1. Freeze drying
Subtitle
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2. Freeze Drying Drying heat-sensitive substances to preserve taste
Example: Coffee
Preserve a perishable material
Example: Blood plasma
Make more convenient for transport
Example: Astronaut food

3. Freeze Drying Phase diagram: Pressure vs. Temperature
S = Solid Phase
L = Liquid Phase
G = Gas Phase
Conventional drying (green)
Freeze drying (blue)
Supercritical drying (red).

4. Freeze Drying Phase diagram: Pressure vs. Temperature
Triple Point
Critical Point
Phase diagram: Pressure vs. Temperature
S = Solid Phase
L = Liquid Phase
G = Gas Phase
Conventional drying (green)
Freeze drying (blue)
Supercritical drying (red).

5. Freeze Drying Freeze drying (blue)
Triple Point
Freeze drying (blue)
Sublimation of an element or compound is a transition from solid phase to gas phase with no intermediate liquid stage

6. Freeze Drying Sublimation of water ice in a vial Vapor Domain
Ice Domain

7. Freeze Drying Heat conduction in both Vapor Domain Ice Domain

8. Freeze Drying Diffusive transport of vapor in Vapor Domain
Ice Domain

9. Freeze Drying
Thermodynamic equilibrium at ice-vapor interface. Vapor pressure above the solid follows an equilibrium law, for example. This constitutes the boundary condition at the surface for the mass transfer.
Vapor Domain
Ice Domain

10. Freeze Drying The interface is moving with time!
Heat + Mass Balance at ice-vapor interface gives the velocity of the interface:
Qs is discontinuity in heat conduction rate (due to latent heat of fusion)
L is latent heat of sublimation
Vapor Domain
Ice Domain

11. Freeze Drying Moving Mesh Needed The interface is moving with time!
Heat + Mass Balance at ice-vapor interface gives the velocity of the interface:
Qs is jump in heat flux
L is latent heat of sublimation
Vapor Domain
Moving Mesh Needed
Ice Domain

12. Freeze Drying Mass flux of vapor from Ice Domain to Vapor Domain:
Mv =molecular weight of vapor
Vapor Domain
Ice Domain

13. Freeze Drying
Uneven heating of the bottom tray

14. Ice-vapor interface is asymmetric due to uneven heating of the tray.