C o A . N o t e N o . 123
ff Hi\'!SCHE HOGESCHOOL DELFT
VLIEGTUIGBOUWXUNDE' Michiel d« KuyJerwtg 10 - D£LFT
THE COLLEGE OF AERONAUTICS
C R A N F I E L D
A P R E L I M I N A R Y E X P E R I M E N T A L I N V E S T I G A T I O N O F T H E E F F E C T O F S U R F A C E C A T A L Y T I C E F F I C I E N C Y ON STAGNATION P O I N T H E A T T R A N S F E R b y J . R. B u s i n gT H E C O L L E G E O F A E R O N A U T I C S C R A N F I E L D
A P r e l i m i n a r y E x p e r i m e n t a l Investigation of the Effect of Surface Catalytic Efficiency on
Stagnation Point Heat T r a n s f e r b y
-J . R. Busing. B . E . , B . S c . , D . C . A e .
SUMMARY
R e s u l t s of an e x p e r i m e n t a l investigation to m e a s u r e the difference between the heat t r a n s f e r r a t e to a catalytic wall and to a non-catalytic wall a r e p r e s e n t e d . Using thin film t h e r m o m e t e r techniques, a s s o c i a t e d with an e l e c t r i c a l analogue, d i r e c t m e a s u r e m e n t was made of the heat t r a n s f e r r a t e to a chemically deposited platinum film and a vacuum evaporated silicon monoxide film. These films w e r e formed n e a r the stagnation point of a pyrex g l a s s s p h e r e and the e x p e r i m e n t s w e r e done in the College of Aeronautics shock tube. The m o d e l s w e r e designed so that the heat t r a n s f e r r a t e s w e r e m.easured under identical flow conditions.
The r e s u l t s obtained indicate that the heat t r a n s f e r r a t e to the platinum film i s significantly higher than the heat t r a n s f e r r a t e to the silicon mionoxide film.
This r e p o r t was p r e s e n t e d at the Fifth Scientific Conference of the Polish Academy of S c i e n c e s , Jablonna, Poland. 1961.
CONTENTS 1. 2 . 1 . 2 . 2 . 2 . 3 . 3 . 4 . 5. 5 . 1 . 5 . 2 . 5 . 3 . 6. 7, S u m m a r y Introduction Shock Tubes Models Instrumentation T h e o r y R e s u l t s 1
Comparison of T h e o r e t i c a l and E x p e r i m e n t a l Results The flow in the boundary l a y e r is not frozen
Page 1 1 2 3 3 5 6 6 I n c o r r e c t value for the catalytic activity of
silicon monoxide
The flow outside the boundary l a y e r i s not in equilibrium Acknowledgements References F i g u r e s 7 7 8
1. Introduction
Stagnation t e m p e r a t u r e s encountered by hypersonic v e h i c l e s and r e - e n t r y s a t e l l i t e s a r e of the o r d e r of s e v e r a l thousands of d e g r e e s Kelvin. This i n t r o d u c e s a s e v e r e heating p r o b l e m , p a r t i c u l a r l y at the stagnation point.
At t h e s e elevated t e n a p e r a t u r e s the gas behind the bow shock wave i s highly d i s s o c i a t e d . T h u s , in addition to the n o r m a l aerodynamic heating by m o l e c u l a r conduction one m u s t consider the effect upon the heat t r a n s f e r of the diffusion of a t o m s and the e n e r g y that they l i b e r a t e upon recombination. If the density i s sufficiently low, the a t o m s m a y diffuse a c r o s s the boundary l a y e r and r e a c h the wall before recombining, i . e . the flow i s "frozen". They m a y then r e c o m b i n e on the wall and the energy thus li be r at ed could g r e a t l y i n c r e a s e the r a t e of heat t r a n s f e r to the s u r f a c e . C o n v e r s e l y , if a wall of low catalytic activity is used then the heat t r a n s f e r r a t e should be considerably r e d u c e d .
Stagnation conditions which a r e developed in flight can be reproduced in the shock tube and considerable work h a s been done on high t e m p e r a t u r e gas flows with this specialised facility.
The effect of dissociation in such flows h a s been extensively studied both t h e o r e t i c a l l y and e x p e r i m e n t a l l y . A t h e o r y of stagnation point heat t r a n s f e r h a s
been developed notably by L e e s (Ref. 1) and by F a y and Riddell (Ref. 2). E x p e r i m e n t a l investigations have been performed by Rose and Stark (Ref. 3) and many o t h e r s ,
which confirm the t h e o r e t i c a l p r e d i c t i o n s .
It h a s been pointed out in t h e o r e t i c a l studies by Scala (Ref. 4) and Goulard (Ref. 5) that the catalytic efficiency of the surface can have a s t r o n g influence on the heat t r a n s f e r . That i s , the higher the catalytic efficiency of the s u r f a c e , the m o r e e a s i l y do atoms recombine t h e r e and l i b e r a t e t h e i r e n e r g y of dissociation.
The e x p e r i m e n t s to be d e s c r i b e d l a t e r have been designed to produce flows with a high d e g r e e of dissociation at r e l a t i v e l y low d e n s i t i e s , in an attempt to produce frozen conditions in the boundary l a y e r . Thin film t h e r m o m e t e r s have been used to m e a s u r e heat t r a n s f e r r a t e s to a b a r e platinum film and a l s o to a platinum film coated with silicon monoxide. T h e s e two films should have different catalytic efficiencies and hence t h e r e should be different heat t r a n s f e r r a t e s to them under frozen flow conditions.
2 . 1 . S h o c k Tubes
The unsteady flow which is set up in a shock tube, when the diaphragm s e p a r a t i n g high p r e s s u r e from low p r e s s u r e b u r s t s , is well understood and i s i l l u s t r a t e d in F i g . 1.
This idealised flow d i a g r a m is modified in p r a c t i c e by the effect of v i s c o s i t y and the associated boundary l a y e r which f o r m s behind the moving shock wave. The contact surface is a c c e l e r a t e d and diffuses rapidly into the hot region. As a r e s u l t the length of hot flow is considerably reduced. These effects a r e m o s t s e v e r e at low d e n s i t i e s .
The College of Aeronautics shock tube i s made from s t a i n l e s s steel of 5 c m . internal d i a m e t e r and about one c m . wall t h i c k n e s s . The tube is mounted v e r t i c a l l y with the high p r e s s u r e section at ground level and the working section at first floor
l e v e l . The dump c h a m b e r and vacuum equipment a r e on the second floor. The m a i n dimensions a r e shown in F i g . 2. Fig.3a shows the charging equipment which i s r e m o t e l y controlled from the first floor and the high p r e s s u r e section which can be swung to one side to change d i a p h r a g m s , whilst F i g . 3b shows the dump tank, diffusion pump, backing pump and control v a l v e s . F i g . 4a shows a close up of the model mounted in the working section in the unexpanded flow, and F i g . 4b i s a view of the working section and associated e l e c t r o n i c equipment for r e c o r d i n g initial tube p r e s s u r e , shock velocity and heat t r a n s f e r r a t e s .
D i a p h r a g m s of v a r i o u s t h i c k n e s s e s made from pure copper, aluminium o r p l a s t i c film a r e used. The m e t a l ones a r e p r e s c r i b e d to e n s u r e s y m m e t r i c a l petalling without l o s s . The d i a p h r a g m s a r e allowed to b u r s t naturally using cold hydrogen a s the d r i v e r gas at p r e s s u r e s up to 75 a t m o s p h e r e s . The channel o r low p r e s s u r e section of the tube i s n o r m a l l y evacuated to about 10"^ T o r r and a i r o r other gas admitted to the d e s i r e d p r e s s u r e . The p r e s s u r e s r i s e in the s y s t e m due to l e a k s is about 10"^ T o r r p e r m i n u t e . This i s acceptable at initial p r e s s u r e s of 0.05 T o r r . P r e s s u r e s a r e m e a s u r e d with an "Alphatron" vacuum gauge which depends for its operation on the variation of alpha r a y absorption with change of gas p r e s s u r e . This gauge will m e a s u r e total p r e s s u r e s in the range 1000 T o r r to 10"^ T o r r with a c c u r a c i e s of about 2%.
Shock velocity is m e a s u r e d by r e c o r d i n g on a microsecond counter the t i m e i n t e r v a l r e q u i r e d for the shock to t r a v e l 20 cm. The shock wave i s detected by thin film r e s i s t a n c e t h e r m o m e t e r s , which give r e l i a b l e t r i g g e r i n g at Mach n u m b e r s a s low a s 1.1 into a i r at 200 T o r r . (This c o r r e s p o n d s to detection of a t e m p e r a t u r e r i s e of about 0.05°C at the wall).
2. 2. Models
All the models used w e r e made from 1.27 c m . d i a m e t e r polished pyrex g l a s s s p h e r e s . The heat t r a n s f e r gauges w e r e thin film r e s i s t a n c e t h e r m o m e t e r s formed from platinum paint (Hanovia 05X) baked onto the pyrex at a t e m p e r a t u r e n e a r the softening point of the g l a s s . The films w e r e approximately 10"^ m m . thick and about 0.2 m m . w i d e . They were drawn a s an open c i r c l e approximately 1.2 m m . dia. around the g e o m e t r i c stagnation point. This c o r r e s p o n d s to a 10 angle subtended at the s p h e r e c e n t r e . The tetniperatüfe coefficient of r e s i s t a n c e of the films was 2.5 m i l l o h m s / o h m pef C Gauge r e s i s t a n c e s were about 100 ohms and were used with a steady c u r r e n t of 15 m i l l i a m p s flowing through them. Copper plated platinum l e a d s w e r e used to connect the signal w i r e s to the gauge.
Initially, a single gauge was used with e i t h e r b a r e platinum o r silicon monoxide coated platinum a s the sensing e l e m e n t . However, it was found that identical flow conditions could not be reproduced in the shock tube at low densities and so a model having two sensing e l e m e n t s was m a d e . F i g u r e 5 shows the two types of model and the method of mounting in the working section. The silicon monoxide was deposited by vacuum evaporation and in t h i c k n e s s e s of about 5 x 10"^ m m . was v e r y adherent and r e m a r k a b l y robust.
These models lasted for five or six r u n s , after which the gauge was open circuited probably by a d i r e c t hit from a dust particle c a r r i e d along by the contact s u r f a c e .
2. 3 . Instrumentation
When m e a s u r i n g heat t r a n s f e r r a t e s in a shock tube it is usual to r e c o r d the surface t e m p e r a t u r e variation with t i m e by m e a n s of a thin film r e s i s t a n c e t h e r m o m e t e r . A fairly lengthy n u m e r i c a l integration of points r e a d off the film i s then r e q u i r e d to obtain the v a r i a t i o n of heat t r a n s f e r r a t e with t i m e . Meyer (Ref. 6) h a s suggested the use of the e l e c t r i c a l analogue for the d i r e c t m e a s u r e -ment of heat t r a n s f e r r a t e . He has used his design successfully in a gun tunnel. A s i m i l a r analogue, but with much s h o r t e r time resolution, h a s been used in
t h e s e e x p e r i m e n t s and i s shown in F i g . 6. The diffusion of charge into this network closely a p p r o x i m a t e s to the diffusion of heat into a semi-infinite solid. Hence, the voltage developed a c r o s s the first r e s i s t o r is d i r e c t l y proportional to the heat t r a n s f e r r a t e . The sensitivity of t h i s network is such that a heat t r a n s f e r r a t e of 100 w a t t s / c m will give an output of one millivolt. In p r a c t i c e this network will show v a r i a t i o n s in heat t r a n s f e r r a t e s which a r e impossible to obtain from the t e m p e r a t u r e r e c o r d s because of the i n a c c u r a c i e s in film reading and integration. F i g . 7 shows the t e m p e r a t u r e r e c o r d and equivalent heat t r a n s f e r r a t e obtained via the analogue network.
The circuit for r e c o r d i n g the heat t r a n s f e r r a t e s from the composite model is shown d i a g r a m m a t i c a l l y in F i g . 8. The power supply and balance network »vere used to equalise the output from the two gauges and also to adjust the gauge voltage in the event of the r e s i s t a n c e i n c r e a s i n g during a r u n .
Since heat t r a n s f e r r a t e s could be m e a s u r e d d i r e c t l y the models were cilibrateii in the shock tube at a low shock Mach n u m b e r . The heat t r a n s f e r r a t e s wer-^
calculated using F a y and Riddell's r e s u l t and the gauge s e n s i t i v i t i e s d e t e r m i led. 3. Theory
The boundary l a y e r equations, including the effect of chemical dissociation, have been formulated by L e e s , (Ref. 1) and F a y and Riddell (Ref. 2). They
considered that heat i s t r a n s f e r r e d to the wall by n o r m a l m o l e c u l a r conduction and in addition by diffusion of atoms which r e c o m b i n e , either in the gas s t r e a m or on the wall. T h e r e a r e two e x t r e m e s possible - a v e r y fast recombination r a t e m
which the gas is in equilibrium throughout the boundary l a y e r o r a slow recombination r a t e where the atom concentration r e m a i n s constant through the l a y e r . F o r these two e x t r e m e c a s e s L e e s simplified the boundary l a y e r equations and then solved them approximately. F a y and Riddell solved the equations n u m e r i c a l l y for all values of the recombination r a t e . Both L e e s and F a y and Riddell, however, assumed that the boundary condition at the wall was that the atom concentration i s z e r p ; this
c o r r e s p o n d s to an infinitely efficient catalyst.
In general Goulard (Ref. 5) aissumed that the atom concentration at the wall m u s t be g r e a t e r than z e r o . F r o m naass conservation principles he deduced that, for equilibrium, the m a s s flux of a t o m s diffusing towards the wall must equal the r a t e of atom m a s s lost by recombination at the wall. F o r a first o r d e r reaction this r e s u l t s in the equation
p D
f l ^ ^
=ip {c
p )4
-w h e r e p = density
D = diffusion coefficient c = atom m a s s fraction
y = co-ordinate perpendicular to wall ^ = catalytic r e a c t i o n r a t e constant s u b s c r i p t w denotes conditions at wall.
Goulard proceeded from h e r e to solve the boundary l a y e r equations for the case of frozen flow. He obtained the following e x p r e s s i o n for the heat t r a n s f e r r a t e
[
1 +(Le='^ - 1 ) - ^ se where <p /9 0.47SC 1 + (2/9/j p ^ se '^se T ) " w ^wd i p \
^ e s e sand Le - = Lewis number = p
R Sc
= heat of recombination = Schmidt number PD
ti = v i s c o s i t y
Ujo = velocity ahead of b a r shock wave d = nose d i a m e t e r
s u b s c r i p t s e denotes conditions outside boundary l a y e r s denotes stagnation conditions.
F is a function of the flow v a r i a b l e only and will cancel when comparing heat t r a n s f e r r a t e s to s u r f a c e s of different catalytic efficiencies. F o r the c a s e of
<l> =1 the equation r e d u c e s to thai obtained by L e e s .
G o u l a r d ' s r e s u l t s were used to calculate the ratio of heat t r a n s f e r r a t e for finite catalytic activity to heat t r a n s f e r r a t e for infinite catalytic activity. Actual heat t r a n s f e r r a t e s for s e v e r a l different catalytic activities w e r e also calculated. Shock Mach number and initial channel p r e s s u r e were used a s v a r i a b l e s . The equilibrium gas p r o p e r t i e s at the stagnation point were taken from Ref. 7. The r e s u l t s a r e given in F i g s . 9 and 10.
4 . R e s u l t s
When planning t h e s e e x p e r i m e n t s an o r d e r of magnitude analysis was made to decide on suitable p r e s s u r e s to give frozen conditions through the boundary l a y e r . P r e v i o u s studies of Couette flow by Clarke (Ref. 8) indicated that a
stagnation p r e s s u r e of not m o r e than 0.1 a t m o s p h e r e s should give frozen conditions. T h i s im.mediately d e t e r m i n e d the r a n g e of initial channel p r e s s u r e s to lie between 0.01 T o r r to 0.1 T o r r for shock Mach n u m b e r s from 15 to 10. P r e v i o u s e x p e r i m e n t s indicated that the testing t i m e available would be v e r y short at these low densities due to thick boundary l a y e r s . Some m e a s u r e d v a l u e s , a s de t e r m i n e d from
stagnation point heat t r a n s f e r r e c o r d s , a r e given in F i g . 1 1 . This gave r e a s o n for concern a s it was felt that t h e r e would be insufficient t i m e for the flow to become steady. However, heat t r a n s f e r r e c o r d s show that almost constant heat t r a n s f e r r a t e i s obtained in m o s t c a s e s . This s e e m s to indicate that the s t a r t i n g p r o c e s s e s a r e v e r y fast and that heat t r a n s f e r r a t e at the stagnation point i s insensitive to non-equilibrium conditions.
Runs w e r e done initially with only one type of uncoated gauge to check the e l e c t r i c a l analogues. By determining the heat t r a n s f e r r a t e s from F a y and Riddell's curve at the low calibration shock Mach n u m b e r s , the heat t r a n s f e r r a t e s at the higher Mach n u m b e r s could be d e t e r m i n e d . The r e s u l t s have been c o r r e c t e d for v a r i a t i o n s in initial p r e s s u r e and a r e shown in F i g . 12. It can be seen that the r e s u l t s a r e consistently higher than those predicted by P a y and Riddell. This m a y be due to a gas adsorption effect which will be d i s c u s s e d l a t e r . The important conclusion from t h e s e r e s u l t s i s that the b a r e platinum behaves a s an efficient catalyst and if the flow i s frozen óomplete recombination m u s t be taking place at the wall.
E x p e r i m e n t s w e r e then done with s i m i l a r models but this t i m e the platinum was coated with silicon monoxide. It was soon r e a l i s e d that because it was i m p o s s i b l e to r e p r o d u c e identical flow condition^ in the shock tube, the catalytic effect, which appeared to be s m a l l , would be masked by i n a c c u r a c i e s .
Consequently the composite model was made s o that the two s u r f a c e s could be tested under identical conditions. T e s t s w e r e made using amplifiers with the s a m e sensitivity and r i s e t i m e , and the heat t r a n s f e r r a t e s for the two gauges w e r e displayed on the double beam o s c i l l o s c o p e . The calibration runs showed that within the a c c u r a c y of m e a s u r e m e n t the heat t r a n s f e r r a t e s were the s a m e . T h i s was expected for undissociated flows. However, for flows with appreciable dissociation a difference was observed, the silicon monoxide coated gauge r e c o r d i n g a lower heat t r a n s f e r r a t e as in F i g . 13. To improve the a c c u r a c y of m e a s u r e m e n t the two signals w e r e fed to a difference amplifier which could be set to a higher sensitivity. At the same time the signal from the uncoated gauge was displayed on the oscilloscope. F i g . 14 shows that the difference for the calibration run i s z e r o , whilst for the dissociated flow t h e r e is a positive diïference until behind the contact surface when the difference is also z e r o ,
It is apparent, from these r e s u l t s , that the b a r e platinum and silicon monoxide s u r f a c e s have significantly different effects on heat t r a n s f e r r a t e s in hot dissociated g a s flows.
1 6
-5. Comparison of T h e o r e t i c a l and E x p e r i m e n t a l Results
The following table gives the r a t i o of heat t r a n s f e r r a t e s a s calculated from G o u l a r d ' s t h e o r y and corresponding e x p e r i m e n t a l v a l u e s .
M s 8.7 14.6 15.0 16.2 18.1 ^— P j ( T o r r ) 0.052 0.047 0,039 0.024 0.024 q exp. 0.97 0,93 0.84 0.90 0.83 ^ h e o r . 0.70 0.42 0.40 0.35 0.34
Rate of heat transfer to silicon monoxide
Rate of heat transfer to platinum
\ =1
= w I
% = 10^w
Although the e x p e r i m e n t a l r e s u l t s show the s a m e t r e n d s a s t h e o r y the reduction in heat t r a n s f e r r a t e is not n e a r l y a s l a r g e a s expected. The r e a s o n for the s m a l l e r difference in the m e a s u r e d values could be one or all of t h r e e . 5. l . T h e flow in the boundary l a y e r is not frozen
If p a r t i a l recombination takes place in the boundary l a y e r then the atom concentration at the wall will be lower than expected. Thus the reduction in
heat t r a n s f e r r a t e to a non-catalytic wall would be l e s s than for frozen conditions. As a r e s u l t of this conclusion a m o r e careful e s t i m a t e using the approximate r e s u l t s in Ref. 8 of the chemical reaction t i m e s compared to the atom diffusion t i m e s was m a d e . The r e s u l t s a r e shown in F i g . 13 and for the working p r e s s u r e range the
chemical t i m e s a r e s e v e r a l o r d e r s of magnitude g r e a t e r than the diffusion t i m e s . It would appear that under the conditions of the p r e s e n t e x p e r i m e n t s , the flow is
completely frozen at the stagnation point, (This r e s u l t is also v a l i d for non-equilibrium conditions).
5. 2. I n c o r r e c t value for the catalytic activity of silicon monoxide
T h e r e is little doubt that the platinum film, as deposited, is in a highly active catalytic s t a t e . It is probable that the catalytic activity is about 10"* c m / s e c . a s given by Goulard and o t h e r s ( F i g . 10) The catalytic activity of silicon monoxide was taken a s one c m / s e c , as it was thought that it would behave like a g l a s s and have low catalytic activity. However, even if silicon monoxide has a value c h a r a c t e r i s t i c of m e t a l l i c oxides, i . e . between 10 c m / s e c . and 10 c m / s e c . t h e r e would be negligible change in the t h e o r e t i c a l values a s the most m a r k e d changes occur between l O ^ c m / s e c . and 1 0 ^ c m / s e c . Nevertheless an uncertainty r e m a i n s as to the c o r r e c t value of the catalytic activity for silicon monoxide and further experiments need to be made to clarify this point.
5. 3 . The flow outside the boundary l a y e r i s not in equilibrium
The argument applied to frozen flow also applies to non-equilibrium conditions w h e r e the atom concentration will be lower than the equilibrium v a l u e . Cammac and o t h e r s (Ref. 9) have m e a s u r e d r e l a x a t i o n t i m e s for oxygen in shock heated a i r using u l t r a violet absorption t e c h n i q u e s . T h e s e r e s u l t s have been extrapolated to lower p r e s s u r e s and a r e shown in F i g , 16. It is i m m e d i a t e l y seen that for the m e a s u r e d flow lengths the flow ahead of the bow shock wave i s far removed from equilibrixim. Even though the flow will have longer to equilibrate behind the bow shock, where the velocities n e a r the stagnation point a r e v e r y low, the t i m e s involved a p p e a r to be too short for the flow to r e a c h e q u i l i b r i u m .
This then a p p e a r s to be the m o s t probable r e a s o n for the d i s c r e p a n c y between t h e o r y and e x p e r i m e n t , i . e . the a s s u m p t i o n s of the t h e o r y a r e not reproduced in p r a c t i c e ,
In conclusion t h e r e a r e two additional factors about which little i s , at p r e s e n t , known and which m a y m a t e r i a l l y affect the flow p r o c e s s e s involved in these
e x p e r i m e n t s .
F i r s t l y , it is known that h e a t s of adsorption, i . e . the e n e r g y involved when a gas molecule or atom is bound to a solid s u r f a c e , can be a s l a r g e a s dissociation e n e r g i e s . Little i s known of r a t e s of adsorption and whether these a r e of the s a m e t i m e scale a s has been d i s c u s s e d . One of the m o s t r e c e n t t e s t s done in the shock tube was to pump the tube down for s e v e r a l hours with the diffusion pump. F i g . 17 shows the heat t r a n s f e r r a t e s to the two films after prolonged outgassing for t h r e e h o u r s . The t r a c e s b e a r little r e s e m b l a n c e to the previous t r a c e s but after two m o r e runs without prolonged pumping r e t u r n e d to n o r m a l . This effect may be due to adsorption.
Secondly, Schlieren photographs show that the bow shock does not r e a c h its final position until about 5 m i c r o s e c o n d s after the a r r i v a l of the p r i m a r y shock wave. In addition the t i m e s r e q u i r e d for the boundary l a y e r to become steady a r e unknown. It i s difficult to see at this stage what effect, if any, these p r o c e s s e s will have on heat t r a n s f e r r a t e s n e a r the stagnation point. N e v e r t h e l e s s , it will be n e c e s s a r y to have some knowledge of them if e x p e r i m e n t s a r e to be done in such s h o r t testing t i m e s .
6. Acknowledgements
The author wishes to acknowledge useful d i s c u s s i o n s with J . F . Clarke and the p r a c t i c a l help of E . T a y l o r .
7. R e f e r e n c e s
8
-1. L e e s , L . L a m i n a r heat t r a n s f e r over blunt-nosed bodies at hypersonic flight s p e e d s .
J e t P r o p , v o l . 2 6 . No. 4 , April 1956, pp 259-269. 2. F a y , J . A. ,
Riddell, F . R .
T h e o r y of stagnation point heat t r a n s f e r in dissociated a i r .
J . A e r o . S c . v o l . 2 5 . No. 2, F e b . 1 9 5 8 , pp 7 3 - 8 5 . 3 . R o s e , P . H . ,
Stark, W . I .
Stagnation point heat t r a n s f e r m e a s u r e m e n t s in dissociated a i r .
J . A e r o . S c . v o l . 2 5 . No. 2, F e b . 1 9 5 8 , pp 86-97. 4. Scala, S.M. Hypersonic stagnation point heat t r a n s f e r to
s u r f a c e s having finite catalytic efficiency. P r o c . 3rd U . S . Con,App.Mech. pp 799-806, 5. Goulard, R. On catalytic recombination r a t e s in hypersonic
stagnation heat t r a n s f e r .
J e t P r o p , v o l . 2 8 , No, 11, Nov, 1958, pp 737-745. 6. M e y e r , R . F . A he a t - f l u x - m e t e r for use with thin film surface
t h e r m o m e t e r s .
N . R . C . of Canada. A e r o . Rep. L R - 2 7 9 , A p r i l 1960. 7. F e l d m a n , S.
8. Clarke J , F .
Hypersonic gas dynamic c h a r t s for equilibrium a i r . AVCO R e s e a r c h L a b o r a t o r y , J a n . 1957.
E n e r g y t r a n s f e r through a dissociated diatomic gas in Couette flow.
ARC Report 19,624, Sept. 1957.
9. C a m m a c , M. et a l . Chemical relaxation in a i r , oxygen and n i t r o g e n . I . A . S . P r e p r i n t No. 802, J a n . 1 9 5 8 .
DISTANCE ALONG TUBE
FIG. I. WAVE PROCESSES IN A SHOCK TUBE
DUMP CHAMBER. EDWARDS PUMP. DIAPHRAGM HIGH PRESSURE SECTION.
FIG.2. THE COLLEGE OF AERONAUTICS. SHOCK TUBE.
FIG 3Q. CHARGING EQUIPMENT AND HIGH
PRESSURE CHAMBER. \
FIG.4b. WORKING SECTION, OPTICAL AND
ELECTRONIC EQUIPMENT
SILICON MONOXIDE COATING-Thin platinum film aroui itagndtion point LEADS SOLDERED TO COPPER-PLATED-PLATINUM , . (a)
HEAT TRANSFER GAUGES ON PYREX SPHERE MODELS
F I G . 5 . STING MOUNTING OF MODELS IN SHOCK TUBE
AV THIN FILM GAUGE.
«^è R
> y A / V \ A i A A A A A — j A A A A A T-d=Lc i c zbc
R = 3 , 0 0 0 Q. C = 3 3 0 p F .Time constant — Insec.
Running time (24sections)Ji5flOO/isec.
_ AV (ftQtk-)^^2__
where <^ = rate of heat transfer. Vo= initial voltage across gouge. AV= output from analogue circuit. RC=time constant of analogue circuit.
oc = temperature coefficient of resistance of platinum film.
/ * = density of pyrex. Cp= specific heat of pyrex.
k = thermal conductivity of pyrex.
FIG. 6. ELECTRICAL ANALOGUE FOR OBTAINING HEAT TRANSFER RATES.
0 - 2 mV
lO^iSec.
RUN 437 MODEL A Ms=2.34 p,=50Torr
CONTACT SURFACE
lOmV
\* *\ 2jiS«c.
RUN 438 MODEL A M,=9-45 p = 005Torr FIG7 COMPARISON OF SURFACE TEMPERATURE
AND HEAT TRANSFER RATE
UNCOATED GAUGE. COATED GAUGE. }//
I
I
POWER SUPPLY AND BALANCE NETWORK, ANALOGUE ANALOGUE. PRE AMPLIFIER ( T E K T R O N I X N \\2\) DIFFERENCE AMPLIFIER. (TEKTRONIXN Il2y' DOUBLE BEAM OSCILLOSCOPE. TEKTRONIX 5 5 1 .p= O-1 Torr p= O O I Torr O O I 6 8 lO SHOCK MACH FIG.9. STAGNATION ASSUMING BOUNDARY 12 14 NUMBER 16 M, POINT HEAT TRANSFER EQUILIBRIUM LAYER AND FLOW FROZEN OUTSIDE FLOW THROUGH IT. l O ' l O ' f^ cm. sec: l-O 0-8 0-6 0-4 0-2 O
Ms=6-1 _
1 0 - ^
\2-<l8^^<^
1 4 - ^
\6^
_^—-^
^^^-:;^^^^
W
T = O-l Torr. — i„=300°K.
d= l-27cm. 1 lO lO^ lO^ if cm. secT'FIG.IO.REDUCED HEAT TRANSFER.
oo
\ =
I ^ H R ce
Torr
6 8 lO 12 14 16 SHOCK MACH NUMBER
FIGLII. MEASURED RUNNING TIMES IN 5 cm. Dia. SHOCK TUBE AT LOW INITIAL PRESSURE
2 4 6 8 lO 12 141618
SHOCK MACH NUMBER Ms FIG.I2.STAGNATION POINT HEAT TRANSFER FOR
INITIAL CHANNEL PRESSURES BETWEEN O-Oi Torr AND O-l Torr.
|- <{ K)MSCC.
RUN 4 5 0 MODEL B M5-233 p, =
50Ton-SHOC3C CONTACT SURFACE
RUN 453 MODEL B M,= I6.2 p,=0.024 Torr
FIG.I3. STAGNATION POINT HEAT TRANSFER RATES
0-2mV
0.2it.Y !
1"—^—20/1SCC.
RUN 4 6 2 MODEL D M, = 2 3 4 p = 50Torr
SHOC:K CONTACT, SURFACE
5mY
RUN 455 MODEL B M,= l4-6 p.=0-047Torr
\ , ^ \ \ ^ ^ FRC '////// ^
,^R=c
ZEN F / / / / / /p=o-o
•1 Torr .OWV / / / J
1 Torr / / / / / - • / / / / / / / l 1 1 1 L 1 6 8 lO 12 14 16 SHOCK MACH NUMBER M ,• o w £. -H CC tu 1 -ÜJ 2 < a. < a tu t-< cc
lo'
q lO"^ A KJ 3 lÜ tch.m/ ^ J Q . ' / *diff. p O Body diameter d = 1-27 cms.Recombination rate Xr = lO cc. mok secT Boundary layer thickness S
FIG.I5.RATE PARAMETER VARIATION WITH MACH NUMBER' AND CHANNEL PRESSURE
O Q: U-U O I
o
z
X liJu
u
z
^ en « 0-0-5 " lO II 12 13 14 SHOCK MACH NUMBER M.FiqieiDISTANCE BEHIND SHOCK FRONT FOR OXYGEN TO REACH A GIVEN DEGREE OF DISSOCIATION
r> *\ 5/iSec.
RUN 463 MODEL D M,= I3-I p-0.047Torr
FIGI7 EFFECT OF PROLONGED OUTGASSING ON STAGNATION POINT HEAT TRANSFER RATES
