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Water Expansion/shrinkage

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philired1

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I have done a test with my boil kettle to try and determine the expansion and shrinkage rate. My kettle is a Big W 19.5l 310mm diam. I used a set amount of tap water being 15.75ls being 200mm in depth. This was taken to the boil and took another reading and got 16.14ls 205mm. The .005 difference is about .377ls. This is roughly 2.4% expansion. It was boiled for 60 mins where the evap was 50mm which is about 3.77ls leaving 12.37ls hot with a depth of 155mm. It was left to cool overnite as for no chill. The depth was 145mm cooled. This gave me a shrinkage rate of 4.8%. Are the expansion and shrinkage rates the same and does volume determine the expansion and shrinkage rate. These volume figures are worked out by 3.14x.0240(radius2)xdepths. Hopefully some can shed a little bit more light on this.
 

MHB

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The "standard" figure used in breweries everywhere is 4% contraction between boiling and 20oC.
Two points, that 4% isn't exact but its a close enough approximation for most brewing.
Pots are rarely exactly parallel unless they are fabricated (welded up out of sheet), if they are pressed or spun they are usually slightly tapered to make it easier to get them off the die/form. You would need to measure top and bottom very carefully.
If you want to play silly buggers with contraction, here is the equation for water from 0-100oC. That should copy/paste into excel, replace the t with a link to a cell, put a temperature into that cell... The answer will be in density that's mass/1 (1=kg/L) so 0.995 would be 0.995kg/L.

=(999.83952+(16.945176*t)+(-0.0079870401*t^2)+(-0.000046170461*t^3)+(0.00000010556302*t^4)+(-0.00000000028054253*t^5))/(1+0.01689785*t)

Good question about volume, its the same proportionally for any volume (as say a%), you get more volume (L) for a larger starting volume.
If you are working in L, measuring in decimeters will give the answer directly in L, saves keeping track of quite so many 0's
310mm is 3.1dm r = 1.55^2*Pi = 7.5476*h (200mm or 2dm) = 15.1L
Mark
 

kadmium

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I have done a test with my boil kettle to try and determine the expansion and shrinkage rate. My kettle is a Big W 19.5l 310mm diam. I used a set amount of tap water being 15.75ls being 200mm in depth. This was taken to the boil and took another reading and got 16.14ls 205mm. The .005 difference is about .377ls. This is roughly 2.4% expansion. It was boiled for 60 mins where the evap was 50mm which is about 3.77ls leaving 12.37ls hot with a depth of 155mm. It was left to cool overnite as for no chill. The depth was 145mm cooled. This gave me a shrinkage rate of 4.8%. Are the expansion and shrinkage rates the same and does volume determine the expansion and shrinkage rate. These volume figures are worked out by 3.14x.0240(radius2)xdepths. Hopefully some can shed a little bit more light on this.
Also don't forget in a no chill scenario the cube is sealed so you get no further evaporation.

If the pot was taken off the boil and measured, then measured the next morning if it was not covered you would have had evaporation from the cooling process. Being pedantic the pot would have expanded too, being so thin and heating up. This would throw your calculations off too I suspect.

I would factor a 4% and really just be chasing other efficiencies to gain. Look at evap, its so hard to predict unless you take very accurate measurements for each brew day and note down the environmental factors.
 

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