c1_1_mot so khai niem co ban

NHIT NG LC HC

S tit hc: 42 tit ko di trong 8 tun

- Tun 1 4 : 5 chng u tin

- Tun 4 : KIM TRA gia hc k

- Tun 5 8 : 5 chng cui

- THI CUI HC K

20%20%

80%80%

B mn: Cng ngh Nhit Lnh Khoa C Kh

Ngi son: TS. H anh Tng HBK tp HCM

1/2009

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Mc ch mn hcNm vng nhng qui lut v bin i nng lng (ch yu l

nhit nng v c nng) nng cao hiu qu s dng nng lng

l mn c s nghin cu v thit k cc loi my nhit ni ring v cc h thng nhit ng ni chung

VD: - Cc loi ng c nhit: C t trong, C phn lc- HTHKK, T lnh- Cc thit b sy, l hi- Bm, my nn- Cc h thng s dng nng lng mt tri, vv.


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Ni dung mn hcChng 1: M t s khai nim c ba n Phng trinh trang thai cua cht khi

Chng 2: nh lut Nhit ng th nht (Nguyn l bo ton nng lng)

Chng 3: nh lut Nhit ng th hai

Chng 4: Cht thun khit

Chng 5: Mt s qu trnh c bit ca kh v hi

Chng 6: Khng kh m

Chng 7: Qu trnh nn kh v hi

Chng 8: Chu trnh thit b ng lc hi nc

Chng 9: Chu trnh ng c t trong

Chng 10: Chu trnh my lnh


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Ti liu tham kho1. Hong nh Tn L ch Hip, Nhit ng lc hc kthut, NXB i hc quc gia Tp HCM, 2007.

2. Hong nh Tn Bi Hi: Bi tp Nhit ng lc hcKT & truyn nhit, NXB HQG TpHCM, 2008.

3. Hong nh Tn, Nhit cng nghip, NXB i hc quc gia Tp HCM, 2001.

4. Cengel, Y. A. Boles, M. A., Thermodynamics: An Engineering Approach, 5th Edition, McGraw-Hill publisher, 2006.


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CHNG 1 (Phn 1):

Mt s kha i ni m c ba n

1.1 Cc vn chung

1.2 Nhng khi nim c bn

1.3 Thng s trng thi ca mi cht


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1.1 Cc vn chungTt c cc bi ton v NHIT chung qui cng ch nhm:

Xc nh NNG LNG ca h thng cng nh S CHUYN HA NNG LNG trong h thng

VD1:

m

VD2: Bm xe p nng ln khi bm


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1.2 Nhng khi nim c bn

1.2.1 Nhit lng v cng

1.2.2 H nhit ng

1.2.3 My nhit


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1.2.1 Nhit lng v cngNhit lngNhit lng: l lng nng lng i xuyn qua b mt ranh gii khi gia cht mi gii v mi trng c s chnh lch nhit - Qui Qui cc: + Vt nhn nhit: Q (+)

+ Vt thi nhit: Q (-)

CngCng: l lng nng lng i qua b mt ranh gii c kh nng dch chuyn mt vt no .- Qui Qui cc: + Vt sinh ra cng: W (+)

+ Vt nhn cng: W (-)

n v on v o: - H SI: 1 J (jun) = 1N.m = 107 erg ; 1 cal (calo) = 4.18 J

- H khc: 1 Btu = 1055 J = 252 cal ; 1 Wh = 3.413 Btu


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Mechanical Equivalent of Heat

Joule demonstrated that water can be heated by doing (mechanical) work, and showed that for every 4186 J of work done, the temperature of water rose by 1C0 per kg.

p.9p.9


1.2.21.2.2 H H nhit ngnhit ng

- H nhit ng (HN) khong khng gian c cha mt lng nht nh cht mi gii ang c kho st bng cc bin php nhit ng.

V d minh ha

Khi xem xt mt

HN cn ch :

Cht mi gii ?? Ngun nng ?? Ngun lnh ??

Cng v nhit lng trao i khi cht mi gii bin i trng thi

B mt ranh gii ngn cch gia cht mi gii v mi trng ??


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Mt s v d v h nhit ngMt s v d v h nhit ng (1)(1)


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Phn loi h nhit ngPhn loi h nhit ng

- HN kn: lng cht mi gii trong h thng c duy tr khng i, cht mi gii khng th i xuyn qua b mt ranh gii ngn cch gia h thng v mi trng. ( VD: my lnh)

- HN h: cht mi gii c th i vo v i ra khi h thng xuyn qua b mt ranh gii. ( VD: ng c t trong, tuabin kh, ng c phn lc, etc.)

- HN on nhit: trong h thng ny, cht mi gii khng c s trao i nhit vi mi trng trong qu trnh hot ng.

- HN c lp: trong h thng ny, cht mi gii v mi trng hon ton khng c bt k s trao i nng lng no trong qu trnh hot ng.


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V d v h nhit ng V d v h nhit ng knkn


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V d v h nhit ng V d v h nhit ng hh


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V d v h V d v h c lpc lp


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1.2.31.2.3 My nhitMy nhit

y l loi my dng nhit sinh cng. Trong loi my ny, cht mi gii s vn chuyn nhit lng theo chiu thun t ngun nng n ngun lnh v gin n sinh cng. ( VD: ng c t trong, ng c phn lc, tuabin, vv..)

Ngun nng

Ngun lnh

ng c nhit

Q1

Q2

W

Xt bo ton nng lng cho ng c nhit:

WQQ += 21

Hiu sut nhit:1

2

1

2

1

11qq

QQ

QW

===

A/ ng c nhit:


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V d v ng c nhitV d v ng c nhit


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B/ Bm nhit, my lm lnh:

y l loi my nhn cng t bn ngoi vn chuyn nhit lng theo chiu ngc t ngun lnh n ngun nng.

(VD: my lnh, bm nhit)

Ngun nng

Ngun lnh

Bm nhit,My lm lnh

Q1

Q2

W

Xt bo ton nng lng cho bm nhit hay my lm lnh: WQQ += 21

H s lm nng (cho bm nhit):21

1

21

11

qqq

QQQ

WQ

=

==

H s lm lnh (cho my lnh):21

2

21

22

qqq

QQQ

WQ

=

==

1>


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My iu ha nhit My iu ha nhit


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T lnh - Refrigeration Animation


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Bm nhit My HKK


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1.31.3 Thng s trng thiThng s trng thiTi mt iu kin bt k, trng thi ca cht mi gii c th c xc nh = 2 thng s trng thi c lp (V d)

Cc thng s trng thi thng dng l:

- Nhit T

- p sut p

- Th tch ring v

- Ni nng u

- Entanpi i

- Entropi s


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V d v thng s trng thiV d v thng s trng thi


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Nhit Nhit TT

Thng s trng thi th hin mc nng lnh ca vt

n v:

Dng c o: Nhit k

- NK thy ngn, NK ru: da trn s gin n ca cht lng

(NK) - NK in tr: da trn s thay i in tr- Thermocouple: da trn s thay i dng in

- bch phn (oC): ( )3295

= FC oo

- Fahrenheit (oF): 328.1 += CF oo

273+= CK oo- Kelvin (oK):


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Tng quan gia cc thang nhit Tng quan gia cc thang nhit


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Absolute Zero and the Kelvin Scale

The pressure-temperature relation leads to the design of a constant-volume gas thermometer. Extrapolation of measurements made using different gases leads to the concept of absolute zero, when the pressure (or volume) is zero.

t (oC)


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p sutp sut ppLc tc dng ln mt n v din tch b mt ranh gii theo

phng php tuyn vi b mt . (V d)

Dng c o:

- Manometer (p k): dng o p sut d pd, phn p sut ca cht kh ln hn p sut kh tri- Parometer: o p sut kh tri pkt- Vacumeter (chn khng k): o p sut chn khng pck, phn p sut ca cht kh nh hn p sut kh tri

ppp ktck =

n v:1 Pa (Pascal) = 1 N/m21 bar = 105 Pa = 750 mmHg1 at = 9.81 x 104 Pa = 0.981 bar = 10 mH2O = 735.6 mmHg1 mmHg = 133.3 N/m21 mmH2O = 9.81 N/m2


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V d v p sutV d v p sut (1)(1)


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V d v p sut V d v p sut (2)(2)

2

1

2

121 A

AFFpp ==


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V d v p sut V d v p sut (3)(3)

p s: 111.7 kPa


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V d v dng c o p sutV d v dng c o p sut


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Nguyn l hot ng ca Nguyn l hot ng ca ParometerParometer

VD: vi 1mm H2O

PamNxxghOmmH 81.9/81.9001.081.910001 22 ====


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Nguyn l hot ng caNguyn l hot ng ca ManometerManometer

VD: vi kPaPcmhmkg atm 96;55;/850 3 ===

kPaxxghPP atmGas 6.1001055.081.985096 3 =+=+=


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V d: dng Manometer o chnh p sut ca dng chy

( ) ghgaPhagP 21211 ++=++Ta c:( )ghPP 1221 =


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Th tch ringTh tch ring vvTh tch ng vi mt n v khi lng

GVv = (m3/kg)

hay:1

=v

trong : + G: khi lng ca khi cht mi gii ang kho st (kg)+ V: th tch chon ch ca khi cht mi gii (m3)

+ : khI lng ring ca khi cht mi gii ang kho st (kg/m3)

Lu : th tch ring v mi l thng s trng thi, cn th tch V khng phi l thng s trng thi


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V d v tnh th tch ringV d v tnh th tch ring


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Ni nngNi nng uuL loi thng s trng thi khng o trc tip c m phi

tnh ton Ni nng U ca mt h thng bao gm:

- ng nng Ud do chuyn ng tnh tin, chuyn ng quay ca cc phn t, v do cc dao ng trong ni b phn t bn trong h thng

- Th nng Ut do lc tng tc gia cc phn t trong h thng

td UUU +=Nu kho st 1kg khi lng cht mi gii:

td uuu +=

trong : ud l ni ng nng; ut l ni th nng ca 1 kg khi lng cht mi gii

(kJ/kg)


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td uuu +=

Theo thuyt ng hc phn t:

- Ni ng nng ud ch ph thuc nhit - Ni th nng ut ph thuc khong cch trung bnh gia cc phn t, tc ph thuc vo th tch ring

),( vTfu =i vi kh l tng: lc tng tc gia cc phn t c xem bng

khng, do ni nng ca kh l tng ch ph thuc vo nhit .

n v: kJ, kcal, kWh (h SI) hoc BTU (British Thermal Unit)

Lu : trong cc bi ton v nhit ng, ni chung khng cn bit gi tr tuyt i ca ni nng m ch cn bit lng bin i ni nng


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Ni thm v ni nng UL nng lng bn trong, gy ra do chuyn ng v tng tc gia cc phn t trong vt th.

V d: - i vi vt rn


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V d: (i vi cht kh)


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EntanpiEntanpi iiL loi thng s trng thi khng o trc tip c m phi

tnh ton

Entanpi ca 1 kg khi lng cht mi gii uc tnh theo cng thc:

pvui += (kJ/kg)

i vi kh l tng, do u v pv ch ph thuc vo nhit nn i cng ch ph thuc vo nhit

Lu : trong cc bi ton v nhit ng, ni chung khng cn bit gi tr tuyt i ca entanpi m ch cn bit lng bin i entanpi


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EntropiEntropi ssLng bin i entropi ds ca 1 kg khi lng cht mi gii

trong 1 qu trnh thun nghch uc tnh theo cng thc:

Tqds =

trong : - l nhit lng trao i gia cht mi gii v mi trng trong qu trnh thun nghch v cng b

- T l nhit tuyt i

hayTQdS = cho G kg cht mi gii

(dS = G ds)

n v: kJ/kg.K, kcal/kg.KLu : = 0ds- d chu trnh l thun nghch hay khng

0= TQ- nu chu trnh l thun nghch

0

---------------------------------------

HT CHNG 1(Phn 1)


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NHIT NG LC HCMc ch mn hcNi dung mn hcTi liu tham khoCHNG 1 (Phn 1):1.1 Cc vn chung1.2 Nhng khi nim c bn 1.2.1 Nhit lng v cngMechanical Equivalent of Heat1.2.2 H nhit ngMt s v d v h nhit ng (1)Mt s v d v h nhit ng (2)Mt s v d v h nhit ng (3)Phn loi h nhit ngV d v h nhit ng kn V d v h nhit ng hV d v h c lp1.2.3 My nhitV d v ng c nhitMy iu ha nhit T lnh - Refrigeration Animation Bm nhit My HKK1.3 Thng s trng thiV d v thng s trng thiNhit TTng quan gia cc thang nhit Absolute Zero and the Kelvin Scalep sut pV d v p sut (1)V d v p sut (2)V d v p sut (3)V d v dng c o p sut Nguyn l hot ng ca ParometerNguyn l hot ng ca ManometerV d: dng Manometer o chnh p sut ca dng chyTh tch ring vV d v tnh th tch ringNi nng uNi thm v ni nng U Entanpi iEntropi s---------------------------------------

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