multiple pot ridges and black paint to better absorb the he

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SSGHawk
Posts: 82
Joined: Mon Apr 14, 2014 11:05 am

multiple pot ridges and black paint to better absorb the he

Postby SSGHawk » Wed Apr 16, 2014 10:02 pm

When I last was i the testing mode I was thinking AND A FULL HEIGHT WINDSCREEN but was wondering how much heat the windscreen gives up to the wind or the ambient air. I was considering putting a thin layer of firebox insulation or even Carbon fiber to add as an insulator.

I understand that I am not heading toward backpacking lite but I want to see if the principles work and then will worry about the weight.

Experience, experiments and thoughts ladies and gents?

Regards to all
paul

sudden
Posts: 1058
Joined: Tue Apr 06, 2010 5:33 pm

Re: multiple pot ridges and black paint to better absorb the

Postby sudden » Wed Apr 16, 2014 10:34 pm

Most of the answers will probably come from zelph. The only thing I ever found that interested me was the idea of dimples in the windscreen. The idea being turbulent air next to the pot allowing more heat transfer. Beyond that you get into rocket stove territory and a lot more weight to gain efficiency.
"People are not persuaded by what we say, but rather by what they understand."

SSGHawk
Posts: 82
Joined: Mon Apr 14, 2014 11:05 am

Re: multiple pot ridges and black paint to better absorb the

Postby SSGHawk » Thu Apr 17, 2014 7:44 am

Dimples. I had not thought of that. That's an easy fix.
Thanks,Sudden.
Paul

SSGHawk
Posts: 82
Joined: Mon Apr 14, 2014 11:05 am

Re: multiple pot ridges and black paint to better absorb the

Postby SSGHawk » Thu Apr 17, 2014 6:02 pm

Mr. Heater,
Thanks.
I thought that a laminar flow would not transmit as must neat as a turbulent flow. I guess I thought that once the laminate flow had transmitted its heat that it would not be replaced by hotter exhaust unless there is turbulence.

Thanks again.

sudden
Posts: 1058
Joined: Tue Apr 06, 2010 5:33 pm

Re: multiple pot ridges and black paint to better absorb the

Postby sudden » Fri Apr 18, 2014 9:12 am

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 :DP:
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 :ugeek:


Chapter 6:
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
H
=200-15000. Analysis of the flow structure showed
that
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
H
=100 to 4,000, covering the laminar to fully turbul
ent flow regime.
"People are not persuaded by what we say, but rather by what they understand."

sudden
Posts: 1058
Joined: Tue Apr 06, 2010 5:33 pm

Re: multiple pot ridges and black paint to better absorb the

Postby sudden » Fri Apr 18, 2014 9:23 am

You might find this interesting too. This guy built his own wind tunnel. He wanted to test something called a KF airfoil.
What's interesting for us is the way KF causes a turbulent airflow with just a simple stepped wing.
Turn that into a stoves outside wall and all you have to do is make the bottom of your stove fat, with a quick step down to a smaller diameter.
In theory it would act like this KF wing. I have no idea if it would transfer more or less heat but it would be a lot easier to test than dimples.
"People are not persuaded by what we say, but rather by what they understand."

SSGHawk
Posts: 82
Joined: Mon Apr 14, 2014 11:05 am

Re: multiple pot ridges and black paint to better absorb the

Postby SSGHawk » Wed May 07, 2014 10:51 pm

When you say dimples does it have to be exactly dimples or can it be Dan's old style Starlyte windscreen that was vertically ridged every 1'8" of so?
Regards and thanks
Paul


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