86
'
'
*FREEZE—DRYING .
:
'
__
To vacuum pump
-,
,
_
'
To
_
'
“
_
,
_
_
_
.
,,
vacuum
_
‘0
,.
_
»».'
:,
î
’
"
_
-
,
;
:
_
_
’
-
…
.
—Fre—'eze—dried- «,
;ÏL'ï
:
,
'
VO'L‘Û-‘l‘hEÎFÎC ‘
:
':
"
,,
‘NeoprÏe‘ne,
‘f00d sample
_
Re9Ulat°r…
…
…
tuba
—
;
rU|;>ber,
«
,_
î
valve
' _
‘_‘_J
'
‘
'
‘
‘
'
”
_
.
_
_
UOQ
_
_
_';î
'
'
or…“
'
"
'
"’
'
.
tyuer
Sample
'
_
_
_
_'
'
_
_
holder
'
.
*
‘
manom
Nitrogen
'
_
.
'
cylinder
_
Mercury
_
…
_
_
'
manometef
*,“
“
x…;
.
Rubber buUb'
valve
,
.
of soapy
,
water
_
FIGURE
Permeabitÿ apparatus.
-
Operation was e”ected by_adjusting‘the'regulator't'o obtain atmospheric pressure in the
owmeter, at the same time adjusting the needle _vä1ve
to CaUSe“the soap lm to move
.
over a measured volume in a given time.; Both thé…VaCuum gauge and oil manometer were
then read.
_
_
_
,
'
The permeabity coeîcient Ka for di‘erent mean vacuum pressures P was calculated
using the formula :
‘ _
‘
‘
,
'
V1 P1 [
Ï
,
K
=
————cm2‘sec
.
17
_
_
°
AApt
_
,
[ ]
Where V1/t = owmeter reading
_
_
_
‘
,
'
‘
_
Pi
=
absolutepressure
l
=
sample thickness
_
_
A
=
sample
'
,;
pc?;
—
êp = pressure di‘erence
,
':i
P
_
=
mean vacuum presSure
across the sample.
_
,
__
Ï
__
_
Ko_ values in real permeabity umts(viz. g cm/émztorr sec) are obtained by multiplying _
Aplot of Koagamst Pg1vesa curve(F1gure5)wh1ch 1s l1near >—over themed1um pressure
"
sl@Pemthetransüwalshpowregwn,weretheeanfreepath OfthegasmŒeŒÏes
actually does so _is,
investigated.
_