Ohmic heating: models and measurements

Abstract

Ohmic heating is a process in which electric current is passed through a food; the material heats as a result of its electrical resistance. The process has been studied intensively over the last 25 years as a result of commercial processes being developed by EA Technology and APV in the UK. The aim of this chapter is to outline and review the work on the modelling of ohmic heating and experimental work that has been conducted. Models have been written to describe the heating of simple solid-liquid mixtures, and it has been shown (both experimentally and by modelling) that solids can heat faster than liquids. This makes the process very attractive for heating solid-liquid mixtures quickly. Modelling the flow and heating of two-phase mixtures is very difficult, but some approximate models have been written to simulate the process, and these have been validated by experiments using methods such as temperature mapping with MRI. As well as sterilisation and pasteurisation processes, ohmic heating has been shown to be effective in processes such as thawing and in enhancing mass transfer between solids and liquids.

Dielectric, ohmic and infrared heating

“…For example, when a particle that has a lower conductivity than the liquid is heated the liquid heats faster, but if the density of the particle is higher, the heating rate may exceed that of the liquid (Sastry and Palaniappan 1992). Mathematical models are described by Salengke and Sastry (2007), Samprovalaki et al (2007) and Ye et al (2004) and are reviewed by Ruan et al (2004). The calculation of heat transfer is therefore very complex, involving the simultaneous solution of equations for changes in electrical fields, thermal properties and fluid flow, and is beyond the scope of this book.…”