[Stoves] Question regarding calculations

Frank Shields franke at cruzio.com
Sun Oct 4 21:10:34 MDT 2015


Thanks Crispin. I needed to be reminded of that - again. : )

Sent from my iPhone

> On Oct 4, 2015, at 7:59 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:
> 
> Dear Frank
> 
> Thanks for clarifying that. 
> 
> It doesn't take any energy to keep water hot. It is only necessary to overcome the losses from the pot by radiation, convection and conduction, the last being negligible. 
> 
> Prof Annegarn showed that ‎the heat lost from the pot is dominated by the colour and surface texture. If you overcome that it remains hot. 
> 
> It makes no difference what quantity of water is in the pot. This was shown with a high degree of precision - four 9's - by Yixiang Zhang at CAU. 
> 
> Regards 
> Crispin
> 
> Dear Stovers
> Re-read my question and now see the problem. I ment to say ' keep water at 80c' and does that require the same energy at sea level as it does at 1500 meters? Sorry. Not 'boiling'!
> 
> Maintain a boil at 1500 meters takes less energy than boil at sea level I think.
> 
> And ask one question leads to ten more. 
> 
> Thanks
> Frank
> 
> 
> 
> Sent from my iPhone
> 
> > On Oct 4, 2015, at 2:18 PM, ajheggie at gmail.com wrote:
> > 
> > [Default] On Tue, 29 Sep 2015 20:17:29 -0700,Frank Shields
> > <franke at cruzio.com> wrote:
> > 
> >> Greetings Stovers, 
> >> 
> >> Wanting to know if it takes less energy to keep water boiling at 80 deg. C at 1500 meters than at sea level?
> > 
> > Frank I've waited before ploughing in because I couldn't understand
> > the reasoning behind your question.
> > 
> > The thing is at 1500 metres above sea level the pressure is still 96%
> > of pressure at sea level, so to boil water you have to raise the
> > temperature of water until it's vapour pressure equals the ambient air
> > pressure, and that is at 98.6C
> >> 
> >> Also; It take 4.186 j/g/deg.C to raise water from 20c to 80c at sea level. But is it the same at 1500 meters? or is it less than 4.186?
> > 
> >> From Prof Lloyd's post the specific heat of water varies with
> > temperature and is probably thus not variable with pressure.
> > 
> > So my view would be to keep water at 80C at 1500 metres asl in a
> > saucepan with tight fitting lid, so no vapour escapes would be the
> > same power as at the same ambient temperature as at sea level.
> > 
> > AJH
> > 
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