[Stoves] Question regarding calculations

Frank Shields franke at cruzio.com
Thu Oct 1 11:55:19 MDT 2015


Greetings Prof. Lloyd,


Wondering if you would explain the following interesting graph so that I can understand it? 

I’m just going to use the 4.186 good to three decimals as if I know what I am doing but how did that come from the following graph? and what is going on before 40c that increases the heat capacity of water? and increasing after 40c? What is so great about 40c?

Is the average increase of 4.186 /g water per deg. C based on going from 20c > 95c?

To increase water from 85c (4.20) to 95c (4.21) a more accurate value is the average of 4.205 j/g/deg.c? 



To increase water from 15c (4.19) to 30c (4.18) do you suck heat out at a rate of 4.185 per gram per deg. c? Ha! 

What is happening at 40c to make water have the lowest specific heat capacity?

No need to answer if it is real complicated and beyond my understanding because I am happy using the value 4.186.

Thanks

Frank











> On Sep 29, 2015, at 11:58 PM, Philip Lloyd <plloyd at mweb.co.za> wrote:
> 
> The thermal capacity of water is not a constant. At 1 atmosphere pressure a good correlation is 
> <image002.jpg>
> https://syeilendrapramuditya.wordpress.com/2011/08/20/water-thermodynamic-properties/ <https://syeilendrapramuditya.wordpress.com/2011/08/20/water-thermodynamic-properties/>
> which, of course, you have to integrate over the delta T to get the effective value. 
> <image001.gif>
> The thermal capacity is less sensitive to pressure over the range you are concerned about – the change to 1500m altitude will affect the 3rd decimal place in value calculated at constant pressure.
>  
> Hope that helps
>  
>  
> Prof Philip Lloyd
> Energy Institute
> Cape Peninsula University of Technology
> PO Box 1906
> Bellville 7535
> Tel: 021 959 4323
> Fax: 086 778 0257
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>  
>  
> -----Original Message-----
> From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Frank Shields
> Sent: 30 September 2015 05:17
> To: Discussion of biomass cooking stoves
> Subject: [Stoves] Question regarding calculations
>  
> 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?
>  
> 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?
>  
> Thanks for any understanding help
>  
> Frank
>  
> Frank Shields
>  
>  
>  
>  
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