75
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_
.
FREEZE—DRYING
"
Vapeur may diffuse
in
or
there may be»a
ash of vapeur, such -”'as occurs ât*‘the beginning*ôf freeze drÿi‘ng, and recently it has been
_
_
…
.
:
shown that freeze dry1ng can take placewhen a succession
of vapeur ashes are 1nduced
by cyclic“variation of the vacuum“
I
'
ANALYSIS OF THE
BOUNDARY
Vapeur Pressure Equation
Before deriving an equation for the drying rate, the water vapeur pressure and its relation—
ship to position in the dry layer and to time must be known; the vapeur pressure difference
between the içe interface and surface of the product must also be known. From these
,
_
the drying rate equation can be integrated to give the amount of ice sublimed. In the
!
present paper equations are rst derived for di‘usive ow; from these, equations for other
types of vapeur ow are derived simply by changing the ow coeîcients and making other
suitable modications.
.
'
Basic Concepts
.
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sublimation rroce…ss may… be sens9rsd
£hwsh…thedti
pu utly f thpdut fmfm……b…ndmg tth
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ntth bndybtwnthdyndfzenptfthpdutbmg mmtn
duringŸthe“œurse of frè‘éîè drÿigf1n s1abs”ôf food'iÜhich‘ârë”reas“oably‘fthin" and_homo—
,
,
gsns9us this m9eeëwn@&ry .may bersærd9@ as °°ntmuous
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ofsubhmaüonwhenthe icè aggregaæsmsmapœkets
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…In …the.…99mæ…cfyfrsr«zs :ërrma the. Water
Whç
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dry…layer î…yanss ……‘Y?Êh
distan°eandümeaccœdmg t0 theequaü°
‘(ÎÏ…Q
P:————£
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°° 0
…
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;" f…-Ïà—fîl
theouter
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S“ffaœohedry1&yer f
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°f
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Asrmarequatwnhasprekuslybeenderivedforthetemperaturemthedry
.