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my thy lc

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Phn I

My thu lc

Chng IKhi nim chung v my thu lc

MTL l danh t chung ch cc my lm vic bng cnh trao i nng lng vi cht lng theo cc nguyn l thu lc hc ni ring v c hc cht lng ni chung.

(1. Phn loi my thu lc.

1. Theo tnh cht trao i nng lng

ng c thu lc: tip thu c nng ca cht lng ko mt my khc lm vic khc, c tc dng nh mt ng c.

My bm: truyn c nng cho cht lng to nn p sut hoc vn chuyn cht lng.

My thu lc thun nghch.

2. Theo nguyn l tc dng ca MTL vi cht lng

MTL cnh dn: trao i nng lng gia my v cht lng c thc hin bng nng lng thu ng ca dng cht lng qua my.

MTL th tch: thc hin trao i nng lng vi cht lng theo nguyn l nn cht lng trong mt th tch kn di ASTT.

(2. Thng s c bn ca my thu lc

C 4 thng s c bn: H; Q; N; .

1. Ct p:

Th hin mc chnh lch nng lng n v ca dng cht lng hai mt ct trc v sau MTL.

(2-1)

H>0: dng chy c cung cp thm nng lng (my bm)

H w2).

dng cht lng qua bnh cng tc c n nh th cnh dn phi c kt cu sao cho: = const

5. Lu lng.

(1-3)

D - ng knh ngoi ca bnh cng tc.

d - ng knh trong ca bnh cng tc.

cm vn tc hng trc ca dng cht lng.

H ct p ton phn ca bm (H < HLT)

kc h s vn tc: kc = 0,0055ns2/3Chng VI

My thu lc th tch

(1. Nguyn l lm vic ca cc my thu lc th tch.

My thu lc th tch thc hin trao i nng lng vi cht lng theo nguyn l nn cht lng trong mt th tch kn di p sut thu tnh.

Bt k MTL th tch no cng c th lm vic thun nghch.

Nguyn l lm vic MTL th tch kiu pittng:

Khi Pittng 1 sang tri, th tch bung lm vic a tng ln, p sut gim, nn cht lng t ng ht 5 qua van mt chiu 4 vo xi lanh 2.

Khi Pittng 1 sang phi, cht lng trong xi lanh b nn di p sut p, qua van mt chiu 5 vo ng y.

Nu bung lm vic hon ton kn v bm cng sut th p sut lm vic ca bm ch ph thuc vo p sut cht lng trong ng y.

Phn loi.

+ Theo kt cu v dng chuyn ng:

Loi pittng: c chuyn ng tnh tin.

Loi rto: c chuyn ng quay.

Loi pittng rto: va c chuyn ng tnh tin, va c chuyn ng quay.

(2. Cc thng s c bn ca my thu lc th tch.

1. Lu lng: l tng th tch lm vic ca my trong mt n v thi gian.

QL = qL.n

(2-1)

trong :

qL lu lng ring ca my trong mt chu k lm vic

(th tch my trong mt chu k)

n s chu k trong mt n v thi gian.

QL lu lng trung bnh l thuyt.

2. p sut.

Trong MTL th tch thng dng p sut biu th kh nng ti ca my. Quan h ct p v p sut l:

H = p/

(2-2)

p sut trong my ph thuc lc tc dng hay mmen quay ca my:

Vi MTL c chuyn ng tnh tin:

P = p.S

(2-3)

P - p lc tc ng ln pittng.

S din tch lm vic ca mt pittng.

Vi MTL c chuyn ng quay:

M = kM.p

(2-4)

M mmen quay tc ng ln my.

kM h s mmen, l hng s vi 1 my nht nh,

ph thuc vo kt cu v kch thc my

Tm kM?

cng sut l thuyt: NLT = QL.H = QL.p/ = QL.p. (1)

li c:

NL = .M ( - vn tc gc) (2)

t (1) v (2):

(3)

t (2-4) v (3):

(2-5)

3. Hiu sut v cng sut.

Hiu sut ton phn: = H Q cVi MTL th tch tn tht thu lc tng i nh (H) nn = Q cCng sut:

Cng sut lm vic ca bm thng xc nh bng cc thng s thu lc:

N = QL.H/

(2-6)

Cng sut lm vic ca ng c thng xc nh bng cc thng s c kh:

+ ng c c chuyn ng tnh tin: N = P.v

(2-7)

v vn tc pittng.

+ ng c c chuyn ng quay: N = M.

(2-7)

(3. Bm Pittng.

1. Khi nim.

Loi bm pittng c chuyn ng tnh tin trong xilanh ht v y cht lng qua hai van.

Hai im B1 v B2 ca pittng tng ng vi hai v tr C1 v C2 ca tay quay. Khi trong bung lm vic 5 cha y cht lng, nu tay quay t v tr C2 quay theo chiu mi tn th pittng di chuyn t B2 v pha tri. Th tch bung 5 tng dn, p sut p trong gim i v b hn p sut mt thong b cha. Do cht lng t b ht qua van ht 6 vo bung lm vic 5, trong khi van y 4 ng. Khi pittng chuyn ng t B2 n B1 bm thc hin qu trnh ht. Khi tay quay n C1 (Pittng n B1) th qu trnh ht kt thc.

Sau , tay quay tip tc t C1 n C2 (Pittng i t B1 n B2). Th tch bung lm vic gim dn, p sut cht lng tng ln, van ht 6 b ng, van y 4 m, cht lng chy vo ng y. y l qu trnh y.

Qu trnh ht y ca pittng gin on v xen k nhau. Mt qu trnh ht v y k tip nhau gi l mt chu k lm vic ca bm.

Bm pittng khng cn mi.

2. Lu lng.

a) Lu lng trung bnh l thuyt.

Vi bm tc dng n:

+ Th tch lm vic trong mt chu k: q = S.L

S = D2/4 din tch lm vic mt pittng.

L hnh trnh pittng.

Lu lng l thuyt trung bnh:

(3-1)

n s vng quay ca trc bm trong 1 pht.

Vi bm c tc dng nhiu ln ta lp tng t.

b) Lu lng trung bnh thc t.

Q = Q.QL

(3-2)

c) Lu lng tc thi:

Q = S.v

(3-3)

v vn tc tc thi ca pittng.

3. iu chnh lu lng.

c 4 cch:

Thay i s vng quay ca ng c lm thay i chu k lm vic.

iu chnh bng kho tho cht lng t bung y v bung ht.

Thay i din tch mt lm vic ca pittng bng cc c cu c bit.

Thay i hnh trnh lm vic ca pittng.

(4. Bm bnh rng.

1. Khi nim.

Bm bnh rng gm 2 bnh rng n khp vi nhau trong v bm. Loi n gin gm 2 bnh rng bng nhau. S rng thng l z = 8 12.

Bnh ch ng gn lin vi trc chnh ca bm, n khp vi bnh b ng, c hai bnh t trong v bm. Khong trng A gia v bm, ming ng ht v 2 bnh rng gi l bng ht. Khong trng B gi l bng y.

Khi bm lm vic, bnh ch ng quay lm bnh b ng quay theo, cht lng cha trong cc rnh a gia cc bnh rng ngoi vng n khp c chuyn t bng ht ln bng y theo v bm. V th tch cht lng trong bng y gim khi cc bnh rng n khp, nn cht lng b chn p v dn vo ng y vi p sut cao. y l qu trnh y.

ng thi vi qu trnh y, th bng ht th tch cha cht lng tng (khi cc rng ra khp) p sut gim xung thp hn p sut mt thong b cha lm cht lng i vo ng ht.

Theo nguyn l trn, ta thy: nu bm khng c khe h th p sut cht lng ch tng khi no cht lng c chuyn n bng y. Nh vy, p sut do bm to ra ch ph thuc vo p sut trong ng y.

Nhng trong thc t, bao gi cng c khe h nn cht lng c tng p trc khi n bng y.

Chnh cc khe h ny lm tn tht lu lng trong bm, hn ch kh nng tng p. Nu p sut trong ng y qu cao s lm Q = 0.

V vy, hn ch p sut ln trn ng y thng lp mt van an ton. Van s t ng m cho cht lng thot v b ht khi ng y b tc hoc p sut qu mc quy nh.

2. Lu lng.

Coi khong trng ca rng v b bm bng th tch mt rng:

QL = 2.D.m.b.n.

n s vng quay trong n v thi gian.

b chiu di rng (chiu rng bnh rng).

m mun ca bnh rng. m = D/z.

z s rng.

Khi s rng 2 bnh khng nh nhau th z l s rng ca bnh ch ng.

My thu lc

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