Hochfrequenzerhitzung viskoser, partikelbefrachteter Lebensmittel

A prototype tubular radio-frequency (RF) heater for liquid foods with 25 mm and 50 mm tube has been investigated experimentally. Thermal runaway heating has not been observed even at maximum heating rates of 7 °C/s, stability of heater operation seems to pose no problem. Heating of laminar flowing liquids in most cases leads to temperature profiles with high temperatures at the tube wall due to residence time distribution of the laminar flow. However, practical heating rates up to 3 °C/s seem possible with still fairly uniform temperature distributions. Suspended particles in most cases heat fairly similar to the surrounding liquid. Only when relation of electrical conductivity of particle and liquid exceeds a factor of 2, noticeable differences in heating occur. A circular symmetric numerical model of the laminar tube flow for non-newtonian liquids and of RF-heating has been developed and can be used to make predictions on heating performance and to support up-scaling.