Measurements of temperatures, ice evaporation rates and residual moisture contents in freeze-drying.

The temperature measurements during freezing and freeze-drying are described, and the results obtained using thermocouples and resistance elements (Pt 100) are compared with the barometric temperature measurements (BTM). The BTM is checked with a mass spectrometer, thermoelectric instruments and an absolute capacity measuring gauge. The temperature measurements are also shown as a function of the location of the sensors in the product. The evaporating rates of ice are given as a function of operating pressure. It is shown that the residual moisture content is a function of the temperature of each product. The equilibrium vapour pressure as a function of temperature is shown as desorption isotherms. Therefore, the residual moisture content can be determined by measuring this equilibrium vapour pressure (or at least a pressure very close to the equilibrium vapour pressure).