Pharmaceutical drying, convective heat

Fig. 2 Convective heat transfer applications in pharmaceutical dr5dng (A) tray-drying of a static solids bed and (B) fluid bed-drying of a spherical particle.

The two types of processes currently used in dry-heat sterilization include 1) dry-heat batch sterilization/ oven sterilization and 2) dry-heat tunnel sterilization. Process 1 is the type of dry heat unit widely used in the pharmaceutical industry it uses the principle of convective heat transfer to heat the load. Process 2 is only found in large-scale processes, and the main application of this process is in the sterilization and depyrogenation of glass.f ... 

The heat transfer in the temperature range used in pharmaceutical freeze-drying, -60°C to +60°C, is dominated by contact between surfaces and by convection of the gas between the surfaces. The possible effect of radiation will be studied later. 

It is noteworthy that sometimes one can operate the same apparatus in direct, indirect, or combined modes. For example, a vibrated fluid bed dryer can be purely convective (e.g., drying of tea), purely conductive (e.g., vacuum drying of pharmaceutical granules), or combined direct-indirect (e.g., drying of pulverized coal with immersed heating tubes). The drying medium could be steam for such products as coal. 

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