foam-mat freeze drying of egg white and ... - McGill University

N
D
in = − win,
e
∂C
∂x
pin
N t = v p ( C pw + C pin )
⎛
+ ⎜
⎝ C
pw
C
pin
+ C
pin
⎞
⎟N
⎟
⎠
t
This model can be used for determining overall mass transfer by applying the
boundary conditions; this model also helps to include the effect of radiation heat transfer.
Some of the key assumptions made by the researchers (Liapis & Bruttini 1995;
Liapis & Sadikoglu 1997; Jafar & Farid 2003; Khlloufi et al. 2005) to develop
mathematical model for freeze drying are,
i) The maximum permissible surface temperature (Ts) is reached
instantaneously
ii) The surface temperature is maintained constantly by adjusting external
heat output
iii) Sublimation occurs parallel to the surface at the interface
iv) At the interface the concentration water vapour and the ice are in
equilibrium
v) Solid layer is semi-infinite
vi) Binary mixture of water vapour and inert gas pass through dried layer
vii) In the dried layer, the solid and the enclosed gas are in thermal
equilibrium
viii) Partial pressure variation inside the drying chamber is negligible
ix) There is no heat loss; all the heat input is used for sublimation of water
33
……………… (3.10)
……………… (3.11)