Comments by "seneca983" (@seneca983) on "Ultra-Fast Dryer -BUSTED!" video.

  1. I'm only guessing but here's what I think. In a freeze dryer the temperature is very low which means the saturated vapor pressure of water is also very low. For the sublimation of the water to happen at a reasonable rate the actual partial pressure of the water vapor needs to be below that. The surrounding air will probably have much higher partial pressure of water vapor because it's much warmer and therefore won't be good for drying in subzero temperatures. Raising the saturated vapor pressure by heating is out of the question for obvious reasons. Therefore sucking out the water vapor by a vacuum pump might be the only option. Also sucking out the air in addition to water vapor isn't necessary as such but vacuum pumps cannot selectively only suck out the water vapor.
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  2. I'm only guessing here but here's what I think. In the subzero temperature of the freeze dryer, the equilibrium partial pressure of the water vapor is going to be very low and you need to get the actual partial pressure to be clearly below that for the sublimation to happen at a reasonable rate. The surrounding air likely to have a higher partial pressure of water vapor because it's much warmer so it's not much help. The normal dryer mechanism of using heat is out of the question for obvious reasons. Therefore sucking the water vapor out with a vacuum pump might be the only practical choice. Also sucking out the air as well might not be necessary as such but in practice, the vacuum pump is going to do that as well as a side effect.
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  3.  @tullgutten : "it's sold as a ultra fast dryer, not an efficient dryer 😜" I would guess that sublimation isn't very fast either.
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