ABSTRACT
Transient: Charts, p. 771). The two dimensionless num-
bers used in the graphical techniques are the Biot and the
Fourier numbers.
BIOT NUMBER
The Biot number (Bi0) is a dimensionless number and is
described as:
Bi0 ¼ hx1 k
ð5Þ
where h is the convective heat transfer coefficient, x1 is
the characteristic dimension that represents the shortest
distance from the surface and the center (x1 is equal to
radius/3 for a sphere, radius/2 for an infinitely long cylin-
der, and thickness/2 for an infinitely long square rod).[3]
When a food product is heated or cooled, the heat transfer
resistance is due to a combination of the heat transfer
coefficient at the surface of the food (external heat trans-
fer resistance) and/or due to the thermal conductivity of
the food material (internal heat transfer resistance). The
Biot number compares the relative values of internal
conduction resistance and surface convective resistance
to heat transfer (more information on Biot number is
available in the entry Biot Number). When Biot number
is less than 0.1, the internal heat transfer resistance is
negligible and the external heat transfer resistance
becomes the rate-limiting factor in determining the tran-
sient temperature distribution within the food product.
