OHMIC PROCESSING OF SOLID LIQUID-MIXTURES - HEAT-GENERATION AND CONVECTION EFFECTS

Ohmic heating allows large food particles to heat at the same rate as liquids, and enables 'high-temperature short-time' sterilisation of foods containing up to 25-mm particles. The rate of heat generation depends on the local electric field strength. Around materials of high or low electrical conductivity, the electric field can be distorted. Depending on fluid viscosity and solids fraction, this distortion may cause local temperature variations in the liquid around the particle which might affect both the heating rates and thus the process time of food particles. Experiments have been conducted to determine the magnitude of temperature variations in the liquid both in ideal cases and for real foods. A number of possible models to predict liquid temperatures have been tested, in which various amounts of convection are assumed.