Measuring liquid

[farmskis]

I plan on measuring my water, wort, etc with a ruler or calibrated stick. Can anyone tell me how much expansion I would get between room temp water and say wort that was just mashed or boiled? Is it really enough to compensate for? My typical volumes would be around 4-5 gal. If I just base my measurements off of a temp somewhere in the middle will this be close enough?

 

[Onkel_Udo]

Not enough to worry about.

 

[day_trippr]

4% shrinkage from hot to cool, more or less.
That's what Beersmith uses...

Cheers!

 

[doug293cz]

4% shrinkage from hot to cool, more or less.
That's what Beersmith uses...

Cheers!

4% is for boil to room temp. Mash temp to room temp is about 2%. If your volume measurements have 4% error, then any calculations you do with those measurements will have at least 4% error.

Brew on

 

[timdillon36]

I have read many times about people talking about the shrinkage from cooling but what exactly are we measuring.

I don't think we can just put a number on it and say, yep my 5.2g in the bk will be 5.0 in the fv. The bk also expands and contracts with temp change and the shape effects this measurement as well. Also an al pot will change is size more than a ss pot.

To be accurate you really need to test your own system.

 

[doug293cz]

I have read many times about people talking about the shrinkage from cooling but what exactly are we measuring.

I don't think we can just put a number on it and say, yep my 5.2g in the bk will be 5.0 in the fv. The bk also expands and contracts with temp change and the shape effects this measurement as well. Also an al pot will change is size more than a ss pot.

To be accurate you really need to test your own system.

Theoretically the vessel thermal expansion will affect the results, but in real life the affect is insignificant. Read on...

Water changes 41,600 ppm over the range from 68˚ to 212˚F, or about 289 ppm/˚F by volume, which works out to 289/3 = 96 ppm//˚F linearly (known as the coefficient of thermal expansion, or CTE.) Aluminum has a linear CTE of about 13 ppm/˚F, and 304 SS of 9.6 ppm/˚F.

Let's work an example using an aluminum pot with a diameter of 15.000" at 68˚F. If we put 5.000 gal of water in the pot at 68˚F, the height of the water will be:

231 in^3/gal * 5 gal / (pi * (15 in / 2)^2) = 6.535963" [or, 1.307193 in/gal]​

If we heat the pot to 212˚F (ignoring any evaporation that takes place), the water volume will increase to:

5 * 1.0416 = 5.208 gal​

The pot depth per gallon will decrease to:

1.307193 in/gal * (15 in / 2)^2 / ((15 in + 144˚F * 13e-6 in/˚F) / 2)^2 = 1.306866​

So the error of ignoring the thermal expansion of an aluminum pot would be

(1.307193 - 1.306866) / 1.306866 = 0.00025 or 0.025%​

Thus we can safely ignore the effect of pot's thermal expansion when making volume measurements by depth at different temperatures.

Brew on

 

[timdillon36]

Thank you very much doug293cz for doing the math and explaining it as you did.

 

[doug293cz]

Thank you very much doug293cz for doing the math and explaining it as you did.

Before I did the math, I thought it would be an insignificant effect, but I was surprised at just how small an effect it is.

Brew on

 

[Smellyglove]

I got curious. i guess I know the answer, that the pot will expand (in every dimension) since heat is applied to it..

But will it even if you have a "buffer"? Most stainless pots have a concave bottom, just slight. This is so it can expand when heated. Will the side walls still expand, the height, diameter? That's why you hear a ripple-sound at the start when doing induction. The bottom hasn't expanded yet so it vibrates against the other layers in the bottom "sandwich", afaik.