tl;dr I like both, since they work together in different ways in different devices to satisfy individual tastes and needs. It's the balance between convection and conduction that will determine the extraction/flavour profile at any given device temperature setting. If a dry herb vaporiser tastes like crap, there might be something you can do to improve the balance.
Some physics:
- Hot air can't go through solid bits of weed.
- It has to flow around them.
- Convection can only carry heat to the outer surface of each weed fragment where it flows by.
- Heat can only get inside the fragment by conduction of that originally convected heat
- Same goes for "pure" radiation heating.
So any satisfactory "convection" device is probably relying on conduction to get heat inside each crumb of flower. Doesn't really make sense to me to think of conduction versus convection. A balance is what I am really after for a satisfactory extraction profile.
Personal observations:
- DDave glassware on an old Arizer EQ desktop and a Freight Train pid/coil/ball injector - both pretty much "pure convection" setups I use regularly. Best for me when the load is at least slightly packed together. It might just be me, but the stock FT glass adapter screen arrangement does not extract as efficiently as a lightly packed DDave stainless mesh cup.
- Same for my other rotation - a more "conduction and convection" steel stem on an underdog - weed needs to be lightly packed for best extraction for me.
- Arizer EQ stock glassware convection "cyclone" bowl. Weed crumbs bounce around in hot air, mostly heated at the surface, so even slower to extract than a similar setup in the stock Freight Train adapter. Of course, each crumb mass will conduct heat internally over time. But it seems to work much better when the weed is held together, even in the crappy (IMHO) stock EQ elbow pack.
So, what does
packing the weed in a convection vape have to do with conduction?
Theory:
A packed load has many more physical contact opportunities for the entire mass of plant to heat by conduction.
Lightly packed so decent convection heating can take place from a large volume of hot air passing through.
Depending on the weed particle size and degree of compression, increasing conduction between contact points allows the entire packed mass to heat more efficiently from any given amount of convected heat. Packing/grinding is where you can modulate the conduction heat transfer rate in the extraction profile for most convection devices. Limited range because too tight => lower air flow and lower rate of convected heat transfer.
(Side note: Interesting that for my other favourite drug, for any given machine, setting and roast, the grind and pack modulate the espresso extraction profile too.)
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