[Stoves] Question regarding calculations

Philip Lloyd plloyd at mweb.co.za
Wed Sep 30 00:58:09 MDT 2015


The thermal capacity of water is not a constant. At 1 atmosphere pressure a
good correlation is 

C_p(T)={4.214-2.286\times10^{-3}T+4.991\times10^{-5}T^2-4.519\times10^{-7}T^
3+1.857\times10^{-9}T^4}

https://syeilendrapramuditya.wordpress.com/2011/08/20/water-thermodynamic-pr
operties/

which, of course, you have to integrate over the delta T to get the
effective value. 

https://syeilendrapramuditya.files.wordpress.com/2011/08/water_specific_heat
_capacity_vs_temperature.gif?w=540&h=330

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

Cell: 083 441 5247

PA: Nadia 021 959 4330

 

 

-----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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