I don’t think many vapes, including this one, are really BOILING THC. In the sense that THC vapor pressure > atmospheric pressure. Concentrate ones may be, but operate at higher temperatures. As this article says:
The vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with the liquid phase.36 At a given temperature, more volatile liquids have higher vapor pressures. The vapor pressure increases nonlinearly with the temperature, according to the Clausius–Clapeyron equation.37Figure 1 presents vapor pressure dependency on temperature for some of the terpenes, based on this equation. The temperature at which the vapor pressure of a compound reaches the atmospheric pressure (760 torr, 100 KPa) is the boiling point of that compound, also referred to as the normal boiling point. At this temperature, the vapor pressure becomes sufficiently high to overcome the atmospheric pressure and to lift the liquid to form bubbles, which is referred to as boiling.
Vapor pressures of some terpenes at various temperatures, based on Clausius–Clapeyron equation. The vapor pressures of monoterpenes are markedly higher than those of sesquiterpenes and greatly higher than those of cannabinoids. The critical role of vapor pressure in determining the evaporation or preservation of a compound explains the actual composition of the various cannabis products.
Under vacuum, lower temperatures are sufficient to bring the vapor pressure to the external one, so that at high vacuum of 0.05 torr, THC boils at about 155°C.
There is no practical direct way of measuring the temperature at which the vapor pressures of THC and CBD reach normal room pressure (about 760 torr), since at such elevated temperatures, these cannabinoids are instable and decompose. The normal boiling points can, however, be estimated by extrapolating vapor pressure at lower temperatures, using the Clausius–Clapeyron equation. For example, the vapor pressures of THC at 155°C and 190°C are about 0.05 torr and 0.3 torr, respectively, leading to boiling points higher than 400°C, in agreement with the results of McClements, Umnahanant et al., and Lovestead and Bruno.38–40
Rather, the THC comes into the air by a process of evaporation, or is carried by the terpenes in an azeotropic mixture with a lower boiling point.
The rate of evaporation depends on several variables, because it depends on the concentration gradient at the interface where the evaporation occurs. The vapor pressure gives the concentration at the interface, or at equilibrium, but does not say anything about the rate. Evaporation is a diffusion-limited process, where in order to evaporate more vapor, the vapor must be moved away from the interface to allow more to fill in. Study of the rate of evaporation is in the discipline of heat and mass transfer. I agree in this device that the vapor pressure is a good approximation, because this device should have time to reach equilibrium, while waiting for the pressure to rise back up, but I am very curious what @ForgeHavenVape has to say about it.
I just tested again with .1g and only pumped down to 60% ATM. The needle walked back to zero after about 10 minutes and reaching 140C chamber temp, process temp expected 30+ delta (unmeasured). Vapor was full of flavor and cool enough to enjoy without a bubbler. Not as primed as the full vacuum sessions, but it was 5 less minutes of vaporization.
Instead of the strongest pull being two or three, using full vacuum makes the first pull strongest, followed by lesser density, naturally
The vacuum levels we are working with here’s not enough to really change the boiling point. The pumps that get low enough vacuum, cost a few hundred bucks.
The method of heating here is just never going to be faster than conduction or induction, but I can make marginal improvements. The herb is inside a quartz bowl, inside another quartz tube sealed in a vacuum. Heater is outside of the vacuum entirely.
Do you know what the pressure gets down to, for reference? It will help my geeky research methods.(again, once sober… tonight is a bust after a heck of a work week but I’m floating happy at least)
Haha nice, as you should be on this forum! Well really what I am getting at is just the difference between boiling and evaporation.
The reality and science of vaporizers is quite complex indeed. Also worth keeping in mind that we inhale a suspended aerosol and not a true vapor. After evaporation, at least some of actives and aromatics re-condense into much larger droplets. These refract and reflect light, which is why the vapor is visible. If we inhaled a true gas, it would be invisible. And the vapor is a mix of different chemicals all with different vapor pressures that also interact with and somewhat modify each other. That graph shows the different vapor pressures at any given temperature vary widely between terpenes and cannabinoids.
This is true, but critically, boiling is not the only way in which a vapor can form. Boiling point is a critical temperature at which the rate of vaporization greatly increases, due to the boiling occurring throughout. Evaporation however can occur at any temperature above absolute zero, but only at the surface.
In the case of vapes, we do not see any huge difference in output when crossing over any temperature threshold, which we would expect to see if the boiling point was within the range of vaporizer temperatures.
If you decide to learn more later, here are some background terms you can search for:
Kinetic Theory of Gases
Vapor Pressure / Equilibrium Vapor Pressure
Thermodynamic Equilibrium
Partial Pressure
Clausius-Clayperon Equation/Relation
Maxwell-Boltzmann Distribution
Concentration Boundary Layer
Azeotrope
Volatility
Whole college courses are taught on this science of heat and mass transfer. I’m happy to answer any questions to the best of my ability, but I’m far from an expert. It’s good to clear up misconceptions though.
Honestly i was skeptical at first, but i am starting to think that we are all ging to vape at lower pressures in the future.
For the heatup time I personally think up to 3min is acceptable especially if you compare the device to a ball vape or a dab setup.
I use around 100w for my diy PID heater system that gets me to 260 c in 3min or in 1min30s if I overheat something like 20%. I measure the temp on the outside so the inside won’t get to hot even with overheatin that might be interesting for you as well. But you will need to find some way to measure the temp inside the chamber for the development. Maybe you can try measure the temp of the herb by getting to temp equilibration to then remove it and check with a thermal cam. Or just measure at atmospheric pressure by inserting a probe from the top. I think for a vape in that price range it is quite important to get temperature right.
One more thing I am quite noise sensitive and I am thinking if its possible or maybe even cheaper to have a hand pump instead of an electrical one.
I know it will take longer at lower pressure to heatup except if you can apply conduction heat directly. One way would be to wrap some stainless around the chamber or use a stainless chamber and use induction to heat.
I did a quick test with a vaccum chamber with a heat plate underneath. I dropped in some rosin, pulled vacuum and started heating. 5min later I opened the valve and had vacuum chamber full of vapor. It looked to me like most of the vapor was produced by opening the valve. The process is a bit different since the volume of the chamber is so big that the pressure is not rising. I thing that its better to have some more volume so that the vaporization happens completely at low pressure.
Maybe something like this inductive banger could work as a bowl. This banger already works with a vaping induction tool called the Wand, powered by 2x18650 cells. You’d swap the quartz for high quality boro that encloses a metal cylinder. You could then induce a current in it from a coil outside the quartz chamber. Could this be a solution to more rapid heating?
The way I see it, you finish a bowl in 1-3 hits, benefitting from dense tasty vapor for all of them due to the negative pressure. Then you also profit from the hits being cool and easy on the throat due to the reduced temps. That’s probably something special. I’d try that.
Thats a great idea. I may have to buy one to play with it. Keep the ForgeHaven walls warm like 120C to prevent condensation then pump down, cap off the bowl (where the mouth piece is now) and heat. I could probably extract the full dose in one or two shots that way, as long as heat transfer in the center is okay.
Funny thing because the hand pumps get to lower vacuum than the cheap motor driven pumps. I used a brake bleeding pump with my concept feasability experiments.
Most devices that are heavily convection biased (popular these days) need a lot of surface area to be effective and don’t do well with whole nugs so grinding is more common than not I would say.
Only devices with a good amount of radiant and conductive heat handle whole nugs well but I gotta say, the color and consistency of your vaped nugs look exceptional. If you find ways to get that time-to-vape down, either by more effective heating or a better pump, it’d be a unique device in the DHV space.
That sounds really great! When you say 2X the original power, are we talking about the vacuum or the heater?
3-4 min is really zeroing in on a good time people would be willing to wait between bowls. The lower the better. Of course if the vapor quality is really mind-blowing, people might be willing to wait.
Yeah, I think we were just underpowered. Most of the wait time was the oven preheating. I can keep that preheat fast, then smooth out later on to get uniformity back.
I do like the idea of getting heat closer, but thats a larger redesign. I’ll consider that for next gen.
The 3–4 minute heat-up time completely changes the game. At that point, we’re getting into the same kind of territory as good ball vapes, so it’s definitely manageable. It’s something vaporizer users are already used to.
A 10-minute heat-up time would probably have put off quite a few users, but 3–4 minutes is absolutely within an acceptable range, especially when you compare it to ball vapes.
I also noticed that the heater has gone from 70W to 140W, which is very encouraging. That puts it right in the power range of some of the hardest-hitting portable vaporizers. For comparison, the Frolic uses a 120W heater, and we already know how much performance that thing can deliver.
So between the much more reasonable 3–4 minute heat-up time and the jump to a 140W heater, this is looking a lot more promising.
And honestly, it’s really great to see how responsive the designer of this device has been. He’s actively consulting the community, listening to our feedback, and apparently taking it into consideration as the device evolves. That’s always very encouraging to see.
