EugeneOregon
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You have an excellent question and I pondered a while about this. I think I can explain what I am seeing in my unit. This is indeed about as optimized as it gets for a short path seperation. However there are important and subtle points of difference between this and a short path head. The unit runs a vacuum deep enough to effect the mean free path of the gas molecules so they no longer interact with one another and they then tend to travel in straight line random directions. In this state the gas travels until it hits a surface inside the apparatus and if enough energy is present it again takes off as a gas in a random direction. This means it could go right back the direction it came from as a gas. This would not work in a distillation apparatus that had packing or a bend or corner for the gas to flow around (they all do) because in free molecular flow circumstances gas cannot flow around anything - only straight lines. This is one key difference and there are others. Your question though refers to the phase changes of the compound.
I use the term sublimation simply to avoid confusion with distillation which this is not, even though it is pretty close in most respects. Sublimation here occurs only at the cold finger surface. At all the other surfaces that the gas contacts condensation occurs. As I use the term, sublimation simply refers to a gas changing phase to a solid or a solid changing phase to a gas without a transitional liquid phase. Condensation is the transition from gas to a liquid, and evaporation is the transition from a liquid to a gas (like when it boils).
So in this sublimation apparatus much of what occurs at any given time at the cold finger is indeed condensation from a gas into a liquid and not sublimation into a solid. However ice water is at a temperature that causes Delta 9 THC to become solid. In fact when I harvest it from the cold finger there is no way to even chip it off at that temp without a brief thaw first. The exact temp at which it becomes liquid again is unknown to me except that at room temperature it is liquid. I define a liquid as anything that flows on a surface tilted vertically, however slow.
What happens in the sublimation unit is the gas escapes the boiling puddle via evaporation and contacts the cold finger and sublimates as a solid because the cold finger is colder than the freezing point of THC, building a layer. As the layer gets progressively thicker the latent heat of evaporation that is released into the layer from new incoming gas being sublimated into a solid warms the layer. The heat is continuously removed by the ice water in the cold finger, but at a certain thickness (about 4-5 grams worth in this unit) the heat can no longer be carried away from the surface of the building layer fast enough. So the surface is no longer cold enough to sublimate and instead the gas condenses as a liquid. Sublimation ceases at that point. It is at this point that the unit must be harvested. When condensation begins the unit simply begins to reflux continuously from all the condensing gas and can hold no more compound.
The finger can hold a few grams more as liquid on top of the solid layer in my experience as a highly viscous fluid. As a rule at first drip off the cold finger I shut down and harvest. Thanks for the question and comment.
