12.1 Introduction
Heat transfer is perhaps the most widely used unit operation applied within the
food industry and many key processes such as pasteurisation and sterilisation are
based around it. Heat transfer can be applied on either a batch or continuous
basis and the mechanisms involved can be convection, conduction or radiation,
but are usually a combination of these. In addition, heat transfer can take place
either through direct contact with the service medium or indirectly across a heat
transfer surface.
The most typical practical operations involving heat transfer are:
∑ heating;
∑ cooling/chilling;
∑ freezing;
∑ evaporation;
∑ condensation;
∑ radiation;
∑ drying.
Heat transfer operations can therefore involve a change of phase in the case of
evaporation, freezing and drying. These changes of phase processes are complex
operations in their own right and the scope of this chapter is limited to heat
transfer equipment for applications with no phase change.
Heat transfer can take place in vessels and tanks but the most common
equipment used is the heat exchanger. A wide range of heat exchanger
geometries are available in practice and the major ones used for food applica-
tions are classified in Table 12.1.
12 Improvingthe hygienic designof heating equipment
A. P. M. Hasting, Tony Hasting Consulting, UK