An optimisation framework for drying of heat-sensitive products

An equipment model for a two-stage evaporator system has been presented and validated. A material model incorporating liquid and vapour migration as well as the heat transfer in a potato slice, as a model heat-sensitive product, was formulated and validated. Combining the two models, optimisation of the heat pump drying process was conducted for intermittent air temperature drying cycles. The independent parameters considered were the mean starting temperature, Tm, and the intermittent cycle ratio of the drying air, τon/τcycle. The constraints imposed were the desired moisture content, drying time, ascorbic acid (AA) content and non-enzymatic browning (NEB). The objective functions were minimising the loss of AA content and NEB degradation, and maximising the heat recovery of the two-stage evaporator system. The implications of relaxing implicit and explicit constraints on heat recovery and product quality parameters (AA and NEB) were also studied.