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What are the benefits of convection vs. conduction?

Discussion in 'Ask FC' started by MauiWowee, Jan 20, 2009.

  1. Nosferatu

    Nosferatu Well-Known Member

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    But if you leave the clouds bowl in the whole sesh would it be somewhat conduction or does the ELB keep a low enough temp? Not sure if Vapexhale had commented on this in the past?
  2. satyrday

    satyrday Well-Known Member

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    I think it's funny how people draw a hard line between the two. It's usually a mixture, especially with "conduction" vapes because in most cases as soon as you draw vapor from the bowl there is convection.
    hoptimum likes this.
  3. VapeHead.com

    VapeHead.com Well-Known Member Retailer

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    One of the early MAPS vaporizer studies compared a Volcano to a hot-plate vaporiser, but I'm having trouble finding a copy of the study.

    The rate of extraction, and what is delivered simultaneously vs. consecutively (and in what ratio each active is delivered), all comes down to the subjective preferences of the user, what effects they're looking for etc. So opinions are utterly useless here.

    Objective data could include any harmful combustion by-products like Carbon Monoxide, Particulates, Tar etc. Those are produced at certain temperatures, so really you can make an approximation of this by asking which vaporizer holds a stable and reliable temperature. The vaporizers that when set to 200 degrees celcius, but which actually operate with a wide range of say 190-210 at that setting, are going to produce more harmful by-products than one which only varies between 198-202.

    However, until studies are directly comparing Conduction vs. Convection vs. Radiation, i.e. not comparing products (most of which employ a combination of Conduction, Radiation and Convection just in differing ratios) but controlling all other variables so that we can directly compare the method of temperature transmission... probably the best that we can do is infer those results, based on a vaporizer's ability to hold a steady and reliable temperature.

    Conduction vaporizers expose some of the herb to hotter temperatures, compared to other parts of the herb, based on its distance form the conduction source. So the range of temperatures that the herb is exposed to is relatively high compared to Convection, all other things being equal. You can adjust the surface area of the conduction plate, the depth of the herb, the grind etc. so there are many, many variables here that would need to be properly controlled to answer the OP's question definitively. Probably too many. Your best option would be to design a vaporizer specifically to test each of these 3 temperature vectors - say to be able to set Convection to 60%, Conduction to 10%, Radiation to 28% - and to then cycle through all possible combinations with the same conditions (same herb, same ambient temperature, same warm-up time from ambient, etc. etc.). That's a huge project in itself. Maybe a Physics / Engineering vaporist can chime in on the theoretical transmission side of things - does it all just come down to a calculation, all other things being equal?

    My own observation is that a good (primarily) Convection vaporizer like the VHW or Volcano provides a consistent and reliable temperature all of the way through the herb - mostly regardless of its depth or height, or at least it has a higher tolerance for difference depths/heights. Conduction vaporizers are much more vulnerable to differences in herb depth/height, so the more herb you're using the higher the chance that it is being heated unevenly. Yet if the maximum temperature that any part of the herb is exposed to, remains below the point of those harmful combustion by-products, the difference between Convection and Conduction (as a general rule) is pretty much the rate and efficiency of extraction.

    Convection is going to extract more consistently, and more reliably (greater tolerance to grind/height/area variables), as a general rule. But most people will probably never notice or care, and the circumstances in which they're using their device (grind, load, ambient temperature and humidity, height above sea level, pre-heat and length of session etc.) are all relatively unique.

    Use whatever you prefer, but I get the best performance from the VHW which is primarily convection - but there is definitely Radiation and (after 2-3 hits) a noticeable amount of Conduction starting.

    As for evidence - I doubt we'll ever see any that could answer this definitively, but the sheer number of people who prefer Convection, and the anectodal evidence we have here on this forum - it certainly indicates that Convection is "better".
  4. Hippie Dickie

    Hippie Dickie The Herbal Cube Manufacturer

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    purely anecdotal ... i have a much better vape session when i arrange the herb to maximize the convection: very lightly loaded in the vial. i.e. no grinding, nothing that causes the herb to end up in a dense pile. this provides maximum airflow around each trichome.

    i have thought for the longest time that the ideal would be using concentrates. now i think this is wrong -- at least for my vape. i can use dry sift, but it must be scattered on bits of herb to be sure it is maximally exposed to the air flow.

    so now my thinking is that the cannabis plant knows what it is doing by having the trichomes arrayed along the plant material in a single layer, not all jumbled up like in a concentrate -- or even dry sift. and a convection vape is able to easily harvest each trichome.

    i still need to stir after the first half dozen hits ... this releases even denser vapor for the next 6 to 10 hits. my theory is the waxy shell of the trichomes fuse together and block exposure of the remaining thc to the air flow. the stir breaks this up.
  5. luchiano

    luchiano Well-Known Member

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    770
    You are correct in your thinking!. I thought the same thing about the plant knowing what it's doing when dealing with substances it makes.

    This fusing together of the trichomes is exactly why people need high heat when using most concentrates. If you want to get a good effect when using concentrates/dry sift, just use a SPECK in your vaporizer. I know it sounds crazy to use such a small amount, but if you have a flat screen or base, once you spread that little speck across, it will vape fast, and evenly, as long as you inhale slowly to keep the concentrate in place. When people use concentrates they tend to use the same amount that they would use with herb, but this isn't necessary.

    Also, it's good to raise the temperature in increments as this helps keep the trichome from melting too much. When you start at low temperatures, and then raise it in time, you release only what is on the surface of the concentrate that the hot air is touching, and this keeps the trichome from melting. It will bubble, but it won't melt all over the place. If you start out at a high temperature, the concentrate melt due to the lower temperature oils forcing their way out of the dense area, along with the medium, and high temperature oils.

    You will notice you will get more out your concentrate this way then using a big glob, and boiling at a high temperature from the start of your sessions.
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  6. SameOldTim

    SameOldTim Previously Known as 'ThermoCoreTim' Manufacturer

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    Im a fan of Convection, Not just in our products but in all my history of Vaporizing i've always preferred Forced air Convection desktop units.

    Like Vapehead was saying there is a study comparing the Volcano vs a hot plate style vaporizer, it has some very useful information about both styles. The problem though is that its mostly comparing two models as one is vastly superior technology. Ill try to dig the study up, from my records.


    Cheers,
    Tim
  7. max

    max This space available Staff Member

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    The 'hot plate' type vape is the original conduction design, and a truly inefficient one. It's also what I think of, any time conduction vaping is mentioned. As with cooking a hamburger patty, pancake, etc., if the herb on a conduction plate just sits there, undisturbed, it won't get thoroughly cooked throughout, without overcooking/burning the side that's down. You also suck a lot of hot air with not a lot of vapor per hit- a very unenjoyable vaping experience. No company has designed a vape using this vaporization method in many years. Even conduction designs like the Magic Flight and FlashVape use screens, allowing some good air flow.

    Some of the portables with enclosed heating chambers, that get described by some as conduction models, are really more convection than conduction, since they're designed to get hot air flow through the heating chamber, and thus through the herb load.
    VapeHead.com, RUDE BOY and hoptimum like this.
  8. m0sh

    m0sh Singer Song Writer Stoner

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    Since the solo cooks evenly, I guess it is this example...correct?
  9. OO

    OO Technical Skeptical

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    I came up with a very interesting theory when reading this.

    First though, I want to address the idea of uneven heating, I don't have much knowledge in the area of fluid dynamics, but I don't believe that most "convection dominant" vapes are very even in their heating, just far more-so than "conduction dominant" equivalents. I think you would agree with that.

    Now, on to the theory. With anecdotal evidence, I have found FAR greater expression of the X-factor with my primarily conduction dominant vape. I mean a far more potent experience is achieved, and I believe it comes down to evenness of heating, and more objectively, evenness of the spectrum of compounds vaporized. I think having higher proportions of higher boilers greatly potentiates the effects.

    This is compared to other vaporizers that are either very similar, but convection dominant, or quite different.

    The net result I have observed is as stated above, much more tame effects from vapes which heat more evenly/ deliver spectrum in much more narrow slices, versus vapes that have a large spectrum bias and much more profound experiences.

    I think conversation has finally started to nail down the cause of this difference. If someone wants to experience what I am talking about, and has the will to learn a difficult vape, try using a vapionic without the test tube, and apply the heat directly to the glass surrounding the material. Don't operate heavy machinery, you will be amazed at the distinct difference between typical vapes and this conduction dominant style.
  10. pakalolo

    pakalolo RoboMod v3.17 (ticking) Staff Member

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    There is a major problem of metrics presented here. While there are somewhat objective measures of pain that let us compare analgesic effects, there is nothing I'm aware of that yields a consistent objective measure of psychoactivity. I'm also of the opinion that the psychoactive effects vary depending on mood and state of mind, therefore exactly the same strains and temperatures can produce different effects in independent sessions. I think that if you believe in this difference strongly enough, then you will experience it. If you look for it, you will find it.
  11. OO

    OO Technical Skeptical

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    I agree with your assessment of error potential. I think if you try it you will find much truth to what I speak.
  12. luchiano

    luchiano Well-Known Member

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    770
    I get what your saying, but I think it has more to do with temperature, and how you load the bowl, then conduction giving a more powerful effect then convection. Remember if you using a lighter, that is a very hot temperature touching the glass, so it will release a lot of cannabinoids quickly, but you can do the same with an even better chance of getting the actives with very little burn, with a convection vape if you use a temperature over 410f, and load your bowl small, and loosely, so air can go through your herb efficiently.

    You also have to take into account, a lot of the thc turns into cbn when it sits in the "globe" as vapor is being released, and this may give the stone a lot of people like, as opposed to a strong "high". This was one of the things found when using conduction vaporizers with the fish bowl top. Here's a piece about it:

    http://www.ukcia.org/research/pipes.php

    The vaporizer results appeared more promising, but confusing. The two vaporizers were the only devices to outscore unfiltered joints in terms of raw cannabinoid/tar ratio. The electric hotplate vaporizer did best, with a performance ratio about 25% higher than the unfiltered joint. The hot air gun was just marginally superior, but might have done better had it not been for its water filtration component.
    However, the situation was complicated by the fact that the cannabinoids produced by the electric hotplate vaporizer were unusually high in CBN, leaving 30% less THC as a percentage of the total cannabinoids than with the other smoking devices. Since CBN is not psychoactive like THC, recreational users might be expected to consume more smoke to make up for the deficit. (The situation may be different for medical users, who could experience other, medicinal benefits from CBN). For this reason, it seemed advisable to recompute the performance efficiencies of the vaporizers in terms of THC, rather than all cannabinoids. When this was done, the electric hotplate vaporizer turned out to have a lower THC/tar ratio than the unfiltered joint, while the hot air gun was still marginally higher.
    The reason for the excess CBN from the hotplate vaporizer remains unexplained. Because CBN is produced from THC by chemical oxidation, it has been suggested that the device somehow exposed the sample to too much oxygen. However, there is no evidence that this was the case."
    "
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  13. pakalolo

    pakalolo RoboMod v3.17 (ticking) Staff Member

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    My current two devices of choice are the LB, which is mostly conduction, and the FV with the S2 spacer, which is pretty close to 100% convection. I haven't noticed much difference in effects between the two, however I haven't looked for them either. I'll try some experiments but as I said, I don't know how to measure the outcomes.
  14. Hippie Dickie

    Hippie Dickie The Herbal Cube Manufacturer

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    that vape is essentially what my vape is. Except -- instead of butane i have a nichrome coil that is digitally controlled to maintain a setpoint temperature.

    i agree that increasing the heat -- which invariably happens when trying to use a torch lighter to hit vape temperature -- will give an effect more like smoking, but without the combustion (usually), although i suspect it is quite easy to combust with that design. until you get the hang of it. once again, the old learning curve.

    edit: luchiano beat me to it!
    OO likes this.
  15. VapeHead.com

    VapeHead.com Well-Known Member Retailer

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    It tends to feel like this, to me: convection can heat up a mass uniformly, with good airflow penetration, in a rapid amount of time. Unfortunately this tends to result in this gradual decarboxylation, and produces more of an early THC high then CBD etc. later, with the most aromatic volatiles at the beginning all of the flavour. Teasing it out like this is what convection excels at, as the temperature is relatively stable with an evenly dense grind the only real variable is airflow speed.

    Conduction's more like an Oven, and the cool thing about ovens is that you can get them up to temp first - then put in your food to cook. That way you get more of an instantaneous vaporisation of the full spectrum of actives and flavours all at once. Dabs seem to be the logical extreme in this direction.

    The cool thing is you don't have to go one or the other, you simply have to find the right tool that is capable of both - while still giving you a large amount of choice in the variables. Soak-time, for example, you can choose to get your element up to temp quicker or even to go higher than the normal temperatures with that tool. Airflow's the yin to its yang. But a nice third variable that you don't get in a lot of products, and they should all have them imho, the ability to 'pulse' the heat either by hitting off and on again to the beat of a drum to fine-tune the temperature, or being able to lift the heat source away from the bowl during use.

    Yep totally agree with you.

    The Vaponic's great, I was actually quite impressed by it in many ways. All he needs to do is get glass blowers to make cigarette look-alikes, and someone will eventually make a gas powered oven "cigarette packet" to heat it up say on a table.

    But yeah - my vote has long been the VHW, I've still not found any other tool that has come close to my personal ideal, quite literally because it allows the most generous range of analogue and manual control and it can actually go quite a bit hotter if you use it with its Stand. The bowls start warming up gradually, so you get Radiation and eventually some nice Conduction, for free. The only real upgrade I can see from here is to coat the inside of the bowl with 24k gold as an IR reflector, and to also mount an IR thermometer on the Shorty to get a digital temperature readout on the side while you're using it and dialing in the other variables that you prefer.

    Now I dab, but thankfully they complement each other quite nicely! :)
    OO likes this.
  16. Hippie Dickie

    Hippie Dickie The Herbal Cube Manufacturer

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    that is what a pulse width modulator does to maintain a setpoint temperature. but from my experience it is anything but rhythmic -- it is a very dynamic environment in the middle of the herb and the algorithm must constantly readjust the pulse rate. and, of course, that action changes the dynamic. there is a fair amount of trial and error to get sufficiently correct gains to maintain the temperature. +/- 0.5°F is possible.
  17. luchiano

    luchiano Well-Known Member

    Messages:
    770
    A conduction won't give an instantaneous release of all substances because hot air won't be able to get around, and through the herb, unless you let the herb sit in the bowl for a while, but then you have to worry about oxidation of certain substances. We are inhaling these substances, which mean we need to turn them into a gas, which means we need air to carry them into our lungs. If the air doesn't get up to temperature correctly, then we won't get what we want to extract out of the herb. A convection WILL give a quick extraction if you load the bowl loosely, and have the correct temperature with the air. The only thing is you will degrade some substances, because in order to have a quick release of ALL the actives you will need a hot temperature, and some substances are very fragile, so they need a very low temperature to boil off, and a low temperature to start oxidizing. This is another reason why convection is best to me, you can control the temperature accurately, and extract what you want without degrading it with the use of excess heat.

    You also can get what you want very quickly, when you need to have it. When I watched the video of the guy using the vaponic, he needed to heat up the glass for a good while, and still only got a few hits. He might have not extracted everything, being that the herb was tight in the glass, and a lot of air didn't get into the middle of the herb. Plus, there is a good chance some of the thc oxidized into cbn being that it was in contact with such a high heat for so long. I would have been done when using a quality convection vaporizer with accurate temperature control, and know what temperature I'm using to make sure I'm at a proper temperature to get everything I want. You can't just go by the color of the herb, because that is just chlorophyll degradation that turns the herb brown, and has nothing to do with the herb being spent when vaporizing. You can get brown herb, just by letting herb sit in the sun for a while, when it is harvested.

    I think what needs to be done is more vaporizers need to find ways to make sure the AIRFLOW temperature is the temperature they dialed in, so people won't have so many different experiences form the same product. Some people inhale too hard so they don't release a lot of substances that they want so they don't like vaporizers. Some pack the bowl too much, so the airflow temperature isn't up to temperature quick enough, and they don't extract what they want. I think that's what needs to be the next thing done to vaporizers, precise AIRFLOW temperature as soon as you start inhaling, regardless of how hard you inhale. This way bong smokers, joints smokers, as well as medical users who just want a light inhale, all would be happy with vaporizers.
  18. stickstones

    stickstones Wasted Staff Member

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    8,070
    ^^^
    the herbalizer (not out yet) is making the claim to be able to do this.

    the Ion claimed to be accurate within 2C, but I doubt it was measuring the airflow temp.
    luchiano likes this.
  19. luchiano

    luchiano Well-Known Member

    Messages:
    770
    Do you have a link to the herbalizer?

    The Aromed does this, but you can't inhale hard, so bong smokers are not crazy about it.

    EDIT:
    I found it. It sounds REAL NICE. If I can change the heater when it goes bad, like the aromed, I think this will be my next best thing!.
  20. OO

    OO Technical Skeptical

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    Thank you very much for that, it is quite interesting, and possibly quite the explanation of the observed effects.

    I wouldn't try to measure, it's not like measurement is necessary, as the effects are profoundly different. The Conduction dominant technique I described is quite the powerhouse, but I use a slightly different piece of glass, with a much more narrow-long chamber, which should emphasize the conduction effect.

    The technique is quite sensitive in multiple ways, it is very easy to combust (long learning curve), and the form of the vape will radically change the effect. I use the Hammer as a DD, and literally millimeters of distance (between heating element and material) can completely change the observed effect. Otherwise all other factors should be nearly identical between the two vapes I've compared.

    Quite right, quite right.
    Yes, it is quite easy to combust, and no, I don't always use a torch lighter. I first used candle-flame bics with this technique, but found it easier to control with micro torches. Your design is quite similar, have you done the comparison between conduction effects and convection effects?
    When your vape is ready for the market, I would love to review it.


    I like where your head is at VH, as you seem to understand this thing I am talking about, especially with the comparison to dabs, which often yield similar results, and yet if concentrate is consumed in the "snake in the grass" fashion (thin line of concentrate covered in plant material), even in the vape I refer to, the effect is far less profound, and far more similar to the effects of conduction dominant vapes, even though the technique is still greatly conduction dominant. I can only explain this observation with the idea that the concentrate contributes far more lower boilers to the equation in proportion to the higher boilers, which makes perfect sense, as the snake should melt and cause the lower boilers to preferentially vaporize, where in the pure plant matter example, the amount of vaporizable material is so small, with such a high surface area, that a much wider amount of volatiles have to be vaporize in order to quench the heat source's transfer.

    That will take a few reads to make sense of. This discussion is quite enlightening.

    Luchi, with your latest post, there are many claims made, many of which I find fairly hard to believe until more evidence is obtained, but your theory does have some strengths to it, I just want some form of evidence to corroborate.
  21. 420GanjX

    420GanjX Active Member

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    91
    I'm digging the solo but I'm finding its much less efficient than my SSV due to it being mostly conduction based
    I feel like I'm loosing vapor while the Solo it not being hit from the constant heat.
    Also due to the conduction aspect the solo also seems to rip through a bowl much faster, and because of this it has been easy to slowly (without purpose) up my usage.
    I feel that since mostly switching to my Solo from the SSV I am using more weed.
  22. rayski

    rayski Well-Known Member

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    293
    The Solo is not a conduction based vaporizer; more like convection based with some conduction.
    You can remove the stem between hit's and reduce the limited conduction quite a bit. I think some conduction may be good because it can keep the bowl from taking heat from the passing air, and material that would be shielded from the air stream will be heated by conduction, maybe contributing to more even heating.
    What wand do you use with your SSV?
  23. 420GanjX

    420GanjX Active Member

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    91
    I have two seperate standard wands that vary slighly in size. I do enjoy the SSV but I love how easy the Solo can milk my bong
    for dry hits though I still prefer my SSV but due to the convinience of the Solo I find my self using it much more often
  24. rayski

    rayski Well-Known Member

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    293
    With the Solo, maybe you use more because you use it more.
  25. 420GanjX

    420GanjX Active Member

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    91
    Im just wondering why even at high temperatures, the SSV cant get a bowl as roasted, and couldnt even get through half a bowl in the time the Solo rips through one. The Solo just seems to produce bigger clouds, and stay at a higher constant heat (slight conduction in the bowl) so it in that aspect just seems less efficient to me. But dont get me wrong I love the Solo, and its my daily driver atm

    Edit: Sorry for jacking the thread, IME the Solo is an amazing vape and you would be very pleased with it. I havent tried the thermovape yet but have only heard good things so far on FC

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