The Convection Thread

[JBone65]

i agree with the need for temp control and PID - has been my passion since 2009.

what i have found is that if the battery is sufficiently high current - i.e. LiFePO4 can deliver 70 amps - it is not possible to drop the temperature regardless of the inhale speed - the PID is rock solid. before PID my vape would drop 50 degs with a hit.

However, i think what happens with my heater geometry is turbulent vs laminar air flow ... thinking about your comment, i realized why a slow draw delivers more vapor - the air flow is flat against the heater, while a fast inhale will be more turbulent, so the air does not get a chance to fully get up against the heater and absorb the heat, before passing into the vial with the herb. so, faster hit is thinner vapor vs a slow hit is thicker vapor.

and, the session is only about 3 minutes, so minimal waste of material, despite being in the middle of the heater - the oven tube, between draws.

I'm guessing the slow draw also provides an extra few seconds for the load to heat up and for compounds to absorb heat, in a wave beginning closest to the heater. The end result (with my io) is lungs filling slower with a richer vapor. I like to click it off and continue drawing thru it until cool.

A good objective might be too start at a low enough temp and step slowly enough so that you always need to draw a little longer, maybe 12-15 seconds in my case.

In contrast, if you start a fresh load at a higher temp, you can make milky vapor and maybe cough a little, in as little as 5-6 seconds, but possibly waste 2-3 good hits in the process.

For me, the terpenoid and flavonoid compounds might be more enjoyable (and more absorbable) when using just enough heat to extract slowly.

Edit: With the io, the weed next to the heater always gets blackened. I end up getting a couple of long, slow hits at 430°f to finish the load. On the last one I'm trying to get the entire MP hot to extract compounds from the weed further from the heater.

 

[Dan Morrison]

I feel like the only temperature measurement that matters is the temperature of the air at the exact moment that it contacts your dry herb in the chamber. That's a difficult thing to measure and standardize between different vapes. So, I'd be careful talking about exact temperatures as it'll likely result in confusion, unless we are all talking about the same vape, and temp calibration between each unit is consistent.

What I like about temp stepping is that you get to experience the various fractions of terpenes that are released at different temp ranges. By temp stepping you can seperate them out and taste them individually.

If you extract all of the compounds in one or two hits, the flavors all meld together... and some of those lighter flavors are completely overpowered.

In the end, I like both. I like a robust one hit extraction sometimes, and I also like a more drawn out multi-hit temp step. It all depends!

With temperature, I think it's very subjective. I don't think there is a best method here.

 

[GoldenBud]

If you extract all of the compounds in one or two hits, the flavors all meld together... and some of those lighter flavors are completely overpowered.

I second this
when the heating process is being done with a conduction device, some of the flavour will be gone, like wanting to press Ice-o-lator hash to Rosin, some of the terps which are having boiling temperature of like 105-120 will be gone (i know the pressing temp is like 70c but some molecules will be gone... some) , but with convection device the terps are already mixed in the vapor although with high temps we can't taste them. That's why I think convection will bring better high, ALWAYS

I vape these days at very high temps and the flavour sometimes is gone but still exist in the mix of vapor

 

[Hippie Dickie]

I'm guessing the slow draw also provides an extra few seconds for the load to heat up and for compounds to absorb heat, in a wave beginning closest to the heater. The end result (with my io) is lungs filling slower with a richer vapor. I like to click it off and continue drawing thru it until cool.

A good objective might be too start at a low enough temp and step slowly enough so that you always need to draw a little longer, maybe 12-15 seconds in my case.

In contrast, if you start a fresh load at a higher temp, you can make milky vapor and maybe cough a little, in as little as 5-6 seconds, but possibly waste 2-3 good hits in the process.

For me, the terpenoid and flavonoid compounds might be more enjoyable (and more absorbable) when using just enough heat to extract slowly.

Edit: With the io, the weed next to the heater always gets blackened. I end up getting a couple of long, slow hits at 430°f to finish the load. On the last one I'm trying to get the entire MP hot to extract compounds from the weed further from the heater.

i always wait 90 to 120 seconds before taking my first hit - specifically to allow the vial and the herb to "heat soak". As an assist, the vape software waits 90 seconds from the time the heater measures at the setpoint temp - usually 10 seconds to get to 400°F - and then signals "take a hit" by allowing the green LED to come on when the heater is at or above setpoint temperature.

my typical draw is 15 seconds.

I feel like the only temperature measurement that matters is the temperature of the air at the exact moment that it contacts your dry herb in the chamber. That's a difficult thing to measure and standardize between different vapes. So, I'd be careful talking about exact temperatures as it'll likely result in confusion, unless we are all talking about the same vape, and temp calibration between each unit is consistent.

i agree the actual temperature is difficult to measure with any accuracy, but it can be consistent between sessions. so, although my 420°F may be someone else's 400°F, i know how it responds reliably.

i measure heater temperature using a k-type thermocouple located at the hottest point of the heater coil (12.5" of 1/8" wide nichrome80 ribbon) - the middle. the BBQ display thermometer's RT thermocouple is right next to it. after 30 seconds or so it should be thermally stable from heater to glass.

when i measure the temp in the vial, it is about 50°F below the heater temp and rises to the setpoint temp in the first 5 seconds of the draw. so, kind of sweeps through the terps on its way to extracting the thc.

i need to repeat this measurement - it has been a while.

 

[JBone65]

i always wait 90 to 120 seconds before taking my first hit - specifically to allow the vial and the herb to "heat soak". As an assist,

The 65w io heats incoming air to the desired temperature, but only when drawing air.

The heaters are directly in the air path, 1-2 mm before the load. Hot air directly on the herb "strips" aromatic compounds.

I also have a Davinci IQ conduction vaporizer. It's for sale, very lightly used.

 

[Hippie Dickie]

my heater coil is 0.3 ohm, so it hits 120 watts max with the 6v power pack. this is throttled by pulse width modulation - an "app" built into the PIC 12F683 architecture.

air path is isolated from everything - except herb - by glass. very clean taste.

to stay on topic ... i think my design is convection since there is very little contact between the herb and the hot vial walls, the heat to the herb mostly from the air flow during the draw. however, if the cube just sits with no draw, wisps of vapor drift out the top of the vial - i hold the draw tube against the open vial end to prevent this between draws ... i'm kind of anal about wasting vapor.

i do like the instantaneous speed of the io - i doubt i will ever have an on-demand vape design. heated glass takes more time than metal to reach temperature equilibrium with the heater coil, me thinks. my design(s) will always be all glass.

 

[invertedisdead]

think my design is convection since there is very little contact between the herb and the hot vial walls, the heat to the herb mostly from the air flow during the draw. however, if the cube just sits with no draw, wisps of vapor drift out the top of the vial

If it can vaporize on its own without drawing air it’s a hybrid.

Nothing wrong with hybrids they’re pretty cool as they do half of the extracting for you by already holding the herb at vaping temp.

The last vape I built was a hybrid, though it can also vape from a lower screen further away from the heat source for full convection too.

 

[GoldenBud]

how did I miss this vape eh ? the Supreme ... huge heater with laminar airflow ... when it's big and heavy, only 169c is needed eh ?!

 

[Hippie Dickie]

If it can vaporize on its own without drawing air it’s a hybrid.

yes, i think this is what is happening.

i tried a test: half loaded vial, packed/compressed downward, toothpick to make a hole in the middle of the pack and force the herb against the vial walls. started a session ... at 60 seconds when i normally see whiffs of vapor, there was a lot more this time ... took two hits but the vapor was relatively thin ... stirred the vial and the next several hits were more normal - thick with vapor. so, pretty clearly hybrid operation.

for normal use i never compress the herb in the vial because i like the thick vapor on the first hit. i can use a lower temp vs what would be required with a packed vial to get the same thick vapor.

 

[Abysmal Vapor]

how did I miss this vape eh ? the Supreme ... huge heater with laminar airflow ... when it's big and heavy, only 169c is needed eh ?!

The probe was in the herb chamber,so the actual temp on the block is actually higher. Actually it is quite wasteful on gas.
Alu is pretty good at thermal transfer but by the time the bowl reaches 169 the heater is above that.

 

[GoldenBud]

The probe was in the herb chamber,so the actual temp on the block is actually higher. Actually it is quite wasteful on gas.
Alu is pretty good at thermal transfer but by the time the bowl reaches 169 the heater is above that.

gotcha, the temp shown is not the temp of the heater, but the bowl?
bro, when a manufacturer say the flow within his vape is laminar/turbulent, you think somebody really calculated Reynolds number? how did they calculate the velocity of the draw? lol

 

[Stu]

the temp shown is not the temp of the heater, but the bowl?

The temp probe is at the base of the heating block, not the bowl.

I did run a test years ago measuring both bowl and block temps for shits and giggles.

 

[XpeeN]

I have a question for you. Imagine a tight long pipe with a heater at the center of it, and air passing inside the pipe, near that heater (pretty similar to glass symphony but tighter and without the balls ofc). Let's say we're keeping the heater's temp at a specific temp, and that for simplistically the pipe itself doesn't affect the temp, and that the air reached that temp after passing 2/3 of the way, so the air still has 1/3 of the pipe's length to pass. Will the air's temp will stay the same or rise? I'm pretty sure it'll stay the same, but I have the slightest doubt, so I have to ask lol

 

[GoldenBud]

I have a question for you. Imagine a tight long pipe with a heater at the center of it, and air passing inside the pipe, near that heater (pretty similar to glass symphony but tighter and without the balls ofc). Let's say we're keeping the heater's temp at a specific temp, and that for simplistically the pipe itself doesn't affect the temp, and that the air reached that temp after passing 2/3 of the way, so the air still has 1/3 of the pipe's length to pass. Will the air's temp will stay the same or rise? I'm pretty sure it'll stay the same, but I have the slightest doubt, so I have to ask lol

the air inlet = 25c
the heater = 230c
once the air is flowing into the heater it's getting hotter
and the heater is getting colder

we can calculate it by -
q=m*cp*dt=-m*cp*dt (q for the energy, m for mass, cp for specific heat, dt for the delta temp, must be positive number)

that's why Glass Symphony is so strong, the mass of the heater with all these glass soakers is huge. although, the cp of glass is pretty low... but the mass and the energy of the GS compensate

 

[Farid]

Has anyone here ever thought about some kind of anti-combustion cutoff systems for convection vapes?

As it stands, there are temperature regulated convection vapes that regulate the heat output from the heater itself.

What I've been thinking about is a valve which is activated when a certain temperature is reached. This valve being opened would bypass the heater and flood the flower with cold air.

It could be done with electronic components, or with mechanical components like a bimetalic flat coil (like whats used in many bimetalic thermometers).

Any system like this would need to have very rapid reaction time. It would need to be tweaked a lot to be accurate and not suffer from the other variables at play (environmental temerature for instance).

If it is even technically possible, would it have value? Or is it a solution to an issue that nobody really cares about?

 

[Razhumikin]

Has anyone here ever thought about some kind of anti-combustion cutoff systems for convection vapes?

As it stands, there are temperature regulated convection vapes that regulate the heat output from the heater itself.

What I've been thinking about is a valve which is activated when a certain temperature is reached. This valve being opened would bypass the heater and flood the flower with cold air.

It could be done with electronic components, or with mechanical components like a bimetalic flat coil (like whats used in many bimetalic thermometers).

Any system like this would need to have very rapid reaction time. It would need to be tweaked a lot to be accurate and not suffer from the other variables at play (environmental temerature for instance).

If it is even technically possible, would it have value? Or is it a solution to an issue that nobody really cares about?

Its an interesting idea, but ultimately i think it suffers from the KISS (Keep It Simple, Silly) of death, in that it would be an incredibly overengineered solution to a problem that doesnt really exist. Like, there would have to be, by design, so many points of potential failure in that system, that it would create a lot of room for malfunction in any vape that employs it. The alternative is just, you know, take your finger off the button.

 

[checkyourlibido]

Has anyone here ever thought about some kind of anti-combustion cutoff systems for convection vapes?

As it stands, there are temperature regulated convection vapes that regulate the heat output from the heater itself.

What I've been thinking about is a valve which is activated when a certain temperature is reached. This valve being opened would bypass the heater and flood the flower with cold air.

It could be done with electronic components, or with mechanical components like a bimetalic flat coil (like whats used in many bimetalic thermometers).

Any system like this would need to have very rapid reaction time. It would need to be tweaked a lot to be accurate and not suffer from the other variables at play (environmental temerature for instance).

If it is even technically possible, would it have value? Or is it a solution to an issue that nobody really cares about?

I like the idea. But I wonder what application it would work best with? Dynavap, especially when you are new, can combust. But there are no electronics on there.

Then there are others like the TP80 and the TM, which have electronics, but I don't know of people complaining about combusting with them. Then there's the Nomad/Toad that have the bare minimum of electronics, that's the perk of this unit, so I don't think that your idea would play here either.

But I do like the idea, just wondering where you think it's needed most?

 

[Farid]

This wouldn't have to be electronic. It could be accomplished with pretty simple mechanical components.

I've had way bigger issues combusting with convection vapes than conduction. With something like a Dynavap you learn quickly how to avoid combustion, since you heat then hit, and have the click to go by. Convection has more variables that can lead to combustion (mostly related to the flow velocity). It's also a lot more enticing to push the line, since you're heating while hitting it, and essentially have to choose when to "pull out" so to speak.

I don't have the P80, but I had the original Tubo and I combusted a lot. Same with the lotus, and logs.

Now whether there is a real demand is something else. These types of vaporizers fill a very niche audience that tends to be willing to deal with a learning curve. It also could be annoying to be getting a great hit and suddenly have it ruined by a flood of cool air, especially if you felt "I could have kept going"

 

[invertedisdead]

Has anyone here ever thought about some kind of anti-combustion cutoff systems for convection vapes?

I put one in a Brick style butane vape I had made 2 years ago, the goal was to design something that would be nearly impossible to combust.

It worked really well for the most part, I actually broke the part using a bigger dab torch trying to induce combustion.

 

[Zuhdj]

I've been diving down the rabbit hole of convection heating techniques and I think there is a ton of cool stuff to talk about. So, this is an attempt to dump my thoughts and start some discussion.

This will only cover 100% convection heating. Everything changes when you introduce active conduction heating. Hybrid devices are relevant, but for the sake of keeping things simple I think it's best to omit them in this thread.

______

The convection process, in theory, is simple. You've got hot air flowing through a chamber that is packed with loose leaf/flower particles.

In an ideal world the flow of hot air would be totally uniform over each individual leaf particle, resulting in a perfectly even extraction of the entire packed chamber.

In reality, convection heating can often result in uneven extraction.

When convection goes right, It's absolutely sublime...... so what can we do to increase our chances of success?!

______

For the sake of this thread I think our goal could be to figure out what we can do to reach the highest possible "total extraction". Meaning the percentage of active compounds that end up in the vapor stream, relative to the weight of the extracted material.

This extraction should happen evenly throughout the entire chamber load.

And finally, that this extraction happens without manual stirring. (Perhaps it will be proven that stirring IS needed for absolute best results, but I am really hoping that is not the case) I'd still like to hear thoughts on stirring, as I know some people actually enjoy stirring.... but y'all are crazy. In my opinion, stirring is a sign that uneven extraction is happening. I believe it's better to treat the cause of that unevenness in the first place.

So, what are the variables that affect total/even extraction?

One obvious one is grind size.

______

For this first post, I am going to focus on the variable of grind size.

Theoretically, the finer the grind size the more surface area you have available to extract, and so the more extraction you should be able to achieve with a fixed volume of hot air. From my experience this doesn't translate into the real world.

With a fine grind I typically get very quick extraction. Vapor density is high, seemingly because of the large surface area of the small particles. But the evenness of the extraction can be poor if you try to extract too quickly. Since I prefer faster extractions, I often get uneven extraction.

My working theory is that the fine particles restrict airflow, causing channels to open up where you get regions of high air flow, surrounded by regions of reduced airflow. This usually presents as "hot spotting", where one small area is over extracted.

______

I recently watched THIS video discussing an espresso extraction study. The main focus being grind size and how it relates to the extraction of coffee beans.

While this is all dealing with coffee beans and hot water, I felt like there were a lot of parallels between this process and the process of extracting loose leaf with hot air.

When you think about it, an espresso machine functions similarly to a convection vaporizer, just replace water with air. Instead of the pressure coming from a water pump or hand operated lever, the pressure comes from our lungs.

Since "Air behaves in a fluid manner, meaning particles naturally flow from areas of higher pressure to those where the pressure is lower" (wikipedia), we can likely still assume that there are useful bits of information to borrow from the espresso process, despite the fact that it's using water instead of air. Since espresso has been around for over 100 years, I feel like there are some insights that come with that maturity.

In short, the study found that total extraction (and more specifically the evenness of extraction) dropped with finer grind settings.

From the video,



As mentioned above, I seem to have the same experience with fine grinds. If pushed to extract quickly, uneven extraction is almost guaranteed.

Conversely, coarse grinds, in my experience, have the opposite effect, resulting in more even airflow over the entire herb load. Even when pushed to extract quickly, the airflow remains more even throughout the load.

The above video cites that water flows more evenly through a bed of coarser coffee grinds.... so it seems like my experiences are mirrored in the espresso world.

But... you can only go so coarse. At the extreme end, you can vaporize whole flower. I find that this can work fantastically... but it really depends on the density of your flower material. With dense flowers you've got a lot of nooks and crannies hidden away inside the flower that are not getting good exposure to the hot air flow. These whole flowers may require mid-session grinding and stirring to achieve a high total extraction.

From the video,



I think this pretty much sums up my thoughts on grind size and convection heating.

So, where is that crossover point?

I think it's somewhere in the medium - coarse grind size for my particle vaporizer and usage style. If I'm shooting for perfection, sifting the particles into uniform sizes will result in an incredibly even distribution of particles in the chamber. I use zero tamping, which is very important to preserve the air pockets around each particle.

Thoughts? What is your preferred grind size?

I also feel like it's worth mentioning what vaporizers you're using, so as to get an idea of how each device may affect these variables.

For future posts (and I invite anyone to start their own here) I think it'd be cool to discuss the other variables; chamber size/geometry, air speed, temperature, etc.. In fact, it might be useful to discuss exactly what variables exist in the first place, haha.

From the same creator of the above video, he has a series on "Understanding Espresso" where he outlines all the variables involved. He lists; Dose (weight of ground coffee), Ratio (coffee to water), Brew time, Grind size, Brew temperature, Pressure.

For our purposes, I'm not sure if we can use all those variables, or which ones make sense and how to translate them.. but I guess this is all a work in progress!

So, what variables do you find most important?

There's a lot of interesting parallels between convection vaping and espresso making as they both deal with flowing fluids and they both have the challenge of avoiding "channeling" or air/water taking a path of least resistance rather than an even path through the herb/coffee. In both cases you get an uneven extraction. Weird how that works

 

[Farid]

^Yes! In many ways getting good results with espresso is harder than with vaping because the target between underextracted and overextracted is so small. With vaping, if you underextract you just hit it again, but you can't do that with espresso.

We can also learn from the fact that with espresso the goal isn't go get the most extraction possible. As bud becomes cheaper and more available, I've stopped worrying about extracting everything, and focus instead on their desired results.

I've found that manual expresso machines are a lot like on demand unregulated vapes. They give the user control of all the variables, which increases the learning curve, but allows you to eventually dial in really good results.

 

[Razhumikin]

^Yes! In many ways getting good results with espresso is harder than with vaping because the target between underextracted and overextracted is so small. With vaping, if you underextract you just hit it again, but you can't do that with espresso.

We can also learn from the fact that with espresso the goal isn't go get the most extraction possible. As bud becomes cheaper and more available, I've stopped worrying about extracting everything, and focus instead on their desired results.

I've found that manual expresso machines are a lot like on demand unregulated vapes. They give the user control of all the variables, which increases the learning curve, but allows you to eventually dial in really good results.

Ive never wanted a manual espresso machine more than after you made me realize its the milaana of coffee. Aeropress, here I come!

 

[Dan Morrison]

@Farid , I like where your head's at with the heat sensor for unregulated convection. I've always liked unregulated because it feels like a puzzle to solve the formula for achieving consistent results. One way to solve it is with electronics of course, but for whatever reason I'm more attracted to the mechanical solutions.

I've always liked the espresso machine comparisons. It's neat to see where coffee tech is after many decades of refinement... it sort of hints at what the future holds for vaporizers.. maybe.