ra cua tdc nhdn say T2 = 33°C, gid Sli nhidt do ra cua xe day va phdn: T e n ^ 31 C.
Nhu vay, tdn that do xe day mang di trong 1 gid la:
TAP CHI CONG NGHIEP NONG THON - SO 19 - 2015 31
KHOA HQC - CONG NGHE
a.
" . J >= Q " f e n -?'</1) _ 240X0,46X(31 - 2 3 )/ 2,5 Va t6n thit do phSn tre mang di trong 1 gio la:
^ >",. X C,> X fe7 - T„,) _ 300 X 1,65 X (31 - 23) 353,28 kJ/h
2,5 Do do, t6n thit do thiet bi chuyen tai bang:
S,., =353,28 + 1584 = 1937,28 kJ/h Va t6n that do thiet bi chuyen tai tinh cho 1 j a m :
Q„ _ 1937,28
= 1584 kJ/h
c^('^,,)'<(r,-r,)
; , - A
9CT ^ = 33,39 kJ/kgam
57,2 J.-/. J. vVdc dinh gid Iri A
Tong dai so t6n that nhiet va gia nhiet bo sung A tinh theo cong thiic [1]:
Tren co so phuong trinh can bang nhiet ctia mpt he thong say thuc, gia tri A, entanpy I2 va nhiet lupng tieu hao q dupc tinh nhu sau:
'^ = ?».v + C „ X r^, - {q^ +q,+ q„ ) A^
/ T,-T'
Trong do:
do = 0,0124 kg im/kgkk;
Cdx(do) = 1,027 kJ/kg.K;
Tl la nhidt dp vao ciia tac nhan siy = 45''C;
T2 la nhiet dp ra cua tac nhan siy = 33°C;
12 la entanpy ciia hoi nuac 6 nhiet dp T2:
, = r + C ^ x 7 ; = 2 5 0 0 f 1,842x33=256079 kJ/kg Nhu vay, tinh dupc:
l,027x(45-33)
rfj=0i0124+ =0,0149 kg am/kgkk
= /,
= ( / , - A ) x l
2560,79-(-297,79,0!
b) Entanpy cua tac nhan say sau khi ra khoi buong s^y, I2
I2 ^Cpi.>'T2-^<k^h =l,004<33+aOI49<256q79=7l29 W/kg c) B 6 am tuong d6i ciia tac nhan say sau khi ra khoi buong say, c|>2
Ap sudt bao hod ung vdi nhidt do T2 = 33"C la Pb2 ^ 0,05 bar va lugng chiia am cua tac nhdn sdy d trang thai nay la d2 ^ 0,0149 kg dm/kgkk.
Do do dp am tuang ddi cua tdc nhan say sau khi ra khdi budng sdy bdng:
760 „ „ , , „ Bxd^
T,~T,
Trong thidt ke, may say khong dupc cap nhiet bo sung nen qBs = 0
T a c o :
Cp„ = 4,18 kJ/kg.K Tvi = To = 20°C qBs = 0
qBC = 333,84 k J / k g i m q v = 14,16 k J / k g i m qcT = 33,87 k J / k g i m Xac djnh dupc:
A=0+4,18x20-(333,84+14,16+33,39)=-297,79 kJ/kg jm ( A < 0 )
3.4.4. Xdc dinh cdc Ihdng sd cua tdc nhdn sdy sau qud Irlnh sdy Ihuc
a) Luong chira am dz ciia tac nhan s i y Lupng chiia am d2 cua tac nhan siy khi ra khoi buong say dupc xac dinh theo[l]:
32 TAP CHi CONG NGHIEP NONG THON
- r = 0,475 ''' /•„ X (0,621 + rf J 0,05 X (0,621+0,0149)
Nhu vay tp2 = 47,5% nam trong khoang 55% ± 10%, thoa mSn yeu ciu. Do do, nhiet dp T2 = 33 C la chap nh^n dupc nen khong phai chpn va tinh lai niia.
Cac ket qua tinh toan dupc nhu sau:
- Dp chiia i m : d2 = 0,0149 kg am/kgkk;
- Entanpy: I2 = 71,3 kJ/kgkk;
- Dp i m tuong d6i: 92 = 47,5%.
SO 1 9 - 2 0 1 5
KHOA HQC - CONG NGH?
TIT cac kdt qud tinh todn tren, xac dinh cdc thdng sd cdn lai la lugng khdng khi khd thuc.
Ndu coi tac nhan sdy khdng bi rd ri trong he thdng say thi cdc phuong trinh can bdng dm ciia qua trinh sdy ly thuyet vdn dung cho qud trinh say thuc. Do dd, cac gia tri do va dj vdn khdng thay ddi (do = 0,0124 kg dm/kgkk va d2 0,0149 kg dm/kgkk).
d) Lirong khong khi khd can thiet de bay hoi 1 kg am
/ = = =400 kgkk/kgam d^~d^ 0,0149-0,0124 ^ ^ e) Lirgng khong khi kho can thiet L de bay hoi am trong 1 gicr
i=/^xG> = 400x57,2 = 22.880 khkk/h 3.4.5. Kiem tra lgi tdc do tdc nhdn sdy trong buong sdy
Sau khi cd cac ket qua tinh todn ciia qua trinh sdy thuc, tidn hanh tinh tdc dd thuc cua tac nhan di trong budng sdy nham kidm tra tinh chinh xac cua tdc dp da gia thidt.
Vdi cac thdng sd: T2 ^ 33''C va (p2 = 47,5%, thd lich vc ^ 0,910 m^/kgkk. Do do, Iuu Iupng thd tich sau budng say bang:
p;=ixv^ =22.880x0,91 = 20.820,8 m^/h Thl tich cua tdc nhan sdy trudc khi vdo budng sdy VB = 0,923 m^/kgkk (iing vdi nhiet dp 40"C vd dp dm 27%). Do dd luu lugng thd tich tnrdc budng sdy la:
)/^ = Lxv^ =22.880x0,923 = 21.118,24 m^/h Tit dd luu lupng thd tich trung binh di trong budng say dugc tinh bang:
j^+j^^2Q.82a8+21.1ia28^ ^ 3 ^ 2 2
- (5,82 mVs)
Vdi didn tich tu do cua budng sdy Fid = 9,784 m^, tdc dp tnmg binh cua tdc nhdn sdy trong qud trinh sdy thuc v bang:
V = — = A ^ = 0,595 m/s F,, 9,784
Nhu vay, cd sai lech khdng dang kd so vdi tdc dg tac nhan sdy da gid thidt khi tinh tdn thdt nhiet nen mpi tinh toan cd thd xem la diing.Do dd, luu lugng cua tac nhan sdy V = 20.970 m^/h la CO sd de chgn quat sdy.
3.5. Tinh toan can bdng nhiet
3.5.1. Tong nhi^t luang tieu hao cho viec sdy. Q
Vdi I = 400 kgkk/kg dm; Ii = 72,1 kJ/kg va IQ = 51,5 kJ/kg, tdng nhidt Iugng tidu hao cho 1 kg dm tinh dugc la:
^ = /x(/,-/o) = 400x(72,l-51,5) = 8240kJ/kgdm Do dd, tdng nhidt lugng tieu hao bang:
e = ^xfi) = 8240x57,2 = 471.328 kJ/h Nhiet lupng cd ich dd bde hoi 1 kg dm dugc tinh nhu sau:
?i =h~Cp.xTy, Vdi i2 = 2560,79 kJ/kg; Cpn = 4,18 kJ/kg.K vaTvi = To = 20°C, tinh dupc: 2477,19 kJ/kg dm
Do dd nhidt lugng cd ich:
Q = ^ , x c j = 2477,19x57,2-141.695,3 kJ/h 3.5.2. Ton thdt nhiet do tdc nhdn sdy mang di.Q2
Tir cac thdng sd cua tac nhdn say sau qua trinh say thuc, cd the tinh dugc tdn that nhidt do tac nhdn say mang di nhu sau:
fi2=ixc^x(n-rj
Vol L = 22.880 kgkk/h; Cpt = 1,004 kJ/kg.K;
T2 = 33°C va To = 20°C, ta dupc:
a =22.880xl,004x(33-20) = 298.629,8 kJ/h Do vay, ton that tinh cho 1 kg am se la:
g; _ 298.629,8
?2 = - = 5220,8 kJ/kgam
57,2
3.5.3. Tdng nhi^l luang linh lodn q' Tong nhiet lupng tinh toan la tong tit ca cac ton that va nhiet lupng co ich bao g6m:
TAP CHi CONG NGHI|P NONG THON - SO 19 - 2015 33
K H O A H Q C - C O N G N G H f q' = qi + q2 + qec + qv + qcr
Trong do:
- T6n thit qua k i t ciu bao che:
qec = 338,84 kJ/kg i m - T6n thit do vat lieu say mang di:
q v = 14,16 k J / k g i m - T6n thit do thiit bi chuyin tai mang di:
qcT = 33,87 kJ/kg i m - T6n thit do tac nhSn s^y mang di:
q2 = 5.220,8 kJ/kg i m - Nhiet lupng co Ich:
q i = 2.477,19 kJ/kgim.
Nhu v^iy tong nhiet lupng tinh toan bang:
q' = 2477,19 + 5.220,8 + 338,84 + 14,16 + 33,87 = 8.084,86 kJ/kg i m
Q' = q' X CO = 8.084,86 x 57,2 = 462.453,99 kJ/h Qua cac tinh toan tren, lap dupc bang can bing nhiet nhu sau:
TT 1 2 3 4 5 6 7 8
Bang can bing nhiet Bai lirgng
Ton that qua ket cau bao che Tin that do v^t lidu s&y mang di Ton that do thiet bi chuyen tai mang di T6n that do tac nhan say mang di Nhiet Iupng co ich
Tong lupng nhiSt tinh toan Ting nhiet lupng tieu hao ly thuyet Sai lech ly thuyet va thuc te
Q(kJ/h) 19.381,37
809,95 1.937,28 298.629,80 141.695,30 462.453,99 423.594,60 4Q = 38.859,39
Ty le (%) 4,19 0,17 0,42 64,58 30,64 100 8,4
-
IV. KET LUAN
DS nghien ciiu tinh toan, nhidt can thidt cho qua trinh say cho ket qud:
- Tdng lugng nhidt tieu hao dd bay hoi dm trong 1 gid la Q = 462.453,99 kJ/h, va dd bay hoi 1 kg dm la q = 8.084,86 kJ/kg Im. Va hieu sudt sir dung nhidt cua budng sdy tinh dugc T] = 30,6%
- Lugng khdng khi khd can thidt dd bay hoi dm trong 1 gid Id L=22.880 kgkk/h, va dd hdc hai 1 kg dm la I = 400 kgkk/kg dm. Luu lugng trung binh cua tdc nhan say la: v = 20.970 m^'/h (= 5,82 m^/s).
Trdn co sd tinh toan nhiet tren cd thd tinh toan, lira chpn dugc cac thdng sd chinh cho cdc thidt bi ben trong buong sdy. Dua ra dugc thdng sd tinh toan chinh ciia thidt bi budng sdy, la co sd dd thidt kd dupc cac thidt bi bdn trong va dua ra dugc bdn ve Idp, ban ve chd tao phuc vu cho
qua trinh chd tao chi tiet va lap rap thidt bj budng say sau nay. Tinh todn trd luc cua h?
thdng, cdng sudt quat gid yeu cdu, chpn qugt dling theo chd do cua quy trinh cdng nghe say mien dong dEit ra.
Tai lieu tham khao
1. Hoang Vdn Chudc, Ky thuat sdy, nha xuat ban Khoa hpc vd KJ thu|it, 1999.
2 .http ://www.khoaluan.vn/demo/Demo2/abd911 ca-df31-45c5-8308-2c99f2b5a080.pdf
3.http://123doc.org/doc-cat/99-giao-duc-dao- tao.htm
Ngaynhan bai: 26/8/2015 Ngay phdn bifn: 15/9/2015
Ngiroi phan bifn: TS. Doan Xuan Thin, Hoi co kill nong nghiSp Vi?t Nam.
34 TAP CHi CONG NGHIEP N 6 N G THON - SO 19 - 2015
