Thermal Food Processing

148 Thermal Food Processing: New Technologies and Quality Issues
engineering, but have been applied to an ever-increasing list of industrial situations,
including food and bioprocessing applications. In thermal processing, CFD
packages can be used not only to analyze an existing process, but also to optimize
the process and to explore scenarios of new, more effective operations. There is
no question that food processing problems are complex and also, in most situations,
involve transient, three-dimensional conditions. Analytical approximation
and solutions may no longer be appropriate, and the CFD approach combined
with chemical or biochemical kinetics equations is necessary. So far, only very
limited thermal processing problems have been investigated using CFD, so there
is a scope of further development that will no doubt be beneficial for the improvement
and modernization of the current food industry to make it safer for consumers.
Though powerful in many ways, in using the CFD approach, it is always
necessary to be able to understand the underlined physics and chemistry in simple
terms and indeed to conduct appropriate experiments to validate the calculations
for the situations of interest.
NOMENCLATURE
A Preexponential factor (sec –1 )
c Concentration (mol·m –3 or kg·m –3 )
Cp Specific heat capacity (J·kg –1 ·K –1 )
d Diameter or characteristic dimension (m)
DT Decimal reduction time at temperature T (min)
D Diffusion coefficient (m2 ·sec –1 )
E Activation energy (J·mol –1 )
F Thermal death time (min)
Gr Grashof number,
g Gravity acceleration (m·sec –2 )
H Height of the can (m)
h Heat transfer coefficient (W· m –2 · K –1 )
k Thermal conductivity (W·m –1 ·K –1 )
Nu Nusselt number,
p Pressure (N·m –2 or Pa)
Pr Prandtl number,
r Radius or radial coordinate (m)
R Radius (m) or the universal gas constant (J·mol –1 ·K –1 d3ρ2gβ⋅∆T Gr =
µ 2
Nu = h d
k
)
T Temperature (°C)
⋅
Cp
⋅
Pr =
k
µ