Companion forum thread to:

Heat Exchanger Stove Shootout: Part 1
Introduction and Test Method

Would it be too much to ask for you to include temps. in fahrenheit ? Granted we are the minority in the world using that system. But the majority of BPL members must be in the US.. What do you think? Good article though.

20c=68degrees

Edited by kthompson on 08/04/2009 16:53:29 MDT.

Looking forward to part 4 part on the pot diameter.

I wish I could get reliable R^2 values like that in my ecology work...

One thing im interested in as well as well as the jetboil/etapower etc. is attachable systems like the MSR one, which can easily be homemade. Steve House used a similar set up made of aluminium on an fast climb of K7, it looked rather like the NOLS oven thing they use to save a little fuel as well.

It is great to see photos of experimental setups, wood jigs supporting test fixtures. Makes me want to run out and get to work too. Thanks for all the work and actual data!!

Roger,

Could you test the 1.5 L. JetBoil "Flux Ring" pot v.s. the 1.5 L.Primus Eta heat exchanger pot v.s. a "plain aluminum" 1.5 L. pot?

I think this would settle a lot of questions about the efficacy of these new pot-bottom heat exchangers in an unbiased manner.

Eric

"Would it be too much to ask for you to include temps. in fahrenheit?"

How about getting truly scientific and use the only real unit for temperature, Kelvin?

Eins

>How about getting truly scientific and use the only real unit for temperature, Kelvin?

Celsius temperature is an SI derived units

http://physics.nist.gov/cuu/Units/units.html

Note on degree Celsius. The derived unit in Table 3 with the special name degree Celsius and special symbol °C deserves comment. Because of the way temperature scales used to be defined, it remains common practice to express a thermodynamic temperature, symbol T, in terms of its difference from the reference temperature T0 = 273.15 K, the ice point. This temperature difference is called a Celsius temperature, symbol t, and is defined by the quantity equation

t= T- T0.

The unit of Celsius temperature is the degree Celsius, symbol °C. The numerical value of a Celsius temperature t expressed in degrees Celsius is given by

t/°C = T/K - 273.15.

It follows from the definition of t that the degree Celsius is equal in magnitude to the kelvin, which in turn implies that the numerical value of a given temperature difference or temperature interval whose value is expressed in the unit degree Celsius (°C) is equal to the numerical value of the same difference or interval when its value is expressed in the unit kelvin (K). Thus, temperature differences or temperature intervals may be expressed in either the degree Celsius or the kelvin using the same numerical value. For example, the Celsius temperature difference t and the thermodynamic temperature difference T between the melting point of gallium and the triple point of water may be written as t = 29.7546 °C = T = 29.7546 K.

Tony

I'd be interested in seeing if overall pot volume affects efficiency or boil times as well. In other words, if you filled a 550ml pot w/500ml of water and a 900ml pot w/500ml of water, would you get different time/efficiency results? I'd assume that the time would be the same if the pot diameter were the same? Perhaps we'll see...

Hi Brad,

>I'd be interested in seeing if overall pot volume affects efficiency or boil times as well. In other words, if you filled a 550ml pot w/500ml of water and a 900ml pot w/500ml of water, would you get different time/efficiency results? I'd assume that the time would be the same if the pot diameter were the same? Perhaps we'll see...

I did some work on pot diameter and flux ring pots last year, results on this thread.

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=11467&skip_to_post=87803#87803

Tony

Is having the windshield surrounding the pot 2.5 cm from it, half way up considered the best way to use a windshield? I would be interested to know for my own stove use, thanks

This is what I love about backpacking: the utter simplicity and the way it affords a chance to escape from the complexities of daily life in the modern world. =:o)

Hi, Tony-
Thanks for your response. Good info on that thread. The question I have beyond that, though, is if two pots of roughly equivalent diameter, but of differing volumes, would have different boil times/efficiency. The BPL 900 vs 1100 pots, for example... both with, say, 500 ml of water... and perhaps a 600ml pot of the same diameter? I don't know why I care, but I am interested...

Hi Brad,

Interesting question, without doing specific testing I would say technically yes as the larger pot has larger surface area that can loose/gain heat but it would be a very small difference.

Tony

As an electrical engineer, I'm quite impressed with the electronics that went into the test setup. A few questions though:

It looks like there's a AC-DC conversion at the top of the test bed, any particular reason for doing this yourself or do you not like 'wall warts'?

Did you measure the resistance of your resistors across which I'm guessing the measurement was taken?

Did you use op amps of the cmos or instrumentation variety if high input impedance was needed given the high output impedance of the AD590 (small potatoes, I know)?

-jim

Hi Guys

First of all, I should explain that I have been away for 6 weeks, walking in the Swiss Alps with my wife. We got back late last night - or at least my body did. My brain may still be at 30,000' between London and Hong Kong ...

We had a wonderful time with almost no rain. A lot of sunscreen was used. I took my little experimental stove (remote inverted canister) which has been seen in a previous posting and my 1.5L MSR Ti pot. The stove weighs 105 g complete and works with ANY gas canister. Doubtless more details will come out later on. Promise. :-)

Now, to Eric's question about pots: see Part 2!

Cheers
Roger Caffin

Hi Brad

> if you filled a 550ml pot w/500ml of water and a 900ml pot w/500ml of water, would
> you get different time/efficiency results?

Good question.
My guess is that performance would be identical.
But part 4 should address that.

Cheers

Hi Michael

> windshield surrounding the pot 2.5 cm from it, half way up considered the best way to use a windshield?

Now you are getting really detailed. :-)
I suspect but have no data to confirm that an airgap above 2.5 cm would not be as good. What is optimum? don't know, but a good question.

Cheers

Hi James

> AC-DC conversion, wall-warts
It was really a case of reaching into the cupboard and grabbing a good stable +/- 15 V PS unit with spare capacity. Wall warts are not that stable, so I often bypass them for analog stuff. The unit used was 'ex stock'.

> Did you measure the resistance of your resistors across which I'm guessing the measurement was taken?
The temperature sensors are semiconductor devices.
The load cell is a new commercial unit I bought myself. Internally it is a conventional Wheatstone bridge of platinum wires.

> op amps of the cmos or instrumentation variety
The op-amps were mostly National J-FET units or AD units, with attention to the input drift characteristics. Again it was a case of 'looking in the cupboard' to see what was suitable in stock.

What I DID find was that I needed to allow about 10-15 minutes for thermal stabilisation after power-up. Only when playing with very high impedances and CMOS amps can you avoid the initial thermal drift in my experience.

Cheers