2. Theory: determination of heat transfer coefficient
Heat transfer coefficient is defined as the ratio of convected heat
transfer flux to the driving force of temperature difference through
the product surface–fluid interface (Alvis et al., 2009). Lumped system
methodology is one common method to determine heat transfer
coefficient experimentally where high thermal conductivity
materials are used to eliminate conduction resistance. Heat flux
measurement is another method where surface temperature and
heat flux change are used to estimate the heat transfer coefficient.
These methods are not immediately applicable for frying since
the significant effect of bubbling on boundary layer mixing can
not be easily accounted. Hence, applying an energy balance between
fried samples and frying medium can be used (Hubbard
and Farkas, 1999) for experimental determination of the heat
transfer coefficient based on moisture losses. Assuming the steady
state condition for this purpose: