4.5. Calculation results and comparison with experimental data
Calculations were carried out with the properties estimated as above (see Table 3), and the resultant drying curves are shown in Fig. 7. Experimentally obtained drying curves are also plotted in this figure. The CV values from experimentally obtained and simulated drying curves were 3.4%, 2.4% and 2.3% for the heater temperature setting to 60, 90 and 125 °C, respectively. It can be concluded that the present model is reasonably successful in predicting the experimental results. With the heater temperature set to 60 °C, deviations between experiment and predicted results were seen in the middle stages of drying, whereas no significant deviations were seen for higher heater temperatures. At the higher heater temperature settings, the contribution of radiative heat to the total heat input is higher. The ratios of Qice to Qdry are plotted in Fig. 8 as a function of time and remaining moisture content. It can be confirmed that, in the present freeze-drying system, the radiative heat was the dominant heat source for drying, and that the contribution of conductive heat from the shelf dramatically decreased after ca 40% of the frozen fraction was sublimated. Interestingly, the profiles did not significantly differ among the different heating conditions. It means that the radiation heat and conductive heat synchronously changes depending on the heating condition.