Perturbation solutions for the effect of prandtl number on heat transfer from a non-isothermal rotating disk

Perturbation solutions for the effect of prandtl number on heat transfer from a non-isothermal rotating disk

LETTERS IN HEAT AND MASS TRANSFER Volume 4, Pages 53-62, Pergamon P r e s s , 1977. Printed in Gt. Britaln. PERTURBATION SOLUTIONS FOR THE EFFECT OF ...

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LETTERS IN HEAT AND MASS TRANSFER Volume 4, Pages 53-62, Pergamon P r e s s , 1977. Printed in Gt. Britaln.

PERTURBATION SOLUTIONS FOR THE EFFECT OF PRANDTL NUMBER ON HEAT TRANSFER FROM A NON-ISOTHERMAL ROTATING DISK

Sun-Yuan Tsay and Yen-Ping Shih Department of Chemical Engineering National Cheng Kung University Tainan, Taiwan, China

(C~l,,unicated by Y. Mori)

ABSTRACT A general pertubatlon method for the analysis of the effect of Prandtl number (Pr) on the steady state heat transfer across laminar incompressible boundary layer is proposed. The method is applied to the heat transfer of a rotating disk with step discontinuity of temperature. The method is a combination of coordinate pertubatlon to d e a l l ~ t h the step discontinuity of temperature and parameter (Pr- " ) perturbation to study the effect of Prandtl number on heat transfer. The zero-order solution is the Lighthill solution. The coefficients are universal functions. The convergence is satisfactory for Pr ~ i.

Introduction

This paper s t u d i e s

the s t o a d y o s t a t e hoot t r a n s f e r s c r e e n l ~ s i n a r

inoosrpromsible o o n s t a n t p r o p e r t y boundary l a y e r o f a r o t a t i n K d i s k with a a t o p disHsontinuity o f temperature in a l a r g e body o f qaencont f l u i d . The extreme e a s e o f t h i s problem with i n f i n i t e s t u d y by Smyrl and No~mn [ 1 ] , solution Shill

P r a n d t l number has been

and i s known as L i g h t h i l l

[ 2 ] ° R e c e n t l y , Chso [ ~ ] ,

a p p r o x i m a t i o n t o the s t u d y o f h e a t t r a n s f e r

umiak a two term r e p r e s e n t a t i o n o f the v e l o o i t y step discontinuity

approximation

and Chao and G r i e f [~] extended LiKhfrom r o t a t i n K body

field.

For ~ d g e

flow with

o f s u r f a c e temperature, Chao and Cheean [~3 used a

c o o r d i n a t e p e r t u r b a t i o n t e c h n i q u e t o a n a l y s e the s t e a d y s t a t e h o s t t r a n s f e r s However, t h e P r a n d t l number e f f e c t

on t h e temperature d i s t r i b u t i o n

l o c a l h e a t t r a n s f e r r a t e was not f i l l y

and

investiKatod.

a c o m b i n a t i o n o f the c o o r d i n a t e p a r t u r h a t i o n o f Chao and Chasms [~3

53

54

S.Y. T s a y a n d Y . P .

and p a r a m e t e r p e r t u b a t i o n p a p e r . The c o e f f i c i e n t m ate perturbation

heat transfer

Vol. 4, No. I

w i t h P r "~ a s p a r a m e t e r i n p r o p o s e d i n t h i s

a r e shown t o be u n i T s r s a l

taken care of the discontinuity

whereas the parameter perturbation on h e a t t r a n s f e r ,

Shih

functions. of surface

deals with the Prandtl

The c o o r d i n temperature,

nusber effect

T h i s t e c h n i q u e would be a p p l i e d t o o t h e r b o u n d a r y l a y e r

problems, The Governing Equations

Under t h e b o u n d a r y l a y e r a p p r o x i m a t i o n t h e e n e r g y e q u a t i o n and boundary oonditions as referred

~T

4. W

U - -

~T - -

to Fig.

k

1

|~"s

~tT

(z)

=

T(r,O)

= T~

r ~

T(r,O)

= Tw

r ~r

re

(2)

e

(3)

T(r, oo) ..T~

The s o l u t i o n

of the Telocity

u = r~

~C7) -

r~

field

is

[6]

(-,mC~/)) 2 (6) Z

w

FIG. i Rotating Disk

VOI. 4, NO. i

HEAT TRANSFER FROM A R3T~TING DISK

55

whore (7)

H(~?) . - . 9 , ,

a ~ 6 ÷ 000

(8)

with

a = 0.510, Introduo~

b ,, - 0 . 6 1 6

of

(9)

g = Tw--T.

r

.

[1-

tol

i.

¢~,].,t-

~. ,-, ,,~ -~.,

(1o)

,. ~,~

gqo. ( 1 - 1 0 ) b e o o w |

~

¢1-1,~21A pr- -I- ~-H,(~z) j

[ R ,,¢

,~" (11)

._ A,I

~¢1-R,)

H,('~)

m

e(R,O) O(R,~)

~O.o "~ R

1

.

.

(12)

0

(15)

"

Perturbation 1~t

i,,o

j,,o

Solutlon

56

S.Y. Tsay and Y.P. Shih

Vol. 4, No. 1

Inserting Zq. (14) i n t o Eqs. (if-I}) and oquatiug tho © o e f f i c i n e t ~ of equal powerB of Ri P r ' ~ yield ~;',,

+ 3 ~'~,o

e~',, + 3 ~'W,,

(3.9

" o

-

~

i A. ~ , W . . ~e,. = ~-

O~',, + 3 ~"Qi', " 6~'Q,,,

1

= T A,

(16)

~',Q,,,, + T

b

A,

~V,, (17)

eJ',, + 3 ~'e~,, - 9 y ~ ,, " T

b A, ~-'Q, ,, A, ~-,~, ,, - A, ~.,Q, ,, - ~..

+ ~

e:,,,

+ )~"w,.,

Q;"

- 12 ~,,,,,

=-~A,.

~-,Q.,,.

- )~.,~, ,,,

¢la)

(19)

~ t4

Zb A' ~,O, ,, " ' i ~ 3

with ,o ( o )

~,o(m)

= ",,

t , ,,, ( o )

. e,,,,,(~)

= ~ ,,,, ( o )

= e,,,,,(~)

. . . . .

.....

o

o

(21)

(2z)

Vol. 4, NO. 1

HEAT TRANSFER F R O M A R C E A T I N G

Oi, j a r e u n i v e r s a l

functions.

~,o

is the Lighthill

DISK

57

approximation nolution

a s g i v e n by S m ' y l and Newnan [ 1 ] . N o t i c e t h a t t h e nonvaninhinK c o e f f i c i e n t s are 0i, i, i l O, i, 2, ... , and 0i+3, i , i = I, 2, 3, . . . . Eq.

Therefore,

(l~) gives

O(~'|~l)

• 01, |

"~" ( 0 | | |

"1" 0 1 ) , ,

i~|)])

]pll-- ]

..1- ° ° .

i ÷ ( G i , i + e l + 3 , i R ) ) R i P r ' ~ - ÷ ...

The a n a l y t i c a l

solution

(23)

o f ~ ,o and • I ,, arc

(2k)

(25) lo

o t h e r e l , j a r e o b t a i n e d by n u m e r i c a l i n t e & T a t i o n o F i g . 2 show8 t h e l ~ m a l t s . Typi©al t e m p e r a t u r e d i s t r i b u t i o n s the series

truncated at i >~0

a r e shown i n F i g . 3 u s i n g Eq. (2}) w i t h

The c o n v e r p n e e

o f Eqo (2~) i n s a t i s f a c t o r y

for Pr~l.

Rate of Heat Transfer

The l o c a l h e a t t r a n n f e r

q.

rate,

q, in

- k ( ~~T ' ~ ) S l O = h(T w

T. )

(26)

and t h e l o c a l N u s s e l t number, Nu, i s

lu.

-~

--

~.o

(27)

58

S.Y. Tsay and Y.P. Shih

I'0

,

,

,

,

,

Vol. 4, No. 1

,

,

,

,

,

,

0"9 0"8

0"7 0"6 0-5 0-4 0"3 0'2

t

0,.,(,jf-~---~

O0

(~4

0'1 0'0

(>8

1"2

2"4

2"0

1~5

¢

0"6

0'4

0"2

-

Oa s(¢)

Oi,j(¢) 0'0

-0'2

"0"40-0

~__~ I

I

0"4

J

I

0-8

I

I

1"2

I

L

1"6

06,31~'1XIO

i

I

2-0

FIG. 2 Universal functions of rotating disk with step discontinuity of surface temperature

Z

i

2"4

V o l . 4, NO. 1 Substitutlns

HEAT TRANSFERFRC~ARDTATINGDISK Eq.

(2~)

i n t o Eq. ( ~ )

~u = - A"~ R"~ P ~

59

one o b t a i n s

Q'(O,R)

(28)

with

o,(o,~) . e,,,,(o) + [ e . . ( o ) + ...

+ e~,,(o)~, ] ~ ~r'~

+ {@I,i(O) + Q[+},i(O)R) ] Ri pr'~ + . . .

whops

@~,. (0) = -

1.1198%

~',4

e;,,(o) .

o.3539~

@~ , t ( 0 )

0~ ,e (0) .

0.0695615

,5 ( o ) . - o . o o 6 ~ 2

e~ ,, (o) .

o.0181006

,~ (o)

e~,, (o) =

0.00000o26

In the calculation @4,,

~,~

---

of ~(0,R),

.

.

= 0.005?965

. o.oo~2o3

soles

the coefficients

.

.

o f R~ i n t h e b r a o k e t l ,

f o r m i l l 1 1 R.

t s a n be n o s l s c t e d I'0

(o) . o.oo8747o6

.

.

.

.

.

.

.

r./r'07"~t r oJJo (>9

~%,

005 ,_

O, ~,

r./r-oo6

e (>~

\~'

(>4

"'-."

-

~'

~

,,,~

-.. ~ ~____~ ~ ~

"~"

o,

...

o., • (>0 0

~.~_'~ 0-4

, Oe

"--.~.-.-'y~._~ 1.2

. . . . 1"6

20

2~

FIG. 3

Temperature distribution of rotating disk with step discontinuity of surface temperature

60

S.Y. Tsay and Y.P. Shih

Vol. 4, No. i

Conclusion

The perturbation method proposed in this paper is a general method which can be applied to other forced flow boundary layer heat transfer problems. The coordinate perturbation in terms of R deals with step change of surface temperature whereas the parameter perturbation in Pr -V3 shows the effect of Prandtl number.

The coefficients are universal functions.

Acknowledgment

The authors appreciate the financial support of National Science Council.

Nomenclature

a, b

flow c o n s t a n t s d e f i n e d by Eq. (8)

A

(~)}-- defined by ~ . (10)

Cp

Specific heat

F, H h

d i m e n s i o n l e s s v e l o c i t y f u n c t i o n s d e f i n e d by Eqs. ( 5 - 6 ) local heat transfer coefficient at r

k Nu

thermal conductivity

Pr

P r a n d t l number,

l o c a l Nmsselt number a t r NPC~k

radial

coordinate

radial

c o o r d i n a t e a t whioh the t e m p e r a t u r e has a d i s c o n t i n u e d

s t e p change R

t r a n s f o r m e d d i m e n s i o n l e s s cOOrdinate d e f i n e d by Eq. (10)

T

temperature

m~

v

v e l o c i t y components i n r-and z - d i r e c t i o n s ,

respectively

F(n)

coordinate norlal gamma f u n c t i o n =

~(n,x)

incomplete gamma function =

r

t r a n s f o r m u d d i m e n s i o n l e s s c o o r d i n a t e d e f i n e d by Eq° (10)

s

to disk surface -~tn-le'tdt ~x

tn-le-tdt

dimensionless coordinate dsfinedbyEq.

(7)

G

d i m e n s i o n l e s s t e m p e r a t u r e d e f i n e d by ER. (9)

p

kinematic viscosity

P

density azimuthal coordinate a n g u l a r v e l o c i t y o f d i s k in

J-direction

Vol. 4, NO. 1

HEAT T R A N S F E R F R O M A R O r A T I N G D I S K

61

References

1. W. H. SQyrl and J . Newman, R i n g - d i s k and S e c t i o n e d d i s k e l e c t r o d e s , J . E l e c t r o c h e m , Soc. ~l~, 212-219 ( 1 9 7 2 ) . 2. M. J .

Lighthill,

C o n t r i b u t i o n s t o the t h e o r y o f h e a t t r a n s f e r

a l a m i n a r boundary l a y e r ,

P r o c . Roy. S o c . , London, A 20_2, 359-~77 (19~0).

~. B. T. Chao, An improved L i g h t h i l l ' s boundary l a y e r s ,

through

a n a l y s i s of heat t r a n s f e r

I n t . J . Neat Mass T r a n s f e r , ~ ,

through

907-920 ( 1 9 7 2 ) .

4. B. T. Chao and R. G r e i f , Laminar f o r c e d c o n v e c t i o n over r o t a t i n g T r a n s . ASME J . Heat t r a n s f e r

bodies,

C, 96, 46~-466 ( 1 9 7 4 ) .

~. B. T. Chao and L. S. Cheema, F o r c e d c o n v e c t i o n in wedge flow with nonisothealal

surfaces,

I n t . J . Heat Mass T r a n s f e r , ~4, 1363-1375 ( 1 9 7 1 ) .

6. W. G. Cochran, The flow due t o a r o t a t i n g

~., ~5-375 (19~).

d i s c , P r o c . Camb. P h i l ,

Soc.