[Stoves] Question regarding calculations

Dr.-Ing. Dieter Seifert doseifert at googlemail.com
Mon Oct 5 10:49:05 MDT 2015


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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