water temp

[RodfatherX]

I've been searching all through google for the formula to calc the water temp for say if I have 3 gallons of water at 200 degree F and I add it to 2 gallons of water at 40 degree F.......what will the temp come out to be. I could probably find the formula if I could remember what this is called. Anyone know the formula or even better a online calc

 

[k1v1116]

I think if your just adding water to water you can simply do an average (200+40)/2 = 120f but I have to double check this. I think you would simply divide or multiply the temperature to reflect the ratio between the two volumes in this case 2/3 so two thirds of 40 is 26.666 then average that with 200 and it should come out to 113.33f. It gets more complicated if your adding water to grain or water to alcohol or water and sugar solution, the heat mass changes so the energy stored in the liquid / solid at any given temperature varies and so does the effect on temperature changes.
Im not completely sure of this, and I also cant remember what its called so hopefully someone else will either confirm this or correct me.

EDIT: ok this is the closest I can find http://www.scienceforums.net/forum/showthread.php?t=18500
I hope you can make sense of it.

 

[RodfatherX]

Thx for the help I'll test it soon..............I searched for like 3 days before I posted in the forums lol

 

[Funkenjaeger]

It's a simple weighted average, a math tool rather than anything special related to thermodynamics. Of course that's only true if you're mixing water with water (though wort is likely close enough for a ballpark figure at least).

(T1*V1+T2*V2)/(V1+V2)
Where T1, T2 are the temps, and V1, V2 are the volumes.

A practical example - mixing a partial boil with cold top-off water:
2 gallons @ boiling mixed with 3 gallons @ 50F:
(2*212+3*50)/(2+3) = 114.8F

 

[Bobby_M]

Yes, weighted average works as long as you have no ice. Ice changes everything. You can't consider a mass of ice as 32F water because it takes a lot more energy to melt it.

 

[SkinnyShamrock]

(T1*V1+T2*V2)/(V1+V2)
Where T1, T2 are the temps, and V1, V2 are the volumes.

Thank you! I was just trying to figure that out yesterday when my ice-filled sink wasn't quite cooling the wort off fast enough...

 

[BrosBrew]

As a general rule do you want to cool the wort as fast as possible?

 

[Funkenjaeger]

As a general rule do you want to cool the wort as fast as possible?

Yes. The faster you chill it the more cold break you get, as the sudden temperature change makes proteins coagulate and drop out of solution. It'll make a difference in the clarity of your finished beer.

 

[BrosBrew]

So preparing a bath with ice water and salt would be a good thing?

 

[Funkenjaeger]

So preparing a bath with ice water and salt would be a good thing?

Well it's certainly better than just using cold tap water alone. It'll at least be sufficient for partial boils of 2-3 gallons or less, but by the time you start looking at full boils, ice baths aren't really good enough anymore.