[Stoves] Question regarding calculations

[Dr.-Ing. Dieter Seifert]

Dear Crispin,

We should mention that there is an extensive literature about how to 
keep the pot content hot, known as “fireless cooking” or “cooking with 
retained heat” e.g. 
http://solarcooking.wikia.com/wiki/Heat-retention_cooking.

Kind regards

Dieter



Am 05.10.2015 um 05:10 schrieb Frank Shields:
> 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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