Vapor Pressure R134a R22

8/9/2019 Vapor Pressure R134a R22

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838 Goodw in Defibaugh and W eber

systematic changes become important at lower vapor pressures. Thus, we

measured low vapor pressures using a method that depends on boiling

known as ebulliometry [1 3]) and that continuously degases the sample.

In comparative ebulliometry the condensing temperature of the sub-

stance under study and a reference fluid are measured when the liquids are

boiling at the same pressure [4]. These boilers are connected via liquid

nitrogen cold traps to avoid cross-contamination of the substance being

investigated and the reference fluid. The advantage of this technique,

particularly at low pressure, is that it avoids the necessity of measuring

pressure directly; instead, the pressure is calculated from the condensing

temperature of the reference fluid and its known pressure-temperature

behavior. In addition, provided that the temperature measuring equipment

is sufficiently sensitive, irregularities of the condensation temperature may

reveal further inadequacies in the sample or reference fluid) purity [2]. Of

course, an azeotrope may not be detected with this approach. The sym-

metry of the apparatus implies that certain errors tend to be self-canceling.

In our work allowance is always made for the hydrostatic heads of

vapor [2, 4].

In comparative ebulliometry, a buffer gas subjects the sample and the

reference fluid to identical pressures. The influence of the buffer gas used in

the ebulliometric experiment was investigated by Ambrose et al. [5] with

their measurements of the vapor pressure of benzene. They found no

difference between values of the vapor pressure obtained when helium

was used as the buffer gas and those obtained when nitrogen was used.

The methods of determining vapor pressure, including comparative

ebulliometry, have been discussed extensively in the literature [2, 3].

For our work at low reduced temperatures corresponding to pressures

below 220 kPa, we have used comparative ebulliometry to supplement the

data from our static apparatus for vapor-pressure measurements. Here

we report our ebulliometric vapor-pressure measurements on 1,1,1,2-

tetrafluoroethane R134a) and chlorodifluoromethane R22), both of

which are expected to play important roles in the design of future refrigera-

tion systems. The ebulliometer used here is a refined version of an earlier

design reported by one of us [6] and is adapted from designs described in

the literature [1-4, 7-9]. To our knowledge, neither has this technique

been applied to these refrigerants previously nor has it been used at such

low temperatures.

In addition, we report static measurements made with our Burnett

apparatus [10-12] of the vapor pressure for 1,1,1,2-tetrafluoroethane

R134a) at pressures between our earlier static results [13] and the present

ebulliometric results. All these results have been combined to provide a

correlation for the vapor pressure of 1,1,1,2-tetrafluoroethane R134a) on



Vapor Pressure of R134a and R22 839

the International Temperature Scale of 1990 (ITS-90) [14, 15] at tem-

peratures from 215 K to the critical temperature, which corresponds to

vapor pressures from 17.3 to 4055.1 kPa. For chlorodifluoromethane (R22)

we have combined our results with those already published [-16-18] to

provide a correlation (on ITS-90) from 217.1 K to the critical temperature.

Because of the importance of these two fluids, their vapor pressures

have been reported in the literature numerous times [16-25]. Important

references for 1,1,1,2-tetrafluoroethane (R 134a) include Magee and Howley

[19], Zhu and Wu [20], Baehr and Tillner-Roth [21], Piao et al. [22],

Maezawa et al. [23], Basu and Wilson [24], and Kubota et al. [25] as

well as our earlier work [13]. We argue that certain published vapor

pressure data for R134a are in error by as much as 0.024p. We suspect that

the errors resulted from inadequate degassing of the samples used in

previous work. For the sake of brevity, these compounds are referred to

with the numbering scheme used by the refrigeration industry [26] and

shown in parentheses above.

2. EXPERIMENTAL

2 1 E b u l l i o m e t e r

The ebulliometers are similar to those described by Ambrose et al.

[2, 3, 7, 8]. The apparatus used in the present work has been described in

detail elsewhere [-6]. Only the important differences, required to operate at

lower temperatures and higher pressures, are given here. The sample

ebulliometer, shown in Fig. 1, was constructed from borosilicate glass and

fitted with four bubble-caps with a total internal volume of about 50 cm 3

(the reference boiler was identical). A brass passive radiation shield was

placed around the upper outer portion of the boiler. The entire

ebulliometer and radiation shield were housed inside a second cylindrical

shield, whose temperature was controlled to 0.01 K by circulating chilled

methanol through a coil wrapped around the shields outer surface. We

found, after carefully insulating feed and return pipes, that we could reach

195 K. The thermostat shield was capped with 0.05-m-thick polystyrene

foam disks. Fiber-glass insulation was wrapped around the outside of

the shield to complete the isothermal environment. Although the vapor-

pressure measurements were insensitive to the exact shield temperature, we

always maintained it about 10 K below the fluids condensing temperature.

The sample ebulliometer was connected, via a condenser cooled with a

mixture of carbon dioxide and propanone and two traps cooled with liquid

nitrogen, to the reference boiler and a ballast volume using helium as the

transfer gas. The connections were made with 10-mm-external diameter



840 Goodw in Def ibaugh and W eber

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m e a s u r e d , w i t h a q u a r t z p r e s s u r e t r a n s d u c e r . T h e h i g h e s t v a p o r p r e s s u r e

t h a t w a s m e a s u r e d i n t h e gl as s e b u l l i o m e t e r w a s 2 15 k P a . T h e l i m i t w a s a n

o b v i o u s s a f e t y p r e c a u t i o n .

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d e t e r m i n e d w i t h t w o Y e l l o w S p r i n g C o . 2 l o n g - s t e m p l a t i n u m r e s is t a n ce

t h e r m o m e t e r s [ M o d e l 8 1 63 Q B , se ri al n u m b e r s L 9 S 4 6 09 ( H 2 0 ) a n d

F 9 1 3 5 5 ( s a m p l e ) ] c a l i b r a t e d b e t w e e n 8 3.8 a n d 6 9 2.7 K o n I T S - 9 0 . T h e

r e si s ta n c e m e a s u r e m e n t s w e r e m a d e w i th a d i g it al D C m u l t i m e t e r ( H e w l e t t

P a c k a r d C o ., M o d e l 3 4 5 7 A ) o p e r a t i n g a t a c u r r e n t o f 1 m A , w i t h a r e s o l u -

t i o n o f 0 .0 1 m l 2 , f o r r e s i s t a n c e s u p t o 3 0 .3 s F o r r e s i s ta n c e s g r e a t e r t h a n

3 0.3 s b u t le ss t h a n 3 0 3 ~ , t h e r e s o l u t i o n w a s 0.1 m s T h e m a n u f a c t u r e r s

2 I n o r d e r t o d e s c r i b e m a t e r i a ls a n d e x p e r i m e n t a l p r o c e d u r e s a d e q u a t e l y , i t i s o c c as i o n a ll y

n e c e s s a r y t o i d e n ti f y c o m m e r c i a l p r o d u c t s b y m a n u f a c t u r e r s n a m e o r l a b el . I n n o i n s t a n c e

d o e s s u c h i d e n t if i c a ti o n im p l y e n d o r s e m e n t b y t h e N a t i o n a l I n s t i t u t e o f S t a n d a r d s a n d

T e c h n o l o g y , n o r d o e s i t i m p l y t h a t t h e p a r t i c u l a r p r o d u c t o r e q u i p m e n t i s n e c e s s ar i ly t h e

b e s t a v a i l a b le f o r t h e p u r p o s e .




s t a t e d a f r a c t i o n a l a c c u r a c y o f 6 .5 x 1 0 - 5 f o r t h e r a n g e w i t h a n u p p e r

b o u n d o f 3 0 .3 12 a n d a f r a c t i o n a l a c c u r a c y o f 4 .5 x 1 0 5 f o r r e s i s t a n c e s

b e t w e e n 3 0.3 a n d 3 0 3 12. W h e n t h e c u r r e n t w a s r e v e r s e d , n o d i f fe r e n c es

w e r e o b s e r v e d i n t h e m u l t i m e t e r r e a d i n g . A l t h o u g h t h e t e c h n i q u e f o r

v a p o r - p r e s s u r e m e a s u r e m e n t i s c o m p a r a t i v e , a n d o n l y s h o r t - te r m p r e c is i o n

a n d s t a b il i ty a r e r e q u i r e d o f t h e m u l t i m e t e r , w e c o m p a r e d t h e

m e a s u r e m e n t s o f t h is d e v i c e i n t w o w a y s . F ir s t, t h e m u l t i m e t e r w a s c h e c k e d

f r e q u e n t l y a g a i n s t t w o c a l i b r a t e d R o s a s t a n d a r d r e s is t o rs w i th n o m i n a l

r e s i s t a n c e s o f 10 a n d 2 5 12 t h a t w e r e h o u s e d i n a t h e r m o s t a t e d e n c l o s u r e ,

t h e t e m p e r a t u r e o f w h i c h w a s m e a s u r e d w i t h a m e r c u r y - i n -g l a s s th e r -

m o m e t e r . T h e m u l t i m e t e r w a s c h e c k e d a f te r co m p l e ti n g t h e v a p o r - p r e s s u re

m e a s u r e m e n t s a n d , a t b o t h s t a n d a r d r e si s ta n c e s, f o u n d t o b e 0 .6 6 m 1 2 h i g h ;

w h e n t h e m u l t i m e t e r w a s s h o r t e d t h i s d i s c r e p a n c y w a s n o t o b s e r v e d . A l l

t h e m e a s u r e m e n t s w e r e c o r r e c t e d f o r t h is s m a l l s y s t e m a t i c e rr o r . S e c o n d ,

t h e c o m b i n e d s t a b il it ie s o f t h e t h e r m o m e t e r s w i t h t hi s m u l t i m e t e r w e r e

c h e c k e d f r e q u e n t l y i n a t r i p l e - p o i n t - o f - w a t e r c e l l . T h e t r i p l e - p o i n t r e s i s t a n -

c es d i ff e re d f r o m t h e o r i g in a l c a l i b r a t i o n b y l es s t h a n 1 i n K . T o i m p r o v e

t h e r m a l c o n t a c t b e t w e e n t h e t h e r m o m e t e r a n d t h e c o n d e n s i n g f l u i d s , t h e

g l a s s - t h e r m o m e t e r w e l l s w e r e f i l l e d w i t h e i t h e r n - o c t a n e , s i l i c o n e o i l , o r

1 , 2 - d i h y d r o x y e t h a n e .

T h e e b u l l i o m e t e r s a n d b a l l a s t v o l u m e w e r e e v a c u a t e d a t a t e m p e r a t u r e

o f 3 0 0 K w i t h a r o t a r y v a c u u m p u m p u n t i l th e p r e s s u r e w a s b e l o w 1 P a ,

w h i l e t h e s e a l e d s a m p l e c y l i n d e r w a s a t t a c h e d t o a s i de a r m . A f t er 1 2 h t h e

5 0 - c m 3 l i q u i d s a m p l e w a s d i s t il l ed i n t o t h e b o i l e r . S u f f ic i e n t t i m e w a s

a l l o w e d f o r t h e a p p a r a t u s t o r e a c h s t e a d y s t a t e , a s i n d i c a t e d b y t e m -

p e r a t u r e d i f f er e nc e s b e t w e e n e a c h r e a d i n g o f a b o u t l m K , b e f o r e a s e ri es o f

c o n d e n s a t i o n t e m p e r a t u r e s w a s m e a s u r e d , u s u a l l y a t 6 0 - s i n t e r v a l s d u r i n g

0 . 3 h .

2 2 B u r n e t t A p p a r a t u s

T h e s t a t i c m e a s u r e m e n t s w e r e p e r f o r m e d w i t h a n a u t o m a t e d B u r n e t t

a p p a r a t u s d e v e l o p e d a t t h e N a t i o n a l I n s ti t u te o f S t a n d a r d s a n d T e c h n o l -

o g y N I S T ) , w h i c h h a s b e e n d e s c r ib e d in d et a i l s e v er a l t im e s [ 1 0 - 1 3 ] . A ll

r e s u l t s w e r e a c q u i r e d i n a n a u t o m a t e d f a s h i o n . T e m p e r a t u r e s w e r e

m e a s u r e d w i t h a n i m p r e c is i o n a n d i n a c c u r a c y o f 1 m K u s in g a p l a t i n u m

r e s i s t a n c e t h e r m o m e t e r , a n d p r e s s u r e s w e r e m e a s u r e d u s i n g a q u a r t z s p i r a l

b o u r d o n g a u g e f i t t e d w i t h a n o p t i c a l n u l l d e t e c t o r t o a n i n a c c u r a c y o f

a b o u t 0 .1 k P a . I n a d d i t i o n t o t h e p r o c e d u r e s l is t e d i n S e c t i o n 2 .3 , b e f o r e

c o m m e n c i n g m e a s u r e m e n t s , t h e s a m p l e c el l w a s fi ll ed t o a b o u t t h e c r i ti c al

d e n s i ty , c o o l e d b e l o w 2 7 3 K , a n d t h e g a s e x p a n d e d a n d e v a c u a t e d

r e p e a t e d l y u n t il a d d i t i o n a l e x p a n s i o n s h a d a n e g l ig i b le e ff ec t o n t h e

m e a s u r e d p r e s s u r e .




2 .3 . S a m p l e P u r i t y

D i s t i l l e d w a t e r f r o m t h e l a b o r a t o r y s u p p l y w a s u s e d a s t h e r e f e r e n c e

m a t e r i a l . T h e 1 , 1 , 1 , 2 - t e t r a f l u o r o e t h a n e ( R 1 3 4 a ) w a s s u p p l i e d b y E . I . D u

P o n t d e N e m o u r s a n d C o . w i t h a s ta t e d a n a l y si s f o r t h r e e i m p u r i ti e s :

x ( C 2 H F s ) = 1 .5 6 x 10 - 4 , x ( C F 3 C H 3 ) -- 1 .5 9 x 1 0 - 4 , a n d x ( C C I H 2 C F 2 H )

= 1 .5 x 1 0 - 4 . G a s - c h r o m a t o g r a p h i c a n a l y si s o f t h is s a m p l e d e t e c t e d a m o l e

f r a c t i o n o f 2 .1 5 • 1 0 - 4 f o r w a t e r [ 2 7 ] . T h e s a m p l e w a s d i s t il l ed f r o m t h e

s u p p l i e r s c y l i n d e r in t o a p r e v i o u s l y e v a c u a t e d s te e l am p o u l e . A n a l y s is o f

t hi s s a m p l e w i t h a g as c h r o m a t o g r a p h r e t u r n e d x ( H 2 0 ) = 1 .0 5 • 10 - 4

[ 2 7 ] . N o a t t e m p t w a s m a d e t o p u r i fy t h e R 1 3 4 a f u r t h er . A l iq u o t s o f t h is

s a m p l e w e r e u s e d f o r t h e v a p o r - p r e s s u r e m e a s u r e m e n t s r e p o r t e d h e r e a n d

i n R e f . 1 3 , a s w e l l a s t o d e t e r m i n e t h e c r i t i c a l t e m p e r a t u r e [ - 2 8 ] , t h e

g a s e o u s ( p , V m , T ) b e h a v i o r [ 1 3 ] , a n d g a s e o u s s p e e d - o f - s o u n d m e a s u r e -

m e n t s [ 2 9 ] . T h e c h l o r o d i f l u o r o m e t h a n e ( R 2 2 ) w a s o b t a i n e d f ro m A l li ed

S i g n al C o r p ., f r o m b a t c h B R l l 9 1 A , w i t h a s t a t ed m o l e f r a c t io n p u r i t y o f

g r e a t e r t h a n 0 . 9 9 9 5 . T h e a n a l y s i s c e r t i f i c a t e p r o v i d e d b y t h e m a n u f a c t u r e r

r e p o r t e d a m o l e f r a c t i o n p u r i t y o f 0 .9 9 9 68 a n d t h e p r e s e n c e o f f iv e

i m p u r i t i e s , o f w h i c h f o u r w e r e i d e n t i f ie d : x ( C C 1 2 F 2 ) = 0 . 0 0 0 1 8 , x ( C H F 3) =

0 .0 0 01 3 , x ( C H C 1 2 F ) = 0 .0 0 0 01 , a n d x ( H 2 0 ) = 3 x 10 - 6 . O t h e r u n s p e c if ie d

h y d r o c a r b o n s m a d e u p t h e r e m a i n d e r . G a s - c h r o m a t o g r a p h i c a n a l y s i s o f

t h e s t o c k m a t e r i a l u s i n g a n o n p o l a r s t a t i o n a r y p h a s e a n d a t h e r m a l c o n -

d u c t i v i t y d e t e c t o r i n d i c a t e d t h e p r e s e n c e o f t w o i m p u r i t i e s w i t h f r a c t i o n a l

a r e a s o f 1 9 x 10 - 6 a n d 4 .9 x 1 0 - 4 , r e s p e c t i v e l y ; b o t h e l u t e d p r i o r t o t h e

m a j o r p e a k . N o f u r t h e r a n al y s is o r p u r i f i c a ti o n w a s a t t e m p t e d .

3. R E S U L T S A N D A N A L Y S I S

T h e v a p o r p r e s s u r e o f w a t e r , w h i c h w a s u s e d a s t h e r e f e r e n c e f lu i d f o r

o u r e b u l l i o m e t r y , w a s c a l c u l a t e d f r o m b o i l i n g t e m p e r a t u r e s o n I T S - 9 0 [ 1 4 ,

1 5 ] , w i t h t h e e q u a t i o n d i s c u s s e d i n S e c t i o n 3 . 1 . N o i r r e g u l a r i t i e s w e r e

d e t e c t e d i n t h e t e m p e r a t u r e o f t h e w a t e r e b u l l i o m e t e r , th i s s u g g e st s t h e

s a m p l e h a d n o s i g n i f i c a n t c o n t a m i n a n t s .

A s a c h e c k o n t h e i n t e r n a l c o n s i s t e n c y o f t h e e b u l l i o m e t r i c re s u l ts , a n d

t o p r o v i d e a n o r m a l b o i l i n g t e m p e r a t u r e a t a p r e s s u r e o f 1 0 1 . 3 2 5 k P a , w e

f it o u r e x p e r i m e n t a l v a l u e s t o a n A n t o i n e e q u a t i o n ( a p p l ic a b l e in t h e r a n g e

1 0 t o 2 0 0 k P a )

I n ( p )

= A + B/ T+ C)

1 )

w h e r e p i s i n k P a a n d T is i n K . T o p r o v i d e a n e q u a t i o n f o r th e fl u id ra n g e

f r o m a p r e s s u r e o f a b o u t 1 0 k P a t o t h e c r it ic a l p r e s su r e , w e c o m b i n e d o u r

e b u l l i o m e t r i c r e s u lt s w i th o u r s t a t ic m e a s u r e m e n t s f o r R 1 3 4 a. F o r R 2 2 o u r




e b u l l i o m e t r i c v a l u e s w e r e c o m b i n e d w i t h h i g h e r - p r e s s u r e d a t a f r o m t h e

l i t e ra t u r e t h a t j o i n e d s m o o t h l y w i t h o u r r e s ul ts . F o r e a c h f l ui d, t h e

c o m b i n e d s e t w a s u s e d t o d e t e r m i n e t h e c o e f fi c ie n ts i n th e e q u a t i o n

r e c o m m e n d e d b y W a g n e r [ 3 ( ~ 3 3 ] :

i n p i p e )

= (n 1z + n2 z l s

+ n~3 + n~) T c /T

( 2 )

where z = (1 - T / T c ) , T c i s t h e c r i t ic a l t e m p e r a t u r e , a n d c , d a n d t h e n s a r e

a d j u s t a b l e p a r a m e t e r s . I n o u r a n a l y s i s , w e a s s u m e d t h a t t h e v a p o r p r e s s u r e

c o u l d b e r e p r e s e n t e d b y t e r m s w i t h p o s i t i v e p o w e r s c a n d d , a n d u s i n g a n

a d a p t i v e r e g r e s si o n a l g o r i t h m [ 3 4 ] , w e s e le c te d t h e m o s t s i g ni fi c an t te r m s

f r o m the ba nk ~2, r2 .s , ~3.o .... ~9. W e we igh te d e a c h e bu l l i om e t r i c ob se r v a -

t i o n b y 6 T x d l n p / d T , w h e r e 6 T = 1 .4 x 10 3, w h i c h w e c o m b i n e d i n q u a d -

r a t u r e w i t h t h e u n c e r t a i n t y in t h e v a p o r p r e s s u r e o f w a t e r. W e w e i g h t e d

o u r s t a ti c m e a s u r e m e n t s b y 0 .1 5 ( k P a / p ) , w h e r e 0 .1 5 k P a is o u r e s t im a t e o f

t h e u n c e r t a i n t y i n p . T h i s s c h e m e e n s u r e d t h a t t h e e b u l l i o m e t r i c re s u lt s

r e c e i v e d a w e i g h t a b o u t a f a c t o r o f l 0 g r e a t e r t h a n t h e s t a t ic r es u l t s a t a

s i m i l a r p r e s s u r e . F o r R 2 2 t h e l i t e r a t u r e r e s u l t s w e r e w e i g h t e d b y a n

e s t i m a t e o f t h e u n c e r t a i n t y p r o v i d e d b y t h e s o u r ce s . In E q . ( 2 ), e a c h t e r m

e n t e r e d w i t h a h i g h d e g r e e o f s i g n i fi c a n c e a n d n o o t h e r s i g n i f ic a n t t e r m s

w e r e f o u n d . T h e p r o c e d u r e s r e q u i r e d t o p e r f o r m t h e s e c a l c u l a t i o n s h a v e

b e e n d e s c r i b e d i n d e t a i l e l s e w h e r e [ 3 5 ] .

T a b l e I g i v e s t h e v a p o r p r e s s u r e , t o g e t h e r w i t h d e v i a t i o n s f r o m t h e

A n t o i n e a n d W a g n e r e q u a t i o n s , d e t e r m i n e d a t e a c h t e m p e r a t u r e o n I T S - 90 .

S m a l l c o r r e c t i o n s h a v e b e e n a p p l i e d t o a c c o u n t f o r t h e f l u i d h e a d i n e a c h

e b u l l i o m e t e r ; f o r R 1 3 4 a w e u s e d a s t a t i c - h e a d c o r r e c t i o n f a c t o r o f 1 . 0 0 0 1 3 9 ,

wh i l e f o r R 22 we use d 1 .000124 .

3 .1 . V a p o r P r e s s u re o f W a t e r o n I T S 9 0

A l t h o u g h t h e r e a r e n u m e r o u s e q u a t i o n s f o r t h e v a p o r p r e s s u r e o f

w a t e r o n I T P S - 6 8 [ 3 6 3 8 ] , w e w e r e n o t a w a r e o f a n y c o r r e la t in g e q u a t i o n

w i t h t e m p e r a t u r e s o n I T S - 9 0 . T h e r e f o r e , w e u s e d t h e b e s t e x p e r i m e n t a l

r e s u lt s ( f ro m t h e N a t i o n a l B u r e a u o f S t a n d a r d s , t h e p r e d e c e s s o r to N I S T )

r e p o r t e d b y O s b o r n e e t al. [ 3 9 ] , S t i m s o n [ 4 0 ] , a n d G u i l d n e r et a l. [ 4 1 ]

a n d c o n v e r t e d t h e t e m p e r a t u r e s t o I T S - 9 0 u si n g t h e r e c o m m e n d a t i o n s o f

S a t o e t a l. [ 4 2 ] . T h e c o n v e r s i o n fo r m u l a [ 4 3 1 i s a c c u r a t e t o 1 m K a b o v e

2 7 3 .1 5 K a n d t o 1.5 m K b e lo w . W i t h t h e r e g r e s si o n p r o c e d u r e d e s c r i b e d

a b o v e , w e s e le c te d te r m s t o d e t e r m i n e a W a g n e r e q u a t i o n f o r w a t e r . E a c h

o b s e r v a t i o n w a s g i v e n a w e i g h t o f u n i t y i n t h e r e g r e s si o n a n a l ys i s, e x c e p t

f o r t h e m e a s u r e m e n t s o f S t i m s o n [ 4 0 ] a n d G u i l d n e r et a l. [ 4 1 ] , w h i c h

w e r e g i v e n a w e i g h t o f 10. W e u s e d t h e c r i t i c a l t e m p e r a t u r e o f 6 47 .1 K ( o n




Table I. Vapor Pressures p and Deviations

A p l = p - p c a l c . )

from Eq. 1) and A p 2 = p - p c a l c . ) from Eq. 2)

at Tempera ture s T for 1,1,1,2-Tetrafluoroethane R134a)

and Chlorodifluoroethane R22)

T p ZJpl z~p2

K) kPa) Pa) Pa)

Chlorodifluoromethane R22) ebulliometer

217.086 46.651 - 1 1 - 2 6

217.118 46.738 - 5 -2 1

218.307 49.888 8 - 6

220.217 55.272 4 - 9

221.873 60.315 5 - 5

223.409 65.309 2 - 7

224.861 70.331 1 - 5

226.227 75.331 2 - 4

227.529 80.358 5 - 1

228.828 85.632 4 0

229.978 90.529 5 4

231.225 96.095 17 16

232.206 100.664 28 30

232.151 100.319 - 5 5 - 5 5

234.240 110.609 - 1 7 - 1 1

235.712 118.364 35 - 7

236.188 120.899 - 8 1

238.205 132.295 - 31 - 2 1

238.461 133.848 17 25

239.615 140.779 - 1 8 - 7

242.718 160.936 6 20

242.742 161.070 - 2 2 - 1 0

244.060 170.274 - 21 - 1 2

245.584 181.443 - 4 9

245.464 180.565 20 29

248.502 204.388 33 36

1,1,1,2-Tetrafluoroethane R134a) ebulliometer

214.435 17.301 3 1

216.869 20.179 4 1

218.289 22.033 4 2

223.588 30.219 - 6 - 4

226.340 35.365 - 6 - 4

228.866 40.691 - 1 0 - 8

228.824 40.596 - 10 - 9

231.025 45.749 - 6 - 4

230.996 45.676 - 7 - 6

232.785 50.230 - 9 - 8

232.798 50.269 - 5 - 4

233.849 53.121 3 4

233.881 53.208 1 2



Vapor Pressure of R134a and R22

Table I. Continued)

T p dpl Ap2

K) kPa) Pa) Pa)

234.625 55.291

234.668 55.432

235.317 57.317

236.287 60.203

236.293 60.226

236.582 61.133

238.084 65.932

239.610 71.106

239.635 71.196

241.675 78.628

242.972 83.669

242.951 83.579

244.861 91.450

244.879 91.534

247.149 101.649

249.243 111.742

251.123 121.471

252.951 131.554

254.558 140.955

256.289 151.655

258.660 167.348

261.048 184.401

262.599 196.175

264.727 213.242

Static

265.609 220.860

266.152 225.480

267.134 234.160

268.151 243.390

269.167 252.880

270.132 262.140

271.153 272.270

272.182 282.590

273.135 29Z710

273.167 293.030

276.166 326.250

281.151 387.700

285.171 443.310

289.181 504.720

293.146 571.560

297.130 645.190

301.150 726.680

305.162 815.530

309.162 912.080

313.204 1017.710

--10 --9

7 9

10 11

--16 --13

--10 --9

6 8

9 11

8 9

9 11

14 14

16 12

9 19

9 9

13 16

10 13

4 5

2 5

2 --1

1 2

--9 --12

--3 --12

I

--18

--5 --29

--40 --76

118

69

112

129

137

129

170

22

172

153

197

208

135

130

96

- 1 7

0

41

157

- 117

845





V a p o r P r e ss u re o f R 1 3 4 a a n d R 2 2 8 4 7

~ 0

-5

I

2 2 0

9 0 0 9 0 0 0 0

F i g . 3 . F r a c t i o n a l d e v i a t i o n s

I

9 9 O -

9

e 9

I

250

T , K

zlp/p= [p-p calc.)]/p

o f t h e

e x p e r i m e n t a l v a p o r p r e s s u r e s f r o m E q . 1 ) f o r c h l o r o d i f l u o r o -

m e t h a n e R 2 2 ). O , T h i s w o r k .

tions from Eq. 1) with the coefficients given in Table II. The normal boil-

ing temperature, at a pressure of 101.325 kPa, calculated from Eq. 1) with

the coefficients of Table II is 232.351 + 0.005) K on ITS-90. The standard

deviation of the fit was 21 Pa, or 4 mK in temperature. Only at 232.2 K did

the result deviate from Eq. I) by more than 10 mK. Removal of this point

from the regression did not alter the normal boiling temperature.

There are several measurements of the vapor pressure of R22 in the

literature [16-18, 46-51] and most have quoted imprecisions of about

0.001p. All values were compared on ITS-90 [43, 52]. At temperatures

that overlap our range, most agree within the uncertainty of those

measurements. For example, the static measurements of Zander [ 16] are in

excellent agreement with Eq. 1) in the overlapping range. At 222.905 K his

T a b l e I I. C o e f f ic i e n t s a n d S t a n d a r d D e v i a t i o n s s f o r E q s . 1 ) a n d 2 ) O b t a i n e d b y

A n a l y s i s o f t h e N V a p o r P r e s s u r e s o f C h l o r o d i f l u o r o m e t h a n e R 2 2 ) a n d

1 , 1 , 1 , 2 - T e t r a f l u o r o e t h a n e R 1 3 4 a ) a

Eq . 1 ) A B C N s P a )

R 2 2 1 4.0 37 98 - 1 8 9 0 . 6 4 1 - 3 1 . 6 4 0 2 6 2 1

R 1 3 4 a 1 4 .2 14 7 5 - 2 0 1 3 . 9 5 1 - 3 7 . 2 1 7 3 7 11

Eq . 2 ) P c kP a ) n a n 2 n 3 n 4 N s P a )

R 2 2 4 9 8 7 . 1 + 1 .2 - 7 . 0 3 5 5 1 1 . 4 5 97 6 - 1 . 8 1 20 - 2 . 9 6 4 4 1 0 6 8 7 7

R 1 3 4 a 4 0 55 .1 + 0 . 3 - 7 . 6 1 7 0 2 1 .6 9 46 4 - 2 . 5 0 8 1 - 3 . 4 9 1 5 7 9 16 7

U n c e r t a i n t i e s a r e o n e s t a n d a r d d e v i a t i o n .



848 Goodwin, Def ibaugh, and W eber

3

I I I L

AT= 25 mK v 9

- 9 " " - - - - - - - ~ ~ 9

~ 0 ,

9

v v v

' , r - " I " l - v 9 v v V "

_ 2 F I I I I I

200 250 300 350

T , K

Fig. 4. Fractional deviations

Ap/p= Ep-p calc.)]/p

of the experimental

vapo r pressures from Eq. 2) for chlorod ifluorom ethane R2 2). Tb is the

boiling temperature at a pressure of 101.325 kPa. 0 , Th is wo rk; , , Ref. 17;

A, Ref. 16; V, R ef. 18; , the error arising at ea ch temp erature from a

chang e of 0.025 K.

r e s u l t d e v i a t e s b y l es s t h a n 4 P a , a t 2 3 2 . 3 9 0 K b y 1 .2 P a , a n d a t 2 3 4 .2 2 5 K

b y - 7 P a . T h e e x c el le n t a g r e e m e n t b e t w e e n o u r v a p o r - p r e s s u r e

m e a s u r e m e n t s a n d t h o s e r e p o r t e d b y Z a n d e r [ 1 6 ] s u g g es ts t h a t b o t h s et s

o f m e a s u r e m e n t s a r e f r ee f r o m s y s t e m a t ic e r ro r s .

W e c o m b i n e d o u r v a l u e s w i t h t h o s e r e p o r t e d i n R e f s . 1 6 - 1 8 a f t e r

c o n v e r t i n g t h e t e m p e r a t u r e s t o I T S - 9 0 [ 4 3 ] . T h e s e d a t a s e t s , a s s h o w n i n

F i g. 4 , j o i n e d s m o o t h l y w i t h o u r r e su l ts a n d w e r e o b t a i n e d w i t h s a m p l e s

o f s i m i l a r p u r i t y . W e f ix e d T c a t 3 6 9 .2 7 5 K , a s r e c o m m e n d e d b y A m b r o s e

[ 5 3 ] c o n v e r t e d to I T S - 9 0 [ 4 3 ] ) , a n d f it E q . 2 ) t o t h e c o m b i n e d d a t a

w e i g h t i n g t h e l i t e r a t u r e v a l u e s b y 0 .0 0 1. T h e r e g r e s s i o n r e t u r n e d c = 2.5 a n d

d = 5 . T a b l e I I l is ts t h e co e f f ic i e n ts o f E q s . 1 ) a n d 2 ) d e t e r m i n e d f o r R 2 2 ,

t o g e t h e r w i t h t h e s t a n d a r d d e v i a t io n s a n d n u m b e r o f v a p o r p r e ss u r es in

e a c h r e g r e s s i o n .

3 .3 . 1 , 1 , 1 , 2 - T e t r a f l u o r o e t h a n e R 1 3 4 a

F o r R 1 3 4 a t h e 37 e b u l l io m e t r i c m e a s u r e m e n t s o f t h e v a p o r p r e s su r e

w e r e u s e d t o a d j u s t t h e c o e f fi ci e nt s o f E q . 1 ). T h e s t a n d a r d d e v i a t i o n

o f th e f it w a s 11 P a , o r 2 .9 m K i n t e m p e r a t u r e . T h e n o r m a l b o i l in g

t e m p e r a t u r e , a t a p r e s s u r e o f 1 0 1 . 3 2 5 k P a , c a l c u l a t e d f r o m E q . 1 ) is

247 .082 _+ 0 .00 5) K .

W e w e r e u n a b l e t o e x t e n d t h e s t a t i c e x p e r i m e n t t o a t e m p e r a t u r e



V a p o r P r e s su r e o f R 3 4 a a n d R 2 2

8 4 9

lower than 265.6 K, about 0.9 K above the highest ebulliometric tem-

perature. Consequently, the pressure ranges did not overlap. The static

measurements reported here extend to a temperature 48 K below the

lowest temperature reported by us previously 1-13]. These pressures

deviated from the smoothing equation, discussed below and shown in

Fig. 5, within a factor of 0.9 of the estimated accuracy of the pressure

gauge.

We combined our ebulliometric measurements and static results,

including those from Ref . 13, with the critical temperature observed by

Morrison and Ward [28] of 374.179 K. A small correction was applied to

convert the temperature reported in Ref. 28 to ITS-90 [-43]. We obtained

c= 2.5 and d = 5 from a weighted regression analysis with Eq. 2) and a

standard deviation of 167 Pa, or of 1.39

x 1 0 - 4

in in p. Figure 5 shows the

experimental results as deviations from this smoothing equation. It is clear

that there are inconsistencies in the results from static and ebulliometric

experiments which, although small, far exceed the imprecision of any one

value. We suspect that the presence of air in the sample is responsible.

However, the deviations show a systematic, albeit small, undulation from

Eq. 2), which implies that the functional form is not entirely suitable.

While the difference between the ebulliometric and the static results at

265 K suggests that our static measurements were affected by the presence

of a volatile impurity, no additional significant terms remained unselected

i @ [ ] i i

[]

~-

I l l I - ' ~ [ ] , o . , ' _ ~ i - - _ _ _

0 9 ~ "

I ' I , .

-5 Tb r c

I i i i i

2 0 0 2 5 0 3 0 0 3 5 0 4 0 0

T , K

F i g . 5 . F r a c t i o n a l d e v i a t i o n s Ap/p=Ep--p calc.)]/p o f t h e

e x p e r i m e n t a l v a p o r p r e s s u r e s f r o m E q . ( 2 ) f o r 1 , 1 , 1 ,2 - t e tr a f lu o r o -

e t h a n e ( R 1 3 4 a ) . T u i s t h e b o i l i n g t e m p e r a t u r e a t a p r e s s u r e o f

1 0 1 .3 2 5 k P a . 0 , T h i s w o r k , e b u l l i o m e t r i c ; [ 3 , t h i s w o r k , s t a ti c ;

i , R e f. 1 3, s a m e s a m p l e ; - - , t h e e r r o r a r i s i n g a t e a c h t e m p e r a t u r e

f r o m a c h a n g e o f 0. 0 05 K .




a t t h e c o n c l u s i o n o f t h e r e g r e s s io n . T h e d i s c o n t i n u i t y , s h o w n i n F i g . 5,

c o u l d r e s u l t f r o m a m o l e f r a c t i o n o f a i r o f 1 0 - 5 . N e v e r t h e l e s s , t h e a g r e e -

m e n t b e t w e e n t h e r e s u lt s o f t w o s u c h d i f fe r en t te c h n i q u e s i s e x c e p t i o n a l a n d

i n d i c a te s t h a t t h e v a p o r p r e s s u re s c a n b e o b t a i n e d t o b e t t e r t h a n 3 x 1 0 - 4 p .

T a b l e I I g i v es t h e c o e ff i ci e n ts o f E q s . 1 ) a n d 2 ) f o r R 1 3 4 a , t o g e t h e r

w i t h t h e s t a n d a r d d e v i a ti o n s a n d t h e n u m b e r o f v a p o r p r es s u re s in e a c h

r e g r e s s ion .

4 . D I S C U S S I O N

F o r b o t h R 1 3 4 a a n d R 2 2 o u r a n a l y s i s p r o c e d u r e h a s s e l e c t e d t h e f o r m

o f E q . 2 ) r e c o m m e n d e d b y A m b r o s e [ 3 5 ] a n d r e t u r n e d c o e ff ic ie n ts w h i c h

a r e ty p i c a l i n m a g n i t u d e o f s u c h a n e q u a t i o n [ 3 5 ] .

4.1. Chlorodif luoromethane R22

T h e r e a r e s e v e ra l o t h e r p r e v i o u s m e a s u r e m e n t s o f t il e v a p o r p r e s s u re

f o r c h l o r o d i f l u o r o m e t h a n e [ 4 6 - 5 1 ] , m o s t t h a t ar e a v a il a b le [ 47 , 4 9 - 5 1 ]

d e v i a t e f r o m E q . 2 ) b y m o r e t h a n 0 . 00 5 p. O n l y th e m e a s u r e m e n t s o f

O g u c h i e t al . [ 4 6 ] a n d T a k a i s j i e t a l. [ 4 8 ] d i f fe r b y le ss t h a n 0 . 0 0 1 p f r o m

o u r c o r r e l a t i o n .

A s s u m i n g t h e c ri ti ca l t e m p e r a t u r e r e c o m m e n d e d b y A m b r o s e [ 5 3 ]

a n d a l s o b y H i r a t a e t a l. [ 5 4 ] a n d K o h l e n e t a l. [ 1 8 ] ) , w e c a lc u l a te f r o m

E q . 2 ) a c r i t ic a l p r e s s u r e o f 4 9 8 7 .1 _ 1 .2 ) k P a , 1 6 . 1 k P a a b o v e t h e v a l u e

g i v e n in R e f. 5 3. T h e m e a s u r e m e n t o f K l e t s k i i [ 1 7 ] l ie s 1.1 k P a b e l o w , w e l l

w i t h i n o u r e s t i m a t e d u n c e r t a i n t y , w h i le th e v a l u e o f Z a n d e r [ 1 6 ] is 2 .9 k P a

a b o v e , t h e c r i ti c a l p r e s s u r e c a l c u l a t e d f r o m E q . 2 ) .

4 .2 . 1 , 1 ,1 , 2 - Tet ra f luo ro e t ha ne R 1 3 4 a )

T h e v a p o r p r e s s u r e s r e p o r t e d b y o t h e r w o r k e r s a r e s h o w n i n F i g . 6 , a s

d e v i a t i o n s f r o m E q . 2 ) , w h e r e t h e o r d i n a t e s c al e h a s b e e n c o m p r e s s e d b y

a f a c t o r o f 1 0 0 c o m p a r e d w i t h F i g . 5 ; a l l v a l u e s w e r e c o m p a r e d o n I T S - 9 0 .

T h e r e a r e l a rg e d i f fe r en c e s b e t w e e n t h e v a l u e s o f p a t t e m p e r a t u r e s b e l o w

3 0 0 K w i t h d i f fe r e n c e s u p t o 0 .0 2 4 p . S u c h e r r o r s i n t h e v a p o r p r e s s u r e

c o u l d a r i s e f r o m i n c o n s i s t e n c i e s b e t w e e n t h e t w o t h e r m o m e t e r s u s e d f o r

o u r e b u l l i o m e t r y . F o r e x a m p l e , a n u n c e r t a i n t y o f 0 .0 5 K a t 2 6 5 K o r 0 .3 8 K

a t 2 1 5 K w o u l d b e l a r g e e n o u g h t o c a u s e s u c h d i ff er en c e s; h o w e v e r , b a s e d

o n o u r m e a s u r e m e n t s , d i s c u s s e d i n S e c t i o n 2 . 1 , o u r t h e r m o m e t r y w a s

s h o w n t o b e a c c u r a t e t o a f e w m i l l i k e l v i n a n d w e a r e a b l e t o r u l e o u t t h i s

a s t h e s o u r c e o f t h e d i f fe re n c es . A t t e m p e r a t u r e s b e l o w 2 5 0 K w e a r e a w a r e

o f t w o o t h e r i n d e p e n d e n t s et s o f v a p o r p r e s s u r e m e a s u r e m e n t s i n th e



V a p o r P r e s su r e o f R 3 4 a a n d R 2 2 8 5

3

2 1 9 9

-1 L . ~ A T = o . ] K 9

200 300 400

T , K

Fig. 6. Fra cti on al deviations

Ap/p=[p--p calc.)]/p

of the

experimental vapor pressures fr o m Eq. 2) for 1,1,1,2-tetra-

fluoroeth ane R13 4a). O, Ref. 19; L Ref. 20; O, Ref. 21; D,

Ref. 22; A, Ref. 23; V, Ref. 24; A , Ref. 25; -- , the error arising

at each temp erature from a change of 0.1 K.

l i t e r a t u r e 1 -1 9, 2 4 ] b o t h , a r e s h o w n i n F i g . 6 , a n d w e r e o b t a i n e d w i t h a

s t a t i c t e c h n i q u e . S y s t e m a t i c e r r o r s i n s t a t i c v a p o r p r e s s u r e m e a s u r e m e n t s

c o u l d a r i s e f r o m e r r o r s i n t h e p r e s s u r e m e a s u r e m e n t o r f r o m t h e p r e s e n c e

o f v o l a t il e i m p u r i ti e s. T h e d i s c r ep a n c i e s b e t w e e n e q u a t i o n 2 ) a n d t h e s t a ti c

m e a s u r e m e n t s o f B a s u a n d W i l s o n [ 2 4 ] a r e le ss t h a n t h e e s t i m a t e d e r r o r s

i n t h e p r e s su r e m e a s u r e m e n t s o f t h e l a tt e r. B a s u a n d W i l s o n [- 24 ] d e g a s s e d

t h e i r s a m p l e b y a r e p e a t e d f r e e z i n g , p u m p i n g , a n d t h a w i n g p r o c e s s u n t i l

t h e p r e s s u r e w a s b e l o w 7 P a . W e e s t i m a t e t h a t t h e d i s c r e p a n c y o f 0 .0 2 4 p a t

2 1 0 K , b e t w e e n e q u a t i o n 2 ) a n d t h e r e su l ts r e p o r t e d i n R e f. [ 2 4 ] , c o u l d b e

a c c o u n t e d f o r w i t h a m o l e f r a c t i o n o f a i r o f 3 x 1 0 5. M o s t o f t h e s t a t i c

m e a s u r e m e n t s r e p o r t e d b y M a g e e a n d H o w l e y [ 1 9 ] d if fe r f r o m o u r v a p o r

p r e s s u r e e q u a t i o n w e ll w i t h i n t h e i r e r r o r e s ti m a t e s. M a g e e a n d H o w l e y

[ 1 9 ] u s e d a s a m p l e o f R 1 3 4 a t h a t c o n t a i n e d a m o l e f r a c t io n o f a i r o f a b o u t

1 x 1 0 6. A t t e m p e r a t u r e s b e t w e e n 2 4 0 a n d 2 5 0 K t h e r e a p p e a r s t o b e a

s te p d i s co n t i n u i t y i n th e m e a s u r e m e n t s o f M a g e e a n d H o w l e y [ 1 9 ] , t h a t

a r o s e f r o m c h a n g i n g p r e s s u r e g a u g e s . S e v e r a l o t h e r s e t s o f r e s u l t s a g r e e

w i t h E q . 2 ) t o w i t h i n 0.1 K a t t h e n o r m a l b o i l in g t e m p e r a t u r e . A t h i g h e r

t e m p e r a t u r e s t h e m a j o r i t y o f t h e r es u l ts d e v i a t e f r o m E q . 2 ) b y le ss t h a n

0 . 0 0 2 p , o r l e s s t h a n 0 . 1 K . F o r e x a m p l e , t h e r e s u l t s r e p o r t e d b y B a e h r a n d

840/13/5 8



8 5

G o o d w i n , D e f i b a u g h ,

a n d W e b e r

Tillner-Roth 1-21] differ by less than 0.0001p from Eq. 2) at temperatures

up to the critical. Such agreement between independent vapor-pressure

measurements is truly remarkable. In contrast, the measurements of

Kubota et al. [25] appear to have a systematic error with differences

between 0.004p and -0.005p. The recent measurements of Zhu and Wu

[20] between 279 and 363 K show a similar trend to those of Kubota et

al. [25]. The vapor-pressure equations given by the Japanese Association

of Refrigeration JAR) 1-55] and by Baehr and Tillner-Roth [21] were

both derived from information independent of ours and Ref . 19. These

equations predict vapor pressures below 300 K that are much too high but

tend toward agreement with our data at higher temperatures. The JAR

[55] correlation was derived with data reported by Basu and Wilson [24],

while that attributed to Baehr and Tillner-Roth 1-21] used data of Bier et

al. [56] at lower temperatures. In view of the excellent agreement between

our measurements of the vapor pressure of R22 with those reported by

Zander [16] and for R134a with the precise static measurement of Magee

and HoMey [19] at temperatures below 250 K despite the slight discon-

tinuity in their results), we conclude that the measurement of Basu and

Wilson [24] and the correlations of JAR [55] and Baehr and Tillner-Roth

[21] are in error by as much as 0.02@ at 220 K.

Assuming the critical temperature to be that observed by Morrison

and Ward [28] and adopted by McLinden et al. [57]) we calculate from

Eq. 2) a critical pressure of 4055.1 _+ 0.3)kPa, 12.9 kPa below the value

given in Ref. 28, but only 0.9 +_ 10)kPa below Ref. 57 and well within

twice the combined uncertainty; Weber reported po = 4055.9 kPa [13]. The

critical pressure reported by Kubota et al. [25], from an extrapolation of

their vapor-pressure equation a Chebyshev polynomial), and that adopted

by Tang et al. [58], for use in a simplified crossover model for the critical

region, is 9.9 kPa above our value.

ACKNOWLEDGMENTS

One of us A. R. H. G.) would like to thank Drs. Douglas Ambrose

and Michael Ewing for stimulating his interest in ebulliometric measure-

ment of vapor pressure that began at University College, London, with

Ref. 9.

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Vapor Pressure R134a R22