An explanation of Volumes of CO2

[iverasp]

Hi,

When trying to make a spreadsheet containing all the info I needed for brewing I had some problems making an easy formula for calculating desired head pressure from Volumes of CO2. After putting it all together I thought I might share the basics behind the calculations as I did not find any good explanation searching the internet.

Enjoy

http://dl.dropbox.com/u/13029232/Ca... based on“Volumes of CO2” and temperature.pdf

PS: If any of my logic is flawed please provide feedback.

 

[Dr Malt]

Are you looking for something like this for you use?

http://www.kegerators.com/articles/carbonation-table-pressure-chart.php

In a commercial brewery, they measure the temperature and pressure in a bottle or keg and use the chart to determine volumes of CO2. The apparatus is called a zahm Negal.

Dr Malt

 

[iverasp]

Nope, I wanted a simple spreadsheet where I input the fridge temperature and volumes of CO2 and get the needed pressure calculated for me without looking at charts.

 

[ajdelange]

The ASBC table is quite well fit by

V = 3.4384 – 0.66441*T + 0.12838*P + 0.00040505*T^2 – 0.0010092*T*P – 0.00001234*P^2

where temperature is in Fahrenheit and Pressure is in psig. This is easily solved for P

[Edit] Even simpler to solve for P than the polynomial fit is the exponential one:

V = (P + 14.695) * ( 0.01821 + 0.090115*exp( -(T-32)/43.11 ) ) - 0.0033

which is as good as the polynomial in the rms sense but has lower peak errors. Also, as it models the Henry coefficient as a function of temperature, it is probably safe to use outside the range of the ASBC table to which it represents a fit.

Formulas from: http://ajdel.wetnewf.org:81/Brewing_articles/CO2 Volumes.pdf

They are just fits to the ASBC table.

 

[iverasp]

Great article, thanks! As said I did not find any such info using google. Maybe I should have asked here first