This is way too technical (see below quote) but studies have shown that dimpled surfaces work.
All of these stove building trials we diy have to follow the same rules these guys did for turbines.
Things like Reynolds numbers (low reynolds numbers in our case) are always mentioned in the RC airplane world.
Corialis effects are studied too.
I started out being interested in zelphs stove designs and following everyone's discussions about improvements. I ended up getting interested in RC airplanes
It's the same thing. Flow of gas over a surface and it's connection to the surface. With the RC planes you worry about wing stall so the shape and angle of attack become important. You can't fly if the flow over the wing releases so you play around with different wing shapes but this gets complicated by low or high speeds. It just goes on and on like diy stove tech. The idea for both is to keep the flow of gas connected to the surface for as long as possible. Now i have another new hobby
Summary and Conclusions:
High fidelity time dependent calculations were util
ized to investigate different
heat augmentation surfaces with modified dimples/pr
otrusions for compact heat
exchangers (Part I) and rotating turbine cooling ap
plications (Part II). Part I consisted of
three phases: Phase I considered dimpled continuou
s surfaces, Phase II considered
dimpled plate fins, and Phase III investigated a no
vel fin shape, the split-dimple fin.
Phase I considered a channel with aligned dimples a
nd protrusions for heat
augmentation in compact heat exchangers. Two geome
try cases were considered to study
the channel height effect. Calculations of the dim
pled channel covered the laminar to
fully turbulent flow regime, Re
=200-15000. Analysis of the flow structure showed
heat enhancement near the dimple surface is driven
by separated shear layer reattachment
inside the dimple cavity and vortex shedding out of
the dimple cavity. Whereas flow
impingement, acceleration, and wake reattachment on
the protrusion side were the main
heat enhancement mechanism. While the smaller fin
pitch geometry was found to have
better performance in low Reynolds number applicati
ons, heat transfer and pressure drop
were almost insensitive to fin pitch for the fully
turbulent flow regime.
Phase II investigated the application of dimples as
surface roughness on plain fin
surfaces. The dimple imprint diameter and perforat
ion effect on flow structure and heat
transfer from the surface were tested using three g
eometries. While the dimple imprint
diameter did not produce any effect on the flow str
ucture and heat transfer from the fin,
the dimple perforation had a significant effect on
the flow structure and heat transfer
levels of the fin. Perforated dimple resulted in
flow redirection between the top and
bottom sides of the fin, reduced flow recirculation
inside the dimple cavity, and further
increased boundary layer regeneration from the fin
surface, which resulted in higher heat
transfer from the fin. Although the heat transfer
levels of the perforated fin are
comparable to those of the plain fin, it provided a
10% increase in the heat transfer area,
which adds to its attractiveness as a viable option
of heat enhancement.
Phase III investigated a novel fin design, the spli
t-dimple fin, over a wide range of
Reynolds number, Re
=100 to 4,000, covering the laminar to fully turbul
ent flow regime.