Water flow rate, secondary drying

Willemer (1991) proposed to relate the pressure increase as a consequence of the PRTduring secondary drying to the residual moisture content using this measure to stop secondary drying. An improved approach is that proposed by Oetjen (2001) using two successive measurements of desorption rate, calculated from the water flow rate M ... 

Gieseler et al. utilized tunable diode laser absorption spectroscopy to detect water vapor concentrations, gas velocities and mass flow during freeze-drying of pure water at different pressure and shelf temperature settings and of a 5%w/w mannitol solution. The analyzer was interfaced to the spool that connected the dryer chamber to the condenser. The reported method was advantageous in that primary and secondary drying end-point control based upon mass flow rate was independent of freeze-dryer size and configuration. ... 

Other methods proposed in the past to monitor secondary drying are based on the estimation of the solvent flow rate that can be obtained, for example, from the PRT. This technique can be tracked back to the early 1960s, as was proposed by Kan (1962) for detection of the drying endpoint. In fact, the mass flow rate of water (or solvent) Mw can be calculated from the slope of the curve of chamber pressure vs. time at the beginning of the PRT ... 

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