Faster Boil Times with a Polished Windscreen

Wow! How cool is that!! Thanks for posting!

Please describe your polishing technique?

Also would you please tell us your distance between screen and pot? EDIT, retracted, it's a cone.

Impressive boost in speed David!

This IS cool.

Well I'll be trying this the first chance I get. ie: When I get off work ;)

I always polish stuff up just cuz it looks cool anyway, who knew it was useful :)

For polish, I just use the metal polish found in the auto section for polishing mag wheels.

As a sidenote, I notice you have no upper holes. I found that with a 1/8" gap, I was able to use a hole pattern almost identical to that.

Delmar: I use a hand drill with a 6" cotton buffing wheel and a stick of fine green polishing compound, both obtained from my local hardware store.

Glenn: For this test I used a non-contact windscreen because I happened to have two identical unused ones in my shop. The gap is about 3/16". When I've built a couple of contact windscreens I plan to try the same test on them.

Interesting footnote: in a different series of tests, I tried a polished stove versus an unpolished stove with soda graphics. The shiny stove was a whole minute slower, presumably because it is reflecting heat that would otherwise be absorbed and boil the alcohol a little faster.

David,
Since I'm a scientist and care about things like statistical significance, I quickly ran your data through my stats program to see if you might have gotten your difference by chance…

Even though your sample size is quite limited for both groups (n=5), it looks like the difference in mean boil times between the polished and unpolished windscreen conditions is actually quite statistically significant (p<0.0001).

Congratulations, it looks like you actually have a real effect!

Pretty cool stuff. An 8% increase in efficiency is nothing to scoff at. I'm actually kind of surprised that you are getting such a big effect, but it is what it is. Very cool.

I don't have a drill buffing wheel, but my hand buffing didn't result in such a drastic improvement. Maybe just not quite shiny enough.

I don't think buffing Ti will be very effective. I've never used it, but every image I've seen of a used windscreen made of Ti, it has been blued quite heavily. So any shine would get tempered right out of it is what I'm thinking.

"An 8% increase in efficiency…"
Does this really show an increase in efficiency? Increased boil time is often accompanied by a decrease in efficiency. The OP says that 15ml of fuel was used, but it appears that is the amount of fuel loaded at the start, but we don't know how much was left when the boil started.
I once tested an aluminium cone (unpolished) against a titanium one with the same pot and stove set-up and found the aluminium cone faster but slightly less efficient. It may have been other factors, but I assumed that the reflected heat from the shinier aluminium sped up the boil, but also heated the stove more leading to decreased efficiency.
+1 on not thinking a titanium wind shield will hold a polish for long.

Neither Ti nor SS have really good reflectivity. Aluminum is about the best for most of us. Gold is somewhat better, but costs a lot more. As is mercury and or nickle (roughly the same as aluminum) but both are toxic to work with. A couple of the heavier metals are better than aluminum, but, again, are toxic. NASA did a study on this back in the 60's.

"Does this really show an increase in efficiency? Increased boil time is often accompanied by a decrease in efficiency. The OP says that 15ml of fuel was used, but it appears that is the amount of fuel loaded at the start, but we don't know how much was left when the boil started."

I agree William. I am really enjoying David's reports, but he is not reporting efficiency. He is reporing boil time. It would be nice if he measured total burn time too. Assuming a similar burn rate profile we could at least make a guess at the efficiency between the two processes. Did you happen to measure total burn time David?

Rats, should have recorded burn time too. Did not record burn time since assumption was that 15 ml of fuel represented a pretty good bench mark for efficiency. I will run another set of tests and will either record total burn times, adjust the amount of fuel needed to achieve a boil, or snuff the stove as soon as boil is achieved and see how much is fuel is left, in order to compare efficiency. Perhaps all three, to see if results for the different test methods are comparable.

Do you think Simichrome would work on Ti?

http://www.amazon.com/Nunn-Finer-Simichrome-Metal-Polish/dp/B00BSJYQ9S

KJ

> Perhaps all three…

Wait, I'm confused. Seems to me we are interested in time-to-boil (power/speed), and time-to-extinguish per fixed amount of fuel (efficiency/economy). Isn't that all that's needed?

If I get into this testing, I pretty much have to use the "time-to-extinguish per fixed amount of fuel" measure because I use a StarLyte, which is NOT conducive to pouring off unused fuel.

Myself I'm much more interested in efficiency than speed, as long as speed is reasonable. You'd understand if you saw the car I drive…!

PS David: I've been on the receiving end of "you should collect this data, too" research comments plenty of times. Don't mean to be a pain, do what you can, ignore the rest.

You'll find asking nitpickers like me for donations to fund your research really helps.

"PS David: I've been on the receiving end of "you should collect this data, too" research comments plenty of times. Don't mean to be a pain, do what you can, ignore the rest.

You'll find asking nitpickers like me for donations to fund your research really helps."

As a professional nitpicker, I couldn't agree more!

"If I get into this testing, I pretty much have to use the "time-to-extinguish per fixed amount of fuel" measure because I use a StarLyte, which is NOT conducive to pouring off unused fuel."
Delmar, weigh the Starlyte + fuel at the start. Extinguish when the water boils and weigh the Starlyte + remaining fuel.

As long as we're proposing experiments for others : )

Pour (and weigh) enough fuel to almost boil. Measure temperature before and after.

Multiply weight of fuel * nominal temp difference / actual temp difference

Maybe nominal temp difference would be 80 C or 90 C – in actual use water starts out above 0 C, and I normally heat water to maybe 90 C and let it sit for a minute with lid on to kill any bugs.

If your water boils before fuel runs out, re-do experiment with less fuel.

Ran some boil tests trying ascertain efficiency.

Parameters:
500.0 g/ml 70* F water
14.20 g (16.00 ml) fuel
Air, fuel and surface = 60* F
Relative humidity = 70%
Barometric pressure = 29.83 inHg
No wind
Polished Al windscreen & base sheet
4" diameter Thermofelt pad under base sheet
2" diameter Thermofelt pad on top of base
2" diameter Thermofelt pad on same size Al pot lid
(Thermofelt pads add 9.33 g = 11.83 ml of fuel)

Results:

5:01 min boil, 5:16 burn time
5:06 min boil, 5:22 burn time
5:04 min boil, 5:20 burn time
5:08 min boil, 5:12 burn time
5:03 min boil, 5:18 burn time

Average boil time = 5:04.4 min (max deviation = 8 sec = 2.6%)
Average burn time = 5:18.4 min (max deviation = 12 sec = 3.8%)

It looks like a bit less than 16 ml of fuel would still achieve a boil, but the difference would be almost impossible to measure in the field with a little dosing cup. And I'm kind of burned out on tests for awhile, so to speak.

Here is my estimate at efficiency of your system:

Average time to boil 5:04
St Dev 0.002

Average burn time 5:17
St Dev 0.003

Fuel (g) 14.2
Fuel to boil (g) 13.61
Lower Heating Value (kJ/g) 25
Energy released (kJ) 340.2

initial Temp (°C) 21
Final Temp (°C) 100
Mass H2O (g) 500
Specific Heat H20 (kJ/g-C) 0.0042
Energy absorbed (kJ) 165.9

Efficiency 48.8%

Ben, thanks for the quick analysis.

Very interesting. The "mushroom cap" pot lids are slightly more efficient. That always seems to be the case, that more speed = less efficiency. So it just depends on which a person prefers.

Awright. Which of you guys is going to get me out of the dark ages, and teach me how to do this percentage-based efficiency calculation? Is there an existing Excel sheet for it?