ŸAPOUR TRANSFER PROBLEMS
_
79
0
.
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|___-_—
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8 |___—_
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1'“...
3%
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3
0—5
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1
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2
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3
t.
5
Time
(Minutes)
'
FIGURE 1. Variation of vapeur pressure dierence Ap‘W'ith a Sudden change in vaCuum pressure P
vapeur pressure within the product… Consequeny; there is instantaneously a sudden,
outward hydrodynamic ow of water vapeur.
_
Measurements shown in Figure 2 also make_it clear
that follewmg the commencement
of sublimation quasi-equilibrium is reachedwrthm
a reasonably short
trme. When th1s
stage is reached the saturation vapeur
the
1ce‘ mterface
rs closely appreachmg
the vacuum pressure, and the vapeur pressure‘at‘
of the product rs not
much
lower than that within it.
Of vapeur transfer agam reverts
.
to normal diffusion of vapeur
product.
_
The principles outlined above provided thehasrs
for attemptmg ‘cychc pressure freeze
drying, a process by means of whrchthetrans1ent condÎrüons edenducrve
to ash transfer
«
could be reproduced repeatedlyædurmghG course 0f " reeze rymg.
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