The estimation of freezing time req

The estimation of freezing time requirements is criti-
cal in the operation and control of cryogenic systems.
Different thermodynamic models have been developed
to describe the freezing process and provide methods to
estimate the ‘‘dwell time’’ requirements for a product to
be frozen. The two main thermodynamic models are the
?heat conduction with temperature-dependent thermal
properties model’ and the ?unique phase-change front
model’ (Valentas, Rotstein, & Singh, 1997). The latter
model is based on the assumption that all the latent heat
is released at a unique temperature at a sharp phase-
change front. This front moves from the outside to the
thermal center of the object being frozen. The model
further assumes that the thermal properties in the re-
gions before and after the front are constant but dif-
ferent. Due to the above-mentioned assumptions, the
model incorporating temperature-dependent thermal
properties is considered to be more realistic than the
second approach.