Two-Way Coupling of Fluid-flow, Heat-Transfer and Product Transformation during Heat Treatment of Starch Suspension Inside Tubular Exchanger

When a liquid product is subjected to thermal treatment under continuous flow, its transport properties can evolve as a consequence of changes occurring on the product constitution (continuous phase, particles...). This two-way coupling is implicitly considered when the residence time distribution (RTD) associated with the product is studied through experimental work. For a number of liquid food products, there is experimental evidence that the minimum residence time decreases as the transformation state progresses. In this study, modeling work is employed for assessing the influence of transformation on the RTD associated with a starch suspension under continuous heat treatment. After including the impact of starch granules swelling on the suspension viscosity, the minimum residence time decreases from 55 % to 41 % of the mean value. The role played by the transformation in driving the RTD cannot be neglected if the transport properties evolve with the product transformation state.