Three ways of heat transfer in one photograph (ROLAND)

The following contribution comes from ROLAND.

This is a  view of the interior of the chamber of a freeze dryer where the lyophilization process take place. these are vials with a pharmaceutical product during the ramp of freezing.In this example the three mechanism of heat transfer are involved.

Conduction: From the product to the vials and  then to the shelf in direct contact to the vials.  Higher heat transfer rate.

Convection: From the product to the shelf surface through the air occluded between the shelf surface and the bottom of the vial in the case of concave vials. Lower heat transfer rate.

Radiation: This mechanism is more significant during primary drying of the lyophilization process than the freezing step, because exist a major gradient of temperature between  the surface of the shelf above the vials, walls, front door and the product surface. The product placed at the edge of the shelves have a higher heat transfer coefficient than the center ones.