H THNG IU HO KHNG KH KIU TQu trnh x l nhit m khng kh bng thit b
trao i nhit kiu b mt c u im l thit b gn nh, n gin vv. . . Tuy nhin
x l nhit m bng thit b trao i nhit kiu b mt, b hn ch bi kh nng x l
khng kh, n khng c kh nng tng dung m khng kh trong phng. Trong nhiu
trng hp i hi tng m cho khng kh, chng hn nh trong cc nh my dt c nhng
giai on cng ngh i hi m kh cao, t c trng thi yu cu, cn tin hnh phun
m b sung, tng i phc tp, tn km v hiu qu khng cao. Trong trng hp ny,
ngi ta thng s dng thit b x l khng kh kiu hn hp hay cn gi l thit b x
l khng kh kiu t. Thit b khng kh kiu t l thit b trao i nhit m kiu hn
hp kh v nc, thng c gi l thit b bung phun. Vic phun m khng thc hin
trc tip trong phng m thit b x l khng kh nn hiu qa v quy m ln hn
nhiu.Trong chng ny, s tin hnh nghin cu cc c s l thuyt v trao i nhit
m gia khng kh v nc; cc nhn t nh hng n qu trnh ; cc thit b bung phun
thng s dng v tnh ton thit k cc thit b .CC QU TRNH X L NHIT M KHNG
KHMt s gi thit khi nghin cu qu trnh trao i nhit m ca khng khQu trnh
thc x l nhit m kh phc tp, tin li cho vic phn tnh v tnh ton, khi
nghin cu qu trnh trao i nhit m ca khng kh v nc, ngi ta gi thit nh
sau:- S tip xc gia nc v khng kh l l tng, thi gian tip xc bng v
cng.- Khng c tn tht nhit v m ra bn ngoi h trong qu trnh trao i nhit
m.- Kch thc ht nc nh nhit ng u trong ton th tch ht.Vi nhng gi thit
nh vy c th suy ra nhit khng kh trong lp bin (lp mng st b mt git nc)
t trng thi bo ho c cng nhit vi nhit git nc, m khng kh u ra thit b t
trng thi bo hi ng vi nhit cc git nc u ra.Ngi ta nhn thy, s thay i
trng thi ca khng kh ph thuc nhiu vo chiu chuyn ng tng i gia nc v
khng kh. Di y chng ta s kho st qu trnh trao i nhit m gia nc v khng
kh trong hai trng hp nu trn.Trng hp nc v khng kh chuyn ng cng
chiuXt trng hp trao i nhit m gia nc c nhit ban u l tn, khng kh c
trng thi A(tA, A) trong thit b trao i nhit m kiu hn hp. u ra thit b
trao i nhit m, khng kh t bo ho t =100%, nc v khng kh c cng nhit
tnk(trng thi AK BK).
Hnh 7.1. Trao i nhit m gia khng kh v nc khi chuyn ng cng chiuTa
nghin cu s thay i trng thi khng kh trong qu trnh trao i nhit m dc
theo chiu di ca thit b. thy r qu trnh thay i trng thi , ta chia
thit b trao i nhit m thnh k on (hnh 7.1).Trong qu trnh trao i nhit
m nhit nc tng t tnn tnk, khng kh thay i trng thi t trng thi ban u
A(tA, A) ti trng thi bo ho Ak(tnk,100%), v nh gi thit trn qu trnh
trao i l l tng v thi gian v cng nn trng thi khng kh khi ra bung
phun c nhit bng nhit nc tnkv t trng thi bo ho vi m = 100%.- Xt qu
trnh trao i nhit m vng 1Khng kh u vo c trng thi l A(tA,A) v nc c
nhit tn. Do qu trnh trao i nhit m vi cc git nc, lp khng kh ti lp
bin tip xc vi cc git nc t trng thi bo ho (=100%) v nhit bng nhit nc
t = tn(trng thi B). Cc phn t khng kh ngoi lp bin coi nh vn gi nguyn
trng thi ban u A(tA,A). Nh vy ra khi vng th nht khng kh c trng thi
A1l hn hp ca 2 khi kh c trng thi A(tA,A) v B(tn,100%). Theo tnh cht
ca qu trnh hn hp, im A1nm trn on AB, ng thi do c trao i nhit nn
nhit ca nc tng ln tn1.- Vng 2Khng kh u vo vng 2 l A1v nc c nhit
tn1. Bng cch phn tch tng t, ta thy trng thi khng kh u ra A2ca vng 2
l hn hp ca 2 khi kh c trng thi A1v B1(tn1,100%). Nh vy im A2nm trn
A1B1v nhit nc tng ln tn2.C phn tch tng t nh vy ta thy, trng thy
khng kh u ra thit b s c trng thi bo ho, c nhit bng nhit nc tnk(trng
thi AkBk)Ni tt c cc im A, A1, . . . Akta c ng cong biu th s thay i
trng thi ca khng kh trong qu trnh trao i nhit m vi nc. Cc im B, B1,
. . .Bntng ng l cc trng thi khng kh trong lp bin ca cc git nc, c
nhit bng nhit nc. Lp bin ln dn, n cui thit b x l nhit m s chim ton
b dng khng kh.
Hnh 7.2. S thay i trng thi khng kh khi chuyn ng cng chiu vi ncNh
vy qu trnh thay i trng thi ca khng kh xt v l thuyt l mt ng cong. i
vi thit b trao i nhit m kiu song song cng chiu, n l c cong lm. Tu
thuc nhit nc u ra m dung m ca khng kh c th tng hoc gim. Nu nhit nc
u ra c nhit ln hn nhit ng sng ca khng kh u vo th dung m ca khng kh
tng, tc l c mt lng hi m khuych tn vo khng kh v ngc li. Khi chuyn ng
song song cng chiu, kh nng lm tng dung m rt ln do nhit nc tng dn v
nhit nc u ra c nhiu kh nng ln hn nhit ng sng.Tuy nhin trn thc t do
chnh nhit gia nc v khng kh khng qu ln v ngi ta ch ch trng n trng
thi cui nn thng biu din qu trnh thay i trng thi ca khng kh theo ng
thng. Mt khc do trao i nhit m khng t l tng, thi gian tip xc l hu hn
nn m ca trng thi cui ch t ti c 90 - 95%, tc l khng kh ch ti im O no
m khng t ti B.Ngi ta nhn thy qu trnh thay i trng thi ca khng kh cng
xy ra tng t khi n trao i nhit m vi thit b trao i nhit.Trng hp nc v
khng kh chuyn ng ngc chiuTrng hp khng kh chuyn ng ngc chiu, ta cng
chia thit b thnh k on (hnh 7.3).Trng thi khng kh u vo cc on 1, 2, .
. k ln lt l A, A1, A2. . . Ak-1. u ra cui cng l trng thi Ak.Nhit nc
u ra cc on 1, 2, . . k ln lt l tn, tn1, tn2. . .tnk-1. Nhit nc u vo
on k l Ank. Cc im B, B1, B2, . . .Bktng ng ln lt l trng thi khng kh
bo ho trong vng bin ca cc git nc c nhit tn, tn1, tn2. . tnk.
Hnh 7.3. Trao i nhit m gia khng kh v nc khi chuyn ng ngc
chiuKhng kh thay i t trng thi ban u A qua cc trng thi trung gian
A1, A2v cui cng l trng thi Ak. Trng thi cui cng Akt bo ho v c nhit
bng nhit nc u vo thit b tnk. Ni tt c cc im A, A1, A2. . .Akta c ng
cong biu th s thay i trng thi ca khng kh khi trao i nhit m vi nc.
Kt qu cho thy, l ng cong li, trng thi khng kh u ra l bo ho.Nu nhit
nc u vo kh nh, nh hn nhit ng sng ca khng kh th qu trnh x l nhit m s
lm gim dung m. Ngc li, nu nhit nc x l cao th s lm tng dung m. Trn
thc t, nu s dng nc lnh, th thng nhit nc nh hn nhit ng sng. Ngc li
nu s dng nc thng th nhit nc ln hn nhit ng sng. Nh vy, gim dung m
phi s dng nc lnh, mun tng m s dng nc thng.Qua nghin cu, qu trnh x l
nhit m khng kh trong hai trng hp nc v khng kh chuyn ng cng chhiu v
ngc chiu, ta nhn thy:- Trng thi ca khng kh thay i theo dng ng
cong;- Trng thi u ra ca khng kh ph thuc vo nhit nc x l v chiu chuyn
ng tng h gia nc v khng kh. Dung m ca khng kh c th tng hoc gim.Trn
thc t chnh nhit ca khng kh u vo tAv u ra tAkkhng ln v trong cc tnh
ton thng ch quan tm trng thi u v cui. V vy ngi ta coi qu trnh thay
i trng thi theo dng ng thng.Khi lng nc phun v cng ln v thi gian tip
xc = th qu trnh thay i trng thi ca khng kh tun theo quy lut ng
thng.
S thay i trng thi khng kh khi chuyn ng ngc chiu vi ncTuy nhin,
trn thc t do lng nc phun v thi gian tip xc l hu hn nn trng thi cui
qu trnh x l khng kh khng t trng thi bo ho Akm ch t trng thi O c m
O= 9095%.Gii hn ca qu trnh x l khng kh bng nc phun.Trong thc t trng
khng kh cui qu trnh x l khng kh bng nc phun khng bao gi t ti m =1,
m ch t = 0,9 - 0,95. l trng thi cui ca khng kh khi ra khi bung
phun.Ngi ta chng minh c rng trn th I-d khng kh c trng thi A th mi
qu trnh nm ngoi tam gic cong AMN khng th thc hin ch bng nc phun.
Tam gic cong AMN c y l on MN trn ng cong =1 v NN, AM l cc tip tuyn
t A ti ng cong =1.
Hnh 7.5. Gii hn qu trnh x l khng khV d:- Qu trnh AB trn ng d=dA=
const ch thc hin bng caloriphe (sy nng ng dung m)- Qu trnh AF: thc
hin qua 2 giai on, tng m on nhit bng nc phun AP v sy nng ng dung m
PF.- Qu trnh AC trong tam gic AMN c th thc hin bng nc phun.THIT B
IU HO KIU TKhi nim, phn loi v cu to.Bung my iu ha khng kh cn gi l
bung iu khng l thit b c s dng x l khng kh trc khi thi vo bung myC
nhiu cch phn loi bungTheo cch b tr: bung ng, nm ngang, kiu thng v
ngot.Theo p sut lm vic (ty thuc vo v tr t qut): Kiu ht, thi, v kt
hpThit b bung phun kiu nm ngang Cu to1- Ca iu chnh gi vo2- Bung ha
trn3- Lc bi4- Caloriphe5- H thng phun nc6- Bung ha trn7-
Caloriphe8- ng gi ra9- ng hi gi cp 110- ng hi gi cp 211- ng ng gi
ra12- Bm nc phun13- Mng hng nc
Hnh 7.6. Bung phun kiu nm ngang Nguyn l hot ngKhng kh bn ngoi c
a qua van iu chnh vo bung ha trn 3 ha trn vi khng kh tun hon, sau c
a vo bung phun lm x l nhit m. Nu cn si nng th s dng caloriphe.
Trong bung phun c b tr h thng ng dn nc phun v cc vi phun. Nc c phun
thnh cc ht nh d dng trao i nhit m vi khng kh. trnh nc cun i theo
dng khng kh v lm m t cc thit b, pha trc v pha sau bung phun c b tr
cc tm chn nc dng dch dc. Khng kh sau khi x l xong c a vo bung ha
trn 10 tip tc ha trn vi gi hi cp 2. Caloriphe 12 dng si khng kh nhm
m bo yu cu v sinh khi cn. Nc c x l lnh c bm 15 bm ln cc vi phun vi
p sut phun kh cao. Nc ngng ng s c hng nh mng 14 v dn v li tip tc lm
lnh.Cc tm chn nc c dng dch dc c tc dng ngn v gt ri cc git nc b cun
theo dng hi. N c t 2 pha ca bung phun. V vt liu cc tm chn c th ch
to t cc tm tn trng km hoc inox mng c gp mt vi ln. S np gp cng nhiu
th hiu qu tch m ln nhng tr lc tng. Thng ngi ta ch gp 2-4 np.
Hnh 7.7. Cu to bung phun kiu nm ngangChi tit vi phun quyt nh kch
thc cc git nc phun v do nh hng quyt nh n hiu qu trao i nhit m.
Nguyn l lm vic ca cc vi phun l s dng lc ly tm x ti cc git nc.Trn
hnh 7.9 l cu to ca vi phun thng c s dng. Nc c p sut ln i theo ng dn
2 vo bung xoy 3 theo phng tip tuyn. Trong bung xoy nc chuyn ng xoy
vi tc ln v thot ngoi qua l 4. Tc l 4 rt ln, i ra vi phun c dng hnh
cn v tc gim ngt v c x ti thnh nhng git nh. Mi phun 5 c lp vo thn vi
phun bng ren v c th d dng iu chnh c bung xoy ph hp nht.
Hnh 7.8. Cc chi tit ca bung phun1,5- Vch chn nc; 2- Trn bung
phun; 3- ng gp phun; 4- Vi phun; 6- Bm nc phun; 7- Mng hng nc;
8,9,11- ng nc; 10- Van 3 ng
Hnh 7.9. Chi tit tm chn Cc c im ca bung phun kiu thng- Hiu qu
trao i cao do tc tng i gia gi v nc cao v thi gian trao i cng kh
lu;- Thch hp cho h thng ln trong cng nghip;- H thng cng knh chim
nhiu din tch lp t.
Hnh 7.10. Chi tit vi phun1- Thn vi phun; 2- L nc vo; 3- Bung
xoy; 4- Mi phun; 5- Np vi phunBung ti Cu to1- Qut ly tm vn chuyn
gi2- Chn nc3- Lp vt liu m: G, Kim loi, snh s .4- Ca ly gi5- Bm nc6-
ng nc vo ra7- Dn lm lnh nc
Hnh 7.11. Bung ti Nguyn l hot ngKhng kh bn ngoi c ht vo ca ly gi
6 vo bung ti nh qut ly tm 5. bung ti n trao i nhit m vi nc c phun t
trn xung. tng cng lm ti nc vag tng thi gian tip xc gia nc v khng kh
ngi ta thm lp vt liu m t gia bung. Vt liu m c th bng cc ng st, gm,
snh s, kim loi, g c tc dng lm ti nc v cn tr nc chuyn ng qu nhanh v
pha di ng thi to nn mng nc.Nc c lm lnh trc tip ngay mng hng nh dn
lnh 7. Cc c im ca bung ti- Hiu qu trao i nhit m khng cao lm do qung
ng i ngn.- Thch hp cho h thng nh v va trong cng nghip.- Chim t din
tch lp t.
Hnh 7.12. Cc loi vt liu lm ti ncNHNG NHN T NH HNG N HIU QU TRAO
I NHIT MH s hiu qu trao i nhit m H s hiu qu trao i nhit m.Trn thc t
trng thi khng kh cui qu trnh trao i nhit m vi nc phun khng th t
trng thi = 100%, m ch t mt trng thi O vi = 0,9 0,95 m thi. c trng
cho hiu qu ca qu trnh trao i nhit m gia nc v khng kh trong bung
phun ngi ta a ra mt i lng gi l h s hiu qu trao i nhit m, K hiu l
E.(7-1)H s trao i nhit m c th xc nh theo thng s trng thi ca khng
kh.T O, B ta k cc ng tO v tB ct ng dA cc im O' v B'. Ta c th coi cc
ng tOv tBsong song vi nhau, khi :(7-2)i vi qu trnh on nhit : tB=
t,(7-3) H s hiu qu trao i nhit m vn nngTrong mt s trng hp ngi ta s
dng i lng gi l h s trao i nhit m vn nng E':(7-4)H s hiu qu trao i
nhit m vn nng thng c s dng tnh ton thit k thit b bung phun.Ngoi ra
ngi ta cn a ra h s Ennhm nh gi hiu qu trao i nhit m ca bung
phun.(7-5)Nhng nhn t nh hng n hiu qu trao i nhit mAnh hng ca h s
phunH s phun l t l gia lu lng nc phun Gf(kg/s) vi lu lng khng kh c
x l G (kg/s). H s phun c k hiu l .(7-6)Khi h s phun tng, hiu qu
trao i nhit m tng. Khi < 4, h s hiu qu trao i nhit m tng ng k
khi tng . Khi > 4, vic tng h s trao i nhit m E tng khng ng k,
nhng chi ph in nng cho bm nc phun ln, nn khng kinh t. Trn thc t ngi
ta ch vn hnh vi h s phun < 2.Anh hng ca kt cu bung phunKt cu
bung phun c nh ln n hiu qu trao i nhit m ca bung phun. Cc thng s kt
cu nh hng ti hiu qu trao i nhit m bao gm: S dy vi phun dc theo chiu
chuyn ng ca bung phun: Khi s dy vi phun tng th hiu qu s cao hn S vi
phun trn mt dy: Khi s vi phun tng th hiu qu s cao hn Chiu phun nc
so vi khng kh: Phun ngc chiu nc s tng hiu qu trao i do vn tc tng i
tng ln.Bng 7.1Dng kt cuH s Emax
+ S dy z =1, thun chiungc chiu+ S dy z =2, thun chiu + thun
chiungc chiu + ngc chiungc chiu + ngc chiu+ S dy z
=30,550,55>1,0>1,0>1,01,50,6 0,70,65 0,750,85 0,90,9
0,950,9 0,950,98
Anh hng ca ch phun ncKhi ht nc phun cng b th b mt trao i nhit m
tng nn hiu qu trao i nhit m tng ln.Ty theo kch thc ht nc c phun ra
m ngi ta phn ra thnh 3 ch phun khc nhau: Phun mn Phun trung bnh
Phun thThc nghim v l thuyt chng minh rng mn ca nc phun ra ph thuc
vo ng knh mi phun do v p sut d ca nc trc mi phun pf.Kch thc do v p
sut pf cng ln th ht nc phun ra cng mn. Tuy nhin khi i hi nng lng dn
ng tng v vi phun d b tc.Theo kinh nghim- Phun mn khi: do= 1,5 - 2
mm pf> 4 bar- Phun trung bnh khi: do= 2 - 3 mm pf= 2 - 4 bar-
Phun th khi: do= 2 - 6 mm pf< 2 barVic chn ng knh mi phun v p
sut cn ty thuc vo nng sut yu cu.Anh hng ca tc dng kh.Khi tc ca khng
kh tng s lm tng trao i nhit m. Nhng nu kqu cao th c kh nng cun theo
cc ht nc vo gian my. Trong k thut ngi ta khng ch ktheo tr s lu tc
kmt cch hp l. Thng chn k= 2,8 - 3,5 kg/m2.sAnh hng ca chiu di qung
ng dng kh.Khi tng chiu di qung ng i ca khng kh th thi gian tip xc
ln khi E tng. Tuy vy kch thc ca bung phun tng nn lm tng gi thnh v
vn hnh lp t kh khn. V vy ch khi thc s cn thit ngi ta mi tng l, v d
nh khi khng kh ban u c m qu b.Thi gian tip xc hp l gia nc v khng kh
l 1 giy.Quan h ph thuc ca h s hiu qu trao i nhit m vo h s phun c
biu th theo cng thc sau y:- Khi phun mn:, kg/kg (7-7)- Khi phun
trung bnh v th:, kg/kg (7-8)trong z- S dy phun;pf- Ap sut d ca nc
phun, bar ;k- Lu tc ca khng kh, kg/m2.s;E- H s hiu qu trao i nhit
m.TNH TON BUNG PHUNTnh thit kNhim v bi ton thit k bung phun l xc nh
cc thng s k thut v kch thc ch yu ca bung phun, khi bit trc cc thng
s nhit ca khng kh vo ra, lu lng khng kh cn x l.. c th: Cc thng s
ban u- Lu lng gi cn x l G, kg/s;- Trng thi khng kh u vo (t1, 1) v u
ra (t2, 2);- Nng sut lnh yu cu ca thit b Qo, kW;- Nhit nc lnh u vo
tnl Cc thng s cn tnh ton- Kch thc bung phun: Chiu cao h (m); chiu
rng b(m) v chiu di l (m);- Lu lng nc phun Gf, kg/s; Cc bc tnh
tonChn lu tc khng kh i qua tit din ngang ca bung phunkThng thng ngi
ta chn k= 2,8 3,2 kg.m2/s. Nu qu nh th hiu qu trao i nhit m thp,
nhng cao qu th c kh nng cun theo cc git hi m. Khi lng ring ca khng
kh khong 1,2 kg/m3, do tc chuyn ng ca khng kh nm trong khong k= 2,3
2,7 m/s. Chn K= 2,5 m/s.Xc nh cc kch thc c bn ca bung phun- Tit din
ngang ca bung phun:, m2(7-9)trong h - Chiu cao ca bung phun, chiu
cao h cn chn hp l trong khong 2 2,5 m. Nu qu cao th s phn b lu lng
gi kh u, ngc laih nu chn qu thp th b rng ln, chim nhiu din tch;b-
Chiu rng bung phun, m;G - Lu lng gi c cho trc hoc xc nh c khi thnh
lp s ddoof iu ho khng kh, kg/s.Xc nh cc thng s c trng khc ca bung
phun- Chn s dy phun Z: Trn c s kch thc s b ca bung phun, chn s dy
vi phun. S dy vi phun, nh bit nm trong khong 13 dy;- Chn cch b tr
cc dy vi phun. C 2 cc cch b tr sau: thun chiu, ngc chiu v kt hp c 2
cch trn. Cc trng hp c th b tr trnh by trn bng 6-1;- Chn ch phun:
Phun th, trung bnh v mn;- Chn loi mi phun;- Chn ng knh mi phun do:
3; 3,5; 4; 4,5; 5; 6mm;- Chn mt mi phun trn tit din ngang ca bung
phun n. Theo kinh nghim s mi phun trn 1m2din tch nm trong khong
1824 ci;- Tnh s mi phun: N = fb.Z n, ci.Tnh h s phun,h s hiu qu E v
lu lng nc phun xc nh quan h- Xc nh h s hiu qu trao i nhit m vn
nng:(7-10)tu1, tu2- Nhit nhit k t ng vi trng thi khng kh vo v ra.-
Xc nh h s phun da trn h s hiu qu trao i nhit m vn nng. Tnh theo cc
cng thc (7-7) v (7-8) nhng thay E bng E.Tnh nhit nc phun xc nh nhit
nc phun ta da vo phng trnh cn bng nhit. Nu b qua cc tn tht th nhit
lng lm lnh khng kh ng bng nhit lm tng nhit nc t nhit tnn tn.Qo=
G.(I1-I2) = Gnl.Cpn.(tn-tn) (a)Mt khc, ta c biu thc(b)Kt hp (a),
(b) v cho bit Gf= Gnlta c:
Gi tr tnphi tho mn iu kin tn 5oC, nu ln qu phi tng h s phun v xc
nh li gi tr En.T suy ra:tn= tn+ tnNhit nc vo c suy ra t cc biu thc
(7-3) v (7-10):
Tnh lu lng nc phun v lu lng nc lnhH thng cp nc b phun c th thc
hin theo mt trong hai cch sau:- Nc c lm lnh v a n phun trc tip bung
phun. Trong trng hp ny lu lng nc phun bng lu lng nc lnh.- Nu nc lnh
c cp ti b cha v t y nc c bm n phun bung phun. Trong trng hp ny nc c
tun hon theo hai vng khc nhau v c th lu lng nc phun v nc tun hon
khng ging nhau (do bm hoc tr lc h thng khc nhau).a). Lu lng nc phun
(nc lnh) c xc nh theo cng thc:Gf= G., kg/s (7-11)b). Lu lng nc lnh:
Nc lnh c cp vo b cha t c bm phun bm vo bung phun trao i nhit m. Lu
lng nc lnh c th khc lu lng nc phun.(7-12)trong :tn, tnl- Nhit nc
phun u ra (bng nhit nc lnh hi v) v nhit nc lnh vo b nc phun;Qo- Cng
sut lnh yu cu, kW.Xc nh p sut trc mi phun v s mi phun N- Nng sut
phun ca mi mi phun c xc nh theo cng thc sau:, kg/s (7-13)Nng sut
phun c nh hng ti p sut d trc cc mi phun v quan h c xc nh nh sau: i
vi mi phun kim loi:, l/h (7-14) i vi mi phun nha:, l/h (7-15)trong
do - ng knh mi phun, mm;pf- Ap sut d ca mi phun, at.T gi tr gfc th
xc nh c p sut d nh sau: i vi mi phun kim loi:, at (7-16) i vi mi
phun nha:, at (7-17)Quan h gia p sut d v nng sut phun ng vi cc loi
vi phun c ng knh khc nhau biu th trn hnh 7.11 di y. Theo yu cu k
thut p sut d trc cc mi phun khng nn qu ln, v nu ln th yu cu v ct p
ca bm phi cao. Thc t nn chn pf< 2,5at. V vy khi tnh ton, nu p
sut d ln qu th phi tng s mi phun N, gim p sut d. Trong phn ny tu
theo iu kin thc t m c th chn p sut d pfnh trc v xc nh s mi phun cn
thit. Tuy nhin nu chn s mi phun nhiu, p sut gim, ch phun chuyn sang
phun th, hiu qu trao i nhit m gim.
Hnh 7.13. Cc loi vt liu lm ti ncB tr dn phunC th tham kho cch b
tr dn phun ca Nga nu trong ti liu [ ]. B rng chn nc trc a = 120mm;
B rng chn nc sau b = 185 250mm; Cc kch thc khc: c = 200mm; l =
1500mm; m=660mm; n=400mm; p=600mm; v = 900mm; Khong cch gia cc cc
phun t 250350mm. Khong cch gia cc mi phun theo chiu ng khong
400600mm.
Hnh 7.14: B tr bung phun ca Ngaa- Mt dy phun thun chiu; b- Mt dy
phun ngc chiu; c- Hai dy phun ngc chiu;d-Hai dy phun thun v ngc
chiu; e- Ba dy phunTnh kim traCc bc tnh ton kim traXc nh nng sut
phun ca cc mi phun gftheo dov pfda vo th hnh 7.11 hoc theo cc cng
thc (7-13) v (7-14)Tnh lu lng nc phun Gn:Gn= gf.N, kg/sTnh h s
phun:=GnG, kg/kgTnh tc lu lng khi lng ca khng kh, kg/m2.sXc nh Eb,
Ebv khc.E = Eb.khcEn= Eb.khcTnh nhit nhit k t ca khng kh sau khi x
lt2= (1 - En).(t1- tn) + tntrong tnc xc nh theo cng thc sau:tn= tn+
(m1.t1- m2.t2)/trong m1v m2- cc h s t l ph thuc vo nhit c cho theo
bng di y ly theo p sut kh quynBng 7.2t,oC51015202528
B=760mmHg0,890,6980,670,6850,730,764
B=745mmHg0,900,710,6780,6920,7350,77
xc nh m2cn xc nh t2do cn phi tin hnh tnh lp. Cc bc tnh lp c thc
hin nh sau: Tm ly mt gi tr nc ra no theo kinh nghim: tn= tn+
(35)oC; Xc nh nhit t2 theo cng thc:t2= (1 - En).(t1- tn) + tn Tra
bng 7.2 xc nh gi m1theo t1v m2theo t2; Tnh li gi tr tntheo cng
thc:tn= tn+ (m1.t1- m2.t2)/Nu sai s khng ln th c th chp nhn c.- Xc
nh t2theo gi tr tnxc nh cXc nh I2theo t2trn th I-d: ng I2 = const i
qua im bo ho c nhit bng t2.Xc nh t2theo E theo cng thc:t2= t2+
(1-E).(t1- t2)Theo t2v I2(hoc t2) xc nh im 2 trn I-d v cc thng s
trng thi khc: 2, d2;Xc nh nng sut lnh ca thit b x l khng kh:Qo=
G.(I1- I2)Kim tra nhit lng nc lnh nhn cQn= Gn.Cpn.(tn- tn)So snh gi
tr Qov Qn; sai lch khng qu 10%.* * *
