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What are the benefits of convection vs. conduction?

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

  1. vaporonly

    vaporonly Well-Known Member

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    probably because on the ssv 1) the wand/stem doesn't sit on top of heat (heat rises) 2) the traditional ssv wand/stem doesn't 'stay' next to heating element like on the solo.

    if you only put the solo stem on the heating element right before hitting it and remove it right away afterward you can minimize conduction.
     
  2. Stu

    Stu Maconheiro Staff Member

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    IMO, what causes the Solo to continually "cook" the load has more to do with radiation than conduction. Conduction seems to get a lot of credit for the work of its cousin radiation. Both are definitely involved in almost all vaporizers and the Solo is no different.

    Try this thought experiment (do not actually do this):

    You place a fresh nug of herb suspended on a string in your kitchen oven. Yeah, I know string might burn away, but it's just a thought experiment so bear with me.

    Crank the oven up to 400F, shut the door and let the suspended-in-mid-air nugget cook for 15 minutes.

    What do you expect to see when you take the nugget out? ABV of course. An ABV nug.

    Did it get vaped by convection? No hot air was blowing through it as this oven has no interior fan at all.

    Did it get vaped by conduction? It did not come into contact with any part of the oven as it was suspended by a magic piece of string.

    It got vaped by radiation. Just like most of the weed in the Solo bowl is getting vaped by radiation IMO. The air is not pre-heated per se (air is heated some by going down the sides of the oven wall and past the floor - but very little IMO) so there is not really a lot of convection or conduction happening.

    /radiation rant

    Edit: I have since run some experiments (about a year after making this post) measuring the temperature in the load during a draw with the Solo. I stand corrected to the extent my statement below is not entirely true:

    I found that the air is pre-heated and increases the temperature at the bowl by about 50°F during a hit. Now that means that the "idle" temperature of the bowl is still hot enough to produce vapor by radiation and it's a necessary part of the vaporization process of the Solo. Without standing on the shoulders of the pre-heated bowl (caused largely by radiation), the amount of convection occurring during a draw would not be significant by itself to get the load up to vaporization temps.


    :peace:
     
    Last edited: Aug 31, 2014
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  3. Tweek

    Tweek Well-Known Member

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    Stu's been watching alot of PBS these days.
     
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  4. VaPooRize

    VaPooRize New Member

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    I am trying to wrap my head around this concept. can someone classify these portable vaporizers as conduction or convection, and explain where the heating element is and how it works for the: Arizer Solo, Pax, GrassHopper, and magic flight? Also, a short summary of you personal preference for conduction or convection and why?
     
  5. SpruceGruve

    SpruceGruve Bag of sand in hand,Eyeing up the gold statue

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    Conduction is when the heat source actually touches the herbs.
    Convection is when hot air passes through the herbs without and heat source touching it.

    MFLB is conduction.
    Grasshopper is advertised as convection(I don't think anyone has tried it yet to confirm)
    Pax is "primarily" conduction
    Solo is "primarily" convection
     
  6. CentiZen

    CentiZen Evil Genius in Training Accessory Maker

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    http://www.portablevaporizers.net/w...3/05/Conduction-vs-Convection-Infographic.jpg

    I think that this infographic provides the best introduction to these two different types of heating methods.

    The Arizer Solo is about a 50/50 split between convection and conduction heating, and is heated via wires wrapped around the metal or ceramic bowl at the top. Air is routed through and around it before being fed into the heating chamber, which is where the convection effect comes from

    The magic flight and pax are both totally conduction based units. The MFLB heats up a mesh screen while the pax heats up a steel heating wall. In both cases the herb is heated by close proximity to a heated surface and there is minimal convection effect.

    The grasshopper claims to be totally convection, which is something that would require them to break the laws of physics to achieve the way they describe it.
     
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  7. grokit

    grokit power cosmic

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    Nasa engineers are constantly re-defining the laws of physics!
    :popcorn:
     
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  8. placetime

    placetime Well-Known Member

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  9. pakalolo

    pakalolo RoboMod v3.17 (ticking) Staff Member

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  10. Jor-el

    Jor-el New Member

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    I favour convection because if it works correctly you're only vapourising when you're drawing-in air (ignoring fan-based units for now), potentially allowing for better titration and (probably) using less, which for me is desirable both for economy's sake and because I don't like being noticeably more stoned than my optimal level.
     
  11. KeroZen

    KeroZen Chronic vapaholic

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    @CentiZen : I know this infographic isn't yours, but I tend to disagree with what it says. From my experience with the Firewood and also by reading the LSV, the Firefly and the Elevape threads, it appears all these "mostly convection" vapes require a lot of stirring otherwise you can get a "burnt hole in the middle" of some kind and get tiny particles in the load to combust over time (ie black speckles in the ABV)

    Whereas with "mostly conduction" vapes, like Pax, Indica, Ascent, FlowerMate, you don't have to stir and the load is uniformly cooked. Also excepted with the Pax, all the vapes I listed can't combust, how hard you might try.

    So:
    - higher risk of combustion for conduction > not what I see
    - require stirring with conduction > not what I see
    - harder for a novice with conduction > hell no! all the convection vapes I listed have a learning curve and a "technic" to develop, whereas all the conduction ones I listed are super user friendly (the FlowerMate being the most)

    - more even heating of the load with convection > not what I see
    - lower risk of combustion with convection > not what I see

    - more accurate temp control with convection > I don't know from where they got that, in one case the bowl temp is monitored, in the other it's the air or heating element, but in all cases it's never the load temperature that is measured... I'd say none is better, but the debate is open...
     
  12. pakalolo

    pakalolo RoboMod v3.17 (ticking) Staff Member

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    Most vapourizers benefit from stirring. Some require it, some don't. You can't sort them out using the heating method. Your convection examples simply suffer from a design that doesn't spread the hot airflow well enough. Perhaps they concentrate it too much when hit hard.

    I'm not aware that there is much combustion risk with convection designs. I'm not saying it doesn't happen, but black speckles in the ABV isn't good evidence of combustion at all. Thorough vapourization can produce black ABV that clearly isn't ash.

    It's true that you don't have to stir many of today's conduction designs. It's also true that all of them benefit from stirring. You've named several that employ constant heating, so of course if you heat the load long enough it will eventually all turn a uniform colour. That doesn't mean it vapourized evenly. Under conduction, the load in contact with the heating surface must vapourize before the middle does. That's simple physics. Cannabis is a poor conductor, so heat only reaches the interior of the load after the edges have long been vapourized. It's easy to prove this: simply look at the load from any of your examples after the first hit or two.

    Combustion risk isn't a matter of convection vs. conduction, it's a matter of temperature control. Good control for conduction vapourizers is a fairly recent innovation. If that chart is more than a year or two old (which I think it is) then in general, the point about more accurate control with convection was true when it was prepared. The highest combustion risk comes with designs that do not feature temperature control. The FlashVAPE is a heat-on-demand device that, when used with batteries, requires careful attention to avoid combustion. I mention this example because the FV can be either convection or conduction, depending on whether you use the S2 spacer. Regardless of which mode you use, the FV is so powerful that you can easily reach combustion. I've gotten combustion using the FV upside down, which means the load is nearly 2 cm away from the heater.
     
  13. JCat

    JCat Well-Known Member

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    Although sorta' true ... the NASA engineers aren't actually re-defining any laws of physics that apply at the standard molecular level (at this point the re-definition of the laws of physics is more limited to the sub-atomic level and the vacuum of space and beyond) The standard laws of physics hold true for pretty much all matter until it gets unimaginably large or unimaginably small :) ... I'm pretty sure the 3 forms of heating (conductive, convective, and radiant) all conform to the standard laws of physics and don't venture into the sub-atomic :)
     
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  14. grokit

    grokit power cosmic

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    ^ I knew I would get called on that someday ;)
     
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  15. KeroZen

    KeroZen Chronic vapaholic

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    @pakalolo : I stand corrected! You have a lot of good points here.

    It's true that they all benefit from stirring, but to keep the same examples I used (and I'm selecting two extremes here I know) I can get a couple extra (and rather wispy) hits from my FlowerMate if I stir the bowl after it appears to be fully spent, but in the Elevape (and IIRC also the LSV) thread, they say they need to stir every couple of hits. So that's quite a difference!

    As for the black speckles, when I get them in my Firewood it's usually uber tiny plant particles that were somehow ground too small. They don't really ignite per se, but I believe there is partial combustion happening or something close to that, and they are always associated to that well known (and strong) popcorn taste, and can compromise an otherwise overall green-looking bowl.
     
  16. RUDE BOY

    RUDE BOY Space is the Place

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    I've been havin' a good time the last few days rotating between two very different Vaporizers.

    First off with the Daisy, which is as far as i can see 100% convection. It gives me a a giant quick big long- lasting head and Body buzz with pretty big clouds (huge giant clouds if i wish)strain specific taste the whole way through along with perfectly evenly golden browned AVB as long as I stir every couple hits.

    Next off I'm using the Vapman basic which I'd say is mostly conduction with a bit of radiant heating (the bowl is so small i can't stir with out losing most of the load so no stirring). Just got it days ago so for now i'm still not getting lots of visible vapor and on occasion still blackening a little of the load, the taste for the first few his is amazing then it takes on that conduction roasting taste for the last few. I don't really notice much of a buzz until 10-15 after I've finished a load and Then I find I'm well baked on such a small load, maybe 1/4 of what I'm loading in Daisy. I've remembered what a member here( @pakalolo ?) used to say often; went something like;

    " take three(two) hits then wait 15 minutes, see where your at".

    with the Vapman my avb is always very dark brown (near black) the buzz off one load is good but off of three or four it gets me as high with the same effects as one Bowl in the Daisy. But the same amount of bud in the daisy bowl only takes 3-5 minutes (although in reality you could do it in 1-2 minutes or make it last hours or days actually), using the same amount in The Vapman It takes me an hour or two mainly because I pause 15-20 minutes between sessions.

    the main "benefit" I see from convection is the taste, although i for one also enjoy the change in the taste profile of my herbs through a conduction vape session.

    I see No real Difference in effective extraction of goodies if both a convection and conduction vape is well designed.

    :leaf:
     
    Last edited: Sep 5, 2014

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