An analysis of heat transfer through thermal insulating material

VACUUM Classified Abstracts

I --

General

Science

and

Engineering

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I

Abstract No.

',uld References

Contd.

A n A n a l y s i s of H e a t T r a n s f e r t h r o u g h T h e r m a l I n s u l a t i n g M a t e r i a l

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T h e e f f i c i e n c y of h e a t i n s u l a t i n g m a t e r i a l s h a s b e e n i n v e s t i g a t e d . T h e e x p e r i m e n t s w e r e c a r r i e d o u t o n a n 8 i n c h . g u a r d e d h o t - p l a t e b u i l t i n a c c o r d a n c e w i t h t h e s p e c i f i c a t i o n s of t h e B u r e a u of S t a n d a r d s a n d e n c l o s e d i n a c y l i n d r i c a l t a n k , t h e a i r p r e s s u r e of w h i c h o m l d b e v a r i e d f r o m 80 i n c h . H g t o 0.1 i n c h . H g . R a d i a t i o n w a s i n v e s t i g a t e d first. T h e r e s u l t s of t e s t s a r e g i v e n i n T a b l e I r e p r o d u c e d b e l o w in a b b r e v i a t e d form. I t is s h o w n t h a t t h e a i r cells t e s t e d w h i c h h a d a size of 8 ;< 8 . 1 i n c h t r a n s m i t 7 4 % of t h e t o t a l h e a t b y r a d i a t i o n ( a f t e r a l l o w a n c e h a s 1)een m a d e for t h e e m i s s i v i t y of t h e m e t a l l i c f o i l ) Canada.

Table [ Mean Tel*t pe~'tlteti'e

Npecim en

o 12.

Air Cell : Paper Surfaces Aluminium Foil Surfaces Aluminium Foil Surfaces

Temperallo'e Difference "l,'.

( !ondactivity lc

25.7 36.0 IO.8

1.06 0.278 9.27~

82.0 90.7 71;.2

O I n v e s t i g a t i n g c o n v e c t i o n t h e a u t h o r e m p l o y e d t h e n l e t h o d of v a r y i n g t h e a i r d e n s i t y i n t h e p o r e s or cells of t h e insulating material. As a p r e l i m i n a r y m e a s u r e cells of t h e s a m e size as before, f a c e d o n b o t h s i d e s w i t h a l u m i n i m n foil w e r e t e s t e d , filled a n d u n f i l l e d , a t d i f f e r e n t a i r p r e s s u r e s w i t h t h e r e s u l t s as s h o w n in T a b l e [ I reproduced below. Table II

......

[

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Air Cell (vae) : Both sides faeml with aluminimn foil

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O

S

~tyrofoam " : Density L.31 tb./eu. ft.

A ir t'ressm'e inch. Hg

Jle'a~t l'emperatu,'e { F.

T e m pfrature D~fferenee ° l.'.

Conductrinity

29.91. 24.27 9.06 4.4.I 2.69 1.72 l. 18 0.294 0.220 (). 153

7d.2 83. I 8:1.1 85.4 92.2 !),i. I I}8. I .~}2.9 92. I 9k[ )

10.~ -18.(; t4.2 49,9 60. I 57.8 ,13.5 55.2 59.8 67..1

0.276 0.249 0.225 0.212 0.20B 0.192 0.19 I 0.202 0.20O 0.192

29.9 1.0

8 [.4 80.7

33.1 34.3

0.307 0.301

1,:

A m o n g t h e v a r i o u s p o w d e r s of s m a l l g r a i n size i n v e s t i g a t e d w a s S a n t o c e l , a S i l i c a \ e r o g e l p()w(ler w i t h b l a c k fillet'. R e s u l t s a r e sh(}wn in T a b l e I i I (see below). Table III

A ir .Y f~e¢.[ l,~e tl

" Sautoeel " (SAN) (Silica Aerog(.I) (with Black Filler) : Density 3.88 lb./cu, ft l'arti,h~ Size 20-40 Mq~sh (U.& Standard)

Pressure i~wh. t l g

29.72 21.5 12.7 9.28 2.77 1.81 0.23

Mean "l'em])eraDtre

Teqitperatt~*e

( 'ollch¢c-

Difference

tit:i#! I.:

o F.

Io7.0 103.3 107.3 108 () 106.9 112.0 1258

~il.l d5.8 1~7.9 73.2 Sl') 2 76.4 I I6.7

0.185 0.179 0.170 0.162 0.155 0.149 0.10-t

T h e c o n d u c t i v i t y uf 0.185 o b t a i n e d a t a t m o s p h e r i c p r e s s u r e is v e r y close t o t h a t of s t i l l a i r as g i v e n b v K e c n a n a n d 1,2aye. S i m i l a r t e s t s w e r e m a d e o n g l a s s w o o l of v a r i o u s r l e n s i t i e s a n d o n t i g h t l y p a c k e d w a x - c o a t e d d r i n k i n g s t r a w s . P r e v i o u s i n v e s t i g a t i o n s i n d i c a t e d t h a t , if t h e size of t h e cells w a s l a r g e a s c o m p a r e d w i t h t h e m e a n free p a t h of t h e gas, t h e r e c i p r o c a l of a b s o l u t e p r e s s u r e p l o t t e d a g a i n s t t h e r e c i p r o c a l of c o n d u c t i v i t y

Oclobcr, 1 9 5 2

Vacuum Vol. I I No. 4

408

VACUUM Classified Abstracts

I ---

General

Science

and

Engineering

--

I

Abstract No. all('] R,efel'ellees

Contd.

.~a~e a s t r a i g h t line. T h i s w a s c o n f i r m e d b y e x p e r i m e n t s in a i r u p t o a p r e s s u r e of a b o u t 8 inch. m e r c u r y . B e y o n d t h a t p r e s s u r e t h e r e w a s a n i n c r e a s i n g d e v i a t i o n l r o m t h e s t r a i g h t line r e l a t i o n s h i p o w i n g t o t h e i n c r e a s i n g i n f l u e n c e of c o n v e c t i o n . K a n n u l u i k a n d M a r t i n w o r k i n g on p o w d e r s c o n f i r m e d t h e s e c o n d i t i o n s a n d d e v e l o p e d t h e f o r m u l a p / k - - a p 5 b w h e r e p is t h e a b s o l u t e p r e s s u r e of t h e gas, k is t h e t h e r m a l c o n d u c t i v i t y a n d a a n d b c o n s t a n t s . P l o t t i n g t h e c u r v e of p / k a g a i n s t p a n d d r a w i n g a s t r a i g h t line t a n g e n t i a l l y t o t h e l o w e r e n d of t h e c u r v e g i v e s t h e h e a t t r a n s m i t t e d b y c o n v e c t i o n as t h e d i s t a n c e b e t w e e n t e s t c u r v e a n d s t r a i g h t line. T h e c u r v e s d r a w n fror S a n t o c e l w e r e p r a c t i c a l l y s t r a i g h t a t h i g h e r p r e s s u r e s i n d i c a t i n g t h a t t h e r e is n o a p p r e c i a b l e t r a n s m i s s i o n b y c o n v e c t i o n . T h i s is p r o b a b l y t r u e for m o s t fine p o w d e r s . T h e r e s u l t s r e p o r t e d here a p p l y o n l y t o t h e size of air cell e m p l o y e d in t h e s e e x p e r i m e n t s . T h e effects of c o n v e c t i o n w()uhl p r o b a b l y be g r e a t e r if l a r g e r a i r cells w e r e used. S o m m a i r e : R a p p o r t des e s s a i s de l a b o r a t o i r c u t i l i s a n t la t e c h n i q u e de v i d e p o u r ia ( h - t e r m i n a t i , m de la v a l e u r d e s d i f f d r e n t s t y p e s de m a t d r i a u x i s o l a n t s h la c h a l e u r .

O

On New Methods of Insulating Very Low Temperature A p p a r a t u s Russia. P a r t i a l l y e v a c u a t e d " m i p o r a ", a n e x p a n d e d u r e a f o r m a l d e h y d e p l a s t i c ( d e n s i t y 18-22 k g m : L p o r o s i t y 97-98°.o) c o m b i n e s t h e c h e a p n e s s a n d d u r a b i l i t y of s o l i d i n s u l a t i o n w i t h t h e e x c e l l e n t p r o p e r t i e s of h i g h v a c u u m as t h e r m a l i n s n l a t i o n for l o w - t e m p e r a t u r e a p p a r a t u s a n d c o n t a i n e r s for l i q u i d , O, H, N, CH, etc. P l o t t e d t e s t r e s u l t s s h o w t h e r a t e s of e v a p o r a t i o n of l i q u i d a i r a n d l i q u i d H f r o m a c y l i n d e r i n s u l a t e d b y h i g h v a c u u m (10-Smm. H g ) , p a r t i a l v a c u u m " m i p o r a " a t a t m o s p h e r i c p r e s s u r e , e v a c u a t e d " m i p o r a " (to 10-2mm. H g for l i q u i d air, a n d (l.2 ram. H g for l i q u i d H) a n d " m i p o r a " a t l i q u i d a i r t e m p e r a t u r e s f r o m 0.022 t o 0.0025 k c a l / m h r ' C . ( ScieJ~ce . t t, stracts) . ' ; o m m a i r e : N o u v e l l e s m6th()des d ' i s o l e m e n t d ' a p p a r e i l a t r b s b a s s e t e m p e r a t u r e .

O

A n Optical Cell for Use w i t h Liquid H e l i u m U n i t e d S l a t e s . T h e a u t h o r s d e s c r i b e a cell s p e c i a l l y (levelot)ed for t h e s t u d y ()f t h e o p t i c a l p r o p e r t i e s ()f a l k a l i h a l i d e s a n d t h e a b s o r p t i o n s p e c t r a of m a t e r i a l s w h i c h c o u l d b e s u p p o r t e d b e t w e e n or d e p o s i t e d on a l k a l i h a l i d e c r y s t a l s . T h e cell is 6 inch. w i d e a t t h e t o p b u t n a r r o w e r a t t h e b o t t o m so t h a t t h e s a m p l e is o n l y 1 i n c h f r o m t h e o u t s i d e w i n d o w . I t c o n s i s t s of t h r e e s e c t i o n s , a n o u t e r v a c u u m j a c k e t i n c l u d i n g t h e w i n d o w s , a l i q u i d n i t r o g e n c o n t a i n e r a n d r a d i a t i o n s h i e l d a n d a l i q u i d h e l i u m c o n t a i n e r a n d s a m p l e holder. A c o m m o n v a c u u m is l n a i n t a i n e d b e t w e e n all s e c t i o n s . T h e l i q u i d h e l i u m c o n t a i n e r is t h e i n n e r m o s t s e c t i o n , h o l d i n g 1 l i t r e of h e l i u m a n d is s u s p e n d e d f r o m a s t a i n l e s s s t e e l t u b e ~ i n c h d i a m e t e r a n d 17 inch. l o n g w h i c h is s o l d e r e d to a c o l l a r f i t t e d t o t h e t o p e n d p l a t e . C o n c e n t r i c t o t h e l a t t e r is a s t a i n l e s s s t e e l t u b e of 1 i n c h d i a m e t e r , t h e h)wer e n d of w h i c h t e r m i n a t e s i n a s y l p h o n b e l l o w s . T h i s t u b e c a n b e r a i s e d a n d l o w e r e d b y m e a n s of a c r a n k rack and pinion assembly and by this means the helium container can be raised and lowered by approximately 2 i n c h . T h e n i t r o g e n c o n t a i n e r is s u s p e n d e d f r o m t h e t o p p l a t e of t h e a s s e m b l y . A t t h e l o w e r e n d is a c o p p e r h e a t s h i e l d w h i c h is k e p t a t 77~K b y c o n d u c t i o n c o o l i n g . E x c e p t for t h e r a d [ a t i o n t h r o u g h t h e w i n d o w s t h e l i q u i d h e l i u m v e s s e l ' sees ' n o t h i n g w a r m e r t h a n t h a t . T h e o u t e r h o u s i n g is m a d e f r o m s t a i n l e s s steel. A f t e r e v a c u a t i n g t h e cell t o 10 4 r a m . H g l i q u i d n i t r o g e n is filled i n t o t h e n i t r o g e n c o n t a i n e r a n d , for t h e p u r p o s e s of p r e - c o o l i n g , i n t o t h e h e l i u m c o n t a i n e r . A t t h i s s t a g e t h e p r e s s u r e s h o u l d h a v e d r o p p e d t o 1()-5 ram. Hg. T h e cell is t h e n r e m o v e d f r o m t h e v a c u u m line, t h e l i q u i d n i t r o g e n in t h e h e l i u m c o n t a i n e r b o i l e d a w a y a n d h e l i u m filled in d i r e c t l y f r o m a Collins l i q u i d h e l i u m c r v o s t a t . T h e cell is f i t t e d w i t h r o c k s a l t wind})ws a n d ~)ne I ) e r v l l i u m w i n d o w . T h e c r y s t a l h o l d e r c a n c a r r y t w o s a m p l e s . A d i f f e r e n t d e s i g n is d e s c r i b e d for use w i t h s a n i p l e s in v a p o u r fi)rm, l , i q u i d s a m p l e s , too, c a n be used. I n o r d i n a r y c i r c u m s t a n c e s (me c h a r g e of h e l i u m will l a s t for a b o u t 20 h o u r s . One f i l l i n g of n i t r o g e n , a p p r o x i m a t e l y 1.5 litres, l a s t s 12 h o u r s . T h e o u t s i d e of the cell r e m a i n s a t r o o m t e m p e r a t u r e d u r i n g o p e r a t i o n , a n d if t h e cell is s u f f i c i e n t l y v a c u u m t i g h t , t h e l i q u i d h e l i u m c o n t a i n e r a c t s as t h e v a c u u m p u m p t h u s m a k i n g t h e cell c o m p l e t e l y p o r t a b l e . ,S'ommaire : C u r e ()pti(]ue p o u r l l l e s n r e a n \ b a s s e s t e l n p d r a t l l r e s d a n s ]e ( l o n l a i n e (le la st)ectr()scopie i n f r a rouge.

An'ticle by l';. A. Allcnl Euff,g.

2q2:I

~rl :,tic by A II Fradkov. l)okL A k a d . '.Yauk 8~'5' R

8t, No. 4, 1951 5,U)-51

2( ):}: I

Article by \~. ]I. Duerig & [ I,. Mador l,'e#. Net. l n s t r u m .

23, Aug. 1952, 421-424

Filters for the Infra-Red Region See A b s t r a c t No. : 1 9 2 / I I I

2o I / r

Theoretical Study of the Interference Filter I : r a n c e . T h e s o l u t i o n is g i v e n of t h e p r o b l e m of t h e p r o p a g a t i o n of a p l a n e m o n o c h r o m a t i c l i g h t w a v e t h r o u g h a n i n t e r f e r e n c e f i l t e r c o n s i s t i n g i n a p e r i o d i c s y s t e m of a n y n u m b e r m of ( h m b l e l a y e r s w i t h i n d i c e s nt a n d n 2 a n d t h i c k n e s s e s d t a n d d 2 w i t h o u t t a k i n g a c e ( r a n t of a b s o r p t i o n . T h e t r a n s m i t t e d i n t e n s i t y ( w h e n n t d t = n 2 d a for n o r m a l i n c i d e n c e ) is e x p r e s s e d a s a f u n c t i o n of w a v e l e n g t h . B y s u p e r p o s i t i o n of t w o ()f t h e s e filters, one c a n o b t a i n a p r a c t i c a l l y n l o n o c h r o m a t i c f i l t e r of h i g h t r a n s m i t t a n c e . (.',ch',cc . I bslracts) .%m~maire : l:.tude t h d o r i q u e d u zndcallisnle d e f ( > n c t i o n n e m e u t (le filtres i n t e r f d r e n t i e l s .

2o5/I

()ctobcr, 1 9 5 2

Vacuum Vol. I I .Vo. 4

.I.,

35, .\u~. 1952:

.krt,icle hy D. G. Frau ( Them'. Im~h'~tm,) 3 z, April I.~)52 Id[-lq;!)

409