Chng 3. S DNG IN TRONG SN XUT NNG NGHIP3.1 S dng in nhit trong sn xut nng nghip3.1.1 Khi qut chung Nghin cu ng dng in nhit trong sn xut nng nghip l mt trong cc nhim v c ngha c bit quan trng. Trn 40 qu trnh sn xut trong nng nghip s dng nng lng in cho mc ch si m nui gia cm, gia sc, trong trng trt v t nng gia cng, ch bin nng sn thc phm...Nng lng dng cho khu vc nng nghip, nng thn chim khong 70-80% chi ph nng lng chung. Ngoi vic s dng in nng trong chuyn ng in, tu thuc cch thc chuyn i v s dng, nng lng in cn c bit n nh ngun pht nhit (in -nhit) v s dng nng di dng dng in hoc in t trng (cng ngh in). 3.1.1.1 in nhit Bn cht ca in - nhit l bin i in nng thnh nhit nng, gm cc dng chnh sau: -

t nng bng in tr, c trng bng nng lng in i qua in tr ca dy dn rn hoc lng u trong mch in pht nng. t nng bng h quang in: in nng chuyn thnh nhit nng nh h quang in, duy tr trong mi trng kh (t nng bng tia h quang in trc tip, gin tip v thit b h quang in plasma). t nng kiu cm ng: in nng bin thnh nhit nng trong cht rn hoc lng, nm trong t trng bin i nhanh (50Hz n 500kHz) di tc ng ca dng Phuc. t nng kiu in mi: in nng bin thnh nhit nng trong cht rn hoc cht lng nm trong in trng bin i nhanh (0,2 n 50MHz) di tc ng ca dng in phn cc v dch chuyn. t nng kiu in t: in nng bin thnh nhit nng khi vt cn nung gp dng in t tng tc trong in trng, c mt nng lng cao (n 5.10 8kW/cm-2, cao hn hng nghn ln tia h quang in). t nng quang hc: Xut hin khi vt cn t nng gp bc x tp trung ca my pht lng t nh sng (laser) - tia nh sng n sc trong di nh sng. Nng lng ca xung lng nh sng rt nh (n 30J) nhng v ng knh tia sng rt nh (1 8 m), tn ti trong thi gian cc ngn (phn triu ca giy) nn c th t nng n vi nghn 0C. Yu im l hiu sut thp (di 0,5%).96

-

-

-

-

3.1.1.2 t nng bng in Do d thc hin v c hiu sut chuyn i kh cao, t nng bng in tr ngy cng c nghin cu ng dng ph bin trong cc ngnh kinh t quc dn. Cc i tng cn c t nng trong sn xut nng nghip thng l nc, khng kh, sn phm nng nghip, thc phm, thc n gia sc, g u im c bn ca phng php t nng bng in l: - Thao tc v tc ng nhanh, d iu khin khng ch theo yu cu c bit ca cc cng ngh khc nhau. - B qua giai on chun b (tch nhit), tit kim thi gian v cng sc. - D thc hin ti u ho cc qu trnh cng ngh nhit, nng cao nng sut, hiu qu v cht lng sn phm trong trng trt, chn nui v ch bin. Da vo c im v mi quan h gia vt cn t nng v phn t pht nhit, phn bit lm hai kiu t nng trc tip (i tng cn t nng cho dng in i qua trc tip pht nhit) v t nng gin tip (i tng pht nng ring bit - dng in khng i qua vt cn t nng. Nhit lng pht ra t cc phn t in tr pht nhit bng in c tnh theo cng thc Q = I2Rt trong : Q - nhit lng to ra, J; I - dng in chy qua si t kiu in tr, A; R - in tr ca phn t pht nhit, ; t - thi gian lm vic, s Thit b chuyn i in nng thnh nhit nng bng in tr thng thng gm c ba b phn ch yu nh phn t t nng, v cch in v thit b iu khin. 3.1.2 Phn t pht nhit bng kim loi Phn t pht nng bng kim loi c cu trc h hoc kn trong v bc bng gm, thch anh hoc kim loiVt liu in tr phi c nhit lm vic di hn cao, n nh, c in tr sut cao, h s thay i v nhit thp, tc xy ho b mt si t chm, chng chu ho cht, cht cch in v du m Vt liu lm phn t pht nhit khng qu t, d ch to. Nhm vt liu sau y cho trong Bng 3.1, p ng tt cc yu cu trn c s dng kh ph bin. (3-1)

97

Bng 3.1 - Nhm vt liu ch to phn t t nng

in tr sut nhit Nhit cho php, 0C STT K m hiu Gii hn Ti u 200C, mm2/m 1 X25H20 (Crm - St tng cng) 1 900 800 2 X15H60 (Crm ba) 1,1 1000 900 3 X20H80 (Crm hai) 1,11 1100 1000 4 X20H80 (Crm hai vi Titan) 1,27 1150 1000 Nhit nng chy ca Crm l 1390 - 14000C, khi lng ring 8,2 8,4g/cm3, h s nhit , 0,09x10-3 n 0,35x10-3 (mc X25H20). Nhm vt liu hai hp kim St - Crm - Nhm (Phekhral) vi thnh phn Fe: 70 - 75%, Cr: 12 - 15%, Al: 3,5 - 5,5% c nhit lm vic n 700 0C. Nhm Kantal c thnh phn Fe: 72%, Cr: 20%, Al: 5%, Co: 3% c nhit cho php n 13000C. Nhm vt liu th ba, hp kim Constan cha ng - Niken - Constant ph hp cho di nhit thp di 100 3500C. Nhm Molipden v nhm Volfram c nhit lm vic n 20000C v 30000C. Trong thit k thit b pht nhit thng thng s dng cc cng thc tnh ton sau: Nhit lng ca mt si t q (W), tnh theo biu thc q = .C.l. trong : - h s truyn nhit, W/m2K; l, d, C - chiu di, ng knh v chu vi si t (dy in tr), m; - nhit si t, K. Cng sut tiu th P (W) c tnh theo cng thc P = p.C.l trong : p - cng sut ring b mt si t, W/m2 ng knh dy in tr si t, tnh theo biu thcP dd = 0,74 . U p2

(3-2)

(3-3)

(3-4)

trong :

- in tr sut ca dy in tr si t, .m;

Thng thng ng knh ngoi ca l xo dy in tr chn trong khong Dng = (5I8)d, nhng ng knh trung bnh Dtb khng nh hn 15mm; bc l xo h > d, nhng khng nh hn 8mm; s vng l xo w = l/h, vi l v lw k hiu chiu di ca ton b v chiu di dy in tr ca mt vng l xo. Chiu di ca l xo L = w.h. C th xc nh s vng l xo theo cng thc sau:W= 1000.1 h 2 + ( D tb )2

(3-5)

98

Ngoi cc phn t t trn trong thc tin ph bin cc si t dng ng d s dng v an ton hn, c tui th n 104h, c bit l si t dng ng trong bnh nu hi nc, thit b Karapu, thit b bc x nhit 3.1.3 Phn t t nng phi kim loi Thng s dng cc thanh t Silit (SiC) dng que hay ng (dn, d v) c th t nng n 14500C. n 8000C h s nhit ca phn t t ny m, nhit trn 8000C h s nhit ca n dng. duy tr nhit xc nh cn tng in p cung cp bng bin p iu chnh (v cng sut, t l vi bnh phng in p: P = U2/R) Phn t Kantal - Super lm t MoSi2 lm vic trong chn khng hu nh khng b xy ho, dn d v, c th lm vic n 1600 17000C. c tnh n nh, c h s nhit dng, tng nhanh khi nhit tng. Cc phn t t nng phi kim loi (gm hoc gm kim loi) c ch to theo cng ngh c bit. Trn nhn c ghi cng sut, in p, dng in lm vic v in tr, kch thc. Khi tnh cng sut ch cn t hp (ni tip hoc song song). S lng phn t t c xc nh theo biu thc:n= l 1 a

(3-6)

Trong :

n - s phn t pht nhit; l - chiu di lm vic ca phn t, m; a - khong cch b tr, chn a = 4d (ng knh thanh/ng pht nhit).

Kim tra sc ti nhit b mt cho php i vi thanh t Silit theo iu kin: Ps = P0/ .d.l Trong : P0 - Cng sut ca mt thanh in tr (phn t pht nhit): ti 1100 12000C: Ps 22W/cm2, ti 1250 13000C: Ps 16W/cm2, ti 1250 14000C: Ps 6W/cm2. T xc nh cng sut ton phn: Ptp = N.P0 (3-8) Trong cc thit b gia nhit nhit cao thng s dng cht cch nhit nh azbest, Cliua, ct thch anh, xit manh nng chy, p ng cc yu cu trn, nhit lm vic n 10000C, sau xit manh l xit nhm. (3-7)

99

3.1.4 Tnh chn si t v qut gi cho my sy nng sn My sy l thit b dng lm kh nng sn (ht nng sn, rau qu, thc phm) n m thp (v d: di 14% i vi thc v di 12% - i vi rau c) c th m bo iu kin bo qun an ton, lu di ngay c khi thi tit xu... Tu theo mc ch v cht lng nng sn m xc nh nhit sy cho thch hp. Thng thng, chn nhit sy cao hn nhit mi trng khng kh khong 3 300C (trong mt s trng hp, nhit sy cao hn 800C). Qut gi c tnh ton v chn theo cc thng s lu lng v ct p khng kh. Lng khng kh cn thit lm bay hi nc trong nguyn vt liu sy nng sn, tnh theo cng thcV= B bh , 1 0 vi B bh = 100 m1 2

(3-9)

trong :

V - lng khng kh, m3; Bbh - lng hi cn lm bay hi, kg; m1 - khi lng nng sn a vo sy, t; 1, 2 - m tng i ca nguyn vt liu trc v sau khi sy, %; - Kh nng cha m ca khng kh, g/m3 (tra bng xc nh theo biu i-d, ng vi m khng kh tng ng. V d: ti m khng kh 55 60%, gi tr l V tcT20 RH

= 20g/m3 ng vi nhit 200C, kh nng cha m ti aT50

= 17g/m3, cn 500C:

= 83g/m3 v 900C -

T90

= 428g/m3.

Nng sut qut (lu lng khng kh) L (m3/h), tnh theo biu thc:L=

(3-10)

trong :

tc - Thi gian sy cn thit (thng chn tc = 4 12h); (3-11)v 2 h lh 2g

Ct p ca qut H (m), xc nh theo cng thc: H = Hv + H1 + H2 + Hll trong : Hv - Ct p vn tc, H v =

- t trng khng kh (ti nhit 950C: 95 = 0,95), kg/m3; hlh - p sut bo ho khng kh nhit xc nh; v - tc lung khng kh (tc nhn sy), chn bng 3 10m/s; Hvl - tn tht ct p qua lp vt liu sy, m;T Ho - tn tht ct p trn thnh ng ( H o = 4' d .H vl ), m; T

L

100

- h s ma st, i vi ng bng kim loi v bng g: = 0,0034; dT, LT - ng knh v chiu di ng, m; H2= Hv - tn tht ct p ti cc c cong ( - h s thc nghim). Cng sut ng c qut P1(W) c xc nh theo biu thcP1 = L.H.k z 102 .3,6.10 3 td q

(3-12)

Trong :

L - nng sut qut, m3/h; H - ct p, m; kz - h s d tr (kz = 1,1 1,5); td

- hiu sut..

q - hiu sut qut gi (chn q= 0,4 0,6). Xc nh nhit lng tnh tonQ tt 2 = m1 .p 1 2 100 2

(3-13)

trong :

p - nhit lng ho hi nc (p = 2674kJ/kg);B bh .p m k

Nhit lng ca thit b gia nhit c xc nh theo cng thcQk =

(3-14)m

trong :

m

- hiu sut ca my sy (

= 0,5 0,7);

k - hiu sut ca thit b pht nhit ( k = 0,9 0,98). Cng sut thit b in cung cp nhit (Kaloripher) P2, W c xc nh theo biu thcP2 = Qk 3600 k

(3-15)

Cng sut ca mt phn t pht nhit Ppt , tnh theo cng thc Ppt = trong :P2 3n

(3-16)

n - s phn t nhit (in tr) u song song.Ppt

Dng lm vic qua mi si t (phn t pht nhit), tnh theo cng thcIp t

= U pt

(3-17)

Chn ng knh si t bng dy in tr Crm-niken , trn c s dng in v nhit lm vic ca dy in tr theo thit k: t 200 0C n 8000C (Bng 3.2).V d: Thng

101

thng, chn nhit lm vic 6000C, v nu dng in lm vic tnh ton (theo thit k) l 5,4A, tra bng chn dy Crm-niken ng knh 0,6 mm, tit din 0,283 mm2.Bng 3.2 - Hng dn chn dy in tr Crm-niken theo dng in v nhit lm vic

Dng in v nhit lm vic ca si dy in tr, 0C 200 400 600 800 1,00 1,63 2,13 2,78 1,50 2,35 3,10 4,05 1,95 3,15 4,20 5,45 2,48 4,00 5,40 7,05 3,00 4,90 6.64 8,75 3,55 5,80 7,95 10,50 4,10 6,80 9,40 12,40 4,70 7,80 10,90 14,40 5,90 9,80 13,70 18,70 7,30 12,00 17,00 23,20 8,70 14,40 20,20 27,80 10,20 17,00 23,80 32,70 11,90 19,70 27,60 37,90 15,40 25,40 35,70 48,70 19,30 31,50 44,50 60,00 21,20 34,50 49,00 66,00 25,40 41,80 58,50 79,00 32,20 53,20 74,20 99,00

Tit din dy dn 0,0707 0,1257 0,1963 0,2827 0,3848 0,5027 0,6362 0,7854 1,1310 1,5394 2,0106 2,5447 3,1416 4,5239 6,1575 7,0786 9,0782 12,5669

ng knh dy dn 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,2 1,4 1,6 1,8 2,0 2,4 2,8 3,0 3,4 4,0

Xc nh chiu di dy in tr ca mt phn t pht nhit, theo biu thcl pt = d t pt 0,5( t 2 + t 1 )

[

3600 Ppt

]

(3-18)

trong :

tpt - nhit phn t pht nhit, 0C; t1, t2 - nhit ln nht v b nht ca khng kh trong di lm vic, 0C. - h s truyn nhit i lu, kJ/h.m2.0C.V

= 11,3 trong :

v d

; vi v = 3600 F , (thng thng v = 5I10 m/s)k

V - lng khng kh i qua cc phn t pht nhit, m3/h; Fk - mt ct ngang ca bung pht nhit, m2.

S vng ca cun dy si t tnh theo mc 3.1.2. V d: Hy thit k thit b cp nhit cho my sy, nui t li in cng nghip 220/380V. Nu bit nhit lng yu cu l Qk = 50000kJ/h. GII: Gi s hiu sut ca thit b cp nhit l k = 0,95, cng sut ca thit b t nng102

P=

Q 50000 = =14 ,6kW 3600 .k 3600 .0,95

Nu b tr mi pha hai phn t t nng (hai cun dy in tr), cng sut ca mi phn tPpt = 14 ,6 = 2,43 kW 3. 2

Dng in qua mi phn t t nngI pt = Ppt U pha = 2,43 =11,1A 220

Gi s chn dy crm-niken vi nhit t nng 6000C, tra bng c: ng knh dy in tr d = 1,0 mm (tit din 0,7854 mm2). Chn tc gi 5 m/s, tnh gn ng h s truyn nhit i lu =11 ,3 5000 = 799 kJ / h.m 2 .o C 1,0

Chiu di si dy in trl pt = d[ 600 0,5( 50 + 70 ) ] 3600 .Ppt = 3600 .2,43 .1000 = 6,457 m 3,14 .1,0.799 .540

Chiu di ton b dy in tr L = 3.n.6,457 = 3.2.6,457 = 38,74 m Tnh bc l so: h = (2I4)d = 2I4 < 8 mm, chn h = 8 mm. Tnh ng knh trung bnh ca l xo: Dtb = (5I8)d = 5I8 < 15 mm, chn Dtb= 15 mm. Xc nh s vng dy trong mt phn t pht nhit (cun dt in tr)w= 1000l pt h + ( D tb )2 2

=

1000.6,457 82 + 3,14.152

(

)

= 135

Chiu di ca l xo si t (phn t phat nhit): LPT = 1000.h.w = 1,08 m.

3.2 Chiu sng trong sinh hot v sn xut nng nghip3.2.1 Khi qut chung Con ngi nhn bit cc vt th xung quanh, trong mi trng sng hay lm vic bng cc gic quan. Nh c quan th lc con ngi cm nhn nh sng pht x hoc phn x t cc vt, to khi nim v hnh dng kch thc v v tr ca chng trong mi trng lm vic xung quanh. Con ngi c th nhn bit 80% thng tin t mi trng sng, nh hng, vn ng, tip cn v cm nm, iu khin cng c lao ng nh th lc. Cc gic quan cn li thng ch ng vai tr b sung, lm phong ph hn khi nim c th ca103

cc vt th. V d, thnh gic v khu gic cm nhn m thanh v mi v, cn nh xc gic c th s m khng nh chc chn hnh ging, kch thc v v tr... C quan th gic cm nhn cc vt th quan st v mi trng sinh hot, lao ng cng tt, khi lng nh sng pht hoc phn x t cc vt v mt phng nn cng ln. Bi vy, chiu sng, biu th bng lux c xem l thng s c bn ca mi trng lm vic i vi cc hot ng sn xut. Trong cc cng trnh nh , gian sn xut, ngoi nh sng (chiu sng) t nhin, cn phi s dng cc ngun chiu sng nhn to, nh cc loi n in si t, n hunh quang, n chn khng, n kh km...Chiu sng bng in d thc hn, gi thnh hp l, s dng thun tin v nht l c th to ra cc ngun nh sng gn ging vi nh sng t nhin v nh sng c ph nh sng thch hp... Cn c vo i tng chiu sng, phn lm hai loi chiu sng-

Chiu sng dn dng: Cn h gia nh, phng c c quan, bnh vin trng hc, khch sn...; Chiu sng cng nghip: Khu vc nh xng sn xut, ch bin, trang tri, kho bi...Cn c vo mc ch chiu sng. Chiu sng chung: To nn sng ng u trn ton b din tch cn chiu sng (phng khch, hi trng, nh hng, phn xng); Chiu sng cc b: Tp trung nh sng vo mt im hoc mt din tch nh (bn lm vic, chi tit cn gia cng chnh xc nh tin, khoan, ng ch my khu); Chiu sng s c: Chiu sng d phng khi xy ra mt in li nhm mc ch m bo an ton cho con ngi trong cc khu vc sn xut hoc ni cng cng (nh ht, hi trng).

-

Cn c vo mc ch chiu sng, phn lm hai loi: -

Cn c vo mc ch chiu sng, cn phn lm cc kiu: chiu sng trong nh, ngoi tri, chiu sng trang tr, chiu sng bo v Mi loi hnh chiu sng c c im v yu cu ring bit, dn ti phng php tnh ton, cch s dng loi n, b tr n khc nhau cho iu kin c th. 3.2.2 Cc i lng c trng chiu sng 3.2.2.1 Quang thng Quang thng l phn nhn thy c (sng in t c bc sng trong khong = 380- 780nm) ca ngun nh sng pht ra (pht x). i vi ngun c ph nh sng t qung104

=

1 M td

V P=1

n

= 683 ( V1P1 + V2 P2 + ... + Vn Pn )

(3-19)

trong : - quang thng (lung sng), lm; Mtd =1 lm / W - h s tng ng c hc ca nh sng; 683

V - nhy ca ph nh sng (c trng cho r); P - cng sut pht x nh sang n sc, W; n - s ph nh sng n sc ca ngun nh sng. i vi ngun c ph nh sng lin tc = 8632 =760

1 =380

V p

d,

(3-

20) trong : p = e = 683.p ). c trng chnh ca bng n in bao gm: cng sut nh mc Pm (W), in p nh mc Um (V) v quang thng nh mc m, ph nh sng...do nh ch to cung cp. T cc s hiu ny, ta c th nh gi so snh la chn n trong thit k ph hp cho cc mc ch ng dng c th, v tit kim chi ph u t, chi ph in nng... 3.2.2.2 Cng nh sng Trong trng hp chiu sng ng u ca lng quang thng (lm) trong gc khng gian (sr)I= d d

dP , (trong thc t tnh ton i khi s dng i lng d

(3-21)

trong :

I - cng nh sng, cd/sr;d d

trong trng hp khng ng u, tnh cng nh sngI=

(3-22)

trong :

d - quang thng, lm; d - gc khng gian, sr.

Gc khng gian bao quanh tm O ca bng n trn (sr) c xc nh theo biu thc105

d =

dS r2

(3-23)

trong : r, dS - bn knh, m v din tch phn ct ca mt cu, m2. Cng thc ny cng ng cho trng hp gc khng gian bao quanh mt cu tm O (khi din tch S c thay bng din tch ton b mt cu). V d: Tnh cng sng I ca mt tri, ng vi mt lng quang thng xung tri t d = 1,45 .1019 lm, trong mt gc khng gian d = 5,55.10- 9sr. GII: Cng sng ca mt tri chiu xung qu t l I = d /d = 1,45.1019 / 5,55.10- 9 = 2,61.1027 cd 3.2.2.3 ri v trng ri E l phn quang thng ti trn mt n v din tch dS, tnh theo biu thc, biu th bng lux (lx)E= d dS

(3-24)

trng R ca ngun sng c quang thng d , phn b u trn mt din tch gii hn dS, cng c tnh theo biu thc trn nhng biu th bng lm/m2 Nu mt vt phn x hay cho qua ton phn ngun sng chiu ti ri trn vt E lun nh hn trng chiu ti n.lHnh 3.1 - Minh ho xc nh ri

Gi thit c ngun sng C, din tch c chiu sng tuyn N (Hnh 3.1). Thng lng ca ngun C i qua din tch dS l d = Id .d = dS cos l2

dS c phng theo php

(3-25)

trong : l - khong cch t C n tm dS,m. Thay vo cng thc (3-25) trn c:E= d IdS cos I cos = = dS l 2 dS l2

(3-26)106

ri ca ngun sng t l thun vi cng nh sng, t l nghch vi bnh phng khong cch t ngun ti tm din tch c chiu sng v ph thuc vo hng ti ca ngun sng. Khi mt quang thng u chiu ti mt phng xc nh, mt quang thng ri trn n v din tch b mt, tnh theo biu thcE= S

(3-27) - quang thng ca ngun sng, lm; S - din tch chiu sng, m2.

Trong :

Bng 3.3 gii thiu mt s tr s ri cho khc khu vc khc nhau c quy nh cc nc pht trinBng 3.3 - Tr s ri quy nh cc nc pht trin

i tng chiu sng Phng lm vic, bn giy Nh ng ph, chiu sng cng cng Ca hng, kho tng Phng n Phng hc, phng th nghim Phng v thit k, siu th Cng nghip mu Cng vic t m vi cc chi tit nh

ri, lx 400 600 150 300 20 50 100 200 300 300 500 750 1000 > 1000

Sau y cho mt s tr s ri c trng: Ngoi tri, bui tra h tri nng Ngoi tri, tri c my, ma ng m trng rm Phng lm vic Nh ng ph 100.000 0,25 300 500 150 300 20 30 lx lx lx lx lx 2000 3000 lx

V d: Mt lp hc c chiu rng a = 7,5m, chiu di b = 11,5m, c chiu sng bng 6 b n, mi b n c 2 ng hunh quang 1,2 m (cng sut P = 36 W, = 3350 lm. Bit h s s dng quang thng ksd = 0,65. Tnh ri trn b mt lm vic (b mt ngang bn hc, cch nn nh 0,8 0,85 m). Gii:107

Din tch b mt lm vic : S = b.a = 11,5 7,5 = 86,25 m2 Theo nh ngha, h s s dng quang thng l : ksd = s / t trong : vic, lm; t - quang thng, thu c t tt c cc ngun sng, lm. S ng hunh quang trong lp N l: N = 6 2 = 12 (ng hunh quang) Tng quang thng ca tt c cc ng hunh quang t = Nn = 12 3350 = 40200 lm T , xc nh quang thng nhn c trn b mt lm vic s = ksd t t = 0.65 40200 = 26130 lm ri E trn b mt lm vic l : E = s / S = 26130 / 86,25 = 303 lx 3.2.2.4 H s phn x , h s thu x , h s hp th Ngun nh sng ri ti mt vt th, phn tn thnh cc thnh phn phn x, xuyn qua vt th, v mt phn b vt th hp th. Do vy quang thng c c trng bi cc h s sau: a) H s phn x H s phn x ca b mt vt th c tnh theo biu thc = p / s trong : p - quang thng phn x; s - quang thng ri ti b mt. b) H s thu x H s thu x ca vt th, c tnh theo biu thc = x / s 29) trong : x - quang thng xuyn qua vt th. H s thu x cn gi l h s dn quang108

s -

quang thng nhn c trn din tch b mt lm

(3-28)

(3-

c) H s hp th H s hp th quang thng ca vt th = h / s (3-30) trong : h l quang thng hp th bi vt th. V tng quang thng phn x p, quang thng xuyn qua x, quang thng hp th h bng quang thng ri ti b mt s, c p + x + h = s Chia c hai v cho s ta c: 31) Cc h s ny ph thuc vo mu ca vt th, khi thit k c th c lng da vo mu sc ca vt th theo cc ch dn chn % nh sau: - Mu trng sng, thch cao trng - Mu trng nht, cc mu rt sng - Mu vng, xanh sng, mu xi mng - Cc mu rc r, mu gch - Cc mu ti, knh 3.2.3 Thit b chiu sng v thit b khi ng, iu khin to ra ngun sng, ngi ta thng dng cc loi n in, thng dng nht l n si t v n hunh quang (n tup, n neon). Hin nay, s lng n si t ang c s dng trn th gii ln khong gp 5 ln cc loi n khc. Nht Bn, n hunh quang c s dng ph bin, c s lng tng ng n si t... 3.2.3.1 n si t n si t cn gi l n dy tc do Thomas Edison pht minh nm 1879, do c cu to v iu kin s dng n gin, lp t d dng nn c dng rng ri trong khp cc lnh vc. Nguyn tc lm vic ca n si t da trn c s bc x nhit. Khi dng in i qua si dy tc, t nng n nhit rt cao (khong 2700 3100 K) v pht sng. Dy tc bng n thng lm t si trn volfram, tungsten hoc vn xon c, mc dch dc trn cc cc treo v c cung cp ngun in qua hai cc chnh. Trong mi trng cha kh tr hoc chn khng, nhit ca dy tc trong c th ln n 2500 - 30000C (ht chn khng i vi bng n cng sut nh, cn bng n109

+ + =1

(3-

80% 70% 50% 30% 10%

cng sut ln trn 75W - np kh tr nit, argon hay kripton chng xy ho v tng nhit lm vic ca si t). Tuy nhin, khi c kh tr trong bng n, tn tht dn nhit tng ln, cng sut n tng ln v hiu sut pht quang gim. Ngy nay ngi ta s dng cng ngh lm si t hoc xon xon kp ba,Hnh 3.2 - Cu to n si t ui xoy (a) v ui ci (b)

gim bt tn tht nhit v hiu sut pht quang ca n tng ln ng k, t 10 n 20 lm/W v tui th khong 1000h. n si t c u im l gn nh, h s cos = 1, nhng hiu sut pht quang ca n kh thp. T nhng nm 60, s dng kh halogen, cho php t nhit lm vic ca si t ti trn 3100K, tng hiu sut pht quang ti 20 I 27 lm/W, v tui th ti 2000h. V bng n si t thng dng, cng sut t 15 n 300W lm bng thu tinh pha ch. gim chi n si t cng sut, nh bn trong n ph lp bt m mn, c kh nng lc mu ngun sng v hp th t 1% n 4% ngun sng. Trng mt lp bc hoc nhm vo v tr thch hp trn v thu tinh ca n to lp gng phn chiu, c th nh hng c chm nh sng ca n. n halogen c kt cu c bit, lm bng thch anh hoc hai ln v, c kh nng pht sng cao, thng dng lm n pha xe t, n chiu phim v cho cc cng trnh vn ho th thao. Sau y l mt s k hiu thng dng ch cc loi n thng dng: A, k hiu n tiu chun; G - n hnh cu; PAR - n parabol; R - n phn quang; PS,P - n qu l v T - n ng.

110

Trong Hnh 3.3 gii thiu cc dng ui n xoy v ui ngnh khc nhau gp. cho sut, ng ui mi cn ch thng xoy cng ui dng i

dng ph bin

n ngnh - thcho cng sut d150W. Khi ui lp n, lp n vo ni n c ui vi

ngun in. Nhc im ch yu ca n si t l Hnh 3.3 - Hnh dng mt s n si t tn in v pht nng. Ngoi ra, tnh nng ca n thay i ng k theo bin thin in p ngun. Mi bin thin in p dn ti bin thin dng in v do bin thin si t nng lm nh hng n quang thng v tui th ca n. V d: Nu in p gim i 10% tui th n l 3700h, khi qu in p 5% tui th ca n nh hn 500h. Thi gian s dng n si t, thng thng Tm = 1000I2000 h. c tnh k thut ca n ph thuc nhiu vo in p cung cp. Khi in p thay i, dn n dng in thay i, ko theo s pht nng, quang thng v tui th ca n cng thay i.

Bng 3.4 - Thng s k thut chnh ca bng n si t

Cng sut, W 10 15 25 40 60 75 100

12V 100 500 -

Quang thng, lm 30V 110V 66 124 200 222 376 670 904 1327

220V 111 197 336 506 684 1004

Thi gian s dng Tm, h 1000

111

150 200 300 500 750 1000 = 1000h

-

-

2217 3100 4926 6715 12375 30500

1722 2528 4224 7640 10875 18300

V d: Cho n si t Um = 220V; Pm = 40 W; m = 430 lm; Tm a) Tnh quang thng ca n, khi n lm vic vi in p U = 200V b) Tnh tui th ca n khi n lm vic vi in p U = 240V GII: a) p dng cng thc tnh quang thng ta c: = m . (U / Um )3,67 = 430 . (200/220) vi in p nh mc 220V. b) p dng cng thc tnh tui th ca n: T = Tm . (Um / U)-14,8 = 1000. ( 220 / 240 )-14,8 400 h Ta thy rng, khi in p tng 10% (U = 240V), tui th ca n , gim gn 3 ln (Tm = 400 gi) so vi in p nh mc 220V. Bng 3.5 l c tnh cng sut v quang thng ca n si t chun v n si t halogen loi Um = 220VBng 3.5 - c tnh cng sut v quang thng ca n si t chun3,67

320lm

khi U = 200V, quang thng ca n gim rt nhiu so vi khi lm vic

n si t chun 220V P, W , lm P, W , lm 15 120 150 2200 25 220 200 3000 40 430 300 5000 60 740 500 8700 75 970 1000 18700 100 1390 1500 27700 3.2.3.2 n hunh quang a) Cu to

P, W 100 300 500 1000 1500 2000

n halogen , lm 2100 6300 10500 22000- 26000 33000 44000- 54000

n hunh quang (n tup) c hnh ng tr thng, hnh xuyn tit din trn v nhiu hnh dng khc nhau... Ph bin nht l loi n c hnh ng (Hnh 3.4)112

V n thng c lm t ng ng thu tinh 1 (di 0,6m; 1,2 m; 1,5 m; 2,4m), bt kn hai u c hai chn in cc mi bn, mt trong ph mt lp bt hunh quang 2. Trong ng np kh tr (argon) p sut thp v vi git thu ngn 3. Hai in cc bng vonfram hai u ng c ph lp oxit bari, kch thch pht x in t 4. b )

Hnh 3.4 - Cu to n hunh quang

Nguyn l lm vic Khi cung cp in p lm vic, s phng in gia 2 in cc trong mi trng c hi thu ngn p sut thp lm ion ho hi thu ngn v pht ra cc tia t ngoi (khng nhn thy). Tia s cp (t ngoi) tc dng vo lp bt hunh quang thnh ng, to ra cc bc x th cp c ph sng nh sng trong di nh sng nhn thy. Mu ca nh sng ph thuc vo tnh cht v liu lng ca lp bt hunh quang. c) c tnh Cng sut tiu th ca n ng hunh quang c ng knh ng 38 mm truyn thng kh ln. Ngy nay, nh ch to c lp bt hunh quang mn, c kh nng pht x th cp tt, hiu sut pht quang tng hn 4 5 ln n si t, cho php gim nh ng knh ng (t 38 mm xung 32 mm, 26 mm n di 26 mm) c cng sut tiu th gim (t 20W xung 18W, 40W xung 36W, 65W xung 58W) m vn c quang thng pht ra ln hn (Bng 3.6).Bng 3.6 - Quang thng ca mt s loi n ng hunh quang , lm

n ng th h 1 0,6m 1,2m ng knh ng 38 mm 20W 40W nh sng trng 1350 3200 nh sng ban ngy 1000 2450 nh sng trng Z 930 2450 nh sng trng cng 1150 3200 nghip n ng th h 2, ng knh 26 mm nh sng ban ngy 1350 3200 nh sng trng 1400 3350

1,5m 65W 3750 5100 5100 5300

2m 105W 8950 6300 8900

113

Hiu sut pht quang t khong t 40 lm/W 90 lm/W. Tui th ca n ph thuc vo s ln bt tt n - t khong 6000gi. So vi n si t, n hunh quang c u im hn l tui th di hn, hiu sut pht quang cao hn, s dng n hunh quang s tit kim in nng hn, v th n ng hunh quang c s dng ph bin chiu sng trong nh, lp hc, cng s, nh my... Tuy nhin, n ng hunh quang c nhc im l gi thnh cao cn thit phi c thit b iu khin (mi thp sng) v lp t phc tp... Cng nh cc loi n phng in khc, n ng hunh quang ch lm vic tt in p nh mc n nh. c) Mi in kch sng V khong cch gia hai in cc n phng in ln, khi ng n vo ngun in tn s 50Hz, cc n phng in khng pht sng lm vic ngay c m cn phi mi phng in bt n sng. C th s dng mt trong cc phng php v thit b mi phng in sau: Chn lu in t: Chn lu in t gm mt cun dy, qun quanh li thp, t trong hp bo vA 1 B 3

Hnh 3.5 - Chn lu t

(Hnh 3.5) Hin nay, thng dng loi tcte kh, gm c hai in cc nm trong bng thu tinh nh. Cc ng l cc2

4

Hnh 3.6 - S u ni mch in n hunh quang 1 - n hunh quang; 2 - Chn lu; 3 - Tcte; 4 - T b cos

lng kim (gm 2 ming kim loi c h s gin n v nhit khc nhau, ghp cht vo nhau). T in 4 c tc dng chng nhiu cho mch. S u ni mch in n ng hunh quang cho trong Hnh 3.6.114

Khi cung ng ngun cung cp, in p t gia hai in cc A-B ca n kh ln cha iu kin n bt sng. in p ng thi t vo hai cc ca tcte, bt u qu trnh phng in, cc cc ca tcte b t nng, cc ng un cong dn v chm vo cc tnh - ng mch tcte, khp mch dng in chy qua chn lu - in cc n hunh quang - in cc chn lu v ngun cung cp. Dng in ny c tc dng si m 2 in cc A v B ca n hunh quang v tch lu nng lng t trng trong cun in cm (chn lu). Sau khi 2 cc tcte ni mch (chp vo nhau), qu trnh phng in gia 2 cc tcte chm dt, cc ng bt u ngui dn v tr tch ra khi cc tnh (lm h mch cc tcte). Do dng in qua chn lu b ct t ngt, xy ra hin tng qu in p ln t ln 2 cc n hunh quang, qu trnh phng in trong n bt u v duy tr ngun sng. Bnh thng, do chn lu ng vai tr b san p (thay i in p ri trn trn lu), in p t ln n v dng in c duy tr n nh trong khong cn thit, bo v c in cc v n lm vic n nh lu di. Nhc im ca chn lu in cm l lm cho h s cng sut mch in n thp (c 0,45 0,55), phi dng t in C b sao cho h s cng sut t trn 0,85 0,9. Tn hao cng sut trong chn lu in cm chim khong 15%I25% cng sut n). Chn lu in t: Chn lu in t thc cht l b bin tn cng sut nh, bin i in p tn s cng nghip 50Hz thnh tn s c 20 - 30kHz, cung cp cho n. tn s cao, qu trnh phng in bt sng n din ra thun li (n d rng bt sng ngay sau khi ng in), hiu sut pht quang ca n c pht huy (tng thm c 10%), h s cng sut cao - t khong 0,9 m khng cn t b cos , ng thi tn hao cng sut trong chn lu in t nh. Chn lu in t c nhiu u im, ngy cng c xu th s dng rng thay cho chn lu in t. Khi thay i in p trong gii hn cho php, quang thng gim khng ng k (1%).Bng 3.7 - Thng s k thut ca n tup

Cng sut, W 30

in p, V 220

nh sng trng nh sng ban ngy Quang thng , Quang thng , lm/W lm/W lm lm 1230 41 1080 36

Thi gian s dng, h 2500115

40 100 200

220 220 220

1720 10990 -

43

1520 4000 8000

38 -

Ngoi cc yu im ni trn, yu im ca n hunh quang l quang thng ca n ph thuc vo nhit ca n (tcte lm vic kh khn di 150C). 3.2.3.3 n compact Mc d cc n phng in, n ng hunh quang c ci tin lin tc, c c tnh k thut ngy cng cng tt hn, nhng cc yu cu v h thng kch sng v iu khin cng nh v tr v din tch lp t lm cho kh nng ng dng ca cc loi n ny b hn ch cho mc ch chiu sng trong nh. Gn y, p dng lp bt hunh quang mn c cht lng nh sng tt, hiu sut pht quang cao cho php thu nh hn na ng knh ng, ng thi phi ghp chn lu vi ui xoy thnh mt b phn lm cho n c kt cu gn nh (compact) vi nhiu c tnh ni bt, gi ngn gn l n compact (Hnh 3.7). Nh c trang b ui xoy truyn thng, n compact c th thay th trc tip n si t vi hiu sut pht quang cao hn (vo khong 50 lm/W), tit kim in nng , tui th cao hn (vo khong 7000h) so vi n si t (Bng 3.8).

Hnh 3.7 - Hnh dng mt s loi n compact thng dng Bng 3.8 - c tnh mt s loi n compact

Loi n

Chiu di, mm

Cng sut P,W

Quang thng ,

Hiu sut pht quang, 1m/W116

n compact bng hnh tr, ui xoy

148 9 47 158 13 46 168 18 50 178 25 48 n compact ng knh bng hnh 165 12 700 58 trn, ui 165 18 1000 55 xoy 216 24 1450 60 n compact ngy cng c thc tin chp nhn v s dng rng ri

lm 425 600 900 1200

thc hin chiu sng hiu sut cao. 3.2.3.4 n phng in p sut a) n natri p sut thp Cu to ca n natri thp p bao gm mt ng thu tinh cha natri, np vo mi trng c kh neon p sut thp (khong 4.10- 3 mm Hg). vi p trong ). Thoy u, khi ngui natri c dng ht. Sau khi mi vi pht, natri bc hi pht ra nh sng mu vng da cam. n loi ny c hiu sut pht quang cao, t n 190 lm/W - ng hng u cc loi ngun sng in, ph hp cho chiu sng ng ph, xa l v sn kho...nht l cc nc x lnh, c sng m. Tuy nhin, ch s v trung thc mu sc km, khng thch hp cho chiu sng trong nh v ni c nhu cu cao v trung thc mu sc v nt. Tui th t khong 8000 gi.

117

Hnh 3.8 - n natri cao p Hnh 3.9 - n thu ngn cao p

b) n natri p sut cao Cu to ca n natri p sut cao gm v thu tinh bn ngoi hnh van v ng phng in bn trong bng thu tinh alumin, c kch thc tng i nh. p sut hi natri trong ng phng in khong 250 mmHg. Trong Hnh 3.8 cho hnh dng n natri cao p ui xoy. Hiu sut pht quang ca n t ti 120 lm/W. Ch s th hin mu thp. Tui th t khong 10 000h . nhit trn 10000C v p sut cao, n natri cao p pht ra nh sng mu trng m, c s dng ch yu chiu sng ngoi tri, chi sng cc khu vc cng cng, ng ph, bi xe, cng trnh vn ho, th thao... c) n thu ngn cao p Cu to ca n thu ngn cao p gm v bng bng thu tinh bn ngoi v ng phng in bn trong. S phng in trong ng thch anh c hi thu ngn p sut cao t 1 n 10 at to ra nh sng trng. Ngoi ra, mt trong ca bng thu tinh ngoi c ph mt lp hunh quang, cc bc x t ngoi bin thnh bc nh sng (Hnh 3.9). n thu ngn cao p c hiu sut pht quang t 40 n 60 lm/W, ch s trung thc mu sc trung bnh. Do c hiu sut thp118

hn, n thu ngn cao p (trc y c s dng nhiu trong chiu sng cng cng, ngoi tri v trong cng nghip) dn oc thay th bi n natri cao p ... 3.2.3.5 n halogen kim loi n ny c nguyn l lm vic da trn s phng in cao p trong hi thu ngn v halogen (ioua natri, ioua tali), c ph nh sng trng ging nh sng ban ngy. Hiu sut pht quang t ti 95 lm/W. Ch s trung thc mu sc tng i tt. Tui th t khong 4000h. n halogen kim loi c s dng chiu sng cng cng, cc cng trnh vn ho th thao c yu cu cht lng chiu sng tt, c nhu cu tip pht truyn hnh mu... 3.2.3.6 Thit b chiu sng Trong thc tin, t khi s dng ngun sng in trn, m s dng thm chao n bo v, ci thin cht lng ca ngun sng v chiu sng (che chn, phn x, khuch tn...) v to ra cc hiu ng m thut v k thut cn thit. Thit b chiu sng c phn loi tng i nh sau: a) Chiu sng trc tip Thit b ny c c im hng trn 90% quang thng xung pha di (b mt lm vic). y l phng php chiu sng kinh t, song thng gy chi mt v ri phn b khng ng u. Phng php chiu sng trc tip hay c s dng trong cng xng, nh kho, vn phng, ca hiu... b) Chiu sng bn trc tip c im: hng 60% 90% quang thng xung b mt lm vic v 10% 40% quang thng hng ln trn, phn x tr li xung b mt lm vic v.v. Phng php ny khng kinh t bng phng php chiu sng trc tip song chi mt, s dng cho chiu sng vn phng, nh , lp hc ... c) Chiu sng hn hp c im: hng 40% 60% quang thng xung b mt lm vic, cn 60% 40% quang thng hng ln trn, ri phn x phn b tr li . d) B n chiu sng bn gin tip119

c im: hng 10% 40% quang thng xung b mt lm vic, cn 90% 40% quang thng hng ln trn, ri phn x phn b tr li. e) Chiu sng gin tip c im: hng trn 90% quang thng ln trn ri phn x li phn b cho ton phng. Phng php chiu sng ny khng kinh t, song c u im l khng gy chi mt, rt tin nghi cho ngi s dng, thng dng chiu sng phng biu din, phng khch ... 3.2.3.7 Chao n Chao n l b phn bao bn ngoi, c chc nng phn phi li quang thng t ngun sng ca bng n mt cch hp l, theo cc yu cu chiu sng nht nh. V d: Chao n gi cho mt khi b chi, bo v bng khi va p, chng bi bn hoc cc kh n mnChao n c chia ra lm ba loi chnh: Chiu trc tip: c th tp trung hn 90% quang thng ca ngun sng xung pha di; Phn x: tp trung hn 90% quang thng ca ngun sng ln pha trn ri phn x tr xung; Khuych tn: to ra nh sng khuych tn, khng chiu sng trc tip. 3.2.4 Phng php thit k chiu sng theo h s s dng Thit k chiu sng trong nh, thc cht l thc hin tnh ton la chn ngun sng, s lng b n (thit b chiu sng), b tr v phn b cc b n trn trnv.v. Phi tun th cc yu cu c bn trong thit k chiu sng, m bo:-

ri E cn thit, lx; Tin nghi cho ngi s dng (chiu sng ng u, mu sc ph hp, khng gy chi hoc lo mt...; M thut v kinh t.

3.2.4.1 H s s dng ksd H s s dng ph thuc vo kiu b n, c tnh kch thc hnh hc v c tnh phn x ca a im (phng hc, vn phng, nh , xng ...). Di y a ra bng tra cu h s s dng cho thit k chiu sng trong nh (Bng 3.9).Bng 3.9 - H s s dng trung bnh cho mt s kiu b n

Phng php chiu sng kiu b n

ch s K

H s phn x Trn: 70% Trn: 50% Tng: Tng: 50% 30% 10 50 30 10%120

0,6 0,8 Chiu sng trc 1 tip b n cng nghip cho bng 1,25 hunh quang 1,5 2 2,5 3 4 5 0,6 Chiu sng trc tip b n chn 1 trong trn ng hunh quang 1,25 1,5 2 2,5 3 3 5 0,6 Chiu sng trc tip b n cho ng hunh quang 0,8 1 0,8

0,49 0,58 0,64 0,69 0,73 0,78 0,81 0,84 0,87 0,88 0,31 0,39 0,45 0,51 0,56 0,62 0,67 0,70 0,74 0,76 0,32 0,38 0,42

0,42 0,51 0,56 0,60 0,64 0,68 0,71 0,73 0,75 0,76 0,24 0,31 0,37 0,42 0,46 0,52 0,56 0,59 0,63 0,65 0,27 0,32 0,36

% 0,3 9 0,4 8 0,5 3 0,5 8 0,6 1 0,6 6 0,6 9 0,7 2 0,7 4 0,7 6 0,2 0 0,2 8 0,3 3 0,3 8 0,4 3 0,4 9 0,5 3 0,5 6 0,6 1 0,6 3 0,2 5 0,3 0 0,3 4

% 0,4 6 0,5 4 0,5 9 0,6 2 0,6 5 0,6 9 0,7 2 0,7 3 0,7 5 0,7 6 0,2 8 0,3 6 0,4 1 0,4 6 0,5 0 0,5 5 0,5 8 0,6 1 0,6 4 0,6 5 0,3 0 0,3 5 0,3 8

% 0,4 2 0,5 1 0,5 5 0,6 0 0,6 3 0,6 7 0,7 0 0,7 2 0,7 4 0,7 5 0,2 3 0,3 1 0,3 6 0,4 1 0,4 5 0,5 1 0,5 5 0,5 8 0,6 2 0,6 4 0,2 7 0,3 2 0,3 6

0,39 0,48 0,53 0,57 0,61 0,65 0,69 0,71 0,73 0,74 0,20 0,27 0,33 0,38 0,42 0,48 0,53 0,56 0,60 0,62 0,25 0,30 0,33121

1,25 1,5 2 2,5 3 3 5 0,6 Chiu sng hn hp b n cho n si t 0,8 1 1,25 1,5 2 2,5 3 3 5 0,6 Chiu sng hn hp hai ng hunh quang 0,8 1 1,25 1,5 2 2,5

0,46 0,48 0,52 0,55 0,57 0,59 0,61 0,37 0,45 0,52 0,58 0,63 0,69 0,74 0,77 0,82 0,85 0,21 0,28 0,33 0,38 0,42 0,48 0,53

0,40 0,42 0,45 0,47 0,49 0,51 0,52 0,30 0,37 0,42 0,48 0,52 0,58 0,62 0,65 0,69 0,72 0,16 0,22 0,27 0,31 0,35 0,40 0,44

0,3 7 0,4 0 0,4 3 0,4 6 0,4 7 0,4 9 0,5 1 0,2 6 0,3 2 0,3 8 0,4 4 0,4 8 0,5 4 0,5 9 0,6 2 0,6 6 0,6 9 0,1 3 0,1 9 0,2 3 0,2 7 0,3 1 0,3 7 0,4

0,4 2 0,4 4 0,4 6 0,4 8 0,4 9 0,5 1 0,5 2 0,3 3 0,4 0 0,4 5 0,5 0 0,5 3 0,5 9 0,6 2 0,6 4 0,6 7 0,7 0 0,1 9 0,2 4 0,2 9 0,3 2 0,3 5 0,4 0 0,4

0,3 9 0,4 1 0,4 4 0,4 6 0,4 8 0,5 0 0,5 1 0,2 8 0,3 5 0,4 0 0,4 6 0,4 9 0,5 5 0,5 8 0,6 1 0,6 5 0,6 7 0,1 5 0,2 0 0,2 4 0,2 8 0,3 2 0,3 6 0,3

0,37 0,39 0,43 0,45 0,47 0,49 0,50 0,24 0,31 0,36 0,42 0,46 0,51 0,56 0,58 0,63 0,65 0,13 0,18 0,22 0,25 0,29 0,3 0,37122

3 3 5

0,56 0,60 0,63

0,47 0,51 0,53

3.2.4.2 Cc bc thit k chiu sng trong Bc I:-

1 0,4 4 0,4 8 0,5 1 nh

3 0,4 5 0,4 7 0,4 9

9 0,4 2 0,4 5 0,4 7

0,39 0,43 0,45

Xc nh cc thng s hnh hc ca khu vc chiu sng: Chiu rng a; chiu di b; chiu cao t trn n nn H, chiu cao t "n" n b mt lm vic h H - h - 0.85;

-

Xc nh ch s khu vc KK= ab h (a + b)

(3-32)2

-

Xc nh cc h s phn x ca trn 1, ca tng 3.8;

theo bng

Xc nh ri E cn thit theo Bng 3.10 (nu khng c cc quy nh v yu cu ring bit).Bng 3.10 - ri cn thit cho mt s i tng chiu sng

i tng chiu sng Trang tri chn nui gia cm, gia sc Chiu sng chung khu nh ng giao thng, bn bi xe, nh kho Xng c kh, ch bin; Khch sn, phng n Phng hc, th nghim, trin lm, th vin Phng thit k; Lp rp thit b in-in t; Siu th Gia cng, lp rp c kh chnh xc; Cng nghip mu Bc II: kim tra:-

ri cn thit 30 75 lx 130 lx 100 150 1x 200 500 1x 300 500 1x 500 750 1x 1000 1x

T cc kt qu tnh ton ti bc I, la chn cc hng mc v tnh ton Ngun sng in (loi n); Phng php chiu sng v thit b n; Quang thng ton phn t; S lng thit b chiu sng; Phn b v b tr thit b chiu sng.123

-

V d: Tnh ton chiu sng cho phng hc c kch thc nh sau: chiu rng a=6,85m; chiu di b=8,6m, chiu cao t trn n nn H = 3,9m. n c gn vo trn, khong cch t ngun sng n b mt lm vic tnh theo cng thc: h = H - 0,85m. GII: Khong cch t ngun sng n b mt lm vic h=3,9 - 0,85 = 3,05 Ch s kch thcK = ab 6,58 .8,6 = h( a + b) 3,05 (6,85 +8,6)

Xc nh h s phn x - trn trng sng - tng xanh nht Xc nh tr s ri - cho lp hc chn E=3001x Ngun sng: Chn thit b n ng hunh quang, chiu sng trc tip gn vo trn. Tng quang thng tng t cho ton lp hc.K= ES dt k sd2 1

= 0,7

= 0,5

trong : S = ab - din tch phng hc kdt - h s b quang thng, do quang thng n gim theo thi gian: kdt=1,2 1,6 H s khu vc K = 1,25. Tra bng h s phn x trn phn x tng 2 1

= 0,7, h s

= 0,5. H s s dng ksd = 0,46.

Tnh tng quang thngt = 300 .6,85 .8,6 .1,3 = 499451 m 0,46

Chn thit b n hunh quang th h 2, nh sng ban ngy (Xem bng thng s n hunh quang) n=3200 lmden = 49945 = 156 16 ng n , 3200

Cho b n c hai ng, s b n l:124

N 16 = = 8b n 2 2

Kim tra li ng u ri. Theo tiu chun m bo ng u ri, khong cch m gia 2 b n khng c vt qu 1,5h mmax = 1,5.3,05 = 4,575m Trong thit k ta c khong cch 3,8m. Vy tho mn iu kin ng u d ri. 3.2.5 Phng php thit k chiu sng theo nh mc cng sut nh mc cng sut (cng sut ring) l i lng c tnh bng biu thcp= P S

(3-33)

trong : p - nh mc cng sut, W/m2; P - cng sut ton b ca bng n, W; S - din tch mt bng cn chiu sng. Phng php nh mc cng sut da trn c s cc bng cng sut ring (nh mc) cho trc, khng i hi trnh t tnh ton nh phng php h s s dng. Tng cng sut chiu sng c tnh t cng sut nh mc tra bng P = pS T tng cng sut chiu sng theo yu cu, xc nh c s bng n (ngun sng)N= P P0

(3-34)

trong : N, P0- s lng v cng sut ca mt ngun sng (bng n hoc thit b chiu sng); T xc nh s thit b chiu sng v phn b cc b n trn trn nh v d 7. Phng php tnh ton n gin, chnh xc khng cao, ph hp cho cc tnh ton chiu sng chung trong nh xng ch bin, kho bi...hoc tnh ton kim tra, tnh ph ti in cho trm bin th. 3.2.6 Phng php thit k chiu sng im

125

Bng phng php chiu sng im c th xc nh c sng mi mt im ca mt phng b tr cc ngun chiu sng, dng tnh sng cc b, ti ch mt bng thong, k c mt phng nghing v thng ng. ri ca cc mt phng nm ngang bng phng php chiu sng im c tnh theo trnh t sau: 1. B tr cc ngun sng trn bn v thit k nh xng, v nh du cc im cn kim tra c sng c coi l nh nht trn mt phng cn chiu sng; 2. i vi mi im nh du xc nh ri E (lx), c lng trn c s bng n c quang thng 1000 lm theo biu thcE=3 I 0 cos 2 Hp

(3-35)

trong : I0 - Cng nh sng ca ngun sng quy c (1000lm) theo hng im c chiu sng, xc nh trn ng cong phn b nh sng ca cc ngun sng hay tra bng; - Gc gia trc ngun sng vi phng ca tia sng.

Hnh 3.10 - Minh ho tnh ton chiu sng trn mt phng ngang

Trn Hnh 3.10, cho s tnh ri bng phng php chiu sng im, khi mt phng c chiu sng t mt ngun sng. Nu im tnh ton A c chiu sng bi nhiu ngun sng th ri ti im A c xc nh bng cng thc: EA = EA1 + EA2 + ... + EAn trong : ngun sng hu hn, ch yu quanh im tnh ton). Ly im c ri c lng nh nht thc hin tnh ton cc bc tip theo. 3. Xc nh quang thng ca n theo cng thc= 1000 E min.k (lm) E A

(3-36)

EA1, EA2,... EAn - ri ti cc im c trng, tnh t mi ngun sng (s

(3-37)126

Trong :

Emin - ri nh nht cho php theo nh mc, lux; Kdt - h s d tr (chn nh phng php h s s dng);

- h s ri b sung, c tnh n tc dng ca cc ngun sng xa v quang thng phn x (tra bng). 4. Chn bng n c cng sut tng ng quang thng tnh ton (t cc catalog).

Hnh 3.11 - Minh ho tnh ton chiu sng i vi mt phng nghing

Trn Hnh 3.11 cho s tnh ri ca cc b mt nghing v mt thng ng. ri ca b mt khng nm ngang c xc nh theo cng thc l E = E n = cos sinE n Hp

(3-38)

trong :

l - khong cch ngn nht t trc i xng ca ngun sng n ng ct mt phng nghing Fn hay mt thng ng Fd i qua im A. - Gc nghing ca mt phng cn tnh so vi mt phng nm ngang. Cho mt phng thng ng: = 900, khi l Hp

=

trong :

Hp - chiu cao treo ngun sng so vi mt phng chiu sng.

3.2.7 Thit k mch in chiu sng Bn thit k chiu sng, thng thng c cc ni dung cng vic sau 1. La chn loi n (ngun pht sng), cng sut v xc nh s lng bng n; 2. B tr n trong khng gian cn chiu sng; 3. Thit k li in chiu sng, gm-

S nguyn l li in chiu sng; La chn cc thit b bo v: aptomat, cu ch.127

-

a) Chn aptomat theo cc iu kin in p v dng in sau:

UmAp UmL ImAp Itt IcmAp IN trong : UmAp, ImAp, IcmAp - in p, dng in nh mc, dng in ct ca aptmat; UmL,Itt, IN - in p, dng in tnh ton, dng in lm vic ca mch chiu sng. Chn cu chy theo cc iu kin in p nh mc ca cu chy v li in, dng in nh mc cu chy v dng in tnh ton: UmCC UmL IdmCC Itt Khng cn kim tra iu kin ct dng ngn mch khi cu ch h p t xa bin p ngun (dng ngn mch nh). Cu ch cp trn phi c sao cho m bo iu kin tc ng chn lc. Tuy Aptomat c cu to phc tp v t tin nhng lm vic tin cy v thao tc d rng, ng li nhanh (thi gian mt in ngn) ngy cng c s dng nhiu trong li in chiu sng dn dng v cng nghip. b) Tnh chn chn dy dn Dy dn trong li in chiu sng h p chn theo dng pht nng cho php: K1K2Icp Itt trong : (3-39) K1 - H s hiu chnh gia nhit quy nh v lm vic (tra bng theo hng dn ca nh ch to); K2 - H s hiu chnh nhit , k n s lng dy hoc cp i chung ng (hoc mt rnh); Icp - Dng cho php ca dy ng vi tit din cn chn (tra bng theo hng dn ca nh ch to). Kim tra dy dn chn theo iu kin kt hp vi thit b bo v.K 1K 2 I cp 1,25 I dmAp 1,5

, trong trng hp bo v bng aptomat v

K 1K 2 I cp

I dmCC , trong trng hp bo v bng cu ch. 0,8

Khi cn thit, phi kim tra dy dn theo iu kin tn tht in p (nu ng dy di) v iu kin n nh nhit dng ngn mch (nu gn ngun).

128

Chiu sng chung cc khu vc nh sng sinh hot nh nh , hi trng, trng hc, c quan, vn phng i din, ca hng, siu th, bnh vin, khng i hi tnh ton thit k chnh xc, c th p dng phng php cng sut ring. Tu theo kh nng kinh ph, mc yu cu m quan c th s dng mi loi n: n si t, n tup, n halogen, n natri cao, thp p. Trnh t thit k chiu sng nh sau: 1. Cn c vo tnh cht ca i tng cn chiu sng, chn sut ph ti chiu sng p (W/m2) thch hp. T y tnh c tng cng sut chiu sng cho khu vc c din tch S (m2). P = P0.SP P0

(3-40)

2. Chn loi n, cng sut n P0, xc nh tng s bng n cn lp trong khu vc:N=

(3-41)

3. Phi cn c vo din tch cn chiu sng, s lng bng n v tnh cht yu cu s dng nh sng chn kiu b tr n cho thch hp (ri u, theo cm, s lng bng trong mi cm). 4. V s mng in chiu sng (t bng in n tng bng n). 5. La chn v kim tra cc phn t trn s (aptomat, cu ch, thanh ci, dy dn). V d: Thit k chiu sng cho mt nh xng c din tch 10x20 = 200m2. GII: Gi s, yu cu mc chiu sng trong gian sn xut kh cao. Chn sut chiu sng (cng sut ring): p = 30W/m2 Tng cng sut chiu sng: P = p.S = 30.200 = 6000W Chn n tup di 1,2m, cng sut 40W. Tng s bng n tnh theo biu thcn= 6000 = 150 40

Tng s n tup tnh c l 150 chic c b tr lm 10 dy, mi dy 15 bng n chia lm 5 cm, mi cm 3 bng. S nguyn l li in chiu sng cho siu th nh sau:

p t mt tng 50A p t mt nhnh 5A129

x 10 Dy cch inAT

i, li ng mm 10 xVC(2x1)A1 A2 A10

Hnh 3.12 - S b tr mch in chiu sng

La chn aptomat tng AT:I dmAT I tt = 6000 = 34 ,1A 220 .0,8

Chn aptomat c Im = 50A. La chn cc aptomat nhnh: C 5 nhnh, dng tnh ton cho mi nhnh l dng ca 15 n:I dmAi I tt = 15 .40 = 3,409 ( A) 220 .0,8

Chn dng 10 aptomat vi Im = 5A. Thng s k thut chnh ca cc aptomat tnh chn (v d ca hng LG) nh sau: Tn aptomat Um, V Im, A Loi S cc Icm, kA S lng 50AF ABE53a 3 2,5 1 16AF BKM C10 3 2,5 5 Kiu

AT 600 30 600 5 A1 A10 Gi s ph ti chiu sng xa ngun, khng kim tra iu kin ct ngn mch. La chn dy dn cho 10 dy n: K1K2Icp Itt = 3,409A

D nh dng dy ng bc nha h p, li mm nhiu si do Trn ph ch to, i ring r: K1 = K2 = 1. Chn dng dy i mm trn 2x1, vi Icp = 10A. Kim tra iu kin kt hp aptomat bo v:I cp = 10 A > > 1,25 I dmAp 2,5 = 1,25 .5 2,5

130

Vy dy 2x1 trn tho mn iu kin dng in cho php i vi cc dy n. Khng kim tra iu kin tn tht in p v n nh nhit dng ngn mch v xa ngun v v ng dy ngn. Sau y gii thiu mt s s mch in chiu sng thng dng

n mc ni tip

n mc song song

Hnh 3.13 - S mc n chiu sng ni tip v song song

Hnh 3.14 - S ng ct hai n hai v tr khc nhau dng mt cng tc

S khai trin

S kin trc

Hnh 3.15 - S mc n chiu sng xu chui chiu sng cu thang

Hnh 3.16 - S ngt mch chiu sng hai v tr

131

Hnh 3.17 - S mc n hunh quang v n c kh

Hnh 3.18 - S mc n hunh quang v n c kh

132

3.2.8 Vn hnh chm sc v bo dng thit b chiu sng bn ca n ng ph thuc vo cht lng lp t, iu kin s dng v ch bo qun. Nguyn nhn trc tip lm hng n l do b t dy tc. Khi tc n b t, thay th n mi l tt nht Phi tun th qui nh ca nh ch to v quy cch trong thi cng lp t cc thit b chiu sng, c bit l i vi cc loi n ng c cc ph tng, mch iu khin i km. Sau y l mt s quy tc chnh u ng s v m bo cht lng n hunh quang sau lp t:-

Kim tra m bo thng mch dn t dy pha ca ngun in i qua cng tc n chn lu, i qua din cc vo ca u tc n, qua stcte, ri qua in cc ra ca cc n cn li, khp mch v dy ngun (dy trung tnh). Nu mch c t in b cos , hai cc ca t in ni vi hai u dy ngun ca mng in chiu sng;

-

Nu s i dy ng, khi ng thi xoa nh tay xoay bng n n v tr cc in cc ca n tip xc tt vi cc in cc n - tcte s pht sng, gi nguyn v tr ny n s kch sng. Nu n khng kch sng, nguyn nhn c th l do khng tip xc in n, dy tc bng n b t hoc tcte khng lm vic (dng ng h vn nng hoc bt th in kim tra thng mch); C th dng bt th in kim tra thng mch nh sau: ni mt u in cc (si dy tc) vo dy la ca ngun cung cp, chm bt th in vo u in cc cn li, nu bt pht sng nh khi cm vo dy pha l dy tc in cc khng b t (tuyt i khng cm trc tip hai in cc bng n vo hai l cm, s lm ngn mch v chy dy tc). Nu in cc n cn tt, kim tra thay tcte, nu cn.

-

Kh nng pht x in t ca catt (in cc) ca n gim dn trong qu trnh lm vic, khi kh nng pht x ca catt khng n kch sng, gy ra hin tng phng in trong n...thc y qu trnh lo ho ca n v lm hng tc te, nu khng kp tt n v thay th. Bng n thng c tui th 5000h. Tui th ca n hunh quang, n kh ph thuc nhiu vo s ln khi ng n v kh nng pht x ca n mau b tiu hao, gi ho, gim kh nng pht sng...Nu tcte chc nng khng bnh thng s gy ra hin tng chp chn (n lc tt lc sng), lm n gim rt nhanh tui th. in p ngun, nhit mi trng lm vic qu cao hoc qu thp cng u nh hng su ln c tnh k thut v bn s dng ca n. Trong qu trnh s dng n loi ny, phi thay th ngay tcte hoc cc b phn i km nu b hng hc. Sau y, gii thiu mt s hng hc thng gp, nguyn nhn v bin php khc phc (Bng 3.11).133

Bng 3.11 - Mt s h hng thng thng, nguyn nhn v bin php x l

TT Hin tng 1 n khng sng, u n en, n nhp nhy 2 Mt hay hai u n c vng en sm rng 3 C vnh en 2mm st u n 4 n s dng cha lu c vnh en, c hin tng lc sng lc tt Kh khi ng, nhng n vn sng

5 6 7 8 9 10

11 12

Nguyn nhn Cch x l n ht thi gian s Thay mi dng n ht thi gian s Thay mi dng Thu ngn ngng t n lm vic mt lc s t ht - Tcte hng - Thay mi - Tip xc u n khng - Sa li ch tip xc tt. - Hng in dung stcte. - Thay stcte. - in p ngun qu cao, - Dng n p. qu thp. - Thay chn lu thch hp. - B hn ch khng ph hp Trn ng n c vt en Nhit na di thp Xoay n quanh trc na lm thu ngn ngng t vng. Khi tt n, n vn sng T in trong tcte chp. Thay tcte u ni sai s Kim tra, u ni li n sng nhp nhy, ht thi gian s dng Thay mi lc sng lc ti Mch 2 n khi lm u sai tcte u ni li s vic ch sng 1 n n khng ln hoc Dy tc b t, hng tcte, Thay tcte/thay n mi, khng th khi ng t dy ngun hoc in u ni hoc nng in p c p qu thp ngun. nh sng n c hnh - n mi: do hi thu - Dng vi ln s ht xon c, hnh sng ngn cha n nh hoc hoc gim in p cho ph do in p ngun qu cao; hp; - B tcte c hin tng - Thay mi tcte hoc chn d in qua tip im lu. hoc chn lu khng hp. Cng pht sng yu - Nhit n lnh hoc - Che chn gi nhit hoc qu cao; thng gi; - in p ngun qu cao. - Gim in p. Chn lu qu nng - Chn lu khng hp; - Thay chn lu mi; - T in tcte b chp; - Thay stcte mi; - in p ngun qu cao. - Gim in p.

3.3 Chiu x trong sn xut nng nghip3.3.1 Khi qut chung Bc x tia hng ngoi c hiu sut truyn nhit cao hn hn phng thc truyn nhit i lu, bc x cc tm v bc x nh sng nhn thy, tng ng vi thit b t nng bng134

in. K thut bc x hng ngoi c hiu sut cao, d thc hin iu khin theo cc yu cu cng ngh gia nhit n 3000C, nng cao n k cht lng sn phm... c s dng rng ri cho mc ch sy nng sn, rau qu, si m gia sc, gia cm. Bn cht tia hng ngoi l dao ng sng in t c bc sng =0,76 420 m (chia lm ba di vi ph bc sng tng ng: di ngn tb ngn

= 0,76 2,5 m, di trung bnh

= 2,5 25 m v di di

di

> 25 m).

Bc x nhit l tnh cht chuyn i nhit nng thnh dao ng sng in t, truyn t ngun pht vo mi trng xung quanh v cc vt th... Cc vt th tip nhn ngun nng lng di dng tia bc x sng in t, kch hot cc chuyn ng nguyn t, phn t bn trong - lm tng nhit ca vt. Nhit lng truyn dn theo nh lut Stephan-Bonsman sang vt cn t nng, t l vi cn bc bn nhit ngun pht bc x hng ngoi. Hiu sut truyn nhit ca bc x hng ngoi t ngun pht nhit trn 400 - 5000C, ln hn so vi truyn nhit i lu bng khng kh... (Hnh 3.19).RT

K K K

Hnh 3.19 - Phn b ph bc x hng ngoi ca vt en tuyt i

u im ca bc x hng ngoi trc tc nhn khng kh l:-

Hiu sut ny cn cao hn 4 -5 ln khi nhit pht x hng ngoi nhit 25000K, v cn tng hn na khi nhit bc x tng n khong trn 35000K; Lung bc x nhit d dng tp trung v mt pha nh c cu gng, tng hiu sut t nng; Bc x nhit hng ngoi cho php thanh kh trng sn phm nng nghip bng cch tc ng nhit c la chn, ln i tng t nng: tng dn t ht thc kh my, n ht thc lp lng m cao hn v mnh nht - ln c th su mt (c th cha nhiu nc) da trn tnh cht hp th bc x hng ngoi ca nc v hi nc.135

-

Bc x hng ngoi c kh nng xuyn su vo lp vt liu (vt cn t nng).

3.3.2 Tnh chn phn t pht bc x hng ngoi sy nng sn Trong trng hp chung, s dng cm nng chuyn ngnh, da vo cc nh mc ch tiu k thut cc ngun (n chiu x), cng sut v ph tn x, chi ph nng lng in (Hnh 3.40).W/cm2

h=80cm cm

Hnh 3.40 - Hnh dng v c tnh chiu x ca n hng ngoi C-250W

V c bn, bng n pht tia hng ngoi c cu trc tng t bng n si t, lm vic nhit khong 15000C (n si t lm vic 2800 35000K). Khi cn ngun pht x hng ngoi ln trn 250 500W thng s dng n hng ngoi c bit lm vic trong mi trng kh Iod. Trong mt s trng hp, c th s dng n si t thay th n hng ngoi, tuy nhin hiu sut bc x b gim st. V tia hng ngoi ch chim 60 - 80% pht x nh sng chung ca n. Nhit lng Q cn thit lm nng v sy sn phm (lm bc hi nc) xc nh theo cng thc: Q = Q + Q Trong : (3-42) Q - nhit lng cn thit lm nng G kg vt liu t nhit t1 n t2, J; Q - nhit lng cn thit sy G kg vt liu t m W1% n W2%, J. Nhit lng tnh ton (chn h s d tr k = 1,4). Qtt = 1,4Q Nu Qtt c n v o l J/h, xc nh cng sut theo cng thc:P= Q tt 3,6.10 6

(3-43)

(3-44)

Trong :

P - cng sut, kW;P= Q tt 860

Nu n v o ca Q l kcal:

(3-45)

136

Nu s dng ngun pht bc x hng ngoi l vt t nng (l so, thanh hay tm), lng nng lng pht ra trn 1m2 nhit T0K theo nh lut Stephan-Bonsman i vi vt en tuyt i. R = T4 Trong : = 5,67.10-8W/m2K44

(3-46)

Trong thc t i vi vt en khng tuyt i s dng cng thc gn ng: T R ' = A.C S 100

(3-47)

Trong :

CS = 5,67W/m2K4 - hng s; A - kh nng hp th nhit ca ngun pht. i vi vt en khng tuyt i A < 1. i vi vt liu dy in tr pht nhit l xo nhn A 0,9.

3.3.3 Tnh chn phn t pht bc x tia hng ngoi si m gia sc Ln con n 15 ngy tui s pht trin thun li nu duy tr nhit trong chung nui 25 - 270C. nhit di 210C ln con s b nhim lnh nu mt mnh. Di 150C, ln con kh gi cn bng thn nhit. Duy tr nhit nn chung ln 200C trong ma lnh bng cc phng php gia nhit khc l vic lm kh v tn km v hiu sut nhit thp. S dng phng php chiu x hng ngoi l ph hp nht. Mt chiu x hng ngoi c xc nh thng qua cng sut tnh ton nhit lng bc x hng ngoi b nhit lng cn bng nhit cho mt n ln con 2 tun tui v din tch sn 400cm2/con:P* = 4,6 W = 0,011W/cm 2 400cm 2

(3-48)

Nu s dng n pht x hng ngoi 3C-250 (Hnh 3.41) ng vi cng chiu sng 0,0011W/cm2, n cheo cao 1,6m trn sn.

a)

b)

Hnh 3.41 - B tr n hng ngoi si m cho ln a) dng treo; b) gn c nh

137

Kt cu ca mng n si cho ln phi c thit k sao cho ph hp vi cc ng dng c th. Cn ngun pht nhit bc x hng ngoi c th chn bng n hng ngoi, thanh hay tm pht x (da vo cc thng s v c tnh k thut do nh ch to cung cp). m bo an ton ngun chiu x hng ngoi phi treo cao t nht 1m trn nn sn chung ln v xa vt liu d chy. 3.3.4 Tnh chn phn t pht bc x tia hng ngoi si m gia cm i vi g con nui th t do trn sn: Chn chiu cao thch hp theo biu Hnh 3.42 v Bng 3.12 di yW/m2

ngyHnh 3.42 - Biu nh mc cng sut chiu x g con, ph thuc ngy tui v theo nhit mi trng Bng 3.12 - Chiu cao v mc chiu x si gia cm di 1 tun tui

Loi n pht x hng ngoi Nhit Kiu 3C-1, 3C-3 Kiu UK3 khu vc Din tch Din tch cao trn cao trn chiu x chiu x, chiu x, sn, m sn, m m2 m2 16 37 - 25 0,9 0,37 18 37 - 26 0,95 0,46 0,6 0,23 20 36 - 25 1,0 0,52 0,65 0,3 22 37 - 26 1,1 0,68 0,7 0,39 24 37 - 26 1,15 0,78 0,8 0,51 Ch thch: Sau mi tun l, cao treo n hng ngoi c nng ln thm 0,1m. Nhit khng kh trong nh nui Chp n treo c hnh chp ct, ng knh phn di 1,6m; trong gn 4-5 bng n hng ngoi. Bng n cn c b tr sao cho thot nhit tt tng tui th ca ui n.

3.4 Dy chuyn ch bin htKhi thu hoch bng my lin hp lng tp cht trong ht c th ln n 15-18% v m ca ht trong iu kin thu hoch khng thun li: trong khong 28-30%. Thng thng iu kin bo qun tt, m ht khng c cho php vt qu 13 16%. 138

tch tp cht, ht lp lng cha m cao, cn thit phi tin hnh lm sch, phn loi ht cc cng on: trc, trong hoc sau khi sy... cc c s sn xut nh, cha c dy chuyn gia cng ch bin ht nng sn hon chnh thng c trang b n l cc loi my lm sch phn loi dng sng kt hp kh ng, bn phn loi theo khi lng gia cng ht ging. Ngoi ra cn trang b my sy, bng ti, gu ti vn chuyn ht... Khi c trang b dy chuyn ch bin hon chnh, c kh nng t ng ho cao, gim ng k chi ph ch bin ht. S cng ngh sy, lm sch phn loi ht gm cc khu chnh sau: vn chuyn ht t my gt lin hp a v trm tri, cn , bc d t t vo thng cha, lm sch v phn loi, sy lm kh ht n m bo qun an ton, vn chuyn trung gian gia cc my (cng on gia cng), vn chuyn ph ph phm, cn v a ht c gia cng vo kho, thang my vn chuyn hay t... Ph thuc vo m ht, qui trnh cng ngh gia cng c th xy dng theo s sau: 1) Khi m ht thp hn v n 16% : lm sch s b - lm sch tinh; 2) Khi m t 17 n 21%: lm sch s b - sy - lm sch tinh; 3) Khi m trn 21%: lm sch s b - sy hai giai on - lm sch tinh. Hnh 3.43 gii thiu s truyn ng in cc ng c in a), s cng ngh b) v s mch iu khin c) ca dy chuyn gia cng ht ca Nga (v d: t hp my 3AB20) gm : t ben Gaz-2, hai my lm sch phn loi 3BC-10b, hai trng phn loi, thp cha, h thng ng ng dn kh v t iu khin ng c in. Khi lm vic vi my t hp my sy trong dy chuyn cn c trang b my lm sch s b OBB-20. T hp my c th lm vic theo su s cng ngh Hnh 3.43b S iu khin hnh 3.43c lm vic theo nguyn tc sau: a) Cung cp in cho cc ng c in lm vic, theo trnh t "ngc" so vi dng chy ca quy trnh cng ngh. Ngc li, khi dng my - theo chiu ngc li. b) Khi ngt s c mt my no , th ton b my trong dy chuyn u t ng ngt. c) C kh nng iu khin tng my ring bit, khi tin hnh sa cha v iu chnh. Sau y, minh ho trnh t khi ng cc my gia cng ht trong dy chuyn lm vic theo s cng ngh I (trong s ny, tt c cc my u lm vic, ngoi tr my lm sch 8 v thp gu ti 9): Trnh t vn hnh dy my c thc hin nh sau: n nt KC, pht tn hiu ci thng bo "dy chuyn thit b chun b hot ng". Tip theo, t chuyn mch ch lm vic PP vo v tr cc tip im PP2 v PP3 ng mch cun dy khi ng t 3K-6K , mch 7K h, chuyn mch PP1 t v tr trung gian. n nt khi ng 1KP v 2KP, ng 1K v 2K khi ng thp gu ti "ht sch" v "ph phm", ng thi ng139

tip im kch hot mch rle trung gian RP-2 v RP-2, cp in cho khi ng t 3K v 4K iu khin trng phn loi lm vic. B tip im ca 3K v 4K ng mch chun b cho khi ng t 5K v 6K sn sng hot ng, sau khi n nt 5KP v 6KP a ng c my lm sch vo hot ng, tip im ca khi ng t 5K v 6K ni mch chun b sn sng cho khi ng t 7K lm vic: ch ch n nt 7KP l ng ng c in cho gu ti ca vo lm vic. n dy qu trnh khi ng dy chuyn hon tt. Khi ngt s c mt my no , tt c cc my khc cung cp vt liu pha trc t ng ngt. Nhng my nm pha sau trong dy chuyn vn tip tc hot ng. V d, khi s c my lm sch 6 khi ng t 6K m tip im trong mch ng c ca my c s c v ng thi ngt tip im mch cun dy khi ng t 7K, dng thp gu ti ca my lm sch. Trng phn loi v thp gu ti ng ph phm v ht sch tip tc lm vic cho n lc ngi vn hnh ch nh tt chng.

a) Thp Thp Trng Trng My gu gu phn phn lm ti ti loi loi sch ht ph bn bn bn sch phm tri phi tri My OBB- Thp Thp lm 20 gu gu ti sch lm ti ht bn ht nguyn sch phi s b lm liu sch

140

b)Hnh 3.43 - S mch chnh ng cc ng c in (a), s cng ngh lm sch ht (b) v s mch iu khin (c) t hp my lm sch 3AB-20

Khi iu chnh v sa cha, chuyn mch PP-1 chuyn sang v tr ng mch cun dy rle PP-4 lm ngt tip im mch ngun nui khi ng t 3K -7K, tip im ca 3K7K ngt ngun nui cun dy rle PP-2 lm h mch khi ng t 3K-6K. v tr ny iu khin c lp tng my.

3.5 Cc phng php mi s dng in nng trong nng nghip3.5.1 Khi qut chung Vo nhng nm gn y, song song vi cc lnh vc cng ngh truyn thng s dng in nng trong sn xut hnh thnh mt hng mi, mang tn "cng ngh in t ion" da trn c s ng dng cc lc tc ng tng h ca in trng v in tch iu khin chuyn ng cc phn t ht ca cht rn v cht lng mt cch c trt t. im ni bt ca cng ngh in t - ion l cc qu trnh ni trn xy ra trong khng gian ca cc thit b cng nghip, trong mi trng kh quyn ti ni sn xut, ch khng phi trong mi trng chn khng ca ng phng n in t. Trong thit b cng ngh in t - ion, ng dng cc tnh cht ca trng in t, c bit l trng phng in coron v trng tnh in. Trng in t l dng vt cht c bit, mang nng lng, c trng v tun th cc tnh cht ca t trng v in trng. Trng tnh in l mt dng c bit ca trng in t, to bi nhng in tch tnh ti (so vi ngi quan st) phn b trong khng gian v khng thay i theo thi gian. Phng in coron xut hin trong in trng mt chiu hoc in trng xoay chiu khng ng nht. Khi tng in p gia cc in cc n mt gi tr xc nh ln, bt u qu trnh ion ho mnh, nh thng khng kh gia cc in cc. Gi tr in p ny ph thuc vo cu trc v hnh dng ca in cc, mt v nhit ca cht kh. Phng in bt u nh thng khng kh gia cc in cc gi l phng in coron, cn hiu141

ng ca n gi l hiu ng coron. Khi phng in nh thng ton phn khng kh gia cc in cc gi l phng in tia la. Cng ngh in t - ion tuy mi ra i nhng c ng dng rt rng ri trong cc lnh vc sn xut cng nng nghip: t tuyn qung, lc bi n phn loi lm sch ht nng sn, kch thch ht ging ny mn, cy trng pht trin, bo qun ht ging, tr dit c di, kh trng, x l nc thi... Nm 1930 phn loi bng in c ng dng thnh cng trong cng nghip thc phm lm sch v phn loi sn phm ht nh c ph, ht ci... Nm 1947 Canada, n , ng c c v nhiu nc khc nh Megleria cng ngh in t - ion c ng dng thnh cng trong phn loi lm sch qung cng nghip cng sut t 6 triu tn/nm v ch bin ht nng sn. T nhng nm 1954 Lin X c my phn loi coron tnh in, in mi c nghin cu s dng i tr trong cc ngnh tuyn m sa khong v lm sch, phn loi ht ng cc, ht rau qu trong nng nghip. nc ta, Vin C in Nng nghip thit k ch to my phn loi ht bng in trng u tin dng phn loi ht thc ging (nm 1981 - 1984). Giai on 1991 1995, Vin C in Nng nghip ch tr ti nghin cu khoa hc Cng ngh cp nh nc m s KC-04-14, thit k ch to my phn loi bng in trng. Kt qu nghin cu cho thy, phn loi ht bng in trn my PL-1D do Vin ch to c th lm sch ht n >99%, chn ra nhng ht ging thc v ht rau qu c cht lng nng sinh cao... ng dng in trng c cng cao lm sch, phn loi vt liu ri c nghin cu pht trin theo ba hng: -

Trng tnh in; Trng phng in corona; T hp cc trng v cc tc ng khc.

3.5.2 Thit b v cng ngh lm sch v phn loi ht nng sn S dng my phn loi bng in trng trn c s tnh cht in ca ht c nhng u vit ng k so vi c kh, cho php tng nng sut v gim chi ph sn xut ht ng cc c yu cu cao v cht lng v sch ht ging:-

Lm sch, tch c ht c di m my c kh khng th hoc rt kh thc hin; Chn nhng ht ging c cht lng gieo trng tt nht (da trn c s cht lng gieo trng lin quan mt thit voi c tnh in ca ht);

142

-

X l ht bng in trng lm tng (kch thch) cht lng gieo trng ca ht ging.

3.5.2.1 Phn loi ht bng trng phng in coron Nguyn l lm vic ca my lm sch ht bng trng phng in coron th hin Hnh 3.44.3 _ _

3 Fc 2 1Flt Fe P

+

P

F

2

1

4 I II III I II III

4

a)

b)

Hnh 3.44 - S nguyn l my phn loi ht bng trng phng in coron a) in cc phng; b) in cc trng quay; 1,2 - H in cc; 3 - mng phn phi; 4 - mng hng;

Da vo cc thng s trng thi ca ht trong in trng nh: thm in mi, dn in, kh nng phn cc, kh nng np/phng in tch ca ht. Cng in trng gia cc in cc, chn khong khong 2 4kV/cm. a) Phn loi ht kiu coron in cc phng Ht t phu cha 1, c a vo gia in cc coron v cc lng, b tr song song vi nhau, ni vi cc cc dng v m ca ngun cao p nh c cu phn phi 2 (Hnh 3.1a). Cu to ca in cc coron gm nhng dy dn c ng knh 0,3mm, mc song song v cch nhau khong 100mm. Khi in p gia cc in cc cao, xung quanh dy dn mnh xut hin hin tng phng in coron, ion ho cc phn t ca khng kh (giai on u phng in ca in cc) to thnh nhng ht mang in: in t v ion gia cc in cc coron. Di tc dng ca in trng, cc in t v ion chuyn ng v pha in cc lng (ni t) v tch in cho ht t phu ri xung. in tch m ht nhn c khi trc di ca ht nm dc theo ng sc in trng, c xc nh theo cng thc:Q= 0 .E.d 2 4K

(3-49)

trong :

Q - in tch ca ht, C;143

E - cng in trung, V/m; K - h s hnh dng ph thuc vo t s gia chiu ngang trn chiu thm in mi ca ht; d - ng knh ht, m. Nh vy trong khong cch gia cc in cc chu tc dng ca hai lc thnh phn: Lc trng trng F1 v lc in trng FE, biu th bng Niuton (N) tnh theoF1 = mg

di ht v

(3-50) m - khi lng ht, kg; G - gia tc trng trng, m/s2.

trong :

v

FE = Q.E

(3-51)

Phng trnh chuyn ng ca ht trong in trng:F = F1 + FE = mg + Q.E

(3-52)

T (3-52) cho thy ht c in tch cng ln th lc in trng cng ln. Mt khc, in tch cn ph thuc vo h s hnh dng. Trong trng hp ny, phn loi ht trong da trn c s du hiu hnh dng, thm in mi v khi lng ca ht. Cc ht c v tnh cht c l v tnh cht in khc nhau s ri vo cc khc nhau ca mng hng... b) Phn loi ht kiu coron trng quay Ht t phu c a vo in trng gia in cc coron v trng quay, ni vi in cc ni t. Sau khi nhn c in tch t in cc coron quay trn, ht b ht dnh vo trng do tc ng ca lc in trng (Hnh 3.1b). in tch ca ht c xc nh theo biu thc:Q= 0 E.a.d 4K

(3-53)

trong :

a, d - chiu di v ng knh ht, m.

Khi ht b mt in tch (phng in bi dn in), ra khi vng in trng tu thuc lc qun tnh, sm hay mun s ri khi trng ri vo cc mng hng. Qu trnh phn loi trong thit b coron trng quay (Hnh 3.1b), ht nm trn trng in cc ni t, chu tc ng ca lc ly tm Plt, tng hp cc lc in trng F, lc cm ng Fax, lc ly tm v lc trng trng (biu th bng N)Plt = F + Fax + PT

(3-54)

144

trong :

F =E.Q ,

lc ny p ht vo mt trng, N;

Fax =

Q2 2

, lc ny ko ht p vo mt trng, N; (vi - bn knh ca ht, m);

v kch thc ca ht rt nh so vi bn knh ca trng quay, lc ly tm c tnhPlt = 2mv 2 D

(3-55)

trong :

m - khi lng ca ht, kg; v - vn tc tip tuyn ca trng in cc, m/s; D - ng knh trng, m.

PT - trng lc, gm hai thnh phn ph thuc vo gc tc ng so vi phng thng ng khi ht nm trn trngPT = P cos

(3-56)

Thay (3.7), (3.8), (3.9) v (3.10) vo (3.6) ta c phng trnhPlt = QE + Q2 + mg cos

(3-57)

Khi in p t vo h in cc v s vng quay khng thay i, gc ri ca ht ph thuc vo hnh dng v hng s in mi ca ht. Do tnh cht c l v tnh cht in ca cc ht khc nhau, trong in trng chng ri cc gc khc nhau vo cc mng hng. 3.5.2.2 Phn loi ht bng trng tnh in1 2 2 1

3 3

a)

b)

Hnh 3.45 - S nguyn l ca my phn loi ht bng tnh in a) mt trng; b) hai trng 1 - Phu cp liu; 2 - Trng phn ly; 3- Mng hng; 4 - Trng in cc

145

Phn loi ht s dng trng tnh in c ng dng rng ri vo thc tin sn xut t nhng nm 1930 trong cc lnh vc tuyn qung, lc bi v lm sch phn loi ht c ph, ht ci trong ngnh cng nghip thc phm... Nguyn l lm vic my phn loi lm sch bng trng tnh in cho s Hnh 3.45. Qu trnh phn loi trong my bng trng tnh in da vo tc ng tng h gia in trng cao p v ht mang in. Du hiu phn loi ht trong in trng da trn s khc bit v tnh cht c l (trng lng, hnh dng, kch thc...) v tnh cht in ( dn, thm in mi...), dn n lc in trng tc ng ln ht khng ging nhau do cc ht nhn c in tch khc nhau. a) My phn loi ht dng mt trng v hai trng My phn loi tnh in n gin nht ch c mt trng quay (Hnh 3.45a). Ht t phu 1 c a vo trng c tch in s nhn c in tch cng du vi trng. Nhng ht c dn ln (m hn) tch in rt nhanh v b y ri ra xa khi mt trng, cn nhng ht c dn in thp (kh hn) - ri gn hn hoc thm ch b ht dnh vo trng (lc tng h gia cc in tch). My phn loi dng ny c s dng vi nguyn vt liu, ht kch thc nh. Thng thng s dng my phn loi tnh in trng quay hai in cc tri du lm sch, phn loi nhng ht c kch thc ln hn (Hnh 3.45c). Nguyn l lm vic cng tng t loi mt trng, nhng y cng in trng mnh hn v c th iu chnh c. Qu o chuyn ng ca ht ph thuc vo dn v cng in trng tnh in gia cc in cc. in tch ht nhn c khi trc di ca ht nm dc theo in trng c xc nh bi biu thc:Q= 0 hE b2 1 + ( h 1) (K ) 4

(3-58)

trong :

h

- thm in mi ca ht, F/m ;

b - di trc ngn ca ht, m; (K) - h s gim phn cc ca ht. in tch ca ht khi trc ngn ca ht nm dc theo ng sc in trngQ= 0 hE a2 . 1 + ( h 1) (K ) 4

(3-59)

Ht nm trn trng phn ly chu tc dng ca trng lc P, lc ly tm Flt(N), lc in trng Ft (N), lc nh x gng Fax (N) c m t bng biu thc Fms = (P1 Flt Fdt Fax )f (3-60)

146

trong :

P1 - trng lc theo phng php tuyn, N:

P1 = mg cos

(3-61) (3-62)

P2 - trng lc theo phng tip tuyn, N: P2 = mg sin vi - Gc gia lc php tuyn thnh phn v lc tng hp, ; m - khi lng ca ht, kg; g - gia tc trng trng, m/s2.

Flt - do kch thc ht nh so vi bn knh ca trng nn lc ly tm c xc nh theo cng thc, NFlt = 2mv 2 D

(3-63)

trong :

v - vn tc chuyn ng ca ht, m/s; D - ng knh ca trng, m. Fdt - lc in trng do khi tip xc vi trng in cc, ht tch in vi i lng Q:

Fdt = E ( ) Q

(3-64)

trong :

E( ) - cng in trng ph thuc vo v tr ca ht trn trng (l hm s ca gc ), V/m; Fax - Lc nh x gng, N:

Fax =

Q2 Q2 Q2 = 2 d2 0 (d 0 + 2l) 2 0 9 0 0

(3-65)

trong :

d - khong cch gia hai tm in ca ht, m; d0 - khong cch gia hai tm hnh hc ca ht, m; f - h s ma st (f = tg = const); 0 - bn knh ca ht, m; d0 = 2 0.

Lc in trng ph thuc vo in tch ca ht v cng in trng v khi lng cu ht. Nhng ht in tch khi lng khc nhau s ri cc mng khc nhau.

147

b) My phn loi dng sng Ht a vo phn loi, chuyn ng theo chiu rung lc ca sng i qua in trng c cng cao. Sng c gn vi cc dng, cn tm kim loi pha trn v di sng gn vi cc m ca ngun in cao p, sao cho ng sc ca in trng vung gc vi sng. Di tc dng ca in trng, nhng ht di b phn cc v nh hng trc di ca n theo chiu ca ng sc. Mmen quay M (Nm), tc dng ln ht c xc nh theo biu thc0 E 2 .0,42 M= Vh 2 8

(3-66)

trong :

Vh - th tch ca ht, m3; 2 - h s c trng cho s bin thin ca in trng ph thuc vo hnh dng v thm in mi ca ht; 0

- thm in mi ca khng kh, F/m;

E - cng in trng, V/m; - gc nghing trc di ca ht (elip quay) so vi mt phng in cc. Khi t l gia chiu ngang trn chiu di ca ht cng nh, mmen quay tc dng ln ht cng phi ln c th dng ng ht ln. Nhng ht c trc di, nu c nh hng vung gc vi mt sng s d lt qua l sng. V vy, s dng in trng nng ht ng ln trong qu trnh sng lc, cho php nng cao cng sut v cht lng lm sch phn loi ca my. 3.5.2.3 Phn loi ht kiu in mi Trong cng ngh phn loi ht s dng trng tnh in, phn loi kiu in mi c pht trin thnh nhnh ring v ng dng rt rng ri trong thc tin tuyn qung, tch lm sch phn loi ht nng sn. Phng php phn loi kiu in mi da vo s khc nhau v ln v phng ca lc in tc dng ln ht b phn cc trong in trng khng ng nht c to bi h in cc dy qun cch ly song song vi cu hnh khc nhau. Hnh 3.46 my phn loi ht kiu in mi trng quay. Ht t phu 1 c a vo b mt trng 2 vi h dy qun cch ly song song 3 ni vi cc in cc tri du to thnh in trng khng ng nht. Khi trng quay di tc dng ca lc in trng ht b ko vo dy qun 3. Do trng lc v lc ly tm ht bt khi trng v ri cc mng hng khc nhau. Nhng ht nng to v va ri vo ngn II v nhng ht km nht, nh vo ngn III.148

3 2 1

F lt P Fe

4 I II III

Hnh 3.46 - My phn loi ht kiu in mi

Lc in trng tc dng ln ht c xc nh theo biu thc:2U 2 d 0 ( h 1) Sab cos (2a h + l d ) 2 2

Fdt =

(3-67)

trong :

d,

h

- thm in mi ca lp cch in dy qun v ca ht, F/m;

U - in p t vo h dy qun, V; a - b dy ca lp cch in dy qun, m; l - di trung bnh ca ng sc qua ht, m; - gc gia hai lc tri du ca dy qun n tm ca ht, ; Sab - din tch tip xc hu ch gia ht v lp cch in ca dy qun, m2. 3.5.2.4 Phn loi ht ging bng t trng Nguyn l hot ng ca thit b ny da vo tnh cht bm dnh bt t vo b mt nhm ca ht ging c khi qua nam chm s b ht bng t trng. B phn chnh ca my l trng nam chm in. My phn loi ht bng t trng lm vic nh sau: hn hp ht x l qua bt t c a vo b mt trng (ch to bng vt liu phi t tnh). t cc cc nam chm in mnh vo bn trong trng, sao cho chon na ng trn t trn xung di (Hnh 3.47). Nhng ht bm dnh bt t c ht gi li trn mt trng s ri xung v pha di trng, cn ht trn (khng bm bt t) ri ngay v mt pha - bn trn.

149

Hnh 3.47 - S nguyn l thit b phn loi ht bng trng in t 1 - v; 2,4 - khung t; 3 - cun dy; 5 - khe h khng kh; 6 - ; 7 - trc quay; 8 - vng m cao su;

Lc gi ht trn trng F phi ln hn tng i s lc ly tm Flt (N), tc dng ln ht v hnh chiu lc trng trng P ca ht c xc nh bng biu thcF Flt + PHC

(3-68)

trong :F =

F - lc gi ht bm bt t c xc nh theo cng thc, NB.m l2

(3-69)

trong :

- h s thm bt t; B - cm ng t ph thuc s ampe-vng ca cun kch thch, T; mbt - khi lng ca bt t, kg; Flt - lc ly tm, N;

PHC = m.g. cos Flt = m 2 R

(3-70) (3-71)

trong :

m - khi lng cc ht b t ht, kg; - vn tc gc ca trng, rad/s; R - bn knh trng, m; g - gia tc trng trng, m/s2; - gc gia hng lc ly tm v trc thng ng, .

Khi :

F m R +m.g. c s o

(3-72)

150

T (3-68) v (3-69) cho thy, gi c ht trn trng, cm ng t phi tho mn iu kin:B g cos + 2 R 2 l p

(3-73)

trong :

p=

m bt m

gi c ht di trng:B g + 2 R 2 l p

(3-74)

gim chi ph nng lng in cho vic to t trng trng phi quay vi vn tc nh, gim thiu khong cch gia thnh trong ca trng v nam chm in. Nng sut my c xc nh theo cng thc:Q =3,6 .h.v.m .b

(3-75)

trong :

- t trng ca ht, kg/m3; b - b rng c ch lm vic ca trng, m; h - dy lp ht ( dy lp ht khng vt qu hai ln b dy ca ht), m; v - vn tc tip tuyn ca trng, m/s.

Ngoi ra, vi kt cu thch hp, t trng nam chm cn loi c vt kim loi, inh, on dy st c chiu di khong 100mm... 3.5.3 Phng php x l ht ging cy trng bng in t trng Nng sut ma mng cy trng, cy lng thc tim n ngay trong giai on u sinh trng pht trin ca cy non bao gm cc qu trnh thc mm, xung ging, hnh thnh h r... Giai on khi u pht trin tt, to tin thc y qa trnh trao i cht, m hoa kt tri... tng nng sut v cht lng cy trng. T lu, x l ht ging trc khi gieo c bit v ng dng rng ri trn th gii nh bin php u tin tng nng sut v n nh ma mng cy trng. Ty thuc phong tc tp qun canh tc v trnh pht trin khoa hc k thut ngi ta p dng nhng bin php khc nhau nh phi nng, ngm nc nng hai si ba lnh, x l bng ho cht, cc tia vt l, phng x... S dng nhiu ho cht dn n mt cn bng sinh thi, gim lng vi khun c li, gy c hi cho ng vt v con ngi. Hin nay, cc phng php x l ht ging trc khi

151

gieo thng dng sng in t c vch ph khc nhau: ion ho, tia cc tm, tia phng x, tia nng tp trung, in cao th, cao tn (Bng 3.13).Bng 3.13 - c tnh c bn ca mt s tc ng vt lS TT i lng Tn s, Hz Min thng s Cng chiu x, W/m2 in T trng, trng, kV/cm A/m 2-5 2-3 1-2 600 - 900 (1,2 - 3,0)x103 (11 - 73)x103 1,5 1,6 - 3 30 - 160 Thi gian chiu x, s 0,2 - 3 3-4 10 - 35 300 - 900 360 - 600 60 30 - 160 0,6 - 1 Nng lng ht hp th, J/m3 10 - 103 3x10 - 6x103 9x106 - 5x108 6x106 - 4x109 7x104 - 9x105 4x103 - 4x104 105 - 3x106 -

1 2 3 4 5 6 7 8

in mt chiu in xoay chiu T trng m tn Tia hng ngoi Tia nng tp trung Tia laser Tia cc tm Hydro - Plasma

0 50 12 - 103 (1,2 - 4,05)x1014 (1,3 - 10)x1014 (3 - 9)x1014 (0,75 - 10)x1020 (0,75 - 10)x1015 -

Hiu qu tc ng ph thuc vo liu lng v ch x l u nhm kch thch qu trnh chuyn i ho sinh bn trong mm ht v qu trnh sinh trng pht trin, hnh thnh hoa tri, tng nng sut cy trng. Mi i lng vt l c trng bi s tc ng qua li ca mt s cc ch s lin quan. Ch cn thay i t l thnh phn cu thnh nh tn s, cng , thi gian tc ng... t c hiu qu tc ng ln nht. Ht ging c xem l ht in mi c m hnh cu trc cho trong Hnh 3.48

Hnh 3.48 - Mt ct a) v phn b in trng bn trong v ngoi ht la b) 1 - v tru; 2 - v cm ; 3 - nhn go; 4 - phi mm;

X l ht ging bng in trng cao p c nhiu u im nh khng gy t bin gen di truyn, tng kh nng trao i cht v chng chu su bnh, ngoi cnh, tng nng sut cy trng v khng gy nhim mi trng. T nhng nm 1940 - 1950, tc ng trc tip ca in t trng ln i tng vt nui cy trng, bo qun nng sn quan tm nghin cu ng dng. Nhng nm 1960 Lin X, M, Nht Bn... t c nhng thnh tu to ln trong vic x l kch thch ht152

ging bng in trng, tng sn lng cy trng 10 - 15% ht v 20% khi xanh. Cn tc ng mt cng in trng thch hp i vi m ca c cht ht, cng nh duy tr thi gian sau x l i vi cc loi ging ht khc nhau t kt qu tt. nc ta, nm 1981 - 1985, Vin C in nng nghip tin hnh nghin cu ng dng kch thch ht ging bng in trng cao p, kt qu thu c mt s c s sn xut cho thy khi xanh tng n 20% v nng sut la tng 5 - 7%. 3.5.3.1 X l ht ging trc khi gieo bng trng coron Ht la m ging trc khi gieo em x l vi thi gian l chiu 1s trong trng phng in coron vi cng 2 - 3kV/cm, lm tng kh nng sng v chng chu tt cc bin ng xu ca iu kin ngoi cnh, tng nng sut ma mng 10 - 15%. Hiu qu tc dng ca in trng dng in mt chiu in p cao ph thuc vo cng trng v i lng in tch m ht nhn c. Ht mang in tch m c hiu ng tt hn ht mang in tch dng, cha hm lng m cao hn. 3.5.3.2 X l ht ging trc khi gieo bng trng tnh in X l ht c tin hnh bng dng in xoay chiu trong bung gm hai bn cc phng ni vi bin th cao p (Hnh 3.49).

1

2

KV

3

Hnh 3.49 - S nguyn l thit b x l ht ging trc khi gieo bng in trng 1, 2 - ngun in cao p; 3 - h in cc

Ng ging, sau khi x l trong in trng c cng 2kV/cm, thi gian x l 10s, nng lng sinh trng tng 23%, trng lng khi cy xanh tng 20 -27% v nng sut tng 40% so vi i chng. Tng t, hiu ng tt cng t c i vi x l ht ging la m, la nc v nhng ging khc 3.5.4 ng dng ozon x l bo qun lng thc, thc phm v ht ging 3.5.4.1 Khi qut chung Ozon l cht kh c cng thc ho hc O3 gm ba nguyn t oxy. Ln u tin nm 1785 c nh vt l H Lan Marum pht hin khi nghin cu s phng in trong khng kh. Ozon c v tanh v l cht oxy ho mnh, d dng thit lp lin kt vi cc cht hu c. Do vy c kh nng kh trng, kh mi rt tt. Nm 1874 gio s A. P. Dobroslavin xut s dng ozon kh trng nc v khng kh. Mi hai nm sau N. Keldus chng minh s dng thnh cng ozon trong thc tin. n nm 1911, ln u tin chu

153

u trm cp nc dn dng x l bng ozon c a vo s dng ti thnh ph Saint Perterburg. Ozon nhit v p sut tiu chun l mt cht kh mu tm nht, tnh cht l ho ca n c c trng bi cc s liu sau: Khi lng phn t, g: Khi lng ring ( nhit 00C v p sut 0,1MPa), g/l: Nhit ng c, 0C: Nhit nng chy, 0C: Nhit lng ring (kh nng to nhit), kJ/mol: ho tan trong nc nhit 00C: nhit 200C: in th oxy ho-kh, V: Bc sng hp th ti a tia cc tm, m: 48 2,154 111,9 192,5 192,5 0,49 0,29 2,07 2,537.10-7

Phm vi v lnh vc ng dng ca ozon ngy cng m rng. Mc d c nhiu nghin cu ng dng v kt qu cng b v s dng ozon trong cc ngnh kinh t quc dn: lm sch nc n, nc thi, bo qun rau qu, c tht, kh mi, kh trng lm sch khng kh mi trng v lm kh bo qun nng sn, ht ging... c ch tc ng sinh l hc ca ozon ln c th sng ng thc vt vn cn ang c tip tc nghin cu. Ozon khng nhng c ng dng trong cc ngnh cng nghip thc phm, y t... m ngy cng c quan tm nghin cu ng dng trong sn xut nng nghip v x l nc thi, bo v mi sinh. Nm 1997 U ban qun l thuc v thc phm M (FDA) tuyn b cp nhn an ton GRAS, cho php s dng ozn lm mi cht trong ch bin, bo qun thc phm... nng 1mg/m3 ( 0,5ppm), ozon c kh nng dit khun. Hiu qu dit khun trong mi trng bi sng cao hn mi trng bi kh. i vi trc khun ng rut ch cn nng 0,2g/m3 l b t lit (mt kh nng phn hu ng, gim tc ng men katalaza). Trong khi vi trng cm b tiu dit nng 0,2mg/m3 cn trng t cu cn 1mg/m3. Nng ozon thp hn 3mg/m3 khng gy tc ng r rt, nhng nng 30mg/m3 tiu hu ngay c cc t bo t nm. Ozon c dng thanh kh trng, kh mi, mu v nc sinh hot, nc thi cng nh nc cng nghip. Ozon c s dng di dng lng v kh trong kho bo qun, bung lnh, ng lnh v lm sch phng lm vic.

154

ng dng ca ozon rt phong ph v a dng, ph hp cho cc quy m cng nghip ln, va, nh v quy m h. Ozon c kh nng oxy ho cc mnh ng sau Flo v 7 ln mnh hn Clo. c bit ozon khng to ra sn phm ph c hi trong qu trnh x l, s dng. Kh nng lm sch v bo qun ca ozon cho trong Bng 3.14Bng 3.14 - Khuyn co nng kh ozon trong lm sch mi trng bo qun

Lnh vc Ca hng Ch bin thc phm Bnh vin Trang tri chn nui Nh

i tng T lm lnh quy hng Nh bp, nh ng gi kho bo qun tm

Mc ch bo qun Tht, rau qu Lm sch mi trng, dng c nh bp v qun o (thanh kh trng, kh mi...) Chng ti vim nhim (thanh kh trng, kh mi...) Chng nhim trng v kh mi

Nng ppm 0,1 - 0,5 0,04 - 0,4 0,1 - 0,5 0,1 - 0,4 0,02 - 0,5

V sinh 0,2 mi trng Nng ozon cn c iu chnh tu theo mc ch v s c mt ca con ngi v vt nui. Nng an ton cho php i vi ngi khng qu 0,1ppm i vi M v Nht Bn, tiu chun Nga - 0,05ppm (Hnh 3.50). , mg/ m3 2.104 2.103 2.102 2.101 2.100 2.10-1 10-1 100 1 101 102 103 t, min 2 4 3 5

Phng khm, phng ch, phng m Nui ln, nui gia cm Phng khch, phng Dit vi sinh c hi, chng nhim ng, nh bp, kho, trng vt nui trong nh, kh mi nh v sinh, ng vt nui trong nh Nh cha rc x l Kh mi

Hnh 3.50 - Vng cho php v mc c hi i vi con ngi

Khi x l bo qun tht nng ozon phi c iu chnh v duy tr thp hn mc cho php gi ti v khng lm gim cht lng. Bng 3.15 khuyn co nng cng ngh cho bo qun mt s thc phm: tht, cc, sa, rau qu...155

Bng 3.15 - Khuyn co nng kh ozn bo qun mt s thc phm rau qu ti

Thc phm Nng ozon, g/1000m3 Tht m, tht c nhiu m, b sa 1,0 - 2 Kho mt bo qun trng nhit thp 1,5 - 3 X l ozon lin tc bo qun hoa qu ti 2,0 - 4 Tht nc 3,0 - 5 kh trng, kh mi trong phng lm vic, phng khch cn c qut i lu hn hp khng kh v ozon nng thp khi c ngi hoc vt nui. tng hiu qu x l kh mi, thanh trng khng kh cn nng ozon cao hn... 3.5.4.2 ng dng ca ozon nc Cc ng dng in hnh ca nc ozon nc cho trong Bng 3.16 cho mc ch thanh trng kh mi v kh mu nc sinh hot v nc thi cng nh trong chn nui gia sc, gia cm, c v ch bin thc phm...Bng 3.16 - Khuyn co nng ozn nc trong x l, bo qun

Lnh vc Cung cp nc Nc thi Nh cng cng Cng nghip thc n ti

i tng Nc sinh hot, nc ung Nc cng thnh ph, bnh vin v nc nhum Thp nc lnh, b bi C v nhuyn th chng ng bng thc phm ng lnh, lm sch rau v nh xng thc phm B c, nc nui ln, gia cm Ht ging, rau qu Thit b y t X l trong nha khoa

Mc ch Thanh trng, kh mi, lm sch bn cha nc, tng v ca nc (dng than hot tnh) Kh mu, mi, thanh trng, x l Thanh trng, kh mi cho nc, ngn nga ru to Thanh trng, nc bao gi, kh mi, gi ti, thit b nh bp, sn nh

Nng , mg/lit 0,4 - 0,5 1,0 - 40 0,1 - 0,5 0,4 - 3,0

Trang tri chn nui Trng trt Y t

Tng lng oxy ho tan, thanh trng, tng v (than hot tnh) Thanh trng, lm sch Thanh trng Chng vim ming

0,4 - 0,5 0,4 - 3,0 0,4 47 - 61

Thi gian bn phn r ca ozon (khong thi gian m nng Ozn gim 50%) trong nc (nh hn so vi trong khng kh): khong 10 pht trong nc trung tnh nhit 156

mi trng bnh thng, v nh hn nhiu mi trng c nhit , pH cao, cng nh ni c nhiu tp cht hu, v c (ch c vi giy). Ngc li mi trng axit v nhit thp thi gian bn phn r di hn, c th lu gi tm thi v vn chuyn. Cc yu t ny lin quan cht ch vi cc tham s cng ngh Ozn. 3.5.4.3 Phng php to kh ozon Ozon c cng thc phn t O3, c to thnh t ba nguyn t oxy. Hin nay ozon c tng hp theo mt s phng php nh: in phn, quang ho, phng php in... Ozon c to ra khi cho dng in mt chiu chy qua cc vai cu c kt cu c bit v cht in phn H2SO4, HClO4 hay NaClO4, KClO4... Cc oxit hay mui ca chng trong phn ng in phn khng gii phng phn t oxy m to kh ozon v cc ion, cc gc (radical) H2O + O2 = O3 +2H+ + 2ein phn cc dung dch axit tuy cho php nhn ozon vi nng 30 - 38% (1% 20mg/m3). Nu in phn cc dung dch mui, nng ion thu c s cn cao hn. Phng php ny phc tp, ch ph hp cho iu kin tnh ti, kh p dng rng ri. 3.5.4.4 Tnh chn nng sut my pht ozon Hiu qu tc ng ca zon ln cc i tng x l trong min cng ngh, c xem nh hng s ozon

ca tch s gia nng =ozon

ozon

v thi gian tc ng

ozon

ozon

.

ozon

(3-76)

Nh vy, nng zon thp cn thit phi tng thi gian tc ng tc ng lu, nhng nu nng thp di ngng xc nh, s khng t c hiu qu cn thit). Khi tnh chn my pht zon phi m bo sao cho mi trng x l, bo qun c c nng cng ngh cn thit. Nng sut zon cho khng gian h, tnh theo cng thc Nozon = Q. trong : Nozon - nng sut my pht zon, g/h; - nng zon cn thit, g/m3 hay mg/l. Nng sut zon cho bung kn, tnh theo cng thc Nozon = 0,7.V. /T trong : (3-78) T - thi gian bn phn r (thng thng trong mi trng sn xut nng nghip T < 0,4I0,2), h. (3-77)

157

CU HI N TP1. c im chnh ca cc phn t pht nhit bng kim loi v phi kim loi. Nu phng php tnh chn si t v qut gi cho my sy nng sn. 2. Nu cc i lng c trng chiu sng c bn v thit b chiu sng v thit b khi ng, iu khin. Trnh by cc phng php thit k chiu sng theo h s s dng, nh mc cng sut, chiu sng im. V v gii thch nguyn l lm vic mt s s chiu sng thng dng. 3. Nu cng dng v c im ca tia bc x hng ngoi. Cc phng php tnh chn phn t pht bc x hng ngoi sy nng sn, si m gia sc v gia cm. 4. Nu c im ca cc phng php mi trong gia cng x l v bo qun ht, nng sn. V s v gii thch nguyn l lm vic ca thit b v cng ngh lm sch v phn loi ht nng sn, x l ht ging cy trng bng in t trng v ng dng ozon x l bo qun lng thc, thc phm v ht ging.

158