NHIỆT ĐỘNG LỰC HỌC KỸ THUẬT - CHƯƠNG 1

1/22/2013

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thermodynamics

NHIT NG LC HC K THUT

(Thermodynamics)

HUNH PHC HIN

B MN CNG NGH NHIT LNH

KHOA C KH

1

thermodynamics

GII THIU CHUNG V MN HC

2

Thi lng/s tn ch: 14 tun/2 tn ch

Cch thc nh gi kt qu hc tp:

2 bi kim tra trc nghim (15%/mt bi)

Kim tra gia hc k: 20% ( thi trc nghim thi gian: 45 pht ).

Thi cui k: 50% ( thi vit thi gian: 90 pht ).

Ti liu tham kho:

[1] Hong nh Tn , L Ch Hip - Nhit ng lc hc k thut, NXB KHKT 1997.

[2] Hong nh Tn, Bi Hi - Bi tp Nhit ng lc hc KT v truyn nhit, NXB HQG Tp HCM - 2002.

[3] Yunus A.Cengel, Micheal A. Boles - Thermodynamics, An Engineer Approach, International Edition - 1994.

[4] David Halliday- Robert Resnick- Fearl Walker - Fundamentals of Physics, Wiley Publisher.

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thermodynamics

CHNG 1: M U

3

thermodynamics

Ni dung

4

Gii thiu mn hc

Khi nim & nh ngha

Thuyt ng hc phn t

Cc thng s trng thi

Phng trnh trng thi ca vt cht th kh

Hn hp kh l tng

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thermodynamics 5

1. Gii thiu mn hc

C Nng Nhit nng

Nhit

ng lc

hc k

thut

thermodynamics

2. Cc khi nim v nh ngha

H nhit ng

H nhit ng kn.

H nhit ng h.

H nhit ng on nhit.

H nhit ng c lp.

Ngun nhit

Ngun nng

Ngun lnh

ng c nhit

My lnh

Bm nhit

6

Cht mi gii

Trng thi v trng thi cn bng

Qu trnh thun nghch v khng thun nghch

Pha v cht thun khit

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thermodynamics


7

H nhit ng

H nhit ng

Khi lng Cng Nhit

lng

Kn 0

H

on nhit 0

C lp 0 0 0

thermodynamics


8

Ngun nhit ng c nhit, my lnh, bm nhit

Q1

Ngun lnh

Ngun nng

Ngun nng

Ngun lnh

Q2

Cng W ng c

nhit

My lnh,

bm nhit Cng W

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thermodynamics 9

Cht mi gii

Kh l tng:

Th tch bn thn ca cc phn t kh bng khng.

Lc tng tc gia cc phn t kh bng khng.


Cht thun khit

thermodynamics

3. Thuyt ng hc phn t ca cht kh

10

M hnh ca Joule

Cc phn t kh ch chuyn ng tnh tin, tc ca cc phn

t bng nhau theo mi phng.

B qua tng tc gia cc phn t, b qua nh hng ca trng

trng

Phng trnh biu din trng thi ca cht kh:

. =

..

Vi

.. = ()

Nu p =const, V t l thun vi T (L Charles v Gay Lussac)

Nu T = const, p.V = const (nh lut Boyle)

M hnh ci tin ca Clausius

Tnh n nh hng ca tng tc gia cc phn t.

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thermodynamics

4. Cc thng s trng thi

11

Nhit

p sut

Th tch ring v khi lng ring

Ni nng

Enthalpy

Entropy

thermodynamics 12

Nhit

L thng s biu th mc nng hay lnh ca mt vt.

Thng s quy nh mc chuyn ng ca dng nhit.

L thc o ng nng trung bnh ca v s cc phn t ang chuyn ng tnh tin (i vi kh l tng)

. . =

..

k = 1,3805.1023 J/K - hng s Boltzmann

Video


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thermodynamics 13

Nhit

Cc thang o nhit

Cc thit b o nhit in hnh


Thang nhit

bch phn

(Celcius scale)

Thang nhit

Fahrenheit

(Fahrenheit scale)

Thang nhit tuyt i

(Thermodynamic temperature scale)

Thang nhit Kelvin Thang nhit Rankine

n v oC oF K oR

Chuyn

i t(oC) t(oF) = 1,8.t(oC) +32 T(K) = t(oC) + 273,15

T(oR) = 1,8.T(K)

T(oR) = t(oF) + 459,67

thermodynamics 14

p sut

L p lc tc ng ln mt n v din tch b mt ranh gii theo phng php tuyn vi b mt .

= (

)

n v:

H SI: N/m2(Pa); kgf/cm2, mH2O, mmHg, bar, at.

H I.P: inHg, psi, tonf/in2.

Bng chuyn i n v: bng 1.1/trang 23, TL[1]

Phn loi:

p sut d pd (gage pressure)

chn khng pck (vacuum pressure)

p sut kh quyn po (atmosphere pressure)

p sut tuyt i p (absolute pressure)


p sut d

p sut tuyt i

p sut

tuyt i

p sut

chn khng

p sut kh quyn

Chn khng tuyt i

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thermodynamics 15

Thit b o p sut chn khng: Vacummeter

Thit b o p sut kh quyn:Barometer.

Thit b o p sut d: Manometer,


p sut

Cc thit b o p sut

thermodynamics


16

Th tch ring v khi lng ring

Th tch ring v (m3/kg)

=

Khi lng ring (kg/m3)

=

Trong :

V: th tch (m3)

G: khi lng (kg)

0

2000

4000

6000

8000

10000

12000

14000

16000

Khi lng ring (kg/m)

Nc

Du

Thy ngn

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thermodynamics


17

V d: s dng p k dng ch U o p sut kh trong bnh nh hnh bn. Bit mi cht lm

vic bn trong ng ch U l nc, c khi lng

ring = 1000 kg/m3. Chnh lch mc cht lng

gia hai nhnh l h = 10 cm. Xc nh:

p sut d v p sut tuyt i ca khi kh

cha trong bnh.

Nu mi cht s dng bn trong ng ch U l

thy ngn c = 13600 /3, xc nh li gi tr h? C nhn xt g v kt qu nhn c?

thermodynamics 18

Ni nng: L tt c cc thnh phn nng lng ca h nhit ng lin quan n cc

phn t vi m ca h (nguyn t v phn t).

U = f(T,v)

i vi kh l tng: U = f(T)

n v: H SI (International system of unit): J (Joule)

H I.P (Imperial unit): BTU (British thermal unit)

1 BTU = 1,055 kJ

* Tnh cho mt 1kg mi cht u = U/G (J/kg)


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thermodynamics 19

Enthalpy:

L mt thng s trng thi c tnh gin tip qua biu thc:

I = U + p.V (J)

Tnh cho 1kg mi cht: =

= + . (

)

i vi kh l tng: i = f(T)

Entropy: entropy l mt hm nhit ng.

dS = 0 khi QT thay i trng thi ca mi cht l on nhit

thun nghch.

dS =

(J/K) khi QT thay i trng thi l thun nghch.

Tnh cho 1 kg mi cht: =

(

.)


thermodynamics

5. Phng trnh trng thi ca kh l tng

20

Kh l tng

Phng trnh trng thi ca kh l tng Quan h gia cc thng s trng thi p,v,T ca kh l tng

Phng trnh Clapeyron (1799 1864):

. = .

. = . p.V = G.R.T

Trong : p: p sut tuyt i ca cht kh (N/m2, Pa)

: th tch ng vi 1 kmol cht kh (m3/kmol).

v: th tch ring ca cht kh (m3/kg).

: hng s ph bin ca cht kh - = 8314J/(kmol.K)

R: hng s cht kh R =

=

.

G: khi lng khi kh (kg)

T: nhit tuyt i ca khi kh (K)

Video

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thermodynamics

6. Hn hp kh l tng

21

Hn hp kh l tng: cc mi cht thnh phn bn trong u l

kh l tng v c trn ln li theo kiu c hc.

Vd: khng kh, sn phm chy

VD: Khi khng kh c cha trong bnh kn c th

tch V = 1m3 v nhit t = 35oC. Xc nh nhit v

th tch ca cc kh thnh phn trong khi kh ni trn.

thermodynamics 22

Hn hp kh l tng gm n kh thnh phn.

Thnh phn khi

lng =

=

=

=/

()

Thnh phn th tch =

=

=

Thnh phn mol =

=

=

6. Hn hp kh l tng

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thermodynamics 23

nh lut Gibbs-Dalton p sut ring phn

=. .

=

=

;

Video

nh lut Gibbs Dalton cng c pht biu cho enthalpy v entropy v ni nng ca kh l tng

=

=

=

=

;

=

=

6. Hn hp kh l tng

thermodynamics 24

Cc i lng c trng ca hn hp

6. Hn hp kh l tng

Hn hp kh c n kh, thnh phn khi lng v th tch ca kh th i l: gi, ri.

Theo thnh phn khi lng Theo thnh phn th tch

Khi lng tng ng

vi 1kmol hn hp (kg/kmol)

=

(/= )

= .

=

Hng s cht kh R ca

hn hp Rhh (J/kg.K) = . ( )

=

= .

=

= /( . )

=

Th tch ring ca hn

hp (m3/kg) = /

=

Khi lng ring ca hn

hp (kg/m3) = .

=

Phn p sut ca cc kh

thnh phn pi = . .

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thermodynamics

KT THC CHNG 1

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NHIỆT ĐỘNG LỰC HỌC KỸ THUẬT - CHƯƠNG 1