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Freeze drying Subtitle © 2011 COMSOL. All rights reserved.

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Presentation on theme: "Freeze drying Subtitle © 2011 COMSOL. All rights reserved."— Presentation transcript:

1 Freeze drying Subtitle © 2011 COMSOL. All rights reserved.

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 – S = Solid Phase – L = Liquid Phase – G = Gas Phase Conventional drying (green) Freeze drying (blue) Supercritical drying (red). Triple Point Critical Point

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

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

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

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

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

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

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

13 Freeze Drying Uneven heating of the bottom tray

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


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