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Capacity Basis Converter
Two freeze dryer quotations can both quote kilograms of water per square metre per hour and still differ threefold, because the figures sit on different bases. Put the number you were given into the converter, say which basis it is on, and read the equivalent on the other three.
Used to relate a peak figure to a cycle average. Change it if you know your own split.
A 20 % solids recipe loses about 80 % of its mass as water.
—Average dehydration, kg/(h·m²)
—Peak sublimation, kg/(m²·h)
—Rated capacity, kg water per hour
—Wet product per batch, kg
Why the bases differ
| Basis | What it measures | What it hides |
|---|---|---|
| Average dehydration | All the water removed, divided by the whole cycle and the shelf area | Nothing — but it looks small next to a peak figure |
| Peak sublimation rate | The fastest moment of primary drying | That it cannot be held across pre-freezing, the ramp and secondary drying |
| Rated sublimation capacity | A machine rating in kg of water per hour | That it means nothing until you know the tray area it goes with |
| Wet product per batch | What you load | Loading density and cycle time, without which it says nothing about output |
Published figures for large food freeze dryers give peak sublimation above 3 kg per m² per hour as an alternative operating point to running at low vacuum, not as a continuous throughput. A published porridge dryer table gives 1.0 kg per hour per m² as an average dehydration figure. Both can be true of comparable machines.
The question to ask every supplier
- Which of the four bases is your number on?
- What tray area does it go with?
- Does the cycle time include pre-freezing and secondary drying?
- How is the endpoint moisture measured?
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