Maximum product temperature

If the product temperature approaches T%- from lower temperatures, the viscosity changes rapidly (within a few degrees) by several decimal powers. Since also the product temperature can be measured only with a certain accuracy (see Section 1.2.3), one has to account for both uncertainties. It is recommended that the maximum product temperature during main drying 3 to 5 °C below T. be chosen. 

Thermal analysis data also dictate the maximum product temperature allowable during primary drying. Shelf temperatures and chamber pressures are then selected to assure that the product remains below this critical threshold temperature during primary drying. Secondary drying conditions necessary to achieve the desired residual moisture content are also identified. Determination of these processing parameters requires numerous process studies and corresponding stability studies to define optimal conditions. 

Product Temperature Trace The traces of the different batches should be compared and found in reasonable agreement. Using the method shown in Figure 1, one can tabulate the maximum product temperature at the end of primary drying and the product primary drying time (individual probes and the mean of all). 

The choice of co- or countercurrent drying is determined by the product properties. Cocurrent drying leads to high drying rates and limits the maximum product temperatures, while countercurrent drying allows lower final moisture contents to be achieved. 

Maximum air temperature Depends on heat sensitivity of product Maximum product temperature must be specified... 

Fig. 4.18 Example of the application of the feedbackcontrol strategy that uses the observer to estimate the maximum product temperature (the freeze-dried product is skimmed milk dv= 14.2 X 10 m, Lp = 8 X 10 m,...

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