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TRUYN NHIT
S tit hc: 42 tit ko di trong 16 tun
GV: TS. H ANH TNG B mn Cng ngh nhit lnh
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.1p.1
- Tun 1 7 : 4 chng u tin
- Tun 8 - 9 : KIM TRA gia hc k
- Tun 10 16 : 4 chng cui
- THI CUI HC K
20%20%
80%80%
Mc ch mn hcNm vng s truyn nng lng xy ra gia cc vt v trong thit b do
s chnh lch nhit gy nn 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.
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.2p.2
Ni dung mn hcChng 1: Nhng khi nim c bn
Chng 2: Dn nhit
Chng 3: Nhng khi nim c bn v trao i nhit i lu
Chng 4: Trao i nhit i lu trong mi trng 1 pha
Chng 5: Trao i nhit khi cht lng bin i pha
Chng 6: Trao i nhit bng bc x
Chng 7: Truyn nhit
Chng 8: Thit b trao i nhit
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.3p.3
Ti liu tham kho1. Hong nh Tn, Truyn nhit & Tnh ton thit b trao i nhit, NXB Khoa hc v K thut, 2007.
2. Hong nh Tn, Bi Hi Bi tp Nhit ng lc hcK thut & Truyn Nhit - NXB HQG TpHCM. 2002
3. Hong nh Tn, C s Nhit cng nghip, NXB i hcquc gia Tp HCM, 2006.
4. M. Mikheyev - Fundamental of Heat Transfer - Mir Publisher, Moscow, 1968.
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.4p.4
Bi 1Chng 1 (Phn 1): Nhng khai nim c ban
1.1 Khi nim chung v Truyn nhit
1.2 3 dng Truyn nhit
1.3 Bi ton Truyn nhit tng hp
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.5p.5
1.4 Gii thiu v Thit b trao i nhit
- Dn nhit- i lu- Bc x
1.1 Khi nim chung v Truyn nhitL dng truyn nng lng khi c s chnh lch v nhit
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.6p.6
NHIT LNG
VD:
Bi ton truyn nhit :- Xc nh nhit ti 1 v tr no trong vt
- Xc nh Nhit lng Q truyn qua vt
Joule: J = N.m
Watt : W = J/sQ : n v
1.2 3 dng truyn nhit c bn
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.7p.7
B. i lu
C. Bc x
A. Dn nhit- Xy ra do chnh lch nhit gia cc vng trong vt rn hoc gia 2 vt rn tip xc nhau.
- Xy ra do chnh lch nhit gia 2 vt t cch xa nhau
- Xy ra do chnh lch nhit gia b mt vt rn vi mi trng cht lngxung quanh n.
A. Dn nhit
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.8p.8
N: l qu trnh truyn nhit khi c 2 iu kin:
- T vng c To cao n vng c To thp
- v gia cc phn ca 1 vt hay gia cc vt tip xc nhau.
(y l qt truyn nhit in hnh trong vt rn: bn cht do s truyn ng nnghay va chm gia cc phn t, nguyn t)
Q
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.9p.9
Dng nhit truyn qua vt (trong 1s) theo phng x c tnh theo L Fourier:
Tit din F
x
Qx
xTFQx
= (W) x
TFQ
q xx
== (W/m2)
- Qx l dng nhit truyn theo phng x trong thi gian 1s (W)
- qx l mt dng nhit truyn theo phng x trong thi gian 1s (W/m2)- T l nhit tuyt i ca vt (K)- F l din tch tit din vung gc vi phng x (m2)- l h s dn nhit ca vt (W/m.K)
vi:
V dV d: : Tnh ton dn nhit Tnh ton dn nhit qua qua vch phngvch phng
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.10p.10
Q
T1T2
- Vch phng c:
+ Din tch F (m2)+ B dy (m)+ H s dn nhit (W/m.K)+ Nhit 2 b mt vch T1 v T2
TFQ =
L Fourier (W)
hay /
Tq = (W/m2)
(R c gi l nhit tr dn nhit ca vch phng)
L OhmRUI =
T1 T2
=R
ng dng phng php nhit trng dng phng php nhit tr
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.11p.11
321
41
RRRttq++
=
H H s dn nhit s dn nhit ca vt liuca vt liu
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.12p.12
Trong thc t c th xem l hng s ng vi nhit trung bnh ca vt ttb
T ttb ca vt tra bng suy ra
ph thuc vo nhit
)1( bto +=
Mt s ng dng ca hin tng dn nhitMt s ng dng ca hin tng dn nhit
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.13p.13
Vt liu cch nhit (c nh) Lp nc c tc dng cch nhit chng hi lnh xm nhp
B. B. Trao i nhit Trao i nhit I LUI LU
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.14p.14
N: l qu trnh trao i nhit xy ra khi gia mt b mt vt rn tip xc vi mi trng cht lng (kh) c nhit khc nhau c s chuyn ng ca cht lng
V d:
Mt s v d v trao i nhit i luMt s v d v trao i nhit i lu
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.15p.15
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.16p.16
Trao i nhit i lu khi khng kh tip xc dn nng, dn lnh
THC NGHIM
tnh trao i nhit i lu tnh trao i nhit i lu ththng dng dng cng cng thng thc c NewtonNewton::
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.17p.17
Q
FTw
Tf( )fw TTFQ = (W)
hay/1Tq = (W/m2)
trong : - l h s ta nhit i lu (W/m2.K)- F l din tch b mt trao i nhit (m2)
- Tw l nhit trung bnh ca b mt ( K hoc oC)- Tf l nhit trung bnh ca cht lng ( K hoc oC)
1
=R
Tng t qu trnh dn nhit t
l nhit tr i lu
Tw
TfRS :
C. C. Trao i nhitTrao i nhit BC XBC X
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.18p.18
N: l qu trnh trao i nhit xy ra gia cc vt c nhit khc nhau t cch xa nhau Nng lng bc x truyn trong khng gian di dng sng in t
Tnh cht ca nng lng bc xTnh cht ca nng lng bc x
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.19p.19
- Mi vt lun pht ra nng lng bc x v nhn nng lng bc x t cc vt khc n
- Nng lng bc x pht ra t vt t l vi nhit tuyt i ly tha bc 4
E ~ T4
- Vt en tuyt i s nhn nng lng bc x ln nht
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.20p.20
A White sifaka Lemur
To warm up in the morning, they turn their dark bellies toward the sun.
tnh trao i nhit bc x tnh trao i nhit bc x ccng thng thcc StefanStefan--BoltzmannBoltzmann::
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.21p.21
( )424112 TTFQ = (W)
( )( )( ) ( )2131122122212112 4 TTTFTTTTTTFQ ++=
trong :
- 12 l h s chiu x (12 < 1)
- F l din tch trao i nhit (m2)
- l hng s Stefan-Boltzmann ( = 5,6697.10-8 W/m2.K4)
- 1, 2 l nhit tuyt i ti b mt hai vt 1 v 2 (K)
( )21 TTFQ bx = haybx
Tq/1
=
Trong trng hp T1 T2
1.3 Bi ton Truyn nhit tng hp
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.22p.22
Q = kF(tf1 tf2) k: He so truyen nhiet (W/m2.K)
1.4 Gii thiu v Thit b trao i nhit
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.23p.23
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.24p.24
ng c t trongng c t trong
My iu ha nhit My iu ha nhit
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.25p.25
---------------------------------------
HT BI 1
Ngi son: TS. H anh Tng HBK tp HCM
8/2009
p.26p.26
TRUYN NHITMc ch mn hcNi dung mn hcTi liu tham khoBi 11.1 Khi nim chung v Truyn nhit1.2 3 dng truyn nhit c bn A. Dn nhit Dng nhit truyn qua vt (trong 1s) theo phng x c tnh theo L Fourier: V d: Tnh ton dn nhit qua vch phngng dng phng php nhit trH s dn nhit l ca vt liuMt s ng dng ca hin tng dn nhitB. Trao i nhit I LUMt s v d v trao i nhit i lu tnh trao i nhit i lu thng dng cng thc Newton:C. Trao i nhit BC XTnh cht ca nng lng bc x tnh trao i nhit bc x cng thc Stefan-Boltzmann:1.3 Bi ton Truyn nhit tng hp1.4 Gii thiu v Thit b trao i nhitng c t trongMy iu ha nhit ---------------------------------------