- T\X NDP den 64"C dien trd suat giam tuan theo quy luat ciia chat band an gia tr
3.4.1.Phúang trinh nhiet trong hieu iing tU dot nong
Dat dien dp len mdu mang mdng VO2, khi cd dong dien chay qua mau dUdc cung cap
mot nhiet lUdng lam thay đi nhiet do cua chiing. u vung nhiet do T < x^ mang VOo cd do
d^n nhát dinh, cdn d vung nhiet do T > T^ do d^n cua mang tang len rat nhieụ De mo ta hien tUdng chuydn pha BDKL qua cac phUdng trinh giai tich, chung ta dung cac ky hieu sau day de bieu dien cac dai lUdng vat ly lien quan den hieu iing tU đt ndng m i u :
Nhiet do tai toa do x, y, z d thdi diem t la: T = T(x,y,z, t)
He só đn nhiet cua vat la: }, = X (T)
Nhiet dung rieng (J/kg.K): C = CT
Khdi lUdng rieng: 7 ÔS^^'^^ )
Cdng suat rieng cda nguon nhiet: W = PÂ,
Giai bai loan can hdng nhiet [S] trong trUdng hdp he sd dan nhiet khdng doi va dien trUdng phan bd trong mau mot each dong deu, nhan dUOc phUdng trinh:
>.,V-T-rW = C . 7 — (2)
dt
Do: vdi mot he mang mdng, 06 the gidi phUdng trinh tren cho he toa do mot chieu ly ttiong. xei trong truong nhitU dung, chung ta cd:
•^ _r'
£ L . o Vd V " T = = ^ ^3j
d! C'X". Pbtidng trinh cf\n hdng nhiet cd dang:
LL=-J^ (4)
5A- - >-'''
Do hien !udn- rhuvGn pha BDKL khdng xdy ra đng thdi Lrong mang. cho nen đng đi mau duọ: iunii^thdnh dUdi dang dong sdị G.di phUdng trinh (4) cd the nhan dUdc bieu thuc lien he -.^lua kich thudc va đ Idn cua đng sdi naỵ
Goi a ki hieu \y sd gida be rdng cda dong sOi (2/) va kicii thudc cua đi tidp xdc d'^.en cUc / T i p - VO c^'O thi: a - ~— - — . cung eac didu kien bu-n: X = f-> Ty= T, va I > 1,..
'••^ •" 2 ' j j < o
\nki thdc tdiu: qua;, hen h6 ;;iaa kich thuoc va do Idn cua dong soi dudi dang phifong trnih
Linh kien quang dii2n lír Iron ccf -•<d., 13
| ! [ a - l f + i2(2a-l)Jxá^-[(a-l)(i*^ x 2 a - ( i ^ - l ) = 0
100.
t r o n g đ i = I / Ic ; p o / P s = ^^ )) ^ Ldi giai c u a phUdng t r i n h la:
(a - l ) ( i " - l ) ± i a V i - - 1 a = (2a - l ) ( i - - D - h a - (5) .65 0 * ^-^£CAii:.ị:axZ;i 20 I imV. 30 40
Tii bieu thiic (5) de n h d n t h a y : Khi n a n g d d n g dien q u a m a u . b a t d a u t d gia
tri I = I^, tiic / = 1 , d a n den a ~ 0, d n g vdi
thdi d i e m d o n g sdi b a t d a u h i n h t h a n l i .
Tiep tuc t a n g I, d e n k h i I » ! , , (i-> ỵ) t h i
a =1/2, tUc la be r o n g c u a đng sqi d a t gia (adsbygoogle = window.adsbygoogle || []).push({});
tri 16n n h a t va b a n g nUa kich thUdc c u a dai tiep xuc. TrUdng h d p ndy chi cd y n g h i a t o a n hoc, t r e n t h u c te d d n g dien chi
cd t h e t a n g len den gia tri tdi h a n n a o đ k h o n g gay n e n h u h d n g tiep xuc c u n g nhU c a u t r u e
t i n h thé c u a n h i e t d i e n trd. Do vay, be r o n g c u a d d n g sdi thUdng hi r a t be so vdi kich t h u d e cua m a u m a n g m d n g .
Hinh 5. Dudng dac trUng Von-Ampe cua mang mong VO; do tai nhiet do 30'=C (A); 40=C (B); 50'C (C);
60'C(D);65'C(E)va70°C{F)
100i
Uiiil.'
40