Thermal Food Processing

38 Thermal Food Processing: New Technologies and Quality Issues
T
T1
dT
dx
x1 x2
(a)
Cross area: A
T2
q
x
Total surface
T1
Total surface
area: A 1
(c)
area: A2
Boundary layer
T Ts
Bulk fluid
Cross area: A
FIGURE 2.1 Schematic of three basic heat transfer modes. (a) Heat conduction through
a uniform slab. (b) Heat convection through a vertical wall. (c) Heat radiation between a
surface, 1, of a body and the surroundings, 2.
Radiation does not require a medium for transferring heat but uses electromagnetic
waves emitted by an object for exchanging heat. The energy emitted
from a surface depends on the temperature of the surface, which can be described
using the Stefan–Boltzmann law:
q= σAεTK 4
T2
T
(b)
δ
q
x
(2.4)