Bg Ky Thuat Lanh

8/2/2019 Bg Ky Thuat Lanh

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Gio trnh k thut lnh dng cho sinh vin ngnh in Cng Nghip

BAI 1. KHAI NIEM CHUNG VE NHIET ONGLC HOC

I. NHIET ONG HOC VA PHNG PHAP NGHIEN CUNHIET ONG HOCNhiet ong hoc la mon khoa hoc nghien cu nhng quy luat bien

oi nang lng trong cac qua trnh vat ly, hoa ly khac nhau, trongo chu yeu la cac qua trnh bien oi nhiet nang va c nang.Nhng c s nhiet ong hoc a phat minh t the ky XIX khi xuathien cac ong c nhiet

Nhiet ong hoc c xay dng tren hai c s hai nh luat thnhat va nh luat th hai cua nhiet ong hoc

nh luat th nhat thc chat la nh luat bao toan va chuyenhoa nang lung ng dung trong pham vi nhiet, no at trng ve matso lng cua nhng qua trnh bien oi nag lng. nh luat th haxac nh chieu hng tien hanh cua cac qua trnhtrong t nhien,ieu kien vamc o bien hoa cuanang lng, cu the la bien haogiai nhiet va cong, no at trng cho mat chat lng cua cuanhng qua trnh bien oi nang lng

II. CAC KHAI NIEM VE QUA TRNH NHIET ONG:1. Cong va nhiet lng

Khi cac vat tac ong lan nhau, chung trao oi cho nhau mot nanglng nao o. S truyen nang lng c thc hien bang hai cach

Thc hien mot cong cua vat nay oi vi vat kia. Luc o nanglng cua mot vat tang len mot lng ung bang long vat kia

mat i. Cong trong nhiet ong ky thuat k hieu la L va qui c congdo vat sinh ra la dng, va ngc lai cong do vat nhan c la congam.

Nang lng truyen t vat nong sang vat lanh khi chung tiep xuctrc tiep vi nhau. Nang lng c trao oi di dang nay c goila nhiet lng. Nhiet lng trong nhiet ong ky thuat c ky hieula Q va qui c nhiet lng do vat nhan c la nhiet dng va vatnha ra la am. n v o cong va niet lng la Joul (J), trc aynang lng c o bang n vla calo (cal), gia cal va J co quan henh sau:

1cal= 4,1868 J

2. He nhiet ongTap hp tat ca cac vat co trao oi nhiet lan nhau va vi mo

trng xung quanh goi la he nhiet ong. Neu he nhet ong khongtrao oi nhiet vi moi trng xung quanh goi la he oan nhiet. Hekhong trao oi nhiet va cong vi moi trng xung quanh c goi lahe co lap

Bin son: KS Nguyn Hong Phong Trang 1


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3. ong c nhiet, bm nhiet va may lanhong c bm nhiet: la loai may nhan nhiet va sinh cong. Cac

may nay nhan nhiet t nguon nong e bien mot phan nhiet lngnay thanh cong va nha phan nhiet con lai cho nguon lanh. V dunh cac ong c ot trong, cac ong c phan lc, cac thiet b ong

lc hi ncBm nhiet va may lanh: ve nguyen ly bm nhiet va may lanhgiong nhau. Cac may nay nhan cong t ben ngoai e chuyennhiet lng t moi trng co nhiet o thap hn en moi trngco nhiet o cao hn. Nh ve muc ch th bm nhiet va may lanh cos khac nhau. Ve bm nhiet ngi ta quan tam en nhiet lng manguon nong nhan c, con may lanh ngi ta quan tam lng nhietnhan t nguon lanh.

4. Chat moi gii va trang thai cua chat moi giie thc hien qua trnh chuyen hoa gia nhiet va cong va

chuyen tai nang lng trong cac he nhiet ong ngi ta phai dungmot chat trung gian c goi la chat moi gii. Chat moi gii thnggap trong ky thuat dang kh hoat hi, v the kh co kha nang thayoi the tch rat ln do o co kha nang sinh cong ln. nhngieu kien khac nhau chat moi gii se co cac trang thai khacnhaubieu th bang cac ai lng vat ly thng at trng bi nhieto (T), ap suat (P), the tch rieng (v). Cac thong so dung e xacnh trang thai cua chat moi gii c goi la thong so trang thai. mot trang thai xac nh th cac thong sotrang thai cung conhng gia tr xac nh. trang thai ma cac thong so trang thaco gia tr giong nhau bat ky iem nao trong toan bo khoi kh th

ta goi la trang tha can bang, va ngc lai ta goi la trang thai khongcan bang.

5. Cac thong so trang thai cua chat moi giia. Ap suatAp suat la lc tac dung cua vat chat len 1 n v dien tch cua

thanh bnh cha. Ap suat c ky hieu la P, n v N/m2

2m

N

S

FP ==

Khi ta at mot vat ran len mot dien tch th ap suat se phanng tren dien tch o.

Khi ta cha nc trong bnh th ap suat di ay bnh bang nhaunhng ap suat thanh ben giam dan theo chieu cao cot nc.

Khi nen kh (hoac hi) vao trong mot bnh kn, hi se tac dung lenmoi pha bnh vi gia tr ap suat giong nhau.



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Trong ky thuat co mot so khai niem ap suat nh sau: ap suatkh quyen, ap suat chan khong, ap suat d va ap suat tuyet oi.

p

Pd (ap suat d)Ptd (as tuyet oi)

Pck as chan khong P0(as kh quyen)

Ap suat kh quyen (P0): c o bang Barometer 1 atm vat lyc bieu th qua cot thuy ngan cua Baromer cao 760mmHg,

dien tch cua ong o la 1cm2

. (Baromer at tren mat nc bien 0oC) Trong lng thuy ngan: 13,6x0,076 = 1,033kg. Vay ap suatkh quyen Po = 1 atm = 1,033 kg/cm3 (atmosphe vat ly)

Ap suat chan khong (Pck): la ap suat o bang Vacummeter,Tr so ap ke nho hn ap suat kh quyen Pck < Po

Ap suat d (Pd): la ap suat o bang Manometer, tr so ap keln hn ap suat kh quyen Pd > Po

Ap suat tuyet oi: khong o at c ma ch co the tnhtoan c t ap suat kh quyen, ap suat chan khong

o Ptd = Po + Pdo Ptd = Po Pck

b. Nhiet oNhiet o la ai lng vat ly, no bieu th mc o nong lanh

cua vat chat. Nhiet o chnh la mc o van ong hoac rung ongtrung bnh cua cac phan t trong noi bo vat chat thi iem o.

Neu lam lanh vat chat en nhiet o -273,15oC th tat ca cac rungong phan t se bien mat. Nhiet o t = -273.15 oC c goi lanhiet o khong tuyet oi

He n v quoc te SI s dung nhiet o bach phan (Celcius) vanhiet o Kelvin oK lam n v o nhiet o

Thang nhiet o Celcius xay dng tren c s lay iem nc atan 0oC va nc soi la 100oC ieu kien chuan (P = 1atm =760mmHg)

Trong ky thuat ngi ta s dung nhiet o Kelvin oK. oK ng vnhiet o khong tuyet oi 0oK = -273.15oC. Do o:

o T0K = toC +273.15 He n v Anh My s dung nhiet o Fahrenheit (oF). Quan he

gia nhiet o toF va toC nh sau:o toC = 5/9(toF 32)



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o toF = 32 + 9/5toCc. The tch riengMot kh co khoi lng la G kg va choang mot the tch la V m3

the tch rieng cua khoi kh o c nh ngha nhu sau:

G

Vv = m3/ kg

Ta co khoi lng rieng la:vV

G 1== kg/m3

III. KH LY TNG VA PHNG TRNH TRANG THAI CUA KHLY TNG

1. nh ngha ve kh l tngMot chat kh la tap hp vo so cac phan t, gia cac phan t

luon luon co lc tng tac, va ban than cac phan t co mot thetch nhat nh. Nhng mot chat kh ta bo qua lc tng tac gia cacphan t va bo qua the tch ban than th chung c goi la kh l

tng.

2. Phng trnh trang thai cua kh l tng phng trnh viet cho 1 kg

pv = RT Phng trnh viet cho G kg

pV = GRTTrong o:p = (N/m2); v= m3/kg; V= m3; T= (0K)R: Hang so chat kh

8314

=R

(J/kgK) : Phan t lng cua kh (kg/kmol)G: Khoi lng kh (kg) Phng trnh viet cho 1 kilomol kh

pV = R T= 8314 TTrong o:V : The tch cua 1 kilomol V = . (m3/kmol)R = 8314 J/kmol.0 K Phng trnh viet cho M kilomol kh

pV = M.R T= 8314MT

M: So kilomolIV. CAC QUA TRNH C BAN CUA KH LY TNG:1.QUA TRNH ANG TCH:

Qua trnh ang tch la qua trnh xay ra khi the tch khong thay oi V= Const va so mu a bien n = . Nhiet dung rieng cua qua trnh CvTrong qua trnh nay ta co moi quan he sau.

+ Quan he gia nhiet o va ap suat



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1

2

1

2

p

p

T

T=

+ Cong thay oi the tch

l12 = 0+ Cong ky thuat

lkt = -(p2 p1) = (p1 p2)+ Nhiet cua qua trnh

Q = GCv(T2 T1)+ o bien oi Entropi

1

2lnT

TGCS v=

2.QUA TRNH ANG AP

Qua trnh ang ap la qua trnh ch xay ra khi ap suat khong thayoi p = const va so mu a bien n = 0, nhiet dung rieng cua qua trnhCp. Trong qua trnh nay ta co cac quan he sau:

+ Quan he gia nhiet o va the tch:

1

2

1

2

=

T

T

+ Cong thay oi the tch:l12 =p( 2 1)

+ Cong ky thuatlkt = 0

+ Nhiet cua qua trnhQ = GCp(T2 T1)

+ Bien oi Entropi

1

2lnT

TGCS p=

3.QUA TRNH ANG NHIETQua trnh ang nhiet la qua trnh xay ra khi nhiet o cua qua

trnh khong thay oi. T = Const va so mu a bien n = 1. Nhiet dung

rieng cua qua trnh la C = . Trong qua trnh nay co cac quan hesau:+ Quan he gia ap suat va the tch

2

1

1

2

v

v

p

p=

+ Cong thay oi the tch va cong ky thuat



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2

1

1

212 lnln

p

pRT

v

vRTll kt ===

+ Nhiet cua qua trnh

2

112 ln

p

pGRTlQ ==

+ Bien oi Entropi

2

1lnp

pGRTS =

4.QUA TRNH OAN NHIET

Qua trnh oan nhiet la qua trnh xay ra khi khong kh trao onhiet vi moi trng q = 0 va dq = 0, so mu a bien n = k, Entropicua qua trnh khong oi S = const va nhiet dung rieng cua qua trnhC = 0. Trong qua trnh nay ta co cac quan he sau:

+ Quan he gia nhiet o, ap suat va the tch

2

1

1

2

vv

pp =

( )( )1

2

1

1

1

2

2

1

=

=

kk

k

v

v

p

p

T

T

+ Cong thay oi the tch( )

=

k

k

p

p

k

vpl

1

1

211

121

1

+ Cong ky thuat( )

==

k

k

ktp

p

k

kRTll

1

1

2112 1

1

5.QUA TRNH A BIENQua trnh a bien la qua trnh xay ra khi nhiet dung rieng cua qua

trnh khong oi. Cn = Const va c xac nh bang bieu thc.

1

=

n

knCC vn

Trong qua trnh nay ta co cac quan he sau:+ Quan he gia nhiet o, ap suat va the tch.

n

v

v

p

p

=

2

1

1

2

( )( )1

2

1

1

1

2

1

2

=

=

nn

n

v

v

p

p

T

T



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+ Cong thc thay oi the tch( )

=

1

1

21112 1

1

nn

p

p

n

vpl

+ Cong ky thuat( )

==

1

1

2112 1

1.

nn

ktp

p

n

nRTlnl

+ Nhiet cua qua trnhQ = GCn (t2 t1)

+ Bien oi Entropi

1

2lnT

TGCS n=

V.NH LUAT NHIET ONG LC HOC.1. NH LUAT NHIET ONG HOC 1:a.Phat Bieu:

nh luat nhiet ong th nhat thc chat la nh luat bao toanva chuyen hoa nang lng ng dung cho cac hien tng nhiet vac phat bieu nh sau: Nang lng khong mat i va cung khong tsinh ra, no ch co the bien oi t dang nay sang dang khac trongnhng qua trnh vat ly va hoa hoc khac nhau. Noi mot cach khac,tong so cac dang nang lng trong mot he co lap bat ky lakhong oi.

Trong pham vi nhiet ong, mot lng nhiet nang nao o mat ith sinh ra mot lng c nang xac nh va ngc lai.

nh lut nhit ng I pht biu: Nhit lng cp vo cho h mt phndng thay i ni nng, mt phn dng sinh cng:

dq = du + dl (1-9)- ngha ca nh lut nhit ng: nh lut nhit ng I cho php ta vitphng trnh cn bng nng lng cho mt qu trnh nhit ng.

b.Cc dng biu thc ca nh lut nhit ng

nh lut nhit ng I c th c vit di nhiu dng khc nhau nh sau:Trong trng hp tng qut:

dq = du + dl (1-10)i vi 1 kg mi cht:

q = u + l (1-11)i vi G kg mi cht:

Q = U + L (1-12)Mt khc theo nh ngha entanpi, ta c: i = u + pv,



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Ly o hm ta c: di = du + d(pv) hay du = di - pdv - vdp, thay vo (1-10)vch dl = pdv ta c dng khc ca biu thc nh lut nhit ng I nh sau:

dq = di - pdv - vdp + pdvdq = di - vdp (1-13)

Hay: dq = di + dlkt (1-14)i vi kh l tng ta lun c:du = CvdTdi = Cp dT

thay gi tr ca du v di vo (1-10) v (1-13) ta c dng khc ca biu thcnh lut nhit ng I :

dq = CvdT + pdv (1-15)dq = CpdT - vdp (1-16)

i vi h h:

(1-17)

c.Noi Nang Cua Chat Kh:

Batky he nhiet ong nao bao gom nhieu vat tac dung len nhaueu co nang lng tong E. Nang lng tong nay bao gom ongnang cua toan bo he E ac trng cho s chuyen ong cua toan bohe, the nang cua toan bo he Et ac trng cho v tr cua toan bo

he trong trng lc nao o ( v du nh trong trng, ien trng.)va noi nang cua toan bo he at trng cho nang lng cua cacphan t nho be cau tao nen vat

Noi nang bao gom hai thanh phan chnh: Noi ong nang U: la ong nang chuyen ong tnh tien va

chuyen ong quay cua cac phan t vanang lng dao dongcua cac nguyen trong phan t. Theo thuyet ong hoc phan tnoi ong nang ch phu thuoc vao nhiet o va tang len khnhiet o tang

Noi the nang Ut: la the nang cua lc lien ket gia cacphan t. Noi the nang phu thuoc vao khoang cach gia cacphan t, ngha la phu thuoc vao the tch rieng cua khoi khKhi the tch rieng cuakhoi kh thay oi, khoang cach gia cacphan t thay oi, do o noi the nang Ut thay oi

2. INH LUT NHIT NG HC II:2.1.Mt vi cch pht biu ca nh lut nhit ng II



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- Nhit lng khng th t truyn t vt c nhit thp n vt cnhit cao hn. Mun thc hin qu trnh ny th phi tiu tn mt phnnng lng bn ngoi (chu trnh ngc chiu).

- Khi nhit T1 = T2 = T th hiu sut ct = 0, ngha l khng thnhn

cng t mt ngun nhit.Mun bin nhit thnh cng th ng c nhit phi lm vic theo chutrnh vi hai ngun nhit c nhit khc nhau. Trong mt ngun cpnhit cho mI cht v mt ngun nhn nhit mi cht nh ra. iu cngha l khng th bin i ton b nhit nhn c t ngun nng thnhcng hon ton, m lung phI mt mt lng nhit thi cho ngun lnh. Cth thy c iu v: T1 < v T2 > 0, do ct < ctCarno < 1, ngha lkhng th bin hon ton nhit thnh cng.- Chu trnh Carno l chu trnh c hiu sut cao nht,

- Hiu sut nhit ca chu trnh khng thun nghch nh hn hiu sut nhitca chu trnh thun nghch. kTN < TN .

2.2.Chu trnh carnot:a.khi nim v nh ngha chu trnh nhit ng:

Khi nim chungTrong cc chu trnh nhit, mun bin nhit thnh cng th cn c mi

cht lm cht ti nhit v cho mi cht dn n sinh cng. Mi cht dnn mI c v kch thc thit b c hn. V vy, cho mi cht dn n nmt trng thI no , ngi ta li nn mi cht n tr li trng thi ban

u ri tip tc cho dn n v nn lp li nh ln u, qu trnh c lpi lp li nh vy . . . . Khi mi cht thay i trng thi mt cch lin tc ri litr v trng thi ban u, ta ni mi cht thc hin mt chu trnh hay mt qutrnh kn.

Hnh 1-17 th p-v ca chu trnh Hnh 1-18 th p-v ca chutrnh



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carnot thun nghch thun chiu carnot thun nghch ngcchiu

Trn th trng thi, nu chu trnh tin hnh theo chiu kim ng hthgi l chu trnh thun chiu (hnh 1-17).

chu trnh ny mi cht nhn nhit sinh cng, nn cng c du dng(1 >0) . Cc thit b nhit lm vic theo chu trnh ny c gi l ng cnhit.

Nu chu trnh tin hnh theo chiu ngc chiu kim ng h th gi lchu trnh ngc chiu (hnh 1-18). chu trnh ny mi cht tiu hao cnghoc nhn nng lng khc, do cng c du m (1 < 0) . Cc thit b nhitlm vic theo chu trnh ny c gi l my lnh hoc bm nhit.b.Chu trnh thun nghch v khng thun nghch

Cng ca chu trnh l cng m mi cht sinh ra hoc nhn vo khi thchin mt chu trnh.

Cng ca chu trnh c k hiu l L khi tnh cho Gkg mi cht hoc

khi tnh cho 1kg mi cht.Nhit lng v cng ca chu trnh bng tng i s nhit lng v cngca cc qu trnh trong chu trnh .

(1-114)

(1-115)

Lng bin thin u, i, s ca chu trnh u bng khng v u, i, s lccthng s trng thi, m chu trnh th c trng thi u v cui trng nhau.

Theo nh lut nhit ng I th q = u + l, m y u = 0, nn vi chu trnh ta lun c:

(1-116)

c.Chu trnh thun chiu* nh ngha:

Chu trnh thun chiu l chu trnh m mi cht nhn nhit t ngunnng



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nh cho ngun lnh v bin mt phn nhit thnh cng, cn c gi l chutrnh sinh cng. Qui c: cng ca chu trnh thun chiu l > 0. y l cc chutrnh c p dng ch to cc ng c nhit.* th:Trn th hnh 1-17, chu trnh thun chiu c chiu cng chiu kim ng

h.* Hiu qu chu trnh: nh gi hiu qu bin i nhit thnh cng ca chu trnh thun

chiu, ngi ta dng h s ct, gi l hiu sut nhit ca chu trnh.Hiu sut nhit ca chu trnh bng t s gia cng chu trnh sinh ra v

nhit lng m mi cht nhn c t ngun nng.

(1-117)

y: q1 l nhit lng m mi cht nhn c t ngun nng,q2 l nhit lng m mi cht nh ra cho ngun lnhl l cng chu trnh sinh ra, hiu nhit lng m mi cht trao i v

ngun nng v ngun lnh. Theo (1-116) ta c:

d. Chu trnh ngc chiu* nh ngha:

Chu trnh ngc chiu l chu trnh m mi cht nhn cng t bn ngo ly nhit t ngun lnh nh cho ngun nng, cng tiu tn c qui c lcng m, l < 0.* th:

Trn th hnh 1-18, chu trnh ngc chiu c chiu ngc chiu kim ngh.* H s lm lnh:

nh gi hiu qu bin i nng lng ca chu trnh ngc chiu,ngi ta dng h s , gi l h s lm lnh ca chu trnh.

H s lm lnh ca chu trnh l t s gia nhit lng m mi cht nhnc t ngun lnh vi cng tiu tn cho chu trnh.

(1-118)

trong : q1 l nhit lng m mi cht nh cho ngun nng,q2 l nhit lng m mi cht nhn c t ngun lnh,l l cng chu trnh tiu tn,



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e. Chu trnh carno thun nghchChu trnh carno thun nghch l Chu trnh ly tng, c kh nng bin

inhit lng vi hiu qu cao nht. Tuy nhin, nu p dng vo thc t th nc

nhng nhc im khc v gi thnh v hiu sut thit b, do xt vtng th th hiu qu kinh t khng cao. Chnh v vy n khng c pdng trong thc t m n ch lm mc tiu hon thin cc chu trnh khcv mt hiu qu nhit, ngha l ngi ta phn u thc hin cc chu trnhcng gn vi chu trnh Carno th hiu qu chuyn ho nhit nng cng cao.Chu trnh carno thun nghch lm vic vi hai ngun nhit c nhit khcnhau T1 v T2, nhit cc ngun nhit khng thay i trong sut qu trnhtrao i nhit. Mi cht thc hin 4 qu trnh thun nghch lin tip nhau:hai qu trnh ng nhit v hai qu trnh on nhit tin hnh xen k nhau.Sau y ta xt hai chu trnh Carno thun nghch gi tt l chu trnh Carnothun chiu v chu trnh carno ngc chiu.

f. Chu trnh carno thun nghch thun chiu th p-v v T-s ca chu trnh Carno thun chiu c biu din trnhnh 1-19. ab l qu trnh nn on nhit, nhit mi cht tng t T2 nT1; bc l qu trnh dn n ng nhit, mi cht tip xc vi ngun nng cnhit T1 khng i v nhn t ngun nng mt nhit lng l q1 = T1(sc -sb); cd l qu trnh dn n on nhit, sinh cng l, nhit mi cht gim tT1 n T2; da l qu trnh nn ng nhit, mi cht tip xc vi ngun lnhc nhit T1 khng i v nh cho ngun lnh mt nhit lng l q2 =T2(sa - sd).

Hnh 1-19 thp-v v T-s ca chu trnh carnot thun chiu

Hiu sut nhit ca chu trnh thun chiu c tnh theo cng thc (4-4) .Khi thay cc gi tr q1 v |q2| vo ta c hiu sut nhit ca chu trnh Carnothun nghch thun chiu l:



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(1-119)

* Nhn xt:T biu thc (1-119) ta thy:- Hiu sut nhit ca chu trnh Carno thun chiu ch ph thuc vo nhit ngun nng T1 v nhit ngun lnh T2 m khng ph thuc vo bncht ca mi cht.- Hiu sut nhit ca chu trnh Carno cng ln khi nhit ngun nngcng cao v nhit ngun lnh cng thp.- Hiu sut nhit ca chu trnh Carno lun nh hn mt v nhit ngunnng khng th t v cng v nhit ngun lnh khng th t n khng- Hiu sut nhit ca chu trnh Carno thun nghch ln hn hiu sut nhitca chu trnh khc khi c cng nhit ngun nng v nhit ngun lnh.g.Chu trnh carno thun nghch ngc chiu

th p-v v T-s ca chu trnh Carno ngc chiu c biu din trnhnh 1-20. ab l qu trnh dn n ng nhit, mi cht tip xc vi ngunlnh c nhit T2 khng i v nhn t ngun lnh mt nhit lng l q2 =T2(sb - sa); bc l qu trnh nn on nhit, tiu tn cng nn l l, nhit mi cht tng t T2 n T1; cd l qu trnh nn ng nhit, mi cht tipxc vi ngun nng c nhit T1 khng i v nh cho ngun nng mtnhit lng l q1 = T1(sd - sc); da l qu trnh dn n on nhit, nhit mi cht gim t T1 n T2.

Hnh 1-19 thp-v v T-s ca chu trnh carnot ngc chiuH s lm lnh ca chu trnh ngc chiu c tnh theo cng thc (1-

118). Khi thay cc gi tr |q1| v q2 vo ta c h s lm lnh ca chu trnhCarno thun ngch ngc chiu l:



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(1-120)

* Nhn xt:T biu thc (1-120) ta thy:- H s lm lnh ca chu trnh Carno ngc chiu ch ph thuc vo nhit ngun nng T1 v nhit ngun lnh T2 m khng ph thuc vo bncht ca mi cht.- H s lm lnh ca chu trnh Carno cng ln khi nhit ngun nngcng thp v nhit ngun lnh cng cao.

- H s lm lnh ca chu trnh Carno c th ln hn mt.

2.3. H s chu trnh nhit ng ca my lnh v bm nhit:Chu trnh thit b lnh chy l chu trnh ngc chiu, nhn nhit t

ngunc nhit thp, nh nhit chongun c nhit cao. Mi cht s dng trongcc lm thit b lnh thc t thng l hi ca mt s cht lng c nhit si thp p sut bnh thng, h s to nhit ln, r tin, khng c hi. Tutheo phng php tng p sut ca mi cht ta chia ra hai loi: chu trnh thitb lnh c my nn v chu trnh thit b lnh hp th (khng c my nn).a.Chu trnh thit b lnh c my nn

Mi cht thng dng trong my lnh c my nn l Amoniac (NH3) hayFron F12, F22 (c cng thc: CmHxFyClz). Amnian thng dng trong my lnhcng nghip sn xut nc hoc lm lnh thc phm, v nhit n hohI ln nn c th ch to vi cng sut ln. Fron thng dng trong my lnhgia nh nh t kem, t lnh gia nh v khng i hi cng sut ln, khngmi v khng c hi.

S nguyn l ca my lnh c my nn c th hin trn hnh 1-20.Hi mi cht trng thi bo ho kh t bung lnh IV c p sut p1 c mynn ht vo v nn on nhit n p sut p2, nhit t2. Sau i vobnhngng II ngng t ng p p sut p2, nh lng nhit q1 cho khng kh

haync lm mt. Lng ngng t t dn ngng II i qua van tit lu III, gim psut t p2 xung p1 v chuyn t dng lng sang dng hi m. Hi m tip tci vo bung lnh IV nhn nhit lng q2 ca vt cn lm lnh p sut p1 =const bin thnh hibo ho kh v chu trnh lp li nh c. Cc qu trnhca my lnh dng hi c my nn c biu th trn th hnh 1-21.1-2 l qu trnh nn on nhit trong my nn, p sut tng t p1 n p2,2-3 l qu trnh ngng t ng p p sut p2 = const, nh lng nhit q1



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cho khng kh hay nc lm mt,3-4 l qu trnh tit lu trong van tit lu, p sut gim t p2 xung p1,4-1 l qu trnh bc hi dn bc hi trong bung lnh, mi cht nhn nhitlng q2 p sut p1 = const.



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Hnh 1-20 s my lnh nn hi Hnh 1-21 th T-s chu trnhmy lnh nn hiH s lm lnh:

v trong qu trnhtit lu i4 = i3, do :

(1-121)

Nng sut lnh ca my nn:

Cng sut ca my nn:N = G.l

y: G l lu lng mi cht trong chu trnh, kg/s.b.Bm nhit:

Bm nhit cn c gi l my iu ho hai chiu. Bm nhit c thlmlnh, ht m v cng c th si m, hin c dng kh ph bin minBcnc ta. Khi dng vi chc nng si m, bm nhit s tit kim c innngrt nhiu so vi dng l si in tr.

Nguyn l lm vic ca bm nhit nh sau: Mi cht trng thi bo hokh t bung lnh IV c my nn ht vo v nn on nhit t p sut p1n



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p sut p2, nhit t2. Sau i vo dn ngng II ngng t ng p psut p2, nh lng nhit q1 bin thng lng. Lng t dn ngng II i qua vantit lu III, gim p sut t p2 xung p1 v chuyn t dng lng sang dng hm, ri vo dn bay hi nhn nhit lng q2 . Nu s dng nng lnghu ch t dn bay hI (dn lnh, c b tr trong phng) th my lm vic

theo ch lm lnh; Nu s dng nng lng hu ch t dn ngng (dnnng, c b tr trong phng) th my lm vic theo ch si m (bmnhit). Trong thc t cc dn c b tr c nh, ch cn i chiuchuyn ng cu dng mi cht nh van i chiu.

S nguyn l ca bm nhit c th hin trn hnh 1-22. Ch cnthayi vai tr ng, m ca cc van, thit b c th lm lnh hoc si m.Thit b chnh gm my nn C, hai dn trao i nhit A v B, hai dn nythay nhau lmdn lnh (dn bc hi) hoc dn nng (dn ngng t); van tit lu D v ccvan

ng m t 1-8 thay i chc nng lm vic ca my. Mi cht c th lFron hoc Amniac. xt nguyn l vn hnh ca thit b, ta coi dn A ttrong phng.

2.4.Nhiet dung rieng:a. nh ngha:Nhiet dung reng cua mot chat nao o la nhiet lng can thiet

e nang nhiet o cua 1kg chat o len 1 0Cb. Cac loai nhiet dung rieng: Nhiet dung rieng khoi lng, ky hieu la C n v la J/kg 0C Nhiet dung rieng the tch, ky hieu la C n v la J/m3kg0K

Nhiet dung rieng kilomol, ky hieu la J/kmol0KQuan he gia cac nhiet dung rieng:

CCC == 0'.

v0 : the tch rieng ieu kien tieu chuan vat ly m3/kgNhiet dung rieng ang ap Cp, CP, C nhiet dung rieng xay ra ap

suat khong oi p= constNhiet dung rieng ang tch Cv, Cv, Cv nhiet dung rieng khi qua trnh

xay rao the tch khong oi V= const

Quan he gia nhiet dung rieng ang ap va nhiet dung rieng angtchCp Cv = RCp = kCv= k.R/k-1, J/Kg.K

k: he so mu oan nhiet , R : hng s cht khc. Nhiet dung rieng la hang so va nhiet dung rieng trung

bnh



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Vi kh ly tng, nhiet dung rieng khong phu thuoc vao nhiet ova la hang so c xac nh theo bang sau:

Vikh thc

nhiet dung rieng phu thuoc vao nhiet o nen ta co khai niem nhietdung rieng trung bnh. Nhiet dung rieng trung bnh t 00C en t0C c khieu tC

0va cho trong cac bang phu luc. Nhiet dung rieng trung bnh

t t1 en t2 c k hieu2

1

t

tC

hay Ctb, c xac bang cong thc tong quat [ ]122

1 010.2

12

1 tttt

CtCttt

C

=

2.5.Nhiet lng:Nhiet lng la lng nang lng dang nhiet co the lam thay

oi nhiet o hoac trang thai(pha) cua mot vat.Ngay nay ngi ta nh ngha nhiet la nang lng cua nhng

chuyen ong hon on cua cac phan t vo cung nho cua vatchat. ot nong mot vat len ngha la ta cap nhiet lam cho cac

chuyen ong cua phan t vat o tang len va khi lam lanh motvat len, ngc lai ta lam cho chuyen ong cua cac phan t giam iNhiet lng lam nong hoac lam lanh 1 vat c k hieu la Q n

v la Jun (J). nh ngha mot n v nhiet (J)

Joul (J) la n v nang lng (nhiet hoac cong). Mot nang lng 1Jc thc hien khi cho dong ien co cng o 1A chay qua day danvi ien the 1Vtrong thi gian 1 giay.

1J = 1W.S = 1N.mNhiet lng con co n v la cal. Mot cal la nhiet lng can thiet

e nang nhiet o cua 1 gam nc t 13,5oC len 14,5oC.He o lng Anh My s dung n v nhiet lng la BTU (British

Thermal Unit). Mot BTU la nhiet lng can thiet e nang 1 bl nc(454g) len 1oF (t 39oF len 40oF).

1 BTU = 252 cal

Cach tnh nhiet lng theo nhiet dung rieng khoi lng:Vi qua trnh ang ap:

( )12. ttCGQ p =


Loai kh Trso k

Kcal/kmol.0K KJ/kmol.0KCv Cp Cv Cp

Mot nguyen tHai nguyen t(N2,O2.)Ba hay nhieunguyen t (CO2,H2O)

1,61.41,3

357

579

12,620,929,3

20,929,337,7


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Vi qua trnh ang tch:( )12. ttCGQ =

Vi qua trnh a bien:

( )12. ttCGQ n =Trong cong thuc tren: Q: nhiet lng KJ Cp : nhiet dung rieng khoi lng ang ap, kJ/kg.0K Cv : nhiet dung rieng khoi lung ang tch, kJ/kg.0K Cn : nhiet dung rieng khoi lng a bien kj/kg.0K

a.Nhiet an nong chay va nhiet an bay hiL lng nhit cp cho vt cht, lm cho vt cht thay i trng thi(ha hi hoc ngng t)

Nhiet an hoa hi cua mot chat, la nhiet lng can thiet elam cho 1 kg chat o trang thai ran chuyen hoan toan sang trang

thai long ( ieu kien nhiet o va ap suat nhat nh), k hieu la qhl, kJ/kgNhiet an hoa hi cua mot chat la nhiet lng can thiet e

lam 1kg cua chat o trang thai long bien hoan toan thanh hi ieu kien nhiet o va ap suat khong oi, qua trnh ngng tunhiet lng thu c ung bang nhet lng hoa hi o, k hieu la r,kJ/kg

t 0CNhiet an hoa hi

1000

C Nhiet an ngng tu

Nhiet an hoa long00C

Nhiet an hoa ran-200C

10 90 190 559 Q,kcal

b.Nhit hin :L lng nhit lm cho nhit ca vt tng ln, nhit hin l lng nhit cung cp cho v

cht nhng vt cht khng thay i trng thi (lng rn, hoc ngc li)

CU HI V BI TP :A.CU HI :1. Lm lnh hoc t nng khng kh trong bnh kn, l qu trnh g ?



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2. Hy phn bit s khc nhau gia ng c nhit, bm nhit v my lnh ?3. Pht biu nh lut nhit ng hc 1 ?4. Pht biu nh lut nhit ng hc2 ?5. Th no l th tch ring ?6. nh ngha p sut, thit lp cng thc tnh p sut tuyt i ?

7. nh ngha kh l tng ? trnh by cc phng trnh trng thi ca kh l tng ?8. nh ngha chu trnh thun chiu ? trnh by hiu qu s dng nng lng ca chu trnh ?9. nh ngha chu trnh ngc chiu ? trnh by h s lm lnh ca chu trnh ?10. nh ngha v phn loi nhit dung ring ? trnh by cng thc tnh nhit dung ring trungbnh ?11. Hy gii thch v cho bit s khc nhua gia nhit n v nhit hin ?



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B.BI TP :Bai 1: Kh O2 ieu kien nhiet o t oC; ap suat d pbar.Biet ap suat kh quyen la 1 bar. The tch rieng (lt/kg) ?t=50

pd=100

B=1

=

32Bai 2: 1kg khong khco p1 (bar), t1 (oC), sau khi nen oannhiet ap suat tang len 10 lan. Tnh The tch rieng v2(m3/kg)?

Bai 3: 1kg khong kh co p1 (bar), T1(K), sau khi nen oannhiet ap suat tang len 5 lan. Tnh Cong ky thuat lkt(kJ/kg)?p1=

1

T1=2

88

p2=

5

=2

9

k=1.

4

Bai 4: Cho qua trnh a bien co V1(m3), p1(bar), V2 (m3), p2(bar). Tnh So mu a bien n?V1=12

V2=2.4

p1=1

p2=6

Bi tp 5: Xc nh th tch ring, khi lng ring ca kh N2 iukin tiu chun vt l v iu kin p sut d 0,2 at, nhit 127 0C.Bit p sut kh quyn 760 mmHg.Bi tp 6: Xc nh th tch ca 2 kg kh O2 p sut 4,157 bar, nhit 470C.Bi tp 7: Xc nh khi lng ca 2 kg kh O2 p sut 4,157 bar,nhit 470C.Bi tp 8:Tm nhit dung ring khi lng ng p trung bnh vnhit dung ring th tch ng tch trung bnh t 200 0C n 800 0Cca kh N2.



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BI 2CC PHNG PHP LM LNH NHN TOI. Khi nim chung:

Con ngi bit s dng lnh cch y rt lu. V ma ng ngi ta tr bng tuyttrong cc hang ng bo qun thc phm vo ma h. Ngi c Ai cp cng bit i hakhng kh bng cch qut cc bnh gm xp cho nc bay hi. Cch y 2000 nm, ngi n v trung quc bit trn mui vo bng tuyt to nhit thp.

Tuy nhin lm lnh nhn to vn l ch yu, c ng dng rng ri trong cc lnh vc kinht, k thut khc nhau.

Lm lnh nhn to bt u vo cui th k 18 v pht trin mnh m th k 19Nm 1824, Micheal Faraday khm ph nguyn l lm lnh hp thNm 1834, Jacob perkin, k s ngi m, ng k pht minh u tin v lm lnh nn hiNm 1910, t lnh gia dng hot ng bng tay xut hin. Xut hin t lnh t ng u tin

vo nm 1918Mt s kin quan trng cho s pht trin k thut lh l nm 1930, hng Dupont sn xut ra

cc mi cht h FREON, c cc tnh tnh cht nh khng chy, khng n, khng c hi v ph hpvi chu trnh nhit ng ca my lnh.

Ngy nay bn cnh vic tm ra cc mi cht mi khng ph hoi tng zon, k thut lnhpht trin theo hng hon thin h thng iu khin tin cy, nh iu khin bng lp trnh PLC, ng vai tr rt ln trong k thut lnh hin nay.II.Cc phng php lm lnh nhn to:1. Phng phap hoa tron :

a. Cc dung dch lm lnh:ay la phng phap lam lanh n gian, co the tao moi

trng nhiet o thap t nhng vat chat co nhiet o cao hnNc lnh + mui _ nhit gimng dng : dng trong dnh c bien .vvv

Th du : khi tron muoi an Nacl vao nc a xay nhuyen vi tle thch hp, ta se co dung dch nc muoi 21 oc

b. ng dng:Do tnhcht n gin, phng php ny c s dng nhiu trong thc t nh: bo qun

kem, bo qun c..Cc dung dch v nng khc nhau s cho nhit khc nhau. Dung dch thng gp l

NACL, Cacl22. Phng php bay hi khuych tn:

a. My lnh hp th:My lnh hp th s dng trc tip ngun nhit nng, nh: nhit tha, th cp, mt tri, nhit thicng nghipb phn chuyn ng duy nht l cc bm dung dch, gii nhit.

Khuyt im l h thng lnh hp th c h s lm lnh nh, nn tn hao nng lng ln, chimdin tch ln khi lp t v tiu th nc gii nhit ln.

Phn loi v nguyn l lm vic ca my lnh hp th:Da theo nguyen ly lam viec cua MLHT H2O-LiBr ngi ta chiachung ra lam 4 loai:

Single Effect:



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Double Effect

Triple Effect

Half Effect

S o nguyen ly cua may lanh hap thu H2O-LiBr loai SingleEffect c trnh bay Hnh 1.6. Trong s o nay, ta goi A la bnhphat sinh (Generator), B la bnh ngng tu (Condenser), C la bnh bayhi (Evaporator), D la bnh hap thu (Absorber), HE la thiet b traooi nhiet va E la bm dung dch.

N c l am m at

N c can lam l a nh

B m c ha n k h o ng

N c lam m a t

O ng chon g k e t tinhH E

D

O n g gi am ap

H i g i a nh i e t

C

A

B

Hnh 2.1 May lanh hap thu H2O-LiBr loai SingleEffect.

Qua trnh thc hien cua may lanh hap thu H2O-LiBr da vaoac tnh cua dung dch H2O-LiBr nhiet o thap no hap thu hnc rat manh, con nhiet o cao lai giai phong hi nc ahap thu. Da vao ac tnh nay e hoan thanh chu trnh congtac.

Dung dch loang trong bnh hap thu D c bm qua HE vao bnhphat sinh A, dung dch c hi nc gia nhiet, v nc co nhieto soi rat thap so vi LiBr do o dung dch loang c gia nhieten nhiet o nhat nh. Hi tac nhan lanh trang thai qua



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nhiet bay ra t bnh phat sinh vao bnh ngng tu B c lam matbang nc giai nhiet va ngng tu thanh long tac nhan lanh.

Long tac nhan lanh i qua ong tiet lu ch U vao bnh bay hiC va c bm len phun thanh giot nho tren be mat chum

ong bay hi.Nc tac nhan lanh hap thu nhiet cua nc can lam lanh vabay hi, hi tac nhan lanh i qua tam chan phan ly nc roi ixuong bnh hap thu D. Dung dch trung gian trong bnh hap thuc bm ay phun giot nho e hap thu hi tac nhan lanh vatr thanh dung dch loang, trong qua trnh hap thu co san sinhra nhiet nen can phai lam mat cho bnh hap thu.

S o cap dch noi tiep

H E 2

N c l am m at

O ng gi am ap

A PG P

E P

D

H E 1

N c ca n l am l a n h

N c l a m m a t

A B C

B

H i g i a n hi e tA

Hnh 2.2. May lanh hap thu H2O-LiBr Double Effect cap dch notiep

S o nguyen ly cua may lanh hap thu H2O-LiBr loai DoubleEffect c trnh bay Hnh 1.8. Trong s o nay, ta goi A la bnhphat sinh (Generator), AB la bnh phat sinh ngng tu, B la bnh ngng



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tu (Condenser), C la bnh bay hi (Evaporator), D la bnh hap thu(Absorber), HE1 & HE2 la thiet b trao oi nhiet, GP la bm dungdch cho bnh phat sinh, AP la bm tuan hoan cua bnh hap thuva EP la bm tuan hoan cua bnh bay hi.

Thong thng bnh phat sinh bao gi cung che tao rieng motthung. Phan con lai co the che rieng hoac ghep vao nhau.

S o cap dch song song

H E 1

G PP

D

E

N c l am la nh

T

H i g i a n h i etA

A P

N c gi ai nh iet

E P

H E 2

H E 3 N c ng ng

N c g ia i n hie t

A B

B

Hnh 2.3. May lanh hap thu H2O-LiBr Double Effect cap dchsong song

Dung dch tuan hoan

Trong s o nay ng dung dch loang t bm phat sinh chia ra

lam 2 ng:- ng th nhat: Dung dch loang c ay qua TBTN

nhiet o cao HE1, dung dch c gia nhiet en nhiet o t 3, oan2-3 la qua trnh gia nhiet dung dch loang trong TBTN nhiet ocao. Sau o dung dch loang c ay vao bnh phat sinh A e gianhiet en trang thai 3 va soi ap suat ph tao nen hi tacnhan lanh, nong o dung dch thay oi dan en ci (iem 4) trang



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thai 4 la trang thai cuoi cua qua trnh phat sinh dung dch trongbnh phat sinh A. oan 3-3-4 la qua trnh thc hien trong bnh phatsinh A. Dung dch trung gian t bnh phat sinh A (iem 4) chay qua

TBTN nhiet o cao HE1 b lam lanh en iem 5 co nhiet o t5va chay ve bnh hap thu, trong qua trnh chay vao bnh hap thu

ap suat giam xuong ap suat p0 (trang thai 6), tren o th h-cxem iem 6 va iem 5 trung nhau nhng iem 6 bieu th trangthai hi am ap suat p0, con iem 5 la dung dch qua lanh ap suat ph.

- ng th hai: Dung dch loang chay qua TBTN nhiet othap HE2 c gia nhiet va ra trang thai 7 (nhiet o t 7, nongo khong thay oi) roi chay qua TBTN phu c gia nhiet eniem 8 (nhiet o t8), ap suat dung dch iem nay cao hn apsuat p0. bnh phat sinh ngng tu AB dung dch c gia nhiet vasinh hi, hi tac nhan lanh bay ra va dung dch tr thanh dungdch am ac co nong o cs, oan 9-9-10 la qua trnh cuadung dch xay ra trong bnh phat sinh ngng tu AB.

Dung dch am ac trang thai 10 chay qua TBTN nhiet othap HE1, nhiet o giam xuong en t11 nong o khong thayoi (trang thai iem 11), sau o chay vao bnh hap thu, trongkhi chay vao bnh hap thu ap suat tiet lu giam xuong p0 (trangthai iem 12). Tren o th iem 12 va iem 11 trung nhau,nhng iem 12 la trang thai hi am co ap suat p0.

Dung dch c bm hap thu hut vao la dung dch bao hoa

iem 6 va iem 12 (iem 6 va iem 12) hoa tron vi dungdch iem 1 (iem 13 nam tren ng noi lien iem 6, 12 va1). Dung dch trang thai 13 qua bm c tang ap (13-14) nhngnong o khong thay oi, nhiet o c ban cung khong thay oi,iem 13 va 14 trung nhau, dung dch nay c phun giot lenchum ong truyen nhiet cua bnh hap thu, hap thu hi tacnhan lanh va tr thanh dung dch loang iem 1.

ng dung dch mac noi tiep

Bm phat sinh ay dung dch loang t bnh hap thu qua thiet

b trao oi nhiet (TBTN) nhiet o thap HE2 roi qua TBTN nhieto cao HE1 sau o i vao bnh phat sinh A. Trong bnh phat sinhdung dch c gia nhiet va sinh ra hi tac nhan lanh dung dchloang bay hi va bien thanh dung dch co nong o trung gian,dung dch nay chay qua TBTN nhiet o cao HE1 roi i vao bnhphat sinh ngng tu AB. bnh phat sinh ngng tu AB dung dchtrung gian c gia nhiet sinh ra hi tac nhan lanh co nhiet o



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thap va dung dch con lai la dung dch am ac sau o dungdch am ac i qua TBTN nhiet o thap HE2 roi i vao bnhhap thu.

ng hi tac nhan lanh

Hi tac nhan lanh i ra khoi bnh phat sinh A i qua chum ongtrao oi nhiet bnh phat sinh ngng tu AB, nha nhiet an hoahi va bien thanh nc tac nhan lanh va chay vao bnh ngngtu.

Hi tac nhan lanh t bnh phat sinh ngng tu AB cung i vaobnh ngng tu B, c lam mat bang nc giai nhiet va ngngtu thanh nc tac nhan lanh.

Nc tac nhan lanh

Nc tac nhan lanh t bnh ngng tu B i qua c cau tiet lu

ch U chay vao bnh bay hi. ay nc tac nhan lanh soi ap suat thap va lam lanh nc can lam lanh. Hi tac nhanlanh sinh ra bnh bay hi co ap suat thap i vao bnh hap thu,b dung dch am ac hap thu va bien thanh dung dch loang.

b. T lnh hp th khuych tn:

Trong nguyn l my lnh va kho st, i vi cng sut nh, vn t ra l lm saoloi b bm dung dch thun tin hn trong s dng, dn bay hi p sut thp, dn ngngt p sut cao, bm dung dch dng thng chnh lch p sut ny.



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Hinh 2.4 My lnh hp th khuych tn

Hnh trn m t nguyn l lm vic ca my lnh hp th khuych tn. H thng nydng cp mi cht NH3/H2O v cht khuych tn l H2. khi cung cp nhit cho bnh sinhhi 1, hi NH3 v H2O thot khi bnh sinh hi, theo ng 2 n b phn tch (separator)3nc ha lng v v b hp th(absorber) trong khi hi NH3 tip tc theo ng n b ngngt (condenser) bin thnh NH3 lng. NH3 lng chy vo b bc hi(evaporator) bchi sinh lnh. Hi NH3 tr v b hp th v gp H2O, bin thnh dung dch no v tr v

bnh sinh hi tip tch chu trnh.

Qu trnh hp th s gii phng kh H2 v kh H2 khng ha ln vo H2O, v rt nh nntheo ng ng pha trn b hp th tr li b bc hi..

Tm li, ta c th gii thch nguyn l lm vic ca t lnh hp th khuych tn nh sau:ti mi im ca h thng, p sut tng bng p sut ngng t nhng p sut ring phn ca

NH3, H2O, v H2 thay i sao cho NH3 c th ngng t v bc hi cc nhit tngng



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3. Phng php hiu ng nhit :

Phng php ny cn c gi l hiu ng peltier(M). nu cho dng in mt chiu i quavng dy dn gm 2 kim loi khc nhau th mt u s nng ln, mt u ngui i. lhiu ng ngc vi pin nhit in. hiu ng nhit in c th t n 60K.

Hnh 2.5 Phng php hiu ng nhit in

Khi c Ito nn th = 1 - 2

u im chnh ca loi my lnh dng hiu ng nhit in l khng c phn chuyn ngnn khng n, gn nh, khng cn mi cht lnh, nhng hiu sut thp, gi thnh cao.

4. Phng php bay hi chu trnh:

Qu trnh bay hi cht lng gn lin vi qu trnh thu nhit. cht lng bay hi ng vai trquan trng trong k thut lnh nh l mi cht lnh v cht ti lnh. Cc mi cht lng my lnh nn hi, hp th, l NH3, nc, Freon u thu nhit ca mi trng khi ngng t nhit cao v p sut cao

Do o neu s dung cac chat long co nhiet o soi cangthap, cam giac lanh cang ro ret, cac chat co nhiet o bayhi thap nh C4H10 ( gas bat la) ap suat kh quyen co nhieto soi 0,4oc, nit co nhiet o soi ap suat kh quyen en-196oc. Khi can nhiet o soi cao hn ta phai lap them van ekhong che.

5. Phng php gin n kh c sinh ngoi cng:

y l phng php lm lnh nhn to quan trng. cc my lnh lm vic theo nguyn lgin n kh co sinh ngoi cng gi l my lnh nn kh. Phm vi ng dng rt rng ln t

my iu ha khng kh cho n cc my s dng sn xut Nit , oxy, ha lng khng khv tch kh, ha lnh kh t..

Nguyn l lm vic ca my lnh nn kh:



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Hnh 2.6 My lnh nn kh

My lnh nn kh gm 4 thit b chnh: my nn, bnh lm mt, my gin n kh v bunglnh. Mi cht lnh l khng kh hoc mt cht kh bt k. khng bin i pha trong chutrnh. Khng kh c nn on nhit S1 = Const t trng thi 1 n trng thi 2. chu trnhlm mt my thi nhit cho mi trng p sut khng i n trng thi 3, sau cgin n on nhit s3 = const xung trng thi 4 c nhit thp v p sut thp.

Trong bung lnh, khng kh thu nhit ca mi trng p sut khng i v nng dn lnim 1, khp kn vng tun hon

Nh vy chu trnh my lnh nn kh gm hai qu trnh nn v gin n on nhit vi hai qutrnh thu v thi nhit ng p nhng khng ng nhit.



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BI 3

MY NN LNH1.Cng dng ca my nn

Trong h thng lnh, my nn c cng dng:

- Ht hi t TBBH v, nhm duy tr 1 p sut bay hi khng i Po trong TBBH.

- Nn hi ln p sut cao, nhit cao PKTKy vo TBNT.

- Bo m 1 lu lng mi cht tun hon lin tc trong h thng lnh, ph hp vi phti nhit ca dn bay hi v dn ngng t.

Yu cu: My nn phi lm vic n nh, c tui th v tin cy cao, khng n, khng rungng, r tin, c ph tng thay th..

2. Phn loi

C nhiu cch phn loi my nn nh sau:

a. Theo cu toMy nn piston, my nn Rotor, my nn xon c , my nn tuabin, my nn trc vt, MN ly

tm.

b. Theo tc nhn lnh

My nn Amoniac, my nn Freon

c. Theo nng sut lnh Qo v cng sut u trc N

My nn nh: Qo 8000 Kcal/h ; N 5 KW ( 7,5 HP )

My nn trung bnh: 8000 Kcal/h < Qo < 50 000 Kcal/h; v 5KW < N < 20 KW.

My nn ln: Qo 50 000 Kcal/h ; v N 20 KW.( thng t 30 HP tr ln)

Nng sut lnh

L nhit lng m my lnh ly c t mi trng cn lm lnh trong 1 n v thi gian.

K hiu: Qo. n v: Kcal/h ; BTU/h.; Kw ; Tn lnh.

d. Theo nhit bay hi

Khi To = +10oC -25oC (my nn 1 cp)

Khi To = -30oC -110oC (my nn 2 hay nhiu cp)

e. Theo cch b tr, sp xp xilanh

My nn c xilanh nm ngang.

My nn c xilanh thng ng.

My nn c xilanh ch V, W

f. Theo cch chuyn ng ca hi gas qua xilanh



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My nn trc lu (Thun dng): L MN c dng hi chuyn ng khng i hng trongxilanh.

My nn khng trclu ( Ngc dng): L MN c dng hi b i hng trong xilanh.

g. Theo s xilanh

My nn c 1 xilanh My nn c nhiu xilanh

h. Theo kn v kh nng tho rp

My nn kn: Phn c v phn in nm chung trong 1 v kn, khi sa cha phi ca vmy..

My nn na kn: Phn c v phn in nm chung trong v my nhng vn tho rp c.

My nn h: Phn c v phn in c lp vi nhau. Tho rp d dng. My nn vn hnhc phi nh 1ng c in ko qua trung gian ca dy cuaroa.hay khp ni.

i. Theo s vng quay My nn quay chm: n < 550 vng/pht.

My nn quay nhanh: n 1500 vng/ pht.

3. Phn loi theo hnh dng:

3.1.My nn h :

My nn h l my nn c cm bt kn u trc , ng c in v my nn c t ring vtruyn ng = dy ai.

Hnh 3.1a My nn h



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Hnh 3.1 b My nn h b ct

u im :

- C th thay i tc my nn bng cch thay i iu khin bnh ai do c th thayi c nng sut lnh ca my nn

- ng c v my nn c t ring nn lp t, sa cha, bo tr

Nhc im :

- Din tch lp t ln

- D x h du v gaz qua cm pt kn qua u trc

3.2.My nn na kn :

ng c in v my nn c lp ng trc.



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Hnh 3.2 My nn na kn

My nn ny gii quyt c vn c bn l chuyn v tr bt kn c trc quay sang m knmt bch tnh

Thng ngi ta b tr ng ht i ngang qua ng c s dng sc lnh ca hi ht v

lm mt ng c

Nhc im:

- Khng thay i c tc vng quay ca my nn.

- Khng s dng c tv nhn l Amoniac.

3.3.My nn kn :

My nn kn thng c s dng trong cc h thng lnh nh, cc thit b thuc in lnhgia dng v thng nghip. Hin nay, cng sut ca lc kn c th t c 15 HP



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Hnh 3.3. My nn kn

My nn c gi l kn v tan b ng c v my nn c t trong v hn kn

u im : nh gn, d s dng, khng x h, lm vic vi cao

Nhc im : kh sa cha.So snh My nn h , kn v kn

Cng sut X h Sa cha bo tr

My nn h Ln D x h D

My nn kn Trung bnh t x h Trung bnh

My nn kn Nh Khng x h Kh

4. Phn loi theo nguyn l lm vic:

4.1.My nn pittong thng:

4.1.1.My nn piston ng thun dng

a. Cu to

Hnh 3.4: Cu to My nn Piston

ng thun dng



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Hi mi cht vo ra xilanh theo thng t di ln trn . My nn ng thun dng thngl c trung bnh v c ln dng NH3 l tc nhn lnh.

b. Hot ng:

Hi gaz s i vo gia xilanh , clap ht c b tr trn nc Piston, khi Piston di chuyn t

trn xung di do qun tnh clap ht s c n ra, hi gaz NH3 s i t di Piston xuyn quaPiston vo trong lng xilanh , khi Piston i t di ln trn clap ht s ng li , hi gaz trongxilanh s nn ln p sut P m clap y that ra ca y

c im : V s dng tc nhn lnh NH3 nn p sut cui qu trnh nn rt cao nng xilanhrt nng cho nn gii nhit cho xilanh ngi ta b tr o nc lm mt

trnh va p do ht bi tc nhn th lng ngi ta b tr mt tm chn v l xo an ton.Nu tc nhn ht vo th lng p sut trong lng xilanh s rt ln tm chn s b i ln tc nhnlnh s that ra ngoi ra ca y

Ch : L xo phi chu c p sut ln ngng t PK

u im :

- Khng c tn tht trao i gia khoang ht v khoang y

- C kh nng thit din clap ht v y

- Clap ht hat ng t tn tht do ng m theo qun tnh

Nhc im :

- Hi gaz s i xung di cacte ha tan vi du lm gim kh nng bi trn

- Khi lng ca Piston ln do lc qun tnh v lc ma st s ln kh ch to mynn ng thun dng vi tc vng quay ln

- Do clap ht b tr trn np Piston ch to kh khn hn v cng knh hn dn n unn thng cao so vi my nn ngc chiu

4.1.2.My nn piston ngc dng

a. Cu to

Hnh 3.5 Cu to My nn Piston

ngc dng

b. Hot ng



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My nn piston ngc dng da vo nguyn l hot ng :Bin chuyn ng quay trn cact my (trc khuu) thnh chuyn ng tnh tin ca piston trong xilanh:.

Hi mi cht c ht vo xi lanh qua spp ht khi piston i t trn xung di, lc spp nnng li, khi piston vt qua im cht di i ln trn th spp ht ng li, hi mi cht cnn ln p sut cao ri y ra ngoi qua spp y

4.2. My nn roto:

Hin nay ang c pht trin mnh , thng c cng sut b , s dng rng ri trong my iuha gia dng v mt s t lnh c ln. C 2 loi my nn Roto thng dng l my nn Roto ln vmy nn Roto tm trt

a. My nn Roto ln:

Hnh 3.6: Cu to My nn My

nn Roto ln:

Hot ng : khi piston lntrong xy lanh s tn ti hai khoang , khoang ht s tng dn khoang

y s nh dn ,khi piston trn nh th tch khoang y s bng 0 th tch khoang ht l lnnht .khi Piston ln qua khi nh xy lanh th li bt u qu trnh nn , khoang y v khoang ht lixut hin

u im :

- Lu lng ht y ln, kch thc v trng lng nh

- t chi tit chuyn ng

- C th gn trc tip MN v ng c nn s lm vic n gin.

Nhc im :

- Kh ch to do i hi chnh xc cao- mi mn ca tm trt ln

- Kh bi trn

b. My nn Roto tm trt :



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Hnh 3.7: Cu to My nn My nn Roto tm trt

Hat ng:

My nn rotor quay c trc ca rotor khng trng vi trc xilanh, trn rotor c x rnh cctm chn trt c. Khi rotor quay, di tc dng ca lc ly tm, cc tm chn s trt theo rnhra ngoi v ta vo mt trong ca xilanh chia ct khong trng gia xilanh v rotor thnh nhiukhoang ring bit, phn trn c th tch ln nht, phn di c th tch nh nht. Hi t ng htc cc tm chn ht vo v nn trong cc khoang, ri tin n ca y vt qua spp nn thotra ngoi.

4.3. My nn trc vt:

L loi my nn c hai trc quay nm song song vi nhau c rng xon hnh xon c mttrc mt rn li (lm) mt trc 56 rng lm. C hai trc c t trong mt thn my c caht v ca y



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Hnh 3.8 a my nn trc vt

Khi chuyn ng gii hn gia hai rng s gim dn thc hin qu trnh nn. Hin naymy nn trc vt c s dng trong cc h thng my ln .



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Hnh 3.8b My nn trc vt b ct



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u im:

- Nh gn , cng sut ln

- T s nn cao do khng c khong cht.

- kn rt cao.



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BNG SO SNH S KHC BIT GIA MN PISTON V MN ROTOR.

5.Tho lp my nn pittong:

1.3.1. Thn my:

Thn my cn c gi l cacte hay block cacte, n l v bc ngoi ca my nn, c nhim vg cc b phn nh bm du, bc n, trc khyu, piston, xilanh. Do yu cu thn my phi nng v n nh. Bn trong thn my phi c khng gian rng cha du bi trn, quan st lng du ngi ta lm mt ca king. Ngoi ra ngi ta cn lm mt ca thao tc sacha

Thn my c bng gang xm v ch to bng = phng php c. Khi c yu cu gim nhkhi lng ta c th ch to thn my bng hp kim nhm

Cc v tr gia cng c kh trn my nn phi m bo chnh xc cao nh ng tm, vunggc

1.3.2. Xilanh:

Xilanh l b phn c nhim v cha hi gaz ht vo i vi my nn nh xilanh c c cngvi thn my. i vi my nn ln th xilanh c c ring bng vt liu cht lng cao. Sau c lp vo thn my ta gi l smi xilanh.


MY NN PISTON MY NN ROTOR

* u im- Chnh xc, rt bn.

- u y nn trc tip.

- Tc gas i nhanh.

- Thng dng cho h thng lnh c lnh su

*Khuyt im

- Kt cu cng knh, phc tp, cngngh ch to i hi tnh chnh xc caoca chi tit my.

- Gi thnh cao

* u im- Kt cu n gin, gn, nh.

- Khng c spp ht, nn gin tip.

- Thng dng cho my lnh

- Cn bng tt nn c th b tr trn cao.

- t chi tit chuyn ng nn c tin cy trongvn hnh. Gi thnh r

*Khuyt im

- u ht ca xilanh v rotor phi kn.- Cc tm chn d b mi mn, khng dng cho h

thng lnh c lnh su

- Khng bn


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Hnh 3.9 XILANH

Xilanh c ch to vi chnh xc cao, khe h gia xilanh v Piston loi c xc mng =1/1000 ng knh , xilanh c ng knh b hn 5mm th ngi ta khng dng xc mng , trongtrng hp ny khe h = 3/1000 ng knh .

B mt ca lng xilanh c gia cng rt bng, bng t c l cp 1013 v phi qua qutrnh my nghin. i vi my nn NH3 v i khi R22 , do nhit cui qu trnh nn rt cao nnu xilanh c b tr o nc lm mt . Cc my nn khc c b tr cch tn nhit , mt s trnghp khng cn cnh tn nht

1.3.3. Piston:Piston c dng hnh tr, thng c ch to bng nhm hoc hp kim nhm gim qun

tnh . trnh mi mn xilanh v piston , vn tc ca Piston khng vt qu 4m/s . Vi my nn nhtc c th tng ln. Loi Piston dng cho my nn ngc chiu khng c clap ht b tr trn uPiston gi l Piston khng thng



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Hnh 3.10 PITTONG

Loi Piston dng cho my nn thun chiu u Piston c gn clap ht gi l Piston khngthng, hi gaz c th i xuyn qua Piston .

1.3.4. Xc mng:

Xc mng c nhim vu bt kn khang h gia piston v xilanh dn ddu bi trn ln uxilanh, tng ng vi hai nhim v c 2 Xc mng l Xc mng du v Xc mng kin

Hnh 3.11. SECMANG



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Hnh 3.11 b cch lp t semang

Xc mng kn c th lp t hai n bn chic . Xc mng du c th lp t 12 chic vtrong c khoan cc l phn b du bi trn

Xc mng c lm bng vt liu n hi v chu c s mi mn

1.3.5. Tay bin:

Tay bin : bin chuyn ng quay ca trc khyu thnh chuyn ng tnh tin. Tay binc lm bng thp c hai l, l nh trn c lp c Piston, l di c lp vi trc khyu. chng mi mn ngi ta lp bc cc trc khyu .



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Hnh 3.12 Tay dn

1.3.6. Trc khuu:



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Trc khyu : l trc chnh ca my nn . Trong cc my nn c va v c ln, mt trc uca trc khy c lp bnh ai, u kia c lp bnh rng truyn ng cho bm du. Hai u trcc lp trn hai . gia c lp vi tay bin ty theo s xilanh ca my s tay bin s tngng , trong trc c khoan l hay lm rnh dn du bi trn n cc b mt ma st

Hnh 3.13 Trc khy

Trc c ch to bng thp, cc l trc phi ng tm, cc phn lp rp phi c bng caov c ti chng mi mn

1.3.7. Cc van ht v y:

Lm vic t ng theo hiu p sut khi p sut ht trong xilanh gim xung nh hn p sutht trn 0,3Kg/cm2 th van ht t ng m. Nu p sut trong xilanh tng cao hn p sut tng y

0,7Kg/cm

2

th van y t ng m. Cc l van c ch to bng thp n hi c dy 0,2

2mm trng thi cn bng cc van t ng kn nh lc n hi ca chinh n hay lc l xo . hn chng m ca cc l van ngi ta ch to cc ca van gn .



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Hnh 3.14 l van ht v y



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1.3.8. Cm bt kn c trc:

Cm bt kn c trc c nhim v bt kn cc trc quay trong my nn h mi cht trong khng l r ra ngoi v trnh khng kh t ngai vo trong my nn . B phn ny phi chu cnhit cao v s n mn ca du gaz

1.3.9. Van an ton:Van an ton c nhim v m bo p sut y khng vt qu mc cho php gy nguy himh hng thit b

Hnh 3.15 Van an ton

1.3.10. Van khi ng:

Van khi ng i vi my nn ln gim ti khi khi ng. Khi khi ng lm cho mynn khi ng d dng, ngi ta b tr mt van khi ng . Khi khi ng ngi ta ng van ht vvan y v m van khi ng lm cho u ht v u y ca my nn thng nhau lc cngnn khng cn ng k , cng sut ng c ch khc phc ma st v qun tnh cc chi tit khcsau khi khi ng xong ngi ta m cc van y v van ht ri kha van khi ng li .

1.3.11. C cu bi trn:

C tc dng lm gim ma st v mi mn cc chi tit . C 2 phng php bi trn l btrn =t du v bi trn =bm du

a. Phng php t du:

C nhng cch t du c b tr trc khy. Khi trc khy quay cc cnh ny s t du lncc b mt chi tit bi trn



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b.Phng php bm du:

Bm du l ht du v bm ln p sut nht nh sau du s theo cc ng bi trn ncc v tr cn tht, c hai loi bm du: bm du bnh rng v bm du Roto

Hnh 3.16. Bm du



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Bai 4 :THIET B TRAO OI NHIET4.1THIT B NGNG T

4.1.Cng dng & phn loi

a. Cng dng: TBNT l TBTN dng :

Gii nhit cho hi mi cht p sut, nhit cao, ngng t thnh lng cao p.

Thi ra mi trng xung quanh 1 nhit lng Qkm h thng lnh ly c phng lnh.

i khi trong TBNT cng xy ra s qu lnh lng mi cht.

TBNT cng c nhim v nh 1 bnh cha cao p trong vi loi HTL t hp.

b. V tr

TBNT c Lp t lin k sau my nn.

c. Phn loii. Theo cht gii nhit

Thit b ngng t gii nhit bng khng kh (i lu cng bc hay t nhin)

Thit b ngng t gii nhit bng nc (i lu cng bc)

Thit b ngng t gii nhit bng khng kh v nc.

ii. Theo qu trnh lm mt

Thit b ngng t lm mt cng bc

Thit b ngng t lm mt t nhin

iii.Theo cch ngng t TBNT c mi cht ngng t b mt trong ng trao i nhit

TBNT c mi cht ngng t b mt ngoi ng trao i nhit.

iv. Theo cu to

Thit b ngng t ng v trm nm ngang

Thit b ngng t ng v thng ng

Thit b ngng t ng lng ng.

TBNT kiu bay hi.

TBNT kiu phn t.

TBNT kiu xi ti.

4.1.1.Thit b ngng t gii nhit bng nc:

a. Thit b ngng t ng v chm nm ngang

i. Cu to



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Hnh 4.1: Cu to thit b ngng t ng v chm nm ngang

ii. Hot ng

Bnh ngng t kiu ng v nm ngang thng c s dng cho cc h thng lnh va vln (20KW tr ln).

Hi mi cht c p sut, nhit cao t my nn ti c a vo pha trn ca bnh ngngqua van s 3 v chim y khng gian gia cc ng trao i nhit , c lm mt nh nc chytrong ng, mi cht b ngng t li thnh lng c ly ra t pha y bnh (ng ng s 10). Bnhngng c 2 np 2 u trn c 2 ng nc vo ra v nhng vch ngn to hnh trnh chonc gii nhit.

i vi bnh ngng NH3 th ng trao i nhit lm bng st, thp v khng c cnh.( ngtrn )

i vi bnh ngng Freon th ng TN lm bng ng, c cnh.

b. Thit b ngng t kiu ng lng phn ti. Cu to



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Hnh 4.2: Cu to thit b ngng t ng kiu ng lng phn t

ii. Hot ng

L TBNT gm nhng phn t ring bit ghp vi nhau thnh t hp. Mt phn t ging nh

1 TBNT ng chm nm ngang. Cc phn t c ghp ni tip nhau theo ng hi mi cht vghp song song theo ng nc gii nhit.

Nc lm mt c a t pha di ng gp dn qua cc phn t v ra ng gp pha trn.Hi mi cht c a vo phn t trn cng in y khng gian cc ng di chuyn t trn xungdi v ngng t chy xung bnh cha.cao p.

iii.u nhc im:

u im : Chc chn v nh nhng., d lp t.

Nhc im : Kh lm sch cu, cn trn b mt trao i nhit.

c. Thit b ngng t kiu ng lng ng

i. Cu to

Hnh 4.3: Cu to thit b ngng t kiu ng lng ng

ii. Hot ng

Thit b ngng t kiu ng lng ng thng gii nhit bng nc gm c 2 ng lng vonhau, ng ngoi c ng knh 57 mm, ng trong c ng knh 38 mm. Ty theo loi m mi chtlnh s di chuyn ng trong hoc ng ngoi (Tng t vi nc gii nhit) nhng nguyn tc di

chuyn gia nc v mi cht lnh phi ngc chiu nhau nhm tng cng s trao i nhit.iii.u nhc im:

u im : Hiu sut ngng t rt ln.

Nhc im : Kh lm v sinh ng ng nc gii nhit, d b x v pha nc gii nhit.

4.1.2.Thit b ngng t gii nhit bng nc v khng kh

a. Thit b ngng t kiu xi ti



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i. Cu to

Hnh 4.4: Cu to thit b ngng t kiu xi ti

Hot ng :

Thit b ngng t kiu xi ti c gii nhit bng nc, ti t trn xung di ph y ccng trao i nhit thnh tng mng mng bao quanh ng.

Hi mi cht c p sut cao, nhit cao i trong ng ta nhit ra cho nc lm mt. Nc bbay hi nh khng kh, 1 phn ri xung b nc. Nh vy phi b p bng 1 lng nc b sung,lng mi cht ngng t xong c a vo bnh cha cao p t n van tit lu vo dn lnh lm lnh.

ii. u im

Khng nguy him, ch to d dng, c th s dng nc khng qua x l, thng c tngoi tri, li dng gi tri lm mt nc, tit kim in nng .

iii.Khuyt im

Nc gii nhit ph thuc vo mi trng xung quanh , thit b cng knh, nhiu cu bn vc n mn ln.



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b. Thit b ngng t kiu bay hi

i. Cu to v Hot ng

Nhm lm gim lng nc phi bsung (Cng l lng nc tiu hao) v gim

in nng tiu th, ngi ta dng TBNT kiubay hi. Khng kh c cng bc chuynng nh qut gi ht t di ln ngcchiu vi nc lm mt ti t trn xungdi to thnh mng xung quanh ng trao inhit. Nc lm nhim v gii nhit hi micht, cn khng kh va lm mt hi micht, va lm mt nc, do nhit nclc vo v ra gn nh khng thay i .

Hnh 4.5: Cu to thit b ngng t kiu bayhi

Hi mi cht vo ng trao i nhit ta nhit cho nc v khng kh, sau ngng t li thnh lng,chy vo ng gp lng ri ti bnh cha. Lng nc b sung nh 1 van phao b p lng nc b cuntheo gi.

i. u im

Gn, nh, hiu sut ta nhit cao, thng c s dng cho h thng lnh va v nh.

ii. Khuyt im

Nhit khng kh ti ni t thit b ph thuc vo mi trng xung quanh.

4.1.3.Thit b ngng t lm mt bng khng kha. Lm mt t nhin

Hnh 4.6: Cu to thit b

ngng t lm mt

t nhin bng khng kh

Ch s dng cho h thng lnh nh v rt nh nh T lnh gia nh. Thit b ngng t loiny phi t ni thong mt d i lu khng kh.



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b. Lm mt cng bc

Hnh 4.7: Cu to thit b ngng t lm mt bng khng kh cng bc

Hot ng:

Trong cc loi Thit b ngng t ny, ngi ta dng cc ng trao i nhit thng bng ng (haythp) v co ch U lin kt chng thng nhau. Mi thit b c 2 hoc nhiu ng ni song song vinhau. Cnh tn nhit thng c lm bng nhm, c chiu dy 0,3 mm v bc cnh l 3,5 mm.Khong cch gia 2 ng l 26 mm. Khng kh s c qut cng bc i xuyn qua TBNT. Hi tcnhn c a vo pha trn Thit b ngng t , cn lng tc nhn c ly pha di.

4.2.THIT B BAY HI

a.nh ngha

L thit b trao i nhit dng lm lnh mi trng no , nh vo s bay hi nhit thp ca tc nhn lnh trong ng trao i nhit.

b.Phn loi:

C nhiu cch phn loi nh sau:

1.Theo mi trng lm lnh

Thit b bay hilm lnh cht lng .vd : (Nc, nc mui)

Thit b bay hilm lnh khng kh .

2.Theo cch vn ng (S trao i nhit)

Thit b bay hilm lnh trc tip (Tc nhn lnh si trong ng trao i nhit)

Thit b bay higin tip (Cht ti lnh chy trong ng trao i nhit)

3.Theo cch chon ch ca tc nhn Thit b bay hikiu ngp

Thit b bay hikiu khng ngp

4.2.1.Thit b bay hi lm lnh cht lng

a. Thit b bay hi ng v kiu ngp

i. Cu to



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Hnh 4.8: Cu to Thit b bay hi ng v kiu ngpii. Hot ng

Thit b bay hing v kiu ngp c dng trong h thng lnh c nng sut lnh c va vln tr ln. Mi cht lnh c s dng l NH3 hoc Freon 22

Cht lng (Nc hay nc mui) cn lm lnh chuyn ng trong ng trao i nhit v micht lnh si bn ngoi ng trao i nhit, ngp trong khng gian ca bnh. khng ch mc ngp,ngi ta dng b iu chnh c van phao khng ch s ng m van in t. Sau khi thu nhit cacht lng, bay hi, lm lnh, hi mi cht c my nn ht v t bu hi pha trn.

i vi bnh dng NH3, mc ngp ca tc nhn cho php ln n 0,8 ng knh bnh.

vi mi cht lnh l Freon 22, mc ngp ln n 0,5 0,7 ng knh bnh.b. Thit b bay hi ng v chm ng thng, mi cht si trong ng

i. Cu to v Hot ng



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Hnh 4.9: Cu to Thit b bay hi ng v kiu ngp

ii. Hot ng

Nguyn tc lm vic trong loi TBBH ny l mi cht lnh si,bay hi, bn trong ng traoi nhit, thu nhit ca cht lng di chuyn bn ngoi lm lnh cht lng. Mi cht lnh tit luvo thit b theo ng s 1 phn b u trong cc ng trao i nhit, nc mui vo ng s 7 v rang s 3, cc vch ngn s 4 to thnh dng chy zic zc cho nc mui nhm tng cng s traoi nhit. Sau khi bay hi lm lnh, hi mi cht c ht v my nn theo ng ng s 9.

u im ca thit b loi ny l khng b ng bng trong ng ng.

Ton b thn, np v ng ng dn vo bnh u phi bc cch nhit.

4.2.2.Thit b bay hi lm lnh khng kh

a. Thit b bay hi lm lnh khng kh (dn lnh kh)

Cu to v hot ng.

loi ny, tc nhn lnh i trong ng traoi nhit, thu nhit ca khng kh bn ngoi bay hi lm lnh bng cch tip xc trc tip (DLt lnh), hoc i lu cng bc (DL my iuha khng kh ).

Cc loi TBBH ny cn gi l dn lnh kh,cc ng trao i nhit c th b tr thng nghoc nm ngang gm 1 hay nhiu dy ng. Khngkh lu ng qua cc ng trao i nhit bng ilu t nhin hoc cng bc nh qut gi, micht lng c a vo pha di, sau phnphi ng u cho cc ng trao i nhit. Sau khibay hi lm lnh, mi cht c my nn ht v( ly ra pha trn ).

Hnh 4.10 : Thit b bay hi lm lnh khng kh



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b. Thit b bay hi kiu hn hp

Cu to v Hot ng

TBBH kiu hn hp lm lnh khng kh, traoi nhit bng cch tip xc qua b mt ng

ng nh 1 qut lng sc, khng kh ht vo sc lm lnh nh mi cht si trong ng vnc lnh ti t trn xung. Nhm gim bt stiu hao nc cun theo gi, khng kh lnh trckhi ra khi TBBH phi qua 1 tm m chnnc., mi cht thng dng: R12 ; R22

u im : n gin, d ch to. Khng khlnh c gia m.

Khuyt im : dn ng d b mc, c tingn ln.

Hnh 4.11: Thit b bay hi kiu hn hpc. Thit b bay hi lm lnh khng kh kiu t.

Hnh 4.12: Thit b bay hi lm lnh khng kh kiu t.

Hot ng

y l TBBH lm lnh kiu tip xc gia khng kh v nc lnh., nc sau khi c lm lnh t bnhbay hi, c dn vo bung phun sng ( bung iu khng) theo ng ng (6), nc lnh c phunsng nh cc dn phun hnh ch U c gn cc bc phun.,. khng kh, c qut gi (3) ht vo t bnngoi, i qua cc tm chn ( 1 ) vo bung phun sng trn vi hi nc lnh v c lm lnh. Khngkh sau khi c lm lnh s c qut gi a ti cc phng cn lm lnh. Nc sau khi nhn nhit lmlnh kkh, c dn v bnh bay hi theo ng s 9 lm lnh tr li.



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Thit b ny thng c dng trong cc h thng iu ha khng kh trung tm, nh my dt, ngnhng, siu thv.v..( cn gi l AHU )( Air Handing Unit ).

4.3. Kho st, vn hnh thit b ngng t:

4.3.1. Cc h hng thng gp thit b ngng t

Thit b ngng t b lng dn ng (x) , B mc nt.

Bm nhiu cu cn bn. - Nght dn ng.

H thng gii nhit tun hon b h hng (bm hay qut trc trc).

4.3.2.Cc nguyn nhn tng p PK thit b ngng t

Do b mt thit b trao i nhit b bm bn

H thng lnh b lt kh khng ngng vo.

Do nc lm mt khng hoc h thng nc phn phi khng u, bm yu, lc d.

Din tch trao i nhit khng cho ng ng.

Van tit lu m ln.; dn ng trao i nhit ngp du

H thng lnh b nght hoc np d gas..; nhit mi trng xung quanh tng.

4.4.Cc nguyn nhn lm thay i p sut bay hi poa. Trng hp PO tng bt thng

- Ph ti nhit dn lnh thay i t ngt.( tng )

- VTL m ln .

b. Trng hp Po gim bt thng- Ph ti nhit dn lnh gim. - VTL b nght, m nh.

- Tuyt bm qu dy dn lnh .- Dn lnh b ngp du.



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Bai 5:THIET B TIET LU5.1. Cong dung, phan loai:

Van tiet lu t ong am bao nhiet o va ap suat bay

hi ieu kien toi u, tranh cho may nen khong b huthi am.Van tiet lu t ong c chia ra lam 3 loai:

Van tiet lu t ong can bang trong.Van tiet lu t ong can bang ngoai.Van phao tiet lu t ong.

5.2. van tiet lu t ong can bang trong :a. S dung:

Cho cac thiet b BH co o chenh ap au vao va rakhoi dan, thiet b BH nho: po < 0,3 KG/cm2.

b. Nguyen ly lam viec:Van tiet lu lam viec da vao s thay oi nhiet o cuamoi chat sau BH, ngha la da vao s thay oi phu tai lanhcua BH. Moi chat cha trong ong xi phong va ong maodan la ga lanh F12 va F22 .

Hnh 5.1 van tiet lu can bang trongHot ng:

Gi P1 l p sut ca kh trong ng cm nhit, P0 l p sut ca dn lnh. TEVhot ng da vo tn hiu qu nhit hi ht v MN, to ra s so snh gia P1 vP0.

http://opt/scribd/conversion/tmp/scratch6304//D:/MR%20PHONG/VAN%20TIET%20LUU%20CAN%20BANG%20TRONG%20%20(NOP).exehttp://opt/scribd/conversion/tmp/scratch6304//D:/MR%20PHONG/VAN%20TIET%20LUU%20CAN%20BANG%20TRONG%20%20(NOP).exehttp://opt/scribd/conversion/tmp/scratch6304//D:/MR%20PHONG/VAN%20TIET%20LUU%20CAN%20BANG%20TRONG%20%20(NOP).exe


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Khi dn lnh thiu gas, hi ht v MN b tng qu nhit, kh trong ng cmgin n, P1 > P0 y mng p sut vng xung, kim van m ln l tit lu, gas v dnlnh nhiu.

Khi dn lnh gas P1 > P0, mng p sut phnh ln ng bt l tit lu lm

gim lng gas v dn lnh.Van TEV khng bao gi ng kn. Nh c iu chnh c l xo, ngi th c th

chnh sao cho qu nhit hi ht nm trong khong t 50 n 80C l ti u ( dn lnhc khai thc ht)

5.3.van tiet lu can bang ngoaia. S dung:

oi vi cac dan BH co ton that ap suat au vao vaau ra ln (chang han: P 0,3 bar) th nhiet o sau BHkhong phan anh chnh xac ap suat moi chat sau tiet lu,do o neu s dung TPB can bang trong tao nen sai so ln,lu lng cap cho BH se nho hn can thiet. Trong trnghp nay ta s dung van tiet lu can bang ngoai.

b. Cu to, nguyn l lm vic:

Hnh 5. 2: Cu to TEV cn bng ngoiCac lc tac ong len mang an hoi gom co 3 lc sau:

Ap lc cua ga ong xi phong (lay theo nhiet o cua moichat sau BH), ap lc cua moi chat sau BH, ap lc cua loxo.

TEV cn bng ngoi c dng cho nhng dn lnh ln, ng ng di vnhiu co ct, lc ny p sut ng v b tn tht ch cn l Po < Po. Do , ngita so snh P0 vi P1 mi chnh xc cho m kim van tit lu.

http://opt/scribd/conversion/tmp/scratch6304//D:/MR%20PHONG/VAN%20TIET%20LUUCAN%20BANG%20NGOAI%20(NOP).exehttp://opt/scribd/conversion/tmp/scratch6304//D:/MR%20PHONG/VAN%20TIET%20LUUCAN%20BANG%20NGOAI%20(NOP).exe


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5.4.Van tit lu in t:Nguyn tc c bn ca van tit lu in t l ly tn hiu qu nhitv c th thm tn hiu p sut ht a qua b x l in t iukhin van tit lu c ng c truyn ng ng m kim van ty theo

mc mi cht lng cn cp cho dn bay hi.Hnh 3.11 gii thiu s iu chnh thit b bay hi s dng vantit lu in t

Hnh 5.3 S iu chnh thit b bay hi s dng van tit lu in t.MPS - B vi x l, T-PC - iu chnh nhit v p sut, RTC-

Van tit lu in t iu chnh bng ng c, AF1-u cm nhit hoc

p sut, BH Dn bay hitn hiu iu khin bng ng c bc , hai thermistor c lp u vo bchi v u ht ca my nn . b iu khin vi mch s so snh nhit ca haithermistor iu khin ng c bc quay tng ng . nu chnh nhit nyln hn chnh nh th ng c m ln van tit lu . chnh nhit nh ,ng cng bt van tit lu li . khi my nn dng , mch iu khin van ng li trnh mi cht lng vo b bc hi v van ch m ra sau khi my nn chy mtthi gian ( 50 s) . ngoi ra mch iu khin khng cho p sut bc hi qu cao trnh qu ti my nn



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BAI 6THIET B PHU

6.1.Khai niem:Nhng thiet b phu cua he thong bao gom : bnh tach dau, bnh

cha dau, cac loai bnh cha moi chat lanh nh bnh cha cao ap,bnh cha ha ap, bnh cha thu hoi, bnh cha tuan hoan, bnh trunggian, bnh hoi nhiet, bnh tach long, bnh qua lanh long, phin loc, phinsay, thiet b xa kh khong ngng, bm, quat, ng ong.Cung vcac thiet b chnh(may nen, dan ngng, dan boc hi, van tiet lu)cac thiet b phu giup cho he thong lanh trong tng trng hp ngdung cu the lam viec vi o tin cay cao hn, an toan hn, hp ly vakinh te hn, tao ieu kien thuan li hn cho viec van hanh maylanh.Mot he thong lanh khong nhat thiet phai co tat ca cac thietb phu ma tuy theo moi chat lanh, che o van hanh co the canthiet b phu nay ma khong can thiet b phu kia.6.2.Bnh Tach Dau:

Hnh 6.1.Mot so kieu bnh tach dau vi cac nguyen ly lam viec khacnhau

a) kieu tam chan oi hng ; b) kieu zyclon ; c) kieu khoi em va lammat bang nc ;

d) kieu ra hi trong amoniac long ; e) kieu non chan.1 ca hi vao; 2 ca hi ra; 3 tam chan; 4 tam dan hng;

5 tam chan luong hi; 6 khoi em; 7 ong xoan lam mat bang nc;



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8 bnh gi nc long; 9 ong chay tran; 10 bnh cha; 11 bnh ngng;12 loi dau i; 13 non chan.

Hnh 6.2. Bnh tach dau co van phao hoi dau t ong.

May nen lanh can co dau boi trn e boi ntrn cac be mat masat trong o co be mat xilanh va secmang. Khi may nen lam viec,luon co mot lng dau b cuon theo hi nen vao ng ay roivao bnh ngng tao mot lp tr nhiet tren be mat trao oi nhietcua bnh ngng, bnh boc hi lam giam hieu suat may lanh acbiet oi vi loai moi chat khong hoa tan dau nh amoniac.e tranh hien tng tren ngi ta bo tr bnh tach dau lap at trenng hi nen t may nen en bnh ngng.

1. Nhiem Vu:Bnh tach dau co nhiem vu tach dau cuon theo hi nen

khong cho dau i vao dan ngng ma dan dau quay tr lai may

nen (hoac bnh gom dau)2. Nguyen Ly Lam Viec : (Hnh 6.1)Nguyen tac chu yeu la giam toc to dong hi t 18 25m/s

xuong 0,5 en 1m/s ngoai ra :Thay oi hng chuyen ong bang cach bo tr cac tam

chan vuong goc vi dong chay hoac xoan kiey zyclon e cacbui dau mat ong nang Tch tu lai va chay xuong ay bnh



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Lam mat hi nen xuong nhiet o thap 50 600C bang ongxoan ruot ga cho nc lam mat chay ben trong.

Ra hi nen lan dau bang amoniac long oi vi he thonglanh aoniac

Hnh 6.1 gii thieu mot so kieu bnh tach dau vi cac

nguyen tac lam viec khac. Hieu qua tach dau cua a va bthap nhng cua c va d co the at ti 90%.3.ng Dung:

Bnh tach dau chu yeu cho cac he thong lanh co moi chatkhong hoa tan dau nh amoniac, R13, va cac moi chat hoatan dau han che nh R22 oi khi ca R12.

Bnh tach dau ch s dung trong cac he thong lanh ln, ratln va co nhieu may nen mac song song. Rat t khi dung chocac he thong lanh trung bnh va nho.

Bnh tach dau thng sdung cho cac he thong lanh

co ng ong dan t maynen en dan ngng xa. ay bnh tach dau va ongvai tro giam xung, tieu amcho ng ong va tranhngng tu long tren ungay trng hp may lanhdng.

4.Phng Phap Hoi Dau VeMay Nen

Co the xa nh ky dau

tr lai may nen khi mcdau trong may nen tutxuong di mc yeu cau.

Co the bo tr c cau tong hoi dau ve may nenv du s dung van phao. Trng hp moi may nenco mot bnh tach dau cothe s dung van phao bo trngay trong bnh tach dau.

Khi dau trong bnh tach dau dang len, van phao m e dau

phut tr lai may nen nh hieu ap suat gia bnh tach dauva cacte may nen (ky hieu) . trng hp nhieu may nen cochung mot bnh tach dau th phai bo tr van phao pha may nen.Khi may nen thieu dau, mc dau tut xuong, van phao m edau hoi t ong t bnh cha dau ve may nen.

e tranh a dau co nhiet o qua cao (> 600C) quay tr vemay nen, can phai bo tr van ien t tren ng hoi vathermostat kiem tra nhiet o dau. Thermostat ch m van ien


Hnh6.3. Bnh tach dau co vanphao hoi dau t ong


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t cho hoi dau ve may nen khi nhiet o dau di mc chophep

Hnh 6.3 gii thieu s o nguyen tac hoi dau t ong vemay nen kieu van phao at trong tach dau.

5.V Tr Lap at :

Bnh tach dau c lap gan may nen tren ng ay tmay nen en bnh ngng.Bnh tach dau luon at ng va vuong goc vi ng ay.

Tuy theo thiet ke, ng hoi dau co the nam pha tren hoacpha di bnh. Ong hoi dau co the co ng knh 6, 10 hoac12mm ong ong noi theo kieu loe.

Loai co phao khi lap at can o u dau vao bnh e th knvan phao (thng khoang 0,75ml). Neu van phao khong kn, kh nenlien tuc x ve cacte lam giam nang suat lanh cua may nen.Ngoai ra can o dau vao e hieu chnh mc lam viec cuavan phao.

Neu may nen khong co mat dau nen bo tr mat knh uan sat dautren ng hoi. Tng hp dau qua nhieu trong cacte, dau bocmanh va van phao lien tuc m e hoi dau. Neu co knh tren nghoi, co the phat hien va xa bt dau khoi he thong v khi van phaom lien tuc, se co ton that nang suat lanh oi vi may nen.

Ch lap at mot bnh tach dau cho toi a 3 may nen.

6.3. Bnh Cha Cao Ap:1. Nhiem Vu :

Bnh cha cao ap thng at di bnh ngng dung e chalong a ngng tu va giai phong be mat trao oi nhiet cua

thiet b ngng tu, duy tr s cap long lien tuc cho van tiet lu.2. Cau Tao : (Hnh 6.4)

Bnh cha cao ap la mot bnh hnh tru at ng (dung chocac may nho) hoac at nam ngang (dung cho cac he thonglanh ln) co cac ng noi phu hp.

Bnh cha cao ap can bo tr cac ng ong noi long t bnhboc hi en 8, va ng long dan en tram tiet lu 2, ngcan bang hi vi bnh ngng tu 5,ng noi vi bo tach khkhong ngng 3, 4,ng noi ap suat 6 va ng noi van antoan 7. e kiem tra mc long can co bo ch th mc long(ong thuy 9), ngoai ra con ng xa dau 10 va xa can 11, ap

suat lam viec la 1,8Mpa.



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Hnh 6.4. Bnh cha cao ap1 than bnh , 2 ong long ra , 3 ong xa kh khong ngng, 4 ong hoi long t bo xa kh , 5 can bang hi ,6 ap ke , 7 noi van an toan , 8 long vao , 9 ongthuy , 10 xa dau , 11 xa can , 12 chan.

3. V Tr Lap at :Bnh cha cao ap c at sau thiet b ngng tu va trc van

tiet lu.

6.4.Phin say loc:.1 Nhiem Vu :

Phin say va phin loc conhiem vu loai tr cac can ban c hocva cac tap chat hoa hoc ac biet la nc va axid ra khovong tuan hoan moi chat lanh. Phin say va phin loc c lapca tren ng long va ng hi cua he thong lanh.

Can ban c hoc co the la at cat, r set, vay han, mat kimloai. Cac can ban nay ac biet nguy hiem cho may nen khchung lot vao xilanh va cac chi tiet chuyen ong. Cac canban cung nguy hiem oi vi van ac biet van tiet lu, chunggay tac ban.



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Cac tap chat hoa hoc ac biet la am (nc) va cac axidtai trong vong tuan hoan co the la han r, an mon cac chitiet may. Nc co the ong a bt kn van tiet lu gay tacam.

2.Cau Tao :Co nhieu dang cau tao tuy thuoc vao cong suat may, moi

chat lanh Hnh 6.5 gii thieu 1 phin loc dung cho moi chatFreon c nho va c trung. Bo phan loc va say n gian lamot khoi zeolit nh hnh bang keo dnh ac biet at trong motvo han kn.

Phin loc cua cac he thong ln thng co than hnh tru bang

thep han hoac uc, bo tr ng vao va ra cho hi hoac long.Mot au hnh tru co bo tr nap e de dang thao phin ra vesinh. Neu co them chc nang say, ngi ta bo tr them cachat hut am tng ng (zeolit, silicagel ) vao ben trong li loc.

3.V Tr Lap at :Phin say loc ng hi thng bo tr ngay au hut may nen

e loai tr can ban i vao may nen, tren ng long thnglap trc van ien t (neu co) va ac biet la van tiet lu egi cho cac van nay hoat ong bnh thng khong b tac.

6.5.Knh long mat gas:.1 Nhiem Vu :

Mat gaz la knh quan sat lap tren ng long (sau phin sayloc) e quan sat dong chay cua moi chat lanh. Ngoai viec chth dong chay, mat gaz con co nhiem vu :- Bao hieu u gaz khi dong gaz khong b sui bot.- Bao hieu thieu gaz khi dong gaz b

sui bot manh.- Bao hieu gaz khi thay suat hien

cac vet dau tren knh.


Hnh 6.5. Phin say loc choma lanh Freon c nho va


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- Bao o am moi chat qua s bien mau cua cham mau trentam mat gaz so sanh vi mau tren chu vi mat gaz xanh :kho(dry) ; vang : than trong (caution) ; nau : am(wet). Neu b amnhat htiet phai thay phin say mi.

- Bao hieu hat hut am

b ra khi thay gaz bvay uc, khi o cungphai thay phin say loce phonh van tiet luva cac ng ong btac.

.2 Cau Tao :Hnh (6.6) gii thieu

cau tao cua mat gaz.Mat gaz co than hnhtru pha di kn con

pha tren c lap matknh e co the quansat dong gaz chay bentrong.

.3 V Tr Lap at :Lap gaz c lap tren

ng long sau phin say loc,trc van tiet lu.

Trng hp mat gaz long tng oi phu hp ng knh lapmat gaz, co hte lap ngay tren ng ong(hnh 6.7).

trng hp ng ong long ln, phai lap tren ng ong

nhanh song song vi ong chnh (Hnh 6.8).

Hnh 6.7.Nap mat gaz len ng long chnh Hnh 6.8Napmat gaz len ng phu


Hnh 6.6. Cau tao

mat gaz


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6.6. Van ien t:Van ien t dung e ong m lo thoat ng ong dan moi chat,moi chatTL va nc, thuoc loai ieu khien t xa. Van ien t cothe chia ra lam 2 loai:

LOAI TAC ONG TRC TIEP: Thanh sat t (ty van) c m

hoan toan nh t trng cua dong ien. ay la cac van ien tco lo thoat be.LOAI TAC ONG GIAN TIEP: Thanh sat t m van nh t

trng ket hp vi ap lc cua moi chat i qua van. ay la cac vanco lo thoat ln, lc t trng khong u ln e t m van c.1.Van ien t tac ong trc tiep:

Cau tao- nguyen ly lam viec:Khi co dong ien vao cuon day 1 th loi sat t 2 c hut len,

do lo thoat be nen lc t trng thang lc ep cua ap lc moichat trc van, ca van 4 c m thong hoan toan va moi chat iqua van. Khi ngat ien di tac ong cua lc trong trng loi thep

ri xuong ong van lai, ap lc sau van giam nen van c ep chatnh ap lc moi chat trc van.

Hnh 6.9 van ien t tac ong trc tiep

2. van ien t tac ong gian tiep:( hnh mo phong)oi vi cac van ien t co lo thoat ln, khi van ong ap lc e

len van rat ln (co the at ti vai tram KG) do o khong kinh tekhi che tao cuon hut ln a trc tiep m van bang t trng. cau tao- Nguyen ly lam viec:


1.Cuonhut.2.Loi satt.3.Vocach ly.4.Cavan.


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Bnh tach long n gian la mot bnh hnh tru at ng vac cau tao nh hnh 6.11

cac may nen nho ngi ta s dung bnh tach long(accumulartor) e tach long va dau ve ot ngot sau o tietlu dan ve may nen va tranh c va ap thuy lc, va ha

c nhiet o cuoi tam nen.

3. Tr Lap at :Bnh tach long c lap at tren ng hut t thiet b boc

hi ve may nen.

6.8.Thiet b hoi nhiet:Thiet b hoi nhiet dung e qua lanh long moi chat sau

ngng tu trc khi vao van tiet lu bang hi lanh ra t dan bochi trc khi ve may nen trong cac may lanh Freon nham tanghieu suat lanh chu trnh.


Hnh 6.11. bnh tach long (accumulatorhoac liquid trap)


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Hnh 6.12.Hoi nhiet)a nguyen ly cau tao ; b) hoi nhiet cua Danfoss (an Mach)

1 hi vao ra ; 2 long vao ra ; 3 khong gian ben trong ; 4 khong

gian 2 vo.Hoi nhiet co nhieu dang khac nhau nhng eu chung nguyen

tac la mot thiet b trao oi nhiet ngc dong, trong o hi pha ngoai ong xoan, long i trong ong xoan. Hnh 6.12 mo tamot thiet b hoi nhiet n gian. e tang hieu qua trao onhiet, co the tang dien tch trao oi nhiet bang cach bo trnhieu tang ong xoan pha trong.

6.9.Cac loai van, ong dan:1. Ong Tieu Am :

May nen pittong lam viec theo chu ky hut ay nen co runong ca hai ng hut ay gay tieng on. e tieu am chng hut va ay ngi ta bo tr cac ong tieu am.

Hnh 6.13 gii thieu cau taon gian cua 1 ong tieu am chomay nen lanh. Ong tieu am c lap ngay pha trc va phasau may nen tren ng hut va ay.

2. Van dch vu :

Hnh 5.17.Van tap vu


Hnh 6.13 Ongtieu am


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a) loai 4 bulong bat len may nen ; b) loai 2 bulong batlen may

b) mat cat qua 1 van tap vu ; d) hnh cat phoi canh1 than , 2 e van , 3 tam chan di , 4 em kn truc , 5 em nap , 66 nap ;

7 truc van , 8 au noi lay tn hieu ap suat hoac e hutchan khong, nap gaz, nap dau9 au noi vao dan ngng hoac dan boc hi , 10 tai co nhvao au may nen ,11 vong siet , 12 au vuong , 13 tam chan tren , 14 aunoi vao may nen.

Hnh 6.14 cac loai van dch vu

Van dch vu (service valve) la van lap ngay tren ng maynen ng hut va ng ay, van tap vu la loai van 3 nga.Khi van het xuong la ong ng hi t dan boc hi hoacdan ngng en may nen nhng thong may nen vi au noi

au nap hoac ap ke. Neu van het len la ong au noing nap hoac ap ke va thong vi dan. Neu e van lngchng th ca 3 nga thong vi nhau. Van tap vu dung e baodng, sa cha, nap dau, nap gaz, hut chan khong cung nhe phuc vu viec o ac kiem tra may nen (kiem tra ap suatay va hut )

Hnh 6.14 gii thieu mot so loai van tap vu.Van tap vu co the b h hong. Neu em kn co van b x h,

co the thao ra e thay em kn mi hoac ch can siet chatla van kn.Tam van hoac tam chan cua van neu b h th khongsa c ma phai thay van mi.

3. Van Mot Chieu :Trong mot so he thong lanh ngi ta thiet ke chu trnh chcho long va hi i theo mot hng nhat nh va khi a i vaothiet b th khong c phep quay tr lai v du : khi hi nen ai vao bnh ngng th khong c phep quay tr lai may nen,long a qua bm cung khong c quay tr lai (e phongtrng hp may nen, bm hong ot ngot) Van mot chieuco nhieu loai khac nhau nhng eu lam viec da tren nguyentac chenh lech ap suat. Khi ap suat au vao ln hn, van tong m cho dong hi hoac long i qua, nhng khi ap suat auvao giam nho hn pha au ra, van van t ong ong lai. Hnh

6.15 gii thieu hnh dang mot so van mot chieu c nho.



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Hnh 6.15. Mot so loai van mot chieu1 loi vao , 2 loi ra , 3 e van , 4 lo xo nen , 5 coc van , 6 g dan

hngkhi ca vao co ap suat, lo xo b nen lai, coc van b ay len cho moi

chat i qua. Khi ca vaomat ap suat p1 p2 lo xo t ong dan ra ay coc xuong di e ong

van lai.

Khi van hanh bao dng may lanh can thiet phai khoa

hoac m dong chay moi chat lanh tren dong tuan hoan mochat lanh. Cac van khoa, van chan am ng nhiem vu o.Van khoa va van chan co rat nhieu dang khac nhau tuy theo

chc nang, cong dung, kch c, dong chay, moi chat lam kn,vat lieu, phng phap gia cong Theo chc nang co the phanra van chan ng ay, van chan ng hut, van chan nghi van chan ng long. Theo dong chay co the phan ra vanthang dong, van goc, theo moi chat phan ra van NH3 van Freontheo phng phap lam kn co the phan ra loai co lam kn, vongem kn, kieu mang, kieu hop xep (khong co khoi em kn),theo vat lieu co the phan ra gang, thep hoac ong, theo phng

phap gia cong co the phan ra van uc, van han. Hnh 5.1 giithieu van chan kieu gang uc, thang dong dung khoi em kn,cho amoniac va Freon.

4.Van Khoa, Van Chan:


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